To solve the problems of fluidization safety and ultra-low NOx emission of supercritical CFB boiler under ultra-low load,flue gas recirculation technology was introduced.Taking a supercritical 350 MW CFB boiler as the research object,a flue gas recirculation auxiliary peak-shaving system after semi-dry desulfurization was built.Based on the data of field operation,the effects of operating parameters such as the average bed temperature,separator inlet temperature,exhaust temperature,NOx,CO mass concentration of outlet flue gas,combusti-ble content of fly ash and bottom ash,steam-water parameter at 30％-60％load were studied under the flue gas recirculation.The results show that under the coordination of flue gas recirculation,the final emission of NOx at 30％-60％load is less than 50 mg/m3 after SNCR,the original NOx emission is less than 50 mg/m3 at 30％load;the bed temperature is reduced by 15-22 ℃,the boiler exit flue temperature increases 10-13 ℃,and the primary and reheat steam temperature is above 558 ℃.With the decrease of boiler load,the carbon content of fly ash and bottom slag increases,and the mass concentration of CO does not increase significantly.The NOx is reduced about 15 mg/m3 by SNCR arranged at secondary air;the minimum change rate of load rise/fall is 1.23％Pe;the boiler keeps dry operation above 30％load,the maximum deviation of water wall temperature is 55 ℃ at 30％load,the maximum deviation of overheated and reheated heating surfaces is 55 and 47 ℃ respectively,and no over-temperature appears.
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