Full Scale Validation Of A High Pressure Ratio Centrifugal Compressor

Abstract

The present paper describes the test activities which have validated a new compressor architecture, developed by the OEM, which is able to deliver a higher pressure ratio in a single casing with respect to traditional configurations. The major differences with respect to the typical technologies used for high pressure machines are in the rotor design: Rotor stacked configuration with impellers connected through high precision toothed joint and a pre-stretched tie-rod; Shrouded and unshrouded impellers on a multistage between-bearings compressor; High peripheral speed journal and thrust bearings. The combination of unshrouded and shrouded impellers allows achieving same pressure ratio in a shorter bearing span, giving the possibility to increase the number of sections for each unit, making possible to reduce the number of casings. A full scale prototype has been built and tested to validate the new machine architecture. The prototype has been designed to fulfill a compression service made of three compression sections with a single unit; the same service could only be performed with at least two units if a standard compressor design was applied. The service requires serial compression of natural gas, characterized as follows: Design inlet volumetric flow close to10800m3/h; Design pressure ratio close to 30; Absorbed power~14MW; Design speed of 17619 RPM (MCS = 18500RPM, mos = 14095 RPM); First section comprises 2 open impellers; second section comprises 3 closed impellers and third section has 2 closed impellers. Impellers for first and second sections are in stacked configuration; third section’s impellers are mounted through shrink fitting. Considering the increased speed requirement, the prototype has been tested in conjunction with an epicyclic gear, which allows for improved efficiency for high gear ratio (12.34 in this case) with respect to standard parallel axes gears.