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Show X -L-External and Internal Flue Gas Recirculation: A Comparison with Respect to Flame Stability and NOx Emission B. Martien Visser and Howard B. Levinsky N. V. Nederlandse Gasunie The Netherlands Abstract This study compares external and internal flue-gas recirculation with respect to their effects on combustion stability and the potential for NOx reduction. Towards this end, mixtures containing natural gas, air and flue-gas in various proportions and temperatures between 20°C and 500°C have been burnt. In addition, calculations of the laminar burning velocity of these mixtures have been performed, and the results have been compared with the experimental data on flame stability. The results presented in the paper indicate that internal (hot) flue-gas recirculation may lead to lower NOx emissions than external (cold) flue-gas recirculation. The experimental data also suggest that, in the relatively cool flames under investigation, the NOx in the flue-gases which was present in the initial mixture is not reduced. A relation between the adiabatic flame temperature and the NOx production by flames burning mixtures of air, natural gas and flue-gas is presented. The data presented in the paper contain information useful for burner manufacturers for the design and/ or optimisation of natural gas burners employing some form of flue-gas recirculation. 1. INTRODUCTION Worldwide, stringent legislation to limit pollutant emissions from combustion equipment has been introduced. And, even for a clean fuel like natural gas, a more stringent legislation is |
