US1760444A - Method of drying materials - Google Patents

Description

May 27, 1930. F. A. SECORD 1' ,7

' METHOD OF DRYING MATERIALS Original Filed Opt. 30, 1919 as 30 a2 l8 l5 A268 Ina/2 7130? Eedera'cX. See-cord,

UNITED STATES PATENT OFFICE FREDERICK A. SECOBD, OF PORTLAND, MAINE METHOD OF DRYING MATERIALS Original application filed October 30, 1919, Serial No. 25, 1922, Serial No. 531,722.

produce waste or checking. The invention will be best understood by referring to the accompanying drawings which disclose mere ly for purposes of illustration one embodiment of an apparatus for carrying out the various steps of the process embodying this invention, the scope of the said invention being more particularly pointed out in the appended claims.

In the drawings: Fig. 1 is 'a side elevation partly in section of-the drying apparatus; and

Fig. 2 is a transverse section of the same taken on a. vertical plane extending transversely of the apparatus immediately at the right of the headers 17 in Fig. 1.

The methods heretofore employed in drying various materials, particularly lumber, have necessitated the extension of the drying operations over a long period of time and so have resulted in a large percentage of waste due to many reasons but principally to the factthat the outer surfaces of the materials that are being dried become dry much quicker than the interiors, thereby causing uneven shrinkage and consequent checking of the outer surfaces thereof. Furthermore, the contraction of the outer surfaces of the lumber has resulted in the closingof the pores to such an extent. as greatly to retard the completion of the drying operation. Such defects have been largely due to the subjecting of the material to currents of highly tempered air which remove the moisture from the outer surfaces of the material much faster than the moisture from within can be transmitted by capillary attraction to said outer surfaces toereplace'that carried away by the drying medium. The present invention contemplates the production and maintenance of certain ranges of temperatures between the Renewed October 19, 1929.

material that is being dried and the dry-- ing medium, so as to maintain a more nearly perfect equilibrium between the vaporization of the moisture upon the surface of the material and the transmission of the moisture from the interior portions of the material by capillary attraction, thereby avoiding unequal contraction and the inevitable premature closing of the outer pores of said ma teri'al. In the present example, means are provided for transmitting heat'of a desired temperature to the material to be dried and then in surrounding said material or in subjecting it to the action of a drying medium, preferably of a lower temperature than that of said material, for moisture travels from hot to cold. I

Moisture laden materials when suddenly subjected to the application of a drying medium of a predetermined temperature will retain, due to the moisture therein, a tem perature a number of degrees lower than that of the drying medium, but as the moisture is gradually removed from the material the 4 temperature thereof will more nearly approach that of the said drying medium. In view of this gradual change, it is desirable that the range or difference in temperatures bet ween the drying medium surrounding the material and that of the heat supplying medium be maintained substantially uniform and that the temperature of said drying mcdium be increased from time to time in accordance with the changes in temperature of said material. Therefore, means are shown for increasing the temperature of the drying medium from time to time. a

The apparatus herein disclosed for carrying out the steps of the process embodying this invention includes a casing 1 of any suitable design or construction capable of enclosing the matcrial that is to be dried, the dimension of said casing varying according to the capacity desired, as well as to the nature of the materials that are being treated thereby. In the present example, the casing 1 is of sufiicient length to receive a carrier 2, consisting of a frame 3 provided with wheels 4 arranged to roll along tracks 5-5, which tracks extend longitudinally of the casing 1. The carrier 2 is herein shown comprising a perforated top 6 upon whichthe material is piled in such a manner as to permit circulation of air around the greater portion or substantially all "sides of each separate article mounted thereon. For example, in Fig. 2 the carrier is loaded with strips 7 of lumber arranged in layers, each layer separated from the preceding layer by separators or what are commonly known as sticking 8 in the manner ordinarily used in piling lumber. The various tiers of said lumber are separated from each other by vertical spaces 9, permitting the drying medium to circulate freely through all parts of the stack. The carrier such as described together with its load is rolled into the casing 1 and said casing is then closed by means of suitable doors 10, 10 arranged at opposite ends thereof, or

at appropriate points, and the material mounted upon said carrier is thenheated to a desired temperature, which temperature may be varied according to the condition and to the nature of the material. As an example, however, let it be assumed that the'temperature of the material is approximately 140, this temperature being given, however, merely as an example and not for purposes of limitation. Means shown herein for heating said material consistof a coil or coils 11, preferably of steam pipes arranged beneath the carrier 2, said pipes being heated to the desired temperature and the heat thereof transmitted to the material upon the carrier through the erforations in the top thereof. During the rst stages of drying, the material naturally contains considerable moisture,

' hence the temperature of the coil must be considerably higher than that required for thea material itself, in order to produce the desired results, that assaid moisture is removed by the process hereinafter described, the temperature of said material will gradually in-- crease or approach the temperature of the coils, although an equal temperature of said material and drying medium will not be reached until the material is practically dried. By arranging the heating coils 11 close up to the bottom of the carrier, the'heat from said coils will be imparted to said carrier and be transmitted or radiated therefrom throughout the several layers of the lumber piled thereon, although naturally the temperature of the various layers will gradually decrease toward the top of the load. The drier each layer becomes the more perfect the same becomes as a medium for transmitting the heat from the source to the layers thereabove. When the desired temperature has been reached, at least in the lower layers, the present method contemplates the supplying of a drying medium with as little pressure as possible to said casing. Obviously as the lower layers of the material on said carrier become dried or approach a completely dried ent supply pipes. The have suitable discharge orifices 16 for directmitted at points where it will contact with a lower or hotter layer of the material, and for this purpose the casing or drying chamber is divided into Zones, each zone having its own drying medium supplying means, consisting in the present example of pipes 12, 13, 14, and 15 respectively, herein four in number which may obviously be increased or diminished in size or number according to the circumstances or prevailing conditions. The pipes referred to are herein shown as duplicated on opposite sides of the casing and correspond in length with the casing; that is they are made substantially the length of the carrier 2, but should a number of carriers be arranged in the same casing, each carrier would preferably have its independpipes 12, 13, 14 and 15 ing the drying medium against the material immediately adjacent thereto. Each of said supply pipes is herein shown as communicating with a header 17 through a suitable valve 18 whereby the supply of drying fluid to each cf said pipes may be regulated or entirely cut off. The header 17 extends down- Wardly and is connected with a supply pipe 19 through which the drying medium is conducted from any suitable source not shown, said supply pipe being arranged in the present example centrally of the casing so that a uniform supply will be provided for each side thereof. l

The coils 11 beneath the carrier 2 are herein arranged within a liquid container 20 having suitable supply and discharge pipes 21 and 22 respectively, whereby the said container may be'flooded, as hereinafter described. The container 20 also has connections through a pipe 23 with the supply pipe 19, and a valve 24 is arranged in this pipe to regulate communication with said supply pipe. Thevarious pipes 12, 13, 14, 15, 19 and 23 are, as previously stated, for the purpose of conducting the drying medium to the various zones of the casing and it is desirable that this drying medium be at times at a lower temperature than the material so as to produce the vaporization of the moisture upon the surface of said material and to ef feet the drawing out of moisture from the interior thereof in accordance with the theory that moisture travels from hot to cold, or from a high temperature to a relatively lower temperature. For example, if the material in the lower layer or layers upon the carrier is approximately 140, the drying medium may be supplied to said casing at the temperature approximating or thereabouts, although it is distinctly to be understood that this range is given merely as an example and not for purposes of limitation. If delivered to the casing at a lower temperature than the material, the drying medium will tend to settle, and as it contacts with the warmer moisture covered surfaces of the material, this moisture will immediately take the form of vapor and being warmer than the drying medium will impart more or less heat thereto. Furthermore, said drying medium, as it approaches the heated area at the bottom of the casing,'w-ill accumulate still more heat and when sufficient heat has been acquired, said drying medium will be forced upwardly due to the circulation produced by the incoming cooler current and will discharge through openings 25 at the top of the casing. As hereinbefore stated, it is desirable that the drying medium be admitted to the drying chamber at a pressure sufiicient only to carry away the moisture from the surface of the material at substantially the same speed that it is drawn by capillary attraction to the outer surfaces ofthematerial. The difference in temperature between the material and the drying medium tends to cause said drying medium to settle toward the bottom of the casing until it has become sufficiently heated from the higher temperature of the material to cause it to change its-course and move to the top of the casing where it will be discharged through the openings 25. To provide the'desired force necessary to deliver the drying medium from its source of supply to said casing, I have herein provided a blower 26 arranged at a suitable point in the supply pipe 19. the speed of said blower being capable of variation to increase or decrease the pressure or force of said drying medium.

As previously stated the temperature of the material within the casing is increased as the moisture therein is removed because the presence of moisture in said material has a tendency to depress or lower the temperature, hence as said moisture decreases in volume, the temperature automatically increases: Therefore, when it is desirable to 'maintain a uniform range or difference of temperatures between the material and the drying medium, meansmust be provided for varying from time to time the temperature of said drying medium. In the present example, means are provided for accomplishing this result which consistsof a conductor 27', having connection with any suitable source capable of supplying adryingmedium of relatively low temperature. For example, where the drying medium is to be air, as it preferably is in the present case, said conductor 27 may be connected to a suitable refrigerating plant, or directly with the atmosphere, where the temperature of the same is low enough to accomplish the desired results. Uniting with "said conductor 27 is a conductor 28,

herein shown as connected with a chamber 29 within which are arranged coils 30 preferably of steam pipe,-whereby the air which is conveyed through said chamber 29 and through said conductor 28 may be heated to the desired temperature. The conductors 27' and 28 are provided with dampers 31 and 32 respectively, so that the desired proportion of hot and cold air may be established in the conductor 33, connecting said conductors 27 and 28 with the blower 26. By this and other -means a suitably tempered drying medium may be supplied to the casing wherein is the material to be dried, and this drying medium may be constantly varied in temperature as the drying operations progress and a predetermined range of temperatures be maintained between said material and said drying medium.

The arrangement of the casing and the construction of the carrier are such as to confine most of the heat supplied by the coils 11 with in the space beneath said carrier, so that the heat therefrom instead of being circulated upwardly through the casing will be transmitted directly through the material surmounting said carrier and to the several layers thereon. Naturally the lower layer will be of a much higher temperature than successive layers and as the moisture is removed from the lower layers they will become more nearly the temperature of said coils and will in consequence thereof form a more perfect conductor for the heat to the layers thereabove. By providing perforations in the top plate 6 some of the heat will be permitted to circulate upwardly through the spaces provided between the various articles or pieces of material, and thus assist in drying all the upper layers of the same, and the air which is permitted thus to escape will increase the temperature of the drying medium entering through the ports 16 as it descends toward the bottom of the drying chamber and assist in changing the course of said drying medium and ultimately increase its moisture carrying capacity.

Obviously the drying of the material would be greatly expedited if the various zones hereinbeforereferred to, were provided with independent supplying means whereby the temperature of the drying medium to said several zones could be independently varied, and an example of a simple device adapted to carryout the invention includes the conductors 27 and 28 and heating coils 30, connected with the main supply pipe 19 although it is to be distinctly understood that the invention is not limited to the application shown.

Preferably the drying operations are begun at the bottom of the carrier and proceed up ward layer by layer or by groups of layers until the entire load is dry enough to be removed from the casing and in following out this process communication is preferably cut of the material within the casing approximates 140, these temperatures being given merely as examples and not for purposes'of limitation, for obviously they maybe varied according to-the character of the material that is to be dried. At the beginning of the drying operations where the material is sur charged with moisture and heated to 140 the temperature of the coils 11 must necessarily be much higher, owing to the fact that the evaporation of moisture from the material has a substantial cooling effect thereon, but as this moisture is gradually removed through vaporization when subjected to the action of a cooler drying medium admitted through the pipes 12 the temperature of said material will gradually be increased until it approaches the temperature of the heating coils 11.

Upon the removal of all the moisture from the material of the lower layers, communication with the lowermost pipes 12 and the supply pipe 17 will be cut off and communication with the next upper pipes 13 provided by opening the valve 18 therefor. Naturally the temperature of the material in the second or next upper zone will be lower than that of its predecessor in the drying operation due to its distance from the source of heat, namely the coils 11. Therefore, in order that the desired range of temperaturebetween that of the zone in which the drying is to take place and its drying mediumbe maintained, adjustment of the dampers 31 and 32 will be necessary to effect a decrease in temperatures of the drying medium consistent with the lower temperature of the material of the next course or layer. When the drying of the material within the zone supplied by the pipes 13 has been com leted, communication between said pipes and the supply pipe may be cut ofi and the operations repeate successively in the zones thereabove until the entire stack of material has been completely dried. It is within the scope and purpose of the invention to increase the temperature of the coils 11 rather than to decrease in the desired proportipn' the drying medium as it is being supplied through the several tiers of pipes 12, 13, 14 and 15, the main object being to maintain a predetermined range in temperature of the material and the drying medium throughout the entire operation. I

Itis desirable to maintain the various temperatures hereinbefore described comparatively low in order that the lumber be not exposed to excessive heat, such as would cause an unequal expansion between the outer and partially dried sections and the innermost sections, but the lower the temperature of the air the lower will be the moisture carrying capacity thereof. For example, assume the air at will carry about 8 grains of moisture to the cubic foot, while air at 180 will carry about 166 rains to the cubic foot, hence it would seem that the higher the temperature the more rapid will be the drying of the inaterial, but such is not the case, for where excessive heat is allowed to contact with the outer surface of the wood or other materials that are being dried, said outer areas will be dried so rapidly that the process of drawing the moisture from the interior by capillary attraction will not keep pace with the removal of the moisture from the outer surfaces, resulting in an unequal contraction between the pores of said outer areas and the inner areas and producing serious checks in the material, whereas a much slower removal of the moisture from the exterior will maintain the drying forces in equilibrium, that is the moisture will be removed from the outside no faster than will be the rocess of withdrawing the moisture from the interior. In order to speed up the drying of the materialwithout producing the results just described, a coil 34 preferably of steam pipe has been provided in the upper part of the casing, and this coil may be kept at an exceedingly high temperature, much higher if desired than that of the coils 11. The heat from said coil 34 passes upwardly and discharges through the openings 25 rovided in the top of the casing and by so oing the circulation of the heating and drying mediums within the easing will beincreased as will also the temperature of the moisture laden air rising from the material into the zone of said coil 34, and

by heating said moisture laden air its carrying capacity will be increased and assisted in discharging from the top of the casing. The

heat from said coil 34 will form, as it were, a blanket at the top of the casing, which forces the relatively cooler air entering through the several pipes 12, 13,114 and 15 downwardly against the material until the same has acquired suflicient heat to cause it to change its course and rise to the zone of said coil 34.

Very often material will be brought to the casing for drying that has been exposed more or less to the atmosphere and has acquired a comparatively dry outer surface, the pores having become contracted and consequently greatly retard the drawin of the moisture from the interior by capil ary attraction or otherwise. When these conditions exist, it is desirable to treat such material so that the several steps hereinbefore described may take place, and one method of treating such material is to provide a coating of moisture upon the surface thereof. This may be accomplished either by condensation or by filling the entire casing 1 with water, said casing being made water-tight for this purpose, or the container 20 may be flooded with suitable liquid, as for example water, and into said liquid, steam may be discharged to produce vapor which will pass upwardly and cover the exterior surfaces of the material within the casing. For this purpose, perforated steam pipes 35 are arranged within the con tainer 20 among the loops of the coils 11, whereuponwhen steam is turned on vapor will rise from said container into contact with the material and result in the softening of the surface of the wood or the opening of the pores thereof in preparation for the various steps of the process hereinbefore described. Should the temperature of the material be higher than desired for beginning the steps of the above process, this temperature may be reduced by supplying through the pipe 19 air of apredetermined or desired temperature, the latter being admitted to said container through the valve 24 and pipe 23. Obviously the latter means may i also be used to supply the necessary amount of heat to the material upon the carrier in place of the steam pipes 11.

It is to be understood that the method of drying is not limited to the maintenance of the ranges of temperature above described throughout the drying operation, fo r such ranges may be increased at intervals when all danger of warping or checking of the material is passed. As for example, in the drying of lumber the starting of the process may be at temperatures not very far apart say 20 and this range may be maintaine until a certain proportion of the moisture, say 10 per cent has been removed, after which all danger of checking being past th e range may be increased either gradually or very abruptly as desired, according to the nature or character .of the-material. Furthermore, steam may be admitted directly to the casing through the perforated pipes 35 without using water or other liquid in combination therewith, the steam passing upwardly through the openings in the perforated plate 6 and into direct contact wlth the material upon the carrier.

Although I have described the above operation in connection with the drying of lumher or like substances, it is distinctly to be understood that within the scope and purpose of the invention, grains, fruits, clay products, peat and in fact practically all substances requiring drying may be treated with equal success.

Claims:

1.- That method of drying which consists in raising the temperature of the moisture substantially throughout the mass to be dried and then in subjecting different layers of the mass to lower temperatures varying according to the positions of the layers relatively to the source of heat to cause moisture therein to move to its surface.

2. That method of drying which consists in tempering the material to be dried and in directing against said tempered material at selected levels a drying medium of selected temperature having a relatively lower temperature than the material at said levels, to effect the vaporization of the moisture in said material. y

3. That method of drying which consists in moistening the surface ofthe material to be dried, then in bringing said material to a predetermined. temperature, then in subjecting different layers of said material severally to the action of a drying medium having a temperature lower than that of said material, to effect the vaporization of moisture on the surface of said material.

4. That method of drying which consists in moistening the surface of the material to be dried and in bringing the temperature of said material to a predetermined point, then in subjecting said material, for a predetermined period, to the action of a drying medium having a temperature less than that of said material to vaporize the moisture on said material, and then in increasing the temperature of said moisture laden 'dryin medium to facilitate the removal thereo 5. That method of drying which consists in arranging the material to be dried in a casing; then in supplying heat at the bottom of the mass of material to bring the latter to a predetermined temperature; and then in supplying a drying medium of relatively lower temperature from opposite sides of the material and at dilferent levels to draw the moisture from the interior of the material and remove said moisture from said material.

6. That method of drying which consists in arranging the material to be dried in a casing; then in supplying heat to said casing to heat the material throughout; and then in supplying a cooler medium at a plurality ing and later to be increased in temperature and assisted in discharging from the top of the casing.

In testimony whereof, I have signed my name to this specification.

FREDERICK A. SECORD.

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