Characteristic of coal combustion in oxygen/carbon dioxide atmosphere and nitric oxide release during this process

Combustion characteristic of a bituminous coal and an anthracite coal in oxygen/carbon dioxide (O2/CO2) atmosphere is investigated in a thermogravimetric (TG) analyzer. The characteristic parameters, which are deduced from the TG–DTG (differential thermogravimetric) curves, show that the coal combustion process is basically kept consistent in O2/CO2 and O2/N2 atmosphere at the O2 concentration of 20%. The Coats–Redfern method with the reaction order of 1.25 could perfectly describe the combustion process in these two different atmospheres through the calculation of the kinetic parameters for the two coals. Nitric oxide (NO) release is concentrated in a narrower time period in O2/CO2 atmosphere compared with the one in O2/N2 atmosphere during the coal combustion process. Though the high value of the NO release rate peak, the total conversion of the fuel-N to NO is strongly depressed in O2/CO2 atmosphere, and at 1473 K, the conversion is reduced by 28.99% for the bituminous coal and 22.54% for the anthracite coal, respectively. When O2 concentration is increased from 20% to 40% in O2/CO2 atmosphere, the coal combustion property is obviously improved with the shift of the whole process into the lower temperature zone and the more intensive of the reaction occurrence in a narrower temperature range. However, the total fuel-N to NO conversion is increased accordingly. For bituminous coal the increase is 17.22% at 1073 K and 20.51% at 1173 K, and for anthracite coal the increase is 15.73% at 1073 K and 16.19% at 1173 K.