Oxy-fuel combustion: Effect of recycled CO₂ on pyrolysis behavior and char reactivity

Oxy-fuel combustion is a promising technique to achieve significant reduction of CO₂ emissions. However, due to change in the combustion medium from N₂ (inert) to CO₂ (reactive), significant changes in heat transfer, pollutant emissions and combustion behavior are expected. These changes have caused concerns for successful commercial application of this approach. In this paper, the effect of gas media on pyrolysis and combustion behavior is studied experimentally by conducting tests in a drop tube reactor, and numerically by computational fluid dynamics code FLUENT. Similar weight loss values were obtained when gas was switched from inert N₂ to CO₂ during the pyrolysis tests. To obtain the intrinsic char oxidation rate parameters three well known approaches were used: average reactivity up to certain burnoff range, reactivity at a fixed burn off and maximum reactivity. The reactivity parameters obtained using these approaches were then used to predict the char burnout at different furnace temperatures of a DTR using a FLUENT computational fluid dynamic code (CFD). The predicted results have suggested a significant effect of these rate parameters on the char burnout.