Removing oxygen from water using nitrogen sparging
Removing oxygen from water using nitrogen sparging
(OP)
Hi,
I am having a difficult time understanding why sparging water with nitrogen removes the dissolved oxygen in it.
Could someone please help me understand the concept behind it?
I am having a difficult time understanding why sparging water with nitrogen removes the dissolved oxygen in it.
Could someone please help me understand the concept behind it?





RE: Removing oxygen from water using nitrogen sparging
Using N2 gas as a stripping medium also help to increase the interfacial mass transfer coeff and speed up the transfer.
Using N2 as a stripping medium in this application is the basis for a process license for better large volume sea water de aeration for a large petroleum EXPRO company.
RE: Removing oxygen from water using nitrogen sparging
I guess I don't understand the O2-H2O vapor phase aspect. If I have no oxygen in the vapor phase, how can adding N2 lead to a reduction in oxygen's partial pressure?
RE: Removing oxygen from water using nitrogen sparging
Matt
RE: Removing oxygen from water using nitrogen sparging
If you start with a batch of water, and sparge with a large amount of completely oxygen-free nitrogen, eventually the water will be scrupulously free of dissolved oxygen. You'll also lose some water to evaporation into the nitrogen.
In a continuous contactor, the ratio of gas to liquid flow, the number and arrangement of contact stages, the effective area of the gas/liquid interface, and fluid properties affecting the mass transfer coefficient, are all important to determine how much stripping of the target molecule occurs.
It's important to realize that concentration gradients are the driver for mass flow by diffusion even if there is a pressure gradient which you might think would drive the flow in the other direction. While it is possible to make diffusion "stand still" or even to reverse it by means of a large advective (pressure difference-driven) flow of something else, diffusion under static conditions doesn't care about pressure-only about concentration. Helium-neon laser tubes contain mixtures of helium and neon in a sealed glass assembly, but over a period of years, helium diffuses straight through the glass boretube and through the glass/mirror seals and glass-electrode seals to leave the tube, because the concentration of helium in the tube is much higher than the concentration of helium in the atmosphere. The diffusivity of helium is high, and as good a job as you do to make that glass assembly impermeable, it isn't absolutely impermeable to something as small as helium. Another example is oxygen diffusing through teflon tubing into pressurized hydrogen- it can be very surprising just how much, and how fast, even those big oxygen molecules diffuse through the teflon.
RE: Removing oxygen from water using nitrogen sparging
RE: Removing oxygen from water using nitrogen sparging
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Removing oxygen from water using nitrogen sparging
I understand that Oxygen would diffuse to Nitrogen.
I am just still confused about the partial pressure aspect. How can the partial pressure of Oxygen decrease if there is not Oxygen in the vapor Phase to begin with?
All of the Oxygen is dissolved in the my water...
RE: Removing oxygen from water using nitrogen sparging
@Latexman - Thanks for the answer, I was refreshing myself on Fick's Law just as I came to check this thread.
RE: Removing oxygen from water using nitrogen sparging
p = partial pressure of oxygen in the vapor phase
H = Henry's constant
x = mole fraction of oxygen in the liquid phase.
During the sparging, you may not be at equilibrium, but the system will move towards equilibrium, and the oxygen will move into the vapor phase.
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Removing oxygen from water using nitrogen sparging
Thank you so much for the detailed explainations!
RE: Removing oxygen from water using nitrogen sparging
While my dissolved Oxygen Needs to Transfer to the Nitrogen to be removed from the water...
Can I just consider the Diffusion of Oxygen in Nitrogen to determine my mass Transfer coefficient or would it be better to consider the Diffusion of Oxygen in water?
I guess it would be best to the use the one that is the smallest since this will be the one limiting the rate of my mass Transfer.
Does this seem Logical?
RE: Removing oxygen from water using nitrogen sparging
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Removing oxygen from water using nitrogen sparging
Sparging the tank with nitrogen will increase both interfacial area and liquid mixing GREATLY, relative to just replacing the headspace gas.
Pulling a vacuum on the headspace is a different matter. Vacuum can be a very effective de-gassing measure if it is done properly.
RE: Removing oxygen from water using nitrogen sparging
This method will remove all gasses other then nitrogen (such as CO2).
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P.E. Metallurgy, Plymouth Tube
RE: Removing oxygen from water using nitrogen sparging
RE: Removing oxygen from water using nitrogen sparging
RE: Removing oxygen from water using nitrogen sparging
RE: Removing oxygen from water using nitrogen sparging
Boiling is often undesirable because of the greatly increased water loss.
Though if you have live steam available you can just build a DA like power plants use.
Basically sparging with steam and using and eductor to pull exhaust the gasses.
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P.E. Metallurgy, Plymouth Tube