Thermochemical energy storage with the solid-gas reaction of SrCO ₃ improved with CaCO ₃

Abstract In the context of thermochemical energy storage (TCES) for concentrating solar power (CSP) applications, metal carbonates’ reversible calcination and carbonation are gaining prominence, particularly in the SrCO 3 /SrO system. This system is notable for its high theoretical energy density of 10.61 GJ/m³ and operational temperatures up to 1,200 °C. However, like the CaCO 3 /CaO system, SrO experiences a significant drop in reactivity during cycling due to sintering and agglomeration of particles. In this work is proposed that the conversion effective will be improved by mixing the strontium carbonate with calcium carbonate. The best mix found was 80/20 SrCO 3 /CaCO 3 with the operating parameters of calcination-carbonation temperatures of 1,200 °C and 900 °C, respectively. This reaction has a notably better stable conversion rate than pure strontium carbonate. The study was carried out using thermogravimetry analysis. The mixture was subjected to 9 cycles, and for the ninth cycle, there was an effective conversion of 33.14 %, which, compared to pure SrCO 3 , was 2.33 %; that was improved noticeably during the carbonation process. There was an increase in the percentage effective conversion of 30.81 %. Volumetric energy density was reduced from 6.93 to 2.81 GJ/m 3 in the first and after nine cycles. The XRD analysis of the unprocessed mixture after 4 and 9 cycles showed no formation of new or secondary compounds, only the expected compounds: SrO, SrCO 3 , CaO, and CaCO 3 . This important change is explained during the carbonation looping because the CaO remains encapsulated in the SrCO 3 and does not react completely at 900 °C. As a hypothesis, this encapsulation delays the sintering of the SrCO 3 . Using a T carb = 850 °C promotes the carbonation of CaO. By promoting CaO to react, the CaO encapsulated is released rapidly, and the material was sintering faster than the T carb = 900 °C. Comparing the seventh cycle at a T carb = 900 and 850 °C, it is observed that the effective conversion decreases from 0.4431 to 0.4202 and, in the same proportion, the volumetric energy density.