Turboexpander Fundamentals

A turboexpander generates the deep, low-temperature refrigeration industrially used for gas separation and liquefaetion, and a number of related purposes. It does so by the meehanism of eonstant entropy expansion, together with the produetion of power (a byproduet). The power is generated from the deerease in enthalpy of the stream itself. A turboexpander is a high effieieney turbine with numerous speeial features. These features make it eonveniently usable and reliable for small volumetrie flows at the low temperatures (and often rather high pressures) usually found in these applieations. 

Reciprocating expansion engines have been used since the early twentieth century and are still used to some extent, especially for volumetric flows below 10 ft /min. Reciprocating machines often suffer from high maintenance, excessive size, valve problems, and tlie fact that liquid will damage the valves. For these reasons they have largely been replaced by turboexpanders, even down to sizes around 1 hp. 

The success of expanders was predicted in the 1940s. More recently, processes similar to those used in air separation have been applied in other fields. These new applications have progressed as a result of the parallel development of new processes and improved heavy-duty turboexpanders. 

Moreover, there have been improvements in the economics of the processes themselves. The following review of turbine technology recaps the evolution of the turboexpander. 

Sueeessful eommereial expander proeesses depend on the design and produetion of suitable high-speed turbine rotors and nozzles eapable 

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