예열공기 조건의 대향류 확산화염에서 배기가스 재순환 방식에 따른 NO 배출 비교
Comparison of NO Emission with Flue Gas Recirculation Methods in Preheated Air Condition
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External flue gas recirculation has been applied to achieve ultra-low NOX combustion in industrial boilers. In this paper, three recirculation methods were studied numerically in methane-air counterflow diffusion flames, which flue gas was diluted in fuel (FIR), air (FGR) and both (FIR+FGR) sides. Burned gas was used as a diluent, and NOX emission was calculated in ambient and preheated air to simulate the practical boiler conditions. As a result, the maximum flame temperature of FIR was the lowest, and the flame extinction limit of FGR was the widest. Before the flame zone, NOX consumption reaction steps occurred near the nozzles, especially the fuel side. To eliminate this effect, emission index of NO (EINO) was calculated at the flame zone and it is compared with original EINO. EINO of FIR was the lowest, and the tendencies of FIR and FIR+FGR were similar. It can be seen that the recirculation of fuel-side is greatly influenced on the flame zone and effective in reducing NO. Finally NO emission was evaluated through NO formation mechanism.
Abstract
External flue gas recirculation has been applied to achieve ultra-low NOX combustion in industrial boilers. In this paper, three recirculation methods were studied numerically in methane-air counterflow diffusion flames, which flue gas was diluted in fuel (FIR), air (FGR) and both (FIR+FGR) sides. Burned gas was used as a diluent, and NOX emission was calculated in ambient and preheated air to simulate the practical boiler conditions. As a result, the maximum flame temperature of FIR was the lowest, and the flame extinction limit of FGR was the widest. Before the flame zone, NOX consumption reaction steps occurred near the nozzles, especially the fuel side. To eliminate this effect, emission index of NO (EINO) was calculated at the flame zone and it is compared with original EINO. EINO of FIR was the lowest, and the tendencies of FIR and FIR+FGR were similar. It can be seen that the recirculation of fuel-side is greatly influenced on the flame zone and effective in reducing NO. Finally NO emission was evaluated through NO formation mechanism.
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