US3491954A - Air flow regulator for a pulverizer - Google Patents

Description

Jan. 27, 1970 E, c, MILLER 3,491,954

AIR FLOW REGULATOR FOR A PULVERIZER Filed March 22. 1966 EARLE C. MILLER Y INVENTOR.

United States Patent AIR FLOW REGULATOR FOR A PULVERIZER Earle C. Miller, Worcester, Mass., assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Filed Mar. 22, 1966, Ser. No. 536,373 Int. Cl. B02c 15/06, 23/00; B07b 11/04 U.S. Cl. 241-41 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a pulverizer and, more particularly, to ball-and-ring type pulverizing apparatus having means to regulate the air flow over the grinding elements.

It has been common practice in the past to grind solid material, such as coal, by use of a so-called ball-ring or roller-ring pulverizer. In such pulverizers, an annular track which is concentric to a vertical axis and lies in a general horizontal plane receives the coal and over this track pass rolling elements, such as a ball, roller, or the like. The coal is introduced to the inner periphery of the ring and moves outwardly by centrifugal force and air flow to its outer periphery where it is entrained by a vertical blast of air passing upwardly on the exterior of the ring. This flow of air is introduced by means of generally vertical orifices which permit the air to entrain the comminuted material and to carry it upwardly to the burners of the steam generating unit or the like. The difficulty is that, if the orifices are sized properly for full load operation, then, when the mill is reduced to low load operation, the velocity of the air becomes quite low. The coal then falls downwardly through the orifices, accumulates there, and tends to plug the air duct. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outsanding object of the invention to provide a pulverizer using a rolling element and a track which will operate effectively at all loads.

Another object of this invention is the provision of a rolling element track-type pulverizer having orifices for directing entrainment air which orifices are not subject to plugging at low load.

A further object of the present invention is the provision of a pulverizer which has means for adjusting the flow of air for comminuted material entrainment in accordance with the load on the mill.

It is another object of the instant invention to provide a pulverizer having a novel method for adjusting air flow nozzles.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional view of a pulverizer embodying the principles of the invention, and

FIG. 2 is a horizontal sectional view of the pulverizer taken on the line 11-11 of FIG. 1.

In general, the pulverizer built in accordance with the present invention, provides adjustable orifices in the airflow plate. This is done by providing a second orifice plate overlying the first one and by adjusting the upper one to control the size of the net orifice which exists at any given load. The adjustment would be such that the orifices in the upper plate would exactly match those of "ice the lower plate at high load to give the largest aperture and would be at least partially non-registered at low load to reduce the size of the effective orifice. The smaller orifice gives a higher velocity at low load and this prevents the coal from falling into the orifice.

Referring to the drawings, the pulverizer, indicated generally by the reference numeral 10, is shown as provided with a vertical tubular housing 11 in which is fixedly mounted a grinding ring 12 having a upwardlydirected annular track 13. Supported over the track and adapted to roll around the track is a roller 14 which is one of a plurality of similar rollers which are mounted for rotation on a support 15. They are normally resiliently pressed downwardly onto the track 13 by spring means (not shown).

Mounted in the housing 11 and extending between the inner surface of the housing and the outer periphery of the grinding ring 12 is an air-flow plate 16. The air-flow plate is provided with a series of apertures 17. The plate 16 is provided with an upwardly and inwardly directed conical surface 18, the apex of the cone being located on the central axis a of the apparatus below the track 13. An annular regulator plate 19 overlies the air-flow plate 16 and has a conical undersurface 21 which contacts and slides over the conical surface 18 of the air-flow plate. The regulator plate is provided with apertures 22 each aperture lying adjacent to a corresponding aperture 17 in the air-flow plate 16.

The regulator plate is capable of adjusting movement relative to the air-flow plate 16 to permit the selection of the amount of overlap between each aperture 22 and its corresponding aperture 17. As is evident in the drawings, the annular track 13, the regulator plate 19, and the airflow plate 16 lie in the same general horizontal plane and are concentric with the vertical axis A of the pulverizer. The apertures 17 in the air-flow plate are of generally pointed form, while the apertures 22 in the regulator plate 19 are rectangular. Each aperture 17 in the air-flow plate 16 is formed as a nozzle-shaped passage which is directed toward an area exterior of the rollers 14 and track 13 to permit the air to entrain comminuted material. The axis of the nozzle-shaped passage is generally perpendicular to the conical surface 18. The outer periphery of the airflow plate 16 is provided with an annular recess 23 and the regulator plate extends radially outwardly to overlie this recess with its outer edge closely adjacent to the housing 11. The conical undersurface 21 of the plate is provided with three arcuate-shaped racks 24. Mounted for rotation on the surface of the housing 11 is a shaft 25 for each such rack on the inner end of which is mounted a pinion gear 26. On the outer end of one of the shafts is mounted a handwheel 27. It will be understood that in place of the handwheel 27 it would be possible to use a positioning motor which would be controlled by a signal transferred from the feeder control for the pulverizer, this being the same control which controls the air damper for controlling air flow through the pulverizer.

A skirt 28 extends inwardly from the inner surface of the housing 11. Its inner edge closely overlies the upper surface of the regulator plate 19. At the bottom of the recess 23 a series of small passages 29 extend downwardly to the apertures 17. In this way, a small amount of air flows from the apertures 17 through the passages 29 to the recess 23. From there, the air flows through the gap between the inner edge of the skirt 28 and the upper surface of the plate 19. This small amount of air flow prevents coal from entering the recess 23 and affecting efficient operation of the racks 24 and pinions 26.

The operation of the apparatus will now be readily understood, in view of the above description. With the pulverizer 10 operable, the rollers 14 are carried about the axis a and roll over the track 13. The material to be ground is introduced into the center of the ring and directed toward the track 13. As it is ground, the fine material passes radially outwardly under the action of centrifugal force and of air-flow and, when it reaches the outer periphery of the track 13, it is picked up by air flowing upwardy through the apertures 17 and through the apertures 22. At high load, the plate 19 would overlie the airflow plate 16 in such a way that the maximum net aperture would result. At low load, the handwheel 27 will be operated to rotate the pinion gear 26 and operate on the rack 24 to cause the plate 19 to rotate about the axis a. The contact between the conical surfaces 18 and the conical surfaces 21 provides an effective bearing for this rotation. At an intermediate stage, the apertures 22 and 17 would be out of registry and the net aperture would be reduced considerably. At extremely low load, the matching between the apertures would be quite small, so that the air velocity would be maintained at a high value despite the fact that it is necessary to reduce the total air flowing through the pulverizer at low load to be commensurate with the smaller amount of fuel passing through the pulverizers to the burners. The fact that the apertures 17 are non-rectangular and are generally pointed means that it is possible with this combination to provide for a non-linear relationship between the size of the aperture and the particular load selected, or between the size of the aperture and the position of rotation of the plate 19 relative to the aperture 17. This means that, even though the relative movement between the plate 19 and the plate 16 takes place in a linear relationship to the change in load, the size of the net aperture will not change linearly and, as a matter of fact, will be made considerably smaller in proportion at the low end of the load range for a given increment of movement between the plates.

It can be seen that by use of the present invention it is possible to provide a pressure drop at high loads which is a much ower value and requires less primary air fan power. In the past, it was necessary to use high rates of flow at high load of the pulverizer in order that at low load the flow would be suflicient to keep the orifices clear of fuel. By use of the present invention, the velocity through the apertures can be maintained at a high value at all loads without increasing the fan power at high loads. The present construction lends itself to automatic control. In other words, plugging at low loads is removed, as well as possible entry of the fuel into the lower air chamber portions of the pulverizer. There is a saving in fan power since the pressure drop at high load is the determining factor rather than at low load as in the past.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. A pulverizer, comprising (a) a grinding ring forming an annular track,

(b) rolling elements supported to roll over the track for the comminution of solid material,

(c) an air flow plate extending around the outer periphery of the track and provided with a plurality of apertures,

(d) a regulator plate mounted adjacent the air flow plate for movement relative thereto on occasion, the regulator plate having an aperture corresponding to each aperture of the air flow plate, the said movement permitting the selection of the amount of overlap between the apertures in the air flow plate and the apertures in the regulator plate to determine the flow of air therethrough, and

(e) control means for simultaneously and uniformly etfectuating said movement between all of said apertures in said regulator plate and said apertures in said air flow plate.

2. A pulverizer comprising (a) a grinding ring forming an annular track,

(b) rollin elements supported to roll over the track for the comminution of solid material,

(c) an air flow plate extending around the outer periphery of the track and provided with a plurality of apertures,

(d) a regulator plate mounted adjacent the air flow plate for movement relative thereto on occasion, the regulator plate having an aperture corresponding to each aperture of the air flow plate, the said movement permitting the selection of the amount of overlap between the apertures in the air flow plate and the apertures in the regulator plate to determine the flow of air therethrough and wherein the air flow plate and the regulator plate have surfaces that lie in conical surfaces concentric with a vertical axis.

3. A pulverizer as recited in claim 2, wherein the apertures in the regulator plate are generally rectangular and the apertures in the air flow plate are pointed.

4. A pulverizer as recited in claim 2, wherein each aperture in the air flow plate forms a nozzle-shaped upwardly-directed passage which is directed toward an area relative to the balls and track to entrain the comminuted material.

5. A pulverizer as recited in claim 2, wherein an arcuate rack is fastened to the outer periphery of the regulator plate and a manually-operated pinion gear is mounted for rotation on an axis which is fixed relative to the air flow plate to bring about the said movement.

6. A pulverizer as recited in claim 2, wherein the air flow plate is provided with a conical surface which is concentric with the said axis and wherein the regulator plate is provided with a similar conical surface to rest on and slide over the conical surface of the air flow plate.

7. A pulverizer as recited in claim 6, wherein the apex of the conical surfaces lies below the annular track and the surfaces of the nozzle-shaped passages in the air flow plate lie generally at right angles to the conical surfaces.

References Cited UNITED STATES PATENTS 1,523,881 1/ 1925 Kreutzberg 241-59 X 1,977,771 10/1934 McMahan 241-59 X 2,206,145 7/1950 Wood 241-59 X 2,378,681 6/1945 Bailey et al 241-60 3,169,712 2/1965 Schauer et al 241-49 X 3,199,794 8/1965 Poole 241-59 3,326,476 6/1967 Izquierdo 241-59 X FRANK T. YOST, Primary Examiner US. Cl. X.R. 241-59

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