Gas separation: processes – Solid sorption
Reexamination Certificate
1999-12-30
2002-06-11
Smith, Duane (Department: 1724)
Gas separation: processes
Solid sorption
C096S121000, C096S147000, C096S151000, C055S512000, C055S515000
Reexamination Certificate
active
06402811
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a filter for use with an air-purifying apparatus. More particularly, it relates to an inexpensive, granular sorbent material filter having a non-dusting attribute.
In recent years, there has been a growing interest to improve environmental air conditions in homes and in commercial settings such as offices, restaurants, taverns, bowling alleys, hospitals, laboratories, lavatories, and the like. As more information has been made available to the public concerning the hazards of indoor air pollution, there has been an increased demand for filtering devices that can be used to effectively improve air quality.
With respect to commercial settings, a popular filtering technique entails placement of a self-contained, stand-alone air-cleaning or filtration unit over the room of interest. The air filtration unit can assume a variety of forms, but typically includes a housing maintaining a fan or blower and one or more applicable filter materials. The housing defines an inlet, at which the filter(s) is disposed, as well as an outlet or exhaust port. Most commercial settings include a false ceiling, such that the housing is easily “hidden” above the ceiling, with only the intake or an associated grille being visible to persons within the room. During use, the fan or blower is operated to draw room air through the filter material(s) via the inlet. The filter material removes undesirable air-borne particles and/or odors such as dust, smoke, pollen, molds, etc. from the airflow. Following interaction with the filter material, the now “cleansed” air is forced, via the fan or blower, into the room through the outlet port. A continuous intake and supply of air preferably generates a desirable air re-circulation pattern within the room.
Certain types of filter media, or combinations of different filter media, have been identified as being highly proficient in removing unwanted airborne contaminants. To this end, airborne contaminants are generally categorized as particulate (e.g., pollen, molds, bacteria, smoke, etc.) or gaseous (e.g., odor, carbon monoxide, formaldehyde, volatile organic compounds (VOCs), etc.). A particulate filter is employed to remove airborne fibers and particles, and is typically “rated” according to filtering efficiency and resistance to airflow. For example, a well-known particulate filter is a high efficiency particulate arrestance (HEPA) filter. HEPA filters are generally comprised of intertwined, small (less than 1 micron) glass fibers and have a minimum efficiency of 99.97% relative to 0.3 micron dioctyl phthalate (DOP) particles. Alternatively, the particulate filter may assume other forms (with lower efficiencies), such as cellulose, wool felt or glass fibers filters with efficiencies ranging from 30%-95% ASHRAE rated dust spot efficiency. For enhanced filtration of gas molecules and odors (e.g., tobacco smoke odors, cooking odors, volatile organic compounds (VOCs), etc.), a sorbent material-based filter (or “sorbent filter”) is normally employed. The sorbent filter typically includes a relatively large volume of an appropriate sorbent material, in granular form, or a combination of granular sorbent materials. The sorbent material adsorbs odor-causing gases and other gaseous contaminants, thereby removing the contaminant from the air. Sorbent materials identified as being most effective in removing odors include charcoal or carbon, potassium permanganate and zeolite. In fact, an extremely popular sorbent filter material is available under the trade name CPZ™, generally composed of 60% charcoal or carbon, 20% potassium permanganate and 20% zeolite.
With the above filtering medias in mind, it has been found advantageous for a commercial air filtration unit to include a pre-filter, a primary particulate filter (e.g., HEPA filter, 95% ASHRAE filter, etc.) and a sorbent filter. The pre-filter is normally an inexpensive, low efficiency (e.g., on the order of 15% dust spot efficiency) impingement filter, such as open cell foam, employed to capture relatively large particles, thereby extending the useful life of the primary particulate filer. Regardless, the primary particulate filter is normally disposed upstream of the sorbent filter to optimize overall filtering performance.
Installation and replacement of the above-described primary particulate filter is highly convenient due to the filter's construction. For example, a BEPA filter is generally formed as a continuous sheet, and can be installed with relative ease. In contrast, sorbent filters are normally quite large and unwieldy. Further, during installation and/or replacement, the individual sorbent material granules constantly contact and abrade against one another, generating a fine dust. This dust is highly undesirable, having many adverse effects including possible respiratory problems, unsightly stains on nearby persons and objects, reduction in unit airflow capacity immediately following installation, etc.
Efforts have been made to overcome the dusting problems associated with sorbent material filters. For example, the sorbent material can be formed as a foam. While eliminating dust, the foam sorbent filter has a highly diminished particle/odor retention capacity. Alternatively, the granular sorbent material may be loosely placed within a sealed, rigid encasement. A series of panels or trays are similarly disposed within the case to better maintain the sorbent material as well as to achieve a desired air flow pattern. Even with this encased configuration, some dusting still occurs. Further, the case is quite bulky, rendering installation difficult. Also, the sorbent material is typically unevenly dispersed within the case, leading to diminished filter performance. Additionally, at the end of sorbent material's useful life, the entire filter device must be replaced. As a point of reference, encased sorbent filters are relatively expensive, making replacement a costly proposition.
Air-purifying devices, and in particular commercial air-purifying units incorporating a sorbent material filter, are extremely popular and beneficial. However, certain potential drawbacks associated with sorbent filters, including undesirable dust generation and high replacement costs, have been identified, yet remain unresolved. Therefore, a need exists for a cost-effective sorbent material filter that generates little or no dust during installation and use.
SUMMARY OF THE INVENTION
One aspect of the present invention relates to a filter for use with an air-purifying apparatus. The filter comprises a flexible bag and a sorbent material in granular form. The flexible bag defines at least one storage region. The sorbent material is disposed within the at least one storage region. With this configuration, the bag is formed of a porous material configured to allow passage of air such that the air, including air-borne particles and/or odors can interact with, and be adsorbed by, the sorbent material. However, the porous material used for the bag limits passage of sorbent material. As such, the filter generates little if any dust during handling. In one preferred embodiment, the flexible bag forms a plurality of storage regions and is selectively attached to a separate frame that in turn is designed for mounting within the air-purifying apparatus. With this design, the frame can be re-used such that sorbent filter replacement requires only a new flexible bag containing the granular, sorbent material.
Another aspect of the present invention provides a method of assembling a sorbent filter for use with an air-purifying apparatus. The method includes providing a flexible bag and then forming at least one storage region in the bag. A sorbent material in granular form is disposed into the storage region. The storage region is then closed. Upon final assembly, the bag substantially prevents release of sorbent material dust from the storage regions. In one preferred embodiment, a plurality of storage regions are formed in the bag, with the sorbent material being evenly disperse
Bahn Richard R.
Monnens Patrick J.
Schwarz Edward L.
Shanks Anthony E.
Greene Jason M.
Smith Duane
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