Release of nitrogen during coal pyrolysis and combustion

NOx (NO+NO2+N2O) emissions from power plant or industrial, boilers represent a health hazard and an environmental concern, especially for N2O emissions. N2O has been identified as an active absorber of the earth's radiation in the troposphere, contributing to the global green house effect. This gas is particularly harmful because of its long lifetime in the atmosphere (similar to 150 years). The major advantages of fluidized bed combustion (FBC) are fuel flexibility and low emissions of SOx and NOx (NO+NO2). The low emission of NOx is partly due to the low combustion temperature, and partly to the staged combustion principle of FBC. Coal microstructure research has indicated that for fresh coal, pyrolic nitrogen is the most abundant form of organically bound nitrogen, followed by pyridinic, quaternary, and amino types. Some of the quaternary nitrogen species initially present in coal are lost upon pyrolysis, prior to hydrocarbon devolatilization. These quaternary species are attributed to pyridinic or basic nitrogen species associated with hydroxyl groups from carboxylic acids or phenols. In order to obtain a better understanding of the relationship between NOx emission and nitrogen behavior in coal during pyrolysis and combustion, a bench scale fluidized bed combustor and a TGA-FTIR system were used for experiments. The effects of coals, temperature, excess air ratio and heating rate on the emission of NOx were studied.