Fume Hood and Storage design

[dsmith2828]

Was looking for some input on the design of a fume hood / storage cabinet that I have come up with along with a two stage scrubber. I am by no means an engineer so please let me down easy if this design is completely ridicules. So with that said here is what I have.



The first image is of the hood / storage. As you will notice I have designed it along the lines of a sand blasting cabinet. The top section, reaction chamber, would be somewhat sealed with with a 4" opening for fresh air and a 2" opening for an exhaust manifold exit to the scrubber. The chemical gloves will be attached to the cabinet with the opens at the front. Again just like a sand blasting cabinet. The bottom will be for storage with an exhaust port to pull the fumes from the chemicals into the second stage of the scrubber.



This image is of the two stage scrubber that I was looking to use. The primary scrubber, the larger of the two, would handle the reaction chamber and then feed into the secondary scrubber. The secondary scrubber would handle any fumes coming off the chemicals in the storage area, mainly HCL, AP and the Bleach / HCL mix, and any fume left over coming from the primary scrubber. This then would feed into a charcoal filter and back into the garage. The mix to reduce the fumes down with in the primary and secondary scrubbers would be water saturated with sodium carbonate. Both scrubbers would be made of 6" PVC with either 2" or 3" PVC connecting everything.

As you can probably noticed, this is a modified version of the one that 4metal's posted.

I am looking to build the cabinet out of plywood and the scrubber out of PVC. Not sure on the fan units as of yet. Really was looking to see if this was a safe design for a small operation in a garage attached to a house. So again, any feedback would be appreciated.
Thanks in advance.

 

[4metals]

I would consider exhausting out of your work area, you will never get complete scrubbing and you will always have an odor of some chemical essence coming out of the top.

Using a sand blasting cabinet design will limit your ability to do some things because of the limited dexterity with those big gloves on. On the other hand the low air change of the hood will allow for better scrubbing. I can't picture me picking up a sheet of pH paper with those gloves on.

 

[dsmith2828]

The area that I would be able to exhaust it out to would be to my side yard through a window. The window has an alumimum frame and I have the AC unit out there as well. Which leads to the question, do you think the scrubber design that I have will reduce the fumes enough so I will not have to worry about those items?

As for the gloves, you are right, it will be a little difficult to work with on small items. But it is something that I will have to put up with considering the work space that I have. That couple with not having to worry so much about the chemicals being stored in the garage is a benifit for me.

So over all do you feel that it is a good design and one that is workable?

 

[4metals]

It's hard to say if the scrubber will be effective. It depends on the chemistry in the scrubber, what quantities you are processing, the retention time in the scrubber and the list goes on.

If you have built this already, and if I remember you live someplace warm like Florida, why not set it up outside, remove the charcoal filter or enclose it so you can place a length of un-painted aluminum duct after the discharge. Run a typical lot and check for signs of attack on the aluminum.

The aluminum is acting as a test indicator for your scrubbers effectiveness, if you get no corrosion, I would consider it safe to discharge outside and keep the stub of aluminum to test occasionally. Inside could be a real issue, I would never trust it. If the attack is very mild you could elevate your discharge above your rooftop.

 

[dsmith2828]

Yeah currently I am looking at small amounts using AP and then HCL / bleach in 2 gallon buckets. Overall about 4 cups of chemicals at a given time. Nothing really more than that being that I am just starting out.

As for building anything, it is all theory at the moment. Wanted to make sure that it is a safe design before building. It is a lot easier to change it on paper than it is after the unit is built. :lol:

I do like that idea of putting aluminum in where the charcoal filter is as a test indicator. Would be a quick way to verify things once it is built. Not sure on placing it outside though. Would have to run electrical for the fans to make it work, will have to look into that though or like you said just run a vent out just above the roof line. Being that it will be PVC, won't have to worry about lightning strikes.

I will have to start working out what to use for fans next and make sure that it is not pulling the fumes through to quickly. Make sure they stay in the scrubber as long as possible. With that said, do you see any issues with using sodium carbonate to reduce the fume and if that is OK how often do you have to add to it to keep the PH up on it for this type of scrubber?

 

[4metals]

Building blowers like described in this thread http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=8994&p=93013#p93013
will keep the blower away from the corrosive fumes. If you get good enough suction you may be able to replace the glove holes with an open front that closes when you aren't manipulating the solutions in the hood. You also have to leave an opening for fresh air to come into the hood while you are exhausting through the scrubber.

as far as how much carbonate to use, pick up an inexpensive pH probe at a hydroponics store and keep the solution at a pH >7. If you track how much alkaline you add per unit of acid you will end up knowing how much carbonate to add before you start a reaction.

 

[dsmith2828]

4metals, thanks for all the information. I will change the primary scrubber fan so it pushes the fumes through the scrubber instead of pull. Well actually both the primary and secondary scrubber fans. Be able to keep the fan motors around a lot longer.

With that, it would be nice if it does produce enough suction so the front could be open with a door as you said. Easier to work with.

As for the fresh air inlet, do you think the 3" opening is enough as drawn or should I go to a 4" opening to allow enough air flow?

 

[4metals]

Why not drill a 4" hole and cover it with a hole saw waste circle from a 5 or 6 inch hole saw attached with 1 screw at the top so it can be either opened full or closed partially as needed by swiveling the cutout circle.

 

[dsmith2828]

Excellent idea. You are definitely all over this. I will draw up some new plans and post them. Thanks again for all the great ideas and direction on this.