Scrubber concept help

[Aubee]

Hey guys!

I'm trying to understand the concept of the NOx scrubber described by 4metals on page 3 of the gallery of home built hoods. I think I generally understand the concept but there is a few things that are still unclear and was hoping some of you guys can help me wrap my noob head around it.

Please let me know if my understanding of this is correct so far. As far I understand, the closed circuit water flow in the reservoir in combination with the venturi tee will create a vacuum in the tube attached to it, which will draw the fumes away from the reaction, through the 3 PVC tubes filled with the tower packing material of choice, which will slow down the flow of fumes and allow them to react with the hydrogen peroxide respectively with the sodium hydroxide solution on their way up inside the tubes, scrubbing them. The clean air will be sucked backed through the venturi tee into the water reservoir and from there it will be vented out through the blue pipe (as per the drawing).

What I'm trying to understand is, how is the scrubbing solution coming in contact with the fumes? Are the PVC pipes filled up with the NAOH solution? Is the tower packing sitting submerged in the high pH solution while the fumes are bubbling through the liquid and are obstructed by tower packing? Is this correct?

Please pardon my ignorance, total noob here.

Thank you!
Aubee

 

[4metals]

Are the PVC pipes filled up with the NAOH solution? Is the tower packing sitting submerged in the high pH solution while the fumes are bubbling through the liquid and are obstructed by tower packing? Is this correct?

Yup, that is exactly what is happening. For small systems the tubes are filled with the liquid and the packing slows the airflow through the tubes.

For larger commercial systems the tubes (much larger) are filled with the fume and air and the tower packing provides an air water interface for the liquids which are pumped over the packing and recirculated.

Welcome to the forum.

 

[Aubee]

Thank you very much for clearing that up for me!

I'm thinking in terms of a very small system, something like 2-3 lbs of e-scrap on a weekend once in a while. At the moment I'm still in the learning phase, trying to make a plan and figure out what exactly is involved. I want to do it the right way, I want to understand every step of every process. I'm especially interested in the procedures of safe disposal of waste and the scrubbing. I want to do it responsibly.

The next detail I'm interested in is what kind of vacuum are we after? something like 20-25 inHg? i believe that would give us around 80% vacuum, would that be enough? I'm trying to figure out what kind of water pump I would need to generate this. I'm looking at different venturi tees, it looks like on a 1/2in nozzle, most of them would require a 25 gpm pump. That is 1500 GPH. And I need this at a height of about 4-5 feet (where my venturi would be sitting), because pumps are rated at the pump and the flow is decreasing with height. So I think I would need a 1/2 hp pump that is rated around 2200 GPH, which would do around 1600 GPH (26.6 GPM) at 5 feet head. Does this sound about right?

I see that in your drawing, the pump is sitting on the outside of the 30 gal reservoir. Would I be able to get away with a corosion resistant submersible utility pump instead? I saw a nice little 1/2 hp pump all thermoplastic including the impeller for a decent price, was wondering if it would work.

Thanks!
Aubee

 

[4metals]

I always think along the lines of refiners who do this for a living and as a result I prefer corrosion resistant pumps and most of them are not submersible. But commercial refiners are usually not up on their change out the corrosive liquids maintenance. You will have protection of the scrubbing chambers before the vacuum to get the majority of the fume scrubbed (if you keep up with the solutions) but to be on the safe side, put a few inches of marble chips in the vacuum reservoir to neutralize any pass over fumes. Then submersible should work.

 

[4metals]

The next detail I'm interested in is what kind of vacuum are we after? something like 20-25 inHg? i believe that would give us around 80% vacuum, would that be enough?

That should be enough vacuum. At 20-25" Hg you will get enough to serve as a vacuum source for transferring solutions and wastes as well as filtering as long as you split the system to either power the scrubber or use the vacuum for filtering. Just not both at the same time.

 

[Aubee]

Thank you again for your reply, much appreciated!

One more thing I've been thinking about is, how would the top cap of the PVC pipes be fastened? I would assume that I'd need to have a treaded cap that I could unscrew when I want to fill the tubes with the solution and have it closed tight when the scrubber is on. I was looking at philddreamer's pictures and I see that the bottom cap is glued with pvc cement, but the top doesn't seem to have any treading or glue.

 

[4metals]

Phildreamers tops come off if I remember correctly. I do not know how easy that process is. I suggested using thread on caps which can be unscrewed and you can add chemicals. It also has a bottom drain to drain the solution to start over. IN my drawing I attempted to show threads on the to end of the tubes but no threaded plug.