A wide variety of processes use radial or horizontal flow reactors to effect the contact of particulate matter with a gaseous stream. These processes include hydrocarbon conversion adsorption and exhaust gas treatment. In most of these processes, contact of the particulate material with the fluid decreases the effectiveness of the particulate material in accomplishing its attendant function. In order to maintain the effectiveness of the process, a system has been developed whereby particulate material is semi-continuously withdrawn from the contacting zone and replaced by fresh particulate material so that the horizontal flow of fluidized material will constantly contact particulate material having a required degree of effectiveness. Typical examples and arrangements for such systems can be found in U.S. Pat. No. 3,647,680, U.S. Pat. No. 3,692,496 and U.S. Pat. No. 3,692,496, U.S. Pat. No. 3,706,536, and U.S. Pat. No. 5,130,106.
A good example of the way in which moving bed apparatus has been used for the contacting of fluids and solids is found in the field of petroleum and petrochemical processes especially in the field the hydrocarbon conversion reactions. One such process that uses a radial-flow bed for the contact of solid catalyst particles with a vapor phase reactant stream is found in the dehydrogenation of light paraffins to form olefins. This process uses one or more reaction zones where the catalyst particles enter the top of the reactor and flow downwardly under gravity flow and are transported out of the first reactor. In many cases, a second reactor is located either underneath or next to the first reactor. Catalyst particles again move through the second reactor under gravity flow. After passing through the second reactor, the catalyst particles can go through a further series of reaction zones and are collected and transported to a regeneration vessel for the restoration of the catalyst particles by the removal of coke and other hydrocarbon by-products that are produced in the reaction zone and accumulate on the catalyst. In the dehydrogenation of hydrocarbons using the moving bed system, the reactants typically flow serially through the one or more reaction zones. The dehydrogenation reaction is typically endothermic so the reactant stream is heated before each reaction zone to supply the necessary heat for the reaction. The reactants flow through each reaction zone in a generally horizontal direction through a bed of catalyst. In most cases the catalyst bed is arranged in an annular form so that the reactants flow radially through the catalyst bed. Many other hydrocarbon conversion processes can also be effected with a system for continuously moving catalyst particles under gravity flow through one or more reactors having a horizontal flow of reactants. One such process is the reforming of naphtha. The catalyst particles in each reaction zone are retained between an inlet screen and an outlet screen that together form a vertical bed and allow the passage of vapor through the bed.
Radial-flow reactors typically include a reactor shell with an annular catalyst retention space. Gaseous fluid flows either radially inwardly or outwardly through the annular catalyst retention space to contact the gas with the solid catalyst within the catalyst retention space. The annular catalyst retention space is typically defined by a partition assembly including 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 may include, for example a mesh, either wire or other material, or a perforated or punched plate. The screened surface includes an inner screen and an outer screen with the catalyst retention space defined therebetween. 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. In moving bed systems, catalyst particles are typically introduced at the top of the reactor, and flow downward through the catalyst retention space and are removed at the bottom through catalyst removal nozzles or ports. Typically catalyst transfer pipes communicate with the catalyst retention space and extend through the catalyst removal ports to facilitate the flow of the moving bed of catalyst out of the catalyst retention space where it can be transferred to another reactor, regenerated in a regeneration portion of the process, or removed from the system. The screens and the catalyst transfer pipes are preferably constructed of a non-reactive material, but in reality the material often undergoes some reaction through corrosion, and over time problems arise from the corroded screen or mesh.
In order to minimize corrosion of the screens and transfer pipes and damage to the catalyst particles, the catalyst contact surfaces of the screens and catalyst transfer pipes are typically designed to provide a generally smooth surface over which the catalyst particles can flow. For example, in some reactors wires of the screens have a wedge shape with the flat face facing the catalyst retention area for minimal attrition with respect to catalyst particles which are moving downwardly by gravity during use.
Experience has shown that it is difficult to assemble radial flow reactors due to their large sizes and mating parts that preferably fit together with tight tolerance specifications and minimal obstruction or resistance to the flow of catalyst once the reactor is assembled. For example, once a portion of the reactor shell is in place, a crane may be utilized to individually lift lower the outer screen and inner screen into place. The catalyst transfer pipes extend down from the bottom of the partition assembly, usually an outer screen assembly. Crew members guide the transfer pipes into the corresponding catalyst transfer port openings as the screen assembly is lowered. The transfer port openings include annular guides or rings with center openings for centering the catalyst transfer pipes within the catalyst discharge ports. It has been identified that due to the length of the catalyst transfer pipes, they are typically not perfectly straight readily aligned with the catalyst transfer ports. In this regard, during installation the ends of the catalyst transfer pipes often get stuck on the rings, in particular where the rings meet with the inner surface of the ports, so that staff members must manually try to move the transfer pipes to fit through the central openings. Further complicating installation is that installation typically requires installation of several catalyst transfer pipes, which must be centered and lowered at the same time into corresponding ports. For example, sometimes three or four field workers are needed to center the several transfer pipes as the screen assembly is lowered. In this regard, significant amounts of time and man power are required for lowering the screen assemblies into place.