So should I have 2 fume hoods or 1

[PreciousMexpert]

I would like to build a fume hood similar to this.
I am wondering whether to have 2 blowers or 1.
The reason whether to have the second blower is that what happens when you remove the tube from the reaction vessel some gas will escape into the air and that might be bad for me and the environment.
So should I have 2 blowers or 1.
Also where do I place the second blower if I decide to have a second one
Thanks


http://goldrefiningforum.com/phpBB3/memberlist.php?mode=viewprofile&u=9899

 

[4metals]

I always like to have 2 blowers, one scrubbed and one not. In a conventional hood the exhaust requirement of 100 cfm per square foot of opening means you need a huge blower for the hood you show in the picture. A 4 x 8 opening needs 3200 cfm for good exhaust.

The scrubbed exhaust is only sucking out of the ends of all of the tubes so even if you give yourself a factor of 10 the area of a 2" diameter drop is 31.4 sq inches, you can have 3 drops per 100 CFM of blower. In an 8 foot hood, having 6 drops should be adequate. So a blower giving you 200 cfm after the resistance of the scrubber would do fine.

For the hood itself, you can place sliding doors so the hood can be closed off partially. If you arrange your doors so you always have it half closed you can get by with 1600 cfm for the main blower.

Once your chemicals are added and the reactions are cooking, sealed reactors can allow you to shut off the main blower and just scrub the reaction. Big benefit in putting up reactions at night because you can shut down the main blower. Where I've done most of my refining, that means not coming in to ice in the refinery in the winter.

 

[PreciousMexpert]

Hi 4metals!
Thanks for your help

 

[PreciousMexpert]

I notice that he does not have a condenser and he probably closes the passage of the holes partially.
Is that good

 

[4metals]

If you look at the picture closely you will see that every flex tube has a shut off valve at the top to regulate flow. I'm sure the exhaust goes to a scrubber. A condenser doesn't eliminate the need for scrubbing it only lowers your nitric consumption by condensing the fume back into the reactor. Usually a condensed aqua regia reaction will go to completion with aqua regia at a 5:1 ratio.

 

[PreciousMexpert]

Hi 4metals
When you say
condensed aqua regia reaction will go to completion with aqua regia at a 5:1 ratio.
what would be the approximate ratio for something like what you see in the picture
Exactly what do you mean by 5:1 ratio
Thanks for your help

 

[4metals]

In a condensed reactor the condensed fume, mostly nitric, falls back into the reactor essentially replenishing the nitric. For stone removal I like it because you can really heat up the reaction and dissolve up those last bits of chloride encrusted metal so cleanup is easier. For digesting cornflake shotted gold I don't see the same benefit. Karat gold scrap which has been melted and has a silver assay below say 9% does not have to be heated above 130 degrees and the savings in nitric are minimal.

The ratio is the amount of hydrochloric compared to the amount of nitric 5:1 condensed. Without a condenser anywhere between 3.5:1 to 4:1 works. It is always best to measure out your acids, add all of the HCl and 1/3 of the nitric and slowly add the excess nitric until the reaction stops. This way you can avoid adding too much nitric and dealing with all of the aggravation getting rid of it before you drop the gold.

 

[PreciousMexpert]

Hi 4metals
Thanks for your help
I tried to find a plastic container to use a hood and couldn't
how about using Plexiglas
http://en.wikipedia.org/wiki/Poly%28methyl_methacrylate%29
I said I should make a smaller version of what you see in the picture maybe
4 feet by 3 feet
I thought about making the walls with Plexiglas and attaching them together with plastic nuts and bolts and gluing everything with acid resistant glue
Thanks again

 

[4metals]

Build one out of plywood and get it coated inside and out with the coating they use to spray bed liners in pickup trucks. Check with your surfing buddies, all the surfers where I came from use the spray on bed liners to keep the salt water from rotting out their pickup truck bed.

Quite a while ago I posted on how to build a hood then a scrubber was added into the mix.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=4776

 

[PreciousMexpert]

Hi 4metals
Thanks for your help
I appreciate it very much

 

[PreciousMexpert]

Hi 4metals

Place a stop so the door always stays 3 or 4 inches up from the bottom,

Is this to create a draft.
how about blowing compressed air into that opening
Here is something about that idea
http://www.ehs.ufl.edu/lab/fumehood.htm#design

Do not position fans or air conditioners so as to direct airflow across the face of the hood. This can interfere with airflow and containment of hazardous chemicals.

This is written right underneath the picture

 

[qst42know]

Compressed air could work but it would take a very large compressor. I have a 5hp compressor that won't run a pneumatic Gast vacuum generator to capacity. A blower will give the velocity and volume required more efficiently.

 

[goldnugget77]

qst42know that is very helpful thanks
I know a situation where refining is done and right above where this is taking place there are heating pipes
and other plumbing pipes in the ceiling which is about 5 feet away from the fume hood.
The person just started doing this so we don't know what the effect will be.
My question is that will any harm be done to these pipes
and how can the pipes be protected
Thanks

 

[qst42know]

I don't have any experience running or designing a refinery but I would expect a good coat of paint would go a long way in protecting nearby metals.

 

[goldsilverpro]

In my experience, most paints don't stand up too well on hoods, even epoxy. One place I worked had acid proof tile/mortar on the floor and inside the fume hoods. Worked great, easy to keep clean, but hell on glassware. I have seen wooden fume hoods coated with several coats of boat resin (applied on fiberglass cloth). One place sent their wooden hoods out to have a coating of PVC "chopped" on them. These "chop" guns can apply many types of pure plastics dry (but molten), without solvents, at about any thickness you want - not terribly expensive. On some of the wooden silver cells I made, I had a "chopped" PVC coating applied to them - lasted forever if you didn't bang them around.

 

[goldnugget77]

Hi Folks
Thanks for your reply
I am thinking if there could be major damage to these pipes.
They are hot all the time
i said maybe I could make a compartment but I dont know if that will work

 

[qst42know]

Paint isn't a permanent solution but it's better than exposed. Kind of like your car. I get that it's no protection for direct exposure. The better the prep work the longer it will last and at least it is some level of protection for casual exposure.

 

[goldnugget77]

qst42know
What do you think of the idea of making a plastic cover and sealing it all over
that way there is no exposure

 

[qst42know]

I guess I don't understand what you are trying to cover?

Something within the room you are working in, or something in the actual fume hood?

 

[goldnugget77]

what i am trying to cover are steel pipes
they are about 4 inches in diameter
and they are worm or mildly hot
they are in the same room where the fume hood is and are directly exposed to the atmosphere.
there are also smaller pipes 2 inch pipes that are also steel
all this is about 3 to 4 feet away from the fume hood