Alkali-promoted calcium-based heat carriers for solar-driven thermochemical energy storage

Le résumé fourni par la source

Calcium looping (CaL) process can convert solar energy into chemical energy in a concentrating solar power system, which will be further converted to heat energy to generate electricity. The calcium-based heat carrier in the CaL is considered to be a highly prospective future medium for thermochemical energy storage (TCES) because of its excellent energy storage performance, low input cost, and high cycle operating temperature. However, sintering occurs when the heat carriers are cycled at elevated temperatures, leading to a substantial reduction in their energy storage capacity and hindering their practical applications. In this work, the sintering problem was highly mitigated, and the TCES capacity of calcium-based heat carriers was obviously promoted by doping with alkali meal salts, which are usually considered adverse for the carbonation and calcination reaction of the heat carriers. Based on the modification experiments, it can be reasonably inferred that during the high-temperature operation process, part of the alkali metal salts sublimates and escapes to provide abundant porosity for calcium-based heat carriers. Simultaneously, the other part covers the surface of the calcium particles in a molten state to maintain the stability of the pore skeleton, which greatly enhances the energy storage performance of the heat carriers. As a result, "0.5 K 2 CO 3 /CaO" showed the best energy storage performance improvement. During high-temperature cycling, the performance of the heat carrier initially increased gradually, followed by an extremely slow decline. Even after 20 cycles, the energy storage capacity still remained at a high level of 1977.23 kJ/kg. This final energy storage capacity was 2.85 times higher than that of unmodified CaO. The microstructural characterizations showed that the "0.5 K 2 CO 3 /CaO" obtained richer small particles and pore structure after cycles, benefiting from the doping of K 2 CO 3 and providing good pore channels for carbonation to inhibit sintering. Therefore, CaO-based heat carriers promoted by alkali metal salts hold significant potential for advancing the application of the TCES system in concentrated solar power plants. • Alkali metal salts were doped into calcium-based heat carriers for enhanced solar energy storage. • A high energy storage capacity of 1977.23 kJ/kg was maintained even over 20 cycles. • K 2 CO 3 was demonstrated to be the better dopant for calcium-based heat carriers.

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