US2434037A - Material classifier - Google Patents

Description

n- 1948- G. B. EBERsoLE ET AL 2,434,037

MATERIAL CLASSIFIER Filed April 2, 1943 5 Sheets-Sheet 1 A ITORNE Y 1943- I r G; B. EBERSOLE arm. Q037 MATERIAL CLASSIFIER Filed April 2, 1943 5 Sheets-Sheet 2 INVENTORS George B. Ebersole f BY Lester L. Leach ATTORNEY Jan. 6,1948. e. B. EBERSOLEIEI'AL. 2,434,037

v MATERIAL CLASSIFIER Filed April 2, 1943 3 Sheets-Sheet 3 Fig. 3

37 2 5/ I 3 pr" INVENTORS Geo rge 'B. fbersole 1 BY LesterLLezc/z A TTORNE Y Patented Jan. 6, 1948 7 2,434,037, MATERIAL CLASSIFIER George B. Ebersole, Akron, and Lester Barberton, Ohio, asslgnors to The Babcock 8rv I Wilcox Company,

tion of New Jersey Rockleigh, N. J., a corpora- Application April 2, 1943, Serial No. 481,518

4 Claims. (01. 209-139) I The present invention relates in general to the construction and operation of stationary classifiers adapted to selectively separate solid particles in suspension ina gasstream, and more particularly to classifiers of thistype adapted for use in the outlet end of pulverizers in which the pulverized material is carried out of the puverizing or grinding zone in suspension in a gaseous carrier medium. The classifier of our invention is particularly designed and especially useful in pulv'erizers f the general type shown in U. S. Patent No. 2,275,595, in which the material treated is coal, phosphate rock,.and the like. In such pulverizers, the pulverizing elements are relatively movable upper and lower grinding rings between which a circular row of grinding balls is horizontally arranged, and the pulverized material is removed from the grinding zone by an annular stream of carrier air passing upwardly through a restricted annular throat and picking up pulverized material discharged from the outer circumferential edge of the lower grinding ring.

The. general object of our invention is the provision of a material classifier which is capable of effectively classifying suspended material at high capacity rates with a relatively low pressure drop through the classifier. A further and more specific object is the provision of an air-swept pulverizer having a classifier of the type described which is capable ofsubstantially increasing the circulating load of the pulverizer while substantially reducing the air pressuredrop through the grinding zone.

The various features of noveltyi 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 operatingadvantages andspecific objects attained by its use, reference should be hadv to the accompanying drawings and descriptive matter in which we have illustrated and described preferred embodiments of our invention. I

0f the drawings:

Fig. 1 is a sectional elevation of a pulverizer incorporating a stationary classifier constructed and arranged in accordance with our invention;

Fig. 2 is an enlarged horizontal section, partly broken away, taken on the line 22 of Fig. 1; and

Fig. 3 is a sectional elevation of a portion of a pulverizer with a modified form of classifier, parts of the pulverizer being omitted for purposes of clarity.

The classifier of our invention is illustrated in Figs. 1 and 2 as incorporated in the top :or outiii . 2 let section of an air-swept pulverizer, the grinding parts of which are enclosed in a cylindrical casing Ill. The pulverizer has a vertical drive shaft ll carrying a generally conical drive yoke 12 on its upper end. A lower grinding ring I4 is mounted on flattened lower portions of the yoke and its surface shaped to form a track for a circular row of grinding balls I5. The halls l5 support a nonrotary upper grinding ring l6. An annular spider I! mounted on the upper ring is provided with lugs l8 arranged in vertical guides IS! on the inner wall of the 'casing III for preventing rotation, but permitting vertical movement, of the spider and upper ring. A resilient grinding pressure is exerted downwardly-0n the grinding parts by a number of coil springs 20 engaging the spider.

The material to be pulverized is supplied through a feed spout 2| to the inner side of the spider and upper grinding ring and falls on the inclined upper surface of the drive yoke 12, being distributed throughout the grinding area by the rotation of the drive yoke and associated parts. The material flows outwardly over the upper surface of the yoke and lower grinding ring, is pulverized between, the relatively moving balls and grinding rings and discharges over the outer edge of the lower grinding ring at an oblique angle to the periphery thereof depending upon the ring speed. I

- The pulverizer disclosed is of the airswept type having an annular stream of primary or carrier air passing upwardly at the discharge side of the pulverizer grinding'zone and through astationary classifier hereinafter described to a central outlet 22 for the material laden air stream. A cylindrical turret 23 forms an upward continuation of the outlet opening 22 and has one or more valve controlled discharge pipes 24 symmetrically connected into the turret top plate, The carrier air is normally preheated and supplied under pressure by a suitable forced draft fan (not shown) to an involute wind box 25 surrounding the casing [0 opposite the grinding zone. The carrier air flows into the pulverizer through casing passages 26 at the outer side of the drive yoke and then upwardly through an annular throat passage 21 formed between the outer side of the lower grinding ring and an annular throat plate 28 mounted onthe inner side of the casing. Relatively unpulverizable material, such as pyrites, leaving the grinding zone drops through the throat and is collected in a compartment 29 in the base section of the-pulverizer.

The material leaving the pulverizing zone includes a large percentage of oversize or coarse bolts 33 extending are used in the embodiment particles which must be returned to the pulverizing zone ior regrinding, ii the material distribution to the discharge pipes is to be of the desired fineness and uniformity. Various types of classifiers of various degrees of effectiveness have been installed between the pulverizer grinding zone and discharge pipes for the purpose of selectively classifying the suspended material and returning oversize particles to the grinding zone. A relatively high percentage of returned material or circulating load is desirable for optimum operation of pulverizers of this type. The return of rejected oversize particles to the grinding zone is hindered by the varying air pressure conditions in different parts of the pulverizer, and particularly by the pressure drop through the classifier, necessitating the passage of rejected material from a low pressure zone to a higher pressure zone. A further normal obstruction to the return of rejects is the travel of the rejected particles across the path of now of the material laden air stream approaching the classifier, which tends to cause previously rejected particles to be swept up and again passed through the classifier without intervening regrinding. I

The improved classifier of our invention is of the stationarytype and comprises apair of frusto-conical members or truncated cones 3d and 3| arranged coaxially oi the pulverizer outlet 23. The outer cone 33 has a top flange 32 held in contact with the pulverizer casing top plate by eye through the top plate. The flange extends inwardly from the outer cone to the perimeter of the outlet 22. The inner cone 3| is spaced from the outer cone a distance equal to the width of the flange 32, with its upper end spaced therefrom to provide an annular opening 34 into the downwardly flaring annular space 35 between the cones.

The lower part of-the space within the inner cone 3! is occupied by a central hub or cover member 31 and a series of symmetrically arranged overlapping inclined segmental blades 38 extending radially from the hub 31 to th inner side of the lower end of the inner cone 3|. Each of the blades 38 is inclined in a clockwise direction. Twelve'blades are shown and each blade when developed has a true angle of- 40, so that a considerable overlap of adjacent blades is provided. V

The annular opening 34 at the upper .end of the intercone space 35 is occupied by a circular series of short inclined deflector plates 40 symmetrically spaced circumferentially. Sixteen of such plates illustrated, each being inclined 45 in both plan and elevation, with the'outer edge advanced in a clockwise direction. a The space 35 between the cone members is di-c vided into three double chutes by inclined plates 42, the lower end of each chute opening into a depending trap 43 having a hinged flap valve or gate 44 at its lower end. The traps 43 are inclined inwardly sufficiently to bring their lower ends above the inner side of the ball row. A portion of the outer cone 30 is cut away to avoid obstructing the feed spout 2 l.

The effective flow area of the annular opening the lower end of the turret and adapted to be moved downwardly, as indicated in broken lines, to close ofi all or a part of the'opening 34. Externally adjustable support rods 41 are provided for this purpose.

When a pulverizer of the character described is used in a direct fired pulverized coal system, the

. amount of carrier air supplied is substantially dition of the larger size particles.

34 is made variable by a sleeve 46 positioned in rectly proportional to the amount of coal to be pulverized. The air velocity in the throat will vary with changes in load, but at all times will be suflicient to lift the pulverized material out of the pulverizing zone. Normally a mass of pulverized material will be maintained in a. floating condition above the throat and from which the rising air stream continuously picks up pulverized material. The clockwise rotation of the pulverizer yoke and lower grinding ring tends to promote a swirl oi! the material laden air in that direction, so that the stream passing upwardly along the outer side of the upper grinding ring and spider will have a general clockwise movement. In order to reach the pulverizer outlet 22, the material laden air stream must pass through the passagesformed between the, stationary blades 38 and due to the shape and inclined arrangement of these blades receives -a substantial additional swirling effect in a clockwise direction which causes the larger size particles to be thrown outwardly tov outwardly into the op and in effect are skimmed ed the moving stream by the plates and enter the space 35, thereby increasing the average fineness of the remaining particles in suspension. The amount of material so eliminated is proportional to the effective port area of the opening 34, so that the sleeve 33 can be adjusted to control that area and thereby the effective time in which the oversize particles can separate from the stream. The fineness of the suspended material passing to the turret and discharge pipes is thus.

variable.

The annular opening 34 also acts as an outlet for oversize material separating out of the stream when in the turret. Due to the substantial height and cylindrical shape of tend to form in the upper part thereof, which together with the retarding action of the turret walls, have been found to effect further separa- 'These oversize particles dribble down the sides of the turret wall and control sleeve and pass out through the annular opening 34.

The oversize or rejected material entering the intercone space 35 falls down the chutes therein to the traps 43, from which it discharges through the flap valves whenever the head of material is suflicient to overcome the existing pressure differential between the pulverizing zone and the interior of the classifier. The rejected material drops into the space at the inner side of the ball row and again passes through the pulverizing zone.

The described construction and arrangement of the classifier has been found to result in the maintenance of a desirably high circulating load in the pulverizer, while reducing the amount of material in flotation above the throat substantially to the minimum necessary to operate the usual differential pressure control of the associated feeden. .The selective separation obtained with the described classifier is highly effective in eliminating oversize material with little, it, any, added fan power consumption.

In the modification illustrated in Fig. 3, the

the turret, eddy currents assaosr 5. increased and the level of the reject opening raised to more efiectively utilize the swirl effect created by the stationary blades 38. The general arrangement is similar to that in Figs. 1 and 2, with the body of the classifier formed by spaced inner and outer truncated cones 50 and 5| respectively enclosing an annular space 52 divided into chutes by inclined plates 53 leading intofiap valve controlled bottom traps 54, The turret 60 is flared upwardly and the inner cone member 50 provided with an upwardly flaring extension 5| to provide a continuation of the space 52. The upper end of the turret has a top plate 82 in which discharge pipes 53 are symmetrically arranged. The inner cone extension 8i stops short of the top plate 52 to provide an annular exit opening 65 for the rejected material into the annular space 52. An inverted irustoconical baflie 56 is positioned at the inner side or the exit opening 65 to facilitate the separation of material flowing along the surface of the extension member 5l, while requiring an abrupt change in direction of material in the peripheral portion of the stream to reach the discharge pipes 53. The baiile 86 is supported from the top plate by rods 68 which are externally adjustable to vary the position or the heme and thereby the eflective entrance area of the exit opening 85. The higher the position or the cone, the greater will be the fineness of the material reaching the discharge pipes.

While in accordance with the provisions of the statutes we have illustrated and described herein the best forms 01. the invention now known to us, those skilled in the art will understand that changes may be made in theform of the apparatus disclosed without departing from the spirit of the inventioncovered 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, theword air" is intended to generically cover any gaseous carrier medium suitable for removing pulverized material in the manner described.

We claim:

1. A material classifier comprising a pair 01' vertically. extending inner and outer upright frusto-conical casing members arranged'to form an annular space therebetween and inlet and outlet openings for air-borne material at the lower and upper ends respectively of saidinner casing member, the upper part of said inner casing member being formed to provide a separate substantially annular entrance for oversize material into said annular space. stationary baille means in said inlet opening constructed and arranged to swirl the entering air-borne material upwardly through said inner casing member, avertically adjustable baiiie for varying the efiective height of said annular entrance, means subdividing at least the lower portion of said annular space into chutes, and a valve controlled trap at the lower end of each chute.

2. A material classifier comprising a pair of vertically extending inner and outer upri ht frusto-conical casing, members arranged to form an annular space therebetween and inlet and outlet openings for air-borne material at the lower and upper ends respectively of said inner casing member. the upper part of said inner casin member being formed to provide a, separate substantially annular entrance for oversize material into said annular space, means in said inlet opentrance, means subdividing at least the lower portion of said annular space into chutes, and a valve controlled trap at the lower end of each chute.

3. A material classifier comprising a pair of vertically extending inner and outer upright frusto-conical casing members arranged to form an annular space therebetween and inlet and outlet openings for air-borne material at the lower and upper ends respectively of said inner casing member, the upper part of said inner casing member being formed to provide a separate substantially annular entrance for oversize mate- 'rial into said annular space, stationary baiiie means in said inlet opening constructed and arranged to swirl the entering air-borne material upwardly through said inner casin member, deflector plates in said annular entrance for de-' fleeting material into said annular space, a vertically adjustable battle for varying the eflective area of said annular entrance, means subdividing at least the lower portion or said annular space into chutes, and a flap valve controlled trap at the lower end of each chute.

4. In combination, a casing having an outlet in its upper end for material-laden air, and a stationary classifier positioned in said casing below and symmetrically arranged relative to said outlet, said classifier comprising spaced inner and outer upright irusto-conical members relatively arranged to form an annular space therebetween having an annular opening thereto above said inner frusto-conical member, stationary baifle means within said innerfrusto-conical member constructed and arranged for eflecting a swirl of entering material-laden air, deflector plates positioned in said annular opening and arranged to deflect material into said annular space, plates subdividing said annular space into chutes, a flap valve controlled trap at the bottom of each chute, and an adjustable sleeve bafilc arranged to vary the efi'ective area of said annular opening. GEORGE B. EBERSOLE.

LESTER. L. LEACH.

REFERENCES CITED in the UNITED STATES PATENTS Number Name. Date 857,988 Fuller June 25, 1907 1,965,186 Hardgrove July 8, 1934 1,724,041 Plaisted Aug. 13, 1929 452,580 Morse May 19, 1891 465,548 Shelley Dec. 22, 1891 1,214,249 Williams Jan. 30, 1917 2,079,155. Crites May 4, 1937 429,347 -Haslrell June 3, 1890 750,088 Child Jan. 19, 1904 1,367,637 Sturtevant Feb. 8, 1921 2,211,274 Kuck -1 Aug. 18, 1940 2,275,595 Schwartz Mar. 10, 1942 2,087,645 Hermann July 20, 1937 FOREIGN PATENTS Number Country Date 813,690 ca June 20, 1929

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