Multivariable optimization of reaction order and kinetic parameters for high temperature oxidation of 10 bituminous coal chars

In industrial pulverized fuel combustion, char oxidation is generally limited by the combined effects of chemical reactions and pore diffusion. Under such conditions, char oxidation is frequently predicted by power law models, which despite their simplicity, are widely used in the comprehensive CFD modeling of pulverized coal boilers. However, there is no consensus on the apparent reaction order given by such models. This study developed a systematic approach which gives consistent values over a range of conditions. Apparent reaction orders for 10 bituminous coal chars were investigated with three different oxygen concentrations, ranging from 4 to 12 vol.%, and a gas temperature of 1223 K for each char. Experimental burnout profiles of the chars were obtained by means of an Isothermal Plug Flow Reactor operating at industrially realistic heating rates (104 K/s). For various reaction orders between 0.05 and 2.00, kinetic parameters were independently determined, following numerical procedures recently suggested in the literature. The resulting values were incorporated into an empirical power law model and compared to experimental data for the 10 chars, over a burnout range of 0–75%. The best fit to the experiments occurs with apparent reaction orders of around one for all the chars.