US 3348779 A
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Och 1967 N. H. ANDREWS 3,348,779
METHOD AND APPARATUS FOR COMMINUTING MATERIALS 4 Sheets-Sheet 1 Filed Oct. 2, 1964 WWQ w lIlllll A M I A g //V Vf/VTOI? NORM 00D H. ANDREWS er Q p06,! 5 'waza' 06L 1967 N. H. ANDREWS 3,3
METHOD AND APPARATUS FOR COMMINUTING MATERIALS Filed Oct. 2, 1964 4 Sheets-Sheet 2 nvvewrom NORWOOD H. ANDREWS W WM ATTORNEYS.
Oct. 24, 1967 N. H. ANDREWS 3,348,779
METHOD AND APPARATUS FOR COMMINUTING MATERIALS Filed Oct. 2, 1964 4 Sheets-Sheet 5 //VV/V70/? NORWOOD H. ANDREWS ATTORNEYS.
Oct. 24, 1967 N. H. ANDREWS 3 7 METHOD AND APPARATUS FOR COMMINUTING MATERIALS Filed 9st. 2, 1964 4 Sheets-Sheet A "VVE/VTOF IVOPWQGD IV. ANDREWS ATTORNEYS.
United States Patent 3,348,779 METHOD AND APPARATUS FOR COMMINUTING MATERIALS Norwood H. Andrews, Box 68, Moorestown, NJ. 08057 Filed Oct. 2, 1964, Ser. No. 401,191 22 Claims. (Cl. 24139) This invention relates to an improved method and apparatus for comminuting materials. More particularly, this invention relates to an improved method and means of reducing a wide variety of pulverant materials to extremely fine sizes using a re-entrant circulatory stream together with jets of high pressure gaseous fluid.
The 4th Edition of Perrys Chemical Engineering Handbook, Section 8, page 42, states that fluid energy grinding mills may be classified in terms of'the nature of the mill action. In one class of mill, the fluid energy is admitted in fine high velocity streams at an angle around a portion or all of the periphery of a grinding and classifying chamber. In another class, the fluid streams convey the particles at high velocity into a chamber where at least two streams impact upon each other. This invention relates to the former class of mill.
The use of the term-re-entrant circulatory stream and endless casing is directed to the first-mentioned class and the limitations of such terms may be more fully understood from subsequent statements of the actions and operations of this invention.
The present invention relates to a pulverizer for subsieve grinding such as is described in Patent 2,032,827 which describes the basic principles of a jet pulverizer of the re-entrant circulatory type. Although the present invention is most readily applicable to those types of pulverizers as exemplified by Patent 2,032,827, the principles can also be applied to those forms of re-entrant circulatory stream pulverizers as exemplified by FIGURE 6 in Patent 2,219,011.
The type of pulverizer being discussed operates on the general principle of causing coarse material to circulate about the outer periphery of a confined gas stream, then causing the material to be picked up and projected at an angle into the stream by a jet or jets positioned adjacent the outer periphery. The relation of centrifugal force in the particles versus the entraining efiect of the gas as it leaves the periphery and moves toward an outlet, determines the classification in these types of devices.
Many modifications of these devices have been made. In general, in order to improve the efficiency of such devices, attempts have been made to try to concentrate a greater proportion of the circulating unground material into the jets at their point of discharge. This has been done because it is a fact that most of the energy of the fluid jets is dissipated within the first couple of inches of the point of discharge. Furthermore, the greatest percentage of reduction is in the first few inches of the jets intersection with the circulating stream. Some of the earliest pulverizers have used narrow peripheral walls and divergent top and bottom plates to improve the efiiciency of operation. In fact, some of these types of pulverizers have used peripheral walls so acutely V-shaped that the flat vertical part is very little more than the diameter of the nozzles. Thus, in Patent 2,590,220, FIGURE shows the use of a restricted configuration for the purpose of improving the efliciency of comminuting.
Although such prior attempts as indicated above have met with moderate success in improving the efiiciency of pulverizers, it is a general object of the present invention to provide a novel method and appartus for comminuting particles which will greatly increase the efliciency of the re-entrant circulatory stream type of pulverizer.
It is another object of the present invention to provide 3,348,779 Patented Get. 24, 1967 a jet stream pulverizer wherein a greater production of finely ground material can be obtained at a lower energy ratio to new surface produced.
Another object of the present invention is to provide a jet stream pulverizer that is capable of producing in commercial quantities, particle sizes below that now considered economically practical.
Another object of the present invention is to provide a jet stream pulverizer which effectually controls and, with many materials, eliminates the random oversized particles usually obtained in these types of mills.
Still another object of the present invention is to provide a pulverizer which is capable of reducing many materials to sizes hereto-fore considered impractical due to the build-up of cake or accumulated masses within the mill.
It is yet another object of the present invention to provide a method and apparatus for largely eliminating the build-up or caking of material within a mill chamber for most materials.
A further object of the present invention is to provide a method and appartus to substantially maintain the velocity of the circulating stream independent of slight increased variation in feed.
It is still another object of the present invention to provide a jet stream pulverizer capable of providing a more uniform product.
Yet another object of the present invention is to provide a pulverizer which concentrates more feed material in the jet stream.
Still another object of the present invention is to provide a jet stream pulverizer that more efficiently causes 7 partially ground particles to re-enter the jet stream.
Other objects will appear hereinafter.
For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.
FIGURE '1 is a longitudinal sectional view of one form of the present invention.
FIGURE 2 is a transverse sectional view of the embodiment shown in FIGURE 1 taken along the line 2-2.
FIGURE 3 is a longitudinal sectional view of another form of the present invention.
FIGURE 4 is a transverse sectional view of the inventive form shown in FIGURE 3 taken along the line 44.
FIGURE 5 is a longitudinal sectional view of another modification of the present invention.
FIGURE 6 is a transverse sectional view of the embodiment shown in FIGURE 5 taken along the line 6-6.
FIGURE 7 is a sectional View of another embodiment of the present invention.
FIGURE 8 is a transverse sectional View of the embodiment shown in FIGURE 7 taken along the line 88.
FIGURE 9 is a sectional view illustrating still another embodiment of the present invention.
FIGURE 10 is a sectional view illustrating yet another embodiment of the present invention.
FIGURE 11 is a sectional view of an embodiment similar to the one shown in FIGURE 1 with a modified arrangement of the injector, taken along the line 11-11 of FIGURE 1'.
In order to more fully understand the principles of the present invention, it should be noted that there are two types of gaseous energy in the re-entrant circulatory type of pulverizer. One form of gaseous energy is represented by the jet streams, which are of a very high energy concentration. The other forms of gaseous energy is represented by the expanded gasses resulting from the jet streams and circulating as a stream of relatively low energy. It is important to note that it is thelow energy gas stream that is depended upon to circulate material to be ground and partially ground materials into the jets and yet have a high enough energy to classify the material to the desired particle size. Consequently, any design of a jet stream mill that improves the efiiciency of the circulatory gasses will improve their material-carrying capacity and hence provide a greater efiiciency in loading the jets, as well as improving the efficiency of classification.
Patent 2,376,747 represents a type of pulverizer which is directed to a reduction of the friction on the circulating stream. However, the mill represented by Patent 2,376,- 747 suffers from several serious handicaps. In particular, it is very difiicult to maintain the extremely close clearance between the rotating bottom plate and the angular floor ring necessary for successful operation. And with the necessary gas pressure on the underside of the rotating fioor plate, as mentioned in the specification, any but the closest clearance causes an extreme amount of gas to flow up into the grinding chamber to the. detriment of the grinding as well as to the classifying of the material. When the pressure is lowered on the underside of the plate in Patent 2,376,747, then part of the ground material escapes from the circulating stream and accumulates in the space between the said plate and the annular floor plate thus causing the rotating plate to jam. Because of these problems the mill never became operative as a commercial mill.
The means of feeding material to be ground into the mill often presents several problems. In nearly all commercial applications of thetype of mill under discussion an injector type of feed means is used. This type of feed means is similar to that shown in Patent 2,032,827. In using such an injector means, it has been found that the amount of energy necessary to seal the throat of a large venturi when certain bulky, easy to grind materials are fed, reaches extensive proportions and in certain instances represents up to one-third the total gas energy of the mill. It has been found that when such large volumes of gas are used, it is desirable to have the expanded gas from the injector have a velocity in the direction of the general gas stream. Several patents have been directed toward reducing the energy for the injection of material as well as reducing the amount of entrained gas by substituting a screw feeding means. Thus, for example, see Patents 2,763,437 and 2,596,088. The screw type of feeding while overcoming some of the abovementioned problems, pre sents some problems of its own. For example,- there is an advantage in having the material to be ground enter the circulating gasses in a dispersed state. The screw feed mechanism does not provide the desired dispersion of particles.
Another problem with the screw feed injector might best be pointed out by indicating that it introduces the entire feed in a static condition in the circulating gas stream. Theacceleration ofthis feedfrom a static condition imposes an enormous burden upon what is already a secondary low grade gas force. Since this secondary force is the force that feeds material to the jets to be ground, it should be apparent why the screw feed type of injector has not been widely adopted.
It has been found that there are two types of feeding or loading of the jet, which is the arts term for describing the material to be ground that is picked up by the jets at the point of discharge and angularly projected into the circulating stream. One type of loading is caused by feed material that is newly introduced into the mill and into the jets. The other type of loading is caused by material that is partially ground but not sufiiciently so for the particular grinding operation and which must be retained in the mill and re-introduced into the jets. This is called recirculated material.
A general mixing of the two materials occurs quite rapidly under any circumstances, but the quicker and more evenly distributed and mixed the feed material is with the i e-circulated material, the more eflficient the operation. Thus, in the broadest concept, the two main principles of this invention are (1) the substitution of mechanical means for a large portion of the energy of accelerating the distribution and mixing of feed material with the re-circulated material'in the re-entrant circulatory stream, and (2) mechanical means for maintaining in the peripheral portion of the grinding chamber a higher velocity of the re-entrant circulatory stream by either or both direct physical contact with the material or by the increase in the velocity of the gas supporting the circulating stream of material as it causes the material to approach the jets.
Although the velocity of various gasses issuing from a nozzle can be easily computed, given pressure, temperature, nozzle shape, etc., there is no way to actually evaluate the velocity of different size particles circulating adjacent the periphery of the grinding chamber of a circulating gas stream pulverizer. Patent 2,032,827 gives some indication of gas velocities in an empty mill in order to illustrate the general type of flow, but it does not indicate the velocity of the various parts of a circulating load in an operating mill. It is known that the circulating velocity slows up rapidly as material is fed into the mill, but the exact extent of the slow-up is not known.
In fact, the knowledge that slow-up occurs has been used to introduce material into an empty mill on starting up. Thus, without material in the mill to slow down the rotational velocity of the gas, a high peripheral pressure, resulting from centrifugal velocity is frequently obtained. This high peripheral pressure is such that the injector means selected for subsequent operation cannot overcome it. Therefore, the energy of the gas to the mill is reduced until some material is introduced into the mill thereby slowing down the gas and reducing the peripheral pressure. This is called priming the mill.
The foregoing problems and their solution can best be illustrated by referring now to the drawings wherein like numerals indicate like elements.
Referring now to FIGURES 1 and 2, there is shown a preferred form of the invention capable of producing much more surface area per unit of energy input than previous jet pulverizers. As shown, the mill comprises a grinding and classifying chamber 56 of substantially circular cross section formed by the side plates 58 and 60 mounted on peripheral wall 62. A plurality of nozzles 64 are spaced around the peripheral wall 62 and communicate with header 66. A pipe 68 connects the header 66 to a gas supply through which air or steam is forced into header 66 and through nozzles 64. The nozzles 64 are angularly directed so that the jet streams created thereby are tangent to a circle of lesser diameter than the inner periphery of wall 62.
An opening 70 is centrally located in plate 60. Opening 70 is of suflicient size to allow the discharge of pulverized products together with the circulating gas. A collector means (not shown) may be connected to pipe 72 mounted in opening 70.
The material to be pulverized is introduced into the chamber 56 by means of a feed assembly 74. The feed assembly 74 comprises a nozzle 76, a venturi 78, and a funnel 80.- A gas supply, attached to nozzle 76, passes through venturi 78 and carries material from funnel 80 into the chamber 56. The material is discharged against disk 94.
A shaft 82 is rotatably mounted on bearings 84 and 86 ture superheated steam is used. In that case, it is also.
necessary to pack the stuffing box 88 with a high-temperature-resistant material. The pulley 90 and belt 92 are adapted to cause shaft 82 to rotate when driven by a motor (not shown).
A disk 94 is threadedly mounted on the end of shaft 82 and rotates therewith. A plurality of vanes 96 are fixedly attached about the periphery of disk 94. Thus, the rotation of shaft 82 causes the disk 94 and vanes 96 to rotate within chamber 56.
As material is forced into the chamber 56 it impinges on rotating disk 94 and is dispersed. As it is dispersed the vanes 96 pick up the material and accelerate it radially into impact with peripheral wall 62. The relationship of the vanes 96 to the peripheral wall 62 causes a forced circulation of the gas and material adjacent thereto and a general movement or flow towards and into the jets. The material is immediately picked up by the jets and projected angularly inwardly away from the wall. Those particles which are already of a size small enough to be classified with the size product desired are carried out of the outlet 70 by the gasses leaving the chamber. On the other hand, a major part of the material which is not yet of a size to be classified with the size product desired will be centrifugally returned to the periphery.
It should be noted that the vanes 96 extend on both sides of disk 94. Thus, a portion 97 of the vanes 96 which is on the outlet side of disk 94 will aid the circulating stream of gasses and increase the centrifugal force on the re-entr ant materials which are to be directed back into the jet stream. Thus, the vane portions 97 intercept and accelerate a considerable portion of the material being returned to the jet streams for further grinding.
The portions 97 are located on the outer periphery of the disk 94 and thus do not affect the inwardly spiralling classifying stream but mechanically aid it in accelerating the particles into the jet streams. The jet streams pick up both the recirculated material and the feed material and hurl it back into the circulating gas stream wherein it impacts upon other particles and breaks up into fine particles.
In the construction of the vanes 96, it is to be noted that they extend radially inwardly from a reasonably close clearance with the inner periphery of wall 62 to a point about half-way to the shaft 82. It has been found that this distance is sufiicient to not only help in the introduction of feed by the fan action created by said vanes 96 but also in the acceleration of the material against the peripheral wall '62 in a radial direction. This action is helpful in reducing some of the particles that may be of undesirably large size.
In one example, the inner diameter of the inner pe riphery of wall 62 was 21 inches at the jet location and 20 inches at the intersection of plate 58. The disk 94 was 18 /2 inches in diameter so that there was a clearance between the periphery of disk 94 and the inner periphery of wall 62 of of an inch. It should be noted that such dimensions are by way of example and it is not intended to imply that slight variations of these dimensions would be critical.
The clearance between the end of the vanes 96-97 and the inner periphery of wall 62 was /3 of an inch. The vanes 96 were A of an inch in width measured between plate 94 and wall 58 and twenty in number.
The portion 97 of the vanes extending towards the jet side of disk 94 do not have to be an integral part of the vanes 96, but such construction has been found to be much simpler. It is the inner portions 97 of the vanes 96 that intercept and accelerate a considerable portion of the material being returned into the jet stream for further grinding as a result of centrifugal force from the classification section. I
It should be readily understood that the rate of rotation of disk 94 and vanes 96 will create a forced circulation of the gasses within the chamber 56. Various rates of speed can be adapted to properly load the jets for most efficient operation on a wide range of materials. The
speeds chosen can be mechanically applied by means of a motor attached to belt 92 and pulley and do not depend on the low order of energy of the aforementioned circulating gasses created by the jet streams issuing from nozzles 64.
The action of vanes 96 which pick up the dispersed feed material and direct it along inner periphery of wall 62 into jet streams issuing from nozzle 64 also aids in preventing a build-up of material between said jet streams.
The rotational speed of the vanes 96 is of particular importance. Experiments have shown that there is no way of predicting the optimum speed for a wide range of products of different grindability to produce different desired low particle sizes. It is possible, however, as a result of tests made over a fairly wide range of materials of different specific gravities and grindability as well as differences in particle size, using both compressed air and superheated steam as a grinding medium, to give sufficient information so that one schooled in the art can obtain the benefit of the invention. From many tests, it can be stated that in general, a higher rotational speed of vanes 96 is indicated in a given mill when material of low specific gravity and easy grindability is processed.
For any given material it has been found desirable to feed the same quantity of material relative to the gas energy as would normally be done in a conventional mill, while rotating the vanes at a relatively low speed. After operation has begun, then the feed rate is increased until a product comparable to the normal production product in a conventional mill is obtained. When this point is reached, then the speed of the vanes 96, 97 is increased. As a finer product is produced then the feed rate is again increased. This sequence of first increasing the speed of vanes and then the feed rate is continued until the maximum production of a desirable size is obtained with a minimum of energy, including the energy of rotating the vanes.
It is well understood by those skilled in the art of re-entrant circulatory stream pulverizers that the only way to change the product size for a given material in a given mill with a given fluid energy is to change the rate of feed, oralternately for any set condition of feed rate of the material in a given mill, by changing the gaseous energy supplied to the mill. As a result of the present invention, a new variable is introduced whereby the rate of circulation of a large portion of the gas and material at or adjacent to the periphery can be substantially maintained, irrespective of considerable variation in the rate of feed. In order to better illustrate this result, reference is made to the following tests on the mill shown in FIGURE 1, using both air and steam as the gas energy.
In this first test, using air at 100 pounds gauge pressure and feeding 600 pounds per hour of chrome green and rotating the plate 94 so that vanes 9697 had a tip speed of approximately 280 feet per second, an ammeter attached to the motor driving belt 92 indicated 22 amps. The number of amperes required to drive the motor was considered to be indicative of energy 'being added to the circulating stream. When the rotational velocity of disk 94 was increased so that the tip speed of the vanes was slightly over 500 feet per second (with all other factors being the same) the ammeter showed a reading of 60 amperes. However, when the feed rate was cut in half, the reading on the ammeter dropped off to 28 amperes.
In another test, using steam at pounds pressure and 500 F., a micaceous silicate was fed into the mill at the rate of 630 per hour with a tip rotational velocity for the vanes 96 of slightly over 200 feet per second. Under these conditions the reading on the ammeter was 32 amperes. When the tip velocity was increased to 360 feet per second the ammeter rating built up to 100 amperes. As in the previous test, when the feed rate was reduced to approximately one-half or to 350 Present invention (percent increase of -inch mill equal quality product Rotor (standard commercial) for same proportion of (energy used) steam energy from same (amps) grade of feed material) Barytes 46 28-32 Micaceous silicate 25 -37 Gulf red oxide. 100 2938 \Vhiting 1-. 17-18 Spanish oxide 31-33 In each of the above-described examples, there were twenty vanes of approximately inch thickness, leaving about 2 /2 inches between vanes at the periphery of plate 94. More or less vanes of greater or less thickness have only a slight effect on the operation. Also, as shown, the peripheral wall 62 and vanes 96 are tapered outwardly toward the jet openings. A greater or lesser taper might modify the results, but the important thing is that the design be such that feed and re-circulated material must be mechanically directed into the jets at the point of discharge.
In the illustration shown and described in FIGURE 1 the vanes 97 extended /1 of an inch from the face of disk 94 towards the nozzle 64 opening. The radial length of the edge of vanes 96 nearest the nozzles 64 is /2 of an inch, tapering to of an inchat the plane of the face of disk 94.
It should be noted that the vanes 97. do not extend very far radially inwardly toward the center of disk 94 on the side closest to opening 70. Thus, the vortex at the center of the classification zone 56 is not substantially affected by the vanes 97. The vanes 97 are widest close to the periphery of wall 62 in order to have the greatest circulatory effect on the gas and material close to the jets.
In general, those skilled in the art consider that reentrant circulatory type jet devices are most efficient for producing a product under the 30 micron size, whereas in the ZOO-mesh and coarser range, hammermills, ball mills, tube mills, ring roll, etc., are considered more efficient. There are those heat-sensitive materials, however, as for example certain types of plastics, which heretofore have been ground in the generally inefficient range of jet devices because they will not withstand the temperature rise incidental to the mechanical grinding devices. Since the vanes 96 accelerate the material into impact with the peripheral wall 62 a hammermilling effect is produced in that portion of the apparatus. Ac-, cordingly, it is possible to adjust the energy of the jets in order to have a cooling effect upon the material which compensates for the temperature rise resulting from the hammermilling. In this manner the advantages of hammermilling the temperature sensitive material are achieved. If desired, the peripheral wall 62 may be serrated to increase the efficiency of the hammermilling.
Another advantage'in using the vanes as designed is that the operation of the vanes in forcing the re-circulation of material into the jets allows a mill of greater axial extent to be used than would be normal. Normally, when the axial height of the mill becomes too great then the material will not be efficiently re-circulated into the jet streams. Further, there would be a slowing up of the circulation by friction of the added peripheral surface. Reference is made to Patents 2,376,747 and 8 3,005,594 for a more detailed discussion of the effect of mill height upon the circulating gasses.
As has been indicated previously, in those instances where large quantities of easily ground material are to be treated, and other cases for other reasons, it may be desirable to introduce the feed by means other than an injector-venturi. As previously mentioned, screw feeding is not novel in itself, but it has heretofore been largely avoided in commercial application for the reasons previously stated. In the embodiment of the invention shown in FIGURE 5, however, a mechanical screw feed means is shown in combination with a re-entrant circulatory mill in which none of the aforementioned objectionable conditions are present.
As shown, the screw feed means 100 is provided in place of the venturi type feed assembly shown in FIG- URE l. The screw feed consists of a hopper 102 and mechanical screw 104 adapted to convey pulverant material along pipe 106 into classifying and grinding chamher 110. As shown, the classifying and grinding chamber 110 is substantially identical to the embodiment shown in FIGURE 1. Hence, prime numerals have been assigned to like elements andidentify said like elements as having a function that is the same as that described with regard to the embodiment shown in FIGURES 1 and 2.
In this embodiment, the shaft 82 is extended through the chamber 56, through the outlet 70' of the mill as well as through a fan casing 112. A hearing provides additional support for the added length of shaft 82.
Within the fan casing 112 a disk 114 is mounted on the shaft 82 and rotates therewith. A plurality of fan blades in the form of paddles 116 are mounted about the periphery of disk 114. The fan casing 112 communicates with the classifying chamber 56' through the exhaust opening 70. The gasses circulated within fan casing 112 are exhausted through outlet opening 118.
The fan casing 112 and paddles 116 are of such size as to be capable of handling all the gas discharged from the chamber 56 and in addition have enough excess capacity to cause the flow of gas from the outside of the mill into the chamber through the opening 120 thereby eliminating the stuffing box 88 shown in FIGURE 1. In
this way, means are provided'to assist in the dispersal and flow of material from the screw feeding means 100 into the vanes 96 which disperse the material into impact with the outer peripheral wall 62. This additional dispersal of the pulverant material carried in by the screw feed means together with the dispersing effect of the fan blades 96' is sufficient to overcome any of the disadvantages previously encountered with regard to screw feed means.
In FIGURES 3 and 4 there is shown a modification of the present invention wherein a small number of unusually large jets may be used or where the jet angle to the circulating stream is madevery aoute. Grinding mills of this type are sometimes desirable where extremely difficult-togrind materials are used.
As shown in FIGURE 4, the jets 122 are spaced about only one-third of the periphery of the chamber wall 124.
This arrangement is possible because, as previously described, the re-entrant gasses are assisted in the circulation by the vanes 126 rather than solely by the jet streams issuing from the nozzles 122. Gas is forced through the nozzles 122 by means of pressure developed in header 128 connected to a gas supply means (not shown). The vanes 126 are mounted on a disk 130 which is rotated by means of shaft 132 in accordance with the principles previously discussed. Material to be pulverized is fed into the classifying and grinding chamber 134 by any conventional means such as the venturi means previously described with respect to the embodiment shown in FIGURES 1 and 2.
In accordance with the invention of the present embodiment, the outlet pipe 138 projects into the classifying chamber 134. As shown, the portion of the outlet pipe 138 which is radially opposite the nozzles 122 extends all the way up to the disk 130 with only a minimum clearance therebetween. The radial portion of outlet pipe 138 which is away from the nozzles 122 extends only partially into the chamber 134. In this way large random particles deflected by impact with the jets issuing from nozzles 122 will not enter the outlet. Rather, they will be deflected by the outlet pipes into the circulating stream. Otherwise, the operation of the pulverizers shown in FIGURE 3 is substantially the same as that described with respect to the pulverizers shown in FIGURES 1 and 2 except for the use of a limited number of oversized nozzles 122 and the use of a specially constructed outlet pipe 138.
Referring now to FIGURE 7 there is shown a pulverizer wherein the fundamentals of the present invention are applied to a device such as is shown in FIGURE 6 of Patent 2,219,011 or in Patent 2,590,220. Devices of the type shown in these patents cannot classify to as low a particle size as can the devices previously described. However, they have certain advantages under some circumstances. For example, when a longer time element of contact of the material under treatment with the gaseous medium is desired devices such as are shown in FIGURE 7 have particular utility.
The device shown in FIGURES 7 and 8 comprises a feed means 140 of the venturi type similar to those previously described. The feed means 140 in this illustration communicates with the bent portion of a return feed pipe 142 which communicates with the chamber 146. A shaft 168 extends through the walls 148 and 150 of the chamber 146 and has hub 152 mounted thereon.
The pipe 153 is connected to a supply of gas which feeds the gas under pressure into header 154 and through nozzle openings 156. The nozzle openings 156 are angularly directed. The angular direction of the nozzles 156 provides jets with a greater shearing, tearing and impacting effect because they are angularly disposed with respect to the circulating stream of material. It should be noted that the wall 158, through which nozzles 156 extend, is curved and forms the end section of an elliptical form. The chamber 146 is in communication with straight pipe 160 which in turn is connected to a semi-circular section 162. The semi-circular section 162 is in communication with the straight section 142 and the outlet opening 167.
In all of the devices herein described, it should be realized that the feed can be introduced at a variety of points and still secure some of the benefits of the invention. However, the maximum benefit is obtained when the feed material is introduced more or less axially of the rotating vanes so that less energy is required to introduce the material into the mill by avoiding the fan action of the vanes. Further, the vanes have an opportunity to act directly on the feed material.
The pulverant material fed into the chamber 146 impacts on disk 164 where it is radially dispersed into the vanes 166 and radially accelerated outward to impact against the wall or periphery 158 of chamber 146. This action is provided by means of rotataing shaft 168 to which hub 152 is attached. The action of nozzles 156 is substantially the same as described in Patent 2,219,011. That is, the jet streams issuing from nozzles 156 cause the pulverant material circulating through chamber 146 and pipes 160, 162, and 142 to impact 'upon itself and thereby become finely ground.
The embodiment shown in FIGURE 9 is substantially the same as that shown in FIGURES 7 and 8. However, the chamber 170 is specially V-shaped adjacent the nozzles 172 so as to provide more efficient loading of the jet streams issuing therefrom. Further, the vanes 174 mounted on disk 176 which in turn is fixed to shaft 178 by means of hub 180 are specially shaped so as to concentrate the pulverant materials about the jet streams issuing from nozzles 172. Thus, the vanes 174 are provided with extensions 174A which cooperate with the inwardly angled portion 182 of the chamber wall so as to cause the pulverant material to be driven towards the jet streams.
In certain cases, particularly where the combination of hammer milling and jet grinding is desired, the peripheral walls of the devices shown in FIGURES 7, 8 and 9 may be serrated at that portion where the vanes are closely adjacent to the peripheral Wall. Thus, for example, in FIGURE 9 the peripheral wall 158 may be serrated over the area extending from the point marked to the point marked 182. In fact, serrated walls may be provided for any of the embodiments shown herein.
The improvement provided by the embodiment shown in FIGURES 7, 8 and 9 is that in addition to impacting the material against the casing as indicated above, it is circulated in the direction of rotation of the vanes and the returning gas from straight pipe 142 or its equivalent is also circulated by cooperation of the vanes and the casing. The flow of material is along the casing into the jets, which act as previously referred to in the description of FIGURE 1, and then through the apparatus towards the outlet 166.
The remainder of the gas and insufiiciently ground material, previously called re-circulated material, returns through the return pipe 142.
It should be pointed out that the tip speed of the vanes may generally be of a higher velocity in the device represented by FIGURES 7 and 8 than in the device represented by FIGURE 9.
As has been noted above, the operation of the vanes allows the mill to have a greater axial height. It has been found that such additional height is advantageous in certain operations in that a series operation, such as is desirable for certain grinding operations may be provided. Heretofore, most attempts to provide series operations have been unsuccessful due to the fact that jets in the second stage have to dissipate too much of their energy in accelerating or continuing the circulation of the considerable weight of gas and pulverant provided from the first stage and insufficient energy is available for classification. At this point it would be well to point out again that as the volume of gas in a given mill increases, the entrained force toward the outlet tends to carry larger particles out as a product. Increasing the height of the mill to slow this down has detrimental effects in that the loading of the jet streams is decreased. Due to the fact that in accordance with the present invention it is now possible to mechanically accelerate the gas and material from the first stage before it approaches a jet of the second stage and therefore increase the height of the mill, it is now possible to successfully arrange for multiple staging.
FIGURE 10 shows an example of a multiple stage grinding mill which has been found to be particularly effective in grinding certain materials. The mill comprises a first stage having a classifying and grinding chamber 200 through which shaft 202 extends. A stuffing box 204 connects the shaft 202 and provides a seal between the wall 206 of chamber 200. A gas supply 208 supplies gas into 'header 210 and through nozzle 212 in the manner which has previously been described. A feed assembly 214 of the venturi type feeds the material into the chamber 200.
The operation of the first stage of the device shown in FIGURE 13 is substantially the same as in the prior are devices. Thus, reference is made to Patent 2,032,827 for an explanation of the grinding operation within chamber 200.
The second stage of the device shown in FIGURE 10 consists of a grinding and classification chamber 220 which is substantially the same as the chamber shown in FIGURE 1. Thus, the disk 222 has vanes 224 mounted thereon and the disk is caused to rotate by shaft 202. A gas supply 226 supplies gas through header 228 and nozzle 230.
The vanes 224 capture the gas and pulverant mixture escaping through outlet 236 of chamber 200- and direct the pulverant material against the peripheral wall 238 in the same manner as described with regard to the embodiment shown in FIGURE 1. The pulverant material is forced to move along peripheral wall 238 into jet streams issuing from nozzles 230 and is thereby caused to break up into small pieces. The gas and product become entrained in the circulating vortex and eventually when it is classified to the correct size it escapes through outlet 240.
The two-stage mill tested has the same supply of energy to the jets in each of the two stages, although for certain materials desired at different particle size, more or less energy to one or the other stage might be desirable.
When using an injector type of feed, it has been found that for many materials an improved result is obtained when the direction of the injector is angularly opposed the plane in which the vanes are rotating. This is illus trated in FIGURE 11 which shows substantially the same mill as illustrated in FIGURE 1 except the injector 300 is arranged to feed material to be grounded into the mill at an acute angle relative to the disk 394.
The numerals used to describe the embodiment shown in FIGURE 11 are the same as those used in FIGURE 1 but with a 3 in front of each numeral. Therefore, operation of the mill is the same.
However, it is to be noted that the injector 300 feeds material into the mill at an acute angle with respect to the disk 394 and in a direction opposed to the direction of rotation of disk 394 and vanes 396;
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.
1. Apparatus for reducing material to a finely divided form comprising an endless casing, means to introduce into the outer portion of said casing at least one stream of high velocity elastic fluid, said stream having a component of movement which is forward in a rotational direction and a component of movement which is transverse to said rotational direction, means to introduce material to be ground into said casing, a grinding zone abutting the outer periphery of said casing, rotatable vanes positioned within said casing to cause a substantial portion of the material to be ground to be circulated closely adjacent at least a portion of the periphery of the casing which includes said high velocity stream, the periphery of at least a portion of said vanes being in the outer portion of the grinding zone, and discharge means spaced inwardly of the periphery of said casing.
2. Apparatus for the reduction of material to finely divided particles comprising an endless curved chamber, means to introduce a stream of gaseous fluid adjacent the periphery of said curved chamber, said stream being directed to have both rotational and radial components of movement, means for introducing into said chamber and into said gaseous stream feed material to be divided, said gaseous stream having sufiicient energy to impose centrifugal force on the gas and material flowing therein, a grinding zone abutting the outer periphery of said chamber, first rotatable vanes within said casing positioned to forcibly mix feed material with material circulating in said stream, second rotatablevanes positioned closely adjacent the periphery of said chamber to cause circulating material and a portion of said gas stream to flow along and adjacent at least a portion of the periphcry of said curved chamber, the periphery of at least a portion of said second vanes being in the outer portion of the grinding zone, and means disposed radially inwardly of said periphery for the discharge of said gas and divided material.
3. In a pulverizing apparatus, an endless casing pierced by nozzles for the introduction of a gaseous fluid directed to cause a high rate of circulation of the gasses within the casing, means, to introduce a material to be ground into the casing so that it will circulate adjacent a peripheral wall of the casing as a reentrant circulatory stream, a rotatable element within said casing havinga multiplicity of vanes, said vanes being spaced in close relationship to the inner periphery of the casing and being of sufiicient width in relationship to that part of the re-entrant circulatory stream which is adjacent the inner peripheral wall to cause an increase in velocity of flow of both the gas and re-entrant circulatory stream at the casing periphery as they flow toward the nozzles.
4. In an apparatus for the comminution ofmaterials, an endless casing having at least one nozzle piercing the periphery of said casing and adapted to supply at least one jet of an elastic fluid at high velocity into said casing which include said jet, a grinding zone abutting the outer periphery of said casing, said grinding zone being traversed by said elastic jet, a rotatable element provided with a multiplicity of vanes mounted at least at the periphery of said element, said vanes being spaced in close relationship to atleast a portion of the inner periphery of said casing, means to feed material into said rotatable element so that the vanes will cause said material to impact against at least a portion of the inner peripheral wall of the casing, the periphery of said vanes being in the outer portion of the grinding zone, and gas and material withdrawal means spaced inwardly of the periphcry of the casing.
5. Apparatus according to claim 3 wherein said feed means is positioned to direct material against said rotatable element.
6. Apparatus according to claim 3 wherein said feed means is positioned to introduce feed material directly into the vanes on said rotatable element.
7. Apparatus according to claim 3 wherein said feed means is positioned to direct material against said rotatable element and in a direction opposite to the direction of rotation of said element.
8. Apparatus according to claim 3 wherein at least that.
portion of the peripheral wall adjacent the nozzle is tapered outwardly towards the nozzle.
9. Apparatus according to claim 8 wherein said vanes are tapered to conform to the tapered portion of said wall.
10. Apparatus according to claim 3 in which at least that portion of the casing against which the feed material is impactedhas a roughened surface.
11. Apparatus according to claim 3 in which the rotating element is a disk and the vanes are mounted adjacent to the periphery of said disk.
12. Apparatus in accordance with claim 3 in which that portion of the vanes which is closest to the nozzles is shaped to be spaced away from the impact of the jets created by said nozzles.
13. In an apparatus for the comminution of materials, an endless casing having at least one nozzle piercing the periphery of said casing, means adapted to supply an elastic fluid at high velocity through said nozzle into said casing, a rotatable element provided with a multiplicity of vanes at least at the periphery thereof, said vanes being spaced in close relationship to at least a portion of the inner periphery of said casing which includes said nozzle, said vanes being positioned axially to the side of said nozzles, feed means for introducing material to be comminuted into said casing, gas and material outlet means spaced inwardly of the periphery of the casing, a housing mounted in communication with said outlet means, and fan means within said housing for causing air to flow into said casing adjacent said feed means.
14. Apparatus, in accordance with claim 13 in which material is fed into said apparatus by a mechanical forcing means.
15. A pulverizing device of the gaseous fluid jet type comprising a first grinding chamber having at least one gaseous jet means adjacent its periphery, feed means for feeding material to be ground into said chamber, and outlet means for discharging gas and ground material from said first chamber, a second grinding chamber in communication with said outlet means, at least one gas jet means adjacent the periphery of said second chamber, a plurality of rotatable vanes mounted within said second chamber, said vanes being positioned to rotatably accelerate into the second mentioned jet the gas and partially ground material discharged from said first grinding chamber into said second grinding chamber, and discharge means mounted inwardly of the periphery of said second grinding chamber to discharge gas and ground material from said second chamber.
16. Apparatus for the comminution of materials comprising a passage which closes upon itself to define an endless passage, angularly directed gas jet means for causing gas to flow in said passage, said gas jet producing means being in at least a portion of the periphery of said passage, the gas flow area immediately adjacent said periphery which includes said jet means defining a grinding zone, means to feed material to be comminuted into said passage, rotatable mechanical means positioned to accelerate the material and gas flowing along the wall of said passage at the grinding zone and to force said material into said jet means, and discharge means on a remote portion of said endless passage.
17. In an apparatus for the comminution of materials, an endless casing having a plurality of nozzles piercing the periphery of said casing and being adapted to supply jets of elastic fluid at high velocity into said casing, said nozzles being spaced about substantially less than the entire periphery of said casing, a rotatable element provided with a multiplicity of vanes mounted on at least the periphery thereof, said vanes being spaced in close relationship to at least a portion of the periphery of said casing, means to feed material against said rotating element, a portion of said vanes extending radially inwardly from the periphery of said element and on the side of said element on which said material impacts, whereby said radial portion of said vanes causes said material to impact against at least a portion of the inner peripheral wall of said casing, and gas and material withdrawal means spaced radially inwardly of the peripheral wall of said casing and the opposite side of said rotatable element from said feed means, said withdrawal means comprising a conduit mounted in a casing wall, a portion of said conduit which is spaced closer to said jets having a greater axial length than the remainder of said conduit.
18. In an apparatus for the comminution of materials, an endless casing having at least one nozzle piercing the periphery of said casing and being adapted to supply a jet of elastic fluid at high velocity into said casing, a rotatable element within said casing provided with a multiplicity of vanes mounted on at least the periphery thereof, means to feed material into said casing adjacent said rotating element, whereby said vanes will cause said material to be circulated adjacent at least a portion of the periphery of the casing, and gas and material withdrawal means, said gas and material withdrawal means including a second casing in communication with said first-mentioned casing, said second casing being in communication with said first-mentioned casing at a position spaced radially inwardly of the peripheral wall of said first-mentioned casing, and a rotatable exhaust means within said second casing.
19. Apparatus for the reduction of material to finely divided particles comprising an endless curved chamber, a plurality of nozzles in a peripheral wall of said chamher to introduce jets of gaseous fluid adjacent the periphery of said curved chamber, said nozzles being positioned to create a gaseous stream having both rotational and radial components of movements, means for introducing into said chamber feed material to be divided, said gaseous stream having sufiicient energy to impose centrifugal force on the gas and material flowing therein, rotatable mechanical vanes disposed between said means for introducing feed material and said nozzles, said rotatable mechanical vanes being positioned closer to said peripheral wall than the inner extent of the major force of said jets and the zone of greatest intensity of said stream created by said jets to cause circulating material and a portion of said gas stream to flow along and adjacent at least a portion of the periphery of said curved member and to force said circulating material into said jets, and means disposed radially inwardly of said periphery for discharge of said gas and divided material.
20. Apparatus according to claim 19 wherein said rotatable mechanical vanes comprise a disk having a plurality of vanes mounted on either side thereof, said vanes mounted on the side of said disk adjacent said feed means being positioned to engage said feed material and cause it to impact against at least a portion of the inner peripherai wall of said casing, and said vanes mounted on the side of said disk adjacent said stream of gaseous fluid being spaced in close relationshi to at least a portion of the inner periphery of said casing and being positioned to accelerate said stream and circulating material entrained in said stream toward said peripheral wall.
21. Apparatus for the communition of materials comprising an endless casing, said casing including a grinding chamber and a classifying section, said grinding chamber including a curved wall, a plurality of nozzles piercing said wall, said nozzles including gas supply means cooperating therewith to create jets of elastic fluid, the angle of said nozzles with respect to a tangent to said wall being such as to create a component of gas flow along said wall, a plurality of rotatable vanes within said grinding chamber, said vanes being positioned close to at least a portion of said wall for accelerating material and gas flowing along said wall and into the jets, said classifying section including a curved conduit communicating at one end with said grinding chamber at a position to receive material and gas flowing from said nozzle and communicating at its other end with said grinding chamber at a position spaced radially inwardly of the periphery of said rotatable vanes, gas and material discharge means in said classifying section, and material feed means opening into said grinding chamber at a position spaced radially inwardly of the periphery of said vanes.
22. Apparatus in accordance with claim 19 wherein said peripheral wall is conical, the axis of the cone defining the wall being parallel to the axis of curvature of said peripheral wall, and the wall converging inwardly to said nozzle.
References Cited HARRISON L. HINSON, Primary Examiner. HARRY F. PEPPER, JR., Examiner.