Low Emission Burner Techniques

The reduction of NOx emissions from fired equipment has been driven by environmental regulations for over a quarter of a century. During that time period, various techniques have been developed to achieve the sometimes mandatory reductions. These techniques include the use of a variety of "low NOx" burner designs, staged combustion techniques, flue gas recirculation, and post treatment of the combustion products. Most, if not all of the burner designs and staged combustion techniques reduce the temperature of combustion which, in turn, decreases the thermal NOx. Flue gas recirculation adds mass to the combustion zone which suppresses the combustion temperature which reduces NOx emissions. The effect of steam injection into the combustion zone either mixed with the fuel or the combustion air on NOx reduction is well documented. The purpose of this paper is to discuss the use of certain "low combustion temperature fuels" to reduce thermal NOx formation. These fuels are usually by-products of plant processes that can, in addition to reducing the generated thermal NOx, provide greater operating flexibility by reducing the impact of excess air on NOx generation. Correlations are presented that characterize the reduction in thermal NOx emissions that result from the use of the low combustion temperature fuels. Additional correlations and detailed discussion are presented that provide insight on the effect of excess air in combination with these fuels.