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.

Low-NO X combustion is the main technology for reducing NO X 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 NO X 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 NO X 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. • Combustion system modification and operating parameters optimization were adopted. • The arrangement of different air jets was optimized. • The NO X at the furnace was reduced from 1527 mg/m3 to 773 mg/m3. • The overall boiler efficiency remained nearly constant after optimization. [ABSTRACT FROM AUTHOR]