Refrigeration is widely used in chemical and petrochemical industries especially in low temperature processes such as the liquefaction of natural gas. There are many processes available commercially which are used in the LNG industries. These processes are energy intensive and require a significant amount of capital investment. Gas-phase refrigeration processes have certain advantages over conventional refrigeration processes like the single mixed refrigerant process or the cascade refrigerant process.

It was found that pre-cooling of the process stream with a propane refrigeration loop improves the efficiency of the process significantly. However, due to the propane pre-cooling cycle the liquid hydrocarbon inventory in the process increases, and hence, the hazard potential of the overall process increases. Therefore, there is a trade/off between the energy efficiency and the inherent safety of the process. To analyse this trade/off, a multi-objective optimisation study is performed on the propane pre-cooled dual independent expander process. The objectives are the minimisation of the total shaftwork and the minimisation of the propane refrigerant inventory. The multi-platform multi-language environment along with NSGA-II is used for the optimisation.