UNABLE TO LOAD TURBO EXPANDER OF ASU
UNABLE TO LOAD TURBO EXPANDER OF ASU
(OP)
Dear all,
We are having a turbo expander in cryogenic air separation plant. Few days ago, the lube oil pump tripped due to some electrical issues and the turbine tripped. Mean while the bearing temperatures of the turbine and booster bearings gone upto 180 deg C. After rectifying the electrical issues, we re started the turbine and the vibration levels are found to be high ( 56 microns in place of 4 microns under normal conditions). Hence we replaced the turbine cartridge with new cartridge.
On running the new cartridge, the rotor reaches its full speed of 58000 rpm for inlet pressure of 35 bar G and IGV opening of 34%. This is highly unusual as the normal operating condition is that the roto will reach max. 52000 rpm for inlet pressure of 42 bar and IGV opening of 50%.
Since the equipment has reached its full speed for such lower inlet conditions , we are unable to load the equipment further.This affects the plant's production drastically.
What may be the reason for such abnormality????
Note : Old and new cartridges are of same specification and of same make
We are having a turbo expander in cryogenic air separation plant. Few days ago, the lube oil pump tripped due to some electrical issues and the turbine tripped. Mean while the bearing temperatures of the turbine and booster bearings gone upto 180 deg C. After rectifying the electrical issues, we re started the turbine and the vibration levels are found to be high ( 56 microns in place of 4 microns under normal conditions). Hence we replaced the turbine cartridge with new cartridge.
On running the new cartridge, the rotor reaches its full speed of 58000 rpm for inlet pressure of 35 bar G and IGV opening of 34%. This is highly unusual as the normal operating condition is that the roto will reach max. 52000 rpm for inlet pressure of 42 bar and IGV opening of 50%.
Since the equipment has reached its full speed for such lower inlet conditions , we are unable to load the equipment further.This affects the plant's production drastically.
What may be the reason for such abnormality????
Note : Old and new cartridges are of same specification and of same make





RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
is your IGV system hydraulically actuated and fed by a common lube oil circuit (control oil and lube oil) or is it pneumatic ? just speculating here: if the IGV does not adjust to 50% (suppose this is the set point), then the capacity controller would increase the speed to reach the desired outlet pressure. Again just brainstorming..
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
The indicated pressure is the inlet pressure of the turbine.
The other side of the turbine is a gas booster.
We do not have any auto capacity controller, IGV (pneumatical) of the turbine is controlled manually.
Let me explain our process for better understanding.
# We will start the turbine by opening the IGV manually (upto 50%) with inlet gas at 42 bar where it expands to 5 bar causing a Temp. drop of 50 deg.C
# we will watch the other side of the turbine (gas booster) to do its work - Compresses the gas from 42 bar to 60 bar. We do not give any set point or any other auto control input to the booster. The above mentioned compression will be pertaining to the speed of the turbine (normally 52000 rpm).
# And now, we have opened the IGV of the turbine only upto 35 % with inlet gas at 35 bar, but the rotor has reached its full speed of 58000 rpm.
# And also for such higher speed the gas booster is compressing its fluid from 41 bar to 47 bar only. This outlet pressure of the gas booster is important for us to achieve full production from the plant.
Thus we are not getting the rated discharge pressure of 60 bar from the booster, but the rotor has reached its full speed.
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
Best regards, Morten
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
Thus my question: how confident are you on the accuracy/reliability of the measured 58000 rpm speed?
How is you speed measurement system set up / what type of speed probes are you using; my point is, is there any chance that things may have been affected/upset during bearing replacement procedure ? Also, has the inspection revealed any noticeable damages on the other rotor components apart from damage on bearings?
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
Some one has changed the setpoint on this brake side compressor discharge PIC from 60barg to 47barg - why?
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
# we will watch the other side of the turbine (gas booster) to do its work - Compresses the gas from 42 bar to 60 bar. We do not give any set point or any other auto control input to the booster. The above mentioned compression will be pertaining to the speed of the turbine (normally 52000 rpm).
unquoted
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
This change is a significant process modification, and there is nothing stated so far on what this may be. Anyway, it is now clear that this is the cause for not being able to load up the expander to design flow at 52000 rpm.
The author of this process change in this plant is probably well aware of this bottleneck.
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
A complete dissembly, repair and dynamic rebalancing of this turbine-compressor assembly at 52000rpm or so at the manufacturer's shop may be a likely scenario for this machine.
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
on thorough analysis of the entire system, we found that the speed transducer is malfunctioning - it is giving higher feedback of the speed than the actual (Reading 58000 rpm in place of the actual 39000 rpm).
Hence all through this period we were running the equipment at 39000 rpm only. Not as what the transducer read 58000 rpm.
Operating parameters of the turbine and the gas booster are normal for this actual speed of 39000 rpm.
We replaced the speed transducer with new one.
Now we loaded the equipment to 52000 rpm and we are getting 60 bar at outlet of gas booster.
Thus our problem in loading the equipment is solved now.
Still, the reason for the malfunctioning of the speed transducer is unknown.
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU
RE: UNABLE TO LOAD TURBO EXPANDER OF ASU