Resolved-particle fixed bed CFD with microkinetics for ethylene oxidation

The incorporation of an ethylene oxidation microkinetic model into fixed-bed CFD is studied using two different approaches. The first is based on mapping pre-calculated reaction rates into quadratic splines under steady-state conditions without any further assumptions or simplification of the elementary steps. The second approach uses conventional reaction engineering assumptions such as quasi-equilibrium (QE) and hybrid steady state (HSS) to reduce the kinetic model and generate lumped rate expressions. Both kinetic models are implemented for illustrative resolved-particle CFD simulations in a randomly packed bed of 120 spheres. It is shown that the QE and HSS assumptions are not valid throughout the range of reacting conditions. Comparison of the temperature and species profiles for these two approaches shows that the strong gradients inside the bed cause significant deviations in the reduced model compared to using the splines method with full microkinetics, which produces accurate results without increasing the computational time. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 87-94, 2017