US3224686A - Impact pulverization-classification - Google Patents

Description

Dec. 21, 1965 c. WALLACE, JR 3,224,635

IMPACT PULVERIZATION-CLASSIFICATION Filed April 27, 1962 3 Sheets-$heet 1 INVENTOR CURT1S C.WALLACE, JR-

ATTORNEY 3 Sheets-Sheet 2 Filed April 27, 1962 NQE A mm L m 5 MW c Q S H w W Y B hm ATTORNEY r Dec. 21, 1965 c. c. WALLACE, JR 3,224,686

IMPACT PULVERIZATION-CLASS IFICATION Filed April 27, 1962 3 Sheets-Sheet 3 INVENTOR CURTIS C.WALL.ACE, JR.

ATTORNEY United States Patent U 3,224,686 ill/[PACT PULVERllZATION-CLASSIFICATION Curtis C. Wallace, Jr., Newark, Del., assignor to E. l. du lPont de Nemours and Company, Wilmington, lDeL, a corporation of Delaware Filed Apr. 27, 1962, Ser. No. 190,761 14 Claims. (Cl. 241-49) This invention relates to a method and apparatus for impact pulverization-classification, and particularly to such a method and apparatus wherein the classification is conducted immediately after the impact size reduction, while the pulverized product is still completely dispersed in the carrier gas with which the apparatus is swept.

The practice in the impact pulverization art has hitherto been to conduct size reduction and product classification as completely independent operations, within different pieces of apparatus. This has not only been expensive in terms of equipment cost but, more important- 1y, has necessitated redispersion of the pulverized product within a carrier gas before classification could be effected as a separate step. It has been found that freshly pulverized material is subject to agglomeration to a serious degree in the course of collection and that redispersion in gas prior to classification does not by any means yield the sharp product classifications obtainable when pulverization and classification follow one another in rapid sequence without intervening product collection. Some advantage of this principle has been taken in mills which, though varied, conduct their solids disintegration by a vortex action wherein the effective comminuting agency is inter-particle rubbing, such as the design taught in US. Patent 2,963,230. However, there has apparently been no appreciation or utilization of the concept in impact pulverization per se. I have found, as a matter of fact, that sequential pulverization-classification is very much more beneficial when impact pulverization is the effective size reduction agency, because full advantage can now be taken in the classification of the centrifugal forces acting on the several masses of particles, which centrifugal forces are either not generated in vortex pulverization or are of such small magnitude as to be uni'rnportant.

Accordingly, an object of this invention is to provide a method and apparatus for impact pulverization-classification wherein the classification is effected immediately after the pulverization and while the particles are in dispersion in the carrier gas stream. Another object of this invention is to provide a pulverization apparatus which is low in cost and maintenance, compact, and one for which the power consumption is low. Another object of this invention is the provision of a pulverization apparatus adapted to the interchangeable utilization of different types of close-coupled classification apparatus therewith. The manner in which these and other objects of this invention are obtained will become apparent from the following detailed description, and the drawings, in which:

FIG. 1 is a side elevation view of a preferred embodiment of complete impact pulverization-classification apparatus according to this invention,

FIG. 2 is a sectional side elevation view of the impact pulverization-classification zone of the apparatus of FIG. 1, with the connections to recycle ducts omitted,

FIG. 3 is a sectional side elevation view of the pulverization-classification zone of a second embodiment of apparatus especially adapted to the processing of materials the particles of which have a relatively high tendency to agglomerate, the showing being limited solely to the left-hand half of the apparatus, the right-hand half being identical,

Fatented Dec. 21, 1965 FIG. 4 is a fragmentary plan view taken on line 44 of FIG. 2,

FIG. 5 is a longitudinal section of a preferred design of classification fluid nozzle adapted to use with the apparatus of FIG. 3, and

FIG. 6, which is a section on line 66, FIG. 3.

Generally, this invention comprises a method and apparatus for impact pulverization-classification of solids comprising, in sequence, subjecting the solids to centrifugal impact pulverization in the presence of a concurrently flowing stream of carrier gas, thereby effecting the throwout of coarse pulverized solids by the combined effects of centrifugal force and gravity, and the entrainment of fine dispersed pulverized solids in the carrier gas, introducing an additional quantity of carrier gas in vortical flow to the carrier gas entraining the fine dispersed pulverized solids in suflicient quantity to effect a classification of the dispersed pulverized solids into a first fraction of fine particle size concentrated centrally of the vortical fiow and a second fraction of coarse particle size concentrated peripherally of the vortical flow, and withdrawing at least the first fraction as a separate pulverized product.

Impact pulverization can be conducted most efficiently in rotary mills, such as those generally shown in US. Patent 2,694,492 and 2,981,490, employing a rapidly rotating disk provided with peripherally disposed teeth past which solids to be pulverized are flung under extreme centrifugal force loadings against either circumferential anvil surfaces, or past interdigitating stationary or counter-rotating teeth which, in themselves, constitute anvil surfaces, thereby effecting solids pulverization by very high energy impact. It is this type of impact pulverization which is intended by the term centrifugal as used herein, it being obvious that a great variety of designs of such pulverizing apparatus now exist or can be devised to meet specific pulverization requirements. In every case, the rapid rotation of the pulverizer disk acts as a fan impeller and, accordingly, drives a considerable amount of air through the mill along with the solids in the course of pulverization. This air constitutes a carrier vehicle for the finer-sized products of pulverization, and that which is supplied to the centrifugal mill feed inlet is hereinafter referred to as carrier gas, whereas that which is added after the pulverization to provide the high speed vortical classification medium is denoted additional carrier gas. It will be particularly understood that the identity in terms is purely functional, in the sense that the additional carrier gas need not be of the same composition as the carrier gas supplied with the raw feed and, in fact, in the embodiment of apparatus shown in FIG. 3 is steam, as distinguished from air for the gas introduced at the feed inlet of the mill.

An important advantage of my method and apparatus is the conservation of energy imparted to the carrier gas during the centrifugal impact pulverization, so that the latter complements and greatly reinforces the classification effect obtained by the introduction of the additional carrier gas in vortical flow immediately following the pulverization. Even more important is the fact that classification is, by this invention, obtained immediately after impact pulverization and before there is any intervening agglomeration of the freshly pulverized material. Performance tests have shown that products of vastly improved properties are thereby obtained, especially as regards heat-sensitive materials which suffer thermal degradation in the usual grinding equipment and also substances which must have uniform particle fineness throughout, such as grit-free paint pigments and the like.

Referring to FIGS. 1 and 2, one embodiment of apparatus according to this invention, utilizing air as the carrier gas throughout, is provided with a rotary impact ice pulverizer having a drive motor and frame such as that shown in US. Patent 2,981,490 hereinbefore mentioned. Thus, the apparatus frame 10 is built up from circular pipe lengths 11 as uprights and rectangular or square cross-section tubes 12 as horizontal members, several of which latter are broken away to better show the details of inter-component staying. The pulverizer drive motor 16 is supported with drive shaft vertical by attachment to a channel member 17 (cut away vertically in FIG. 1), and the drive is via sheave 18, belt-connected to sheave l9 keyed to the pulverizer shaft 20. Inter-bracing of drive motor 16, frame 10 and the shaft housing 21 of the pulverizer is secured by turnbuckle fitting 22.

The pulverizer is suspended from horizontal I-beam supports 26 welded or otherwise attached to tubes 12, the housing indicated generally at 27 constituting both the impact pulverization zone and the classification chamber, whereas housing 28 immediately thereunder constitutes the fine product oiftake volute communicating, via connection flange 29, with a screening bag air exhausting auxiliary not shown.

A double-ended motor 30 is mounted with drive shaft upright so as to drive, at one shaft end, a suction fan 31 (FIG. 2) and, at the other shaft end, a similar classification air supply fan 32, shown only partially in broken line representation within air supply volute housing 33, through keyed connections at the two shaft ends. The classification air supply line is duct 34, typically 6" inside diameter, opening into the intake of fan 32. Classification air is delivered through duct 35 discharging into the annular air supply receiver 38 (FIG. 2) encircling housing 27, while ducts 39 are optionally provided for recycle of coarse pulverized solids to the impact pulverization zone. Port 40 constitutes an inlet for fresh solids feed to the apparatus, it being understood, of course, that one or more of the ducts 39 may be disconnected to thereby afford additional fresh feed supply inlets if these are required in preference to recycle.

Referring to FIG. 2 particularly, the impact pulverizer disk 45 consists of a generally circular imperforate plate fixedly attached to the lower end of shaft 20 by nut 46. A multipilcity of radially disposed solids-directing vanes 47 are provided around the entire upper face of disk 45, which vanes not only impart high centrifugal energies to solids introduced to pulverization but also draw in a large amount of carrier air through port 40 as well as through ducts 39. The actual pulverization is effected by solids impact, either direct or ricochet, against stationary pins 48 depending from stator ring 49, or against the lower encircling face 50 thereof. An enhanced pulverizing effect is frequently obtained by provision of a row of rotating pins 51 integral with disk 45.

The inside periphery of air supply receiver 38 is provided around its entire circumference, at intervals in the range of about to 15, with a plurality of additional carrier gas supply louvers 55 (FIG. 4), typically fifty in number, each defined by a pair of pivotally mounted plates 56, which can all be adjusted simultaneously by provision of an interconnecting ring (not shown) shiftable manually from outside housing 27. These louvers supply classification air from receiver 38 to classification chamber 57 along tangential lines. For the design detailed, the vortical flow of classification air is generally counter-clockwise, as viewed in top plan view, thereby matching the ascribed directions of rotation of disk 45 and fan 31, indicated by adjacent arrows. Obviously, these directions are a matter of choice and could be just as conveniently all opposite in sense.

As an aid to classification, there is provided an annular plate 60, which is typically 2" wide x A" thick, tapered to the outside edge from the underside at an angle of about 15". This plate is attached to the underside of pulverizer disk 45 by lugs 61, which lugs are preferably extended below plate 60 to support annular lower plate 62 defining the floor of chamber 57. Thus, disk 45 and plates and 62 all rotate together by virtue of the rigid common attachment afforded by lugs 61. Plate 62 is cut away centrally at 63 to provide open communication with the intake side of fan 31. Also, the periphery of plate 62 is machined to form short length air propulsion vanes 64 between which coarse solids thrown out from the impact pulverization, or ejected outwardly during classification, can both pass into a circularly extending trough 65, and thence via ducts 39 connected therewith to recycle.

It will be seen, from FIG. 2, that the radially inward under-extremity of plate 62 is adjacent to the shroud ring 66 of fan 31, and the shroud ring is formed with an upstanding cup extension 67 interposed between a pair of depending lips 68 on plate 62, to thereby provide a labyrinth seal between the two rotating members. The top of housing 28 is closed off by a thin gage stack piece 69, which is fixedly supported from the radially inward edge of the upper wall of the housing, as by welding or screw attachment, not detailed. The construction is such that vanes 64 of plate 62 and the vanes of fan 31 both apply moderate suction on the opposite sides of the labyrinth seal, thereby sweeping it clear of any particulate solids which might otherwise collect there, and at the same time keeping the air of the room in which the apparatus is located clean of the products of pulverization.

In operation, it will be understood that fresh solids to be pulverized, introduced through port 40, and recycled solids returned for re-pulverization via ducts 39, both enter the apparatus by delivery to the center region of disk 45. From here the solids are thrown outward violently under the high speed of rotation of disk 45 (typically 3000 rpm. for a disk 16 in diameter), impacting against teeth 48 or 51 and also against ring face 50, thereby effecting a high degree of pulverization. Delivery of pulverized solids is directly into classification chamber 57, which is in open communication with the pulverized product discharge side of impact pulverizer disk 45. Relatively coarse non-entrained solid particles travel more or less 00- parallel to the surface of face 50 extended and quickly impinge on vanes 64, to be immediately ejected from housing 27 via trough and ducts 39 connecting therewith, thus being recycled through the impact pulverizer. The finer particles resulting from the pulverization are entrained in the swirling carrier gas drawn into the pulverizer by vanes 47 and are further subjected to the high velocity vortical sweep of additional carrier gas, preferably supplied at about 0.1 to about 0.9 sonic velocity, introduced through louvers 55.

Under these conditions an exceedingly efficient classification action is attained within the central chamber 57, uniformity in velocity gradient from top to bottom of the chamber being preserved by the flat plate 60. The fraction made up of coarse particles is impelled outwardly until it reaches the vicinity of the periphery of chamber 57, whereupon it is ejected by vanes 64 and passed to recycle in the same manner as that hereinbefore described for the coarse material derived directly from face 50. On the other hand, the fraction of fine particles resulting from the classification is concentrated centrally of the vortical flow and withdrawn from chamber 57 by fan 31, which delivers the fine product still entrained in air through the product delivery volute 36 encircling the inside of chamber 28 and thence via connection flange 29 to the nextfollowing equipment in sequence, usually a bag filter for product separation from the air stream.

In the design detailed there was no disadvantage in bulking the coarse, non-entrained material immediately thrown out by the impact pulverizer with the coarse particle fraction resulting from the classification within chamber 57, since recycle of each was desired anyway. However, it is obvious that a separate collection trough similar in design to trough 65 can be provided between trough 65 and face 50, such as immediately below the lower edge of face 50, to thereby collect and withdraw the coarse material immediately segregated by the pulverization, reserving trough 65 solely for the coarse particle fraction resulting from the classification. It is in this sense that the coarse and fine fractions from classification are re ferred to as separate pulverized products, since it is of no consequence what the ultimate utilization of either fraction might be, as, for example, a recycle of the coarse fraction for additional pulverization. Also, the floor 62 for chamber 57 is preferably driven in rotation at the same speed as disk 45 and plate 69, so as to equalize the frictional drag on the vortically moving classification air as well as impel coarse material from chamber 57 by the rotation of vanes 64. However, obviously, plate 62 can be made stationary if desired and, in fact, this latter arrangement is particularly advantageous Where a heavy, low tensile strength, extremely hard substance is used as a material of construction and, additionally, where a relatively coarse-grade central roduct of classification is desired.

In some cases it is desirable to drive plate 62 from fan 31, instead of from disk 4-5, so that the latter can be driven at much greater speed-s in the interests of more intensive impact pulverization without the drag imposed by the power drawn off to simultaneously rotate the classification elements. This is readily accomplished by providing a ported driving collar, similar to that hereinafter described for the embodiment of FIG. 3, fixedly secured at the upper end of the shaft of motor 30, directly connected to the inside periphery of plate 62, to thereby drive this plate at the same speed as fan 31. With this alternate construction the upper ends of lugs 61 connecting disk 45' with plate 60 are simply dispensed with, and the rotational effort for plate 60 is instead supplied by the lower lengths of the lugs based on plate 62.

A typical set of performance tests was conducted on two different solid pigment substances with the apparatus of FIGS. 1, 2 and 4. By way of comparison, identical tests were run on the same pigments in a commercially available hammer mill which has been widely employed conventionally in pigments size reduction and thus constitutes something of a standard. The test procedure in- Volved, first, subjecting individual half portions of the same identical pigment samples to pulverization in the hammer mill and in the impact pulverizer-classifier apparatus of this invention to substantially equal pulverizing exposures in terms of H.P.-hr. expenditures per lb. of solids throughput and, second, removing the pulverized products, dividing them into three separate portions and dispersing each in a suitable vehicle in conventional dispersive equipment for different periods of time adapted to evaluate the utility of the resultant product as a paint, in this case 2, 4 and 8 minutes for separate samples. The comparison of results obtained was on the basis of fineness in terms of a conventional linear paint scale (Hegman gauge) extending between the limits 0 to 10, i.e., from the coarsest, poorest grade to the finest, most desirable gra-de, respectively.

Time of Dispersing in Vehicle (Minutes) Pigment No. l-Fineness1 Hammer Mill 1 4 7% Impact Pulverizer-Classifier... 8% 9% 1O Pigment No. 2-Finenessz Hammer Mill 0 0 0 Impact Pulverizcr-Classifier 7 8% 9% such as TiO for example, are more readily dispersed in other gaseous media. For such products the apparatus of FIG. 3 is especially preferred, the additional carrier gas employed to effect the classification being in this instance steam. In addition, some pigments require a superadded size reduction operation as a finishing step in order to reduce grit to a minimum, and the apparatus of FIG. 3 is effective also in such cases.

Referring to FIG. 3, the impact pulverizer proper is identical with that hereinbefore described with respect to the embodiment of FIGS. 1 and 2, and the several elements thereof are accordingly denoted by the same reference numerals. However, the classification is entirely different and this is conducted within housing 74, substituted for housing 27 and all following equipment of the first embodiment. Housing 74 is provided around the outside periphery with an annular steam chest 75, and the housing is drilled to receive evenly spaced outwardly disposed plugs 76 for convenience in assembling the inwardly oriented steam introduction nozzles 77 (typically 16 in number) mounted in line therewith, with longitudinal axes generally coparallel with the plane of disk 45. Nozzles 77 discharge steam as the classification fluid into generally circular cross-section classification chamber 78, and a powerful vortical sweep is obtained by disposing the nozzles along lines tangential to a circle concentric with chamber 78, with outlets all disposed in a common sense preserving the swirl imparted to the carrier gas (air) drawn in by the impact pulverizer disk 45. In a typical apparatuse, nozzles aligned 30 away from radii drawn from the center of chamber 78 gave good results.

The embodiment of apparatus shown in FIG. 3 is adapted to utilize steam at from about 90 to 300 lbs./ sq. in. gauge pressure, whereupon the introduction via nozzles 77 to chamber 78 is either at, or well above, sonic speeds. Under these conditions it is desirable to dispose the nozzle outlets somewhat farther outwards radially from the periphery of disk 45, and, accordingly, a ring 49' of somewhat greater terminal diameter than ring 47 is preferably substituted for the latter.

The remaining construction of the classifier is very similar to that already described for the first embodiment, incorporating a rotating chamber floor plate 79 suspended from circular cross-section lugs 80. Floor plate 79 is not machined with peripheral air propulsion blades, such as blades 64, FIG. 2, nor is a coarse solids trough 65 incorporated in the design of FIG. 3, for the reason that recycle is not contemplated with this embodiment. The finely pulverized product is swept off through central exhaust vent 82, which is in open communication with chamber 78 but offset therefrom 90, from whence it can be collected in a bag filter, or passed to other following equipment in train, in the same manner as hereinbefore described for the first embodiment.

It is preferred to provide a preloaded stiffening support for floor plate 79, and this can conveniently consist of four spokes 83 carried by a hub 85 and spaced apart one from another, which assembly is slipped on the end of shaft 20 before nut 46 is screwed on. Spokes 83 are preferably round in cross-section at the inner and outer extremities, for lengths of approximately one diameter extent, and therebetween are machined to a rectangular cross-section such as indicated at 84, FIG. 6, disposed at an angle of approximately 45 with the longitudinal axis of the spokes. Thus, the lengths 84 function as suction vanes in the course of rotation of spokes 83, assisting in the withdrawal of the fine classified fraction from chamber 78. The lengths of spokes 83 are proportioned such that the outboard ends abut the inside periphery of floor plate 79 with a tight shrink fit, facilitated by heating one part and cooling the other as conditions require, so that plate 79 and spokes 83 are, in effect, a single piece, even though not joined together. Consequently, when disk 45 is brought up to speed, carrying plate 79 with it, spokes 83 minimize flutter of the plate occasioned by the high rotational speeds and mechanical shocks resulting from impacts with particles, while also providing a portion of the torque-transmitting effort from shaft 20 to plate 79.

The underside of plate 79 is preferably machined with a plurality of concentric grooves 86 mating with the ends of upstanding ring portions 87 provided on the top face of stationary circular base member 88, thereby providing a labyrinth seal against steam and particle leakage from chamber 78.

Nozzles 77 can have a variety of designs, depending upon the velocities which are desired within classification chamber 78. Thus, a straight cylindrical bore nozzle produces classification gas velocities in the approximately sonic range, Whereas a converging-diverging nozzle, such as that shown in FIG. and covered in copending U.S. Patent application Ser. No. 189,927, which has now matured into US. Patent 3,178,121, is capable of introducing steam at velocities Well above sonic, such as, typically in the range of 2.2 times sonic for 300 p.s.i.g. steam and 1.8 times sonic for 150 p.s.i.g. steam. The specific design of nozzle 77 in FIG. 5 has diametral dimensions a (inlet) 0.5", 11:0.155" to 0.157, and c (outlet) =O.238 to 0.240 (dimensions b and c thereupon defining an expanding divergence in the nozzle outlet of 6 radially), and length dimensions of (1:1.020, e=0.156" and f:0.359". The transition from the inlet bore to the nozzle throat is accomplished through a neck defined by rounding to a A radius drawn over a length of A3", thereby providing smooth flow for the steam supplied from chest 75 to classification chamber 78.

In operation, the solids feed is introduced into the apparatus of FIG. 3 in the same manner as hereinbefore described for the embodiment of FIGS. 1, 2 and 4. The classification is again effected by a vortically flowing additional carrier gas, in this case steam, but at considerably greater velocities than obtained with the air flow through louvers 55. Under these conditions the classification is so efficient that the classification assistance plate 60 can be entirely dispensed with, centrifugal forces of the order of 20 10 to 180x10 times the force of gravity being applied to particles in entrainment, as distinguished from forces in the general range of only about 0.6 to 10 10 times gravity attained in the apparatus of FIGS. 1 and 2. At least equally important, however, is the superadded grinding action obtained within chamber 78 resulting from the violent interparticle shear and collision, due to the fact that the gas vortex functions as a very efficient fluid energy pulverizing agency completely apart from its classification effect. Accordingly, there is no need to recycle any coarse particles back to the impact classifier incorporating disk 45, and any over-size material is simply retained within chamber 78 until it be comes sufficiently reduced in size to join the rest of the fine particle material drawn off as product through vent 82.

The use of steam or a similar hot fluid as the classification gas is especially advantageous where slurries are to be pulverized and then dried, as these operations can be concomitantly effected in apparatus such as that detailed in FIG. 4.

In the usual situation, as hereinbefore described, it is preferred to effect the final size reduction of particles within the classification zone of the embodiment shown in FIG. 3. However, in some instances it may be desirable to remove the coarse fraction segregated peripherally by the vortical flow, as where this fraction is itself a desired product, or where recycle to the impact pulverization section is advantageous as, for example, where a preselected quality of raw feed is obtained by return of at least a portion of the coarser pulverized product for admixture therewith. Under these circumstances, it is entirely practicable to provide a peripheral trough similar to trough 65 for the embodiment of FIG. 2, adapted to take off a controlled amount of the coarse particulate solids from the peripheral region of chamber 78.

An important practical advantage of the design of apparatus hereinbefore described is the fact that the same impact pulverization mill can very conveniently be utilized interchangeably to achieve subsonic velocity classification using the classification adjunct shown in FIGS. 1, 2 and 4, or sonic or supersonic velocity classification using the classification adjunct shown in FIG. 3, by simply substituting one for the other. It should be further mentioned that it is by no means necessary to arrange the apparatus components so that pulverization and classification are conducted in horizontal planes, because the centrifugal forces developed in each operation are of such large magnitude that gravitation imposes little limitation as regards equipment arrangement.

It will be understood that additional carrier gas in aid of classification can be supplied to the classification zone in a variety of ways, and that the louvers of FIG. 2 and the nozzles 77 of FIG. 3 are each to be considered representative, and not restrictive. It is also practicable to utilize diverse gas introduction means, such as, for example, one or more steam nozzles 77 interspersed with air louvers 55, or the like, so that precise preselected velocity or temperature patterns can be preserved within the classification zone, as where temperature-sensitive materials are being processed or where a concomitant steam distillation effect removing adhering solvent from particulate solids is advantageous. This readily enables the use of two or more different gases as components of the additional carrier gas, which can be highly desirable.

A completely unanticipated advantage derived from impact pulverization-classification according to this invention is the marked increase in efficiency in the over-all pulverization effort as compared to that obtained where impact pulverization and classification are conducted as separate operations. This is displayed in greatly improved uniformity of particle size in the products obtained and also in the power required for a given degree of pulverization. Apparently, the immediate, essentially complete removal of fine particle solids with elimination of their dwell within, as well as their return to, the pulverization zone frees the coarse material from any accompanying burden of energy-absorbing fines which could interfere with the maximum application of energy to pulverization per se.

It will be understood that the apparatus designer has great freedom as regards the supply of carrier gas to the impact pulverization section of the apparatus. Thus, this gas can be supplied in whole or in part, and singly or collectively, by air drawn in from the room through port 40, air reinjected into the pulverization zone via recycle ducts 39, or even by gas introduced from entirely different sources, as might be required where inert atmospheric blanketing of operations is essential. In the extreme case the apparatus can, in fact, be completely sealed off, so that the carrier gas is then supplied exclusively internally by return flow adjacent ring face 50. Accordingly, introduction of carrier gas to the pulverization section is, of course, completely independent of raw or recycle solids feed to the apparatus, the only requirement being that the carrier gas in this section proceed radially outward of the impact rotor together with any solids in course of pulverization.

From the foregoing, it will be apparent that the method and apparatus of this invention can both be modified extensively within the skill of the art without departure from the essential spirit of the invention, and it is intended to be limited only by the appended claims.

What is claimed:

1. A method of impact pulverization-classification of solids comprising, in sequence, subjecting said solids to centrifugal impact pulverization in the presence of a concurrently flowing stream of carrier gas, thereby effecting the throwout of coarse pulverized solids by the combined effects of centrifugal force and gravity and the entrainment of fine dispersed pulverized solids in said carrier gas, introducing an additional quantity of carrier gas in co-rotational vortical flow to the carrier gas entraining said fine dispersed pulverized solids in sufficient quantity to effect a classification of said dispersed pulverized solids into a first fraction of fine particle size concentrated centrally of said vortical flow and a second fraction of coarse particle size concentrated peripherally of said vortical flow, and withdrawing at least said first fraction as a separate pulverized product.

2. A method of impact pulverization-classification according to claim 1 wherein said second traction is recycled to said centrifugal impact pulverization.

3. A method of impact pulverization-classification of solids comprising, in sequence, subjecting said solids to centrifugal impact pulverization in the presence of a concurrently fiowing stream of carrier gas, thereby effecting the throwout of coarse pulverized solids by the combined effects of centrifugal force and gravity and the entrainment of fine dispersed pulverized solids in said carrier gas, introducing an additional quantity of carrier gas in co-rotational vortical flow to the carrier gas entraining said fine dispersed pulverized solids in sufficient quantity to effect a classification of said dispersed pulverized solids into a first fraction of fine particle size concentrated centrally of said vortical flow and a second fraction of coarse particle size concentrated peripherally of said vortical flow, and withdrawing said first fraction and said second fraction as separate pulverized products.

4. A method of impact pulverization-classification of solids comprising, in sequence, subjecting said solids to centrifugal impact pulverization in the presence of a concurrently fiowing stream of carrier gas, thereby effecting throwout of coarse pulverized solids by the combined effects of centrifugal force and gravity and entrainment of fine dispersed pulverized solids in said carrier gas, introducing at a plurality of points spaced not in excess of about 15 one from another around the periphery of the zone receiving said fine dispersed solids in said carrier gas and at a velocity within the range of about 0.1 to about 0.9 sonic velocity an additional quantity of carrier gas in co-rotational vortical flow to the carrier gas entraining said fine dispersed pulverized solids in sufficient quantity to effect a classification of said dispersed pulverized solids into a first fraction of fine particle size concentrated centrally of said vortical flow and a second fraction of coarse particle size concentrated peripherally of said vortical flow, and withdrawing said first fraction and said second fraction as separate pulverized products.

5. A method of impact pulverization-classification of solids comprising, in sequence, subjecting said solids to centrifugal impact pulverization in the presence of a concurrently fiowing stream of carrier gas, thereby effecting throwout of coarse pulverized solids by the combined effects of centrifugal force and gravity and entrainment of fine dispersed pulverized solids in said carrier gas, introducing an additional quantity of carrier gas at substantially sonic velocity or above in co-rotational vortical flow to the carrier gas entraining said fine dispersed pulverized solids in suflicient quantity to effect a classification of said dispersed pulverized solids into a first fraction of fine particle size concentrated centrally of said vortical flow and a second fraction of coarse particle size concentrated peripherally of said vortical flow, and withdrawing at least said first fraction as a separate pulverized product.

6. A method of impact pulverization-classification of solids according to claim 5 wherein said additional quantity of carrier gas consists of a different gas than that in which said centrifugal impact pulverization is conducted.

7. An apparatus for impact pulverization-classification of solids comprising, in combination, (1) a centrifugal impact mill incorporating a power-driven rotary pulverizer disk provided on its outboard surface with radially disposed solids-directing vanes imparting extreme centrifugal force loadings to solids moved therepast mounted generally co-axial with respect to a stator ring having an axially oriented face encircling the periphery of said pulverizer disk at close clearance therewith, means for introducing solids to be pulverized, and means for introducing carrier gas in concurrent fioW with said solids radially outward past the vanes of said pulverizer disk, and (2) a generally circular cross-section chamber disposed axially adjacent of and in open endwise communication with the interspace between said stator ring and the periphery of said pulverizer disk, said chamber being provided with a centrally disposed port on the end remote from the inboard surface of said pulverizer disk for the withdrawal of fine pulverized solids entrained in carrier gas exiting from said interspace, and a plurality of gas inlet ports disposed in the peripheral wall of said chamber introducing additional carrier gas into said chamber to thereby maintain a vortical flow of carrier gas within said chamber effecting a particle size classification of pulverized solids delivered from said interspace and dispersed in said carrier gas.

8. An apparatus for impact pulverization-classification of solids according to claim 7 wherein the end wall of said chamber provided with said centrally disposed port consists of a plate driven in rotation c-o-directional with said pulverizer disk of said impact mill.

9. An apparatus for impact pulverization-classification of solids comprising, in combination, (1) a centrifugal impact mill incorporating a power-driven rotary pulverizer disk provided on its outboard surface with radially disposed solids-directing vanes imparting extreme centrifugal force loadings to solids moved therepast mounted generally coaxial with respect to a stator ring having an axially oriented face encircling the periphery of said pulverizer disk at close clearance therewith, means for intro ducing solids to be pulverized, and means for introducing carrier gas in concurrent flow with said solids radially outward past the vanes of said pulverizer disk, and (2) a generally circular cross-section chamber disposed axially adjacent of and in open endwise communication with the interspace between said stator ring and the periphery of said pulverizer disk, said chamber being provided with a peripherally disposed port for the withdrawal of coarse pulverized solids thrown out from said pulverizer disk and a centrally disposed port on the end remote from the inboard surface of said pulverizer disk for the withdrawal of fine pulverized solids entrained in carrier gas exiting from said interspace, and a plurality of gas inlet ports disposed in the peripheral wall of said chamber introducing additional carrier gas into said chamber to thereby maintain a vortical flow of carrier gas within said chamber effecting a particle size classification of pulverized solids delivered from said interspace and dis persed in said carrier gas.

10. An apparatus for impact pulverizadon-classification of solids comprising, in combination, (1) a centrifugal impact mill incorporating a power-driven rotary pulverizer disk provided on its out-board surface with radially disposed solids-directing vanes imparting extreme centrifugal force loadings to solids moved therepast mounted generally co-axial with respect to a stator ring having an axially oriented face encircling the periphery of said pulverizer disk at close clearance therewith, means for introducing solids to be pulverized, and means for introducing carrier gas in concurrent fiow with said solids radially outward past the vanes of said pulverizer disk, and (2) a generally circular cross-section chamber disposed axially adjacent of and in open endwise communication with the interspace between said stator ring and the periphery of said pulverizer disk, said chamber being provided with a peripherally disposed port for the withdrawal of coarse pulverized solids thrown out from said pulverizer disk and an end wall remote from the inboard surface of said pulverizer disk consisting of an annular plate driven in rotation co-directional with said pulverizer disk of said impact mill having a central aperture of a size permitting withdrawal of fine pulverized solids entrained in carrier gas exiting from said interspace, said chamber being further provided with a plurality of gas inlet ports disposed in the peripheral Wall of said chamber introducing additional carrier gas into said chamber to thereby maintain a vortical flow of carrier gas within said chamber effecting a particle size classification of pulverized solids delivered from said interspace and dispersed in said carrier gas.

11. An apparatus for impact pulverization-classification of solids comprising, in combination, (1) a centrifugal impact mill incorporating a power-driven rotary pulverizer disk provided on its outboard surface with radially disposed solids-directing vanes imparting extreme centrifugal force loadings to solids moved t-herepast mounted generally co-axial with respect to a stator ring having an axially oriented face encircling the periphery of said pulverizer disk at close clearance therewith, means for introducing solids to be pulverized, and means for introducing carrier gas in concurrent flow with said solids radially outward past the vanes of said pulverizer disk, and (2) a generally circular cross-section chamber disposed axially adjacent of and in open endwise communication with the interspace between said stator ring and the periphery of said pulverizer disk, said chamber being provided with a peripherally disposed port for the withdrawal of coarse pulverized solids thrown out from said pulverizer disk and an end wall remote from the inboard surface of said pulverizer disk consisting of an annular late driven in rotation co-directional with said pulverizer disk of said impact mill having a central aperture of a size permitting withdrawal of fine pulverized solids entrained in carrier gas exiting from said interspace, and a plurality of gas inlet ports disposed in the peripheral wall of said chamber introducing additional carrier gas into said chamber to thereby maintain a vortical flow of carrier gas within said chamber effecting a particle size classification of pulverized solids delivered from said interspace and dispersed in said carrier gas, said gas inlet ports constituting nozzles oriented generally tangentially of circles concentric with said chamber with the axes of said nozzles generally coplanar with said pulverizer disk of said impact mill.

12. An apparatus for impact pulverization-classification of solids according to claim 9 wherein said gas inlet ports have a pitch spacing one from another in the range of from about 5 to about 15 measured angularly of said chamber.

13. An apparatus for impact pulverization-classification of solids according to claim 7 wherein said gas inlet ports constitute nozzles oriented generally tangentially of circles concentric with said chamber, with the axes of said nozzles generally coplanar with said pulverizer disk of said impact mill.

14. An apparatus for impact pulverization-classification of solids according to claim 10 wherein said chamber is further provided with a flat plate classification element interposed intermediate said inboard surface of said pulverizer disk and said annular plate driven in rotation co-directional with said pulverizer disk of said impact mill, said flat plate classification element being also driven in rotation co-directional with said pulverizer disk of said impact mill.

References Cited by the Examiner UNITED STATES PATENTS 1,159,122 11/1915 Steckle 241 X 2,092,307 9/1937 Gaffney 24156 X 2,342,255 2/1944 Doyle 24l61 3,015,391 1/1962 Sharples 241-275 X 3,023,973 3/1962 Conley et al. 241-275 ROBERT C. RIORDON, Primary Examiner.

ROBERT A. OLEARY, J. SPENCER OVERHOLSER,

Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,224,686 December 21, 1965 Curtis C. Wallace, Jr.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 26, for "Patent" read Patents columr 3, line 42, for "multipilcity" read multiplicity column 6, line 39, for "47 read 49 column 7, line 25, for "0.359" read 0.395 column 9, line 9, for "traction" read fraction Signed and sealed this 3rd day of January 1967.

( AL) Anna:

ERNEST w. swmER EDWARD J. BRENNER Arresting Officer Commissioner of Patents

Claims (2)

1. A METHOD OF IMPACT PULVERIZATION-CLASSIFICATION OF SOLIDS COMPRISING, IN SEQUENCE,. SUBJECTING SAID SOLIDS TO CENTRIFUGAL IMPACT PULVERIZATION IN THE PRESENCE OF A CONCURRENTLY FLOWING STREAM OF CARRIER GAS, THEREBY EFFECTING THE THROWOUT OF COARSE PULVERIZED SOLIDS BY THE COMBINED EFFECTS OF CENTRIFUGAL FORCE AND GRAVITY AND THE ENTRAINMENT OF THE FINE DISPERSED PULVERIZED SOLIDS IN SAID CARRIER GAS, INTRODUCING AN ADDITIONAL QUANTITY OF CARRIER GAS IN CO-ROTATIONAL VORTICAL FLOW TO THE CARRIER GAS ENTRAINING SAID FINE DISPERSED PULVERIZED SOLIDS IN SUFFICIENT QUANTITY TO EFFECT A CLASSIFICATION OF SAID DISPERSED PULVERIZED SOLIDS INTO A FIRST FRACTION OF FINE PARTICLE SIZE CONCENTRATED CENTRALLY OF SAID VORTICAL FLOW AND A SECOND FRACTION OF COARSE PARTICLE SIZE CONCENTRATED PERIPHERALLY OF SAID VORTICAL FLOW, AND WITHDRAWING AT LEAST SAID FIRST FRACTION AS A SEPARATE PULVERIZED PRODUCT.

7. AN APPARATUS FOR IMPACT PULVERIZATION-CLASSIFICATION OF SOLIDS COMPRISING, IN COMBINATION, (2) A CENTRIFUGAL IMPACT MILL INCORPORATING A POWER-DRIVEN ROTARY PULVERIZER DISK PROVIDED ON ITS OUTBOARD SURFACE WITH RADIALLY DISPOSED SOLIDS-DIRECTING VANES IMPARTING EXTREME CENTRIFUGAL FORCE LOADINGS TO SOLIDS MOVED THEREPAST MOUNTED GENERALLY CO-AXIAL WITH RESPECT TO A STATOR RING HAVING AN AXIALLY ORIENTED FACE ENCIRCLING THE PERIPHEREY OF SAID PULVERIZER DISK AT CLOSE CLEARANCE THEREWITH, MEANS FOR INTRODUCING SOLIDS TO BE PULVERIZED, AND MEANS FOR INTRODUCING CARRIER GAS IN CONCURRENT FLOW WITH SAID SOLIDS RADIALLY OUTWARD PAST THE VANES OF SAID PULVERIZER DISK,

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