Compensation valve compressor/expander combination

[cryotechnic]

In our plant we have a few compressor/expander combinations to produce cold.
The expander is driving the compressor.

One of this combinations has a "compensation valve" the use of this valve is clear. At the start-up it compensates the axial forces who are generated by the expander, since the compressor is still running in bypass and does not create his own axial forces to compensate the ones of the expander.

Ok, that's clear to us. Now I have a question. Why has only this particular combination the "compensation valve"? The others don't have one.

We are thinking it is that because this machine is running on much higher pressures then the others, but also this one is the oldest combination we have, so it can also be something which is used in the past.

Does anyone know the answer?
Thanks,
Cryotechnic

"Math is the ruler of your potential succes...."

 

[asukid99]

Can you describe how this valve is piped in to the expander process? Do you also have a recirculation valve on the compressor-side of the unit? Have you tried starting the unit without opening the valve? Can you monitor the compressor-side bearing temps during startup?

 

[cryotechnic]

When the compensation valve is opened, gas from the compressor inlet is fed to a chamber where a piston (disc mounted on the shaft) is, and so creating a force with a direction away from the turbine.

There is no compensation valve at the turbine, and there is no bypass at the turbine.
There is only a bypass at the compressor.

I am not sure if it is possible to start the combination when the compensation valve is closed... I will check that.

What I do know is that we have to close the compensation valve manually after the start-up, so in that case it's possible to run the combination with the compensation valve opened. In my opinion, that's not a recommend situation, because then your actually have 2 forces (1 too many) on your compressor. Then you have the compensation force and your "normal" force.

It's a good point to check the temperatures of the bearings. We don't have a good read out since this machine is very old one, but we do have a temperature read-out. (too bad, we don't have a trending)

Thanks in advance,
Cryotechnic.

"Math is the ruler of your potential succes...."

 

[cryotechnic]

Ok, I checked the compensation valve. The valve opens automaticaly at low RPM's. (why they have choosen RPM's we don't know, our idea was: they have to let it switch on something.......)
So opening is automatic, closing is manual.

Cryotechnic


"Math is the ruler of your potential succes...."