Modeling and thermal economy analysis of the coupled system of compressed steam energy storage and Rankine cycle in thermal power plant

To facilitate the integration of greater amounts of renewable energy into the power grid, it is crucial to enhance the peak shaving capabilities of conventional thermal power units. This paper proposes a novel system that combines compressed steam energy storage with the Rankine cycle of a thermal power plant (referred to as the coupling system), and focuses on modeling a 200 MW thermal power unit. The performance evaluation and parameter selection of the coupling system are conducted through comprehensive energy analysis, exergy analysis, and economic analysis. The results indicate that the energy storage cycle in the coupled system can prevent boilers and turbines in the Rankine cycle from operating at extremely low loads during deep peak shaving. Specifically, when the boiler and steam turbine operate at 66.45 % of their design load, the external power of the coupling system can be reduced to 30 % of the rated power. This results in a reduction of coal consumption by 63.42 g/W * h compared to direct peak shaving of the original thermal power unit, and an improvement in exergy efficiency by 2.99 %. In this study, a 1300 m3 energy storage circulating water storage tank capacity is used as an example, and it is found that the 200 MW unit can achieve continuous deep peak regulation operation for 8.58 h. The study also reveals that a 1 % increase in the isentropic efficiency of energy storage cycle compressors can lead to a reduction in coal consumption by 2.4 g/kW*h. Moreover, economic analysis suggests that maintaining a compressor efficiency of 86 %, utilizing 7 compression stages, and prioritizing the effectiveness of the heat exchanger are optimal for maximizing the system's revenue. These factors collectively result in a shorter payback period for the coupling system and an overall increase in total income.