System Optimization And Experimental Study Of Mid-low Temperature Organic Rankine Cycle

Using Organic Rankine Cycle (ORC) to transfer low-grade heat resources into high quality electricity is the trend of low-grade heat energy utilization. This work will take theoretical optimization and experimental study on mid-low temperature ORC system.Firstly, this work built up thermodynamic model of ORC system and main equipment. And the main thermodynamic properties of organic working fluids were introduced. Then evaluating indicators and comprehensive evaluation method of ORC system optimization were summarized. It shows that the number of indicators that need to be considered into working fluid selection is a little bit more, and both qualitative indicators and quantitative indicators are employed. Therefore, multi-level non-structure fuzzy decision making method was used for fluid selection of ORC. This work built an ORC system driven by 150℃ heat resource,5 organic working fluids were chosen as the candidate,8 indicators were employed as the criteria. Pair-compare method was used to determine the relative membership degree and weighting of criteria. The results showed the optimum sequences, R123 and R245fa were the best two recommended candidates.Secondly, this work built models of evaporator, condenser, pump and turbine of an ORC system with working fluid of R245fa. Multi-objective genetic algorithm optimization method was used to study the optimization model considering ORC system operation parameters and heat exchangers’ structure parameters simultaneously. For the case of plate heat exchangers,3 operate parameters and 6 structure parameters were chosen as the variables. The system first law efficiency and specific investment cost were chosen as the objective functions. Pareto solutions were presented by GA. The analysis of Pareto solutions would contribute to decision making.Finally, An ORC experimental installation was designed and built. Orthogonal experimental method was employed to calculate the values of main parameters. And the equipment of the ORC installation was chosen according to the values above. Working fluid of this ORC installation is R245fa. And heat released from condenser will be taken away by a water chilling unit. High-temperature oil was chosen as heat recourse medium. The performance testing experiment of ORC and its equipment can be taken out by this experiment installation. After the completion of the ORC installation, a preliminary experiment was taken under a steady operation condition. The output work of turbine was 2 kW, and efficiency can reach to 12% in this working condition.In this paper, the theoretical optimization of the research conclusions can provide reference for the optimization design of ORC system at low temperature, the experimental installation is set up to provide the conditions for the follow-up study.