Experimental and theoretical calculations study on heterogeneous reduction of NO by char/NH3 in the reduction zone of ammonia co-firing with pulverized coal: Influence of mineral Fe

• NH 3 co-firing with coal promotes NO heterogeneous reduction in the reduction zone. • Fe reduces the efficiency of reducing NO with char and NH 3 . • Fe is not conducive to the adsorption of NH radicals and NO on the char surface. • Fe plays a catalytic role in NH/char/NO heterogeneous reduction system. • Fe increases the energy barrier of the rate-determining step in NO reduction. As a carbon-free fuel, NH 3 can be co-firing with pulverized coal to reduce CO 2 emissions in pulverized coal-fired boilers, which has attracted increasing attention in recent years. However, the source of N in NH 3 can lead to the increase in NO emissions. Studies on the NO reduction mechanism in the reduction zone by the co-firing of NH 3 in a pulverized coal-fired boiler have been reported rarely. The mechanism for the heterogeneous reduction of NO with char and NH 3 in the reduction zone is still not known, and the influence mechanism of mineral Fe on the char/NH 3 /NO heterogeneous reaction system is still not clear. In this study, high-temperature tube-furnace experiments and quantum chemical theoretical calculations are used to investigate the NO heterogeneous reduction mechanism in the reduction zone of NH 3 co-firing with pulverized coal, and in-depth analysis of the influence mechanism of mineral Fe on the heterogeneous reduction of NO by char/NH 3 . Experimental results revealed that the heterogeneous reduction efficiency of iron-impregnated char/NH 3 to NO is less than that of demineralized char/NH 3 to NO. Fe inhibits the reduction of NO by char and NH 3 in the reduction zone. Theoretical calculation results revealed that Fe is not conducive to the adsorption of NH and NO on the char surface. In the heterogeneous reduction of char/NH 3 /NO, Fe increases the activation energy of N–H bond dissociation and OH formation on the char surface, resulting in a 32.34 kJ/mol higher energy barrier value for the rate-determining step in the heterogeneous reduction of NO on the iron-impregnated char surface (IM2-Fe3 structure) than that for the heterogeneous reduction of NO on the surface of the iron-free char (IM2 structure). Fe is not conducive to the reduction of NO by char and NH 3 . This study provides new insights into the NO reduction mechanism in the reduction zone by the co-firing of ammonia in the pulverized coal-fired boiler and provides theoretical support for the application of this technology.