Refrigeration System Synthesis and Optimization

Refrigeration system holds an important role in many chemical/petrochemical processes. The traditional cascade refrigeration system (CRS) used in ethylene plants contains multiple refrigerants working at multiple temperature and pressure levels. We have technology know-how for the optimal process synthesis of a CRS based on exergy analysis. The process synthesis procedure involves four stages of work: (i) refrigeration system exergetic analysis; (ii) optimization model development for simultaneous synthesis of refrigeration system and heat exchanger network (HEN); (iii) HEN configuration identification; and (iv) final solution validation based on rigorous simulations.

In recent years, we have also systematically studied the mixed-refrigerant system (MRS). The MRS has shown salient advantages comparing to CRS. A MRS operates within smaller temperature differences at the lower limit. Thus, it leads to a smaller increase in entropy and consequently a smaller loss in energy. Besides, an MRS also requires a simpler unit configuration and less maintenance. Based on CRS technology know-how, we also developed methodology to study MRS used in ethylene plants based on exergy analysis. Exergy-based mixed-integer linear programming (MINLP) models have been developed to maximize the energy efficiency of each system, where multiple refrigerant combinations and their recycling loops are simultaneously addressed and all of cooling demands are fulfilled as inputs for a heat exchanger network synthesis.

Selected References

Xu, C. X, Zhang, J., Dinh, H., Xu, Q., “Process Synthesis of Mixed Refrigerant System for Ethylene Plants”, Industrial & Engineering Chemistry Research, 56(28), 7984-7999, 2017.
Dinh, H. D., Zhang, J., Xu, Q.*, “Process Synthesis for Cascade Refrigerant System based on Exergy Loss Minimization”, AIChE Journal, 61(8), 2471-2488, 2015.
Zhang, J., Xu Q.*, Li, K. Y. “Operational Optimization for Mixed-refrigerant Systems”, Hydrocarbon Processing, 91(4), 59-64, 2012.
Zhang, J., Xu, Q.*, “Cascade Refrigeration System Synthesis Based on Exergy Analysis”, Computers & Chemical Engineering, 35(9), 1901-1914, 2011.
Zhang, J., Wen, Y. Q., Xu, Q.*, “Multi-Objective Optimization for Design and Operation of the Chilling Train System in Ethylene Plants”, Industrial & Engineering Chemistry Research, 49(12), 5786-5799, 2010.
Dinh, H., Xu, Q.*, “Coupling Refrigeration System Synthesis and Heat Exchanger Network Design”, Proceedings of the 8th International Conference on Foundations of Computer-Aided Process Design, p297- 302. FOCAPD 2014, July 13-17, 2014, Cle Elum, Washington, USA.