Optimization of energy consumption in liquefaction process of mixed refrigerant for propane pre-cooling

The C3/MRC process, i.e. liquefaction process of mixed refrigerant for propane pre-cooling, is most popular in basic-load natural gas liquefaction unit. Through thermodynamic analysis, it is found that pressure and composition of the mixed refrigerant are major factors influencing the energy consumption in the process. To reduce such energy consumption, HYSYS, the simulation software of chemical process, is used to establish the model of liquefaction process of mixed refrigerant for propane pre-cooling. Then, the process is optimized by taking LNG power consumption ratio as the objective function and the pressures of high pressure refrigerant and low-pressure refrigerant and the composition of the refrigerant as the decision variables, and optimal values of such parameters and corresponding process parameters are obtained. Through comparing the process parameters before and after the optimization, it is found that, given the constant natural gas liquefaction rate and LNG product quality, the required refrigerant flow is reduced by 12.1% and the LNG power consumption ratio is reduced by 22.9% after the optimization, indicating higher economic efficiency.