Deaeration/O2 removal 2

[bigdog50]

Hello ENG. Can anybody tell me if there is a DA system that removes 100 % O2 by mechanical means? I'm working with an ALSTOM condenser with a side mounted DA. and I'm little confused why the operators are continuing to run Pegging steam to the system when they are a steady state. The manager of the facility says its because they want to removes all of the Oxygen! and they want to eliminate the use of limanox! In my exp. this is not possible, I think all DA's System only remove up to 7 ppb of O2. and rest is chemical removal. Thanks for any imput in this matter!

FLORIDA,
BIGDOG50

 

[rmw]

Some higher temperatures DA's can get down to 5 ppb. 7 ppb may be your limit with your vacuum deaeration, but no deaerator is 100% efficient. Life doesn't work that way.

What you have described is a deaerator for the cycle make up. Condensers have limited capacity to function as deaerators. I suspect that your cycle does not have a stand alone spray or tray type DA in the feedwater stream.

If you were to have a system where you did not have to add any make up, the condenser would eventually remove all the air from the system except what enters through the leaks.

When you add aerated make up, however, it brings more air in than the condenser can get out effectively with its design. Condensers are good at condensing, but not so good at deaerating.

Hence the side mounted DA, where the make up is heated and deaerated before being added to the hotwell condensate.

The oxygen soluability of water decreases as the temperature rises. But, I cannot remember where it ever goees to zero. Some chemist can tell us.

Everything I have said assumes that you have a constant make up requirement, even at steady state.

rmw

 

[bigdog50]

Yes that is correct rms, and I thank you for your response. I have never worked with a vacuum Da. before, all my experience is in direct contact/stray type DA's and we only ran steam to it on start up for heating and striping. once pressure reached 20 psig then pegging steam was removed. On this VAC. DA. We run Steam Continuesly is this the correct way to run the Vac. DA.?

FLORIDA,
BIGDOG50

 

[rmw]

No, actually, the reason this is side mounted is so that the turbine exhaust steam can provide the vacuum deaeration of the make up stream. The pegging steam would only be needed when there was no, or in some cases possible very little turbine exhaust available to do the deaeration. I agree with the PM about not running this steam all the time.

Now, possibly, there is something wrong with the DA, so the operators run the pegging steam, instead of relying on the turbine exhaust, or maybe it is just easier to leave it on, rather than having to switch after getting on line each day.

Try it without the pegging steam after you are on the line, and see what the results are.

I also assume that this side mount has its own vacuum system, separate from the main air removal equipment for the main condenser. Make sure that is all up to snuff.

If it is a liquid ring, try to get the coldest water in the plant to your seal water cooler, if it means running well water instead of cooling tower (if that is what you have) to it. Liquid rings derate fast in the summer time, as CW sources get hotter.

rmw