A Four-Hierarchy method for the design of organic Rankine cycle (ORC) power plants

Abstract

In this paper, a practical and general-adapted optimization and decision-making method is proposed for thermal systems designed for a wide range of energy field regarding organic Rankine cycle and thermodynamic cycles. This method is composed of four progressive hierarchies including modelling, optimization, scheme comparison and decision-making. To demonstrate the Four-Hierarchy method, performance of a basic trans-critical ORC and a recuperative trans-critical ORC are analyzed and compared. The NSGA-II algorithm is adopted to obtain the Pareto optimal frontier. Four decision-making methods which are Shannon Entropy, modified LINMAP, TOPSIS and TLFDM are applied for evaluating the Pareto set points. Furthermore, the final Pareto-optimal solution is determined by the root-mean-square difference, correlation coefficient and standard deviation in the Taylor diagram. The optimal results indicate that the final Pareto-optimal solution often appears at LINMAP and TLFDM points. In contrast with basic trans-critical ORC, the recuperative trans-critical ORC can always improve the system’s thermodynamic performance. But the techno-economics is only enhanced when the energy grade of heat source is sufficient. The most beneficial improvement is the average reduction of heat transfer area per net output power by more than 27.0% and 30.0% in the medium temperature and high temperature geothermal reservoirs, respectively. Based on the case study, the presented method has proved its application value, and has shown its promising applicability in a wide range of energy field regarding organic Rankine cycle and thermodynamic cycles for energy conversion.