Fume Hood

Jmk88

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Jul 7, 2019
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Dear All,

I am currently in the process of building a fume hood; I have an enamelled cooker good which I will set on acid resistant (treated) timber. I will place hepa layers above and contained charcoal.

This will vent into a second space which I intend to vent externally with an extract fan into a scrubber.

Does anyone have any information on how to make an effective dry scrubber?

Kindest Regards
 

rickbb

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Apr 4, 2013
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I doubt a "dry" scrubber will do the job. The fumes are wet vapors and need to condense back to a liquid to remove the NOX.
 

4metals

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Generally you need water and chemicals, usually caustic to neutralize the fume, combined with a proper flow rate and fume retention time in the packing of the scrubber.
 

orvi

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Apr 13, 2021
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acid fumes are mostly relatively easy to scrubb (take empty HCl canister, fill with little water, cap, shake vigorously for like half minute and you will see negative pressure inside it - HCl vapor absorbed to water very quickly). NO2 or NOCl from AR treatment (i assume this will be a big portion of "fumes" created) are a bit more tough ones to deal with.
as 4metals said, caustic solution will be needed to get into close contact for relatively long period of time to adsorb and neutralize all of these gasses. in industry, they use nozzles to spray the absorbent countercurrent to gas flow (caustic solution of soda, NaOH or cheaper Ca(OH)2 or even pulverized limestone slurry) in the absorption towers or columns. big in diameter, relatively low flow of gases, long retention time, recirculation of the scrubbing solution... it could also be a packed column design, where a big contact surface area is created with proper filler medium. scrubbing solution/slurry is then applied on top of the column and flow down, giving gases plenty of time "touch" the wet surface and eventually react.
it is also possible to bubble the gasses through the solution of scrubber, but this approach have some serious drawbacks when you consider high flowrate in good fumehood.
also, freezing out the gasses and let them condense is another option, but also when you take it realistically, it will consume way too much electricity in cooling, in combination with high airflow... not pleasant to design :)
and of course, this isnt a 100% process. you cannot absorb 100% of gases with 1 stage scrubber, but it can be done to that extent they dont pose immediate risk when vented out :)
it need quite a bit of space and elaboration to make some working prototype of scrubber, but it can be done :)
i will firstly try to dig up some industrial papers, publications or literature dealing with this issue. not reinventing the wheel, big guys figured this out many many years ago :) find some designs, count the diameters, airflows, types of contaminants... suitable materials... elaborate some user friendly substitutes from local hardware store and properly plan it :)
 
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