Exergy analysis of an ethylene bog re-liquefaction system.

The present study aims to achieve a thermodynamic analysis of an ethylene cascade re-liquefaction system. The system consists of two subsystems: a liquefaction cycle using ethylene as the working fluid and a refrigeration cycle operating with a hydrocarbon refrigerant. Hydrocarbon refrigerants considered are: propane (R290), butane (R600), isobutane (R600a) and propylene (R1270). A computer program, written in FORTRAN, has been developed. The program calculates the parameters for the characteristic points of cycles and then the system performance. The system performances have been determined and analyzed by numerical examples according to the refrigerant condensation temperature, the temperature in the tank and the temperature difference in the cascade condenser. Results show that R600a performs the best followed, in order, by R600, R290 and R1270. Furthermore, it is found that the increase of the tank temperature improves the system performance. However, an increase in the refrigerant condensation temperature deteriorates the performance of the system. It is also advantageous to run the system at low temperature difference in the cascade condenser.