CFD simulations of Industrial Steam Cracking Reactors: Turbulence–Chemistry Interaction and Dynamic Zoning

Abstract

Modeling finite-rate chemistry in turbulent reacting flows is challenging because of the large span in length and time scales. Reynolds-averaged Navier–Stokes equations-based simulations do not resolve turbulent fluctuations and hence neglect their effect on the reaction rates. Turbulence–chemistry interaction was accounted for in RANS simulations via quadrature-based integration of the reaction rates, calculated using a temperature probability density function with a presumed Gaussian shape and transported mean and variance. The effect on light olefin yield was 0.1–0.2 wt % absolute. A dynamic zoning method was implemented to reduce the computational cost by performing chemical rate calculations only once for thermodynamically similar cells. Speedups of 50–190 were observed while the relative error on conversion remained below 0.05%. The advantages of the presented methodology were illustrated for a large-scale butane-cracking U-coil reactor.