ENVIRONMENTAL ENGINEERING:TOTAL-ENCLOSURE CONCEPT FOR FUGITIVE AIR EMISSIONS

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TOTAL-ENCLOSURE CONCEPT FOR FUGITIVE AIR EMISSIONS

Most if not all industrial operations result in the generation of air pollution emissions to the atmo- sphere. The emissions may be partially captured by a ventilation hood and be taken to an oven, incinerator, baghouse, or other air pollution control device. The air pollutants not captured by the ventilation hood escape into the workplace and are referred to as fugitive emissions. These fugitive emissions eventually reach the outdoor atmosphere either through roof ventilation fans, open win- dows, doors, or exfiltration through the walls of the building structure itself. Ultimately, all the air pollutants generated by the industrial process reach the outdoor atmosphere. For this reason, the EPA and state regulatory agencies require an industrial process that generates air pollutants to be mass- balance tested prior to approving an air pollution operating permit. In other words, either the fugitive emissions must be quantified and figured in the overall destruction and removal efficiency (DRE) of the air pollution controls or it must be demonstrated that the ventilation hood(s) form a 100% per- manent total enclosure of the pollutants. With 100% permanent total enclosure demonstrated, it is known that all air pollutants generated by the process are captured by the hood(s) or enclosure and taken to the ‘‘as-designed’’ air pollution control device, whether it be an integral oven, external incinerator, baghouse filter, electrostatic precipitator, or some other tail gas cleanup device.

Criteria for 100% Permanent Total Enclosure of Air Pollutants The United States Environmental Protection Agency has developed a criterion for determining 100% total enclosure for an industrial operation, EPA method 204 (EPA M204 2000). It requires that a series of criteria be met in order for a ventilation hooded industrial process to qualify as 100% permanent total enclosure. These criteria are:

1. The total area of all natural draft openings (NDOs) must be less than 5% of the total surface area of the enclosure.

2. The pollutant source must be at least four equivalent diameters away from any natural draft opening (NDO). The equivalent diameter is defined as 2(LW )/ (L + W ), where L is the length of the slot and W is the width.

3. The static pressure just inside each of the NDOs must be no less than a negative pressure of 0.007 in. of water.

4. The direction of flow must be into the enclosure as demonstrated by a device such as a smoke tube.

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