OCR Text |
Show Sensitivity of NOx Production and Combustion Efficiency to Fuel-Air Mixing in a Model Industrial, Natural Gas Fired Burner M. M. Miyasato and G. S. Samuelsen UCI Combustion Laboratory University of California, Irvine Irvine,C1\,92717-3550 U.S.1\. To meet increasingly strict emissions regulations, most industrial burners that utilize in-flame NOx control techniques reduce NOx at the expense of combustion efficiency. 1\dvanced 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 1\ 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. INTRODUCTION .Air pollution in many urban areas is reaching levels that may soon require the exclusive use of natural gas in industrial burners. This regulatory strategy is directed to limiting the emission of pollutants, specifically NOx, from industrial sources. While manufacturers have designed low NOx natural gas burners, the reduction has not been optimized. For example, the role of fuel and air mixing on combustion performance (e.g., stability, NOx emission, and efficiency) has not been addressed to any great extent in practical configurations. Instead, a reduction in NOx is typically achieved today with flue gas recirculation, air staging, reburning, selective catalytic reduction, selective non--catalytic reduction, or a combination of these techniques [1]. This notwithstanding, previous studies have shown that fuel and air mixing in gas-fired burners can affect NOx emission [2-5]. These studies imply that injector and reactor geometries, which dictate the aerodynamics and subsequent fuel/air mixing, are in fact important factors in NOx production. Missing from consideration has been the effect of fuel-air mixing on reaction stability and combustion efficiency. In practical as well as laboratory systems, a reduction in NOx is usually accompanied by a reduction in combustion efficiency. While the mechanism is not fully understood, it is likely associated with the fact that practical burners are non-premixed, and the fuel and air have only a |