Tutorial On Cryogenic Turboexpanders

Abstract

Cryogenic turboexpanders are used in many applications, including ethylene plants, refineries, gas processing plants, and air separation facilities. They frequently produce the coldest level of refrigeration available in the plant, and often operate with turbine outlet conditions where large quantities of liquid are condensed during the expansion process. Turboexpanders have come a long way in the last 20 years. Their high efficiency and reliability have led to widespread use around the world. The use of magnetic bearing in many critical turboexpander application such as ethylene plants has become common, and in the natural gas processing market, they are making inroads as well. Computational fluid dynamics (CFD) programs are providing windows into aerodynamic improvements and new applications that were unheard of in the past. API 617 (2002) now addressed cryogenic turboexpanders in Chapter 4 of the Seventh Edition. Annex 4F of the same document provides guidelines for purchasing equipment using magnetic bearings, and this section is particularly applicable to turboexpanders. The upcoming Eighth Edition will continue the trend with further enhancements to the sections on turboexpanders and magnetic bearings. This tutorial will attempt to broaden the knowledge of engineers regarding cryogenic turboexpanders, briefly covering both their design and application.