Metal finishing Q&As since 1989
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Environmental officer needs suggestions for aluminum bright dip NOx emissions
2007
Q. Hi,
I work as an Environmental Health Officer for a local council in Lancashire, England. Part of my job involves regulating various industrial processes, including a few anodisers. My question concerns a current problem I've got with a plant that carries out chemical brightening prior to anodising.
The brightener they use is Ultralyte 170XL, a mix of phosphoric, sulfuric and nitric acids. The fumes generated when the works are lifted out of the brightening tank are extracted through two wet scrubbers and washed with a caustic soda
[affil links]
solution, which they currently test the pH of using Drager tubes but is soon to go on a continuous pH monitoring unit.
My problem is that the plant has a permit to operate that includes conditions about not emitting odour and discoloured fumes outside of the site boundary. However, I am getting complaints from nearby residents about "toxic fumes". Every time a jig is lifted out of the brightening tank (about 4 times an hour), the emission from the scrubber stack turns a really horrible looking yellow/brown for about 5 minutes. The guys at the plant say they're doing everything they can to minimise it (keeping pH of liquor at correct level, maximising residence time in scrubber etc).
Really though, I would like to see the emission remain as close to white as possible, but don't know what to suggest. Any ideas would be greatly appreciated.
cheers,
Richard
Regulator - Pendle Brough Council, Lancashire, UK
A. Chemical brightening of aluminum is necessary business (we wouldn't have street light reflectors or dental lights without it), but it's nasty business. The brown color is NOx fumes, and indeed "Nox"ious. The basic problem, I believe, is that this gas is soluble in water to the extent that simple fume scrubbing probably passes too much though. I have seen 2 packed-bed wet scrubbers used in series to good effect, but I hope that a ventilation equipment manufacturer or another bright dipping shop can give us both some ideas.
Would that more of our USA regulators adopt your "working together" attitude!
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007
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2007 A. Spike some ferrous sulphate ferrous sulphate
[affil links] into the scrubber liquid?  Dave Wichern Consultant - The Bronx, New York 2007 A. Hi Richard !  Freeman Newton [deceased] (It is our sad duty to advise that Freeman passed away April 21, 2012. R.I.P. old friend). |
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A. The scrubber was not designed properly. It takes a residence time of the NOX in the scrubber to get it to come out of the gas phase into a dissolved phase. Caustic speeds up the process, but it is not the final answer. There are a number of retrofits that will work, but they are dependent on the space you have available as well as the amount of money, not to mention the down time for the retrofit. James Watts- Navarre, Florida 2007 2007 A. Does the Ultralyte 170XL include a fume suppressant? Commonly used bright dip fume suppressants are ammonium sulphate or monobasic ammonium phosphate. I believe urea has been used, too. 'Nitrogen oxides scrubbing with alkaline solutions,' D.Thomas and J.Vanderschuren, Chem. Eng. Technol., Vol.23, pp. 449-455 (2000). - Goleta, California 
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from. |
A. Hi
We have used a commercial product called BioNOx Solver with success
thanks
- Auburn, Washington
2007
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