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Modeling FCC spent catalyst regeneration with computational fluid dynamics

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aRaj Singh, aEsebius Gbordzoe<

aTechnip Stone & Webster Process Technology

Regeneration of spent catalyst is key to the successful operation of the fluid catalytic cracking (FCC) unit. The coke laden spent catalyst from oil cracking in the FCC riser is burned off in the regenerator. The heat generated raises the circulating catalyst temperature and, in turn, helps crack the oil to valuable products in the riser. Efficient regeneration depends on good spent catalyst and combustion air distribution. Ideally, the combustion air is designed to match the spent catalyst distribution.
The FCC regenerator has been modeled using various techniques. Technip Stone &Webster Process Technology (Technip) is using computational fluid dynamic (CFD) techniques to develop a tool that simultaneously models both hydrodynamics and coke combustion in the FCC regenerator. Descriptions of the coke burning kinetics are provided through proprietary combustion kinetic equations with appropriate kinetic constants. The results provide detailed qualitativemapping of the regenerator’s behavior in termsof flue gas composition, temperature distribution including afterburning, regenerator bed density in both axial and radial planes. The CFD, coupled with spent catalyst regeneration kinetic model, is used is to evaluate the regenerator performance of a commercial regenerator. The results were used as basis to recommend hardware and operational modifications. The proposed modifications were subsequently modeled using the CFD kinetic tool to quantify the benefits.