A zero-dimensional model of porous char gasification in supercritical water: Experiments and mathematical modeling

Abstract

This work aims to develop a zero-dimensional model of porous char gasification in supercritical water which can serve as the char conversion sub-model in reactor-scale modeling and simulation. Experiments were firstly carried out to obtain the evolution of specific surface area of char, based on which the structure parameter ψ in random pore model was calculated. Then, a kinetic model with detailed coal conversion pathways in supercritical water was proposed, with the evolution of specific surface area specifically considered. This model was applied to fit the experimental results to calculate the intrinsic kinetic parameters. The obtained structure parameter ψ and kinetic parameters were finally used to develop the sub-model. The established sub-model was evaluated through model predication of 0.25–4 mm sized char particles gasified at 1000–1800 K. The results showed that this model gave a reasonable predication of the gasification transition from zone Ⅰ to zone II/III regime with the increase of temperature and particle size, and the development of particle size, apparent density and specific surface area was well described. Besides, the convection was found to obviously promote the gasification in zone II/III regimes mainly by enhancing the mass transfer process, while its effect was negligible in zone Ⅰ regime. Similarly, the effect of ash content on the burnout time became more obvious from zone Ⅰ to zone II/III regime.