Numerical simulation of a reacting porous char particle in supercritical water with structural evolution

Abstract

A deep understanding of the particle conversion behavior is necessary for reactor-scale simulation and design, and the unqiue properties of supercritical water make it different from traditional gasification/combustion process. A 2-D transient numerical model coupling flow, heat transfer, species transport and porous structure evolution was therefore developed in this paper for supercritical water gasification of a single porous char particle. The gasification behavior was studied from 873 to 1023 K for particles of 0.1 and 0.5 mm, and the effects of convection and structural parameters were discussed. The results showed that the gasification shifted from kinetically controlled regime to diffusion controlled regime as temperature and particle size increased, and the conversion characteristics in each regime were quite different with the comprehensive effects of temperature and species distribution and porous structure. Under convective conditions, both heat and mass transfer was enhanced which significantly promoted char gasification, and asymmetric conversion was observed. Besides, the increase of the structural parameter ψ in random pore model and initial porosity shortened the char conversion time and showed more significant impact in kinetically controlled regime.