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Chromium Plating Facilities April 1995 Technical Disclaimer References to abatement equipment technologies are not intended to represent minimum or maximum levels of Best Available Control Technology (BACT). Determinations of BACT are made on a case-by-case basis as part of the New Source Review (NSR) of permit applications. BACT determinations are always subject to adjustment in consideration of specific process requirements and recent developments in abatement technology. Additionally, specific health effects concerns may indicate stricter abatement than required by the BACT determination. The represented calculation methods are intended as an aid in the completion of acceptable submittals; alternate calculation methods may be equally acceptable if they are based on, and adequately demonstrate, sound engineering assumptions or data. It is the responsibility of applicants to remain abreast of regulation developments which may affect their industries. TNRCC Rule 116.111(3) in Regulation VI requires that BACT be applied to all facilities that must obtain a permit. BACT is defined as any control method which is technically feasible and economically reasonable. BACT determinations are made on a case-by-case basis. The applicant is encouraged to talk with a TNRCC NSR Permit Engineer to determine the BACT for the facility. Current BACT practices are: 1. Use of well designed capture hoods over chromium plating and acid pickle tanks. 2. Chromium emissions exhausted to an appropriate abatement device or system like scrubbers, mist eliminators, etc. 3. Use of a fume/foam suppressant in chromium plating and acid pickle tanks. Chromium Emission Reduction Techniques 1. The principal techniques used to control emissions for chromic acid mist from decorative and hard chromium plating and chromic acid anodizing operations include add-on control devices and chemical fume suppressants. 2. Since electroplating and anodizing operations are normally conducted in open-top tanks, a system of slot hoods or canopy hoods are usually constructed to capture the chromic acid mist. The slot hoods are the more prevalent. The ventilation rates in cubic feet per minute for either type of design must be adequate to ensure the capture efficiency. Technically acceptable hoods should be designed and built in accordance with the (Industrial Ventilation) handbook or an equivalent configuration that is acceptable to the permit engineer. Hoods designed in the above manner can be assumed to have a ninety-eight percent capture efficiency of the chromic acid mist being entrained from the gassing at the surface of the tank(s). The correct design of the hood system and air flow rate (velocity across the surface) are as necessary as the correct abatement device. 3. The hood(s) must ventilate to an acceptable abatement device(s). The control devices most frequently used are mist eliminators and wet scrubbers that are operated at relatively low pressure drops. If the device requires periodic was down with fresh water (no caustic) and the water returned as makeup water (returns lost chromic acid to plating bath), then the manufacturer's literature, test data and details on the washdown cycle should be clear. Once-through water or recirculated water is used as the scrubbing liquid because chromic acid is highly soluble in water. Typically, the wet scrubbers used in chrome plating operations are single and double packed-bed scrubbers and less frequently fan-separator packed-bed and centrifugal-flow scrubbers. Scrubbers remove chromic acid droplets from the gas stream by humidifying the gas stream to increase the mass of the droplet particles, which are then removed by impingement on a packed bed. 4. Chevron-bladed and mesh-pad mist eliminators are the types of mist eliminators most frequently used to control chromic acid mist. The mechanism by which mist eliminators remove chromic acid droplets from gas streams is the inertial impaction of droplets onto a stationary set of blades or a mesh pad. Mist eliminators are usually operated as dry units that are periodically washed down with water to clean the impaction media. 5. Chemical or mechanical fume suppressants can be added to decorative or hard chromium plating tanks and chromic anodizing baths. The manufacturer's claim as to reduced emissions should be supported by test data and a warranty. Manufacturer's emission reduction claims of ninety-nine percent are common. For some hard chromium applications, some fume or foam suppressants cause pitting in the plating and consequently require a mechanical approach for a suppressant. A common mechanical suppressant is to float polypropylene balls (ping pong balls) on the surface of the tank, usually in two layers. Polypropylene balls are generally used on hard chromium plating baths to reduce evaporation of plating solution and inhibit misting. They are generally not used in automated plating or anodizing operations because plating racks drag the balls out of the baths. The balls tend to be pushed away from the anodes and cathodes where the surface of the bath is agitated by gassing, thus reducing their effectiveness for inhibiting misting. These levels are guidelines to help the applicant get an idea of what the TNRCC is currently considering as BACT; however these control levels are subject to change. Part D of section VI of the PI-1 form requires the applicant to submit a BACT analysis. Any BACT proposal that is different from the requirements stated above needs to be explained in detail. Any control system alternative evaluated should be well designed and engineered for its application.