Desorption kinetics of CO in char oxidation and gasification in O2, CO2 and H2O

Char carbon oxidation in mixed atmospheres of O-2, CO2 or H2O results in the formation of carbon-oxygen surface complexes that desorb to CO and CO2. In this study it is investigated whether desorption of CO can be modeled with the same kinetic parameters in char carbon reactions by O-2, CO2 or H2O. Modeled char carbon conversion rates of single particles are compared to experimentally-derived measurements from a single particle reactor. Experiments were performed at temperatures between 800 and 1050 degrees C with various concentrations of CO2, H2O or O-2 in the gas. In the single particle model, radial profiles of gas species and temperature are considered. Adsorption and desorption steps are considered inside the particle and homogenous chemistry is considered outside the particle. There is good agreement between the modeled results and the measurements, implying that the CO desorption occurs in the same way regardless of whether the char carbon reacts in O-2, CO2 or H2O. Based on these results, a new simplified mechanistic char carbon oxidation model is suggested applicable to gasification, combustion and oxy-combustion conditions.