BLENDER WITH VIRTUAL BAFFLE OF PARTICULATE MATERIAL

Abstract: A blending apparatus, inexpensive in construction and requiring a minimum of recirculation, is today essential for economical and thorough blending of particulate material, for example, plastic pellets of virgin material and of pellets that have been reconstituted from recycled material. Construction of the blender is low in cost not only because the customary receiver, and its piping, conventionally installed below the blender are eliminated, but because the rigid baffle of the prior blender has been replaced by a virtual baffle (626) of particulate material, which forms a toroidal block within: the conically walls (610) of the blender; the converging blended conduits (602) adjacent thereto; and the structural supporting matrix. The baffle of particulate material (626) serves: 1) as a termination surface for the conventional perforated blending conduits; and 2) retains a toroidal annular volume of particulate material in position between the upper outer surface of the baffle and the inside wall of the blender.

Description: BLENDER WITH VIRTUAL BAFFLE OF PARTICULATE MATERIAL BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to blenders and more specifically to methods and apparatus for thoroughly blending particulate or granular materials, a portion of the unblended material forming a toroidal block, constituting a virtual baffle to the downward flow of any particulate material except that passing through the blending tubes themselves. DEFINITIONS baffle--(noun) a plate, wall, screen, or other device to deflect, check, or regulate flow. virtual baf le—herein defined as a barrier, formed of particulate material, in combination with a supporting structural matrix, to the downward flow of particulate material, except through blending tubes which penetrate the barrier. matrix—herein defined as blender walls, metallic plates and cones, blending conduits, all coacting with the particulate material to provide the virtual baffle. voussoir—(diet . ) one of the wedge-shaped pieces forming an arch or vault. Used herein to graphically describe the cross section of the virtual baffle, at some point on the toroid or segment. bridging—the tendency of particulate solids, flowing downward through a channel with converging sides, to bridge across the channel, blocking the channel, causing all of the material flowing out of the blender to flow through the blending tubes. toroidal block—herein, a toroidal mass of particulate material, having a voussoi r-1ike crossection, supported between the outer wall of the blender and the downwardly converging metal baffles of FIGs. 6 and 9. Also called a toroidal or annular "keystone joist." DESCRIPTION OF THE PRIOR ART Prior to the advent of large scale use of polymers in such applications as continuous film or filament production, the needs of industry for precision blending of bulk solids products were met with mechanical tumbler, ribbon or screw blenders. Capacities of these units ranged from less than one cubic meter to over 100 cubic meters. As the demand for plastics grew, it became apparent that much larger blender volumes were necessary to allow continuous production lines in plastics users 1 plants to operate without frequent shutdowns caused either by (1) variations in physical properties or (2) additive content inherent in the producer's production processes. This led to a demand for tumble blenders in the range of 700 cubic meter capacity. The high cost of large tumble blender installations prompted industry-wide efforts to develop a blending capability in storage silos to comply with the product uniformity requirements of the polymer industry. A number of designs resulted, some silo blenders having capacities in the 3000 cubic meter range. Efficient silo blenders are available today in two broad categories : A. Gravity Blenders These designs generally use either external or internal tubes having openings to allow solids in the bin to flow from the main silo body to a separate blend chamber below the silo. The tube openings in the main body of the silo are randomly located so that material drained into the blend chamber represents a typical composite of the material in the main silo body. B. Internally Recirculated Blenders These units rely on an external source of air to pick up material in the lower part of the silo body by an orifice arrangement, and convey it to the upper part of the main silo. The material flowing vertically down through the silo is randomly sampled by the openings in the tubes and agitated by inverted cones, resulting in homogenization of the silo contents after a period of time. The performance of both Gravity Blenders and Internally Recirculated Blenders can be significantly improved by recirculation while the blender is being filled. As storage bins or hoppers are filled with granular or particulate material, it often happens that an inhomogeneous distribution of material occurs. There may be several reasons for this result. In the first place, as material flows into a hopper, the material beneath the inlet nozzle piles up at the angle of repose of the material. In this case the larger particles often roll down the peak toward the sides of the hopper, leaving the finer particles in the central region. Inhomogeneity can also occur when the hopper is filled with different batches of the same material because of variations of composition of individual batches. When material is drawn off through an outlet at the bottom of the hopper, the material flows from the region directly above the nozzle. Thus the material will not be representative of the average characteristics of the material in the hopper. Prior art attempts at a solution to this segregation problem typically included placing perforated blending tubes vertically within the hopper. Such tubes have openings spaced apart along their axes which allow material from all levels within the hopper to enter the tubes. The lower portion of the blending tubes communicate with the outlet nozzle so that a more nearly homogeneous mixture of the material issues from the outlet of the hopper. In spite of many efforts to completely blend the particulate material, it is usually necessary in prior art blenders to specially treat at least the final portion of the discharge to achieve acceptable results. For example, U.S. Patent No. 4,923,304, discloses that the first and last few pounds are not used, but instead are withdrawn and later remixed with fresh ingredients, and re-poured, with these fresh ingredients, back into the dispensing apparatus. SUMMARY OF THE INVENTION My invention, in two preferred embodiments disclosed herein, in combination with a conventional hopper and conventional blending tubes, can effectively blend a batch of particulate material, including the final portion of the batch. In a third embodiment, my invention simulates the operation of tne full size blender, in an adjustable laboratory size model, enabling experimentation with various particulate densities, compactabilities and annular gaps. My invention does not require ji separate blending chamber. It utilizes the tendency of particulate solids, flowing downward through a channel with converging sides, to bridge across the channel, blocking the channel, causing all of the material flowing out of the blender to flow through the blending tubes. Thus my invention assures that all of the material discharged from the blender represents a truly typical composite of the blender contents. The three preferred embodiments disclosed in this specification rely upon the tendency of particulate solids, in flowing downward through a channel with converging sides, to bridge across the channel. Such bridging may occur in: A. A toroidal block, having a voussoir-1ike crosssection, as shown in the blender of FIG. 6, and equivalent supporting structure for bridging by particulate materials, as shown in FIGs. 2, 4, 7, 8 and 10. B. A similar toroidal block in the apparatus in -FIG. 9, for confirming by empirical tests, the preliminary design proportions for a blender specifically contoured for the density, compactabiIity, and other characteristics of the particulate material, or materials, to be blended; C. A voussoir-like construction for the support of particulate material, as shown in the construction of FIGs. 7 and 11-13, in which the matrix of blending tubes, optional inverted cones, and conical walls of the vessel prβvide a matrix for the support of the virtual baffle of particulate material. The "bridging principle" and the "virtual baff-€e" concept employed in the preferred embodiments are illustrated in the following drawings and explained in the speci ication. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 provides an elevational, sectional view? through the center line of a typical blender of the prior art; FIG. 2 provides an elevational, sectional view through the center line of one preferred embodiment of the gravity blender of the present invention; FIG. 3 provides a schematic diagram of the hopper, piping and pumps, if required for extremely uniform blending within the gravity blender of the present invention; FIG. 4 provides a sectional view from the vertical centerline through the exterior wall of the lower portion of the hopper of an alternate embodiment of the present invention, including a detail of a blending tube and a conduit for exhaust gases, or for structural purposes; FIG. 5 is a section of the conduit of FIG. 4, illustrating the knife-like device for preventing accumulation of particulate matter on the top surface of the conduit ; FIG. 6 is a more detailed view of Embodiment A of the present invention, as combined with terminations of the conventional blending tubes; FIG. 7 is a more detailed view of alternate Embodiments A and C of the present invention as combined with two convex surfaces for better blending of virtually all of the material to be blended; FIG. 8 provides an elevational, sectional view through the center line of a gravity blender of an alternate embodiment A of the present invention, in which one basic convex surface is combined with a cylindrical device, developed further in FIG. 12-13, for further blending; FIG. 9, Embodiment B, provides a vertical, sectional view through the center line of the test apparatus, which substantially duplicates the conditions within, and operations of blending of the present invention? FIG. 10, Embodiment A, provides a sectional view from the vertical centerline through the exterior wall of the lower portion of the hopper of an alternate embodiment of the present invention, including a detail of a blending tube, but without a venting conduit for exhaust gasesj FIG. 11, Embodiment C, provides a fragmented elevational hemicy1indrical inside view, through a section in the plane including the vertical centerline of a blender, utilizing a virtual baffle of particulate material, supported partially on a matrix of converging blending tubes, and equipped with a small inverted cone. Two partial sectional details are provided^ FIG. 11A is a fragmentary section just inside the wall 1112, showing the ends 1114 of the blending tubes 1110 within the toroidal block 1130 of particulate materialj FIG. 11B shows various angles of cut off of the discharge ends 1114 of the blending tubes 1110 FIG. 12, Embodiment C, provides an elevational hemicylindrical inside view, through a section in the plane including the vertical centerline of a blender, utilizing a virtual baffle of particulate material, supported solely on a matrix of converging blending tubes, without an inverted cone, but with a vertical tubular element^ αnα FIG. 13, Embodiment C, provides a generally horizontal sectional view through the blender of FIG. 12, at approximately the level of the virtual baffle of particulate material, supported partially on a matrix of converging blending tubes and the vertical tubular element 1240. DESCRIPTION OF THE THREE PREFERRED EMBODIMENTS OF THE INVENTION In providing a more detailed discussion of the three preferred embodiment of the invention, reference will be first made to components of the blending apparatus from the prior art, insofar as they differ from, or combine with, the new invention for improved and more efficient performance at lower cost. In FIG. 1 is shown a drawing from Patent No. 3,268,215, issued to T.A. Burton for a Blending Apparatus on August 23, 1966. Illustrative of this prior art are tank or hopper 10, blending tubes 24, and separate receiver or collector manifold 28. FIG. 2 shows the similarities and the differences between the prior art of FIG. 1 and the present invention. Similarities include a cylindrical housing 210 superimposed upon and sealed to a conical structure 211. Downcomer tubes 224 however, terminate in perforations 227 through the inverted generally horizontal baffle ' 225, comprising part of the present invention. This means of termination is a significant improvement over the prior art shown in FIG. 1, in which tubes 24 pass entirely through the hopper 10 and terminate in receiver 28. In the annular area 226, between the converging walls of baffle 225 and structure 211, the accumulation of particulate matter forms a toroidal block to the passage of the particulate matter accumulating above the block. The recirculating schemes of the prior art are shown in FIG. 3, diagrams 302 and 303. My invention, as shown in its alternate embodiments, deals with the problem in novel fashion. In FIG. 2, and as more easily seen in FIG. 6, the blending tubes, of which tube 602 is an example, terminate in apertures 603. These apertures are formed in the convex surface 604. This means of termination is a significant departure from the prior art, as shown in FIG. 1, in which tubes 24 pass entirely through the hopper 10 and terminate in receiver 28. Returning to FIG. 6, it should be noted that convex surface 604 is supported upon brackets 606, and is thus spaced away from the exterior cone 610 by an annular gap shown as 605. Now, if the surfaces 604, annular gaps 605, and apertures 603, are designed as will be shown in connection with the description of FIG. 9, the material to be blended will begin to fill the hopper 601, but will form a barrier at the annulus 605, past which barrier the particulate material will not descend, until blending tubes are evacuated. As the blending operation being performed on the batch, or mixture, draws to a close, the level of the material will fall below the seam line 607, and then past a series of apertures 608. The discharge of material from the blender will then flow preferentially from the blending tubes 602, with essentially zero flow through the annulus 605 between the inverted cone and the vessel cone. Flow through this annulus 605 cannot occur until the supply of maternal coming from the blend tubes 602 is exhausted. FIG. 9 is a diagram of the Test Apparatus, i l≠iαistratin< its similarity in construction to the blenders ofurthe present invention. Material 901 is cross hatched. or clarity. Material 902 is shown crosshatched at ββother angle. The inverted cone may be set in a position 911 and provides a smaller annular gap 903 than were it raised to a higher position, say 912. Material 901 is first poured into the inverted cone, upright cone and standpipe at the start of test, filling volumes shown as underlined 1,2,3,4 and 5. Material 902 may be then put in to fill the remainder of the vessel and will fill to the annular surface 909, in "keystone fashion," as a toroidal block, or as a voussoir of particulate material. Material 902 will not flow out of the vessel until the supply of Material 901 is exhausted. In order to make this principle work: a. The flow of material from the center nozzle must be regulated by valve 914 to a rate below that would cause voids to form in material 901. b. Flow properties of material 901 and 902 should be similar. The test procedure, if properly performed, can provide valuable information on the dimensions 903, 909, and other critical factors in full-size blender design. FIG. 11 illustrates the use of an inverted baffle through which the blending tubes 1110 do not penetrate, but which is positioned in such a manner that a voussoir of particulate material is formed between converging surfaces in close proximity to each other. In this blender, particulate material is entrapped within the matrix of conduits 1110 and small inverted cone 1113 mounted on brackets 1106 within the cone of the outer wall 1112. The density, particle shape, compactabi1ity, and a host of indeterminate factors will cooperate to establish a toroidal block of material 1130, thus creating a virtual baffle of particulate material, supported partially on a matrix of converging blending tubes 1110, a small inverted cone 1113, and lower section wall 1112. It must be understood that this drawing is purely illustrative of the inventive concept, and that other variations are within the scope of the following claims. FIG. 12 illustrates the accumulation of particulate material 1230 in this blender, when entrapped within the matrix of conduits 1210, and within the cone of the outer wall 1212. This embodiment is not equipped with an inverted cone 1113, but has instead a vertical tubular element 1240. A voussoir of particulate material 1230 will be formed, creating a virtual baffle, in the form of a toroidal block, between and among the structural members, including the central tubular structure 1240. The diameter of the tube 1240 is drawn too large in comparison with the area 1233 provided for discharge of the particulate material, but the concept is adequately presented. The density, particle shape, compactabi 1ity, and a host of indeterminate factors will cooperate to establish the position, volume, and mass of material 1230. These parameters will be those required to obtain a suitable toroidal block, utilizing a virtual baffle of particulate material, supported partially on a matrix of converging blending tubes 1210 and vertical tubular element 1240. It must be understood that this drawing is purely illustrative of the inventive concept, and that other variations are within the scope the following claims. FIG. 13 provides a horizontal sectional view through the blender of FIG. 12, at approximately the level of the virtual baffle 1230 of particulate material, supported partially on a matrix of converging blending tubes 1210. Further support is provided by the vertical tubular structure 1240. CLARIFICATION OF DIFFERENCES BETWEEN BAFFLES OF THE THREE PREFERRED EMBODIMENTS OF THIS INVENTION In the embodiments disclosed in FIGs. 11-13, the blender uses a number of blending tubes or channels which terminate at the same elevation adjacent to a small inverted cone 1113 as shown in FIG. 11, or without an inverted cone as shown in FIGs. 12 and 13. Although as shown in FIG. 6, the converging blending conduits provide only limited support to the blocking accumulation of the particulate material, in FIG. 11 the major part of the mass of particulate material is supported by the converging matrix of conduits. In FIGs. 12 and 13, the entire mass of particulate material is supported by the converging matrix of blending conduits and the vertical tubular element 1240. Thus a very useful blender can be constructed which can be installed in silos at a much lower cost than blenders that rely solely on separate blend chambers as shown in FIG. 1. FIG. 11 illustrates an alternate embodiment and a more economical method of construction than that of FIG. 7, achieved by eliminating the large baffle 704, and the "hard" terminations of the blending tubes in apertures in the sides of cone 704. The matrix of converging downcoming blending tubes 1110 are mounted close to the conical wall 1112. Blending tubes 1110 do not terminate in apertures or hubs in the surface of cone 1113, but terminate in the approximate region delineated as 1114, which has a variable vertical range as shown by the two-headed arrow at 1123. The base line of the lower end of cone 1113 may vary above or below a typical position 1114, as shown by bidirectional arrow 1123. If proper proportions are selected, such a grid of blending tubes converging toward plane 1114, in combination with the converging wall 1112 of the lower bin section 1101, can support a voussoir 1130 of particulate material, extending slightly downward or upward from reference plane 1114. It is thus possible to achieve the blocking effect of the impervious baffle 604 of FIG. 6 without the expense of physically connecting (measuring, cutting and welding) the blending tubes to apertures in the surface of a large baffle, and in some cases the small baffle 1113 may not be needed. Please refer to FIG. 12. In FIG. 11A, various terminations for the blending tubes may be employed. The intent of this disclosure is to illustrate the concept of a baffle primarily of particulate material, simpler to build and less costly in material. The specific terminations of blending conduits, patterns of the matrix, and use or nonuse of small convex cones are all minor variations contemplated in the general use of this invention. In FIG. 12 is shown an embodiment which does not use the small inverted baffle or cone 1113, a preferred construction being the structural tubing 1240. With some particulate materials, the conical wall 1112 in combination with the blending tube matrix 1110, may ' support the toroidal blocking mass of material 1120 without member 1240. The section shown in FIG. 13 is typical of many usable designs. The intent of this disclosure is to illustrate the concept of a baffle primarily of particulate material, simpler to build and less costly in material. The specific terminations of blending conduits, patterns of the matrix, and use or nonuse of small convex cones are all minor variations contemplated in the general use of this invention.

Claims: WHAT IS CLAIMED IS: 1. A method of inducing, within a gravity blending device, the formation, from a portion of the particulate material to be blended, of effective baf le means to the unrestricted downward flow of the remainder of said particulate material, said baffle means of said particulate material being secured in a voussoir-like matrix by at least one downwardly converging structural element within said blending device; said voussoir-like matrix continuing to secure said particulate material within said baffle means, until said unbaffled portion of said particulate material has been discharged from said blending device. 2. A method of inducing, within a gravity blending device, of the type having blending tubes, the formation, from a portion of the particulate material to be blended, of effective baffle means to the unrestricted downward flow of the remainder of said particulate material, said baffle means of said particulate material being secured in a voussoir-like matrix by at least one downwardly converging structural element within said blending device; said voussoir-like matrix continuing to secure said particulate material in bridging form within said baffle means, until said unbaffled portion of said particulate material has been discharged from said blending tubes of said blending device. 3. A gravity blender apparatus, having: in its upper portion, bin means operable to receive and store a mass of particulate material; 8a generally horizontal baffle, in the form of an upwardly convex-shaped dome-like dish, similar in circumferential shape to the internal circumference of said bin means and smaller by the width of a preselected annular gap between said ' bin and said baffle, said baffle having a plurality of perforations adjacent the base of said convex shaped domelike dish, said baffle serving as a nominal divider between said upper portion and the lower portion of said bin; a plurality of blending conduits extending downward from top of said bin means, said conduits terminating in at least some of said perforations in said baffle, said conduits operable to convey particulate material from said mass toward said lower portion of said bin means ; and said annulus serving as voussoir to support a keystone-joist-1ike mass of particulate material until said blending tubes and said open perforations have released final portions of said particulate matter through said blending tubes and through said perforated apertures into said lower portion of said bin. 4. A gravity blender apparatus, of the type recited in claim 3, having blending zone means disposed generally within said lower portion of said bin means. 5. A gravity blender apparatus, of the type recited in claim 3, in which said annulus is generally circular. 6. A gravity blender apparatus, having: in its upper portion, cylindrical bin means operable to receive and store a mass of particulate material; in its lower portion, a downwardly converging conical section, sealed to the lower cylindrical edge of the upper portion; a plurality of blending conduits extending downward from the upper portion of said bin means, said conduits mounted internally and vertically within said upper portion; said blending conduits operable to convey particulate material from regions of said blender above top of said virtual baffle to discharge from said blender; said baffle of particulate material remaining in position until said blending tubes have released said final portions of said particulate matter through said blending tubes into said lower portion of said bin; and the outlet ends of said conduits terminating at points on a virtual plane, said plane constituting a virtual bottom of said virtual baffle. 7. A gravity blender apparatus, having: in its upper portion, cylindrical bin means operable to receive and store a mass of particulate material; in its lower portion, a downwardly converging conical section, sealed to the lower cylindrical edge of the upper portion; within said lower portion, a vertical tubular element centered axially therewithin; a plurality of blending conduits extending downward from the upper portion of said bin means, said conduits mounted internally and vertically within said upper portion, said blending conduits adjacent said converging conical walls, said blending conduits converging downwardly toward the vertical center line of said blender, said lower open ends of said conduits terminating in a generally circular and horizontal pattern; an upwardly converging conical surface, having a maximum diameter substantially of the diameter of the circular pattern of said lower open ends of said conduits, the conical surface projecting upward within said circle of said open conduit ends; said convergence of said blending conduits, said conical walls of said of said lower section and said axial vertical tubular surface, all, in combination, creating voussoir-like accumulations of particulate material in said converging channels between said conduits and between said conical walls and said conduits ; said voussoir-like accumulations serving additionally as the base of a virtual baffle, said virtual baffle being formed solely of said particulate material supported upon a matrix of said converging blending conduits, said conical lower portion of said bin walls, and said tubular surface; said blending conduits operable to convey particulate material from regions of said blender above top of said virtual baffle to discharge from said blender; said baffle of particulate material remaining in position until said blending tubes have released said final portions of said particulate matter through said blending tubes into said lower portion of said bin. 8. A test apparatus and procedure to predetermine the parameters for optimum performance of a blender for blending particulate materials, of a first type (for example, white), and of a second type (for example, black), said materials having similar flow properties, said test apparatus, as shown in FIG. 9, comprising: (i)an external vessel, having an upper cylindrical end and a lower downwardly-tapered conical frustum end, both centered about a common perpendicular axis, the upper circumference of said cone sealably joined to the lower circumference of said cylinder, said smaller frustum end having discharge valve means; (ii)an upwardly-tapered inverted funnel-like section, centered axially within said surrounding cylinder, said funnel connected to a conduit nipple, the upper end of said nipple surmounted by a particle feeding hopper ; ( ii i )assembly of said funnel, said hopper, and said nipple, said assembly having adjustable mounting means to top of said cylinder, whereby said slidable funnel may be positioned, at the least, at any preferred level within dashed and solid line positions shown in FIG. 9; (iv) said inverted funnel-like section having a maximum diameter less than the diameter of said cylindrical upper end, said maximum diameter of said funnel having been predetermined empirically by the parameters of said particulate materials to be processed therethrough; (v) said maximum diameter of said funnel-like section having vertical positioning adjustment means within the plane of the lower edge of said generally cylindrical upper end, and having adjustment means for raising and lowering said inverted cone, said preliminary adjustments having been predetermined empirically by the parameters of said particulate materials to be processed therethrough; and said test procedure comprising: (a) closing said discharge valve, and filling the volumes cross hatched 901 with said first type, white, particulate material level with the top of hopper 925; (b) filling said generally cylindrical volume 902, surrounding said upwardly tapered inverted funnel-like section with said second type, black, particulate material, to a predetermined proper level, said level corresponding with the level of the lowest aperture in one of said blending tubes; (c) opening said discharge valve, which controls the flow of blended particulate materials, to a rate below that which would cause voids to form in said material of first type, white, while manually filling said hopper so there is always white material 901 in standpipe 925 ; (d) observing the flow of, the distinctive color of, the level of, the surface of, and weighing material of second type, black, to confirm that no black material is crossing the annular keystone joist 909 formed of said second type, black, material; (e) emptying enough of said first type, white, material to confirm by visual inspection of said second type, black, material in the keystone annular joist 903 at surface 909, that a stable voussoir of particulate material remains in bridging position.

Inventors: AVERY HUGH E JR, AVERY, HUGH, E., JR.
Applicants: AVERY HUGH E JR, AVERY, HUGH, E., JR.
Application year: 1992
Main classification: B01F5
IPC codes: B01F5