Hello,

I am working in combine cycle power plant. We have 260MW four STG available at our plant. We are facing problem in STG condenser level transmitter. we have DP type level transmitter with condensate pot.

In each STG we have three DP transmitter with individual condensate pot available at our plant. it has observed that at normally 15 to 20 we found transmitter reading drifting in one out of three transmitter. during checking found its condensate pot empty.

We checked following things to solve problem
- check transmitter installation found ok
- leakage checked and found no leakage
- check insulation of condensate pot and found normal

One observation is that for all three condensate pot we have common isolation valve. after isolation valve we have individual isolation valve for each condensate pot. Is this one reason for level transmitter reading deviation?

Please advise and suggest what to do.

 

Several questions here--

Has this problem just surfaced, or has it been an ongoing problem since construction?

How long has this unit run without a major outage? Have you had any chemistry excursions in the last year?

How long has it been since the turbine has been inspected (specifically the hotwell?)

Since you have three sensors, I'm assuming it takes two out of the three to initiate a shutdown--has this occurred? A rigorous sensing arrangement would use three separate sensing lines, dedicated to the three sensors.

As this seems not the case, and you have a common valving arrangement for the sensors, I might suspect some clogging/trash in the lines causing your problem. The sensing lines and pots should be fabricated of stainless steel, preferably of 304 Stainless at minimum.

 

Hi there,

Flush the lines properly. go for open inspection of hotwell and cleaning.

then see the results.

 

hi

thank for showing interest and supporting us

I will give you point wise reply-

-- Yes this problem is since construction. plant commission since last 3 years.

--- Still no major outage. on an average every year 5 to 6 month unit is running.

--- Hotwell was last inspected before 1 year.

--- Yes two out of three logic will initiate shutdown. hence our continuous monitoring we are doing. if mismatch we observe between transmitter then we force logic and once closing isolation valve we are filling condensate pot and after once taken in line reading again appear normal.

--- Yes line and pot are SS316 material

--- we have also checked by flushing impulse line but still problem persisting.

please advise what may be the issue with the transmitters.

 

Are you sure that the conditions promote condensation under a vacuum?
What is the temperature and pressure of the condenser?
What is the pressure and temperature of the condensate pot?

Perhaps you can run it as a dry leg, either that or cool the pod down some way.

 

You might use an infrared imager to look at the three transmitters installations for differences or something out of the ordinary that might indicate what the problem is.

William (Bill) L. Mostia, Jr. PE
ISA Fellow, SIS-TECH Fellow,
FS Eng. (TUV Rheinland)
SIS-TECH Solutions, LP

"No trees were killed to send this message, but a large number of electrons were terribly inconvenienced." Neil deGrasse Tyson

Any information is provided on Caveat Emptor basis.

 

I would agree with this. Seems like you may have leftover gunk in the hotwell that may be migrating to the level pots.

>Flush the lines properly. go for open inspection of hotwell
>and cleaning.

When inspecting make sure the hotwell joints at the steam interface are free of contaminants. there are usually "H" shaped joints where the hotwell structure is fused to the steam dump metal from the turbine that can fill up with garbage--metal/sand/old welding rods, etc. you should have seen the results of this in the hotwell chemistry monitoring program if you have one.

 

Hi,

Here's some points may help:

- check the isolation valves and replace if needed.

- flush and clean the lines and condensate pots.

- try not to fill the condensate pot with water , close the transmitter manifold isolation valves and let the steam condensate to fill the condensate pot to be sure that the lines and isolation valves are ok

- flush and clean the transmitters manifolds.

Kind Regards,
---------------------------------------------------------------------
Eng. /Ali Mohamed Soltan
Electrical & Automatic Control Services
General Manager Assistant
Assuit Oil Refining Co. [ASORC]

 

This almost seems like you may have a condensate contamination problem-putting contaminates into the level pots.

What is the condensate chemistry? Do you have high levels of silica in the feedwater? or maybe Chlorides in the water? a condenser leak?