APPARATUS FOR BLENDING PARTICULATE MATERIAL

Abstract: Disclosed is an apparatus for blending solid particulate material comprising a vertically oriented vessel (10) having an upper part and a lower part (11) and an outer wall and an inner wall (116). The apparatus has an inlet (13) for particulate material to be blended and an outlet (17) for blended particulate material. The apparatus preferably has a vertical lift column (20) centrally mounted in the vessel (10) including an inlet (22) located in the lower part (11) thereof and an outlet (23) in the upper part of the vessel (10), and at least one improved tubular vertical blending channel (30) having a passageway through which solid particulate material passes by gravity. The blending channel (30) is formed by bringing a substantially rectangular, open-ended convex shaped member (125) in communication with the inner wall (126) of the vessel (10).

Description: APPARATUS FOR BLENDING PARTICULATE MATERIAL BACKGROUND OF THE INVENTION The present invention relates to an improvement in a blending apparatus for particulate material such as plastic pellets. Typically, such blenders are commonly used to homogenize the feed stock of resin molding plants. Generally, the apparatus utilizes the blending concept of withdrawing material from a plurality of points within a vessel through vertical blending channels, or downcomers, which are basically tubular shaped through which such material flows by gravity. Preferably the vessel will also incorporate an internal recirculation system utilizing gas under pressure to recirculate the thus withdrawn material back to the top of the vessel through a central lift pipe. Most preferably, the present invention is an improvement over my co-pending U. S. Patent Application Serial No. 06/848,005 filed April 3, 1986. More particularly, the present invention relates to an economical design of vertical do ncomers that are utilized in the above and other blending apparatus. The blender design disclosed in my prior above referenced U.S. Patent application includes a conical bottom vessel with tubular extension on the bottom. A vertical lift pipe is centrally mounted in the vessel and extends from the upper part of the vessel into the tubular extension. Blending air is supplied to the bottom of the vessel for entraining material to be blended and conveying it up the center lift pipe for circulating material through the vessel. The tubular extension and lift pipe are dimensioned to define a seal leg to prevent blending air from bypassing the vertical lift pipe and flowing directly into the vessel. The vessel also contains a plurality of blending channels, also referred to as "downcomers", that are circumferentially spaced around the inside of the vessel. Each of these channels may have a plurality of vertically spaced apart inlet openings which may have baffles positioned therein. Material that is already in the vessel moves by gravity down through a passageway within the blending channels to the area of the seal leg for entrainment with the incoming material up through the center lift pipe or the blending column. The outlets of the blending channels are placed near the top of the seal leg and the inlet for the lift column is placed near the bottom of the seal leg. The blending channels or downcomers are of a tubular structure. In such a blending apparatus, and, in fact, in other designs of blending apparatus that utilize blending channels but do not utilize the lift pipe concept, it has been discovered that a significant portion of the material costs can be attributed to both the material utilized to manufacture the blending channels and the material utilized to manufacture any supports and guides that may be deployed within the blender itself to hold such channels in place. Aside from the material costs involved, such supports and guides can, at times, and depending upon the nature of the material being circulated and the design of the blending apparatus, cause a certain amount of build-up of material within the blender which would decrease the performance characteristics of the blender and create maintenance problems. It would be advantageous, therefore, to provide for tubular blending or downcomer channels which can be advantageously utilized in a blending apparatus but which are not as material intensive as prior art channels. It would be preferably advantageous to provide for a design which is capable of utilizing the advantages of my prior invention yet would reduce material cost attributed to the design of the downcomer channels and any supports required therewith while giving similar or improved performance characteristics. SUMMARY It is therefore the object of this invention to provide an apparatus for blending particulate material which utilizes downcomer channels that are less material intensive than channels typically employed within prior art blenders and additionally enhance performance characteristics. In general, the foregoing and other objects will be carried out by providing an apparatus for blending particulate material that employs a plurality of downcomer channels. Each downcomer channel is formed by placing or bringing an open backed member in communication with the inner wall of the blending vessel to thereby form a substantially vertical and tubular channel. The term "in communication with" as used herein means that the member is either positioned on the wall or is placed in close proximity to the wall. The open-backed member will preferably be manufactured from a basically rectangular piece of a suitable material which is formed in a basically convex shape relative to the inner wall of the blending vessel. The term "convex" is used herein in a general sense to connotate a shape such that when the member is attached to or placed in close proximity to the inner wall of the vessel the member, in combination with said inner wall, will define a channel through which material will flow vertically by gravity. The member can be formed in any of a number of shapes, such as, for example, a v-shape, an arch, or three sides of a rectangular or square. The member will be positioned on placed in close proximity to the inner wall of blender so that the length of the generally rectar.- lar member will be in the vertical plane, with the edges along the length thereof being in contact with or in close proximity to the inner walls of the blender and the edges along the width of the member being bent away from the inner wall of the blender. When positioned on or placed in close proximity to the inner wall of the blender the member will define, in combination with said inner wall, a vertical passageway through which the particulate material contents of the blender can freely pass. The member is specified as being "open-backed" because it does not, by itself, define an essentially closed tubular shape, which shape will be defined only by the combination of the member and the inner wall of the blending vessel. The unobstructed tubular cavity thereby formed will allow material to freely pass in a downward direction through the blender. The member can be fashioned from any material that is compatible with the blender inventory, the processing demands inherent with moving the inventory through the blending vessel and the inner wall of the vessel, if, for example, it is desired to physically attach the member to the inner wall, such as by welding it thereto. The choice of material used for the member is not an aspect of the present invention and is within the ability of those skilled in the art. The preferred blending apparatus of the present invention will comprise a vertically oriented vessel having an upper end and a lower end and an inner wall and an outer wall; with a vertical lift column mounted in the vessel with gaseous fluid under pressure supplied to the bottom of the column for entraining material in the vessel and lifting it up through the column to circulate material within the vessel. The apparatus also includes an arrangement of defining a seal leg at the bottom of the vessel to facilitate proper recycle of material through the apparatus. The apparatus preferably is used with a bottom filling arrangement so that the energy used for supplying material to the vessel is utilized for blending material; and a plurality of vertically oriented downcomers are mounted in said vessel and terminate above said seal leg. The downcomers are constructed by the positioning of an open-backed member to the inner wall of the blender or bringing said member in close proximity to said inner wall so that the open-backed member, in combination with said inner wall, will define a channel having a tubular cavity therethrough, which channel is basically vertically oriented within the blender. The exact shape of the channel's cavity or passageway, as viewed in cross-section, will be dependent on the shape of both the open-backed member and the inside blender wall to which it is attached or in close proximity. The cross-sectional shape of the cavity within the downcomer defined by the blender wall and the open-backed member is not a crucial element of the present invention, as long as the downcomer is generally tubular in shape and material can freely pass therethrough via gravity. The above describes a preferred embodiment of the present invention. However, the novel blending channels of the present invention can also be used in blenders that do not utilize a lift pipe or a seal leg. In such blenders, the flow exiting such blending channels will enter an area within the bottom of the vessel typically located in the volume within the tubular extension of the blending vessel wherein further mixing occurs. As indicated, the open-backed member can either be "positioned on " or in "close proximity to" the inner wall of the vessel. The term "positioned on" is used in its literal sense to mean that the member will, to some extent, actually be touching the inner wall. More specifically, the vertical edges only of the member will be in contact with the inner wall of the blending since, obviously, if the entire member were placed flush against the inner wall, a cavity would not be formed between the wall and the member. When the member is "in close proximity" to the inner wall of the vessel a gap exists from which the longitudinal edges of the member are spaced from the wall. Obviously, such a gap or separation from the wall should not be so large so as to destroy the integrity of the passageway or cavity formed by the combination of the open-backed member and the inner wall. Ideally, the gap will, however, be sufficiently large to promote free flow through the gap at the upper surface of the inventory. When utilized in such a manner, the gap will function as a "moving port" in that free flow through the gap will begin at a point level with the surface line of the inventory of the material within the blender when such material is being withdrawn from the blender. In such a manner, material to be withdrawn will be obtained from all the submerged exit ports within the blender and from the top surface of the blender, thus promoting better blending. The open-backed member utilized in the present invention can be spaced out from the wall by any of a number of methods which are well within the ability of those skilled in the art. For example, the open-backed member may be spaced away from the wall by short tabs which are attached to the inner wall of the blender. Alternatively, the open-backed members may be hung from the top of the blender by tension links, and when such members are segmented, as described below, the segments can be interconnected by tension links. BRIEF DESCRIPTION OF THE DRAWING The invention will be described in connection with the annexed drawing wherein: Fig. 1 is a diagramatic view of the blending system according to the present invention; Figs. 2 and 2A are a sectional view of the blender according to the present invention with Fig. 2A being a continuation of Fig. 2 at the line A-A. Figs. 3a-3b are cross-sectional views of prior art blending channels. Figures 3c-3e are cross-sectional views of various blending channel configurations of the present invention. Fig. 4 is a side view of a segmented blending channel of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, the blending system according to the present invention includes a blender generally indicated at 1, a source of particulate material to be blended indicated at 2 and a source 3 of gaseous fluid under pressure such as a motor operated blower. A conduit 4 extends between the blower 3 and the inlet 13 of blender 1 for supplying gaseous fluid under pressure and entrained fresh material to be blended from the source 2 to the blender 1. Material from the source is supplied to the conduit 4 by any of the several means known in the pneumatic conveying art. A vent conduit 5 is connected to a high efficiency dust collection system 6 and a fan 7. The blending vessel 1 is supported by legs 8. Referring to Figs. 2 and 2A, the blender 1 includes a vertically oriented vessel 10 having a hopper shaped bottom or lower end 11 and a downwardly extending tubular extension 12 centrally positioned in the lower part of the vessel 10. In the preferred form, the vessel includes a solid particulate material inlet 13 in the bottom of the tubular extension 12. This inlet 13 is connected to the conveying conduit 4 by means of a diverter valve 15. A cutoff valve or gate 16 is interposed between the conveying line 4 and the material inlet 13. With the use of the diverter valve 15, the inlet opening 13 also serves as the blender outlet. Thus, when it is desired to supply material to the blending vessel 10, material is supplied from the source 2 by entrainment in the gaseous fluid under pressure supplied from 3 and conveyed through line 4 through diverter valve 15 and open gate 16 to inlet 13. When it is desired to discharge material from the vessel 10, the diverter valve 15 is repositioned to close the passage from line 4 to inlet 13 and open a passage from opening 13 to diverted outlet 17 to permit material to flow from opening 13 through open gates 16 to outlet 17. Thus, in this preferred embodiment of the present invention, the inlet and outlet of the vessel are coextensive. In the apparatus depicted in Figures 2 and 2A, the vessel 10 includes a vertically oriented, centrally mounted blending or lift column 20 which extends downwardly into the tubular section 12 as illustrated in Fig. 2A. This blending column or lift column 20 is mounted in the vessel 10 by means of support bracket (or brackets) 21. The column 20 is hollow and open ended and has a lower end 22 near the opening 13 within the tubular extension 12 and as an upper end or outlet 23 which is near the top of the vessel 10. A distributing cone 24 may be positioned in the top of the vessel. As shown in Fig. 2, the vessel includes an outlet 25 connected to vent line 5 and high efficiency dust collector 6 (Fig. 1) . The blending apparatus also includes a plurality of recycle channels or downcomers 30 circumferentially spaced apart that are attached to or in close proximity to the inner walls 32 of the vessel 10. In Figures 2 and 2A, downcomers 30 are formed by attaching member 31 to the inner walls 32 of vessel 10, which attachment in the depicted embodiment is accomplished through the use of brackets 33. While in the preferred form the invention includes a bottom inlet for material to be blended, it should be understood that the invention is also applicable to a blender where material is supplied to the top of the vessel and blending is achieved totally by material recirculation within the blender to be hereinafter described. In addition, the downcomers of the present invention may be utilized in a top-filled blender that does not contain a central lift pipe and through which material to be blended travels by gravity both down through the body of the blender and down through the downcomer channels. In such an instance, the volume within the tubular extension 12 would function as a mixing chamber for collecting all the flow from the blending channels. The downcomer channels of the present invention are shown in better detail in Figures 3C-3E, with Figures 3A and 3B illustrating prior art downcomer channels. Figure 3A illustrates, in cross-section, a tri-sected downcomer tube configuration depicted by numeral 101 which is believed to be the most common tube shape used at present for downcomers. In this design, the inner passage or channelway of tube 101 is divided into three internal sections 102, 103 and 104 through the use of partitions 105, 106 and 107. The tube is supported within the blender through the use of support struts 108 which are connected to inner wall 109 of the blending vessel at points 110. Figure 3B illustrates a prior art circular downcomer 111. This figure also illustrates a tube being supported within the blending vessel by support struts 112, which are attached to the inner wall 113 of the blending vessel at points 114. Figure 3C illustrates the downcomer of the present invention, wherein downcomer passageway 115 is defined by the combination of inner wall 116 of the vessel and member 117, which member is attached to inner wall 116 at points 118. While figure 3C shows member 117 as being fashioned in the form of an arch, such a member can be formed in any of a number of other shapes, so long as an internal passageway is formed through which material can pass when the member is attached to or placed in close proximity to the inner wall of the vessel. For example, figure 3D shows member 120 in the form of a v and figure 3E shows member 125 in the form of three sides of a rectangle. Thus, the attaching member can be of any of an infinite number of possible configurations, the only requirement being that the solid particulate inventory within the blender must be able to freely pass down by gravity through the downcomer channels formed by the attachment of the member to the inner surface 32 of vessel 10. Blending channels constructed according to the present invention will not, therefore, need to be supported by the elaborate struts utilized for prior art blending systems. In addition, blending channels having the same cross-sectional flow area as the generally circular prior art blending channels which are exemplified in Figs. 3A and 3B, for example, can be formed utilizing less material that is used to form such prior art downcomers. When it is desired to place member 31 in contact with inner wall 32, the method of attaching member 31 to said inner wall 32 of vessel 10 will be dependent on the needs of the individual practitioner of this invention. For example, member 31 may be attached with brackets as depicted in Figure 2. Alternatively, member 31 may be welded to inner wall 32. It is, however, not necessary to physically attach member 31 to wall 32 at every point along edge 33 of member 31. Generally, it is only necessary to attach the top portion of member 31 to wall 32, as depicted in Figs. 2 and 2A, since, when the vessel is full of material, member 31 will be forced against the inner wall of the blender by the solids content within the blender. Such a method of attachment is advantageous when the contents of the blender are drained, since the channels will relax and move away from the wall, thus releasing entrapped material. The downcomers of the present invention will preferably include a plurality of sections which are separated from each other by a narrow gap, which in Figures 2 and 2A are depicted by numeral 35. The purpose of using a plurality of sections separated by a gap is to allow for differential thermal expansion between the vessel walls and the tubular channels and, also, to preferably form, in each downcomer, at least one and preferably a plurality of vertically spaced apart openings in the upper part of the vessel 10. In addition, each of the downcomers includes an outlet in the lower part of the vessel. In the embodiment illustrated, the inlet openings are uniformly spaced along the vertical length of the downcomers. In addition, in the embodiment illustrated, the openings in the downcomers 30 are spaced at uniform levels in the vessel 10, but the invention would also be applicable to spacing the openings at various levels. In the preferred form, the downcomer outlets are generally located at the top of the tubular extension. Each of the openings includes a baffle mounted therein. In one embodiment, this baffle is a fixed element which extends into the interior of the downcomer. As is generally known in the prior art, when material is filled in the vessel 10 to a given level, material will flow into the downcomers primarily through the top most opening which is below the level of material and little material will flow into an opening below that top most opening. If a baffle element is positioned in a lower opening, then material will flow into the downcomer not only from the uppermost opening but also from a next lower opening that includes a baffle element. The baffles in the downcomers of the present invention are similar to those specified in my U.S. Serial No. 848,005 except that they can be constructed to be much stronger than is currently possible with the circular blend tubes specified in the present invention. This is possible because the baffles can be welded to the blend tube from the flow side of the tube. As indicated above, the blending channels of the present invention can be segmented, with a narrow gap between each of the segments of each channel. Additional mixing can be promoted if the segments have varying cross-sectioned flow areas. To promote the best blending characteristics, such segments would be co-axially positioned vertically in a sequence with the segments with the largest cross-sectional flow areas being located at the bottom of the blending vessel and the segments to having the smallest cross-sectional flow areas being located at the top of the blending vessel. Thus, each segment of a given blending channel will have a larger cross-sectional flow area than the one immediately above it. As indicated each segment is positioned so that a small gap exists between the lower end of the upper segment and the upper end of the lower segment. As material is thereby withdrawn from the lowest segment, the same flow velocity exists in all the subsequent segments. Such segmented blending channels are shown in Figure 4, which depicts segments 131 and 132 of a blending channel which are respectively formed by members 133 and 134 in combination with inner wall 135 of the blending vessel. Segment 131 is located closer to the upper portion of the blending vessel than segment 132 and has a smaller cross-sectional flow area than does segment 132. The segments are separated by gap 136. To promote better mixing characteristics between the contents of the blending channels and the inventory present in the rest of the vessel, the ends of the segments are preferably cut at an angle relative to inner wall. The angle at which the lower end of a given segment is cut will preferably be an obtuse angle relative to the inner wall, as exemplified by angle A for segment 131, with the upper end of any segment immediately beneath such segment being cut at an angle which basically supplements said first angle, as exemplified by angle B for segment 132. It is intended that the foregoing description be that of a preferred embodiment and that the invention be limited solely by that which is within the scope of the claims as set forth herein.

Claims: CLAIMS 1. In an apparatus for blending solid particulate material comprising a vertically oriented vessel having an upper part and a lower part and an outer wall and an inner wall, an inlet for particulate material to be blended, an outlet for blended particulate material; a vertical lift column centrally mounted in said vessel including an inlet located in the lower part thereof and an outlet in the upper part of the vessel; at least one tubular, vertical blending channel having a passageway through which solid particulate material passes by gravity, said channel having at least one inlet for receiving particulate material from the upper part of the vessel and an outlet for returning particulate material to the lower part of the vessel; means for supplying gaseous fluid under pressure to the bottom of said lift column for entraining material in the lift column and upwardly through the lift column whereby material is discharged from the outlet of said lift column into the upper part of the vessel, the improvement comprising forming the vertical blending channel by bringing a substantially rectangular, open-ended convex shaped member in communication with the inner wall of the vessel. 2. The apparatus of claim 1 wherein the member is in contact with the inner wall of the blending chamber. 3. The apparatus of claim 1 wherein the member is in close proximity to the inner wall of the vessel. 4. The apparatus of claim 1 wherein at least the upper portion of said member is attached to the inner wall of the vessel. 5. The apparatus of claim 1 wherein the member is in the form of an arch. 6. The apparatus of claim 1 wherein the member is in the form of three sides of a rectangle. 7. The apparatus of claim 1 wherein the member is v-shaped. 8. Apparatus for blending solid particulate material according to claim 1 which further comprises a tubular extension having a top portion and a bottom portion, which tubular extension is located on the lower part of said vertically oriented vessel into which the lower part of said vertical lift column, including the inlet thereto, extends, wherein said tubular extension and the lift column are further dimensioned to define a seal leg to enable a major portion of said gaseous fluid to be directed upwardly through the lift column, wherein further the outlet of the blending channel is connected to the top of the tubular extension and the means for supplying gaseous fluid under pressure is connected to the bottom portion of the tubular extension. 9. Apparatus for blending solid particulate material according to claim 8 wherein the inlet for particulate material of the vessel is positioned in the bottom portion of said tubular extension, co-axially aligned with said lift column, and said means for supplying gaseous fluid under pressure entrains fresh material to be blended to the lift column inlet and upwardly through said lift column and entrains material already in the vessel through the lift column. 10. Apparatus for blending solid particulate material according to claim 9 wherein there are a plurality of circumferentially spaced apart vertical blending channels located around the outer periphery of said vessel. 11. Apparatus for blending solid particulate material according to claim 10 wherein the outlet of the vessel is coextensive with the inlet of the vessel and valve means is provided in said inlet. 12. The apparatus according to claim 1 wherein the at least one blending channel is comprised of a plurality of vertical segments. 13. The apparatus according to claim 12 wherein the segments have differing cross-sectional areas with each segment having a larger cross-sectional flow area than the one immediately above it. 14. The apparatus of claim 13 wherein the ends of each segment are cut at an angle relative to the inner wall of the vessel. 15. In an apparatus for blending solid particulate material including a vertically oriented vessel having an upper part, a lower part, an inlet for material to be blended located at the upper part of said vessel and an outlet for blended material located at the lower and at least one generally vertical blending channel having a passageway therethrough associated with said vessel having at least one inlet communicating with the upper part of the vessel and an outlet, communicating with the lower part of said vessel, the improvement comprising defining the blending channel by bringing a substantially rectangular, open-ended convex shaped member in communication with the inner wall of the vessel. 16. Apparatus of blending solid particulate material according to claim 15 wherein there are a plurality of vertically spaced apart inlet openings in said at least one vertical blending channel, each communicating with a progressively lower level of said vessel. 17. The apparatus according to claim 15 wherein there are a plurality of circumferentially spaced apart vertical blending channels located around the outer periphery of said vessel. 18. The apparatus according to claim 15 wherein the blending channel is comprised of a plurality of vertical segments. 19. The apparatus according to claim 18 wherein the segments have differing cross-sectional flow areas with each segment having a larger cross-sectional flow area than the one immediately above it. 20. The apparatus of claim 19 wherein the ends of each segment are cut at an angle relative to the inner wall of the vessel.

Inventors: PAUL KERMIT D, PAUL, KERMIT, D.
Applicants: FULLER CO, FULLER COMPANY
Application year: 1991
Main classification: B01F13
IPC codes: B01F13