Abstract:

The CaCO₃/CaO thermochemical energy storage system is promising in the field of clean energy power generation because it helps to peak carbon dioxide emissions and achieve carbon neutrality as soon as possible. In this study, CaCO₃/CaO composite heat storage materials doped with TiO₂ were prepared by employing the physical mixing method. The effects of TiO₂ doping on the cyclic stability and the reaction performance in the exothermic and endothermic processes were then systematically investigated. The composite exhibited the best cyclic stability at a molar doping ratio of 100∶2.5 (Ca∶Ti). Its conversion rate was 1.65 times that of the control group after 15 cycles. Characterization showed that the CaCO₃-TiO₂ composite heat storage material with the best doping ratio had a smaller particle size and more developed pores, leading to a better anti-sintering ability in the cycle process. In the exothermic process of carbonation, CaCO₃-TiO₂-2.5 illustrated higher reaction conversion rate and thermal release/storage enthalpy ratio at a high temperature range (i.e., 750 ℃. and 800 ℃). However, its enthalpies in the exothermic and endothermic processes decreased due to the low CaCO₃ content in the composite material. During the isothermal decarbonation process, the TiO₂ doping increases the reaction rate and reduces the reaction time in the N₂ atmosphere, and decreases the initial decarbonation temperature and promotes earlier reaction in the CO₂ atmosphere. In contrast, during the non-isothermal decarbonation process (10 ℃/min), the TiO₂ doping reduces the initial decarbonation temperature of the pure CaCO₃ from 897.16 ℃ to 870.92 ℃ in the CO₂ atmosphere. The TiO₂ modification is generally of far-reaching significance for the practical application of the CaCO₃/CaO thermal storage technology.

Key words: CaCO₃ thermochemical energy storage, TiO₂ modification, cyclic stability, exothermic carbonation, decarbonation process