(737f) Optimal Synthesis of a Heat Integrated Mixed Refrigerant System for Maximum Energy Savings in Chemical/Petrochemical Industries

Authors: 
Xu, C., Lamar University
Zhang, J., Lamar University
Xu, Q., Lamar University
Refrigeration system is one of the most important and critical operating system in the chemical and petrochemical industries. The tradition cascade refrigeration system (CRS) has been used for decades in ethylene plants. However, the use of the multiple refrigerants in the CRS requires a very number of separate compressors, heat exchangers, pumps and associated pipes for each temperature and pressure level. Mixed refrigerant system (MRS) has been introduced for decades, where the pure working fluids are replaced by mixed working fluids. MRS is more efficient in energy saving and less capital cost than CRS and has been widely applied in liquefaction of natural. However, because of the complexities of ethylene manufacturing process and refrigerant systems aforementioned as well as possible intellectual copyright concerns, the in-depth studies for a complex mixed refrigeration system design and operation are still lack of reporting.

In this study, a general methodology has been developed for the simultaneous synthesis of MRS and heat exchanger network (HEN) design. The methodology involves four stages of work: (1) the development of process superstructure containing all the possible pressure levels and the arrangement of all units; (2) the development of mathematic model with HEN to minimize the total compressor shaft work of MRS, where multiple pressure levels satisfying all the cooling/heating demands are simultaneously addressed; (3) the design of a detail HEN configuration according to the pinch design method; (4) solution validation examined by rigorous simulations for the entire MRS and its associated HEN. The efficacy of the developed methodology is demonstrated by a case study, where the capital is respectively saved by over 20.0%; and the compressor shaft work is also reduced by 11.2% compared with the CRS.