Rotor dynamic response of a centrifugal compressor due to liquid carry over: A case study

• Liquid carry over in centrifugal compressors has negative effect on the vibration amplitude.
• Medium molecular weight has a direct effect on the vibration amplitude at critical speed.
• The presence of liquid in the compressor impellers changes the rotor balance state particularly at start-up.

This paper presents a case study in which a high speed gas lift centrifugal compressor experienced significant vibration problems associated with start-up and operation. The two-stage 8-impeller unit was used to compressor natural gas associated with oil production. During operation the unit experienced significant levels of vibration that made its continued operation impossible. A rotor-dynamic analysis of the compressor unit confirmed the presence of significant unbalance mass, a direct result of liquid within the process gas (‘liquid carry over’). Results of the rotor dynamic analysis was validated with field data. In addition, the paper shows the difference in rotor vibration synchronous response for varying molecular gas weights, particularly at critical speed.