Stripping of Dissolved Oxygen from Water

[chin19]

Dear all,

I work on a beverage plant and am looking into the possibility of stripping dissolved oxygen from water using nitrogen instead of carbon dioxide, which is what we currently use.

So long as we have the same operating pressures and temperatures, would the removal rate of dissolved oxygen be the same so long as the molar flow rate of the nitrogen is the same as what we currently use for the carbon dioxide? Also, someone suggested to me that more nitrogen would be needed to remove the same amount of dissolved oxygen since the solubility of nitrogen in water is far less than that of carbon dioxide, but I thought that the dissolved oxygen was removed predominantly by the stripping gas reducing the partial pressure of the dissolved oxygen. Therefore wouldn't the main difference from using nitrogen instead of carbon dioxide just be that the stripped water would have less dissolved nitrogen than it currently has dissolved carbon dioxide. Thanks

Best regards,
Chin19

 

[moltenmetal]

No time to do a detailed calculation for you, but the flux of gas OUT of the tower would be higher for a given flux of gas into the tower if you used N2 rather than CO2. My guess, though I wouldn't put money on it without dusting off my mass transfer text, would be that for a given volumetric flux of N2 relative to CO2 (i.e. much less mass of CO2 as well), you'd remove more oxygen because almost none of the N2 would dissolve whereas at least some of the CO2 does. Dissolution of CO2 into water will not affect the oxygen solubility noticeably.

 

[Compositepro]

I agree with moltenmetal. I'm wondering how using CO2 or N2 compares economically with steam stripping, which I believe is a far more common process?

 

[EdStainless]

With N2 (well actually with any gas) the bubble size will be important.
And with N2 it will likely be different than for CO2.
I am with Compositepro here, I would think that heat and a slightly lower pressure would be just as effective and cost less.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Your predictions appear to be reasonable, given CO2 dissolves into water much more than N2. But we also know that CO2 dissolution in water also decreases pH, while N2 has no effect on pH. Check if you can find data on how / if O2 solubility in water changes with pH. Agreed, also read up you Uni mass transfer text to see if there is any change in mass transfer coeff for this switch.