US2431201A

US2431201A - Drying of porous masses

Info

Publication number: US2431201A
Application number: US532030A
Authority: US
Inventors: Donald W Ross
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-04-21
Filing date: 1944-04-21
Publication date: 1947-11-18
Anticipated expiration: 1964-11-18

Description

Nov. 1 8, 1947. D. w. ROSS -bRYING oF Ponous mssEs F11e'd`Apr11 21. 19444 d LIV., P IL .Jh l .f u r. T. a? l -i 2. 2x,

. in the finer pores.

invention proceeds.

Patented Nov. 18, 1.947J

vUuifi-'rino fsTATE-fs iftramitar:-"r oF-Fics DiiriNGon PonoUs Ms'sEs v .A Ross, Weighing-toni a.

Application anni 21, 1944,'se'riai Nofsabo 3 Claims.

` if, .2 l. f.; @This.inventionrelates to` the drying of 1iquidcontaining porousmasses, and nds practical application in the drying of articles of erarnicLware, including refractories, particularly large ,refractory bodies, such.res.tank:b1ocks `used in .the Side 5 @weils @f elassfurnaceslpafter.they have been `s hapedand lbefore they have been red. The

application for this patentjconsisted in a continuation yin p art ofniyV application Serial No. \323,92,5 nl ed March,l4, 19,40, and notice Ais also given, of Letters. Patent ,No.2201474l granted t0 .mefJune l, 1 943, and,of application, Serial No.

484. ,5 4 7, l ed bym@ April 26, 1943, relating to the same general subject.

In the accompanying drawings:

Figure lis a diagrammatic view in perspective of a tank-block within a chamber, and in condi-` A,porous material,A the' air rst penetrates the coarser pores, and that the water continues longer laries, and upon this other principle my present When a, capillary is partially lled with water, menisci are formed at the ends i of `the column ,of water; if then there be a dif. `ferencein temperature at the ends of .the water column (having equal menisci) ,the cooler meniscus. will exert a greater surface tension, and the column will tend to. ow inthe capillary in a di- .rection from the warmer to the cooler end of the i mass and thev control of the temperature drop.

between that portion ofl the surface and remainder of the surface, together control the pull of surface tension from the warm portion of the surface tothe cooler portion.

When articles of ceramic ware are taken from, the molds in which they have been formed they still are burdened with water, and, before their introduction into the kilns, they have to be dried.

It is usual practiceto introduce the `Water-con- .taining articles as theyome from. themolds into, o

a drying chamber: the articles in relatively cold I have perceived another prin-i ciple that expresses itself in Water-lled capilstate are brought into a'relativly warm atmosphere.r Under such yconditions the surfacetensionfaction that I have described tends to carry the water, not outward toward the surface, where itrnayevaporate, but inward; furthermore', superfiicial drying tends to bring'about a case-hardened condition, thathiriders and delays Vsubsequent eine, e

present invention consists' in controlling a l` watergradient from a'relatvely warm portion of the surface of aporous mass to the cooler portion. 'I accomplish this; as" `noted above, by controlling the heat gradient from th warmer' to thecooler portion of surfacef'and I accomplishthe control of heat gradient, in turnfby controlling the ternperatures and humidi'ties of both the warmer and ycooler portions ofk the surface. In acoomplishing this end'I'maypunderprope'r conditions; lettem- 'perature and humidity at" the cooler portion of :'the"surface,` vary with fthe' weather. Alternatively, I ,maycontrol either'temperaturev orhumidity'y orbothternperature and humidity, at the cooler portion'of ths'urface. 'In any'case I conftrOl automatically (and vary) the conditions at the warmer'port'ioiiof the surface,l so`as `to insure.

suitable 'heat and `water gradients froml the ,warmer to the coolerV portionfa's'described hereiriafter.

The supplying of heat maybe effected in Various'rways, thessential thing being that a heat gradient-,is vestablished and1maintained that descends froml theport'ion of ythesurfac'e so heated -V'to thefree or nheated (cooler) portion. When such aheat gradient is established, the water contained iny the mass will iiowl from the warmer portion of the surface andthrough the substance ofthernass to the cooler portion of the surface. 'Such acceleration of flow is apparently due to the condition described above. That is to say, the

4o-heating. 0f 'minute columns of water within the ,mass sothatthepull of the menisci at the heated 4 er'ids is less ,than the pull of the merlisci at'the J coc'iier ends of 'these minute columns, creates a tendency for vthe water to migrate towardthe cooler surface.

Necessarily, the heating of the porous 'mass V over a portion offit's surface will, unless preventive measures are taken, induce superficial evaporation; that portion of the surface will become unduly dry; localized shrinkage will occur; and the risk of lossby 'crackingvfwll be brought about. Such a conditionlpr'event by maintaining 4"the humidityof the atmosphere atthe heated surface `..Sniiicientlvlbien ',Substantiallrtq Prevent @raporation. Necessarily, as the drying of the rriass As the drying progresses, the humidity over the` heated portion of the surface may be lowered. Heat may 4be applied by radiation, by convection, or by conduction, or by space heaters, or by warm air, or by other warm Substances in contact with the surface. It is possible to provide apparatus automatically to control the rate at which heat is impartedeto the warmer portion of the surface according to humidity and temperature conditions over the cold portion of the surface, it being desired to effect such control in order that the rate at which moisture is driven to the cooler portion of the surface will be adequate to prevent the cooler portion of the surface from becoming dry and shrinking, with the harmful consequences known to the art.

Referring t Figure 1, a tank-block that may be understood'to be moist is arranged within a chamber 2, and rests upon the floor thereof. A partition within the chamber extends in the plane a, b, c, d, and extends to the block, along the line e-f-g-h. On the two sides of this partition, by means lof heating and circulation apparatus, the conditions of relative temperature and humidity that are specified may be maintained; and control apparatus may be pnovided, for attaining such conditions,for maintaining them, and for varying them as drying progresses.

It will be understood that conditions of relatively great humidity and relatively high temperature are to -be maintained upon the near side of the partition, while conditions of relatively low humidity and relatively low temperature are to be maintained .on the remote side. A fan 3 and a Vent 4 may be provided, by means of which air, drawn from the outer atmosphere, is delivered through the portion of the chamber on the near side of the partition. The air so delivered is heated and moistened (if need be) so that the conditions of humidity and temperature, to which the body of the block on the near side of the partition is exposed, may be controlled and varied as the drying operation progresses.k In the line of air flow from the outer atmosphere into the chamber, means may be provided for affording the desired control of humidity and temperature, and, in exemplary way, I show in Figure 1 a burner and a water spray 8 for such purpose. As already indicated, the temperature of the air delivered by fan 3, will be substantially higher than the temperature of the air on the far side of the partition, and the relative humidity of this warmer air will `be substantially 100%, so thatl practically no evaporation will occur from the portion of the block on the near side of the partition.

On the far side of the partition, the flow of air through the chamber is eiected by means of an exhaust fan E, which draws air into the chamber through an inlet duct 5. f

Ordinarily, the air drawn through the chamber on the far side of the partition is untreated atmospheric air, and the desired heat gradient through the block I is obtained by regulating the temperature of the saturated air delivered to the chamber on the near side of the partition. In

case the natural atmospheric air in a particular region, or in a particular season, is too humid for effecting the desired evaporation of moisture from the position of the block on the far side of the partition, the air may be passed by way of a branch 5U through a refrigerating unit 9 and its humidity lowered to proper value. The humidity of the air entering the chamber may also be controlled by means of a heater lil that is arranged in a Valved branch line '5l of the duct 5. Indeed, by regulation of the refrigerating and heating eiects of the units 9 and Ill, the desired condition of temperature, as well as humidity, may be maintained in the stream of air entering the chamber 2 on the remote side of the partition. Thus, migration of water within the body of the block may be maintained in direction from the near side toward the far side, and it will be understood that the humidity of the air on the far side of the partition may be adjusted and maintained at such degrees as to eiect evaporation from the block at rates suited to the conditions of wetness of the surfaces of the block on the far side.

In such an article as that illustrated in Figure 2, no dividing partition is required when the moist article is brought within a drying chamber. The wall of the article may suice Ito separate the inner and outer chambers. As between such inner and outer chambers, the conditions of relative temperature and humidity that are specified may be established, maintained, and varied; with the effect that drying is thorough, rapid, and so carried out that the integrity of the article is not endangered.-

The drying of porous masses with the practice of the invention which is here described is applicable throughout a wide range of practical procedure. By observation of a thermometer and psychrometer, the conditions of temperature and humidity on the cooler side of the article can be determined, and from such data the proper temperature to establish on the warmer side of the article can be ascertained. Indeed, the latter temperature can be established by means of known and available automatic temperature-humidity control apparatus, a consideration of which aph paratus is not essential to an understanding of this invention. In practice the temperature of the cooler surface may range from below the freezing point to above the boiling point of the moisture to be removed from the mass, and the relative humidity may range from 0 to 95 per centum. In the drying of certain masses or articles the temperature of the warmer side of the article need be only 1 degree higher than the cooler side, and in some cases the temperature dierence must vary several degrees. In the case of relatively dry articles, temperatures as high as 257 F. have been maintained on the warmer side of the article, while the temperature on the cooler side was 70 F. In cases where the center of the body of the article contains a substantial quantity of moisture, the relative humidity of the air on the warmer side of the article must be as high as 98 per centum, but if the article is or becomes relatively dry the relative humidity of the air on the warmer side of the article may be lower, in some cases as low as 75 per centum. The quantity, temperature and humidity of air to be passed over the opposite sides of the porous article may be ascertained by a consideration of the Willis Carrier psychrometric charts, as given in Marks Engineers Hand Book, third edition, page 352. The rate of flow of moisture through porous masses depends upon a number of independent variables, including temperature diierence between the opposite sides of the mass, the kind of porous material through which the flow is eected, the thickness of the mass in which flow is promoted, and the change of pore size caused by shrinkage during the drying process. Calculations of temperature and humidity are, therefore, not given in this specication. They would involve assumptions of rates of flow for given temperature differentials between the opposite sides of the mass or article at successive time intervals throughout the operation. Suffice it to say that persons skilled in the art, and having this specification before them, may readily avail themselves of the invention.

With this specication in hand, persons skilled in the art will fully understand how to practice the invention and obtain the advantages described.

The invention will prove useful in the removal of water from other bodies than porous masses, and may be useful in the removal of other liquids than water. Within the scope of the appended claims many variations and modifications are held in contemplation.

I claim as my invention:

1. The method herein described of controlling the drying of a water-containing porous mass, which consists in passing over one portion of the surface of the mass a stream of air of humidity substantially preventative of evaporation and simultaneously passing over another portion of the surface of the mass a stream of air that is cooler and dryer than that of the rst named stream, and as drying progresses reducing the humidity of the air of the first named stream.

`two surface areas of the mass to a different atmosphere, one atmosphere being a variable rela tively cool evaporative atmosphere and the other being a relatively warm and substantially nonevaporative atmosphere, and controlling and varying, in accordance with variations in the temperature and humidity of the relatively cool evaporative atmosphere, the temperature and humidity effective upon the surface area of the mass exposed to the relatively warm non-evaporative atmosphere DONALD W. ROSS.

REFERENCES CITED The following references are of record in the illev of this patent:

UNITED STATES PATENTS Number Name Date 942,150 Tiemann Dec. '7, 1909 1,509,533 Thelen Sept. 23, 1924 1,572,849 Secord Feb. 9, 1926