The NOx produced during combustion mainly includes fuel type, thermal type and rapid type. As for gas fuel, the NOx produced by gas combustion is mainly of the rapid type and thermal type due to the little nitrogen in the fuel. From the perspective of reducing thermal type and rapid type NOx, the core technology of low nitrogen combustion is to rationally optimize the mixing process of fuel and combustion air and control the local high temperature in the furnace.
At present, low-nitrogen gas burners generally adopt technologies such as graded combustion and thick-light combustion, etc. Although NOx production can be reduced to a certain extent, it cannot meet the existing environmental protection standards [3]. On the basis of the existing technology, the new low-nitrogen gas burner integrates the most advanced ultra-low nitrogen combustion technologies, such as subsonic supermixing and strong and weak cyclone hedging dynamics [4-5] (FIG. 1 -- FIG. 3). On the one hand, fuel and air are fully mixed, local high-temperature zone in the furnace is eliminated, and the residence time of flue gas in the high-temperature zone is reduced. On the other hand, it enhances the combustion stability and provides a favorable guarantee for increasing the flue gas external circulation technology. In order to meet the standard that NOx emission mass concentration of gas boiler is lower than 30 mg/m3, flue gas recirculation technology must be added on the basis of existing low-nitrogen burners to achieve the emission standard of gas boiler. Flue gas recirulation will be low temperature flue gas boiler tail into the combustion air, and fully mixed with the combustion air to participate in combustion, can effectively reduce the volume fraction of oxygen in the combustion air, thus reducing the initial mixing combustion intensity and combustion temperature in the furnace, and finally reduce the furnace thermal NOx generation effect.
Considering the flue gas recirculation effect and the influence of combustion stability, a new type of low nitrogen gas burner design makes the gas fuel in the throat section into plane distribution, combustion flame along the radial and axis from the inner to the outer layers of support, superior combustion stability, and overcome the existing low nitrogen gas burners in after adding flue gas recirculation combustion efficiency is low, the problem of the flame, and can effectively control quality of NOx emission concentration under 30 mg/m3. New type burner with low nitrogen recycling flue gas is mainly in guarantee under the condition of combustion stability, reduce the combustion air oxygen volume fraction, burner combustion intensity decrease throat area, makes the fuel part turned back along the depth of the chamber of a stove or furnace combustion, flame length longer, can make full use of furnace space to reduce the flame temperature, thus inhibiting type thermal NOx formation.
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