Gas separation: processes – Liquid contacting – And deflection
Reexamination Certificate
1999-09-20
2001-06-05
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
And deflection
C055SDIG003, C095S217000, C095S222000, C096S273000, C096S325000, C096S328000, C096S355000
Reexamination Certificate
active
06241809
ABSTRACT:
This invention relates to cleaning contaminants or undesirable constituents from an airflow or from a gas flow. More particularly, the present invention relates to a new and improved method and apparatus for water or liquid scrubbing contaminants, such as particulate matter and gases, from an air or gas flow. A consequence of the present invention is highly effective air and gas cleaning.
BACKGROUND OF THE INVENTION
Modern society has imposed numerous requirements for filtering contaminants and undesirable constituents from air and gas flows. Environmental concerns and regulations demand that most business and industrial concerns clean any discharged air before the air passes into the ambient environment. One particularly challenging example is the requirement to filter high concentrations of smoke and fat airborne contaminants from the cooking exhaust of restaurants and food preparation facilities. Burning fossil fuels in the generation of electrical power is another, large-scale example. A variety of different filters and cleaning devices have been developed for addressing some of these needs and requirements.
Static high efficiency particle (HEPA) filters are commonly used for relatively small volume cleaning and filtering applications. In conditions with very high contaminant concentrations in the air or in very high flow volume situations, however, HEPA filters are not practical, because HEPA filters will become clogged with particles too rapidly and have to be replaced or serviced too often. HEPA filters are also very expensive.
Scrubbers are a well-known type of cleaning apparatus. Contaminated air or gas passes through a water mist curtain, a waterfall-like flow of water or cleaning liquid, packed beads or electrostatic precipitators and some of the airborne contaminants become entrained in the water or cleaning liquid, or on beads or charged plates of the precipitators, while the partially cleaned air or gas passes from the device. The accumulated contaminants are flushed out periodically, and the scrubber is otherwise cleaned out, typically with hot water and detergent, achieving a level of self-cleaning functionality. Since the contaminants are removed by the cleaning fluid or water and continually washed away, there are no filters or other similar components which need to be replaced or serviced on a periodic basis. Scrubbers are usually preferred for high volume and heavy contamination applications because of their ability to operate continuously without intense maintenance. Scrubbers have also been used as a pre-filter for removing contaminants from an airflow prior to fine-filtering by one or more HEPA filters.
In general, scrubbers have not been fully successful in removing a sufficiently large percentage of airborne contaminants to be practical in certain high contaminant concentration or high volume airflow situations. For example, water scrubbers that have been used to clean the cooking exhaust of a restaurant or the coal dust in the air of a coal mine have had to rely on HEPA or other filters for their primary air cleaning due to the low efficiency of cleaning from the water scrubbing effect. Another difficulty with water or liquid scrubbers is that they introduce relatively large quantities of water or other cleaning liquid into the exiting air or gas flow. Such scrubbers often require a separate filtering or screening section simply to remove the excess moisture or cleaning fluid before it is discharged into the environment. Additionally, electrostatic precipitators can cause fires or explosions.
It is with respect to these and other considerations, that the present invention has evolved.
SUMMARY OF THE INVENTION
One improvement available from the present invention is a scrubber with an improved ability to remove contaminants from the airflow or gas flow caused by enhancing the gas and liquid mixing. Enhancing the gas and liquid mixing causes a larger proportion of the contaminants to be mixed with the cleaning fluid and removed from the air or gas flow. The improved efficiency of the present scrubber makes it possible for the scrubbing function to achieve the primary cleaning action on the air or gas flow, without necessarily having to rely on additional HEPA or other filters.
To achieve the enhanced scrubbing, the scrubber comprises a baffle-defining structure which includes a plurality of vertically spaced and interdigitated deflection plates that define a serpentine-shaped flow passageway through which contaminated gas flows generally upward. A liquid distributor is positioned above each passageway to flow liquid cleaning agent downward through each passageway and onto the deflection plates. The deflection plates are vertically spaced and extend generally horizontally in the passageway. Each deflection plate has a main downward sloping portion and an outer end lip portion extending from the main portion. Vertically consecutive deflection plates in the passageway extend horizontally in opposite directions with respect to one another and interdigitate with one another. The lip portions horizontally overlap the main portions of at least one vertically adjacent deflection plate to form the serpentine passageway which has repeated alternating-direction turns around the lip portions of the deflection plates. The liquid flows off the lip portion of each deflection plate into and through the gas flow turning around the lip portion to mix the gas and the liquid and entrain contaminants in the gas flow with the liquid. Preferably, at least a portion of the liquid flowing from the lip portion of the deflection plate is driven upward from the lip portion with the gas flow and mixed with the gas, preferably in a gas/liquid mixing zone in the passageway between vertically adjacent deflection plates where a vortex motion of gas flow increases the contact of the contaminants with the liquid. The liquid is maintained for a longer time in the airflow path, where the opportunity for contaminant/liquid collisions is greater, which results in a greater removal of the contaminants by the liquid. The high turbulence also enhances the atomization of the liquid drops into many smaller liquid droplets, thereby maximizing the surface area and distribution of the liquid suspended in the airflow path. A greater surface area of the liquid leads to a greater likelihood that contaminants will encounter a liquid surface and become entrained therein or chemically react therewith to remove the contaminants from the gas.
Another improved aspect of the present invention relates to an improved method of liquid scrubbing contaminants from a gas flow flowing generally upward through a passageway while flowing a cleaning agent liquid generally downward through the passageway. The method includes turning the gas flow in the passageway through a serpentine-shaped flow path around exterior lip portions of overlapping deflection plates located in the passageway, flowing the liquid generally off of the lip portions of the deflecting plates, mixing the liquid flowing off of the lip portions in the gas flow turning around the lip portions, and entraining a substantial portion of the contaminants in the liquid. Other preferable aspects of the method involve lifting liquid upward from the lip portion during mixing with the gas flow turning around the lip portions of the deflection plates, preferably into a gas/liquid mixing zone between vertically adjacent deflection plates, and flowing the gas flow in the mixing zone in a vortex motion to increase contact of the contaminants with the liquid. Still other preferable steps include inducing the vortex motion by deflecting a significant portion of the gas flow in the passageway with the shape or configuration of the deflection plate, removing a substantial majority of a liquid mist from the gas flow after the gas flow flows through the serpentine-shaped passageway, whirling the gas flow in a circular motion to force the liquid mist to coalesce into liquid by centrifugal force, and forcing contaminants in the gas flow into the coalesced liquid while the
Ley John R.
Lindsay L. Jon
Smith Duane S.
LandOfFree
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