Experimental Study of Cyclic Vibration of an Integrally Geared Centrifugal Compressor for Air Separation Application

Integrally geared centrifugal compressors are widely found in air separation plants to serve as main air compressors, pressure boosters and production gas compressors. High cyclic vibration was detected on the top pinion with two booster stages of an integrally geared centrifugal compressor, which was driven by a 4850 KW induction motor and assisted by a 1843 KW cryogenic turbo-expander. The cyclic vibration was characterized with a long quiet period, sharp jump and then settle down. Sometimes vibration peaks were above a prescribed shutdown limit and the compressor was tripped and then the air separation plant. A vibration survey was conducted with proximity probes but no key phasor for some reason. Spectra showed this cyclic vibration is dominated by synchronous vibration component, which was closely related to synchronous instability or Morton effect. A new signal processing technique was proposed to analyze the incomplete vibration data and get reliable and meaningful information for the diagnosis. An experimental study of this vibration phenomenon was meanwhile conducted on the machine in operation. The mechanisms of this high cyclic vibration were disclosed. An effective remedy measure was therefore taken so that this compressor has been smoothly running for over two years. This study gives an alternative method to diagnose this synchronous instability using limited vibration data and demonstrates how to design this type of compressors with robust rotordynamic performance and resistance to such cyclic vibration.