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We have a steam turbine driven oil free CO2 screw compressor installed at our site, with the below said specifications

  1. Male rotor RPM : 3000
  2. Female rotor RPM : 2000
  3. Direct coupled through shim pack with steam turbine
  4. Forced oil lubrication
  5. Sleeve bearings at male & female rotors, drive and non drive end side
  6. Active and inactive thrusts at coupling side (discharge side/drive side)
  7. Compressor body has cooling water jacket

 

The compressor faced the first major failure 3 months after commissioning, against thrust bearing damage for the male rotor. Once compressor was restored back to operation, 1 RTD at the male rotor thrust bearing temperature, showed a higher degree of temperature than the other one, 78 & 64.93 (@ 2400 rpm, alarm : 80 C , Trip: 90 C)

The temperatures remain stable at the developed threshold and fluctuates only when RPM change, otherwise there is no spike or slow increase/decrease to the temperature.

All other parameters, including axial movement, bearing temperature vibrations, operational characteristics are acceptable and show no significant change to previous running.

There are two concerns right now 1: is that the compressor can not be operated to its full RPM without causing the temperature to move into alarm range (something that I am not comfortable in doing). Maintenance teams have checked the below and found no abnormality

  1. Resistance for RTD
  2. Axial run-out for thrust collar
  3. Bearing inspection

 

2: The thrust pad shown in the attachment is combined with the radial bearing through a dowel pin inserted at its back, and hangs on it. This dowel pin has frequently failed multiple times in the past causing the pad to rotate with the shaft, however we have been lucky enough not to cause any damage to the compressor.

 

What may be the possible reasons for both the problems above?  We need to be sure before we shut the equipment down over the checks to be done, so your experience & advice would be much appreciated. 

Attachments

Images (1)
  • Thrust pad
Tags: RTD, Screw, temperature, thrust, compressor

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