Nitrogen oxide reduction in pressurized oxy-coal combustion

Abstract

Pressurized oxy-coal combustion is one of the promising technologies for carbon capture in power plant. NOx control is one of the main challenges during solid fuel combustion, which has attracted more interest at higher pressure. Previous results reported that lower NOx emissions were tested during pressurized oxy-coal combustion, however, fundamental studies regarding the NO reduction by coal/char at elevated pressure are scarce. In this paper, NO reduction behaviors during coal combustion in pressurized oxy-environment were systemically studied. Experiments were carried out at pressures from 1 atm to 7 atm, and temperatures of 800 K, 1073 K, and 1273 K, respectively. Equivalence ratios in the range of 0.5 to 1.5 were arranged to evaluate the oxygen effect on the interaction of coal/char with NO. Results show that the high reduction capacity of combusting particles at higher pressure and temperature can significantly reduce the NO concentration in the furnace. A large difference in NO reduction efficiency is also found among coal types at elevated pressure. The influence of equivalence ratio shows marked differences between 1 atm and higher pressure. The reduction tests by char show that the NO reduction activity is notably lower than coal at elevated pressures and varied equivalence ratios, which is due to the much higher reduction efficiency by homogeneous reaction by volatile matter at higher pressure. Compared with the char produced in fixed bed, reduction efficiency of char samples produced in drop tube furnace is much active at 4 atm. ROP analysis shows that the dominant pathway of reducing NO by volatiles is NO+HO2O2+OH among cases, while the main reactions occurred in volatile-NO interaction are not changed, although the global kinetic rate is enhanced obviously at higher pressure.