Rotordynamic Stability Of A 9500 Psi Reinjection Centrifugal Compressor Equipped With A Hole Pattern Seal-Measurement Versus Prediction Taking Into Account The Operational Boundary Conditions.

Special Paperpg. 251-260Extensive stability measurements were performed during the full-load, full-pressure factory testing of a five-stage inline centrifugal compressor. The compressor, tested up to a maximum discharge pressure of 655 bar (9,500 psi), is equipped with a hole-pattern balance piston seal. The purpose of the test was the validation of the predicted rotordynamic stability with the consideration of all available boundary conditions (including the analytical determination of the correct seal geometry). In order to validate the prediction of the internal pressure distribution, the compressor thrust force and the balance piston leakage flow were measured and compared to the analytical results. The test arrangement included a magnetic exciter attached to the free end of the compressor shaft. An asynchronously rotating force was injected into the rotor to excite the first forward and backward precession modes. The measurement results demonstrated the good stability behavior of the compressor throughout the complete performance curve, a large rise of the first natural frequency even at very low pressure levels, and the insensitivity of the stability characteristics to the pressure ratio or level. Generally, a good correlation is obtained between the test results and the analytical predictions even though the predicted damping ratio is underestimated in most cases