Comparisons of pulverized coal combustion in air and in mixtures of O2/CO2

Pulverized coal combustion in air and the mixtures of O2/CO2 has been experimentally investigated in a 20 kW down-fired combustor (190 mm id×3 m). Detailed comparisons of gas temperature profiles, gas composition profiles, char burnouts, conversions of coal-N to NOx and coal-S to SO2 and CO emissions have been made between coal combustion in air and coal combustion in various O2/CO2 mixtures. The effectiveness of air/oxidant staging on reducing NOx emissions has also been investigated for coal combustion in air and O2/CO2 mixtures. The results show that simply replacing the N2 in the combustion air with CO2 will result in a significant decrease of combustion gas temperatures. However, coal combustion in 30% O2/70% CO2 can produce matching gas temperature profiles to those of coal combustion in air while having a lower coal-N to NOx conversion, a better char burnout and a lower CO emission. The results also confirm that air/oxidant staging is very effective in reducing NOx emissions for coal combustion in both air and a 30% O2/70% CO2 mixture. SO2 emissions are proved to be almost independent of the combustion media investigated.