New fume scrubber design

[Lou]

SBrown:
Beautiful hood and a great deal you got there! Wish you did my shopping!




As far as bed packing media...we just make Raschig rings out of PVC pipe sections. More surface area, better flow through, more turbulence, more scrubbing efficiency in a countercurrent column. Problem is you need a greater pressure drop on your blower.

I've seen one very industrious well-known refiner here on this forum build one out of two 55 gallon drums and make his own PVC manifold--as good as the Italians make and about 10^2 cheaper.

 

[overdriv]

Any ideas on the best way of connecting the scrubber without cutting into the metal if I can help it? I was thinking about having taps plastic fabricate a bottom ring that the hood would set on, out of polypropylene and put the scrubber pipes through that into the inside of the hood and then just simply pipe them inside to wherever I needed suction.

Any ideas on that?

1.How you get the suction into the fume hood is up to you. Try not to over think this thing. There are two things to remember. Your fumes when hot will rise easily and air flow/ suction is important at the top. Mine is not perfect and I would change some things. If you do have a pipe coming up from below inside the hood then you have less room for beakers with reactions. Also you have now a hole in the floor for PGM's to spill out if you have an accident. Try to find a spot on the side up high, on top or on the back up high.
a. Also the acid fumes when you are not heating them will tend to drop down to the bottom of the lab hood.
b. Provide an air supply that is equal to the air you are drawing.. Notice the air intakes on the front of the lab hood. Mine should be bigger. Although, I can watch the reactions happen with the window open or with the window closed.

2. The pipes that I used on top of my lab hood are really too small.... They work well and are acid proof. A 2", 3" or 4" pipe would suck more air. Schedule 40 or 80 would work well for this.

3. The air flow into the Scrubber is NOT bubbling. You have the Bio Balls and they will increase the area that the fumes will have to react with the wet spray. If you notice that the pipes going into the scrubber are not at the bottom and there for there is NO bubbling. The lawn sprayers that I used will spray a curtain of water and the spray created a mist as well. Using 55 gallon drums was overkill.... way overkill. With your Bio Balls you should be able to get away with 30 gallon drums.

4. If you proceed to go down the path of bubbles floating up through the Bio Balls, you will run into two problems.
a. You will have to either have to create a pump pushing the TOXIC FUMES into the scrubber or through the water. The first will probably force the toxic fumes to leak out and the second will cause your plastic drums to collapse (trying to suck the fumes through the drums collapsed mine).
b. You will make the thing not as simple to operate.

I am assuming the pump is a submersible in the small blue container on the cement in front of the reservoir rack?

There is a acid resistant pump in the bottom of the front reservoir. Make sure it is powerful enough to pump the water vertically up to the sprayers. This is only for spraying water and does not suck the air from the lab hood.

Or is that wrong, I see the fan, and the large 12" conduit, I am assuming that the conduit is expelling offgas and the fan facilitates by pushing rather than pulling? That way it doesn't have to be acid resistant?

Yes, it should be acid resistant or just be prepared to buy new ones later. The fan you can not see is pulling the air through lab hood and through the scrubber (the sprayer wash) and outside very clean. It is also pulling air out the the lab.... You will appreciate this when you start pouring acid outside of your lab hood. Also it is mainly aimed at the floor scooping up fumes at the floor level and at the torch/melting/table. The fumes from this area is equally toxic.

Do I need two? I was going to use one, and then make a 6-7 ft spray down tower with the spray nozzle at the top and make it out of 12" conduit. If I split the pump like you have, into two 6ft tall, 12" PVC conduit and had them come out of the top of the barrel would that be enough? Or do you think I should just use two 55 gallon barrels?

1.The first barrel with a sprayer on top and bioballs in the middle and crushed marble at the bottom of the barrel should (estimated) take out 90% of the toxic fumes. The second barrel configured the same will further reduce the toxic fumes.
2. I am not a guru on this stuff so if someone else has more knowledge than me please chime in.
3. Remember the fan should not be dedicated solely to the lab hood and scrubber. By making it take air from the lab as well you will provide a safety valve for the fan in case of a blockage in the scrubber or lab hood. You actually increase the pulling power of the fan for the scrubber, (this is as long as you choose a fan that is oversized).

One tall chamber will have one inherent problem. The sprayer will spray out at an angle and probably hit the walls of the PVC. The water will then run down the walls and not react with the bioballs or the fumes. If you use two 55 gallon drums like I did then fill the drums with bioballs up to the point where the sprayed water will splash evenly over the balls and concentrate on the walls or the center/middle of the drum. This allows the fumes to react with the water soaked bioballs and become a weak acid. Dripping down to the crushed marble and becoming neutralized.

http://www.usplastic.com/catalog/search.aspx?search=fans,%20acid%20resistant&page=1


Remember the lab hood, the scrubbers are the tools, the fan is the life saver.

Crushed marble can be found at building materials yard.

 

[NobleMetalWorks]

Thank you for correcting and clarifying, I really appreciate it.

if you look at the hood, the two sides have open holes, I have pieces of polypropylene plastic it came with that fit, with acid resistant seals, in the holes. I am planning on having holes cut large enough and attaching two - four pvc suction pipes, the top has a hole where the vent used to attach, it covers about 3/4 of the distance across the top of the hood. I am planning on fitting a piece of polypropylene in the vent hole, and dropping a PVC pipe into the top part of the inside of the hood to suck gas that reaches the top (heated NOx, etc). On the back, I am planning on setting the hood on a polypropylene collar that will allow PVC pipe to suck from the back, and nothing in the bottom of the hood, you are right I didn't think about any spilled aqua regia wasting down an outgas vent.

I might decide to use sheets of 1/2 polypropylene cut to spec by taps, and fabricate the scrubber myself. If I can use some type of clear plastic, so I can see everything going on in the scrubber, I may go that route unless there is something I am missing or should know? Taps sells a bonding liquid that fuse the parts together using a regular propane torch, no plastic welding.

I will have another hood that is 6ft across, similar to the hood I just purchased. I bought it from a different person, paid to have it shipped to me but I no longer need it. It arrives tomorrow, if anyone is interested let me know and I will snap pictures and post all the information, manufacturer, model number, etc tomorrow. I am only going to ask what I actually paid for the hood, plus what it cost to ship it to me. Also, I am having Taps Plastic fabricate some of the pieces I am going to use, if anyone is interested in the hood I could have parts fabricated at the same time, and just charge you for the cost. I live in the San Francisco Bay Area, so if there is someone in the area that is interested you can pick it up in person. If not, I would be willing to drop it off at a freight company within a reasonable distance from me, that will band it to a pallet and ship it to you. I would just ask, since I am going to sell it for what I paid and shipped it for, to pay for any gas past 30 miles so that I am not loosing money. I don't mind selling it for what I paid on this forum, but after a week I will put it on eBay for double the price, and still be way under what you can but the hood for, from anyone else, used.

 

[overdriv]

Thank you for correcting and clarifying, I really appreciate it.

I might decide to use sheets of 1/2 polypropylene cut to spec by taps, and fabricate the scrubber myself. If I can use some type of clear plastic, so I can see everything going on in the scrubber, I may go that route unless there is something I am missing or should know? Taps sells a bonding liquid that fuse the parts together using a regular propane torch, no plastic welding.

On your scrubber think KISS. The more you make it complicated the more that can go wrong with it. Like leaks....... water and gases. Think of it as exhaling all the bad fumes you do not want to breathe... outside. Yes, processed to do your part environmentally. That is why I used two 55 gallon barrels. However two 30gallon barrels the way you are doing it would be way overkill. What really is there to see inside the scrubber? Water splashing around. Pretty dark in there unless you are going to put in a light. The fumes would become very transparent in that environment.

Good luck.

Nick

 

[NobleMetalWorks]

Thank you for correcting and clarifying, I really appreciate it.

I might decide to use sheets of 1/2 polypropylene cut to spec by taps, and fabricate the scrubber myself. If I can use some type of clear plastic, so I can see everything going on in the scrubber, I may go that route unless there is something I am missing or should know? Taps sells a bonding liquid that fuse the parts together using a regular propane torch, no plastic welding.

[\quote]

On your scrubber think KISS. The more you make it complicated the more that can go wrong with it. Like leaks....... water and gases. Think of it as exhaling all the bad fumes you do not want to breathe... outside. Yes, processed "bad fumes" to do your part environmentally, "Thou shall not kill thy neighbor". That is why I used two 55 gallon barrels. However two 30gallon barrels the way you are doing it with bio balls would be way overkill. What really is there to see inside the scrubber? Water splashing around. Pretty dark in there unless you are going to put in a light. The fumes would become very transparent in that environment.



Umm, did you mean the fume hood or the scrubber? I would use a 1/4 inch glass on the fume hood to look in. That makes it very nice to see what reactions are happening in the fume hood. Make such window at the least 2ft wide.
Good luck.

Nick

The fume hood has a counterbalanced glass door, here is a picture.

And if you notice on the left hand side it also has an airflow meter, and on the right, on the glass and the supporting frame there are arrows that when matched up, are suppose to be the operational level the glass door should be drawn down to.

The reason I thought clear poly is because in the plan it asks for windows in the spray down tower, so you can see what is going on. I thought instead of adding a view port, and making the fabrication more expensive, I could make the entire scrubber out of clear poly so that I can see everything working properly and would not have to use any view ports anywhere on the scrubber. All I would have to do is use a band like you have, or clamps, or some other way to fix the spray down tower to the reservoir. In that way I can get rid of the access port, and the view port and save on fabrication costs, and have the added extra benefit of being able to make sure the spray down tower sprayer, and all the other components, as well as the reservoir, substrate, etc were all working properly. The filters on my salt water reef tanks are all clear, here is what one looks like.

That is a reef filter that I just use for my sharks, the reef filters that I use for my reef tanks are a little more complex, but you can see what I am talking about. Here are some pictures of my old venturi protein skimmer and a new one I am replacing it with I just had modified by Taps. I figured since I was switching them out I would post some pictures so everyone understood what I have been blabbing about.

This is what I was trying to explain, about the bubbles, but I am not going to attempt anything like this anytime soon. I need to do a lot more reading before I can figure out if this would actually work, or be beneficial at all. It kind of works on a similar principle as the venturi scrubber, except the scrubber exhausts air, where the protein skimmer captures nitrates/nitrites in the catch.

You can see all the sludge, the negative charged nitrates and nitrites that float to the top, then when the bubble pops it's cause in the catch. I had thought, if a ventruli filter could be made to do the same with the Nitric or other acid values in the water of the scrubber, it would be easy to balance the PH, because you would actually be removing them from the water. I just don't know enough to know if this can actually be done or not, and you are right it would make the scrubber that much more complex. But running the reef filter, and the ventruli protein skimmer, makes the water so pristine that my tanks shimmer.

I am just going to adapt the bio balls for now, and try other things out after I have a good solid working system.

 

[overdriv]

Well my friend you are truly amazing and my hat is off to you on the aquarium thing. The aquarium tank with the bioballs in it would probably work fine. (I AM OUT OF MY LEAGUE HERE, so please others that know better chime in.) The acid fume will be strongest in the pipe going to the scrubber and of course in the lab hood. Once it hits the water it will become a very weak acid. Once it hits the base elements it will start to neutralize.

I can not wait to see your good results. If I do not understand what you did I will ask about it and maybe I can learn from you. Good luck.

Nick

 

[NobleMetalWorks]

Well, if I was going to use the tank, I would have to do something with the fish, lol, but thank you for the kind words.

I think I am going to take your advice and start off simple, I was only using the pictures to illustrate what I was talking about a little better. I read through what I posted, and I couldn't even understand it, ha. No, I knew what I was trying to say, but I just wasn't able to make it clear enough. Maybe if I had a stick and bare earth to scratch it out on, but pictures are the next best thing!

I know I'm going to have a lot of questions still, but I don't think I'll have too much of a problem putting a scrubber together. And thanks for the support!

 

[butcher]

Beautiful saltwater reef tank, I know you have had to learn a lot, to be able to have that nice of tanks, and to keep them critters alive, my daughter just started learning salt water tanks, and said she is learning the chemistry to take care of them, she said it was like listening to me talk about gold refining chemistry.

I believe from what you know of the salt water chemistry it will not be hard to use that knowledge in the gold refining, although we do not work with the organic bacteria changing ammonia to nitrate, there are similarity's in the chemistry, I can see your already using the knowledge in this field to build your scrubber.

The little nitrate factory you have there, it is beautiful and impressive.

 

[NobleMetalWorks]

Hey, thanks a lot, I love it when people enjoy my tanks. I have had some of them since 1991. And you're right, salt water tanks have all kinds of chemistry going on, biological in nature for the most part but also inorganic as well, like charcoal, it's used to absorb ammonia as water passes through it. If you ever need help with anything to do with salt water aquariums I would be more than happy to try and help.

 

[butcher]

Thanks, I will let my daughter know.
Now we just need to learn to make nitric acid from that tank skimmer sludge.

 

[Lou]

SBrown, do you know Bill Wann?

He makes a mean scrubber and is an excellent source for reasonably priced big glassware.

 

[4metals]

SBrown,

Very nice reef tank. From what I gather from quickly reading your posts is you are thinking that a protein skimmer type device will scrub your nitric fumes and enable you to somehow reconstitute your nitric.

Nitric is removed from the air column in a scrubber by oxidation in the air on the surface of the tower packing (bio balls) The alkaline pH of the solution which has wet the fume on the packing neutralizes the fume. In reality a caustic only scrubber is at best 50% efficient at neutralizing NOx. adding peroxide either to the scrubber or the reaction can increase the efficiency. The big key is retention time in the scrubber. 8 seconds is good. If you think about it passing all of the air moving through the hood you will need to scrub a lot of air. I recommend a general exhaust for the hood and a manifold from closed reaction vessels directed to a smaller scrubber with the proper retention time.

I have seen devices similar to your protein skimmers used in refining of electronic scrap. Parts with exposed gold plating were granulated and etched in a solution containing 50% nitric acid to release the foils of gold. The solution also contained potassium phosphate and citric acid to act as a frothing agent. The froth acted like scrubbing bubbles to release and float the gold particles in the froth where they were collected. The system is more efficient at removing the gold foils and the separation is effective. The protein skimmer on fish waste is an example of foam fractionation working on a hydrophilic compounds in the aquarium water. The foam fractionation to collect the gold flakes is an example of stripping non surface active particles from the waste stream. The reason I say this is not an effective method of scrubbing NOx is while watching the process, visible red fume passes right through the foam layer and is pulled into a classic fume scrubber.

 

[NobleMetalWorks]

If my hood is fairly air tight, couldn't I lower the shroud enough to only allow as much air flow as the scrubber can handle going in? So long as the shroud face has positive air flow into the hood? I have 2 air flow meters, I was thinking I could use one on the outgas exhaust conduit, and one on the hood for air intake, balance them so that the two match and the hood is only bringing in as much air as the scrubber can handle? The only problem I see with that is the air flow meter being damaged by NOx. In your opinion should I scrap that idea (no pun intended "scrap") and just make a reaction vessel out of poly?

On the protein skimmer, the way you describe it, I can make that work. I have been designing and building protein skimmers for my own personal use and a few close friends for about 20 years, it's only been recently that I have purchased them. I probably have enough old protein skimmers to test several different designs. I might play around with that after I have a working system put together. Thank you so much for all the information! It's a very interesting concept at the very least.

 

[4metals]

Don't get your hopes up for the hood being tight, those laboratory hoods have an airflow pattern that remains constant. If the door is down the full CFM flows over the top vents into the hood and vened through the blower. If the door is open, the top vents are blocked and the air influx is through the door. My guess that's a 6 foot hood so the full opening is likely at least 6 feet by 2 feet.

Conventional exhaust protocol will require a 1200 CFM blower for that hood. An efficient scrubber for that hood will be huge if you want to scrub all of the air. To give you an idea of size, if you had 2 full 55 gallon drums, one atop the other and filled to the gills with bioballs, your CFM capacity to hold the fume in the scrubber for 8 seconds will be 110 CFM.

I would opt for 1, 55 gallon drum of balls and a 50 cfm blower running through a manifold in the back of the hood. A sealed "reactor" can be as simple as a 5 gallon Spackle bucket with a bulkhead fitting close to the top on the side where a hose hooks up to carry the fume to the manifold. you can easily remove the lid and add chemicals or scrap to the bucket and replace it to regain suction. All the while the main exhaust will remove any fugitive fume. Plastic band heaters will warm the acid in a plastic pail nicely if necessary.

 

[NobleMetalWorks]

Thank you, makes perfect sense. I was thinking of a reactor that I could remove or insert as needed. I have a poly base I milled a round slot that fits the lip of a 5 gallon plastic bucket. If I used that with PVP pipe from the bucket to the scrubber I would have a cheep and easy, and most important safe reaction chamber I think.

I was also thinking about something like this http://www.ebay.com/itm/Nederman-Fu...029?pt=LH_DefaultDomain_0&hash=item1c1875b315 to connect the scrubber to so that I can easily move it around in the hood but it would be out of the way when I didn't need it. Any thoughts of this?

And thank you again for the help!

 

[4metals]

The arm can only exhaust one reaction at a time, I would run a 4" manifold across the back of the hood with 6 inch and a half drops, each with their own shut off valve all leading into the scrubber inlet. This way you can have some digestions cooking on one or two drops while precipitating gold on another drop.

You could also build a foam fractionator to collect your foils and scrub the fume coming off.

You never mentioned what type of refining you're doing or the size of your process lots so it could very well be you only need one collection point.

 

[NobleMetalWorks]

I am very new to this if you couldn't already tell. I paid off my initial investment so I have stopped processing for the time being, and am concentrating on getting my work area the way I want it, hood, scrubber, lighting, ventilation, etc. I am primarily recovering gold from e-scrap, however I have run some plated jewelry through an HHO cell with awesome results. I am not planning on growing big enough that I have to hire employees, been there, done that, bought the t-shirt and it's just not for me. I only want to do this to supplement and perhaps eventually make a living this way, or maybe a little more. But I am not expecting, nor am I intending to make millions doing this, anytime in the near future.

However, I am set up, or will be, to be able to deal with large quantities of scrap. I have beakers up to 4000 ml, so whatever I do has to be able to encompass beakers that size, I am using two heat pad/stirrers and I have to tell you, I love the stirrers, makes a huge world of difference. When I am running I usually have 6-8 large 2000 - 4000 ml beakers at different stages of processing. I was doing anything that was reacting, giving off gas, outside. But I was starting to process so much that I was afraid if the wind blew the wrong way, I would be polluting my neighbors air, not to mention the fact that when you do large amounts, you create huge amounts of NOx. I was reacting 10lbs of pins/finger boards at a time.

I think your suggestion is probably better than my fancy costly solution, it makes a lot more sense, I could also use the same lines for suction, for Buchner filters, so long as I attach a fitting for the rubber hose.

So, I am recovering and refining, reacting large amounts in large beakers, and I have several going all at the same time, at different points in the recovery or refining process.

Did I answer everything?

 

[4metals]

Then you definitely need to be doing more than 1 thing at a time (someday) . This is an example of the manifold, a change, made since this was made, is to have the tee's extend to the back of the hood horizontally into a shut off valve and then a 90 degree elbow and the hose. This does 2 things, one it allows lines to be shut off increasing suction to others and two it prevents condensate from running down the next inlet down the line.

A tee replaced the manifold elbow that goes up with a reducer and a 1/2" valve to drain the "scrubber juice." There is definitely value in scrubber juice, so always check it with stannous.

 

[NobleMetalWorks]

That makes sense!

What type of material is the flexi hose made of? Is that PCV or is it Poly or some other material?

I was wondering who made the hood, I see in the upper right hand corner the tag of whoever made it. Did they also design it, or is the design your own? It looks very well built, best custom hood I have seen, and lately I have seen a lot of hokey systems for sale.

I am going to end up trading in the three 6ft hoods I have, for one 4ft poly hood, and a few other items/money. Not positive but I speak with the guy again tomorrow. Anything other than being made out of Poly with the glass sash I should be aware of? I am going to make sure I get an air flow meter/alarm. Is there anything else besides the scrubber that I should think about and maybe ask him to throw in on the trade?

 

[4metals]

The flex hose is polyethylene off the shelf item from US Plastics.

http://www.usplastic.com/catalog/item.aspx?itemid=23022&catid=567


The hood shown has a plexiglass eye shield which folds up. generally it is down and the main exhaust is sized for the opening with the shield down.

This hood is made by Chem Tec form Long Island NY http://www.chemteksys.com/Fume-Hoods.html