Improving compressed air energy storage efficiency via chemical reactions
To recover the heat generated during air compression operations, American scientists have suggested using a thermochemical energy storage (TCES) technology that stores energy in chemical bonds. They claim that this innovation might raise compressed air energy storage's round-trip efficiency to 60%.
Researchers at Oregon State University in the United States have suggested recovering the thermochemical heat generated by facilities using compressed air energy storage (CAES) as a way to increase the technology's efficiency.
According to Nicholas AuYeung, the corresponding author of the study, "conventional CAES has relatively low cost compared to all kinds of batteries and we would imagine that this technology should only improve that advantage," pv magazine reported. "A comprehensive techno-economic analysis is something we are interested in doing, but cost analysis has not yet been completed."
The novel approach involves recovering the heat produced during air compression operations by using a thermochemical energy storage (TCES) technique that stores energy in chemical bonds. This process is detailed in the paper "Thermochemical heat recuperation for compressed air energy storage," which was published in Energy Conversion and Management. The paper states that "any chemistry that can operate under high pressures could be considered," but "TCES systems based upon metal oxide redox reactions which can release oxygen under high partial pressures of oxygen are especially of interest." "Solid-gas reactions are usually the form these schemes take."
The researchers suggested using three distinct approaches—direct heat transfer via a reactive bed of TCES materials in a solid-gas reaction, indirect heat transfer between hot air and the TCES system, and a combination of direct and indirect heat transfer—to specifically employ resistance heating to break down barium oxides in the charging step of CAES.
According to AuYeung, "We looked at TCES with packed beds filled with rocks and barium oxides." Because of the comparatively low heat capacity and heat of reaction for the barium oxides, our results demonstrated a similar round-trip efficiency comparing beds with and without TCES.
He claims that the suggested system configuration may guarantee a round-trip efficiency of 60% and a storage time of 20 hours following charging. This is in contrast to standard CAES, which only achieves round-trip efficiencies of 40% to 50%. "We developed a hypothetical material with the same heat capacity as rocks but a thermochemical storage capacity three times that of barium oxides, and we looked at that hypothetical material in our model to better illustrate the potential of the concept," AuYeung continued. The findings indicated that longer storage times and a possible round-trip efficiency improvement of more than 5% may be attained. In addition, 45% less filler volume would be required to reach storage capacity comparable to that of beds filled with rocks.
The research team intends to look into additional materials in the future. "We looked at hypothetical properties like high heat capacity and high heat of reaction in non-oxygen chemistries like carbonates and hydrates, but as of yet we haven't identified one for a redox material that operates on oxygen swing," AuYeung said in her conclusion.
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