Thrust Bearing Failure in a Large LNG Refrigeration Compressor

Authors

Ed Wilcox
Senior Principal Machinery Engineer
Chevron Technology Center
Houston, TX, USA

Bruce R. Fabijonas
Research & Development Manager
Kingsbury, Inc.
Philadelphia, PA, USA

Matthew Marchione
Chief Engineer Aftermarket
Kingsbury, Inc.
Philadelphia, PA, USA

Summary

Two large refrigeration compressors at a liquified natural gas (LNG) facility experienced several damaged thrust bearings in the past eight years, one of which caused a significant Lost Profit Opportunity (LPO) in 2017. During normal operation the load on the bearing is quite low. However, when the compressor shuts down, it experiences a rapid increase in thrust load due to the settle-out conditions inside the compressor. Increases in the discharge pressure of the compressor do not substantially increase the thrust load while running, but it greatly increases the transient thrust load. During the design phase of the compression package a dynamic simulation was not performed which could have identified the transient thrust load. A complete solution would be to install a hot gas bypass valve that would have quickly equalized the pressures in the compressor casing during shutdown. However, to install a valve of this size and nature would be very difficult to justify and possibly extend the duration of the turnaround (TAR).

Talk to a Kingsbury Expert

To improve the reliability of the compressors the following changes were implemented:

• A modified active thrust bearing with higher load capacity was installed on both compressors during 2022. The new bearing was a direct replacement of the existing bearing that required no housing modifications.
• The performance controller high discharge pressure limit control setpoints were lowered slightly. This change reduces the transient load on the bearing during shutdown, although calculations have shown that the pressure can still be high enough to fail the original bearing.

With these two changes, the compressors have operated since 2022 with less high temperature transients and no thrust bearing failures.



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