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

Abstract

There has been renewed interest in evaluating NOx emission control by selective non-catalytic reduction (SNCR) combined with biomass co-firing to meet impending enforcement of NOx emission limits for power generation plant. Oxygen enrichment for the concentration of CO2 in the flue gas has been observed in this work to have benefits for NOx emission control. This paper presents new information on the effect of combining biomass co-firing with SNCR under various oxygen enriched and air-staging conditions performed in the 20 kW combustion facility. Biomass has a higher tendency to generate CO and produced better reductions 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 coal (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 power station boilers would result in lower NOx emissions and higher CO2 concentration for efficient scrubbing with better carbon burnouts.