Analysis and treatment of difficulties in NOx emission control of a supercritical 660 MW circulating fluidized bed boiler
It is difficult to control NOx 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 NOx 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 NOx emissions of the CFB boiler were relatively low,with a maximum of 120 mg/m3(standard condition)during full load operation and a NOx mass concentration below 50 mg/m3 during medium and low loads.However,there was a significant deviation in NOx mass concentration between the front and rear ends of the furnace,and the NOx in flue gas was mainly generated in front of the furnace.The reason why NOx 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 NOx emissions at full load.Currently,the power plant cannot achieve uniform coal feeding without renovation,but the original NOx 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％.
circulating fluidized bed boilerNOx emissionSNCRcoal feeding
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