Cocurrent diffusion (can't be this hard....)

[KarenRei]

Thank you for the derivation - that was very thorough. I can't imagine how long it would have taken me to come into something like that on my own.

Re α: Aha, that was the bug - I was just using total surface area, not surface area per unit volume. Now all of the numbers make sense. Excellent.

I'm very concerned about your suggesting that the volume fraction of liquid is only 0.0004. With that small a value, the liquid does not have enough capacity to remove much of the undesirable species from the gas, even if the two phases equilibrated in the scrubber. What does your Eqn. 20-eq tell you about the ratio of the final- to the initial concentration of CO2 in the gas, assuming that f = 0.0004 and CL0 = 0? I get virtually no change.

That was just a starting point. After working with the numbers all morning I'm currently looking at 0.12% (0.0012). As examples of the capture rates I'm getting:

CO2: 0.017%
N2: 7.35E-06
Ar: 2.39E-05
H2SO4: 100.00%
CO: 1.62E-05
He: 6.43E-06
SO2: 1.67%
Ne: 7.71E-06
H2O: 9.30%
HCl: 43.36%
H3PO4: 95.99%
OCS: 0.036%
...
HF: 68.61%
...

... and so forth. It might benefit to being upped some more to catch more of the H2O, HF, HCl, etc, but it's already catching all of the sulfuric and essentially all phosphoric acid. They have extremely high Henry's constants. You're absolutely right that it doesn't capture much CO2. But I don't want to capture much CO2; CO2 is the bulk gas, my interest is the minor acidic species. And the interest in their acquisition, not in purifying the exhaust stream; the exhaust doesn't need to be "clean".

I had initially had some big concerns about my HCl numbers, they were a small fraction of this. But digging through papers looking into the issue I found that Henry's Law doesn't adequately describe it well at low concentrations; it has a "reactivity" component as well as an "absorption" component that needs to be factored in, and thus greatly increases how well it's absorbed at low concentrations. Technically there's many species that would be ideally represented like this, but I'm not sure how much of the table I'll be able to fill in that way. At least it means that the data I'm working with is a pessimistic case.

I had also initially had some huge concerns about the power requirements the spreadsheet was coming up with for recycling the liquid stream (outgassing via heating; the solubilities vary greatly with temperature). But I realized I had forgotten to account for the heat exchanger; when that's factored in the numbers come out much more reasonable.

I think this will get me where I'm needing to go - thank you :)