Need a little advise. The steam power plant im working ats vacuum has dropped consistantly over the last week or so. Ive trended in/outlet condenser circulating temps, vacuum, load, gland seal steam pressure and temps etc. I cant get a hotwell temp on the trend so that out of the question. Would warn labrynth seals on the LP end of the turbine aid in the dropping vacuum? We havent had a turbine casing pulled in way too many years, so I have no clue.

Typical loss off vacuum is caused by air leaking into the surface condenser through the joints or packing glands. If you have an air ejector, make sure its assisting with drawing proper vacuum. Most issues related to the air ejector can be attributed to the nozzle errosion, the strainer protecting the nozzle is clogged, or the steam pressure to the nozzle is too low.
What are the temps of the seals on the LP end? hotter than normal temps could enlarge clearances and effect the seal. What is the rate of decay from the normal operating vacuum? What type of turbine do you have?

I suggest double checking your valve lineup if you are cycling your unit but if it was online when the problem occured, its not likely related to a lineup issue but hardware degradation, instrumentation, or controls.

We do have a steam jet air ejector in service as well as our hogging jet to keep the vacuum as high as possible right now. When I got off shift the other week vacuum was fine and when I returned it started to slowly degrade. Vacuum has not changed for a couple days, but is still very low. This was also after a cycle of the unit. We vented the water box recently with no change in vacuum.

The temps going to the steam seals on the LP turbine are around 300*F and are usually at that temperature (startup is 500*F). The decay of vacuum is very gradual and bumps around the +/- 26.20" HG mark. With lower loads, the vacuum will improve by about .5"HG.

The turbine is a Westinghouse, tandem compound reaction with reheat (curtis stage in the HP as well) (HP,IP, and LP sections) rated at 145 MW. Last turbine outage to look at bearing/seals... was many a moons ago.

One last thing is that I trended the condenser circulating outlet temps for both our units which have split condensers on each. On the other unit, both outlet temps from the condenser were pretty close to each other and within reasonable range. On one of the sides of the low vacuum condendser there is about a 5-6*F difference in temperature from the other side of the condenser. Im not familiar to what should be the reasonable limit so Im not sure if tube pluggage is to blame or maybe theres air in the box.

Thanks for the help!

Also, intrumentation both mechanical and electrical (honeywell) show the same temps and pressures.

Im going to find out the last time the air ejectors had work on them as soon as I can. Night shift doesnt work too well in my favor haha.

have you done a helium test to determine if there is any LP turbine or condenser leakage? Or you could simply use the rag on a broomstick method to determine leakage.

We have not done a helium test yet because no one knows how to use the kit (Im new to the plant and i know its pathetic that no one can run the test successfully haha). I have tried the rag on the end of a long poll trick, but only to find out i still cant get into too many areas with it to check for suction.

based on my experience:

1. you check condenser surface area, make sure it is clean (you can do inspection for one room while the other still in service and you need to reduce load) this is if possible with your business operations

2. check for leakage around flanges, gaskets, valves etc, near ejector and condenser

3. check MP steam pressure which drives the ejector (is it according to the required pressure)??

4. check ejector drain and steam trap which send the condensate back to condenser (plug-up or not)??

5. check if someone has opened chest valve / valve after governor drain, maybe drain valve is open instead of steam trap, because condensate which goes back to condenser should pass steam trap, not through drain.

6. check your vacuum breaker is not in service

7. check level of condenser, it should be good, and check temperature of cooling water for condenser, it should be low enough to condenser steam

We had the unit cycled off the other day. While returning it back online we had good initial vacuum until load increased. This is also happening today after a cycle. So what ever it is, its load dependent. We are going to try and see if theres a leak at the expansion joint from the LP turbine to the condensor. Ill also check the above suggestions, thanks guys.

Also, one of the operators trended the regulator operation to the gland seals, and over the past month it has been opening alot more than normal and staying that way. Could it be bad labrynth seals?

Also, I asked about the turbine governor valves. I guess they leak main steam (chest) to the hotwell. increased hotwell temp could raise vacuum, but would this be enough to cause it to increase?