Modeling of Single Porous Char Particle Gasification in Supercritical Water

A deep understanding of the gasification behavior of porous char particle is the premise of the reactor-scale modeling, but there are few studies on the gasification characteristics in supercritical water. Thus, a numerical model for porous char particle gasification in supercritical water was developed in this work, and the effects of particle size, inflow temperature and inflow velocity were studied. Simulation results showed that gasification of the small particle of 0.1 mm lay in zone I regime where the particle radius kept unchanged due to uniform reactions inside the particle and the effectiveness factor increased rapidly after the gasification began due to easy accessibility of supercritical water into the particle. The gasification of the large particle of 1 mm showed typical characteristics in zone II regime that the particle began to shrink at a certain conversion degree, and smaller effectiveness factor was observed due to larger supercritical water concentration gradient inside the particle. As the increase of temperature and particle size, ambient fluid became difficult to flow through the unreacted core, and the Stefan flow was observed to obviously modify the hydrodynamic boundary layer at low Reynolds number. Besides, it is unreasonable to assume isothermal particle for gasification with large particle and high temperature because of the significantly overestimated particle consumption rate.