US3508714A - Multiple section fluid energy grinding mill - Google Patents

Description

April 28, 1970 N. N. STEPHANOFF 3,508,714

MULTIPLE SECTION FLUID ENERGY GRINDING MILL Filed Feb. '7, 1968 3 Sheets-Sheet 1 INVENTOR NICHOLAS N. STEPHA/VOFF ATTORNEY April 28, 1970 N. N. STEPHANOFF 3,508,714

MULTIPLE SECTION FLUID ENERGY GRINDING MILL Filed Feb. '7, 1968 3 Sheets-Sheet 2 INVENTOR NICHOLAS N. STEPHANOFF A TTORNEY April 28, 1970 N. N. STEPHANOFF 3,503,714

MULTIPLE SECTION FLUID ENERGY GRINDING MILL Filed Feb. '7, 1968 3 Sheets-Sheet 5 INVENTOR NICHOLAS IV. STEPHANOFF A T7'ORNEY United States Patent Int. Cl. B02c 19/06 U.S. Cl. 24139 5 Claims ABSTRACT OF THE DISCLOSURE A fluid energy mill utilizing at least two opposed generally annular mill portions. Solid particles are fed to either one or both mill portions and high velocity, high pressure fluid, either a gas or vapor, is propelled into the bottom of each mill portion to entrain the particles and to project the particles against each other. The impact of the streams of particles from the two mill portions are substantially angular and may be effected in an area between the two mill portions for a more direct impact, or the streams may be projected in the same annular path for a less direct impact and a greater degree of blending to form a circulating vortex.

This is a continuation-in-part of pending application Ser. No. 455,265, now Patent No. 3,456,887, issued on July 22, 1969, filed May 12, 1965.

This invention relates to an apparatus for grinding or pulverizing solid material, and it particularly relates to the so-called fluid energy method of grinding wherein a high velocity elastic fluid, such as a gas or vapor, is utilized as the grinding medium in a so-called double mill.

As stated in the aforementioned parent application, the ordinary fluid energy type of grinding mill comprises a curved or annular duct having a feed inlet adjacent the bottom portion for feeding the granular solid raw material into the mill and a plurality of tangentially arranged inlet nozzles at the bottom through which the elastic fluid is inserted at high velocities. This bottom portion constitutes the primary grinding chamber wherein the raw solids are caught up and hurled against each other by the incoming gaseous fluids which form a vortex because of the tengency of the fluid nozzles. The solid particles are pulverized by these impacts. The pulverized particles, because of the centrifugal force imparted thereto by the high velocity gases, together with the gaseous vortex, are impelled upwardly from the bottom grinding chamber through the so-called upstack portion of the curved or oval mill. The less finely ground particles, being relatively heavy, are impelled by their centrifugal force to the outer periphery of the vortex and continue to pass through the mill in accordance with the curvature thereof. The more finely ground particles, being relatively light, are entrained in the gaseous vortex and are carried by the viscous drag of the gases around the inner periphery of the mill. As the solid particles and gaseous vortex pass around the upper portion of the mill and then into the curved classifier portion, the lighter particles are carried by the used-up gases, or those which have lost a large part of their vortex energy, through an outlet duct opening from the inner periphery of the mill to a collection station, while the heavier particles and remaining vortex gases are carried by their centrifugal force around the outer periphery back to the grinding chamber where the heavier particles are again subjected to im act by freshly fed solids.

The above-described type of apparatus, although greatly more effective for its purposes than other heretofore known grinding devices, has certain disadvantages which prevent the full and most effective utilization of the fluid energy grinding method. For example although the grinding or pulverizing effect of this method largely depends on the momentum produced on the particles by the high velocity gases, it has rarely been possible, heretofore, to achieve a fluid velocity in the grinding chamber even approximating the velocity of the fluid entering through the nozzles. One of the main reasons for this is that when the fluid issuing from the nozzles picks up the solid particles from the feed means, the fluid must expend a substantial portion of its own energy in order to provide an impetus on the particles. Furthermore, in order to entrain the particles, it is necessary to effect an expansion of the fluid as it leaves the nozzle so that circumvallating eddy currents are formed which suck the solid particles into the fluid. Without such eddy currents, the velocity of the fluid as it leaves the nozzle would be so high that a high intensity dynamic barrier would be formed therearound. This barrier would prevent entrance of the particles into the fluid stream. Conversely, the decrease in fluid velocity deleteriously effects the number and force of impacts between the particles and results in a diminution in possible grinding effect.

In addition, the use of tangentially or angularly arranged fluid nozzles, while necessary to form the fluid vortex and to impel the particles through the mill, permitted the particles to collide with each other at relatively acute angles whereby there were often only glancing 'blows between the particles so that the full force of headon collisions was lost and the resultant grinding or pulverization was less effective.

Moreover, in the curved or oval mill, it has been found that the maximum mill circulating velocity obtainable is about 25% that of the velocity of the fluid as it leaves the inlet nozzle. This is due to the fact that although the velocity of the fluid and particles on the outer periphery of the vortex is increased because of their centrifugal force, the velocity on the inner periphery is so low as to measure zero or even negative velocity at times, especially when an insufficient amount of fluid enters through the nozzles so that there is not enough circulating fluid to fill the void created by the centrifugally outward shift of the fluid. The total velocity of the circulating fluid is, therefore, consideraly diminished relative to the entrance velocity. In practice, the circulation also depends, to some extent, on the frangibility of the material being processed, the weight and size of the particles, and the amount and rate of feed of the material, the heavier the load borne by the fluid, the slower the circulation.

It is, however, most desirable to obtain as rapid a circulation as possible because the higher the velocity, the more vigorous the vortex turbulence and the greater the degree of separation of the lighter finer particles from the heavier coarser particles. However, in the ordinary mill, not only is the velocity of the fluid diminished for the above reasons but the more rapid the circulation the less grinding effect is obtained due to the fact that the grinding is caused by opposed impact of the particles against each other whereas the circulation moves the particles in the same direction and, therefore, decreases the probabilities of impact.

The aforementioned parent application discloses a double mill assembly which overcomes the above and other problems of prior fluid energy mills and comprises a mill assembly wherein two generally annular mill portions are provided, each extending in an opposite direction from the other, but both joining at a common central upstack. Solid particles were fed into each mill portion from opposite directions and fluid nozzles were provided to inject high velocity fluid, such as air, steam or the like, into the mills. These fluids propelled the opposed streams of solid particles toward each other to effect a collision between them below the central upstack. The forces generated by the collisions served to pulverize the particles, which then passed up through the central upstack. The stream of pulverized particles including both the finer, lighter particles and the larger, heavier particles, then separated into two streams at the upper end of the upstack, one stream passing through one mill portion and the other stream passing through the other mill portion. As each of the streams passed through the respective mill portion, the lighter particles were centrifugally separated and passed from the mill, while the heavier particles passed down to be entrained in new fluid jet streams, together with newly fed particles, to be propelled against each other for further collisions.

The above-described double mill has been found to be very effective for its purposes. However, it has been found that, in addition to impacting against each other, the high velocity streams impacted against the chamber walls of the mill and caused excessive wear thereon because of the abrasive effect of the particles. Furthermore, the resultant ground particles were, for the most part, very jagged and irregular, and although this might be immaterial for some types of product, it could not be satisfactorily used for products where the particles were required to be relatively smooth and rounded. In addition, at least some of the energy generated in the mill was not fully utilized, thereby not attaining the utmost efl'iciency.

It is one object of the present invention to overcome the above disadvantages by providing a double mill wherein abrasion of the mill chamber walls is substantially obviated.

Another object of the present invention is to provide a double mill which is effective to produce particles of smooth, generally rounded surfaces.

Another object of the present invention is to provide a double mill" wherein the energy produced is substantially fully utilized in the grinding process.

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 double mill embodying the present invention.

FIG. 2 is a cross-sectional view taken on line 22 of FIG. 1.

FIG. 3 is a cross-sectional view taken on line 33 of FIG. 1.

FIG. 4 is a sectional view of a modified form of the mill of FIG. 1.

FIG. 5 is a sectional view of an alternative form of mill embodying the present invention.

Referring now in greater detail to the various figures of the drawings wherein similar reference characters refer to similar parts, there is shown in FIGS. 1, 2 and 3 a double mill, generally designated 10, comprising a right hand mill portion 12 and a left hand mill portion 14.

The mill portion 12 includes a downstack 16 integral with a curved inlet chamber 18 at the bottom. A feed duct 20, for feeding solid particles, leads into the top of the inlet chamber 18.

The inlet chamber 18 is provided with a plurality of fluid inlet nozzles 22 in fluid communication with a manifold 24. The manifold 24 is supplied with fluid under pressure, such as air or steam or any other desired gas or vapor, from a header 26 having one or more inlets 28 adapted to be connected to a source of the fluid under pressure (not shown).

It is to be noted that the nozzles 22 are arranged at progressively more acute angles relative to the horizontal, from right to left as shown, so that although the most left hand ones are directed to project a stream almost horizontally, they gradually direct their streams angularly upward so that the bulk of the total stream moves not only leftward but upward, the mean vector force bein g at an angle of approximately 40-45 The mill portion 14 is similar to mill portion 12 and also includes a downstack 30 integral with a curved inlet chamber 32 provided with a solids feed duct 34. The inlet chamber 32 is also provided with a plurality of fluid nozzles 36 arranged in gradually changing angular directions similar to the nozzles 22 but in opposite direction thereto. The nozzles 36 are also in communication with the manifold 24.

Both inlet chambers 18 and 32 merge into an upstack 38, and the fluid streams from the nozzles 22 and 36 blend (as shown in FIG. 1) to form a convergent stream passing upwardly into the upstack 38. The upper end of the upstack 38 is integral with two oppositely extending, curved elbow portions 40 and 42 which form the classifier sections of the mill. These classifier sections 40 and 42 merge with the upper ends of the respective downstacks 16 and 30, and at the areas of merger are provided the respective outlets or exhaust ducts 44 and 46 leading to a common or separate collection station or stations (not shown).

The mill portions are not annular in cross-section but are provided with contours best adapted to their functioning. In this respect, it is to be noted (as best seen in FIG. 2) that the downstacks 16 and 30 have a crosssection wherein the walls taper outwardly as they progress toward the center of the mill. This is for the purpose of concentrating the heavier particles, which pass in the outer peripheral portion of the mill, to provide greater pulverizing eifects in that area. The upstack 38 is, on the other hand, provided with its walls tapering inward toward the center since the upcoming stream of pulverized particles and fluid are concentrated at the center. FIG. 3 shows the cross-sectional contour of the two inlet chambers 18 and 32 and the dispositions of the fluid nozzles 22 and 36 therein.

The operation of the mill 10 is clear from the drawing. Briefly, the solid particles are fed through inlets 20 and 34, and, as they pass into the respective inlet chambers 18 and 32, they are entrained by the high pressure, high velocity fluid from the respective nozzles 22 and 36 and projected in the paths shown in FIG. 1. As seen in FIG. 1, although the opposite streams of particles impact against each other, the major portion of such impacts are angular rather than direct. In other words, there is a sort of blending. The sum vector force is therefore upwardly. This has various important results. One result is that there is very little, if any, bombardment of the chamber walls, thereby increasing their longevity. Another result is that the upward flow through the upstack is increased because of the total upward direction of the streams. This provides for increased velocity of the circulating vortex. A third result is that because of the tangential impact of the major portion of the particles against each other, there is a sort of rolling effect between the particles which causes a smooth, rounding thereof rather than the formation of jagged edges such as would be caused by direct cross-impact.

As the stream passes upwardly through the upstack 38, it separates at the top into two opposed streams, one passing through the classifier section 40 and the other through the classifier section 42. The streams passing through these sections have the lighter, smaller particles on the inner periphery and the heavier, larger particles on the outer periphery. The lighter particles pass through the respective exhaust ducts 44 and 46, while the heavier particles pass down, while in turbulence, whereby additional pulverization continues to take place, toward the respective inlet chambers 18 and 32. During this passage, they are intermixed with newly fed particles from the respective inlets 20 and 34 and are recycled therewith for another pass through the mill.

In FIG. 4 there is shown a double mill, generally designated 100, which is, in most respects, identical to the mill shown in FIGS. 13, except that there is only one feed duct 102 leading into the right hand mill portion 104, and only one exhaust duct 106 leading from the same mill portion 104. The left hand mill portion 108 has neither a feed inlet nor an exhaust duct.

Both inlet chambers 110 and 112, respectively, are provided with fluid nozzles 114 and 116, respectively, which are identical to those shown in FIG. 1. The re sultant paths of impact are, therefore, the same. However, since the particles are all initially travelling from right to left, the pulverizing action is primarily due to the vortex action of the impinging streams rather than direct counter-impact of the particles. The bulk of the smaller, lighter particles then pass up through the upstack 118. However, a large proportion of the larger, heavier particles, while still under the initial velocity due to their direction of feed and the fluid from nozzles 114, kick over into chamber 116 and pass up through the stack 120 of the left hand mill, which, in this case, also acts as an upstack. These heavier particles then circulate, While in turbulence, through the stack 120 and the elbow portion 122, pulverization taking place meanwhile. As they pass from elbow portion 122, they descend into the top of upstack 118 and there they are impacted by the rising stream of lighter particles and the high energy fluid passing upwardly through the stack 118. This results in further pulverization somewhat like that which takes place between the opposed streams in mill 10 in FIG. 1. There is also much turbulence at this area. The resulting pulverized particles, blended together, then pass through the classifier section 124 of the right hand mill portion and separation takes place whereby the lighter particles pass through the exhaust duct 106 while the heavier particles pass down through downstack 126 for another pass.

FIG. 5 illustrates another embodiment of the invention wherein the mill, generally designated 200, is almost identical to that shown in FIG. 4 with only one feed duct 202 leading into the right hand mill portion 204 and one exhaust duct 206 leading from the same mill portion 204, the left hand mill portion 208 having no inlet or outlet. However, although the fluid nozzles 210 of the inlet chamber 212 are identical to those in FIGS. 1 and 4, the nozzles 214 in the chamber 216 are slanted in the same direction as the nozzles 210.

In the mill 200, the solid particles are fed through duct 202, entrained in the jet streams from nozzles 210 and a portion thereof, consisting of the lighter particles, pass upwardly through the central upstack 216, as indicated in the drawings. The remainder kicks over into the chamber 216 of the mill portion 208 and is further accelerated by the force of the jet streams from the nozzles 214. They then pass through the stack 218, in turbulent stream, where they pulverize each other in the same manner as in the ordinary single mill. The stream then passes through the elbow portion 220 and a portion thereof descends through the upstack 216 to impact with the portion of the particles ascending therethrough together with the ascending fluid from the nozzles 210, the

remainder passing into the classifier section 222 by centrifugal force. The particles impacting against each other in stack 216 further pulverize each other and then pass upwardly, under pressure of the fluid from nozzles 210, into the classifier section 222. The stream then passes through the mill portion 204, the lighter particles passing through exhaust duct 206- and the heavier particles passing down through downstack 224 for another pass.

As indicated above, although the apparatus described herein has been illustrated in each case as having a central upstack with consequent upwardly circulatory movement, it is equally within the scope of the present invention to use a central downstack with downwardly circulatory movement.

The invention described above has been illustrated as utilizable for grinding or pulverization of solid particles. However, any of the above-described apparatus can also be used for effective mixing of different types of particles as well as for coating particles whereby the particles to be coated are projected from one side and the coating material from the other so that coating is effected by impact under the high velocities present. In the same manner, particles can be metalized or cold-welded together. This apparatus may also be used for the removal of liquids and for dehydrating, especially if additional heat is provided. Such additional heat energy may be provided by heated elastic fluids or auxiliary heating means. It is, furthermore, possible to effect certain chemical reactions in this manner without the heat energy usually required although, if desired, heat energy can be simultaneously supplied by using heated elastic fluids or auxiliary heating means in the grinding chamber. In this respect, it is to be noted that liquids for coating, chemical reaction, quenching, etc., may be ejected through the booster orifices into the fluid and particle streams, if so, desired.

It is further to be noted that although the apparatus, as described above, has, in each case, consisted of two opposed ductworks, it is within the scope of the present invention to provide three or more opposed impact streams intersecting at a central impact area and a corresponding number of three or more recycling ductwork systems.

Obviously, many modifications of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

The invention claimed is:

1. Apparatus for treating solid particles comprising at least two generally arcuate mill portions connected by a common stack forming part of each mill portion, at least one mill portion having an inlet for feeding solid particles to be treated into the mill in a selected path and an outlet for exhausting centrifugally separated relatively light particles resulting from the treatment from the mill, each mill portion having an inlet chamber, a plurality of nozzles in each inlet chamber, each of said nozzles being in fluid communication with a source of fluid under pressure, the nozzles in each inlet chamber being constructed and arranged in such manner that each nozzle is at a different angle relative to said selected path of feed of the solid particles than the nozzles adjacent thereto, the angles of the nozzles varying gradually from one nozzle to the next.

2. The apparatus of claim 1 wherein the nozzles in each inlet chamber are arranged in substantially equal but opposite angles relative to the corresponding nozzles in the other inlet chambers to provide opposing fluid streams that impact and blend in said common stack, the angles of the nozzles being such that the major impact forces are substantially tangential.

3. The apparatus of claim 2 wherein each mill portion is provided with an inlet and outlet, the outlet in each mill portion being positioned at approximately the juncture between an arcuate classification section and a corresponding downstack leading to the corresponding inlet chamber, each classification section extending between and merging with said common stack at one end and the corresponding downstack at the opposite end.

4. The apparatus of claim 2 wherein only one mill portion is provided with an inlet and outlet.

5. The apparatus of claim 1 wherein the nozzles in each inlet chamber are arranged at substantially the same angles as the corresponding nozzles in the other inlet chambers to effect an acceleration of at least a part of the fluid flow from one chamber to the next.

ROBERT C.

D. KELLY,

References Cited UNITED STATES PATENTS RIORDON, Primary Examiner Assistant Examiner

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