Long-Residue Processing in a Riser Pilot Plant

Abstract

A number of different types of laboratory scale units have been developed to simulate commercial catalytic crackers. These include fixed bed (MAT), fluidized bed, and riser units. In particular, for simulating commercial riser FCC units which process residue, a riser pilot plant is the preferred choice. In this type of unit, the catalyst and oil are in plug flow and the contact time is short. Secondary reactions are thus avoided and catalyst deactivation by coke formation is properly simulated. The resulting product selectivity is similar to commercial units. Experimental results from a laboratory scale unit can thus be translated to commercial units. By paying particular attention to FCC pilot plant design and operating procedures, feedstocks containing significant amounts of residue can be successfully processed in a small-scale unit. The critical aspects can be itemized as follows: atomization of oil to small droplet sizes; feed temperature adequate to avoid coke formation in the feed system; use of hot catalyst to supply heat to the system, as is done in commercial units; consistent catalyst flow rate to the feed/catalyst mixing zone by selecting fluidizing nitrogen flow rate to stay below the minimum bubbling velocity of the catalyst; uniform mixing of the feedmore » and catalyst in the bottom of the reactor to ensure quick vaporization and avoid coke formation in the mixing zone; optimized design and operation of the spent catalyst stripper to ensure that coke yields are minimized without diluting the product gas more than necessary; and proper selection of condenser operating temperature in order to avoid retaining the heavy, viscous fraction of the product on the condenser tube walls.« less