An experimental and theoretical study of NO heterogeneous reduction in the reduction zone of ammonia co-firing in a coal-fired boiler: Influence of CO

The co-firing of ammonia (NH3) and coal in boilers and furnaces has attracted increasing attention worldwide. However, only a few studies have been reported on the mechanism of NO reduction in the reduction zone of coal and ammonia co-firing. This work adopted theoretical calculations and experiments to explore the mechanism of NO reduction by char and NH3 and the role of CO. Theoretical results indicated that CO exhibits a synergistic effect with the amino agent on NO reduction. In char/NH/CO/NO system, the hydrogen-rich environment created by H atoms weakens the energy of N-C bond, thereby promoting NO heterogeneous reduction. However, CO occupies the active sites on the char surface and slightly inhibits the NO heterogeneous reduction in char/NH/CO/NO system. Experimental results revealed that CO improves the NO reduction efficiency in the NH3/char/NO system. CO plays different roles in the heterogeneous reduction of NO by NH on the char surface in high-temperature furnace experiments as well as in theoretical calculations. These results are attributed to the fact that the homogeneous reduction rate of NO by the amino and CO in the ammonia and coal co-firing is greater than the heterogeneous reduction rate of NO by CO-coordinated char.