It is difficult to control NO_x emissions during full load operation of a 660 MW supercritical circulating fluidized bed(CFB) boiler in a certain power plant

and its instantaneous value is prone to exceed the ultra-low emission limit. In addition

the selective non-catalytic reduction(SNCR) system has a high ammonia consumption and severe ammonia escape issues. To solve these problems

on-site experiments on NO_x original emissions

SNCR denitrification efficiency

CO mass concentration and bottom slag combustibles were conducted

and optimization experiments on secondary air volume layout were also performed. It was found that

the original NO_x emissions of the CFB boiler were relatively low

with a maximum of 120 mg/m~3(standard condition) during full load operation and a NO_x mass concentration below 50 mg/m~3 during medium and low loads. However

there was a significant deviation in NO_x mass concentration between the front and rear ends of the furnace

and the NO_x in flue gas was mainly generated in front of the furnace. The reason why NO_x emissions are difficult to control is due to the low denitrification efficiency of SNCR and uneven coal feeding in the furnace. The SNCR denitrification efficiency at inlet of the 6 separators was all below 50%

among which the denitrification efficiency of four separators B

C

E

and F was below 40%. Furthermore

according to the distribution of parameters in the furnace depth direction

such as the bed temperature

the content of combustible materials in bottom slag

and the variation of CO mass concentration

it can be determined that the uniformity of coal feeding in the furnace also had a significant effect on the control of NO_x emissions at full load. Currently

the power plant cannot achieve uniform coal feeding without renovation

but the original NO_x generation can be reduced by adjusting the secondary air volume ratio in the depth direction of the furnace

with a reduction of up to 9.77%.