In order to improve the flexibility of coal-fired units

a flexible peaking operation method is proposed by combining the heat storage by extracting the reheated steam and secondary air heating by extracting the main steam. Taking the ultra-supercritical 660 MW indirect air-cooled unit as the object of study

the performance of the unit under different peaking schemes at 30% BMCR operating conditions

the energy reuse rates under different heat release conditions and the performance of the combined load reducing operation mode are analyzed. The results show that the energy reuse rates of extracting main steam heat storage

extracting main steam heating secondary air and extracting hot reheat steam heat storage are 55.13%

84.74% and 46.24%

respectively

at a peak-load shaving capacity of 20 MW with 75% THA heat release condition. Under the premise of ensuring the safety of boiler combustion and heating surface

the combined load reducing operation mode can achieve a peak peak-load shaving capacity of 46 MW

and the energy reuse rate can reach 74% when the heat release condition is 75% THA. This study can provide a reference for flexible peak-load regulation of coal-fired units.