Combustion Performance and NO Emission in Industrial Furnace under Preheated Air Condition with Different Excess Air Ratio

Abstract

The effect of excess air ratio on combustion performance in an industrial furnace with a swirling burner was numerically modeled. The simulation was carried out at inlet oxygen fraction of 8% and a preheated air temperature of 1273 K for natural gas. The gas combustion process was calculated by a Beta function PDF (Probability Density Function) combustion model. The transportation of the turbulent flow in the furnace was modeled by Reynolds Stress Model (RSM). The radiation was simulated by a Discrete Ordinates method. The NO chemistry was simulated by thermal NO model. The effect of excess air ratio on NO emission, temperature, O2 and CO distribution in the furnace was investigated. Results showed that thermal NO emission increased from about 5 ppm to 70 ppm when the excess air ratio increased from 1.05 to 1.25. The burnout of natural gas was improved at increased excess air ratio, i.e., CO emission decreased. The maximum and average temperature in furnace did not change much at different excess air ratio. When the excess air ration is 1.1, both good burnout of fuel and low thermal NO emission (<15 ppm) were achieved.