Air staged combustion technology transformation was conducted on combustion system of the 1 025t/h coal-fired boiler in Xiangtan Power Plant.A part of nozzles for the original secondary air were blocked to increase the reduction zone area.The separated over fire air(SOFA)nozzle was installed at water wall tubes at upper part of the reduction zone.The boiler efficiencies and NOx emission characteristics were experimentally investigated

with the SOFA putting into service and not

under conditions of different kinds of coal and different unit loads.The results show that

for the coal with high heating value and low ash content

when the SOFA was put into service

well air staged combustion condition is formed in furnace

resulting in drop of the NOx emission by 41%

which is significant.