Experimental and numerical investigation on nitrogen transformation in pressurized oxy-fuel combustion of pulverized coal

As a cutting-edge high-efficiency combustion technology, pressurized oxy-fuel combustion (POFC) has attracted worldwide attention. Although extensive investigations have been performed on POFC to clarify the effect of different operating parameters under high CO2 partial pressure conditions, the NOx emission behaviour is not entirely understood. Experimental analysis and numerical simulations were conducted in this research to understand the nitrogen transformation mechanisms for different operating parameters. When the system pressure was increased from 0.1 MPa to 1.6 MPa, the NO emissions decreased by 41%, which was caused due to both homogeneous and heterogeneous reductions. NO emissions increased by 1.56 times after a temperature increment from 700 °C to 1100 °C. It was also discovered that NO emissions increased by 5.32 times as the oxygen concentration went up from 10% to 60%. Numerical results were highly consistent with the experimental findings, which indicates that NO emissions were primarily impacted by six elementary reactions that involve multiple intermediate species, including NCO, HNO, and NH. The main reaction pathway from fuel-N to various N products was studied through a rate of production analysis. These results show the importance of understanding the impact of operating parameters on NOx emissions in pressurized oxy-fuel conditions, which will help to facilitate the application of POFC technology in large-scale boilers.