Techno-economic analysis of a novel heat-power decoupling system of molten salt coupled steam accumulator used in gas-steam combined cycle CHP unit

With the rapid development of renewable energy power generation systems, heat-power decoupling technology has garnered increasing attention in recent years, as it resolves temporal and spatial mismatches between the electrical energy and thermal energy output of the combined heat and power units. A conventional approach employs steam-molten salt thermal storage; however, this technology is limited to storing only the sensible heat of steam, neglecting latent heat. To realize full utilization of steam thermal energy, an integrated system combining molten salt and steam accumulator is proposed. In this design, molten salt stores high-grade sensible heat from superheated steam, whereas the steam accumulator stores both the residual sensible heat and the latent heat released during steam condensation. Multi-criteria analyses of the thermodynamic and economic performance of the molten salt coupled steam accumulator system are performed to assess the techno-economic feasibility of the system, and the operational flexibility during a typical day is investigated. The results demonstrate that the heat storage proportion of the conventional steam-heated molten salt system is only 5.6 %, requiring 12 h of charging to supply 4.7 h of steam. In contrast, the molten salt coupled steam accumulator system realizes full energy storage with significantly enhanced capacity: merely 3 h of daytime charging sustains 10.5 h of continuous steam supply at night. The proportion of heat storage, overall energy efficiency, and exergy efficiency of the molten salt coupled steam accumulator system are 63.7 %, 63.5 %, and an impressive 84.7 %, respectively. The system can save 13.3 million Nm3 of natural gas annually, resulting in a 75.8 % reduction in natural gas consumption, while also reducing CO2 emissions by 27,755 tons per year. The net present value, static and dynamic payback period are 6.1 million dollars, 4.1 years, and 4.4 years, respectively. The rate of return on investment and the internal rate of return are 11.2 % and 32.1 %, respectively, demonstrating excellent techno-economic feasibility.