Effect of H2O on Preheating Combustion Characteristics in O2/CO2 and O2/N2 Atmospheres

This study explores the effect of H2O on the characteristics of the oxy-fuel combustion process preheated by a circulating fluidized bed. The preheating and combustion characteristics have been studied in O2/CO2/H2O and O2/N2/H2O atmospheres. It was observed that the preheating temperature decreased with adding steam. Meanwhile, the addition of steam enhanced the C-H2O gasification reaction, while weakened the C-CO2 gasification reaction. As a result, the H2 concentration was increased, while the CO concentration was reduced. H2O was conducive towards increasing the surface area and pore formation of the preheated char, though it had an insignificant effect on the particle size. Moreover, H2O enhanced the preheated char activity, which was helpful for ignition and stable combustion. The NOx emission was observed to increase from 68 to 79 mg/MJ and 62 to 81 mg/MJ in O2/CO2 and O2/N2 atmospheres, respectively, after adding steam.