Expander Configurations and Torsional Analysis

Lateral rotor-dynamic behavior is often discussed as one the critical aspects in determining the reliability and operability of rotating equipment. However, as multiple equipment are coupled together to form trains for centrifugal pumps, fans/blowers, compressors, steam or gas turbines and motors or generators, torsional behavior requires a thorough analysis. As per industry standards, torsional response is sought only for train units comprising of three or more coupled machines (excluding any gears).Blog 6

The configurations of the expanders used in the oil and gas industry makes it not only ideal but mandatory to perform train torsional analysis.  Expander trains are commonly used in CCU and FCU units and in the production of nitric acid. Serving the purpose of energy recovery, various arrangement for power recovery train are illustrated to the left:

As part of torsional analysis, the drive-train critical speeds (rotor lateral, system torsional, blading modes, and the like) need to be established to ensure they will not excite any critical speed of the machinery and the entire train is suitable for the rated speed and starting-speed hold-point requirements of the train. Finding frequency margins (torsional natural frequencies and torsional excitations) and if necessary undertaking stress analysis is mandated to demonstrate that resonances do not have  an adverse effect.RD

Such analysis requires modelling complexities of flexible supports, foundation, rotor seal interaction, instabilities etc. of the entire train and their interaction. SoftInWay’s CAE tool AxSTREAM® RotorDynamics is comprehensive, user friendly, and fully integrated with modules for flowpath and blade design making it unique to undertake train torsional analysis. Further information about the software is available by following the link

Leave a Reply