US2906467A - Pulverizing apparatus - Google Patents

Description

Sept. 2 9, 1959 E. M. POOLE PULVERIZING APPARATUS Filed April 22, 1957 INVENTOR- Edward M. Poole- ATTORNEY A A 2,906,467 Patented Sept. 29,1959

PULVERIZING APPARATUS Edward M. Poole, Barberton, Ohio, assignor to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Application April 22, 1957, Serial No. 654,229

3 Claims. (Cl. 241-5 3) The present invention relates in general to improvements in the construction and operation of pulverizers, and more particularly to pulverizers of the general type shown in U.S. Patent 2,275,595 in which horizontally arranged rolling grinding elements are circumferentially positioned between and in contact with upper and lower grinding rings. a

In the pulverization of any material, particularly in air swept pulverizers wherein the material is pulverized and continuously air swept to remove the finished prodnot, the arrangement of parts must'besuch as to obtain maximum grinding effect without overgrinding the material being processed. Many variables enter into the efliciency of pulverization, where one of the variables relates to the material being ground and its general grinding characteristics. However, on any particular material, the efliciency of pulverization is largely influenced by the amount of effective grinding surface available for pulverization. Ordinarily, an increase in the surface area available for grinding will increase the pulverizing capacity of a unit, providing the pulverized material is removed from the grinding substantially as it is produced and overgrinding is avoided.

The amount of grinding surface available in any pulverizer is limited, for practical reasons, to the effectiveness of the removal of the finished product from the grinding zone so as to avoid overgrinding of the material. Thus, an efficient pulverizer is largely a compromise between the area available for pulverization and an arrangement of parts whereby the finished material may be efiiciently removed from the grinding zone.

In the present invention, the capacity of a pulverizer is increased with an actual reduction in the grinding area available for pulverization. The results of the reduction of surface area are entirely unexpected in that while it would be expected the pulverizer capacity of a unit would be reduced by a reduction in grinding surface area,'actual operation has shown that the capacity has been increased. Actually, while the surface area available for pulverization has been decreased, the position of the grinding surfaces has been slightly altered in relationship to the structures heretofore in use without adversely affecting the grinding capacity of the unit.

The various features of novelty which characterize my 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 I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a perspective, partly in section, of a pulverizer constructed and arranged according to the present invention; and

Fig. 2 is an enlarged elevation, in section, of a portion of the grinding surfaces shown in Fig. 1. a a

In general, the pulverizer illustrated includes a cylindrical upper housing 10 and a lower section 11 supported on a foundation 12. The lower section encloses the pulverizer gear drive which includes a horizontal pinion shaft 13 arranged to drive a vertical drive shaft axially disposed in the section 11 and the housing 10. The drive shaft extends upwardly through supporting bearings (not shown) arranged in a base plate 14 forming the top of the base section 11. The upper housing is detachably secured to the base plate and encloses the grinding parts of the pulverizer which comprises a drive yoke-15 of generally frusto-conical form keyed on the upper part of the drive shaft and a lower annular grinding ring 16 supported upon'and dowelled to a flattened lower portion of the drive yoke 15. The upper face of the grinding ring 16 is shaped to form a circular track for a-row of rolling grinding elements, preferably balls 17 of wear resistant alloy. The halls support a non-rotary upper grinding ring 18 having a circular ball track formed in its lower face. The upper grinding ring is provided with lugs 20 formed adjacent its upper surface at circumferentially spaced positions where the lugs are each provided with a socket for the insertion of a coil spring 21. The upper end of the coil spring 21 is inserted in a socket formed in the lower end of'a vertically adjustable support element 22. The assembly described is arranged to exert a resilient downward grinding pressure on the grinding parts, and as disclosed in U.S. Patent 2,595,587, the springs are also utilized to restrain rotational movement of the upper grinding ring 18.

-The material to be pulverized is supplied by a feeder 23. of the rotating table type, Where the discharge from the feeder enters through the upper portion of the pulverizer housing 10. The raw material falls through the influence of gravity to the inclined surface of the yoke 15, and the yoke rotation distributes the material circumferentially to the grinding zone formed by the grinding rings 16 and 18 and the circular row of balls 17. Due to the efiect of centrifugal force, the raw material tends to flow outwardly through the grinding zone and to discharge therefrom at an oblique angle to the periphery of the grinding elements. The angle of discharge of the pulverized material from the grinding zone depends upon the rotational speed of the lower ring 16.

As shown in Fig. l, the pulverizer is of the air-swept type wherein a stream of primary or carrier air passes through the pulverizer from an external source such as a blower (not shown). The air is delivered to the pulverizer at a superatmospheric pressure through the duct 26 to an annular wind box 27.v The primary air is ordinarily preheated to a temperature of from to 600 F., depending upon the moisture content of thematerial being pulverized. The annular wind box 27 surrounds the lower portion of the pulverizer housing 10 and is' provided with an annular inlet passage 28 through the housing having a plurality of circumferen-. tially.spac ed vanes 30 therein, which areinclined so asv to cause a swirling of the air in the same direction as the rotation of the lower grinding ring 16.

As shown particularly in Fig. 2, the air entering the pulverizer housing is directed upwardly through a reing ring 16. The throat passageway 31 is inclined upwardly. and outwardly so as to direct a high velocity stream of carrier air passing therethrough toward thewall of the housing 10. A circumferentially spaced series of plows 34 are attached to the annular stationary mem-' ber of the throat 31 at a position upwardly spaced from the rotating lower grinding ring 16. As hereinafter de-- scribed, the plows are utilized to prevent the accumulation of an air suspended mass of relatively coarse material adjacent the discharge opening of the throat 31.

Immediately above the throat 31 and the plows 34, the cross-sectional area for flow of air and entrained pulverized material is increased. Thus, the reduced velocity of the carrier air will permit a separation of the coarser particles of pulverized material from the carrier air stream. These coarser particles have a tendency to drop out of suspension on the upper grinding ring 18 of the grinding zone. As hereinafter described, the upper grinding ring 18 is constructed and arranged to facilitate the recirculation of the coarser particles back to the grinding zone. The finer pulverized material, maintained in suspension in the carrier air stream, passes upwardly through the upper portion of the pulverizer housing to enter a classifier 35.

As shown in Fig. 1, and disclosed in US. Patent 2,762,- 573, the classifier is of the stationary type and consists of an upper cylindrical portion attached to the cover plate 36 of the pulverizer and provided with a circumferential series of adjustable deflector vanes 37 positioned in the wall thereof. Immediately below the cylindrical portion of the classifier is provided an inverted frustoconical portion 38 which merges into a lower cylindrical neck 40 which extends below and encircles the upper end of the rotating yoke 15. As disclosed in said patent, the upper end portion of the yoke is provided with rejector vanes 41, which tend to discharge coarse material separated in the classifier downwardly onto the upper surface of the voke 15 for recirculation to the grinding zone.

Within the classifier, the fine particles of pulverized material which remain in suspension in the carrier air stream pass upwardly through a centrally positioned. depending cylindrical baflle 42 and an outlet 43 in the cover plates 36 into a two-way distributor 44. The distributor is provided with a pair of upwardly extending discharge pipes 45 and 46 for the transportation of the air entrained pulverized material to burners or other points of use. Each of the bifurcated outlet branches 47 and 48 from the pulverizer distributor 44 is provided with a flap valve 50 such as shown in branch 47 so that one or the other or both of the pipes 45 and 46 may be tightly closed.

In accordance with the present invention, the upper grinding ring 18 is provided with a plurality of ports 51 extending upwardly and outwardly through the upper grinding ring 18. As shown particularly in Fig. 2, the grinding ring 18 is provided with an annular recess 52 opening to the lower grinding surface 53 of the ring where the recess 52 opens to each of the circumferentially spaced ports 51 so that any recirculated coarse materials discharging downwardly through the ports may be distributed throughout the circumference of the grinding zone formed between the rings 16 and 18, and the balls 17. The recess 52 is formed in the ring 18 for fabrication purposes, so as to permit an economical arrangement for supporting cores and chill plate in casting the ring. Actually, the recess has no substantial functional effect on the use of the ring in the grinding zone. The ports 51 are elongated circumferentially of the ring and have a radial width substantially equal to the radial width of the recess 52. In the illustrated embodiment of the invention, the pulverizer is constructed with a pitch diameter of 70 inches center to center of the balls 17. The balls, as originally installed, are 10 inches in diameter, and the upper grinding ring 18 has a radial arc of contact with the balls of approximately inches while the ports 51 and the recess 52 have a radial width of 2 /2 inches adjacent the grinding surface of the ring. In the ring 18 shown, the length of each port 51 is approximately 8 inches, with a spacing between circumferentially adjacent ports of approximately 3 inches. It will be recognized that the dimensions of individual ports will vary with the dimensions of the rings, but the radial width dimension should be maintained as near as 2 to 2 /2 inches, even in smaller rings, consistent with structural strength requirements of the ring.

As shown in Fig. 2, the upper grinding ring 18 is shaped with a lower annular grinding surface which contacts the upper segment of the circumferential series of grinding balls 17. The ring 18 is of upwardly increasing diameter, and in cross-section the inner surface 54 curves upwardly and outwardly for a maximum thickness of approximately 9 inches. The outer surface 55 inclines upwardly at an angle of approximately 70 degrees with respect to the horizontal to join the upper surface 56 of the ring which inclines outwardly and downwardly at an angle of approximately 45 degrees. The circumferential row of ports 51 is offset outwardly of the ball centerline about inch and the ports 51 are curved outwardly, parallel to the inner surface 54 of the ring, to a flared opening in the top surface 56.

With the construction described, the wear on the contact surfaces of the rings 16 and 18, and balls 17 will be substantially vertical and the entire assembly will move downwardly as wear occurs, while maintaining effective surface contact between the relative moving contact surfaces of the assembly. The outwardly flared section of the ring aids in maintaining the vertical wear movement of the assembly.

In the operation of the pulverizer described, a material such as bituminous coal is delivered through the pulverizer to the feeder 23. The raw coal discharging upon the upper surface of the yoke 15 will move outwardly into the grinding zone formed by the rings and balls, and will be pulverized by the rolling action of the grinding elements. As the coal is pulverized, the material passing through the grinding zone is discharged outwardly into the high velocity stream of carrier air passing upwardly through the throat 31. The carrier air entrains and lifts the pulverized material and discharges the material toward the inner surface of the pulverizer housing 10. The coarser materials discharged upwardly by the air will have a tendency to fall out of suspension and to discharge inwardly of the pulverizer into the ports 51 formed in the upper grinding ring 18. The coarser materials falling through the ports 51 will be discharged to the ring and ball assembly and will be distributed to the grinding zone. A major portion of the grinding effect of the grinding zone on such recirculated coarse coal will occur between the balls 17 and the surface 53 of the grinding ring 18. The remaining portion of the finer pulverized coal will be discharged into the classifier 35 where a further separation of fine and coarse material occurs, with the fines being discharged through the pipes 45 and 46, and the coarser material being recirculated to the pulverizing zone. While the total area of contact between the balls 17 and the upper grinding ring 18 has been reduced substantially in proportion to the contact area removed in forming the ports 51, as compared with upper grinding rings heretofore in use, the capacity of the unit has actually been increased as much as 5 to 10%.

While the exact reasons for this increase in grinding capacity is not known, it is believed that the improvement in the operation of the unit results from an improved separation of coarse material from the mass discharged fromthe grinding zone and the prompt recycling of the major portion of the coarsest material back to the grinding zone. This immediate separation of the coarsest material from the grinding zone in the annular space immediately above the pulverizer throat eliminates any tendency to maintain a suspended mass of pulverized material immediately above the throat 31 which would thereby tend to choke the pulverizer discharge. It has also been observed that the upper grinding ring constructed in accordance with the present invention has increased the service life of the ring as compared with the rings of the same material heretofore in use. This again is probably due to the freedom for recirculation of the coarse material to the grinding zone so that any tendency to choke the grinding zone is substantially eliminated under normal conditions of air 110w and fuel flow to the unit.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

The claims are:

1. A pulverizer comprising a housing, a plurality of rolling grinding elements arranged for rotational movement in a horizontal circular path between the grinding surfaces of upper and lower opposed grinding rings, the radial external dimension of said upper ring being less than said lower ring to define an increased area between the periphery of said upper ring and said housing, means for rotating one of said rings about the axis of said circular path, means for passing an annular stream of carrier fluid upwardly past the outer periphery of said rings to entrain pulverized material discharging from said grinding elements, the increased area adjacent the periphery of said upper grinding ring reducing the velocity of carrier medium flow past said upper ring to de-entrain coarser pulverized materials therefrom, the upper grinding ring having a lower surface of contact bearing substantially on the apex of said rolling grinding elements, and means defining a plurality of circumferentially spaced ports extending through said upper ring and opening to the grinding surface thereof for downward and inward movement of said de-entrained material through said ports.

2. A pulverizer comprising a housing, a plurality of rolling grinding elements arranged for rotational movement in a horizontal circular path betweenthe grinding surfaces of upper and lower opposed grinding rings, the radial external dimension of said upper ring being less than said lower ring to define an increased area between the periphery of said upper ring and said housing, means for rotating the lower of said rings about the axis of said circular path, means for passing an annular stream of carrier fluid upwardly past the outer periphery of said rings to entrain pulverized material discharging from said grinding elements, the increased area adjacent the periphery of said upper grinding ring reducing the velocity of carrier medium flow past said upper ring to deentrain coarser pulverized materials therefrom, the upper grinding ring having a lower surface of contact bearing on an upper segment of said rolling grinding elements, and means defining a plurality of circumferentially spaced ports extending through said upper ring and opening to the grinding surface thereof for downward and inward movement of said de-entrained material through said ports.

3. A pulverizer comprising a housing, a plurality of rolling grinding elements arranged for rotational move.- ment in a horizontal circular path between the grinding surfaces of upper and lower opposed grinding rings, the radial external dimension of said upper ring being less than said lower ring to define an increased area between the periphery of said upper ring and said housing, means for rotating the lower of said rings about the axis of said circular path, means for passing an annular stream of carrier fluid upwardly past the outer periphery of said rings to entrain pulverized material discharging from said grinding elements, the increased area adjacent the periphery of said upper grinding ring reducing the velocity of carrier medium flow past said upper ring to de-entrain coarser pulverized materials therefrom, the upper grinding ring having a lower surface of contact bearing substantially on the upper apex of said rolling grinding elements and having an upwardly and outwardly flaring cross-sectional configuration with an upwardly and inwardly inclined upper outer surface, and means defining a plurality of circumferentially spaced ports extending through said upper ring ring from said inclined upper outer surface and opening to the grinding surface thereof for downward and inward movement of said de-entrained material through said ports.

References Cited in the file of this patent UNITED STATES PATENTS 935,161 Nix Sept. 28, 1909 2,092,310 Hardgrove Sept. 7, 1937 2,762,573 Culp Sept. 11, 1956 FOREIGN PATENTS 573,163 Germany Mar. 23, 1933 573,582 Germany Apr. 4, 1933

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