Certain aluminum anodize lines include a very aggressive process commonly referred to as Aluminum Bright Dip, which provides an extremely bright decorative finish to aluminum components. Such components could be aluminum awnings, residential trim for shower doors, or could be used for aerospace components or anywhere bright corrosion resistant aluminum is required.
Due to its chemistries and tank solution temperatures, the Aluminum Bright Dip process produces Nitric Oxide (NO) and Nitrogen Dioxide (NO2) as an off-gas. These are combined as NOx. The NO2 evolves as a brown/orange plume that is highly toxic. Therefore, it must be exhausted using the maximum control velocities and specially designed enclosures to effectively capture the plume. Furthermore, a traditional wet scrubber is not highly effective at removing NO2. Therefore, multi-stage scrubbing combined with high efficient composite mesh mist elimination may be necessary to maximize removal efficiency.
Capturing the NOx gas is critical
Most Bright Dip applications require a very special Exhaust Hood design. It is recommended to locate the Bright Dip tank at the very end of the anodizing line to enable a complete enclosure hood to be designed. This is sometimes referred to as a ‘Garage Hood’. The enclosure hood should encompass both the Bright Dip Tank and the rinse tank. This hood must be designed to effectively capture the off gassing during aluminum immersion and also the travel of the aluminum’s rack to the rinse. Therefore the air volumes to exhaust a Bright Dip Operation cannot be under designed. Capture of all of the orange NO2 gas is critical.
Because NOx cannot be exhausted into the atmosphere with a visible opacity, bright dip scrubber parameters are all larger and greater than that of a standard acid scrubber, including a much larger diameter for additional resonance time, 3 times the packing height, and a required recirculation/irrigation rate that is 3-4 times greater than a standard acid scrubber. It is also required to add reagents to the scrubber irrigation for NO oxidation and NO2 de-oxidation
A standard acid scrubber cannot achieve the required reduction of emissions of NOx, and only a custom designed KCH specially enhanced scrubber for NOx will enable zero visible NOx emissions from the Aluminum Bright Dip process.
Please contact KCH for details on the enhanced exhaust/ventilation and also the enhanced scrubber parameters to control the off-gassing Bright Dip NOx fumes.
See also the NOx case study for further information of NOx scrubbing.