Design and control of a cryogenic multi-stage compression refrigeration process

Abstract

Providing refrigeration at very low cryogenic temperatures requires the use of several stages of compression refrigeration with progressively lower boiling point refrigerants in the various stages. The cascade of cycles ultimately rejects heat to cooling water, but the working fluid at each stage removes heat from a lower-temperature source and rejects this heat plus the compressor work in that stage to a higher-temperature sink. The design of these systems appears to be only qualitatively discussed in the literature, and no discussion of their plantwide dynamic control has been found.This paper presents a quantitative design of a three-stage compression refrigeration process that uses methane, ethylene and propylene as the working refrigerant fluids in the three stages. Heat is removed in the condenser of a cryogenic distillation column separating carbon monoxide and methane. The bubble-point temperature of carbon monoxide at 13.9bar is −158°C. The distillation column condenser is cooled by evaporating boiling liquid methane at −163°C. The second stage has an evaporator with boiling ethylene at −106.7°C. The final stage has an evaporator with boiling propylene at −25.9°C. An effective plantwide control structure is developed and tested.