1. Field of the Invention
This invention relates generally to ventilating gases containing condensable vapors from enclosed spaces; and more particularly to a method and apparatus for exhausting mixtures of gases, entrained particulates and vapors, such as air ladened with particulate and vapors of oils, greases, fat, solvents, and smoke.
2. Description of the Prior Art
Domestic and commercial kitchens, machine shops, factories and similar work spaces with ovens, roasters, ranges, painting and welding booths, industrial furnaces and the like, usually have ventilating systems installed to prevent the buildup in the air of smoke, fumes and vapors to which exposure may be injurious to health as well as become a fire hazard. The contaminant mixture is typically exhausted from the space through a duct to the outdoors by a motor-driven fan, but the carbonaceous particles and flammable droplets of grease, oil and solvents tend to rapidly accumulate in various parts of the ventilation system including the hood, ducts, and exhaust fan and on adjacent building surfaces. Filters and traps are commonly used to capture these contaminants but do not completely solve the problem.
One exhaust system frequently installed in kitchens is equipped with replaceable filters such as disclosed in U.S. Pat. No. 2,886,124 to G. A. Scharmer. Other systems as described in U.S. Pat. Nos. 2,889,007 to K. E. Lunde and 2,494,146 to P. A. Spanos employ a trap in which grease particles are removed by gravity. Still another system disclosed in U.S. Pat. No. 3,911,895 to Q. H. Van Schoyck collects and isolates the grease and other contaminants in a mesh liner removably attached to the interior of a hood and exhaust duct. In each of these systems, the exposed components must be cleaned or replaced periodically to prevent clogging and to minimize resistance to the air flow.
U. S. Pat. No. 4,987,882 to A. S. Kaufman discloses still another system in which a roof-mounted exhaust fan diverts the grease-laden air past a scoop. The grease adheres to the surface of the scoop and drains into a collector below the scoop where it can be separated by a flotation trap from any rain water which may accumulate.
U.S. Pat. No. 3,827,343 to W. J. Darm utilizes a heat exchanger for condensing the grease and oil vapors with cooling air drawn from outside the building. The temperature of the cooling air is raised reclaiming sufficient heat for returning to the building. As in the other systems, the heat exchanger and ducts must be periodically cleaned of accumulated grease condensate.
The ventilation system described in U.S. Pat. No. 3,785,778 to Bernstein et al. removes the grease and oils from the exhausted air by combustion. An electrically-heated, catalyst-coated refractory block is located between the intake and the exhaust fan. Combustible vapors drawn through the block are heated to their ignition temperature, and the products of the combustion are then exhausted. Such a system, of course, should be very carefully regulated to prevent fire.
From all of the above, it is apparent that such systems offer only partial solutions to the problems that they attempt to solve. Either they do not completely prevent the accumulation of fire-hazardous pollutants, or extreme cautionary measures must be taken to maintain safe operation. However, if these pollutants were first exhausted outside of the building using air as the carrier, many well-known fluid-separating techniques, such as absorption, adsorption, extraction, precipitation, filtration and combustion can be used.