Centrifugal Compressor Rotordynamics in Wet Gas Conditions
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A new technology challenge in centrifugal compressor design and operation is the condensate phase management. End users (especially in offshore and subsea operations) are more and more interested to have a Wet Gas Compression system which is able to tolerate liquid in the process gas. Authors’ Company has initiated for several years a research program aiming to investigate the impact of the liquid phase on centrifugal compressor operability (mainly thermodynamics, rotordynamics, erosion, axial thrust). As an introduction, the Authors’ Company past experiences and more recent experimental tests [Ransom D. et al. 2011], [Bertoneri M. et al. 2012], are reviewed in order to show how the rotordynamic behaviour of a centrifugal compressor may be affected by the wet gas. However in the core, this paper is focused on the novel rotordynamic experimental outcomes of a wet gas single stage compressor test campaign. The machine was equipped with the following special instrumentation: Pressure and temperature probes along the flow path and internal seals; Magnetic lamination installed on the shaft end to allow for stability test through a magnetic exciter; Load cells installed in the thrust bearing; Torquemeter installed at the compressor coupling. The explored test conditions were: Wet gas = Air and Water mixture up to 3% of Liquid Volume Fraction (LVF); Suction pressure levels = 10, 15, 20 bar-a; Maximum Continuous Speed = 13500 rpm. The compressor went through an extensive test campaign where the following aspects were thoroughly investigated: Rotordynamic behaviour during steady state wet operation; Rotordynamic stability (through magnetic exciter); Transient phenomena: response to liquid load variations (LVF up to 8%), start-up/shutdown from wet conditions, start-up with stratified flow into suction pipe. The compressor dynamic behaviour was monitored both from lateral viewpoint (using no contact probes located close to bearing locations) and axial/torsional viewpoint (through the special instrumentation described above). Overall the compressor was able to withstand a huge amount of liquid phase, with an increased vibration level with respect to dry conditions but still in the safe area, both in steady and transient tests. Finally, major differences were found only at high flow – high liquid/gas density ratio conditions where an unexpected subsynchronous vibration (SSV) was showing up. The nature of this SSV was deeply investigated and finally it was fixed through a balance piston seal geometry change.
Vannini, Giuseppe; Del-Vescovo, Giuseppe; Bertoneri, Matteo; Wilcox, Melissa (2014). Centrifugal Compressor Rotordynamics in Wet Gas Conditions. Texas A&M University. Turbomachinery Laboratories. Available electronically from