Experimental and Density Functional Theory Investigation of the No Formation Mechanism During Ammonia Combustion in a Pulveri Z Ed Coal-Fired Furnace

Doping the carbon-free fuel NH 3 into pulverized coal furnaces is a feasible approach for reducing CO 2 emissions during thermal power generation, but the NH 3 co-combustion increases NO x emissions. Therefore, it is necessary to study the formation mechanism of NO during the NH 3 -pulverized coal co-combustion. In this study, the mechanism by which NH 3 doping influences the formation of NO was investigated by a combination of experiments and quantum chemical calculations. The experimental results showed that mixing a small amount of NH 3 greatly increased the NO emissions. The peak NO emissions at different temperatures corresponded to different NH 3 amounts. In the combustion system, the peak NO emissions first increased and then decreased as the temperature increased. The incorporation of NH 3 inhibits the conversion of coal-N to NO and reduces the conversion rate of fuel-N to NO. Theoretical calculations deeply analyzed the formation mechanism of NO in the NH 3 homogeneous system and the coexistence system with pulverized coal, revealing at the micro level that the formation of NH in NH 3 →NH→NO is one of the factors restricting ammonia combustion. NH oxidation on the char surface first occurred in the NH/pulverized coal/O 2 combustion system, and realizes the conversion of N to NO, HNO and NO 2 through different reaction paths. Then, the char-N and the residual oxygen on the char surface or O 2 in the system are oxidized to NO in a heterogeneous oxidation. The results of thermodynamics and kinetics both show that compared to the heterogeneous oxidation of char-N and O 2 , the process of combining char-N with residual oxygen on its surface into NO is more likely to occur. This study is the first to use experiments combined with quantum chemistry methods to explore the mechanism of NH 3 -coal co-combustion to generate NO, and provide new insights into the mechanism of N migration and transformation in ammonia combustion in pulverized coal furnaces