US2042042A

US2042042A - Pulverizer

Info

Publication number: US2042042A
Application number: US609167A
Authority: US
Inventors: Frisch Martin
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1932-05-04
Filing date: 1932-05-04
Publication date: 1936-05-26
Anticipated expiration: 1953-05-26

Description

May 26, 1936 y AM. FRISCH '2,042,0425

PULVERIgER v Filed May 4, 1932 2 sheets-sheet 2 ha@ N @f MAMA,

fs ATroRNEY Patented May 26, 1936 .l

PATENT oFFlcE 1 PULVERIZER Martin Frisch, New York, N. Y., assignor to Foster Wheeler Corporation, NewYork, N. Y., a corporation of New York Application May 4.1932, serial no. 609,167

My invention relates to the art of pulverizing and particularly tothe art of pulverizing coal or similar material by subjecting it to the action of I rapidly rotating members. I

One of the objects of my invention is to provide a pulverizing apparatus or mill wherein the material to be pulverized is subjected a plurality of times to the action of the same rotating members, whereby extremely line pulverizing is effected by an `apparatus of size.

Another object of my invention is to eliminate foreign materials, thereby minimizing the danger of breakage of pulverizing members.

A further object of my invention is to increase lf the air flow through a' pulverizing mill so that the mill may be operated with a smaller exhauster, or the same exhauster may deliver more air therethrough than was formerly the case.

Other objects and advantages of my invention will be apparent from the following description considered in connection with the accompanying drawings, which form a part of this specication, and on which:

Fig.l 1 is )a central vertical longitudinal' section, partly in "elevation, through the main portion of a mill embodying the invention;

Fig. 2 is a transverse sectional view, taken on line 2-2 of Fig. 1; A

Fig'. 3 is a transverse sectional view taken on line 3-, 3 of Fig. 1;-

Fig. 4 is a fragmentary view of certain parts shown in Fig. l;

Fig. 5 is a view similar to Fig. 4 but showing l a modied arrangement of certain parts;

bers and I2. The casing is provided with end` walls I1 and 63, each being formed with a central opening therethrough. An exhauster casing I6 o is supported by end wall I1 and the bed-plate.

Extending through the casings I5 and,l I6 is a shaft I8 mounted in

suitable bearings

20 and 2| carried by lsupports I3 and I4, respectively.

Mounted on shaft I8 within casing I5 is a hub 32. In the embodiment shown, two annular Fig. 6 is a 'view taken on line 6-6 of Fig. 5;

discs or wheels and 3| are rigidly secured toV hub 32 by means of

bolts

33 and 34, respectively, and by means of

rings

35 and 36 secured to hub 32 by

bolts

31 and 38, respectively. Wheel 3| has-a larger 'diameter than wheel 38. A plurality 5 of hammers 46' and 42 are pivotally secured to

wheels

38 and 3| by pins 4| and `43, respectively.` so as to have limited swinging movement about the pins.

Arranged around wheel 3| and hammers 48 is l0 a scroll-shaped member 62 made upof two parts 62' and 62" supported on end wall 63 by bolts 64. A pocket 82 for tramp metal or other foreign material such as stone is formed in the scrollshaped member 62 between parts 62' and 62". A. 18 series of louver grids or targets 83 are provided in the side ofthe pocket. `These grids permit the passage of air and partially pulverized coal but stop larger particles of foreignv material, which thus are trapped. A drop gate 84 is iixed` 20 to a shaft 85. Shaft 85 extendsthrough the end' wall 63 and a boss 86. A lever 81 held invplace by a s top 88 is fixed to shaft 85. The frotation of shaft 85 causes' any material trapped in the pocket'to be discharged through an opening 96 g5 in the casing I5.` Communicating with opening su is a conduit 9|. The opening of th conduit is closed by a slide 82, which may be raisedto remove tramp metal.'

- Wheel 30 and its associated parts constitute 30 a first stage, and wheel 3| and its associated parts constitute a second stage. The first and second stages constitute what may be termed a cruhing zone. I

Fine grinding elements constitute a thirdstage, 35

There is thus formed by the plate 53 and webs I and 5| a series of pocketswhich provide means `for redirecting air, and pulverized material. The 45 stationary bars 44, webs 50, 5| and 52 and plate -53 are conveniently made in four sections, two of which,designated by-reference characters 46 and 41, are shown bolted together at 48. Each sec tion may be cast Vin one piece and is bolted to 50 the pulverizer casing I 5" by bolts 54 and 55. The four sections taken `together constitute the set of stationary bars. f

The rotating bars 45 are mo ted on a disc 56 and are held rigidly in place by bolts 51. The

disc is secured to hub 32 by bolts 58. An additional fastening ring 60 prevents disc 56 from moving axially. Discv 60 is fastened to the hub by screws 81|.

The bars have been shown as round but it will be understood that. they may be given any dey sired cross-section, such as square or triangular.

As shown, thereare twenty-'four stationary bars and twenty-three rotating bars. This prevents zontally split end wall liner 66 is secured adjacent t6 end wall 63 outside of the scroll-shaped liner 62 and is held in place by the liner..65 to- 4 To the left gether with a flange 61 on liner 62.

of web 52, as viewed in Fig. 4, is the liner 68. A

partition 10 formed with a central opening is secured to the pulverizer casing I5. The liners and partition 10 may be made of steel or other suitable wear resisting material. v

A classiiler cone 1| and an annular member 12 are bolted to partition 10 adjacent to the central opening therethrough by bolts 13. Between the annular member 12 and the partition 10 is a plurality of shims 14 for spacing the annular member 12 away from the rotating bars 45. Associ- Vated with the classier cone 1| is a set of radially extending vanes 80. 'I'he vanes are mounted on a hub 8| which is keyed to the shaft 8.

All parts fastened to the upper half of the pulverizer casing are split horizontally so that by

unfastening bolts

15 and 16 the entire upper half of the pulverizer with the exception of partskeyed `to shaft I8 may be swung upwardly `on the pivot 11 of the'hinge 18. This allows inspection of the interior of the pulverizer and permits replacement of certain parts which may be worn' out.

' A conduit 94 communicates through an opening 93 with the space between partition 10 and the end wall I1. The end of theconduit 94 may be closed by an adjustable slide 95. Opening 93 will hereinafter be referred to as an air inlet and admits air between'the fine grinding zone `and the exhauster. By adjusting slide 95 the size of theopeningof the air inlet may be changed to 'vary the amount of air admitted atthis point.

Where the pulverizing mill is used to supply pulverized coal directly to a burner it is desirable to supply additional air through this inlet. It will be understood that the conduit 94 may be connected with any suitable source of heated air. f

Mounted on shaft lvwithin exhauster casing i6 is a hub 24 having arms 25 to which are secured fan blades 26. Casing |6'is formed with a cen` trally located inletopening 22 and a tangentially located discharge conduit 23. A liner 28 is provided within casing |6.

A feed inlet chute 96 is fastened to end wall 63 by bolts 91 and communicates with the centralv opening in the end wall. A conduit |00 from lchute 96 to a table feeder V98 is fastened to the `feeder. Table feeder 98 comprises a. flat circular table |0| fitting; closely in a circular feeding chamber |02. Thev table is rotated by a shaft |03 which is slidably mounted in a worm gear |04. .A

bevel gear |05 is mounted on the shaft I8. A transverse shaft |06-carries a worm |01 meshing with worm gear m and a. beveigear Ins mesh.

vcarried upon this deilecting cone is a scraper- II! vl 0 which is held from rotating by a stationary abutment I3. A lever I4 pivotally mounted on bracket ||0- engages a collar on shaft I 03 for raising and lowering the table |0| to vary the amount of material enteringl the feeding chamber |02 15.

from hopper 1. I'he lever ||4 is held in any desired position by engaging a latch I5 with rack II6. A slide ||8 held in adjustment by wing nut |20 varies the quantity of air fed to the pulverizer 2o with the material tobe pulverized.

Fig. 5 shows a modification of certain parts in the ilne grinding zone. Like reference characters in Figs. 1 and 5 'indicate lar elements. The stationary bars |2|A 'ay be cast in four sections with webs |22, |23 and |24 therebetween. 25

Upper and lower pairs of sections are bolted togetherat |25. Between webs |23 and |24 there are more bars than between webs |22 and |23. As shown, there are twice as many bars between webs |23 and |24 as there are between' webs 22 30 and |23, but this proportion may beyaried.' This allows'a wide clearance |26 for air and pulverized material between webs |22 and |23. Each section 65 and `68 by bolts |21 and |28.

The rotating radial bars are made separate and interchangeable. These' bars are provided with a neck portion |3| around which a pair of clamps |32t. As thereare, in the device shown, twenty-three rotating bars, eleven pairs of clamps are constructed to hold a pair of bars each, while one pair of clamps |33 holds only a single bar.

The clamps are fastened rigidly to the disc 56 by bolts |34.

The ribs or vanes on disc |36, besides causing aportion of the air and pulverized material tobe thrown outwardly toward the pulverlzer casing, also cause flow to be again redirected intokstationary and rotating bars.

'The arrows in Figures 4 and 5 indicate in general the path of flow of air and pulverized ma# terial through the ne grinding zone.

The operation of the pulverizing mill is as follows:

For the purpose of illustration let vit be assumed that coal is the material to be pulverized. Relatively larger pieces of coal enter the feeder chamber |02 from the hopperl ||1. 'Ihe coal falls on the rotating table |0|1and is swept oil into the chute 96 by the scraper ||2. When lever ||5 is in its lowermost position the capacity of the feeder is a maximum, since the position of the deflecting cone, which is varied by the leverfdetermines the Quantity of coal y discharge into the feeder chamber.

is bolted to the pulverizer casing I5 between liners 35 falling through the hopper u The .coal leaves chute't and enters the first stage which is primarily designed to crush the coal as a result of impact between the hammers 40 and the pieces of coal. Any hard foreign matter, such as tramp metal, which is not broken up by impact with hammers 40 is thrown into the pocket 82 by the hammers or beaters 40. The air and coal is given a whirling motion by the rotation of wheel 30 .and the hammers 40. This whirling motion is carried into the second stage through the discharge opening of the spiral chamber formed by the scroll-shaped 'member 62 sur rounding the rst stage wheel and hammers. Should any tramp metal or hard foreign body enter the second stage the hammers or beaters 42 strike it and cause it` to be thrown through crushing of the coal and accentuate the whirl of the mixture of coal and air, thus aiding the exhauster in drawing the mixture through the mill, while, atthe same time brushing or distributing 4itthrough the stationary radial bars at the inlet to the third or fine grinding stage. These hammers also prevent accumulation or deposit of material in the bottom portion of the casing I5 to the 'right of the stationary radial bars, which would block or obstruct the entrance to the third stage.- i

The final pulverization of the coal occurs by the aid of grinding elements comprising the radial rotating bars rotating closely to the set of stationary radial bars 44. 'I'he arrangementA of the annular member 12 on end wall 10 and web or baille 5| with plate 53 in the iine grinding zone is such that the air and coal leaving the second stage must pass three times across the stationary and rotating radial bars before entering the exhauster. The mixture leaving the second stage to enter the third stage must change from a radial direction to an axial direction in order to pass through the stationary radial bars 44. In this -way the relative'velocity between the coal t'o be the radially outer portion of the stationary and rotating bars and the coal is thereby pulverized. They then are deeoted by the partition 10 and annular member 12 and pass across the rotating and. stationary bars again and into the pockets formed between adjacent stationary bars by webs and 5| and plate 53. From these pockets the air and coal pass once again across the stationary and rotating bars to the central inlet 22 of thev exhauster. It will be noted that this `main path of Ltravel is from the circumference toward the center and hence counter to the direction of centrifugal force which acts on the particles of coal the circumference are setup. Ilhese eddies and l ditional air may be preheated if desired.

they result in the coal coming in -contact with the rotating and stationary bars more often than would be the case if they were not present. Con'- sequently, more grinding and pulverizing is accomplished. Furthermore, thev centrifugal force acting on the larger particles is greater than that acting on the smaller ones; and hence the larger particles are more apt to be caught in the eddies, whereby they are further pulverized. When the particles of coal are minute enough so that the frictional drag' of the air overcomes the centrifugal force, they will be withdrawn from the mill by the exhauster.

Between the mill and the exhauster is the classier or 'rejector ldevice comprising classifier cone 1| and radially extending blades 80 which pre- 'I'he blades 8|) act more or less like the blades of a fan for continuing the rotary movement of the mixture of. coal and air leaving the ine grinding zone, and by centrifugal force throw the coarser material against the sides of the classiiier cone which permits the return of the material to the fine grinding zone for further treatment.

The operation of the modification shown in Fig. 5 is 'similar to the foregoing with respect to vents large particles from entering the exhauster. 9

the first two stages, or crushing zone, but differs with respect to the third stage, or fine grinding zone. In this modication the mixture of coal and air discharged from the second stage enters the rst pass of the third stagerbetween the` outer group of stationary bars |2| and the rotating bars |30. After going through this first pass, the mixture is redirected by end partition 10 and annular member 12 and passes throughfthe second pass between rotating bars |30 and the inner group of stationary bars |2|.- The mixture at the end of this second pass 'is acted upon by the rotating ribs or vanes |38 mounted on the second impact` wheel 3|.. These rotating ribs Acausev a stage. Hence, the portion of the mixture di' vided at the end of the second pass is recirculated through the first pass. The ,highest relative velocity between the rotating and stationary bars is the section comprising the first pass, and hence the maximum' pulverizing eiiectl is obtained by keeping material in this section until fine enough to be carried out of the fine grinding zone by the stream of `air drawn .therethrough by the exhauster.

The amount of additional air'supplied through the damper controlled inlet 93 is determined by the degree of pulverization desired and the use to bemade of the material pulverized. Inasmuch as the exhauster draws in a substantially constant Aquantity of air, if more air is admitted` through -inlet 93, less air is drawn through the crushing and grinding zones of the mill and consequently what is drawn through has alower velocity.

' This results in the coal being ground liner before it is removed from the last stage, inasmuch as the low velocity aircannot remove larger particles against the action of. centrifugal force. The ad- -The pulverized coal discharged by the exhauster may be collected and stored or it may be used directly by any suitable burner.

It will thus be seen that in both modifications the material to be pulverized is passed a plurality of-times across the stationary and rotating bars.

fiov portion of the mixture of. air and coal to pass fil It will be understood that the members constitut-L ing thene grinding stage may be employed independently of the specic means shown for performing the preliminary crushing. The nature of the material may be such that it may be fed directly to the apparatus constituting the third stage of the mill above described.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the parts without departing from the scope of my invention, which, generally stated, consists in a device capable of carrying out the objectsabove set forth, and in the novel parts and combinations of parts disclosed, and as deilned in the appended claims.

Having thus described my invention, what I claim is:

1. A pulverizing apparatus comprising a casing having an inlet and an outlet, means for supplying material to be pulverized to said inlet, means for moving a current of air through the casing, means within said casing for pulverizing said material comprising rotatable members, means for directing said material into contact with the radially outer portions of said members, and means independent of said members for redirecting said material back and forth through the plane of rotation of said members tosaid outlet.

2.- A pulverizing apparatus comprising a casing having an inlet and an outlet', means for supplying material to be pulverized to saidinlet, means y for moving a current of air through the casing, means within said casing for pulverizing said material comprising a set of rotatable members and a set of stationary members adjacent thereto, means for directingsaid material into contact with the radially outer portions of said rotatable and stationary members, and means for redirecting said material into contact with radially inner portions of said rotatable and stationary members.

3. A pulverizing apparatus comprising a'casing having an inlet and an outlet, means for supplying material to be pulverized to said inlet, means for moving a current of air through the casing,

means within said casing for pulverlzing said material comprising a set of rotatable members and a set of stationary members arranged in a plane adjacent and parallel to the plane ofrotation of said rotatable members, and means independent of said members for directing said material back and forth through said planes. 1

4. A pulverizing apparatus comprising a casin4 having an inlet and an outlet, means for supp ing material tobe pulverized to said inlet, means for moving a current of air through the casing, means within. said casing for pulverizing said material comprising a set of rotatable members and a set of rstationary members arranged in a plane adjacent and parallel to the plane of rotation of said rotatable members, means for directing said material into contact with the radially outer portions .of said rotatable members, and means independent of said members and said means for moving a current of air through the casing for redirecting rsaid material back and forth through -said planes to said outlet.

5. A pulverizing apparatus comprising a casing having an inlet and an outlet, means for supplying material to be pulverized to said inlet,

ymeans'for moving a current of air through the 'and stationary members, means for redirecting bers, .means for redirecting a portion of said material into contact with a radially inner portion of said members, and meansfor returning another portion of said material into contact with said radially outer portions.

6. A pulverizing apparatus comprising a casing having an inlet and an outlet, means for supply- (ing material to be pulverized to said inlet, means for.moving a current of air through the casing,t means within said casing for pulverizing .said material comprising a set of rotatable members and-a set of stationary members adjacent thereto, means for directing said material into contact with the radially outer portions of said rotatable l5 a portion of said material into contact with radially inner portions of said rotatable and stationary members, and means for returning another portion of said material into contact with said radially outer portions of said rotatable and 20 stationary members.

7. Pulverizing apparatus comprising a casing having an inlet and an outlet, means for supplying material to be pulverized to said inlet, means for moving a current of air through the casing, 25 means within said casing for pulverizing said material comprising a set of rotatable radial bars and a set of stationary radial bars arranged in a plane adjacent and parallel to` the plane of rotation of said rotatable bars, and means for direct- 30 ing sald'material back and forth through said planes. 'I

8.*Pulverizing apparatus comprising va casing having an inlet and an outlet, means for supplying material to be pulverized to said inlet, means for moving a current of air through the casing, means within said casing for pulverizing *said material comprising a set of rotatable radial bars and` a set of stationary radial bars arranged in a plane adjacent and parallel to the plane of rota- 40 cent to the inlet for crushing the material and 5 0 distributing it to said passage free from relatively large foreign bodies, a set of revoluble and stationary members adjacent to the outlet, and

means independent of said members and said l l0. Pulverizing apparatus comprising a casing having an inlet and an outlet, means for supplying material to be pulverized to said inlet, means -for moving a current of air through the casing, means providing a plurality of pulverizing zones connected by an annular` passage, means including revoluble hammers adjacent tothe inlet for crushing the material and distributing it to said passage free from relatively large foreign bodies, a set of radially extending revoluble and stationary members adjacent to the outlet, and means independent of said means for moving lair through the casing for directing` material from said passage into contact with said members a plurality of times as the material passes against 7 5 passage free from relatively large foreign bodies,

a set of 'radially extending revoluble and stationary members adjacent to the outlet, means .a current of air through the casing, means providing a crushing zone and a fine grinding zone, said crushing zone comprising a rst stage and a second stage, a revoluble wheel arranged in .said first stage, a plurality of hammers mounted on said wheel, and means comprising a scrollshaped liner surrounding said wheel and having an opening communicating with the second stage whereby crushed material is conducted from the rst stage to the second stage while maintaining the velocity of the whirling movement setup in the first stage.

13. A pulverizing mill comprising a casing having an inlet-and an outlet, means providing a crushing zone and a line grinding zone, a plurality of hammers mounted to moveabout an axis in said crushing zone, aset of revoluble and stationary radially extending bars in said fine grinding zone, means for .moving a current of air through the casing from the inlet to the outlet, and means beyond the ne grinding zone zone against the centrifugal force imparted to 'said material by the revoluble bars.

14. A pulverizing mill comprising a casing having an inlet and an outlet, means providing a crushing zone and a ne grinding zone,a plurality of hammers mounted to move about an 8x18 in Said Crushing 2011. a Sei? 0f revlublerarranged on said hub, a pluralityof hammer and stationary `radially extending bars in said ne grinding zone, means for moving a current of air and solid particles through the casing Q from the inlet to the outlet, and means in the fine grinding zone for directing the current-oi' air and solid particles from adjacent to-the'casing, to the axis of rotation'of the revoluble radially extending bars and into contact with said lrevoluble Aand stationary bars a plurality of times. i 15. A pulverizing mill comprising a casing having an inlet and an outlet, means providing' a crushing zone and a fine grinding zone, a .plurality of hammers mounted to move about jan axis in said crushing zone, a set of revoluble qand stationary radially extending bars in said 'fine grinding zone, means formovng a currentof air and solid particles* through the casing from the inlet to the outlet, means providing a plurality of passes for air and solid particles across the revoluble radially extending bars, said passes extending inwardly and concentrically of each other, and means in the crushing zone for distributing material to the first pass.

16. A pulverizing mill comprising a casing having an inlet and an outlet, means providing a crushing zone and a fine grinding zone, a plurality` of hammers mounted to move about an axis `in said crushing zone, a set of revoluble and 6 stationary radially extending bars in said fine ,l grinding zone, means for moving a current of air and solid particles through the-.casing from the inlet-'to the outlet, means providing a series of concentric and interconnected passes in said 10 fine grinding zone, said revoluble radially extending bars tending to carry solid particles from an inner to an outer concentric pass vand said current of air tending to carry solid particles from an outer to aninner pass, and means in said l5 crushing zone for distributing material to the oute of said series of passes.

17. A pulverizing mill comprising acasing havi ing an inlet and anfoutlet, means providing a .crushing zone and a iine grinding zone, a plu- 20 rality of hammers mounted to move aboutman axis in said crushing zone, a set of revoluble and stationary radially extending bars in said lne grinding zone, means formoving a current of air and solid particles through the casing from 25 the inlet to the outlet, means providing three passes for air and solid particles across the revolubleradially extending bars,` said passes ex-y tending inwardly and concentrically of each.

other, means cooperating with the stationary 30 radial bars for causing a portion of the current of air and solid particles leaving the second pass to be returned to the inlet of the first pass,

and means in the crushing zone for distributing material to the first pass.

18. In a pulverizing mill comprising a casing having an inlet and an outlet, a crushing zone and a line grinding zone, suction means for causing a current ofair to ow through said zones for carrying pulverized material, a series of 40 stationary and rotating radial bars in said `iine grinding zone, means beyond the rotating bars for redirecting flow into the vicinity of the stationary bars, and means cooperating with the stationary bars for splitting the redirected ow 45..

and for causing', a split portionto move radially outward for mixture with flow entering the iine grinding zone.

' 19. A pulverizing mill comprising a casing having an inlet and an outlet, a shaft, a hub 5' mounted on said shaft, a rst and second wheel mounted on said wheels, a set of .peripherallyv spaced radial bars iixed to saidv hub, a set of stationary inwardly extending radial bars lo- 5" cated between said second wheeland said first mentioned radial bars, spacing. webs integral with the stationary bars, an annular member beyond said first mentioned radial bars and arranged intermediate said webs, means for vmov- 0 ing a current of air through the casing from the .inlet to the outlet, said webs and annular member causing air to make a plurality of passes catedbetween said second wheel andvsaid rst mentioned radial bars, spacing webs integral with the stationary bars, an annular member beyond said irst mentioned radial bars and arranged intermediate said webs, means for moving a current of air through the'casing from the inlet to the outlet, said webs and annular member causing air to make a plurality of passes across the radial bars, and blade means associated with the second wheel for withdrawing a porti'on of the air leaving the second pass and for returning the same to the first pass.

21. Pulverizing apparatus comprising a casing having an inlet and an outlet, means for supplying material to be pulverized to the inlet, means for moving a current ofair through `the casing, a irst impact wheel having a plurality of hammers,

a second impact wheel having a plurality of ham-y mers extending radially outwardly beyond the hammers on the first impact wheel, a plurality of spaced stationary barsradially disposed in a vplane adjacent and parallel to the plane of the second impact wheel, a plurality of movable bars radially disposed in spaced relationship in a plane adjacent and parallel to the plane of the'stationary bars, means causing the material in the zones of the stationary and movable bars to flow generally in a radially inward direction, and K means for rotating the impact wheels and the movable bars.

22. Pulverizing apparatus comprising acasing having an inlet and an outlet, means for supplying material to be pulverized to the inlet, means for moving a current of air through the casing, a

` g extending radially outward to approximately the same extent as the hammers on the second impact wheel andbeing greater in number than the hammers on the impact wheels, means causing the material in the zones of the stationary and movable bars to ow generally in a radially inward direction, and means for rotating the impact wheels and the movable bars. A

23. Pulverizing apparatus comprising a casing having an inlet and an outlet, means for supplying material to be pulverized to the inlet, means for moving a current of air through the casing, a rst impact wheel having a pluralityof hammers, a'second impact Wheel having a plurality 'of hammers extending radially outwardly beyond the hammers on the first impact wheel, a plurality of spaced stationary bars radially disposed in a plane adjacent and parallel to the plane of the second impact wheel, a plurality of movable bars radially disposed in spaced relationship in a`plane adjacent and parallel to the plane of the stationary bars, means causing the material in the zones of the stationary and movable bars `to flow generally in a radially inward direction,

and means for superimposing on the general path of the materialand air in said zones, supplementary systemsof whirls which tend-to keep the coarser particles in said zones while permitting the` finely pulverized` particles to be'removed thereflm. D

air to flow in a generally radial direction in the 10 zones of said pulverizing elements, and means for superimposing on the general path of the material and air in said zones, supplementary systems of whirls which tend to keep the coarser particles in` said zones while permitting the finely 15 pulverized particles to be removed therefrom.

25. Pulverizing apparatus comprising a casing having an inlet and an outlet, means for supplying material to be pulverized to said inlet, means for moving a current of air through the casing,

means within said casing for pulverizing 'said material comprising a plurality of rotatable pulverizing elements and a plurality of stationary pulverizingelements arranged in adjacent and parallel planes,vmeans causing the material and air to flowin a generally radially inward direction in the zones of said pulverizing elements, and

- means for superimposing on the general path of the material and air in said zones, supplementary systems of whirls which tend to keep the coarser particles in said zones while permitting the finely pulverized particles to be removed therefrom.

' 26. 'I'he method of pulverization which comprises passing the material to Ibe pulverized 'through a crushing zone and a pulverizing zone, 35

causing a current of air to flow through said zones, subjecting the material in the crushing zone to impact with moving crushing elementsv whereby the material is reduced in size and the material and air are caused to whirl, substantially 40 -eliminating the whirling motion of the fuel and air upon leaving the crushing zone and prior to lits introduction into the pulverizing zone, subjecting the material in the latter zone to a greater.

impact with moving crushing elements whereby the material is reduced in size and the material and air are caused to whirl, substantially eliriii-V nating the whirling motion of the fuel and air upon leaving thecrushing zone and prior to its introduction into the pulverizing zone, subjecting the material inthe latter zone to a greater ratel of impact with pulverizing elements than in the crushing zone, causing the material and air to ow centripetally through the pulverizing zone, and superimposing on the path of -movement of the material and air through the pulverizing zone, a supplementary whirling motion to retain v the coarser particles of the material in said zone Y while permitting the iinely pulverized particles to I flow out of'sai'd zone.