US3409273A

US3409273A - Method and apparatus for blending pulverulent materials

Info

Publication number: US3409273A
Application number: US683956A
Authority: US
Inventors: Edgar J Kelly
Original assignee: Amcol International Corp
Current assignee: Amcol International Corp
Priority date: 1967-11-17
Filing date: 1967-11-17
Publication date: 1968-11-05
Anticipated expiration: 1985-11-05

Description

Nov. 5, 1968 E. J. KELLY 3,409,273

METHOD AND APPARATUS FOR BLENDING PULVERULENT MATERIALS Filed Nov. 17, 1967 INVENTOE. Enema 1]. KELLS/ United States Patent O" 3,409,273 METHOD ANDAPPARATUS FOR, BLENDING PULVERULENT MATERIALS Edgar -J. Kelly, Lake Zurich, IIL, assignorto American Colloid Company, Skoki e, Ill., acorporation of Delaware g Filed Nov. 17, 19 67, Ser. No. 683,956

' 7 Claims. (Cl. 259 -4) ABSTRACT OF THE. DISCLOSURE A method and apparatus for mixing pulverulent or finely-divided materials by fiuidizing such materials to reduce the friction between the particles soas to facilitate combining, and recirculating such fluidized materials within an enclosed container so as to'effect complete blending and mixing thereof, permitting discharge' of unsegregated material. 7

Pulverulent or granular materials, such as clays, cements, crushed minerals, coal, etc. are generally composed of particles which differ in size and when a silo or hopper is being filled, larger or coarse particles tend to separate from finer particles. Such segregation results in the initial discharge of material high in fines and a later discharge high in coarse particles, whereas constancy and homogeneity is desired and often essential. Mixing devices have been proposed in the prior art which attempted to 3,409,273 Patented Nov. 5, 1968 flow path of fluidized pulverulent material particles and recirculating such fluidized material by aspirating means.

Another object of the present invention is to blend pulverulent materials with an apparatus having zones or regions of varying pressure within a substantially cylindrical container and having stationary mechanical means disposed within the container for controlling the flow path of the fluidized material.

Still another object of the present invention is to blend finely divided, powdered or granular material either continuously or by a batch process selected by controlling the obtain homogeneity of a single material or a plurality of materials, but such devices were expensive, generally capable of handling only small batches and not satisfactory. The use of stirring arms with and without injected air and the use of air alone in specialized constructions have been tried. Generally, the air was supplied at high pressure thereby increasing the cost, and the mode of operation of these prior devices was not capable of producing satisfactory results.

'It has been found that the particular interior configuration of blenders or hoppers is critical to obtaining a satisfactory mix of the material. In the prior art, the use of nozzles positioned in the lower portion of a container or hopper so as to discharge air under high pressure'has been tried in an attempt to create vortices within the container or hopper so as to effect satisfactory blending. However, there are disadvantages to such prior art devices caused by the turbulence created within the container due to the introduction of high pressure air and difliculty in controlling the flow path of the fluidized material within the container due to such air turbulence.

The present invention provides 'an inexpensive apparatus of large capacity, which may be used to continuously blend and discharge material at exemplary rates of 400 to 600 tons per hour (or in batches of, for example, 30-40 tons each), the apparatus being capable of being used either as a silo or storage container or a blender or both. Segregation of coarse and fine material components is prevented by a novel mode of operation including tangential feed into the upper portion of an enclosed chamber, and the movement of the material in a series of successive inwardly contracting and outwardly expanding spirals to the lower portion of the chamber, followed by axial and upward return for recirculation and effective mixing. The repeated reversal in the direction of movement of the material (inwardly, outwardly, up and down) is facilitated by the use of an aspirator for the upward movement of the material, the presence of air fiuidizing the material and permitting a large tonnage to be mixed within a very short period of time.

Accordingly, it is a general object of the present invenvolumetric or weight rate of flow of materials into an enclosed container relative to the volumetric rate of flow of air supplied to aspirating means used for recirculating and fiuidizing material.

A further object of' the present invention is to mix pulverulent material within a container by introducing material into the upper portion of the container by air transport in a tangential direction and blending such material by controlling the downward flow of the fluidized material and recirculating such material by aspirating means.

Other objects and advantages of this invention will be readily apparent in the following description when considered in connection with the appended drawings.

In the drawings:

FIG. 1 is a side elevation sectional view of an apparatus for blending pulverulent material constructed in accordance with the present invention;

FIG. 2 is a top plan view of the apparatus as shown in FIG. 1, with a portion thereof shown in section;

FIG. 3 is a top plan view of a portion of the apparatus shown in FIG. 1, taken along the line 3-'-3; and

- FIG. 4 is a side elevation sectional view taken along the line 44 of FIG. 3.

The exemplary form of apparatus of this invention shown in the appended drawings is illustrated by the blender and container 10 which comprises an upper cylindrical portion indicated at 11 and a lower portion 12 in the form of an inverted truncated cone, 'this inverted truncated cone being connected to the upper cylindrical portion 11. The lower or discharge portion of the cone 12 is preferably provided with a valved material outlet indicated at 13; the top of the container 10 is provided with a top wall 14 having a central aperture in which there is held a removably attachable, inwardly extending deflector 15 having a conical lower surface 16. Another aperture in the top wall 14 is in communication with a vent pipe 17 which may lead to the atmosphere or to a small dust collector (not shown).

The periphery of the upper cylindrical portion 11, adjacent the top wall 14, is provided with a tangential material inlet 18. It is to be understood that the material supplied to the mixer and blender 10 may be introduced in airborne suspension or the material may be supplied to the blender by gravity or any other means. Pulverate material supplied by air transport is most often employed and therefore inlet line 18 is shown provided with a manually adjustable valve 19, shown in FIG. 2. It may also be noted that the inner surface of the cylindrical portion 11 immediately adjacent the inlet may be lined with a wear pad 20, such wear pad extending for 60-120 of the arc of. the portion 11.

To facilitate blending and eliminate segregation of the particulate pulverulent or granular material being blended, means are provided for controlling and reversing the downward movement of the material supplied. As

shown best in FIG. 1, the blender is provided with an inverted truncated, conical baflie 21 the upper edge 22 of the baflie being attached to the inner surface of upper cylindrical portion 11 slightly below the level of the inlet pipe 18. The lower edge 23 of the baflie 21 opens downwardly. Very good results have been obtained when the diameter of the baflie 21 at its lower or discharge edge 23 is on the order of 0.4 to 0.6 D, where D represents the diameter of the upper cylindrical portion 11 of the blender. The inwardly and downwardly extending directional baflie 21 is maintained in a position by three or more struts, one of which is indicated at 24, the struts being welded or otherwise suitably attached to the walls of the blender and to the baflie.

It will be understood that the upper or inner surface of the baffle 21 directs the incoming pulverulent material towards the center of the blender. Material so directed in a constricting spiral path is then deflected by a second conical baflie 25 (shown held in position by struts, one of which is shown at 26), the upper surface of the baffle 25 being virtually normal to the upper surface of baflle 21 but spaced therefrom, thereby causing the material to be reversed in its direction of downward flow in an expanding spiral towards the inner surface of the lower, inverted cone portion 12 of the blender. Again it has been found that very eflective operation is obtained when the diameter of the lower marginal edge 27 of bafiie 25 is on the order of from about 0.4 to 0.6 D. The conical baflie 25 may be welded or suitably attached at its upper end to the outer wall of aspirator pipe section 34.

It may be observed that by the construction described. whether the incoming pulverulent material is fed by gravity or in airborne suspension, the incoming material is caused to swirl and cascade downwardly, reversing its direction from the external areas of the blender towards the center and then again to the outside and again towards the center. The normal tendency of coarse particles to find their way to the sides of the hopper or container are thus repeatedly thwarted and an effective mixing of coarse and fine particles is obtained.

The blender 10 is also provided with additional mixing and aspirating means which repetitively circulates the material within the blender and facilitates discharge of a homogeneous mixture of particulate material differing in particle size. Such additional aspirating and mixing means comprise the air inlet pipe 28 extending through the lowermost portion of cone portion 12 and terminating in the vertically and centrally oriented nozzle 29 whose upwardly directed open end is of smaller diameter than the pipe 28.

The pipe 28 is preferably supplied with air at a relatively low pressure, for example, to pounds per square inch gauge, but in suflicient quantity ot fluidize the pulverulent material, the volumetric rate of flow of air being controlled through a valve 30. The upwardly directed converging nozzle 29 is positioned and spaced in operative relation to a shroud 31 carried by the lower end of an aspirating pipe 32 which, in turn, is connected by an expanding conical pipe section 33 to the upstanding axial pipe section 34 which terminates below the conical deflecting surface 16 of the deflector carried by the top wall 14 of the blender. Preferably, the upper or discharge portion 35 of the aspirator pipe section 34 is below the level of the supply inlet pipe 18 and approximately at or slightly above the upper edge 22 of the baflie 21, as illustrated.

It will be noted that the upper open end of nozzle 29 is in spaced relation with the inner walls of the shroud 31 whereby the velocity of theincoming air, together with the reduced pressure caused by such velocity, aspirates or sucks in the material contained in the lower portion of cone 12 and causes such material to be conveyed upwardly through the aspirator pipe section 34 and discharged upwardly against the conical lower deflecting surface 16, thereby spreading the fluidized material radially in the upper end of th cylindrical portion 11 of the blender. The aspirating pipe sections may be supported from the walls of the blender by means of struts, one of such struts being indicated at 36.

Disposed below baflle 25 is means to maintain the flow path of fluidized material near the inner wall of the lower cone portion 12 of the blender, indicated generally by the reference numeral 37. Flow path control means 37 comprises a gas pressure inlet manifold pipe 38 connected to a gas pressure source (not shown) located exteriorly of container 10 through an air flow control valve 39. The flow path control means 37 also includes a plurality of toroidal gas discharge pipes 40, each of which has a plurality of radially inwardly directed discharge openings 41, as seen best in FIGS. 3 and 4.

The flow path control means 37 will create a gas pressure zone in the lower cone portion 12 of the blender 10 which exceeds the ambient pressure within the container so that the spiraling cascading pulverulent material passing into the upper end of lower cone portion 12 will be forced to flow in the peripheral area adjacent the inner wall thereof. To prevent the fluidized material, particularly the more coarse particles of such material, from adhering to the inner wall of the lower cone portion 12 of the container, a plurality of fluid injecting pads 42 may be positioned around the periphery of the inner walls of this lower portion of the container. Each of the fluid pads 42 are connected through a coupling to an external gas supply source (not shown).

In operation, pulverulent material is introduced into the blender 10, preferably by air transport through the material supply inlet pipe 18 by opening valve 19 disposed in such pipe. As mentioned above, the material may also be fed into the blender 10 through gravity feed into the peripheral upper end of the upper cylindrical portion 11 of the blender. Simultaneously with the introduction of the pulverulent material, valve 30 in air inlet pipe 28 is opened so that a relatively high velocity, but low pressure, stream of air is introduced into the blender through the recirculation pipe section 34 into the upper portion of the blender. The air discharged from the upper end 35 of recirculator pipe section 34 will impinge upon reflector 16 and spread radially through the upper end of the cylindrical portion 11. Since the pulverulent material is introduced in a tangential direction the material will combine with the radially discharged air so as to form a confluent flow of fluidized pulverulent material moving in a downwardly spiraling direction guided by the baflle 21 towards the center of the blender.

This downward spiraling stream of fluidized material contracts until it passes through the lower opening 23 of battle 21 and is then expanded and directed by baflle 25 into the upper end of the lower conical portion 12 of the blender. The cascading flow of pulverulent material will continue proximate the inner wall of the lower portion 12 of the blender towards the central region in which the aspirating means is positioned by virtue of the higher pressure gas zone created by the flow directing means 37. The fluidized material continues toward the discharge opening in the lowermost end of the cone portion 12, but as it approaches the region of the aspirating means the material will be drawn or sucked into the aspirating means due to the low pressure region existing at the discharge end of the inlet nozzle 29. In this manner, the material will be further fluidized and recirculated to the upper end of the blender 10 through the recirculation pipe section 34.

It will be appreciated that the blender 10 may be operated so as to mix materials either continuously or by a batch method. The weight rate of flow of pulverulent material into the blender through inlet pipe 18 may be selected by means of control valve 19. The volumetric rate of air flow introduced into the blender will also be controlled by selective operation of air inlet control valve 30. The amount of pulverulent material which will collect at the discharge opening of the blender will thus be controlled by balancing the amount of material introduced with the amount of air introduced so thatall, or a portion thereof, may be aspirated and'continuously'recirculated within the container. In operation as a'batch method, theiamo'unt of air introduced will be sufficient so as to continuously" recirculate all materialintroduced into the blender, for a given period ofgtime, and the discharge opening of the blender will be closed. To o'pi'ate continuously,'-'the' amount of 'material introduced relative to the amount of air introducedinto the blender w ill be controlled so that a "pertain-or the pulverulent material will continuously collect at the-discharge opening of the f I blender, which will be open, so that the blended ,unsegregated combined material may be exhausted. I

' An actual example ofuse, of the above-described embodiment of the inv ention will demonstrate the novel blending effectiveness ofthe apparatus. Approximately two hundred tons o f powdered bentonite clay, having a nominal classification of ninety perc'ent 'less 'than"2'0'0 mesh and a bulk density of 55 lbs. per cubic foot, was fed into the apparatus for blending. Sieve analysis indicated that the pulverulent bentonite was one hundred percent less than 150 mesh, ninety percent less than 200 mesh, and five percent less than 325 mesh. Furthermore, bentonite has the property of imparting viscosity to a water solution but natural bentonite clay, i.e. as it is mined, has a great variation in viscosity. This particular bentonite material had a natural unblended viscosity range of from 3 cps. to 26 cps. in a 6%% concentration.

In blending the bentonite by batch process, 650 cubic feet per minute of air was introduced through the mixing and aspirating means at 6 p.s.i.g. Since the entire charge of pulverulent material was fed into the container prior to commencing blending, the material head required 18 p.s.i.g. in the air inlet pipe to overcome the head. However, the pressure required for operation shortly dropped to 6 p.s.i.g. The mixing and aspirating means with this volumetric rate of flow produced a recirculation rate of 600 tons per hour and, for this particular pulverulent material, it was found that ten recirculation cycles yielded a well-blended homogeneous material of differing particle size.

Specifically, sieve analysis of the blended material showed a uniform homogeneous mixture of particle sizes and a viscosity of 13 cps. in a 6 A% concentration.

The above-described material was also used in a test of the apparatus in continuous operation. The container was fed at a rate of fifty tons per hour and the lower portion of the container was allowed to fill to a desirable level by closing the discharge opening. The mixing and aspirating means was operated so as to allow the level of blended material to be maintained after the discharge opening was opened providing a continuous operation. The same uniform homogeneous mixture of blended material was obtained.

In another example of use of this apparatus for both storage and blending, a fifty ton container was filled with silica sand weighing 100 lbs. per cubic foot, and having a No. 90 grain fineness according to American Foundry Society standards. Without blending, it was found that the container when discharged would initially deliver material high in fines and subsequently the coarse part of the material.

However, when the apparatus was operated with 900 cubic feet per minute introduced through the mixing and aspiratin g means :at a starting pressure of 22 p.s.i.g. and an operating pressure of 7 p.s.i. g., a homogeneous mixture was discharged with the grain size graduation consistently plus or minus one-half of one percent.

It will be appreciated from these examples that the present invention provides a blending and storage apparatus of large capacity which by controlled movement of the material will provide an unsegregated, homogeneous, uniform mixture of pulverulent material. It will therefore be seen that many modifications and variations of the present method and apparatus for blending pulver ulent materialsare possible in light of the. above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than specifically described.

I claim: i p 1. A method for producing, storing and discharging homogeneous mixtures of finely divided solid materials comprising the steps of:

introducing finely divided solid material by air transport into the upper end of a cylindrical portion of a container in a tangential direction to create a circumferential flow path of the material; directing low pressure air flow radially in the upper end of the cylindrical portion of the container to create a confluent flow path of fluidized material; H directing the' flow of the fluidized material in a downward spiral path toward the axis of the container cylindrical portion;

re-directin g the downward spiralling flow of fluidized material away from the axis of the container and into the upper end of an inverted cone portion of the container;

reversing the flow of down-ward spiralling fluidized material toward the container axis;

aspirating the fluidized material in the lower region of the inverted cone portion of the container; and

re-circulating the aspirated fluidized material to the upper end of the cylindrical portion of the container to effect complete homogeneous blending of the finely divided solid materials.

2. An apparatus for producing, storing and discharging homogeneous mixtures of finely divided solid material comprising:

-a container housing having an upper cylindrical portion provided with a top wall and a lower inverted cone portion with a discharge opening at the lower end thereof;

a tangential material inlet means in the periphery of the upper end of the cylindrical portion adjacent said top wall;

means within said container housing for reversing the direction of downward movement of the material by a series of successively inwardly contracting and outwardly expanding spirals to the lower portion of said housing, said means comprising an upper inverted truncated conical bathe in said cylindrical portion extending from a zone slightly below said material inlet means and providing a surface for guiding material toward the central axis,

and a lower conical baflle providing a surface adapted to receive material from the upper truncated conical bafile and guide material away from the central axis toward the lower portion of the container housing;

axially positioned, upwardly directed aspirating means in the lower portion of the lower section of the housing, a pipe plositioned in operative vertical axial alignment with said aspirating means and extending through said housiing lower cone portion to the upper end of the cylindrical portion of the housing;

and means for supplying low pressure air to said aspirating means to circulate material from the lower portion of the housing to the upper portion thereof.

3. The apparatus of claim 2 wherein said tangential material inlet means includes means providing air transport of such material into the container.

4. The apparatus of claim 3 additionally including means supported in the lower inverted cone portion of the housing for creating a pressure zone exceeding the housing ambient pressure so as to direct the downward movement of the material outwardly toward the wall of the housing lower portion.

7 5. The apparatus of claim 4 additionally comprising: valve means in operative relation with the tangential material inlet means for selectively controlling the weight rate of material flow introduced; and

valve means in operative relation with the low pressure air supply means for selectively controlling the volumetric rate of air flow introduced,

whereby a selected portion of the downward flow of material may be aspirated and the remainder collected in the lower end of the lower inverted cone portion of the container.

6. The apparatus of claim 5 wherein the lower opening of the upper inverted truncated conical baffle is between 0.4 and 0.6 of the diameter of the upper cylindrical portion of the container and the lower edge of the lower conical bafile has a diameter no less than the diameter of the lower opening of the upper inverted truncated conical 'baffie.

7. The apparatus of claim 6 additionally comprising:

means for providing a fluidized bed of gas on the inner wall of the lower inverted cone portion of the container so as to prevent the material from adhering to the wall; and

means for collecting the fines from the material which are suspended proximate the top wall of the container.

References Cited UNITED STATES PATENTS 1,000,689 8/1911 Paterson 2594 XR 2,718,471 9/1955 Samler 2594 XR 3,164,376 1/1965 Clark 2594