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Author: Subject: Best method for absorption or scrubbing of gases from air
RogueRose
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[*] posted on 17-12-2018 at 12:48
Best method for absorption or scrubbing of gases from air


I'm trying to figure out the best method to scrub certain gases from air and can think of 3 methods to do this and I'm wondering if there are any other methods I should look at and also which method is best.

First is normal bubbling of gases through water or a solution using an air stone or a fritted glass bubbler.

Liquid soaked filter - layers of some type of filter (could be cloth/cotton/nylon/etc, paper like coffee filter, etc) with water or a solution being pumped onto the top of the filter so it will run/soak down the filter to the bottom where it is pumped back to the top of the filter.

Mist spray - spray water or solution in a very fine mist and have the air pass through it at a slow-ish manner. Have a filter at end of misting chamber to absorb the water/solution droplets in air.


I'm planning on trying this out on a few different things like ammonia absorption and a few other things.

[Edited on 12-17-2018 by RogueRose]
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walruslover69
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[*] posted on 17-12-2018 at 12:58


I don't think those types of systems are scaleable to something like a coal power plant. The biggest problem I see with a method like that is the exhaust gasses coming out are quite hot, and so the equilibrium for having a gas dissolved in water is going to be unfavorable. The second is when your gases such as NOx dissolves you now have a lot of really hot nitric acid solution that is going to be a bitch to deal with.

Most power plants use a catalytic converter system similar to a car's catalytic converter to get rid of things like NOx and SOx.
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RogueRose
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[*] posted on 17-12-2018 at 14:31


Quote: Originally posted by walruslover69  
I don't think those types of systems are scaleable to something like a coal power plant. The biggest problem I see with a method like that is the exhaust gasses coming out are quite hot, and so the equilibrium for having a gas dissolved in water is going to be unfavorable. The second is when your gases such as NOx dissolves you now have a lot of really hot nitric acid solution that is going to be a bitch to deal with.

Most power plants use a catalytic converter system similar to a car's catalytic converter to get rid of things like NOx and SOx.


Well coal was just an example and not what I was planning on using it for, lol, just wondering if something like that would work for it. I'm more looking at small scale with various gases like ammonia, amine's, HCl and others.

I would think that it would be possible to have a heat exchanger/absorber that cools the flue gases before it passes through the liquid and then maybe it is either re-heated (with the same heat exchanger maybe??) to cause the draft upwards - possibly in addition with a blower of some type. Or the heat could be used to pre-heat any incoming water for the plant and then a blower used to exit the exhaust.

As for the nitric acid and sulfuric acid, that can be handled with a Ca(OH)2 solution to absorb the acids.

[Edited on 12-17-2018 by RogueRose]
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morganbw
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[*] posted on 17-12-2018 at 14:53


Google industrial air scrubbers. It might give you an idea of what is being done in industry.
Be aware that it is a big field and many chemical engineers devote their lives to such as this.

We used an assortment of air scrubbing technologies at the place I retired from. It included a counterflow packed column for one aspect of it.
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walruslover69
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[*] posted on 17-12-2018 at 15:01


have you thought about a cold trap, using dry ice if its available? Also it wouldn't work for ammonia, but you could just pack coarse Ca(OH)2 or something like it in a tube that all your exhaust gasses have to pass through on their way out.
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RogueRose
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[*] posted on 17-12-2018 at 15:09


The coal thing is about 5% of what I'm interested in. I'm looking at much smaller scale applications.
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AJKOER
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[*] posted on 17-12-2018 at 17:30


Here is a cool idea, low cost, safe, environmentally friendly and likely efficient.

Mix air with the gas to be scrubbed (say H2S) and pass through a tap water solution (rich in transition metals like Fe, Mn,..) in which an electric current flows.

The solution is exited through some microjets and collected. Repeat process on dissolved gas as necessary.

Reactions, first dissolved oxygen and electric current could form some superoxide radical anion:

O2(d) + e- = .O2-

Next some expected chemistry surrounding the Electro-Fenton reaction (background, see https://www.tandfonline.com/doi/abs/10.1080/10643389.2017.14... and free pdf at https://www.researchgate.net/publication/319934098_Modeling_... ) incorporating microjets (replacing the need for acid addition):

Fe(lll) + e- = Fe(ll)

Fe(ll) + O2 = Fe(lll) + .O2- (the superoxide radical)

Using microjets, the pH of the aerosol is now high and .O2- + H+ --> .HO2

.HO2 + Fe(ll) + H+ --> Fe(lll) + H2O2 (in situ created hydrogen peroxide, see p.32, Eq 30, in 'Modeling of Electro-Fenton Process' pdf)

Fe(ll) + H2O2 + H+ --> Fe(lll) + H2O + .OH (See Eq 1, p. 4, where hydroxyl radical is capable of degrading organics, H2S,..)

Related work employing micro jets based Fenton reaction see my thread and sources at http://www.sciencemadness.org/talk/viewthread.php?tid=81667#... and also photo-Fenton https://www.sciencedirect.com/science/article/pii/S004565351... .Example of electro-scrubbing, see http://jes.ecsdl.org/content/163/14/E390.full.pdf+html .

We can collaborate on the patent write-up if you can make a demo!

[Edited on 18-12-2018 by AJKOER]

[Edited on 18-12-2018 by AJKOER]
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Pumukli
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[*] posted on 18-12-2018 at 10:13


You should take into consideration how much pressure drop would be acceptable in your system. The "cold water sprayed into a tower" method causes much less pressure drop than the "wet sponge" method where you try to pass gasses through a wetted absorbent material.


The colder the absorbing medium is the better of course.
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Sulaiman
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[*] posted on 18-12-2018 at 10:28


In my mind, not in reality, I would USE all byproducts or make them suitable for later use.
NOx for example captured by hydrogen peroxide to yield dilute nitric acid.
I've only used Cl2 gas a few times,
each time more escaped than was used.

My plan for next time I set up a gas generator for SO2, Cl2 etc.
Is to do as many experiments requiring that gas as I can manage,
probably the exhaust from some would be the feed for others.




CAUTION : Hobby Chemist, not Professional or even Amateur
(suffering from separation of me and my chemistry stuff)
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Fulmen
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[*] posted on 18-12-2018 at 13:44


This is a common technique used in a wide array of industrial applications. Any good process engineering book should teach you most of what you are looking for. I'm sure there are free online books out there. As for other references it is very comparable to distillation columns.

Designing a good scrubber will probably depend on a wide array of criteria. Capacity, liquid phase (usually water) consumption, recovery and efficiency are just a few I can think of on the top of my head.

I would start by looking at packed columns. It has a good balance between efficiency and pressure drop and are easy to construct.




We're not banging rocks together here. We know how to put a man back together.
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