According to the cooling demand of the ethylene plant

cracking gas cooling-separation process is divided into a variable-temperature cooling process and a constant-temperature cooling process

corresponding to the precooling process of cracking gas and the overhead condenser of towers in the ethylene plant

respectively.In this study

the heat exchange composite curve of the original refrigeration system(ethylene-propylene cascade refrigeration systems)was obtained

indicating that the heat exchange temperature difference between cold and hot streams is massive in precooling process of cracking gas.The heat exchange losses can be reduced by a suitable mixed refrigerant system.Furthermore

a combining multiple mixed refrigerant and cascade refrigeration system was proposed.The combinatorial refrigeration system model was set up with Aspen Plus.And genetic algorithm was adopted as the optimization method

with system variables such as refrigerant components

outlet pressure of compressor

and pressure in outlet of the throttle.Eventually

the compression power in the optimal solution was 3025.5 kW

which was 14.7% lower than that in the pure refrigerant systems.