US2670138A

US2670138A - Air swept ball and ring pulverizer throat and upper ring construction

Info

Publication number: US2670138A
Application number: US124754A
Authority: US
Inventors: Walter C King; Lester L Leach
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1949-11-01
Filing date: 1949-11-01
Publication date: 1954-02-23
Anticipated expiration: 1971-02-23

Description

w. c. KING ET AL 2,670,138 AIR SWEPT BALL AND RING PULVERIZER THROAT AND UPPER RING CONSTRUCTION Feb. 23, 1954 Filed Nov. 1, 1949 2 SheQts-Sheet 1 *1 o 2 I l 2 24-" 21 64 0 37 o 23 22 65 20 37 4 e9 42 20 7 I9 38 J I8 68 INVENTORS WALTER CK/NG BY} wars/e L. ZEACH W ATTORNEY 1954 w. c. KING ETAL 2,670,138

AIR SWEPT BALL AND RING PULVERIZER THROAT AND UPPER RING CONSTRUCTION Filed Nov. 1, 1949 2 Sheets-Sheet 2 4 m 7 \\\\\w i 2 22 5 i 66 45\; 44 /7 42 /.9 "EE 40 I8 45 I F16. 4 4 A 7 b 4 4/ 4 FIG. 3

INVENTORS WALTER 0. KING &

W ATTORNEY BY 55m? L. LEACH v Patented Feb. 23, 1954 SWIllFIT131131 AI-ND RING PUIIVERIZER" THRQ'ATAND UPPER RING CONSTRUC- TION Walter='G.'.Kin-g, Lancaster, S. 0., and Lester. Leach; Akron, Ohim, assig'norsv to The: Babcock 8a Wilcoxw Company,-.Rockleigh, N. J., a corporation ofINew Jersey Application November 1, 1949*, Serial No.- 124,751

18 Claims.

. The presentiinvention. relates in general: to im:-- provements in. the construction and: operation of pulveriz'ers, and more particularly; toipulverizer'si of. the. general type shown in U. S-.. Patent No: 2,275,595 in which. a: housing. encloses a horizon tally arranged; circular series oilrollingt grinding elements positioned between cooperatingrelatively movable upp'er'andi lower grinding; rings re"! siliently pressed: together; the: raw material. to be pulverized being delivered to the inner side of. the: annular grinding: zone, and most of the wholly or partly pulverized material swept: up at the outer: sideof the grinding zone by a.- high velocity. an. nular'streamiof a-gas'eous. carrier medium passing. upwardly through an annular throat. Any' particles oi. suflicient density toadropnthrough the throat: against the carrier gas stream. are col-- lected the subiacentf part of the" pulveriher... The pulverized mateniala suspension; inzthe gaseous carrier medium: is carried. upwardly I to a rotary classifier whichioperates to= separate oversize material. which returns: by. gravity.-towards the grinding zone; while the finer-particles of material are: discharged-in. suspension: in the:

carrier medium from theclassifier outlet through:

the housing pulverized material outlet to -stora-ge one; point of use;

The commercial value of pulverizer'szo'fi the character described is dependent upon: a number of factors including. the originalcost of. the pull-- verizer and. auxiliary equipment; for a given output capacity, power consumption, finenessiofi outputover thepermissible load range adapmbi'lity for operation withmaterials or diflerent grinds ability, feed; size: and moisture. content,- the ex:- tent) of the operating load; range, and: the: amount of the recirculating load, The sizeand power requirements of therein or blower will depend upon the pulverizeri static pressure differential and quantity handled With pulverizers of. thecl'iaracter.- illustrated in said U. S; Patent Not-2,275,595, it. hasnnow been foundthat the pulverizing capacity is limited. by aeration and. consequent fiuidizi-ng of; the material the: grinding zone due-to thedirection 01 the gaseous carrier medium streamirelative-to the. grinding zone, thus preventing the maximum uti.-. lization. of. the grinding capacity of; the. grind.- in partaand the presence oi a relatively-denseslowly, rotating. annular mass of. raw or partly pulverizedparticles at the outer sidaof thei-grind ing. zone. believed to be due toaccumn'lationsin" that area of oversize particles attempting to separat'e bygravity from: the'carrier gaastreana or. rejected bythe classifier and: bypassing; the 55 grinding. zone; The presence-0t this suspended dense annular mass: of. particles. around the outside of the grinding zone results in a relatively-i high static pressure difierential through. the pulverizer; as. the mass fills substantially all oil the:

space between the housing? and the grinding" elements, thus materially o'bstructingcthe. flow path;

of the rising: carrier gas stream. llhe mass acts resistance, resulting: in; an uneven peripheral. distribution. of the suspended: particles to the rotary. classifier; The flow obstructing. effect of the sus-= pended massof particles also-causes a portion of. the. rising: carrier gas stream to flow inwardly through; the row' at rolling. grinding. elements, thus opposing: theioutward flow of pulverized material and. effecting aerationof the material in. the: grinding zone. The material thus fluidized is difficult to pulverizeby'thenorma'l grinding ac--" tion ofthe relatively moving, rolling grindingelements and rings as it tends-to flow out of the path: of. the cooperating grinding; parts.

The general objiecti of'the' present invention.- the. provision of. an: improved construction andoperation of. a pulverizer of the general: type de' scribed which is' characterized by; a: substantial increasein pulverized material output capacity and a decrease in. the statiepressure differential through". the pulveriz'er without any decrease in: finenes of output. or increase in pulverizersize or'cost. A furtherandmore specific object is theprovision of a pulverizer of the type described with animproved construction and arrangement of. the parts defining the" flow path of the gaseous carrier medium adjacent the grinding. zone,.

whereby the tendency towards the formation of.

an annular relatively dense mass of suspended oversizeparticles of" pulverized material around" the grinding zoneis substantially eliminated,

much of the oversize material leaving the grind-- ing zone is immediately recirculated through the;

grinding zone, and aeration of the material in" thewgrinding zone minimized. A still further specific: object is an improved construction and arrangement of the non-rotary upper grinding ring;- whereby the area available for reentrance tothe grinding zone: of material recirculated by the rising stream of carrier gas issubstantially ill-79 creasedt The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of our invention.

Of the drawings:

Fig. 1 is a sectional elevation of the pulverizer, taken on the line il of Fig. 2;

Fig. 2 is a plan section on a smaller scale taken on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged view of a portion of Fig. 1;

Fig. 4 is a side view of one of the deflector plates taken on the line 4-4 of Fig. 3;

Fig. 5 is a plan view of the deflector plate taken on the line 5-5 of Fig. 3; and

Fig. 6 is a horizontal section through one of the classifier blades taken on the line fi-0 of Fig. 3.

In general, the pulverizer illustrated includes a cylindrical upper housing section. I!) and a lower housing section I I supported on a foundation l2. The lower section encloses the pulverizer gear drive which includes a horizontal pinion shaft I3 arranged to drive a vertical drive shaft [4 axially arranged in the housing. The drive shaft i l extends upwardly through bearings arranged to a base plate is forming the top of the lower housing section ii. The housing section ii] is detachably secured to the base plate and encloses the grinding parts of the pulverizer which comprise a drive yoke H of general conical form keyed on the upper part of the drive shaft i l and an annular grinding ring it supported on and doweled to a flattened lower portion of the drive yoke. The upper face of the grinding ring is shaped to form a circular track or race l9 for a row of rolling grinding elements 26, preferably balls of wear-resistant alloy. The ball row supports a non-rotating upper or top grinding ring 2| having a circular ball track 22 formed in its lower face and constructed and arranged as hereinafter described.

At four symmetrically spaced points, arms 23 project radially outwardly from the upper ring and are provided with sockets 24 for receiving dual purpose springs 25. Each spring is formed of a length of spring steel bar stock bent to form a single complete coil turn having a large pitch diameter. The upper ends of the springs 25 fit into corresponding sockets 26 carried by vertical adjusting bolts 27. Each bolt 21 is supported in a sleeve bracket 28 on the housing top plate 29 by means of a nut 30 and retainer 3|. The springs 25 provide a resilient compressive force for the application of a grinding pressure upon the grinding rings and balls as well as a resilient torsional force restraining the rotational and radial movement of the top ring 2! relative to the axis of the bottom ring l8. This dual purpose spring construction is disclosed and claimed in a copending application of applicant Leach, Serial No. 783,248, filed October 31, 194?.

The raw material to be pulverized is supplied by a regulable table feeder through an inclined feed spout 35 extending above the top grinding ring and discharging down the inner side thereof to the upper inclined surface of the yoke H at the inner side of the ball row. The inclined surface of the yoke and the rotation thereof distributes the material circumferentially into the grinding zone. Due to the effect of centrifugal force the material flows outwardly into the ball race l9 where it is pulverized by the crushing action of the relatively moving grinding balls and rings and the attrition action of the particles on one another. The material is pulverized to various finenesses and discharges from the grinding zone at a high speed and tangentially to the periphery of the lower grinding ring, the velocity of discharge depending upon the rotational speed of the lower ring.

The pulverized material is removed from the grinding area by a high velocity annular stream of a suitable gaseous carrier medium, preferably air, and when coal is being pulverized for com- ;bustion purposes, preferably the primary air supply used for combustion in the associated furnace. The air is supplied at a regulated temperature, e. g. -600 F., sufficient to eliminate substantially all of the surface moisture on the raw material undergoing pulverization. The air is preferably supplied under a superatmospheric pressure by a suitable forced draft fan (not shown) to an annular wind box 3! surrounding the lower part of the housing section In. The carrier air passes through passages defined by equi-spaced obliquely arranged vanes 38 opening through the housing wall adjacent to the lower outer side of the lower grinding ring. The vanes 38 effect a swirling movement of the air stream in the same direction as the direction of lower ring rotation as it flows upwardly through the narrow annular passage between the lower grinding ring and housing.

In accordance with the present invention, the lower grinding ring is provided with an annular vertical ledge 4i] held in position thereon in any suitable manner, as by a welded extension plate 4| fitting between the yoke and lower ring. The ledge extends vertically to a level above the lower ring track sufficient to maintain the desired bed of material in the grinding track. For example, in one installation with balls 10%" diameter, the top of the ledge was 2 above the outer top face of the lower ring. In operation, the ledge will act as a dam over which the pulverized material will flow under centrifugal force, the space within the ledge being normally filled with material at an angle corresponding to the angle of the free surface of the forced vortex of the pulverizer material.

According to this invention, the swirling stream of carrier air has its velocity increased to a value at a pulverizer level corresponding to the upper end of the ledge, at which value, e. g. 9000-l0,000 ft./min., substantially all of the pulverized material flowing over the ledge will be picked up and carried upwardly in suspension. For this purpose, a narrow outwardly inclined throat 42 is defined by parallel inverted frusto-

conical plates

43 and 44, the stationary throat plate 43 being mounted on the housing wall by bolts 49 and extending inwardly and downwardly from the housing wall at the top level of the ledge, while the plate 44 is welded to and forms an angular extension of the ledge 40 substantially coextensive with the plate 43. The space between the upper ends of the plate 44 and ledge 40 is closed by an annular plate 45 across which the pulverized material flows to the throat 42. In one embodiment of the invention, the throat was in width and extended at an angle of substantially 30 to the vertical. The space be- .tween the lower end of the plate 43 and housing wall is closed and, an. upwardly tapering, en trance passage for the throatformed,by means.-.

of. a frusto-conical extension48 welded to the lower end of the plate 43iandarrangedopposite the ledge area subjacent to..-the.throat. With the described throat construction. and

arrangement, the swirling. air. stream-passes up-. wardly at a progressively increasing; velocity through the passage .41 and. onenteringthe throat 42 i directedv outwardly. at an-acute angle-t0- carried upwardly in suspension. Thelarger or denser particles swept up .tend-toudrop out of.

the. upfiowingair stream and. the streamof air along the. housing wall tends to direct such particles inwardly. towards. the. grinding zone. Any

small particles of dense .unpulverizable material,

such as pyrites,. will drop through thethroat to the. pulverizer space below the. airentrancepassages defined by. the vanes- 38 and be periodically discharged through ahorizontally slidable gate 50 into a trap or compartment 5|. relative movement between the stationary plate 43. and rotating plate 44 effectively prevents. clogging of the throat 42.

The material laden air stream swirls upwardly along the housing wall at the outer side of the top grinding ringand laterally to a rotary classifier 6.0 of the. type disclosed in said U. S. Patent No. 2,275,595... except that the classifier blades are advantageously formed, as shownin Fig. 6;, by circumferentially spaced vertical Z-bars 6| moving in the direction indicated. Asdisclosed. in

said prior patent, the classifier is arranged to extend across thelower endof the. turret 62 in the top of. which the pulverizedmaterial outlet 63 is located. The classifier is detachably,

mounted on andits rotation .efiected by a supporting structure 64 carried on. the drive yoke H. The supportingstructure is provided with tangentially extending outlets 6.5-, through which.

any material separating out. within the classifier,

is returned to the inner side of the grinding ball row, minglingwith the rawmaterial. therein from the feeder. Thus a major portion of the material to be pulverized, i...e. the raw material from the feeder 35. and. the recirculated ma.-

terial from the classifier 60', isdelivered to-the grinding zone at the inner. side of the. ballrow and flows outwardly through .thegrinding, parts.-

The classifier construction described. effectively separates oversize particles. in suspension in the air stream both by the mechanical action of F the blades and the-windage created, by the moving; blades. The desired finenessof output: is indicated by the usual commercial guarantees of 99% through a U; S. Standard 50'mesh screen.

and 70% through a 200-mesh screen.. Thecuter section of the Z-bars tends to deflect. oversize particles outwardly away from theclassifier and when their lateral'movement is. neutralized. by

the air stream, such particleswill drop towardsthe grinding zone. Other. oversize particles.

reaching the interblade area. of the classifier are.

caught in the V-pockets formed by, the blade middle and inner sections andslideto the bottom of the pockets. and .arethen ejected. by cene triiugal force.

The oversize material so. re'clrculatedby the.

action of gravity and the classifier must be further pulverized before being fit for use. The

recirculating load normally ismany times the rate of discharge or the pulverized material from The.

the pulverizer; outlet,v e. 3; when pulverizingz bituminous. coal. -.-30 :l;. such; material 3 droppingintocthe space. atthe inner. sideoi I the ball row readily; reaches;ther.; grinding;- zone, the. portion heretofore.dropping onand outside the upper grinding ring was greatly, delayed in again ranged substantially tangentialtoa ball radius at an angle of in the upper inner quadrant of the grinding balls. Theiringis sosh'apedthat its ball contact is almost-wholly confined vto the upper inner ball? quadrant: and, extends. onlyv a small arcuate distance beyond the ball vertical center line. For example, with 10 diameter balls, this distance was only, /1! 'in .one installa.-.

tion. The upperend ofthe ring cross-sectionis continuously curved and slopes. downwardly. at

-its.inner sidefor amajorportion of its extent at an angle of approximately 45 tothe vertical.

with. the remaining inner. surfacejsubstantially vertical. The oppositeface is arranged at an ang'leof approximately 30? to. the vertical... With this formationthe geometrical center cv of the top ring will always be located at the inner side of the ball center line.bb duringthe normal life oi, the parts. Atop ring, construction haviing the. desired strength, rigidity and lifeis thus provided. With this ring. construction. substantially the. whole upper outer octantsurf aces of the balls and theintervening spaces are open to receive materialdropping out of the air stream close to the point of initiaILpick-up, as indicated by the arrows in Fig. 3,.or dropping downwardly through the space outside. of the upper ring. The.

desc'ribedrelation of the balls and rings and recirculated material entrance area are not affected.

by the inevitable wear of the grinding. parts.

The described primary recirculation effect is enhanced in the present. construction by the location of stationary. deflectors .or. plows 66 project! ing inwardly from thehousingwall'at four SYIII'. metrically spaced locations adjacent the grinding zone.

is cutaway at onesegmental' section to permit. the installation of a counter weightedrelief gate fiilof. the same contour andpivoted on a shaft. (is to allow large piece of unpulverizable.,ma terial,. such as tramp. iron, to dropinto the sub.-

jacent part of the pulverizer.

The present'ginyention hasbeen found by field.

tests on bituminous coal tobe adapted forsuccessful use in all" the sizesof pulveri-zerstested;

i. e; pulverizers having A d'ifierent' ballroW pitch. di m t r1and"ball 'dial netera Comparative field.

As shown inFigs. 3 -5, each plow is. sloped inwardly and upwardly in the direction of ring rotation at an angle of approximately 30 from the vertical and app oximatelyv 45 from. the radial} so that it will extend at an angle across andimmediately above the throat 42.. With this.

tests of two pulverizer sizes incorporating the present invention with thesame pulverizers constructed as shown in said U. S. Patent 2,275,595 and said Leach application, Ser. No. 783,248 show the following superior performance attained by the present invention in pulverizing bituminous coal:

Pat. i S. N. Inven- 2,215,s95 l 783,248 tion Pulverizer A: i i

Output, Percent 100 113 147. 8 Fineness, Percent Passing 50 M 96. 97. 99. 0 Fineness, Percent Passing 200 M 56. 0 64. 0 74. 0 Static Press. Diti, Percent 100.0 98. 6 90.2 Pulverizer B: i E

Output, Percent ..l 100 104 138 Fineness, Percent Passing 50 M 98. 0 99. 0 99. 1 Fineness, Percent Passing 200 M 68.0 72. 0 73. 0 Static Press. Did, Percent -k Y 100. u 11. 1

The greatly increased output with increased fineness and a decreased static pressure diiferential evidenced by the foregoing operating results are believed to be mainly due to the improved conditions in and adjacent to the grind- 9 ing zone. These conditions are attained by preventing carrier air flow directly into the ball row and thus avoiding aeration and consequent fluidizing of material at the time of pulverization; the maintenance of a bed of material on the grinding face of sufficient thickness to cause adequate pulverization on each passage of a particle through the grinding zone; the rapid scavenging of the undersize particles from the material leaving the grinding zone to prevent overgrinding and consequent useless power consumption, the recirculation of much of the oversize material to the grinding zone by the shortest practical route, i. e. so as to back feed the'balls above their horizontal center line; the elimination of a dense mass of oversize material around the grinding zone; and the intimate mixing of the hot air and partially pulverized material at a point in the circulation path which insures proper drying of thematerial. The improved construction has been found to successfully handle extremely fine sizes of raw coal which previously were considered unusable and to increase the permissible operating load range from 2.5:1 to 9:1 with substantially complete freedom from trap discharge.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features. In the claims, the word air is intended to cover generically air and any other gaseous carrier medium suitable for conveying pulverized material in the manner described.

We claim:

1. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring sup-- ported on said grinding balls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls to sweep up pulverized material discharging therefrom, said air flow directing' means being constructed and arranged to define an annular throat inclined upwardly and outwardly away from said row of grinding balls, and said upper grinding ring being cut away at its outer side to an extent sufficient to lay open a major portion of the upper outer quadrant of said grinding balls for the reception of recirculated material and its lower surface in contact with said balls over a substantially greater arcuate portion of the upper inner quadrant of said balls than its contact with the upper outer quadrant of said balls.

2. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding balls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls to sweep up pulverized material discharging therefrom, said air flow directing means being constructed and arranged to define an annular throat inclined upwardly and outwardly to a point adjacent said housing so as to deflect the air stream away from said row of grinding balls, and said upper grinding ring being cut away at its outer side to an extent suilicient to lay open substantially all of the upper outer quadrant of said grinding balls for the reception of recirculated material.

3. A pulverizer comprising a housing enclos ing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding balls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls .to sweep up pulverized material discharging therefrom, said air flow directing means including an annular stationary throat plate constructed and arranged relative to said lower grinding ring to define therebetween an annular throat inclined upwardly and outwardly to a point adjacent said housing so as to deflect the air stream away from said row of grinding balls, and said upper grinding ring being cut away at its outer side to an extent sufficient to lay open a major portion of the upper outer quadrant of said grinding balls for the reception of recirculated material and its lower surface in contact with said balls over a substantially greater arcuate portion of the upper inner quadrant of said balls than its contact with the upper outer quadrant of said balls.

4. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding balls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means forming a peripheral ledge on and extending substantially above the ball-contacting surface of said lower grinding ring, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls to sweep up pulverized material discharging therefrom, said air flow directing means ingrinding ring being cut away at its outer side to an extent sufficient to lay open-a major portion of the upper outer quadrant of said grinding balls for the reception of recirculated material.

5. A pulverizer comprising'a -housing enclosing -a rotary lower grinding ring, means forrotating said lower grinding ring, a circularrow of grinding balls supported on said lower grinding ring,

anon-rotary upper grinding ring supported on said grinding balls, means for delivering material "to be pulverized mainly to the inners'ide'of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls to sweep up pulverized material discharging therefrom, said air flow directing means'being constructed and arranged to define an annular throat inclined upwardly and outwardly at an acute angle to and terminating adjacent said housing so as to deflect the air stream away from said row of grinding balls, said upper grinding ring being cut away atfits outerside'to an extent sufficientto lay open a major portion of the upper outer quadrant of said grinding balls'for the reception of recirculated material, and -a circum- 'ferential series of stationary plow members mounted on said housing opposite said row of grinding balls and adjacent the upper end of said -throat and projecting inwardly in the direction or lower ring rotation at an angle to said housing 'sufiicient to deflect pulverized material into the upper part of said rowof grinding balls.

"6. A pulverizer comprisinga housing'enclosing "a rotary lower grinding ring, means'for'rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring,

a non-rotary upper grinding ring supported on said grinding "balls, means for-delivering material to be pulverized mainly to the inner side of said row of grinding balls, means forming a peripheral ledge on and extending aioove the upper-surface of said lower grinding ring, means for directing an annular stream of air upwardly past the outer side of said grinding rings-and row of grinding balls to'sweep up pulverizedmaterial .-rdischarging therefrom, said airflow. directing means including an --annular stationary throat tplate constructed .and arranged relative to said illedge-forming means to define .therebetween' an annular throat inclined upwardly andoutwardly rat an acute angle touand terminatingadiaeent said housing :so as to deflect the air stream away .from said row of grinding-balls, andsa-id upper grinding ring being cut away at its outer side to an extent suflicient to lay-open suhstantiallyall of the upper outer quadrant of said grinding balls and interball spaces for the-reception of recirculated material, anda circumferential series of stationary [plow members mounted oni-said .housing oppositesaid row of grinding balls and adjacent the upper end of said thrcat and-pro- Jecting inwardly in the direction of lower ring rotation at an angle .to said housing sufficient to deflect. puluerizedimaterial into ,the upper part of said row. oi grinding -balls..

7. A pulverizer comprisinga housing. enclosing :a rotary. lower grinding ring, means. for rotating said lower. grinding 'ringmlcircular row of mailing {grinding elements supported flower grindingring, a non-rotary upper grinding ring suping means being constructed and arranged to define an annular throat inclined upwardly and outwardly away from said row of'gr'inding elements and terminating at its upper end at the material discharge level of saidlower grinding ring.

8. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of rolling grinding elements supported on saidlowergr inding ring, a non-rotary upper grinding ring supported on said grinding elements, means for delivering material to be pulverized mainly to -the inner side of said row of grinding elements, means for directing an annular stream or air/upwardly past the outer side of said grinding rings and row of grinding elements to sweep up pulverized material discharging therefrom, said air flow directing means including an annular stationary throat plate constructed and arranged relative to the outer periphery of; said lower grinding ring to define therebetween an annular throat inclined upwardly and outwardly *to a point adjacent said housing and terminating at its upper end at the material dischargelevel of said lower grinding ring so as to deflect the air stream away from said row of grinding elements.

9. A pulverizer comprising a housing enclosing a lower rotary'grinding ring, means for rotating said lower grinding ring, a circular rowof rolling grinding elements supported .on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding elements,- means for delivering material to be pulverized mainlyxto the inner side of said row of grinding elements, means above the upper surface of said lower-grinding ring, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding elements to sweep up pulverized material discharging therefrom, said air flow directing means including an annular stationary throat plate constructed and arranged relative to said ledge-formingmeans-to define therebetween an annular throat inclined upwardly and outwardly to a point adjacent said housing and terminating at its upper end at the level of said ledge so as to deflect the :airstream away from saidrow of grinding elements,

10. A pulverizer comprising a housing enclosing a lower rotary-grinding ring, means ferrotating said lower grinding ring, a circular row of rolling grinding elements supported on saidilower grinding ring, anon-rotary u per "grinding-ring supported on said grinding-elements, means for delivering material to he pulverized mainly to the inner side of said row of grinding elements, means forming a peripheral ledge on and extend- .ing above the upper surface of said lower grinding ring, means for directingan annular stream lar stationary throat plate constructed and arranged relative to said ledge-forming means to define therebetween an annular throat inclined upwardly and outwardly at an acute angle to and terminating at its upper end adjacent said housing and at the level of said ledge so as to deflect the air stream away from said row of grinding elements.

11. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding balls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls to sweep up pulverized material discharging therefrom, said air flow directing means including an annular stationary throat plate and being constructed and arranged to define an annular throat inclined upwardly and outwardly at an acute angle to and terminating at its upper end adjacent said housing and at the material discharge level of said lower grinding ring so as to deflect the air stream away from said row of grinding balls, and a circumferential series of stationary plow members mounted on said housing opposite said row of grinding balls and adjacent the upper end of said throat and projecting inwardly in the direction of lower ring rotation at an angle to said housing sufficient to deflect pulverized material into the upper part of said row of grinding balls.

12. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding halls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means forming a peripheral ledge on and extending above the upper surface of said lower grinding ring, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls to sweep up pulverized material discharging therefrom, said air flow directing means including an annular stationary throat plate constructed and arranged relative to said ledge-forming means to define therebetween an annular throat inclined upwardly and outwardly at an acute angle to and terminating at its upper end adjacent said housing and at the level of said ledge so as to deflect the air stream away from said row of grinding balls, and a circumferential series of stationary plow members mounted on said housing opposite said row of grinding balls and adjacent the upper end of said throat and projecting inwardly in the direction of lower ring rotation at an angle to said housing sufiicient to deflect pulverized material into the upper part of said row of grinding balls.

13. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for retating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring having a concavely curved lower surface contacting with and supported on said grinding balls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said'grinding rings and row of grinding balls so as to sweep up pulverized ma- 12 terial discharging therefrom, and said upper grinding ring being cut away at its outer side to an extent sufficient to lay open a major portion of the upper outer quadrant of said grinding l balls for the reception of recirculated material and its lower surface in contact with said balls over a substantially greater arcuate portion of the upper inner quadrant of said balls than its contact with the upper outer quadrant of said balls.

4. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding balls, means for delivering mate rial to be pulverized mainly to the inner side of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said lower grinding ring so as to sweep up pulverized material discharging therefrom, and said upper grinding ring being cut away at its outer side to an extent sufficient to lay open substantially all of the upper outer octant surfaces of said grinding balls and interball spaces for the reception of recirculated material.

15. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding balls, means for delivering material to be pulverized mainly to the inner side of said row of grinding balls, means for directing an annular stream of air upwardly past the outer side of said grinding rings and row of grinding balls so as to sweep up pulverized material discharging therefrom, and said upper grinding ring being cut away at its outer side to an extent sufficient to lay open a major portion of the upper outer quadrant of said grinding balls for the reception of recirculated material and having its lower surface in contact with said balls over a substantially greater arcuate portion of the upper inner quadrant of said balls than its contact with the upper outer quadrant of said balls and its geometrical center located at the inner side of the vertical center line of said grinding balls.

16. A pulverizer non-rotary upper grinding ring adapted to be supported on a circular row of grinding balls arranged to receive material to be pulverized at the inner side of said row, said upper grinding ring having an arcuate ball-contacting surface on its underside, the major portion of the outer side of the ring, extending from the outer end of said arcuate surface, lying in an inverted conical surface of revolution whose semi-vertex angle is not greater than approximately 30 to expose a major portion of the upper outer octant surfaces of said grinding balls when positioned thereon and being free of inwardly projecting parts at the inner side thereof, the outer periphery of said arcuate ball contacting surface being substantially higher than the inner periphery thereof.

1'7. A pulverizer non-rotary upper grinding ring adapted to be supported on a circular row of grinding balls, said upper grinding ring having a lower arcuate ball-contacting surface and being cut away at its outer side from the outer end of said arcuate surface to an extent sunicient to expose substantially all of the upper outer octant surfaces of said grinding balls, be-

ing free of projecting parts at the inner side thereof, and having its major cross-sectional axis upwardly and outwardly inclined and its geometrical center at the inner side of the vertical center line of said grinding balls when positioned thereon.

18. A pulverizer comprising a housing enclosing a rotary lower grinding ring, means for rotating said lower grinding ring, a circular row of grinding balls supported on said lower grinding ring, a non-rotary upper grinding ring supported on said grinding balls, means for delivering material to be pulverized to said row of grinding balls, means forming a peripheral ledge on and extending substantially above the ballcontacting surface of said lower grinding ring. means for directing an annular stream of air upwardly past the outer side of said lower grinding ring to sweep u pulverized material discharging therefrom, said air flow directing means including an annular stationary throat plate constructed and arranged relative to said ledgeforming means to define therebetween an annular throat, and said upper grinding ring being cut away at its outer side to an extent suflicient to lay open substantially all of the upper outer octant surfaces of said grinding balls and the interball spaces for the reception of recirculated material.

WALTER C. KING. LESTER L. LEACH.

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