Vibrations in Turbo Machinery

Paper No. 117

The CO2 compressor is designed to compress wet 99% pure CO2 recovered from the CO2 Capture and Amine Regeneration sections. The selected compressor is an eight-stage, integrally geared, centrifugal machine with an electric motor drive. Before initial startup testing, the primarily concern was the torque in the motor shaft during the synchronous motor start. Measured dynamic torque values and corresponding stresses in the motor and gear shafts during startup were below those predicted by the MDT torsional analysis and were considered acceptable. However, during the first monitored shutdown, the phenomenon of reverse rotation became the main focus of investigation during subsequent testing.

Technical recommendations that can be followed by future projects to prevent reverse rotation include:

• Recognize the number of stages in a compression system and the potential energy stored in inter-stage volumes, particularly when sizing liquid knockout vessels and the impact on shutdown. Integrally geared compression systems may behave differently than inline systems.

• Consider including dynamic modeling of compressor systems in the design phase, or adding physical controls such as check valves, blow-off valves, or recycle lines between each stage. The interaction of the components within the compression package needs to be considered by the system integrator, working with all parties involved.

• Consider the specific behavior of CO2 at high pressures when designing a compressor system for carbon capture.

• The use of bi-directional components in the compressor such as seals and bearings, along with sufficient lubricating oil supply, significantly reduces the risk of damage to the compressor from reverse rotation. Note that there are no measures to stop reverse rotation once it begins, as shutdown systems are no longer effective.

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