Effects of oxygen ratio on pulverized coal combustion under O2/CO2 atmosphere preheated by a circulating fluidized bed

This study assessed the effects of oxygen ratio on preheating combustion characteristics under O2/CO2 atmosphere. The experimental results are discussed based on two aspects: the preheating characteristics and the combustion efficiency. With the increase of oxygen ratio in the primary gas, the preheating temperature increased. The reaction was more vigorously with increasing oxygen volume fractions, so the concentrations of CO, H2 and CH4 in high-temperature gas decreased and the conversion rate of each component increased. In addition, the conversion ratio of fuel-nitrogen to N2 increased as the primary oxygen ratio increased. After preheating, there were more micropores on the surface of char particles and the carbon reaction activity was enhanced. In the combustion stage, the temperature in the down-fired combustor decreased with increasing primary oxygen ratios. What’s more, increasing the oxygen ratio in the primary gas and decreasing the excess oxygen ratio could decrease NOx emissions and reduce combustion efficiency. In addition, the minimum combustion efficiency was still higher than 99%.