US2136870A - Method for drying and treating wet granular materials - Google Patents

Description

METHOD FOR DRYING AND TREATING WET GRANULAR MATERIALS Filed Aug. 11, 1936 2 Sheets-Sheet l //v VENTOR G. A. VISSAC Nov." 15, 1938.

METHOD FOR DRYING AND TREATING WET GRANULAR MATERIALS Filed Aug. 11, 1956 2 Sheets-Sheet 2 //VVNTOI? usTA vg/Q V/SSHF Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE 2,136,870 METHOD FOR DRYING AND TREATING WET GRANULAB. MATERIAIB This invention relates to a method and apparatus for drying and treating wet granular materials, with particular reference -to the drying of wet coal.

Different methods and apparatus for effecting the'drying and preparation of wet granular materials have been suggested and used heretofore. However, the methods and apparatus previously employed have had serious disadvantages. granular materials have been dried in vertical or rotary driers and on screens but degradation of coal, among other things is apparent in the use of rotary driers and, in other types of apparatus, there has been the diiiiculty of penetrating a bed of coal lying on top of a screen or conveyor with currents of air which generally tend to pack the bed and retard or prevent movement of the material. Furthermore, difficulty has been encountered'in controlling the gas temperature while using ordinary types of furnaces. Lack of efficiency has, therefore, resulted.

For many years it has been the practice to treat materials to prevent deterioration and, in the case of coal, it has been well known to subject the product to an oil treatment in order to prevent deterioration and to control the dust. There has been experienced, however, dimculty in distributing the oil over the particles to render the coal dustless when properly dried.

It is an object of the present invention to provide a novel method and'apparatus for drying and treating wet granular materials including coal so as to avoid apparent disadvantages in previously used apparatus and to provide in a simple manner means for the drying and treating of material quickly and efiiciently.

A further object of the invention is to provide 'a method and apparatus which will use a minimum volume of air which may be caused readily to penetrate the bed of material being dried without materially affecting the movement of the material. e

A further object of the invention is to provide for theuse of heated gases for penetrating the bed of material to eliminate the moisture.

A still further object of the invention is to' vide a method and apparatus in which the var-' ious elements co-operating to effect drying and treatment are minutely controlled to such a degree as to provide for a final efliciently dried product and in a large volume comparative to the time of operation.

With these and other objects in view, the invention will be apparent upon a consideration, of 5 the following specification in conjunction with the accompanying drawings which form part of the application.

In the drawings:-

Figure l is a schematic side view of apparatus for drying and treating the material.

Figure 2 is a schematic view of one of the screens employed, to show the course taken by the material under normal conditions during the oscillation of the screen.

Figure 3 is a sectional view of a nozzle construction for mixing and ejecting the treating gases;

Figures 4 and 5 are schematic views to illus-- trate the course taken-by material under conditions imposed by the proposed method of treat- 20 lnent during oscillation of the screen.

Referring more particularly to the drawings,

A and B indicate two compensating shaker screens supported by suitable oscillatable hangers in and I l. The screens are preferably cov- 25 ered with a wire mesh, perforated plates or wedge wire screen surfaces of proper mesh and are connected to eccentrics I! through connected rods l3 disposed preferably at an 180 angle, so that when the eccentric I2 is operated through any 7 suitable source, such as the motor M the screens are subjected to opposed and continuous oscilla-' tion.

The wet granular material is delivered from the chute ii on to screen A, which is divided into two sections CD and DE. The material, after passing over screen A, is transferred to screen B and this latter screen is likewise divided into two sections FG and GH, these sections being defined by the area between the transverse lines indicated by 4 these various letters. On' screen A the material is delivered first of all to section CD, below which is positioned a suitable hood l6 connected by a pipe l'l to a. water sump l8. As the material passes over section CD, the excess moisture carried thereby is caused to pass through the screen by gravity and the momentum of the material owing to the shaking motion of the screen.

After passing over the area CD of the first screen, the partially dewatered material is moved.v over section DE above which is positioned a hood I8 which is connected by a pipe line l9 and 20 with the boiler 2| of a furnace C and'is also connected in a suitable manner by pipe lines 22 and l 23 with the flue-24 of the furnace C so that steam 69 is desired to treat it with oil, an oil and hot flue gases are discharged into the hood and pass downwardly through the bed of coal on the screen. The pipe lines connected with the hood may be arranged in any suitable manner and may take the'form of pipe lines which commonly communicate with the hood as shown. Furthermore, in the case where the coal or other material being dred is also to be treated, other apparatus for treatment may be incorporated at this point. For instance, in the case of coal,if it 7 he Il may be incorporated with-"the-pipes ll an 2! and discharged with the gases through a suitable nozzle, as will hereinafter be described.

The steam and flue gases projected into the hood ll serve to warm the coal and the condensed steam is shaken of! and eliminated with the excess of condensed moisture of the coal..

Below section DE are positioned hoods 20 and 21 communicating through pipes 20 and is with the conduits Ill and SI respectively. These conduits preferably commonly communicate as at II with a suction fan 33 in turn communicating with an evase II which, through the drainage pipe 85, delivers the moisture to the water sump I I. In the conduits I0 and Si, in advance of the fan II, are positioned pulsators I and II respectively which are disposed oppositely to one' another alternately to establish connection between the fan and conduits It and It so that in a particular manner, by means of air currents, the coal is heated and the moisture is withdrawn when the coal is positioned in section DE of the screen A,

as will be described more particularly hereafter.

The coal is then passed from screen A to screen B and is delivered to section FGbver which is positioned a hood ll connected by the pipe 3! with the pipe line 23 so that hot flue gases are passed to hood II and passed through the bed of eliminated when the coal passes from this section.

As the coal moves on to section GH'it is subjected to a final drying and cooling operation. In this instance it will be noted that the pair of hoods M and 45 are positioned beneath section GH and communicate respectively with the conduits l0 and Ii. The upper side of the screen in section GH is completely open to the atmosphere so that through the action of the fan a cool air is drawn downwardly through ,the bed of coal so that a final effective drying operation takes place at this point in addition to the cooling of the coal before it is loaded into barges, etc., thus avoiding possible oxidization during transit due to a heated condition.

It will be realized from the foregoing general explanation of the apparatus illustrated that the method of drying generally consists in producing a flowing bed of the material and separating excess moisture by gravity, then preheating the partially dewatered material by steam and hot gases, subjecting the preheated material to hot drying gases and finally forcing cool air through the heated material finally to dry and cool it.

Having described the method and apparatus in a general way I will now deal with the development in a more specific sense in order that the advances made may be fully appreciated. In order efficiently to dry all the material it is essential that the steam, air or gases, penetrate the entiredepth of the bed, otherwise the surface only of the bed, which comes into contact with the steam, air, or gases is dried. It has been found that if these are forced upwards through the bed, in the case of materials such as coal emerging from a wet washery, which contain a high percentage of moisture, the moisture forms into a heavy fog over the bed which the gases are unable to disperse and which later condenses and falls back onto the coal, thus nullifying to an extent the drying action of the gases. I overcome this disadvantage by subjecting the bed to downward currents of steam, gases and air, and I ensure thorough penetration of the bed by the provision of regulated air pulsations. For coal is discharged onto a shaker screen and subjected to continuous downward current of air, it packs and becomes difficult to move and the air currents cannot penetrate the bed efliciently in intimate contact with all particles of the coal. However, under the present development by the use of proper pulsations of air properly combined with the shaking motion of the screen, having regard to periods of compression and depression of the mass of coal on the screen, a free motion of the coal on the screen is obtained and the air thoroughly penetrates and intimately contacts with the coal particles throughout the bed. The same is true of the gases and steam and a treating agent such as oil, in the case of coal, if used.

On referring, particularly to Figure 2, wherein the motion of the coal on the screen is illustrated, CA represents a coal particle on the surface SA. The particle CA being inert, follows the motion of the screen and reaches the position CB. After the screen has reached the position SB, it stops and then returns to SA but the coal from its momentum continues to position- CC and then under the action of gravity falls to the position CD on' the screen SA. Consequently for each complete oscillation of the screen the coal advances a distance equal to CACD. However, if during this complete oscillation of the screen, a downward current of air or gases is continuously maintained over the surface of the screen, the coal instead of leaving the screen at CB will be continuously pressed on the screen and return with it to CA. To avoid this I employ pulsating currents, which, on the contrary, are established and disestablished in such a way as not to blow down in at least part of the forward and return motion of the screen. Thus the coal will not be heldon the screen but will be permitted to move to an extent such as referred to above, although the relative displacement of the coal will be slightly decreased. Therefore, according to the present development, the air and gases are intimately contacted with the particles of coal making up the bed since the air and gas can readily penetrate the bed as it is agitated and the coal continuously passes along in an eflicient manner through thevarious stages of treatment on the screen.

As an illustration, assume the screen to beoscillating at 240 periods per minute'and air pulsating at the rate of 480 pulsations per minute, this results in one quarter of a second for complete oscillation of the screen whose displacements are positive for the upstroke of the screen (compression of the coal) and negative for the downstroke (compression of the coal). Air and ,/gas pulsations are positive when a connection is established with the fan 83 through the pulsators contrary, with the closure of a pulsatorfa slight upward. current of air is produced due to a returning wave of the air pulsation.

To illustrate the action, reference is made to Figure 1 and Figures 4 and 5, which illustrate the action of a piece of coal lying upon the screen above the hood 26, a similar action occurring above the hoods 21, 40 and ll. Upon referring to Figure 1, it will be seen that hood 26 is illustrated as connected to pipe line it which is closed off from the fan by the pulsator 31. Consequently, assuming that the screen is moving for.- wardlyat this point, it will be realized that there is a negative pressure on the coal, thus when the screen moves one-half the distance of its.

forward movement, the piece of coal CO will reach the position CP (see Figure 5). ,At this point the pulsator 31 is reversed to establish a positive downward pressure of air, whereupon the piece of coal will be moved back towards the screen, reaching substantially the position CQ and, moving upward with the screen, will reach the position CR. At this point the pulsator again changes, establishing a negative or slightly upwardly directed current of air, and as the screen moves back in downstroke through one-half its movement in .this direction, the

piece of coal will be free and reach substantially the position CS. At this point the 'pulsator again changes, establishing a downward pressure of air which will cause the coal to move downwardly to reach substantially the position CT, so that during one complete oscillation of the screen under the conditions referred to the coal will move along the screen a distance substantially equal to (JO-CT. The coal moves this distance in one-quarter of a second, having regard to the ratio as between the air pulsations and screen oscillations, so that during the period of one second the coal will be caused to move substantially four times this distance during which time it will be subjected to four periods of active forward motion, four periods of aeration, four periods of slightly assisting motion, four periods of slightly assisting aeration. A similar action takes place on the other half of the screen section underlying the hood i8 and overlying the hood 21, although the action of the air current is substantially reversed for the reason that the hood2'l is, as illustrated in Figure 1, in direct connection with the fan 30 due to the fact that the pulsator- 36 is in the open position. Therefore, assuming that thescreen is moving forwardly at this point, the coal will be subjected ,to a downwardly directed current during the first part of this movement.

On referring to Figure 4, it will be seen that as the screen moves forwardly a distance equal to one-half its travel the coal CL is subjected to a positive downward pressure so that it will be held on the screen and reach the position CK at the half-way mark. At this point the pulsator 36 reverses and a negative pressure is established so' that, as the screen travels forwardly the last half of the distance, the coal will reach wardly till it reaches the position CN, at the half-way mark in the downward movement of the screen, whereupon. a negative pressure is again established so that it is loose on the screen and when the screen reaches the extreme lower position in its downward movement the coal will reach substantially the position CK. Consequently the coal -moves a distance equal to CL-CX in a similar manner to the operation above referred to. It is apparent, therefore, that there is a constant forward movement of the coal while subjected to varying air currents and thus, in addition to securing proper motion of the coal, there is provided the most efllcient conditions for heating and drying. the coal as well as oiling when it is proposed to give the coal an oil treatment.

The eccentrics I2 have an adjustable stroke which provides for regulation of the total displacement of the coal, due consideration being given to losses due to compression periods to obtain the desired output compatible with the total duration of the treatment periods necessary to obtain the desired results.

An important feature of the invention resides 'in the fact that all the hoods under the screen are of exactly the same shape and size, so that they all can be resonators to the same notes of musicor to the same air pulsations of certain periods; in other words, all harmonics.

The driving motor I4 is designed to provide a very sensitive vari ble speed drive and, when the system is put into operation, resonance is obtained by tuning to the ear. The adjustment of the speed of the motor permits one to catch the desired period of air pulsation for which all the air boxes or hoods are resonators. suits, therefore, in a considerable increase in efficiency; instead of air currents counteracting against each other and waste of energy, there is a considerable amplification of these air currents. Consequently maximum volumes of air are circulatedfor minimum of energy supplied which results in maximum efliciency in heating, drying and oil spraying when this is carried out.

The eificiency of the method and apparatus is readily illustrated by referring to operation with screens of a size to provide a width of 4 feet and lengths of 6 to '7 feet for sections CD, DE, FG and GH, which provide for a tonnage of 50 tons per hour of coals over one-eighth of an inch in size. During passage of this volume of material over the screens the moisture content was reduced on section CD down to 12 to 14% and at the end-ofsection G -H down to a moisture content of 2 or 3%. l

Asa result of the drying process described the coal as it is discharged is just suitable for shipment. It will not freeze in the winter time and not oxidize to any extent. However, during its transportation in barges or railway cars it is liable to deteriorate. Fines will therefore be made, thus producing an objectionable dust when the coal is delivered to the consumer. To control the dust, oil has been used for many years and may be particularly and suitably applied for the present method of treatment. Through its addition with the hot gases in the drying operation the oil, as previously referred to, is introduced through the pipe line to the hood l8. To be eiflcient This rethe oiling must disseminate the oil and throw equally and regularly. This is readily brought about with the introduction of the oil along with the gas during the agitation of the coal as previously described. In other words,'the gases through the pulsating arrangement project through the loose mass of coal so that a large volume travels through the coal and comes into intimate contact with the whole mass. The oil is heated to a fluid and thrown under pressure by a pump as usual, but when ejected in the present process it is carried by a strong and large volume of hot gasses and by steam through the coal as the latter, when loose, is aerated and ejecting construction composed of the pipe line 46, corresponding to pipe l9 illustrated in Fig. 1, into which the oil jet 41, controlled by needle valve 48, is projected. Also communicating with this pipe is the steam conduit 20. Within the pipe 46, below the oil ejector, are positioned the mixing cones 50 and 5| through which the oil is directly ejected, the wide ends of the cones permitting the steam to intermingle with the oil. At the lower end of the pipe 36 is provided further mixing cones 53 and 54 which permit the hot gases in the conduit 22 to pass into intimate contact with the intermixed steam and oil, so that, as the mixture is projected into the hood J0, there is a very fine composite mixture of hot gas, steam and oil which readily penetrates the loose bed as described and contacts with the whole mass of coal equally and regularly.

Moreover, due to the fact that the oil is piped to the hood within the pipe 46, which acts to carry the steam, the oil is readily heated to a proper degree and the construction, in addition to ensuring a good mixing, acts as a blower injector. There is no danger of the oil evaporating as an oil of high boiling point may be selected.

As an example of the air and oil consumption for conditions, sizes and tonnages as above referred to, a volume of around 25,000 cubic feet of air and gases passes constantly through the apparatus and the amount of oil used is two to three pounds per ton.

The heating system provides a marked advance and contributes to the success and effi- .ciency of the method and apparatus disclosed.

Most driers use hot gases from a furnace in coal drying as accomplished at the coal mine, and plenty of low grade and cheap coals are available and used. However, in such furnaces as the gases produced by such coal can 'run as high as several thousand degrees, there use introduces many problems. For instance, most coals begin to oxidize at 200 C. and this oxidization is likely to alter their coking and burning qualities and if carried further will cause ignitions or explosions. According to the present process, however; by employing steam, the heating of the combustion gases is first used to produce the steam and when the gases leave the boiler they are always at a temperature under the danger point so' that they can be passed through the coal mixed with air, if necessary to obtain the desired volume, without any possibility of disadvantageous results. In view of this, quick and eflicient drying is accomplished in a relatively simple type of apparatus. I

As a further illustration of this in an apparatus of the dimensions above referred to, the coal advances oneinch for a screen oscillation of two inches, and therefore when operating at 240 oscillations of the screen per minute, this results in the coal advancing four inches per'second. Thus for a bed of a thickness packed to four inches, an output of 50 tons per hour is achieved.

It is apparent from a consideration of the various steps involved that in addition to the method of drying generally set forth, wherein a percentage of moisture is removed by gravity and the remainder suocessivelyeliminated by heating and preheating with steam and gases, drying with gas and drying with air, the method includes the subjectionof material to controlled pulsations of the air which when combined with the heating provides for quick drying, as well as a steady movement of the material. On the other hand, the heating by way,.of steam and gases in a controlled manner constitutes an important factor.

vided for with relatively small apparatus and small consumption of coal and power. With this, there is provided the most efficient conditions for treatment of the material, such as by oil in the case of coal, inasmuch as the oil may be readily dispersed and brought into intimate contact with the coal particles.

However, it will be realized that while coal has been used as a general illustration of the material treated, the apparatus is generally applicable to the drying of wet granular materials and that where materials are subjected to treatment by special agents, such agents might be brought into contact with the material in a similar manner to the dispersion of the oil as above referred to.

Various modifications may be made in this invention without departing from the spirit thereof vas are disclosed in the prior art or are set forth in the accompanying claims.

What I claim as my invention is: 1. (The method of drying wet granular mate rial, which comprises producing a flowing agitated bed of material, subjecting the bed to a series of controlled air pulsations applied substantially throughout the length of the bed, preliminarily separating excess moisture by gravity, preheating the partially dewatered material by forcing steam downwardly therethrough, subjecting the preheated material to downwardly forced hot drying gases, forcing air downwardly through the heated material as a cooling and final drying step, and discharging the dried cool material from the bed, said air pulsations inducing the passage of the steam, hot gases and air through the bed.

2. The method of drying wet granular material, which comprises producing a flowing agitated bed of the material and subjecting the moving bed to a series of air pulsations alternately directed to different portions of the bed and applied substantially throughout the length of the bed.

3. The method according to claim 2, in which the alternate air pulsations are applied from 0D- posite surfaces of the bed.

4. The method of drying wet granular material, which comprises producing a flowing agitated bed of the material, subjecting the moving bed to a series of air pulsations alternately directed to diiferent portions of the bed and applied substantially throughout the length of the bed,

and forcing hot gases and steam downwardlyinto the bed for drying purposes and carrying the hot gases and steam through the bed into intimate contact with the particles therein by means of said air pulsations.

5. The method of drying wet granular material, which comprises producing a flowing agitated bed of material, subjecting the moving bed to a series of controlled air pulsations directed to different areas of the bed and applied substantially throughout the length of the bed, and correlating the air pulsations with the movement of the bed to amplify the air currents.

6. The method of drying wet granular material, which comprises producing a flowing agitated bed of material, producing steam by means of hot combustion gases, directing the steam downwardly to an area of the bed to preheat the material, directing the-combustion gases to the bed dividing said gases, applying a portion of said gases downwardly to the bed together with the steam in the preheating operation, applying the other portion of the gases downwardly to another area of the bed as a drying operation, and finally drawing cool air downwardly through the bed as a final drying and cooling step.

GUSTAVE ANPRE VISSAC.

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