Wet Gas Compression - Transients
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Today, most of the large and easily accessible oil and gas fields on the Norwegiancontinental shelf has been developed. Future production potential is found in developmentof fields at large depths and cost-efficient methods of improving the recoveryof existing fields at the tail production stage. Development of wet gas compressiontechnology for subsea boosting is one pathway to achieving this. Introducing multiphase flow into the already complex flow pattern inside compressorsmakes it challenging to develop accurate analytical models. Current researchis therefore highly dependent on test data from real scale compressor rigs.One such compressor rig is built at the Department of Energy and Process Engineering. This thesis focus on transients aerodynamics phenomenons in centrifugal compressors.These primarily occur at low flow rate where the compressors performanceis limited by stall and surge. Encountering stall or surge is highly unwanted duringoperation and it is therefore of interest to investigate how wet gas affect them.A compressor that is exposed directly to the wellstream also needs to handle inletinstabilities in the form of liquid content fluctuations, especially if the downstreampipelines are prone to slug formation. This is a unique challenge for wet gas compressors. A vibration approach is taken, and the author has focused on analysis of frequencyspectra, primarily based on dynamic pressure readings in the diffuser. Theresults show a mild increase of noise during wet conditions due to the dispersedliquid droplets causing reflection of pressure waves. Left limit tests suggest that thecompressor encounters impeller rotating stall that is severe enough to cause flowinstabilities, but no signs of surge oscillations are seen. The same is observed forwet gas, but this occurs at a lower flow rate. Slug tests performed in the surge areagives no indication of instability, as the stall cells are immediately re-energized andno excitations are observed around the rotors natural frequency.