Thermo-economic optimization of the thermal energy storage system extracting heat from the reheat steam for coal-fired power plants

Abstract

• Thermal energy storage options with reheat steam as a heat source are introduced. • A energy-exergy-economic comparison of three heat storage options is investigated. • Minimum power load ratio of thermal power system can be reduced by 12%-points. • The largest round-trip efficiency is achieved at 67.54% by two-stage heat storage. • Sensible and latent hybrid heat storage has economic advantages than other options. The load cycling range enlargement of thermal power plants is essential to ensure the power grid stability, which can facilitate the penetration of large-scale renewable power. If a part of reheat steam is extracted from the intermediate pressure turbine inlet to the thermal energy storage system, the minimum power load of the coal-fired power plant can be decreased. Moreover, constructing a thermal energy storage system extracting heat from the reheat steam is relatively easy because no modification on the boiler system is required. The reheat steam carries some sensible heat and much latent heat, and how to store the heat efficiently and cost-effectively is investigated in this study. Three thermal energy storage configurations are introduced: configuration A, as a basic configuration, one-stage sensible heat storage; configuration B applied two-stage sensible heat storage; and configuration C applied sensible and latent hybrid heat storage. Thermodynamic and economic performance of three thermal energy storage systems is evaluated and compared. The results show that integrating the thermal energy storage allows the minimum power load to be reduced from 30% to 17.64% of the rated load. Configuration B achieves the largest equivalent round-trip efficiency (67.54%), which is higher 2.56% than that of configuration A, and configuration C exhibits the lowest total cost of the equipment and storage materials (14.75 million USD) and levelized cost of delivery (143.98 USD/MWh), which is 5.94 million USD and 12.69 USD/MWh lower than those of configuration A.