Adiabatic Compressed Air Energy Storage with packed bed thermal energy storage

TLDR

Adiabatic compressed‑air energy storage has mainly been studied with indirect‑contact heat exchangers and thermal fluids, while packed‑bed storage has been proposed but lacks detailed analysis. This study provides a detailed analysis of A‑CAES with packed‑bed thermal energy storage. The authors develop and validate a numerical model of a packed‑bed A‑CAES system and perform an exergy analysis of a charge–storage–discharge cycle to locate major losses. The analysis predicts an efficiency exceeding 70 %, with the largest losses in compressors and expanders (~20 % of work input), and shows that continuous cycling causes heat buildup in the beds, reducing efficiency by less than 0.5 %.

Abstract

The majority of articles on Adiabatic Compressed Air Energy Storage (A-CAES) so far have focussed on the use of indirect-contact heat exchangers and a thermal fluid in which to store the compression heat. While packed beds have been suggested, a detailed analysis of A-CAES with packed beds is lacking in the available literature. This paper presents such an analysis. We develop a numerical model of an A-CAES system with packed beds and validate it against analytical solutions. Our results suggest that an efficiency in excess of 70% should be achievable, which is higher than many of the previous estimates for A-CAES systems using indirect-contact heat exchangers. We carry out an exergy analysis for a single charge–storage–discharge cycle to see where the main losses are likely to transpire and we find that the main losses occur in the compressors and expanders (accounting for nearly 20% of the work input) rather than in the packed beds. The system is then simulated for continuous cycling and it is found that the build-up of leftover heat from previous cycles in the packed beds results in higher steady state temperature profiles of the packed beds. This leads to a small reduction (<0.5%) in efficiency for continuous operation.