Sorry if this seems a bit too basic but here goes.

Ok basically a problem came up with the placement of our F6 lub oil vent by which supposedly oil was sucked into the mist eliminator..
by my understanding..a gap is usually maintained between the oil level and the vent pipe...

so if anyone can shed some light on how the oil would get sucked in principle, theory, anything..I would greatly appreciate it..

Even a nod in the right direction would be appreciated..so I could research more into this

Thanks in advance

Regards
Shilton

 

Have you looked at the Lube Oil system P&ID (Schematic Piping Diagram)?

Before the introduction of the L.O. Mist Eliminator the L.O. Tank was vented to atmosphere. This meant that L.O. vapours were vented to atmosphere. Sometimes the vent pipe was run to the top of the exhaust duct (on a simple cycle machine) and the exhaust heat was enough to make the vapours seem to disappear--when the unit was running. When the unit was shut down and the L.O. was warm/hot, vapours were still visible coming from the vent.

In many parts of the world, visible vapurs are not permitted. GE and their packagers tried a high-voltage precipitator with mixed results.

That's when the Mist Eliminator started being supplied. The theory is that a motor pulls the vapours from the L.O. Tank through a separator/filter vessel, which causes the vapours to have to make a series of changes of direction which should make the heavy oil vapours frop out of the air stream. There is supposed to be a loop-seal drain between the bottom of the Mist Eliminator vessel and the L.O. Tank, so the condensed oil vapours can drain back to the tank from the Mist Eliminator.

There are also usually some internal filter-like elements which also help to prevent visible vapors from exiting the vent to atmosphere. These require maintenance (see the manufacturer's instructions in the Service Manuals provided with the turbine and auxiliaries).

There is a motor which draws the vapours from the L.O. Tank through the Mist Eliminator vessel and discharges vapour-free air to the atmosphere. There is usually a butterfly valve on the suction of the motor to control the vacuum on the L.O. Tank.

You should find a Note on the L.O. Mist Eliminator P&ID that tells you how to set the butterfly valve, and it usually says to ad-seal just the butterfly valve to maintain a 1-2 in. H2O vacuum on the L.O. Tank <b>when the unit is at Base Load.</b> This means the vacuum on the tank is higher at low loads, and sometimes this means there is a visible vapour stream exiting the Mist Eliminator.

But, presuming the butterfly valve is set properly (and typically GE nor its packagers provide a gauge to monitor the pressure/vacuum on the L.O. Tank!--meaning the owner operator has to install one), the most common cause of visible vapours is lack of maintenance on the vessel internals. Or, some problem with the loop-seal drain piping or valving.

So, consult the P&ID to see how the Mist Eliminator is to be connected to the system and to see how the butterfly valve is to be adjusted. And consult the manufacturer's instructions for maintenance recommendations. And check the loop-seal drain to make sure it's working correctly (there is usually one manual valve in the line--which should always be open except for maintenance or troubleshooting), and also a sight-glass to see if there is oil in the loop. (The loop seal works like the loop seal of any sink or tub or toiler; it serves to provide some isolation between the Mist Eliminator vessel while connecting the vessel to the L.O. Tank.)

Other than that, it sounds like you are just reporting what someone else has said, maybe second-, third- or fourth hand. It's not clear exactly what is happening. But it's really difficult to suck/draw oil into the Mist Eliminator, presuming the loop seal is filled and working properly and the internals are maintained and the butterfly valve is set even remotely correctly.

 

Thanks for your reply...