US2828921A - Material feeder and material relief gate structure for gas swept pulverizers having rolling grinding elements and a stationary upper classifier - Google Patents

Description

April 1958 J. B. WALKER, JR 2,828,921

MATERIAL FEEDER AND MATERIAL RELIEF GATE STRUCTURE FOR GAs SWEPT PULVERIZERS HAVING ROLLING GRINDING ELEMENTS AND A STATIONARY UPPER CLASSIFIER I Original Filed Feb. 13, 1952 2 Sheets-Sheet 1 FIG.1

IN V EN TOR.

/Zzme; 5 Wa/kea/r WZLRNEY p 1958 J. B. WALKER, JR 2,828,921

M RIAL FEEDER AND MATERIAL RELIEF GATE STRUCTURE F GAS SWEPT PULVERIZERS HAVING ROL I G GRINDING ELEMENTS AND A STATIONARY UPPER SSIFIER Original Filed Feb. 13, 1952 2 Sheets-Sheet 2 IN V EN TOR. L/Zzmes 5 M/ken/E ATTORNEY James B. Walker, Jr., Middletown, N. 3., assignor to The Babcock & Wilcox Company, NewYork, N. 1 a corporation of New Jersey Original application February 13, 1952, Serial No. 271,130, now Patent No. 2,710,148, dated June 7, 1955.

Divided and this application February 23, 1954, Serrai No. 411,921

1 Claim. 01. 241-53 7 I 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 No. 2,275,595 in which a housing encloses a horizontally arranged circular series of rolling grinding elements positioned between cooperating upper non-rotating and lower rotary grinding rings resiliently 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 side of the grinding zone by a high velocity annular stream of a gaseous carrier medium passing upwardly through an annular throat. Any particles of sufiicient density to drop through the throat against the carrier gas stream are collected in a subjacent part of the pulverizer. The pulverizer material in suspension in the gaseous carrier medium is carried upwardly to a classifier which operates to separate oversize material which returns by gravity towards the grinding zone, while the finer particles ofmaterial are discharged in suspension in the carrier medium from the classifier outlet through the housing pulverized material outlet to storage or a point of use. The present application is a division of my copending application, Serial No. 271,133,

filed February 13, 1952, now Patent 2,710,148, dated June 7, 1955.

The commercial value of pulverizers of the character described is dependent upon a number of factors including the original cost of the pulverizerand auxiliary equipment for a given outputcapacity, power consumption,

fineness of output over the permissible load range, adaptability for operation with materials of different grindability, feed size, and moisture content, the extent of the operating load range, and the amount of the re-' circulating load. The size and power requirements of the fan or blower will depend upon the pulverizer static pressure differential and quantity handled.

With pulverizers 'of the character illustrated in said U. S. Patent No. 2,275,595, it has been found that the pulverizing capacity is limited by aeration and consequent fiuidizing of the material in the grinding zone due to the direction of the gaseous carrier medium stream relative to the grinding zone, thus preventing the maximum utilization of the grinding capacity of the grinding parts, and the presence of a relatively dense slowly rotating annular mass of raw or partly pulverized particles at the-outer side of the grinding zone believed to be due to accumulations in that area of oversize particles attempting to separate by gravity from the carrier gas stream, or rejected by the classifier and by-passing the grinding zone. The presence of this suspended dense annular mass of particles around the .outside of the grinding zone results in a relatively high static pressure difierentialthrough the pulverizer as the mass fills substantially all of the space between the housing and the 2,828,921 Patented Apr. 1, 1958 ice grinding elements, thus materially obstructing the flow path of the rising carrier gas stream. The mass acts like a filter bed for the rising suspended particles, with some of the suspended oversize particles being caught in the mass and lighter particles in the mass being picked up in the gas stream. The carrier gas flow through the suspended mass is often non-uniform, as the gas stream will tend to follow the flow path of least resistance, resulting in an uneven peripheral distribution of the suspended particles to the classifier. The flow obstructing efiect of the suspended mass of particles also causes a portion of the rising carrier gas stream to flow inwardly through the row of rolling grinding elements, thus opposing the outward flow of pulverized material and effecting aeration of the material in the grinding zone. The material thus fluidized is difficult to pulverize by the normal grinding action of the relatively moving rolling grinding elements and rings as it tends to flow out of their pulverized material output capacity increased and the lugs.

static pressure differential through the pulverizer decreased, without any decrease in fineness of output or increase in pulverizer size or cost, by an improved construction and arrangement of the non-rotary upper grinding ring, whereby the area available for re-entrance to the grinding zone of oversize material discharged from the grinding zone and picked up by the rising stream of carrier gas is substantially increased. For this purpose, the upper ring is made: of vertically elongated crosssection with its major axis arranged substantially tangential to a ball radius at an angle of 45 degrees in the upper inner quadrant of the grinding balls and the ball contact area almost wholly confin d to the upper inner ball quadrant and extending only a small arcuate distance beyond the ball vertical center line. For example, with 10 /2 diameter balls, this distance was only /2" in one installation. The outer face of the'ring was arranged at an angle of approximately 30 degrees to the vertical. With this upper ring construction and arrangement, substantially the whole upper outer quadrant of the balls and the intervening spaces will be open to receive material dropping out of the carrier gas stream close to the point of initial pick-up or dropping downwardly through the space outside of the upper ring.

It has been found that in use, such grinding rings have developed outward wear to such a degree that the grinding balls may not remain in their designed positions in the rotary lower ring race, and thereby cause an outage of the pulverizer, which in turn would cause an outage of the furnace serviced unless another fuel source were available. Any increase in the upper ring thickness to increase'the ball contact area at the outer side of the ball row, i. e. the overhang, sufficient to eliminate this wear problem has been found to materially reduce the pulverizer capacity.

In accordance with the present per non-rotary ring'is provided with an increased overhang relative to the ball row without materially reducng the area available for back-feeding the race by formng the upper ring with a series of special lugsspaced in a particular manner along its outer side, the underside of the lugs being shaped to conform to the ball and form a continuation of the upper ring race profile. The lug faces are arranged at an inclination downward in the direction of pulverizer rotation to utilize the swirling motion of the'material passing theupper ring 'to induce a high rate of back-feeding in the gaps between The lugs are circumterentially spaced on the invention, the up-.

trated and described a preferred embodiment of my invcntion.

Of the drawings: Fig. l is a sectional elevation of a pulverizer embodying the invention;

Fig. 2 is a perspective view of the grinding parts; Fig. 3 is an enlarged view of a portion of Fig. 1; Fig. 4 is an enlarged plan view, in section, of a portion of Fig. 1.

In general, the pulverizer illustrated includes a cylindrical upper housing section and a lower housing section 1]. 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 14 axially arranged in the housing. The drive shaft 14 extends upwardly through bearings arranged in a base plate 15 forming the top of the lower housing section 11. The housing section 10 is detachably secured to the base plate 15 and encloses the grinding parts of the pulverizer which comprises a drive yoke 17 of general conical form keyed on the upper part of the drive shaft 14 and an annular lower grinding ring 18 supported on and doweled to a flattened lower portion of the drive yoke. Part of the upper face of the lower grinding ring is shaped to form a circular track or race 19 for a row of rolling grinding elements 20, preferably balls of wear-resistant ferrous alloy. The ball row supports a non-rotating upper grinding ring 21 having a circular ball track 22 formed in its lower face and constructed and arranged as hereinafter described.

At 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 27 is supported in a sleeve bracket 28 on the housing top plate 29 by means of a nut 30 and retainer 31. 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 upper ring 21 relative to the axis of the lower ring 18. This dual purpose spring construction is disclosed in the L. L. Leach U. S. Patent 2,595,587, issued on May 6, 1952.

The raw material to be pulverized is supplied by a regulable table feeder through a housing opening 36 which is positioned in the upper portion of the housing above the upper grinding ring. As the raw material is deliveredthrough the opening 36 by the feeder, the

material may divide into three portions with the finer particles being swept into the classifier by the rising air stream, and the medium size particles being defiected downwardly and inwardly of the pulverizer by air flow and the force of gravity toward the upper inclined surface of the yoke 17 at the inner side of the ball row. The large particles of raw material and foreign material passed through the opening 36 fall to the outside of the rings and ball row and are gradually worked into the grinding zone by the circulation taking place at the outside of the rings. The inclined surface of the yokeand the rotation thereof distributes the medium size particles circumferentially into the grinding zone. Due to the effect of centrifugal force, the material flows outwardly into the ball race 19 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.

As shown in Figs. 1 and 3, the ball race 19 terminates at its inner side a short distance, e. g. /2", inwardly of the pitch circle of the ball row and the adjacent part 13 of the upper face of the lower grinding ring is cut away to a lower level to form a storage pocket which will tend to feed the material to he pulverized into the lower half of the ball race after the passage of each grinding ball and will result in both grinding and wear in this race area which promotes a wear direction more compatible with the direction of ball thrust.

The pulverized material is removed from the grind ing area by a high velocity annular stream of a suitable gaseous carrier medium, preferably air, and when coal is being pulverized for combustion 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 37 surrounding the lower part of the housing section 10. The carrier air passes through passages defined by equispaced obliquely arranged vanes 38 opening through the housing wall adjacent to the lower outer side of the lower grinding ring. The vanes 38 etfect 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 annu lar passage between the lower grinding ring and housing.

The lower grinding ring is provided with an integral annular vertical ledge 40 spaced from the outer side of the ball row and extending vertically to a level sufficient to maintain the desired bed of material in the lower grinding race. For example, in one installation with balls 9%" diameter, the top of the ledge was at the level of the ball centers. 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.

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, c. g. 9,000 12,000 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 at an angle of 60-70 degrees to the horizontal is defined by the outwardly flaring side of the ledge 40 and a parallel inverted frusto-conical plate 43, the stationary throat plate 43 being mounted for radial adjustment on the housing wall and extending inwardly and downwardly from the housing wall at the top level of the ledge substantially coextensive with the ledge 40. The upper surface of the ledge 40 is inwardly inclined and across which the pulverized material flows to the throat 42. In one embodiment, the throat was in width.

With the described throat construction and arrangement, the swirling air stream passes upwardly and on entering the throat 42 is directed outwardly at an acute angle to the housing wall, whereby the pulverized. material flowing over the ledge 40 is sweptv up by theair stream adjacent the housing wall andjcarried upwardly in suspension. .The larger or denser pa'rticlesswept up tend to drop out of the upflowing air stream and the stream of air along the housingwall tends todirect such: particles inwardly towards the grinding zone. Any small particles of dense unpul'verized material, such as pyrites, will j drop through the throat to the pulverizer space below the air entrance passages and be periodically discharged through a gate 50 into a: compartmentSL, The relative movement between the stationary plate 43 and. rotating ledge 40 effectively prevents clogging of the throat 42'.

The material-laden air stream swirls upwardly along the housing wall at the; outer side of the upper grinding ring and laterally to a stationary classifier 60 of the type disclosed and claimed in an application; of S. W. Culp,

Serial: No. 282,217, filed April 14, 1952, now Patent said application, the classifier is arranged to extendacross the lower end of a turret 62, the top of which. opens to the pulverized material outlets 63. The classifier has a casing 61 of circular cross-section supported in spaced relation from the top plate of the pulverizer, the annular opening therebetween being occupied by a circumferentially spaced series of angularly; arranged separating blades 64,,positioned between upper and lower annular plates 65 and 66, respectively. The upper plate 65 has a depending vertical flange 67 at its inner edge,as shown in Fig. 1. The lower end of the casing 61 surrounds the upper end of the drive yoke 17 which carries a series of curved blades 68 positioned in the ,space therebetween and which act to eject the oversize material separating out in the classifier and dropping to the lower portion of the casing 61. The oversize material is thus returned to the inner side of the grinding. ball row, mingling with the raw material therein from the feeder. j

The oversize material so recirculated by the action of gravity and the classifier must be further pulverized before being fit for use. The recirculating load normally is many times the rate of discharge of the pulverized material from the pulverizer outlet, e. g. when pulverizing bituminous coal, -30:1. Whilesuch material dropping reaches the grinding zone, the portion heretofore dropping 2,762,573, dated September 11., 1956. As disclosed in in Fig, 3, or dropping downwardly through the space outside of the upper ring.

The described primary recirculation effect is enhanced in the present construction by the location of stationary deflectors or plows 69 projecting inwardly from the housing wall at symmetrically spaced locationsadjacent the grinding zone. As shown in Fig. 3, each plow is sloped inwardly and upwardly in the direction ofring rotation at-an angle of approximately degrees from the vertical and, approximately degrees from the radial, so that it will extend at an angle across and immediately above the throat 42. With this construction, the larger oversize particles discharging from the grinding zone which cannot be lifted by the air stream tend to impact on the plows and be deflected back into the upper part of the ballrow, avoiding any tendency towards 'the formation of a. slowly rotating suspended mass outside. of the grinding zone.

As shown H cut away at one or more segmental sectionsto permit the installation of a counterweighted relief gate v7t) of the samecontour and pivotedona shaft 71 to allow large pieces of unpulverizable material, such as tramp iron, to drop into' the subjacent part of the pulverizer. The relief gate ltl is in general vertical alignmentwith the feed inlet opening 36, and with a substantially unobstructed passageway therebetween, heavy materials will fall to the lower portion ofthe unit with the ungrindable lumps discharged through the relief gate 70.

With the grinding balls and rings constructed and arranged as described, it has been foundthat in use such grinding rings have developed outward wear. to such a degree that the grinding balls may tend to move radially on and outside the upper grinding ring was greatly de 1 layed in again reaching the grinding zone. The re-enf trance of recirculated material to the grinding zone is out of their illustrated positions in the lower rotary ring race. This would result not only in a loss in pulverizer capacity, but is likely to cause an outage of the pulverizer out materially-reducing the flow area available for backfeedingthe grinding zone with material dropping out of the carrier gas stream. For this purpose, the upper grinding ring 21 hasa series of circumferentially spaced 'lugsSi) along its inclined outer side projecting outwardly therefrom. The lugs are preferably integrally formed on quadrant of the grinding balls. The ring is so shaped that its ball contact area is almost wholly confined to the upper inner ball quadrant and extends only a small arcuate distance beyond the ball vertical center line. For example, with 9%" and 10 /2" diameter balls this distance was only A2". The upper end of the ring cross-section is continuously curved and slopes downwardly at its inner side for a major portion of its extent at an angle of approximately 45 degrees to the vertical with the f remaining inner surface substantially vertical. The opposite face is arranged at an angle ofapproximately 30 degrees to the vertical. With this formation the geometri to the point of initial picloup, as indicated by the arrows side with the curved upper end of the ring.

the ring and are downwardly flared in width and thickness, as shown in Figs. 2 and 3, from the junction of the outer The underside 81 of the lugs is shaped to conform to the ball profile and to form a continuation of the grinding ring race 22. The opposite faces 82, 83 or" the lugs are inclined downwardly in the direction of rotation of the lower grinding ring to utilize the swirling motion of the material passing the upper ring to induce a high rate of back-feeding of material into the gaps between the lugs. This action more than oifsets the reduction in the flow area for back-feeding the grinding zone caused by the lugs. I The lower ends of the lugs 84) are preferably spaced apart circumferentially an arcuate distance slightly less than the diameter of the grinding balls when new. With this arrangement,

the ball-contacting area of the upper grinding ring is substantially increased without reducing the recirculation of the oversize material to the grinding zone above the horizontal centerline of the ball row. The increased ball-contacting area so located is sufiicient to hold the grinding balls in their designed locations relative to the grinding ring races throughout the designed service life of the grinding rings.

in Fig. 1, a portion of the throat. plate 43 is 7 Pulverizers of the construction described are characterized by greatly increased output with increased fineness and a decreased static pressure differential. The improved conditions in and adjacent to the grinding zone are attained by preventing carrier airflow directly into the ball row and thus avoiding aeration and consequent fluidizingflof material at the time of pulverization; the

' maintenance of a bed of material on the grinding face of sufiicient thickness to cause adequate pulverization on each passage of a particle through the grinding zone; the rapid scavenging of the undersize particles from the mate rial leaving the grinding zone to prevent overgrinding and consequentpower consumption; the recirculation of much of the oversize material to the grinding zone by the shortest practical route; the elimination of a dense mass vof 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 propendrying of the material. 7

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

What is claimed is: v A pulverizer having a housing enclosing a grinding zone in the lower portion and an air-borne pulverized material outlet in the upper portion thereof, a relief gate in said housing adjacent said grinding zone for the discharge of nnpulverizable materials therethrough, means for passing an annular stream of carrier air upwardly through said housing to entrain pulverized material discharged outwardly from-said grinding zone, a stationary classifier positioned in the upper portion of said housing and ar ranged to separate the fine from the coarse material entrained in said carrier air stream with the fine material discharging from said housing outlet with said carrier air and the coarse material being returned to said grinding zone for pulverization, means defining an opening in the side wall of said pulverizer housing at a location above said grinding zone and in general vertical alignment with said relief gate, and a feeder positioned and arranged to discharge material to be pulverized through the side wall opening of said housing and into the annular stream of upwardly moving carrier air within said housing whereby the finer portions of said material to be pulverized are transported by said carrier air into said classifier and the coarser portions of said material fall downwardly through said carrierair toward the lower portion of said housing.

References Cited in the file of this patent UNITED STATES PATENTS 1,737,800 London Dec. 3, 1929 1,952,322 Leach Mar. 27, 1934 2,012,783 Bailey Aug. 27, 1935 2,066,139 Collins Dec. 29, 1936 2,275,595 Schwartz Mar. 10, 1942 2,670,138 King Feb. 23, 1954 2,710,148 Walker June 7, 1955 FOREIGN PATENTS 531,564 Germany Aug. 12, 1931

Images