Optimization and thermodynamic analysis of the dual mixed refrigerant process of natural gas liquefaction

Natural gas liquefaction processes require a lot of investment and operation costs and are part of the energy consuming industries. In this research, parameters such as refrigerant component, inlet and outlet pressure to compressors were optimized in dual mixed refrigerant system to reduce operating costs. The optimized system was then evaluated by exergy to obtain the amount of exergy loss in various components of the system, , Exergy efficiency of the entire cycle was obtained 41/63%, finding illustrate the highest exergy losses were in compressors, heat exchangers, after coolers and throttle valves, respectively. The reason is the high exergy loss in the compressors due to their low polytrophic efficiency. In the analysis of exergy it was found that the exergy loss in the main cycle heat exchanger is 4% higher than that of the pre-cooling cycle heat exchanger, reason is the high temperature difference in the input and output of the currents in the converter. Choosing the right heat exchanger can help reduce investment costs. For this purpose, analysis of the effect of the size of the heat exchanger on the specific power consumption was carried out, results showed that changes in the size of the heat exchanger near the optimum point on the power consumption of the cycle are low and increases with the distance from the optimum point of this effect. However, the main cycle curve will have a greater impact on the power consumption of the cycle due to its lower slope.