Enhanced NOx Reduction by Combined Staged Air and Flue Gas Recirculation in Biomass Grate Combustion

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• 作者：Ehsan Houshfar ; Roger A. Khalil ; Terese L酶v氓s ; 脴yvind Skreiberg
• 刊名：Energy & Fuels
• 出版年：2012
• 出版时间：May 17, 2012
• 年：2012
• 卷：26
• 期：5
• 页码：3003-3011
• 全文大小：492K
• 年卷期：v.26,no.5(May 17, 2012)
• ISSN：1520-5029

文摘

Flue gas recirculation (FGR) is a conventional means of reducing NO_x emissions that involves lowering the peak flame temperature and reducing the oxygen concentration in the combustion region. Staged air combustion is also an effective means of NO_x reduction, especially in biomass combustion. This article reports results on NO_x emissions in a set of experiments combining FGR and staged air combustion in a grate-fired laboratory-scale reactor. Two different compositions of the recirculated flue gas were used: CO₂ and CO₂ + NO. The CO₂ concentration varied between 0鈥? vol鈥? of the total inlet flow rate and the NO concentration varied between 0 and 64 ppm. Two different FGR locations were also tested: above and below the grate. The results are compared with a reference experiment performed without FGR. The NO_x reduction level from staged air combustion at the optimal primary excess air ratio is 70%, while employing FGR can reduce the NO_x emissions by an additional 5%鈥?0%. The optimal primary excess air ratio range is 0.9鈥?. However, FGR more effectively reduces NO_x when employed outside of the optimum primary excess air ratio range, i.e., excess air ratios higher than 1 and less than 0.9. The experiments with FGR located above the grate exhibit higher reduction potential, while FGR located below the grate produces decreased reduction. The recycled-NO conversion factor, which gives a measure of maximal FGR efficiency, at the maximum point, is nearly 100% when FGR is applied below the grate and is 85%鈥?00% in the case of recirculation above the grate.