(751g) Numerical Simulations of PSRI Cold-Flow FCC Stripper Experiment with Subway Grating Baffles

Industrial fluid catalytic cracking units (FCCUs) employ fluidized bed strippers to recover hydrocarbons carried away with the downward flowing spent catalyst particles from the reactor, preventing these valuable hydrocarbons from entering and combusting in the regenerator. In the stripper, steam flows upward counter-current to the catalyst flow direction, stripping the hydrocarbon vapors from and around the catalyst particles before the particles enter the regenerator. Effective stripper operation requires intimate contact between the gas and particle phases. Commercial stripper designs often use internals, such as subway grating trays, chevrons, disk-and-donut baffles, structured packing or other configurations, to promote better mixing of gas and particles and improve stripping efficiency.

Numerical simulations have been performed of a PSRI cold-flow FCC stripper experiment with subway grating baffles. The experimental unit has an internal diameter of 3 feet, and a height of 25 feet. The subway grating baffles within the vessel are intended to promote more uniform fluidization of particles by preventing the formation of large bubbles as well as preventing gas bypassing in the stripper. The commercial computational fluid dynamics (CFD) software Barracuda Virtual Reactor®, which implements the multi-phase particle-in-cell (MP-PIC) numerical method, was used to perform the simulations. Simulation results are compared with experimental measurements of apparent bed density over a wide range of solids flux conditions, at superficial gas velocities typical of industrial FCC stripper operation. The simulation results are in good agreement with the experimental bed density measurements, and are able to predict the experimentally observed trends of bed density variation as a function of gas superficial velocity and catalyst mass flux through the stripper vessel.