Cheap home made scrubbing unit (theoretical design) _fumescrubber_

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samuel-a

samuel-a

Well-known member
Joined
Oct 7, 2009
Messages
2,190
The picture is pretty self explanatory.
What you guys think? Pros, cons, questions, suggestions....

scrubber on the cheap.JPG
 
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try to have the inlet extend into the reservoir at the bottom so it bubbles through the water. Would add just a bit more contact time
I like the idea of alternating: water added to air, air added to water, water added to air. I doubt it would be any better than water to air, water to air, air to water but it just sounds more professional or something
 
I'm sure more contact of gas with the solution will somewhat increase its scrubbing efficiency, but that would probably require quite a powerful blower which may be exensive.
 
The important thing with fume scrubbing is to match up the cubic volume of the packed area with the airflow to maintain a contact time of 8 seconds. So a 1 cubic foot packed section will support up to a 7.5 CFM fan.

A big blower requires a lot of packed bed.

If you perform the reaction in a vessel that can be exhausted through the scrubber the flow can be quite small. A reaction vessel can be a 5 gallon pail with a lid on it and a 1" hole with tubing passing to the scrubber, 7.5 CFM will suffice for fume removal. 5 gallons is only 0.66 cubic feet so you will exhaust all of the air in the bucket 11.36 times a minute or every 5 1/2 seconds. You will likely need a vent hole to prevent implosion if the plastic gets warm and softens.

What are your pipe diameters and fan capacities Sam?
 
Thank you 4metals.

I honestly don't know what is the CFM grading of a given random computer fan... Can you maybe suggest some macgyver methode to masure thier CFM ?
Since my point is to keep the costs as low as possible and easy to build as possible so that any homebrew refiner could build one of those, at least to start his recovery/refining advanture in a safely manner.

I was thinking of making the packed space at about 0.5 (14 liter) cu ft.
I think for trial and error, i will fit a clear PVC pipe at the outlet and just play around with the fan speed.
I know a simple fan will eventually die, the point here is to prolong the inevitable and when comes the time, replace it with another scrap fan.
 
I Googled muffin fans because I have no idea what the CFM of these fans run. Here is a link to a fan supplier and I was suprised at how high some of them flow. http://www.surplussales.com/fans-blowers/fansblow-3.html

The trouble is there is a restriction of the airflow by the packing and the water flow involved in scrubbing and the flow we need to measure is the actual CFM through the system not the fan rating which is likely rated at no resistance.

I would think that using a velometer to measure the velocity of the air moving into the inlet pipe, and knowing the area of the intake pipe opening, one could calculate the flow in CFM. A rheostat on the 12V fan may suffice to adjust the flow rate if it is too fast for the packed area of the scrubber.

It would be interesting to correlate actual CFM to rated CFM for a few popular fan types to make this design a practical reality for small digestions.
 
i know that my question is very much of a ball park question but ... how long is the expected use of the naoh solution for a heavy use? do you intent to regulary check and make ph adjustment on daily basis or wait untils you have mostly plain salt water and just change all the solution at once?
 
ericrm

Theoretically, it could be calculated (according to the gas you are scrubbing and assuming 100% efficiency). But i have no plan on doing that as it is too theoretical, so i think eventually it will come down to trial and error where the prime indicator would be to eye ball the exhaust fumes and maybe even go outside and taking a whiff.

I do plan on taking pH readings at the end of each day.
When pH starts to drop, you know there's at least one mole of NaOH that had been neutralized. Then adding again NaOH (40 gram for each liter solution)
I plan to run the same solution until i reach 50-60% of the solubility of the resulting sodium nitrate.
 
I'm currently using a blower from a steam cleaner I broke down for my first prototype (Not 100% of the cfm but I've seen them to be about 70-90 cfm) Either way it moves some good air. I'll be getting a 55 gallon plastic drum tomorrow for my next prototype scrubber. I'll be mounting the blower directly to the top of the drum to pull the air out and with PVC piping leading into the drum from the fume hood. I was worried about using packing and a water pump so I decided to actually cap the bottom of the pipe that's submerged and drill multiple small holes all through and down the pipe. It works just like a bong does (Tobacco use only). You can adjust the air flow by gradually adding more holes until you get it right. The PVC pipe will lead from a fume hood similar if not just like this homemade one http://www.youtube.com/watch?v=ioVNjuDJRe0 Down into the drum where the diffuser (Pipe with multiple holes) will create lots of small bubbles to maximize surface area to neutralize the fumes in water and sodium hydroxide then out the top where the blower is mounted. The idea is that it can be made for little to nothing and the parts are easily found at garage sales, thrift stores, or Craigslist. I found a 2lb bucket of sodium hydroxide at Lowe's for $15 http://www.lowes.com/pd_146450-331-HD-CRY-6+CRYSTAL+DRA_0__?productId=3465780&Ntt=drain+cleaner&pl=1&currentURL=%3FNtt%3Ddrain%2Bcleaner&facetInfo= I'd like to find it cheaper and not online or in a 50lbs bag. Now I just need to find out the best ratio of water and sodium hydroxide. I'm also thinking of adding another down pipe for adding pH adjustment without having to shut off the system. It would be a open ended pipe submerged with a cap on top. Once you open the cap the air flow is redirected from this pipe. Close it back and its back to coming from the fume hood. Sorry for the long post with no pictures. I have a rough drawing but I'm no artist so I figured I'd spear everyone the having to try and figure out what I drew LOL. Let me know if you have any questions. Looking forward to hearing you input as well.
 
I buy it at the grocery store as generic drain cleaner for about $2 lb. The solution should be 20% NaOh. That's 20 grams NaOh per 100 ml water or .2 grams per ml or 757 grams to a gallon. Or 1.7 lbs NaOh per gallon.
 
If i understand currectly, you want to pass the gas through the solution. I think it is pointless to try and pass the gasses through the solution.
For the gas to dissolve efficiently when it passes through the solution, you would need about 2 ft of solution height. This would require a powerfull and expensive blower.
Sinking the fumes inlet pipe an inch or so into the solution will give very little and take quite a toll on the efficiency of the blower.
 
I'll need to draw up a to scale design. A 55 gallon drum is about 4 feet tall and would be at-least 1/2 full of solution but most likely 2/3. The inlet pipe would go down to the bottom of the drum, so therefore 2 feet is easily accomplished. As for the blower how much force would be needed to pull the fumes? Is there and equation or are you basing that off of personal experience? Sense you mention the depth being so important I can also use a T fitting at the bottom so the fumes are dispersed instead of top to bottom, left to right evenly. That's why I consult the professionals. Also as for it being "pointless to try and pass the gasses through the solution." did i completely miss the idea of what a scrubber is and how it works? I understand using a cylinder with falling solution to have maximum contact time, but wouldn't it do the same in the solution? To reference a bong the idea and design is to do just that, filter off the toxins with water. The smaller the bubbles and the more bubbles you have, the more contact you have which is the reason for the multiple small holes (a diffuser). Has anyone tried this before? I'm a reinvent the wheel kinda guy and I want to design something anybody can build with out spending a lot of money. I also want to add a stack to the blower so that if It doesn't work the fumes will be dispersed upward, but that's another thing I'll talk about once I have time to design it. Once again I take it I'll need to draw a to scale design.
 
Johnny

No, you are not wrong, scrubbing the gas throught the solution is a good way too.
My point is, that you simply can't do it cheaply, thus pointless.

I'm not sure what should be the HP of your blower in order to overcome the weight of 2-3 ft of water in a given pipe diameter and sustain a decent suction of air at the inlet.
I'm sure 4metals can provide better input on this.
But i'm sure this would need forces much greater then the 90cfm blower you have right now. Also, the entire rig should be build very rigidly to withstand the negative pressure, maybe the drum walls will not hold up.
 
butcher said:
You could just add an liquid pH indicator to the scrubber solution, the color change would tell you when the solution pH changed.
Click to expand...

i dont realy know what your taking about. are you saying that there is a ph test strip in "liquid form" that you can add to your "whole" solution and when ph move the solution color will change from green to blue/blue to green over and over simply by the gaz that go tru the solution or the addittion of more naoh?

what i realy trying to ask is if the color of the solution is not permanent once it will be green, gaz will make it blue and and when you add naoh you will be able to get it green again and again, or is it permanent color change?
 
Sam: Yea I'll just have to find out a equation or something to determine how powerful the pump will need to be. I actually found a thread in this forum where the guy was doing almost the exact same design as I'll be doing. I've messaged him to find out if it worked or not and if so what had to be done to do so. I'm interested to hear what 4metals will have to say. I've read a lot of his post and that's one smart guy.

Eric: I actually know what he's referring to and its not a permanent solution as far as I know, but maybe if you added a LOT(That's be pretty cool if it would work though). It's mostly used in hydroponics and is a cheap and fairly accurate reading. Most people take a small sample in a vial and add a drop to clearly see what color it comes out to be, and that tells you your pH. You could most likely add a drop into your solution, see what color it changes to, and there you go. Also I believe electric meters go bad over time where strips and liquid would always give you an accurate reading.
 
Johnny---

I did try what you are talking about, pulling the fume air flow down through a 4" PVC pipe. I used a shop vac, and one of those plastic garbage cans.

At about 1.5 ft deep, the garbage can just collapsed in on itself, and no air was pulled. So I drilled a bunch of 1/4" holes in the PVC, to around a foot high from the bottom of the PVC, making it only about 1/2 foot deep into the water at the top holes. It bubbled, but still collapsed the can, and the air flow was very weak.

I inlarged the holes to 1/2 inch, and got a little more air flow, but the can still ran in a collapsed condition.

It would take a very powerful blower to suck enough air flow through an appreciable depth of water. However, I was using mine on a fume hood. For just a closed circuit reaction vessel one might be able to get it to work using a steel drum.
 
Here's an example of what I'll be using. I feel like there sturdy enough to hold up to the force's. http://www.globalindustrial.com/p/material-handling/drum-barrel/drums-pails/plastic-drum-55-gallon-closed-head?utm_source=pricegr&utm_medium=shp&utm_campaign=Drums-Barrels-Pails-pricegr&infoParam.campaignId=WU
 

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