Design of Hydrodynamic Journal Bearing for Integrally Geared Centrifugal Compressor

With performance considerations driving the design of rotating equipment, operating speeds and journal loads have increased greatly in recent years, often exceeding generally accepted design limits. For high performance applications including integrally geared compressors, tilting pad bearings are often used as they are subjected to both high speeds and loads. This paper presents design of tilting pad bearing for an integrally geared centrifugal compressor where the shaft stiffness and the bearing stiffness are in the moderate range. A rotor model was created to study the response of the system. Critical speed mode shapes, undamped critical speed map and Bode plot are plotted for this rotor model. The analysis is carried out at maximum continuous operating speed of 31000 rpm (± 5%) which lies between the 2nd and 3rd critical speeds. This paper illustrates design of tilting pad bearing along with rotordynamic analysis which helps to explain the rotor response and provide assurance that Separation Margin are within acceptable limits mentioned in API-672. Speed at the vibration probe location of the rotor from the DyRoBeS software and on-site data of the same are compared in which we observed a percentage variation of 3.29% in first stage vibration probe location and 10.9% in second stage vibration probe location which are within acceptable limits.