Enhancing the flexibility of coal-fired power units is crucial for China’s development of a new energy system dominated by renewables. This paper proposes three schemes to improve the fast load ramp capability of subcritical coal-fired units: coupling with a high-parameter hot water storage tank

coupling with a small pulverized coal bunker

and integrating both. Using a 630 MW subcritical unit as an example

the load ramp characteristics of the three schemes are investigated

and the operable region for achieving a ramp rate of 5.1%Pe/min is determined for the small bunker and hot water tank systems(Pe is the rated power output of the unit). Results show that the integrated scheme leverages the advantages of both technologies

achieving ramp rates 12.7% and 30.8% higher than those of the standalone small bunker and hot water tank

respectively. The integrated scheme exhibits a corresponding water-to-coal ratio (approximately 11.1) between the discharge flow from the hot water tank and the coal feed rate from the small bunker. Within the operable region for the target ramp rate of 5.1%Pe/min

gradually increasing the coal output (3.6~17.25 t/h) and hot water discharge (29~201 t/h) ensures rapid load increase at the target rate. This paper reveals the energy matching law in the coordinated operation of the hot water tank and small bunker

and proposes the feasible operating region and control strategy for achieving a 5.1%Pe/min load ramp rate.