Kinetics of pressurized oxy-combustion of coal chars

A kinetic study of oxy-combustion of chars received from two Polish coals, namely lignite and hard sub-bituminous was conducted. The kinetics of char oxy-combustion was examined in the TA Instruments TG-HP150 s pressurized thermogravimetric analyzer at 0.1, 0.5 and 1 MPa of absolute pressure. The experiments were carried out at isothermal conditions and at wide range of temperature (773-1273 K). Mixture of gas containing 20% and 30% of O-2 in CO2 was used as an oxidant. Additionally at temperature 873 K the experiments were performed using 5%, 10% and 40% of O-2 in CO2. A kinetic model of pressurized oxy-combustion of coal char was presented. Kinetic parameters such as activation energy, pre-exponential factor and reaction order in respect of oxygen concentration were computed. Influence of temperature, pressure and O-2 concentration were discussed. The results show a significant shift of the oxycombustion reaction from kinetically controlled regime to diffusion - controlled regime with increasing temperature and pressure. The method of selecting the proper reaction model was presented based on the integral and differential approach of experimental data analysis.