Design of Instrumentation and Control System for the Test Facility of Cryogenic Turboexpander

Abstract

The Helium Refrigerator/Liquefier (HRL) needs turbines as expansion machines to produce cooling effect which is further used for production of liquid helium. Cryogenic turbines are significantly smaller in size compared to those for room temperature applications but rotation speed is high, about few lakhs of rpm and hence they have contactless gas bearings or magnetic bearings. Gas bearing can be of aerostatic and aerodynamic type. Due to this high speed of rotation, for safe and controlled operation of turbines, effect of flow dynamics for associated pipe and valves on turbine speed are necessary. Before using these turbines in the helium plant, it is necessary to simulate the performance for producing cooling effects using ASPEN or other software tools. For different normal and off-normal operations, speeds will be different and hence the flow parameters for bearing gas flow should be controlled via control valves through a developed logic. These turbines will also have gas compression cycle whose pressure also needs to be auto controlled.

Cryogenic cycles like Linde cycle, Claude cycle cover the liquefaction of various gases such as Air, Nitrogen, Helium. This project work involves the work to simulate the cryogenic cycles with the help of the simulation tool ASPEN HYSYS.

This project work involves the design of a control loops and hence development of logic for different operational scenarios of turbine test facility. To operate the test facility in the cryogenic temperatures environment, a number of specific cryogenic temperature, pressure, flow sensors, speedometers are required. Project includes the development of process behaviour in ASPEN HYSYS by understanding the plant cycle, process flow chart (PFC) Operational sequence of different components with rate of opening/closing of valves will be established for safe operation during nominal and off-nominal operations in the test stand. It also includes the study of safety interlock for the reliable fail-safe operation of turbine test facility.