Using an experimentally-determined model of the evolution of pore structure for the gasification of chars by CO2

Abstract

A pseudo-steady state model of reaction and diffusion has been constructed to model the non-isothermal gasification of single char particles by CO2. The model uses a Cylindrical Pore Interpolation Model for intraparticle mass transfer, Ergun’s Langmuir–Hinshelwood equation for the intrinsic rate of gasification, an experimentally determined function f(X) for the pore evolution as a function of the conversion X, the Stefan–Maxwell equations to describe external mass transfer and the equation of energy for energy balance. Experiments were conducted to measure rates and extent of conversion, at various temperature and for various particle sizes, of lignite char and the less reactive activated carbon. The simulation results have been compared with experimental measurements, with excellent agreement being obtained. The results show that for the gasification of chars, the experimentally determined function f(X) predicts the rate of reaction of particles of various sizes well, all being at the same temperature. However, for the CO2 gasification of char particles, at least, an f(X) evaluated at one temperature does not predict experimental measurements well at other temperatures, possibly because there are contributions from multiple types of active sites within the particles. However, multiple sites are also not reflected in most published pore models.