A comprehensive analysis of a thermal energy storage concept based on low-rank coal pre-drying for reducing the minimum load of coal-fired power plants

摘要

In the context of renewables penetration, coal-fired power plants are required to operate at the minimum load in low-demand periods of the grid. However, combustion in the boiler will become unstable in low load conditions, which constrains the load reduction of coal-fired power plants, especially the plants fueled by low-rank coal (LRC). This work proposed a thermal energy storage (TES) concept based on LRC-drying (LD-TES) to reduce the minimum load of LRC-fired power plants (LCPPs). A simple experiment was employed to verify the feasibility of energy storage through LRC drying. The advantage of LD-TES compared with traditional low-temperature TES was revealed based on the thermodynamic analysis. Moreover, an LCPP system integrated with LD-TES was proposed, and the minimum load reduction attributed by LD-TES and the energy/environmental performance of the integrated system is determined quantitatively. To achieve this goal, a thermodynamic model is employed for system simulation and evaluation, and the TES scheme based on hot water tank (HWT-TES) using the same heat source as LD-TES is chosen for comparison. The results show that, pre-drying and storage of LRC is feasible for hourly thermal energy storage, and LD-TES can equivalently store electric power in megawatt magnitude (11.1-25.0 MW) with high round-trip efficiency (92.8%). Besides, LD-TES can also significantly reduce the CO2 emission of LCPP systems.