Refrigeration systems in gas separation plants account for a large contribution to the capital and operating costs. This paper addresses the interactions between the separation and refrigeration systems. Designs must provide the optimal sequence of separations, types of separation operation and associated operating conditions, to separate a feed into the desired products, together with the design of the refrigeration system. This paper focuses on simultaneous design of the refrigeration and separation systems. Optimisation variables, regarding refrigeration system, include the number of evaporation pressure levels, multiple rejection levels, heat loads on each refrigeration level, partition temperature in cascaded cycles, composition in mixed refrigerant systems, etc. Heat pumps can also be included. Stochastic methods have been adopted for optimizing the formulated optimisation problem. Case studies will focus on different separation sequences coupled with various refrigeration techniques. Both pure and mixed refrigerant cascaded refrigeration cycles are considered.

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