Nitrogen for Removal of Oxygen from Water 1

[xcbeast944]

Does anyone know of a standard for how much nitrogen is required to bubble through a unit of water in order to effectively remove oxygen from the water? Trying to decide on an appropriate flow rate of nitrogen through a bulk water tank in order to reduce oxygen pitting in components downstream of the tank. Any help would be appreciated. Thanks!

 

[sshep]

This (thread135-10369) gave some Henry law data sources to make a stripping calculation, including initial O2 loading. The N2 to water ratio required will depend on the temperature (assume atmospheric pressure) and design- you can use a countercurrent stripping tower to get the best effect. Steam is actually your best bet as per a BFW deaereator if you have excess low pressure steam, as solubility of air (incl O2) decreases with increasing temperature. Oxygen scavangers and corrosion inhibitors are another possibility if they are compatable with the process and economical.

best wishes,
sshep

 

[siretb]

Unless you add mechanical agitation, just sparging nitrogen will not be very efficient. It will work, but because the kl.a (mass transfer coefficient) will be lower, to some extent, you waste nitrogen.
As said by sshep, steam is a better choice. Yet just sparging N2 is technically feasible.
As a ball park figure use us (gas slip velocity of 1 cm/s)
us=volumetric rate / cross section

 

[moltenmetal]

You won't get far stripping water with steam until the water is boiling...

Bringing water to a boil to deoxygenate it makes sense IF it's boiler feed water, but not a whole lot of sense for other water use purposes- unless LP steam in your plant is both clean and "free". Don't count on the latter, because the boiler feed water to make that steam isn't free, even if the energy is essentially free.

Yes the kLa will be bad with a single sparger in a big tank. Yes you will "waste nitrogen" relative to what you could achieve in a properly designed continuous contactor. But you don't need to go down to 9 ppb oxygen for the OP's purposes.

How much nitrogen depends on lots of stuff: your target DO level, the purity of the N2, geometry of the tank and sparger, size of bubbles etc. etc. Not a question we're going to be able to answer for you for free with any accuracy on a public forum I'm afraid.

 

[25362]

Have you contemplated the use of vacuum ?
Can you describe the water volumes involved and the purpose of the desorption ? Are scavenging chemicals allowed ?

 

[moltenmetal]

25362 offers good advice on how to "steam strip" the water without heating it to the normal boiling point!

Unlike nitrogen sparging it may not be possible to do this in your tank unless your tank is really a vessel. But if you can de-aerate the water under vacuum and then simply inert the tank headspace with nitrogen, you may be able to get away with this approach.

 

[dogtop]

sshep recommendation can be implemented by using a vertical pipe of a given diameter and using a porous metal disc (

http://www.mottcorp.com/media/default.htm)

as gas sparger.

HTH

 

[bimr]

One would think that nitrogen stripping is unlikely to reduce the oxygen enough to eliminate the corrosion. This would have to be accomplished with a packed bed, not by simply bubbling nitrogen into a bulk tank.

The method used in the power industry is vacuum degasification and nitrogen inerting of the tank.

The degasification unit does not have to be large as a sidestream arrangement can be used on the tank.

 

[xcbeast944]

Thank you for the replies. Please note that the nitrogen sparging is not our primary method of removing oxygen from the water. The problem comes when we need to use makeup water from the tank which is open to atmosphere and contains around 8 ppm oxygen while the water that it mixes with contains less than 10 ppb. Adding in this oxygen rich water throws off the balance temporarily and puts us out of spec. I am just looking to reduce the magnitude of this upset to the balance.

 

[Casimo5]

Have you looked at this process...

http://www.grenlandgroup.com/minoxtm-deoxygenation-system/category365.html

Speaking with a rep from Grenland, I was told that 1:1 volume ration of N2 to Water will strip O2 down to 20 ppb or less. Not sure if it was a 1:1 volume ratio at operating conditions of ~3 - 5 barg, or normal meteres cube per hour of N2.

 

[bimr]

Have you looked at this process:

http://www.liqui-cel.com/product-information/tour.cfm

 

[nevine]

may be by several trials of different quantities, you will reach your desired concentration