Combustion Characteristics and Nitric Oxide Release of the Pulverized Coals under Oxy-enrich Conditions

Instead of using pure oxygen in oxy-fuel combustion, oxy-enrich combustion uses air to replace part of pure oxygen for coal combustion. Compared with oxy-fuel combustion, oxy-enrich combustion uses much less pure oxygen, which may reduce the cost for CO 2 capture due to the reduction of pure oxygen requirement. The thermo-gravimetric technique was used to study the combustion characteristics of three pulverized coals under oxy-enrich atmospheres. The results show that both the ignition and burnout temperatures of pulverized coals decrease with the rise of oxygen concentration, while the combustibility index S increases gradually. Under the same oxygen concentration, the ignition and burnout temperatures in oxy-enrich combustion are lower than those in oxy-fuel combustion due to the different properties between N 2 and CO 2 . A fixed-bed reactor (FBR) was used to investigate the NO emissions of a coal sample at different atmospheres. It is found that temperature has played an important role in NO releasing. With the increase of furnace temperature, the peaks of NO release appear to occur early. For the tested coal, the conversion rates of fuel-N to NO in air are higher than those in oxy-fuel or oxy-enrich atmospheres, which may be due to the effect of CO 2 gasification. The conversion of fuel-N to NO appears to have some complicated tendencies in oxy-enrich combustion, and some possible reasons about this were discussed.