Magnetic Bearings in Turboexpander Applications

Magnetic bearings in turboexpander have become the standard for the installation in gas processing and ethylene plants; there are areas of the design that are challenging to the designer for each application. This paper begins with a review of magnetic bearings, the components and how they operate with a focus on ethylene applications followed by a discussion of enthalpy drop and its relation to the effect on tip speed, and spouting velocity and efficiency and power related to magnetic bearing design. The rotor length for a magnetic bearing is longer than for oil bearing machines and with high tip speed it is possible to hit several machine limits. A discussion on these rotordynamic effects will be covered including dynamic stiffness and tuning.