Aging based design and operation optimization of organic rankine cycle systems

•An aging based model of the ORC system is proposed.•The optimal working fluid considering fluid decomposition is selected.•The working fluid decomposition effects in design of the ORC systems is considered.•The proposed model manages decomposition rate by optimizing system’s operating schedule.•Degradation rate and performance of two working fluids are evaluated. The Organic Rankine Cycle (ORC) is a power generation cycle similar to the conventional Rankine cycle which runs on a working fluid other than water. The selection of a working fluid is a critical part of designing an ORC system. Researchers have selected working fluids based on various performance criteria including thermal efficiency, safety, output power, and investment cost. It should be noted that working fluids are degraded over system operating lifetime, and this will affect the system performance. As a result, working fluid should be selected considering fluid degradation mechanism in long-term operation that is studied in this paper. The objective of this work is to develop a model which optimizes simultaneously the working fluid selection and operation schedule of ORC systems. Firstly, an aging based model of the ORC system is proposed which selects the optimal working fluid considering fluid decomposition over time. Then, an aging based optimization model is developed optimizing operating schedule of the system. The model is applied to a combined gas turbine-ORC system which toluene and cyclopentane are compared as two working fluids. The results revealed that by utilizing the toluene as a working fluid, the degradation rate and cost of electricity generation and maintenance is much higher (about 30%) and using cyclopentane will be more economical during the system lifetime. Finally, this study indicates that selection of working fluid just on the basis of the start point power production is not reliable and the design and optimization of the ORC systems should be evaluated through the long-term operation.