Modeling of char particle size/conversion distributions in a fluidized bed gasifier: non-isothermal effects

Mass and thermal energy balances are developed to describe the time-dependent behavior of reacting char particles distributed in both size and conversion in continuous, steam—oxygen, fluidized-bed gasifier. These relations are solved numerically utilizing the method of orthogonal collocation to simulate both steady-state and time-dependent behavior. The influences of superficial gas velocity, mechanical removal of solids, and reactants gas concentration on steady-state bed characterisctics and particle size/conversion distributions are determined. An investigation is made of particle heating times, and the validity of neglecting temperature profiles in reacting char particles is confirmed. These heating times are compared to the dynamics governing solids flow and particle size/conversion distributions. The transient responses of solids holdup and the distributions are presented to show the dynamic effects of step changes in solids feed rate, superficial gas velocity, and particle-size distribution in the feed.