Abstract: The developments of coal tangentially fired technology are concisely reviewed and technical details of reducing NOx emissions combined with alleviating the gas temperature deviation are discussed for a newly designed combustion system in pulverized coal boiler. Field tests are carried out to alleviate the steam temperature deviation in the crossover pass of a 660 MW boilers, major attention was paid to the coordination of the rotational momentum required for the residual swirl elimination with the air staged flow necessary for reducing NOx emissions by the changes in yaw angles of separated over-fire air. The effects of nozzle tilt angle for reheater steam temperature regulation, pressure difference of furnace with wind box, flow-rates and yaw angles of over-fire air, are quantitatively investigated on steam temperature deviation in division platen superheaters in the upper furnace, it shows that the gas temperature deviation are eliminated in tangentially fired pulverized coal boiler by field combustion optimization, and keeping low NOx emissions of 449.0 mg / m3 and higher combustion efficiency in the meantime. Suggestions of putting steam temperature deviation into automatic control are proposed in large scale, advanced low NOx, tangentially fired pulverized coal boiler.

Key words: Coal combustion, Gas temperature deviation, NOx emissions, Residual swirl, Tangentially fired boiler