Mycom Compound Screw Compressors

[gpeterman]

Need some technical expertise on Mycom 3225 compound screw compressor high stage end. Have a few things I am researching and need to cut to the chase.

Thanks,

[RANGER1]

gpeterman ,
What would you like to know.
Give us as much relevant info as possible.
ie refrigerant ,conditions,etc etc.

Common for high stage to fail if thats your initial problem.

[RANGER1]

gpeterman,
So you have a manual apparently !

What other info do you require?

[gpeterman]

Just had the high stage end crash due to failed thrust bearing. This unit has the long screws and is used for CO2 compression. The thrust bearings had 23,000 hours on them at the time. The suction end of the male screw got into the end housing and removed approximately 3/8" of screw. Discharge end looked good all things considered. Reassembled and restarted plant. Compressor running at 95% load with no excess vibration or heat issues. One rebuild company here is now looking for 5 new high stage ends for 5 different customers. Do you have any recommendations?

14 - 16 weeks to get a new unit from Japan.

[RANGER1]

gpeterman,
What do you think failed , the bearings or inner race spinning or other?
What pressures is it pumping on CO2?

Do you keep 2nd stage fully loaded at all times & just unload 1st stage?

What control do you have on oil injection , any ie % load of 1st stage or themostatic control with solonoid on oil injection ( which would only be on first stage I presume).

Does it have 2 or 3 thrust bearings on male rotor?

After all that I & probably Mycom would strongly recommend overhaul of 2 nd stage every 20000 hrs anyway.

I think 2nd stage is probably oil sensitive causing continual oil compression issues that why it can be necassary to manage oil system with oil injection on first stage & reduce flooding of rotors on start up .



I wonder what Mycom have to say apart from thanks for the order of new 2nd stage?

[gpeterman]

Mycom will say that failures of the high stage end are not common. According to reliable techs here in the States, that is not the case. The high stage on this system, both CO2 and NH3 load 100% and stay fully loaded until shut down. Oil cooling on the discharge end is by injection. This is a manual valve regulating the injection and there is line between too much oil and not enough oil. The inner race was damaged as were the ball bearings. I don't know which failed first but it was a show stopper. The compressor continues to run very smoothly and at about 215 dF discharge temp. at 95% load. The techs didn't think this was possible. Mycom doesn't think there is a problem apparently. I just wish there was someplace stateside that could build and balance a set of screws.

[RANGER1]

All the ones I have heard of fail on high side machine if left to run to long .
I think you have done the right thing with reassembly & would not worry about it .
If its running OK why bother with new rotors, as a lot of it is superficial .
Suction end damage to me does not matter in any way .
Can you advise on all pressures throughout compressor 1st & 2nd stage suction/discharge.

A bit confused , is this an ammonia refrig system condensing CO2 in a heat exchanger?

Is the oil injection on low stage or high stage?
If you are using liquid injection for oil cooling it would be highest priority to get rid of it & instal water cooled or t/syphon . It only complicates a compound unecassarily .

215deg F sounds a bit hot if on ammonia unless its special application .

In the past we have bought complete high stage unit for warranty issues & because of severe damage .

If you want rotors quickly consider buying standard new or s/hand machine , removing rotors & adapting drive shaft to spline coupling. Then instal in existing machine.

[gpeterman]

My apologies. This is a CO2 liquefaction plant with an ammonia compression system for the cooling. The problem was on the CO2 compressor. The oil is injected in the high stage end to cool and lubricate. Suction temp/presure runs 40 dF/5 psi and discharge temp/pressure runs 215 dF/310 psi. The thermosyphon feeds NH3 to a heat exchanger on each machine to cool the oil. A new high stage end has been ordered and will deliver in approx. 3 months. Trying to find a salvage unit with a decent set of screws is the problem. When these things crap out they really crap out. The techs tell me Mycom is aware of the problem but you know how they manage inventory. Poorly

[RANGER1]

Gpeterman you have what you have, but we do the same thing in CO2 recovery in a brewery .
2 stage system with basic shell & tube intercooler , glycol cooling it from NH3 side.
Highside discharge not as high as yours , but running -30 C Ammonia for CO2 condensing .
Running 5 yrs no hint of a problem.

I would say the compounds COULD be misapplied, would have to check selection programme next week as I high discharge pressure might alter use in this application.

To the best of my knowledge they are for ultra low temp applications only -40 C/F & below.

[RANGER1]

mycom programme does not show CO2 but at approx 2000kpa or 285psi it says out of range .
So unless its a special or I don't know what I"m talking about , or both it seems suspect that its running with such a high discharge pressure.