Sensitivity of NOx Production and Combustion Efficiency to Fuel-Air Mixing in a Model Industrial, Natural Gas Fired Burner

To meet increasingly strict emissions regulations, most industrial burners that utilize in-flame NOx control techniques reduce NOx at the expense of combustion efficiency. Advanced techniques will require that combustion efficiency is not compromised. The present paper addresses the trade-off between NOx emissions and combustion efficiency in a model, industrial burner, and the affect of fuel-air mixing on the emission of NOx and CO. Rapid mixing concepts are employed utilizing three gas injection strategies. For a given load, the parameters investigated are gas injection, excess air, and swirl intensity. Due to the different fuel injector geometries, a wide array of operating conditions and emissions result. A performance index is introduced to identify the conditions for which NOx is low and efficiency is high and to provide a common basis to which injectors can be compared. While, in general, combustion efficiency is degraded when NOx is reduced, limited conditions are identified where NOx is reduced and combustion efficiency is not compromised. The results reveal the role that fuel-air mixing strategies can play in low NOx, high efficiency burner designs and operation.