Research on the effects of extracting main steam and reheat steam on enhancing the flexibility of the coal-fired power plants

To mitigate the problems caused by the instability and intermittence of renewable energy generation on the power grid, coal-fired power plants (CFPP) have to undertake more and more peak shaving tasks, which puts high demands on the flexibility of the units. To enhance the flexibility of coal-fired power plants, this paper proposes a heat storage model for deep peak shaving by extracting main steam and reheat steam simultaneously and a heat release model for peak-load operation by adding steam to the reheater. The system is evaluated by choosing 50 % turbine heat acceptance (THA) condition as the basic load for heat storage and selecting various THA conditions as basic load for heat release. The results show that the thermoelectric conversion efficiency can reach a maximum value of 31.56 % in the heat release process. When 200 t/h steam is added to the reheater under the 70 %THA for heat release, the power increment reaches its maximum value, 49.11 MW. Heat storage coal consumption, exceeding 447 g/kWh, increases as steam extraction rises, whereas heat release coal consumption, below 306 g/kWh, drops as the additional steam increases. After a heat storage and release cycle, the minimum unit power is 209.98 MW, while the maximum is 647.51 MW. Meantime, the system can achieve a deep peak shaving duration of 10.28 h, a comprehensive coal consumption of 313.23 g/kWh, and a round-trip efficiency of 70.38 %. This study may provide some references for enhancing the flexibility of CFPP.