A Gibbs reactor approach to the design of thermochemical storage processes: Calcium looping as a case study

Thermochemical energy storage (TCES) based on gas-solid reactions may make use of a wealth of different materials, which may be roughly distinguished between metal carbonates, metal hydroxides, and metal oxides. Each material is characterized by different thermochemical properties, determining the range of operating temperatures and storage capacity. The choice of the most appropriate material depends on such properties, as well as the operating temperature ranges of both the heat source and downhill power block. Here we develop a simple, equilibrium-based, model capable of estimating the performance of a TCES reactor, in terms of outlet gas temperature and solid conversion with respect to time. This model has been validated for the calcium looping process against a more complete model accounting for the dynamics of heat and mass transfer, as well as the rate of the chemical reaction. Following its validation, the model was employed to describe the performance of different reactive systems to provide insight on those that are more promising.