Abstract:
An apparatus is shown for contacting a bed of particulate material with a cross flowing fluid, which maintains the bed of particulate material within a retention volume. The apparatus includes partitions for retaining particles, with apertures disposed within the partitions. The apertures are covered by louvers that extend above the edges of the apertures to prevent solid particles from spilling through inlet apertures. And the apparatus includes baffles to inhibit erosion of the particles by redirecting the inlet gas flow.

Description:
FIELD OF THE INVENTION 
     The present invention relates to improved reactor design, and more particularly to improved reactor design with moving beds of particulate materials. 
     BACKGROUND OF THE INVENTION 
     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. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation. 
     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 beds in place and for aiding in the distribution of pressure over the surface of the reactor 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. 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. 
     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. Corrosion can plug apertures to a screen or mesh, creating dead volumes where fluid does not flow. 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. 
     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 
     The invention comprises a cross-flow reactor or a cross-flow adsorber, where the apparatus has an inlet partition and an outlet partition. The partitions define a particle retention volume where a catalyst or adsorbent is held as a catalyst bed or an adsorbent bed. The catalyst or adsorbent can flow through the apparatus between the inlet and outlet partitions. The partitions have apertures defined therein for allowing the flow of gas or fluid across the solid particulate bed. The inlet partition further includes louvers over the apertures to provide for a screenless inlet partition, which allows for freer flow of the gas. The louvers include a baffle affixed to the underside of the louver for changing the direction of the flow of the gas. The baffle breaks up flow along the louver and redirects and spreads out the flow to prevent high speed impingement of the gas with the catalyst, which erodes the catalyst. 
     Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an embodiment of the invention with baffles on the louvers; 
         FIG. 2  is an embodiment showing the addition of inlet vanes; 
         FIG. 3  is an embodiment with a particle retention screen as a part of the baffle; 
         FIG. 4  is a simulation of the gas flow pattern without the baffles; and 
         FIG. 5  is a simulation of the gas flow pattern with the baffles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Radial flow reactors are designed for the downward flow of catalyst through a catalyst retention area, with a cross flow of gas through the catalyst bed. The typical reactor design entails a screened inlet partition where the gas passes through a screen to the catalyst bed, and the screen has holes of a small enough size to prevent catalyst particles from passing through. Recent developments have created a screenless inlet partition to address some of the problems associated with the screened inlet partition having louvers to prevent the passage of catalyst through the inlet partition, but still admitting the gas. 
     With screenless partitions, a problem was encountered in that there was unacceptable losses of catalyst, and that the losses were in the form of fines. The catalyst was being eroded and creating fines that were being removed from the reactor with the reacted gas. The formation of catalyst fines and loss of catalyst is a significant expense to the operation of an olefin reactor. It was necessary to determine where the catalyst was being eroded. 
     It was discovered that the problem was with the inlet flow of gas, in that the flow was jetting along the underside of the louvers. The jetting flow needs to be broken up as it passes under the louvers. A solution was to place a baffle on the louvers to prevent the gas flow from creating a jet that was causing the erosion of catalyst and subsequent production of fines. 
     The present invention comprises an apparatus for supporting a granular solid in a cross-flow system. The apparatus includes an inlet partition having apertures defined therein and an outlet partition having aperture defined therein, where the space between the inlet and outlet partitions defines a particle retention volume. The apparatus further includes at least one inlet louver, where each louver has an upper edge and a lower edge, and the louver upper edge is affixed to the inlet partition at a position above an inlet aperture, and the louver lower edge extends into the particle retention volume at an angle between about 1 degree and about 85 degrees. The louver further includes at least one baffle disposed on the underside of the louver, and where the baffle projects substantially perpendicular to the louver. The louvers are preferably disposed at an angle that will overcome hydraulic hold up of the catalyst flowing over the louvers. 
     Preferably, the louvers are at an angle between about 10 degrees and about 50 degrees, and the baffles are disposed on the louvers at a position between about 10% and about 90% of the length from the louver upper edge to the louver lower edge. An embodiment of the present invention is shown in  FIG. 1 , wherein the inlet partition  10  comprises a plurality of apertures  20  defined therein, where each aperture  20  has an upper edge  180  and a lower edge  110 . The inlet partition  10  has a gas side, where gas entering the reactor flows, and a catalyst side, where catalyst moves down the reactor as the gas flows across the catalyst in the reactor. The inlet partition  10  further includes at least one louver  30  affixed to the partition  10  on the catalyst side. The louver  30  has an upper edge  60  and a lower edge  70 , and the upper edge  60  is affixed above an aperture  20 , and the lower edge  70  extends downward to at least the height of the aperture lower edge  110 , and preferably below the aperture lower edge  110 . 
     The baffles  200  are positioned on the underside of the louvers  30 , and preferably are positioned below the aperture lower edge  110 . The baffles  200  are for breaking up the jetting inlet flow of the gas and preferably are positioned between about 30 percent and 70 percent of the length of the louvers from the upper edge to the lower edge, and more preferably between about 50 percent and 70 percent of the length of the louvers from the upper edge to the lower edge. The baffles  200  project substantially perpendicularly from the louvers  30 . The baffles  200  extend between about 10% and about 50% of the distance between the louver  30  and the inlet partition  10 , where the distance is determined at the position of the baffle  200  and projecting perpendicularly from the baffle  200  to the inlet partition  10 . Preferably, the baffles  200  extend between about 15% and about 30% of the distance from the louver  30  to the inlet partition  10 . 
     In another embodiment, the apparatus comprises a first baffle  200  and a second baffle (not shown). The first baffle  200  is the baffle affixed to the louver  30 , and the second baffle is a baffle affixed to the inlet partition  10  at a position between the louver  30  and the inlet partition  10 , and disposed below the aperture  20  on the inlet partition  10 . The second baffle provides a barrier to the catalyst during the loading phase of the reactor. During loading, catalyst can rise into the space underneath the louvers, and particularly along the inlet partition. The second baffle prevents catalyst from rising to the apertures in the inlet position. A secondary benefit is that the second baffle can aid in the break up of the flow, and also aids in containment of the catalyst or adsorbent. The second baffle provides a barrier for catalyst lifted along the inlet partition wall due to circulation of the inlet gases. 
     In another embodiment, the apparatus comprises louvers affixed to the outlet partition. The outlet partition has apertures defined therein, and has a catalyst side and an outlet gas side. The catalyst side is the side of the outlet partition where the particle retention volume is defined. The louvers affixed to the outlet partition extend downward from the outlet partition into the particle retention volume at an angle between about 1 degree and about 85 degrees, and preferably at an angle between about 10 degrees and about 50 degrees. Each outlet louver has an upper edge and a lower edge, where the upper edge is affixed to the outlet partition at a position above an aperture in the outlet partition. The lower edge extends to at least the lower edge of the outlet partition aperture covered by the louver. 
     In this embodiment, the apparatus further comprises at least one outlet baffle affixed to an outlet louver on the underside of the outlet louver, and the baffle projects substantially perpendicularly from the louver. The apparatus can also incorporate a baffle affixed to the outlet partition, disposed below the outlet aperture and between the outlet partition and the outlet louver. Baffles in these positions provide the additional benefit of reducing or preventing the carrying out of catalyst with the outflowing gas. 
     In another embodiment, the apparatus further comprises a plurality of inlet vanes. The inlet vanes are disposed on the inlet partition. As shown in  FIG. 2 , the inlet vanes  210  are disposed on gas side of the inlet partition  10 . The inlet vanes  210  provide secondary backup for catalyst, or adsorbent, containment, preventing any catalyst from spilling out of the reactor. The inlet vanes  210  can be made in a variety of shapes, such as an inverted conical shaped structure, or inverted pyramidal structure, or an L-shaped structure affixed to the inlet partition  10 . The inlet vanes  210  have an upper edge  220  and a lower edge  230 , and preferably the lower edge  230  of each inlet vane  210  is affixed to the inlet partition  10  at, or near, the lower edge of the aperture. It is also preferred that the inlet vanes  210  extend upward and away from the inlet partition  10  at an angle between about 20 degrees and about 50 degrees. The choice of design for the inlet vanes is determined by a variety of factors, including, but not limited to, flow considerations, and available space in the inlet flow channel of the reactor. 
     Another embodiment of the invention combines aspects of design that contributes to preventing the erosion of catalyst at the louver where the surface of the catalyst bed meets the louver, and catalyst retainment. In this embodiment, as shown in  FIG. 3 , a perforated particle containment baffle  240  is affixed to the underside of the louver  30 , and extends across the space between the louver  30  and the inlet partition  10 . The baffle  240  is also disposed above the surface of the catalyst bed so as not to be in continuous contact with the catalyst. The perforated particle containment baffle  240  has a relatively large percentage of the baffle open for unrestricted gas flow. The perforated particle containment baffle  240  also is spaced from the inlet partition  10  to allow for particles that manage to get by the baffle  240  to slide down and through the gap  250  between the baffle  240  and the inlet partition  10 . The perforated particle containment baffle  240  has a louver side edge  260  and an inlet partition side edge  270 . The louver side edge  260  is affixed to the louver  30  at a position between about 30% to about 70% of the length of the louver from the louver upper edge  60  to the louver lower edge  70 . The inlet partition side edge  270  is disposed a distance from the inlet partition  10  greater than the characteristic size of the catalyst particles, and at a position below the aperture lower edge  110 . The inlet partition side edge  270  can be held in place by spacers, or other means known to those skilled in the art. A feature of the perforated particle containment baffle  240  is that the baffle  240  also breaks up the flow of the gas and redistributes the gas flow more evenly as the gas flows to the catalyst bed. 
     In another embodiment, the apparatus has an inlet partition with a plurality of apertures defined therein, and an outlet partition with a plurality of apertures defined therein, and the space between the partitions is defined at the particle retention volume. The inlet partition  10  has a plurality of louvers  30  affixed to the inlet partition  10  where each louver  30  has an upper edge  60  and a lower edge  70 . The lower edge  70  of the louvers  30  are affixed to the inlet partition  10  at the lower edge  110  of the apertures in the inlet partition  10 . The louvers  30  extend away from the particle retention volume side of the inlet partition  10  at an angle between about 5 degrees and about 85 degrees, with the louver  30  extending a distance, d, above the aperture upper edge by a distance according to the formula:
 
 d=L *sin(θ)*tan(φ),
 
where L is the length of the louver  30  from the lower edge to the upper edge, θ is the angle the louver extends away from the inlet partition, and φ is the angle of repose for the grandular solid that is disposed within the particle retention volume. The apparatus further includes a baffle affixed to each louver on the upper side of the louver, and projects substantially perpendicularly from the louver. The baffle breaks the jetting gas flow along the upper side of the louver to reduce erosion of the catalyst.
 
     EXAMPLE 
     In studying the problem of erosion of catalyst, it was found that the inlet flows are a cause of fines from the catalyst. A numerical simulation was carried out with gas flowing into the reactor, and the region under the louver was studied. As shown in FIG.  4 , the inlet flows are very rapid along the under surface of the louver  30  and impact the catalyst where the catalyst bed surface meets the louver  30 . The rapid flow of gas at a localized position is having a deleterious effect on the integrity of the catalyst. Therefore, changing the gas flow near the region where the catalyst bed surface meets the louvers can improve the life of the catalyst by reducing catalyst erosion. 
     From the results of the gas flow as shown in  FIG. 4 , the gas flow along the louver needs to be diverted, or reduced in magnitude. A baffle  200  was added to break up the flow along the louver  30 , and to reduce the flow of gas at the junction where the catalyst bed surface meets the louver  30 . The numerical results for one case are shown in  FIG. 5 , where the gas flow is diverted away from the louver  30  with a reduction in the speed of the gas at the junction where the catalyst bed surface meets the louver. 
     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 and equivalent arrangements included within the scope of the appended claims.