Coke combustion and gasification kinetics in ethane steam crackers

A simulation model for the development of the optimal decoking procedure of a steam cracker is constructed. It is based on experimental data for the process gas side coke combustion with oxygen and the process gas side coke gasification with steam, using coke samples taken from an industrial steam cracker. The texture changes of the coke during the combustion and gasification are accounted for. Different kinetic models are combined with a coke porosity model and different gas-solid reaction/diffusion models. The model parameters are estimated from the experimental data and model discrimination is performed. For the coke combustion the kinetic model is based on the dissociative chemisorption of oxygen on the active coke sites, whereas a general gas-solid reaction/diffusion model is required. The growth of the pores and the overlap of the pores during the coke combustion are found to compensate each other. For the coke gasification, the kinetic mechanism is based on the dissociative chemisorption of steam, whereas a uniform gas-solid reaction/diffusion model is used. (c) 2005 American Institute of Chemical Engineers.