Development and comparison of two expander cycles used in refrigeration system of olefin plant based on exergy analysis

In this study, two typical types of low temperature expander cycles for cold section of olefin plant are designed and simulated. In addition, the best refrigerant is selected as the working fluid and the matching of the heating and cooling curves in heat exchangers is also analyzed. Furthermore, the second law efficiency is calculated for systems, as well as the exergy destruction and exergy efficiency for the system components, leading to determination of sources of irreversibility. The results show that the expander cycle with one cooling stage surpasses the expander cycle with two cooling stages. The main irreversibility exists in the expander due to its large pressure difference. Eventually, the significant parameters of the expander cycle with one cooling stage are optimized and the best cycle for the separation system is introduced. The net power of the expander cycle with one cooling stage is 3549 kW, the flow rate is 47.35 kg/s and the overall exergy efficiency is 50.18% for the considered cycle in this research.

► Two low temperature expander cycles are designed using HYSYS.
► The designed cycles are evaluated by amount of the net power of the expander cycle.
► Exergy analyses of designed cycles are carried out.
► Overall exergy efficiency of designed cycles is calculated by two methods.
►  The chosen expander cycle is optimized.