Bright dip stack emissions

A. Bright dips use mixtures of phosphoric and nitric acid, and emit a good deal of NOx fumes. These are not easily removed with a "neutralizing" solution as you might hope. I would suggest talking to the manufacturer of your scrubber, or to another manufacturer such as KCH Services, Midwest Air Products, or ScrubAir Vent Systems, and see if there is any relatively simple and practical way to improve the packing or add an additional stage to your scrubber.

A. Hi Ralph, If I may be frank, it sure seems that your scrubber is not up to snuff. In the 70's the Ont. Min. of the Environment used to 'computor' check out scrubber designs before they were made ... in B.C. they work on the principle of 'It's working, LET'S TEST IT' & see if it will get approved. At Staysa in Brantford in the mid 70's (their name changed to Alumidized, I believe) the 'sulfur' side, ie. the sulfuric fumes went first into a 2 bank horizontal airflow high efficiency mist eliminator ... this was before the scrubber itself. No odour emissions. The INTERESTING thing is that after air quality tests by the Min. of the Environment (unusual but then this Company was in a deep valley) I went to see it and inquire about the NaOH consumption ... because this is what 'everyone else did', This was the THING TO DO, i.e., they used NaOH. To my utter and total HORROR, the guy i/c the scrubber tank told me, again and again, AQUA, AQUA ...only AQUA.. ... in other words they were NOT recharging with sodium hydroxide. Hence, thereafter none of my bright dip designs ever used NaOH but just water. ... and ne'er a complaint. The scrubber itself (a prototype using only mesh!) was not too close to the bright dip tank. The advantage is that nitric 'fumes' can be more easily 'scrubbed' if they are cooler and there is some retention time for some of the varying nitric compounds to 'change' into a form that is more easily 'scrubbed'. My first recommendation to you is to protect your scrubber and make it apparently more efficient by using a high efficiency 2 bank all PVC mist eliminator. This will/should knock out all the sulfuric and much of the nitrous fumes to around l2 microns at full efficiency. Pressure drop? Max. 1" for, as previously said, a well designed unit.

A. Ralph,

I second with Ted's suggestion above as there is much to know and learn about NOx emissions. But to lend some comments:

The sulfur odor is likely the result of the pH (below 7) dropping in the scrubber solution and "stripping" H2S from said solution, given your comments, this is quite common. Caustic for pH and sodium sulfide work well, IF ONLY, you have enough retention time, packing depth, a high liquid to gas ratio, and run the chemical make-up properly. The manufacturers' can help you here. Nitric acid can evolve from the process as a gas AND a mist form as indicated above. The mist eliminator will NOT help with the gas form but does a fine job on the Nitric mist.