US 3856215 A
A device for preventing the encrustation of the outlet duct of a fluid energy type grinding mill comprising a screen positioned adjacent the inner periphery of the outlet duct and means providing a flow of gaseous fluid through the screen to entrain particles passing through the duct in what is, in effect, a fluidized bed.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Van Vliet 1 Dec. 24', 1974 ENCRUSTATION-PREVENTING DEVICE FOR FLUID ENERGY TYPE MILLS  Inventor: Edward Van Vliet, Doylestown, Pa.
 Assignee: Fluid Energy Processing &
Equipment Company, Hatfield, Pa.
 Filed: Oct. 23, 1973  Appl. No.1 408,451
 US. Cl. 241/39  Int'. Cl. B02c 19/06  Field of Search 241/5, 39
 References Cited UNITED STATES PATENTS 4/1916 Wood 241/5 X 2,402,203 6/1946 Pharo v. 241/39 X 2,628,786 2/1953 Piperoux et al.... 241/39 3,559,895 2/1971 Fay 241/5 3,648,936 3/1972 Stephanoff 241/5 Primary Examiner-Granville Y. Custer, Jr. Attorney, Agent, or FirmArthur A. Jacobs, Esq.
[5 7] ABSTRACT A device for preventing the encrustation of the outlet duct of a fluid energy type grinding mill comprising a screen positioned adjacent the inner periphery of the outlet duct and means providing a flow of gaseous fluid through the screen to entrain particles passing through the duct in what is, in effect, a fluidized bed.
10 Claims, 5 Drawing Figures This invention relates to fluid energy type grinding mills, and it particularly relates to an improvement in the exhaust outlet duct to prevent the encrustation of the duct to the point where it interferes with the passage of the treated materials.
Fluid energy type grinding mills are those wherein granular material, either relatively dry or in the form of a slurry, is fed into a generally annular, vertically or horizontally arranged, housing where the material is entrained in circulating gaseous streams which centrifugally whirl the material around the housing in which the grinding or .pulverization treatment takes place. The gaseous material is generally passed into the housing with high velocity (usually at least acoustical velocity) so that the particles of the fed material collide with each other and often with the walls of the housing, whereby the particles are cracked and broken into smaller particles. Since the collisions are somewhat random and since those particles which do break, break into varying sizes, The centrifugal force exerted thereon varies, the larger particles being in the outer peripheral portion of the centrifugal stream and the smaller particles being in the inner portions. An outlet duct is provided at one position of the inner periphery of the housing so that as the smaller particles pass along their centrifugal path, they pass into this outlet or exhaust duct, whereas the larger particles continue on the outer peripheral portions of the path for another pass through the mill. The gaseous streams may be hot or cold but are usually hot, such as steam, in order to increase their velocity.
Although the aforesaid treatment is highly efficient, a serious problem has long existed with respect to the build-up of encrustation in the outlet duct to the point where it seriously interferes with the effective passage therethrough of the finished product. This is an especially severe problem with respect to heat sensitive or sticky types of materials such as waxes, toner powders, thermoplastics, oil bearing materials such as cocoa, soybeans, and other similar fruits and vegetables, and other such substances. These substances tend to adhere to the interior walls of the duct and continue to build up upon each other causing clogging of the duct. In addition, the encrusted materials tend to break off in large lumps at intervals. These lumps then pass through with the finished product and act as contaminants therein. It is one object of the present invention-to provide a device for overcoming the aforesaid build-up of encrusting materials in the outlet duct of fluid energy type mills.
Another object of the present invention is to prevent the formation of large lumps or particles in the finished product.
Another object of the present invention is to provide a device of the aforesaid type which is simple in construction and inexpensive to manufacture and install.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following description when read in conjunction with the accompanying drawings wherein:
FIG. 1 is a sectional view of a fluid energy type mill provided with an encrustation-preventing device embodying the present invention.
FIG. 2 is an exploded view of the encrustationpreventing device of FIG. I and of a portion of the outlet duct.
FIG. 3 is an enlarged detailed elevational view of an alternative embodiment of the present invention.
FIG. 4 is a view similar to FIG. 3 of another alternative embodiment of the present invention.
FIG. 5 is a sectional view showing the encrustationpreventing device installed in another type of fluid energy mill.
Referring now in greater detail to the drawings wherein similar reference characters refer to similar parts, there is shown in FIG. 1 a vertical type grinding mill, generally designated 10, comprising an annular housing including an inlet section 12, an upstack 14, a classification section 16, an exhaust or outlet opening 17 in the classification section, connected to an outlet duct 18, and a downstack 20. A feed conduit 22 is positioned just above the inlet section 12. The feed conduit- 22 may be of any desired type, but is here illustrated as having a Venturi section 24, a hopper 26 and a duct 28 connected to a source of gaseous fluid under pressure. The material to be ground is fed into the hopper 26 and is propelled through the Venturi section 24 into the mill by the gaseous fluid from duct 28. Tangential nozzles 30 propel gaseous fluid, such as steam or air, from a manifold 32 into the inlet section. These gaseous fluids entrain the particles of the material to be ground and whirl them against each other as well as centrifugally through the upstack 14. Gaseous fluid nozzles 34, also connected to the manifold 32, are optionally provided to propel gaseous fluid into the classification section 16 to aid circulation around the outlet opening 17. The smaller particles, on the inner centrifugal path periphery in the classification section, pass through the outlet 17 into the duct 18, while the larger particles, on the outer periphery, pass down through the downstack 20 where they may be joined by additional fresh feed from conduits 22 while they are recycled back through the inlet section 12.
As indicated above, many of the materials being ground are sticky or adherent, especially when hot gases such as steam are being used. In order to prevent adherence of such sticky particles to the walls of the outlet duct and to each other, there is provided in the outlet duct 18 a cylindrical or tubular screen 36, preferably flexible, which is held in position within the duct by any desired means. In FIGS. 1 and 2, the screen 36 is frictionally held in place by an annular ring or manifold 38 which is, itself, held by friction against the internal wall of the duct 18. Instead of friction, screws, nuts and bolts, clamps, pin and slot connections, or any other desirable and feasible connecting means may be used. a
The ring 38 should preferably be as narrow as is feasible in order to obtain as small a space between the screen and the interior wall of the duct as possible. Preferably, this space should be no more than about l/16 of an inch but may be varied as necessary. The drawing shows this space and the width of the ring 38 somewhat exaggerated in size in order to provide a better illustration thereof.
The ring .38 is provided with a plurality of ports 40 on its inner peripheral surface and has an inlet opening 42 on its outer peripheral surface. The opening 42 mates with an opening 44 in the duct 18, both openings receiving a conduit 46 connected to a source of gaseous fluid under pressure, which may be the manifold 32 or any independent source (not shown).
Gaseous fluid, such as air, steam, an inert gas such as nitrogen, or any other desirable and feasible gas or vapor, is passed through conduit 46 into the ring 38, from where it passes through the ports 40 in radial directions. These gaseous streams pass through the screen 36 and provide what is, in effect, a fluidized bed around the screen. This fluidized bed holds any particles which would normally adhere to the screen or the duct wall in suspension so that theycan easily be entrained and propelled out of the duct by the material behind them. This results in a substantially complete avoidance of encrustation build-up.
Although the screen 36 is shown extending through substantially the full length of the duct, this being the preferable form in order to prevent build-up above and below the screen, but especially below, it may, in some instances, be of a relatively short length and positioned either near the inlet end of the duct 18, adjacent the outlet opening 17, or, less preferably, near the outlet end of the duct.
The ports 40 are illustrated as straight or radial so that radial streams of gaseous fluid are propelled therefrom. However, they may also be made tangential, in which event, they provide an additional vortex action which may result in additional grinding and which may also aid in preventing adherence of the particles.
In FIG. 3, there is shown an alternative embodiment of the invention wherein the duct 50, similar to duct 18,
is provided with a tubular screen 52, similar to screen 36, which is held in place by brackets 54. However, instead of an annular manifold ring such as shown at 38, a single gaseous fluid supply conduit 56 is used to supply gaseous fluid behind the screen 52.
In FIG. 5, there is shown another embodiment of the invention wherein the duct 60, similar to duct 18, is provided with an annular manifold ring 62 on the outer peripheral surface of the duct. The tubular screen 64 is held in place by brackets 68, or the like, similar to brackets 54.
The ring 62 is provided with one or a plurality of ports, such as shown at 40 in FIG. 2, and these ports mate with ports 66 in the wall of the duct. Gaseous fluid is passed from a source thereof into the ring 62 through a conduit 70.
This form of the invention permits the screen 64 to be positioned as close to the duct wall as desirable (although still in spaced relationship thereto) since it is not necessary to provide space for the ring 62 within the duct. a
In FIG. 4, the present invention is shown as utilized in a horizontal type mill, generally designated 100. This mill 100 has an annular chamber 102 surrounded by an annular header 104. The header 104 is provided with gaseous fluid, such as air or steam, and this gaseous fluid is propelled in tangential streams into the chamber 102 through tangential nozzles or ports 106. The resulting inwardly whirling gaseous fluid entrains particles inserted through a feed conduit 108 in a radially inward moving vortex wherein pulverization by the action of the particles against each other takes place. The smaller particles move toward the inner periphery of the vortex and eventually pass through a central opening into the collector 110. The freed gaseous fluid passes upwardly through duct 112. However, this gaseous fluid usually entrains some particles and these particles, when sticky, tend to adhere to the inner wall of the duct 112. The tubular screen 114 and ring 116 supplied with gaseous fluid through conduit 118 prevents such adherence, these members being identical to the corresponding members in FIGS. 1 and 2.
Although the screen 114 and its associated ports are disclosed in the drawings as being positioned in the duct 112, they may also be used in similar manner in the collector in order to prevent encrustation of the collector 110.
The invention claimed is: V
1. In a centrifugal type grinding mill wherein granular material is centrifugally passed through the mill in a vortex action by gaseous fluid whereby the particles pulverize each other and are then centrifugally separated into smaller and larger particles, and wherein the smaller particles are centrifugally exhausted through an outlet duct, the improvement comprising an antiencrustation assembly which comprises a screen in said outlet duct, said screen having a cross-sectional contour conforming to the interior cross-sectional contour of the duct but being radially inwardly spaced from the interior wall surface of said duct, and fluid delivery means to deliver gaseous fluid between said screen and said interior wall surface of said duct in a manner to propel said gaseous fluid radially inward through said screen.
2. The invention of claim 1 wherein said fluid delivery means comprises a conduit connected to a source of gaseous fluid, said conduit having an outlet between the screen and said interior wall surface of said duct.
3. The invention of claim 1 wherein said fluid delivery means comprises a manifold surrounding said screen, said manifold being connected to a source of gaseous fluid and being positioned between said screen and said interior wall surface, said manifold having at least one port to propel gaseous fluid through said screen.
4. The invention of claim 1 wherein said fluid delivery means comprises a manifold surrounding the external surface of said outlet duct, said manifold having at least one port in fluid communication with a mating port extending through the wall of said outlet duct to deliver gaseous fluid from said manifold between said screen and said interior wall surface of said outlet duct.
5. The invention of claim 1 wherein said fluid delivery means propels gaseous fluid radially straight through said screen.
6. The invention of claim 1 wherein said fluid delivery means propels gaseous fluid tangentially through said screen.
7. The invention of claim 3 wherein said manifold is provided with a plurality of ports.
8. The invention of claim 4 wherein said manifold is provided with a plurality of ports.
9. The invention of claim 1 wherein said grinding mill is a vertical type mill with an inlet section vertically spaced from a classification section, and said outlet duct is connected to said classification section.
10. The invention of claim 1 wherein said grinding mill is a horizontal type mill with an inlet section surrounding a classification section, said classification section having an outlet opening at the center of the mill, and a particle collection means and a gaseous outlet means leading in opposed directions from said outlet opening, said anti-encrustation assembly being selectively positioned in either or both of said particle collection means and said gaseous outlet means.