Conversion of large coal particles under O2/N2 and O2/CO2 atmospheres—Experiments and modeling

Conversion under O2/N2 and O2/CO2 atmospheres of coal particles of sizes typically used in fluidized bed combustion is studied by means of experiments and modeling. Experiments are conducted for six different fuels in a thermo-gravimetric oven, for different gas atmospheres and temperatures, providing empirical data on devolatilization and char conversion. A model is developed to predict coal conversion (drying, devolatilization, and char conversion), coupling mass and heat transfer and accounting for primary and secondary fragmentation. The validation of the model yields satisfactory agreement between experimental and modeled mass loss curves and conversion rates during devolatilization and char conversion. It is shown that O2/CO2 mixtures give slightly longer devolatilization times and a decrease of char reactivity compared to O2/N2 mixtures.