Blanketing of Boiler Feed Water Tank with Floating Balls? 5

[Htech01]

I am currently doing a study for an economical way to blanket a 5,000 M3 Boiler Feed Water tank. The tank doesn't have a blanketing system at the moment, and is atmospheric tank breathing to air. Therefore the plant experiences corrosion problems caused by the dissolved Oxygen in the water which was introduced by contacting with air at the tank.
The usual way to improve this, I think, is a Nitrogen Blankeing System. But someone says he heard about using floating balls in lieu of N2 Blankting system. To a little bit more explain this: to add floating balls on top of the water in the tank by a few layers, and this floating balls reduces the contact of water with air and thus serves as a simple blanketing system. If this works it will be much cheaper than the N2 blanketing system to operate.

Does anyone out there hear about this? or know anything about this?

It sounds like to work, but it does not completely prevent air contact and thus still have some Oxygen dissolve into the water. Then the question is how much will be the Oxygen content, or by using certain floating balls how much contact surface will be reduced in percentage?

Thanks,
HTech01

 

[Compositepro]

It would help but to work well the water under the balls would have to be near boiling. injecting a little steam into the water would provide some O2 stripping though the "packed bed" of floating balls. If your feed water tank is not hot it will not help much.

 

[cheute79]

You could also look at adding water treatment to scavenge oxygen.

The effectiveness of the balls is also a function of the diameter of the balls.

 

[Htech01]

The water temperature in the tank is close to ambient temp., so it is not warm...

 

[TBP]

I have heard of an application where ping-pong balls were used.

 

[Htech01]

Thanks for your posting TBP,

Can you explain a little bit more?
Do you know how the performance was - reduction of dissolved oxygen or reduced corrosion?
How much layers did they used?

Regards,
Htech01

 

[TBP]

I had no direct involvment with the application. It was someone I worked with years ago, who had seen it done in another plant where he had worked. As far as I remember, the ping-pong balls did the job. And they're cheap, and readily available.

 

[rmw]

Ping pong balls have so much bouyancy that they would only cover a portion of the surface of the water and the rest of it would be exposed to atmosphere, and probably enough so that the ping pong ball effort would be pretty much negated IMHO.

Why not just pour some oil on it? Just be sure to never pump it all the way down. See the tongue in cheek......

rmw

 

[TBP]

My collection is that the balls were several layers thick.

 

[rmw]

That would make a more tortuous path but not a seal.

rmw

 

[Htech01]

I don't think pouring oil will work. Because the oil will dissolve into water even very small amount, and that is not acceptable to boiler feed water.

Having balls floated on the water surface will definitely reduce surface area of air-water contact and thus reduce the oxygen dissolving rate into water. So I have no doubt that it will have positive effect. The question is how much!
Also in either case, oxygen will only dissolves up to the saturation concentration at that temperature. And if the water residence time in the tank is long enough to go to the saturation even at the reduced surface area with floating balls. That is my doubt.

So I am wondering what's the result in the actual applications.

By the way I have mistaken about the water temperature in the Tank. It is actually quite warm at 80deg-C.

Waiting more advices and comments,
Thanks,

 

[unclesyd]

Though I've never seen them used in a situation as in your OP I have used them on some waste recovery tanks for both odor and evaporation and to conserve heat. All the literature I have says they will impede mass transfer and that whats you are looking at. Air water contact is largest mode of O2 transfer in lakes and oceans.

http://www.euro-matic.com/hollow.html

http://www.paradisenw.com/bird_ball_cover.php

 

[unclesyd]

Here is information on the balls I originally used and on this page specifically mentions O2 adsorption.

http://www.ritter-chemie.com/english/01b9a392af1093d01/01b9a392af114a533/01b9a392af114a536.html

 

[unclesyd]

A little more information form the UK.

http://secure.processengineering.co.uk/Articles/274109/A+blanket+of+protection.htm

 

[Htech01]

unclesyd,

Thank you so much.
These are exactly what I am looking for.

 

[btrueblood]

Unclesyd, a star from here too.

Htech01, this is a very interesting question, as we have some open water storage tanks that we use for testing, and have been dosing for corrosion control. Would be interesting to see if you come to any conclusions regarding your question. Could you please post any conclusions you reach here?

 

[Htech01]

It will take some time before I come to the conclusion, around a month.
But I will definitely post my conclusion and rationale later in this Thread.

 

[btrueblood]

Even better, Htech. Looking forward to it.

 

[mxmaciek]

Have you noticed that the mentioned system has the "stabilizing rings" around the each ball?
I think this is the clue of that method. Without it the balls will rotate, (i.e. in case of pin pong balls) and if so, each ball will be covered by thin water film, perfectly expanding the exchange surface, and thus, extending the oxygen and carbon dioxide dissolving process.
If your water already is 80C... well, it's not far form old type degasifier, where steam at 105C was bubbling through the water.

 

[cub3bead]

A couple of things need to be added to this discussion.

The water entering the tank must be deoxygenated or the tank dosed with an oxygen scavenger. The floating balls only reduce the surface area exposed to the atmosphere which limits the rate of absorption of atmospheric oxygen. If the water in the tank is saturated with O2 the balls won't help.

Don't try this with ping pong balls, use HDPE balls. DI water is very corrosive and may attack the ping pong balls. HDPE is virtually immune to this type of corrosion.