Internal Leakage Impact on Compressor Performance

Abstract

Abstract With the discovery of Ekofisk in 1969 the Norwegian oil adventure started and up until today the work both offshore and onshore has given Norwegian industry a unique position in the world. Peak oil was reached in 2001 and a trend is seen towards a more natural gas directed energy society. This combined with a low oil price sees the need for a change in the Norwegian oil and gas industry.

To ensure a sustainable future for the industry the focus will have to be put on enhancing recovery of existing fields and requires development of smaller and more remote fields through cost effective extraction. Wet gas compression in this regard is highly applicable and it has the potential for boosting wellstreams and achieving larger output rates, as well as enabling subsea processing with limited need for separation equipment.

In this thesis research into wet gas compression is documented. It is focused on the effect wet conditions have on the labyrinth seals of a compressor, primarily around the drive shaft. An extensive literature review has been conducted and an overview of the flow regime in the labyrinth seal and the surrounding leakage paths is given. Experimental work was conducted on the wet gas rig at NTNU. This was however limited due to unforeseen downtime on the rig. Part of the testing focused on the validation of a newly installed pressurized buffer seal and this showed an increased leakage for wet conditions. The effect of water on the rest of the labyrinth seal was shown to be somewhat ambiguous, as a positive sealing effect over the fins was indicated, however not conclusive.

In addition to this the implementation of a laser based measurement system has been reviewed in regard to the wet conditions and possibilities on the wet gas rig. Laser Doppler Velocimetry and Particle Image Velocimetry have been the focus of this investigation and it shows great potential for velocity measurements and flow field investigation.