High-pressure versus low-pressure auxiliary condensers in distillation vapor recompression.

• The designs of vapor-recompression distillation columns for the ethylene-ethane separation with high or low pressures in the auxiliary condenser are compared. • High pressure reduces refrigeration cost in the condenser but increases compressor cost. • The high-pressure design has 11% lower total energy cost but requires more capital investment. • The return on investment is quite attractive. A recent paper studied the separation of ethylene and ethane using several types of distillation systems in which cryogenic cooling is required. The economics of a conventional column using a very low-temperature expensive refrigerant in the condenser were compared with several configurations using process compressors. The alternative configurations involve the pressure in the auxiliary condenser and the fraction of the column overhead vapor sent through the compressor. Low pressure in the condenser requires a very low-temperature expensive refrigerant but has lower compressor costs. The purpose of this paper is to show that all of the vapor from the column should be compressed and then split, with some going to the reboiler and the rest going to an auxiliary condenser that operates at high pressure so that a higher-temperature less-expensive refrigerant can be used. [ABSTRACT FROM AUTHOR]