To enhance the deep peak-regulation capability of coal-fired power units and improve the thermal economy under low-load operation

this paper establishes a dynamic coupled model of the flue-gas and water-steam systems of a 300 MW subcritical boiler-turbine unit on the Dymola platform based on the Modelica language. The model is used to quantitatively evaluate the effects of installing a No.0 high-pressure feedwater heater (HPH) on the unit’s fast frequency-regulation response

thermal efficiency

and low-load denitrification performance. Results show that under the turbine heat acceptance (THA) conditions of 75% and 50%

rapid cut-off of the No.0 HPH can increase the unit output by 9.8 and 5.3 MW

respectively

significantly enhancing the auxiliary frequency-regulation capability. Under steady operation with the No.0 HPH in service

the main feedwater temperature increases by 33.46 and 26.75℃

while the turbine heat consumption rate decreases by 99 and 80 kJ/(kW·h)

respectively. Meanwhile

the operation of the No.0 HPH significantly raises the flue-gas temperature at the economizer outlet under various load conditions

which helps maintain the selective catalytic reduction (SCR) reactor within an appropriate operating temperature range. Further analysis at the 75% THA condition indicates that the total exergy destruction of the system decreases from 37.07 MW to 35.79 MW when the No.0 HPH is in service

while the exergy efficiency of the turbine and each regenerative heater stage is correspondingly improved. These results indicate that installing a No.0 HPH provides additional operational flexibility for both enhanced frequency-regulation capability and improved energy efficiency

offering a practical approach for optimizing deep peak-regulation operation of coal-fired power units.