LES simulation of char particle gasification at Reynolds numbers up to 1000

Abstract

The interplay of turbulent flow and heterogeneous gasification reactions of char particles is studied using Reynolds-averaged and large-eddy simulations. Currently available submodels for char gasification are typically developed for laminar flow conditions. For that reason, the simulation results are used to assess the applicability of these models at higher particle Reynolds numbers. Two representative gasification conditions were chosen on the basis of simulation data obtained for two different entrained-flow gasifiers: a 2 mm particle at atmospheric pressure in an O2/CO2/H2O atmosphere at 2006 K and a 263 µm particle at 30 bar in another O2/CO2/H2O atmosphere at 1480 K. The Navier–Stokes equations for the flow field were solved and were coupled with energy and species conservation equations. Six gaseous chemical species, H2, O2, CO, CO2, H2O, N2, and solid carbon, were considered and a semi-global reaction mechanism was applied for the homogeneous gas-phase reactions. Three heterogeneous gas-solid reactions were modeled: the water gas reaction, the Boudouard reaction and the oxidation of carbon to create carbon monoxide. The modification of the reaction zone due to a changing wake structure is presented in this work and the effect of turbulent structures on the overall carbon conversion rate is outlined. The impact of flow oscillations on char consumption and the particle temperature distribution at particle Reynolds numbers of 500 and 1000 is shown to be moderate.