Research on the Operation Flexibility of a Combined Heat and Power Generation Unit with Low-Temperature Return Water

In northern China, photovoltaic power generation peaks around midday, resulting in a concentrated demand for flexible and deep peak shaving over a period of approximately four hours. This study analyzes the heating and power supply capacity, as well as the operational flexibility, of the low-temperature backwater cogeneration unit at the Gujiao Power Plant. It is found that this unit exhibits stronger thermo-electric coupling and lower flexibility than conventional cogeneration systems. By evaluating the applicability of general flexibility enhancement technologies, the impacts of several thermal storage methods, including the user-side thermal storage, the hot water tank storage, and the combined regulation of the tank with user-side thermal storage, are investigated in terms of their effects on unit flexibility, energy consumption, and economic performance. A combined regulation strategy incorporating a tank-based thermal energy storage system with a rated power of 1000 MW and 20% user-side thermal storage is proposed. This approach can reduce the unit load rate by approximately 28% and significantly enhance both peak shaving capacity and economic efficiency. The correlation analysis presented in this study can serve as a reference for research on improving the operational flexibility of low-temperature backwater combined heat and power units.