On the effect of ammonia cofiring with methane; a combined CFD-economic analysis

Abstract

In recent years, there has been a growing emphasis on the co-firing of conventional fossil fuels with carbon-free alternatives to mitigate CO2 emissions. In the current study, a computational fluid dynamics (CFD) simulation was carried out to investigate the co-combustion of ammonia and methane in a combustion furnace located at the University of Lisbon. To examine the interaction between turbulence and chemistry, the Eddy Dissipation Concept (EDC) model was utilized. The fuel mixture consisted of methane and ammonia, ranging from 100 % methane combustion to 100 % ammonia combustion. The fuel proportions were determined based on their respective calorific values, ensuring an equivalent thermal input to the furnace. Subsequently, the CFD results were analyzed from an economic perspective. The research findings revealed that ammonia-methane cofiring led to a noteworthy reduction in CO2 emissions compared to pure methane combustion. However, an increase in NOx emissions during ammonia combustion was observed. Interestingly, as the proportion of ammonia in the fuel mixture increased, the NO and NO2 emissions decreased, while the amount of N2O increased. Based on the economic analysis results, the lowest annual cost (1922 USD y(-1)) was observed from the use of 100 % CH4 fuel, primarily due to the relatively lower CH4 cost compared to the NH3 and NOx reduction system. However, as the NH3-contained fuel was considered, the annual cost increased with the NH3 contained percentage, reaching the highest annual cost (5811 USD y(-1)) in the case of 100 % NH3-contained fuel. Among the economic parameters examined, the cost of NH3 emerged as the most influential factor affecting the annual cost in the co-firing system. Furthermore, the co-firing system proved to be an economically viable option when considering CH4 sourced from landfill gas and the renewable H-2 methanation process.