US2484255A - Vortical gaseous-fluid type classifier for pulverized solid particles - Google Patents

Description

W. A. THOMAS VORTICAL GASEOUS-FLUID TYPE CLASSIFIER @cfi. F11, 1949.

FOR PULVERIZED SOLID PARTICLES 3 Sheets-Sheet 1 Filed Feb. 15, 1946 V ww Get. 11, 1949. w. A. THOMAS VORTICAL GASEOUS-FLUID TYPE CLASSIFIER FOR PULVERIZED SOLID PARTICLES 3 Sheets-Sheet 3 Filed Feb. 15, 1946 BY m, MK

Patented Oct. 11, 1949 UNITED STATES FATE.

VORTICAL GASEOUS-FLUHD TYIE CLASSI- FIER FOR PULVERIZED SOLID PAR'EKCLES William A. Thomas, Pittsburgh, Pa, assigno r to Blew-Knox Company, Pittsburgh, Pa, a cor poration of New Jersey Application February 15, 1946, Serial No. 647,670

6 @laims. i This invention relates to the grinding or pulverizing of solids in an intermediate state of subdivision by impact of the particles with each other and the walls of an endless passage through which they are driven by a suitable motive fluid. In particular, the invention relates to means for separating the particles which have been reduced to sufficiently small size from the remainder of the circulating particles and delivering them to a point of use while returning the oversize particles for further grinding.

Impact grinders or pulverizers of the endlesspassage type have been known for some time but have been found to be subject to serious limitations in respect to capacity, the amount of steam required and the control of the size of the prodnot. In addition, the delivery of the product is pulsating and not continuous. It is impossible to pulverize material having a substantial moisture content in the known apparatus and the latter requires considerable time for gradual shutdown.

I have invented a novel pulverizing apparatus which avoids the aforementioned objections to apparatus of the same general type known heretofore. In a preferred embodiment, I provide a pulverizer of the continuous-passage type with a classifier adapted to be connected in circuit therewith, capable of separating the particles which. have been reduced sufilciently in size from those which require further grinding. The classifier preferably comprises a housing adapted to be connected to the members forming the continuous passage of the grinder or pulverizer so that a descending stream of gas with particles entrained therein is delivered to the top of the classifier. A spreader cone is located in the upper portion of the housing and has a cylindrical baffle or skirt depending therefrom. An outlet duct leads from the cone to the exterior of the housing. A hopper located below the cone and within the baffle collects oversize particles and returns them to the pulverizer. A series of vertical guide vanes spaced around the interior of the baffle impart a circumferential velocity component to the inwardly flowing gas, thereby fa- ,cilitating separation of the oversize particles from those which have been sufiiciently reduced in size. The latter float in the gas and are conveyed by the outflowing stream thereof through the outlet duct.

A complete understanding of the invention may be obtained from the following detailed description when read in connection with the accompanying drawings illustrating the preferred embodiment. In the drawings,

Figure 1 is a side elevation showing the invention in operative relation to means for supplying solid fuel to be ground and means for delivtring the ground fuel to a combustion space;

'larged scale, partly broken away and partly in- Cal . portion of the grinder.

Figure 2 is an elevation of the grinder to ensection along a central vertical plane;

Figure 2a is a vertical section through an injector for delivering to the grinder the material to be ground;

Figures 3 and 4 are transverse sectional views taken along the plane of lines III-J11 and IV--IV, respectively, of Figure 2; and

Figure 5 is a partial vertical section taken through the outlet duct.

Referring now in detail to the drawings and, for the present, to Figure 1, solid material to be ground, in the particular application illustrated, coal or a suitable grade, is stored in a bin ill from which it is delivered by a screw conveyor ll to the inlet I 2 of an injector it. A motor-reducer llla drives the conveyor and an agitator Na in the bin iii.

The injector it delivers the coal into the upperportion of an impact grinder it of the endlesspassage type shown in Figures 6 and 7 of Kidwell Patent 2,219,011. The grinder includes a classifier it from which coal of the desired degree of fineness flows through pipe it to a separator l'l, being entrained ina stream of motive fluid such a steam. The separator delivers the coal downwardly to a burner it from which it is discharged into a combustion space it) by a stream of air delivered to the burner from a blower 20 through suitable piping 2i. The steam from which the coal has been largely separated is discharged from the separator through a pipe 22 to the combustion space.

The classifier i5 is illustrated in detail in Fig ures 2 through 4 along with the injector l3 and the pulverizer it. The injector includes a Venturi throat 23 between the inlet l2 and the upper A scraper 25 is mounted for rotation in the inlet it about the axis of the steam nozzle 25 of the injector to prevent accumulation of material at the entrance end of the Vc-nturi throat. The shaft of the agitator Ha is prolonged and drives the scraper 25 in the inlet l2 through bevel gears 122). This portion of the apparatus is disclosed in greater detail and claimed in my copending application Serial No, 637,819 filed December 29, 1945, Patent No. 2,420,- 388, for Apparatus for feeding granular material into a fluid stream.

The injector discharges coal into the upper portion of the grinder M. The lower portion of the grinder is formed by a jet tube 24 which is an elbow having steam nozzles 28 spaced therealong adapted to deliver jets for driving the coal particles repeatedly around the grinder I l. The latter also includes an arcuate tube 29 with a connection for the injector, and connecting members 30 and 3!,

These several members form a continuous passage the sectional area of which increases gradually in the direction of the flow.

The classifier l5 comprises a housing 32 having its upper end connected to the outlet end of the tube 29 and its lower end to the entrance end of apart and a cylindrical wall therebetween. A

spreader 33 in the form of a conical frustum is disposed in the upper portion of the housing and has a cylindrical baille or skirt 34 depending from the lower edge thereof. A renewable wear plate 33a is placed on the frustum to withstand the impact of particles emerging from tube 23. A hopper 35 is supported in the lower portion of the housing on radial brackets 36. A series of vertical guide vanes 31 is disposed between the hopper and the spreader cone. The vanes have vertical hinge pins, the lower ends of which are journaled in a ring 38 carried by the hopper. The upper ends of the hinge pins are journaled in a base plate 39 secured to the cone 33. The cone 33 and baille 34 are thus supported on hopper 35. A ring 40 rests on the upper ends of the vanes 31. Projections 4| at the inner edges of the vanes extend into radial slots 42 spaced circumferentially of the ring 40. It is thus possible to adjust all the vanes 3! simultaneously by rotating the ring 40. For this purpose, the hinge pin of one of the vanes has an extension 43 projecting downwardly therefrom and through the lower portion of the housing. A lever 44 permits the extension 43 to be turned by hand for effecting the desired adjustment of the vanes 31.

The base plate 39 has a central opening therethrough from which a tubular neck 45 depends. An outlet passage 46 extends from the cone 33 to the adjacent wall of the housing and connects with an elbow 41. As shown vin Figure 1, the delivery pipe l6 communicates with this elbow. A helical flight or vane 48 extends around inside the hopper 35 to cause the particles and steam moving circumferentially of the hopper to descend through the open'lower end thereof and re-enter the tube 24 of the pulverizer.

The operation of the apparatus is as follows. Coal introduced into the tube 29 by the injector I3 is subjected to impact the plate 33a and, after passing the classifier l5 with the result to be explained, against the walls of the endless passage formed by. the members 24, 29, 30 and 3| of the grinder H. The particles are driven along a continuous course by the jets from the nozzles 28 and are delivered by entrainment in the resulting stream to the upper end of the housing 32. The stream of steam and coal particles striking the plate 33a and cone 33 are spread laterally in all directions. Some of the steam and the finer particles entrained thereby flow around the lower edge of the baflie 34 and inwardly between the vanes 31 toward the central outlet through neck 45. As the steam passes around the lower edge of the baflie 34, the larger and heavier particles continue on a downward course falling into the lower portion of the housing and returning to the entrance of the tube 24. The steam and particles which pass between the vanes 31 have a circumferential motion imparted thereto by the angular adjustment of the vanes whereby a vortex is created in the upper portion of the hopper 35. From the center of the vortex a column of steam ascends through the neck 45 carrying with it the particles of coal which have been reduced to such a size as to float in the outflowing stream. The

4 stream flows from the cone 33 through the outlet 46, through elbow 41 and thence by pipe is to the separator l I. The larger, heavier particles which pass between the vanes 31 fall downwardly as they travel about the hopper. 0n striking the helical vane 48, these particles are given a positive downward velocity component and are thereby discharged into the entrance end of the tube 24.

It will thus be apparent that the device effects a two-stage separation of the coal which has been sufllciently reduced in size for combustion. The first separation occurs when a portion of the steam entering the classifier sweeps around the lower edge of the baiile 34. The second stage occurs within the hopper 35, as a result of the circumferential velocity component imparted to the steam and entrained coal particles by the angular adjustment of the vanes 31.

The mixture of steam and coal particles delivered to the separator II from the classifier i5 is divided thereby into a stream of finely divided coal falling into the burner is and a stream of steam with a small percentage of coal delivered through pipe 22 into the combustion space IQ.

The helical vane 48 is an important feature of the classifier because it produces a down draft of steam and oversize particles through the hopper 35, thus preventing an up draft through the hopper which might tend to be produced by direct flow of steam around the cone 33, the baille 34 and the hopperand into the bottom of the latter.

The operation of the classifier may be summarized thus. In the space between the housing and the bailie 34, the coarser particles are separated by the differential in their mass weight as a result of their inertia. This separation is possible because of the reduced velocity of the steam resulting from the large sectional area of the annular passage through the classifier as compared to that of the passage through the grinder. The coarse particles continue undeflected and reenter the grinder for further reduction in size. The steam carrying the smaller particles rises inside the baflle 34 and is subjected to a second separation resulting from the tangential motion imparted by the vanes 31. In this centrifugal separation, the finest particles float on the ascending stream through the outlet while the coarser particles circle around in the hopper and are positively directed downwardly by the vane 48.

The apparatus of my invention has several important advantages over impact pulverizers as known heretofore. In the first place, I am enabled, by my invention, to deliver a greater quantity of finely ground material than has been obtainable heretofore from continuous-passage impact grinders. This seems to result from the fact that the velocity of the circulating steam is reduced in the region where the separation occurs as a result of the enlargement of the sectional area of the passage. My invention also makes it possible to grind a given amount of material with a smaller amount of steam. The delivery of the finely ground material, funthermore, is steady and continuous, and free from the pulsations characterizing the operation of apparatus known before. The apparatus of my invention is also capable of pulverizing materials having a substantial moisture content. This was impossible with the prior apparatus. It is also possible to shut down the pulverizer according to my invention much more quickly than those known previously.

My invention also has the characteristic of delivering material of substantially the same degree of fineness regardless of the rate of feed. This is not true of previous grinders which exhibited a marked change in the fineness of the product if the feed rate is changed materially, the particle size becoming larger as the feed rate is increased. On the contrary, the apparatus of my invention exhibited but very small changes in the percentages of various sizes of particles when the feed rate was varied over a substantial range. This is particularly important in combustion applications since it is frequently desirable to operate at reduced rates without affecting combustion conditions seriously. Considering the entire system as applied to the production of pulverized coal for combustion, the removal of steam in the separator permits cold air to be supplied to the burner without objectionable condensation.

The location of the feed-in connection above the classifier increases the rate of grinding which is particularly important in the case of the harder coals. It also gives better drying of the coal and pulverizer of the endless-passage type delivering downwardly therefrom a stream of gas entraining particles of various sizes, said classifier comprising a housing converging toward its upper and lower ends, said ends being connected to points spaced apart along the pulverizer and iorming a portion of said endless passage, a fixed some initial separation of fines because the entering coal makes one pass through the classifier before grinding begins (except that due to striking the plate 33a).

Fundamentally, my invention makes it possible to withdraw from the grinder substantially all the material which has been ground to the desired fineness. It difiers in this respect from grinders previously known in which it was impossible to withdraw a substantial portion of the material which had been sufiiciently reduced in size. In the embodiment illustrated, my invention removes from the grinder all coal which is in a state of subdivision suificiently small for use .as pulverized fuel. M invention is not only capable of being shut down more quickly than previous grinders but also makes it possible to start up combustion in a much shorter time.

While the invention has been described by reference to a system for the production of pulverized coal for combustion, it will be understood that this is merely by way of example since the apparatus may be used for grinding material other than coal.

Although I have illustrated and described but a preferred embodiment of my invention, changes in the details of construction disclosed may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. In combination, a classifier for separating particles of granular material adapted to be connected in c.osedcircuit relation with an impact pulverizer of the'endless-passage type delivering downwardly therefrom a stream of gas entraining particles of various sizes, said classifier comprising a housing converging toward its upper and lower ends, said ends being connected to points spaced apart along the pulverizer and forming a portion of said endless passage, a downwardly flaring spreader cone in the upper portion of the housing adjacent the gaseous fluid inlet thereto, a skirt depending from the cone,

2. series of vertical guide vanes spaced around the skirt and spaced inwardly thereof, a passage between said vanes and the interior of said cone, an outlet leading from said interior of said cone to the exterior of said housing, and a hopper in the lower portion of said housing and below said guide vanes for returning oversize particles to the pulverizer.

2. In combination, a classifier for separating particles of granular material adapted to be connected in close-circuit relation with an impact downwardly flaring spreader cone in the upper portion of the housing adjacent the gaseous fluid inlet thereto, a series of vertical guide vanes for said gas-entrained particles spaced around the axis of the cone and lying below the cone and within the projection of the base thereof on a horizontal plane, said guide vanes being angularly disposed with respect to the respectively adjacent radii of said cone, a passage between said vanes and the interior of said cone, an outlet leading from said interior of said cone to the exterior of said housing and a hopper in the lower portion of said housing and below said guide vanes for returning oversize particles to the pulverizer.

3. In combination, a classifier for separating particles of granular material adapted to be installed in a descending stream of gas entraining particles of various sizes in an impact pulverizer of the endless-passage type, comprising, a housing for said classifier forming a portion of said endless passage, a fixed downwardly flaring spreader cone in said housing adjacent the gaseous fiuid inlet thereto, a cylindrical baflle coaxial with said cone and extending downwardly therefrom, a passage extending between the interior of said baffle and said cone, an outlet duct communicating with said cone for conducting outflowing gas and particles floating therein, a hopper within said bafiie coaxial therewith and smaller in diameter than the bafile for collecting oversize particles falling through the gas, guide vanes for said gas entrained particles above the hopper for directing the gas entering the space between it and the baifie in a direction circumferentially of the hopper, and an opening in the bottom of said hopper through which said oversize particles are returned to the material passing through said endless passage beyond said classifier.

4. In combination, a classifier for separating particles of granular material adapted to be connected in closed circuit relation with an impact pulverizer of the endless-passage type delivering downwardly therefrom a stream of gas-entrained particles of various sizes, comprising, a housing forming an enlarged portion along the length of said axial passage, 9. fixed frusto-conical spreader concentrically positioned within said housing adjacent the gaseous fiuid inlet thereto, a cylindrical skirt substantially depending from the lower edge of said spreader, a hopper concentrically positioned within said cylindrical skirt and spaced therefrom, a depending tubular neck positioned within said spreader in concentric relation thereto and above said hopper, means defining a plurality of generally radial passages extending between the interior surface of said skirt and the interior of said hopper adjacent the upper portion thereof an outlet in communication with said tubular neck and extending through said housing, a downwardly directing helical vane in the lowermost portion of said hopper, said hopper having an axial opening below said vane, whereby gas-entrained fineparticles make a reentrant turn beneath said skirt and enters said hopper wherein the predetermined finer portion thereof passes out through said neck and said outlet and the coarser portion thereof passes out through said opening at the bottom of said hopper to rejoin material moving through said endless passage.

'5. In combination, a classifier for separating particles of granular material adapted to be con- 1 nected in closed circuit relation with an impact pulverizer of the endless-passage type delivering downwardly therefrom a stream of gas-entrained particles of various sizes, comprising, a housing extending between the base of said spreader and the interior of said hopper adjacent the upper portion thereof, said annular passage being above the bottom of said tubular neck, centrifugal guiding means in said annular passage, and an outj let in communication with said tubular neck'and extending through said housing, said hopper having an axial opening in the bottom thereof, whereby gas-entrained fine particles enter said hopper beneath said spreader with a whirling motion and make a reentrant turn around the bottom of said neck wherein the predetermined finer portion thereof passes out through said neck and said outlet and the coarser portion thereof passes out through said opening at the bottom 1 of said hopper to rejoin material moving through said endless passage.

6. In combination, a classifier for separating particles of granular material adapted to be connected in closed circuit relation with an impact pulverizer of the endless-passage type delivering downwardly therefrom a stream of gas-entrained particles of various sizes, comprising, a housing forming an enlarged substantially vertical portion along the length of said axial passage, a fixed frusto-conical spreader concentrically positioned within said housing adjacent the gaseous fluid inletthereto, a hopper ooaxially positioned beneath said spreader and spaced therefrom, a depending tubular neck positioned beneath said spreader in concentric relation thereto and above said hopper, means defining an annular passage extending between the base of said spreader and the interior of said hopper adjacent the upper portion thereof, said annular passage being above the bottom of said tubular neck, centrifugal guiding means in said annular passage, an outlet in communication with said tubular neck and extending through said housing, said hopper having an axial opening in the bottom thereof, and a downwardly directing helical vane around the inside of said hopper adjacent said axial opening, whereby gas-entrained fine particles enter said hopper beneath said spreader with a whirling motion and make a reentr ant turn around the bottom of said neck wherein the predetermined finer portion thereof passes out through said neck and said outlet and the coarser portion thereof passes out through said opening at the bottom of said hopper to rejoin material moving through said endless passage.

WILLIAM A. THOMAS.

REFERENCES CITED I The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,058,313 Luckenbach Apr. 8,1913 1,367,635 Sturtevant Feb. 8, 1921 1,569,468 Ely Jan. 12, 1926 1,635,527 Barthelmess July 12, 1927 1,698,361 Dreisback Jan. 8, 1929 1,770,850 Hartman July 15, 1930 2,010,128 Arnold Aug. 6, 1935 2,055,385 Noack Sept. 22, 1936 2,219,011 Kidwell et a1 Oct. 22, 1940 2,224,169 Turnbull Dec. 10, 1940 FOREIGN PATENTS Number Country Date 806,771 France Oct. 5, 1936 590,866 Germany Oct. 13, 1930 Certificate of Correction Patent No. 2,484,255 October 11, 1949 WILLIAM A. THOMAS It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 27, for the words a steam read as steam; column 8, line 46, list of references cited, for the foreign patent number 590,866 read 509,866;

and that the said Letters Patent should be read with these corrections therein that the same'may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 7th day of February, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'omr of Patents.

Images