Design of Instrumentation and Control System for Compressors and Oil Removal System of Helium Refrigerator/Liquefier

Abstract

The Helium Refrigerator/Liquefier (HRL) needs compression of helium gas, which is then cooled and expanded to produce liquid helium at 4.5 K. Oil of heavy molecule with higher specific heat is mixed with helium to avoid heating and reduce mechanical efforts during compression. Before using this He gas for refrigeration, it is necessary to reduce the gas temperature to about room temperature and separate the oil from the mixture. For this, there are heat exchangers, bulk oil separator tank, oil recirculation pumps, oil vapour coalescers and oil adsorber beds, filters, valves and other instrumentation are needed. This whole system is called as Compressor and Oil Removal System (CORS). Control of CORS plant involves the design of control system and development of logic for different operational scenarios of Helium plant. To operate the system, a number of temperature controllers, pressure controllers, level controller, flow switches and control valves are required to communicate with PLC. Project includes the development of control system architecture, process flow chart (PFC), design of control algorithms which exhibits the plant start-up conditions with helium gas management in the plant (circuit). An alarm management system is developed for the major parameters of the plant. After that the process data should be store in a data historian and performance analysis logic should be developed on the data historian which give the analytical results for plant performance. Basic characteristic operations regarding compressor control mechanisms are simulated in Aspen HYSYS software.