The role of sensible heat in a concentrated solar power plant with thermochemical energy storage

The calcium looping process is one of the most prospective candidates for thermochemical energy storage system owing to its high energy density, widespread availability and low cost. This paper aims to explore the effect of sensible heat on storage efficiency in the system of thermochemical energy storage based on calcium looping process. Three storage efficiencies in the charging process, discharging process, and total system are defined to quantify the role of sensible heat. The obtained results indicate that the maximum storage efficiencies in the charging process, discharging process, and total system are limited by the amount of sensible heat. Their values can be increased by 45.1%, 32.1%, and 61.59% when the sensible heat is taken full advantage in the charging process, discharging process, and total system, as compared to those without sensible heat. In addition, a sensitivity analysis on the amount of sensible heat is also performed, which demonstrates the amount of sensible heat is determined by different operation conditions. A positive effect is observed on the amount of sensible heat from several dominant parameters including reactor size, reaction temperature, molar flow of calcium carbonate and split ratio, except for carbonation pressure and carbon dioxide storage pressure. Besides, the optimal amount of sensible heat is in the range of 15-40% carbon dioxide percentage of the gas phase under the discharging pressure from 3 to 7 bar. These valuable results can deepen our understanding of the importance of heat recovery in the systems of thermochemical energy storage. More importantly, some meaningful descriptors are established to efficiently assess storage efficiencies for all gas-solid systems of thermochemical energy storage with heat recovery.