Turboexpanders are the heart of cryogenic process cycles everywhere, including air separation and gas liquefaction systems. At the same time, the component that is critical to those processes and is essential to trouble-free system efficiency is the bearing that supports the shaft linking a turboexpander’s barbell-shaped expansion and compression wheel assembly.
Essentially, a turboexpander is a radial inflow ‘expander’ turbine through which gas under high pressure is expanded to produce work that, in turn, can drive a compressor or generate power. The low-pressure, expanded gas that is exhausted from the turbine is very low in temperature, making it useful as a cryogenic refrigerant for many industrial processes or in the distillation and liquefaction of highly useful gases such as oxygen, nitrogen, argon, carbon dioxide (CO2) and helium.
In a manner similar to turbochargers, the construction of a typical turboexpander features a rigid shaft connecting the inflow turbine to a compressor or generator. This shaft, which runs at speeds of 5,000-10,000 rpm for large turboexpanders and up to 150,000 rpm for smaller ones, is supported by bearings. The ‘health’ of these bearings is acutely critical to the functionality of not only the turboexpander they support, but also the cryogenic plant it serves.
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