Expansion turbine for cryogenic rectification system

Abstract

A turboexpander, particularly suited for use in a cryogenic rectification system, comprises a center housing rotatably supporting an elongated shaft to opposite ends of which are mounted a turbine wheel within a turbine housing and a compressor wheel within a compressor housing or a brake within a load housing. The turbine wheel has circumferentially spaced turbine blades. Process fluid is introduced so as to flow through annular nozzles or guide vanes which encompass the turbine wheel. The guide vanes direct the process fluid through the turbine blades and each extends between a leading edge more distant from the turbine wheel and a trailing edge less distant from the turbine wheel. Each guide vane is substantially uncontoured between its leading edge and the trailing edge and is substantially thicker at the leading edge than at the trailing edge. A thermal shield thermally isolates the turbine housing and the process fluid within the turbine housing from the central housing and the lubricant within said central housing. A labyrinth seal construction along the length of the shaft between the bearings and the turbine housing prevents migration of the lubricant along the shaft into the turbine housing and prevents migration of the process fluid out of the turbine housing along the shaft and into the central housing. Sealing gas may also be provided to the labyrinth seal construction as an additional expedient to prevent migration of the lubricant along the shaft and of the process fluid out of the turbine. Superior performance is achieved by the relative dimensioning of certain components.