Design of Turbine for Cryogenic Turboexpander Used for Helium Liquefaction

Abstract

The need for gases like oxygen, nitrogen & helium in their pure form has been amplified due to the demand from industry, medical and research institutes. Cryogenics has been proven to be an effective and economical way for the separation and liquefaction of these gases. Due to advancement in superconductors are used in medical equipment and atomic energy harnessing. There are many successful processes to achieve required cryogenic temperature. Application of turboexpander for cryogenic process is a suitable option in terms of yield and compressed power requirement. Turboexpander is an important part of a liquefaction plant which operates on Claude, Kapitza or Collins cycle. It actually cools down a fraction of working fluid (air) by expanding it isotopically and feed it to downstream. Such that consecutive heat transfer through HX precools the upstream going to expand in J-T valve. Expansion turbines are most actively developed in India for nearly two decades and sizable knowledge base has been created by NIT Rourkela. Institute of Plasma Research (IPR) requires regular consumption of liquid helium for its fusion program. So there is a need of in-house production of liquid helium. To avoid dependence on other countries and organizations IPR, NIT Rourkela has taken up design and modelling of one turboexpander out of three turboexpander used in helium liquefaction thermodynamic cycle as supplied by IPR collaborator. This work is limited to design and understanding of turbine which is most important part of turboexpander.
The design procedure of the turbine is divided into two parts: finding the basic dimensions of the turbine and designing the blade profile. The basics for the design of turbine wheel is based on the method outlined by Balje (1980), which are based on the similarity principle. The two dimensionless parameters: specific speed and specific diameters uniquely determine the major dimensions of the turbine wheel, rotational speed of turbine and the velocity triangle at the inlet and outlet. These velocity triangles help us to determine the blade profile using Hassel Gruber’s approach.