The No. 5 boiler in a power plant is a 670 t/h ultra high pressure natural circulation boiler. In order to improve the depth peak-load regulation capacity of the unit

cold flue gas recirculation system was installed to meet the environmental protection emission standard and run in safety and economic state. Through adjustment and optimization on flow rate of the primary cold gas recirculation and the secondary cold flue gas

the minimum stable load of the unit was reduced from 50% to 34% of the rated load

the flue gas temperature at the SCR denitration system inlet was 316 ℃

the reheat steam temperature reached 519 ℃

the flow rate of the primary cold gas recirculation was 2.0×10~4 m~3/h

and the flow rate of the secondary cold flue gas was 2.5×10~4 m~3/h.Therefore

the unit ran stably

the SCR denitration system worked normally

and the depth peak-load regulation capacity of the unit was improved dramatically.