3D study of a chemically reacting fixed-bed under gasification conditions for non-porous char: Laminar flow

Abstract

This paper reports a computational investigation of the combustion of char particles in a fixed-bed using a three-dimensional model. Numerical simulations were carried out using the commercial software AnsysⓇ Fluent, implementing a six semi-global kinetic scheme, where carbon monoxide combustion, forward and backward water-gas-shift reaction (WGS), Boudouard reaction, and two other heterogeneous reactions take place inside the reactor composed of 85 spherical particles. The diameter of the particles is 5.6 mm. Laminar flow regime (Rein = 50, 75 and 100), inflow gas temperature in the range of 900–1500 K, and mass fraction of oxygen at the inlet (YO2,in) of 0.05, 0.11, and 0.233 are the parameters of interest to study the heterogeneous combustion of carbon char particles inside the unit. The Boudouard reaction and oxidation of carbon monoxide are dominant among heterogeneous and homogeneous chemical reactions, respectively, being the inflow gas temperature a critical parameter to assess, since the kinetic scheme is dramatically activated at higher temperatures. A linear dependency has been found for species concentration and temperature profile in most of the simulations using YO2,in=0.05. Further studies are necessary to extend this research to intrinsic chemical reactions (tracking of porosity and particle radius), and the hybridization of the bed zone by incorporating inert solid particles into the system.