Numerical investigation of ammonia/coal co-combustion in a low NOx swirl burner

Abstract

Co-firing of ammonia (NH3) and coal in boilers is a promising technology to reduce CO2 emissions from power plants. However, NH3/coal co-firing in swirl burners can impact the original flame structures and may lead to serious NOx emission issues due to the high concentration of nitrogen in NH3. In this study, a numerical simulation of a low-NOx swirl burner was carried out to investigate the changes in flame structure, carbon emission, and characteristics of NOx generation. The results show that, when the NH3 co-firing ratio is 10 cal%, the flame retains its original swirl structure, and a significant increase in NO formation is observed in situations with different injection positions. When the co-firing ratio increases to 20 cal% and 30 cal% and NH3 is injected through the central air pipe, the flame changes from a swirl flame to an elongated flame. The injected NH3 is wrapped by the low-temperature primary air, separating the NH3 from the high-temperature zone, and pyrolysis becomes the primary reaction pathway for NH3 consumption rather than oxidation. The NO concentrations measured at the chamber outlet can be reduced to 11.2mg/Nm3, which is lower than that from coal combustion. As the co-firing ratio further increases to 50 cal%, NH3 and air are well mixed and burned, forming a “candle-type” flame. This results in a significant rise in NO emissions.