Figure 1. Effect of main stream inlet temperature on the stability limits of the opposed reacting jet combustor over a range of equivalence ratios.

The fluid centerline nitrogen oxides concentration and carbon dioxide mole fraction profiles are presented in Figure 2 along the length of the gas fired burner. The design controls nitrogen oxides emission by reducing the contact time of the hot nitrogen molecules with atmospheric oxygen and conducting the combustion process at a low temperature. Fuel atomization and mixing of the reactants must be improved to complete the combustion rapidly and therefore reduce the residence time to a minimum for the reacting species that produce nitrogen oxides. The reduction of flame temperature is accomplished by radiating heat away from the flame and by diluting the bulk of the reactants with an inert gas. However, use of intense mixing for improved fuel atomization does not result in a low level of nitrogen oxides emissions, but rather results in a high level of nitrogen oxides emissions. Completing the combustion process near homogeneous stoichiometric conditions, by intensifying the mixing process, further increases nitrogen oxides emissions. There are many combustion and burner modification techniques which can reduce the nitrogen oxides emission of gas-fired burners. These techniques include flue gas recirculation [49], staged combustion [50], ultra-high aeration [51], and burner design or redesign [52], as well as flame inserts and secondary air baffling [53, 54], which may be of particular interest. The total system of the burner would have the potential to enjoy numerous benefits in operation such as: a) achievement of higher furnace throughput by modification of flame shape to both optimize the heat flux profile and improve the balance of heat transfer to individual passes; b) detection of coking; c) altering of the heat flux profile to maximize furnace availability and productivity after the onset and buildup of coking and; d) predictive emissions monitoring. The total system of the burner has several advantages: a) much lower emissions; b) practical designs which can meet substantially all potential user requirements; c) the system is retrofittable into many if not most existing furnaces and process heaters; d) no external flue gas recirculation is required; and e) no special treatment of the gaseous fuel is required to obtain optimal furnace performance.