Thermodynamic Characteristics Of Concentrated Solar Energy System With Chemical Energy Storage Unit

The characteristics of solar energy such as discontinuity,instability,and imbalance greatly limit the efficient use of solar energy.In order to address the shortcomings of discontinuous,unstable,and unbalanced utilization of solar energy resources,it is urgent to establish energy storage systems with high efficiency and strong load capacity.Calcium based cycling（CaL）thermochemical energy storage（TCES）technology has become the preferred energy storage technology due to the advantages of rich and cheap raw materials,high energy density,low heat storage loss,non-toxic,and easy industrial application.The CSP-CaL system built in combination with concentrated solar power（CSP）technology has played an important role in the efficient utilization of solar energy.So far,scholars around the world have developed various efficient and stable CSP-CaL systems,but the drawbacks of CSP-CaL systems are also evident.Excessive waste heat loss of heat exchanger network at the system level and excessive power demand of the compressor led to a significant reduction in the system’s power generation efficiency.The CaO activity at the material level continued to decline with the increase of the number of cycles,damaging the system’s stability.Problems at the system level and the material level limited the large-scale application of the CSP CaL system.Therefore,in this study,first of all,solve the system-level problems,and build two types of CSP-CaL-MR systems respectively by integrating the methane reforming（MR）subsystem into the energy storage（ES）and energy release（ER）unit of the CSP-CaL system to solve the system problems.Then,based on the thermodynamic characteristics,the overall design and optimization strategy of the two CSP-CaL-MR systems are proposed.After considering the power generation efficiency,hydrogen production efficiency and overall energy consumption of the system,we finally made a comprehensive evaluation of the two systems.The results show that the CSP-CaL-MR（ES）system not only realizes the dynamic storage of CO₂,but also improves the power generation efficiency by about 4%by abandoning the compressor used to store CO₂ in the traditional CSP-CaL system.CSP-Cal-MR（ER）system can balance the mass flow of CO₂,CaO and CaCO₃/CaO at the hot and cold ends of the heat exchanger,reducing the waste heat loss of the heat exchanger network by 45%.In addition,the waste heat utilization system integrated in the MR subsystem can provide about 20%of the net output power of the CSP-CAL system.More importantly,the new CSP-CaL-MR system can capture,store and convert carbon.Secondly,to solve the problem of material level,the CSP-CaL-MR（Ca-CaO mild）system using CaO as Ca-based adsorbent under mild conditions was simulated respectively.CSP-CaL-MR（Ca-Al mild）system using CaO-Ca₃Al₂O₆ as Ca-based adsorbent.Under severe conditions,CSP-CaL-MR（Ca-Al severe）system using CaO-Ca₃Al₂O₆ as Ca-based adsorbent.Then the thermodynamic analysis of the cycle process performance of the three systems is carried out.The results show that the CSP-CaL-MR system using CaO-Ca₃Al₂O₆ as Ca-based adsorbent can not only effectively improve the power generation efficiency of the CSP-CaL-MR system,but also greatly increase the system operation stability.Under the severe environment,the power generation efficiency of CSP-CaL-MR（Ca-Al severe）system has declined,but still remains at a high level.The variation of various parameters of the system during the cycle can still ensure the operation stability of CSP-CaL-MR（Ca-Al severe）system.