Numerical study of coal particle gasification up to Reynolds numbers of 1000

Abstract

The influence of turbulent structures on the gasification of coal particles, in particular on the char consumption and surface temperature, is studied . Existing submodels for char gasification are mainly based on results for laminar flow only, therefore the capability of these models to predict gasification at higher particle Reynolds numbers is evaluated using the simulation results. Two representative scenarios were studied: the gasification of a 2 mm particle at atmospheric pressure in a O2/CO2/H2O atmosphere at 2006 K and the gasification of a 263 μm particle at 30 bar in a different O2/CO2/H2O atmosphere at 1480 K. The simulation conditions were based on data obtained from the simulations of two different entrained-flow gasifiers. ANSYS Fluent™ was used to solve the Navier-Stokes equations for the flow field coupled with energy and species conservation equations. The model for the reaction system incorporates six gaseous chemical species H2, O2, CO, CO2, H2O, N2 and solid carbon. A semi-global reaction mechanism was applied for the homogeneous gas-phase reactions and the water gas reaction, the Boudouard reaction and the oxidation of carbon to carbon monoxide were considered as heterogeneous gas-solid reactions. In the present work it is shown how the reaction zone is modified due to the change in wake structure, the impact of the turbulent effects on the overall carbon conversion rate are discussed, and hints how to adjust existing submodels to correctly predict char conversion at high particle Reynolds numbers are given.