Steam turbine vacuum keeps worsening

[1Kuks]

Hi all,

We run a 110 MW steam turbine which has undergone major overhaul.After this overhaul,the vacuum has been very good(below 90mmHg) with only one pump in service.But presently,the vacuum has worsened to 120mm Hg with two pumps in service.The vacuum pump is 2*100 skid.

We have performed several leaks scans to detect any point of leak which might cause the vacuum to worsen but could not detect any leak point..

I really need your inputs to resolve this problem.

Wait on your inputs.

Thank you

 

[ScottyUK]

Liquid ring pumps, or steam ejectors?

Do the instruments on the surface consenser indicate normal conditions for CW flow and inlet / outlet temperatures, hotwell level, and so on? Have you set up trends on your plant historian?

Just because you can't find a leak doesn't mean there isn't one.

 

[JJPellin]

I will describe what I would do if I had this problem on one of our turbines. Inspect for leaks using shaving cream at all flanges, joints and threaded connections. Check the split-line on the low pressure end of the turbine (including around the studs and nuts). Check the sentinel valve for leaks. Verify the proper operation of the sealing steam. Increase the sealing steam pressure to see if the problem improves. Run the hogger (if equipped) and see how the system responds. If the vacuum comes right back down, there is probably an air leak somewhere. Check the mechanical seal in the off-line condensate pump. If they are vertical turbine pumps, the seal normally sees discharge pressure when the pump is running, but vacuum when the pump is off. Start the second condensate pump and run both in parallel for a while to see if the vacuum comes back. Check the water seal on the Atwood Morrel relief valve on the vacuum system.

What type of vacuum pumps are you using? All of ours use eductors/ejectors. I have never seen a system with liquid ring vacuum pumps.

Are your condensers water cooled or air cooled? If water cooled, test the condensate for hardness to see if you are leaking cooling water into the system. If you use air coolers, check the plugs for leaks using shaving cream.


Johnny Pellin

 

[TheTick]

No information about thermal performance? Input and output temperatures versus flow? Energy transferred?

You assume it's a leak, but it could be a clog or something impeding heat transfer.

 

[dougarthur42]

Vacuum is also directly proportional to temperature in the back end of the turbine and the condenser and may also be related to hot well level. more info is need for sure. We also have a 110 Mw steam turbine unit and condensate, it operates better with 1 vacuum pump than with 2. When the second pump is running under normal conditions than it cavitates and break the water seal on the other pump causing lower vacuum. Maybe I am mixed up but isn't 120mm/hg better (more vacuum) than 90mm/hg (less vacuum)because mm/ hg imply negative pressure

 

[dougarthur42]

at least here 28.5 in/hg is better than 24.5in hg.