Scrubber Design

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Tahmoures

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Hello to all,
I'm about to build a fume scrubber and I've designed one but before start I have a question and that is " Is this design correct?"

I have closed system that fumes come out of the reactor to 4 4L gas washing bottles (or sealed buckets).
I'm using nitric acid for base metals, aqua regia for dissolving gold and sodium metabisulfite for precipitating the gold so I have NO, NO2, Cl and SO2 fumes.

First bottle is H2O2 bottle for converting NO to NO2.
the next One is water To make acid from NO2 or Cl Or SO2.
the third one is for Neutralizing the fumes and the forth bottle is trap for the vacuum pump and I have doubt if vacuum pump is needed or not.
and at the end the tube returns to the hood for ventilation If there is remaining gas.

this is picture of my designing

Wet scrubber.png


Please help me If my design is correct or not.

Best regards
Tahmoures
 

speed

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I think the chemistry is right.

Probably the most important bit to make it work is ensuring the gas makes good contact with the solutions. You need very fine bubbles or maybe bubble through some kind if inert media that will promote mixing.
 

4metals

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The critical aspects of fume scrubbing are
1. Chemistry, you have that right but the peroxide is difficult to monitor and maintain
2. Retention time, the amount of time the fumes spend in contact with the chemistry. This is usually done with packing materials inside the scrubber and, as mentioned, small bubbles of gas to increase exposure.

I prefer drawing a vacuum for this type of setup with an PVC eductor which will not be eaten up by the corrosive nature of any un-scrubbed vapors passing through it.

There are some threads about building a scrubber in the library section you can read. The link in my signature line to the library no longer works so I will have to attend to that. In the mean while find it the old fashioned way.
 

Geo

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You should have a large volume of exhaust that is expose to a spray of basic solution. People like columns. Exhaust comes in near the bottom while a spray of neutralizing solution is sprayed in near the top where the fumes exit the scrubber. Monitor the pH of the spray solution and once it is near neutral, add more base or change out the solution if solids starts to form.
 

Tahmoures

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I think the chemistry is right.

Probably the most important bit to make it work is ensuring the gas makes good contact with the solutions. You need very fine bubbles or maybe bubble through some kind if inert media that will promote mixing.
Dear speed
Thanks for your advice

So I'll use packing in the bottles for better contact between liquid and gas.
 

Tahmoures

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Location
Middle east
The critical aspects of fume scrubbing are
1. Chemistry, you have that right but the peroxide is difficult to monitor and maintain
2. Retention time, the amount of time the fumes spend in contact with the chemistry. This is usually done with packing materials inside the scrubber and, as mentioned, small bubbles of gas to increase exposure.

I prefer drawing a vacuum for this type of setup with an PVC eductor which will not be eaten up by the corrosive nature of any un-scrubbed vapors passing through it.

There are some threads about building a scrubber in the library section you can read. The link in my signature line to the library no longer works so I will have to attend to that. In the mean while find it the old fashioned way.
Dear 4metals
I appriciate your reply and your advice.

I found the post that you were talking about in it

I'll add packings to the bottles for better contact between gas and liquid
and is silicon hose be eaten up by corrosive fumes?

and I think a low performance pump is good for suction and is not needed to spend money for high performance pumps, am I correct?
 

Tahmoures

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You should have a large volume of exhaust that is expose to a spray of basic solution. People like columns. Exhaust comes in near the bottom while a spray of neutralizing solution is sprayed in near the top where the fumes exit the scrubber. Monitor the pH of the spray solution and once it is near neutral, add more base or change out the solution if solids starts to form.
I would like to but it costs more than my design and im in the biginning.
 

Tahmoures

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Hello again
this is an edited picture of my designing.
the second water bottle was excess and I removed it, and after that I added extra NaOH bottle for better scrubbing.
 

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Geo

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Hello again
this is an edited picture of my designing.
the second water bottle was excess and I removed it, and after that I added extra NaOH bottle for better scrubbing.
Pulling exhaust through liquid will lower CFM to the point that will make it ineffective. The exhaust needs unrestricted flow except at certain points used to slow the flow to give fumes time needed to be contacted by the neutralizing spray.
 

Tahmoures

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Pulling exhaust through liquid will lower CFM to the point that will make it ineffective. The exhaust needs unrestricted flow except at certain points used to slow the flow to give fumes time needed to be contacted by the neutralizing spray.
What if I only use NaOH in 3 bottles next to each other?
at this situation the first bottle to the end is NaOH and The exhaust has unrestricted flow until contact with NaOH and no other liquid is between fume and NaOH.

I insist on this design because spraying costs too much for me than this design that I'm talking about, but if this doesn't work and its ineffective I should do what you said.
 
Last edited:

orvi

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I think you will be good with sodium carbonate, NaOH is quite caustic and it slowly ruin quite a bit of materials. But if the setup is from PE or PP, it will be OK.
I think you should stick with just basic scrubber. H2O2 is overkill in my opinion, but it can certainly help.

Simple bubbling through solution is quite ineffective, despite it look right. That is why whole industry use shower adsorbers and wet countercurrent packed columns.

All you need is one pump that will withstand basic pH, pipe with suitable diameter, some packing material - glass rings, PP shavings etc - anything that increase surface area and withstand basic pH. And you are good.

Then, you also do not need any vacuum pump, as the gasses from reaction will pass this column freely and slowly, giving them plenty of time to react.

Another thing you can do is purchase aspirator vacuum pump. It will suck the gasses from the reaction and finely disperse and mix them with basic scrubbing solution. Get big plastic drum, make basic solution, and get one membrane pump to cycle the water for the aspirator. Small lab glass ones can be fine with 5L/min flow. But you need pressure to be at least 2 bar. Outgas from the drum can be led directly to the fumehood exhaust as it would be quite nicely scrubbed :)
 

Yggdrasil

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I’m new, why are we using scrubbers for the gases
It was briefly explained in your other thread.
Filters will not stop NOx gases, they need to put into a liquid by "scrubbing" the gases with a Caustic solution like Sodium Carbonate or Sodium Hydroxide.
Study this link and the replies in your other thread.
And while doing that you can study the link in more detail, and answer the question I asked.
 
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