Gasification of Brazilian coal-chars with CO2: effect of samples' properties on reactivity and kinetic modeling

The gasification of coals obtained from important coalfields in Brazil was investigated in 1.0 bar of CO2 using a thermogravimetric analyzer. Tests were carried out in two sequential steps: pyrolysis under N-2 at 1213 K and isothermal gasification under CO2 in the temperature range of 1113-1213 K. The kinetic study was performed in the kinetically controlled regime and three gas-solid models were fitted to the experimental data. According to the results, subbituminous coal-chars presented higher reactivities than bituminous types, with maceral and ash compositions playing a key role in the overall process. The reaction rates increased with increasing temperature, with maximum values found in the conversion range of 10-60%. The random pore model that predicts a maximum point of reactivity over the reaction course suitably described the gasification kinetics. Values of activation energy between 146.63(+/- 0.03) kJ/mol and 215.09(+/- 0.05) kJ/mol were found, which are consistent to literature data of coals gasified worldwide. Despite the relatively high ash content (32-45%), the Brazilian coals appeared to be sufficiently reactive to be gasified, thus indicating the significance of this study to the development of gasification process in Brazil.