Coupled simulation of convection section with dual stage steam feed mixing of an industrial ethylene cracking furnace

A complete coupled simulation of the convection chamber and tubes with dual stage steam feed mixing of an industrial ethylene cracking furnace has been carried out with the computational fluid dynamics (CFD) method for the first time. In the convection chamber, the standard k-epsilon model and discrete ordinates (DO) radiation model were respectively used in the descriptions of turbulence characteristics and radiative heat transfer. In the tubes, renormalization group (RNG) k-epsilon model and volume of fluid (VOF) model were respectively applied to the turbulence flow and the liquid-vapor two phases flow. Simulation results agree well with the industrial data. Based on the coupled result, a dynamic simulation was calculated in the feedstock preheater (FPH). Simulation results show that the velocity and temperature fields are inhomogeneous distributions along the width direction due to the asymmetrical structure of convection chamber. Two recirculation zones occur at the corner both near and away from the entrance to the convection chamber, which will cause a longer residence time of flue gas and local overheating in furnace wall of convection chamber. The process gas temperature, tube skin temperature and heat flux profiles are respectively different along the axial and radial direction of the high temperature coil (HTC-I). The changes of flow pattern from bubble flow to spray flow are effected by gravity and centrifugal force during evaporation. The results will be helpful for the design and operation in cracking furnace. (C) 2015 Elsevier B.V. All rights reserved.