Investigations on combustion optimization and NOX reduction of a 600-MWe down-fired boiler: Influence of rearrangement of tertiary air and jet angle of secondary air and separated over-fire air

Abstract

Low-NOX combustion is the main technology for reducing NOX emission in coal-fired plants. In this work, numerical simulation was conducted on a 600-MWe down-fired lean coal boiler to study the effects of important factors on NOX reduction, namely, the arrangements of tertiary air (TA), the jet angle of secondary air (SA), the separated over-fire air (SOFA) ratio, and the SOFA jet angle. The optimal arrangement was obtained with the original TA moved down; the jet angle of SA (A layer) at 20° (downdip); the SA (F layer) and the TA at 20° and 30° (downdip), respectively; and the SOFA set in the upper furnace, with a 20% ratio and a 30° jet angle. The NOX emissions were reduced from 1527 mg/m3 to 773 mg/m3 in the optimized system. Meanwhile, the exhaust gas temperature decreased from 1387 K to 1369 K, and the unburned carbon content increased slightly by 0.24%, with the overall boiler efficiency kept nearly constant. The in situ measurement results are consistent with the simulation predictions.