Rotary Compressor: High Vibration at 40% Load 2

[RMNKBR]

We are experiencing high vibration at 40% load in an oil flooded rotary screw compressor (Service: Wet Process Gas, Suction= 0 psig, Discharge= 60 psig. Electric Motor Driven, 3600 RPM with suction scrubber and filter installed upstream the compressor):

At 1% load vibration is low.

At 40% load outboard overall vibration is 15 G's. The dominant peak is lobe pass frequency (10 G's @ 14400 cpm). Inboard overall vibration is 8 G's. A reading taken on the slide valve shows also high vibration at lobe pass frequency (8 G's @ 14400 cpm).

At normal operating conditions (100% load) the outboard overall vibration is 3.2 G's and inboard overall vibration is 2.8 G's. The dominant peak is lobe pass frequency (1 G's @ 14400 cpm).

Is there any field experience, vibration study or paper analyzing load condition and dynamics in rotary compresors? And possible solutions (Structural, control or slide valve related?).

Thanks,


Ricardo Medina - KBR
661-763-6919

 

[CESSNA1]

RMNKBR: Oil flooded rotary screw machines are very smooth. I suggest you take it out of service and open it up.

Regards
Dave

http://www.wsec1.com

 

[sms]

Sounds like a pulsation problem. It is not unusual for this kind of machine to have acoustic problems at certain load points. Does it need to run at 40%? Sounds like it is ok at 100%. What kind of pulsation control devices are on the machine?

 

[RMNKBR]

No pulsation control devices are installed. Flow is 6 MMSCFD.

Equipment upstream of Compressor: Suction Scrubber and Suction Filter (Pipe size is 16-in).

Equipment downstream of Compressor: Oil/Gas separator, cooler and discharge scrubber. Pipe size is 16-in.

We are planning to take vibration readings on the compressor outboard (also note that suction pipe is on this side) and on the slide valve at different load conditions from 1% to 100% (increments of 10%. Between 25% and 50% load we plan to take readings every 2% load increments).

 

[TPL]

At 1% and full load vibration is low, so the bearings are good and the rotating elements are not contacting - the advice to take out of service and open it up is poor and should be ignored.

Sounds like a flow/operating problem and investigation of pulsation/acoustic resonance as suggested by SMS is a good step forward. You might try to get hold of a piezo-electric pressure transducer (google for it or try a search for Kistler)and install this at a suitable location - treat as an accelerometer output to get a direct measure of pressure pulsations using your datacollector

 

[RMNKBR]

I'll include the pulsation readings at the same time vibration is taken at different load condition.

Any web link to look for pulsation dampeners in case that is the problem?

Regards,

 

[sms]

I don't know what brand it is, but I would start with the OEM and see what they recommend. I went through a big problem with one of these machines, and it turned out when we got rid of the "engineered" pulsation damper and went to the OEM design, the problem was solved.

Having said that, Burgess Manning is one that I have used:

http://www.burgess-manning.com/Pulse.html

Peerless used to build these, but based on their web site, I am not so sure they do anymore...

http://www.peerlessmfg.com/index.html