Abstract: The problems of serious high-temperature corrosion and reheat steam temperature deviation have been in existence in a 600 MW subcritical boiler since its ultra-low NO_x combustion retrofit. In this paper, by virtue of numerical simulation, the effect of the unevenness of the secondary air on the reductive atmosphere near the water walls, the burnout rate at the furnace outlet as well as the flue gas temperature deviation and the slag volume is studied. Then, the bottom secondary air is optimized. The results indicate that after increasing the degree of the uniformity of the secondary air volume, the CO volume fraction declines from 4% to 3% at most of the rear wall. The burnout rate and the furnace outlet flue gas temperature deviation are improved obviously despite of slight increase of the NO_x volume fraction at the furnace outlet. The slag volume is reduced substantially and the high-temperature corrosion is also expected to be improved with the increase of the bottom secondary air volume.

Key words: coal-fired power plant, boiler, high-temperature corrosion, numerical simulation, combustion adjustment, bottom secondary air, reducing atmosphere