UNIVERSITY OF CALIFORNIA 
 LOS ANGELES 
 
 GIFT OF 
 
 James W. Moncrieff
 
 t 
 
 V 
 
 3 O <b
 
 DRYING CLAY WARES 
 
 BY ELLIS LOVEJOY, E.M. 
 
 Member and Ex-President 
 American Ceramic Society. 
 
 Member 
 
 American Institute of Mining Engineers, 
 National Brick Manufacturers' Association. 
 
 T. A. RANDALL & CO. 
 
 Publishers, 
 Indianapolis, Ind.
 
 Copyrighted 1916 
 
 by 
 A. RANDALL & CO.
 
 TP 
 
 PREFACE 
 
 The following articles which appeared serially in The 
 Clay-Worker were inspired by the fact that there is no pub- 
 lished literature on the subject of drying clay wares. 
 
 The various treatises on heating, ventilation and drying 
 include only in a small measure data applicable to our clay 
 drying problems. In our engineering work we have collected, 
 modified and applied this data to our special needs, and the 
 articles include such engineering data as we have found 
 useful. 
 
 We have tried to make the articles not merely descriptive, 
 nor yet too technical, and hope they will prove of some 
 assistance to both the practical and technical clayworker. 
 
 Credit is due Mr. T. W. Garve, M. E., for all the pen and 
 ink drawings and for the chapter on German clayworking 
 plants. We also wish to acknowledge the assistance of Prof. 
 C. B. Harrop, E. M., in numerous discussions of the problems 
 involved and in checking over and correcting the mathe- 
 matical work. 
 
 Credit has been given in the text to all authorities as far 
 as possible, though in many instances the information is from 
 our engineering data and so interwoven with it that it is im- 
 possible to trace it to any single authority. 
 
 ELLIS LOVEJOY, E. M. 
 
 Columbus, Ohio, January 22, 1916.
 
 TABLE OF CONTENTS 
 
 CHAPTER I. 
 
 Page 
 Classification of Clays ................................... 7 
 
 Water in Clay ............................. g 
 
 How Drying Proceeds ................................ 9 
 
 CHAPTER II. 
 The Work to Be Done ................... 12 
 
 CHAPTER III. 
 The Relation of Air to Drying ...................... 1 6 
 
 Effect of Lamination on Drying ................ 19 
 
 '' 
 
 _ ........ .............. 20 
 
 Preheating Clay ........... .............. 21 
 
 CHAPTER IV. 
 CHAPTER V. 
 
 Shrinkage . . . 
 
 .................... . Zo 
 
 Air Drying ............ ............... 33 
 
 Open Yard Drying of Soft Mud Brick ........ 
 
 Stiff Mud Brick in Open Yard ......... '35 
 
 Rack and Pallet Yard ................. 
 
 Air Drying Stiff Mud Brick.. 
 
 Drain Tile Sheds ..................... '"" ' 43 
 
 CHAPTER VI. 
 Drying Above Continuous Kilns ........ 
 
 Advantages 
 
 Disadvantages . ' ' ' 
 
 ' ' ...................... 61 
 
 CHAPTER VII. 
 Artificial Dryers 
 
 General Principles ...... 
 
 Floor Dryers Hot Floor ] ' .
 
 CHAPTER VIII. 
 Sewer Pipe Floors 62 
 
 CHAPTER IX. 
 
 Periodical Dryers 78 
 
 Steam Pipe Dryers _ _ 78 
 
 The Boss Dryer 103 
 
 The Pipe Rack Dryer 105 
 
 Tender Clay Dryer 107 
 
 CHAPTER X. 
 Pottery Dryer 110 
 
 CHAPTER XI. 
 
 Terra Cotta and Other Special Dryers 115 
 
 The Scott System 118 
 
 Car Tunnel Kilns _ 120 
 
 CHAPTER XII. 
 
 Conservation of Heat in German Factories 124 
 
 Moeller and Pfieffer Dryer 127 
 
 CHAPTER XIII. 
 Progressive Dryers 130 
 
 CHAPTER XIV. 
 Radiated Heat Dryers 133 
 
 CHAPTER XV. 
 Steam Progressive Dryers , 141 
 
 CHAPTER XVI. 
 
 Waste Heat Progressive Dryer 145 
 
 Air Volume of Heat Requirement for Waste Heat 
 
 Dryers 154 
 
 Another Method of Determining Air Volume 159
 
 DRYING CLAY WARES 
 
 DRYING CLAY WARES. 
 
 By Ellis Lovejoy. 
 
 CHAPTER I. 
 Classification of Clays. 
 
 DRYING CLAY WARES is one of the most complex 
 problems with which the clayworker has to deal, and 
 one that is least considered and least understood. We 
 are lacking in a proper classification of clays in their relation 
 to drying and perhaps no accurate classification is possible. 
 Clays may be roughly classified as- follows: 
 
 (1) Clays that may be dried in a few hours, starting with 
 an initial high temperature and rapid drying condition. 
 
 (2) Clays that may be dried in twenty-four hours or less, 
 starting at an initial low temperature in saturated atmosphere. 
 
 (3) Clays that can be dried in twenty-four to seventy- 
 two hours, under conditions of No. 2. 
 
 (4) Clays that require over seventy-two hours under 
 conditions of No. 2. 
 
 (5) Clays that must be slowly heated up in a saturated 
 stagnant atmosphere before advancing into a moving drying 
 atmosphere. 
 
 (6) Clays that cannot safely be subjected to conditions 
 under No. 2 and No. 5, but must be dried slowly, starting un- 
 der drying conditions. 
 
 (7) Clays that cannot be dried under any condition. 
 There are many clays and shales which will rate as No. 1 ; 
 
 clays that can be dried in a pipe rack dryer; that will stand 
 exposure to wind and sun; that can be placed in a periodic
 
 DRYING CLAY WARES 
 
 dryer in which a maximum temperature is maintained from 
 end to end of dryer. 
 
 No. 2 contains a greater number of clays and the pro- 
 gressive dryers in which No. 2 conditions prevail, are the most 
 numerous. No. 2 class shades into No. 3 and No. 4. 
 
 There are many tender drying clays that can be 
 dried safely by first heating them in a saturated atmos- 
 phere, then moving them into conditions No. 2 and No. 4. 
 No. 5 is considered the .method par excellence for very tender 
 clays, but we have found some clays that can be safely dried 
 under somewhat trying conditions, provided they are not 
 first subjected to a moist atmosphere the humidity treat- 
 ment which prevails in No. 2, 3. 4, and especially in No. 5. 
 
 These classes include many clays, but there are many 
 others, perhaps as many, that cannot be dried under any 
 conditions in their raw state, but must first be subjected to 
 some treatment which changes the physical conditions. 
 
 A weak point in any classification is that a clay which 
 may be difficult to dry in one kind of ware becqmes easy 
 to dry in some other ware. We have frequently found clays 
 which in bricks required thirty-six to forty-eight hours to 
 dry safely, yet in drain tile would dry without a flaw in 
 twenty-four, or even twelve hours. In safe drying, drain tile 
 easily leads the list, then comes sewer pipe in small sizes, 
 simple and small hollow ware especially in clays that lamin- 
 ate, bricks, perforated bricks, complex hollow ware, large 
 sewer pipe, roofing tile, terra cotta, etc. 
 
 Water in Clay. 
 *Water in clay exists in three conditions: 
 
 (1) Moisture, fa) free water, fb) water of saturation. 
 
 (2) Hygroscopic water. 
 
 (3) Chemically combined water. 
 We might also add colloidal water. 
 
 Free water is the water which fills the pore spaces in 
 
 the clay mass, and which serves as a lubricant, permitting 
 
 ie grains of clay to slip one on another, and gives the mass 
 
 the mobility necessary for casting or moulding processes 
 
 the water with which we are chiefly concerned in 
 
 *0ne authority classifies the water in clav 
 
 sssSr^ 
 
 y, hygroscopic water, and combined or ch4mi wate
 
 DRYING CLAY WARES 
 
 drying. When it is driven off the clay mass is rigid; it will 
 no longer flow under pressure, but it still looks wet. 
 
 Water of saturation is that water clinging to the surfaces 
 of the grains of clay after the pores have been emptied of 
 their free waters. This water can only be removed by con- 
 tact with some other substance having greater affinity for the 
 water than that of the clay, or by vaporization from the sur- 
 faces of the clay grains. 
 
 We say clay wares are bone dry when they come from 
 the dryer, showing no perceptible wetness. Yet we know 
 that in the water-smoking, there is driven off from the dry 
 wares a considerable volume of water vapor. This is hy- 
 groscopic water and also colloidal water. We have no hint 
 of its presence either in the appearance or feel of the clay. 
 We often use the expression "dry as dust" to express dry- 
 ness, but dust contains hygroscopic water. 
 
 Combined water is a chemical constituent of clay and 
 only appears when we disintegrate the mineral kaolinite by 
 heat. 
 
 To recapitulate: Free water is sensible moisture entrapped 
 in the clay mass, but which may be removed by mechanical 
 means, such as filtering, pressing and capillarity. 
 
 Water of saturation is also sensible water removable only 
 by evaporation but at normal temperatures. 
 
 Hygroscopic water is insensible and is removed only by 
 evaporation at temperatures above normal. 
 
 Combined water is a chemical constituent of the clay min- 
 erals and can only be driven off by a destruction of the min- 
 eral characteristics. 
 
 How Drying Proceeds. 
 
 Clay is porous, and when wet, these pores are filled with 
 water. The pores form zig-zag channels or capillary tubes 
 from the center of the mass to the surface. When there is 
 no drying at the surface, there is practically no movement of 
 the water in the pores osmotic movement not considered. 
 Immediately, however, jthat drying begins on the surface, 
 the water thus evaporated is replaced by capillarity, drain- 
 ing the numerous .minute reservoirs which we call pores. 
 There is no better illustration than a lamp and wick. As 
 long as the lamp contains oil it will be drawn up by the 
 wick by capillarity. When the oil is exhausted, the flow 
 ceases, although there is some oil still clinging to the walls 
 of the lamp. Similarly are the pore reservoirs in a clay mass 
 drained. This is the first stage in drying and the stage in 
 which shrinkage takes place, and if all parts of the clay mass
 
 It' 
 
 DRYING CLAY WARES 
 
 are being drained at the same time, there are no unequal or 
 local strains and the ware does not crack. 
 
 It is almost needless to say that the safety of drying 
 during this first stage depends upon the relative rate of 
 surface evaporation and replacement. 
 
 If we dip different substances in a colored solution and 
 note the rise of the solution in the substances, we will have 
 a clear idea of how in one clay mass, because of its pore 
 channels, the included water will move from one place to 
 another within the mass faster than in another clay ,mass 
 with a different system of pore channels, to replace water 
 removed by surface evaporation. 
 
 Now if the water is evaporated from the surface faster 
 than it is replaced, there must be cracking to relieve the 
 strains, either that or the wet core must be compressed 
 by the dried and shrinking shell, which is very doubtful. To 
 compress such a core will exceed the power of the strongest 
 press, and clay, however strong, has not such strength. 
 There are undoubtedly some strains introduced. It would 
 be folly to claim that drying proceeds absolutely at the same 
 rate throughout the mass, and whenever the strain exceeds 
 the breaking strain of the dried clay, there must be cracking. 
 
 In overcoming minor strains, the physical character of 
 the clay plays a part. Ordinary clays, practically all clays, 
 are made up of a number of minerals fragments of the rocks 
 from which the clays were derived. If the grains are angular 
 and coarse, they may be loosened, partly pulled cut of the 
 imbedding matrix, or under compression will rearrange them- 
 selves into greater compactness, in either case relieving the 
 relieving the strain. Also we must admit that clay has some 
 elasticity which will relieve minor strains. 
 
 The safe removal of the moisture then depends upon three 
 factors: 
 
 (1) The relative rate of evaporation and interstitial 
 movement of the moisture. 
 
 (2) The shape and size of the grains which make up 
 the clay mass viz., the interlocking power. 
 
 (3) Elasticity. 
 
 Having removed the reservoir water, as above described, 
 there still remains the moisture clinging to the walls of the 
 pore passages the water of saturation. This can only be 
 removed under the boiling point. Air will take up and hold 
 orating the water by direct contact with it. 
 
 This brings us to the border land of the second stage of 
 the drying, or more properly, we should make this the second 
 step in the first stage.
 
 DRYING CLAY WARES 11 
 
 When the drying medium has penetrated to the core of 
 the clay mass, the latter is bone dry, as we say, but there 
 is still the hygroscopic and colloidal water that cannot be 
 removed under the boiling point. Air will take up and hold 
 as vapor a certain amount of water for each temperature. 
 We make this statement advisedly. (Without confusing the 
 discussion with technical matters, let us say the air has 
 absorptive power for the moisture, so, likewise, has other 
 bodies, including clay, and which every body has the greatest 
 absorptive power, will remove moisture from the other. We 
 may say that the clay mass may not become dryer than the 
 drying medium, and air is never absolutely Jry. We know 
 that this statement is open to attack, but, relative absorptive 
 powers considered, it is true.) 
 
 There is then some moisture remaining, and especially 
 is this the case when we have lining the pore passages vari- 
 ous salts common to clay besides sulphuric acid. The lat- 
 ter and calcium chloride are commonly used as dessicators 
 to remove moisture from the air, simply because they have 
 greater affinity for moisture than air. Whatever the cause, 
 some moisture remains in the "bone" dry clay mass which 
 can only be removed by temperatures above the boiling point 
 of water, or of the solution whatever it may be. Sulphuric 
 acid, for instance, is only volatilized at 680 degrees Fahren- 
 heit. The removal of this hygroscopic water is the second 
 drying stage and is done in the kilns water-smoking. 
 
 We are not concerned with chemically combined water, 
 since it is never in the form of moisture, and is only expelled 
 by the breaking up of the kaolin at a temperature of 800 
 degrees or higher. It correlates with the expulsion of carbon- 
 dioxide from limestone, or sulphuric anhydride from sulphates, 
 or sulphur from sulphides. 
 
 In the water-smoking stage of the drying there is con- 
 siderable danger. We may generate the vapor so fast 
 that there is considerable pressure, and while it may not 
 rupture the mass as a whole, yet it may loosen the indivi- 
 ual grains and thus cause a rather punky product which 
 otherwise would have the steeUike rjng so much desired. 
 The grains are loosened in their sockets in the matrix and 
 while they may not pull out entirely, yet they cannot con- 
 duct the vibratory motion which is essential if the ware is 
 to ring like steel. A cracked bell or a cracked vase will 
 not ring true, neither will a brick ring true that has an 
 infinite number of minute cracks, or loosened grains. This 
 is why steamed bricks are so often rotten.
 
 DRYING CLAY WARES 
 
 CHAPTER II. 
 The Work to Be Done. 
 
 WE HAVE SHOWN how drying proceeds. It will be in 
 order next to determine the work to be done and the 
 heat required. 
 
 Clays vary in the amount of water they will take up 
 in order to make them plastic. The following table, made 
 up from various sources, gives the percentage of water re- 
 quired for the clays in question: 
 
 Missouri Geological Survey. 
 
 Brick clay 16 19 per cent. 
 
 Fire and potters' clay. ..... .15 33 per cent. 
 
 Flint clay 15 24 per cent. 
 
 Kaolins 18 35 per cent. 
 
 Shales . 14 25 per cent. 
 
 Georgia Geological Survey. 
 
 Brick clays 1 530 per cent. 
 
 Kaolins 30 45 per cent, 
 
 Fuller's earth up to 90 per cent. 
 
 North Carolina Geological Survey. 
 
 All clays 1640 per cent. 
 
 Illinois Geological Survey. 
 
 Paving brick clays 1317 per cent. 
 
 Other clays 1521 per cent. 
 
 Oklahoma Geological Survey. 
 
 Shale .. ..1032 Average 22.5 per cent. 
 
 Light burning clays, " 25.1 per cent. 
 
 Fir 6 cla y " 15.1 per cent 
 
 Surface clays, 15-36 " 24.9 per cent. 
 
 The amount of water in clay ware depends upon the pro- 
 >s as well as the clay. The dry or dust-pressed wares
 
 DRYING CLAY WARES 13 
 
 have very little water. In the semi-dry processes, the clay 
 is damp enough to ball up in the hand, and this is the usual 
 condition of the clay for dry-pressed bricks. 
 
 Stiff mud processes require more water from 10 to 25 
 per cent, of the dry clay. The soft mud has a still higher 
 per cent., and casting processes require that the clay be 
 made up into a thin slip, but as this is absorbed by the 
 plaster moulds, the ware itself has scarcely more water than 
 would be required for soft mud. 
 
 In the several processes, but especially in the stiff mud, 
 the softness of the ware has a wide range. Some clays can 
 only be made into stiff mud wares by working them so soft 
 that they easily dent by the fingers in handling them, and 
 paddles or hand clamps are necessary for the handling. 
 Other stiff mud wares are so hard that in bricks, for instance, 
 they may be hacked ten to fifteen courses high. In several 
 plants, for a number of years, stiff mud bricks have been 
 set in the kiln six to ten courses high and dried therein. 
 Experiments are being made, having in view setting the 
 bricks eighteen to twenty courses high in the kiln, making 
 this the maximum height of the setting and drying in the 
 kiln followed by burning, thus eliminating the dryer just 
 as in the dry-pressed bricks. Clays which will stand this 
 setting must be suitable, and naturally will require little 
 water. 
 
 In our discussion of the work of drying, we will assume 
 that a standard sized brick weighing five and one-half pounds 
 burned, will contain one pound of free water. This may 
 seem low, but it must be remembered that there are three 
 water conditions that enter into loss in weight in burning 
 chemical water, hygroscopic water, and moisture. In dry- 
 ing we are only concerned with the moisture. 
 
 Many people get the idea that because clay wares can 
 be dried readily at normal temperatures in the open air, 
 that very little heat is required for the drying. We wish 
 to state emphatically that regardless of temperature, a cer- 
 tain number of heat units are required to vaporize water, 
 and this heat must be supplied from same source. 
 
 (Note We wish to encumber this discussion with tech- 
 nicalities as little as possible, and make this note to avoid 
 the criticism of some technicist who concerns himself chiefly 
 with technicalities. Water vaporizes at all practical tem- 
 peratures. It will take less heat to vaporize water at 60
 
 DRYING CLAY WARES 
 
 degrees Fahrenheit than 212 degrees or 325 degrees. First, 
 the water is only heated to 60 degrees instead of ^ 
 grees or 325 degrees. This is the sensible heat. Second, it 
 requires more heat to maintain the pressure, the greater the 
 pressure.) 
 
 We are accustomed to say that air absorbs the vapor, and 
 will continue to use that term. Water will evaporate at any 
 temperature until the requisite vapor pressure for that tem- 
 perature is reached, and this takes place in a vacuum prac- 
 tically as well as in air or in any gas mixture. 
 
 We readily appreciate this in boiler practice, where the 
 temperature of the water must be advanced with every ad- 
 vance in gauge pressure. The same is true of temper- 
 atures below 212 degrees, only here the boiler is not in 
 evidence, but the pressure is there just the same. We say 
 the air is saturated, meaning the vapor pressure is satisfied. 
 
 For the benefit of those who wish to figure these ques- 
 tions closely, we insert the following table, giving the heat 
 units of vaporization. 
 
 32 degrees 1092 B. T. U. 
 
 60 degrees 1100 B. T. U. 
 100 degrees 1112 B. T. U. 
 212 degrees 1147 B. T. U. 
 
 307 degrees 1176 B. T. U. 60 pounds pressure. 
 324 degrees 1181 B. T. U. 80 pounds pressure. 
 338 degrees 1185 B. T. U. 100 pounds pressure. 
 350 degrees 1189 B. T. U. 120 pounds pressure. 
 
 We will make use of this table in discussing steam 
 dryers. 
 
 To vaporize a pound of water at 212 degrees Fahrenheit, 
 at sea level, 967 B. T. U. are required. This is the heat that 
 disappears becomes latent. It represents the heat required 
 to keep the pot boiling without any advance in temperature 
 of the water in the pot. One hundred and eighty B. T. U. 
 per pound of water are required to bring the water up to 
 the boiling point from 32 degrees Fahrenheit, or 140 B. T. 
 U. to advance the temperature from 72 degrees to boiling. 
 Add this 140 to 967 and we have 1,107 B. T. U. to vaporize 
 a pound of water at 212 degrees Fahrenheit from 72 degrees 
 Fahrenheit. Let us say 1,100 B. T. U. 
 
 We must generate this heat or rob the atmosphere to 
 the extent of the latent heat for every pound of water we 
 evaporate from our wares.
 
 DRYING CLAY WARES 15 
 
 A pound of coal may have from 8,000 to 15,000 (averaps- 
 12,000) B. T. U., and nearly one pound of coal is required to 
 evaporate ten pounds of water. Ten bricks then require one 
 pound of coal; a thousand bricks require 100 pounds of coal. 
 
 But this is only part of the work. We put in 6,000 pounds 
 of clay (1,000 bricks), at 60 degrees Fahrenheit and take 
 them out at 130 degrees Fahrenheit perhaps. This takes 
 84,000 B. T. U. [6,000 X. 2 (sp. ht. of clay )X 70,] or seven 
 pounds of coal. We put in 800 pounds of iron cars per thou- 
 sand bricks, which requires 6,260 B. T. U. (800X. 11X70), 
 or one-half pound of coal. 
 
 We may use 720,000 cubic feet of air in drying 1,000 bricks, 
 or 57,600 pounds, which requires 967,670 B. T. U. (57,600 X. 24 X 
 70) or 80 pounds of coal. 
 
 Now we have in round numbers 188 pounds of coal. If 
 the radiation loss is ten per cent., the total fuel requirement 
 is 206 pounds, or practically one-tenth ton of coal to dry 
 1,000 bricks.* 
 
 These figures will be surprising to many, but there are 
 many dryers using a greater quantity. In fact, a half more 
 is common practice, and double is not infrequent. Our figures 
 are on the assumption that we get all the heat from the fuel 
 into the dryer. 
 
 If we are drying with steam, we must introduce the boiler 
 losses. 
 
 If we use direct heat, we must allow for the loss in the 
 products of combustion, for imperfect combustion, either 
 through too much or too little air, loss in ash, etc. How- 
 ever we may do the work, there is an absorption of heat, and 
 the fuel required to generate this heat will in some factories 
 exceed the fuel used in burning the ware. 
 
 The fuel consumption in burning is frequently discussed 
 in conventions, but we seldom hear any mention of the fuel 
 used in drying. 
 
 The owners of open yards will often view with envy the 
 modern drying plant of their competitors, its less labor, per- 
 haps less drying loss, but if they could appreciate the fact 
 that the gain is at an expense of ten to fifteen dollars per 
 day in fuel, they would be more content with their old-fash- 
 ioned process. 
 
 *Note The above figures are general, but approximately 
 correct for a direct fired dryer. The heat consumption will 
 vary with the method of application and will be considered 
 in detail in the discussion of the several types of dryers.
 
 DRYING CLAY WARES 
 
 CHAPTER III. 
 The Relation of Air to Drying. 
 
 WE HAVE USED the expression, "the air absorbs 
 moisture," and yet stated that the air plays no 
 part in absorption. We wish to set ourselves right 
 in this matter and have a clear understanding of it. 
 
 Scientists hold that water as vapor is absorbed by air, that 
 it goes into solution just as salt may go into solution in water. 
 Such problems in physical chemistry do not concern us. 
 
 From our standpoint of drying clay wares, we may con- 
 sider that air does not absorb moisture because air is not an 
 essential factor in vaporization. 
 
 If we could inclose a cubic foot of air saturated with 
 moisture and then could remove the air, the moisture would 
 remain suspended in the space as vapor. 
 
 If we fill a long tube closed at one end, with mercury, 
 and invert it in a mercury bath, the mercury in the tube 
 will drop to about 29" or barometric pressure. The space 
 above the mercury in the tube is a vacuum. Now suppose 
 we introduce a drop of water in the tube; the mercury will 
 quickly drop, and this fall is not due to the weight of the 
 water, which is insignificant, but to the vapor from the water 
 which fills the upper part of the tube and which exerts a 
 pressure upon the mercury and depresses it, or in other 
 words, partially overcomes atmospheric pressure, which sup- 
 ports the colujnn of mercury. If all the water passes into 
 vapor, the saturation of the vacuum may not be complete, 
 and the introduction of ,more water will cause further de- 
 pression of the mercury, but finally a point will be reached 
 when saturation is complete and no more water will evap- 
 orate, and no further change will take place in the mercury
 
 DRYING CLAY WARES 17 
 
 level. Suppose we now introduce some other liquid. The 
 space is saturated with water vapor, but not with the vapor of 
 this other liquid, and the latter evaporates and the mercury 
 level is still further depressed. The pressure exerted by these 
 vapors is called vapor pressure. If we cool the tube some of 
 the vapor condenses and the mercury rises, but if we raise 
 the temperature, we increase the vapor pressure (volume of 
 liquid vaporized), and the mercury falls. If we introduce air, 
 the mercury still further falls, and additional vapor is taken 
 up in consequence of the greater space, and perhaps in con- 
 sequence of the introduction of the air. 
 
 Suppose we could take a cubic foot of saturated air from a 
 dryer at 60 degrees, and remove the moisture by dessicators, 
 by cooling, or in any way, we would have a cubic foot of rare- 
 fied air, but less than a cubic foot at atmospheric pressure. 
 Repeat the experiment at 120 degrees, and our remaining 
 air will occupy a much smaller volume, and at 212 degrees 
 there may be no air whatever. 
 
 In other words, while air in a closed space does not inter- 
 fere with the weight of moisture taken up, and indeed may be 
 in some slight degree an aid, yet in free space the water vapor 
 displaces air and at the boiling point or above the air may be 
 entirely driven out. 
 
 From this it will be seen that practically air has nothing 
 to do with evaporation. Evaporation is a function of vapor 
 pressure, and vapor pressure is influenced by temperature. 
 
 The part air plays is mechanical, and very important. 
 Referring again to the mercury tube, suppose we have a 
 stopcock in the top of the tube opening into a larger vacuum. 
 When the mercury has reached its lowest level, due to the 
 vapor pressure, if we open the stopcock the mercury will 
 rise and force out the vapor. Closing the stopcock repro- 
 duces the former conditions and the water will evaporate 
 as before and force down the mercury. With air we can 
 create a draft and sweep away the vapor as fast as it is 
 taken up by space. If it were not removed, drying would 
 cease when the vapor pressure was attained. As the tem- 
 perature rises, the vapor pressure increases, and at 212 de- 
 grees equals the pressure of the atmosphere. We now no 
 longer need any air because the steam will overcome at- 
 mospheric pressure and forces itself out, not because of the 
 air, but in spite of it. Steam will rush out of a boiler with 
 great force, pushing the air away.
 
 18 DRYING CLAY WARES 
 
 If we are working at a low temperature, we must intro- 
 duce a large volume of air because each cubic foot has space 
 for only so much vapor and must be removed when saturated 
 if the drying is to continue. As we increase the temper- 
 ature, the capacity to take up moisture increases, and we 
 need less volume to carry it away. Above 212 degrees we 
 theoretically need no air whatever, but in practice it serves 
 as a convenient medium to conduct the heat from the source 
 to the ware. We say convenient not essential. 
 
 The question may arise, does not the volume of air in- 
 crease with temperature in equal ratio with the vapor pres- 
 sure, and if so, will there not be required the same volume of 
 air for all temperatures? 
 
 Let us glance at this. 
 
 The following table from Seger's formula for vapor ca- 
 pacities has been especially calculated for this paper. 
 Seger's formula is: 
 
 p .623 
 
 V = 1.293 X X =; wt. of vapor in kilos per cu. meter of air 
 760 1+at 
 
 1.293 = wt. of 1 cu. meter or dry air at temperature t. 
 
 p = tension of vapor at temperature t. 
 
 a = 0.00366 = co-efficient of expansion of gas. 
 t = temperature. 
 0.623 = specific weight of water vapor where dry air equals 1. 
 
 We have changed the formula to pounds, Fahrenheit, etc., 
 and we have assumed an altitude of 800' or 29" of mercury 
 instead of 760 millimeters. 
 
 Our formula becomes: 
 
 P' 0.623 
 
 V=1.293X 0.062 X- -X100=wt. of j lb 
 
 29 l+0.002(t'-32) 
 
 per 100 cu. ft. of air 
 
 The column on the left gives the value of p' for the sev- 
 eral temperatures. In the table itself, the first column gives 
 the temperature; the second column is for 100 per cent or 
 complete saturation; the third column is 90 per cent satura- 
 lon, etc. See table on opposite page. 
 
 Now as seen in the second column, in advancing from 
 degrees to 200 degrees, the capacity for moisture in- 
 ten times ~ namely ' from - 2 92 pounds to 
 aCC rdin S ^ the ratio 1+
 
 DRYING CLAY WARES 
 
 This is an increase of 17 per cent, in the volume of air, or 
 rather the air is rarefied to this extent while the carrying 
 capacity of equal volumes has increased over 1,000 per cent. 
 About one-eighth of the air volume is required at the higher 
 temperature to do the same work. 
 
 We will have occasion to refer to the above table in the 
 discussion of some of the types of dryers. 
 
 Having explained the relation of air to vaporization, we 
 
 VAPOR CAPACITY OF 100 CU. FT. OF AIR. 
 
 
 Deg. 
 
 Percentage of Saturation 
 
 p' 
 
 Fahr. 
 
 100 
 
 90 
 
 80 
 
 70 
 
 60 
 
 50 
 
 40 
 
 0.361. 
 
 . 50 
 
 0.060 
 
 0.054 
 
 0.048 
 
 0.042 
 
 0.036 
 
 0.030 
 
 0.024 
 
 0.518. 
 
 . 60- 
 
 0.085 
 
 0.077 
 
 0.068 
 
 0.059 
 
 0.051 
 
 0.043 
 
 0.034 
 
 0.733. 
 
 . 70 
 
 0.117 
 
 0.105 
 
 0.094 
 
 
 0.070 
 
 0.059 
 
 0.047 
 
 1.024. 
 
 . 80- 
 
 0.161 
 
 0.145 
 
 0.129 
 
 0.113 
 
 0.097 
 
 0.081 
 
 0.064 
 
 1.410. 
 
 . 90 
 
 0.218 
 
 0.196 
 
 0.174 
 
 0.153 
 
 0.131 
 
 0.109 
 
 0.087 
 
 1.918. 
 
 .100- 
 
 0.292 
 
 0.263 
 
 0.233 
 
 0.204 
 
 0.175 
 
 0.146 
 
 0.117 
 
 2.578. 
 
 .110 
 
 0.384 
 
 0.346 
 
 0.307 
 
 0.269 
 
 0.230 
 
 0.192 
 
 0.154 
 
 3.425. 
 
 .120- 
 
 0.502 
 
 0.452 
 
 0.402 
 
 0.351 
 
 0.301 
 
 0.251 
 
 0.201 
 
 4.503. 
 
 .130 
 
 0.650 
 
 0.585 
 
 0.520 
 
 0.455 
 
 0.390 
 
 0.325 
 
 0.260 
 
 5.859. 
 
 .140- 
 
 0.830 
 
 0.747 
 
 0.664 
 
 0.581 
 
 0.498 
 
 0.415 
 
 0.332 
 
 7.545. 
 
 .150 
 
 1.051 
 
 0.946 
 
 0.841 
 
 0.736 
 
 0.631 
 
 0.626 
 
 0.421 
 
 9.628. 
 
 .160- 
 
 1.320 
 
 1.188 
 
 .056 
 
 0.924 
 
 0.792 
 
 0.660 
 
 0.528 
 
 10.850. 
 
 .165 
 
 1.476 
 
 1.328 
 
 .181 
 
 1.033 
 
 0.886 
 
 0.738 
 
 0.590 
 
 12.180. 
 
 .170 
 
 1.644 
 
 1.480 
 
 .315 
 
 1.161 
 
 0.986 
 
 0.822 
 
 0.658 
 
 ;.; |M 
 
 .17.-, 
 
 1.826 
 
 1.643 
 
 .461 
 
 1.278 
 
 1.096 
 
 0.913 
 
 0.730 
 
 15.270. 
 
 .180- 
 
 2.029 
 
 1.826 
 
 .623 
 
 1.420 
 
 1.217 
 
 1.015 
 
 0.812 
 
 17.060. 
 
 .185 
 
 2.250 
 
 2.025 
 
 800 
 
 1.576 
 
 1.350 
 
 1.125 
 
 0.900 
 
 19.000. 
 
 .190 
 
 2.486 
 
 2.237 
 
 1.989 
 
 1.740 
 
 1.492 
 
 1.243 
 
 0.994 
 
 20.260. 
 
 . 1!.:, 
 
 2.631 
 
 2.368 
 
 2.105 
 
 1.842 
 
 1.579 
 
 1.316 
 
 1.052 
 
 23.460. 
 
 .200- 
 
 3.024 
 
 2.722 
 
 2.419 
 
 2.117 
 
 1.814 
 
 1.512 
 
 1.209 
 
 shall continue to use the term "moisture absorbed by the air," 
 rather than "moisture in space." 
 
 Effect of Lamination on Drying. 
 
 Lamination, as we know, is due to the slipping of the clay 
 on itself, forming planes or "slickensides" in the clay mass. 
 
 We can hardly conceive a porous plastic mass being 
 slipped on itself without closing up the pores. Where such 
 closing up takes place the effect in drying is serious. 
 
 We have said that safe drying can only take place when 
 the water in the mass is brought to the surface as fast as 
 evaporation on the surface takes place. 
 
 Now if the clay mass is made up of a series of plates 
 as would be the case when laminated, the passages for the 
 water are broken and closed along the planes of the lamina-
 
 DRYING CLAY WARES 
 
 tions In order to dry such masses safely, the rate of evap- 
 oration should only be the same as the rate of the passage 
 of the water across the laminated planes. Suppose the evap- 
 oration rate should he faster than this, let us say at a rate 
 which would be safe if the clay were not laminated, the wate 
 in the outer shell is drawn to the surface at a faster rate 
 than the water can get into this shell from the inner core. 
 The outer shell becomes leather hard and finally bone 
 dry In becoming so, it must shrink or crack, and it naturally 
 cracks The tendency to shrink and the cracking causes the 
 shell to creep more or less on the core and breaks whatever 
 bond there may have been. 
 
 The air enters the cracks and begins work upon the sec- 
 ond shell and the result is duplicated and a second ring or 
 shell is dried, cracked and loosened from the core. The final 
 dried mass is a series of cracked and loosened concentric 
 shells, or, as we say, badly shattered. In order to make such 
 a clay safe drying, or to get a solid product from it, the first 
 step is to overcome lamination. 
 
 Grog. 
 
 Lamination is often discussed and \ve will not enter into 
 it except as it relates to drying. 
 
 The usual remedies for lamination are lubrication, grog, 
 lamination bars, etc. Grog plays quite a part in drying as 
 well as in lamination. It reduces lamination si,mply because 
 of its granular character. It acts as a binder, as a lot of 
 teeth, as a drag to prevent the clay slipping on itself. To 
 serve this purpose it must be relatively coarse and angular. 
 Its effect on drying is first to increase the pore space so the 
 water will flow faster to the surface; second, to reduce shrink- 
 age, thus reducing the degree of strains; third, it increases 
 the strength of the clay because of its binding action and en- 
 ables the clay to withstand the strains. The coarser and more 
 angular the grog, the better it serves as a binder, and the 
 larger the pore spaces. 
 
 Sand, which is most commonly used as a grog because it is 
 most available, is far from the best material. It is deposited 
 from the water, and in consequence it is made up of rounded 
 instead of angular grains, through the rolling and tumbling 
 it gets from its source to the final deposit. The density and 
 smoothness of the surface of the grains do not permit the 
 plastic clay to cling as closely to it as to a rougher and more
 
 DRYING CLAY WARES 21 
 
 porous material. Finally in the burning there can be no bond 
 between the clay and the sand except at high tejnperature, 
 but this does not concern us in the drying problem. 
 
 Crushed quartz or quartzite is a better material than 
 sand because of its angular character, but this is available 
 in very few yards. 
 
 The best grog is crushed burned clay, and often there is 
 enough waste about the plant to make sufficient grog. An- 
 other good material is crushed clinkers from the kiln and 
 boiler furnaces, but it can only be used in common wares. 
 
 Such materials have the advantage of being rough and 
 angular, and in drying have the further advantage of being 
 porous. If we have lamination planes bound together with 
 a lot of porous grog, the water can get across through the 
 binding material if it cannot find its way through the inter- 
 stitial spaces. 
 
 The porous grog, because of its pores acting as a lot of 
 suckers, draws the plastic clay into close contact and forms a 
 much better bond than could exist between clay and sand. 
 
 Where sand suffices nothing further need be said, but 
 where sand fails, as it often does, it is well to know that 
 there is a much better material. 
 
 Preheating Clay. 
 
 Prof. A. V. Bleininger deserves great credit for his work 
 on preheating clays as a means of overcoming drying trou- 
 bles. Preheating a clay .makes it more porous and permits 
 the moisture to escape to the surface. 
 
 The peculiar condition of many clays which makes them 
 difficult to dry is the subject of much study and discussion 
 at the present time and brings us to the borderland of our 
 knowledge. The colloid theory is now generally accepted by 
 clay technicists. Briefly, we assume that the clay contains 
 a great number of cells or sacs which absorb water through 
 their walls, swell and close up the interstitial pore spaces. 
 This puts a stop to any flow of water to the surface, and 
 when the surface dries, it must crack to relieve the strain. 
 The air gets into the cracks and continues the drying pro- 
 cess which at the same time deepens the cracks. The drying 
 cracks in a colloidal clay are irregularly hexagonal in shape 
 and are characteristic. 
 
 The preheating bursts the sacs and sets free the in- 
 cluded water, driving it off, and at the same time so destroys
 
 DRYING CLAY WARES 
 
 the structure of the sac that it cannot take up water and hold 
 it except by surface tension which applies in any case, nor 
 can the colloids now swell and close up the pores in the clay 
 
 Clayworkers have been slow to take up preheating, and 
 there may arise a number of practical difficulties. 
 
 The temperature must be carried considerably above the 
 drying degree, and it remains to be proven whether we have 
 a practical preheating range, otherwise it becomes of ques- 
 tionable value. Clays differ in the degree of preheating re- 
 quired, and the variation ranges from 250 degrees C. (450 
 degrees F.) to 450 degrees C. (810 degrees F.). Suppose 
 a clay is not sufficiently heated at 500 degrees Fahrenheit 
 and tco much plasticity is lost at 600 degrees Fahrenheit, 
 then we must keep within this range, else we will get some 
 cracked ware in drying on one extreme and some loss 
 through weak bonding on the other extreme. Therein lies the 
 uncertainty of preheating the range may be less than we 
 can work within. 
 
 In testing one material, we found that the addition 
 of burned clay grog to the raw clay served the same purpose 
 as preheating, and, if it applies in all cases, will greatly sim- 
 plify the problem. 
 
 It is analogous to the trouble with the Bessemer con- 
 verter in making steel. Originally, it was intended to stop 
 the process when the impurities in the metal had been 
 burned out to a required degree, but it was impossible to 
 stop at the right point, and successive blows differed widely 
 in the character of the .metal. The process became success- 
 ful when the everburning was resorted to and the over- 
 burned metal corrected by the addition of a reducing element 
 which could be added in definite proportions. 
 
 We may not be able to preheat clay to the proper de- 
 gree of uniformity, but if grog will serve the same purpose, 
 we can add it in any determined amount. We think that 
 the part that burned clay grog plays is not only that of 
 opening up the structure mechanically, but, by the absorp- 
 tive power of its pores, it will draw the water from the col- 
 loids, and collapse the cells which clog the pores of the mass.
 
 DRYING CLAY WARES 23 
 
 CHAPTER IV. 
 Shrinkage. 
 
 BEFORE TAKING up a description and discussion of 
 dryers, we wish to consider the question of shrinkage. 
 \Vhy do wet clays shrink? It seems almost a foolish 
 question, but if we could properly answer it we would un- 
 derstand the cause of our drying trouble and perhaps more 
 easily eliminate it. 
 
 What is shrinkage? The answer is easy. It is a drawing 
 together of the particles of clay toward a common center, 
 each particle pulling the next beyond. When the chain of 
 particles is too long, it breaks, causing a crack in the ware. 
 Every break establishes a new center with a shorter chain of 
 particles and we have safe drying only when the mass around 
 each center is proportionate to the forces pulling the particles 
 together. 
 
 There are several forces at work though they all may be 
 grouped under the head of gravitation. It is the attraction of 
 one jnolecule for another in the same material (cohesion), of 
 a molecule in one material for a molecule in a different ma- 
 terial (adhesion), of differential cohesion (surface tension), of 
 adhesion in minute passages (capillarity), that cause a clay 
 to shrink. 
 
 The surface of a liquid is stronger and more difficult to 
 rupture than within the liquid. It is, as it were, an elastic 
 skin or coating, which will support bodies that will not float 
 once the surface is broken and the body submerged. A 
 needle may be floated on water, but sinks immediately when 
 submerged. This surface force, or skin to retain the sUnile, 
 is called surface tension. In any liquid each molecule attracts 
 all surrounding molecules. It is pulling and being pulled in 
 every direction and may be said to be in equilibrium. Being 
 balanced, little force is required to start it in motion. At the 
 surface, however, there are no .molecules above, and in con- 
 sequence the surface molecules are not balanced. They are 
 held down by the attraction between them and the molecules
 
 24 DRYING CLAY WARES 
 
 below, and it requires more force to move them than the sub- 
 merged molecules. Thus we explain surface tension. 
 
 Citing again the floating needle, it remains on the surface 
 because the only forces acting are terrestrial gravity pulling 
 the needle down and surface tension resisting this pull. The 
 water is depressed under the needle, and there is a stretching 
 apart of the surface molecules, but not beyond the limit of 
 elasticity, or more properly, not sufficient to overcome the 
 forces of surface tension. 
 
 Iron is nearly eight times as heavy as water, and it is evi- 
 dent that surface tension which supports such a weight is a 
 force worthy of consideration. The needle must be oiled or 
 waxed to make it float. There must be no adhesion, because 
 if the water can stick to the needle it will immediately begin 
 to climb by capillarity, and we have this force added to grav- 
 ity to pull the needle down. 
 
 Capillarity is a much greater force than gravity. Witness 
 the sap rising in the trees to heights of three hundred feet or 
 more (sequoia trees) directly or indirectly by the force of 
 capillarity acting against gravity and overcoming friction. 
 Here we have a force of ten atmospheres, with apparently no 
 decrease in the acting force. Again if a porous body is 
 placed in a closed vessel and submerged in water, capillarity 
 will take up the water and drive out the air from the body 
 to develop in the vessel a pressure of four to five atmos- 
 pheres. 
 
 Who knows the power of capillarity? 
 
 Of course, capillarity is merely an application of adhesion, 
 and the latter is a force inestimable. Government tests show 
 that nearly 50 per cent, of the water in a clay is retained 
 against a force three thousand times the force of gravity. 
 
 We do not appreciate the power of these forces in connec- 
 tion with time. 
 
 We can tear a mass of wet clay apart with our hands, but 
 no mechanical power can pull the water loose from the clay 
 grains. We may tear the .mass apart, but how much power 
 will be required to compress the mass to the degree of natural 
 shrinkage? But. you will say. the mass is full of water and 
 water cannot be appreciably compressed. True, but if there 
 were no clay, the water would run out the smallest orifice 
 by the force of gravity alone. In a mixture of water and wax 
 >r water and mercury, or any mixture in which there is no 
 adhesion and consequently no capillarity, we could easily
 
 DRYING CLAY WARES 25 
 
 squeeze out the water; but in clay it is impossible, except in 
 small degree. 
 
 Adhesion, cohesion, capillarity and surface tension these 
 are the forces that cause shrinkage, and if we give them the 
 proper assistance they will do their work faithfully. The 
 trouble is that we ask too much of them. We set one force 
 against another, and in the equilibrium which follows our ware 
 ruptures. 
 
 Let us consider a clay body. In a slip prepared for dipping 
 or casting the clay grains are in suspension in the water. The 
 larger or coarser particles settle quickly, but the finer grains 
 may float for days. Here we have widely separated grains of 
 clay in a water matrix. They are moving about, but hardly 
 can come in contact. As two particles approach, the si>ace 
 between decreases, capillarity increases, and a current of 
 water is drawn up between them driving them apart. If two 
 plates of glass are placed on edge in a shallow vessel of water 
 and held like a slightly opened book, it will be noticed that the 
 water will rise highest at the hinge or back edge and will drop 
 in a curve to the natural water level toward the open edges. 
 Closing the angle sends the curve upward, opening causes it 
 to drop. Similarly when grains of floating clay approach or 
 fall apart, the currents set in motion counteract the move- 
 .ment. 
 
 A bed of quicksand looks solid, but the grains are quies- 
 cently afloat in water. Puddle the bed in the slightest degree, 
 and we set the grains of sand in motion in their watery beds. 
 A beach sand, on the contrary, is solid, and one may follow 
 the waves out, scarcely leaving a footprint on the wet sand. 
 The difference is due to size of grain and surface area. We 
 may float a needle on water, but not an iron shot, though 
 they have the same weight. 
 
 In clays we have a large percentage of very fine material 
 (some authorities hold that plasticity is due to fineness of 
 grain, and the flotation of these grains gives the mass its mo- 
 bility). This fine material, vibrating back and forth through 
 the varying capillary currents, will materially aid in keeping 
 the coarser material afloat. 
 
 If we could greatly magnify a drop of slip we would ob- 
 serve a condition something like sketch No. 1. On the surface 
 we would have the wavy conditions as shown. The grains of 
 clay, being heavier than water, do not float, but are held sus- 
 pended at the surface by adhesion of the water to the grain
 
 DRYING CLAY WARES 
 
 surfaces and surface tension of the water. Should two parti- 
 cles approach each other, as at "A," a capillary current is set 
 up between them, the tendency of which is to carry the col- 
 umn of water to a higher elevation, and the pressure thus de- 
 veloped forces the particles apart. Thus No. 1 particle will be 
 driven toward No. 2. Momentum carries it beyond the point 
 of equilibrium and back it goes toward No. 3. 
 
 If we let the slip settle, equilibrium will finally be reached, 
 
 SUP6rnatant water we still find our clay 
 Let us take some of the material and dry it In the firt 
 N"? ^ T &S Sh Wn in No * sketcl ^^ differ- 
 sketch N TJ 11 that the gminS are closer to^er. 
 
 ^^^ 
 are drawn together by surface tension they exert
 
 DRYING CLAY WARES 
 
 27 
 
 a compresive force on the mass below, squeezing together and 
 forcing the water outward. 
 
 In sketch No. 4 we are approaching the final stage. The 
 water is constantly being drawn to the surface and evaporated 
 
 Figure 5. 
 
 and the water in the pores is being drained just as if a wick 
 had been inserted into each pore. The end is reached in 
 sketch No. 5, where all the pores are drained, and there only 
 remains to be removed the water clinging to the surface of 
 the grains.
 
 DRYING CLAY WARES 
 
 This is removed by the air entering the pores and the 
 evaporation takes place from the surfaces of the grains. Even 
 then the drying is not complete. The clay particles cling 
 tenaciously to the water and the last traces of the latter can 
 only be removed by temperatures above the boiling point, but 
 this is done in the kiln and does not concern us in the drying. 
 
 We have illustrated the grains as uniform in size and 
 shape, but in reality they are widely varied, as illustrated in 
 sketch No. 6. As compression takes place the angular grains 
 arrange themselves into greater compactness and the finer 
 grains are forced into the interstices between the larger 
 grains. 
 
 The bond or strength of the dried ware depends upon the 
 
 Figure 6. 
 
 surface area in contact and the forces of adhesion and co- 
 hesion. A lot of marbles, or shot, or rounded grains or washed 
 sand will have little or no bound. There is too little surface 
 in contact. Crush the marbles and mix with them a quantity 
 of infinitesimally fine materials and we will get a bond. Add 
 to this some soluble salt which as evaporation of the water 
 proceeds will crystallize and interlace the mass with its crys- 
 tals and we get a still stronger bond. 
 
 We think of gummy clays which are so difficult to dry as 
 being chemically different from other clays, but the difference 
 is largely a physical one. and by some excellent authorities 
 is considered simply a difference of fineness of grain. The 
 fine grains necessarily involve small pore spaces and the 
 water travels very slowly from the center to the surface of
 
 DRYING CLAY WARES 
 
 19 
 
 the mass and in consequence is troublesome to dry. Others 
 hold that these gummy clays and in fact plasticity in all 
 clays are due to cells or sacs enclosing water and the cells 
 must burst to allow the water to escape and also to provide 
 passageway to the surface of the mass, since the sacs not 
 only hold the water back, but pack the pore spaces through 
 which the water must escape. These amorphous sacs, glue 
 like in their character (colloidal), as drying proceeds coat 
 the larger grains and cement them together. When colloids 
 are abundant (gummy clays) drying is difficult, but the dried 
 ware is very hard. As colloids (colloidal condition) de- 
 crease drying is safest with corresponding falling off in the 
 strength of the dried ware. 
 
 Figure 7. 
 
 After all, these colloidal sacs are built up of molecules 
 and held together by cohesion, and so far as we are con- 
 cerned, fineness of grain, in connection with angularity, 
 soluble salts, cohesive and adhesive forces, suffice to explain 
 the difference in the bond of dry clay ware. 
 
 Why do clay ware crack in drying? Suppose we illustrated 
 in sketch No. 7, that the rate of evaporation is greater at the 
 surface than the rate at which the water is brought to the 
 surface by capillarity. The air will follow the surface of the 
 water into the brick as at "A." The surface particles can 
 only draw together as the entire mass shrinks, and the mass 
 can only shrink as the water is driven out. Consequently
 
 DRYING CLAY WARES 
 
 there is a rupture between the surface grains. The crack 
 started at "A" will go deeper and deeper into the ware as 
 drying proceeds, and will only cease when sufficient pores 
 have been opened by the crack to supply the rate of evapora- 
 tion. 
 
 The cracks in such instances are irregularly hexagonal in 
 shape (see sketch No. 8) and the size of the separate masses 
 depends upon the difference in the rate of evaporation from 
 the surface and the rate of the progress of the water to the 
 surface. 
 
 Many wares, such as bricks, tiles, fire clay blocks, etc., of 
 simple rectangular shape, develop straight cracks across the 
 narrow face, which extend into and across the ware. Such 
 cracks are due to the load being in excess of the forces. As 
 
 Figure 8. 
 
 noted the particles, one acting on another, are all being pulled 
 toward the center of the mass. When the load becomes 
 greater than the strength of the chain, a break occurs, and 
 the load is divided into two sections, or three, or a dozen, as 
 the case may be. 
 
 Time is an important factor. If we tie a string to a load, 
 and give it a quick jerk, we break the string, but if we pull 
 gradually we may move the load. Similarly in drying if we 
 give the acting forces time, we can safely dry any ware 
 
 Irregular shaped ware develops cracks in the weakest 
 Points, due to the shrinkage forces acting in opposite direc- 
 tions. For example, sketch 9 shows a shape that would be 
 ifficult to dry. The forces pulling the two halves together 
 are greatly reduced in the neck with a heavy load on each
 
 DRYING CLAY WARES 
 
 side to be moved toward the center. An "L" shaped piece 
 will crack in the angle because each leg is pulling toward 
 its center and away from the angle. 
 
 Many cracks which develop in drying are due to faulty 
 structure. Lamination, for instance (sketch 10), which has 
 been previously discussed, is really a core within a shell. The 
 structural fault between the two causes a break in the flow 
 of water from center to surface and cracking occurs. 
 
 Figure 10. 
 
 Hollow ware often develops straight cracks the length of 
 the ware, due to weak structure. The cracks may occur in 
 the corner where we have the effect of the "L" shaped ware 
 cited above, and in such cases the trouble is not necessarily 
 due to faulty structure. 
 
 When, however, the longitudinal cracks are in the sides 
 of rectangular ware, and also in circular tile, the trouble is
 
 DRYING CLAY WARES 
 
 generally due to structure. The core bridge splits the ware 
 and while the split is closed up in coming from the die, yet 
 not to have the strength of the other parts of the ware. It is 
 the same condition as sketch 9 the weak neck is present but 
 not visible in the ware as it comes from the die. 
 
 This structural weakness has been experienced in changing 
 frqm one product to another. 
 
 Many manufacturers who have installed new dryers dis- 
 credit the dryer because it will not dry in the time specified. 
 When told to increase the heat or circulation they say it 
 cracks the ware. What they wanted was a dryer that would 
 do the work in a specified time without cracking the ware. 
 The trouble is in the clay, in the shape of the ware, or in 
 some structural weakness rather than in the dryer. 
 
 We have discussed methods of overcoming structural weak- 
 ness, and also methods of improving the drying qualities of 
 a clay, and will not go into that here. 
 
 A few words about drying mediums other than air, and we 
 will close. As seen from the table previously published, the 
 capacity of air for moisture increases very rapidly with ad- 
 vancing temperatures. We can not safely increase the tem- 
 perature in a tender drying clay, because we soon reach a 
 point where the surface evaporation is greater than the in- 
 ternal movement of the water. Suppose, now, that we intro- 
 duce moisture to vapor pressure or saturation. We may then 
 advance the temperature to any degree without harm to the 
 ware. Many tender drying clays become safe drying under 
 this treatment. There can be no cracking, since no drying 
 can take place, and in consequence no shrinkage can occur 
 so long as the vapor pressure is maintained. Meanwhile the 
 heating up of the ware sets the water in motion and pore 
 spaces are cleared for the subsequent escape of the water to 
 the surface when drying begins. Moreover, the grains of 
 clay are being softened and put in condition to adjust them- 
 selves more readily to drying strains. We have only to ad- 
 just the degree of pressure of vapor to correspond with the 
 rate of flow of water to the surface of the ware to insure safe 
 drying. 
 
 This humidity treatment to insure safe drying has been 
 extensively used in terra cotta work and has been applied to 
 common wares with gratifying results in a number of in- 
 stances.
 
 DRYING CLAY WARES 
 
 CHAPTER V. 
 Air Drying. 
 
 AIR DRYING of clay wares is both ancient and modern. 
 The oldest cities of the world, now merely mounds in 
 the plain they once adorned, even the names of which 
 are questions of historical dispute, were built of air-dried 
 bricks, and the .modern city of New York is likewise largely 
 built of the same product. 
 
 By air drying is meant drying without the expenditure of 
 heat except such heat as is naturally in the air, or such as 
 may be derived from radiation from burning and cooling kilns. 
 There are many adaptations of air drying. 
 
 Open Yard Drying of Soft Mud Bricks. 
 
 The original and at the same time the simplest, is to lay 
 the ware on the ground exposed to wind, sun and rain. It is 
 limited to soft mud bricks, and there are many clays which 
 will not stand such severe drying test. It seems strange that 
 in the New England States, New York and New Jersey, where 
 weather conditions are least favorable, we should find the 
 largest and greatest number of open yards, while in the south 
 and west where conditions are extremely favorable, open yards 
 are the exception. Perhaps the clay has much to do with it. 
 Direct exposure of a green piece of ware to the sun's rays is 
 a very trying test, and open yard work is only possible where 
 the clays will come through the ordeal safely. 
 
 The Hudson river district is the jnost notable instance of 
 open yards. For many years open yards only were to be found 
 in this district, but recently the artificial dryers are coming 
 into use. 
 
 The arrangement of open yards is much alike. See Fig. 11. 
 The soft mud machines are widely separatedj and each has its 
 clay mixing rig, thus making a complete plant of each ma- 
 chine. In front of the machine is a broad, practically level
 
 34 
 
 DRYING CLAY WARES 
 
 space, sufficiently large to hold the daily output of the ma- 
 chine with space for hacking. 
 
 Usually the work begins very early in the morning and the 
 daily task is on the yard before noon, oftentimes by 8 or 9 
 o'clock in the forenoon. 
 
 The molds of bricks from the machine are placed on truck: 
 and run to the yard, and are there dumped on the ground, thus 
 covering the ground' with bricks laid flat and spaced the thick- 
 ness of the sides and divisions of the mold. The early start 
 
 , a , ^ 
 
 I \Mach<ne I \M&chinc \ \J 
 
 l~rV U^- U : 
 
 J h 
 
 Figure 11. 
 
 is necessary in order to gel the bricks dried before night. As 
 soon as the bricks are stiffened so they will hold their shape 
 they are edged up with a wooden tool called an edger. See 
 Fig. 12. The divisions of the edger correspond to the divisions 
 in the mold. The edger is placed over six bricks, and by a 
 dexterous twist the six bricks are turned on their edges. 
 
 The bricks on edge dry until later in the day, and are then 
 hacked up in long hacks across the yard from machine to kiln. 
 
 The advantage of open-yard drying is in initial cost of in- 
 stallation and in that no fuel is required. The disadvantages
 
 DRYING CLAY WARES 
 
 35 
 
 are, short operating season with lessened capacity on account 
 of bad weather, and increased labor cost. 
 
 An open yard ware is limited to common bricks, the de- 
 mand for which is light during the winter season, especially 
 in the north, and the summer operation is not a serious handi- 
 cap, since the initial cost of the plant is not large compared 
 with a modern plant of equal capacity, and the overhead cost 
 is correspondingly low. The yards are built in several units 
 and a yard of 50,000 brick capacity may have machine and 
 drying capacity for 100,000 brick. 
 
 During the busy season the output may be pushed above 
 the normal capacity. Usually one or more .machines are idle 
 all the time in order to keep down the labor cost. For in- 
 stance, in Fig. 11, machines 1 and 2 will be operated when 
 setting to the left of the center of the kiln shed and machines 
 
 
 
 
 / 
 
 JJ 
 
 V si 
 
 Figure 12. 
 
 2 and 3 when setting to the right. This gives minimum wheel- 
 ing distance from the hacks to the kiln. 
 
 It can be shown that the cost of putting the bricks on the 
 yard, edging and hacking, on the basis of $2 labor will not ex- 
 ceed 25 cents per thousand. It is also evident that the cost 
 of getting the bricks from hacks to kilns in view of the mini- 
 mum distance ought not be greater than from a mechanical 
 dryer however centrally located it may be. 
 
 The fuel cost in an artificial dryer may exceed the total 
 cost of labor incident to drying on an open yard and in the 
 t most economical operation will equal one-half the open yard 
 labor cost. 
 
 An artificial dryer, however, does not eliminate labor cost 
 entirely, but does reduce it. We are safe in saying that the 
 labor cost will not be less than one-half the cost on an open 
 yard. The labor putting the bricks into the dryer, taking them 
 out, handling pallets, making repairs, etc., will on many plants
 
 DRYING CLAY WARES 
 
 equal the cost on open yard. Then the cost of equipment 
 must be considered tunnels, fans, heaters, piping, racks, cars, 
 tracks, pallets and the total cost of artificial drying will ex- 
 ceed that of natural drying. 
 
 The great advantage of the artificial drying is that the man- 
 ufacturer is independent of weather conditions and may keep 
 the plant in continuous operation throughout the season, or 
 throughout the year if desired. The work may start early in 
 the season and the early product catches the early market 
 when left-over stocks are exhausted, and the late fall operation 
 insures a stock to last until the new product comes in. Thus 
 the artificial drying increases the yearly output and reduces 
 the overhead cost per thousand to more than offset any in- 
 crease in the actual cost of drying. 
 
 It will generally be found that artificial drying costs more 
 than natural drying, but we hold that in the majority of in- 
 stances the net advantage will be in favor of the artificial 
 operation. 
 
 Stiff Mud Bricks in Open Yards. 
 
 The open yard drying is occasionally used for stiff mud 
 bricks. The bricks from the machine are placed on foot pal- 
 lets 60 to 80 bricks and these are carried to the drying yard 
 by lifting trucks and set in rows. 
 
 They are covered with boards as occasion jnay require to 
 protect them from the direct rays of the sun or from rain. 
 When dry they are picked up by the lifting trucks, taken to 
 the kiln and the pallets returned to the machine. 
 
 The pallets and covers are the only equipment over the 
 soft mud open yard and there is an advantage in that the 
 bricks are handled in larger units. All that has been said rel- 
 ative to the soft mud open yard applies to the stiff mud, with 
 the exception that the bricks originate at one place, and in 
 drying must be left on the yard several days to one week. The 
 ground area required for each day is much smaller than for 
 soft mud, since the bricks are hacked on edge eight to ten 
 courses high. 
 
 Rack and Pallet Yard. 
 
 By far the larger number of summer common brick yards 
 use the rack and pallet system. This is necessary because the 
 clay will not stand the severe test of the open yard work. 
 
 Long sheds, cqmmonly called "racks," are built as shown 
 in Fig. 13. 
 
 The uprights are spaced the length of the pallets, each pal- 
 let holding one mold, 6 or 7 bricks. To the uprights are nailed
 
 DRYING CLAY WARES 
 
 ft un Plan*
 
 DRYING CLAY WARES 
 
 horizontal cleats spaced vertically the width of the bricks 
 plus the thickness of the pallet plus clearance. The length of 
 the cleats is sufficient to hold four pallets-two on each side 
 
 The racks are roofed over as shown in Fig. 13, and the 
 space between is covered by hinged doors which may be 
 opened or closed as .weather conditions demand. The racks 
 are built ten cleats in height and each section holds forty 
 pallets, or 240 bricks. The pallets are about 35 inches long, 
 making the section over three feet on centers. A rack 100 
 feet long will have 32 to 33 sections and will hold 7,920 brick. 
 Seven racks are required for a day's run of 50,000 brick, or 42 
 racks for the week's run. 
 
 Figure 14. 
 
 As the racks are spaced 7 feet on centers, the total space 
 required is 29,400 square feet something over half an acre. 
 
 The above described racks (Fig. 13) are extensively used 
 in this country in air drying soft mud bricks, but in foreign 
 countries where labor is cheaper other types of buildings are 
 used. For instance, three or more racks may be put under one 
 roof, but the advantage in quick and uniform drying is with 
 the single rack. 
 
 In Germany large sheds are often used with the racks 
 across the shed (See Figs. 14 and 15), and space is provided 
 for storing the dried or partially dried bricks until kiln space 
 is available. This involves extra handling, but it saves space, 
 and what is more important, it insures a supply of bricks at
 
 DRYING CLAY WARES 39 
 
 all times for the kilns a consideration not to be overlooked 
 where the burning is done in continuous kilns. 
 
 In German practice continuous kilns are more commonly 
 used for caramon bricks than in this country, and to keep the 
 kiln in operation it is necessary that there be a supply of dry 
 bricks, regardless of weather conditions, which requires not 
 only excessive drying space, but space must be provided to 
 store dry bricks in order to take advantage of good drying 
 weather and tide over periods of bad weather. The atmos- 
 pheric conditions in Germany are also less favorable for air 
 drying than in this country, which accounts for the more per- 
 manent structures used in that country. 
 
 
 Figure 15. 
 
 The German bricks are nearly five inches wide and ten 
 inches long (2\/ 2 centimeters by 25 centimeters). Their racks 
 are usually built to hold only two pallets, one on each side, 
 while ours hold four. They also use higher racks than we, 
 which requires that the workmen stand on benches in filling 
 the upper racks. 
 
 In order to economize space, the German sheds are often 
 built two stories high which is never done in this country. 
 
 Because of the unfavorable atmospheric conditions, and in 
 order to protect the ware from early and late frosts, thereby 
 getting a longer drying season, the Germans have largely 
 adopted the method of constructing the drying sheds over the 
 continuous kilns, thus taking advantage of the radiated and
 
 40 DRYING CLAY W T ARES 
 
 waste heat from the continuous kilns. This will be fully de- 
 scribed in a following article. We are beginning to adopt this 
 method in this country, and it is likely that with the adoption 
 of the continuous kiln for conynon bricks this method of dry- 
 ing will largely replace the open yard or yard rack work. Now 
 
 Figure 16. 
 
 we used scove kilns which are independent of drying con- 
 
 k n to st d^ bUUd S6Veral arCheS in ne day or allow the 
 m?y req uir n e " ^^ P6ri d ' as the maki ^ -d drying 
 
 Returning to the subject of racks-at the machine the
 
 DRYING CLAY WARES 
 
 41 
 
 bricks are dumped on flat pallets, usually on a turn- 
 table, and the loaded pallets are trucked to the racks and 
 placed on the cleats. As soon as the bricks are hardened so 
 they will stand handling, they are edged up by hand. When 
 the bricks are dry they are removed from the pallets to bar- 
 rows and wheeled to the kiln. 
 
 The time of drying varies from two to three days up to 
 ten days, depending upon the weather. 
 
 Compared with the open yard work, there is a slight ad- 
 vantage in labor in favor of it over the rack system, -but this 
 is more than offset by the less loss in the rack on account of 
 
 Figure 18. 
 
 the protection from inclement weather. The latest develop- 
 ment in the rack system is to use rope conveyors from the 
 .machine along the front of the racks with cross conveyors 
 down each aisle. 
 
 Air Drying Stiff Mud Bricks. 
 
 In place of the movable covers for stiff mud bricks on open 
 yards we occasionally find a shed with a swinging roof as 
 shown in Fig. 16. Such a shed economizes the labor in han- 
 dling the covers. 
 
 A more permanent structure, however, is usually built for 
 stiff mud bricks. The shed structure, a section of which is 
 shown in Fig. 17 and Fig. 18, covers all the drying ground and
 
 DRYING CLAY WARES 
 
 is a permanent structure. Runners about four inches to six 
 inches high are placed through the shed spaced to receive the 
 pallets and to serve as guides for the two-wheeled lifting 
 trucks. Eighty to one hundred bricks are placed on pallets 
 at the machine and run to the drying shed, and when dry are 
 removed to the kiln. The same method is followed in handling 
 larger units with lifting cars, only the pallet supports (stanch- 
 ions) are higher. 
 
 In the latter case several stanchions on turntables are 
 placed along the take-off belt. The empty pallets are placed 
 on the stanchions and as soon as one side is filled the table 
 is turned 180 degrees, bringing the empty side to the belt. 
 When the pallet is full 400 to 500 bricks the lifting car is 
 
 Figure 19. 
 
 run on the turntable under the load and the latter is picked up 
 and carried to the dryer, and thence, when dry, to the kilns. 
 
 The chief advantage is that the bricks are handled in units 
 of 400 to 500 bricks, and we have the economy of handling 
 which comes from these larger units. 
 
 Occasionally steam pipes are installed under the racks to 
 hasten the drying but more particularly to protect the green 
 bricks fro,m frost in early spring and late fall months. 
 
 It is not uncommon practice to keep off frosts by the use 
 of smudge fires, and the large sheds used in Germany are 
 better adapted to this than our open racks. It is well known 
 that pure air absorbs little or no radiated heat either from 
 the sun or from the earth. Air is heated by conduction in
 
 DRYING CLAY WARES 43 
 
 contact with the earth and is distributed by convection (circu- 
 lation or mass movement). Particles of dust in the air, how- 
 ever, can be heated by radiation and in turn give up their 
 heat to the air by conduction. 
 
 By surrounding the bricks with smoke particles, if we may 
 so express it, we collect the radiant heat from the earth and 
 from objects on the earth and retain it as a blanket protec- 
 ing the bricks. 
 
 Drain Tile Sheds. 
 
 Sheds for drain tile for natural drying are built more sub- 
 stantially than brick racks. A common type is a shed about 
 fourteen feet wide with racks. The racks are on either side 
 with a passage way through the center of the shed. 
 
 The pallets to hold the tile are four to five feet long and 
 are placed in the racks, just as brick pallets are racked. The 
 tile, however, are trucked to the shed and placed on the pal- 
 lets in place. As each pallet is filled, the next pallet is placed, 
 and so on until the rack is full. Fig. 19 shows a section of a 
 drain tile shed. ' 
 
 There are many modifications of tile sheds often same old 
 building being adapted. 
 
 Very little can be said in favor of natural drying for drain 
 tile. The best market is in the late fall, winter and early 
 spring and a tile plant equipped for natural drying only is 
 badly handicapped. A good combination for a small yard is 
 open yard drying for bricks during the summer, when the de- 
 mand for bricks is greatest, and an artificial dryer for tile 
 during the winter. Many tile makers have found the need of 
 artificial drying and have added to the sheds some system of 
 heating. Sometimes steam pipes are placed along the floor 
 under the racks, and we have seen tunnels or flues of sewer 
 pipe built under the racks and heated from a furnace at one 
 end of each tunnel, with draft stack at the other end, or, if 
 the shed be long, the stack is placed midway, with a furnace 
 at each end of the tunnel. 
 
 Such methods of heating are makeshifts and very crude. 
 They art not to be recommended in a new construction and 
 will not be considered in connection with artificial drying.
 
 44 DRYING CLAY WARES 
 
 CHAPTER VI. 
 
 The Drying Above Continuous Kilns. 
 
 y N DRYING ABOVE a continuous kiln, as it is done quite 
 generally in Germany, and to a limited extent in this 
 1 country, there are two main problems involved, viz: the 
 drying and the handling of the ware. 
 
 Prior to the introduction of the continuous kiln, drying 
 was almost exclusively done in sheds or in the open air by 
 sun and wind, but following the successful operation of the 
 Hoffman kiln it was quite natural and logical to go a step 
 farther in the economical performance of this kiln by utilizing 
 its radiated heat to assist the natural air in drying the ware. 
 
 The first dryers thus constructed did not use any other 
 heat source, but merely took advantage of the heat radiating 
 from the kiln and the bricks were stacked all around and 
 above it. 
 
 Such dryers, one, two and even three stories high can 
 still be found in Germany on a number of yards. 
 
 Theoretically, as will be seen later, there is nearly enough 
 heat from a continuous kiln to dry the ware to be burned in 
 the kiln, but practically so much of it is lost in the applica- 
 tion, in sufficiently heating and maintaining the temperature 
 of the air to carry the moisture taken up, in radiation loss 
 from the buildings, in heating the ware itself, etc., that it falls 
 far short of the requirement. 
 
 It has been shown that the radiation loss from a continu- 
 ous kiln is 32 per cent, of the fuel consumed in the burning. 
 If we assume that 200 pounds of coal per thousand bricks are 
 used in the burning, then we will have the value of 64 pounds 
 in radiated heat. On the basis of 12,000 B. T. U. per pound 
 of coal, we have 768,000 B. T. U. in radiated heat. If the 
 bricks (American size) contain one pound of water each,
 
 DRYING CLAY WARES 
 
 which requires 970 B. T. U. to evaporate, then the evapora- 
 tion of the water in 1,000 bricks will consume 970,000 B. T. U. 
 The available heat, if all of it could be used in drying alone, 
 will suffice to dry 800 bricks out of each 1,000 to be burned, 
 but we undoubtedly lose more than half of the heat from the 
 kiln. As the fuel required for burning increases, we have 
 corresponding increase in the available radiated heat, and it 
 may be possible in factories with high fuel consumption and 
 properly constructed buildings, together with the best appli- 
 cation of the heat, to dry the ware during the summer season 
 without auxiliary heat supply. 
 
 It has been demonstrated that in the majority of instances 
 
 Figure 20. 
 
 the radiated heat by no means suffices to dry as much ware 
 as the continuous kiln can burn, and it has been found that 
 factories depending entirely upon radiated heat cannot op- 
 erate during the winter. It is necessary, therefore, to have 
 additional drying facilities, either in outside sheds or by 
 means of other sources of heat than that radiated from the 
 kiln. 
 
 Fig. 20 shows a factory with outside sheds contiguous to 
 the kiln. Even with such outside sheds for additional drying, 
 on many yards the bricks are taken from the racks as soon 
 as practicable and are racked on the ground around the kiln, 
 and near to it, as seen in the illustration, where they may
 
 DRYING CLAY WARES 
 
 become fully dry. Thus advantage can be taken of favor- 
 able drying weather and a stock of dry bricks accumulated 
 to keep the kiln in full operation during bad weather. The 
 photograph is of a German brick plant of average size mak- 
 ing 12,000 to 15,000 (German size) bricks per day. 
 
 The outside drying racks hold about 130,000 bricks; 50,000 
 bricks are placed in racks around the kiln, level- with the top 
 of the kiln, and get the heat radiated from the kiln walls and 
 wickets, besides more or less circulation from the kiln top; 
 an additional 50,000 are placed in portable racks, forming 
 tunnels above the kiln, which will be described later. 
 
 The temperature above the kiln during the summer varies 
 from 20 degrees C. to 40 degrees C. (68 degrees F. to 104 de- 
 grees F.) and the time required for drying is from five to ten 
 days. 
 
 Figure 21. 
 
 In this plant we have 100,000 bricks dried by heat from 
 the kiln and 130,000 bricks dried in outside sheds, with stor- 
 age space in which to accumulate dry bricks during good 
 weather, yet the need of additional drying facilities is urgently 
 felt. 
 
 In such kiln dryers the air regulation is effected by open- 
 ing or closing the windows, according to the wind direction 
 It can readily be seen that the drying, besides being slow is 
 also quite irregular. Sometimes in order to distribute the 
 heat more uniformly a sheet metal lining with openings is 
 Placed below the drying floors and the results have often 
 >een bettered by doing so. Usually the floors under the ware 
 are slotted and only left solid in the aisles to compel the ris- 
 ng heat to pass through the ware before escaping through 
 the windows or louvres of the monitor above 
 
 5 updraft is slow and where condensation occurs under
 
 DRYING CLAY WARES 47 
 
 the roof there are placed a few steam pipes below the monitor 
 to heat up the air, prevent condensation and increase the 
 speed of the rising air. In such cases the main updraft will 
 naturally be directed towards the center and the drying of 
 the ware in the side racks will be neglected. One, or better, 
 two suction fans in the monitor are doubtless more effective. 
 With a stronger draft throughout which the fans will give, 
 it is possible to force the air to the side racks by closing 
 floor openings under the center racks. 
 
 In Fig. 21 we have a system devised and built by Cohrs 
 about thirty years ago. The drying racks are placed on both 
 sides level with the top of the kilns, thus relieving the kiln 
 walls of the dryer load. Vapor stacks are placed intermit- 
 tently betw-een the racks, being connected with ducts below 
 the ware. The heated air, coming from over the kiln, is 
 drawn down through the ware and escapes through bottom 
 openings into the under ducts, thence to the stacks. The dry- 
 ing space is confined to the kiln top level, and hence, if pos- 
 sible, the ware should be delivered from the machine on this 
 floor, so that, after drying, the ware only needs to be lowered. 
 
 Most of the modern kiln dryers make use of the exhaust 
 steam from the engine. There may be pipes under the floors 
 and the natural updraft system be used, or there may be used 
 steam heating coils in connection with a fan or a combina- 
 tion of a heating tank with a hot water system. 
 
 We must mention the fact, however, that European plants 
 do not have the amount of exhaust steam available in our 
 American plants. Their engines do not require over 10 
 pounds of steam per h.p. hour from one-half to one-fourth of 
 the consumption in this country and hence the heat derived 
 from this source is comparatively small. 
 
 Other kiln dryers make use of the heat from the cooling 
 chambers by means of a small fan. Many plants use both 
 exhaust steam and the heat from the cooling chambers. Any 
 heat taken from the kiln, however, is not gratis; it must be 
 replaced in some way and more fuel in the burning is the 
 result. 
 
 It furthermore is a fact that the so-called radiated heat is 
 not always to be considered as being gratis. Whenever an 
 artificial updraft above the kiln is created by fans or any 
 other means and the air taken from the top or surroundings 
 of the kiln, there is bound to be a fall of temperature of the 
 kiln walls and thus indirectly of the chambers and the heat 
 taken must be replaced by more fuel in the kiln. The actual
 
 48 
 
 DRYING CLAY WARES 
 
 Figure 22
 
 DRYING CLAY WARES 
 
 49 
 
 amount of radiated heat, therefore, which has no value in the 
 kiln operation and which is an absolute loss except as It may 
 be recovered in drying, is much less than is generally claimed, 
 but at the same time it may be turned into profits provided 
 its value is not more than offset by increased labor cost. 
 
 As regards the handling of the ware there are several 
 systems in vogue. Frequently a tray elevator is used for 
 getting the ware from the machine below to the upper drying 
 floors. This elevator is located close to the cutter, as we 
 can see from Fig. 22. One man takes off two or three bricks 
 at a time and places them upon the tray at hand. The loaded 
 trays go up and on their downward movement, after passing 
 the head sprockets, are unloaded. It is essential that empty- 
 
 Figure 23. 
 
 ing and filling the racks keep pace with the progress of the 
 fires in the kiln as far as possible in order that the bricks 
 in greatest need of heat shall be over the hottest part of the 
 kiln. Where the drying room has two floors a -man on the 
 upper floor unloads alternate trays, leaving the intermediate 
 trays for the man on the lower floor, thus the racks in both 
 floors are equally filled at the same time. 
 
 There are several ways of conveying the ware about the 
 drying floor, the most common perhaps being the car system, 
 of which there are several in use. We have a series of il- 
 lustrations before us of one such system, not necessarily un- 
 derstood to be the best. In Fig. 23 we see the upper part of 
 the tray elevator. The man in front of it is taking off the
 
 50 DRYING CLAY WARES 
 
 bricks and placing them in the frame to the left, which is 
 standing on two wooden blocks, or footings, on top of a turn- 
 table. The frame consists of seven shelves, each made up 
 of four narrow strips of wood, so that a brick is always rest- 
 ing on two strips. After one side is filled the turntable with 
 frame is swung around 180 degrees and the other side is 
 filled. 
 
 As soon as this is done a man pushes a car of special 
 design under the frame between the footings and, by lifting 
 a lever, catches the frame under the upper shelf on two pro- 
 jecting arms. In Fig. 24 we see the frame just being taken 
 off, while in Fig. 25 we have the car with its leverage to the 
 
 Figure 24. 
 
 rear and the two projecting arms to the front, ready to be 
 pushed under the frame. 
 
 The loaded car is moved to the transfer car and with it 
 
 is pushed along until opposite the space being filled. The car 
 
 run off the transfer, pushed into the space and, by lower- 
 
 ing the lever, the frame is set down on two projecting floor 
 
 earns. In Fig. 26 we see the man setting down the last 
 
 frame and thus filling the space or so-called tunnel 
 
 rowi ey are loaded n wheelbar- 
 
 rows and lowered on a double gravity elevator to the ground 
 
 main " h T *' ChambeFS f the kto " The fra * re- 
 main on the drying floors, and when empty are returned to
 
 DRYING CLAY WARES 
 
 51 
 
 Figure 25.
 
 52 
 
 DRYING CLAY WARES 
 
 the turntable. The location of the gravity elevator can be 
 seen in Fig. 20. 
 
 Instead of this system the frames may be filled in front of 
 the cutter on the ground floor, then the loaded frames are ele- 
 vated to the drying floor, where they are put into place by 
 lifting cars as described, or by similar cars of a better design, 
 and, after the bricks contained therein are dry, are taken 
 down on a gravity elevator. A better plan, which will be de- 
 scribed later, eliminates the portable frames, and the pallets 
 only are handled by the lifting cars. 
 
 Again, another way is to use a combination of tray ele- 
 vator and tray conveyor with the elimination of cars entirely. 
 
 Figure 26. 
 
 There are numerous arrangements adapted to special con- 
 ditions and to take advantage of different methods of handling 
 the bricks and distributing the heat. 
 
 Fig. 27 shows an underground continuous kiln with dryer 
 on the ground level on either side. The bricks are partially 
 dried in the racks around the kiln and are then stacked on 
 the cooling burned bricks for the final drying. They do not 
 need to be elevated; they are delivered by the machine to the 
 racks on the ground floor, thence removed to the kiln, and 
 later lowered into the kiln for burning. This scheme requires 
 a second handling in the drying. In Fig. 28 we have the same 
 kiln with a dryer building above.
 
 DRYING CLAY WARES 
 
 Fig. 29 illustrates a continuous kiln with three drying 
 floors above. It is evident that in this case the load of the 
 dryer upon the kiln walls and piers is rather excessive and 
 first quality masonry and good foundation work are essential. 
 
 Pig. 30 illustrates an arrangement first designed by Schaff 
 and later taken up and now built by Rudolf Witte of Osna- 
 briick, Germany, for drying bricks and especially roofing tile. 
 The tiles are delivered on the upper ends of inclined chutes 
 
 Figure 27. 
 
 BJ- 
 
 Figure 28. 
 
 and gradually slide down as drying proceeds and as the dried 
 ware is removed from the lower ends of the chutes along the 
 outer aisles. Schaff originally used the natural updraft of 
 the hot air within closed chutes, while Witte blows in hot air 
 from the side, taken from the cooling chamber or a heater. 
 The original idea may not be more effective, but it certainly 
 is more interesting on account of its scheme by which the 
 drying medium (the air going up) and the conveying feature
 
 54 
 
 DRYING CLAY WARES 
 
 (the ware coming down) carries out a logical idea which has 
 
 been so successfully applied in our progressive tunnel dryers. 
 
 In Fig. 31 we have the bricks in racks around the kiln at 
 
 Figure 29. 
 
 Figure 30. 
 
 the kiln top level and similar to the Cohrs system shown in 
 Fig. 21, which relieves the kiln of the excessive weight in other 
 systems where the bricks are above the kiln. This system 
 only uses radiated heat from the side walls of the kiln and
 
 DRYING CLAY WARES 
 
 55 
 
 that escaping from the wickets. Under the racks are placed 
 steam pipes enclosed in a box, with admission for air on the 
 sides next to the kiln, and outlets into racks on the opposite 
 
 Figure 32. 
 
 upper side. The principal source of heat in this instance is 
 from the steam pipes, and not from the kiln. The radiated 
 heat from the top of the kiln is used to produce draft through 
 the monitor of the building and is not available for drying.
 
 . 56 DRYING CLAY WARES 
 
 Fig. 32 gives the arrangement as built by F. L. Smith & 
 Co. of Copenhagen and Berlin. There are certain features in 
 the drying as well as in the handling worth describing, and 
 we will follow the ware as it leaves the machine. The bricks 
 are cut from the end of the bar of clay, three at a time, with- 
 out waste, by a hand cutter operated by one man and a ca- 
 pacity of 40,000 to 50,000 German size bricks is attained per 
 
 day a remarkable output for a hand cutter operated by one 
 
 man. Such a cutter is shown in Fig. 25. The bricks are taken 
 off by another man and placed on a pallet which is level with 
 the cutter. There are ten such pallets, each of which will 
 hold fifteen bricks, resting loosely on the frame of an elevator 
 and the filling starts with the lowest pallet. As soon as the 
 bottom pallet is filled the elevator drops the height of one 
 pallet, bringing the second pallet level with the cutter and 
 thus repeating until the frame is full. A pit receives the ele- 
 vator as it descends. A woman on the opposite side of the 
 elevator frame spaces the bricks on the pallets. 
 
 After the frame is loaded the woman shifts the lever of 
 the coupling and the elevator rises to the floor where the 
 bricks are to be dried. Two elevator frames at right angles 
 to each other forming a letter V, the angle of which encloses 
 the cutter, are used. Thus the take-off is at equal distance 
 from both elevator frames and has to make only a quarter 
 turn to place the bricks on either frame. 
 
 When the first frame has reached the upper drying floor 
 the elevator is stopped automatically and a man with a spe- 
 cial car takes off the row of pallets from the elevator by 
 pushing the car with its ten sets of projecting arms into it 
 and raising the pallets from the frame supports by the move- 
 ment of a lever on the car. After the car is loaded and pulled 
 back the elevator frame is filled with (ten) empty pallets and 
 lowered to the first position at the cutter. The drying sec- 
 tions or tunnels are provided with projections to receive the 
 pallets corresponding to the projections on the elevator pallet 
 frame, and the loaded pallets are placed in position by a single 
 movement of the car lifting lever. One man on the dryer can 
 easily handle 30,000 bricks. 
 
 Turning again to our illustration, Fig. 32, we see the dry- 
 ing floor located to one side of the kiln to avoid any load upon 
 the kiln walls. Outside air is coming in from the opposite 
 side, passes over the top of the kiln and becomes heated by 
 contact with the kiln top and by commingling with hot air
 
 DRYING CLAY WARES 
 
 57
 
 58 
 
 DRYING CLAY WARES
 
 DRYING CLAY WARES 59 
 
 rising from the kiln. An air-tight ceiling prevents the heat 
 from escaping into and through the roof, thus forcing it to 
 enter the dryer on the side facing the kiln. The heat, after 
 having passed through the ware, enters a vapor stack pro- 
 vided with regulating dampers and escapes to the open air. 
 
 The speed of the air in the dryer Is about 60 meters (197 
 feet) per minute. The exhaust steam from the engine is also 
 used for drying purposes. The steam is forced into a well 
 insulated hot water tank, which supplies ribbed pipes under 
 the dryer. The circulating water will gradually cool off and 
 return to the tank by its own weight through separate piping. 
 
 The drying chambers are made as small as possible to 
 utilize all the space and to avoid losses of heat. 
 
 A test of such a dryer some years ago during the month of 
 November gave the following data: 
 
 The temperature of the outside air was 11 degree C. (52 
 degrees F.) and its degree of saturation 90 per cent. The 
 temperature of the air entering the dryer was found to be 15 
 degrees C. (59 degrees F.) and its degree of saturation 65 per 
 cent. The temperature rising in the dryer was 23 degrees C. 
 (73 degrees F.). The temperature in the vapor stack was 15 
 degrees C. with a saturation of 93 per cent. The sectional 
 area of the stack was 4.2 square meters (45.2 square feet) and 
 the speed of the air 60 meters (197 feet) per minute. Each 
 of the sixteen chambers contained 7,500 bricks and it took four 
 days for drying. At 59 degrees F. saturated air contains 
 4.7") grains of moisture per cubic foot. In the above data the 
 air entered at 59 degrees F. 65 per cent, saturated and came 
 into the vapor stack at 59 degrees F. and 93 per cent, satu- 
 rated. Sixty-five per cent, and 93 per cent, of 4.75 give us, re- 
 spectively, 3.08 and 4.41 grains, and the difference, 1.33 grains, 
 represents the amount carried out by each cubic foot of air. 
 The stack being 45.2 square feet and the air moving at the 
 rate of 197 feet per minute, we get an air movement of 8,904 
 cubic feet per minute, carrying 11,842 grains of water. In 
 one hour, therefore, about 123 pounds of water are carried 
 out, and in four days 11,808 pounds, which fairly represents 
 the water in 7,500 (German size) bricks. 
 
 Fig. 33 shows the same system for two continuous kilns, 
 for which it works out especially well by getting the dryer in 
 the center. 
 
 In Fig. 34 we have a system of drying which has been in 
 successful operation in this country for a number of years. 
 
 The bricks are set on long trays, which are fastened to a
 
 DRYING CLAY WARES 
 
 iii 
 
 ^ / ' 
 
 fP^h-& 
 
 & 
 
 VK/ 
 
 -k --
 
 DRYING CLAY WARES 61 
 
 continuous double chain conveyor, which passes over and 
 under sprockets the full length of the continuous kiln, as 
 shown in the illustration, and returns to the ground floor, 
 where the dry bricks are removed and wheeled to the kiln. 
 The conveyor is operated by rack and pinions driven from a 
 steam cylinder, as seen in Fig. 35. Alongside one wall steam 
 radiators are placed and the whole dryer is operated at pretty 
 high temperature, higher than in German practice. The 
 bricks are handled three times in small units once from ma- 
 chine to tray, once from tray to barrow and once from barrow 
 to setter. 
 
 Prom our experience with cars and transfers into and out 
 of dryer tunnels and kilns, we believe there will be some 
 economy in labor in the above system. Our continuous kilns 
 are not insulated as are the German kilns, and we will have a 
 greater value in radiated heat, but still far from sufficient to 
 dry the product burned in the kiln. As our kilns are con- 
 structed, operated and maintained they are not adapted to 
 carry heavy loads, especially loads of moving machinery 
 equipment, which must be kept in perfect alignment. 
 
 In a number of plants drying floors have been established 
 over periodic kilns, but the consensus of opinion is that such 
 combination of kilns and drying floors is not satisfactory. 
 
 There have, perhaps, other attempts been made in this 
 country to dry the ware above kilns, of which we do not 
 know. The tendency of our day is directed towards econ- 
 omy in fuel, and we believe that the methods of drying above 
 kilns will in the future more and more be taken into serious 
 consideration. 
 
 In conclusion we briefly wish to recapitulate the advan- 
 tages and disadvantages of the drying methods above de- 
 scribed: Advantages. 
 
 Utilization of space. 
 
 Compactness of arrangement. (Eventually the whole plant 
 under one roof.) 
 
 Economy in fuel. Disadvantages. 
 
 Elevating and lowering of the ware. 
 
 Load upon the kiln walls. (The outer kiln walls should 
 not be loaded under any circumstances.) 
 
 High buildings. 
 
 The radiation alone not sufficient for drying and in conse- 
 quence extensive and scattered auxiliary equipment.
 
 DRYING CLAY WARES 
 
 CHAPTER VII 
 Artificial Dryers. 
 
 AMERICA LEADS in the development of artificial 
 dryers for clay ware, and her advance in this fea- 
 ture of clayworking is due to greater need, or more 
 properly, to greater variety of needs. A need leads to an in- 
 vention to supply it. No two clays are exactly alike and in 
 the variety of clays, America has all the needs in the world. 
 The alluviums of the coasts border and overlap the tertiary 
 and cretaceous deposits, which in turn, extend to the foot- 
 hills of shales, adjacent to the mountains of schists, quartz- 
 ites and hard shales. In and beyond the mountains come 
 the rich shales and fireclays of every kind laid down in 
 Paleozoic times, and these overlap the calcareous shales of 
 the Devonian age. The great glacial cap stretches in a 
 broad belt from coast to coast, nearly three thousand miles. 
 In the broad valleys are the deep terrace and lake deposits of 
 the Champlain period. The mountains are ribbed and seamed 
 with disintegrated dikes of every description. In the Middle 
 West are vast deposits of white cretaceous clay, overlapped 
 by tertiary shales the drying difficulties of which are beyond 
 the ingenuity of the dryer man. Over the plains are found the 
 wind-tossed beds of loess, and the troublesome joint clay. In 
 the South are the washings of the continent, ancient and 
 modern, shales and alluviums, kaolins, Fullers earths, fire 
 clays, bauxite. 
 
 The development of the dryer is also influenced by cli- 
 matic conditions. We have the frozen North and the sunny 
 South, the arid plains and the dripping west coast, and all 
 kinds of climate in between. 
 
 Fuel also must be considered. In a smaller country the 
 variation in cost is less wide than in our broad land where a 
 difference of 1,000 per cent, is not unusual. In the coal dis-
 
 DRYING CLAY WARES 63 
 
 tricts, where coal and clay often come from the same pit, 
 the cost of fuel is of slight consideration, while in the dis- 
 tant districts it must have every consideration. 
 
 High priced labor must be reckoned with, and every effort 
 is made to develop a mechanical operation. 
 
 These conditions in every extreme have led to a wide de- 
 velopment of mechanical dryers. 
 
 All dryers can be placed in two general classes: 
 
 1. The periodic dryer, in which the ware is stationary 
 and the heat and circulating air are brought to it. 
 
 2. The progressive dryer, in which the ware is being ad- 
 vanced from a low temperature, usually humid zone, to a high 
 temperate dry zone. 
 
 The periodic dryers may be separated into: Floor 
 dryers, rack dryers, tunnel or compartment dryers. 
 
 The progressive dryers are limited to the tunnel or com- 
 partment type. 
 
 A further classification introduces the source of heat as 
 follows: 
 
 Combustion 
 
 Introduced direct. 
 Radiation. 
 Convection. 
 Steam 
 
 Direct radiation. 
 Convection. 
 Waste Heat- 
 Steam. 
 
 Cooling kilns. 
 Burning kilns. 
 
 The possible variations, the combinations and the modi- 
 fications, to adapt dryers to all kinds of ware and all varieties 
 of clays, gives us a long list of artificial dryers. 
 
 It is not our purpose to go into a full description and 
 discussion of all the modifications, but instead we will take 
 up the general types and follow with some of the best known 
 and most widely used modifications, but we will not attempt 
 to follow any definite classification. In fact, the division is 
 not always sharply drawn. It is but a step from hot floors 
 to ordinary drying floors in one direction and to radiated 
 tunnel dryers in the opposite direction. Periodical dryers 
 in some instances approach very closely to the progressive
 
 64 DRYING CLAY WARES 
 
 type, some being periodical in construction and progressive 
 in operation. 
 
 General Principles. 
 
 Before taking up the individual dryers, we wish to re- 
 view briefly the general principles of drying even though 
 we repeat what has been said in a previous chapter. 
 
 1. It is important to bear in mind that drying cannot 
 take place without the consumption of heat, and the same 
 amount of heat is required in every instance for equal 
 amounts of water evaporated. The efficiency of a dryer de- 
 pends upon the application of the heat. 
 
 2. Air has nothing whatever to do with drying in a strict 
 sense. We speak of the volume of air required and it. is 
 convenient to do so. It is true that we use air in drying, 
 but not for drying. The air is simply a vehicle to carry away 
 the water vapor, or more properly speaking, it is used to 
 create a current, or a draft, to sweep away the moisture vapor 
 as fast as it is formed. As a matter of fact, instead of air ab- 
 sorbing vapor, the latter, as fast as it forms, displaces air 
 by its pressure, until at the boiling point there is theoretic- 
 ally no air present in a vessel containing the boiling water. 
 Some types of dryers have small air inlets and equally small 
 outlets with no other force moving the air than natural draft. 
 Other types use fans to force the air in through large ducts 
 in which one may walk without inconvenience, and at the 
 exhaust end of the dryer is another fan drawing away the 
 air and moisture through another large duct. These dryers 
 may have equal drying capacity yet there is no comparison 
 in the volumes of air passing through them. 
 
 3. Other things being equal, the greatest economy will 
 come with the shortest connection between the source of heat 
 and the drying ware. 
 
 A direct coal fired combustion dryer will give greater re- 
 turn in heat than a dryer in which the fuel is used to gen- 
 erate steam a hundred or more feet away and the heat value 
 recovered from the steam in or adjacent to the dryer, on the 
 other hand, where the combustion gases cannot be used di- 
 rect, but instead the heat from the combustion must be con- 
 ducted through walls thence by radiation to the ware, the 
 amount of heat which may be led to the ware may be less 
 than by the more complicated steam operation. 
 
 4. Meteorologists tell us that air cannot be heated by
 
 DRYING CLAY WARES 65 
 
 radiation, but becomes heated by contact with hot bodies 
 (conduction), and the movement of the air carries the heat 
 from place to place (convection), and gives it up by con- 
 duction, to the bodies with which it comes in contact. They 
 also inform us that heat waves radiating from a hot body will 
 raise the temperature of any solid body with which they come 
 in contact without, as above stated, heating the intervening 
 air. The Fery pyrometer is perhaps an illustration of this. 
 We focus it on a glowing body in the center of a kiln and it 
 will register the temperature in a galvanometer, but instantly 
 a screen is intervened the temperature drops back, which 
 would not be the case if the intervening air were heated by 
 radiation from the glowing body. We sit in front of a fire 
 and are comfortable so long as a screen is held between us 
 and the fire but without the screen our face will burn. It is 
 evident that the burning sensation does not come from the 
 air. 
 
 5. Dryers, then, must be constructed to get the air in 
 contact with the heated body in the greatest degree and then 
 be brought in contact with the ware to be dried, or if we are 
 relying upon radiation from the hot floor to the ware there 
 should be as little movement of the intervening air as possible 
 because to whatever degree it comes in contact with the hot 
 body and ware it will carry away heat from both, but on the 
 other hand, after the heat has driven the moisture from the 
 ware there should be a current of air to remove the vapor. 
 Herein lies the difference in the quantity of air required for 
 different types of dryers. In one type the air is heated by 
 contact with the hot body and is then brought into contact 
 with the drying ware. In the other type, the ware is heated 
 and the water evaporated directly by the heat radiated from 
 the hot body to the ware and it is only necessary to maintain 
 the vapor condition and sweep it away either by its own ex- 
 pansive force or by a current of air. 
 
 Floor Dryers Hot Floor. 
 
 Clay wares were originally dried on the ground without 
 cover. Shelter was next provided which raised the drying 
 space to the dignity of a floor. It was but a step farther to 
 provide some method of heating the floor and this led to the 
 development of modern hot floors. 
 
 The hot floor, so called, was first used in the manufac- 
 ture of fire bricks and is still the chief drying equipment in 
 such factories. It consisted of a floor of any width and one 
 hundred feet or less in length. At one end was a firing pit 
 below the floor level, and at the other end a stack. The floor 
 was underlaid by a series of parallel flues connected directly
 
 DRYING CLAY WARES 
 
 with coal-fired furnaces in the firing pit, and with the stack 
 by a cross head flue. 
 
 In order to equalize the temperature of the floor, it was 
 made thicker near the furnaces, gradually decreasing in 
 thickness toward the stack. The flues were spanned with 
 bricks, then the thickness was built up with rammed ashes 
 and paved, or with rammed crushed furnace slag without 
 paving, or with concrete finished to a smooth surface. Even 
 at best it was impossible to get the temperature uniform 
 nor was it considered desirable to do so, because some wares 
 required slower drying than others and a suitable temperature 
 for all the product could be found on such a floor. 
 
 The size of the floor per thousand bricks depends upon 
 the time required to dry, and varies from 700 square feet to 
 1,250 square feet. 
 
 In the hand molding process the bricks in the molds are 
 carried by boys from the molder and are dumped flat on the 
 hot floor just as common bricks from soft mud machines are 
 placed on the open air drying ground. 
 
 The bricks are left on the floor from twelve to twenty- 
 four hours or until dry enough to repress. If they show 
 signs of becoming too dry before the repressing gang gets 
 them, they are hacked into piles, or in some instances, simply 
 edged up. This is one instance where the drying may be 
 retarded by edging up the bricks, where usually edging is 
 resorted to in order to hasten the drying process. 
 
 Where the bricks set sufficiently for repressing in eight 
 or ten hours it is the custom for the molders to begin work 
 about 4 a. m. and finish their task by noon, while the re- 
 pressing crew will begin at noon or as early as the drying 
 will permit, and continue until the day's output is complete. 
 From the repress the bricks are again placed flat on the 
 floor, four to eight high, and allowed to remain until com- 
 pletely dry, when they are taken up and wheeled to the kilns. 
 The tunnel dryer is being introduced in fire brick manu- 
 facture, as an adjunct to the hot floor, and in fact has been 
 in use on a few yards for many years. It is used for the re- 
 pressed product and for any struck bricks which do not have 
 to be repressed. 
 
 The advantage of the open floor is that the bricks can be 
 watched and repressed when in the proper condition, and it 
 is retained in all fire brick plants, but the crude direct fired 
 hot floor, expensive in fuel consumption and at best not very 
 efficient, has been replaced by the modern exhaust and live 
 steam heated floor. 
 
 Figs. 37, 38 and 39 show a section, plan, and detail of a
 
 DRYING CLAY WARES 
 
 Figure 37. 
 
 Figure
 
 DRYING CLAY WARES 
 
 modern hot floor. The floor is divided into sections so that 
 each can be heated independently. It has a base of concrete 
 upon which are laid 4-inch hard-burned drain tiles or elec- 
 trical conduits imbedded in and covered with concrete, which 
 is finished to a smooth surface, with the tiles as near to the 
 surface as practical. 
 
 The hot floor is adapted only for low pressures and 
 size and number of tiles under the floor is such that the 
 steam pressure is virtually atmospheric pressure. Exhaust 
 steam is used during the day and low pressure live steam at 
 night, which reaches the floor at a gauge pressure less than 
 five pounds. The main header is connected with the under 
 tiles by %-inch nipples and though the pressure in the 
 header be five pounds the drop will be practically to atmos- 
 pheric pressure in the tiles, being merely sufficiently in ex- 
 cess to carry the steam to the exhaust end of the floor! 
 
 Figure 39. 
 
 The tiles have a grade sufficient to carry away the con- 
 densation and the floor surface follows this grade. 
 
 In modern plants there is a second slatted floor, as shown 
 in Fig. 37, upon which are molded and dried the large and 
 intricate shapes which require careful drying treatment. The 
 temperature is lower in the second floor and the ware cannot 
 come in contact with the hot radiating floor. Moreover, the 
 air is partly saturated with moisture from the ware on the hot 
 floor, and in consequence the progress of the drying on the 
 second floor is slower and safer. 
 
 It is also evident that all ware dried on the second floor 
 is without expense for fuel and further that the hot floor can 
 be kept at a maximum operation on ware that will dry 
 safely under such conditions, so that the combination of a hot 
 floor and upper drying floor is an economy which should not 
 be neglected.
 
 DRYING CLAY WARES 
 
 In a number of yards, waste heat is drawn from the cool- 
 ing kilns by a fan and distributed through the building in 
 galvanized iron pipe so that blasts of hot air can be turned 
 on the stacks of bricks that have reached a drying stage, 
 where they will stand rapid finish. This is the only use in 
 fire brick plants of waste heat from cooling kilns, but with 
 the advent of the tunnel dryer in the fire brick factories, a 
 greater use of this valuable heat will be made. 
 
 Hot floors are sometimes built with brick flues covered 
 with cast iron or steel plates. The steam pressure may be 
 so low that the leakage through the lapped joints of the 
 plates is hardly noticeable. 
 
 The use of hot floors is not uncommon In brick and tile 
 plants. The bricks may be handled on pallets and dumped 
 directly on the floor as with fire bricks, or they may be 
 placed on foot pallets and delivered to the floor by lifting 
 trucks, the bricks remaining on the pallets until dry or flat 
 pallets, lifting cars and supporting stanchions may be used 
 as illustrated under air drying, or the dry floors may be 
 equipped with tracks and standard dryer cars. The latter, 
 however, would hardly be considered. The hot floor is not the 
 most efficient type of dryer, and if a car equipment is to be 
 used, a better type of dryer should be adopted. The advan- 
 tage of the hot floor is that it lends itself readily to the use 
 of pallets and lifting trucks or lifting cars. A good feature 
 of it is that after once in full operation there is a large mass 
 of concrete and earth heated up, which, in a number of plants, 
 suffices to carry the operation through the night without the 
 use of steam, or, in other words, we store up enough heat 
 in the day time to run the plant through the night. 
 
 The hot floor dryer has some advantages in small yards 
 where the operation is not continuous throughout the year, 
 and where no waste kiln heat is available, but is hardly to be 
 recommended for large capacity plants, except in the fire 
 brick industry, where it is necessary to watch the progress 
 of the drying. 
 
 Compared with other types of modern dryers the cost of 
 installation is low, which is usually a consideration; the labor 
 cost is not excessive, especially in small yards where the 
 distances are short; a combination of brick and drain tile 
 very common in small yards, works nicely with the hot floor, 
 since the more easily drying tile may be dried on the upper 
 floor.
 
 DRYING CLAY WARES 
 
 CHAPTER VIII. 
 Sewer Pipe Floors. 
 
 THE DRYING ROOMS for sewer pipe, drain tile and fire- 
 proofing hardly need any description. Manufacturers 
 of drain tile, fireproofing and other hollow ware that do 
 not need to be finished after leaving the machine or press 
 are adopting tunnel dryers for the small sizes of ware, but 
 retain the dry floors for the large sizes. 
 
 A sewer pipe dryer is a large building with three to four 
 floors, including the ground floor. The customary plan in the 
 past, and still largely followed, has the steam piping under 
 the second floor. The press is placed to deliver the ware on 
 this floor, and the large sizes which have to be turned as the 
 drying progresses are lowered by gravity to the ground floor. 
 The steam pipes being overhead, all this ware is heated by 
 radiation from above, and the top of the ware dries first, as 
 it should, and the finishing work is done when the pipes are in 
 the best condition for this work. It is necessary that little 
 or no drying take place in the large pipe at the floor level, 
 because the weight of the pipe would prevent shrinkage and 
 the pipe would crack to relieve the shrinkage strains. As 
 soon as the top is dry, sufficiently so that the danger of crack- 
 ing from any drying which might occur at the floor level is 
 obviated, the pipe is turned, bringing the bottom to the top, 
 and is then left on the floor until the drying is completed. 
 The pipe leaves the press with the socket down, but it is 
 turned at the machine and placed on the shod (pallet) with 
 the socket up and so placed on the floor for the initial drying. 
 The upper floors are always slatted where a single piping 
 system is used, but in some sections the floors are made solid 
 and there is an overhead pipe system for each floor. The 
 slatted floors are made of four-inch strips spaced about one- 
 half inch. The second floor in a single heating system plant
 
 DRYING CLAY WARES 71 
 
 is the most rapid drying floor, and upon it is placed, or should 
 be placed, the small ware which will stand rapid drying. 
 
 The hot air from the lower floors rises through the slatted 
 floors to the upper floors, gathering moisture in its course and 
 finally escapes through monitors on the roof. 
 
 A frequent annoyance is the condensation under the roof 
 and constant dripping on the ware. Steep roofs (one-fourth 
 pitch or more) covered with shingles will not "sweat," but 
 such roofs are not regarded with favor on account of fire risk. 
 To prevent dripping from flat roofs, a ceiling is put in, thus 
 giving air space, and an occasional steam pipe under the roof 
 maintains a temperature sufficient to prevent condensation. 
 
 An average one-press shop has a capacity of from sixty 
 to seventy-five tons per day, and the dry floor space required 
 is from 800 square feet to 1,000 square feet per ton of ware. 
 This means from 50,000 square feet to 75,000 square feet of 
 floor, and the dimensions of a three-story factory will be in 
 round numbers, 100x200 feet. 
 
 It is desirable to have the building rectangular rather than 
 square; first, on account of light, and second, to distribute 
 the ware in front of the kilns in which it is to be set. 
 
 The press Is preferably placed in an annex midway of 
 the length of the dryer. 
 
 The green ware from the press is lowered to the ground 
 floor on gravity drops, and elevated to the upper floors on 
 power elevators. When dry, the ground floor product is 
 wheeled or trucked direct to the kilns, and the upper floor 
 product is lowered on gravity drops, which at the same time 
 return the empty trucks to the floor in question. 
 
 In most instances no provision is made for the admission 
 of air, and the supply depends upon leakage, open doors, ele- 
 vator shafts, etc. 
 
 There is no data in regard to the quantity of piping. Origi- 
 nally the single pipe system used one-inch pipe spaced 12 to 
 15 inches under the entire second floor except around elevator, 
 etc. This would require from 15,000 to 18,000 feet of piping, 
 or 5,000 to 6,000 square feet of radiating surface, not counting 
 mains and headers, verticals and returns, roof piping, etc., 
 which materially increase the radiating surface. It Is ar- 
 ranged in sections and all of it is not necessarily in opera- 
 tion at the same time. Later plants have put in 1^-inch 
 pipe without increasing the spacing beyond 15 inches, which 
 would give in excess of 6,000 square feet of radiating sur- 
 face, not counting the mains, etc. 
 
 In determining the radiating surface required to heat a
 
 72 
 
 DRYING CLAY WARES 
 
 given building, R. C. Carpenter used the following formula: 
 
 NC W 
 
 -+G+ 
 
 in which H = heat units per degree difference in temperature^ 
 C = cubic content of the building; G = glass surface; W - 
 wall surface; N = number of times air is changed per hour. 
 We estimate that a building 100x200 feet, three stories high, 
 has 600,000 cubic feet content, 15,000 square feet wall surface 
 and 2,700 square feet glass surface. For winter work, let us 
 assume the outside temperature as 32 degrees F. and the room 
 temperature 92 degrees F. 
 
 N can be obtained from the volume of moisture to be re- 
 moved. Sixty tons of clay made into pipe will contain fifteen 
 tons, or 30,000 pounds of water, which must be removed every 
 twenty-four hours. If the air enters 70 per cent, saturated 
 and leaves fully saturated, each cubic foot will remove .002 
 pound of moisture, and therefore there must be 15,000,000 
 ubic feet of air pass through the building each day, or air 
 in the building must be changed 
 
 (15,000,000) 
 
 =25 times in 24 hours. 
 (600,000) 
 
 25x600,000 
 
 24 15,000 20,000 
 
 1-2,700-f 1 = 19,810. 
 
 55 4 10 
 
 19,810x(92 32)=1,188,600 B.T.U. per hour. 
 We add to the wall surface the approximate roof area on the 
 the basis of wood construction. In ordinary building heating 
 the roof need not be considered, because usually an attic in- 
 tervenes between it and the rooms to be heated; but there is 
 no attic in a sewer pipe plant. Carpenter assumes a radia- 
 tion value of 280 B.T.U. per hour per square foot of steam 
 radiating surface: 
 1,188,600 
 
 - 4,245 square feet radiating surface. 
 280 
 
 Assume that summer conditions are 82 degrees F. outside 
 temperature, air 70 per cent, saturated. We determine in the 
 same way that 1,295 square feet of radiating surface will be 
 required. In the last determination each cubic foot of air 
 takes out .00108 pound of moisture and 27,800,000 cubic feet 
 will be required daily, or, in round numbers, the air in the 
 building must be changed twice per hour.
 
 DRYING CLAY WARES 73 
 
 These calculations do not take into consideration the work- 
 ing conditions in a pipe dryer. We are heating up seventy- 
 five or more tons of clay and water from some lower tem- 
 perature to 92 degrees F. and evaporating 30,000 pounds of 
 water. We may neglect the sensible heat in the mass, so far 
 as the dryer is concerned, because it presumably heated up 
 in preparation and pressing. There remains 30,000 pounds of 
 water to be evaporated at 92 degrees F. The latent heat at 
 92 degrees is 1,041.1 B.T.U. per pound, and the total heat re- 
 quired per day will be 30,000x1,040.1=31,203,000 B.T.U., or, in 
 round numbers, 1,300,000 B.T.U. per hour. The radiating sur- 
 face required will be 
 
 1,300,000 
 
 = 4,643 square feet. 
 
 280 
 
 Adding this to the radiation losses, we find" 8,888 square feet 
 of radiating surface required for winter work and 5,908 square 
 feet for summer work. 
 
 The problem is merely illustrative, and we have made no 
 attempt to work out the niceties of it, which would only con- 
 fuse the main points which we wish to bring out. 
 
 It is evident that a radiating surface of 6,000 to 9,000 square 
 feet will be required, depending upon climatic conditions. 
 
 It is also evident that the older factories with 6,000 to 
 7,000 feet of radiating surface were not fully efficient under 
 unfavorable weather conditions, and this probably accounts 
 for the increase in piping in the more recent factories. As 
 an offset to this the older factories were wood structures, the 
 conductivity of which is less than one-half that of brick, and 
 
 W W 
 
 in the formula becomes or less, depending upon the 
 4 10 
 
 insulation. 
 
 There is no published data in regard to the power required 
 to operate a sewer pipe dryer. One-press shops usually in- 
 stall three to four boilers with a rated power of 400 to 450- 
 h.p., but when occasion requires one of these can be cut out 
 for cleaning or repairs without shutting down any part of the 
 operation. 
 
 An approximation of the power required for drying may be 
 made from the preceding problems. In the winter problem 
 we have 1,188,600 B.T.U. per hour to maintain the factory tem- 
 perature, and 1,300,000 B.T.U. per hour for the evaporation of 
 round numbers, 1,300,000 B.T.U. per hour. The radiating sur- 
 the water, making a total of 2,488,600 B.T.U. per hour. A 
 boiler horse power is rated at 30 pounds of water from 100
 
 DRYING CLAY WARES 
 
 degrees F. steam at 70 pounds pressure, and this requires 
 33,450 B.T.U. The boiler horse power therefore for the above 
 requirement would be 75, but this is unquestionably too low. 
 There are boiler losses, pipe losses in transmission to the 
 dryer, frictional losses in moving the steam and water through 
 the piping, leakage losses, steajn losses in the return mains 
 and vacuum pump. Allowing 10 per cent, for these losses 
 brings the boiler requirement for drying alone to about 83-h.p. 
 We have no data to determine whether 10 per cent, is even 
 an approximation of these losses. The boiler radiation losses 
 alone have been carefully calculated and even determined 
 direct, and when the boilers are properly protected, are reck- 
 oned at 4 per cent. Besides the actual work of drying, there 
 is the heat required for the plaster and molding rooms, clay 
 preparing room, .press room, etc., which cannot be separated 
 from the actual boiler requirement. 
 
 Waste heat from cooling kilns is not largely used in sewer 
 pipe drying. Three or more plants were built to use waste heat 
 in connection with steam piping, but in one instance at least 
 the method was abandoned. The steam piping was placed under 
 the second floor, as usual in older plants. Figs. 40 and 41 show 
 the methods of introducing and distributing the air in two fac- 
 tories. A plate fan collects the hot air fro.m the cooling 
 kilns, or from sectional steam heating coils, and forces it into 
 the building through galvanized iron pipes (Fig. 41). From 
 the verticals, under each floor, are four small distributing 
 pipes, so placed and of such an extent that each riser suffices 
 for six sections of the floor, or about 1,500 square feet. Fig. 
 40 shows the distributing outlet in another plant. In this in- 
 stance the heat was distributed under the lower floor only. 
 Each perforated pipe was enclosed by a galvanized iron pipe, 
 also perforated to mate with the perforations in the inner pipe. 
 When it was desired to shut off the heat in any section, the 
 outer pipe was turned so the holes missed connection. We 
 believe the hot air system in the latter plant was abandoned, 
 and also in one plant using the distributing pipe system. The 
 difficulty in such hot air system is to get even distribution of 
 the heat. Sections of the floor immediately over and adjacent 
 to the heating pipes will get greater heat than intermediate 
 sections, and if the clay is at all tender there will be excessive 
 loss in cracked ware in the vicinity of the distributing pipes. 
 
 Another method of working out this waste heat problem 
 which is in successful operation, is to have a deep basement 
 under the lower floor, with steam pipes under the first floor. 
 The hot air from the kilns is simply blown into the basement,
 
 DRYING CLAY WARES 
 
 Figure 40.
 
 DRYING CLAY WARES 
 
 in which there is ample space for diffusion before its passage 
 among the steam pipes and up through the slatted floor. 
 There could be no marked changes in temperature from 
 one section of the floor to the next, and one could easily 
 learn what portion of the floor must be reserved for tender 
 drying ware. No ware is placed on the basement floor. 
 
 This recalls another point previously mentioned in regard 
 to sewer pipe plants; namely, that in very few plants is any 
 specific provision made for ventilation. Leakage is relied 
 upon for inlet air and windows in monitors for outlet. 
 
 The use of a fan as above mentioned insures any desired 
 volume of air, and it is practical to distribute it uniformly 
 through the several floors. Natural exhaustion at the top is 
 perhaps satisfactory, but we believe a forced exhaustion by 
 suction fans would be better. 
 
 Many people have the erroneous idea that moisture ladened 
 air is heavier than dry air and attempts have been made to 
 adapt down comer ventilators. This is a mistake. The more 
 moisture air takes up the lighter it becomes, and completely 
 satured air has the least weight per cubic foot, temperature 
 of course remaining the same. Water vapor is lighter than 
 air, and instead of being taken up by the air, displaces it. A 
 cubic foot of dry air when saturated with vapor will occupy 
 more than a cubic foot of space, and the moisture has a lower 
 specific gravity. As air cools, however, it becomes heavier, 
 and the cooling effect should be counteracted by secondary 
 heating, which at the same time prevents condensation of the 
 moisture. The air rising from the first floor, whether the 
 floor be heated or not, is partly saturated with moisture. 
 Passing the pipes under the second floor, it becomes heated 
 and its capacity for moisture correspondingly increased. The 
 ware on the second floor gives up moisture to the air with- 
 out saturating it, but, in passing through the third floor and 
 the fourth floor, both in taking up moisture and cooling, the 
 air becomes saturated, and may have little or no capacity for 
 moisture in the upper floor, and, because of its greater weight 
 through cooling, it acts as a blanket or damper. With steam 
 pipes under the third and fourth floors, we maintain the tem- 
 perature and the air is lighter in consequence of the vapor 
 and becomes lighter with each increase of vapor. Of the 
 capacity of the air to take up moisture, 25 per cent may be 
 used in the first floor, 25 per cent in the second, 25 per cent
 
 DRYING CLAY WARES 77 
 
 in the third, and complete saturation reached in the fourth. 
 The air becomes more buoyant as it rises and we only need 
 to maintain the temperature by steam pipes under the roof 
 until the air can reach the exits, where it will discharge itself 
 fully ladened with moisture and carrying materially more 
 moisture than if heated, only by a single system of piping 
 under the first or second floor. 
 
 We recall only one instance in which a tunnel dryer for 
 small ware was used in connection with dry floors for large 
 pipe, and the operation was not satisfactory. On drain tile, 
 however, which does not have to be rolled and finished, the 
 modern plant uses a tunnel dryer for small sizes and the 
 dryer floors for large tile.
 
 7S 
 
 DRYING CLAY WARES 
 
 CHAPTER IX. 
 Periodical Dryers. 
 
 A NY DRYER, in which the ware remains stationary dur- 
 A ing the drying, is periodical, and the open air and the 
 <* kiln dryers previously described belong in this class. 
 There are two distinct advantages in the periodical dryer: 
 
 1. It is adapted to the use of lifting cars or trucks, or a 
 conveyor system for delivery of the ware into the dryer and 
 removing it when dry. 
 
 2. In some types it permits slow heating up with as little 
 or as much air as may be desired, and when the ware has 
 reached a condition where it will stand rapid drying, the 
 temperature may be advanced to any degree within the limits 
 of the heating equipment and any required volume of air may 
 be introduced. 
 
 Steam Pipe Dryers. 
 
 A combined radiation and convection periodical dryer con- 
 sists of a series of tunnels with steam pipes under the tracks 
 or runways, and sometimes along the sides. With the air 
 inlets and outlets closed, the ware can be heated up by radia- 
 tion with no convection except such air currents as may be 
 occasioned by leakage. When the ware has been heated up 
 and thus put through any desired degree of humidity treat- 
 ment, the air vents may be opened and the drying finished 
 rapidly. With the steam pipes in the dryer tunnels we have 
 no radiation loss except that from the dryer building itself, 
 which is unavoidable in any dryer. 
 
 As will be seen under the description of the progressive 
 type of waste heat dryers, a large volume of air is required 
 to bring in sufficient heat to do the drying. 
 
 In the periodical steam dryer we need very little air,
 
 DRYING CLAY WARES 79 
 
 merely sufficient to sweep out the moisture as it is developed. 
 The problem figures as follows: 
 
 An ordinary tunnel is 100 feet long and holds 7,000 brick. 
 If each brick contains one pound of water, and the drying 
 period is twenty-four hours, we have 7,000 pounds to evapo- 
 rate and remove from the dryer in that period. Assume that 
 the air enters at 60 degrees F. and 70 per cent, saturated, 
 then from the table of vapor capacities, page 19, we find 
 that each cubic foot of air brings in .00059 pounds of moisture. 
 If the dryer is heated to 200 degrees F., which can easily be 
 done with high pressure live steam, the incoming air and 
 moisture expands to 
 
 1 x 
 
 491+ (60-32) 491+ (200-32) 
 From which we find x = 1.27 
 
 from Charles' law that the volume of gas is proportional to 
 the absolute temperatures and a cubic foot of the expanded 
 air will contain 
 
 .00059 
 
 = .00047 pounds of moisture. 
 1.27 
 
 From the same table of vapor capacities we find that satu- 
 rated air at 200 degrees contains .03024 pounds per cubic 
 foot, and therefore each cubic foot of air will remove from 
 the bricks .03024 .00047=.02977 pounds. To remove 1,000 
 pounds of water in twenty-four hours, we must have in round 
 numbers 33,600 cubic feet of air at 200 degrees, or 26,450 
 cubic feet at 60 degrees. 
 
 We determine the radiation loss as follows: 
 A tunnel is 3 feet 6 Inches wide, 4 feet 8 inches high and 
 100 feet long, and contains 1,630 cubic feet, from which we 
 deduct 346 cubic feet for brick and cars, leaving 1,288 cubic 
 feet, and since the air required per tunnel for drying is 
 (7X33600) 235,200 cubic feet, the air in the tunnel must be 
 changed (235,200/1288) one hundred and eighty-two times in 
 twenty-four hours, or 7.6 times per hour. 
 
 In a battery of six tunnels there will be 867 square feet 
 of exposed wall, 233 square feet of iron doors, and 2,500 
 square feet of well-insulated roof, the radiation from which 
 may easily be reduced to one-twentieth that of glass. The 
 radiation from iron is 1.1 times that from glass, and the 
 other factors have been given in the discussion of sewer pipe 
 drying.
 
 80 DRYING CLAY WARES 
 
 Using Carpenter's formula, we get for radiation loss from 
 one tunnel 
 
 7.6 X 1288 233 X 1.1 867 2500 
 
 55 6 4 X 6 20 X 6 
 
 = 277 B. T. U. per degree difference of temperature per hour. 
 The difference in temperature is 200 60 = 140, and the to- 
 tal radiation loss per tunnel will be 277 X 140 = 38,780 B. T. 
 U. per hour, or 930,720 B. T. U. in 24 hours, or 930,720/7 = 
 132,960 B. T. U. per 1,000 pounds of water evaporated. 
 
 It may be noted from what follows that the radiation loss 
 as determined, is about 9 per cent, of the total heat require- 
 ment. It has been customary to estimate dryer losses at 10 
 per cent., and it was also formerly customary to estimate kiln 
 radiation losses at 10 per cent., but some commercial tests 
 have shown kiln radiation losses up to 70 per cent. It is 
 probable that a well-insulated dryer will have a radiation loss 
 less than 10 per cent., and our calculations confirm this. 
 
 The value of such calculations in which there are a num- 
 ber of assumed factors may be questioned, but we hold that 
 any calculation is a better basis for the exercise of one's 
 judgment than a mere guess. 
 
 In the drying we have the following heat requirement per 
 thousand bricks: 
 
 1,000 pounds of iron to be heated from 60 to 200. 
 
 6,000 pounds of clay to be heated from 60 to 200. 
 
 26,450 cubic feet, or 26,450 X .075 = 1,984 pounds of air to 
 be heated from 60 to 200. 
 
 1,000 pounds of water to be evaporated at 200. 
 
 15.6 pounds of water vapor originally in the air, to be 
 heated from 60 to 200. 
 
 The specific heat of iron is taken as .12; of clay, .2; the 
 sensible and latent heat required in changing water at 60 to 
 vapor at 200 is 1118; the mean specific heat of a gas 
 is k + s (T + t). For water vapor the value of "k" is 
 .42 and of "s" is .0001, while for air "k" is .234 and "s" 
 .000012. "T" and "t" are the temperatures less 32. 
 1000 X .12 X 140 = ................... 1 6)8 00 B. T U. 
 
 6000 X .2 X 140 = ......................... 1 68> 000 B. T. U. 
 
 1984 X [.234 + .000012 (168 + 28)] 140 =. . . 65,650 B. T. U. 
 1000 X 1118 (Heat in vapor at 200 60)= 1 118 000 B T U 
 15.6 X [.42 + .0001 (168 + 28)] 140 =. . . 960 B. T. U. 
 
 1,369,410 B. T. U. 
 Adding the radiation loss as previously determined, we
 
 DRYING CLAY WARES 81 
 
 have a total heat requirement of 1,502,370 B. T. U. per thou- 
 sand bricks dried. 
 
 The next problem is to determine the amount of piping re- 
 quired. 
 
 Carpenter's factor of 280 B. T. U. radiation per square 
 foot of radiating surface may be used, but it is only applica- 
 ble to problems in which the current of air passing over the 
 piping is very slow. 
 
 The rule of thumb, in which the quantity of heat given 
 off from steam pipes varies from 1.25 to 3.25 B. T. U. per 
 square foot per hour per degree difference, gives us a basis 
 upon which to exercise our judgment, but it makes no separa- 
 tion of radiation and convection. 
 
 The amount of heat given off depends upon radiation and 
 convection. The radiation value is constant for each temper- 
 ature, but the convection value depends upon the size of the 
 pipe and the number of changes of air. 
 
 It is evident, as will be seen in the discussion of indirect 
 heating, that with increased circulation we get greater con- 
 densation and in consequence greater heat return from a 
 given amount of piping. Richards' "Metallurgical Calcula- 
 tions" adopts the basis that the heat given off varies as the 
 square roots of the velocities and uses the formula, 
 
 A familiar illustration of the advantages of circulation is 
 that of a heater which is insufficient to heat a closed room by 
 natural circulation, but which becomes sufficient if a fan is 
 placed to force the air in contact with it. There is no change 
 in the conditions except greater circulation, which increases 
 the convected heat taken from the heater. 
 
 We can readily calculate the radiation and convection 
 values for natural ventilation, but when we attempt to cor- 
 rect these values for increased changes of air we get into dif- 
 ficulties which make the calculations of little or no value. 
 
 We have the assurance, however, that the piping required 
 for natural ventilation, other things being equal, is in excess 
 of that required for greater velocities of air among the piping. 
 
 We have found the following method the most satisfactory 
 in determining radiation and convection losses. It is based on 
 Peclet's experiments, upon Newton's law of radiation, and 
 upon Dulong's corrections for Newton's law. The data for the 
 calculation will be found in one form or another in several 
 treatises on heating and ventilating (Box "Treatise on Heat,"
 
 82 
 
 DRYING CLAY WARES 
 
 Kent's "Mechanical Engineer's Pocket Book," Carpenter's 
 "Heating and Ventilating Buildings"), but as a rule it is not 
 in convenient form for ready calculation. 
 
 According to Newton's law, the radiation from steam pip- 
 ing varies with the difference in temperature, namely, .64 X 
 difference in temperature = radiation, but this has been found 
 incorrect for wide differences in temperature. 
 
 Fct. c to ~r* J f~o r Heaiuc. lion To l/uion&j Law u/ f/d ai a ff o n 
 
 inference 
 In Ternn^Betw. 
 ffac/iafinq Body 
 GndTheQir, F 
 
 18 
 
 Te 
 
 Si 
 
 mfie 
 <H 
 
 rato 
 50 
 
 reC 
 
 59 
 
 /"T& 
 
 68 
 
 ?<2V, 
 
 77 
 
 -InL 
 
 86 
 
 7e 9 r 
 95 
 
 eej i 
 
 104 
 
 ^a/n 
 n5 
 
 enh 
 
 I2Z 
 
 147 
 
 eit 
 
 I 31 
 I 525 
 
 140 
 
 36 
 45 
 
 3 
 050 
 
 1.0 70 
 92 
 
 1 1 
 
 1 35 
 
 1 60 
 
 ^30 
 
 ;55 
 
 1.325 
 
 1 375 
 
 M25 
 
 TT^T 
 
 1.550 
 
 I.M 
 
 t -- , 
 
 
 07 
 
 15 
 
 
 20 
 
 25 
 
 300 
 
 135 
 
 1400 
 
 MS 
 
 1.515 
 
 1 56 
 
 l.fc+0 
 
 1.70 j 
 
 
 
 
 
 
 50 
 
 
 
 
 151 
 
 1 575 
 
 1.64 
 
 1.700 
 
 1 ~p | 
 
 8\ 
 
 140 
 
 82 
 
 225 
 
 2JO 
 
 330 
 
 3SO 
 
 1450 
 
 147 
 
 1.545 
 
 16 1 
 
 lt>75 
 
 1737 
 
 1 5 I 
 
 90 
 
 16 
 
 05 
 
 .25 
 
 .31 
 
 36 
 
 410 
 
 Mb 
 
 
 
 
 
 1.775 
 
 1 4 1 
 
 99 
 
 165 
 
 32 
 
 280 
 
 535 
 
 
 440 
 
 1.490 
 
 I 55T 
 
 Ifol 5 
 
 Ic60 
 
 1 745 
 
 161 2 
 
 15 60 
 
 [ 17 
 
 235 
 
 " 85 
 
 335 
 
 $90 
 
 450 
 
 500 
 
 1550 
 
 1617 
 
 ltS5 
 
 1752 
 
 I6TO 
 
 I.S90 
 
 l.fl c 
 
 1 26 
 
 Ik 
 
 1 
 
 36 
 
 42 
 
 48 
 
 530 
 
 1.58 
 
 1650 
 
 1.72 
 
 1790 
 
 ICb 
 
 1930 
 
 
 1 35 
 
 230 
 
 40 
 
 .390 
 
 450 
 
 5 I 
 
 562 
 
 1 tl5 
 
 1 68 5 
 
 1.755 
 
 1.827 
 
 1 900 
 
 1 970 
 
 2 :* : | 
 
 1 53 
 
 345 
 
 97 
 
 45 
 
 5! 
 
 570 
 
 630 
 
 ' c : 
 
 1757 
 
 If 25 
 
 1902 
 
 I9f0 
 
 2052 
 
 2.1 lj\ 
 
 1 7 I 
 
 405 
 
 fcO 
 
 .515 
 
 .575 
 
 HO 
 
 705 
 
 1.770 
 
 1.838 
 
 1905 
 
 1.965 
 
 2.065 
 
 2. 1 4 2 
 
 zJJol 
 
 ieo 
 
 .44 
 
 95 
 
 55 
 
 6 1 
 
 es 
 
 7*5 
 
 LSI 
 
 i.eeo 
 
 1.95 
 
 2030 
 
 21 1 
 
 2190 
 
 2.2 7 
 
 1 SZ 
 
 50 
 
 to 
 
 .02 
 
 -69 
 
 75 
 
 .6:0 
 
 1 69 
 
 1 9fc5 
 
 204 
 
 2125 
 
 Z2I 
 
 2.295 
 
 236 
 
 |?I 
 
 57 
 
 50 
 
 69 
 
 7o 
 
 | 
 
 .900 
 
 ,97 
 
 2050 
 
 2 1 3 
 
 2225 
 
 2.32 
 
 2400 
 
 2g 
 
 Z34 
 
 .64 
 
 .705 
 
 77 
 
 "^~ 
 
 90 
 
 90 
 
 20fc 
 
 2.14 5 
 
 2.23 
 
 2.330 
 
 773- 
 
 2510 
 
 7TT 
 
 /?*3 
 
 Z 52 
 
 c/S 
 
 7EO 
 
 I I 
 
 Sfc 
 .<? 
 
 99 
 
 025 
 
 Z.I 05 
 
 2192 
 
 2.280 
 
 2.380 
 
 2<80 
 
 2.5 fc 5 
 
 2fc50 
 
 2fe 1 
 270 
 
 1.79 
 
 6feO 
 
 95 
 
 2.01 
 
 Z09 
 
 2175 
 
 tik 
 
 2.350 
 
 2.44 
 
 2.540 
 
 264 
 
 2740 
 
 2S4 
 
 The factors for correction are given in the following table, 
 and it will be sufficiently accurate for practical purposes to 
 take the factor nearest to the required temperature and de- 
 termined difference of temperature. 
 
 Chart No. 1 gives the convection losses of different sizes 
 of piping for one degree temperature difference per square
 
 DRYING CLAY WARES 
 
 s:; 
 
 foot of surface and Chart No. 2 gives the factors for correc- 
 tion necessary in wide differences of temperature.* 
 
 In .our problem we have a temperature difference of 247, 
 the nearest to which In the first column of the table is 243. 
 The factor for this difference of temperature and for an air 
 temperature of 59, which is nearest our assumed air tem- 
 perature (60), we find to be 1.88. The heat given up by ra- 
 
 l.iO 
 
 Chart lloJ 
 Con v ec t i on 
 
 From Hortjonfat 
 
 for Ct Temp Difference 
 
 ,3 4- 5 6 8 
 
 Oft side Diameter Of ' Pt/ie/n /nche-s 
 
 diation then is .64 X 1.88 X 247 = 297 B. T. U. By interpo- 
 lations to get the exact factor, we find the radiation to be 301 
 B. T. U., which shows that the table is sufficiently extended 
 
 *Our problem is based on the use of live steam at 60 Ibs. 
 pressure, which has a temperature of 307 F.
 
 84 
 
 DRYING CLAY WARES 
 
 for practical problems. Figuring the same problem from data 
 given in "Heating and Ventilating Buildings" (Carpenter), 
 we get 322 B. T. U. 
 
 Convection is determined from the charts No. 1 and 'No. 2. 
 
 -fOO 
 
 C/i aff Tlo 2 
 r ro>-ffect<jct, on TeyDutenajLaw Of Convecfi.in 
 
 -.'300- 
 
 0:5 
 
 Facto 
 
 Our problem assumes that 1-inch pipe will be used, which has 
 1.315 inches outside diameter. 
 
 From Chart No. 1 we find that piping with diameters of
 
 DRYING CLAY WARES 85 
 
 1.3 inches strikes the curve opposite .97 heat units lost. From 
 Chart No. 2 we find that 247 difference in temperature pro- 
 jected to the curve and thence to the base co-ordinate gives a 
 factor of 1.73. 
 
 The convection loss, therefore, is .97 X 1.73 X 247 = 414 
 B. T. U. From the data given by Carpenter, the convection 
 value for the assumed conditions is 380 B. T. U. The total 
 radiation and convection loss from our table and charts is 711 
 B. T. U. and from Carpenter's data 702 B. T. U. 
 
 From our table and charts it is possible to figure the prob- 
 lem for any difference of temperature, for any outside air 
 temperature and for any size of piping, and the results are 
 sufficiently accurate for any practical problem. The result we 
 obtained above, reduced to B. T. U. per degree difference, 
 gives us 2.87 B. T. U. per square foot per hour. 
 
 With a heat development of 711 B. T. U. per square foot 
 per hour, or 17,064 B. T. U. per day, we will require for the 
 estimated heat requirement of 1,502,370 B. T. U. for 1,000 
 bricks, 88.2 square feet of heating surface. 
 
 The average capacity of a tunnel is 7,000 bricks, and there- 
 fore 616 square feet of heating surface will be required per 
 tunnel, or 1,848 lineal feet of 1-inch pipe. 
 
 Low-pressure steam let us say 5 pounds will have a tem- 
 perature of 227 F. and the difference in temperature will be 
 167. From the table of factors we find that the factor for a 
 temperature difference of 171 and air temperature of 59 is 
 1.575 and the heat given off by radiation will be 1.575 X .64 X 
 167 = 168 B. T. U. 
 
 From Chart No. 1 we get for 1-inch pipe the factor .97, as 
 before, and from Chart No. 2, for a temperature difference of 
 167, we get the factor 1.58. The convected heat then is .97 X 
 1.58 X 167 = 256 B. T. U., making the total heat loss 424 B. 
 T. U. per square foot per hour, or 2.54 B. T. U. per degree dif- 
 ference per square foot per hour. 
 
 The piping required under such condition would be 
 
 1,502,370 
 147.6 
 
 424 X 24 
 
 square feet per thousand bricks, or 1,033 square feet per tun- 
 nel, or 3,099 lineal feet of 1-inch pipe per tunnel. 
 
 The above determinations of convected heat are for nat- 
 ural ventilation, and do not take into consideration the in- 
 crease which comes from increased circulation essential in 
 natural draft dryers. The solution of the problem for natural 
 draft dryers requires too many uncertain assumptions to give 
 results of any value, as the following discussion will show:
 
 DRYING CLAY WARES 
 
 In a coil heater we space the pipes 2% inches and the free 
 area will be 1 435 inches. If we have eight pipes in a row we 
 may count nine spaces or 12.915 inches of free area in the 
 row and for a square foot of free area we must have a sec- 
 tion' (144/12.915) 11.15 inches long, in which there will be 
 11 15 X 8 = 89.2 inches of piping, which is equivalent to 2.48 
 square feet of heating surface. We require per tunnel 26,450 
 (page 79) X 7 = 185,150 cubic feet of air per day, or 7, (15 
 cubic feet per hour. If the tunnel is 100 feet long we have 
 
 100 X 12 X 12.915 
 
 = 107.6 
 
 144 
 square feet of free area. The velocity of the air is 
 
 7715 
 
 = 71.7 
 
 107.6 
 
 cubic feet per hour through each square foot of free area. A 
 cubic foot of air requires .018 B. T. U. to raise the tempera- 
 ture one degree the formula is [.018 X .0000009 (T + t) ] 
 ( T _ t) and 71.7 cubic feet will require 1.29 B. T. IT. to 
 raise the temperature one degree. 
 
 Under natural ventilation we have, as previously deter- 
 mined, 414 (page 84) B. T. U. convection value, or since each 
 square foot of free area has 2.48 square feet of piping, we 
 have available 1,028 B. T. U., 
 1028 
 
 1.29 
 which is an impossible temperature from the piping. 
 
 It becomes evident at a glance that the volume of air re- 
 quired to carry out the moisture is not sufficient to carry the 
 heat required in the drying, making full allowance for the 
 heat obtained direct from radiation. It follows that since the 
 incoming air cannot take enough heat from the piping to 
 meet the dryer requirement, there must be circulation within 
 the dryer by which the hot air, after being cooled by the ware 
 and by the evaporation of the water, returns repeatedly to the 
 piping to again become heated, and meanwhile there is escap- 
 ing from the dryer a quantity of air equivalent to that enter- 
 ing. The purpose of this discussion is to bring up the ques- 
 tion of convection relative to the number of changes of air. 
 We have figured the heat values for natural ventilation, and 
 with any increased velocity of the passage of the air over the 
 heating surface the heat loss from the piping due to convec- 
 tion increases and the area of heating surface correspond- 
 ingly decreases. If we were introducing sufficient air for the
 
 DRYING CLAY WARES 87 
 
 heat requirement at a single passage through the piping, then 
 we could determine the velocities for the assumed conditions 
 and for natural ventilation from the formula, 
 
 2 + 
 
 \ 
 
 and could determine within a practical degree of accuracy the 
 increased heat loss from the piping in consequence. 
 
 In the problem in question the quantity of air is such that 
 it attains a maximum temperature before passing all the 
 heating surface, and because of this cannot increase the con- 
 vected heat. 
 
 The circulating air becomes the factor from which we 
 must figure any increased convection, and as this will have a 
 higher temperature than the entering air, we must base any 
 calculations on lower differences of temperature, which means 
 less convected heat per square foot of piping per hour, and in 
 consequence more piping to deliver the requisite amount of 
 heat We cannot determine the velocity of the circulating air, 
 nor the efficiency of its contact with the piping, nor its tem- 
 perature upon its return to the piping. It is not possible, 
 therefore, to figure the problem without several uncertain as- 
 sumptions, and it is best to determine the piping by the 
 method previously set forth from data which can readily be 
 determined, and beyond this to be governed by one's judg- 
 ment or experience in similar equipment, bearing in mind 
 that as we increase the volume of air or the circulation, we 
 increase convection and decrease piping, and as we decrease 
 difference of temperature between the air and the steam we 
 decrease convection and increase piping. 
 
 We have considered only actual steam temperatures in 
 the piping, but there should be some allowance made for loss 
 in transmission from steam to piping, and for conduction 
 through the piping. It is possible to calculate these losses 
 under assumed conditions, but an allowance of 3 to 5 de- 
 grees in the temperature difference will usually fully cover 
 such losses. 
 
 Figures 41 and 42 show plan and sectional elevations of a 
 steam pipe dryer which, as shown and with various modifica- 
 tions, has found frequent use. 
 
 A double row of steam pipes are placed at the floor level
 
 88 
 
 DRYING CLAY WARES 
 
 under the cars of bricks, and a single row is placed along the 
 walls on each side of each tunnel. The dryer is roofed as 
 shown and down comer flues are inserted in the walls at in- 
 tervals. The flues are connected with cross horizontal flues 
 at the bottom, forming an inverted T, which extends under 
 the floor piping. The air supply enters through these flues. 
 Alternating with these air inlets are stacks in the roof of the 
 
 Figure 41. 
 
 tunnels and extending through and above the protecting roof. 
 
 It will be noted that one feature of this dryer is that the 
 air is taken from the space between the tunnel roof and pro- 
 tecting roof, and it is heated to the extent of any radiation 
 from the tunnel roof. 
 
 As much as 3,200 lineal feet of one-inch pipe is used in 
 each tunnel 100 feet long, which is a greater heating surface 
 than that determined by our estimate, but it must be remem-
 
 DRYING CLAY WARES 
 
 bered that actual conditions can only determine the amount of 
 piping. We find in use some dryers with less piping than the 
 theoretical amount calculated by us, and some with more, all 
 dependent upon the work to be done and the time. 
 
 The dryer shown is properly periodical, but where the clay 
 
 Figure 42. 
 
 will stand the severe treatment, the dryer is operated pro- 
 gressively. In the periodical dryer the steam is shut off until 
 the tunnel is filled, and is then turned on and the heat raised 
 as the ware will stand it. If the clay is very tender drying, 
 the air inlets and stacks may be closed until the ware is
 
 90 
 
 DRYING CLAY WARES
 
 DRYING CLAY WARES 
 
 heated up and in a safe condition to stand the admission of 
 air, and only such amount of air should pass through the dryer 
 as may be needed to carry out the moisture. 
 
 In operating the dryer progressively, cars of freshly made 
 ware are put in at the receiving end as fast as cars of dried 
 ware are taken from the delivery end. The steam is on all 
 the time, and the ware from the machine enters at once a 
 drying atmosphere having temperatures of 200 to 250 degrees 
 
 Figure 44. 
 
 F., which many clays will not stand. Another objection to the 
 progressive operation is that it would be difficult to adjust 
 the inlets and outlets so that in each part of the tunnels long- 
 itudinally there will be the economical relation between air 
 and moisture, and in consequence complete saturation is not 
 attained. 
 
 Figures 43 and 44 show plan and sectional elevations of a 
 periodical steam dryer designed exclusively for tender drying 
 clay. The piping is arranged in three rows and the connec-
 
 92 
 
 DRYING CLAY WARES 
 
 tions are such that each row is independent. No effort is 
 made to control the individual air inlets except that the roof 
 space from which these inlets draw the air is entirely en- 
 closed, and when desired they can only get such supply as 
 may be derived from leakage. It is not necessary, however, 
 to have any control of the inlets. The outlets are controlled 
 by slide dampers, which can be operated from either end of 
 the dryer. 
 
 As soon as a tunnel is filled with ware, the slide dampers 
 to the flue leading to the stacks are closed, and steam is 
 turned into the bottom row of pipes, followed by the second 
 
 Figure 45. 
 
 and third row as experience may determine. Thus the ware is 
 heated up in a humid atmosphere, which has proven very 
 effectual as a preliminary treatment in drying tender clays 
 Following this humidity treatment the Me dampers a?e 
 diawn, slightly or fully, as the ware may require, and Se 
 
 Fifu P re C 4 e , h^ * ^ flrSt d6SCribed type of stea ^ dryer 
 in several S^jTVif P r i0diCal Steam dryer which ^ used 
 
 r
 
 DRYING CLAY WARES 93 
 
 taining approximately 14,000 bricks in the length of the tun- 
 nel, or 110 feet. At intervals in the roofs of the tunnels are 
 openings into inclined cross ducts and the latter connect with 
 galvanized iron ducts in the outside walls, which in turn lead 
 under the piping. The moisture ladened air rising from the 
 bricks passes through the openings in the tunnel roof, thence 
 to the flues in the outside walls, where it is presumed to be- 
 come cooled, the moisture condensed and carried away by a 
 drip at the ground level. It is assumed that the air in this 
 way renews its ability to take up moisture, which is true to 
 whatever extent it becomes heated in passing among the 
 steam piping, but it must be evident to any one that the air 
 thus returned to the dryer is fully saturated all the time while 
 the outside air on an average will not be more than 75 per 
 cent, saturated. No heat is conserved, because the air re- 
 turned to the dryer has the same temperature as outside air. 
 Possibly the inventor had in mind that the latent heat in the 
 vapor, which is nearly 75 per cent, of all the heat required, 
 would be returned to the air entering, but instead it is given 
 to the outside air. 
 
 Under progressive dryers will be described one which act- 
 ually gives back to the dryer the heat value of the latent heat 
 in the vapor and the additional heat required is that necessary 
 to maintain the dryer losses exclusive of the evaporation of 
 the water. 
 
 In the dryer, under discussion a small air duct extends 
 along the wall on either side of each tunnel inside the tunnel. 
 These ducts connect with the outside air at the ends of the 
 tunnels and have frequent inlets into the tunnels in their 
 length. The purpose of these is to supply leakage losses, and 
 to restore the air which is carried out by small stacks at the 
 end of the dryers. 
 
 So long as clayworkers continue to build dryers which are 
 palpably wrong in principle, it is evident to us that they need 
 instruction in the principles that govern drying. 
 
 One point possibly favorable to the above described dryer 
 is that it might have some application as a humidity dryer. 
 If we had absolutely dry air at a temperature which would 
 give it a vapor capacity of "J," let us say, and air containing 
 moisture, but at such a temperature that it also had an 
 additional vapor capacity of "J," will the latter be a 
 safer drying medium than the former? This is affirmatively 
 answered by some, and numerous instances are cited 
 where steam injected into the hot air at the delivery 
 end of the tunnels has overcome considerable loss in
 
 94 DRYING CLAY WARES 
 
 the drying. If the temperature is below 212 degrees 
 one can readily see how the steam could be of bene- 
 fit by reducing the rate of drying through increase in 
 the degree of saturation, but under such conditions lower 
 temperatures should accomplish the same purpose, yet do not. 
 If the temperature is above 212 degrees, the addition of steam 
 theoretically could not affect the rate of drying, since above 
 the boiling point the capacity of the air, if we may so express 
 it, becomes infinite, or, in other words, so long as the steam 
 can escape we cannot lower the drying rate by the introduc- 
 tion of more steam. We do not know whether vapor in itself 
 has any influence on the drying. Undoubtedly numerous in- 
 stances of the benefits of steam are to be found, in high volume 
 air progressive dryers, in which, as will be seen under the 
 discussion of progressive dryers, saturation is not complete at 
 the exhaust end. In such instances the steam introduced at 
 the hot end simply serves to increase the humidity in such 
 parts of the tunnel where humidity is needed to prevent loss 
 through too rapid drying. We have seen steam introduced 
 into the hot air entering the dryer in a number of instances 
 with beneficial results, but we must admit that we cannot see 
 what part it plays in safer drying, unless it corrects a fault 
 in the dryer and adjusts the degree of saturation to a safe 
 degree. 
 
 Figures 46 and 47 in plan and section show the general 
 principles of a hot air periodical dryer (Bechtel) which is 
 extensively used in the United States and Canada. 
 
 There are a series of parallel tunnels opening on top into 
 the dryer building. A cross duct at one end connects these 
 tunnels with a fan with steam coils attached. The inlets to 
 the floor tunnels are controlled by dampers hinged at the top. 
 On either side of the open floor tunnels are stringers from 
 four to six inches high above the floor level which serve as 
 supports for the pallets containing the bricks. The pallets 
 are loaded at the machine with eighty to one hundred and 
 twenty bricks each and carried to the dry room on lifting 
 trucks and placed on the stringers over the tunnel. As soon 
 as a tunnel is fully covered, burlap is thrown over the bricks, 
 and the hot air is turned into the tunnel duct. The burlap 
 serves as a blanket to prevent rapid escape of the air and 
 permits the latter to become highly saturated with moisture. 
 
 Waste heat from cooling kilns may be used in connection 
 with the steam coils, and as the latter may be heated during 
 the day by exhaust steam the drying may be largely done 
 with waste heat.
 
 DRYING CLAY WARES 
 
 It is common practice to use eight sections of coils, each 
 section to have four rows of one-inch pipes staggered to in- 
 sure thorough contact with the incoming air. For brick dry- 
 ers the pipes are spaced 2% inches on centers and the free 
 
 1 
 
 
 ""* 
 
 
 r 
 
 i 
 
 
 
 ^" 
 
 
 1 
 
 1 
 
 
 
 
 1 
 I 
 I 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 1 
 
 ~ 
 
 ... 
 
 "~ 
 
 
 
 
 ~" 
 
 ~" 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 1 
 
 1 
 
 
 
 
 
 
 
 
 
 
 1 
 
 1 
 1 
 
 
 
 
 
 
 
 
 _ 
 
 ... 
 
 
 
 ! 
 
 | 
 
 i 
 
 
 
 
 | 
 
 
 
 
 
 ! 
 
 L. 
 
 E 
 
 
 
 = 
 
 ii- 
 
 
 f 
 
 L. 
 
 j 
 
 - 
 
 Fig. 
 
 area so obtained is approximately one and one-half times the 
 area of the fan inlet. 
 
 The fans used are disc, plate, or squirrel cage type, but 
 the latter is the most economical in power consumption and 
 the first mentioned the least economical. 
 
 Carpenter has shown that the economic limit of the num-
 
 DRYING CLAY WARES 
 
 ber of rows of pipes in a heater is between 16 and 24, and 
 in consequence we will get no return from any pipes m ser- 
 ies in excess of twenty-four except at air velocities which 
 
 would not be considered in designing a clay ware dryer. This, 
 of course, applies to a constant pressure. 
 
 As stated above, the common practice is to use eight sec-
 
 DRYING CLAY WARES 97 
 
 tions containing a total of thirty-two pipes but six sections 
 having a total of twenty-four pipes are arranged for exhaust 
 or low pressure steam, and the final two sections are sup- 
 plied with high pressure live steam. In this way we get the 
 value of the large amount of latent heat in the exhaust steam 
 and after the air has reached approximately the temperature 
 of boiling water, it is brought in contact with the high tem- 
 perature live steam pipes and its temperature is raised above 
 212 degrees F. by the sensible heat of the high pressure. 
 
 Figure 48 is a sectional elevation of steam coils, waste 
 heat duct and fan. A damper, or set of dampers, is provided 
 so that any proportion of the necessary volume of air can 
 be obtained from the coils or duct. When there is no waste 
 heat available from the kiln, the duct to the fan is closed 
 and all the air is drawn through the coils involving in many 
 instances the use of live steam to maintain a required air 
 temperature. When the waste heat has an excessive tem- 
 perature it is tempered with air through the coils and oh such 
 occasions nothing but exhaust (waste) would be used in the 
 coils. As the kilns cool the volume of air from them may be 
 increased, and, as needed, live steam is introduced into the 
 coils. 
 
 Figure 49 and Figure 50 show in plan and elevation the 
 general principles of a properly connected heater. Both high 
 pressure and exhaust steam are conducted to the coils and 
 controlled by valves and traps so that we may use exhaust or 
 low pressure live steam in six sections, and high pressure 
 steam in two sections, or all the sections may have exhaust 
 steam or high pressure steam as desired, when suitable traps 
 are provided. 
 
 The condensation water may be drained back to a receiv- 
 er and automatically pumped back into the boilers, or tilting 
 traps may be used to deliver the water from the coils to the 
 boilers. Frequently we use a vacuum pump to exhaust the 
 coils and in this way get greater efficiency. 
 
 There are many modifications in fitting up the equipment, 
 and a variety of traps, impulse valves, etc., which apply un- 
 der different conditions, but it is not the purpose of this arti- 
 cle to discuss them. Every problem should be worked out 
 by a competent steam engineer and installed under his di- 
 rection. 
 
 One advantage of this type of dryer is that there are no 
 steam pipes under the bricks to be damaged and covered by 
 broken bricks falling from the pallets, and such debris in the 
 tunnels can be easily cleaned out from time to time.
 
 DRYING CLAY WARES 
 
 It is very important that the ducts be properly propor- 
 tioned throughout and the openings from the floor ducts be 
 adjusted to insure a uniform pressure in all parts of the sys- 
 tem, otherwise the bricks nearest the cross duct and those 
 over the tunnels nearest the fan will dry first. Since in many 
 installations it is necessary to entirely unload a tunnel before 
 resetting it, and, if the hot air is not properly distributed, the 
 bricks most distant from the fan will be slow drying, and 
 
 Fy.49 
 
 I 
 
 ve.3 
 i 
 
 \-T i o 
 
 r^ TA K 
 
 further, since the capacity of the dryer will be determined 
 by these slow drying parts of the system, it is highly import- 
 of the 6t Pr Per diStribution of the hot air to ^1 Parts 
 
 for ttt this dryer ' or a 
 
 LLh '<r th Ut Consultin S the designers, usually lose 
 
 ration T f "^ ^ ^^ in increased cost of ope- 
 ration, than they save In the installation. The distri-
 
 DRYING CLAY WARES 
 
 button of air volumes cannot be accurately pre-determined 
 and the builder of any equipment requiring the uniform dis- 
 tribution of air or gases who has frequent opportunity to 
 practically adjust the equipment to the highest efficiency can 
 work out the problems of a new installation much more ef- 
 fectively than one whose knowledge of the dryer is based on 
 the operation in a neighboring factory, and the efficiency of 
 a properly constructed equipment will be a profitable invest- 
 ment. 
 
 , /n to. Ke 
 
 H O W I 
 
 G. E.X.MAU >~T 
 
 e. SO 
 
 Fief 
 
 This is the first dryer we have described in which the 
 heating pipes are outside the dryer, but we will find similar 
 heating systems in other types of dryers and a brief discus- 
 sion of this method of heating will not be out of place here. 
 
 In sectional coil heaters used in connection with fan draft, 
 the coils are always placed outside the dryer and the air is 
 sucked through them and forced into the dryer. 
 
 One fact which becomes apparent is that we need no long- 
 er consider the radiated heat, or, at least only in such degree
 
 100 DRYING CLAY WARES 
 
 as the casing and internal construction material other than 
 the piping are heated by radiation and in turn give up the 
 heat by conduction to the air passing through the heater. The 
 radiated heat which we may neglect is not lost, however, ex- 
 cept in part that from the outside casing of the coils, since 
 it passes from pipe to pipe and becomes useful in maintain- 
 ing the temperature of the surface of the pipe, or, in other 
 words, it reduces the condensation which otherwise would oc- 
 cur. In the direct heating system we have radiated and con- 
 vected heat applied to the purpose of drying and each re- 
 quires its proportion of steam condensation. In the indirect 
 heating, convection alone carries heat into the dryer but the 
 radiation by maintaining the surface temperature may be 
 said to be given up to the dryer by convection, not to increase 
 the convected heat but to reduce the condensation loss. The 
 convected heat carried into the dryer is constant for any given 
 difference of temperature and fixed air velocity and we get 
 less heat from the indirect method than by the direct and cor- 
 respondingly less condensation, but we can increase the con- 
 densation and thereby the convected heat by increasing the 
 velocity of the air. We would not think of putting the pipes 
 outside the dryer in a natural ventilation system, because, 
 first, as previously pointed out, the volume of air is insuffi- 
 cient to carry the heat required, and second, even though the 
 air volume were sufficient we would have to greatly increase 
 the amount of piping. Increased air velocity, however, com- 
 pletely changes the situation. 
 
 There are several formulas to determine the temperatures 
 available for steam coils, but they are not convenient for the 
 clayworkers' use. 
 
 The manufacturers of heating and ventilating equipment 
 publish the data in the most convenient form, and the follow- 
 . ing table is taken from Bulletin No. 273, of the American 
 Blower Company, Detroit, Michigan. 
 
 Table No. 1. 
 
 To Determine Temperature Rise for Any Steam Pressure or 
 Initial Temperature. 
 
 T t K=constant as follows. 
 
 R= L l R=rise. 
 
 K ' t=temperature incoming air. 
 
 T=temperature steam. 
 K is as follows for any Pressure and Initial Temperature:
 
 DRYING CLAY WARES 
 
 101 
 
 No. of 
 
 
 
 
 
 
 Sections 
 
 300' 
 
 600' 
 
 900' 
 
 1,200' 
 
 1,500' 
 
 Deep. 
 
 Vel. 
 
 Vel. 
 
 Vel. 
 
 Vel. 
 
 Vel. 
 
 1 
 
 3.9 
 
 4.91 
 
 5.57 
 
 6.2 
 
 6.66 
 
 2 
 
 3.19 
 
 2.76 
 
 3.13 
 
 3.48 
 
 3.75 
 
 3 
 
 1.615 
 
 2.04 
 
 2.30 
 
 2.56 
 
 2.75 
 
 4 
 
 1.333 
 
 1.68 
 
 1.91 
 
 2.12 
 
 2.28 
 
 5 
 
 1.21 
 
 1.46 
 
 1.66 
 
 1.85 
 
 1.99 
 
 6 
 
 1.142 
 
 1.32 
 
 1.49 
 
 1.66 
 
 1.785 
 
 7 
 
 1.11 
 
 1.24 
 
 1.385 
 
 1.54 
 
 1.66 
 
 8 
 
 1.088 
 
 1.19 
 
 1.310 
 
 1.44 
 
 1.55 
 
 9 
 
 1.072 
 
 1.152 
 
 1.26 
 
 1.36 
 
 1.46 
 
 10 
 
 1.06 
 
 1.130 
 
 1.220 
 
 1.305 
 
 1.40 
 
 If "t" is above Zero add to "R" for Final Temperature. 
 
 If "t" is below Zero deduct from "R" for Final Temperature. 
 
 Table No. 2. 
 Properties of Saturated Steam. 
 
 Gage 
 
 
 
 Latent 
 
 Total 
 
 Pressure 
 
 
 B. T. U. in 
 
 B. T. U. in 
 
 B. T. U. in 
 
 inLbs. 
 
 Temp. F. 
 
 Water 
 
 Steam 
 
 Steam 
 
 
 
 212.0 
 
 180 
 
 970.4 
 
 1150.4 
 
 1 
 
 215.3 
 
 183.4 
 
 968.1 
 
 1151.5 
 
 2 
 
 218.5 
 
 186.6 
 
 966.2 
 
 1152.8 
 
 3 
 
 221.4 
 
 189.6 
 
 964.3 
 
 1153.9 
 
 4 
 
 224.4 
 
 192.5 
 
 962.4 
 
 1154.9 
 
 5 
 
 227.2 
 
 195.3 
 
 960.6 
 
 1155.9 
 
 6 
 
 229.8 
 
 198.0 
 
 958.8 
 
 1156.8 
 
 7 
 
 232.3 
 
 200.5 
 
 957.2 
 
 1157.7 
 
 8 
 
 234.8 
 
 203.0 
 
 955.6 
 
 1158.6 
 
 9 
 
 237.1 
 
 205.4 
 
 954.0 
 
 1159.4 
 
 10 
 
 239.4 
 
 207.7 
 
 952.5 
 
 1160.2 
 
 15 
 
 249.7 
 
 218.2 
 
 945.5 
 
 1163.7 
 
 20 
 
 258.8 
 
 227.4 
 
 939.2 
 
 1166.6 
 
 25 
 
 266.8 
 
 235.6 
 
 933.6 
 
 1169.2 
 
 30 
 
 274.0 
 
 243.0 
 
 928.5 
 
 1171.5 
 
 40 
 
 286.7 
 
 255.9 
 
 919.4 
 
 1175.3 
 
 50 
 
 297.6 
 
 267.2 
 
 911.3 
 
 1178.5 
 
 60 
 
 307.3 
 
 277.1 
 
 903.9 
 
 1181.0 
 
 70 
 
 316.0 
 
 286.0 
 
 897.3 
 
 1183.3 
 
 80 
 
 329.9 
 
 294.3 
 
 891.0 
 
 1185.3 
 
 90 
 
 331.1 
 
 301.8 
 
 885.3 
 
 1187.1 
 
 100 
 
 337.8 
 
 309.0 
 
 879.8 
 
 1188.8 
 
 125 
 
 352.2 
 
 324.4 
 
 867.8 
 
 1192.2 
 
 150 
 
 366.3 
 
 338.0 
 
 857.0 
 
 1195.0 
 
 200 
 
 387.8 
 
 361.3 
 
 837.9 
 
 1199.2
 
 102 
 
 DRYING CLAY WARES 
 
 To determine the temperature rise we take the difference 
 between the temperature of the steam at any pressure, (table 
 2) Ind the temperature of the air and divide by the proper 
 actor from table 1, which gives us the desired temperature. 
 
 If we have both low and high pressure steam, we deter- 
 mine the temperature for the low pressure then with this 
 temperature as the value of "t" we determine the tempera- 
 ture from the high pressure sections. 
 
 For example if we have six sections on exhaust steam at 
 5 pounds back pressure, and two sections at 60 pounds pres- 
 sure with the air at 60 degrees and an initial velocity of 9( 
 feet 'per minute, we proceed as follows: Low pressure 
 perature from table 2, 227. 
 
 22760 
 
 =112 F.=gain in temperature 
 1.49 (from table 1) 
 
 112 + 60=172=temperature after passing the six low tem- 
 perature coils. 
 High pressure temperature from table 2, 307 
 
 307172 
 
 =43=additional gain in temperature 
 3.13 
 
 172+43=215=final temperature. 
 
 It is not claimed that these tables give accurate results, 
 but they are sufficiently close for practical work, and they 
 have the advantage of a ready reckoning which the busy man 
 desires. Greater accuracy can be obtained by calculating the 
 velocity for each section from the formula: 
 V x 
 
 491+(t 32) 491 + (T 32) 
 
 and find the factor for the calculated velocity by interpola- 
 tion in table 1. For instance, if in the above example we de- 
 termine the velocity after passing six sections we get a ve- 
 locity of 1,094 feet per minute and the factor for two sections 
 will be 3.35. This factor gives us an additional temperature 
 of 40 degrees instead of 43 degrees as previously determined. 
 The error is appreciable and would be still more so if we were 
 to calculate the velocities after passing each section, but the 
 difference will be well within the margin of safety allowed by 
 engineers especially in problems of this character for which 
 there is not sufficient experimental data upon which to base 
 an accurate estimate. 
 
 The problem of determining the amount of piping required 
 for any given requirement will be worked out in the discus-
 
 DRYING CLAY WARES 103 
 
 sion of progressive dryers and need not be taken up now, 
 except to outline the data. 
 
 If the one inch pipes are spaced 2% inches the space be- 
 tween will be 1.435 inches and 8.37 spaces one foot long re- 
 quiring an equal number of pipes will be found in each square 
 foot of free area. This gives us 8.37-=-3=2.79 square feet 
 heating surface in each row per square foot of free space, or 
 2.79X32=89.28 square feet of radiating surface in an eight 
 section heater for each square foot of free space. If the ve- 
 locity is 900 feet per minute we have this many cubic feet of 
 air per minute heated to a temperature of 215 degrees as prev- 
 iously determined, by 89.28 square feet of radiating surface, 
 or reduced to pounds there will be .074X900=66.6 pounds of 
 air per minute. The mean specific heat of air for volume is 
 
 [.0188-f. 0000009 (T+t)] (T t) 
 and for weight is 
 
 [.2344-.000012 (T+t)] (T t). 
 
 From this we find that we get 1640 B. T. U. per hour per 
 square foot of radiating surface, which is a decided advance 
 over the return in B. T. U. in natural ventilation. Having de- 
 termined the B. T. U. per foot of piping we only need to esti- 
 mate the dryer requirements to ascertain the quantity of 
 piping required. 
 
 The Boss Dryer. 
 
 Fig. 51 shows a recent dryer development (Boss) in which, 
 the lifting car and pallet system is used, but the heating ar- 
 rangement is quite different from any other type of dryer. 
 
 Between the car tunnels are superheating tunnels con- 
 taining auxiliary steam pipes. 
 
 The main heating equipment is a mass of steam pipes in 
 the main air duct in front of the fan. (Not shown in the 
 sketch.) In this dryer, the steam pipes are between the dry- 
 er and fan. Exhaust steam exclusively is used in the piping 
 in the main duct. The air entering through the fan is forced 
 among the pipes in the main duct and becomes heated to the 
 full possibility of exhaust steam. Exhaust steam is used in 
 the heating tunnels of the dryer proper and the air in pass- 
 ing these pipes is brought up to the full temperature permis- 
 sible from exhaust steam. Were it desired, live steam in the 
 auxiliary (tunnel) piping would produce a higher temperature. 
 
 I'uder the szeam pipe tunnels are air ducts with inlets into 
 the heating tunnels, which connect at the receiving end of 
 the dryer with a cress duct from a fan.
 
 104 
 
 DRYING CLAY WARES 
 
 The pallets have double floors, the bottom being tight 
 and the top perforated, in other words, they are flat boxes 
 with perforated tops. When the pallets are in place they 
 form a part of the hot air distribution system, since they 
 cover ducts from the heating tunnels and have openings 
 through their bottoms to admit the hot air into the palle 
 and thence the air rises through the mass of bricks and 
 escapes at the top. To prevent lateral escape of the air mov- 
 
 (Section 
 
 able curtains are adjusted to the sides after the tunnels are 
 fully covered with loaded pallets. 
 
 Waste heat or any heat source is applicable to this sys- 
 tem, in conjunction with the steam heating or independent 
 thereof. 
 
 The drying principle is exclusively up draft, which has 
 long been held by brick makers to be the best method of 
 drying. The upward passage of the air among the bricks is
 
 DRYING CLAY WARES 
 
 105 
 
 retarded to any desired practical degree by close setting of 
 the bricks and the top courses may be set to act as dampers, 
 thus preventing too rapid escape of the air. 
 
 There are no pipes in the car tunnels and the heating tun- 
 nels are covered so that no debris can get into the heating 
 tunnels except such as may fall through the small connection 
 between pallet and heating tunnels when the pallets are re- 
 moved. 
 
 The Pipe Rack Dryer. 
 
 The pipe rack dryer shown in Fig. 52 is used in many 
 yards where the clay will stand such severe treatment. It 
 is so well known to the clayworking fraternity that a de- 
 scription is hardly necessary. 
 
 The dryer is simply a series of steam pipe racks upon 
 
 /=/>. 52 
 
 which the flat steel pallets containing the bricks are placed. 
 
 It is customary to build the racks in four sections each 
 holding 7,500 to 10,000, making the daily capacity of each 
 unit dryer 30,000 to 40,000 bricks. 
 
 The pallets loaded with bricks are delivered into the dry- 
 er in the passageway between the racks on rope conveyors 
 and the empty pallets are returned on the same conveyor 
 using the under return ropes for the empty pallets. 
 
 A thirty thousand capacity dryer will have four quarters 
 each containing eight sections ten feet long and fourteen 
 rows high. In each row there are five one-inch pipes. The 
 total piping therefore for 30,000 bricks per day is 22,400 lineal 
 feet, not including connections and fittings. Reducing this 
 to square feet of heating surface per thousand bricks we
 
 DRYING CLAY WARES . 107 
 
 get 249, which is greatly in excess of the piping requirement 
 as figured for periodical tunnels. 
 
 It is likely that the degree of saturation is not high, but 
 the dryer can be depended upon to deliver its full quota of 
 bricks every 24 hours, which Is a very important factor in 
 economical operations. 
 
 Tender Clay Dryer. 
 
 Figs. 52 and 53 show in plan and section one-half of a re- 
 cently patented periodical dryer, the purpose of which is con- 
 trol of the drying conditions in each tunnel independent of 
 the other tunnels. It has a series of double tracked tunnels, 
 "A," as in some other types of tunnel dryers and under each 
 track is a distributing duct, "B," for the hot air, with grad- 
 uated inlets, "C," through the tunnel floor, similar to the dis- 
 tributing ducts in waste heat progressive dryers. The moist- 
 ure ladened air, after leaving the ware, escapes through a 
 series of ventilators, "D," in the roof of the tunnels. 
 
 There are two main cross ducts "G" and "E" one above 
 the other, to supply the distributing ducts with air. From 
 each cross duct there are damper controlled openings, "I" and 
 *J," into a series of mixing chambers, "K," directly connected 
 with the distributing ducts. 
 
 The lower cross duct, "E," connects with a fan, "F," and 
 the air supply is direct from the outside; namely, cold air. 
 
 The upper cross duct, "G," has a separate fan, "H," draw- 
 ing heated air from any source of heat kiln, auxiliary fur- 
 naces, heating coils, etc. 
 
 The illustrations show the cross ducts in the center of 
 the dryer, but this is not essential. It, however, enables the 
 builder to construct a dryer twice as long as one having the 
 heat and air supply at one end, or in a shorter dryer it in- 
 sures more perfect distribution of the heat and air and in 
 consequence a more equitable temperature from end to end 
 of the dryer, and more uniform drying of the ware. 
 
 Cold air alone, or hot air, or a mixture of cold and hot air 
 in any degree and in any volume, may be forced into each, 
 any, or all tunnels, as desired. 
 
 ' After a tunnel is filled with ware, the damper inlet, "I," 
 from the cold air cross duct may be slightly opened, thus per- 
 mitting a small volume of low temperature air to enter. As 
 the ware will stand more rapid circulation, the cold damper 
 can be opened to greater extent. Following this the tern-
 
 108 DRYING CLAY WARES 
 
 perature of the air can be increased by opening the inlet, "J," 
 from the hot air cross duct and can be carried higher and 
 higher by further increase of the latter opening, at the same 
 time reducing the cold air inlet. 
 
 No. 1 tunnel may be filling and the air inlets will be 
 closed, thus disconnecting this tunnel from the cross air 
 ducts. No. 2 tunnel may be unloading and its dampers also 
 will be closed. The drying in No. 3 may be so far advanced 
 that the full hot air temperature may be used and it may 
 get its supply of air entirely from the hot air duct, while No. 
 4 tunnel may require a mixture of hot and cold, in which 
 case both hot and cold air inlets will have their dampers par- 
 tially opened, and No. 5 tunnel, just starting, may, perhaps, 
 safely use only cold air. It may be that a factory is making 
 two kinds of ware, one of which requires a slow careful dry- 
 ing, while the other will stand rapid treatment. It is claimed 
 that all of these conditions are practicable in this dryer. 
 
 At first glance one would say that a progressive regula- 
 tion would be difficult to control, but regular progression 
 probably is not the intention of the inventor, nor is it neces- 
 sary. The operation would likely be in stages two or at 
 most three and experiment must determine the temperature 
 and duration of each stage for the different wares. Each 
 tunnel is provided with a recording thermometer, and when a 
 tunnel is first connected, the dampers may be adjusted to the 
 desired temperature for the first stage. At the expiration of 
 the first period the dampers may be adjusted to bring the 
 temperature to that required during the second period, and 
 again for the third period, should a third period be required. 
 Intermediate adjustments would be required to correct varia- 
 tions in the temperature of the air from the sources of supply. 
 
 The dryer is essentially for tender drying clays, such as 
 require careful treatment in the start but which may be fin- 
 ished rapidly. The ordinary waste heat dryer has to be 
 adjusted for the careful treatment all through in order to 
 protect the tunnels freshly filled and in consequence the full 
 drying period is excessive, often times impractically so. For 
 such clays a dryer which enables the operator to advance 
 the rate of drying in each tunnel independently, has a decid- 
 ed advantage. For clays which will stand abuse in drying, 
 the temperature can be maintained at a maximum all the 
 time and a single control through the hot air fan would be 
 simpler than any multiple control. This single control is
 
 DRYING CLAY WARES 109 
 
 equally applicable to the above described dryer in which 
 event the cold air fan and duct become superfluous. 
 
 A feature of the dryer, especially for hollow ware, is that 
 the movement of the air is directly upward through the ware 
 and the drying is more uniform and there is less damage in 
 in consequence. There are several dryers, both periodic and 
 progressive, in use, having this updraft feature, and the pro- 
 moters of the horizontal draft types justly claim that one can- 
 not get full value from the heat by a single short passage of 
 the air through the ware in other words, that the satura- 
 tion will not be complete and there will be a waste of heat. 
 This is true, but of no moment, if only waste heat is used in 
 the drying- If heat is generated for the drying, naturally the 
 less degree of saturation will require more fuel, but this may 
 be offset by quicker and safer drying. 
 
 A standardization of sixty-eight Ohio clays showed 15 per 
 cent that could be safely dried in commercial operations in 
 twenty-four hours; 51 per cent required from twenty-four to 
 seventy-two hours; 19 per cent were only safe between seven- 
 ty-two hours and seven days, while the remainder required in 
 excess of seven days. Ohio is a favored state in its clay- 
 working materials, yet the percentage of clays that rank first 
 class in drying behavior is low. There are few states that can 
 make as good a showing as Ohio, and there are some states 
 in which good drying clays are so rare that 2 per cent will 
 probably include all that are first class in drying qualities. 
 There is, therefore, a large field for a tender clay dryer.
 
 110 DRYING CLAY WARES 
 
 CHAPTER X. 
 Pottery Drying. 
 
 UNDER THE HEAD of pottery we include all ware 
 which is the work of the potter white and yellow 
 ware, porcelain, electrical ware, sanitary products, 
 stoneware, etc. 
 
 The drying of these wares requires different conditions, 
 depending upon the size and shape of the ware, upon the 
 mixture and upon the process of manufacture. 
 
 In view of the varying treatment required in the several 
 wares, there is no general type of dryer applicable to all, 
 and it is beyond the province of this article to describe the 
 drying methods in any detail. 
 
 Pottery is largely the product of hand labor and each piece 
 as it leaves the potter's hands, or at most several pieces on 
 a pallet, is taken to the dry room by hand. 
 
 Since hand work enters so largely into the manufacture 
 of pottery, it is essential that the work rooms have abundance 
 of light and air, and in general we find the potters' benches, 
 jollys, jigs, etc., along the outer walls of the factory building. 
 
 Since the ware is moved by hand another essential fea- 
 ture is that the distance from the benches to the dry rooms 
 shall be a minimum. 
 
 In consequence of these two factors we frequently find the 
 dry rooms in the center of the manufacturing room. The 
 distance to the dry room is thus very short, and, of course, 
 equally short from the dryer to the finisher or back to the 
 potter, to whom the molds must be returned. 
 
 A modern arrangement for some lines of ware is the con- 
 tinuous operation plan, now applied to so many industries, in 
 which the raw materials enter at one end and in each stage 
 of the manufacture advance toward the warehouse for fin- 
 ished ware, which places the dry room adjacent to the manu- 
 facturing room and opening into it. The succeeding rooms
 
 DRYING CLAY WARES 111 
 
 depend upon the character of the ware and the process of 
 manufacture. 
 
 The dry rooms for small ware consist of a series of com- 
 partments four or more feet wide, depending upon the size 
 of the ware, and ten or more feet long, depending upon the 
 width of the building and the space required for the potters. 
 On either side of each compartment are shelves spaced to 
 suit the ware in question and extending to the ceiling of the 
 room. The passageway between the shelves is simply wide 
 enough for the workmen who fill and empty the shelves, and 
 is made as narrow as possible in order to get a maximum 
 drying capacity within the allotted space. In some lines of 
 ware the compartments or dry rooms are provided with doors 
 which close the room when not being filled or emptied, but 
 in other lines the rooms are merely racks, with passageways 
 for the workmen distributing the ware. 
 
 The heating is by steam pipes, usually three one-inch 
 pipes along the floor under each set of shelves, or six pipes 
 to each room. As the ventilation is natural, usually very 
 crude and slow, the air within the room is practically heated 
 by radiation, or, more properly should we say, that the fix- 
 tures, walls, shelves, molds, etc., are heated by radiation, 
 and the air is heated by contact with the pipes, and with the 
 fixtures, etc. In some lines of ware which will stand more 
 rapid treatment, the pipes are distributed under each shelf, 
 or each alternate shelf, which brings the heating surface in 
 closer touch with the ware. 
 
 As in other clay industries, insufficient drying room is one 
 of the handicaps of the pottery industry, and potters are con- 
 stantly studying the problem of how to increase the drying 
 operation within the space available, without damage to the 
 ware and without increased cost. 
 
 Instead of the rooms with passageways the dryer becomes 
 more compact in fact, the space occupied is more than 
 doubled in capacity by having the shelves hung on trolleys 
 and overhead tracking, which permit pulling them out for 
 filling and emptying. Thus, each shelf is brought nearer the 
 potter and the distance traveled per day by the off-bearers 
 is lessened. Every foot increase in the distance the ware 
 has to be moved adds to the cost otherwise there would be 
 no question in regard to dryer capacity. At first glance, the 
 movable shelf plan seems the most advantageous, but it 
 must be remembered that there must be a wide space be-
 
 112 
 
 DRYING CLAY WARES 
 
 tween the potters' benches and the shelves to provide room 
 for the shelves when pulled out, besides working room around 
 them. 
 
 It is a question whether the movable shelves with their 
 greater initial cost and greater cost of upkeep have any ad- 
 vantage over the fixed racks with passageways. 
 
 Mr. Herford Hope, in a paper before the sixteenth annual 
 meeting of the American Ceramic Society, and later in a lec- 
 ture before the potters of Ohio in the Ohio State University, 
 presented a new type of pottery dryer adapted to small ware. 
 
 Instead of rectangular rooms with shelves on either side, or 
 rectangular racks which can be moved in and out on trolleys, 
 he suggests a hexagonal closet. In the center of each closet 
 there is a vertical shaft to which the shelves are attached 
 radially, and the whole shelf contrivance can readily be swung 
 around a circle, similar to a revolving clothes horse. The 
 door to this closet is opposite the potter's bench, and the 
 passage into it between any two sets of shelves, is "V" 
 shaped. As the shelves of each section or "V" of the shelves 
 are filled, the apparatus is moved one section. Mr. Hope
 
 DRYING CLAY WARES 
 
 113 
 
 shows that no greater floor space is occupied and that the 
 off-bearers travel less distance per day. If no greater floor 
 space is occupied, and the distance traveled by the off- 
 bearers is reduced, the hexagonal closet is an advance over 
 the rectangular, provided the first cost and the subsequent 
 upkeep are not excessive. 
 
 A vertical shaft properly installed offers no mechanical 
 difficulties, and the upkeep will be practically nothing. The 
 initial cost will be greater than the fixed shelves, but not as 
 great as the shelves attached to trolleys. It seems, there- 
 
 FCy. 55 Ena Eicvatfon 
 
 fore, that Mr. Hope offers to the pottery industry a decided 
 advance in the type and arrangement of the dry rooms. 
 
 Prof. Carl B. Harrop, of the Ohio State University School 
 of Ceramics, in a lecture before the potters of Ohio, on the 
 subject of "Pottery Closet Dryer Calculations," assumes the 
 radiation and convection from the steam piping to be 3.25 B. 
 T. U. per hour per square foot of radiating surface per 1 
 degree difference in temperature. In a note he explains: "In 
 a case of this kind, it is exceedingly difficult to determine 
 just how much of the heat is radiated from the pipes and
 
 114 
 
 DRYING CLAY WARES 
 
 how much is carried away from the pipes by convection (by 
 ^incoming air). Experiments and calculations show tha 
 the radiation will be approximately 1.25 B. T. U. 
 erence 2 B T U. (3.25-1.25), cannot be carried in by the 
 amount of air at 120 degrees, which was calculated as suffi- 
 cient to carry out the moisture. 
 
 "The explanation of this is that there is an internal cir- 
 culation of the air going on continuously inside the dryer, 
 i e some of the air which goes into the dryer, becomes 
 heated rises, gives some heat to the ware, takes up some 
 moisture from the air and escapes. Other portions of the 
 entering air does not escape immediately but cools suffi- 
 ciently to drop to the bottom of the dryer and again passes 
 around the pipes, is reheated and rises again to perform 
 more work." 
 
 This accords fully with our view of the action of a natural 
 
 Fiq.56 <S ide :. leva t ion 
 
 draft steam pipe dryer as expressed in a previous article of 
 this series. 
 
 Prof. Harrop's data is based upon 5 pounds steam pressure 
 and 60 degrees temperature of incoming air, and his calcula- 
 tions develop the preceding diagram Fig. 54 as the heat bal- 
 ance for a white ware pottery dryer. 
 
 The calculations lead to the conclusion that a closet 4 feet 
 3 inches wide (containing shelves on either side and passage- 
 way in the center), 8 feet high and 10 feet long, will require 
 six 1-inch pipes, 10 feet long, which is common pottery prac- 
 tice. 
 
 Figs. 55 and 56 show end and side elevation of the general 
 construction of fixed pottery shelves for small white ware, 
 stoneware, and other ware not too large to be placed in 
 shelves, and which will not permit piping under each shelf.
 
 DRYING CLAY WARES 115 
 
 CHAPTER XI. 
 Terra Cotta and Other Special Dryers. 
 
 IT IS A QUESTION whether we are justified in describing 
 a dryer as typical of terra cotta. We have seen terra cotta 
 modeled in a single piece over 40 feet long and 10 feet 
 high. After the modeling the piece in question was cut into 
 sections to be dried and burned, but each section was so com- 
 plicated that the drying had to be watched and controlled. For 
 such ware, and there is a great deal of it, a dryer of any type 
 is obviously out of the question. 
 
 Monumental pieces of terra cotta can only be dried on the 
 modeling floor, and the drying process involves the use of wet 
 cloths here and there on each piece to insure uniform drying 
 without damage. 
 
 This is equally true of other delicate wares, such as glass 
 pots, flattening stones and retorts, some of which exceed a ton 
 in weight, and the manufacture of which from start to finish 
 requires several months. 
 
 Smaller terra cotta products, such as moldings, etc., which 
 can be cut into small pieces of uniform size, can be dried more 
 quickly, and such pieces may be and usually are removed from 
 the modeling floor to some type of dryer. 
 
 One prominent terra cotta plant has the modeling floor 
 (press room) underlaid by flues from the kilns, and all the 
 heat from the burning kilns passes under this floor. At night, 
 arrangement is made to force into the press room hot air from 
 cooling kilns. This method is economical, but lacks sufficient 
 control. 
 
 In two, perhaps more, installations the press room is under- 
 laid by steam pipes in sections, each section being controlled 
 by valves. 
 
 In several instances special dryers are provided for ware 
 which will stand more rapid treatment than that of the press 
 room. 
 
 Fig. 57 shows a dryer used in the manufacture of terra
 
 116 
 
 DRYING CLAY WARES 
 
 
 : 
 
 ^ 
 
 
 
 
 
 XI 
 
 K
 
 DRYING CLAY WARES 117 
 
 cotta. It is of the tunnel type and two-storied. The lower 
 tunnel receives the terra cotta on cars. In the upper tunnel is 
 a fan and set of steam coils. 
 
 The fan forces the air through the heating coils, thence the 
 length of the upper tunnel, from which it passes into the lower 
 tunnel and returns to the fan. With no outlet for the air 
 there will be no incoming air, and the fan merely creates 
 circulation. When the air becomes fully saturated no drying 
 can take place. 
 
 In one instance the practice was first to continue this cir- 
 culation until the ware became fully heated up, then to open a 
 door, "A," in the end of the upper tunnel leading to the fan, 
 also open the exit door, "D," of the lower tunnel, and close the 
 opening, "C," between the upper and lower tunnels at the fan 
 end. With these changes the fan would draw air from the out- 
 side, force it through the coils and to the end of the upper tun- 
 nel, then down into the lower tunnel and returning to exhaust 
 at the delivery end of the latter. 
 
 In two other installations a small relief or escape hole, 
 "B," is placed at the end of the upper tunnel opposite to the 
 fan. Part of the air, forced through the coils by the fan, es- 
 capes through this relief hole, while the remainder passes 
 through the ware and returns to the fan. 
 
 The quantity of air which escapes through the relief hole 
 must be replaced by outside air through "A." The lower tun- 
 nel doors are kept closed all the time except in filling and emp- 
 tying, and after the inlet and vents are adjusted to the ware 
 no changes are necessary. 
 
 In this dryer we have the most satisfactory conditions for 
 drying difficult ware a rapid circulation of hot, nearly satu- 
 rated air. 
 
 In two factories which have come under our observation 
 all ware that has reached the stage of rapid drying and can be 
 removed from the press rooms (which have steam-heated 
 floors) is taken to drying rooms which have slotted floors and 
 through which air is forced by a plate fan. The air is drawn 
 from the outside through heating coils, or from cooling kilns. 
 It is also provided that hot air, after passing through the dry- 
 ers, may be forced into the press room to maintain the tem- 
 perature of the latter and provide a nearly saturated air, which 
 is desired for the initial drying stages of freshly molded 
 wares, and also during the modeling. 
 
 Typical waste heat progressive dryers are also used in 
 some factories.
 
 118 DRYING CLAY WARES 
 
 The Scott System. 
 
 The Scott system is a method of drying, rather than a 
 dryer, since the purpose of the system is to eliminate the 
 dryer. It is applicable to stiff-mud bricks. Dryer cars, trucks, 
 etc., are replaced by conveyor belts. 
 
 The take-off belt from the cutter is extended along the 
 fronts or ends of the kilns. Opposite the entrance of each kiln 
 a cross-conveyor takes the bricks from the main conveyor into 
 and through the kiln, and from this belt they are taken off by 
 the setters. 
 
 The bricks are set six to eight courses high, or to whatever 
 height they will carry the weight. The floor of the kiln is com- 
 pletely covered to this height, and it is the aim of the system 
 to have the kilns of such size that they will hold one day's run 
 of machine. 
 
 The kilns have a system of under-floor flues, and after the 
 kiln floor is fully covered with the first setting of bricks, hot 
 air by means of a fan is forced through these distributing flues 
 and up through a perforated kiln floor, among the bricks, and 
 escapes from the top of the setting. 
 
 If the clay will stand rapid drying, the bricks so set can be 
 dried during the night sufficiently to carry the weight of a sec- 
 ond setting on top of the first lot. 
 
 In this case the cross-conveyor is raised to the proper 
 height for a second setting, and the total height at the end of 
 the second day is twelve or more courses. At night the heat is 
 again turned in, perhaps completing the drying of the first set- 
 ting, and hardening the second setting sufficiently to carry the 
 weight of a third setting. The operation is repeated until the 
 kiln is filled to the proper height, and the burning begins with 
 the advantage that, except the last setting, the bricks are dry, 
 or nearly so, and heated up. 
 
 If the clays will not stand such rapid work, two kilns are 
 used alternately, thus giving thirty-six hours for drying each 
 setting. 
 
 The take-offs, dryer transfer men and tossers in the kiln 
 are eliminated, except one man is required to remove the waste 
 cut from the belt where cutters making a waste cut are used, 
 and one man is required to transfer the bricks from the main 
 belt to the cross-conveyor. 
 
 Before introducing the hot-air system of drying, it was at- 
 tempted simply to set the bricks in the kiln as high as they
 
 DRYING CLAY WARES 119 
 
 would stand and dry them during the night by means of light 
 fires in the furnaces, but this method of drying failed because 
 it was impossible to properly distribute the heat, and the sys- 
 tem only became practical with the introduction of hot-air dry- 
 ing as worked out by Mr. Scott. 
 
 In one instance, where natural gas was available, gas pipes 
 with a series of jet flames were placed through the arches, and 
 at night these were kept burning to provide heat for drying. 
 We do not know how successful this gas firing method proved 
 to be, but it has not been duplicated so far as we know. 
 
 The gas-pipe method of drying is very simple, but it is only 
 applicable to up-draft kilns, while the Scott system in its en- 
 tirety is equally applicable to up-draft, rectangular down-draft, 
 
 and chambered continuous kilns, and is in operation in yards 
 equipped with these several types of kilns. 
 
 The Underwood system of burning up-draft kilns with pro- 
 ducer gas woAild give a wider use of the Scott system of con- 
 veying and drying, provided it is practical to dry the bricks in 
 kilns with a direct flame, as in the natural gas flame method 
 mentioned above. 
 
 Among brickmakers, especially those using continuous 
 kilns, there has been some discussion in regard to the possi- 
 bility of drying the bricks regularly set in the kiln, thus elimi- 
 nating the dryer. 
 
 The practicability of this is doubtful. In the first place, 
 few clays will In the green state support the weight of regular 
 setting. 
 
 Next arises the difficulty of regulating the rate of burn- 
 ing to that of drying, and this has been found a difficult prob- 
 lem, and an unsolved one in this country, by those who are 
 trying to introduce car tunnel kilns for drying and burning, 
 in which the bricks are set on cars at the machine and the 
 loaded cars travel successively through the several stages of 
 drying, burning and cooling in a tunnel kiln. The discussion 
 of this operation belongs under the head of progressive dryers 
 and will there be considered. 
 
 However, if drying in the continuous kiln becomes prac- 
 ticable, it will lead to a decided change in the construction of 
 our kilns, and in this event a kiln along the lines of the Ger- 
 man zigzag kiln, with its low crowns and convenience for me- 
 chanical setting, would likely be developed. 
 
 Among the economies suggested by those discussing the 
 problem is that of fuel, the claim being made that the drying
 
 120 DRYING CLAY WARES 
 
 could be done entirely with waste heat. This is a mistake. 
 The only waste heat in a continuous kiln is that which escapes 
 through the stack or draft fan, which is very little, and that 
 lost by radiation, which is not recoverable. 
 
 If we succeed in Utilizing the continuous kiln for drying we 
 must increase the present burning fuel consumption from 50 
 per cent, to 100 per cent, which in itself is a problem in many 
 continuous kilns at present operated. In our present knowl- 
 edge, and with the present continuous kiln development, dry- 
 ing stiff-mud products in the kiln is not feasible, except possi- 
 bly in some type of car tunnel kiln, of which there are now one 
 or two promising prospects being worked out. 
 
 Car Tunnel Kilns. 
 
 A car tunnel kiln may combine the processes of drying and 
 burning in one operation. 
 
 The car tunnel kiln dates back more than one hundred and 
 sixty years. The first patent is seventy-five years old, while 
 the more or less successful modern kiln was patented more 
 than forty years ago. 
 
 Several attempts have been made to introduce the kiln in 
 this country with very meagre results in drying. 
 
 The principle of the operation is that the green ware on 
 cars from the machine enters the tunnel at one end and passes 
 successively through drying, watersmoking, heating up, burn- 
 ing and cooling zones, and arrives at the exit end finished and 
 ready for shipment. 
 
 It has been found impractical in general to adjust the ope- 
 ration of the kiln to suitable drying conditions, and the gen- 
 eral opinion in countries where the kiln has reached its high- 
 est development is that the drying must be carried on in a 
 separate compartment. Undoubtedly, some shales and clays 
 in this country will stand the severe drying condition neces- 
 sarily developed in the tunnel kiln in order to keep pace with 
 the rapid burning, but for general application the combined 
 operation in a unit tunnel is not practical in the present com- 
 mercial development of the kiln. 
 
 The practicability of the single tunnel may be questioned 
 for any clay, or at least except in rare instances, aside from 
 the ability of the clay to stand severe drying treatment. 
 
 There are many clays that will stand any kind of abuse in 
 drying, but there is the question of heat and moisture to be 
 considered. Clays contain combined water up to 14 per cent
 
 DRYING CLAY WARES 121 
 
 of their weight, and in the tunnel kiln we have the vapor of 
 this combined water to contend with as well as the moisture 
 vapor which is removed in a dryer. 
 
 In the car tunnel kiln then we must provide heat and air 
 to carry the heat, not only to remove the moisture from the 
 ware, but to carry the additional burden of combined water. 
 Even with air dried ware entering the kiln it was found im- 
 practical to maintain sufficient temperature to prevent con- 
 densation before the combustion gases and hot air reached the 
 end of the drying tunnel. Otto Bock, a German engineer, over- 
 came the condensation difficulty by widening the tunnel at the 
 cold end, and introducing iron partitions between the kiln 
 walls and cars of ware. In other words, he built iron ducts 
 in the sides of the tunnel into which the saturated gases were 
 drawn and the ware within the tunnel was heated by radiation 
 from the ducts. 
 
 It will readily be seen that the development of the car 
 tunnel kiln has many difficulties to overcome. 
 
 The use of separate drying tunnels of any type in which 
 to dry the ware and to serve as a storage room to keep the 
 kiln in operation when the machines are not in operation is 
 the method in successful commercial use. 
 
 The heat from a tunnel kiln, because of the burden of water 
 vapor which it carries, is not valuable for direct drying, but 
 in indirect drying we not only realize the sensible heat in the 
 gases but may also realize the latent heat from any condensed 
 vapor. 
 
 The combination of a tunnel kiln with a radiated heat dry- 
 er of the Moeller and Pfeifer type, or perhaps any type, will 
 result in a maximum economy and this is the present com- 
 mercial development of the car tunnel kiln. 
 
 It is not the province of this discussion to consider receut 
 patents, but we will digress to mention two which give prom- 
 ise to overcome the drying difficulties of the car tunnel kiln. 
 
 The Drayton kiln introduces diaphragms on short cars at 
 regular intervals, which partition the tunnel into separate 
 compartments, or, in other words, in a measure convert the 
 tunnel into a chambered kiln. The firing is down draft, eith- 
 er producer gas, or direct coal fired, but with this we are not 
 here concerned. The movement of the combustion gases is 
 down through the burning compartment, up through the heat- 
 ing up and watersmoking compartment, down through the 
 dehydration compartment, and thus up and down until the
 
 122 DRYING CLAY WARES . 
 
 gases are drawn off by a fan. We do not wish our readers 
 to accept the above statement literally. One compartment is 
 exclusively for the burning, but ahead of that the compart- 
 ments are not reserved exclusively for any particular stage of 
 the process heating up, watersmoking and drying. As in a 
 chambered kiln the gases are drawn ahead through several 
 compartments until the temperature and water vapor burden 
 have reached a minimum and maximum respectively in a 
 word, until the dew point is reached when they are removed 
 from the kiln. 
 
 A preheating flue extends from the cooling compartments 
 behind the fires to the drying compartments ahead of the dew 
 point compartment and the initial drying is done with air of 
 any desired temperature and uncontaminated with combustion 
 gas and also free from water vapor, except that originally in 
 the entering air. 
 
 Another kiln now in the experimental stage covers each 
 car with a muffle and when the cars are connected in the tun- 
 nel the muffles form a series of compartment kilns. The fir- 
 ing is done inside the muffles and the air and combustion 
 gases pass from muffle to muffle as the cars advance through 
 the tunnel. The tunnel is a casing for the moving compart- 
 ment kilns on cars, and a drying tunnel. Each muffle-covered 
 car is loaded mechanically inside the muffle with dried bricks 
 and on top of the muffle is placed a load of green bricks. 
 After the car has passed the firing zone and entered the cool- 
 ing zone, an aperture in the top of each or any muffle may be 
 opened, thus permitting the hot air from the cooling bricks 
 to rise into the drying tunnel and by suction pass longitudi- 
 nally to the end of the tunnel similar to a progressive waste 
 heat dryer. 
 
 The muffles in conjunction form the kiln proper, in which 
 the burning is done. The muffle roofs are the floor of prac- 
 tically a waste heat progressive dryer. The movement of the 
 muffles carries the drying bricks forward and thus the muffle 
 roofs combine the dryer floor and brick carriers. The tunnel 
 enclosing the muffled cars has sufficient head room to include 
 the drying bricks and is at the same time the drying and kiln 
 tunnel. 
 
 As each car leaves the tunnel the burned bricks are re- 
 moved from the inside of the muffle, and the dried bricks on 
 top of the muffle are placed inside, after which the car is run 
 back to the tunnel receiving entrance and again started on
 
 DRYING CLAY WARES 123 
 
 its course through the tunnel after receiving a new load of 
 green bricks on its roof. 
 
 The kiln is still in the experimental stage but the experi- 
 ments have advanced to the extent of trying out the burning 
 features commercially, and, it is reported, successfully. The 
 drying features remain to be proven but it is believed that, 
 with the elimination of the combustion gases and the water 
 vapor which the combustion gases carry, there will be no 
 greater difficulty in the drying than there would be in any 
 waste heat progressive dryer. The bricks will enter a warm 
 moist atmosphere and as they advance the temperature will 
 increase, while the degree of saturation will decrease. Finally 
 they will be subjected to the radiation and convection from a 
 hot radiating floor which should remove the hygroscopic water. 
 
 Since the above was written a commercial kiln, complete 
 in every feature, has been put in operation and the problems 
 connected with successful operation are now being worked 
 out.
 
 124 
 
 DRYING CLAY WARES 
 
 CHAPTER XII. 
 Conservation of Heat in German Factories. 
 
 IN A PREVIOUS article we described some German meth- 
 ods of constructing dryers above continuous kilns to make 
 use of the radiated heat from the kilns. This is seldom 
 done in this country, partly because of the great amount of 
 labor required and partly because of cheaper fuel. 
 
 The Germans build expensive plants where necessary to get 
 
 : 
 
 the full benefit of the fuel consumed, while we are very care- 
 less in this regard often ridiculously careless. 
 
 Pigs. 58, 59 and 60 show plan and section of a German 
 dryer equipment, making extensive use of waste heat 
 
 The main draft flue of a continuous kiln is connected with 
 the stack through a series of flues, covered with corrugated 
 iron plates, under the dryer tunnels, and the steam boiler's
 
 DRYING CLAY WARES 
 
 125
 
 126 
 
 DRYING CLAY WARES 
 
 draft flue is similarly connected. Thus they get the waste 
 heat of all combustion, either in the kiln or the boiler fur- 
 naces, and all the heat of cooling kilns. 
 
 The exhaust steam from the engines is carried through the 
 tunnels in large ribbed pipes (see Fig. 60), which are much 
 better radiators than the ordinary steam piping so largely used 
 in this country. 
 
 The exhaust from the drying tunnels is taken up through 
 the roof of the tunnel into ducts leading to the stack, as shown 
 in Fig. 59, and any condensation of moisture in these ducts 
 gives up the latent heat of vapor to maintain the roof temper- 
 
 Ft, 
 
 -ss <5ect lot 
 
 Fij.60 
 
 6J 
 
 ature and the drying tunnels are not robbed of heat to supply 
 the radiation loss. 
 
 The dryer is for the pallet system, and periodic in opera- 
 tion, and the projections in the tunnel walls are supports for 
 the pallets. The pallets are handled by a lifting rack car or 
 truck, Fig. 61, holding the number of pallets required in the 
 height of the tunnel. 
 
 We do not present this German dryer as one worthy of 
 adoption in this country, but merely to illustrate the degree to 
 which the Germans carry conservation of heat and as a hint 
 to clayworkers of this country that they are allowing com- 
 fortable profits to go to waste.
 
 DRYING CLAY WARES . 127 
 
 Moeller and Pfeifer Dryer. 
 
 In the development of progressive dryers the Germans 
 first advanced the principle that the air. should enter with 
 the ware and that the temperature should advance as moist- 
 ure was taken up. It is evident that the exhaust air leaving 
 the dryer at the hot end would carry a large weight of moist- 
 ure pound for pound, or even more and in consequence a 
 much smaller volume of air would be required than in our 
 progressive dryers. 
 
 A number of German dryers, using this principle, have 
 been developed, the most interesting of which is that of Moel- 
 ler and Pfeifer. It also illustrates the recuperation of heat 
 values characteristic of German industrial operations. 
 
 Figs. 62, 63 and 64 show this dryer in plan, longitudinal 
 section and cross-section. 
 
 In the plan, I is the direct coal-fired furnace at the hot end 
 of the dryer G. The dryer is only partially waste heat, since 
 German operators largely use continuous kilns, in which heat 
 from cooling ware is not available for drying. 
 
 The combustion gases from the furnace pass horizontally 
 through ribbed radiating tubes or flues C, thence into flues H 
 connecting with stack or fan. 
 
 Opposite the furnace is a circulating fan F, in fact, there 
 are a number of these circulating fans, as seen in the plan. 
 
 The fan F draws the air through the ware, forces it back 
 under the dryer floor through the ducts N, up around the 
 radiating pipes C, and thence through the ware, a continuous 
 rapid transverse circulation of the air through the ware, with 
 no tendency to a forward movement by the circulating fans. 
 
 In the plan and longitudinal section we have on the dryer 
 roof at the cold end (X) of the dryer a fan E connecting with 
 a cross duct G, and in turn with down comer ducts D. The 
 ducts D connect with heating pipes A, which parallel the cars 
 of ware from near the longitudinal center of the dryer to the 
 cold end. The ends of these pipes at the center of the dryer 
 enter vertical ducts D, which connect with a cross and longi- 
 tudinal duct K to the hot end over the dryer roof. The duct K 
 enters the vertical duct O at the hot end and this duct O at 
 the bottom opens into the end chamber M into which the un- 
 der ducts N discharge. Thus the circuit with the drying 
 chamber is complete. 
 
 There are no doors at the cold end X and the air here en- 
 ters freely. It is immediately taken up by the first fan F and
 
 128 
 
 DRYING CLAY WARES
 
 DRYING CLAY WARES 
 
 129 
 
 the rotary circulation through the heating pipes and ware 
 started. The suction of the fan E acting through the hot end 
 of the dryer slowly advances the air from fan P to fan P un- 
 til the hot end is reached, and the saturated (or nearly) air 
 is drawn into the duct O and started back toward E. 
 
 The movement of the air in the dryer is that of a spiral 
 with a rapid lateral motion and a slow forward movement. 
 The air, as it advances through the drying room, is being used 
 to take up moisture and thus dry the ware. When it reaches 
 the hot end Y its usefulness as a drying medium is finished, 
 and upon its return through the ducts and pipes its heat is 
 given up to the incoming air. 
 
 Not only is the sensible heat of the air and vapor given 
 
 Fig. 64. Cross Section. 
 
 up but in cooling there must be a large condensation of water 
 vapor from the highly saturated hot air which returns to the 
 dryer the latent heat required in the evaporation. 
 
 The dryer losses are the heat taken out by the cars and 
 the ware; the heat in the low temperature saturated exhaust 
 air the volume of which is very small; the radiation losses. 
 These losses are supplied by furnace I. 
 
 If there is available exhaust steam from the factory en- 
 gine it is utilized in radiation pipes B between the furnace I 
 and the exhaust air heating pipes A. 
 
 In connection with a car tunnel kiln the furnace may be 
 dispensed with. The process in the kiln will be extended to 
 the extent of heating up and watersmoking, and the waste 
 gases from the kiln will have a temperature of 500 degrees to 
 800 degrees P. These gases will be drawn through the radia- 
 tors at the hot end of the dryer, and will supply the heat nor- 
 mally supplied by the auxiliary furnace.
 
 130 
 
 DRYING CLAY WARES 
 
 CHAPTER XIII. 
 Progressive Dryers. 
 
 THE periodic tunnel dryer, as its name indicates, is in- 
 termittent in its operation. A tunnel is filled with ware, 
 then the heat and air are turned in and continued un- 
 til the ware is dry when they are shut off and the ware re- 
 moved. 
 
 A progressive dryer is one in which the air volume is 
 constant and the temperature remains unchanged in so far 
 as it is practical to maintain a constant temperture. In 
 the type used in this country, the heated air enters at 
 one end, passes through the tunnels and escapes at the 
 other end. The ware, usually on cars, enters at the 
 air exit end of the tunnels commonly termed the receiving 
 end, travels through the tunnels to the delivery end where 
 it is removed from the dryer and taken to the kilns. 
 
 The entering air, hot and with great capacity for moist- 
 ure, first comes in contact with the hot dry ware leaving the 
 dryer. As the air passes through the tunnels it successively 
 comes in contact with cooler, wetter ware, until at the receiv- 
 ing end it passes among the cold, damp ware just from the 
 machine. In its passage through the tunnel it becomes cooled 
 thereby lessening its capacity for moisture and at the same 
 time it is taking moisture from the ware. The dew point is 
 presumed to be reached as the air leaves the tunnel at the 
 receiving end. 
 
 The drying condition is theoretically ideal. The entering 
 hot air comes in contact with ware in condition to stand a 
 high temperature and which needs such high temperature to 
 drive off the hygroscopic water in the pore spaces of the clay 
 mass. 
 
 The air leaving the dryer comes in contact with green 
 ware which frequently must be carefully heated up without 
 any drying in order to open up the pore spaces, so that when 
 the ware reaches that portion of the tunnel where drying be- 
 gins the water will be drawn to the surface of the ware by
 
 DRYING CLAY WARES 
 
 131 
 
 capillarity as rapidly as it is removed by evaporation. The 
 humidity drying treatment, so necessary in safely drying 
 many clay wares, is automatically carried out in the progres- 
 sive dryer. 
 
 We fail oftentimes in the adjustment of the dryer and in 
 Its operation. 
 
 The normal condition of a progressive dryer is to be full 
 of ware all the time and this is not maintained in any plants, 
 or at least In very few. 
 
 Also the escaping air should be saturated, or nearly so, 
 otherwise there is a loss of heat. If we assume that a dryer 
 has been properly adjusted to a ware and that the inlet tem- 
 perature is 200 degrees F., while the escaping air has a tem- 
 perature of 100 degrees F., and the temperature midway of 
 
 100' 
 
 /SO 
 
 Figure 65. 
 
 
 the dryer Is, let us say, 150 degrees F., we have the condition 
 illustrated in diagram No. 1, Fig. 65. During the night the 
 heat advances until in the morning we have the condition il- 
 lustrated in No. 2 diagram. After a shut down, Monday 
 morning, for instance, the heat has progressed until the con- 
 dition represented in diagram No. 3 is attained. 
 
 The setters In starting work in the morning may draw 
 several cars from each tunnel, enough oftentimes to keep 
 them occupied until noon. The first bricks from the machine 
 come in contact with a temperature and drying condition not 
 intended, and if they stand it the dryer could be changed to 
 more rapid drying conditions with fewer tunnels in operation. 
 If the bricks do not stand this more severe treatment the 
 fault is not with the dryer but with its operation. A progres- 
 sive dryer should have receiving and delivery tracks for stor-
 
 DRYING CLAY WARES 
 
 age outside the dryer and at intervals during the night cars 
 of dried ware should be drawn and cars of green ware en- 
 tered. It is not practical to store cars equal to a day's out- 
 put, but it is common practice to construct the storage tracks 
 to hold three cars on each track. A tunnel holds fourteen to 
 fifteen cars and on the basis of a twenty-four hour period, 
 three cars per tunnel are equivalent to one-fifth of a day's 
 output. If the dryer has a forty-eight or seventy-two hour pe- 
 riod, the three cars are equivalent to two-fifths or three-fifths 
 of a day's run. These storage cars aid materially in main- 
 taining the normal condition of the dryer. 
 
 Operators often find that the output of the dryer is insuffi- 
 cient to keep up the desired capacity. The first step is usual- 
 ly to increase the temperature which changes the conditions 
 to that shown in diagram No. 2 or No. 3, Fig. 65. If the ware 
 cracks, as often is the case, the difficulty may, perhaps, be 
 overcome by reducing the air volume which retards the ad- 
 vance of the heat without necessarily lowering the tempera- 
 ture at the delivery end. With the higher temperature thus 
 maintained at the delivery end we are enabled to drive off 
 the moisture remaining in the partially dried bricks without 
 damage to the bricks behind, since the latter do not get into 
 the high temperature zone until in a condition to stand the 
 higher temperature. Diagram No. 4 illustrates this condition 
 except that the temperature shading should be deeper to show 
 a higher degree of heat. 
 
 There are a number of ways in which the conditions in 
 the dryer can be changed without altering the construction 
 of the dryer, but when these fail it becomes necessary to 
 make such changes in the construction as will give desired 
 results. These changes will be considered under the discus- 
 sion of the several types of progressive dryers.
 
 DRYING CLAY WARES 133 
 
 CHAPTER XIV. 
 Radiated Heat Dryers. 
 
 THE RADIATED HEAT DRYER is a development from 
 the direct coal-fired hot floor. The first step in the 
 development was to cover the hot floor with tunnels. 
 The next step introduced air around the furnaces and into the 
 tunnels, and improvements have been made from time to 
 time in the air circulation and heat radiation. While the pame 
 "radiated heat dryer" is appropriate, yet the dryer really 
 makes use of convection as well as radiation. The entering 
 air circulates around the hot furnace walls and becomes 
 heated by contact with them. It then passes into the tunnels 
 and gives up the heat to the ware and to the work of evapora- 
 tion. The smoke flues extend the full length of the tunnel 
 under the tunnel floor, and the heat from its walls is radiated 
 to the ware. The improvements in the dryer are toward bet- 
 ter air circulation and contact with the hot furnace walls, 
 and toward smoke flue construction, which will give a maxi- 
 mum radiating surface with minimum wall resistance to the 
 passage of the heat by conduction from the inner to the outer 
 surface of the flue walls. 
 
 The furnaces are at the delivery end of the dryer, in a 
 pit below the dryer tracks, and usually and preferably are 
 built into the dryer, in order that any radiation from the 
 furnaces, ordinarily reckoned as a loss, is available in the 
 tunnels for drying purposes. The furnaces are simple box 
 grates and are coal-fired. 
 
 We have worked out the following table from an article, 
 entitled "A Contribution to the Technology of Drying," by 
 R. H. Minton, in Vol. VT, Trans. Am. Cer. Soc. Mr. Minton's 
 calculations are based on nine-pound bricks, containing in 
 round numbers two pounds of water each. The air is assumed
 
 134 
 
 DRYING CLAY WARES 
 
 p 

 
 DRYING CLAY WARES 135 
 
 to have an Initial temperature of 60 F., and to be 75 per cent, 
 saturated. 
 
 Fuel and Air Requirement Per Thousand Bricks Daily 
 No. Temp. F. Temp. F. Coal in Cu. Ft. Air 
 
 Hot End. Exhaust. Pounds. Per Hour. 
 
 1 82 59 271 246,965 
 
 2 109 68 283 144,309 
 176 86 281 71,888 
 
 4 314 104 264 38,087 
 
 A waste heat dryer in temperatures and air volume will 
 operate somewhere between No. 3 and No. 4, inclusive, while 
 a radiated heat dryer will fall below No. 4. In a waste heat 
 dryer the heat source is outside, and there is no opportunity 
 to recuperate the heat in the dryer. In consequence there is 
 a greater fall in temperature from the entering end to the 
 exit, and, other conditions being the same, the volume of va- 
 por which can be carried out is less. 
 
 In the radiated heat dryer the smoke flue (radiating flue) 
 is constantly giving up heat to replace that used in the drying 
 operation, and because of this heat we can remove more 
 moisture with a smaller volume of air. As has been previ- 
 ously stated, there is no relation between air volume and 
 moisture volume; the air has nothing to do with it, except, as 
 in the case of a waste heat dryer, the volume of heat is de- 
 termined by the volume of air. 
 
 Radiated heat dryers can work with a relatively small 
 volume of air. In one instance we found 28,000 cubic feet of 
 air per hour per thousand bricks, but this is greater than an 
 ordinary radiated heat dryer, because of fan draft in this par- 
 ticular instance, where usually only natural draft is used. 
 
 The quantity of fuel per thousand bricks used in a radiated 
 heat dryer depends upon the volume of water to be evapo- 
 rated, upon the weight of clay and iron to be heated up, upon 
 the dryer losses, and upon the efficiency of the operation. 
 
 The quantities given by Mr. Minton are fairly representa- 
 tive, taking into consideration the volume of water assumed 
 to be removed. Our records show variations from 200 pounds 
 to 380 pounds per thousand bricks, the latter consumption 
 being due to improper construction and inefficient operations. 
 
 Fig. 66 is a longitudinal vertical section through a tunnel 
 of a double track radiated dryer, and Fig. 67 is a plan view 
 below the tracks, and Figs. 68, 69, 70 and 71 are vertical 
 cross-sections of the same. The numerals marked on the sev- 
 eral drawings indicate the following features of the dryer: 
 No. 1 is the firing pit below the track level; 2 is the furnace,
 
 136 
 
 DRYING CLAY WARES 
 
 one for each track in the dryer; 3 is the combustion or smoke 
 flue, which extends the full length of the dryer and connects 
 with the main draft duct, 4. 
 
 The dryer under description differs from the usual radiated 
 
 ^Section a- a Section b-b 
 
 Figure 68. Figure 69. 
 
 Section c-c Section cl-ol 
 
 Figure 70. 
 
 Figure 71. 
 
 heat dryer in that the air and moisture at the exit are drawn 
 down through the ware and out through the floor of the dryer. 
 To accomplish this, double-track tunnels are used, and the 
 two smoke flues (3) are brought into one flue in the center
 
 DRYING CLAY WARES 
 
 137 
 
 of the tunnel near the exhaust end. The air enters through 
 openings in the furnace fronts such openings being on either 
 side and above the furnaces circulates around the furnaces, 
 collects in the hot air chambers, 5, enters the tunnel proper 
 through openings 6, thence rises through the ware and is 
 drawn the length of the tunnel. The entering hot air, instead 
 of rising immediately through the ware, may, by means of 
 sheet-iron plates, with graduated openings under the tracks, 
 be distributed under several cars as in waste heat and other 
 
 
 
 I 
 
 Lonjl 'Section 
 Figure 72. 
 
 hot-air duct dryers. On either side of the single smoke flue, 
 near the exhaust end, are air and moisture ducts 7, with per- 
 forated floor (not shown), which connect with air and moist- 
 ure duct 8. The smoke (4) and moisture (8) main ducts lead 
 to stack or fan at one side of the dryer, and the air and fur- 
 nace drafts are controlled by dampers. 
 
 The smoke flues (3) are brick for a distance of 30 to 40 
 feet from the furnaces, on account of the intense heat, and 
 beyond they have brick walls covered with cast-iron plates.
 
 138 
 
 DRYING CLAY WARES 
 
 The idea is to build these flues of materials having the least 
 conductivity resistance and the largest possible radiating sur- 
 face. The flues must be of bricks near the furnaces, but the 
 walls are only 4 inches thick, and the sides, as well as the 
 crowns, are exposed except buck walls at intervals to sup- 
 port the crowns and to carry the tracks. Beyond the brick 
 flue cylindrical iron pipes have been used to the exhaust end, 
 but the more common construction is that of 4-inch brick side 
 walls covered with iron plates. Sheet-iron plates have been 
 
 ~>r .in m n r 
 
 Figure 73. 
 
 used and sealed with sand; flat, overlapping cast-iron plates 
 make a simple covering, but greater radiating surface is had 
 from curved and corrugated plates. 
 
 A more usual form of radiated heat dryer exhausts the air 
 id moisture through the tunnel roof at the end. Figs. 72 
 and 73 are sections through the exhaust stack of such type 
 As will be seen, the smoke flues (3) connect with an under- 
 ground cross-duct (4), which leads to either side of the dryer 
 thence up the back over the dryer to a center stack. The
 
 DRYING CLAY WARES 
 
 139 
 
 moisture outlets (7) are in the tunnel roof and the exhaust 
 air and moisture are directed into the smoke stack. 
 
 The hot radiating flue under the cars of ware induces a 
 circulation, as indicated in Fig. 74, which we do not get in 
 the typical waste heat progressive dryer, and with this cir- 
 culation there is slow progression of the air toward the ex- 
 haust end. 
 
 The value of this circulation is too often overlooked In 
 the setting of the ware on the cars. The bottoms of the cars 
 become heated by direct radiation, thus giving an upward im- 
 pulse to the returning air flowing under the cars. We fre- 
 quently find the ware set in such a way as to prevent the pas- 
 sage of the air; particularly is this true in paving brick man- 
 
 Figure 74. 
 
 ufacture where standard cars are used. Standard cars have 
 slats proportioned and spaced for standard bricks, and paving 
 blocks on such cars overlap the spaces and close them to the 
 passage of the air. 
 
 A brief 'discussion of the merits and efficiency of a radi- 
 ated heat dryer may not be out of place. We are often con- 
 fronted with the inquiry in regard to the proper dryer. Nat- 
 urally, this cannot be answered without full information in 
 each individual case, but some general principles may be dis- 
 cussed. 
 
 There are many plants with scove, updraft or continuous 
 kilns from which little waste heat is recoverable. (Note: 
 We may be criticised for including the continuous kiln in
 
 140 DRYING CLAY WARES 
 
 this category, since in a number of installations heat for the 
 dryer is taken from a continuous kiln. We hold, however, 
 that it is not waste heat, since it must largely be replaced 
 for the kiln operation, but concede that such a kiln may be 
 an economical place in which to generate heat. However, as a 
 general rule, the greatest economy results when the heat is 
 generated where it is to be used. The absurdity of the con- 
 tinuous kiln waste heat claim becomes apparent when one 
 realizes that in a number of plants less fuel is consumed in 
 the kiln than would be required in the dryer. We cannot rob 
 the kiln of all its fuel value, and more, and have left the nec- 
 essary requirement for heating up, watersmoking and burn- 
 ing the bricks.) If, also, the steam power is low, as is often 
 the case, -or the plant is electrically equipped, a direct coal- 
 fired radiated heat dryer is essential. If the steam power is 
 high, then a steam pipe progressive dryer, which is quite as 
 truly a radiated heat dryer, should receive consideration. 
 
 A steam-driven plant, with down-draft kilns, is no place 
 for a radiated heat dryer, especially the coal-fired dryer, but 
 if the plant is electrically driven and near the coal fields, 
 where fuel is cheap, it may be economy to lose the kiln waste 
 heat in order to save the cost of power required to drive the 
 fans necessary to recover the waste heat. 
 
 The selection of the type of dryer, then, is dependent upon 
 the kind of kilns, the character of the power, the cost of fuel, 
 and also necessarily upon the product to be dried. 
 
 The radiated heat dryer may justly claim efficiency when 
 in its proper place and properly installed. 
 
 The heat carried away in the combustion gases is essen- 
 tial to create draft, both for the furnaces and the tunnels. 
 
 The relative high temperature at the air exhaust end 
 causes loss only in case the saturation is correspondingly low, 
 but in view of the small volume of air, of its slow movement 
 through the tunnels, and of the circulatory tendency, as illus- 
 trated in Fig. 74, there is no reason why the saturation 
 should not be practically complete, in which case the high 
 exhaust temperature becomes an efficiency factor. 
 
 The circulation of the air gives in some degree a vertical 
 movement through the ware which is more satisfactory than 
 horizontal draft, and the slow forward movement in connec- 
 tion with the rotary circulation relieves us of the necessity of 
 fitting the dryer closely to the mass of ware. 
 
 The horizontal movement of large volumes of air through 
 a tunnel dryer requires that there be little free space in or- 
 der that the air may be forced among the ware, otherwise 
 there is little drying and excessive loss. It is difficult to 
 adapt such a dryer to several kinds of ware on the same 
 yard tile on double or triple-deck cars, brick on single or 
 double^deck cars, pallet rack cars and in such installations 
 the radiated heat dryers are more efficient.
 
 DRYING CLAY WARES 141 
 
 CHAPTER XV. 
 Steam Progressive Dryers. 
 
 THE ARRANGEMENT of a steam progressive dryer 
 differs from that of a steam periodical dryer in that: 
 The steam piping is massed at the delivery (hot) end 
 of the dryer, the air enters at the delivery end, moves hori- 
 zontally through the dryer, and, with the vapor, is drawn off 
 through a suitable stack at the receiving (cold) end of the 
 dryer. 
 
 The steam dryer may be a series of tunnels, each equipped 
 with the proper amount of piping and under individual control, 
 or more often it is a single large room. 
 
 The piping is arranged in coils, four to six pipes deep at 
 the delivery end, two to four pipes deep in the next section 
 and two pipes in the section most distant from the delivery 
 end. It may extend the full length of the dryer, or only one- 
 half or two-thirds, depending upon the character of the clay, 
 or as the designer deems best. 
 
 Either exhaust or live steam is used for heating. 
 
 The air volume required is relatively low, since the heat 
 is not dependent upon the volume of air. As the heat is used 
 up by evaporation of the moisture, it is replaced by direct 
 radiation from the pipes under the ware and by circulation 
 of the air around the ware, among the pipes, and up through 
 the ware. 
 
 Fig. 75 is a longitudinal vertical section and Fig. 76 a 
 transverse vertical section of a steam pipe tunnel progressive 
 dryer. The air enters from the outside at the delivery end 
 and is distributed under the piping by a floor with graduated 
 openings. The piping is under the tracks and fully exposed 
 within the tunnel. At the receiving end there is no piping 
 shown and this section of the dryer is used for heating up 
 the ware in a humid atmosphere. If the clay will stand se- 
 vere treatment the piping may be extended fully to the re-
 
 142 
 
 DRYING CLAY WARES
 
 DRYING CLAY WARES 
 
 143 
 
 ceiving end and drying begins very quickly after the ware 
 enters. 
 
 The drawing does not attempt to go into any details of 
 construction and is merely a sketch to illustrate the principle. 
 
 Calculations of heat requirement and amount of piping 
 were made for periodic steam pipe dryers and need not be re- 
 peated here. Both rely upon natural draft and use a small air 
 volume. The draft in the progressive type may be somewhat 
 stronger, thus increasing the heat taken from the piping by 
 
 Figure 76. 
 
 convection, but the difference is not material and is easily 
 within the conditional variations of the problem. 
 
 The steam pipe progressive dryer for very tender clays 
 is sometimes built in two compartments in series. 
 
 The first or receiving compartment is short and without 
 any provision for the admission or removal of air in other 
 words, the first compartment, in which a constant temperature 
 is maintained, is merely a heating-up room. The air in this 
 room is necessarily nearly saturated with moisture since no 
 air escapes except by leakage and wall and roof absorption.
 
 144 DRYING CLAY WARES 
 
 The room also serves as a storage room and it is immaterial 
 whether it is kept full or not, provided the ware remains in 
 the room sufficiently long to become thoroughly heated up 
 and put in condition for the drying process. As ware is re- 
 moved from the delivery end of the dryer proper, and the 
 cars of ware moved forward, the space thus provided at the 
 receiving end is filled from the heating-up room. The dryer 
 proper is truly progressive, and since the ware is previously 
 put in condition to withstand the first stages in drying, the 
 piping may extend from end to end. 
 
 A heating-up section is common in other types of dryers, 
 but in none of them do we go to the extent of a separate 
 closed room. 
 
 In one or two instances in the operation of radiated heat 
 dryers it was found beneficial to enclose the receiving tracks 
 and at the same time remove the original tunnel doors at the 
 receiving end. The smoke and exhaust air and moisture 
 ducts were net extended to the end of the receiving tracks 
 (converted into a receiving room). The ware on the receiving 
 tracks became heated in some measure by circulating air from 
 the tunnels, but it was removed from direct heat radiation 
 from the smoke ducts and also from the draft current of air. 
 The ware in this warm dead air space went through a sweat- 
 ing stage which has been proven of value in preparing tender 
 drying materials for the drying treatment. 
 
 In the single progressive dryer this heating-up space re- 
 sults from not extending the piping to the receiving end, but 
 the ware is subjected to the current of nearly saturated air, 
 although not necessarily so. 
 
 So, too, in progressive waste heat dryers do we provide 
 dead air heating-up space where the ware requires it. The 
 difficulty often is that the need of the ware is not previously 
 determined. A dryer is designed and guaranteed for rapid 
 work and afterward its adaptation to the ware requires ma- 
 terial changes.
 
 DRYING CLAY WARES 145 
 
 CHAPTER XVI. 
 Waste Heat Progressive Dryer. 
 
 THE PROGRESSIVE waste heat dryer has found wide use 
 in this country. As the name implies, it is progressive 
 and uses only waste heat where there is sufficient waste 
 heat for the work and on this score the margin is sufficiently 
 small to make suitable equipment and proper operation im- 
 portant. 
 
 In round numbers under the conditions assumed in a prob- 
 lem to be discussed later, about 1.632,000 heat units are re- 
 quired to dry 1,000 bricks. If the bricks are burned at a tem- 
 perature of 1850 F. (Cone 07) and in cooling the heat is re- 
 coverable down to 500 F., we have an available temperature 
 of 1850500=1350 F. The bricks weigh 6,000 pounds and 
 the specific heat is .2. Thus we get from the cooling brick 
 1350X6000X12=1,620,000 heat units. There will be approxi- 
 mately 1,000 brick in the kiln construction for each 1,000 
 brick burned and the average temperature of these brick will 
 be about 1000 F., half of which, perhaps, is recoverable, or 
 500 X 6000 X. 2=600,000 heat units. This makes a total of 
 2,220,000 heat units, not counting radiation losses, which may 
 be 30 per cent to 50 per cent. If the radiation losses in cool- 
 ing are proportional to those in burning, we have under the 
 above assumption insufficient heat in the cooling kilns to dry 
 the product. Higher temperatures in burning will increase 
 the heat supply and the balance may be better or worse than 
 our figure, depending upon the dryness or wetness of the 
 green bricks. We do not give the above figures as data, but 
 simply as an illustration. 
 
 Besides the waste heat of cooling kilns, there is the waste 
 heat in the exhaust steam. If the factory is using 150 h. p., 
 
 34.5X150X970X10 
 
 we have in the exhaust =1,003,950 heat 
 
 50 
 units per thousand brick.
 
 146 
 
 DRYING CLAY WARES 
 
 34.5 = Pounds of water per h. p. hour. 
 150 = Total h. p. 
 
 970 =Heat units per pound exhaust steam. 
 10 = Hours daily operation. 
 50 = Capacity per day in thousands. 
 
 A waste heat dryer necessarily involves the use of a fan, 
 and the most modern installations use two fans. In consider- 
 ing the steam supply, we only reckoned ten hours operation, 
 but the fan operation will be twenty-four hours per day and 
 every day. 
 
 Probably 30 h. p. will be required to drive the dryer fan 
 engines and from these we will recover 34.5X30X970X24= 
 
 34.5X30X970X24 
 engines and from these we will recover - 
 
 50 
 
 481,896 heat units per thousand brick. This is not in addition 
 to the factory waste steam, but materially increases the total 
 as previously estimated on a ten-hour basis. 
 
 The losses between the engine and the dryer is much less 
 than those between the kilns and the dryer and the value 
 of the steam is a material one in reckoning the available 
 waste heat supply. With the exhaust steam it is evident that 
 there should be sufficient waste heat to do the drying with a 
 safety margin of 100 per cent, yet through improper design, 
 faulty construction and inefficient operation, the waste heat 
 supply oftentimes falls short and has to be supplemented with f 
 additional fuel in some way. Small and complicated hot air 
 ducts between the kilns and fan and restricted kiln connec- 
 tions are frequently the cause of excessive loss in collecting 
 the heat, and failure to approximate the dew point in the! 
 dryer exhaust results in great loss in the application of thei 
 heat. A manufacturer would not load his cars with useles^ 
 dead weight, but complacently moves a dead load of useles$ 
 and expensive air through his dryer. That he may be getting 
 his ware dry is no evidence that the work is being economic- 
 ally done. 
 
 The use of the fans brings up a factor of cost which must 
 be considered. On the basis of five pounds of coal per h. p. 
 hour, the fan engines will require 3,600 pounds of coal per 
 day, which, at. $2.00 per ton, is $3.60, or $0.07% per thousand 
 brick. Maintenance brings this cost above $0.10. In fact, we 
 find many fan installations where the operation cost exceeds 
 $0.15 per thousand brick. 
 
 The progressive waste heat dryer is undoubtedly the most 
 economical mechanical dryer, but one must not jump to a 
 conclusion that it will be most economical in every situation.
 
 DRYING CLAY WARES 147 
 
 We may be burning a low temperature product and not have 
 sufficient heat from the kiln; public service electric power 
 may be available at a less cost than steam; licensed engineers 
 command higher pay. When the waste heat supply is short, 
 we supply the deficiency by direct fired auxiliary furnaces. 
 This introduces fuel cost besides power, and often scumming 
 difficulties. 
 
 Difference in size of kilns and in character of product are 
 frequently annoying factors indeed, they enter into the cost 
 in proportion as they affect the capacity. When a large kiln 
 is cooling there is an excess of heat, but a small kiln may not 
 have enough to carry the drying over until a large kiln is 
 ready to turn in. In changing from hollow ware to brick, 
 the hollow ware does not contain heat enough to dry the 
 heavier ware and the operation of the factory is delayed until 
 kilns of cooling brick are available for drying. 
 
 The use of combustion gases from kilns has not been con- 
 sidered and it would materially change the situation. The 
 combustion waste gases and the heat of cooling kilns would 
 give sufficient heat without considering the engine exhaust. 
 The direct application of combustion gases rapidly deterio- f 
 rates the dryer cars, and frequently causes scumming and in 
 consequence the continued use of combustion gases should be 
 through an economize^ in which the heat of the gases serves 
 to heat air for drying and in this way we get the benefit of 
 the heat without the loss and damage by direct use of the 
 gases. An economizer involves the use of fan draft for the 
 kils. which in itself often would be an advantage over natural 
 draft. 
 
 In the selection of the dryer there are many questions to 
 be considered, and one should canvass the whole situation 
 before reaching a decision. 
 
 Auxiliary furnaces to supply deficiencies in waste heat 
 supply are frequently imperative, although, as previously men- 
 tioned, their use is objectionable. Where wood is abundant 
 its use in the furnace removes the objections since wood con- 
 tains no sulphur and its products of combustion will not in- 
 jure the cars nor cause scumming. Either oil or natural gas 
 may be used, since they are very low in sulphur, but coal or 
 coke give a combustion gas seriously objectionable in clay 
 ware dryers. 
 
 Figs. 77 and 78 show a wood-burning furnace adapted to 
 clay ware drying, or it may be equipped with grate bars for 
 coal burning. The bridge wall is made broad and filled with 
 brick checker work. This checker work assists in maintain- 
 ing a uniform temperature, acting as a regenerator and at 
 the same time brings the gases into intimate contact, thus
 
 148 
 
 DRYING CLAY WARES 
 
 giving better combustion. A chamber is provided back of the 
 bridge wall to serve as a dust collector and spark arrester. 
 Figs. 79, 80 and 81 are plan and sections illustrating the 
 relation of 'steam coils, kiln ducts and auxiliary furnace and 
 duct. All the air, whether from coils, kilns or auxiliary fur- 
 nace comes into a mixing chamber adjacent to the fan, and 
 each source of hot air supply is controlled by damper. We 
 can, therefore, use all kiln heat, all auxiliary furnace heat, 
 
 Figure 79. 
 
 all steam coil heat, or any proportion of each. The kiln ducts 
 are usually placed underground and preferably so, but it is 
 important that the ducts be perfectly underdrained and that 
 they be built moisture proof, as far as possible. 
 
 The proper kiln connection has been a fruitful cause of 
 study and experiment. 
 
 A common method is to connect the dryer duct with a
 
 DRYING CLAY WARES 
 
 149 
 
 stack duct, each under damper control. With the stack dam- 
 per open and the dryer damper closed, the kiln is under nat- 
 ural draft and the products of combustion pass into the air. 
 After the kiln is burned, a change in the dampers shuts off 
 the stack and turns the hot air into the dryer. There are 
 three objections to this method: 
 
 1. It is difficult to keep dampers tight and in consequence 
 
 <Sectional Elevation 
 
 Figure 80. 
 
 Fig. 81. 
 
 combustion gases find their way into the dryer to vitiate the 
 air, scum the bricks and blacken them with soot, and destroy 
 the car equipment. 
 
 2. Less heat is obtained by down draft through the kiln 
 floor. 
 
 3. Some wares are damaged by forced draft among them 
 during the cooling stages.
 
 150 DRYING CLAY WARES 
 
 Regarding the dampers we have found any single damper 
 unsatisfactory and we have tried double dampers without suc- 
 cess. Some yards close the dryer duct with a brick wall, 
 which is replaced before each burn. After a kiln is burned 
 and ready to connect with the dryer fan, the stack is damp- 
 ered off and a hole is punched in the dryer duct wall. This 
 hole is enlarged as the kiln cools down, to keep up the heat 
 supply by a larger volume of air. Obviously this method has 
 no merit. It is not tight, nor is it a satisfactory control. 
 
 In one instance, the dryer duct was below the draft duct 
 and the two were connected by a vertical flue from the bot- 
 tom of the draft duct. The top of the vertical flue was re- 
 cessed and in the recess was bedded a heavy fire clay slab, 
 thus closing the connection. The sulphur gases which leaked 
 by these dampers destroyed the reinforcement in the dryer 
 roof and the roof fell in. This damper looked good on paper, 
 but it failed in practice. A fairly tight sand sealed damper 
 might be constructed in this way, but the deep dryer ducts 
 would be expensive in first cost and difficult to drain. 
 
 The simplest and at the same time fully effective damper 
 is a stub duct connected to the dryer duct by a gooseneck. 
 When the gooseneck is removed, the connection between the 
 kiln and dryer is completely broken and there can be no com- 
 bustion gases leaking into the dryer. 
 
 Clayworkers are familiar with the fact that the bottom 
 of the kiln cools first, even though we may be drawing air 
 down through the ware. This, we think, is sufficient proof 
 that we cannot get all the heat out of the kiln through the 
 floor. 
 
 One argument in favor of the bottom draft is that at any 
 time combustion gases can be turned into the dryer to sup- 
 ply any deficiency. We hold that there should be no occa- 
 sion to use combustion gases from kilns or coal-fired furnaces. 
 If the steam equipment is proper, the deficiency can be made 
 up in live steam, but if the deficiency is excessive and con- 
 tinuous, either the kilns and dryers should be connected by 
 an economizer or the waste heat dryer should be replaced by 
 some other type. 
 
 In one plant the distributing ducts are the full length of 
 the tunnels, as in Fig. 85. Suspended in these ducts, which 
 are very large, are cylindrical smoke pipes connected with the 
 kiln draft flues at one end and with an exhaust fan at the other 
 end. All the combustion gases from the kilns are drawn 
 through these pipes and the heat therefrom is available for 
 drying. The heat from cooling kilns is made use of by means
 
 DRYING CLAY WARES 
 
 151 
 
 of a separate fan in the usual waste heat progressive dryer 
 manner. Thus we have an economizing system as part of the 
 dryer construction. 
 
 This manner of using the products of combustion would be 
 equally applicable to a radiated heat dryer, except both com- 
 bustion gases and heat from cooling kilns would be handled 
 through the smoke flues by the single smoke flue fan. 
 
 The most convenient place to connect the dryer duct with 
 the kiln is through the wicket, and a goose neck connection is 
 simple and effective. In the majority of kiln setting there is 
 some space next to the wicket and there is always space over 
 the wickets and in the crown. The suction of the fan draws 
 the air from around the wares rather than through them, and 
 
 Fig. 
 
 TT7 
 
 Fig. 83. 
 
 we not only get more heat in this way but the wares are not 
 damaged by direct draft through them. 
 
 The most efficient place to connect the dryer and kilns is 
 on top of the kiln crown where we fully recover the heat so 
 far as recovery is possible. The wares under such conditions 
 cool entirely by radiation. It is not convenient to make con- 
 nections through the crown, and we usually compromise on the 
 wicket, or in some instances a furnace connection. 
 
 Figs. 82, 83 and 84 show a plan and sections of a typical 
 waste heat progressive dryer. 
 
 The hot air cross inlet duct from the fan is tapered on bot- 
 tom and one side to correspond with the air volume reduction 
 as each distributing duct receives its proportion. The taper is 
 on the distributing duct side so that the end walls of the dis-
 
 152 
 
 DRYING CLAY WARES 
 
 tributing ducts are in echelon and thereby each duct mechani- 
 cally cuts off a proportion of air for its supply. The distribut- 
 ing ducts have graduated openings under each track for a dist- 
 ance of several car lengths. 
 
 The number of cars subjected to the direct upward blast of 
 hot air through the graduated openings depends upon the ware. 
 
 If the ware will stand severe treatment we extend the dis- 
 tributing ducts a greater distance, even the full length of the 
 dryer, as shown in Fig. 85, but extension to this degree is not 
 good practice because any approach to complete saturation is 
 
 Cross <J e c f t o rt 
 Fig. 84. 
 
 4L__B 
 
 Fig. 85. Elevation. 
 
 impossible under such conditions, and economy of operation is 
 coincident with complete saturation. 
 
 A common practice is to extend the ducts four car lengths 
 so that one car will be over the inlet cross duct and three cars 
 over the graduated opening subjected to the direct blast of hot 
 air. Five to eight car lengths subjected to the direct air blast 
 are not uncommon. Other things being equal, the longer the 
 distributing ducts and corresponding greater number of grad- 
 uated openings, the more quickly the drying will proceed. 
 
 Besides the changes in the distributing ducts there are a 
 number of modifications in the exhaust duct.
 
 DRYING CLAY WARES 
 
 153 
 
 I I
 
 154 DRYING CLAY WARES 
 
 In one installation the exhaust ducts return under the 
 dryer floor to the distributing ducts and there connect with an 
 exhaust cross duct. We get two advantages from this con- 
 struction: It brings the fans close together and both can be 
 housed in a single room and driven from the same shaft. The 
 returning air keeps the floor of the dryer warm. Not only the 
 sensible heat of the air and vapor becomes useful, but also the 
 latent heat of any condensation. If the air is saturated to the 
 dew point at the exhaust end of the dryer, there must be some 
 condensation in the return ducts to the exhaust fan, and the 
 heat from this condensation is given back to the dryer through 
 the dryer floor. 
 
 - A vertical air movement is much better than a horizontal 
 one, especially for hollow ware. In any progressive dryer we 
 have an upward movement of the air from the distributing 
 ducts but beyond that the movement is horizontal to the ex- 
 haust and if the ware is not close to the roof of the tunnel 
 which the hot air invariably tries to follow, there will be poor 
 contact between the air and ware. The exhaust cross duct is 
 generally placed underground in order to pull the air down, 
 but it is not very effective and except at the end of the tunnel 
 over the exhaust duct is without any influence on the horizon- 
 tal movement of the air. 
 
 To get a vertical movement, dryers are sometimes con- 
 structed with exhaust ducts having graduated openings simi- 
 lar to the distributing ducts, as illustrated in Fig. 86. The 
 movement then is up through the distributing ducts' openings, 
 over an intervening space which may be much or little as re- 
 quired, and down through the openings in the exhaust ducts. 
 The exhaust cross duct may be at the end of the tunnels or any 
 predetermined distance from the end in order to provide dead 
 air heating up space, and moreover the exhaust ducts' open- 
 ings nearest the exhaust cross duct may be closed to increase 
 the dead air heating up space, but one which will have its floor 
 heated by the escaping air and vapor. Similarly where the 
 exhaust cross duct is on top as in Fig. 85, it may be placed at 
 any distance from the end of the tunnel and thus provide a 
 heating up space removed from the direct air current. 
 Air Volume and Heat Requirement for Waste Heat Dryers. 
 Assume for 1,000 bricks the following: 
 1,000 pounds metal in cars. 
 6,000 pounds clay in bricks. 
 1,000 pounds water in bricks. 
 The conditions of the problem are: 
 Outside air 80 F., 90% saturated 
 Exhaust from dryer 100 F., 100% saturated. 
 The temperature assumed represents average maximum
 
 DRYING CLAY WARES 155 
 
 summer conditions, which will require the greatest quantity 
 of air. A dryer equipped and adapted for these conditions 
 will have excess capacity at lower temperatures or less de- 
 gree of saturation. 
 
 Data used specific heat:' 
 
 Air .234+.000012 (t-32). 
 
 Vapor .42+.0001 (t-32). 
 
 Clay .2. 
 
 Iron .12. 
 
 Water 1.00. 
 
 The problem is first to find the volume of air required, 
 and, second, the temperature to which it must be heated to 
 do the work. 
 
 From the "Vapor Capacity of Air" table (page 19), we find 
 that air at 80 F. and 90% saturation carries .145 pound of 
 moisture per 100 cubic feet, while at 100 F. and 100% satu- 
 ration the burden will be .291 pound of moisture. One hun- 
 dred cubic feet of air, when raised from 80 to 100 expands 
 to 103.7 cubic feet, from the law that the volume of a gas is 
 directly proportional to its absolute temperature 
 
 100 X 
 
 ( , X=1.037). 
 
 491+8032 491+10032 
 
 After raising the temperature of the original air to 100, 
 a volume of 100 cubic feet at this temperature will contain 
 
 .145 
 
 =.140 pound of moisture, provided no additional mois- 
 1.037 
 
 .140 
 
 ture is taken up, and the vapor pressure will be =48% of 
 
 .291 
 
 1.918=.92t). As moisture is taken up, the volume increases 
 directly as the pressure. The pressure increases 1.918 .920= 
 
 29 
 
 .998, and each unit volume at 100 becomes =1.036. 
 
 29 .998 
 
 The volume increases to 1.037 because of advance in tem- 
 perature, and each unit volume of this increases to 1.036 in 
 consequence of increased pressure, due to additional moisture 
 taken up; therefore, the total volume of each unit of original 
 air is 1.037X1.036=1.074. Since each unit volume at 100 and 
 complete saturation contains .291 pound of water vapor, each 
 unit volume at 80 and 90% saturation when saturated at 100 
 will contain 1.074 X.291=.3125 pound. 
 
 Each 100 cubic feet of incoming air under the changed
 
 DRYING CLAY WARES 
 
 conditions has capacity for .3125 .145=.1675 pound of mois- 
 ture. 
 
 We have 1,000 pounds of moisture to be removed, and 
 
 1,000 
 
 therefore will require X 100=597,014 cubic feet of air. 
 .1675 
 
 A common drying period is twenty-four hours, which deter- 
 mines an air volume of 411 cubic feet per minute per thou- 
 sand bricks. 
 
 The weight of a cubic foot of dry air at 80 F. is deter- 
 
 1.325271XM 
 
 mined from the formula: - (page 584, Kent), in 
 
 459.2+t 
 
 which M equals barometric pressure and t equals tempera- 
 ture. From this, we find the weight of a cubic foot of dry 
 air at 80 F. and 29" barometric pressure to be .071 pounds. 
 Air expands as moisture is taken up, and in one cubic foot 
 of the 90% saturated air at 80 there will be less than .071 
 pound, since the vapor is lighter than air and displaces it. 
 
 29 
 From the formula: we get a value of 
 
 29 (1.025X.90) 
 
 1.0328 cubic feet. This formula is based on Boyles law, that 
 the volume is inversely proportional to the pressure. In the 
 formula, 29 equals barometric pressure, 1.024 equals vapor 
 pressure at 80 F. (From vapor capacity table.) 
 
 .071 
 
 The actual weight of air in one cubic foot will be = 
 
 1.0328 
 
 .06876 pound. To this must be added the weight of vapor 
 from the vapor capacity table, .00145, giving a total of .07021, 
 which is the weight of one cubic foot of 90% saturated air 
 at 80 F. 
 
 We required 597,014 cubic feet, which is 41,916 pounds 
 (597,014 X. 07021) of air, including the moisture naturally con- 
 tained in it. 
 
 The problem now before us is to determine the tempera- 
 ture of the air which will be necessary in order to bring suffi- 
 cient heat into the dryer to do the work. 
 
 This problem can only be solved by a series of approxi- 
 mations. 
 
 The heat units required are as follows: 
 
 1. 1,000 X. 12 X temperature is the heat taken out by cars. 
 
 2. 6,000 X. 2 X temperature is the heat taken out by the 
 bricks.
 
 DRYING CLAY WARES 157 
 
 3. 1,000X20 is the heat absorbed by the water in the 
 bricks. 
 
 4. 1,000X1,035.6 is the latent heat of vapor at 100 F. 
 
 5. 41,051(100 80) [.234+.0000121 100 32+80 32)] is heat 
 taken out by dry air. 
 
 6. 866(100 80) [.42+.0001 (100 32+80 32)] is heat taken 
 out by vapor originally in the air. 
 
 7. Dryer radiation loss estimated at 10%. 
 
 Under items 1 and 2, the temperature is indeterminate. 
 In items 3 and 4, we assume that all the evaporation takes 
 place at the exit at a temperature of 100 F., but in reality it 
 is occurring at all temperatures between the maximum and 
 100 F. However, saturation is not complete until the end is 
 reached. If the evaporation took place at 150, the latent heat 
 would be less and the sensible heat required for the water 
 would be greater. The resulting vapor would have a tem- 
 perature of 150, but as it approached the exit it would cool 
 down and give back to the dryer requirement its excess tem- 
 perature. The heat taken from the dryer, therefore, will only 
 be that required to heat the water to the exit temperature 
 and to evaporate it at that temperature. This also explains 
 why item 4 is not made a part of item 6, the latter item being 
 only the moisture originally in the air, which leaves the dryer 
 at a temperature 20 F. higher than its initial temperature. 
 
 In order to solve the problem, we must assume a tem- 
 perature to which the air must be heated, in order to get 
 values for the heat taken out by the cars and bricks. 
 
 Let us assume a temperature of 300, an advance of 220 
 F. We have then the several items: 
 
 1 26,400 heat units 
 
 2 264,000 heat units 
 
 3 20,000 heat units 
 
 4 1,035,600 heat units 
 
 5 193,260 heat units 
 
 6... 7,460 heat units 
 
 1,546,720 heat units 
 7. Radiation loss, 10% 171,858 heat units 
 
 Tot. heat requirement, 1,718,578 heat units 
 The entering air per degree advance in temperature re- 
 quires: 
 
 41,050 [.234+.000012 (300+80 64) ]=9,761 
 866 [ .42+ .0001 (300+8064)]= 391 
 
 10,152
 
 DRYING CLAY WARES 
 
 1,718,578 
 
 =169 advance in temperature, or a thermometer 
 10,152 
 
 temperature of 169+80=249 F. 
 
 Evidently our assumption of 300 F. was too high. Had we 
 assumed 240, the resultant determination would have been 
 241, and a third assumption of 241 (1,632,044 heat units) 
 gives 241, fractional degrees not considered. 
 
 Suppose we have the inlet and exit temperatures, which 
 can easily be determined in any dryer, and wish to determine 
 the volume in order to adjust the fan to economic condition. 
 
 We will take the temperatures in the previous problem 
 in order to check results. 
 
 A cubic foot of the initial air contains .00145 pound of 
 moisture, and, as previously determined, weighs .07021 
 
 .00145 
 
 pound. A pound of the mixture will contain =.02065 
 
 .07021 
 
 pound of moisture and .97935 pound of dry air. 
 
 The heat, in excess of the initial heat, brought into the 
 dryer per pound of initial air is as follows: 
 
 Air (24180) [.234 + . 000012 (24132+8032)] .97935=37.3823 
 Moisture (24180) [.42+. 0001 (241 32+SO 32) ] 
 
 . . .02065= 1.4818 
 
 38.8641 
 Radiation loss, 10%= 3.8864 
 
 Available heat units per pound of air= 34.9777 
 
 Each pound of air, including the initial moisture, removes 
 from the dryer: 
 
 Air (10080) [.234+. 000012 (68+48)] .97935= 4.6106 
 
 Moisture (10080) [.42+.0001 (68+48)] .02065= .1783 
 
 Total heat unit loss per pound of air= 4.7889 
 
 Available heat for the dryer: 
 
 34.97774.7889=30.1889 heat units. 
 The fixed heat requirement is: 
 
 1. 1,OOOX.12X161= 19,320 
 
 2. 6.000X. 2X161= .. 193200 
 
 3. 1,000X20= 20,'000 
 
 4. 1,000X1,035.6= 1,035,600 
 
 1,268,120 heat units 
 
 1,268,120 
 The number of pounds of air required will be: - 
 
 42,006 pounds of air. 3 ' 1889
 
 DRYING CLAY WARES 
 
 159 
 
 In our original calculation we found 41,916 pounds re- 
 quired, a discrepancy of 90 pounds, due to the use of whole 
 numbers in temperatures. The difference is about one-half 
 of one per cent and is negligible. 
 
 Another Method of Determining Air Volume. 
 
 Another, and perhaps simpler, method of determining the 
 air volume is by use of a formula developed by H. M. Prevost 
 Murphy and published in the Engineering News in 1908. 
 
 The water vapor which a pound of dry air can carry is 
 
 KH 
 
 found by the formula: W - 
 
 -, in which W=pounds of 
 
 2.036P-H 
 
 water vapor per pound of air at temperature t, and pressure 
 P in pounds per square inch. P for 29" barometric pres- 
 sure=29X. 4912=14. 24. 
 
 The values of H 
 
 t| K | H || t 
 
 and K are_given in the following table 
 
 K 1 H 
 
 K 1 H 
 
 .tin:: 
 
 MS9 
 
 78 
 
 r,2"; 
 
 .958511 156| .63201 8.744|| 234| .6463] 45.61 
 
 .6115 
 
 .0481 
 
 80 
 
 .6209 
 
 1.024 
 
 ir,.s 
 
 .ma 
 
 9.177| 236 .6467 
 
 47.32 
 
 .6117 
 
 .0526 
 
 82 
 
 .6211 
 
 1.092 
 
 160 
 
 .MM 
 
 9.628 | 238| .6471 
 
 49.08 
 
 .6120 
 
 .0576 
 
 84 
 
 .6214 
 
 1.165 
 
 162 .6330 
 
 10.10 || 2401 .6476 
 
 50.89 
 
 .6122 
 
 .0630 
 
 86 
 
 .6217 
 
 1.242 
 
 164| .6333 
 
 10.59 
 
 242| .6479 
 
 52.77 
 
 | .6124 
 
 .MM 
 
 88 
 
 .6219 
 
 1.324 
 
 166 .6336 
 
 11.10 
 
 211 .6484 
 
 64.69 
 
 .6126 
 
 .0754 
 
 90 
 
 .6222 
 
 1.410 
 
 168| .6340 
 
 11.63 
 
 21.; .6488 
 
 56.67 
 
 .6128 
 
 .0824 
 
 92 
 
 .6225 
 
 1.501 
 
 170| .6343 
 
 12.18 
 
 248| .6492 
 
 58.71 
 
 .6131 
 
 .11! 
 
 94 
 
 .6227 
 
 1.597 
 
 172| .6346 
 
 12.75 
 
 260| .6496 
 
 60.81 
 
 .6133 
 
 .0983 
 
 96 
 
 .6230 
 
 1.698 
 
 171 .6350 
 
 13.34 
 
 252| .6501 
 
 62.97 
 
 .6135 
 
 .1074 
 
 98 
 
 .6233 
 
 1.805 
 
 176| .6363 
 
 13.96 | 254| .6505 
 
 65.21 
 
 .6137 
 
 .1172 
 
 100 
 
 .6236 1.918 
 
 178 .6357 
 
 14.60 256 .6510 
 
 67.49 
 
 .6140 
 
 .1279 
 
 102 
 
 .6238! 2.036 1801 .6360 
 
 15.27 II 258 .6514 
 
 69.89 
 
 .6142 
 
 .1396 
 
 104 
 
 .6241 
 
 2.161 1 1821 .6364 
 
 16.97 || 260 .6618 
 
 72.26 
 
 .6144 
 
 .1523 
 
 mi; 
 
 .6244 
 
 2.294 
 
 184 
 
 .6367 
 
 16.68 M 262| .6523 
 
 74.75 
 
 .6147 
 
 .1661 
 
 108 
 
 .6247 
 
 2.432 
 
 186 
 
 .6371 
 
 17.43 H 264 .6528 
 
 77.30 
 
 .6149 
 
 .1811 
 
 110 
 
 .6250 
 
 2.578 
 
 188 
 
 .6374 
 
 18.20 || 266 .6532 
 
 79.93 
 
 .6151 
 
 .1960 
 
 112 
 
 .6253 
 
 2.731 
 
 190 
 
 .6377 
 
 19.00 
 
 268| .6537 
 
 82.62 
 
 .filfil 
 
 .212" 
 
 114 
 
 .6256 
 
 2.892 
 
 192 
 
 .6381 
 
 19.83 
 
 270| .6541 
 
 85.39 
 
 .6156 
 
 .2292 
 
 116 
 
 .6258 
 
 3.061 
 
 194 
 
 .6385 
 
 20.69 
 
 2721 .6546 
 
 88.26 
 
 .6158 
 
 .2476 
 
 118 
 
 .6261 
 
 3.239 
 
 196 
 
 .6389 
 
 21.68 274J .6551 
 
 91.18 
 
 .6161 
 
 .2673 
 
 120 
 
 .6264 
 
 3.425 
 
 198 
 
 >,::!:< 
 
 22.50 || 276| .6555 
 
 94.18 
 
 .6163 
 
 .2883 
 
 122 
 
 .6267 
 
 3.621 
 
 200| .6396 
 
 23.46 || 278| .6560 
 
 97.26 
 
 ..;i>;.; 
 
 .3109 
 
 121 
 
 .6270 
 
 3.826 
 
 2"2 .6400 
 
 24.44 
 
 2801 .6565 
 
 100.40 
 
 .6168 
 
 ,3880 
 
 126 
 
 .6273 
 
 4.042 
 
 204 | .6404 
 
 26.47 
 
 282 .6570 
 
 103.70 
 
 .6170 
 
 .3608 
 
 128 
 
 .6276 
 
 4.267 
 
 206J .6407 
 
 26.53 
 
 284 .6575 
 
 107.00 
 
 .6173 
 
 .3883 
 
 I, 'in 
 
 .6279 
 
 4.603 
 
 208| .6411 
 
 27.62 | 
 
 286| .6580 
 
 110.40 
 
 .6175 
 
 .4176 
 
 1!!2 
 
 .6282 
 
 4.750 
 
 21" .6415 
 
 28.75 
 
 2881 .6584 
 
 113.90 
 
 .6178 
 
 .4490 
 
 134 
 
 .6285 
 
 5.008 
 
 212| .6419 
 
 29.92 290| .6590 
 
 117.50 
 
 .6180 
 
 .4824 
 
 i:;t; 
 
 .6288 
 
 5.280 
 
 211 .6423 
 
 31.14 | 292| .6594 
 
 121.20 
 
 .6183 
 
 .f.lXl. 
 
 138 
 
 .6291 
 
 5.536 
 
 216| .6426 
 
 32.38 II 294| .6600 
 
 125.00 
 
 .6185 
 
 .6559 
 
 140 
 
 .6294 
 
 5.859 
 
 218| .6430 
 
 33.67 || 296| .6604 
 
 128.80 
 
 .6188 
 
 .5962 
 
 1 12 
 
 .6298 
 
 6.167 
 
 220 
 
 .6434 
 
 36.01 || 298| .6610i 
 
 132.80 
 
 .6190 
 
 .6393 
 
 1 II 
 
 .6301 
 
 6.490 
 
 222 
 
 .6438 
 
 36.38 
 
 300| .66151 
 
 136.80 
 
 .fiiy.-i 
 
 .6848 
 
 11.; 
 
 .6304 
 
 6.827 
 
 221 
 
 .6442 
 
 37.80 
 
 302| .66201 
 
 141.00 
 
 .!% 
 
 .7332 
 
 148 
 
 .CS07 
 
 7.178 
 
 22C 
 
 .6446 
 
 39.27 H 304| .66251 
 
 145.30 
 
 .6198 
 
 .7846 
 
 150 
 
 .6310 
 
 7.545 
 
 22 S 
 
 .6451 
 
 40.78 || 306| .6631J 
 
 149.60 
 
 .6202 
 
 .8391 
 
 If, 2 
 
 .6313 
 
 7.929 |i 230J .6455 
 
 42.34 M 308 .66361 
 
 154.10 
 
 .6203 
 
 .8969 
 
 154 
 
 .6317 
 
 8.328 || 232| .64581 43.95 || 310 .6641) 
 
 158.70
 
 160 DRYING CLAY WARES 
 
 We determine from the above formula that a pound of in- 
 coming dry air at 80 F. and 90% saturation carries .02046 
 
 . 6209X1. 024X. 90 
 
 pound of water vapor ( =.02046). 
 
 2.036X14.241.024 
 
 The weight of a pound of air with water vapor will be 
 
 .02046 
 1 02046 pounds. A pound of the mixture will have 
 
 1.02046 
 .02 pound of water vapor and .98 pound of air. 
 
 This weight of dry air at 100 F. and 100% saturation will 
 
 .6236X1.918X.98 
 carry - -=.0432 pound of water vapor. 
 
 2.036X14.241.918 
 
 Bach pound of the incoming air mixture has capacity to 
 
 remove from the dryer .0432 .02=.0232 pound of moisture. 
 
 Since there are 1,000 pounds of moisture to be removed 
 
 1,000 
 per thousand bricks, there will be required - =43,100 
 
 .0232 
 pounds of initial air mixture. 
 
 This method of figuring gives us a result of 2.8% higher 
 than the method previously used. 
 
 The weight of a cubic foot of dry air at 80 F. is deter- 
 
 1.325271 M 
 mined from the formula - (page 584, Kent), in 
 
 459. 2+t 
 
 which M is barometric pressure in inches of mercury and 
 t equals temperature. 
 
 From this we determine the weight of a cubic foot of dry 
 air at 80 F. and 29" barometric pressure to be .07128 pound. 
 
 Air expands as moisture is taken up, and in one cubic foot 
 of 90% saturated air at 80 F. there will be less than .071 
 pound, since vapor is lighter than air. 
 
 29 
 From the formula we determine that one 
 
 29 (1.024+.90) 
 
 cubic foot of dry air, in taking up moisture to the degree of 
 90% saturation, expands to 1.0328 cubic feet. This formula 
 is based on Boyles law, that the volume is inversely propor- 
 tional to the pressure. In the formula, 29=barometric pres- 
 sure, 1.024=elastic force of vapor at 80. (H in above table.) 
 The actual weight of air in one cubic foot of the mixture 
 
 .07128 
 
 will be =.069 pound 
 1.0328
 
 DRYING CLAY WARES 161 
 
 A pound of mixed air and vapor, as previously determined, 
 
 mains .98 pound dry air and .02 pound water vapor. The 
 
 weight of water vapor in a cubic foot of air at 80 and 90% 
 
 saturation is found from the proportion: 
 
 X=.00141. By Seger's formula, used in our capacity table, 
 this value is .00145. 
 
 The weight of a cubic foot of the air mixture is .069+ 
 .00141=.07041 pound. 
 
 43,100 
 
 The volume of air required will be =r612,129 cubic 
 
 .07041 
 
 feet per thousand bricks. Under the other method of de- 
 termination, the volume was 597,014, a difference of about 
 10 cubic feet of air per minute per thousand bricks. 
 
 Either method gives results sufficiently accurate for any 
 practical purpose. 
 
 Calculations along this line should be of great value in 
 adjusting a waste heat dryer to the highest efficiency. We 
 can determine the temperature by thermometers, the degree 
 of saturation by wet and dry bulb thermometers or the more 
 convenient diagramatic modifications of the same, and the 
 air volume by anemometers or Pitot tubes. With such data 
 we should be able to properly adjust the operation of the 
 dryer. 
 
 In the waste heat dryer, the highest efficiency will come 
 from an initial high temperature. The advantage comes in 
 several ways: 
 
 1. The high temperature means materially less volume. 
 
 2. Less volume means slower progress through the tun- 
 nels, with consequent proportionately greater reduction in 
 temperatures. 
 
 3. Less volume and lower exit temperature assure more 
 complete saturation. 
 
 4. Less volume takes correspondingly less heat out 
 through the exhaust. 
 
 5. More complete saturation means less trying conditions 
 on the ware entering the dryer. 
 
 6. Less volume means less power to drive the fans. 
 
 The size of the fan is always a perplexing question, and 
 one that usually has to be decided before the exact data in 
 regard to moisture and perhaps temperature can be deter- 
 mined. Fortunately, a fan has a wide range; and, provided, 
 we install one of sufficient size, it can be adjusted to any de- 
 sired volume. 
 
 The capacities of fans, as given by the manufacturers of
 
 162 DRYING CLAY WARES 
 
 such equipment, do not apply to our conditions, nor would 
 any capacity table be of general application. We draw the 
 air through a simple to complex checker work and flue sys- 
 tem, and force it into and through the dryer against a re- 
 sistance much greater than an ordinary heating system. 
 
 It has been our practice to determine the actual air re- 
 quirement under adverse conditions, and then select a fan of 
 double this capacity at three-fourths ounce pressure. 
 
 The piping required for a waste steam heat application 
 will depend upon the weight of exhaust steam. 
 
 Under the discussion of periodic dryers, we presented a 
 
 T-t 
 
 formula (R= ) to determine temperatures possible from 
 
 k 
 
 coil heaters. R=rise in temperature, T temperature of the 
 steam, t=temperature of the air, k=factor from table accom- 
 panying the table. If the steam pressure is 4.3 pounds, which 
 would approximate 5 pounds back pressure on the engine, its 
 temperature will be 225. The temperature obtainable from 
 a""six-section heater with air velocity of 900 feet per minute, 
 
 22580 
 
 air temperature of 80 will be T=(R+80) 1-80=177 
 
 1.49 
 
 F. We ordinarily install eight sections, but the last two are 
 arranged for high pressure steam, to enable us to supple- 
 ment with live steam when there is a shortage of kiln waste 
 heat. 
 
 Each pound of steam condensed at atmospheric pressure 
 delivers 970.4 heat units. 
 
 Each pound of air requires: 
 
 Air (17780) [.234+.000012 (193)] .97935=. . .22.45 heat units 
 Moisture (17780) [.42+.0001 (193)] .20265= .88 heat unit 
 
 23.23 heat units 
 
 970.4 
 
 Each pound of steam, therefore, will heat =41.6 
 
 23.23 
 pounds of air. 
 
 If there are 100 horsepower available, we will have 100 X 
 34.5=3,450 pounds of steam per hour, and this will heat 
 3,450X41.61=143,520 pounds of air per hour, or 2,392 pounds 
 per minute. 
 
 In the discussion of periodic dryers, we determined 2.79 
 square feet of heating surface in each row of pipes per square 
 foot of free area. This gives 2.79X24=66.96 square feet in
 
 DRYING CLAY WARES 163 
 
 six sections, and this radiating surface heats 900 cubic feet, 
 
 2,392 
 
 or .07021X900=63.19 pounds of air per minute. X 
 
 63.19 
 
 66.96=2,534 square feet of radiating surface, or 7,602 lineal 
 feet of one-inch pipe to condense the steam from 100 horse- 
 power. 
 
 This result is only approximately correct, since it does not 
 take into consideration any radiation loss from the coils, and 
 in consequence some of the steam will be required to main- 
 tain this loss; but, as this would reduce the amount of piping 
 required, the result obtained gives us a desired factor of 
 safety, and no correction should be made. 
 
 The addition of two sections using live steam will decrease 
 the radiating surface required. 
 
 T-t 
 
 From the formula =R, we determine that live steam 
 
 k 
 
 at 60 pounds in two sections of heater coils will advance the 
 temperature from 177 to 218. This advance of temperature 
 will require a heat consumption of 9.937 heat units per pound 
 of air. 
 
 We have previously determined that a pound of air from 
 80 to 177 requires 23.33 heat units, making a total of 33.267 
 heat units to heat a pound of air from 80 to 218. 
 
 We found that a pound of exhaust steam heats 41.61 
 
 904 
 
 pounds of air to 177, and similarly determine ( ) that 
 
 9.937 
 
 a pound of live steam will heat 90.96 pounds of air from 177 
 to 218. 
 
 The relative steam consumption is proportional to the 
 weight of air heated, and may be determined from the equa- 
 
 1 1 x 1 1 x' 
 
 tions = and = , in which x equals 
 
 132.57 41.61 132.57 90.96 
 
 .686 for exhaust steam and x' equals .314 for live steam. 
 
 The live steam radiating surface per square foot of free 
 area is 2.79X8=22.32 square feet. 
 
 One hundred horsepower in live steam will heat 3,450 X 
 90.96=313,812 pounds of afr per hour, or 5,262 pounds per 
 
 5,262 
 minute. - X 22.32=1,859 square feet of radiating surface 
 
 63.19 
 to condense 100 equivalent horsepower in live steam.
 
 164 DRYING CLAY WARES 
 
 We found that 2,534 square feet would be required for ex- 
 haust steam. 
 
 If both are used at the same time, the surface of each 
 will be: 
 
 1,859 X. 314= 584 square feet of live steam pipe surface. 
 
 2, 534 X. 686=1,738 square feet of exhaust steam pipe surface. 
 
 2,322 total surface required, or 6,966 lineal feet 
 of piping. 
 
 Making due allowance for uneconomical dryer operation, 
 this amount of piping will suffice for 30,000 bricks per day, 
 each brick containing one pound of water. 
 
 It will be noted that the result bears no relation to the 
 dryer capacity, being simply dependent upon its volume of 
 steam available. 
 
 If we wished to determine the piping required to supply 
 heat to dry 1,000 bricks under the conditions of the original 
 problem, we must first determine the temperature obtainable 
 from exhaust steam, which in the above problem we found to 
 be 177. We will assume that two sections are to be used for 
 live steam. In the formula 
 
 T-t 
 
 R= and the table of the factor k included in the dis- 
 
 k 
 
 cussion of periodical dryers, we know, or can easily deter- 
 mine, the value of R=64, t=177, k=3.13; and from these, by 
 
 T 177 
 
 substitution in the formula (64= ), we determine that 
 
 3.13 
 
 the live steam must ha\e a temperature of 377, which is a 
 boiler pressure of 175 pounds. 
 
 This steam temperature is higher than we would have in 
 practical operation, but it can be reduced by the use of a" 
 greater number of sections of live steam coils. 
 
 The number of sections required is easily determined. 
 The temperature of the air entering the live steam sections 
 is 177, and it must be advanced to 241, an increase of 64. 
 
 T-t T 177 
 
 Substituting in the formula R= , we have 64= 
 
 k 2.30 
 
 T 177 
 
 for three sections and 64= for four sections. The first 
 
 1.91 
 
 equation gives 324 for T, which corresponds to a steam pres- 
 sure of approximately 80 pounds, and the second equation
 
 DRYING CLAY WARES 165 
 
 gives 299, which is slightly in excess of 50 pounds pressure. 
 Either of these pressures are commonly used in brick plants, 
 and for our problem we will use four sections of live steam 
 piping. 
 
 Since the air velocity through the heater is assumed to be 
 900 feet per minute, each square foot of free area passes 
 900 X. 07021=63.2 pounds of air per minute. 
 
 As already shown, the exhaust steam in six sections heats 
 the air to 177 F, and there must be heat developed in the live 
 steam sections to advance the temperature to 241 F. 
 
 The total heat development will be: 
 
 1. 63.2 (17780) [.234+.000012 (193)] .97935=1,418.2 
 
 63.2 (17780) [.42+.0001 (193)] .02065=.... 55.61,473.8 
 
 2. 63.2 (241177) [.234+.000012 (354)] .97935= 943.8 
 
 63.2 (241177) [.42+.0001 (354)] .02065=... 38.0 981.8 
 
 Total heat units per sq. ft. of free area= 2,455.6 
 
 The total heat units required for 1,000 bricks is 1,632,044, 
 which, on the basis of a twenty-four-hour drying period, 
 
 1,632,044 
 
 would be =1,133.4 heat units per minute. 
 1,440 
 
 1,133.4 
 The free area per thousand bricks will be: =.46 
 
 2,455.6 
 square foot. 
 
 The piping included within this area will be 2.79X6X4X 
 .46=30.80 square feet for exhaust steam and 2.79X4X4X.46= 
 20.53 square feet for live steam, making a total of 51.33 square 
 feet, or 154 lineal feet of one-inch pipe for 1,000 bricks. 
 
 X,,te Since tlie weight of air required for 1,000 bricks is a 
 factor in determining the total heat requirement, we can deter- 
 
 41,916 
 mine the free area required direct from the weight of air, = 
 
 29.1 
 
 29.1 pounds of air per minute, and =.46 square foot of free 
 
 , 63.2 
 
 area. 
 
 The amount of piping, as above determined, is that re- 
 quired for perfect operation of the dryers; but dryers are 
 seldom operated economically, and to whatever extent they 
 vary from the theoretical operation, in the same proportion 
 will the heat requirement increase, and correspondingly must 
 the steam heating system be enlarged. 
 
 In many installations, double the theoretical amount of 
 piping is installed, which is an admission that practical opera- 
 tions may be only 50% perfect; but in no instance need the
 
 166 DRYING CLAY WARES 
 
 piping be more than 50% in excess of the theoretical require- 
 ment. 
 
 However, excess piping does not necessarily involve loss 
 of heat, because the steam is condensed only in proportion as 
 the heat is removed from the piping by the air. The greatest 
 loss in waste heat dryers is in using an excess of air, which 
 must be heated up. 
 
 About 12% of the total dryer heat requirement is used in 
 heating the air, and if the air is only 50% saturated, as it 
 leaves the dryer the requirement for the air becomes 24%. 
 
 The boiler horsepower required per thousand bricks can 
 easily be approximately determined, since we only need to 
 divide the heat requirement per hour by the heat value of a 
 
 1,632,044 
 
 pound of steam, =70 pounds of steam, or about 
 
 24X970.4 
 
 2 H. P. A safety margin of 50% would increase this to 3 H. P. 
 Finis.
 
 Economies in Brickyard 
 Construction and Operation 
 
 \]O MATTER how successful you 
 have been in your business, no 
 matter how economically you are 
 operating your plant, no matter how 
 skilled your workmen may be, no 
 matter what good results you are 
 getting from your present methods, 
 the book will prove of inestimable 
 value to you. 
 
 WHY? Because it is practical, cov- 
 ers the field thoroughly, points 
 out economical methods for every 
 department of the business, gives 
 you average cost and shows you 
 what the cost of the manufacture 
 of your brick should be. 
 
 It is the best offer for the price we 
 ever made. 
 
 Price - - $1.00 . 
 
 T. A. Randall & Co. 
 
 Indianapolis, Ind.
 
 CLAYS; THEIR OCCURRENCE, PROPERTIES AND 
 
 USES Henrich Ries $5.00 
 
 THE EFFECT OF HEAT UPON CLAYS 
 
 A. V. Bleininger 2.00 
 
 ECONOMIES OF BRICKYARD CONSTRUCTION AND 
 
 OPERATION Ellis Lovejoy 1.00 
 
 SCUMMING AND EFFLORESCENCE 
 
 Ellis Lovejoy .50 
 
 TABLES OF ANALYSES OF CLAYS 
 
 Alfred Crossley 2.00 
 
 THE CLAYWORKERS' HAND BOOK 2.00 
 
 HOLLOW TILE HOUSES 
 
 Frederick Squires 2.50 
 
 MODERN BRICKMAKING 
 
 Alfred B. Searle 5.00 
 
 CLAY GLAZES AND ENAMELS 
 
 Henry R. Griffen 5.00 
 
 VITRIFIED PAVING BRICK 
 
 H. A. Wheeler 2.00 
 
 ENGINEERING FOR LAND DRAINAGE 
 
 C. G. Elliott 2.00 
 
 TILE UNDERDRAINAGE 
 
 J. J. W. Billingsley .25 
 
 RADFORD'S BRICK HOUSES AND HOW TO BUILD 
 
 THEM William A. Radford 1.00 
 
 Any or all of these books will be mailed, postage 
 prepaid, to ajiy address in the United States or Canada, 
 on receipt of price. 
 
 T. A. Randall & Co. 
 
 Indianapolis, Ind.
 
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