US2275116A - Method and apparatus for treating granular or powdered material - Google Patents

Description

March 3, 1942. M. VOGEL-JORGENSEN 2,275,116

METHOD AND APPARATUS FOR TREATING GRANULAR OR POWDERED MATERIAL Filed June 25, 1939 4 Sheets-Sheet 1 d flVENTOR BY M,

m ATTORNEYS March 3, 1942. M. VOGEL-JORGENSEN METHOD AND APPARATUS FOR TREATING GRANULAR 0R POWDERBD MATERIAL 4 Sheets-Sheet 2 \NVENTOR Filed June 23, 1939 ATTO RN EYS BY ya I M 1942- M. VOGEL-JORGIENSEN 2,275,116

METHOD AND APPARATUS FOR TREATING GRANULAR OR POWDERED MATERIAL I Filed June 23, 1939 4 Sheets-Sheet 3 ATTORNEY5 Mal'dl 1942- M. VOGEL'JORGENSEN 2,275,116

METHOD AND APPARATUS FOR TREATING GRANULAR 0R POWDERED MATERIAL Filed June 23, 1939 4 Sheets-Sheet 4 Patented Mar. 3, 1942 METHOD AND APPARATUS FOR TREATING GRANULAR B POWDERED MATERIAL Mikael Vogel-Jorgensen, Frederiksberg, near Co- Jersey Application June 2:, 1939, Serial In Great Britain October I Denmark, asslgnor to F. L. Smidth & (20., New York, N.

1., a corporation of New No. 286,714 a, 1938 I Claims. (Cl. 3l25) This invention relates to the treatment of granular or powdered material by passing a gas transversely through a layer of the material moving on a plane gas-permeable support.

Heretofore it has been customary to use a stationary horizontal grate, or similar support, over which the material is moved by scrapers, or the like, or to use a travelling grate on which the layer of material moves along with the grate. It has also been proposed to use a'grate, the elements of relatively wide steps each of which supports some of the material in its own horizontal plane. Alternate steps of the grate are stationary while the others are horizontally reciprocated in unison so as to cause the material to be pushed off the steps and to move progressively down the steps by a tumbling action from one step to the next lower one.

When scrapers, or like devices, are used in conjunction with a stationary grate, the layer of material isvery uneven with the result that the treatment is not uniform. Moreover, the action of the scrapers on the material is likely to cause considerable dust when certain materials are treated. For various reasons it is often inconvenient to use a travelling grate. One of the ob-' jections to a step-grate of the kind above mentioned is that there is necessarily a great deal of relative movement between the particles of the material as it tumbles down the steps of the grate,

whichare arranged like a series of and this is likely to cause considerable dust when T certain materials are treated. Moreoventhis relative movement between the particles of the material, together with thefact that the layer of material is not uniform in thickness, results in a non-uniform treatment of the material.

According to this invention an inclined grate, or similar support, is used and is arranged at an angle to the'horizontal which'is less than, and preferably only slightly, less than, the angle ofrepose of the material onthe support. By angle of repose is meant the maximum angle at which a mass 'of the particular material being treated, while being penetrated transversely in the desired direction by the treating gas, will reeither grains or particles of the material moving relatively to one another within the mass, or the whole mass moving relatively to the support under the iniiuence of gravity. The material is main stationary on the inclined support without caused to move down the support by being subiected to an internal force which acts parallel to the inclined support so that thelayer of material moves as a whole without substantial local sliding or relative movement of the particles within the layer of material on the support. It the angle at which the support is arranged is too great the material tends to slide down its surface under the influence of gravity and the movement is therefore irregular so that the resulting treatment is not uniform. If the angle'is too small the conditions approach those which would exist if the support were horizontal and the desired result would not be obtained. If, however, the' that the friction between the grains or particles of the material is greater than the friction between the layer as a whole and the inclined grate, so that the internal force can overcome the latter but not the former.

The angle of repose may be different for different materials and for diflerent conditions 0! the same material. It depends, among other things, on the particle size and the temperature of the material. For instance, it has been found that the angle of repose of cold cement clinker of a certain particle size is about 30 and that inclining the grate at an angle of about 25 gives the desired results, whereas for hot clinker-of a smaller particle size the angle of repose was found to be somewhat less and the best results were obtained by inclining the grate at an angle of about 18. Therefore by the expression slightly less than the angle of repose of the material on. the support, I mean slightly less than the angle of repose of the very material undergoing treatment on the support; When the treating gas passes upwardly through the layer (1. e., in a direction away from thesupport), the support will be inclined at a slightly smaller angle than if the gas at. the proper inclinathe treating gas on the ma- I5 terial because the angle of repose of the material is determined while the gas is passing through it in the same direction that it is to be passed while the material is undergoing treatment as above stated, and the proper inclination fdr the support is slightly less than the angle'of repose of the material so determined.

Preferably, the internal force is applied by a member arranged parallel to the support and which is reciprocated within the layer of material. The member is so shaped that while it applies the necessary impulses to cause the layer of material to move down the support, it can nevertheless slide upwards through the layer without causing any substantial disturbance within the layer. It has been found that the desired result can be obtained by a reciprocating member which comprises a number of bars extending longitudinally of the support and arranged to move lengthwise in their own plane in a direction parallel to the inclined support.

The gas maybe passed through the layer of material in order to preheat it, or cool it, or in order to bring about some chemical change. An example of such a chemical change is the artificial ageing of cement by means of carbon dioxide. However, my method and apparatus are particularly useful and advantageous for the air cooling of cement clinker discharged in a hot state from a rotary kiln, and therefore the invention will be described in its application to that particular use.

Several forms of apparatus embodying the invention, and capable of carrying out the improved method, are illustrated in the accompanying drawings, in which- Figure 1 is a vertical longitudinal section through the discharge end of a rotary kiln showing one form of the improved cooler onto which the kiln discharges. In this form of the invention the cooler is arranged transversely to the axis of the kiln and therefore the cooler is shown in transverse section.

Figure} is a vertical section taken on the line 2-2 of Figure 1. In this figure the kiln is shown in transverse section and the cooler is shown in longitudinal section;

Figure 3 is a diagram of the circuit of the motor which operates the reciprocating member;

Figure 4 is a transverse vertical section taken on the line l& of Figure 2;

Figure 5 as a partial longitudinal section taken on the line 5-5 of Figure 4;

Figure 6 is a vertical section through the discharge end of a rotary kiln showing another form of the cooler onto which the kiln discharges. In this form of the invention the axis of the cooler extends in the same general direction as the axis of the kiln instead of transversely to it as in Figure 1.

Figure 7 is a vertical transverse section on the line 1-1 of Figure 6;

Figure 8 is a vertical transverse section on the line 8--8 of Figure 6; and

Figure 9 is a plan view of the lower portion. of

a few of the reciprocating bars above the grate, illustrating how they .may be modified, if so-desired, tov facilitate movement of the lower and cooler portion of the layer of material.

Referring first to Figures 1 to 5 inclusive, the

casing having walls 3, 4 and 5.

the end portion of the kiln are enclosed by a The cooler comprises an inclinedgas-permeabl support, or grate 6, carried by supports 1, 8 and 9. The grate is preferably made of sheet metal formed with a number of openings I0 (Figure 5) covered by hoods II which may be pressed or otherwise formed out of the sheet itself. The hooded openings permit air to pass upwardly through the grate and yet clinker from the kiln Y moving down the gratewill not pass through the discharge end of a rotary kiln suitable for burnopenings.

The clinker leaves the kiln through an outlet ring I2 and drops onto the surface of a precooling or quenching box I3. This box is made of fire-resistant material and is supported by the end wall 4 and a fire brick wall I4. The box I3 is perforated as indicated at I5 so that cooling air can flow through it. The clinker is swept from the surface of the box I3 onto the inclined grate 6 by flights I6 fixed to a carrier H which is rigid with the kiln. Only some of the flights I6 sweep overthe surface of the box I3 and the rest of them distribute the clinker in a uniform layer over the whole width of the grate 6 at its upper end. The inclination of the grate 6 is such that the layer of material formed in the manner just described would not move down the grate under theinfluence of gravity alone. The angle which the grate forms with the horizontal is less than, and preferably only slightly less than, the angle of repose of the material on the grate as above explained. The internal force by which the layer is caused to move down the grate is applied to the material by a reciprocating member formed principally of bars I8 which are spaced apart transversely of the grate, as best shown in Figures 1 and 4, and which extend longitudinally of the grate and parallel to it as best shown in Figures 2 and 5. The bars I 8 may be connected by cross bars I9. The reciprocating member thus formed is sup ported just above the grate by pendulum-like bars 20 which are fixed at their upper ends to the wall of the casing and at their lower ends to two of the cross bars I9. The bars 21! are of such dimensions that they bend slightly to allow the movable member made up of the longitudinal bars It and cross bars It to reciprocate'as a whole. This member is reciprocated by a crank disk M to which it is connected by the links and arms 22, 23 and 24. The crank disk 2| is rotated by an electric motor represented at 25 in Figure 3. As the motor rotates, thelongitudinal bars I8 of the reciprocating member move lengthwise in their own plane in a direction parallel to the inclined grate. During the down stroke of the bars I8 they cause the entirelayer of material on the grate to move as a whole with them as far as the bars move. Due to the angle at which the grate is inclined, the layer of. material is almost ready to move anyhow and requires only the downward movement of the bars It to cause the whole layer of material to start moving. As previously explained, the friction between the particles of material is greater thanthe'friction between the particles and the grate,

and therefore the downward movement of the bars I8 causes the layer of material to move as a whole without substantial relative movement between the particles of the material. on the return upward stroke of the bars I8 they merely slide through the material withoutmoving the layer or substantially disturbing the particles.

The cooling is efiected by passingair from the space 26 at a pressure slightly above atmospheric pressure through the grate and the layer of material. This air is heated by its passage through the hot material and enters the kiln to be used as secondary air of combustion.

The stroke of the reciprocating member may be varied in any suitable way in accordance with the thickness of the layer of material on the grate. Thus, if the output of the kiln increases, the layer of the material on the grate will become thicker and a longer stroke of the reciprocating member will be required. Means for accomplishing this will be described in connection with the other form of the apparatus illustrated in Figures 6-8.

In addition to regulating the stroke of the reciprocating member its speed may also be varied in accordance with the thickness of the layer of material on the grate and this may conveniently be done automatically. For this purpose a paddle indicator 2! (Figure 1) is provided, the position of which is determined by the thickness of the layer of material on the grate. The paddle indicator is connected to'a box 28 which is rocked when the indicator moves up and down as the thickness of the layer varies. The box 28 contains a number of mercury switches indicated at 23, 30, 3| and 32 in Figure 3. These switches are so arranged that they are successively operated as the box 28 rocks, and each serves to short circuit one of a number of resistances 33, 34, 35 and 36in the circuit of the electric motor 25. A manually operated adjustable resistance 31 is provided so that the motor can be initially adjusted to the desired speed for the normal output of the kiln and capacity of the cooler. The current to the motor supplied through the leads 3!! then passes through a greater or smaller number of the resistances 33-36 in accordance with the position of the mercury switches 29--32 which in turn depends on the position of the paddle indicator 21.

In the form of the invention shown in Figures 6, 7 and 8 the axis of the cooler extends in the same general direction as the kiln axis instead of transversely to it. In other words, the material will travel down the inclined grate in the same general direction as it travels in the kiln. The cooler operates on the same principle as that previously described but is somewhat diiferent in construction.

The discharge end of the kiln and the cooler are enclosed by a casing having walls 3', 4' and The wall 4' is provided with an opening for the fuel pipe A, and a door 39. The material discharged from the kiln first passes onto a grate, the bars 40 of which arev hollow and are cooled by water circulated through them by means of pipes 4i and 42. The large lumps of material will not pass between the bars of the grate 40 but will roll along th grate to the vicinityof the door 39 where they can be removed through this door. The normal clinker will fall between the bars of the grate 40 and through a preeooling or quenching shaft formed between the casing wall 5', a fire brick wall 43 and the side walls of the casing. Below the fire brick wall 43 there is a heat resistant hinged plate 44. A header 45 cooperates with the lower edge of the hinged plate 44 to form a restricted opening through which the clinker leaves the precooling or quenching shaft and by which it is feed in a uniform layer to the inclined grate of the coolerproper. The, hinged plate 44 is free to deflect jam when it passes through the restricted opening under the lower edge of the plate. The cooling or quenching shaft is spanned by precooling or air quenching elements 46 which may be supported by thewalls 5' an 43 of the shaft. These elements preferably ha e the cross section indicated in Figure '7 so that the clinker will accumulate on the top of the elements and so that pockets will be formed in the material under the elements. Air is supplied from a header 4! (Figure 6) by means of pipes 48 to the channels under the elements 46 and to the pockets in the material which form under these elements. The air thus supplied escapes partly through holes which may be provided in the horizontal webs of the elements 46 and partly around the lower edges of the elements thereby precooling or quenching the hot clinker.

The opening between the hinged plate 44 and the header 45, and the arrangement of elements 46, cause the clinker to form a pile in the precooling or quenching shaft as indicated by the dotted line B in Figure '7, and cause the clinker to be distributed uniformly over the entire width of the inclined grate. If occasionally the kiln should discharge more clinker than can be removed through the passage between the plate 44 and the header 45 by the reciprocatingmemher over the inclined grate, the height of the clinker pile will be raised and the excess clinker will discharge through the overflow openings 49 in the transverse fire brick wall 43. Hinged plates 50 may be provided at either side of the clinker pile to prevent the clinker from separating into graduated sizes such as usually happens when clinker is allowed to pile 'up freely.

The cooler proper comprises a gas-permeable grate 6' which may be similar to that employed in the type of cooler previously described. The grate may be mounted on supports 5|. The reciprocating member operating above the grate comprises a number of bars I8 extending longitudinally. of the grate and parallel thereto. These bars are supported at their upper ends by rocker arms 52 and at their lower ends by rocker arms 53 (Figure 6), which, in turn,.are supported on upper and lower shafts 54 and 55 respectively. The shafts 54 and 55 are oscillated by means of arms 56 and 51 respectively which, in turn, are actuated by rods 58. Each rod 58 is reciprocated by an eccentric drive mechanism on a shaft 53, the eccentric bushing 60 of which may be angularly adjusted by the mechanism indicated at iii to vary the stroke of the rod. I

Each rod 58 has a sliding connection with the corresponding arms 58 and 51. Collars 52 and 63 are fastened to the rod 58 in such a way that when the rod 58 moves downwardly the upper collar 62 will act onthe arm 55 to pull the bars l8 upwardly. The sliding connection between the lower end of the rod 58 and the arm 51 prevents any pushing or compressive force from being applied to the lower ends of the bars l8. Likewise when the rod 58 moves upwardly the collar 63 moves the arm 51 and. pulls the bars [8' downwardly while the sliding connection be tween the upper ends of the rod 58 and the arm 58 prevents any pushing force from being applied to the upper ends of the bars l8. Thus the bars i8 are always under tension because when they are moved downwardly they are pulled at their lower ends, and when they are moved upwardly they are pulled at their upper ends. Thus they are never pushed by a compressive force which might tend to bend or buckle them.

When the shaft 59 is rotated, as by an electric motor such as that shown at 25 in Figure 3, the eccentric drive reciprocates the rods 53 and through the connections above described the bars it are reciprocated to cause movement of the whole layer of material down the inclined grate in the manner previously described. If the layer of material on the grate becomes thicker due to an increase in the output of the kiln the length of thestroke of the bars I8 may be adjusted by turning the hand-wheel 6| (Fig. 6). This handwheel is mounted on a shaft which carries a worm 6! which meshes with teeth (not shown) on an eccentric bushing fill. Hence when the hand-wheel 8| is turned, the angular position of the eccentric bushing 80 is shifted to thereby adjust the throw of the rods 58 and consequently the length of the stroke of the bars it,

Air is supplied to the cooler casing by means of a fan '65. That portion of the air which passes through the inclined grate above the hinged baffie plate 65 absorbs so much heat from the clinker that it is suitable for use in supporting combustion in the kiln. That portion of the air which passes through the comparatively cool lower portion of the layer of clinker between the baffie E and a second hinged bailie 66 is discharged through a vertical vent pipe 81. The baffle plate 65 is hinged to allow for variations in the thick= ness of the layer on the inclined grate, and to prevent any jamming in case clinker lumps should accidentally pass oil the grate bars 46. The hinged battle plate 66 is of such a length that it will rest at its lower edge upon the layer of clinker thereby forming an air seal.

The clinker discharged at the lower end of the inclined grate drops into a channel where it is discharged upon a drag conveyor 68 which transports the cooled clinker to a suitable place of storage. Any fine clinker particles which pass through the grate 5" fall into the hopper bot= toms 69 and Hi (Figure 8) of the casing and are discharged by collecting screws H into the chan nel in which the drag conveyor 68 operates.

As above explained, it has been found that the angle of repose of cold cement clinker is greater than the angle of repose of hot cement clinker. When the grate is given the proper inclination for cooling hot clinker the movement of the clinker layer at the lower portion of the grate may tend to be less than at the upper portion due to the fact that the clinker near the lower portion of the grate has been cooled thereby giving it a greater angle of repose. To compensate for this the lower portions of the reciprocating bars l8 and It may, if desired, be provided with suitable projections so shaped that they increase the effectiveness of the bars in moving the clinker near the lower portion of the grate but do not unduly disturb the clinker layer when the bars are moved upwardly. Projections of this character are represented at E2 in Fig. 9. The number of these projections to be used, and the distance that they extend up the bars will depend among other things on how much compensating action is required of them and the approximate point in the travel of the clinker where the temperature of the clinker becomes sufilciently changed to tend to slow up its movement.

It will now be noted that in both forms of the apparatus the inclined grate so supports the material that it is capable of a bodily. sliding movement dowu the grate, as distinguished from the way in which the material is supported on the relatively wide horizontal surfaces of a stepgrate of the kind above referred to which does not permit of a bodily downward sliding movement of the material. The preferred inclination of my grate is such that the angle which the grate forms with the horizontal is slightly less than the angle of repose of the material on the grate, as hereinbefore explained, so that when the bars above the grate move ina downward direction the entire layer of material moves as a whole with them without substantial relative movement between the particles of the material. When the bars move upwardly the layer of material remains stationary and there is practically no disturbance of the particles.

The distance that the reciprocating bars are spaced from the inclined grate should preferably be at least equal to the size of the clinker particles, as otherwise the clinker is likely to jam. Furthermore, it has been found in practice that the best results are obtained, when clinker is being treated, if the reciprocating bars are spaced apart transversely of the grate not more than 120 mm., as otherwise there is danger that the layer may not move as a whole.

It will also be noted that the series of reciprocating bars when moving downwardly not, only apply a force to the layer of material at a number of points spaced apart transversely of the layer, but also along a number of spaced lines extending lengthwise of the layer. In other words, the reciprocating bars distribute the force to the material not only transversely of the layer but throughout the length of the bars.

Since the layer moves uniformly as a whole, the treatment with the gas is uniform and effective. Moreover, there is no formation of dust as the material moves down the support in contrast to methods in which parts of the layer move relative to one another, as in the scraper method and the step-grate method, in which considerable dust is likely to he developed. The avoidance of dust is particularly important in the cooling of cement clinker, or like material, discharged in a hot state from a rotary kiln. My apparatus is, therefore, particularly adapted for that use, and when so used the air that is employed for the cooling may be used as secondary air of combustion. in the kiln. This air has been heated by its passage through the clinker on the inclined grate-and itis'a'dvisablc to conduct it to the kiln without its coming into substantial contact with the hot clinker being discharged from the kiln because it is advantageous to give the hot clinker leaving the kiln a sudden uenching before the gradual cooling on the inclined grate. If the air used for cooling the clinker on the inclined grate made substantial contact with the hot clinker being discharged from the kiln, the resulting cooling of the clinker would not be great enough to constitute the quick quench-= ing that is desired. This result is accomplished in both forms of the apparatus herein described by providing quenching means to act on the hot clinker as soon as it leaves the kiln and con ducting the air that has been used for cooling the clinker on the inclined grate to the kiln by a path which keeps it out of substantial contact with the hot clinker leaving the kiln. In the form of apparatus shown in Figs. 6, 7 and 8 this is accomplished very effectively because after the cooling air passes through the clinker on the inclined grate, it passes upwardly to the left of the wall 63 (as viewed in Fig. 6) and contact with the hot clinker leaving thekiln,

and the other through which the hot clinker from the kiln passes and in which it is 'quenched immediately after leaving the kiln.

I claim:

1. Apparatus for treating granular or powdered material comprising a gas-permeable support on which the material may be moved, and means for feeding material to the support comsupport without substantial local prising a shaft through which the material passes before it reaches the support, and a plurality of stationary elements spanning said shaft and extending longitudinally of the support, said elements being located in the path of the material assing to the support and arranged to distribute the material laterally so that the layer of material on the support will be substantially uniform throughout the width oi'the support.

2. In a method of treating ,granular or powdered material by passing a gas transversely through a layer of the material, the improvement which comprises supporting the portion of the layer through which the gas is passed at an angle to the horizontal, applying a force within the layer of material in. a downward direction parallel to the inclined support, the angle at which the material is supported being so chosen that it is less than but close to the angle of repose of the material on the support, and said force being such that by and during its application said portion of the layer of material will start and continue to move as a whole on the support without substantial local relative movement between the particles of the material.

3. In a method of treating granular or powdered material by passing a gas transversely through a layer 01' the material, the improvement which comprises supporting the portion of the layer through which the gas is passed at an angle to the horizontal, applying a force. in a downward direction parallel to the inclined support at a' number of points within the layer of material, the angle at which the material is supported being so chosen that it is less than but close to the angle of repose of the material on the support, and said force being such that by and during its application said portion of the layer of material will start and continue to move as a whole on the support without substantial local relative movement between the particles of the material.

4. In a method of treating granular or powdered material by passing -a gas transversely through a layer of the material, the improvement which comprises supporting the portion of.

the layer through which the gas is passed at an angle to the horizontal, applying a force in a downward direction parallel to the inclined support at a number of points within the layer and spaced apart transversely thereof, the angle at which the material is supported being so chosen that it is less than but close to the angle of repose of the material on the support, and said force, being such that by and during its applirelative movement between the particles of the material.

5. In a method of treating granular or powdered material by passing a gas transversely through a layer of the material, the improvement which comprises supporting the portion of the layer through which the gas is passed at an angle to the horizontal, applying a force in a downward direction parallel to the inclined support along a number of lines within thelayer that extend lengthwise thereof and are spaced apart transversely of the layer, the angle at which the material is supported being so chosen that it is less than but close to the angle of repose of the material on the support, and said force being suchth'at by and during its application said portion,

dered material by passing a gas transversely through a layer of the material, the improvement which comprises supporting the portion of the layer through which the gas is passed at an angle to the horizontal, applying impulses within the layer of material in a downward direction parallel to the inclined support, the angle. at which the material is supported beingso chosen that it is less than but'close to the angle of repose of the material on the support, and said impulses being such that by and during each impulse said portion of the layer of material will start and continue to move as a whole on the support without substantial local relative movement between the particles of the material,

cation said portion of the layer of material will start and continue to move asa whole oh the and controlling the rapidity of said impulses in accordance with the thickness of the layer of the material on the support.

7. Apparatus for treating granular or pow: dered material comprising an inclined support for a layer of the material, a number of bars spaced above the support and extending longitudinally thereof and spaced transversely of the support, means to hold said bars in spaced relation to the support, and means for reciproeating said bars comprising a source of power, means connected to one end of said bars to pull them in one direction when said reciprocating means is actuated from said source 01' power, and means connected to the other end of said bars to pull them in the other direction when said reciprocating means is actuated from said source of power, whereby duri'ng'reciprocation oi the bars they are maintained under tension and are not subjected to longitudinal compressive forces.

. 8. Apparatus for treating granular or powdered material comprising a gas-permeable support for a layer of the material, said support being inclined to the horizontal at an angle which is slightly less than the angle of repose of the material on the support, means arranged to act on the material within the layer above the plane of its contact with the support to apply a downward force to the material in a direction parallel to the inclined support, the means acting on the material within the layer consisting of parallel bars longitudinally inclined downwardly parallel to the inclined surface of the support and spaced along their entire length from the inclined support a distance less than the thickness of the layer or material ordinarily to betreated, means tor maintaining said bars in said spaced relation to the inclined support, and means for reciprocating said bars.

9. Apparatus for treating granular material comprising a gas-permeable support for a layer of the material, said support being inclined to the horizontal at an angle which is slightly less than the angle of repose of the material on the support, means arranged to act on the material within the layer above the plane of its contact with the support to apply a downward force to the material in a direction parallel to the inclined support, the means acting on the material within the layer consisting of parallel bars longitudinally inclined downwardly parallel to the inclined surface of the support and spaced along their entire length from the inclined support a distance at least equal to the size of the particles of the material but less than the thickness of tha layer of material ordinarily to be treated,

means for maintaining said bars in said spaced 20 relation to the inclined support, and means for reciprocating said bars.

10. Apparatus for treating granular or pulverulent material comprising a gas-permeable grate adapted to support a layer of the material and which is inclined to the horizontal at an angle which is slightly less than the angle of repose of the material on the grate, means arranged to act on th material withinthe layer above the plane of its contact with the grate to apply a downward forceto the material in a direction parallel to the inclined grate, said means acting on the material within the layer consisting of a number of parallel bars longi-

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