Abstract:

The Ca(OH)₂/CaO thermochemical heat storage system has the advantages of high energy density, low cost, and inter-temporal storage. A more in-depth revelation of the multi-physics field coupling mechanism of the reaction will help to improve the performance of the system. In this work, for the exothermic process of Ca(OH)₂/CaO system, a biaxial stirred reactor was proposed and its heat and mass transfer and chemical reaction processes were numerically investigated. The feasibility of the biaxial stirred reactor was analyzed, and the exothermic characteristics of the system were discussed. In addition, the effects of the reaction conditions, such as heat transfer coefficient, stirring speed, initial and inlet temperatures, steam pressure and filling height, on the exothermic process were investigated in detail by analyzing the variation of the conversion, the exothermic power and the bed temperature, so as to provide directions for the determination of suitable reaction conditions. The results show that the biaxial stirred reactor with stable flow and temperature fields improves the heat and mass transfer performance of the exothermic reaction. The conversion of the exothermic process of the system during 1200 s is 0.49, the peak and the stable exothermic power can reach 5.4 kW and 3 kW, respectively. The reaction temperature zone of the system can be controlled by adjusting the steam pressure, whereas a lower initial and inlet temperature accelerates the reaction and reduces the additional preheat of the system. The heat exchange capacity of the reactor will significantly affect the exothermic process, especially under the reaction conditions of high speed and high filling height. In practical applications, the needs should be considered to match the appropriate heat exchange device. The model and results in this work could help optimize the stirred reactors and provide theoretical guidance for future large-scale heat storage applications.

Key words: thermochemical heat storage, biaxial stirred reactor, exothermic process, multi-physics field coupling, numerical simulation

摘要：

针对Ca(OH)₂/CaO热化学储热体系的放热过程，提出了双轴搅拌反应器并对其“三传一反”过程进行了数值研究，揭示了体系反应的多物理场耦合机理，分析了双轴搅拌反应器用于热化学储热的可行性，讨论了体系在双轴搅拌反应器内进行放热反应的特性。结果表明，双轴搅拌反应器改善了体系放热反应的传热传质性能；体系1200 s放热过程的转化率为0.49，峰值放热功率和稳定放热功率分别可以达到5.4 kW和3 kW；通过调节水蒸气分压可以控制体系的反应温区，而较低的初始进口温度不仅可以加快反应进程，还能减少体系的额外预热量；反应器的换热能力会明显影响放热过程进行，特别是在高转速和高填充高度的反应条件下，实际应用中应考虑需求来匹配合适的换热装置。

关键词: 热化学储热, 双轴搅拌反应器, 放热过程, 多物理场耦合, 数值模拟