Where the
world gathers for metal finishing
Q&As since 1989


-----

Regulations for Anodize/Cr Exhaust Fumes

We are just now starting to vent the fumes with a system specifically for our process tanks (before this we just used part of our paint booth system to extract and exhaust the fumes on our anodize tanks).

I am looking at the different regulations that we need to stay within, but I'm stuck at a large stumbling block right at the start line! I need to know the "emissions rate" for our exhaust. How do I measure this? Can we do it with our in-house lab? Can we sample the exhaust and have it analyzed or do we need to have some one come here to analyze it?

Our processes are a standard sulfuric anodize w/ dichromate seal @ 190 F, Boric Sulfuric anodize w/ a dilute seal @ 200 F, Alodine 1500, Amchem #7/17 Cr deox, and an acid etch containing HN03 and Hydrofluoric (@ 1% of 48%).

Any suggestions?

Benjamin Jon Curto
- Ponderay, ID, USA
2001

---

2001

Benjamin,

I feel sorry for you as you are somewhat between a rock and a hard place.

If you go to a reputable mfgr. of mass transfer packing, they will ask WHAT are your concentrations of acids, WHAT are your airflows and then ask 'WHAT degree of efficiency of removal do you want?'. To the latter question were you to say l00%, then you'd have to sell the Company's Rolls Royce and Bentley ... after all, their job is to sell packing and they will be very helpful in telling you 'what' the diameter of your scrubber will be and 'what' the packing depth has to be and 'how much' alkaline reagent you'd have to use.

Coming back to all your 'chemicals', there is one point to consider regarding ambient or nearly ambient emissions of acids ...these emissions in MOST CASES are neither gaseous nor fumes. NEITHER. They consist of invisible low micron sized droplets. The exceptions are some of the many nitric compounds, but not all (a very unstable acid!)and partially HCl.... although with Assay applications these ordinary CT-120/2 eliminators meet specs re HCl and aqua regia.

In the Canadian province of Ontario the Air Management people (who parallel EPA on requirements) will demand to see a design drawing. They will then 'enter' this data into their computer and tell you ... it's OK ... it needs to be larger ... your stack height is too short ... you need to increase your alkali recirculation rate ... etcetera. In other words they'd be knowledgeably very helpful!

In British Columbia the authorities take a different tack. They don't care a hoot about the design ... only about the emissions and will demand on-site emission testing to comply with regulations.

In your case ... and may I suggest that all your ducting is made of PVC ... the approach I'd take (assuming you know all the airflow parameters) is to do some pre-empting work. If you did nothing at all, the authorities would come down on you like a brick shipyard. If you did something, something reasonably good, albeit inexpensive, you might well get away with it.

CASE HISTORY .... ALUMIDIZE Company (once called STAYSA) in Brantford, Ontario. l975 era. They were exhausting bright dip (at least 4% nitric) and sulfuric. The plant was situated in a narrow high valley necessitating quite a high stack with a good O.V.

I was experimenting to see if one could improve the capture efficiency of a l2 micron (blade type, horizontal airflow) mist eliminator by using a sprayed coalescer section (using PP mesh) before the eliminator. The sulfuric fumes, which are easy to control, bypassed the mesh and went directly into the eliminator. Because of the nature of bright dip, everyone said, EVERYONE, that one has to use an alkali to neutralize it.

A year goes by during which time the tough Air Management people OK the emissions, so I decide to revisit that plant and check on the alkali consumption as well as on the ventilation design, too.

The 'operator' of the alkali make-up tank is a recent Italian immigrant. I ask him how often is the alkali changed. 'No kapeech', he replies, 'only Aqua, aqua' !

So here we have a pretty common bright dip environment which passes all emission tests AND is located in a geographically bad news narrow valley ... and they are using W A T E R Ordinary tap water. Needless to say, thereon after all my bright dip designs used only 'aqua' and never alkali.

For the eliminators, try Munters in Florida. They have the German designed T-120/2 or try Allanco Environmental in New Westminster, B.C. who call their slightly improved design a CT-120/2.

I sincerely hope that this is of some help to you ... as with every battle (with the environment), a good pre-empt often works

Others follies teach us not
Nor much their wisdom preaches
Of sterling worth is what
Our own experience teaches. Author unknown.

Cheers !

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).