Control of Compression Refrigeration Processes with Superheat or Saturated Boiling

Publication date: Available online 11 March 2019Source: Chemical Engineering and Processing - Process IntensificationAuthor(s): William L. LuybenAbstractCryogenic separation processes typically use compression refrigeration systems to achieve the desired low temperature levels for heat removal in the condenser. Many compression refrigeration systems are designed to produce slightly superheated refrigerant vapor leaving the evaporator. The liquid expansion valve is manipulated to control the amount of superheating. Commercial refrigeration systems must often handle drastic changes in operating conditions of refrigerant load and condenser temperature, which subject the superheat control loop to severe rangeability issues that complicate control due to nonlinearity and saturation.Some compression refrigeration systems have boiling liquid refrigerant in the evaporator with saturated vapor fed to the compressor. The liquid expansion valve controls the liquid level in the evaporator. The control structure is simplified and more robust.The contribution of this paper is to provide a rigorous quantitative comparison of the design and control of these alternative configurations. The fluid mechanics (plumbing) problems encountered when the superheated design is employed are demonstrated. Realistic simulations of the desuperheating, condensing and subcooling in heat exchangers are used.

Source: Chemical Engineering and Processing: Process Intensification - March 12, 2019 Category: Chemistry Source Type: research