The Characteristics of Recycled-NO Reduction in O₂/CO₂ Coal Combustion

O₂/CO₂ coal combustion is a promising technology for easy CO₂ recovery and low NO_x emission. O₂/CO₂ coal combustion system has very high CO₂ concentration, and so O₂/CO₂ ratio is very important parameter in this system. In this study, the effect of CO₂ concentration on recycled NO reduction was investigated experimentally and numerically. It was revealed that the recycled NO reduction ratio was increased with decreasing CO₂ concentration. This was because high CO₂ concentration enhanced the reaction to produce OH radical (CO₂ + H → CO + OH). Both calculations and experiments showed OH radical increased with an increase in CO₂ concentration. However, increasing OH radical enhanced the consumption of H₂ which is needed for the reduction of secondary NO. It was shown that high CO₂ concentration inhibits recycled-NO reduction from the new point of CO₂ reactivity.