Hi guys,

We are using GE MS9001E Gas turbine. We have problem on low output after smoke coming out from the extraction pipe from bearing #2.After running for 1 hour in base load, the output has started to decrease, from 110MW to 99MW.

There are some data recording during the event:

CTIF, inlet temperature: 31DgC

CPD, compressor discharge pressure has dropped from 10.2 to 9.5 bar

Bearing #1/#2/#3 has higher lube oil temperatures, increase about 10 dgC from normal value.

Highest is at bearing #2, for 97.72dgC. Compressor discharge temp; 382dgC.

Bearing metal temperature for bearing #2 increased up to 92DGC. Normally temperature is around 87DgC.

The air for cooling and sealing is taken from the extraction of Stage 5 from the compressor. I am quite confused whether the cooling/sealing air had low pressure or the bearing #2 itself. Need assistance on how the output has affected, and root cause of the problem, either the cooling air low pressure or the Bearing #2 has damaged.

Thank you. Cheers.

 

Dear Fayzl

Do mention the Lube oil header pressure and temperature vibration siesmec as well as proximeter on bearing#2 and overall train is affected if comparatively high.

Did you receive any alarm in alarm summary?

Mention Filters Total DP and IGV opening degree.
What are observations regarding smoke from bearing 2 at base load normal or high smoke?
What are turbine compartment and load compartment and load tunnel temperatures?
Also do check purge air control valves either bypass is in open state or closed?

 

Fyzal,

How long was "smoke" seen coming from the vent pipe?

Is there any idea how long smoke had been coming out of the vent pipe and when it started?

"Smoke" coming from the #2 Brg. vent pipe is not a good indication. It was most likely caused by oil overheating because of a lack of cooling and sealing air, but why that happened is not clear. Some machines have a pneumatically-operated valve that opens and closes to ensure there is sufficient air flow during starting, shutdown and low load operation. I can't recall the designation of the valve, but there was usually at least one limit switch which annunciated a Process Alarm if the valve didn't change position. What alarms were/are present (both Diagnostic- and Process) before, during and after the "smoke" was observed?i

Did this problem occur after a maintenance outage?

After a turbine trip from load and a re-start?

Can you say what caused the "smoke" to stop?

It's presumed the unit is being operated with Base Load selected and enabled/active, with the IGVs fully open and that the data you are reporting is with the IGVs fully open and Base Load active. The drop in CPD would cause the output to decrease.

The elevated bearing drain and/or metal temperatures (it's not clear which you are referring to) are indications of a problem with cooling and sealing air flow. High flow could be the problem as easily as low flow, but the position of the #2 Brg. sealing air valve (if so equipped) is critical to know and understand. It may have "stuck" and is now in the correct position, but damage may have been done.

Also, what was the grid frequency/turbine speed doing during the smoking?

In general, this is not a good condition to continue operating the turbine in without understanding the cause and effects on internal components. Unfortunately, the only way to examine the internal components is to disassemble the machine to get to them.....

Please write back to let us know how the situation is progressing and how it is eventually resolved.

 

Fyzal,

If I recall correctly some Frame 9E machines also had a strainer/separator underneath the forward end of the axial compressor, which had isolation valves which could "accidentally" (though there's really no such an occurrence as an accident) left in the wrong positions.

But, again, since the output is significantly affected there is something amiss--unfortunately the only way to really determine what's wrong and the extent of any damage is to open the unit. A borescope might help increase the need to open the machine (by seeing some indication of a problem).

Wish the recommendations were better.

 

Dear SB,

The lube oil pressure is 1.85 bar, and temperature (LTTH-1) is 66.6dgC.
At bearing #2, we have only siesmic measurement which is normal, 4.6mm/s.
There is no alarm obviously at the alarm summary. make it more difficult to troubleshoot.
For air intake total dp, as we have just replaced the cartridge filters (donaldson), the DP is 0.01 Dapa.IGV opening is 83.4dgA during base load.

Regarding the smoke at the vent pipe during base load, the smoke is high, i would say because the smoke could be sucked in by the neighbour GT intake house.

the temperature measurement at both turbine compartment and load compartment is still below the high temp alarm which is less than 145dgC.While at the load compartment the temp is below 200dgC.

About the purge air valve, which purge valve are you referring to ?

 

Hi CSA,

Smoke is seen from the venting pipe since from Full Speed no load, and getting worse when it is in base load.

We have had rectification on the stator bars on the generator, and the unit has been OFFLINE for more than 2 months.


Obviouly, when the unit has shut down, the smoke will slowly went off.

The data given was at Base load, on gas. and Maximum angle of IGV .

At the bearing #2,
Lube oil temp bearing drain : (LTB2D) = 97.72dgC
Bearing #2 metal temp (BTGJ2) : =91.92dgC

Frequency is 50.05Hz and speed is 2999rpm.

At the moment, the decisions still have not been made by our management, and the unit is still declared available, and as today, the unit has its worse output at CTIF 31dgC, when the load is only 95MW after prolonged base load the day before.

[email protected]

 

At the moment, we are planning to check the extraction pipes for the sealing air, which taken from stage 5 of the compressor, move on to the valves, orifices and also the strainer/separators.

Will update you guys soon.
thanks

 

Fyzal,
If this is a problem with some kind of L.O. leak in the #2 Brg. area (which is what I suspect), then if the smoking is continuous and as bad as you say then the L.O. Tank level would be decreasing and would require replenishment of the L.O.

Has anyone checked the L.O. Tank level during this incident?

In my estimation the smoking is caused by burning L.O., which is not being properly contained in the #2 Brg. housing, probably because of failed seals due to some issue with Cooling and Sealing Air.

And don't rule out a problem with the L.O. Mist Eliminator, either.

Still, this is not a minor incident, especially with the load decreasing.

 

Fyzal,

Lube oil header temperature is quite higher, I think that it should be in 50~55C, try to adjust lube oil header temperature in above mentioned range then observe the behaviour of smoke.CSA highlighted very good observations as usual.

1- Check lube oil tank level and suspicion of leakage of lube oil at bearing 2

2- Check Mist eliminator either working or not? Note down the lube oil tank vacuum reading, its normal range is -100~-150mmH2O.

Sorry Actually I have to write Atomizing air bypass valve instead of purge air, as you did mention that CPD is decreasing. if this valve is remained open it will impact on CPD and give raise in purge air pressure. again a significant loss in out put is not suspected due to bearing N.2 smoke. There may be air leakage from axial compressor output lines or any abnormal opening of normal close valve. These will not contribute to such a high power output loss

What is load tunnel (TTIB) Temperature if it is on higher end it will also tend to decrease the turbine load? and what is position of Turbine frame cooling blowers 88TK1/2? Is turbine running on open cycle or combined cycle? if combined cycle then what is back pressure? What is condition of excitation and generator RTD's?

Turbine is on base load and if frequency remains on higher end >50HZ, load limit is activated that will hold the load of GT at the time of frequency memorized. Is there any status like this?

 

Hi all,

Some updated from site by our Mech team.

We managed to drain some amount of water trapped in the water separator, (at the AE5, extraction of Compressor stage 5). The sealing air pressure has increased from 0.6 to 1.2 bar. Which in turns improving the sealing at the labyrinth seals at bearing no 2.

Vacuum pressure at the oil mist eliminator has been improved by taking out some filters, until the vacuum pressure is -50.9mmH2O.

As a result the smokey mist at Bearing no 2 has gone,after running up the unit for 4 hours on base load. The output has improved from 97MW to 104MW at 32DegC.

But, the output still comparatively lower compare to other units, which @32degC the load shall be 108.5MW.

We noticed that the CPD still suffering at 9.8-9.9 bar at baseload operation. The pressure normally at 10.1 bar during baseload.

What else can cause the CPD pressure drop out? I don't think its the bleed valve, or else the vibration will be very high because of imbalance pressure.

suggestions are so much welcome

 

Fyzal,

Thanks for the update.

As for what could be causing the drop in CPD, quite often when some disturbance or event like the one being experienced occurs the lost CPD is not recoverable. Once cooling and sealing air flows have been interrupted, it's likely the internal clearances of various components of the machine have changed, and will not return to normal when the problem is corrected.

Also, it's not very common for similar units, installed and commissioned at the same time, to all produce exactly the same power output (and CPD). There are too many factors which affect axial compressor efficiency and machine conditions for multiple units to all operate exactly the same. If the maintenance outages were all done at exactly the same intervals, and the procedures all performed exactly the same, and the reassembly procedures were all identical, and the inlet air filters of all the units were operating at exactly the same differential pressure, and the units were all operated identically (the same loads for the same periods of time between maintenance outages), then it might be conceivable the units SHOULD operate at the same power (and CPD) but it still wouldn't be likely. All internal clearances would have to be exactly the same all the time, and that just isn't likely.

As for compressor bleed valves passing, that's not too difficult to check--using an infrared heat sensor ("gun"). If the unit has been running for some time, the temperature measurement on both sides of the compressor bleed valve should be the same (indicating there is no flow through the valve). If the valve is passing, then the temperature on the upstream side of the valve would likely be higher than the downstream side (because of the pressure/temperature drop across a throttling valve).

The problem with using an infrared heat gun/sensor on compressor bleed valves mounted in the turbine compartment is that it's very difficult to get a good measurement on all the valves in roughly the same location on all the valves.

I have seen compressor bleed valves fail full open when the unit is producing power on line, and there has been little or no increase in vibration. When the compressor bleed valves are open at rated speed the result is a loss in efficiency because compressed air is "vented" to the exhaust and the energy used to compress the air is lost, in addition to the lost mass flow (of air) through the machine.

Again, thanks for the update.

 

Please check the tell tale drain valve of Bearing no. 2 under the machine if situation permits for being OPEN. if it remains closed and leakage happens, it can flood the bearing housing...

Logivlover

 

Dear sir,

we are facing some problem mention above in FRAME -VI 9171E.

1) when we start machine, our tank vacuum is OK. But when machine reach FSNL its vacuum became zero, and smoke is coming from bearing-2 vent line ,so again we have to adjust the vacuum.

2) Last time when machine run near about 80 MW for approx 3 hrs then its automatic load reduced automatically 15 MW due to inner barrel temperature was found 230 deg. C. So machine kept on this load and start extra VG fan and watch the load tunnel temperature. same time when machine on higher load, BRG-2 vibration was found near varying 7-11.5 mm/sec which was not noticed earlier (seismic type).

3) After 3 hrs IGV temp kept off so load increasing margin get and machine run for 80 WM with inner barrel temperature 220 deg. C. Bearing-2 vibration was on same range as mention above.

please help me to solve the issue.

1)can we check 5th stage extraction filter as mention in this solution?

2) bearing-2 inspection is required?

3) reason for inner barrel temperature increasing?

4) lube oil tank vaccum was going down from starting to FSNL?

mail me on [email protected]
thanks in advance.