Thermo-economic comparison of subcritical organic Rankine cycle based on different heat exchanger configurations

The cost of heat exchangers account for a large proportion of total investment in organic Rankine cycle (ORC). In this paper, plate heat exchanger (P), shell-and-tube heat exchanger (S) and finned-tube heat exchanger (F) are used as evaporator and condenser of four subcritical ORC configurations: ORC-PP, ORC-SS, ORC-FP and ORC-FS. The thermo-economic models are built and a thermo-economic evaluation and comparison of four ORC configurations is presented in order to recover the low-temperature waste heat. The optimal evaporating pressure, pinch point temperature difference, net power output and dynamic payback period corresponding to the minimum electricity production cost (EPC) are obtained for different ORC configurations under different heat source temperatures. Results show that the EPCs of ORC-PP and ORC-SS are apparently higher than that of ORC-FP and ORC-FS. Among them, ORC-FS is the most cost-effective configuration. The optimal pinch point temperature difference in evaporator has a decreasing trend with the increase of critical temperature of working fluid for ORC-FS and ORC-FP, while the optimal pinch point temperature difference in condenser keeps nearly constant.