High electrical Current in Turbo Exapnder

[Youcef-OilGas]

Hi,

We have just started a new LPG train with AMB Magnetic bearing TurboExpander Technology. However, we noticed that there is a high electrical current in Recompressor side in this new TurboExpander, (Recompressor Side 17 to 20Amps; Turbine side 5 to 8Amps. This means since the current difference is big that there is high axial thrust. On the other hand, the existing Turboexpander are having (recompressor side 14amps, turbine 10amps) for the same process parameters (Flowrate 8million Std /Day, Inlet pressure 88bar & Inlet temp 5 to 10°c), so, small current difference.
Please if anyone can give us his point of view to solve this issue.

NB: The trip condition is 30Amps.

Regards,

 

[georgeverghese]

High axial thrust is usually an indication of some plugging due to ice or some high freezepoint chemical that may have happened during a recent process upset. See if you can run the standby expander, shutdown this unit and thaw / defrost it out. Then dry it with a stream of warm to hot nitrogen before restart. Hope fully the axial thrust differential amps will be less.

 

[Youcef-OilGas]

Thanks georgeverghes,

We tried what you proposed by depressurizing it and drying it with Nitrogen, However, still having the same problem.

For your information, we are having this unbalancing after reaching the inlet flowrate 300,000Stm3/hr @ the speed of 13000rpm, that means before this, we have balanced Rotor 12 Amps, 12 Amps on both sides of the Expander.

Regards,

 

[georgeverghese]

Well, in that case, there may be mechanical damage:
a) Some failure of automatic thrust control
b) Some failure of the rotor seal on the process gas side, which may be caused by dust or dirt in the expander side feed gas

or it may even be both of these.

These machines are highly sensitive to unbalance since they run at high rpm, so do not attempt to fix this problem yourself through your plant mech maintenance team; I doubt your plant has dynamic balancing equipment and maintenance skills for expanders. You may ruin the machine altogether ( which is what happened in my plant a long time ago). Call up the manufacturer and have them take it away for repairs. And find out the root cause for this mech failure. Btw, do you have a expander side suction strainer ?

 

[Youcef-OilGas]

Thanks again,

We have contacted the vendor specialist and waiting for the feedback.
We have strainer in suction side of Expander.

Regards

 

[pierreick]

Hi,
You should always contact the manufacturer, especially in the period time where the equipment is under guarantee.
Collect all the data (DCS/PLC) to support your findings.
My 2 cents
Pierre