Abstract:
An apparatus is presented for contacting a bed of particulate material with a cross flowing fluid, and which maintains the bed of particulate material within a retention volume. The apparatus includes panels for covering fluid inlet and outlet apertures and for retaining solid particles within the contacting bed. The apparatus is designed to promote the flow of solid particles through the bed and to prevent solid particles from spilling through inlet and outlet apertures.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the field of fluid particle contact and to an apparatus for contacting fluids and particles. More specifically, this invention relates to a moving bed of particles with a cross-flowing fluid. 
       BACKGROUND OF THE INVENTION 
       [0002]    A wide variety of processes use radial flow reactors to provide for contact between a fluid and a solid. The solid usually comprises a catalytic material on which the fluid reacts to form a product, or an adsorbent for selectively removing a component from the fluid. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation. 
         [0003]    Radial flow reactors are constructed such that the reactor has an annular structure and that there are annular distribution and collection devices. The devices for distribution and collection incorporate some type of screened surface. The screened surface is for holding catalyst or adsorbent beds in place and for aiding in the distribution of pressure over the surface of the reactor, or adsorber, and to facilitate radial flow through the reactor bed. The screen can be a mesh, either wire or other material, or a punched plate. For a moving bed, the screen or mesh provides a barrier to prevent the loss of solid catalyst particles while allowing fluid to flow through the bed. The screen requires that the holes for allowing fluid through are sufficiently small to prevent the solid from flowing across the screen. Solid catalyst particles are added at the top, and flow through the apparatus and removed at the bottom, while passing through a screened-in enclosure that permits the flow of fluid over the catalyst. The screen is preferably constructed of a non-reactive material, but in reality the screen often undergoes some reaction through corrosion, and over time problems arise from the corroded screen or mesh. 
         [0004]    The screens or meshes used to hold the catalyst particles within a bed are sized to have apertures sufficiently small that the particles cannot pass through. A significant problem is the corrosion of meshes or screens used to hold catalyst beds in place, or for the distribution of reactants through a reactor bed. Reactions can take place that cause a buildup of material on the screens which in turn plugs holes in the screen. Corrosion can also plug apertures to a screen or mesh. This creates dead volumes where fluid does not flow, and there is poor or no fluid-solid contact, and subsequently a loss of efficiency as well as wasted catalyst. Corrosion can also create larger apertures where the catalyst particles can then flow out of the catalyst bed with the fluid and be lost to the process increasing costs. This produces unacceptable losses of catalyst, and increases costs because of the need to add additional makeup catalyst. 
         [0005]    The design of reactors to overcome these limitations can save significantly on downtime for repairs and on the loss of catalyst, which is a significant portion of the cost of processing hydrocarbons. 
       SUMMARY OF THE INVENTION 
       [0006]    New reactor designs can accommodate existing reactors, such that during upgrades of equipment, the reactor internals can be replaced when a new reload of catalyst is provided. Reactors using a catalyst flowing through the reactor with a fluid contacting the catalyst comprises an outer cylindrical partition having apertures defined therein. The reactor further includes an inner cylindrical partition having apertures defined therein, where the inner and outer cylindrical partitions are arranged in a concentric manner and form a toroidal space that defines a particle retention volume where catalyst can flow through. The reactor further includes a plurality of toroidally shaped outer louvers having a leading edge affixed to the outer cylindrical partition. The outer louvers have a leading edge affixed at a position above the apertures in the outer cylindrical partition, and a trailing edge extending downward into the particle retention volume. The reactor further includes a plurality of toroidally shaped inner louvers, with each inner louver having a leading edge affixed to the inner cylindrical partition at a position above the apertures in the inner cylindrical partition. The inner louvers have a trailing edge that extends downward into the particle retention volume of the reactor. 
         [0007]    Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a first embodiment of the invention; 
           [0009]      FIG. 2  is an annular configuration of the first embodiment of the invention; and 
           [0010]      FIG. 3  is a second annular configuration of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Recent investigations into radial flow reactors for olefin cracking have indicated corrosion in likely to be substantial, and that corrosion products and precipitated material such as coke from upstream of the reactor are generated. These materials present significant corrosion and fouling problems for the reactor. 
         [0012]    In one embodiment of the invention as shown in  FIG. 1 , the moving bed reactor  10  comprises a particle retention volume  14  where solid catalyst particles flow downward through the reactor  10 . The phrase particle retention volume is used to describe the region where solid catalyst particles temporarily reside during the process, as the catalyst flows through the reactor, and is not meant to limit the term to a region where the catalyst resides without moving. The reactor  10  is made up of at least one reactor bed unit  12  where each reactor bed unit  12  has at least one solid particle inlet  16 , and at least one solid particle outlet  18 . The reactor  10  has a fluid inlet  20 , that is covered by a panel  22  which prevents solid particles from the reactor  10  exiting through the fluid inlet apertures  20 . The panel  22  extends into the particle retention volume at an angle between 10° and 60° degrees from vertical. The fluid flows into the reactor  10  and across the particle bed and exits a fluid outlet  24 . The reactor bed unit  12  is shaped to direct the flowing solid particles to a solid particle outlet  18  of the unit  12 . Typically, this will entail a slanted wall, or a conically shaped region, at the bottom of the reactor bed unit  12 , and preferably the wall will have an angle greater than about  45  degrees from horizontal. This embodiment can comprise multiple units  12  stacked in a manner such that the particle outlet  18  from an upper unit  12  is the particle inlet  16  to a lower unit. The fluid inlet  20  can comprise apertures in fluid communication with the reactor feed, or can comprise channels underneath the panels  22  where the channels are in fluid communication with the reactor feed through a manifold or other means. The fluid flows up through the reactor bed  14  and out the fluid outlet  24 . The depth of the contacting zone, D, should be greater than 0.5 times the width, W, of the contacting zone. This is to promote good distribution of the fluid through the solid particle bed for good contacting of the fluid with catalyst within the bed. 
         [0013]    In a variation of this embodiment, the reactor  10  can have an annular configuration, as shown in  FIG. 2 . With an annular configuration, the reactor  10  comprises an external cylindrical partition  26  and an inner cylindrical partition, or centerpipe,  30 . The space between the external cylindrical partition  26  and the centerpipe  30  defines the particle retention volume  14  for holding solid catalyst particles that flow through the reactor. The reactor  10  comprises a plurality of reactor bed units  12  which are annular sections that hold the solid catalyst particles in a reactor bed. In the annular configuration, the reactor unit outlet  18  comprises two annular louvers  32   a,    32   b.  An inner annular louver  32   a  has a leading edge affixed to the centerpipe  30  at a position above a fluid outlet  34 . The leading edge of the louver  32   a  is defined as the upstream edge relative to the flow of catalyst through the reactor  10 . The louvers  32   a,    32   b  extend into the particle retention volume at an angle between about 10° and about 60° from vertical, and the trailing edge of the louver  32   a  extends below the leading edge. In one variation, the louvers  32   a,    32   b  further include vanes  38 , where the vanes  38  have a leading edge affixed to the trailing edge of the louvers  32   a,    32   b  and extend vertically downward from the louvers  32   a,    32   b.    
         [0014]    The annular configuration for the reactor  10  provides a benefit of using the center pipe  30  as the outlet manifold for collecting the reactor effluent stream. In another variation with the annular configuration, the center pipe  30  can be used to direct the feed stream to the reactor inlet with the reactor effluent drawn off from around the external cylindrical partition. 
         [0015]    In a preferred embodiment, the reactor  10  of the present invention has an annular configuration as shown in  FIG. 3 . The reactor  10  comprises an external cylindrical partition  26  and an inner cylindrical partition, or centerpipe,  30 , with the space between the partitions defining the particle retention volume, or reactor. The fluid inlets  20  are defined in the external cylindrical partition  26 , and have an annular panel  22  that covers the inlets  20 . The annular panel  22  is a structure that has an angled top portion  34  and a substantially vertical portion  36 . The angled top portion  34  has an orientation of between 10° and 60° from vertical, and the vertical portion  36  extends to a position below the bottom of the inlet aperture  20 . The panel  22  distributes the fluid entering the reactor  10  over the surface of the catalyst. The fluid outlets  24  are covered with a louver  32  that has a leading edge affixed to the centerpipe  30 . In a preferred configuration, the louvers  32  extend into the particle retention volume about 50% of the spacing between the external cylindrical partition  26  and the inner cylindrical partition  30 , and at an angle between 10° and 60° from vertical. This facilitates the mixing of the catalyst such that catalyst will not get stranded in dead zones. It is preferred that the depth, D, of the contacting zone be at least 0.5 times the width, W, of the contacting zone. The reactor  10 , optionally, includes vanes  40  disposed under the louvers  32 . The vanes  40  have an edge affixed to the inner cylindrical partition  30  at a position below the fluid outlets  24 , and extend upwards away from the catalyst bed into the region underneath the louvers  32 . The vanes  40  can be shaped and sized to control the flow of the fluid exiting the reactor, and can provide protection against catalyst rising under the louvers  32  during periods of start up or cooling down in the operation of the reactor  10 . 
         [0016]    The annular panel  22  can also be made of two pieces, a first piece  34  comprising having a leading edge affixed to external cylindrical partition  26  and a trailing edge extending downward into the particle retention volume at an angle between 10° and 60° from vertical. The panel  22  is further made up of a second piece  36  having a leading edge that is affixed to the trailing edge of the first piece  34 , and extends substantially vertically downward from the first piece  34 . 
         [0017]    In an alternative embodiment, the reactor includes a first partition, where the first partition has apertures defined therein. The reactor further includes a second partition spaced from the first partition to define a particle retention volume, and where the second partition has apertures defined therein. The particle retention volume is a space where catalyst resides during the operation of the reactor. The catalyst can flow through the particle retention volume during operation with a fluid flowing over the catalyst. The apertures defined in the first partition include first louvers. The first louvers have a leading edge affixed to the first partition in a position above an aperture, and the louver has a trailing edge that extends into the particle retention volume at an angle between 10° and 60° from vertical. The trailing edge extends to a position at least as low as the lower edge of the aperture to which the louver is covering. The leading edge and trailing edge are referenced with respect to the flow of catalyst through the reactor, where the leading edge is the edge upstream of the trailing edge in the stream of catalyst. The apertures defined in the second partition include second louvers, where the second louvers have a leading edge affixed to the second partition above an aperture in the second partition. The second louvers have a trailing edge that extends into the particle retention volume at an angle between 10° and 60° from vertical and extends to a position at least as low as the lower edge of the aperture to which the louver is covering. 
         [0018]    The operation of this reactor can be controlled through controlling the pressure at the inlets  20  and controlling the pressure drop across the system. Specific operations can also be controlled through variations in design, such as decisions regarding the number and locations of the inlets  20  and the outlets  24  of the reactor  10 . In one operation regime, the fluid enters through the inlets  20  of the reactor  10 , rises through the catalyst bed  14  and the reacted fluid exits through the outlets  24 . In an alternate operation, the fluid can enter the reactor with the catalyst at the top of the reactor and flow down with the catalyst, separating from the solid catalyst particles and exiting through the reactor outlets  24 . 
         [0019]    While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications of the plates, combinations of plates, and equivalent arrangements included within the scope of the appended claims.