To reduce nox emissions, gas burners adopting diffusion combustion generally adopt such low nitrogen technologies as fractional combustion, flue gas recirculation, positive and negative oxygen combustion. In order to realize the low nitrogen combustion technology above, structure design should be adopted to improve the flow velocity of gas jet and air jet, so as to strengthen the mixture of gas and air. Meanwhile, cyclone design should be adopted to increase the turbulence level of flame and improve the stability of flame.
Flame stabilization is achieved by two methods. One of them is called hydromechanics method. By reducing the axial flow velocity of fuel and combustion air in the burner, the mixture will not leave the burning area too quickly, which will lead to defiring. The second method, called chemical kinetics, is to form a persistent ignition source at the root of the flame that can ignite the gas at the temperature, such as the flame reflux zone, so that the flame can continue to burn. These two methods are often used in combination.
Low nitrogen burners have strict requirements on the air-fuel ratio, especially the design scheme using positive and negative oxygen combustion technology. The air-fuel ratio in different combustion zones with different concentrations directly affects the production of nitrogen oxides.
Turbulent free efflux can continuously suck in surrounding gases, making them mix quickly. To evaluate the mixing efficiency of turbulent free jet, the ratio of the total mass flow rate of the jet after a certain point on the jet path to the mass flow rate of the jet outlet can be used to represent, that is, the ratio of the mass flow rate of the jet outlet.
Diffused low nitrogen burners are generally combined with flue gas recirculation technology, in which part of the flue gas is redirected back to the burner through the external circulation pipeline for dilution of combustible mixture and inhibition of nitrogen oxide formation. With the increase of the relative opening of the flue gas external circulation valve, more and more backflow flue gas is introduced and less nitrogen oxide is produced.
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