A gallery of home built hoods and fume scrubbers _hood_

[Jaykii Lam]

I drew this up for making the scrubber out of PVC.

View attachment 63694
If you want I can make up a similar drawing for the vacuum by venturi setup

Hi 4metals and everyone,
Please help clearing for me this, if the 6" pvc tube filled with neutralized liquid (Di water / caustic ), and the red tube go down 48" to the bottom of the scrubbing tube, is it first be flooded with caustic/water, will the vacumn could draw this water out of red tube first, then followed by the Nox fume and bubbling through the drilled holds on 5 ways Tee?

 

[Yggdrasil]

Hi 4metals and everyone,
Please help clearing for me this, if the 6" pvc tube filled with neutralized liquid (Di water / caustic ), and the red tube go down 48" to the bottom of the scrubbing tube, is it first be flooded with caustic/water, will the vacumn could draw this water out of red tube first, then followed by the Nox fume and bubbling through the drilled holds on 5 ways Tee?

The drawing shows the tube a bit full.
The idea is that the vacuum draws the fumes into the bottom and then are bubbling up to the surface. What ever fumes are left will go out the top and over to the next tube or vacuum pump.

 

[Jaykii Lam]

The drawing shows the tube a bit full.
The idea is that the vacuum draws the fumes into the bottom and then are bubbling up to the surface. What ever fumes are left will go out the top and over to the next tube or vacuum pump.

Yggdrasil,
First, thank you for replying.
In big picture, i could understand how to fume being sucked out and passing the flask train. But my stucking point is, when the pump stop working, there is no vacumn at all, the red pipes (1/2") those go down at the bottom, will being flooded back physically for a length of nearly 48" height of the 6" pipe (x3 1/2" red pipes in x3 6" pipes). I've just wondered when starting the pump in the next day of work, will the vacumn could easily clear out the flooded liquids first, then come after NOx fume in bubbles form.

Sorry if i could not make my question more clear

 

[Yggdrasil]

Yggdrasil,
First, thank you for replying.
In big picture, i could understand how to fume being sucked out and passing the flask train. But my stucking point is, when the pump stop working, there is no vacumn at all, the red pipes (1/2") those go down at the bottom, will being flooded back physically for a length of nearly 48" height of the 6" pipe (x3 1/2" red pipes in x3 6" pipes). I've just wondered when starting the pump in the next day of work, will the vacumn could easily clear out the flooded liquids first, then come after NOx fume in bubbles form.

Sorry if i could not make my question more clear

If you run a water driven venturi system the vacuum end is not important.
And if you fear a drawback to the reaction vessel put an empty "bottle" in front of it.
Anyway the risk is negligible since it is run open in the reaction end.
If the vacuum fails, it just stops.

 

[4metals]

If the venturi eductor you choose is properly matched with the pump it should have no issues pulling the scrubbed fume through the flooded cylinders. But in the description of the venturi tank, notice there is a vent valve. If you do not vent the suction line when you shut the pump, it will draw up liquid from the reservoir and require draining to get suction line to draw properly.

 

[Jaykii Lam]

Much appreciate for you advices.
I will give it a try of building this setup from now.

 

[J.Najam]

Hello Sir @4metals ,

I'd like to clear a couple of queries :

1, :

If the venturi eductor you choose is properly matched with the pump

How do we figure this one out? I was about to order the venturi device, but now I need to be sure of the right item.

2, Earlier you said that the scrubber may get clogged, how do we figure that out or what is the tell that it may be clogged even if we have a way to check the pH?

3, You mentioned that you kept the chemistry pH of the caustic fed scrubber at 9. I guess about a 100 grams of NaOH in a litre of water would shoot the pH to around 12 easily with that being a suitable pH for a fight between the acid fume and the base for efficient scrubbing. So what was the reason when you decided to keep it at 9?

Many thanks for your time once again

 

[4metals]

How do we figure this one out? I was about to order the venturi device, but now I need to be sure of the right item.

Flex PVC carries a reasonably inexpensive venturi and they even have a you tube video about how it works and how to size it. See that HERE

2, Earlier you said that the scrubber may get clogged, how do we figure that out or what is the tell that it may be clogged even if we have a way to check the pH?

The fumes react with the caustic and form a sodium nitrate salt which builds up in the scrubber. Eventually it gets to the concentration where the salts start to drop out of solution because it is over saturated and this is what clogs a scrubber. I normally deal with much larger scrubbers where the water trickles down over the packing as the fume moves up past the packing. With these scrubbers you measure the pressure drop with a manometer to determine when the airflow is diminishing and the solution needs changing. I suppose you could put a manometer on the feed into the scrubber and do the same thing, I have never have done this with a small scrubber as we described in this thread, I just learned how much caustic would start the airflow to diminish and kept track of caustic use and changed the scrubber fluid as needed.

3, You mentioned that you kept the chemistry pH of the caustic fed scrubber at 9. I guess about a 100 grams of NaOH in a litre of water would shoot the pH to around 12 easily with that being a suitable pH for a fight between the acid fume and the base for efficient scrubbing. So what was the reason when you decided to keep it at 9?

Again I am used to larger scrubbers and all are controlled with dosing pumps and pH controllers so a pH of 9 is sufficient because it is controlled and maintained automatically. Smaller systems with manual additions will perform well even at a pH of 12 as it will go down as it is used.

 

[Jaykii Lam]

Hi 4metals,
I've read one of your thread posted in 2009, about a built-in eductor packing tower scrubber, same as which you mentioned in this thread, but at that time, the cylinder train, which could neutralize most of the NOx fume, was not counted.

Is it appropriate to put this kind of tower instead of the 35 gallon barrel one you first put in the sketch of this thread. If not, whenever it would be suit for?

Hope this point would not make you guys fed up.

Thank you,
Lam

 

[4metals]

I've read one of your thread posted in 2009, about a built-in eductor packing tower scrubber, same as which you mentioned in this thread, but at that time, the cylinder train, which could neutralize most of the NOx fume, was not counted.

I am not sure what thread you are referring to here. In any scrubber the time the fume spends in contact with the scrubber fluid is what is used to figure out the flow the scrubber can handle. I am not sure what you mean by cylinder train.

 

[Jaykii Lam]

I am not sure what thread you are referring to here. In any scrubber the time the fume spends in contact with the scrubber fluid is what is used to figure out the flow the scrubber can handle. I am not sure what you mean by cylinder train.

The old posted about built-in eductor packing tower is here : https://goldrefiningforum.com/threads/new-fume-scrubber-design-_fumescrubber_.22553/post-236355

And i thought the 3 scrubbing cylinders below called cylinder-train (flask train)

Back to my question, i wonder if i could replace the reservoir on the right of the picture by the packing tower in your old post?

 

[Jaykii Lam]

My purpose of this replacement is just try to absorb all the toxic fume as possible.

 

[4metals]

Back to my question, i wonder if i could replace the reservoir on the right of the picture by the packing tower in your old post?

The designs differ in that the design from a 2011 thread uses a packed tower over the vacuum reservoir. The tower is larger and can support more CFM airflow and as such scrub multiple reactions. Plus the packed tower is not full of solution, the gas flows up through the tower and scrubber water flows down over the packing. Because the wetted surfaces of the tower packing offer more surface area when the gas travels over wetted but not submerged packing, I would say the design from 2011 will be more efficient. The design also pressurizes the reservoir forcing the fume up through the packing after it passes through the reservoir. The 3 cylinder design sucks air through the cylinder by vacuum.

The smaller 3 cylinder scrubber in this thread is for smaller operations, most of which are hobby refiners not needing the scrubbing capacity and more important not having the space the 2011 design takes up in their refining space.

One design uses a venturi to pressurize the tower and force the scrubbed air out through the top and the 3 cylinder design uses a venturi to suck gas through flooded cylinders before it enters the reservoir.

Your choice of scrubbing style will depend on what you are doing and quantity of work you process, you are a new member here so we do not know much about your intentions or existing setup. Welcome to the forum.

 

[Jaykii Lam]

The designs differ in that the design from a 2011 thread uses a packed tower over the vacuum reservoir. The tower is larger and can support more CFM airflow and as such scrub multiple reactions. Plus the packed tower is not full of solution, the gas flows up through the tower and scrubber water flows down over the packing. Because the wetted surfaces of the tower packing offer more surface area when the gas travels over wetted but not submerged packing, I would say the design from 2011 will be more efficient. The design also pressurizes the reservoir forcing the fume up through the packing after it passes through the reservoir. The 3 cylinder design sucks air through the cylinder by vacuum.

The smaller 3 cylinder scrubber in this thread is for smaller operations, most of which are hobby refiners not needing the scrubbing capacity and more important not having the space the 2011 design takes up in their refining space.

One design uses a venturi to pressurize the tower and force the scrubbed air out through the top and the 3 cylinder design uses a venturi to suck gas through flooded cylinders before it enters the reservoir.

Your choice of scrubbing style will depend on what you are doing and quantity of work you process, you are a new member here so we do not know much about your intentions or existing setup. Welcome to the forum.

Thank you so much for sharring these, 4metals.
Since I'm learning from scratch, its better to start with small setup first.
For short introduction, im from Vietnam, a saleguy of a diamond wholesale, in my local and most part of my country, nearly no one use fume hood for refinery. I recently have visited two big jewery companies and witness refining of 15kg of polishing dust, i directly saw they proceed the work without fume hood, gas mask, and just letting the toxic fume floating around the rooftop. After coming back, I decided to find a way to start building the thing right, first to study, then will start up a business, who know!
[Belows are some pictures where the works took place]

So its my pleasure to know this forum and great teacher are ready to help.

Thank you for your time.
Lam

 

[Jaykii Lam]

Old fume hood there, but its useless. A fumehood chinese company sold this to the jewelry company. And they never used it. What a waste!

 

[4metals]

Without vacuum filtration and a crude setup, you should inquire if they want to sell their residues after refining. You can make a lot of money properly refining refining residues that have been poorly processed.

The purple coloration on the equipment is what residue from red rouge polishing dust looks like. Do they burn it before they put it in acid?

 

[Yggdrasil]

Thank you so much for sharring these, 4metals.
Since I'm learning from scratch, its better to start with small setup first.
For short introduction, im from Vietnam, a saleguy of a diamond wholesale, in my local and most part of my country, nearly no one use fume hood for refinery. I recently have visited two big jewery companies and witness refining of 15kg of polishing dust, i directly saw they proceed the work without fume hood, gas mask, and just letting the toxic fume floating around the rooftop. After coming back, I decided to find a way to start building the thing right, first to study, then will start up a business, who know!
[Belows are some pictures where the works took place]

So its my pleasure to know this forum and great teacher are ready to help.

Thank you for your time.
Lam

Are you doing this in a residential building in a city?
The fumes may weaken and maybe even destroy the structures over time.
There should not even be a smell of acids if you do it like this.
Concrete and any exposed metal are attacked by the fumes from HCl and in time it may start eating at the rebars as well.
If you are working like this you will need an oversized scrubbing system to ensure nothing leaves the "building"
Another thing is that you need a separate room/space for mixing and pouring the acids and that needs to be included in the scrubbed air.

 

[4metals]

The hood with the scrubber alongside in the first photo is the way old school fume scrubbing worked. 100% of the fume went through the scrubber for scrubbing. The issue was to get sufficient flow for good exhaust, the scrubber needed to be huge to give them the retention time needed for good scrubbing. So the trade off was less flow overall (which causes the corrosion in the facility that Ygg was describing not to mention the effect on the workers) or inefficient scrubbing because the fume can't stay in the scrubber long enough.
What we propose is a general exhaust to get the hood to move enough air for worker safety and a fume scrubber to selectively pick up the majority of the nasty fumes over the reaction itself. So this requires a hood exhausted directly out of the workspace. Typically upward above the roof height. And a scrubbed exhaust, also exiting above the work space.

 

[J.Najam]

Flex PVC carries a reasonably inexpensive venturi and they even have a you tube video about how it works and how to size it. See that HERE

Thanks for this, I just checked it and to be honest it is a little confusing but I'll keep going through it till I may begin to understand.

The fumes react with the caustic and form a sodium nitrate salt which builds up in the scrubber. Eventually it gets to the concentration where the salts start to drop out of solution because it is over saturated and this is what clogs a scrubber.

So basically if I don't have the meter on hand, I may have to rely on manual checking for this too I suppose. Or one of the tells is the sound of my pump which almost silences down if the vacuum is not being pulled through properly. I also decided to let go of the spiral had you not pointed out otherwise I would have been stuck in a confusion as to why there is no pull. Your educational logic combined with the sound of my pump had me moving in the right direction. Also I've now decided to use 1/2 inch pvc pipe cut into an inch and use these as my scrubber packing. The marbles were actually giving the bubbles a tough time to head up and without them the airflow is just so much more smoother.

I just learned how much caustic would start the airflow to diminish and kept track of caustic use and changed the scrubber fluid as needed.

Here, I believe it may be a matter of experience more than textbook knowledge because we probably won't know for sure how much material we may be processing hence the formation of NOx is unanticipated?

Again I am used to larger scrubbers and all are controlled with dosing pumps and pH controllers so a pH of 9 is sufficient because it is controlled and maintained automatically. Smaller systems with manual additions will perform well even at a pH of 12 as it will go down as it is used.

Ah yes, well aware of the fact that you used the tower scrubbers and initially about a year ago I'd only known that and was in love with the design. Had it not been for Yggdrasil to point out the flask train scrubbers I would have gone on to build myself one of those. Talking and discussing always helps! And that is what this forum has been all about.

Many thanks for your time again

 

[Jaykii Lam]

Are you doing this in a residential building in a city?
The fumes may weaken and maybe even destroy the structures over time.
There should not even be a smell of acids if you do it like this.
Concrete and any exposed metal are attacked by the fumes from HCl and in time it may start eating at the rebars as well.
If you are working like this you will need an oversized scrubbing system to ensure nothing leaves the "building"
Another thing is that you need a separate room/space for mixing and pouring the acids and that needs to be included in the scrubbed air.

Sorry for replying you late, Yggdrasil
Obviously, we can see that the working space there is no safety at all. You wouldnt imagine that when they pour to mix AR, the acid spilled a lot on the floor; and the workers there told me they got acquainted with breath in the fume whenever they do refining once a month . And they were just few of the bad things i mention here.
By the way, i noticed that you regarded to an oversized scrubbing system, so could you please give me any hints about this setup?

How about applying the setup with double - packing tower srubber (each tower : 12" pipe x 8' height, filled with bio balls and a spiral nozzle on top of) ? If it is possible, do I need any further calculations for the exhaust fan?