US3550868A - Fluid energy milling solid granular material - Google Patents

Description

United States Patent inventor Nicholas N. Stephanofl Haverford. Pa. Appl. No. 813,590 Filed Apr. 4, 1969 Division of Ser. No. 455,265, May 12, 1965, Patent No. 3,456,887. Patented Dec. 29, 1970 Assignee Fluid Energy Processing 8: Equipment Co.

Lansdale, Pa.

a corporation of Pennsylvania FLUID ENERGY MILLING SOLID GRANULAR MATERIAL 6 Claims, 9 Drawing Figs.

US. Cl 241/5 Int. Cl. B02c 19/06 Field of Search 241/5, 39, 40

References Cited UNITED STATES PATENTS 2,735,626 2/1956 Trost 241/39 Primary Examiner-Robert C. Riordon Assistant Examiner-Donald G. Kelly Attorney-Arthur A. Jacobs ABSTRACT: The pulverization of solid particles by propelling two opposed streams of the particles against each other by means of high-pressure fluids. The impact between the particles is effected in a central impact chamber which is in communication with a perpendicular stack. The pulverized particles pass through this perpendicular stack and are separated into two opposed streams. The opposed streams pass in opposite directions through opposed centrifugal mills where separation of the lighter and heavier particles takes place, and from each of which the heavier particles are returned to the impact chamber for further impacts with each other as they travel in opposed directions.

PATENTEU UEB29 I976 SHEET 1 OF 3 INVENTOR. Nicholas N. Stephanoff A T TOEE Y PATENTED UEE29 I970 SHEET 2 OF 3 INVENTOR. Nicholas NS fePhunoH.

ATTORNEY PATENTEU'UEEZS m0 SHEET 3 OF 3 INVENTOR. Nicholas N. Sraphano A T TORNE Y FLUID ENERGY MILLING SOLID GRANULAR MATERIAL This is a division of applicationSer. No. 455,265, filed May 12, 1965, issued as U.S. Pat. No. 3,456,887 on Jul. 22, 1969.

This invention relates to a method and apparatus of 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.

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 grandular 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 tangency 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 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, whil'ethe 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 impact by freshly fed solids.

The above described type or 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 evenapproximating 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 c'ircumvallating 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 head-on 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 percent that of the velocity of the fluid as it leaves the inlet I 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 cir culating fluid to fill the void created by the centrifugally outward shift of the fluid. The total velocity of the circulating fluid is, therefore, considerably diminished relative to the en trance 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 isthe 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.

- and, therefore, the maximum separation and classification of 'plates shown in FIG. 5.

finer and coarser particles is obtained.

Another object of the present invention is to provide a method and apparatus of the aforesaid type which can be effectively utilized not only for grinding or pulverization but also for various other purposes such as coating, mixing, metallizing cold-welding, etc.

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 anapparatus embodying the present invention.

FIG. 1A is a cross-sectional view taken on line lA-IA of FIG. 1.

FIG. 2 is a fragmentary sectional view of a modified form of the apparatus of FIG. 1.

FIG. 3 is a sectional view of a second embodiment of the present invention.

FIG. 4 is a sectional view of a-third embodiment of the presentinvention.

FIG. 5 isa sectional view of a fourth embodiment of the present invention. Y

FIG. 6 is a front elevational view of oneof the nozzle orifice FIG. 7 is a sectional view of a modified form of the apparatus shown in FIG. 5. 1

FIG. 8 is a sectional view of another modified form of the apparatus shown in FIG. 5.

In accordance with the present invention, two opposing streams of high velocity fluid having substantially the same linear velocity and intensity and having solid particles entrained therein, are directed toward each other to impact at a common intermediate or central impact area. A common upstack or downstack, as the case may be, leads from the impact area into separate and opposed curved classifier sections where the finer particles 'are separated and passed to a collection station while the heavier particles are recycled through separate and opposed retum'ducts back into the respective opposed fluid streams for regrinding.

It is highly important that the two opposing streams be of substantially equal velocity and strength since only in this manner can the maximum opposed kinetic energy be utilized to secure maximum impact and, therefore, maximum pulverization. As a consequence it is also important that there be a common upstack (or downstack) leading laterally from the central, intermediate, common impact area since the full energies of the two fluid streams, after impact, merge and are directed laterally into the upstack. This maximum energy is translated into a rapid movement of the fluid vortex and pulverized particles through the upstack and around into the classifier section and then back through the return ducts. In this manner, not only is maximum grinding or pulverization obtained but also maximum circulatory velocity and, therefore, maximum separation and classification of the fluid and solid particles.

Referring now in greater detail to the various FIGS. of the drawings wherein similar reference characters refer to similar parts, there is shown in FIG. 1 a mill, generally designated 10, comprising a straight grinding chamber 12 having an inlet duct 14 at one end and an opposed inlet duct 16 at the opposite end. The chamber 12 is preferably provided with a trapezoidal cross-sectional contour, such as shown in FIG. 1A, wherein the lower portion is relatively narrow and the sides taper upwardly and outwardly to a relatively wide upper portion. With this type of cross-sectional configuration, if there is less than a maximum amount of material in the chamber it will be concentrated in the lower portion of the chamber so that the probabilities of impact between the particles will be greater. However, the grinding chamber 12 may also be of circular configuration or of any other configuration which is desirable and feasible.

The ducts l4 and 16 are identical, each comprising a Venturi tube with one end opening into the grinding chamber 12 and the other end being closed except for an aperture through which projects an inlet nozzle, indicated at 18 and 20 respectively. Each inlet nozzle 18 and 20 is connected to a source (not shown) of elastic fluid (gas or vapor) under high pres sure. A hopper, as at 22 and 24 respectively, opens downwardly into the respective venturi duct adjacent the inlet end of the respective nozzles 18 or 20.

At the center of the grinding chamber 12 is provided a central impact area 26 substantially equidistant from the two opposed ducts 14 and I6. Extending upwardly from this impact area 26 is a common upstack 28 which may be either of the same cross-sectional shape as shown in FIG. 2 or of circular or other desirable shapes. The upstack, at its upper end, divides into two separate and oppositely curved arcuate classifier sections, respectively designated 30 and 32, which are preferably circular or oval-shaped but which may be of the same crosssectional shape as the upstack 28. These classifier sections 30 and 32 are each provided with an exhaust duct, as at 34 and 36 respectively, which lead to a common or separate collection stations. Each classifier section also merges with a corresponding return section, as at 38 and 40 respectively, leading back into the grinding chamber 12 adjacent the respective duct 14 or 16.

A pair of annular headers 42 and 44, one on each side of the central impact chamber 26, are optionally provided. These plates are connected to a source of elastic fluid under pressure and each is provided with at least one, but preferably a plurality, of nozzles, designated 46 and 48 respectively, which extend into the grinding chamber 12 and act as high pressure fluid nozzles. Fluid jets from these nozzles, entering the grinding chamber, serve as boosters to accelerate the flow of the opposed streams before they collide in the impact chamber.

Instead of an upstack, a downstack may be used with corresponding classifier and return sections, whereby the apparatus would be a reverse form of that shown in FIG. 1 but would function in the same manner..

The solids feed means are here illustrated as hoppers for gravity feed. However, any other desirable and feasible type of feed means can be substituted such as a screw feed, a fluid pressure or suction feed, a rotary valve type feed, etc.

In operation, high velocity streams of elastic fluid such as compressed air, steam, or the like, are passed through the nozzles 18 and 20, the force of the two streams being substantially equal so that they impact in the central area 26. At the same time, solid particles are fed through the hoppers 22 and 24 and are entrained in the high velocity fluid streams, adjacent the inlets of the respective nozzles 18 and 20. The two fluid streams, with the solid particles entrained therein, then pass through the venturi ducts, which increase their velocity, into the grinding chamber 12 where they impact at 26. Since the particles collide head on, rather than with glancing blows as in the case where tangential fluid nozzles are used, and since the forces of momentum thereon are substantially equal and opposite, the maximum amount of pulverization is obtained.

As indicated above, the orifice plates 42 and 44 are optional and there is no necessity, in most cases, for the their use. However, in those cases where it is desirable to use them in order to further increase the velocity of the opposed streams, they are very effective in restoring most, if not all, of the velocity lost by the fluid in entraining and moving the solid particles fed thereinto. I

Since the upstack 28 leads directly from the central impact chamber or area 26, the fluid vortex resulting from the impact and the solid particles, both of which constitute the impact residue, pass directly up through the upstack under maximum energy conditions. Consequently, the circulatory forces are at a maximum.

When the fluid vortex and solid particles reach the upper end of the upper end of the upstack 28, one part thereof passes through the classifier section 30 and the other part passes through the classifier section 32. The larger, heavier particles, having a greater centrifugal force, remain on the outer periphery of the fluid vortex and pass down through the return sections 38 and 40 to the grinding chamber 12 where they are caught up in the fluid streams issuing from the ducts l4 and 16. The smaller, lighter particles are caught up by the viscous drag of the vortex fluid and remain on the inner periphery thereof to be carried out through the exhaust ducts 34 and 36.

It should be noted that the classifier and return sections are preferably of gradually diminished width because as man many of the solid particles become ground into finer sizes requiring less space, and are then exhausted, leaving still more space, the reduction in width of the ductwork acts to better concentrate the particles of relatively large size and fluid being recycled.

In FIG. 3 there is shown a modified form of the invention wherein the apparatus is essentially similar to that of FIG. 1 except that the venturi portions of the opposed fluid pressure nozzles are incorporated directly into the grinding chamber and the return ducts lead directly thereinto instead of into the separate venturi passages shown in FIG. 1.

In FIG. 2 there is shown a modified form of the apparatus of FIG. 1 wherein the opposite portions of the grinding chamber 12A are inclined upwardly toward the impact chamber 26A from which leads the upstack 28A.

This inclination is sometimes desirable because it-provides an upward as well as horizontal movement of the opposing streams which increases the upward velocity of the impact residue through the upstack 28A and, therefore, increases the circulatory velocity through the apparatus.

The apparatus of FIG. 3 is generally designated 50 and comprises opposed nozzles 52 and 54 leading from a source of high pressure elastic fluid (not shown) into the otherwise closed ends, shown at 56 and 58 respectively, of a grinding chamber 60. The ends 56 and 58 are relatively wide and are each provided with a solids feed inlet, as at 62 and 64.

Extending between each end 56 and 58 and a central impact area or chamber 66 is a relatively narrow throat portion, as at 68 and 70 respectively, from 'which extends a gradually widening passage, as at 72 and 74 respectively. This construction provides a pair of oppositely-disposed venturi passages which actually serve as opposed convergent-divergent nozzles for propelling the fluid streams, with the-particles entrained throat portions 68 and 70. Since the pressure in these throat portions is at a minimum, there is a suction effect provided that helps draw. the return fluid and particles into the opposed impacting streams and, therefore, increases the return flow which, in turn, increases the circulatory flow.

The grinding chamber in this form of the device and in thosehereinafter described, are of circular rather than trapezoidal shape but a trapezoidal shape may be used, if desired.

In FIG. 4 there is illustrated a form of the invention which is similar to that of FIG. 3 except that the solids feed inlets lead directly into the return ducts. By passing the'solids directly into the return ducts, the particles are given an initial acceleration which is added to the further acceleration provided by the fluid inlet nozzles, thereby increasing their velocity and providing a greater circulatory velocity.

The particular structure embodying this form of the invention, as shown in FIG. 4, comprises a mill, generally designated 100, having a grinding chamber 102 with opposed high-pressure fluid nozzles .104 and 106 at opposite ends 108 and 1100f the grinding chamber 102. The grinding chamber 102 then narrows to form throats 112 and 114, after which it again widens from either end toward the relatively wide central impact area 116, whereby a venturi or convergent-divergentduct is formed. An upstack 120 leads from the central im- 1 pact area 116 upwardly to an upper end where it divides into two oppositely curved classifier sections l22and 124. Each classifier section 122 and 124 is provided with an exhaust duct, as at 126 and 128 respectively, and then merges with a return duct, as at 130 and 132.

Each return duct 130 and 132 is provided witha solids feed inlet, as at 134 and 136. respectively. The inlets 134 and 136 are illustrated as being of the venturi type with fluid pressure nozzles, as at 138 and 140, leading thereinto from a source of high pressure fluid (not shown). The high-pressure fluids from the nozzles 138 and 140 entrain the solid particles from the hoppers of inlets 134 and 136 and are then given increased velocities as they pass through the inlet venturi passages. However, any other type of desirable feed means, such as screw feeders, rotary valve feeders, and the like, may be substituted.

The fluid streams with the entrained solid particles pass through the inlets 134 and 136 and are caught up by the circulating fluid vortex descending the respective return ducts so that the fed raw materials receive an added impetus prior to entering the grinding chamber 102 and then receivea further impetus as they pass through the throats 112 and 114 of the grinding chamber.

In FIG. 5 there is shown a form of the invention, generally designated 150. that comprises a grinding chamber 152 similar to that shown at 102 in FIG. 4 in that it comprises two opposed venturi or convergent-divergent sections, one on each side of the central impact area 154, each encompassing a throat portion, as at 156 and 158 respectively. Intermediate each throat portion and the corresponding return duct is an annular header or orifice plate. as at 160 and 1 62 respectively. Each of these. headers. shown in front elevationin FIG. 6, is in fluid connection with a source of elastic fluid under pressure (not shown) and is provided with at leastone, but preferably aplurality, of tangential orifices indicated at 164 for plate and at 166 for plate 162.

The central impact area opens up into the common upstack 168 leading into the oppositely curved classifier sections 170 and 172, provided with exhaust ducts 174 and 176 respectively, and leading into return ducts 178 and 180 respectively.

Solids feed inlets I82 and 184, similar to inlet inlets 134 and 136, are connected to the respective return ducts 178 and 180.

In this fonn of the apparatus, the opposed fluid nozzles are entirely eliminated and only the circulatory velocity of the fluid passinginto the grinding chamber from the return ducts is utilized. However, not only is a large amount of energy expended by the fluid in 'entraining and moving the solids fed through the inlets 180 and 182, as explained above, but, in addition, some of the. circulating fluid is lost by exhaustion through the exhaust ducts. The orifices 164 and 166 are, therefore, used not only as booster nozzles to increase the velocity of the fluid as it passes from either end of the grinding chamber toward the central impact area, but also to replenish spent and exhausted recycling fluid. The convergent-divergent construction of the two opposite portions of the grinding chamber also aids in increasing the velocity of the fluid.

Between each of the return ducts 220 and 222 and its respective chamber portions 204 and 206 are provided at least two orifice plates, designated 224 and 226 on the one side and 228 and 230 on the other. Between the plates 224 and 226 is a I duct portion 232 which tapers inwardly so that it forms a socalled abrupt nozzle section between the two orifice plates. The same is true of the opposite duct portion 234 between the orifice plates 228 and 230. These abrupt nozzle portions, supplied with high pressure elastic fluid from the orifices in their V respective plates 224 and 228, boost the velocity of the return fluid from the respective return ducts 220'and 222 back to approximately acoustic velocity. This boosted fluid then receives a further boost into the superacoustic velocity range as it passes through the throat portions of the chamber sections 204 and 206 where they are subject to the additional force of the high-pressure elastic fluid issuing from the orifices of the respective plates 226 and 230.

i The orifice plates 224, 226,. 228'and 230 are connected through valved conduits to a manifold 236 which is, in turn, connected to a source of fluid under pressure not shown).

The solids feed is provided by inlets 238 and 240 connected to the respective return, ducts 220 and 222, these inlets being preferably of the same type as those shown in FIGS. 4 and 5.

Although two orifice plates are illustrated at each side, it is to be understood that as many as desired may be used in series, depending on the amount of boosting action desired.

The apparatus of FIG. 7 is particularly adapted for most effective treatment of large, heavy or relatively nonfrangible solid particles that require the force supplied by superacoustic velocities. However, where smaller, lighter or more frangible material is being processed, it is usually preferable to use an apparatus such as illustrated in FIG. 8.

The apparatus of FIG. 8, generally designated 250, is very similar to thatof- FIG. 7 in that it includes-a central impact area 252 from'which leads an upstack 254 dividing into oppositely- curved classifier sections 256 and 258 having respective exhaust ducts 260 and 262' and leading into return ducts 264 and 266 that are. respectively provided'with solids inlets 268 and 270. It' is also similar in that between each of the respective return ducts and their respective opposed grinding chamber sections 272 and 274 there is provided a pair of ori-.

effect is in the vicinity of acoustic velocity rather than superacoustic as in the apparatus of FIG. 7.

In this apparatus, too, the number of orifice plates in series on each side may be varied as desired.

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 metallized 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.

lclaim:

1. A method of treating solid particles which comprises propelling at least two fluid streams with solid particles entrained therein toward each other at substantially equal velocities to effect an impact at a central impact area, passing the impact residue comprising the resultant fluid and both lighter and heavier solid particles away from said impact area in a direction transverse to the directions in which said fluid streams were propelled toward each other, dividing said impact residue into at least two diverging streams, separating and removing the lighter particles from said diverging streams, intermixing each of said diverging streams with fresh solid particles and propelling each of the resultant mixtures toward each other at substantially equal velocities to effect further impact at said impact area.

2. The method of claim 1 wherein said diverging streams of impact residue are each entrained in a fresh mixture of fluid and solid particles while said fresh mixtures are being propelled toward each other.

3. The method of claim 1 wherein said fresh solid particles are added to the respective diverging streams prior to the entrainment of said diverging streams in fresh propelled fluid streams.

4. The method of claim 1 wherein each of said resultant paths of travel toward each other.

6. The methods of claim 1 wherein said resultant mixtures are propelled toward each other at initial velocities which are increased by passing each of said resultant mixtures through at least one constricted passage.

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