6' Fume Hood

[devala]

Greetings! I have not posted before, but I have been reading for several weeks now. This forum is by far the best on PM refining I've seen anywhere on the web, bar none. Thanks to all that have worked so generously in bringing this information together in one place and sharing it so freely.

I was looking into some DIY hood designs, after reeling from the very high prices on pro hoods, and I came upon this thread. I've been intrigued by the Venturi designs some of you have proposed, but I have some concerns about face velocity. In doing some research today I came across these Allegro blowers, both axial and centrifugal, and I was impressed by the design, cost, and high output of these units. I wanted to share what I've found and ask for your feedback concerning the feasibility of using one of these for a DIY fume hood.

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Allegro Axial Blower 1842 cfm 12" $375 + s/h

http://www.ebay.com/itm/Allegro-Axial-Blowers12-Plastic-Blower-/190543729570?pt=LH_DefaultDomain_0&hash=item2c5d4a93a2#ht_1202wt_925
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Allegro Centrifugal 3/4HP 1570 cfm 8" $850 + s/h:

http://www.wayfair.com/Allegro-High-Output-Centrifugal-3-4HP-Electric-Blower-9504-50-OAO1171.html?refid=GPA49-OAO1171&gclid=CNH6iZysz64CFWwGRQod9RNbWg

Only $550 + s/h on eBay:
http://www.ebay.com/itm/Allegro-Axial-Blowers12-Plastic-Blower-/190543729570?pt=LH_DefaultDomain_0&hash=item2c5d4a93a2#ht_1202wt_925
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These blowers are described as chemical and corrosion resistant, but I believe they all have ABS housings. I'm not sure about the inner materials, but while ABS is very resistant to HCL, it is not at all resistant to HNO3 and H2SO4; so I was thinking these might not be suited as inline blowers but that they could be low cost, high cfm candidates for the Venturi designs being discussed here.

 

[devala]

Here's another possibility:

Allegro Venturi Blower $450 on eBay:

http://www.ebay.com/itm/Allegro-Industries-9518-08-14-1-4-in-diameter-Venturi-Blower-BRAND-NEW-/280836508901?pt=LH_DefaultDomain_0&hash=item4163290ce5#ht_724wt_1141

From Allegro:
http://www.allegrosafety.com/

The Venturi Blowers are a perfect solution to moving air in refineries, utility and power plants, shipyards, paper and pulp plants, the marine and steel industry and manhole operations. Anywhere where fumes that may be poisonous, explosive or hazardous from process towers, tanks, large pipes or confined space need to be removed. You can cool workers in elevated temperature conditions, or heavy equipment. Our line of high-performance, lightweight Venturi Blowers help to create a safe, healthy working environment leading to greater efficiency and productivity. Welding fumes, hot air, gases and smoke can all be removed quickly and easily.

Compressed air or saturated steam is the power source for our Venturi Blower line. Small volumes of high velocity air (from the compressed air source) run through the casting and out the nozzle jets, creating a venturi action or pulling action that creates large volumes of air through the venturi and out the air diffuser.

A 1/2” hose with a “crows foot” connection is recommended from your air supply source to the side inlet connection. The compressor size required can be determined by checking the chart on air consumed at various inlet pressures. Operate this Venturi Blower on air or steam lines limited to 140 psi.

Choose from Metal or Anti-Static Plastic Linear Low Density Polyethylene (LLDPE)
Lightweight construction
Convenient carry handles for one-person portability to any location
No guards required
Multiple inlet ports
Sturdy steel galvanized steel diffuser
All models include a crow’s foot inlet connection
Static ground is attached to the base of all blowers

These require compressed steam or air as the power source, so a steam generator or air compressor also would be part of the setup, plus an external blower on the roof perhaps. What I like about the steam approach, assuming it could work, is that the gases are diluted with steam before exiting the stack, and it may even be possible to alkalinize the steam before it contacts the gas, thereby moving the fumes and scrubbing in one operation.

Here is a 24KW 3PH steam generator for under $800, but there is no information given concerning the steam pressure it provides; so it's unknown if it could power the Allegro Venturi blowers. Steam generators get expensive quickly with increased capacity, so the steam approach could be impractical if the steam velocity requirements necessitate too costly a steam generator. But assuming this is possible then perhaps an alkaline solution (weak NaOH) could be fed with the steam into the Venturi blower using an inline aspirator, like an airbrush. If one then used a method of in-process scrubbing, like 4metals has described, or in-process gas recycling, as several members have discussed, then the quantity and strength of the fumes entering the hood would be greatly reduced, so that what finally comes out of the stack is PH neutral and fairly clean.

http://www.ebay.com/itm/24-KW-STEAM-GENERATOR-SHOWER-SAUNA-BATH-HOME-SPA-/320654311499?pt=LH_DefaultDomain_0&hash=item4aa87c804b#ht_2641wt_925

Even if using steam is not doable, it may still be possible to inject alkaline into the Venturi blower using compressed air. The spec for the Venturi blower indicates line pressure of 140 psi or less, which can be maintained easily using a medium sized tank, and air compressors are relatively cheap.

 

[devala]

Um, strike that last bit about air compressors being relatively cheap. It looks like an 75 cfm or higher compressor would be called for, and these are not at all cheap!

For instance, to get more than 2000cfm using the 9518-16 (plastic) blower requires a minimum 73 supplied cfm from the compressor, if I'm reading the allegro site correctly. Goto
http://www.allegrosafety.com/
and select Venturi Blowers from the side menu.

 

[Noxx]

It takes a lot of energy to make steam... Also, it's harder to control your fan. With my AC drive, I can dial 5% for the night then 100% when I operate both hoods.

 

[DONNZ]

All kind of options out there one can draw from when setting up a vent system. Woodworking, plumbing, etc.

Inductor 4 in. In-Line Duct Fan
http://www.homedepot.com/buy/building-materials/heating-venting-cooling/inductor/4-in-inline-duct-fan-62960.html

Dust Collection Blast Gates
http://www.ptreeusa.com/blastgates.htm

All kinds of squirrel cage blower out there. Most efficient way to move air. I would adopt one and wire in a rheostat.

http://www.grainger.com/Grainger/blowers/hvacr/ecatalog/N-8sq?ef_id=8A9O-OjnV3wAAI3w%3A20120306140802%3As&gclid=CJrRw5G50q4CFYwj7AodbQ1iDA

PVC clean outs would work well when connecting two systems together. Look around, you have options.

I could do a drawing on this type of layout. Would need to know if it has a filter.

 

[Plasticman]

Hi everyone just thought I'd give my professional opinion. I don't process any ore myself, but I design and build Assay Fume Hoods for big mining companies up in Canada. You can build your hoods and complete exhaust systems including fans and scrubbers using PVC. We've built them for 40 years or so from type 1 grade 1 PVC which you can buy from many distributors in every major city. With a little creative ingenuity you could line any wooden hood with this and extend the life of your hood. If you are using hotplates inside the hood, ensure that you have at least 100 to 125 CFM face velocity at the hood or you could start to burn the PVC. 6' hood should need a 1000 to 1500 cfm blower/fan, depending on the size of opening, ducting, and amount of elbows in the system.