Yes, I would like to see it as well.
A gallery of home built hoods and fume scrubbers _hood_
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This is the configuration for the venturi powered off a reservoir and pump. Since this is drawing water through your scrubbers it is always possible you will overpower the chemistry in the tubes (by not checking it daily and making additions) and some NOx will enter the reservoir. Emptying a bag of marble chips into the reservoir base is not a bad idea. The vent for the vacuum ties into your fugitive exhaust and any odors will be drawn away. For a small setup the vacuum can be dual purpose as it will also provide suction for vacuum filtration, just not when you are using it to scrub NOx fumes. 
The venturi's from flexpvc.com are inexpensive and they have a detailed tutorial to determine sizing. For a scrubber this size (3 tubes) a 10 CFM flow will work fine.
The venturi's from flexpvc.com are inexpensive and they have a detailed tutorial to determine sizing. For a scrubber this size (3 tubes) a 10 CFM flow will work fine.
And all together it would look like this.
I would connect the piping between the tubes with clear heavy vinyl tubing so you can see if red NOx passes over. (telling you to check your scrubber chemistry)
The tubes are filled 90% of their volume with tower packing like bio balls or something similar.
I would connect the piping between the tubes with clear heavy vinyl tubing so you can see if red NOx passes over. (telling you to check your scrubber chemistry)
The tubes are filled 90% of their volume with tower packing like bio balls or something similar.
skinny
Well-known member
i found a few things i wanted to run by you after studying your drawing for a minute i found a circulating vacuum pump that basically does what you have illustrated but what i didnt see on the machine or in any reference was how to apply something to take care of the fugitive fumes the scrubbers miss im guessing thats the blue vent in your diagram? i also found these gas scrubber glass pieces and some medium i was hoping you could evaluate the setup and let me know how to construct it and what else i might need ill use caustic lie and water in one scrubber and hydrogen peroxide and water in the second with the third being empty
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The machine you showed is basically the same venturi setup but I notice it has brass fittings. Sooner or later your chemistry will run down and corrosive fumes will get to your vacuum generator. The one you show is not vented because it is meant to pull vacuum for laboratory experiments and apparently they don't worry about corrosion. It may last for many years but as far as corrosion goes, refiners see a lot of it. But the reason I vent the one I showed is in the event that your chemistry is consumed you are covered. I said as much in the text box. But the emissions that pass thru the scrubber are considered scrubbed emissions as the flow rate and chemistry in the scrub tubes takes care of the NOx.
Fugitive emissions are fumes that never make it to the scrubber, it's the whisp of fume when you open a bottle of acid or when you remove a watch glass. They are removed with your general exhaust blower. Once a reaction is running and the exhaust pickup is set the worst of the fumes go through the scrubber.
You can do your reactions in a sealed reactor and connect the vessel directly to the scrubber if you use something like this. These sealed reactors like this 2 liter reactor will handle a dissolve of about 9 1/2 ounces while maintaining a safe reaction chemical rise. But when you fill the vessel, or empty it to filter it or transfer solutions you will still have fugitive emissions.
Fugitive emissions are fumes that never make it to the scrubber, it's the whisp of fume when you open a bottle of acid or when you remove a watch glass. They are removed with your general exhaust blower. Once a reaction is running and the exhaust pickup is set the worst of the fumes go through the scrubber.
You can do your reactions in a sealed reactor and connect the vessel directly to the scrubber if you use something like this. These sealed reactors like this 2 liter reactor will handle a dissolve of about 9 1/2 ounces while maintaining a safe reaction chemical rise. But when you fill the vessel, or empty it to filter it or transfer solutions you will still have fugitive emissions.
Why an empty container? And why use the caustic solution in the first one? Looking back at the whole post it has been mentioned to use distilled water and peroxide in the first, and caustic in the last two. By using the H2O/peroxide first it captures some NOx and converts to a weak nitric acid solution, making it reusable. The last two can work at neutralizing the remaining fumes before releasing them back into the atmosphere.
Martijn
Well-known member
The first could be empty as a water trap to prevent backflow into the reaction vessel.
The reason there are 3 tubes 48" long is to give the necessary retention time in the area where the NOx is reacting. 3 tubes is a good number for a 10 CFM venturi. If you are concerned about back-flow a small 1 liter vacuum flask between the reaction flask and the first cylinder would be better.
If I were to set up the system as shown above I would run a length of 1 1/2" PVC pipe across the top rear of the hood to make a scrubber pickup manifold. I would add at least 3 tees which reduce to 1" for the pick up tubes to drop from. Each pickup needs a shut off valve so you can throttle the exhaust. I am accustomed to larger vacuum systems in 8 foot hoods. This smaller 10 CFM flow can handle more than 1 reaction at once which is why I would add additional pickups. Spacing them across the hood allows you to work all across the hood to maximize the space.
I mentioned earlier that this system can also provide vacuum for filtration but not both scrubbing and filtration at the same time. For filtration I would bypass the scrub section and hook up suction close to the venturi. I would have a tee, or a true wye and have a valve to shut each off individually. This will allow you to keep the scrubber hooked up to the manifold and simply shut one off and open the valve to the filtration vacuum line. The vacuum lines are typically 1 1/2" PVC as well to act as a vacuum reservoir. The tee's go to 1/2" ball valves to allow 2 suction ports, one close to each end. Your vacuum hose slips on to PVC barb fittings that connects to the glass barb on the vacuum flask.
I mentioned earlier that this system can also provide vacuum for filtration but not both scrubbing and filtration at the same time. For filtration I would bypass the scrub section and hook up suction close to the venturi. I would have a tee, or a true wye and have a valve to shut each off individually. This will allow you to keep the scrubber hooked up to the manifold and simply shut one off and open the valve to the filtration vacuum line. The vacuum lines are typically 1 1/2" PVC as well to act as a vacuum reservoir. The tee's go to 1/2" ball valves to allow 2 suction ports, one close to each end. Your vacuum hose slips on to PVC barb fittings that connects to the glass barb on the vacuum flask.
I put them all together and resized them so they are close (not to scale) to what the setup will look like. The main red pipe is inch and a half PVC and the drops 1". The piping thru the scrubber is still 1/2" but the flow is less restricted in the larger pipe.
The blue line is vacuum and is selected at the valve by the vacuum generator. Each 1/2" vacuum port needs a shut off valve and a PVC barbed fitting.
The fatter pipe provides a vacuum reservoir but when you shut the system, that reservoir can suck water from the reservoir and flood the pipes and become a general pain to deal with. The vent valve by the vac generator solves that. Open it to drop the vacuum and then shut the pump and it will not draw water.
I also have the tubes about 18" off the floor so a bucket can go underneath them to drain into when changing fluids.
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skinny
Well-known member
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Can you please keep your posts on this subject in one thread?
Now we are jumping back and forth with the same subject in different threads.
AlteredLimbs
New member
This is great 4metals! Thanks for posting this. I’m looking to build a fume hood and potentially use a similar design for neutralizing the NOx gases. Do you know how effective your system is at this? How often do you have to change each solution?
Two things will effect the way these scrubbers work, first is the amount of caustic or peroxide in the system to neutralize the NOx. This can be judged by using clear hose between the columns to judge the amount of red fume passing through the column. But after a point, the liquid in the system can crystallize out and clog the airpath and prevent the necessary airflow. That is when you need to empty out the liquid and rinse with hot water to dissolve the nitrate crystals and start over.
My way of operating these tubes would be to add caustic every morning to bring the pH to 11 or 12. Then check it daily and maintain the pH with once daily additions. When a certain quantity of caustic has been added (historically verified) I would drain the system, rinse it with hot water, refill and restart. Then you never have to deal with airflow clogs. A good starting point for the total caustic added would be 1 gallon per cylinder. But this should. be verified with actual usage vs thru put.
The peroxide cylinder is just routinely drained and refilled with distilled water and peroxide and the liquor drained can be distilled to concentrate and generate re-usable nitric acid.
My way of operating these tubes would be to add caustic every morning to bring the pH to 11 or 12. Then check it daily and maintain the pH with once daily additions. When a certain quantity of caustic has been added (historically verified) I would drain the system, rinse it with hot water, refill and restart. Then you never have to deal with airflow clogs. A good starting point for the total caustic added would be 1 gallon per cylinder. But this should. be verified with actual usage vs thru put.
The peroxide cylinder is just routinely drained and refilled with distilled water and peroxide and the liquor drained can be distilled to concentrate and generate re-usable nitric acid.
bloodmoneybullion
Member
I don't remember who it was that said they used a traffic cone as a coupler but you sir are a god among men. Just need to pipe it to the roof now using 6"PVC with a PVC roof cap and I'm still waiting on the flasks for the wet vacuum scrubber but it's coming along nicely!
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I am a bit confused.
Aren't you just sucking through the fan here?
Where is your cone?
bloodmoneybullion
Member
It's a corrosion resistant PVC fan it's made for chemical fume hoods so I didn't see a reason to not have the fan directly pulling fumes there was one metal bolt and nut inside the fan that I covered in silicon. The cone I used as a coupler on my 10 to 6 reducer.
Then there is no need for the traffic cone.
The purpose for the traffic cone is to create a restriction,
so one can utilize the venturi effect to suck from the hood without dragging the corrosive fumes through the fan.
bloodmoneybullion
Member
I tried to plumb it that way as well as a few others and I got back draft instead of the Venturi effect so I decided to go with a direct vent system and beefed up the wet scrubber design. But when I got the fan on top of the hood the exhaust was smaller than any coupler I had so I used a traffic cone as a means to connect my 10 to 6 reducer to the fan it's self I never would have thought about using a cone with out one of the members here. I will be using a wye joint and adding on a booster fan directly over the exhaust to my vacuum pump and that will work to capture any left over fumes from the wet scrubber as well as add fresh air to the mix while exhausting out of my roof.
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Just a word of caution here, check the temperature of that motor that drives your blower. I had not one, but TWO, of those things reaching very high temps very quickly. When I emailed the amazon seller they tried to tell me the unit had thermal protection, but it was over 200 degrees in a very short amount of time and nothing was triggered. I bought a second one, exact unit somewhere else, same thing.
