Deaeration/02 removal, Can Mechanical remove 100% 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


FLORIDA,
BIGDOG50

 

[Fizzhead]

BigDog50:

Well, you are right and then again not quite so right. By raising the temperature of the water, you can indeed drive off what would be "chemical oxygen" (i.e., dissolved oxygen), but only to a certain extent. As long as air is still present inside the DA, the air and water will try to maintain equilibrium. Raising the temperature decreases the equilibrium concentration of oxygen in the aqueous phase, but cannot drive it all the way to zero. but it can get mighty close. I bet this is what your manager is referring to and maybe, though I wouldn't have thought so, they are keeping levels low enough to either eliminate, or dramatically reduce scavenger chemical needs.

 

[cub3bead]

You get down to 0.005 cc/l (7 ppb by weight)with the type DA you are describing. Getting lower takes chemical scavenging.

Improtation of oxygenated treatment from Europe especailly for supercritical units seems to be attracting a lot of attention. O2 is added into the feedwater after the condenser but it is controlled. This treatment technology is intended to assist in controlling Flow Accelerated Corrosion (FAC).

You should turn off the pegging steam after the STG is loaded sufficiently to provide the DA stripping steam.

 

[bigdog50]

Thanks Cup3bead, I have been trying to relay this message. I called the Vender today to request additional info, they were supposed to email it today. Will wait and see what happens. Thanks again.....

FLORIDA,
BIGDOG50

 

[rmw]

cub3bead,

Is your statement true with a side mounted vacuum deaerator deaerating aerated make up, operating at 26" hg vac,. or 3" HgA? Does the difference in the oxygen soluability of water at 116F vs 250F for a 15 psig DA permit this?? I just can't remember. It has been a long, long time since I learned all that stuff.

I know that condensers are designed to keep hotwell condensate that low, but, they are just removing small amounts of air inleakage, free air that won't begin to saturate the water if it is kept from subcooling.

If condensers encounter adverse conditions, such as very very cold CW, or low steam flows, or both, then they have to introduce stripping steam through spargers to reheat the condensate above subcooled temps.

rmw

 

[cub3bead]

Graham's DO2 condenser was the first followed by Ecolaire's design(now Alstom)to use steam from the condenser shell as the stripping steam source for deaerating condensers. These designs came out in the late 80's early 90's when the cogen businesss was really taking off.

Conventional surface condensers always offered some degree of dearation but couldn't keep up with the O2 load when you had a high makeup rate as in a cogen plant.

Graham has an external vessel for doing the deaerating while Ecolaire shared some of the vapor space inside the condenser shell.

There are a number of technical papers on the Graham web site that detail the technology.

http://www.graham-mfg.com/techlib.html

The payoff in cogen plants for these condensers is by getting rid of the pressurized DA you can get much lower stack temperatures thereby increasing the overal plant efficiency.

rmw you are correct that at part load and/or in the case of low CW temp you may have to turn on the sparging steam to get proper deaeration.

 

[rmw]

I am not sure that the sparging steam does any deaeration, just that it heats the conensate, and prevents it from subcooling, and absorbing O2 while subcooled.

In other words, does sparging prevent aeration of subcooled condensate, by keeping it at a saturated temperature, or does it actually deaerate.

In my mind, if sparging steam was a good deaerating method, then DA's would simply be water storage tanks with spargers. I ask this as a question seeking input as I have had this discussion with some condenser designers several times, and they know condensers, but wouldn't know a deaerator from a boiler.

Some of my clients bring their make up in over the tube bundle, and spread it over the bundle, so that it can fall through the bundle, much as water falls throught the tray section of a DA, and by getting all the steam contact with the droplets, they think they get better deaeration of the make up.

comments??

rmw