On site we have a steam turbine. The Lube oil skid is equiped with 2 mist eliminator fans. The OEM of ST states that there should be a 5mbar vacuum to ambient. in order to get the oil bak in the tank and not lose it. We usually worked with higher vacuum (20mbars). Also we experience the fact that the pipes of the discharge of the mist eliminators (common for both fans) have not only fumes but also oil coming out. This means that oil does not condensates and goes out on the atmosphere. Can you advise on that issue?

 

Please give the following,

Oil temp to/from cooler,

Level of lub oil tank.

Oli temp set points.

Bearing header pressure.

Output/% bypass.

 

Many times the OEM doesn't have all the facts, meaning they don't know exactly what is occurring and what is not occurring. Is there something which is contributing to a high pressure and requires a high suction pressure/flow to control or reduce? Lots of times, people ask questions like this without providing all the data for the actual operating conditions, and the OEM just presumes the question is regarding design operating conditions.

Also, OEMs aren't *generally* in the business of operating their equipment. They just design it, manufacture it, install it, and sell spare parts and service. So, sometimes, the design criteria just isn't quite what it should be. Sometimes, even though everything else in the system is operating as expected and to design parameters, the real requirements dictate that the operation requires a little "tweaking" to obtain proper operation.

Sometimes, the auxiliaries just don't work as required. A lot of OEMs are out-sourcing the design and production of auxiliaries, just providing vendors a document which says "Your equipment must do this or that." Many times the equipment works as required; sometimes it doesn't.

We just don't have enough information about the system and auxiliaries in use at your site, the design criteria, the actual operating conditions, the condition of the equipment (sometimes it wasn't installed or configured correctly), etc. Are you absolutely certain the mist eliminators are working correctly? Do they have loop seals which are properly installed and filled? Do they have dampers which are properly installed and adjusted? Do they have orifices which are properly sized and installed?

Has the OEM been to site to observe the conditions, take data, make adjustments, and then make recommendations? Do you know what the pressure on the L.O. tank is without the mist eliminators running? Is it higher or lower than the OEM anticipates or designed the mist eliminators to work with?

If the mist eliminators are manufactured by someone other than the OEM, have you contacted them to make sure they are properly installed, configured, and working correctly?

You also need to be aware of other criteria that the OEM may or may not be making you aware of: the negative effects of excessive vacuum on the system. Sometimes there are rupture disks on L.O. tanks; there's also the vapor pressure at which vapors can become volatile; etc.

So, it's not always just about a single value. It's about the system and how the system should be operated.

 

We have 200MW Alstom steam turbines on our site with two vapor extractors on each tank. One extractor pulls about a 2 inch water column vacuum. After 6 years of operation and no preventative maintenance having been performed, things started getting pretty messy from flex hose leaks and excessive oil vapor coming out of the atmospheric exhaust. Being an E&I that was tired of working in the oily pooled up oil, I read the book.

Turns out that contrary to popular belief, these Swedish built units do require annual maintenance. The blower squirrel cage also acts as a centrifuge. A felt lining on the interior of the drum apparently absorbs the oil in the air stream and directs it do a drain in the blower casing. Access to the felt is easy.

There is also an expanded aluminum screen that further helps prevent the oil from being blown out. To change this you have to pull the blower drum off which requires a special puller. Both the felt and screen are supposed to be changed out annually. Seven years is pushing it.

We ordered the tools and parts seven months ago and they still haven't paddled their way over from Sweden, but when they do, and the summer peak is over there'll be some mechanics jumping right on it I'm sure...