A gallery of home built hoods and fume scrubbers _hood_

[Shark]

ill use caustic lie and water in one scrubber and hydrogen peroxide and water in the second with the third being empty

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]

The first could be empty as a water trap to prevent backflow into the reaction vessel.

 

[4metals]

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.

 

[4metals]

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.

 

[4metals]

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.

 

[AlteredLimbs]

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?

 

[4metals]

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.

 

[bloodmoneybullion]

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!

 

[Yggdrasil]

I am a bit confused.
Aren't you just sucking through the fan here?
Where is your cone?

 

[bloodmoneybullion]

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.

 

[Yggdrasil]

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]

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.

 

[AuggieDog]

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.

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.

 

[Martijn]

My hood. It is made of plywood coated with boat lacquer and an epoxy trespa sheeted piece of wood as a work bench. It does not like sulfuric.
The backplate has a wooden air devider to suck air from the top and the bottom, sliding the back to set the ratio.

The curved door with acryl windows slides up and is balanced with some lead sheets rolled around a threaded steel rod. The rolls are held in place by nuts and big washers. A piece of pvc pipe guides it up and down.
My fan blows air in a venturi so any corrosive fumes don't go through the fan.
The venturi is made of a pvc Y-piece and a tapered plastic cup inside, bottom taken out off course.

The lighting is a watertight outdoor armature to keep corrosive gases out.

I had some sockets inside to connect power leads for electrolysis in the top left, but they corroded fast, so I don't use them anymore.
All together it served me well the past ten years.
I recently expanded my lab to make room for a sulfuric cell and a silver stripping cell and more storage room. The cells only need good ventilation so there is no hood on that side.

 

[4metals]

I never would have thought about using a cone with out one of the members here.

I used a traffic cone for making an eductor, and my son never let me forget stealing his traffic cone! I used it for a venturi but not a reducer. It can work as a reducer as long as you cut open the discharge side so as not to restrict airflow.

 

[bloodmoneybullion]

well either way you solved the problem i had, i tried to use it to create a venturi but i failed every configuration i tried even added a duct booster fan and still got back draft i think i restricted the air too far too fast but with this style blower there was no way to make it work. going from 10" to 4" didnt cut it im thinking about just going 6" from the blower all the way to the roof instead of 4". i really dont expect to be using the hood very much ill be lucky to get a batch to refine once a month and probably not alot at any one time so im hoping my wet scrubber will capture most everything safely.

 

[bloodmoneybullion]

Here it is with a working Venturi effect using the cone. It's inserted in the top wye joint and pulls any excess fumes off the vacuum powered wet scrubber as well as pulls from the fume hood. I know I can now use the Venturi to save my blower but I really am not worried about it it's pretty well protected as long as the motor doesn't over heat like it did for auggiedog.

 

[4metals]

To be clear, it appears that you have the blower mounted on its side so the air intake is 100% over the hood exhaust port? If this is true it will never function as a venturi as the concept of a venturi is to compress the air as it passes over the hood exhaust port and allow the air to decompress and draw extra air from the hood exhaust port. Since you are taking 100% of the intake air, or so it appears, all the cone is doing (aside from allowing you to fit different size pipes together) is restricting airflow. If you cut the cone narrow opening so it is the size of the pipe, you will draw more air, not as a venturi, but as a less restricted air path.

 

[Yggdrasil]

I think his venturi is on the side branch to vent the fumes from the vacuum system.
But by restricting the blower he will get less effect in the main hood.
Another thing is that he might want to run the intake in the hood behind a baffle plate so it sucks the air from the bottom back.

 

[4metals]

OK so the orange coupling isn't the cone it is just a coupling. The venturi is totally enclosed in the pipe. That can work. Usually I try to get the full force of the fan as close to the cone as possible. I'm sure @bloodmoneybullion will let us know how it works.