关键词: 储能技术, 热化学, 钙循环, 碳酸化反应, 放热性能强化

Abstract:

Owing to the fluctuating and intermittent nature of renewable energy, the development of advanced energy storage technologies has become imperative. Among various pathways, the calcium looping (CaL) thermochemical energy storage technology, compatible with concentrated solar power (CSP), holds significant application potential for long-term energy storage. This is attributed to its high energy storage density, elevated exothermic temperature, and the ready availability of low-cost raw materials. However, the Ca-based materials suffer from severe performance degradation during cyclic operation. Neither the effect on exothermic characteristics nor the underlying causes of performance decline are clear. And existing research on energy carrier performance predominantly focused on integral metrics like carbonation conversion and energy storage density, paying insufficient attention to the exothermic temperature—a critical parameter that determines the quality of thermal energy for downstream applications. To address this gap, this work established an experimental test platform centered on a bubbling fluidized bed reactor equipped with a temperature measurement module. Using natural Ca-based particles as the energy carrier, the exothermic performance was comprehensively evaluated from both the carbonation conversion and particle temperature. Then, the effects of key operational parameters, including CO₂ volume fraction, carbonation temperature, superficial gas velocity, and particle size, were systematically investigated. Results indicated that high CO₂ concentrations and elevated reaction temperatures contribute to the generation of higher-grade thermal energy. For instance, at a carbonation temperature of 800℃ and a CO₂ partial pressure of 1 atm, the energy carrier could achieve a maximum particle temperature of 892.28℃ and an average temperature of 861.33℃. But the energy release temperature at atmospheric pressure rarely exceeds 895℃ due to the equilibrium CO₂ partial pressure. Since the carbonation reaction of the energy carrier would absorb large amounts of CO₂, leading to abnormal particle flow state inside the reactor, it is recommended to control the superficial velocity of the fluidized bed within 2 to 4 times the critical fluidization velocity. Additionally, moderately reducing the particle size of the energy carrier could also help enhance its heat release performance. Furthermore, the decay characteristics of the carrier over multiple storage/release cycles were analyzed. It was found that the carbonation conversion underwent severe degradation, dropping by nearly 77% after 15 cycles, with the most significant attenuation occurring within the first two cycles. Characterization via SEM and BET revealed that this performance decay primarily stems from the sintering phenomenon. Repeated high-temperature loops caused agglomeration and fusion of grains, leading to pore blockage, a reduction in specific pore volume (from 0.2732 cm³·g⁻¹ to 0.1631 cm³·g⁻¹ after 10 cycles), and a drastic decrease in specific surface area, which fell by 41% after the first cycle. Importantly, refreshing a portion of the energy carrier after each cycle was shown to effectively improve the performance of particle flow. In conclusion, this work provides experimental insights into the exothermic characteristics of calcium-based energy carrier in the fluidized bed reactors, emphasizing the importance of temperature quality. It offers practical guidelines for optimizing operational parameters and proposes a viable solution to fluidization challenges. The identified severe sintering-induced decay underscores the necessity for future work on particle modification, doping, or granulation to enhance long-term cyclic stability for commercial application.

Key words: energy storage, thermochemistry, calcium looping, carbonation reaction, exothermic performance enhancement