关键词: 系统工程, (火用), 优化设计, 夹点技术, 乙烯, 复叠制冷

Abstract: The separation process of an ethylene plant should be operated at low temperature,and a refrigeration system supplies the cooling demand. The refrigeration system in an ethylene plant is a closed cycle system independent of the separation process. The energy efficiency can be effectively improved if the separation process and refrigeration system are optimized simultaneously. Cascade refrigerating systems are most widely used in ethylene plants. In this paper,Aspen Hysys is used to simulate and analyze an ethylene separation process with a cascade refrigerating system. The exergy analysis showed lower efficiency of heat exchanger and compressor sections,whose exergy loss contribute 83% of the whole loss of the system. So energy conservation work should focus on the two sections. Then pinch technology is used to analyze refrigerant configuration. It is found that refrigerant usage above -56℃ is far more than the theoretical minimum quantity,and refrigerant usage below -56℃ is reasonable. A novel design method by using multi-pass exchangers for heat exchanger networks is proposed and the refrigerant usage is reconfigured. The new design can reduce about 30% propylene compressor work and some ethylene compressor work consumption,reducing the energy consumption of the ethylene separation significantly.

Key words: systems engineering, exergy, optimal design, pinch, ethylene, cascade refrigerating system