Numerical studies of a water-cooled premixed burner for low NOx combustion of natural gas

Abstract

Natural gas, known for its high combustion efficiency and low CO2 emissions, is experiencing a significant increase in both market share and application range. Despite these advantages, there are also challenges emerged during the combustion process, including occurrence of high flame temperature, difficulty in controlling nitrogen oxide emissions, combustion instability, and a tendency to backfire. To address these issues and achieve clean and stable burning, a novel 14 MW water-cooled pre-mixed burner has been developed. In-depth simulations are conducted to assess the impact of various structural and operating parameters on combustion and pollutant emission characteristics. Results indicate that the combustion temperature follows a “W" shape with height of the low cooling component while its width governs combustion stability. Gas inlet spacing influences the flame center position and anti-backfire performance. The flare angle of gas channels determines the minimum ignition energy of the mixed gas fuel which affects ignition point and flame center position. Although large height of high cooling component contributes to low NOx emissions at the gas outlet, the resultant low temperature is undesirable for combustion stability. Further examinations of operating parameters through simulations reveal that combustion temperature initially decreases and then increases with excess air coefficient, while a significant decrease is noted with lower operating load. The premixed water-cooled technology could achieve low-NOx emissions to 2.89 mg·Nm−3 with the combustion temperature controlled at 1642K. This study provides valuable data for the design of low-NOx gas burners, serving as a reference for achieving clean and stable combustion of gas fuel.