US2078515A - Method and means for drying material - Google Patents

Description

April 27, 1937. R. L. SUTHERLAND" METHODAND MEANS FOR DRYING MATERIAL Filed June 29, 1935 6 Sheets-Sheet l ET L.

R. 1.. SUTHERLAND 2,078,515

METHOD AND MEANS FOR DRYING MATERIAL April 27, 1937.

Filed June 29, 1955 6 Sheets-Sheet 2 INVENTOR B0B TL. THEELAND 57 6 VSZZO-o/L ATTORN 5Y5 April R. L. SUTHERLAND 2,078,515

METHOD AND MEANS FOR DRYING MATERIAL Filed June 29, 1935- 6 Sheets-Sheet 3 3 IN VENTOR E05 TLJuTHEEL AND J MM {g B) AT TOHN 5Y5 April 27, 1937. R. L. SUTHERLAND 2,078,515

METHOD AND MEANS FOR DRYING MATERIAL Filed June 29, 1933 6 Sheets-Sheet 4 115.4

a I i I INVENTOR- E08EETL.5UTHEELAND 7 ATTORNEYS April 27, 1937- R'L. SUTHERLAND 8, 1

METHOD AND MEANS .FOR DRYING MATERIAL Filed June 29, 1953 6 Sheets-She't 5 April 27, 1937. R. L. SUTHERLAND 2,078,515

METHOD AND MEANS FOR DRYING MATERIAP 6 Sheets-Sheet 6 Filed June 29. '1933 mhw-Q mrwofu T m hwbwwd mmwrlL [Emmi D J l e w Q W I nwwfi 2 U I 5% w k Patented Apr. 27, 1931 MATERIAL Robert L. Sutherland, Winnipeg, Manitoba,

ada, assignor to Northern Coal P roducts co Minneapolis, Minn., a corporation of Delaware ApplicationJune29, 1933, Serial No. $78,151, I

1 Claim. This invention relatesto a method and means for drying materials of various kinds, and finds a particularly valuable application in the drying of combustible materials such as coals, including lignite. r Objects of the invention are: to prevent degradation of the material being dried; to dry quickly without firing the material; and to obtain even and thorough drying. I

In my jexperience'in drying coals. and lignites of higher-moisture content, I have learned that the following basic facts must be taken into account:

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First-Practically all coals when mined are saturated with moisture, the normal or inherent moisture'content depending, on the geological age, chemical. composition, and physical structure the younger coals and flignites containing progressively greater amounts of moisture. Moreover in mining and/or subsequent handling and transportation of the coals, additional or extraneous moisture may adhereto the surface of the coal particles.

Second-Because of the free moistureon the surface of the coals and lignitespwhen heated unsaturated gases are brought in contact with the materials, the heat in the. gases is practically all used in thefevaporation .of moisturefrom the surfacesyand therefore there is little or no penetration of heat into the interior .of the-lumps.

In many "solid, fuels, surface drying results in greater shrinkage of the surface layersthanof the interionand 'checlgingia'nd 'spallingofi of the surface layers takes place.

Third.-When such material is dried -to a moisture content below that in which the vapor pressure of the moisture in the material is less than the'vapor pressure of the moisture in the surrounding atmosphere, moisture is re-absorbed from the atmosphere, which re-absorptionis a heat-generating or exothermic reaction. The amount of heat 'so .generated maybe sufficient to raise the temperature ofthe fuel to the ignition temperature causing spontaneous combustion. 1

Fourth-Goals and lignites'of higher initialmoisture content, are particularly subject to degradationwhen in contact {with atmospheres of low moisture saturation.

Fifth.- Coals and lignites of a higherinitial moisture content, when dried, are subjectto spontaneous combustion due to the greater reactivity of the combustible elements. 'Thisreactivity maybe reduced by a treatment with an,

inert gas or with a gas of low oxygen concentra- (Cl. 34-34) I tion, during or f ollowing the dryingprocess. vA feature the use of such an-atmosphere.

Sirth;Coals .and lignites .of higher initial moisture .content are sensitive-to atmospheres containing appreciable amounts of oxygen at higher temperature, the ignition temperature varying from a minimum, in pure oxygen, to

higher temperatures depending upon of oxygen present. 1

Briefly, my method includes the first-step of heating the material tobe dried tothe desired temperature of evaporation in a substantially inert atmosphere of high moisture content, to

the, amount minimize surface drying, and to effect-heating of j the interior of the lumps, and later maintaining a humidity gradient between the vaporpressures of the moisture in the materiaL'and in the drying atmosphere, as I drying xproceeds, by controlling the rate of flow of the drying. medium through or past the material. I .Drying may be effected without including a final cooling operation, or the first stage .of'drying may be carried out under conditions which will include cooling of the .material before discharge from the apparatus.

Objects, features and advantages of the invention will be set forth in the descriptionof the drawings forming a partof this applicatiomand in said drawings--- -Figure 1 is a plan section ofone form of deg vice by use of which thepresentmethod can be carried out; r

Figure 2 is a-vertical section approximately 'on line 2--2 of Figure-Lillustrating the manner of controlling the introduction ofdrying medium; at different points alongthe line of travel: of-the bed of material to bedried; I

Figure 3 is a vertical section taken approxi-. mately on line 3 -3 of Figure 1; i 1 Figure 4 is an edge view of one of the'slotted passage-forming plates; 1 l Figure 5, is a face view ofthe plate'of Figure 4;v Figure 6 is an enlarged detailvertical section taken approximately on line 6-4, of Figure 3, illustrating oneof the dust sheds in,relation' to the slots of the passage-forming plates;

Figure 7 is a flow-chart diagram illustrating the drying-without-cooling method; and

Figure 8 is a flow chart diagram illustrating the drying-with-cooling method, and showing,

diagrammatically, a modification ofthe appae carrying out my new method is constructed as follows: Numeral I generally designates a vertically elongated structure, the outer walls of which are formed of any suitable material. Adjacent and at the outside of the structure is diagrammatically shown a furnace 2, as means for burning fuel to supply a substantially inert drying medium. Centrally arranged within the structure i are a series of vertical passages downwardly through which the material to be dried is moved. This structure includes a series of vertically superposed flanged metal end panels 4-5 forming two opposite vertical walls, of a ma terial-controlling structure. and lower edges of these panels are clamped plates 7 having I tical walls which define a series of alternate vertically arranged passages l8, 19, respectively for receiving and distributing the drying medium to be circulated, and for confining and guiding the.

material to be dried as it travels by gravity during the drying operation. The passages 19 for the material are downwardly divergent for causing the bed or body to become thicker as it tray-- els. The purpose of the divergence is to insure flow of the material} It: is noted that there is no division of coal bed or body in any passage, thatis the arrangement is such that there are no obstructions to flow of the material being dried, except a control valve at the bottom of each column. There are two-types of panels respcctively indicated at 4-5, see Figures 1. and 2. The flanges of the panels are suitably bolted together to form a solid structure, the bolls not being herein shown. Eachplate I has two series of horizontal slots 8. The drying medium, introduced into passages I8, passes through these slots into passages l9, thence through the bed of material to corresponding slotsat the opposite side of the bed. The panels 4 are horizontally wider than the panels 5.

Within the chamber i', see Figures 2 and 3,jand at the outer side of one of thepan'eldormed walls, there are arranged horizontal partition plates 9, to provide vertically superposed chambers respectivelydesignated H, l2, l3 and M, from which drying medium is delivered to the materialto be dried. These division plates'are held between the flanges of the panels as best shown in Figure 3. The wall i is provided, see Figure 3, with cleaning openings each closed by a door IS, an opening for each chamber H, I2. 13 and I4. The panels 5 are providedwith openings I! through which drying medium enters the gas passages l8. Referring to Figure 2, it is noted that only every other els 5 of this side are provided with the openings IT. The gases pass through the openings I! into the chambers l 8, through the slots 8 in the plates 1, through the material in the chambers l9, through the'slots' of the plates at the opposite side of the chambers and thence through vertically elongated openings 20 'of the panels 5 of theopposite side. Thus, see Figure 3, the gas is forced to'take a tortuous course through the material. 20, the cooled drying medium from all levels is discharged into a common chamber 2!, from which the mixed products are removed by a'sui'table fan; I

The substantially inert gases "which are products'of combustion of furnace 2, are, see Figure. chambers Ii, l2, l3

1, delivered to the various and I4 through pipes 25, see Figure 1, valve seat casing 28, pipe 21, vertical manifold pipe 28 and Between the upper their edges engaged to form vera one of the pan pipes .35., manifold 36, pipe "38 to fan 40.

After passage through the openings in the same direction as when the valves are in from the manifold through separate pipes 29 to respective chambers H, i2, I3 and [4. Each manifold branch pipe 29 is provided with a damper 30 for regulating the rate of flow or volume of the drying medium to the chambers I, l2, l3 and 4.

The chambers H, i2, i3 and I4 extend the iull longitudinal length of the structure 1, see Figure 1, and each chamber has leading therefrom at that end opposite pipes 29, a passage or pipe 35 communicating with another vertically disposed manifold 36 connected by pipe 3! with valve seat casing 38 in turn connected by suction pipe 35 with suction fan 4i; which, in this embodiment, is thesole means for circulating and rte-circulating the drying medium, and mixture of drying medium and moisture from the material being dried.

The fan 4G delivers into pipe 4%! which, in turn, delivers into pipe 25. Pipe 41 has a branch pipe 43 leading to the atmosphere. and also has a "branch pipe 44 leading into the furnace 2, as

best shown in Figure 3 Each pipe 35 is provided with a suitable damper 46, for the same purpose as'dampers 30. Pipe M is provided with a damper 4? located between pipe and pipes 43 and 44.

Pipe 43 is provided with a suitableldamper 48 and pipe 44 is provided with a suitable damper The purpose of damper 41 is to control the amount of eiiiuent drying medium being returned to the allluent medium of the system. Damper 48 in pipe 43 controls the amount or proportion of eiiiuent medium discharged. to the atmosphere. "Damper 49 controls the amount of effluent medium discharged into the furnace 2, to regulate its temperature. By means of the double connection through pipes 41 and 44 it is possible to control the temperature in the combustion chamber of furnace 2.

Referring to Figure 1, means is provided for reversing the direction of flow of the drying material through the various coiurnns or beds of the material to be dried, to obtain even drying at both sides of the beds. Valve seat casings 2E and 38 are provided with valve means so arranged that reversing circulation can be obtained. The valve casing 26 has axially spaced valve seats 50-5l alternately engageable by valve 52 carried by rod 53 slida-bly held in bearings 54. Valve casing 38 is provided with axially spaced valve seats 56-57 alternately engageable by valve 58 also carried by rod 53. V

As shown in Figure l, the valves 52 and 58 are so positioned as to obtain circulation of the prodnets in the direction of the full line arrows. When the valves 52 and 58 are respectively seated at 5056 the how takes the direction of the dotted linearrows, that is from the pipe 25 through casing 26,'seat 5!, across chamber 2|, first through openings 20, then through passages l8, through the bed of material in the passages IQ, then through passages l1,. th'ence through 31, seat 57, casing In this case, the fan is rotating Figure 1. The

' is disposed below the bottoms of the passages l9.

ported at opposite ends by links 64 swingably at- I i l tached as at 65 tochannels. j ure 2, the slots 62 are positioned to permit feed- The beams are carried on rods 63 each supvAs shown in Figj each slot '62 at this time assuming a position in opposition to a corresponding V-shaped element.

'lcc-tion of dust.

Inverted V-shaped shed-plates H,,see Figures 2and6 are arranged in the vertical gas passages 18 for the purpose of preventing the'col- Their surfaces are so arranged with relation to the slots 8fof the plates 1 that dust passes outwardly through these slots into the passages l9, see Figure 6.

There is of course provided a hopper for delivering the material to be dried into the vertical passages 19. The tops of passages I8 are closed by v-shapedcaps lli. Asuitable cleanout opening 16 with door ll is provided for the mixing chamber 2i. v

The apparatus as above described is a feature of the invention and is closely related to the method in that it represents one form of device by which the new'rnethodcan be carried out. j

Drying method without cooling First referring to flow diagram, Figure 7, the

quantitative data of the diagram are only given case only. The fluid temperatures andhumiditics indicated substantially represent an average condition. in winter, more gas will be required for warming the coal. The calculations are made on the assumption that no heat is lost by radiationJ The calculations of the gas quantities refer to one pound of coal with itsoriginal moisture content. h I,

Now referring to Figures 1 to 4 and '7: Assuming, normal operating conditions to have been established, substantially inert gas, produced for example byburning' fuel in furnace 2, is introduced into conduit 25, see Figures 1 and 3. As shown in the example, see flow diagram, Figure 7, this gas may have a dry bulb temperature of 2000" F., and a moisture content correspond ing to saturation at 100 F. Thsfluid is mixed with that amountof recirculated fluid from pipe 4| necessary to produce a mixture of fluidhaving the required dry'and wet bulb temperatures. The material to be dried-before introduction into the drier may have for "example a temperature of40' F., and a thirty-five per cent moisture content.

operation after an equilibrium between quantities of initially introduced fluid, and recirculated fluid has been established.

This gas is delivered through the conduits 25,

Temperatures and humidities shown in Figure 7 represent the normal conditions of.

theentering drying medium. in the diflerent zones. I I

See Figure 7 for data concerning amountsand temperatures of the drying medium, before pas-' sage through the bed of materialin the'dif" Ierent zones.v The gas now enters chambers H,

12, l3, 14. .By reference to Figure "I, it is seen that the dry and wet bulb temperature of the gasin chambers ll, l2, I3, I4 is the same, and Y that the amount of dryingme'dium is successively increased from chamber H to chamber l4. The drying medium,- now passes through the and through the various columns of moving material, thence through the openings 20 of the opposing plates and into .the main chamber 2|, see Figure 1. In this chamber, the drying medium and moistureof the materiallrom the .various zones is mixed, and vmoved-by fan 40 through valve seat casing 38 into conduit 4!. Referring to Diagram '7, it is noted that as the operation proceeds, the relative humidity of the efiiuent fluid decreases fromabove downwardly,

openings l1 into passages 'l8, through slots 8 I being 100, 90, 80 and 70 per cent, leaving cham- After mix- Fluids from power for circulating the' drying medium. 1 From conduit 4 1 part of themixture is discharged to the atmosphere through pipe 43 past damper 48, and part is returnedthrough pipe 4| past damper 4! to conduit 25, where it is mixed with initial incoming hotter and drier fluids :from furnace 2. Figure 7 shows the temperatures and amounts of dry fluid and water vapor in that portion which flows to the atmosphere and also in that portion which is returned to conduit -for mixing with initial incoming fluids. The fluid discharged to the atmosphere has a higher dry bulb temperature, and is less completely saturated with water vapor than the fluid leaving theupper or warming compartment. This condition obtains-when only one fan is used for circulating a drying medium. By the use of asecond fan and a separate compartment for receiving any portion of the fluid which passes from the chamber 1 I through the upper part of the cham- It will be noted that there has not been sub 7 stantial drying of the material as a result ofthe passage of the drying medium through that portion of the material in the first zone. A' differential' has thereafter been maintained be-, tween the vapor pressures ln the material andthe drying medium, which has resulted in a controlled rate of flow of the moisture in the material to'the' drying medium. The temperature-at which evaporation of moisture from the material takes place is determined by the initial dry bulby saturation of the dryingtemperature and medium, after the material has been heated to the temperature of evaporation.

Mixing of fluids (in which the temperature has been .reduced and the humidity increased by contact with the material to be dried) with the initial fluids, in any proportion, does not substantially affect the temperature at which evaporation takes place. I am able from this fact to reduce the temperature of the fluids (initially at a temperature which would cause degradation or ignition of the material) to a temperature below the danger point, and to control the humidity differential between the material and the drying medium by, regulating the flow of fluids through the material.

If desired, the humidity differential can be further controlled by supplying regulated amounts of fluid at different temperature and/or humidity, to be mixed with the principal source of supply of fluid and applied to the material at diiferent stages in the drying process. A novel feature includes the application of a drying medium (preferably substantially inert fluid) at a temperature below which there is danger of degradation or ignition of the material being dried, and at a humidity or saturation which, at the desired temperature, will provide the desired temperature of evaporation and the control of the humidity differential throughout the drying process by progressively changing the quantity of the drying medium applied to the material as drying progresses, either by varying the thickness of the bed to change the resistance to the flow of fluid supplied at constant pressure, or by changing the pressure of the fluid supplied to a bed of constant thickness.

A modification includesthe admixing of gas of other initial temperature and/or humidity and applying in the different zones of the bed as desired, to maintain or aid in maintaining the desired humidity differential, or to reduce the final temperature of the product to the desired point.

Drying with cooling In case the dried material, such as lignite or other fuel, is to be passed directly to a stoker or pulverizer, cooling as part of the drying process is not necessary. However, in cases where the drier is operated at a mine or source of material, it is desirableto cool the material after drying and before storing, or before loading on cars for transportation to point of consumption. In this instance, the last compartment, see flow chart diagram, Figure 8, may be used to supply cooling gas to reduce the temperature of the dried material.

atmospheric temperature or mixtures of air and furnace gases in such proportions as to provide the desired temperature and humidity to effect cooling. The thermal efliciency is higher when the cooling medium is at or near the same tem perature as the material to be cooled, providing the humidity of the drying medium is low.

Figure 8 is a diagram or flow sheet showing the manner of operating when it is desired to bring the material to a lower final temperature than that heretofore indicated. The general operation previously described applies here but a slight modification is made in the apparatus. modification is only shown in the diagram and consists in connecting the lower compartment 80 with a separate exhaust fan lnot shown) which may also serve as a forced draft fan for the fire box, which supplies hot gas to the upper zones. No means is shown for reversal of the fiow of the drying medium. in the cooling zone, but it is obvious from 'my disclosure that this could be done, and that more than one cooling zone could be used. It is noted that in this form of the invention, the lowermost chamber 83 delivers across the bed into a receiving chamber Bi, which is separate from mixing chamber 2 i. The cooling Any number of such compare, merits can be used. The medium maybe air at This" medium enters at 82 and leaves at 83. Inthis instance, as in the first, the moisture in the fluid may be utilized to control humidity, and the desired balance of relative humidity can be obtained by introducing fluid from the furnace 2 or from any other source or sources, and it is intended that the cooling medium, whatever its source, may or may not be ire-circulated.

Although I have herein, for purposes of illustration, shown a form of drying apparatus usable for coal or lignite, and have illustrated my drying'method by reference to the drying of a combustible material such as coal or lignite, and although this particular application of my method is claimed, there is no intention to be entirely limited to the application of the method to combustible substances. It is evident that the principle can be applied to obtain thorough drying of any non combustible moisture-containing =Inaterial, and to the drying. of any material in-a manner to prevent or minimize checking or s'pall ing, and to obtain more uniform drying clear to the middle of a lump, or piece of such material of any shape.

I have shown that the fluid at its highest temperature and lowest relative humidity is introduced into the upper chamber and comes in contact with the entering material when that material is at its lowest temperature and has a maximum moisture content. As drying material being dried is warmed and dried and the drying fluid is cooled and becomes more highly saturated with moisture. The release of moisture from the material is gradual, and the heating and humidity can be so relatively controlled that moisture is driven from the innermost portion or core of the material at any desired velocity. The final temperature of th entering fluid is determined by the number of 'recirculations. In the present method, wet or cooled, partly or completely saturated fluid is mixed with initial hot furnace fluids.

The fluids entering the various boxes have the same dry bulb temperature and humidity; the amount of drying effected is controlled by the rate of flow 'or by the amount of fluid traveling through the various sections of the bed. Thus, by changingthe velocity and volume of the fluid passing through the material, more or less drying can be obtained at will. fluid through the fuel bed in any zone must be suiflcient to produce the desired humidity of the fluids after passage through that zone. For lignite, the humidity is controlled solely by mixing wet or cooled saturated hot furnace fluid. The mixing is accomplished in a single chamber 2|, rather than in a series of chambers. I

In the first section of the bed in which the material enters the apparatus cold and substantially saturated with moisture, it is desirable to have the drying medium applied of sufficient total humidity that after cooling in contact with the material, it will be in a substantially saturated condition in order that there may be substantially no flow of moisture from the material to the drying medium. The function of the drying medium in this section of the apparatus is to preheat the material to the desired. temperature of evaporation without removal of moisture.

In succeeding sections of the bed, such differential between the vapor pressures of the moisture in the drying medium and in the material as is required to cause flow of moisture from the material to the drying medium must; be

proceeds, the 5 The velocity of the fluid with the initial determined by maintained. The differentials between the vapor pressures in successive sections of the bed may be increased or decreased in successive sections of the bed, as desired. Such differentials will be maintained between the vapor pressures in the drying medium and in each succeeding section of the bed as will result in the maximum drying rate with minimum degradation of the material. Obviously, the greater the differential in any section, the more rapid the flow of moisture from the material to the drying medium.

During the operation, when the temperature of the material has reached the desired evaporating temperature, which the boiling point of water for-certain materials, the heat given up by the drying fluid will be used in evaporating moisture. This is accomplished by reducing the vapor pressure of the moisture in the drying fluid below the vapor pressure of the moisture in the :material, as before stated. In this way, a gradual flow of moisture from material to drying medium can be accomplished. Again it is noted that the vapor pressure differential in any section of the bed is the difference between the dry bulb and the wet bulb temperature of the gas, and by the temperature and moisture content of the material. It is therefore evident that the vapor pressure differential may increase or decrease in successive sections of the bed as drying proceeds, the gradient or rate of change being determined by controlling the rate of flow, and therefore time of contact of the drying fluids with the material, As the rate of flow is reduced, the final dry bulb temperature will be reduced, and the wet bulb temperature increased,

There are two ways of operating with the present method. One is to introduce the drying medium at a dry bulb temperature approximately the temperature of the material and at a wet bulb temperature substantially lower than the temperature of the material. In this case, part of the heat of the fluid is used in evaporating moisture with a conseguent reduction in the temperature of the material. The dry bulb temperature will be reduced and the wet bulb temperature increased.

Another way is by using a drying medium at substantially lower dry and wet bulb temperatures than the temperature of the material in perature depending upon will ordinarily be below which case a part of the heat in the material will be used in warming the medium passing therethrough, and a part in evaporating moisture. In either case, the temperature of the material will be reduced, the reduction in temthe quantity of the fluid used and the time of contact.

In practical application the drying medium is supplied at. a temperature such that it will bring the material to be dried up to the desired drying temperature. The material is maintained at this desired drying temperature by adding heat to the circulating medium, and the rate of drying is regulated by regulating the humidity and quantity of the drying medium. Heat is added to the circulating medium both for the purpose of maintaining the temperature of the material and for the purpose of maintaining the humidity of the drying medium. The moisture absorbed by the circulating medium is removed by allowing part of the eiliuent fluid to escape to the atmosphere, and replacing it with an equal weight dry hot fluid from the furnace, which is accompanied by an amount of water vapor depending upon the type of fuel and conditions under which it is burned. It is noted that for success in drying lignite and materials of like characteristicsfit is necessary to operate so that the temperaturesof drying can be controlled, with the ability to increase the humidity gradient during successive stages of the drying operation.

I claim as my invention:

A method for drying combustible material consisting in applying an inert drying medium to the material to be dried, said medium being at a temperature below the point at which there is danger of degradation or of ignition of said material and having a degree of humidity which at the desired dry bulb temperature will provide the desired temperature of evaporation, and controlling the vapor. pressure differential between moistures in the material and in the drying medium throughout the drying process by progressively changing the quantity of the applied drying medium as drying progresses, by varying the thickness of a bed of the material to correspondingly vary the degree of resistance to flow of drying medium supplied at constant pressure.

ROBERT L. SUTHERLAND.

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