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Emission factors pickle bath


I am looking for emission factors for Pickling solution of 3% hydrofluoric acid and 14 % nitric acid.

Lorne Raycroft
- Brockville, Ontario, Canada



You didn't give us all the facts ... What are you pickling and at What temperature and Are you agitating, too?

Even with those figures, mass transfer experts (i.e., the sales side of m.t. packing) will ask What efficiency do you need .... and then proceed to hopefully design something, at some expense, that might work... and it would be very bulky, too.

You have a nasty mix. Initially I'd try to collect and return some (most?) of the fumes using a horizontal all PVC simple l2 micron mist eliminator. I would try to control/sic.reduce the airflow (via a damper) to an absolute minimum BUT, BUT, BUT would 'add' fresh air, say 20% or so, AFTER the fumehood in order to hopefully reduce some/all of the NOX prior to going into said eliminator or into a more sophisticated, say, 3 micron inertial scrubber.

Nitric 'fumes' can (not necessarily will) consist of varying nitric compounds, depending on the process. Some can be knocked out easily, some need a long retention time and oxygen (i.e., air) in order to revert back to a 'scrubbable' state. Most acid 'fumes and gases' in the metal finishing business are NOT fumes nor gases but invisible low micron droplets which is why good, well made 'mist eliminators' can sometimes work as well as expensive mass transfer scrubbers.

Anyhow, maybe this might be of some help to you.

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


As Mr. Newton indicates, information is lacking to provide you with an adequate response.

The emission rate is dependent upon important factors and is a calculated figure. Chemical concentration, temperature, substrate, part size, etc. will determine the emissions. The "hazard rating" and ultimately the exhaust rate is commonly derived (in the US anyway) from the Industrial Ventilation Manual printed by the American Conference of Governmental Hygienists (ACGIH)in Cincinatti, OH. As an added note to Mr. Newton's suggestion, if you still get the Orange/Brown plume from the stack try more transfer units (i.e. more packing) and/or mix in sodium sulfide with the recirculation solution (consult an expert) to reduce the opacity of the NO2. Watch the pH though, if it gets out of balance you'll make H2S.

Rick Hall
- Hickory, North Carolina


Hi Rick Hall,

Your suggestion about the sodium sulfide is interesting. Hadn't heard of that approach before.

The crux to a really nasty NOX is a helluva long retention time. One Italian design (pure nitric reactor) called for 200 or so cfm via 6 tall l2" dia PVC interlocked pipes which had little bleed valves to allow some air, sic. oxygen, to be bled in. The design was based on RETENTION time. Hopefully the fumes had 'reverted' to an eliminatable size at the end where there was a conventional mass transfer scrubber.

However, your idea of adding on more packing is, I think, a no-go. Once down in Cleveland at a steel plant using nitric, the first scrubber was nbg so they ADDED ON another mass transfer scrubber. Also nbg. Then I was asked if my 3 micron LMITS scrubber would do the job. ... Yes, I replied, it would remove a wet brown plume but I'd need some additional air (i.e., more oxygen!) after the failing scrubbers ... but I could not guarantee that all the fumes were wet.

Once in a plating plant in Toronto (silver electrical contacts) they had various plating acids AND a brown plume. To the customer's surprise and satisfaction, an ordinary l2 micron eliminator knocked that out ... but here we had OTHER acids, not pure nitric and hence the ventilation mix meant that the nitric tank's fumes were diluted due to the general ventilation and that there was more 'oxygen' available.

As you know, the 'books' say that to knock out nitric, you need lots of cold air at minus 80 °C (or F, I forget!) Theory is one thing, practice is another. Yup, I know that the Ventilation Manual is a Tome of excellence ... but heck some of their recommendations could do with updating ... ie. Perchlorics for one!

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

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