CFD Analysis on the Effect of Ammonia Addition on Oxyfuel Coal Combustion in a Swirl Burner

Abstract

Oxyfuel firing technology has proven to be a successful approach for capturing CO2 in power plants that burn fossil fuels. In addition, in recent years, there has been increasing interest in cofiring fossil fuels with carbon-free fuels as a means to reduce CO2 emissions. In this study, a combination of these two promising strategies was examined using computational fluid dynamics (CFD) simulation techniques. The two-phase Eulerian-Lagrangian method was applied to analyze the interaction between gas and particles. Different mixture compositions of ammonia and coal, ranging from pure coal to 50% ammonia, were accounted for, which were determined based on the fuels' calorific values to ensure the same thermal input to the furnace. The findings reveal that the addition of ammonia to the fuel causes the hot region to shift downstream of the furnace. Furthermore, due to the rapid reaction between NH3 and oxygen, the burnout of char is suppressed as the proportion of ammonia in the cocombustion increases. By replacing 50% of the calorific value of coal with ammonia in the fuel mixture, the concentration of carbon dioxide at the furnace exit decreases from about 0.013 kg/MJ to around 0.065 kg/MJ. Moreover, it was observed that the concentration of NO increased with an increase in the ammonia blend up to 10% (by calorific value) but remained relatively unchanged with further additions of ammonia to the fuel mixture. Therefore, given the manageable NO levels and the sufficiently high proportion of CO2 in the flue gas in the cofiring scenario, the technology of oxy-cofiring coal and ammonia can be considered to be a promising mitigation strategy for the carbon footprint.