Emission Characteristics of Syngas Flames
Synthesis gas or "Syngas" is being recognized as a viable energy source worldwide, particularly for stationary power generation due to its wide flexibility in fuel sources and superior pollutants characteristics. Although its composition may vary significantly, it generally contains CO and H2 as the dominant fuel components with varying amount of methane and diluents. There are, however, gaps in the fundamental understanding of syngas combustion and emissions, as most previous research has focused on flames burning individual fuel components such as H2 and CH4, rather than syngas mixtures. To ensure the environmental feasibility of syngas, the harmful emission, especially NOx, must comply with current and future regulations. In addition, the combustion of syngas occurs at elevated pressures and inlet temperatures. Most published research has considered the combustion of syngas constituents at atmospheric conditions. This paper presents a numerical investigation to gain fundamental understanding of combustion and emission characteristics of syngas with varying composition, pressure and inlet temperatures. Two representative syngas fuel mixtures, 50% H2/50% CO and 5% H2 / 95% CO (% vol.), are chosen based on fuel composition data from multiple power generation plants worldwide. Three detailed chemical kinetic models are used namely, GRI 3.0, Davis and Dryer mechanisms. Results indicate that for both representative mixtures an increase in reactant temperature leads to a significant increase in NOx due to increase in flame temperature caused by an increase in inlet temperature. As the pressure is increased from 1 to 6 atm, the peak NO increases rapidly, and then becomes nearly independent of pressure. This can be attributed to a similar trend in radical species responsible for NO production such as HCN and OH which both show the most significant increase at low pressures. The emission index for these flames is also found to follow a similar behavior with pressure.