Improving the Energy Efficiency of Industrial Refrigeration Systems

When designing a cooling process for low temperature (about -30℃ or less), multi-stage refrigeration cycle is usually used. A lot of study has been progressed to increase a cooling efficiency by introducing an additional device (vessel, heat exchanger, etc.) at the multi-stage refrigeration cycle. However, most studies have been conducted in consideration of only using a single refrigerant. Therefore this study focused on whether we can improve a cooling efficiency by using a mixed refrigerant while maintaining the overall structure of multi-stage refrigeration cycle. In this study, we simulated four refrigeration cycles by using a UniSim^® (one base case, three retrofit cases) and optimized each refrigeration cycle so as to minimize the amount of energy requirement. Optimization was performed by the genetic algorithm (GA) provided in MATLAB^® after linking MATLAB^® and UniSim^®. Simple analysis resulted from this study shows that it is economical in terms of energy cost when switching from pure to mixed refrigerant and adding a heat exchanger for self-cooling at the multi-stage refrigeration cycle.