The new wet gas compression technology provides a big potential for improved recovery from new and depleting gas/condensate fields. The current technology is based on centrifugal and axial compressor principles, which offers both the benefits of well-known concept design and the drawbacks of erosion, fouling, surge and instabilities.

These concepts are based mainly on the design of a traditional compressor. This partly reflects performance requirements for handling pure gas and partly the lack of a fundamental understanding of wet gas behaviour through an impeller stage. Process and operating conditions may vary considerably during start-up at gas only or completely filled with addition of liquid with an inlet and/or discharge transient flow regime.

An advanced wet gas test rig has been designed to identify the fundamental mechanisms related to wet gas compressor surge and instability behaviour. The open-loop wet gas rig includes a single overhung impeller, sections of visualisation for the wet gas impeller inlet, discharge and diffuser.

The paper reviews and exposes the instabilities and surge flow behaviour at the impeller eye. Main focuses are the shift in inlet flow regime, the impact on overall compressor stage performance and the ability to handle wet transient inlet conditions. Any flow separation and/or slip across the inlet and impeller eye section will alter the established dry gas design guide lines for compressors. Visualisation of the impeller inlet during surge progression is the focal point of the present study. The investigation is supplemented by fast Fourier transform (FFT) analyses and high-speed measurements.

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