EP0538445B1

EP0538445B1 - Blender with virtual baffle of particulate material

Info

Publication number: EP0538445B1
Application number: EP92910728A
Authority: EP
Inventors: Hugh E. Avery, Jr.
Original assignee: Jansens and Dieperink BV
Current assignee: J&D Beheer BV
Priority date: 1991-04-10
Filing date: 1992-04-09
Publication date: 1997-10-29
Anticipated expiration: 2012-04-09
Also published as: CA2087178C; HK1003826A1; EP0538445A1; EP0538445A4; AU1887592A; DE69222920T2; DE69222920D1; ES2109356T3; WO1992018229A1; CA2087178A1

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conventionally installed below the blender are eliminated, but because the rigid baffle of the prior blender has been replaced by a virtual baffle (626) of particulate material, which forms a toroidal block within: the conically walls (610) of the blender; the converging blended conduits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

The invention relates to a gravity blender comprising a bin operable to receive and store a mass of particulate material, said bin consisting of an upper portion and a downwardly converging lower portion, a generally horizontal baffle in the form of an upwardly convex-shaped dome-like dish similar in circumferential shape to the internal circumference of the bin and smaller by the width of a pre-selected annular gap between the bin and the baffle, the baffle having a plurality of apertures and serving as a nominal divider between the upper portion and the lower portion of the bin, a plurality of blending conduits extending downward from top of the bin and terminating in apertures in the baffle, said conduits operable to convey particulate material from the upper portion towards the lower portion of the bin.
Such a gravity blender is disclosed in US-A-4285602.

Definitions:

Baffle-- a plate, wall screen, or other device to deflect, check, or regulate flow.
Virtual baffle-- 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-- 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 brigde across the channel, blocking the channel, causing all of the material flowing out of the blender to flow through the blending tubes.
Toroidal block-- a toroidal mass of particulate material, having a voussoir-like crossection, supported between the outer wall of the blender and the downwardly converging metal baffle of figure 5. Also called a toroidal or annular "keystone joist."
Dynamic structure--that portion of the structure of a voussoir composed of particulate material, and therefore capable of forming, dissolving and reforming to build a structural combination of rigid material and particulate material.
Prior to the advent of large 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' 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 tuble 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:

I. 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.

II. Internally recirculated blenders.

These units reply 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 performances 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 to 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.
US-A-4353652 describes a two storage vessel of conventional metal construction, in tandem, for adequate blending. 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.
The object of the invention is to avoid this disadvantage and to provide a gravity blender apparatus according to the preamble, which can effectively blend a batch of particulate material, including the final portion of the batch.
According to a first embodiment according to principle A of the invention the gravity blender is characterized in that said apertures are located adjacent the base of the baffle and that said annular gap is dimensioned so as to serve as voussoir to support a keystone-joist-like mass of particulate material until the blending conduits and the apertures have released the final portions of the particulate material into the lower portion of the bin.
The invention does not require a 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, until the last of the unbaffled portion of the particulate material has begun to be discharged or has been discharged. All the material discharged from the blender represents a truely typical composite of the blender content.
The apparatus may further comprise an upwardly converging conical surface located below the baffle, the conical surface projecting upwards substantially towards the circle of apertures in the baffle.
A second embodiment (according to principle B) relates to a gravity blender having a cylindrical upper portion operable to receive and store a mass of particulate material, and a lower portion defining a downwardly converging conical section sealed to the lower cylindrical edge of the upper portion, the lower and upper portions being centered in a single vertical axis, a plurality of blending conduits extending downwards from the upper portion, the blending conduits continuing downwardly adjacent said converging conical section and the blending conduits converging downwardly towards said vertical axis of said blender apparatus.
Such a blender is also disclosed in US-A-4353652.
The object of the second embodiment is the same as the object of the first embodiment: to provide a blender according to the preamble, which can effectively blend a batch of particulate material, including the final portion of the batch.
According to the invention the second embodiment is characterized in that the blending conduits have lower open ends which terminate in a generally circular and horizontal pattern, said convergence of the blending conduits and said conical walls of the lower section creating and supporting in operation a virtual baffle of particulate material in combination, said vertical baffle consisting of voussoir-like accumulations of particulate material in said converging channels between the blending conduits and between the conical walls and the blending conduits, the baffle of particulate material remaining in position until the blending tubes have begun to release the final portions of the particulate material through the blending tubes to blend with the particulate material of the vertical baffle as both pass into and through the lower portion of the bin.
The above blender apparatus in accordance with principle B may comprise an upwardly converging conical surface, having a maximal diameter substantially that of the diameter of the circular pattern of the lower open end of said conduits, the conical surface projecting upwards towards the circle of open conduit lower ends, said conduits being spaced above a bottom of said conical surface, whereas the virtual baffle is formed solely by the particulate material supported upon a matrix of said converging blending conduits, said conical lower portion of the bin walls and said conical surface projecting upwards.
In the second principle according to principle B the apparatus may further comprise within the lower portion a vertical tubular element centered axially therein, the vertical baffle being formed solely of the particulate material supported upon a matrix of converging blending conduits, said conical lower portion of the bin and said tubular element.
The bridging principle and the virtual baffle concept employed in the preferred embodiments are illustrated in the following drawings and explained in the specification.
Figure 1 provides an elevational, sectional view through the center line of a typical blender of the prior art (US-A-3268215).
Figure 2 provides a schematic diagram of recirculating schemes 302 and 303 of the prior art comprising hoppers, pipings and pumps, if required for extremely uniform blending within the gravity blender of the present invention.
Figure 3 provides a sectional view from the vertical center line 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.
Figure 4 is a section of the conduit of figure 3 illustrating the knife-like device for preventing accumulation of particulate matter on the top surface of conduit.
Figure 5 is a more detailed view of embodiment A of the present invention, as combined with terminations of the conventional blending tubes.
Figure 6 is a more detailed view of an alternate embodiment A of the present invention as combined with two convex surfaces for better blending of virtually all of the material to be blended.
Figure 7 , embodiment B, provides a fragmented 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 partially on a matrix of converging blending tubes, and equipped with a small inverted cone.
Figure 7A 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 material.
Figure 7B shows various angles of cut off of the discharge ends 1114 of the blending tubes 1110.
Figure 8, embodiment B, 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.
Figure 9, embodiment B, provides a generally horizontal section of view through the blender of figure 8, at approximately the level of the virtual baffle of particulate material, supported partially on a matrix on converting blending tubes and the vertical tubular element 1240.
In providing a more detailed discussion of the two preferred embodiments 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 figure 1 is shown a drawing from US-A-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.
In figure 5 the meaning of the reference numbers is as follows:

600: - bin for particulate materials;
601: - particulate material mass;
602: - blending conduit;
603: - aperture in primary cone for blending conduit connection;
604: - inverted cone barrier;
605: - annular gap;
606: - supporting bracket;
607: - seamline between mating cylindrical and conical vessels;
608: - series of apertures in blending tubes;
626: - cross-section of "annular keystone joist" of particulate material;
610: - supporting surface area for outer wall of voussoir;
621: - void under inverted cone barrier;
620: - venting means to atmosphere;
615: - a lower opening in cone not connected to a conduit, allowing it to sample the particulate mass 601 at lowest possible elevation;
630: - aperture at low elevation;
625: - toroidal cross section interrupted at intersection with blending tube,

As easily seen in figure 5, the blending conduits, 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 figure 1, in which tubes 24 pass entirely through the hopper 10 and terminate in receiver 28.
Returning to figure 5, 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 properly designed, 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 follow 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 material coming from the blend tubes 602 is exhausted.
In figure 6 the meaning of the reference numbers is as follows:

702: - secondary cone barrier;
703, 706, 711, 712: - gussets;
704: - primary inverted cone barrier;
707: - void;
710: - downwardly converging lower portion.

Figure 7 illustrates the use of an inverted baffle 1113 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, compactability, and a horst 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.
Figure 8 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, compactability, 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.
Figure 9 provides a horizontal sectional view through the blender of figure 8, 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.
In the embodiments disclosed in figures 7, 8, 9, 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 figure 7, or without an inverted cone as shown in figures 8 and 9.
Although as shown in figure 5, the converging blending conduits provide only limited support to the blocking accumulation of the particulate material, in figure 7 the major part of the mass of particulate material is supported by the converging matrix of conduits. In figures 8 and 9 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 figure 1.
Figure 7 illustrates an alternate embodiment and a more economical method of construction than that of figure 6 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 (figure 7A).
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 figure 5 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 figure 8.
In figure 7B, 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 figure 8 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 figure 9 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

Gravity blender comprising a bin (600) operable to receive and store a mass of particulate material, said bin consisting of an upper portion and a downwardly converging lower portion (610), a generally horizontal baffle in the form of an upwardly convex-shaped dome-like dish (604, 704) similar in circumferential shape to the internal circumference of the bin and smaller by the width of a pre-selected annular gap (605) between the bin (600) and the baffle (604), the baffle having a plurality of apertures (603) and serving as a nominal divider between the upper portion and the lower portion of the bin, a plurality of blending conduits (602) extending downward from top of the bin and terminating in apertures (603) in the baffle (604; 704), said conduits (602) operable to convey particulate material from the upper portion towards the lower portion of the bin, characterized in that said apertures (603) are located adjacent the base of the baffle (604) and that said annular gap (605) is dimensioned so as to serve as voussoir to support a keystone-joist-like mass of particulate material (626) until the blending conduits (602) and the apertures (603) have released the final portions of the particulate material into the lower portion of the bin (600).
Gravity blender according to claim 1, characterized in that the blender further comprises an upwardly converging conical surface (702) located below said baffle (704), said conical surface (702) projecting upwards substantially towards the circle of apertures in said baffle (704).
A gravity blender having a cylindrical upper portion operable to receive and store a mass of particulate material, and a lower portion defining a downwardly converging conical section (1112, 1212) sealed to the lower cylindrical edge of the upper portion, the lower and upper portions being centered in a single vertical axis, a plurality of blending conduits (1110, 1210) extending downwards from the upper portion, the blending conduits continuing downwardly adjacent said converging conical section (1112, 1212) and the blending conduits converging downwardly towards said vertical axis of said blender apparatus, characterized in that the blending conduits (1110, 1210) have lower open ends which terminate in a generally circular and horizontal pattern, said convergence of the blending conduits and said conical walls of the lower section (1112, 1212) creating and supporting in operation a virtual baffle (1130, 1230) of particulate material in combination, said virtual baffle consisting of voussoir-like accumulations of particulate material in said converging channels between the blending conduits and between the conical walls and the blending conduits, the baffle of particulate material remaining in position until the blending tubes have begun to release the final portions of the particulate material through the blending tubes to blend with the particulate material of the vertical baffle as both pass into and through the lower portion of the bin.
Gravity blender apparatus according to claim 3, characterized in that the apparatus further comprises an upwardly converging conical surface (1113), having a maximal diameter substantially that of the diameter of the circular pattern of the lower open end of said conduits, the conical surface projecting upwards towards the circle of open conduit lower ends, said lower ends being spaced above a bottom of said conical surface (1113), and in that the virtual baffle (1130) is formed solely by the particulate material supported upon a matrix of said converging blending conduits (1110), said conical lower portion (1112) of the bin walls and said conical surface (1113) projecting upwards.
Gravity blender apparatus according to claim 3, characterized in that the apparatus further comprises within said lower portion a vertical tubular element (1240) centered axially therein, the virtual baffle (1230) being formed solely of said particulate material supported upon a matrix of said converging blending conduits (1210), said conical lower poration (1212) of the bin and said tubular element (1240).