Role of calcium looping conditions on the performance of natural and synthetic Ca-based materials for energy storage

Abstract

In this work, the multicycle activity of natural CaO precursors (limestone and dolomite) and Ca-based composites (CaAlO/CaCO and ZrO/CaCO mixtures) has been studied for Thermochemical Energy Storage (TCES) in Concentrated Solar Power (CSP) plants by means of the Calcium-Looping process (CaL), using two integration schemes proposed elsewhere that differ in the calcination stages. Under CSP-He conditions, calcination for CaO regeneration is performed under pure He at low temperatures (725 °C) while under CPS-CO conditions calcination is carried out under pure CO at high temperatures (950 °C). The latter avoids the use of selective membranes to separate He from CO even though it requires the use of more expensive materials for solar receptors. Carbonation/calcination conditions drastically affect the multicycle CO uptake of the materials tested. Effective multicycle conversion is higher in CSP-He tests due to the mild conditions employed for calcination, which mitigates CaO sintering. On the other hand, the harsh calcination conditions used in CSP-CO tests enhance sintering of CaO derived from limestone and the CaAlO/CaCO composite due to the low Tammann temperature of CaAlO. CaO sintering is hindered by the presence of inert oxides with high Tammann temperatures, such as ZrO in the ZrO/CaCO composite and MgO in dolomite. Dolomite derived CaO shows high effective conversion values along the carbonation/calcination cycles when tested under both types of conditions, as compared to limestone and the composites, which suggests that the integration scheme based on CSP-CO conditions would be a feasible alternative to CSP-He if natural dolomite were used as CaO precursor.