Application of an air curtain-exhaust system at a milling process.
Hampl-V; Johnston-OE; Murdock-DJ Jr.
Am Ind Hyg Assoc J 1988 Apr; 49(4):167-175
An air curtain exhaust system for controlling emissions during a rubber milling process was described. The system consisted of a square canopy type hood with a 290 by 254 centimeter (cm) opening. A 41 by 71cm exhaust take off was located at the top of the hood. The air curtain consisted of an air jet from a manifold comprised of a round 10.2cm inside diameter, 239cm long dead end plastic pipe provided with 0.64cm diameter holes on a 7 hole diameter spacing. It was placed at the safety bar (lower edge) or the upper edge of the front opening. The ratio of the total nozzle opening area to the cross sectional area of the manifold was approximately 0.48. Placement at the upper edge of the opening did not result in complete capture by the exhaust, and subsequent testing was done with the curtain placed at the safety bar. In preliminary laboratory tests of a simulated rubber milling operation utilizing smoke and 0.25 percent sulfur-hexafluoride tracer gas as contaminant source and a mannequin, the system significantly reduced emissions, with reductions of about 98 percent for tracer gas and 30 to 70 percent for particulates. When field tested at the drop mill and strip mill of a plastic manufacturer, reductions of tracer gas were 98 to 99 percent in the drop mill for exhaust flow rates of 1.89 or 2.86 cubic meters per second. Average particulate emission reductions of 20 to 50 percent were obtained in the strip mill for the same exhaust flow rates when the air curtain was operating, with reductions of 67 to 75 percent in the drop mill. Some cooling effects were also noted. The authors conclude that the air curtain exhaust system is more efficient than local exhaust ventilation alone, even with reduced exhaust hood velocities, and is cost effective. The system can be used at rubber or other milling facilities that utilize similarly configured local exhaust ventilation systems.
NIOSH-Author; Ventilation-systems; Air-flow; Equipment-design; Control-technology; Occupational-exposure; Exhaust-hoods; Laboratory-testing; Workplace-studies; Plastics-industry; Rubber-processing-equipment
American Industrial Hygiene Association Journal