Experimental study on effect of gas type on performance of FCC stripper

Key words:  adsorption  stripper  stripping efficiency  fluidized bed  experiment

Abstract:

In fluid catalytic cracking (FCC) units, the role of stripper is to replace the different types of hydrocarbons adsorbed in the pores of catalyst particles and entrained in the interparticle porosities using steam. In previous studies on FCC strippers, small-molecular gases, e.g. hydrogen or helium, are mostly used as tracer gases to obtain the measured simulation stripping efficiency as a parameter to evaluate the performance of different strippers. In order to investigate the different performances of strippers to strip different types of gases, a large-scale cold model was setup where three gases with increasing adsorption capacities in zeolite catalysts, i.e. He, CO₂ and R22, were used as tracer gases to measure the stripping efficiencies. Two strippers, i.e. a packed stripper and a baffle-free stripper were both tested. The experimental results indicate that adsorption capacity of tracer gas has a profound effect on the performance of strippers. When the adsorption capacity of a tracer gas increases, the measured stripping efficiency decreases and the improvement on stripping performance using increased superficial gas velocity and adding high-efficiency internals decreases. For the tracer gas with high adsorption capacity in zeolite catalyst, the relative increment of stripping efficiency by the employed high-efficiency packing internals also increases considerably. Based on these findings, a two-stage stripper idea is suggested where different operating conditions are obtained in the two stages for stripping different types of hydrocarbon gases.