Invetigation On Solar-driven ORC Combined Heat And Power System With Heat Storage Tank

Solar-driven organic Rankine cycle(ORC)combined heat and power system(CHP)is an important way to improve the comprehensive energy efficiency of medium/low-temperature solar energy utilization system.Because solar irradiation has the characteristics of low energy density and lack of stability,it is necessary to alleviate the influence of heat source fluctuation on the stability and reliability of the system by incorporating heat storage units.In order to develop the key technologies of efficient and stable solar-driven ORC-CHP system,it is necessary to investigate the operation characteristics by thermodynamic analysis,to improve the working performance of specific facility such as the heat accumulator by optimizing the components,and to guide the design of specific solar-driven ORC-CHP system under different application scenarios by establishing a comprehensive evaluation system.Thus,it will provide technical support for ensuring the more efficient and stable operation of solar-driven ORCCHP system.Based on rules of thermodynamics,the thermodynamic model of three different types of solar-driven ORC-CHP system with stratified water tank as the heat storage unit have been established.Under the condition of satisfying the electricity and heat demand of end users,the influence of operating parameters of the heat storage unit on electricity and heat output performance was analyzed.In typical areas,the whole-year operation characteristics of the solar-driven ORC CHP system with the heat storage unit has been investigated.Aiming at the optimization design and operation of heat accumulator,this paper chooses stratified water tank as the research object,establishes the flow and heat transfer mechanism model of the water tanks with buffer plates inside,investigates the influence of thickness of insulation layer and the process of heat storage/release on the thickness of inclined temperature layer,and analyses the influence of structure and operation parameters of the heat accumulator on the heat storage efficiency.It is found that the water stratification performance inside the heat storage tank is greatly improved by the buffer plates,and the flow velocity is found to have the greatest impact while the temperature difference has the least impact on the heat storage efficiency,respectively.As for the evaluation of solar-driven ORC-CHP system,a hybrid multi-level grey relational comprehensive evaluation method was adopted with the consideration of energy efficiency,economy and environmental impact.This evaluation method is based on fuzzy analytic hierarchy process and grey relational analysis.Taking the typical application in Tibet and Xinjiang as examples with the consideration of the regional irradiation characteristics and environmental temperature,three different type of solar-driven ORC-CHP system have been constructed and investigated.The performances were analyzed and the technical adaptability of specific solar-driven ORC-CHP system was evaluated comprehensively.The results show that the solar-driven ORC-CHP system with heat storage units is not suitable in Xinjiang because of its low irradiation intensity,large heat collection area occupation,high cost and low profit.In contrast,Tibet is a good place for the development of solar-driven ORC-CHP system with heat storage units according to its local meteorological conditions,where the solar irradiation intensity is strong and the solar-driven ORC-CHP system has better technical and economic advantages.Besides,it is indicated that the heat extraction from both the vacuum tube collector and the condenser is the best technology for Tibet.