PROCESS AND APPARATUS FOR IMPROVED SOLIDS FLOWABILITY BY REDUCING THE CONSOLIDATION FORCE

Abstract: There is provided a process and an apparatus utilizing a grid having two or more cells wherein a majority of the cells have a height (H) to effective diameter (ED) ratio (H/ED) equal to or greater than 1.0, preferably equal to or greater than 1.5, for reducing or eliminating consolidation forces on a bulk solid in a vessel such as one used for storage and transport.

Description: PROCESSANDAPPARATUSFORIMPROVED SOLIDS FLOWABILITYBYREDUCINGTHE CONSOLIDATIONFORCE Field of the Invention The invention relates to a process and apparatus for the bulk transport and/or storage of a granular or powdered material that has a tendency to gain cohesive strength and consolidate over time. More particularly, the present invention relates to a process and apparatus for removing cohesive bulk solids from storage and/or shipment vessels. Background of the Invention Until recently, elastomers or rubbery materials such as ethylene-alpha olefins and ethylene-alpha olefm-dienes, as well as polydiolefins and polymers of vinyl aromatic compounds have been prepared from slurry or solution processes which produce a non- granular or non-powdery elastomer product in bale form for commercial use. With the discovery that these elastomers or rubbers can be produced in gas phase fluidization processes, preferably in the presence of inert particulate materials, these elastomers are produced as granules or powders upon exiting the gas phase reactor systems and not in a bale form. However, unlike their bale-form counterparts, these granular or powdery, gas phase produced elastomeric materials exhibit a tendency to gain cohesive strength over time thereby consolidating or compacting when they are stored or transported in bulk. This in turn makes it difficult to unload these materials when they have been stored for periods or time or when they reach their destination. There is a need to alleviate or minimize such materials handling problems and to provide a cost-effective means of delivering these elastomeric polymers, and other similar materials, in bulk to customers. Brief Description of the Drawings Figure 1 is a schematic drawing of grid of cells and a longitudinal view of a cylindrical storage vessel. In Figure 1, 1 = a converging hopper, constructed of any material such as stainless or carbon steel, plastic, glass etc. 2 = a cylinder section vessel wall, 3 = an unloading device (eg., an insert ); and 4 = a vessel outlet. Figure 2 is a schematic depiction of a rectangular transporting vessel, e.g. a hopper car in overview and the grid of cells to be inserted into the vessel. In Figure 2, 1 = a vertical side of the vessel, 2 = a converging hopper, 3 = a vessel outlet, and 4 = an unloading device (the insert), or grid of cells. SUMMARY OF THE INVENTION Accordingly, there is provided a process for improving the flow properties of a bulk solid material in a vessel comprising providing an insert to minimize the compaction of material, especially at or near the bottom or near the outlet of the vessel. In a preferred embodiment there is provided a process for reducing or eliminating consolidation forces on a granular or powder bulk solid in a vessel comprising the steps of (1) determining the internal volume (VI) of the vessel; (2) inserting at least one insert having two or more cells into the vessel; and (3) introducing said granular or powder bulk solid into said cells in the vessel. There is also provided an apparatus comprising an insert having two or more cells installed inside a vessel to minimize consolidation force inside the vessel and to improve the ability of bulk-handling solid materials. These cells of the insert can be rectangular or circular (ring) shaped. For rectangular cells, a majority of the cells have a height to an effective diameter ratio (H ED), or a height to the length of the shorter side of the rectangular cell (H/B), equal to or greater than 1.0, preferably greater than 1.5. For circular cells (e.g., concentric ring-cells), a major of the cells have a height to the distance between any two cells (H/D) ratio, equal to or greater than 1.0, preferably greater than 1.5. The center ring cell of the circular insert has a height to the diameter of the center ring cell (H/d) ratio, equal to or greater than 1.0, preferably greater than 1.5. Detailed Description of the Invention Polymers. Elastomeric or rubbery materials which can benefit from the present invention are, for example, those elastomeric polymers produced in gas phase processes such as those employing a gas fluididzed reactor or a gas fluidized reactor that is assisted by mechanical stirring. Such elastomeric polymers are produced by processes disclosed, for example, in U.S. Patent Nos. 4,994,534; 5,304,588, 5,317,036; 5,453,471; and WO96/04322 and WO96/04323. The elastomers produced in these processes are granular or powdery with an average diameter size ranging from about 0.001 mm to 5 mm, preferably from about 0.001 mm to 2 mm, and most preferably from about 0.001 to 1 mm. Typically these polymers are polymerized at or above their sticking or softening temperature in the presence of one or more inert particulate materials (silica, carbon black, clay, talc, activated carbon, modified carbon blacks, etc.) in an amount ranging from about 0.3-80 wt%, preferably from about 4-75 wt , and most preferably from about 4-40 wt% based upon the total weight of the polymer particle produced. Illustrative of these elastomers that can be employed in the present invention include, but are not limited to, polyisoprene; polybutadiene; a polymer of butadiene copolymerized with styrene; a polymer of butadiene copolymerized with acrylonitrile; a polymer of butadiene copolymerized with isoprene; a polymer of butadiene, isoprene, and styrene; a polymer of butadiene, acrylonitrile, and styrene; a polymer of isobutylene and isoprene; a polymer of ethylene and an alpha olefin having 3 to 12 carbon atoms (e.g., ethylene- propylene and ethylene-butene polymers); a polymer of ethylene, an alpha olefin having 3 to 12 carbon atoms (e.g., propylene) and a non- conjugated diene (such non-conjugated dienes can include, for example, ethylidene norbornene, hexadiene, dicyclopentadiene, and octadiene (e.g., a methyl octadiene); and mixtures thereof. Process. The above-described polymers produced in the gas phase are granular, powdery free-flowing particles upon exiting the reactor. These polymers do not need to be subjected to grinding or pulverizing. However, during storage and transport, in bulk form, these materials have a tendency to consolidate or compact, gaining in cohesive strength with time. Typically the consolidation or compaction ranges from about 0.5 to 10.0 pounds per cubic foot The present process and apparatus limits the consolidation of the cohesive material at rest in a vessel having a bin (the upper section of a vessel have vertical sides) and a hopper (the section between the bin and the vessel outlet with at least one of its sides sloping). Such vessels can include, for example, storage bins and silos, hopper cars, and railroad cars. The principals of this invention are applicable to both rectangular and cylindrical vessels. In a vessel, in the absence of the present invention, in accordance with flow principles developed by Andrew W. Jenike ("Gravity Flow of Bulk Solids," Bull. 108, University of Utah Engineering Experiment Station, October 1961 and Bull. 123, November 1964), the material can be compacted or will be compacted in the vessel, and the degree of compaction depends upon the vessel shape and the packing (compacting) characteristics of the polymer product. When this happens, the material forms an arch (or bridge) that is capable of withstanding considerable stress, thereby transferring the load to the vessel walls or sides with the net result that an arch (dome or bridge) forms preventing any or substantially minimizing the flow of material from the vessel. In this situation, before flow of material can begin, a force needs to be applied to collapse the arch. Since it is impractical to redesign the vessel holding the material, the apparatus of the present invention functions as a flow- corrective device. In the process of the invention, the vessel to which the bulky material is to be introduced is fitted with at least one insert (or grid) having at least two or more cells, preferably a plurality of cells. The grid is installed in the vessel so as to prevent full consolidation of the material near the outlet of the vessel, thus allowing gravity unloading of the cohesive polymeric materials. Once installed into the vessel, the grid may or may not fitted snugly into the vessel. Preferably the grid will fit snugly or securely in the vessel with or without physical attachment, for examples by use of bolts or clamps, to the walls of the vessel. The grid can be constructed of any material appropriate or compatible for a given bulk solid so long as it maintains it shape and form. Typical construction materials can include, for example,carbon steel, stainless steel, plastic, styrofoam, cardboard, etc. In the vessel, the grid may be installed by being welded, glued (e.g, with adhesives), mechanically fastened, or slip-fitted. There can be either one or multiple inserts inside a vessel. When multiple inserts are employed they can be placed in the vessel such that they touch one another or they can be separated by some of the bulk material. When the inserts are separated by some of the bulk material, the amount of material separating the inserts should not generate a consolidation force that exceeds the consolidation force used to calculate the required minimum opening of the cells of the inserts. The converging hopper, cylinder section, and vessel outlet are often fixed in an existing physical form. When this occurs, for the present invention, the unloading grid, is then added to the vessel. Once the grid is placed in the vessel, the solid material is introduced into said cells of the installed grid. Any conventional means can be employed to fill the cells with material. Such means can include, for example, vacuum or dilute phase conveying material then gravity feeding material through a chute into the vessel or the use of mechanical spreaders with gravity loading systems. Apparatus. Suitable apparatus to practice the present invention is depicted in Figures 1 (grids or inserts for cylindrical vessels) and Figure 2 (grids or inserts for rectangular vessels). In Figure 1, there is shown a cylindrical vessel having a converging hopper (1), a cylindrical section vessel wall (2), the unloading device (3) of the invention, and a vessel outlet (4) located at the bottom of the vessel. The vessel shown has an inlet opening (not shown) at the top of the cylindrical vessel. The unloading device (3) consists of multiple concentric rings. The center ring of this unloading device has a diameter (d) equal to or greater than the required minimum bin opening for conical channels based on the instantaneous flow data of the material. The distance (D) between any two rings is equal to or greater than the required minimum opening for plane-flow channels based on the instantaneous flow data of the material. The required minimum bin opening for conical or plane-flow channels is calculated by following the procedures defined by Andrew W. Jenike ("Gravity Flow of Bulk Solids," Bull. 108, University of Utah Engineering Experiment Station, October 1961 and Bull. 123, November 1964). The height (H) of the grid (or insert) is equal to the required minimum opening for conical channels, and preferably it is greater than 1.5. In the present invention, the unloading grid (3) (shown in both circumference and longitudinal view), is preferably added to the vessel. In Figure 2 there is shown an overview of a rectangular transporting vessel having a converging hopper (2), a vessel outlet (3), a vertical side of the vessel (1), and the unloading device (4) or grid of cells of the invention. The opening between the walls (or sides) of the cells of the grid is rectangular or square shaped. The dimension of the opening is represented by L (the longer side) and B (the narrow side). If the ratio of L to B (L/B) is equal to or less than 3.0, the effective diameter for the opening between the walls of the grid is equal to or greater than the required minimum bin opening for conical channels, based upon Jenike's theory as mentioned above. The effective SUBSTITUTE SHEET (RULE 28) diameter is a mathematical construct that relates the area of the cross section of a geometric form to a circle having the same area. The method of calculating the effective diameter of a non- circular form is to determine the diameter of a circle having the same cross sectional area as the form in question. For example, a rectangular cell having the longer side dimension of 2 and the shorter side dimension of 1. The effective diameter of this rectangular cell will be: 4 A E D = π where A equals the area of the rectangular cell (L x B) and E D equals the effective diameter or 1.60 in the above example. If the ratio of L to B (L/B) is larger than 3.0, B is equal to or greater than the required minimum bin opening for plane-flow channels. The height (H) of the grid is equal to the required minimum bin opening for conical or plane- flow channels, preferably it is greater than 1.5. Inlet opening means (not shown) is located at the top of the transporting vessel Preferably, the sides of the individual cells of the grid have a rough surfaces rather than smooth surfaces to provide added friction for the bulk solid. The construction material itself can be rough such as carbon steel or can be sprayed or coated with an abrasive compound such as, for example, Plaite® 4310 from Wisconsin Coatings. The thickness of the grid cell walls do not have a minimum dimension other than that required for mechanical strength such that the cell retains its shape. Typically this thickness may be 0.0635 inches to 0.250 inches. The process and/or apparatus of the invention can be combined with other prior art methods of handling bulk solid materials. These methods can include, for example, transmission of some form of energy to the material to activate flow, usually by breaking up cohesive structures in the material. The use of vibration equipment is the most prominent method in use in industry today. Commercial vibrating devices intended for use on hopper cars or bulk storage bins are available from a number of suppliers. Another popular device uses high pressure gas discharged into the bulk material to break it up and induce flow. The devices are generally known as "blasters" use the energy of compressed gas to break up and induce flow in a cohesive bulk material. The gas is often directed in the direction of the desired discharge. Still another method for inducing flow involves devices that either attempt to fluidize or aerate the bulk solid, thus reducing the friction between the storage vessel and the bulk material itself. U.S. Patent No. 4,617,868 describes a hopper car unloading system that includes a series of fluidizing conveyers in the converging hoppers of the car. U.S. Patent No. 4,880,148 also discloses the use of a fluidizing pad system as a retrofit to the bottom of outlets of a hopper car to reduce factional forces in the area of the outlet. All of these above- described methods do not work very well with highly cohesive materials which are subject to consolidation/compaction. The present invention is fundamentally different in that the unloading grid acts to prevent consolidation of the bulk material near the outlet of the container or hopper car. The result is that the bulk material either flows via gravity or with minor assist from devices as described above. All references cited herein are incorporated by reference. The following examples are given to illustrate the invention and are not necessarily intended as limitations thereof. All parts and percentages are by weight unless otherwise specified. Examples Several experiments were carried out to demonstrate the invention. The experimental procedure involved the construction of a hopper car simulation device. The simulator included a 3 ft. wide by 5 ft long bin. The bin was 3 ft deep exclusive of the converging hopper section on the bottom. The hopper converged in the major length direction at a 45° angle to an outlet measuring 1 ft by 5 ft. The outlet size could be adjusted by the use of plywood closures along the bottom. Two sets of grid were used in the tests. The first grid was constructed using two 5-ft.-long by 1.33-ft.-high and four 3-ft.-long by 1.33-ft.-high sheet metals, which divided the hopper car simulation device into 15 equal-size cells. Each cell is 1 ft. wide, 1ft. long, and 1.33. ft. high. The second grid was a modification of the first grid. The cells adjacent to the long-side of the walls of the simulation device were further divided into two cells. This resulted in the cells next to the long-side walls of the simulation device being 6 in. wide, 1 ft. long, and 1.33 ft. high and the cells in the center of the simulation device being 1 ft. wide, 1 ft. long and 1.33 ft. high. The bulk material to be tested, in this case Union Carbide Elastoflow™ EPDM, was placed into the simulator with or without the grid. Metal weights equal to the weight of a 13-ft height material was placed and evenly distributed on top of the test material to simulate the full load of a hopper car. At that point the simulator would be moved into a constant temperature booth for a specified time for SUBSTITUTE SHEET (RULE 2R) conditioning. The conditions of all tests were set to heat material to 40-45C then maintain material at the set temperature for 3 days. Control Example The control for the series of experiments was a direct gravity unloading from the simulator described above but without installing an unloading grid. Several experiments showed that in the absence of the unloading grid, granular EPDM could only be unloaded under conditions of a maximum temperature exposure of 40° C. Exposure to temperature above 40° C lead to severe consolidation of the EPDM and the inability to unload the simulator by gravity. This condition persisted even while using conventional mechanical devices, including vibrators and air blasters. It did not matter how long vibrators were engaged, the polymer remained in the simulator device. Example 1. The test with the first grid, which had the H/ED equal to 1.2, was partially successful in that although the mass of the test material was easily discharged from the simulator, the material next to the walls experienced consolidation and did not discharge. The cause appeared to be the additional frictional support provided to the material by the converging hopper walls of the simulator. Example 2. Based on the results of Example 1, the second grid was modified to let the outer cells have a higher effective H/ED than those of the first grid. The H/ED of the outer cells of the second grid was 1.67. By using a larger H/ED the consolidation force at the point of the converging hopper was greatly minimized. This modification led to a complete unloading under the same conditions of temperature and pressure as those used in Control Example and Example 1.

Claims: What is claimed is: 1. An apparatus comprising an insert installed inside a vessel to minimize consolidation force inside a vessel and to improve the ability of bulk-handling solid materials. 2. The apparatus of Claim 1 wherein the insert comprises one grid having two or more rectangular cells wherein: the ratio of the longer side to the shorter side of each rectangular cell is less than 3.0; a majority of the cells have a height to an effective diameter ratio, H/ED, equal to or greater than 1.0; and an effective diameter equal to or greater than a minimum bin opening for conical channels. 3. The apparatus of Claim 1 wherein the insert comprises one grid having two or more rectangular cells wherein: the ratio of the longer side to the shorter side of each rectangular cell is equal to or larger than 3; a majority of the cells have a height to a length of the shorter side of the cell ratio, H/B, equal to or greater than 1.0; and the length of the shorter side of the cells is equal to or greater than the minimum opening for plane-flow channels. 4. The apparatus of Claim 1 wherein the insert comprises one grid having two or more concentric ring-cells wherein: a center ring-cell of the insert has the diameter (d) equal to or greater than a minimum bin opening for conical channels; the center ring-cell has a height to diameter, H/d, equal to or greater than 1.0; the distance (D) between any two concentric-ring cells is equal to or greater than the " SUBSTmJTE SHEET (PULE 26) minimum opening for plane-flow channels; and a majority of cells have a height to distance between cells, H/D, equal to or greater than 1.0. 5. A process for improving the flow properties of a bulk solid material in a vessel comprising the steps of (1) determining the internal volume (VI) of the vessel, (2) inserting at least one insert having two or more cells into the vessel; and (3) introducing said bulk solid into the vessel. 6. The process of Claim 1 wherein the bulk solid is a polymer. 7. The process of Claim 6 wherein the polymer is selected from the group consisting of polyisoprene; polybutadiene; a polymer of butadiene copolymerized with styrene; a polymer of butadiene copolymerized with acrylonitrile; a polymer of butadiene copolymerized with isoprene; a polymer of butadiene, isoprene, and styrene; a polymer of butadiene, acrylonitrile, and styrene; a polymer of isobutylene and isoprene; a polymer of ethylene and an alpha olefin having 3 to 12 carbon atoms; a polymer of ethylene, an alpha olefin having 3 to 12 carbon atoms and a non-conjugated diene; and mixtures thereof. 8. The process of Claim 7 wherein the polymer is produced in a gas phase process. 9. The process of Claim 7 wherein the polymer has an average diameter size ranging from about 0.001 mm to 5 mm and contains inert particulate material in an amount ranging from about 0.3 to 80 wt% based upon the total weight of the polymer. 10. The process of Claim 9 where the polymer is an ethylene- propylene-diene terpolymer produced in the gas phase in the presence of an inert particulate material.

Inventors: KANTZ JOHN FRANCIS, KAY THOMAS WAYNE, SCAROLA LEONARD SEBASTIAN, WANG DUAN-FAN, KANTZ, JOHN, FRANCIS, KAY, THOMAS, WAYNE, SCAROLA, LEONARD, SEBASTIAN, WANG, DUAN-FAN
Applicants: UNION CARBIDE CHEM PLASTIC, UNION CARBIDE CHEMICALS & PLASTICS TECHNOLOGY CORPORATION
Application year: 1999
Main classification: B65D88
IPC codes: B65D88