NOx Control in coal combustion by combining biomass co-firing, oxygen enrichment and SNCR

There has been renewed interest in evaluating the effect of biomass co-firing on the multi-pollutant control system such as Selective Non-catalytic Reduction (SNCR) and oxygen enrichment. Emissions savings have been attained by combining SNCR and biomasscoal co-combustion under various oxygen enriched staged air levels. Biomasses with higher tendency of generating CO produced better reduction in NOx emission with and without using SNCR. NO reduction of around 80% were attained using SNCR for 15% and 50% blending ratios of biomasses at 21% overall O2 concentration for unstaged combustion. Whereas, a range of 40%-80% NO reductions were attained for RC2 (a Russian Coal) and 15% co-fired biomasses with 3.1%-5.5 % overall O2 concentration at 22%-31% levels of flame staging. Moreover, it was found that better NOx removal efficiency was attained for higher NOx emission baselines under both oxygen enriched and normal firing conditions. However, SNCR NOx control for both coal or coal-biomass blends was observed to produce higher NOx reductions during O2 enrichment, believed to be due to the self-sustained NOx reduction reactions. Hence, NOx control by SNCR, oxygen enriched co-firing in the furnaces would result in lower NOx emissions and higher carbon dioxide concentration for efficient scrubbing with better carbon burnouts.