TECHNO-ECONOMIC ANALYSIS OF THE SUB-CRITICAL ORC WITH OPTIMIZED HEAT TRANSFER PROCESS

asme-orc2015 Tracking Number 33

A techno-economic analysis of a sub-critical ORC designed for the utilization of geothermal heat is performed. The thermodynamic optimization of the investigated ORC system is based on a new approach, in which thermal match between the heat source and the working fluid is improved by operating an optimal working fluid at near-critical pressures. The Optimal Heat Source Temperature (OHST) method is used to identify suitable fluids for which the pinch point is located at the inlet (or an intermediate point) of the preheater. As a result, R227ea is selected, which performs best under certain defined conditions, while R245fa is also considered as a reference fluid for further thermo-economic comparison. A heat transfer model is proposed for the plate heat exchanger system in order to determine the pinch point position in the case of near-critical fluid parameters, as well as to obtain the heat transfer area which is required for the calculation of Purchased Equipment Cost (PEC). The economic optimization is based on the minimization of the Levelized Cost of Electricity (LCOE) for the considered fluids. Results from the techno-economic optimizations show that for R245fa the optimum is obtained with a system efficiency of 7.306% and a LCOE of 205.7 €/MWh. In comparison, the proposed approach for R227ea leads to an optimum with a system efficiency of 8.607% and a LCOE of 185.9 €/MWh. The comparison suggests that although the proposed approach aims to improve the thermodynamic performance of the sub-critical ORC, it is also promising in terms of the economic profitability.