Acid Digestion Hood

[Clymber]

I am a new facilities engineer at a local university. We have a system (designed by an outside consultant) that uses flow control valves on VAV fume hoods. The hoods are used extensively for acid digestion (boiling off hydrochloric acid, hydrofluoric acid, nitric acid, OR hydrogen peroxide). After operating ~18 months, response on one valve diminished. Investigation revealed a build-up of acidic matter on the low-pressure side of the (vertically-oriented) valve cone. For those who have experience with this type of operation, is a constant-volume hood preferred for this application?

Thanks in advance.

 

[chicopee]

I don't get involved with this type of matter, but that could change in the near future with one of our clients. I am thinking if condensation of acid fumes could be the problem and perhaps raising the temperature of the acid laden air may control this type of problem. Perhaps the buildup of acid matter is a surface corrosion problem?

 

[SAK9]

Have you got wash down rings on the exhaust duct? All acid exhaust ducts need to be washed down with water after use.Generally acid exhaust ducts go straight up to the roof to make the washdown easy.Looks like the flow measuring pitot holes have been blocked by deposits.I have not used valves on acidic exhaust ducts in the past.Even with a wash down nozzle water can get into the holes and stay there inside the tube.

 

[willard3]

You say nothing of the fans on this system. Is the system VAV? Mixing CV and VAV hoods on the same hood may cause problems.

Call the Engineer who designed this, you won't be able to bootstrap as solution on a web forum.