Calcium Looping Process as Thermochemical Energy Storage in CSP Plant: Integration Strategies and Preliminary Analysis

The growing environmental concerns and the necessity to identify alternative energy sources besides traditional fossil fuels have placed increasing emphasis on renewable resources. Their discontinuous nature, however, requires the development of a storage system capable of responding to the demands of users even in conditions of absence of the resource. The primary aim of the following report is to investigate the possibilities offered by the Calcium Looping (CaL) process and its application as thermochemical energy storage system. It consists of the cyclical repetition of reversible chemical reactions of calcination-carbonation using calcium carbonate as raw material, which is extremely abundant and easily available. The process consists in the splitting of CaCO_3 into CaO and CO_2 in the endothermic calcination reaction followed by the subsequent recombination of the two products in the exothermic carbonation reaction. The high energy density offered by the phenomenon and the ease of storage of the substances involved suggest the possibility of applying it to the development of a thermochemical storage system integrated with renewable resource power plants. The analysis focuses on the integration of the Calcium Looping process into a concentrated solar power plant. Given the immaturity of the technology and the absence of similar installations to date, considerable attention is devoted to the two main reactors, calciner and carbonator, as well as the other components constituting the plant. Two different plant configurations are treated, one with high temperature solids storage system and the other with solids stored at ambient temperature. Each is investigated and modelled through the use of AspenPlus software. In both cases, the main power block is characterized by a Joule-Brayton cycle with gas turbine, exploiting the high thermal availability of CO2 resulting from the energy released by carbonation. The discussion continues through the implementation of an exergo-economic analysis of both configurations observed, with the aim of highlighting their strengths and possible opportunities for improvement. Moreover, the two configurations are also compared from an environmental point of view, through the realization of a cradle-to-grave LCA analysis, in order to understand the possible impacts generated. The compilation of the inventory required for the analysis was obtained from the combination of data regarding a comparable design plant (Gemasolar), hypotheses formulated with the assistance of the literature and results obtained from the simulations performed. Finally, the EROI (Energy Return On Investment) and EPBT (Energy PayBack Time) methodologies are applied in order to provide further information on the energy sustainability of the project, defining a valid tool for comparison with other plant technologies already widely established.