Suitable exhaust fan rate in small chemical room?

[sp3d2]

Helo

I am working in small water treatment plant. I used NaCl (10%) and HCL (33%) to regenerate the resin that we used in our plant.

During the regeneration, the acidic fume from HCL 33% canister and moisture of NaCl from brine tank (we gargle the brine so that the salt will dissolve in water) escape freely causing the surrounding steel equipment to rust badly.

Therefore, I would like to design a room with exhaust fan that can contain acidic fume and brine moisture from being spread. The dimension of the room will be 2.5 meter length x 1.2 meter side x 2.15 meter height.

What is the suitable rate of cfm to be used for my exhaust fan? Any fundamentals stuff should i know? Any suggestion on the ducting as the air being moved out is acidic and contains high humidity>

Hope to get the info from you guys. I got no experience related with HVAC before.

Thank you

 

[trashcanman]

Check International Mechanical Code, section 502. It talks about ventilation for hazardouse chemicals. NPFA might also.

 

[ChasBean1]

Those will have guides (e.g., "1 cfm/ft2 exhaust min.) but not specifics. This sounds pretty nasty, not to mention the exposure/inhalation concerns. You should really have someone look at the exact process and design something to suit it.

 

[CountOlaf]

Yeah I'm with ChasBean on this. I also think a better "code" with appropriate formulae and guidelines to come up with the appropriate CFM would be the ACGIH Industrial Ventilation handbook, under the dilution venitalion sections (as opposed to the stuff on source capture, since you're trying to tackle the whole space). The book has stuff regarding TLV, etc. I'll take a look at the text tomorrow to see what other info you'll need to calculate exhaust/ventilation rates.

You could also post under the "local exhaust ventilation" group as opposed to "HVAC/R"; seems more appropriate, although the same "players" probably view each of the forums.

 

[CountOlaf]

OK. I don't know about the salt, but in terms of the hydrochloric acid, the threshold limit value (TLV) is 2 ppm (ceiling). The ACGIH manual has some data on this (mine is a little old), but you can get this from the MSDS's as well.

The formula for dilution ventilation rate is (from that ACGIH Industrial Ventilation manual of recommended practice)...

Q = [(403 x 10^6)(SG)(ER)(K)]/[(MW)(C)]

where

Q = effective ventilation rate, CFM
SG = specific gravity (1.268 in the case of HCl)
ER = evaporation rate of liquid, pts/min
K = factor from 1 to 10 to account for efficiency of mixing and the toxicity of the substance
MW = molecular weight (36.47 in the case of HCl)
C = concentration, ppm (usually the TLV, 2 ppm for HCl)

The K factor is higher if the mixing (of the dilution air) is poor and the toxicity is high. At 2 ppm TLV, the toxicity is very high. Maybe assume 5 for starters.

So, the only thing you have to determine is the evaporation rate of the stuff. In other words, how many pints per minute evaporate into the air.

If the exhaust rate turns out to be impracticaly large, then you'll have to switch to more of a fume hood (point source capture) method.

If you get "practical" numbers for air flow, see how many air changes per hour this equates to for your specific room as well as CFM/SF and make sure this is higher than any other code guidelines (like 10 ACH or 1 CFM/SF example that Chasbean was talking about -- these aren't the specific numbers by the way, just examples).

In terms of materials, check with fan vendors who sell laboratory exhaust systems --- Greenheck is one. For ductwork, I don't think galvanized or stainless steel will do, but perhaps galvanized steel coated with PVC or epoxy. The fan manufacturer will have ideas based on what type of fan they would recommend for hydrochloric acid handling.

 

[mauricestoker]

I'd recommend looking at lateral exhaust, pretty much as the ACGIH recommends. Cahpter 10, VS-70, should be helpful. Local containment wil save you CFM hence money (as well as better IAQ).

If you are looking at a lab fan, then you proably will need to make sure you discharge at high velocity, 10 feet above any maaintenance activity. I'd recommend looking at where the exhuast will be heading to.

I have an older copy of the ACGIH, 23rd edition. Has the STEL changed along with ceiling? Old copy doesn't have a TWA, just STEL and Ceiling.

 

[CountOlaf]

mauricestoker:

I was thinking the dilution ventilation would prove to be impractical. It's kind of a small room so perhaps the whole space can be treated like a paint booth. My ACGIH is 22nd ed. (1995), so even older. It had the STEL/Ceiling values only as well (5 and 7.5 respectively), but I got the 2 ppm from an on-line MSDS (effective date 11/21/08).

What's the title of the figure your referring to? Those numbers like VS-70 change with every version.

 

[mauricestoker]

VS-70-01, old number VS-503, Open Surface Tanks.
VS-70-02, old number VS-503.1, Open Surface Tanks
VS-70-10, old number VS-504, Push-Pull Hood Design Data for Widths Up To 10 Feet

 

[CountOlaf]

mauricestoker:

Thanks...I guess I have the same VS numbers in my version as yours.