Abstract:
A low profile pipe connection improves process performance or substantially reduces reload time for partitioned beds of particulate material separated by distribution/collection grids. This invention is a multi-sectored grid arrangement that connects piping from an intermediate point on each grid sector with a central or peripheral fluid distribution point through the use of a low profile connection. The reduction in diameter of the low profile connection over the usual flanged connection is substantial.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Provisional Application No. 60/113,295 filed Dec. 22, 1998, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to piping components for distribution and collection of fluids from grids supporting particulate material such as adsorbents or catalyst. The invention is specifically directed to fluid distributor-collector devices which are placed at several intermediate points in a cylindrical bed of solid material to allow the addition or withdrawal of a liquid stream at any of these several points. 
     2. Description of the Prior Art 
     Fluid-solids contacting apparatus are in widespread commercial use as reactors and as adsorption zones. These devices are normally cylindrical columns containing a cylindrical mass of the solid contact material. The solid contact material may be catalyst or solid adsorbent. The fluid flows through the cylindrical mass of solids along the major axis of the column and may flow from one end of the column to another or from one intermediate point in the column to another. To maximize the effectiveness of the intended operation, the fluid should have a uniform composition and flow rate at all points across the cross section of the column to establish a desired “plug flow”. 
     Pressure vessels that contain particulate material for contacting fluids such as gas or liquid process streams are standard features of the chemical and refining industries. In processes for the selective adsorption of components from a multi-component feed and in processes for multi-stage contacting of reactants with a catalyst, partitions commonly subdivide the mass of adsorbent or catalyst in the interior of the pressure vessel into different chambers. The chambers retain a series of adsorbent or catalyst beds comprising discrete particles which permit staged or multiple contacting operations within a single pressure vessel. Such arrangements are routinely used in processes for the simulated moving bed adsorption process. Some fluid-solids contacting columns, especially those used to simulate the movement of the bed of solids, have multiple fluid feed and withdrawal points located intermediate to the ends of the column. At these points it is desired to respectively disperse or collect fluid across the entire cross section of the column. 
     A simulated moving bed adsorbent process exemplifies a process that regularly uses multiple partitions in relatively large pressure vessels. U.S. Pat. No. 2,985,589, the contents of which are hereby incorporated by reference, describes the moving bed adsorbent process in detail. The process distributes and collects process streams from multiple chambers of adsorbent defined by internal partitions located within a pressure vessel and composed of distribution/collection grids. Periodic shifting of the input and effluent streams over the chambers simulates movement of the adsorbent and permits delivery or withdrawal of the streams with a desired concentration profile. 
     Delivering or withdrawing the streams requires flat distribution grids. Common arrangements dispose the grids in a vertically oriented pressure vessel having a vertical centerpipe within the vessel with the grids spaced apart vertically for horizontal fluid distribution. U.S. Pat. No. 4,378,292 shows a typical large-diameter grid arrangement. Each grid is in the form of a flat ring extending between the centerpipe and the vertical outer wall of the vessel and comprises a plurality of grid sectors or semi-annular segments that have an overall wedge shape. Beds of solid particles are located between the layers of fluid distributor grids. Grid sectors at each grid level are placed side by side to fill the annular area between the centerpipe and vessel wall. 
     The grids receive or collect fluid from a plurality of fluid distribution/collection manifolds located in or about the centerpipe at points intermediate the vertically adjacent layers of fluid distributor grids. Requirements for the relatively uniform collection and distribution of fluids from the grids results in the withdrawal or addition of fluid from a central portion of each grid sector. Thus piping is needed to extend from the grid sector through the bed of adsorbent material to the manifold. The term “grid piping” refers to the plurality of fluid distribution/collection pipes that extend from each fluid distributor grid sector to a manifold located above the fluid distributor grid. 
     Most processes need provision for periodic replacement of the particulate material in the beds which requires disassembly and re-assembly of the grids. To facilitate installation, removal, and maintenance of the grid sectors and the grid piping one or more connections are placed along the length of the grid pipes for installation and removal of the piping. Common practice uses bolted flanges to provide these detachable connections. Installing and maintaining the piping in the numerous grid sections and having the piping connections present in the adsorbent poses a number of disadvantages for the process. For example a differential pressure of as little as 2 psi or less across the relatively flat grids can structurally damage the partitions by causing permanent deformation. Structural damage to the partitions has the potential to create leaks in associated connections of the distribution/collection piping. Such leaks typically contaminate the zones created by the partition and reduce the effectiveness of the separation, particularly with respect to the purity and/or yield of the products recovered from the process. 
     The flanges must therefore resist leakage at the piping connections. The size and bulk of the necessary flanges detract from process operations. The volume of the flanges over and above the volume of an equivalent length of pipe displaces additional catalyst or adsorbent from the bed. Any loss of particulate material reduces the effective inventory of the bed for the process application. 
     More importantly, the enlarged profile of the flange relative to the piping disrupts fluid flow through the particulate material immediately upstream and downstream of the protruding flange elements. Adsorbent material downstream of the flange is particularly sensitive to the blocked flow of fluid and results in a “shadowing” effect that renders some portion of the downstream absorbent ineffective for separation and susceptible to extended retention times. The extended retention times further disrupt the desired plug flow of the fluid and can raise the level of impurities in the final products. The degradation of process performance from shadowing usually has the greatest impact when separating viscous materials such as fructose and glucose where the relatively high solids content liquids results being quite viscous as compared to petroleum derived streams. 
     A well known type of piping connection uses a series of machined grooves on the ends of pipes that are connected by bridging links that have complementary grooves for engaging the grooves on the pipe ends. A sleeve or other retaining means is used to hold the link members against the pipes and the cooperating grooves in engagement. Different forms of these types of connections can be seen in U.S. Pat. No. 5,152,556, U.S. Pat. No. 5,265,917, U.S. Pat. No. 5,131,632, and U.S. Pat. No. 4,159,132. These types of connections have not been used in applications that route piping through beds of particulate material. 
     Accordingly, it is an object of this invention to improve the utilization and performance of adsorbent or catalyst in partitioned beds of particulate material separated by distribution/collection grids. 
     It is a further object of this invention to improve the operation of simulated moving bed adsorption process by reducing flow disruption and adsorbent displacement resulting from the presence of grid piping. 
     BRIEF DESCRIPTION OF THE INVENTION 
     It has now been discovered that low profile pipe connections can significantly improve process performance or substantially reduce reload time for partitioned beds of particulate material separated by distribution/collection grids. This invention is a multi-sectored grid arrangement that connects piping from an intermediate point on each grid sector with a central or peripheral fluid distribution point through the use of a low profile connection. The reduction in diameter of the low profile connection over flanged connections is substantial. 
     The low profile connection has an outer radius that is no greater than the 1.25 times inner diameter of the distribution pipe. More typically, the low profile connection provides a mechanical connection having an outer radius that is typically no greater than the inner diameter of the pipe sections that it connects. A flange for a nominal 3-inch diameter pipe has an approximate outside diameter of 8 inches, whereas a typical low profile connection for use in this invention has a diameter of only 5 inches. 
     When subjected to mechanical loads from partition deformation, typical low profile connections resist leakage to a greater degree than most bolted flange-type connections. Deformation of the partitions, particularly to the point of causing structural damage, results in leakage (commonly referred to as “opening up”) of a bolted connection. The connection contemplated for use in this invention can resist such leak producing deformation to about the same extent as the piping that it connects. 
     The use of this apparatus and process can improve the compositional control of a process stream passing into or withdrawn from a processing chamber as well as increasing the contacting capacity of a particulate material contained in the processing chamber. For an adsorption process, compositional control and increased contacting capacity translates into higher recoveries and purities of the product streams. This invention is highly effective in beds where the invention provides a fluid-solids contacting apparatus for utilization in columns in which a vertical oriented cylindrical bed of adsorbent is divided into a large number of zones by means to admix, add or withdraw a fluid and thereby facilitate the movement of adsorption and desorption zones within the bed to simulate a moving bed of the adsorbent. 
     Accordingly, in one embodiment, this invention is a fluid-solids contacting apparatus that includes a cylindrical vessel having a vertical major axis and a plurality of distributor grids spaced apart vertically and extending horizontally for distribution or collection of fluid. A plurality of chambers retains solid particles between the layers of fluid distributor grids. A plurality of fluid distribution pipes extends from each grid into the chamber. Each distribution pipe has at least one mechanical connection for joining separable sections of each distribution pipe. The connection comprises a plurality of grooves defined transversely on each opposing end of the connection and a plurality of cooperating grooves defined transversely on a plurality of links for holding the connection ends in sealed alignment by engagement of grooves on each end of the connection with grooves on each link. A locking member retains engagement of grooves until the connection is broken by removal of the locking member and the links. At least a portion of each distribution pipe usually extends vertically such that at least one mechanical connection is located in the vertically extended portion of the pipe. More often, a portion of each distribution pipe will also extend horizontally and a mechanical connection is located in that horizontal portion as well. 
     In a more limited embodiment, this invention is a fluid-solids contacting apparatus as previously described in described in the previous embodiment that also uses a vertical centerpipe located within the vessel with each grid being in the form of a flat ring extending between the centerpipe and the vertical outer wall of the vessel. Each grid is further divided into grid sectors with a distribution pipe extending vertically upwardly from each grid sector and horizontally over to an inner radius or outer radius of the grid sector. 
     Additional objects, embodiments, and details of the invention are set forth in the following detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of an apparatus containing the grid piping arrangement of this invention. 
     FIG. 2 is a partial section taken along lines  2 — 2  of FIG.  1 . 
     FIG. 3 is an enlarged vertical section of a grid and grid piping taken from FIG.  1 . 
     FIG. 4 is a partial section of the low profile connector for use in this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention may be applied in any process in which it is necessary to contact a segmented cylindrical bed of a solid material, which may be either a catalyst, an immobilized enzyme, or an adsorbent, with a fluid. The fluid may be either a gaseous mixture or a liquid, but it is primarily intended for use with liquid phase conditions. It is, however, specifically intended that the subject invention be utilized in a separation process in which an incoming feed stream containing at least two different chemical compounds or two different isomers of a single compound are passed through a fixed bed of a material which selectively adsorbs one of the two chemical compounds or isomers. Therefore, although the invention is applicable to most all liquid-solids contacting operations, the majority of the description of the subject invention will be described in terms of a separatory process. 
     Adsorptive separation processes and the sequential steps for its performance are well known. The subject invention can be practiced using any type of commercially operable and practical selective adsorbent that is in particulate form. The adsorbent may therefore be a naturally occurring substance or a manmade material and it may be in the form of extrudates, pellets or spheres, etc. The adsorbent can be formed from charcoal, alumina, silica or various clays and mixtures of these materials. The preferred adsorbent comprises a shape selective zeolite commonly referred to as a molecular sieve. Commercially used molecular sieves routinely incorporate a binder such as clay or alumina to produce a stronger and more attrition-resistant adsorbent particle. The adsorbent particles preferably have a size range of about 20 to about 40 mesh. 
     A preferred utilization of the subject apparatus is in a simulated moving bed adsorption process. As mentioned, the movement of the bed of selective adsorptive material is simulated to obtain the effects of the counter-current flow of the bed of solid material and various entering fluid streams such as the feed and desorbent streams. This simulation is performed in part by the periodic movement of the location of various zones such as the adsorption zone along the length of the bed of adsorbent. This movement of the location of the various zones is performed gradually in a unidirectional pattern by periodically advancing the points at which the entering streams enter the adsorbent bed and the points at which the effluent streams are withdrawn from the adsorbent bed. It is only the location of the zones as defined by their respective feed and withdrawal points along the bed of adsorbent which are changed. The adsorbent bed itself is fixed and does not move. 
     It is important to the successful operation of such a simulated moving bed process that the fluid flows through the bed of adsorbent with a “plug flow” flow regime. That is, it is desired for the entire cross section of the adsorbent bed to be evenly swept by the flowing fluid, with the fluid having a uniform velocity and composition at all different points across the entire cross section of the bed. The separational abilities and capacity of any particular adsorbent bed is in part governed by the degree of uniformity of the vertical fluid flow through the bed since nonuniform flow can lead to backmixing, poor utilization of the adsorbent in some areas of the bed, and a dilution of the streams withdrawn from the bed with undesired materials which are also present in the process such as raffmate or desorbent materials. 
     The subject invention is particularly useful for large processing units used to separate different components of water-soluble natural substances such as the separation of fructose and glucose. These substances are normally processed as relatively high solids content liquids. This results in some of the process streams, especially the feed streams, being quite viscous as compared to petroleum derived streams. The large flow rates of these viscous streams and certain other design factors result in large diameter adsorption columns which may be more than 5 meters in diameter. It was observed that these factors lead to an increased tendency toward nonuniform fluid flow and maldistribution of the downward flow of high solids process streams. As previously stated, an uneven flow across different parts of a bed of adsorbent results in a lowering of the optimum performance which may be achieved in terms of the balance between total adsorption and selectivity. It is therefore desirable for the flow rate and composition to be the same at all points across the cross section of an adsorbent bed. More details on the separation of monosaccharides using simulated moving bed techniques may be obtained by reference to U.S. Pat. No. 4,226,639, U.S. Pat. No. 4,226,977, and U.S. Pat. No. 4,206,284. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The structure and operation of the subject invention may be best described by reference to the Drawings. FIG. 1 presents a cross sectional view taken through the vertical major axis of an apparatus built in accordance with this invention. This view shows only a few of the many layers of horizontal grids which are used in an overall apparatus. The apparatus comprises vessel  10  which surrounds the other components of the apparatus. An imperforate centerpiece  12  is located along the. major axis of the outer vessel and supported by a cone-shaped skirt  13  that supports its weight. At the top of the vessel a head volume  17  contains a piping network that delivers or withdraws fluid from an uppermost boundary of the adsorbent chamber as defined by an imperforate plate  15 . Plate  15  receives central support from centerpipe  12 . Above plate  15  the volume  17  of the vessel is usually not used for separation purposes and will not contain adsorbent. Fluid communication between chambers  16  and  17  is established through conduits  18  to balance pressure across the relatively thin plate  15  and prevent distortion. The conduits are arranged to segregate fluid in adsorbent chamber  16  from fluid in volume  17 . Further details of pressure balancing conduit arrangements are given in U.S. Pat. No. 5,415,773. In a similar manner, imperforate plate  23  is located at the bottom of vessel  10  to seal off the lower head volume. Piping system  24  removes or adds fluid at the level of plate  23 . A relatively thin lower plate may be supported by pressure balancing as described in connection with upper plate  15  or by displacement of the empty volume with concrete poured into the lower end of the vessel. The annular volume located above and below plate  15  and  23  is the working volume of the apparatus, and it is in this volume that the adsorbent or other solid particulate material is placed. At the upper and lower ends of the apparatus, a perforate particle-retaining screen may be provided to retain particulate material within the intermediate portion of the apparatus and to provide a hollow annular volume for the collection and distribution of the fluid which is fed to or removed from these terminal portions of the adsorbent bed. 
     The working volume of the apparatus is divided into a number of annular chambers by a plurality of grids  19  which are placed in a layered arrangement. Vertically stacked layers of grids  19  are located below plate  15 . Plate  15  forms the top of an uppermost adsorbent chamber  16  that is ordinarily filled with adsorbent. Uppermost intermediate grid  19  forms the bottom of adsorbent chamber  16  and the top of subsequent adsorbent chamber  11 . 
     Each chamber contains piping for delivering or collecting fluid from each grid  19 . Grid pipes  20  deliver or collect fluid from a plurality of points about each grid. A distribution/collection manifold  21  distributes or collects fluid from all of the grid pipes  20  located in a common chamber. Manifold pipes  22  deliver or collect the process streams that enter or exit the vessel. The grid pipes have low profile connector  28  located in a horizontal pipe segment and low profile connector  29  located in a vertical pipe segment. 
     As shown in FIG. 2, each grid layer is made up of a number of individual wedge shaped sections  25  which are spread around the centerpipe in a circular pattern and which are supported at their inner ends by a support ring  26  fastened to the centerpipe  12  and at their outer ends by a ring  27  attached to the inner surface of the to outer vessel  10 . Each grid layer has a top screen section  30  to support the annular bed of adsorbent which substantially fills the volume between vertically adjacent layers and will usually also have a screen on its bottom portion. Vertical screen support ribs  33  are added as needed to transfer the load on the screen to imperforate bars  34  that serve as side supports. A fluid distributor  32  is located below the inlet/outlet of the grid pipe  20 . 
     FIG. 2 shows a single grid pipe  20  serving each grid segment  25 . The amount of grid piping may be reduced by connecting the vertical portion sections of grid piping  20  from two or more adjacent grid sections to one common horizontal section of grid piping. 
     As shown by FIG. 3, the lower end of each grid pipe is in open communication with a fluid distribution pan  31 . Imperforate pan  31  distributes or collects fluid horizontally from all points of the grid segment and may use fluid distributor  32  to collect or distribute fluid from side to side across the grid segment. An opening  37  communicates both sides of pan  31  with the open end  38  of grid pipe  20 . For example, fluid may flow from a lower chamber into the grid pipe  20  by passing through lower screen  39 , across pan  31  through opening  37  and into open end  38  of pipe  20 . A flow impact plate  35  serves to break up any concentrated jet or stream associated with the open end  30 . Not all of the grid pipes are actively receiving or delivering fluid at all times. When there is no flow through the grid pipe, channeling all of the flow from each adjacent chamber through the opening  37  serves to remix the process fluid as it passes from one chamber to the next. 
     FIG. 4 shows a low profile connection for use in the grid pipes  20 . The connection has a connection half  110  joined to a pipe end  112  and a connection half  114  joined to a pipe end  116 . Pipe sections  110  and  112  are located about a common axis  118 . Each connection half  110 ,  114  also defines a shoulder  150  for engagement with a suitable device, such as a clamp, to provide an axial force and aligning movement to the connection halves during assembly. 
     At least two semi-cylindrical links  120  having contact surfaces  124  and  126  engage contact surfaces  122  and  128  on connector halves  110  and  114 , respectively. A series of grooves defined by transversely extended ribs  130  and  132  on link  120  define the contact surfaces  126  and  124  respectively. Similarly transversely extended ribs  134  and  136  on connector halves  110  and  114  define contact surfaces  122  and  128 . Contact surfaces  122  and  124 , and contact surfaces  126  and  128  may extend perpendicularly from the link or connector halves or may have a small taper to urge connector faces  138  and  140  toward teach other. The contact surface may extend all the way around pipe ends and over the entire transverse length of the link or may be formed as intermediate sections of contact surfaces over only a portion of the transverse length of the links and the connector halves. The use of a cooperating lip structure or other grooves on contact faces  138  and  140  can facilitate the alignment and assembly of the connection. 
     Sealing of the contact faces may also be improved the use of an O-ring in a suitable retaining groove. 
     Links  120  are held in place by an annular sleeve  142  that has a sloped surface  144  for engagement with a complementary sloped surface  146  on the outside of the links  120 . A set screw  148  or other similar attachment device is received by a threaded hole  149  and may be used to keep sleeve  142  in place over links  120 . The types of retaining devices are not limited to structures such as sleeve  142 . Any suitable retaining structure or mechanism could be used such as a clamp arrangement.