Importance of Furnace Mixing on Combustion Optimization and NO_x Reduction for Larger Coal-Fired Boilers

摘要

Coal-fired utility boilers worldwide are continuously challenged by stringent NO_x emission regulations. This paper presents a cost-effective retrofit technology which utilizes specially-designed and high-kinetic-energy air jets to improve furnace mixing for combustion optimization while achieving elevated NO_x reduction. The locations of these air nozzles are determined and optimized through advanced CFD modeling. SNCR agents (e.g. urea) can also be injected deeply into flue gases through these nozzles to improve chemical utilization. The paper also presents a recent application on a 500-MW, twin-tangential boiler burning a blend of Columbian, Russian and US coals in UK. Twelve air boxes were installed at two elevations on the front and rear walls. Three levels of SNCR air boxes were installed for various load conditions. More than 60% NO_x reduction has been achieved in trial testing, and NO_x level have been consistently below 0.16 1b/MMBtu across a wide range of loads while maintaining efficient combustion. The technology has proved to meet the 200 mg/Nm~3 (or 0.16 1b/MMBtu) regulatory requirement set forth by the European IED, but at a fraction of the cost of an SCR system.