US3446218A

US3446218A - Agglomerating finely divided material

Info

Publication number: US3446218A
Application number: US536348A
Authority: US
Inventors: Harold T Stirling
Original assignee: Stirling Sintering Co
Current assignee: Stirling Sintering Co
Priority date: 1966-03-22
Filing date: 1966-03-22
Publication date: 1969-05-27
Anticipated expiration: 1986-05-27

Description

May 27, 1969 H. T. STIRLING AGGLOMERATING FINELY DIVIDED MATERIAL Filed March 22, 1966 FIG.

IN VEN TOR. 6641 040 77 577,94 nvo MSW F|G.30 FIG.3C

United States Patent 3,446,218 AGGLOMERATING FINELY DIVIDED MATERIAL Harold T. Stirling, Pittsburgh, Pa., assignor to Stirling Sintering Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 22, 1966, Ser. No. 536,348 Int. Cl. B01f 5/18, 9/02 US. Cl. 134-57 6 Claims ABSTRACT OF THE DISCLOSURE This application relates to a method and apparatus for handling finely divided particles, and, more particularly, to a device capable of handling and wetting finely divided particles without forming clouds of dust.

During many industrial processes a substantial amount of material is obtained in the form of microscopically fine particles. Heretofore it has been extremely diflicult to utilize these microfines. It has been equally diflicult to dispose of the particles since they are formed in huge quantities. Accordingly a great deal of finely rdivided ma terial has been stockpiled. The cost of the real estate involved in the stockpiling operation has been in and of itself a long standing problem in many industries. Large quantities of this material would willingly be sold at extremely low prices, or even given away, merely to reduce the size and consequent cost of otherwise necessary stockpiling operations.

Recently, operations have been developed in which the finely divided dust-like particles have been pelletized hereby forming agglomerates which can be handled, and thus the finely divided particles are converted into valuable and useful products. In order toform agglomerates or pellets from finely divided particulate material it is necessary to wet the material to a predetermined moisture content such as for example 5 to 20% moisture.

Heretofore the processes used to pelletize finely divided material's involved adding such materials to a pelletizing drum or equivalent apparatus such as a cone pelletizer, disk pelletizer, or the like. Water was then added, in the pelletizer, to adjust the moisture content of the material. It has now been found that the capacity of a pelletizing apparatus can be significantly increased if water is added to the finely divided dust-like particles to adjust the mixture to the desired moisture content before introducing the particles into the pelletizing apparatus. In this manner not only is the pelletizer simplified by elimination of water sprays, water pipes, controls, valves and other miscellaneous equipment, but the necessity of moistening the particles in the pelletizer is eliminated thereby allowing the full capacity of the pelletizer to be used for pelletizing. This results in a significant increase in output. The average residence time of the particles in the pelletizer is also decreased when the particles in the pelletizer are wet when they enter.

It is an object of this invention to provide apparatus for handling extremely finely divided material.

Another object of this invention is to provide means for handling and treating finely divided material to produce particles that have no tendency to form dust clouds.

A further object of this invention is to provide a method and apparatus for Wetting finely divided particles which would normally resist such wetting due to their finely divided nature.

The invention resides in certain novlel features of process and apparatus and in the combination and arrangement of steps and of the parts of the apparatus in which the invention is embodied; land the advantages of the invention will be apparent to those skilled in the art to which the invention pertains from the following description of the embodiments thereof described with reference to the accompanying drawings in which:

FIGURE 1 is an elevational view of the apparatus shown partially in cross section,

FIGURE 2 is a plan view of the wetting drum of the invention,

FIGURE 3 is a vertical cross sectional view of the wetting drum, and

FIGURES 3n, 3b, and 3c are vertical, cross-sectional views showing alternate embodiments of the incoming feed duct and water inlet means taken on lines A-A of FIGURE 3.

Referring now to the drawings there is provided a hopper '10 which is filled from any suitable source with finely divided dust-like particles. Hopper 10 is mounted on means to assist the flow of particles from the hopper generally indicated by reference numeral '12, which in turn is mounted on inlet means 14 of screw conveyor 16. Means 12 is provided to ensure positive flow of the finely divided material from hopper 10 into screw conveyor 16 in any suitable way such as by vibrating the material in the hopper. For this purpose in the embodiment depicted vibrating cone 18 is mounted in casing 20 of means 12 and extends into hopper 10.

Casing 20 is joined to the hopper 10 and to inlet '14 of screw conveyor 16 by flexible means 22, 24 adapted to isolate the vibrations of flow assisting means 12 from both the hopper 10 and the screw conveyor 16. To this end connecting means 22, 24 may comprise flexible rubber sealing means to prevent the discharge of any finely divided material into the atmosphere. A motor 26 or other suitable device is mounted on casing 20 to vibrate cone 18. The use of flow assisting means 12 with its vibrating cone 18 ensures continuous flow of the feed material by eliminating bridging of the fines which otherwise would normally take place when a hopper or bin is filled with finely divided material. Similar equivalent apparatus can be substituted for the above described means 12 but advantageously some device should be used to ensure a continuous flow of the feed material.

The material from hopper 10 is fed into doubledlight screw conveyor 16 which is one-half pitch for the first half of the length and then standard pitch for the remainder. The configuration of the screw operates to control the rate of feed and eliminate gross variations in the rate of feed of the finely divided particles.

In this manner flooding of aerated materials is prevented and the effect of any surges of material from the bin are minimized. The one-half pitch for the first half of the conveyor can suitably be obtained by using a double flight of standard pitch for the first half of the conveyor and a single flight of standard pitch for the remainder. Screw conveyor 16 is provided with variable speed drive means 28 which is operated by a motor 30 or other prime mover. The speed at which the screw conveyor is actuated is controlled by speed controller 31 in accordance with a control system described hereinbelow.

Screw conveyor 16 is provided with two valved

outlets

32, 34. Outlet 32 transfers the material into the next stage of the feed mechanism to the wetting apparatus. If it is desired, however, to bypass the wetting system valve 33 in conduit 32 is closed and valve 35 in conduit 34 opened thereby allowing the material in the screw conveyor 16 to bypass the system, and be delivered to other processing equipment. Material discharged by screw conveyor 16 through outlet 32 is deposited onto continuous conveyor belt means 36 disposed in a dust tight housing 38. Continuous conveyor 36 is driven by any suitable variable speed drive means (not shown).

Referring now to FIGURES 2 and 3 of the drawings, dust wetting drum 40 comprises a rotatable drum having a generally frusto-conical side wall 41. The smaller end 42 of drum 40 opens upwardly to receive feed material, and the larger end 44 forms the base and back wall of the truncated conical member. The open end 42 of drum 40 is provided with a lip 46 to direct the material as it is discharged from the wetting drum onto suitable removal means such as conveyor 55.

Incoming feed is introduced through the small open end 42 of wetting drum 40 through a chute member 50 having its discharge end positioned substantially below the level of material in the wetting drum whereby the incoming dust-like material is fed into the drum below said level of material. Water is sprayed into drum 40 through conduit 45. The incoming dust becomes moist ened because the material in the wetting drum into which the incoming microfines are fed has previously been wetted and the particles therefore have wet, glossy surfaces. Thus the particles in drum 40 either individually or in lumps or agglomerates, are wet with surface moisture. As this wet material rolls past the inlet chute 50 for the dust-like material, the incoming feed attaches to the moistened surfaces almost in the same manner as a magnet will pick up iron powder. Because of this ability of the already moistened material in drum 40 to pick up the incoming feed, a temporary unexpected shutoif of water will not cause a cloud of dust as would be present in a pug mill or the like, and furthermore the moisture content of the material discharged from the wetting drum will always be maintained uniform.

Wetting of hot or cold microfines such as precipitator dust or other very fine material has heretofore been approached with the idea of breaking down the surface tension of the particles with a fine spray of water. This requires a relatively great amount of time i.e., in excess of one minute. By the present system, once the first surge of material is wet, the revolving fines and/or small seed pellets with surface moisture present on the exposed surface thereof begin to gently roll under and around the entry chute. This depth of flowing or rolling material buries the entire entry chute so that the incoming fine dust cannot escape. The continuous rolling action causes the discharge end of the incoming feed duct 50 to be sealed by the flow of wet rolling particles with glossy surfaces from the moisture present thereon. The dry incoming dust is then picked up on the wet sticky surfaces of the gently rolling particles.

Water sprays continuously discharge onto the rolling particles in order to keep them wet so that the surface area will maintain its layer of sticky moisture. Once a wet particle of agglomerate has gone under the incoming feed duct 50 and picked up additional dry dust on its wet surface a portion of its surface moisture is absorbed into the previously dry dust now adhering thereto. The moissurface of the initially wet particles adhering to the surface of the intially wet particle eliminates the water repellency that dry dust particles normally possess. It then becomes possible to further wet the new particle (agglomerate) by spraying the surface of the revolving material with water. This causes the surface of the new particle to become wet and glossy and capable of picking up additional dry dust when it passes under the incoming feed duct. The above described cycle is repeated many times on each particle until it is discharged from the wetting drum. The treated material discharged from the wetting drum had a very uniform moisture content. The particles are, of course, larger than the extremely fine particles originally fed thereto and therefore have no 4 tendency to form clouds of dust, are easily handled, and may be further processed in many ways.

The water added to drum 40 can be added either within dust inlet 50 or directly onto the surface of material in the wetting drum and, if desired, in both locations. To this end water inlet conduit 45 may be provided with two branch conduits 47, 40 (FIG. 3a) each fitted with a spray nozzle. Spray nozzle 51 on branch 47 will desirably form a fine, mistlike curtain of water through which the incoming dust will pass. In this manner the spray helps both to wet the incoming material by starting to break down the surface tension and also to keep the already moist surfaces wet. The fine spray inside chute 50 will also help in keeping the incoming dust from blowing back up the entry chute. At least one one spray nozzle 53 on conduit branch 49 is advantageously adapted to direct a fine spray over a large portion of the surface of material in drum 40. In FIGURE 1, for example, there is shown a modification wherein two spray nozzles 53 are used.

While the embodiment of the invention shown in FIG- URES 2 and 3a utilizes a plurality of sprays it may be desirable to use only a single spray whereupon the spray may be directed only within chute 50 as shown in FIG- URE 3b or the spray may be discharged solely onto t e surface of the material in drum 40 as shown in FIGURE 30. In all embodiments of the invention, even where the sole spray is located within chute 50 the dust is primarily wetted because the rolling wet material picks up the dry dust as the material with a wet, glossy, sticky surface passes the entry chute 50.

In order to control the amount of wetting, a proportioning system should be used in conjunction with the wetting drum. The automatic control system of the invention comprises a weight detector 60 of known design adapted, in combination with computer 62, to continuously measure and derive a signal having a magnitude proportional to the weight of material on conveyor 36. Computer 62 is set to deliver a predetermined rate of feed. A constant feed rate is maintained by varying through speed controller 31, the speed of screw conveyor 16 in accordance with variations in the detected weight of material on conveyor 36. Water proportioning means comprising flow recorder controller 64 is operatively associated with computer 62 and adapted to adjust the rate of addition of water into drum 40 upon variations in the amount of dry material fed thereto as determined by fluctuations in the detected weight of material on conveyor 36.

In one embodiment of the invention the chute 50 is shaped in such manner (FIG. 1) that a maximum of surface is available for contact between the flowing wet particles and the incoming dry dust. Accordingly, the open end of chute 50 is provided with a horizontally extending bottom opening and a second open portion extending generally in the same direction as the bottom 44 of drum 40. To the same end the horizontal cross sectional area of the chute 50 may be larger at the bottom than at the top thereof.

The entire feed system is enclosed in a dust tight housing from the bin 10 to the open end 42 of wetting drum 40. The system described thereby eliminates air pollution. No dust rises from the open mouth 42 of the drum because the surface particles in the drum are sufficiently wet to ensure that none become airborne. The effectiveness of the surface moisture is enhanced due to the depth at which the incoming feed is added.

The drum 40 is adjustably set at an incline of between about 20 and 30 degrees upwards from the horizontal to provide the desired degree of wetting. The bottom 44 of the wetting drum is reinforced by structural means 61. The drum 40 is rotated by motor 63- through reducer 65 and stub shaft 67.

As set forth above, the wetted dust can be further processed and is especially useful as feed material for a pelletizer. For this use the prewet particles increase the I claim:

1. Apparatus for the handling and treatment of dry dust-like material comprising, a hopper for said material, conveyor means for receiving said material frfom said hopper, a dust-tight housing for said conveyor means, downwardly extending chute means for receiving said material from said conveyor means and for delivering said material into a drum for forming a bed of material therein, a drum adapted to receive said material from said chute, and means to spray water onto the material in said drum, said chute extending into said drum and into said bed of material, at a point below the normal surface level of material in said drum whereby the mouth of said chute is sealed by the material already in said drum and further comprising means to rotate said wetting drum to cause the bed of material in said drum to continuously flow past said mouth of said chute whereby incoming solid particles are continually picked up on the surfaces of the wet particles in the interior of the bed of material in said wetting drum.

2. The apparatus of claim 1 wherein said conveyor means comprises, a screw conveyor adapted to receive said material from said hopper, and a continuous belt conveyor adapted to receive material from said screw conveyor and to transfer said material to said chute means.

3. Apparatus as defined in claim 2 wherein said screw conveyor means is divided into two sections, a first section adjacent the inlet thereof having flights, the pitch of said flights being about one-half the pitch of the flights in the second section adjacent the outlet thereof, wherein means are provided contiguous to the connecting means between said hopper and said screw conveyor for vibrating the dust in said hopper to ensure substantially continuous flow of said dust from said hopper into said screw conveyor, and further comprising bypass means to permit said material to bypass said wetting drum.

4. The apparatus of claim 1 in which the downwardly extending chute means extends through an opening in the drum and downwardly below the lowest level of the opening in the drum.

5. The apparatus of claim 4 and further comprising, means to detect the amount of feed material" added to said drum'member, and means to automatically adjust the rate of addition of water in response to changes in said detected amount.

6. The apparatus of claim 4 wherein said means to add water to said drum member comprises means to spray water onto the surface of the bed of material in said drum, and said means to feed material into said drum comprises a chute extending below the surface of said bed of material.

References Cited UNITED STATES PATENTS 2,586,818 2/1952 Harms 23--313 2,834,044 5/ 1958 Antonsin 233 14 3,092,489 6/1963 Smith 23-3 13 2,297,300 9/1942 Hardesty 233 13 2,304,382 12/1942 Shoeld 23313 2,436,771 2/ 1948 Hood 23-3 13 2,860,598 11/1958 Loesche 233 13 2,961,411 11/1960 Klugh 23-313 FOREIGN PATENTS 1,156,013 10/1963 Germany. 612,359 l/1961 Canada.

NORMAN YUDKOFF, Primary Examiner.

US. Cl. X.R.