We planned this book to be an up-to-date overview of turboexpanders and the processes where these machines are applied in a modem, cost- conscious plant environment. Therefore, the text addresses construction features, application criteria, functional parameters, and selection guide- lines. It is clearly intended for the widest possible spectrum of engineer- ing, technical support, maintenance, operating, and managerial personnel in process plants, refineries, air liquefaction, natural gas separation, min- ing, design contracting, and many other industries. The book covers both cryogenic turboexpanders that are used to re- cover power from extremely cold gases, and hot gas expanders that recover power from gases reaching temperatures well in excess of 1,000°E Because energy recovery applications ranging from 75-25,000 kW exist in virtually any process that uses high-temperature and/or high- pressure gases, properly designed turboexpanders will play an increas- ingly important role in modern industry. It is our hope that we have managed to thoroughly explain why, when, and how to use these machines~in both theory and practice. We, therefore, delve into issues and guidelines, overview comments and details, procedures, and tech- niques that most turboexpander owner/operators and specifying engi- neers need to know.