# Cheap home made scrubbing unit (theoretical design)



## samuel-a

The picture is pretty self explanatory.
What you guys think? Pros, cons, questions, suggestions....


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## MysticColby

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


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## samuel-a

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.


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## goldenchild

This is similar to the design that I will build (eventually). I plan to have the packing material in the bucket however. I will be using 7 gallon buckets. One of the blowers on this page should get the job done. I bought the 1 HP. It's surprisingly quiet too. 

http://www.harborfreight.com/catalo...=dust&mode=grid&RequestData=CA_CategoryExpand


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## 4metals

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?


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## samuel-a

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.


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## 4metals

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.


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## ericrm

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?


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## samuel-a

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.


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## butcher

You could just add an liquid pH indicator to the scrubber solution, the color change would tell you when the solution pH changed.


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## Johnnycat535

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.


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## Palladium

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.


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## Johnnycat535

I just got a response back from a guy locally who can supply it to me at $0.75 per lbs!!! Glad I called that guy.


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## samuel-a

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.


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## Johnnycat535

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.


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## samuel-a

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.


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## ericrm

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.



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?


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## Johnnycat535

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.


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## eeTHr

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.


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## Johnnycat535

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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## eeTHr

Johnny---

If you calculate the speed of the air through the pipe in the water, to give you the recommended 100 CFM per square foot of front opening in your fume hood, you will see that the air (and resulting water splash from the bubbles) will be like a hurricane in there. It's quite possible that even a steel drum would collapse under such a vaccum, and your blower will likely suck lots of the lye water.

I would suggest that you test it on a small scale, and find out for yourself.


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## Johnnycat535

I actually already have with the steam cleaner blower (around 93CFM), a vacuum hose, and Rubbermaid container. It does cave in some what but it still keeps a good enough seal to hold up. I used it with water and some baking soda when dissolving my BM's in HCL & H2O2. It's got at least 24 hours of use on it so far. For something I threw together in about 3 hours with stuff I had around the house it works perfectly and with simple PVC framing it can hold up with out much of any caving. I'll post some pictures when I get back from dinner. I also have found that a 5hp shop vac rates in at around 175CFM, give or take. I'll also do my best to draw up a design to hopefully be able to obtain some numbers before the final build. Thanks everyone!!!


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## Johnnycat535

OK so here's my first prototype. Please don't comment negatively about the fume hood. It was thrown together for testing purposes.


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## butcher

sometimes we can learn from the negative as well as the positive, well I guess it is because I am an electrician I think this way.


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## Johnnycat535

It's not that I don't want to learn it's that the fume hood you see won't be involved in my next prototype. I'm going to build the one I listed earlier in this thread. Believe me I know the importance of negative advice. In my opinion its the best kind of advise.


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## butcher

maybe if you give a description of how it works, I see what looks to be a vacuum cleaner motor, a hose from the bottom of the seal-able tub going to a plastic jug.

if the blue tub is the scrubber what are you going to use to keep the gases in solution long enough to react and neutralize, the large hose and high velocity of the vacuum motor would suck those fumes in and out of solution so fast they would be out in the air before they even thought about getting neutralized, where are you exhausting the fumes to away from where you are working

I do not know how long the motor would last in these conditions, and mounting it to the plastic, I would be concerned of fire danger.

just thought I would add some negatives.

now for a little positive,

Good job working on this, with work you will work out the bugs and get a working fume scrubber, I like how you are working to remedy the problem with fumes keep up the good work.


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## Johnnycat535

The heat from the motor was my biggest concern at first so I used high temp gasket sealer. The motor is from a steam cleaner, and doesn't seem to get that hot. The hose's are from a vacuum and the steam cleaner. I'll do my best to draw something up. A lot of your questioned can be answered in my earlier post. I'll be using a 55 gallon plastic drum, and have been made fully aware that the blower will need to be quite powerful. I'm hoping 4metals will have a way for me to calculate what will be needed. I'm hoping using a diffuser to produce multiple small bubbles will help a lot with any lost time in the solution. I have a couple more idea's for that as well. Also in the works is to add a stack for the exhaust to be dispersed about 6' high. I still have a few things I need to figure out, but with everyone's help here I've made a lot of ground in a short period of time. Thanks for the positive as well. I wanna make sure to do it the right way, and come up with a way that is cost effective at the same time. Once I draw it up it'll be easier to understand what I'm going for.


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## Johnnycat535

So here's what I came up with. Let me know if you have any questions or concerns. I included as much detail as I could think to.


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## butcher

John I like the bubblier in that design, it will give more surface are to the bubbles of gases to be scrubbed, that and something inside the column for the bubbles to hang onto for a while would help, one member posted some blue balls (bio balls?) that looked like they would work good (maybe S. Brown).

The taller the coulomb, and the smaller, and harder for the bubbles to escape gives more time for the reactions to work.

Move the fan further from the liquid solution up on top of the exhaust stack, also this means water or condensed fumes can fall back into solution instead going into the fan, do not put motor in path of the fumes.

Possibly add a small chemical pump to pull caustic solution from bottom of the barrel and spray it down from the top this can also help with escaping fumes and mixing as well as keeping fresh caustic solution on rising acid fume bubbles caught in the media.


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## Johnnycat535

Yea I got the idea after Sam's comments. I'm going to mount the blower to the top of the exhaust stack then attach a fan for cooling, and a vent cover to keep it dry. Once I have everything setup then I'll incorporate using some kind of additional filtration in the stack. I think I'll use a 2" pipe for the inlet and a 4" for the stack to better mount the blower. Also I believe that should mean less water in the pipes for when the blower is turned on, and better CFM at the fume hood. I may use instead of a T fitting a X fitting for even better surface area. That way I can drill much smaller holes, and much more of them. Being optimistic I feel this next prototype should be fully functional with only few modifications after testing. I'm excited to begin collecting everything tomorrow to begin assembling. I'll be sure to include pictures as it progresses.


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## Johnnycat535

Step one: I installed the fittings that connects the down pipe and fume hood inlet to the drum. I used a piece of rubber to make a gasket on both sides. The gaskets are sealed with PVC cement. The two fittings screw together as well so it should be enough to create an air tight seal that will hold up to the pressure. Let me know what you think and if you have any questions. Thanks everyone.


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## butcher

Looks like it will work fine, next time see if they have bulkhead fittings.

http://www.google.com/search?hl=en&q=bung+fittings&rlz=1R2RNQN_enUS457&bav=on.2,or.r_gc.r_pw.&biw=1024&bih=539&wrapid=tlif134855575904610&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=2lNhUMvtLMqeiALN0oHwAg#um=1&hl=en&rlz=1R2RNQN_enUS457&tbm=isch&sa=1&q=bulkhead+fitting&oq=bulkhead+fitting&gs_l=img.12...0.0.7.359.0.0.0.0.0.0.0.0..0.0...0.0...1c.ATxx_Bi8DWM&bav=on.2,or.r_gc.r_pw.&fp=4dda7dcaf871ccf&biw=1024&bih=539


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## Johnnycat535

I knew I should of asked about that before I went out buying parts. Live and learn though. I'll be sure to upload more photo's tonight as I progress. I hope to get the connection for the stack on today, but I don't believe they have any 4 inch PVC bulkhead fittings. Or at least I couldn't find them online from Lowe's or Home Depot.


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## goldenchild

That drum makes me think of what I'm going to do for my scrubber. I will be using 7 gallon buckets. Possibly a relay of them that look like this.


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## Johnnycat535

Two questions: First I'd like to reinforce the drum with a couple 2x4's placed inside. I wasn't sure it that would be a problem. Second I'm considering using a rheostat for my motor to better control the system. Would this work? http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380075545605 The blower I'm using is 120v 60hz and 12amps.Thank you all for your help. And I'll more pictures tonight on my progress.


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## Johnnycat535

Latest pictures. My drill died on me so I couldn't finish the holes in the diffuser. I'm also going to use pieces of rubber to put on the ends of the 2x4's with PVC cement to be sure I don't have any unexpected leaks. I'll have it fully assembled tomorrow given no problems occur. Wish me luck!!!


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## butcher

Looking good,

I do not know if will help but Harbor freight sells a cheap plastic welder, they also sell the plastic welding rods, or you can trim some of the same type of plastic from the article your welding to use as rods.


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## Johnnycat535

I thought of doing that to seal my pipes, but then I remembered I'd never welded anything and though it best to stick to what I know LOL. Do you have any knowledge on if that rheostat will work for my blower? And just wait till you see what I rig up to handle it getting over heated. Hopefully I'll be able to start that tomorrow.


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## butcher

The motor speed controller in the link above says:

Will work with any universal AC motor. 
Will not work on induction, shaded pole, soft/slow start, or brushless type motors.

So it depends on what type of motor you are using.


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## Johnnycat535

http://www.totalvac.com/B-010-5970ES.html?zmam=6843742&zmas=1&zmac=57&zmap=B-010-5970ES&gclid=CNLd2KCO07ICFQKCnQod_WAAWQ
That's the motor I have so It'll work. I just wasn't sure if these would damage the motor or not.


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## Johnnycat535

So I've got the holes all drilled, and the support beams screwed in and sealed with gasket sealant. Will the sealant hold up in the scrubber? Also will duck tape hold in the fume hood? I've had to use it and sealant to hold up the intake on the fume hood (Had a couple mishaps). Thanks for all the help I hope to have it and running by Friday.


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## 4metals

Johnnycat

I have used scrubbers that bubble the air through a reservoir and also ones that run it through a wet packed tower where there is more air to water interface. The real scrubbing is done when the fume comes into contact with the oxygen in the air and there is more available oxygen in air than in water. 

You made a comparison earlier to a bong, well if the water was that good at absorbing the fume, nobody would know what a bong is because it would filter out the fume and not much of it would pass through. Apparently its not that effective because I know a lot of people who know what a bong is!

Water is good at cooling a fume off and providing a high humidity enviornment in the scrubber which favors the reaction to decompose the fume. I have posted a fume scrubber design in this section which uses a venturi to pump the air and fume into water and up through a packed tower. http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=9115 The venturi actually causes a positive pressure in the scrubber to force the air through not suck it. My fear with what you are trying is that the negative pressure may implode your drum (cross bracing will help) but after all is said and done, the fume in water will not react as much of the fume as the fume in an air water interface provided by a packed tower. 

I'm not saying what you've done will not work, the NOx you generate may be sufficiently small to allow effective scrubbing the way you are doing it, but the efficiency of a wet, bubble it through water design is limited. Remember a bong cools the smoke but allows it to pass through. Even when filled with Sangria!


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## g_axelsson

4metals said:


> I have used scrubbers that bubble the air through a reservoir and also ones that run it through a wet packed tower where there is more air to water interface. The real scrubbing is done when the fume comes into contact with the oxygen in the air and there is more available oxygen in air than in water.



Do you really mean that? How can oxygen do any scrubbing action? I thought that the scrubbing action was that gases is absorbed into the water phase and neutralized by chemicals added to the water.
We want to have as large area of water-air interface, as long dwelling time as possible and as narrow channels possible to get the best scrubbing action. Gas molecules moves randomly and we want them to hit the water before they pass through the scrubber.

/Göran


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## Johnnycat535

Thanks for getting back to me 4metals. I've got it assembled and have added a check valve to stop the water backing up into the down pipe. I'll try and load some pictures tonight. I'm thinking about adding a water pump and packing to the down pipe and possibly the exhaust stack. I'm going to add a couple more reinforcement 2x4's as well to better help with it collapsing. I may have another blower I can add to it but I'm not sure how I'll be able to do it yet with a venturi. I'll be sure to keep everyone posted.


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## donnybrook

Very interesting John.C. I like the idea of using a venturi. Also on some of the old mercury retorts they added an apron of cloth (like a lantern wick) which drew water up and helped solidify or cool the remaining mercury vapours. Again I like what you are doing and look forward to seeing your final design as I want to build one myself. Regards, donnybrook from down under.


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## butcher

NOx gas can actually be several different types of nitrogen compounds, and they would not act the same, nitrogen monoxide (NO) will not dissolve into water, but it can pick up an oxygen from the air and make nitrogen dioxide (NO2) which will dissolve easily into water forming HNO3, from this we can see we would need to react NO with air before we react it with water.
Nitrogen monoxide (NO) can be bubbled into a solution of H2O2 in which the oxygen in solution will react with the nitrogen monoxide and form nitrogen dioxide (NO2), which then will react with water in solution to form nitric acid (HNO3).

Gases need time to react with water, take a bubble of gas going through water, it can pass through the water so fast very little of the gas has time to react, also the size of the bubble can also make a difference of how much of the gas will react, other factors such as temperature can also make a difference of how it will react.

gases flowing in a very fine mist of water (or solution) can react easier than a large bubble of gas flowing quickly through a solution as the gas and water (surface area has more contact).

HCl is a gas it can dissolve easily into water and make HCL acid, Chlorine is also a gas that can dissolve into cold water, Hot water will not hold much gas, just as hot air holds less oxygen.

Neutralizing acidic gases can generate heat, gases do not absorb into a hot solution as easily as they would a cold solution, (the hot solution can force out gases).


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## samuel-a

4metals put it wonderfully into words. That was exactly the point i was trying to convey.

In closed systems, very little NO2 is produced once the oxygen is depleted in the reactor, hance the need to expose NO to air.
Though, NO will react with caustic solution just as NO2, the scrub time is the main issue still.

There are gasses that will dissolve completly when bubbled through just 4" of cold water, Ammonia and Hydrogen chloride for example.
Oxides of nitrogen do not.


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## Johnnycat535

Hey everyone, I'm not feeling 100% so I'll be short tonight. I just wanted to ask about the need for oxygen. When the fumes are pulled from the fume doesn't oxygen come with it? Would this make for a factor in how efficient the scrubber may be. Maybe even perhaps a ratio of air to gas that's most effective?


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## samuel-a

Johnnycat

I it suckes from the hood, then enough oxygen will be included.


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## Johnnycat535

When you say if its sucked from the hood what do you mean? Where else would the fumes be sucked from? Are you referring to where the blower is mounted?


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## goldsilverpro

Although you get a lot of oxygen in the air exhausted by a fume hood, you get a lot of air dilution of the fumes at the same time. For each square foot of fume hood opening, it takes 100 cfm from a blower to exhaust the fumes. When you have, say, a 2' x 3' fume hood opening, you need 600 cfm of exhaust. The gas released in either the nitric or aqua regia reaction is NO. As butcher said, in order to scrub the NO, it first must be converted to NO2, which is scrubbed quickly. In a standard vertical scrubber, with packing and a sodium hydroxide spray at the top, the NO must be retained in the scrubber at least 8 seconds to be oxidized to NO2. With 6 ft2 of hood opening and open containers generating NO, the scrubber volume would have to be at least 600 x (8/60) = 80 ft3. That's equivalent to a 600 gallon tank. An example of a scrubber this size would be a cylindrical tank 3' in diameter, 11.3' tall.

Therefore, if you want to dissolve metals with nitric or AR in an open fume hood using open containers, you better have a big scrubber. The solution, of course, is to use a sealed dissolving unit with near-zero air dilution. That way, a tiny blower can be used and you would need a very small scrubber.

Another way is to have 2 or 3 scrubber columns, with the first column containing H2O2, which would oxidize the NO. To be able to dissolve in open containers, I've also thought about building a hood that could be sealed while dissolving and using glove-box type gloves.


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## butcher

Thanks GSP for those numbers.

An alternative to fume flowing through the fume hood from a reaction vessel, is to use distillation setup (refluxing) and several small scrubbers (series of jars) where the gases can mix with solutions before escaping into your fume hood.


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## goldsilverpro

My problem when thinking about scrubbers is that most of the refineries I worked in weren't dedicated to just simple stuff like jewelry scrap. They were large "job shop" refineries that accepted anything and everything coming in the door that could turn a profit. This came from many types of industries. They ran a lot of very large items that were difficult to fit into a reaction vessel and they couldn't afford to have dedicated equipment for each type of scrap. It was much more efficient and required less labor to run a lot this stuff in a variety of multi-purpose open containers than in a closed reaction vessel. When you run maybe 100s of different type material, with each requiring a little different cycle and play-it-by-ear chemical additions, a more fixed process done in a closed reaction vessel often doesn't work that well. Therefore, these companies all had huge fume scrubbers that could handle multiple fume hoods, Pfaudler kettles, etc., etc. At one place, one of the scrubbers was 20' tall and 6' in diameter, enough to handle 40 ft2 of fume hoods, kettles, or other exhaust openings. These giant scrubbers were, in essence, the cheapest way to go in the long run. 

From the control tests and calculations I used to make on these scrubbers, the numbers I gave earlier for standard NaOH scrubbers assumed 100% efficiency where, in reality, 70% was closer to the mark.

Whether large or small, though, the same math applies. 

With my limited knowledge in this, the only ways I can see to be able to use a smaller scrubber for a given amount of exhaust cfm is to (1) Oxidize the NO to NO2 before it gets to the NaOH scrubber, (2) Somehow, mechanically separate the NO from the air in the scrubber and retain it for a longer period of time, or (3) Use something other than NaOH. There may be other ways of doing these things that I'm not aware of. I would suggest that you listen to 4metals. He knows more about this stuff than anybody, especially for closed systems.


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## butcher

reactions With HNO2, sulfamic acid reacts to give N2, while with HNO3, it affords N2O.

HNO2 + H3NSO3 → H2SO4 + N2 + H2O
HNO3 + H3NSO3 → H2SO4 + N2O + H2O 

nitrogen and laughing gas :twisted:


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## goldsilverpro

butcher said:


> reactions With HNO2, sulfamic acid reacts to give N2, while with HNO3, it affords N2O.
> 
> HNO2 + H3NSO3 → H2SO4 + N2 + H2O
> HNO3 + H3NSO3 → H2SO4 + N2O + H2O
> 
> nitrogen and laughing gas :twisted:



Does it react with NO? NO is the problem.


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## Johnnycat535

If I where to run the fumes through H2O2 before entering the scrubber, is there a way to tell when the H2O2 is expended?


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## 4metals

Peroxide is a strong oxidizer, it is metered in with a dosing pump controlled by measuring the ORP (oxidation reduction potential) measuring and controlling pH and ORP brings this equipment beyond the range (financially) of a hobbiest or small refiner. 

It is possible to determine a quantity of nitric that can be neutralized by a dose of peroxide.


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## ericrm

i dont understand where the post is going .in first we have this rule, 8 sec will be ok, doesnt the 8 sec rule aply to no or nox?



4metals said:


> 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?



after rereading the gsp post about the 600 gal tank scruber ive understand...


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## goldsilverpro

4metals,

I know you stress the importance of a packed bed. What exactly does the packed bed accomplish? Does it simply separate and retain the NO in the scrubber for a longer period of time? Or, what?


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## Johnnycat535

So H2O2 oxidizes and neutralizes the fumes? And this may be a dumb question but could you just add H2O2 to the sodium hydroxide and water mix in the scrubber? Sorry if I'm coming off as that guy who just doesn't get it LOL. Not to say any of the information provided is contradicting, but it does seem that some things may be circumstantial to how your scrubber is designed.


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## samuel-a

Chris

Though i'm not 4matals, as far as i understand, it all has to do with providing as much surface area as possible in the path of the fumes.

Also, i think we should line ourselves up. Are we talking about closed system or open one?

What i refer to close system is, that the suction applies only to the reaction vessel forming small vacuum environment in it, thus the need to provide some fresh air to the scrubber inlet so any NO will oxidise to NO2 and not to chock the fan.
Though, i'm not sure this is even necessary as NO reacts with NaOH to form NaNO2 and later NaNO3.

An open system i consider a suction from a fume hood, where generated NO had the time to completly react with oxigen in the air to form NO2.
NO react instantly with air to form NO2.

Maybe my terminology is off...?


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## 4metals

Samuel is correct,

The reaction to reduce the fume takes place on the thin well oxygenated layer of water which is running over the packing in the tower. Tower packings are rated by the actual surface area per cubic foot of packing. They give the chemistry in the scrubber more contact area where the chemistry of choice can interact with the fume which is winding its way through the packing. 

Even the scrubber Chris referred to would only handle about 4000 CFM and that was pretty big. Without packing I doubt even that would work but the packing, properly wetted and with the flow redistributed to prevent channeling is the real workhorse.


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## Johnnycat535

Could you add H2O2 to your solution to oxidize the NO better?


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## samuel-a

Johnnycat535 said:


> Could you add H2O2 to your solution to oxidize the NO better?



Yes.
But i would consider this impractical. H2O2 is expensive and will quickly decompose with all the disturbance in the scrubber.


4metals
Do you see a need for oxygenating the scrubbing solution even if it contains NaOH/Lime solution?


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## ericrm

what is a good "inexpensive" material for packing ?


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## goldsilverpro

I always knew about the large surface area needed in the packed column but never understood the mechanism. In the scrubbers I worked with, they used berl saddles or tellerettes (designed by Edward Teller, I think), both of which have maximum surface area in the space they occupy. Also, I think they reduce channeling. In Hong Kong, we used certain shaped rejects from a plastic flower manufacturer as packing. In my copy of Chemical Engineers' Handbook, there are about 25 pages on packed columns. The title of the section this is in is "Gas-Liquid Contacting", which basically says it all. They improve the contact rate of the gas and liquid phases, which are flowing counter-currently. 

One place I worked had a 2600 CFM variable speed blower to exhaust the fume hoods, kettles, etc., with a scrubber sized to match that volume with 8 or 9 second dwell time. They adjusted the blower until red fumes no longer could be seen coming out of the stack. The result was a maximum of about 1800 CFM being possible.


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## ericrm

Plastic Tellerette Ring for gas scrubber tower
Compare
Plastic Tellerette Ring for gas scrubber tower

Min. Order: 2 Cubic Meters FOB Price: US $99-299 / Cubic Meter

Plastic Tellerette Ring
1.High Efficiency of transfer
2.Low pressure drop
3.Sufficiency gas-liquid contact
4.Low weight...

299x2 600$+ shipping is kind of hard for a packing option... any suggestion? or maybe a better deal somewhere?

can garden hose cut in 1/4inch be used or will the acid dissolve it?


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## 4metals

> Do you see a need for oxygenating the scrubbing solution even if it contains NaOH/Lime solution?



Caustic scrubbers are regarded by some to be 50% efficient at best at total NOx reduction, the thing is it is very efficient at removing the nitrogen dioxide from the fume (NO2). To completely (at least 95% or better) destroy all of the nitrogen compounds peroxide seems to be the poison of choice. That is caustic and peroxide together.

Everyone thinks that when the red is gone its all good. The thing is there are still colorless nitrogen compounds remaining like nitrous oxide (N20) which is colorless but considered a major greenhouse gas. The cost of testing a stack gas in unbelievably high and the EPA rarely if ever forces the testing if the fume is clear, hence there are lots of caustic only scrubbers out there.


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## goldsilverpro

In about 1980, a guy I worked for ran a lot of karat scrap. He had 12 hotplates lined up with a 4 liter beaker in a Corning Ware dish on each one. On top of each beaker was a loose fitting (to provide some make-up air for the blower), lift-off flat clear plastic lid, about 1/2" thick, with a vinyl hose (about 3/4" - 1") attached. The other end of the hose was attached to an exhaust manifold above made of plastic pipe. He did it this way because he liked working in open beakers. About the only other thing that was vented was a 50 gallon Pfaudler kettle. It had a loose-fitting fiberglass lid that was about 2/3 hinged for adding or removing material or adding acid. The unhinged portion had about a 3" vent pipe mounted on it. 

All of this was vented to a scrubber in an outside fenced area with a 275 CFM blower mounted at the top. The scrubber was a standard vertical caustic unit with a packed column and spray nozzles at the top. The scrubber was about 4' dia. X 12' high, which was about 4 times larger than what was theoretically needed for the 275 CFM blower. That way, he could add a larger blower and more beakers and/or kettles, if needed. Sitting next to the scrubber was a drum of 50% (6.25#/gal) caustic soda and there was a pH probe in the solution reservoir at the bottom of the scrubber. Some caustic was metered into the reservoir automatically with a peristaltic pump when the pH fell to about 9. An engineering company designed, built, and installed everything including the beaker lids, manifolds, etc. The total cost was about $25K. The refinery was located in a busy industrial park and, after the scrubber was installed, there were no complaints. Inside the building, there were no noticeable fumes or odors, even though there was no fume hood.

_______________________________

There are certain types of scrap that work best in 5 gallon buckets. The particular material I have in mind would react slowly and would generate some NOx, but not much. Also, the acids would be pre-mixed and no additions would be needed during the process. I've often thought about putting a heavy plastic or fiberglass rectangular trough, about 8" deep, in a fume hood. It would be large enough to hold 8 - 12 buckets, in 2 rows. The trough would contain water which would be heated by circulating the water through a pump on a hot water heater. The buckets would be lidded with a small adjustable hole in them for make-up air and vent tubes attached to a manifold above. I haven't calculated it but I don't think it would take a very large scrubber, or 2. There would be 2 separate blowers, a small one on the scrubber and a large one on the hood. The one on the hood would probably only be used when everything has finished, cooled, and when it would be time to manipulate things.


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