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.