Hi Guys,

After a Major outage in one of our GE 9e units we are experiencing heavy white mist oil, when running in base load.
I sometimes appears after 30 min and sometimes after one hour. If the unit is held at 60MW for about an 30 min before going to base load, the heavy mist doesn't appear. We noticed the negative pressure in the L.O tank turns to positive shortly after starting the unit, causing the NRV bypassing the oil mist eliminator to open.
During the outage a refurbished shaft was installed, and house alignment was performed.
Oil samples were taken and the oil is free of water, and with good qualities. (the oil was changed 1.5 years ago).
The oil temp at the bearing drain lines is between 90-100 deg. Celsius. While the outside drain line is at around 70 deg. Celsius.
The mist looks like white smoke, smells like burnt oil and leaves no signs of oil on the surface close to the unit.

Has anyone experienced similar symptoms? overheating of lube oil? excess air in the lube oil return lines?
Any other ideas?

Thank you very much!

 

Bagi,

The Mark* does not control anything to do with the Cooling & Sealing Air system which is what controls the air flow to the bearings which is probably the source of the higher-than-normal pressure in the L.O. tank/reservoir, and it's likely that some orifices in the various lines were not installed or were installed improperly.

Also, it could be a problem with the #2 bearing vent installation (on the roof of the turbine compartment).

But this is most likely not a controls-related issue.

Someone might be able to help if you could provide the .pdf files of the entire Cooling & Sealing Air system and the L.O. system, including the mist eliminator.

 

Bagi, I would agree with CSA that this is most likely an issue with the cooling and seal air system.

I would suggest reviewing the P&ID specific to the system and verifying that all the orifices are installed in the proper locations. These were most likely removed when the turbine compartment roof was removed for work.
It is possible there is an issue with air seals in the #2 bearing area or a problem with the #2 bearing vent pipe assembly causing excess pressure in the housing. The #2 bearing vent pipe is a pipe in a pipe in a pipe, a very interesting design that if not assembled correctly can cause sealing air to over-pressurize the lube mist separator.
The lube oil tank should be under negative pressure at all times. The machine I maintain here in the states is a Frame 7EA which is similar to yours. I have found that for our machine if lube oil tank pressure is more than 1.2" H2O positive an oil leak will develop from the gearbox area.
If your unit uses a valve to port either 11th stage or 5th stage compressor air for bearing sealing make sure it is operating properly. If it is not operating as designed the pressure for bearing seal air will be higher than design.

Again as CSA suggested sharing a P&ID of your system could help us make better suggestions. Over the years I have learned that each machine built by GE may not be the same as the next, so assuming how I think your machine is configured could lead to wrong assumptions.