Heating – With means diluting – purifying or burning exhaust gases
Reexamination Certificate
1998-03-30
2001-02-27
Doerrler, William (Department: 3744)
Heating
With means diluting, purifying or burning exhaust gases
C422S173000, C422S175000
Reexamination Certificate
active
06193504
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and method for abating volatile organic compounds (VOCs). The uniqueness of the invention is that it is portable and is operable from household electrical power. In particular, this invention is concerned with a highly efficient regenerative catalytic oxidizer which in a preferred embodiment is only partially coated with catalyst.
2. Related Art
Treatment of localized air (i.e., indoor air or air surrounding an outdoor source of noxious compounds) is receiving attention in order to reduce human exposure to odor and toxic compounds. Air toxic compounds, such as CO, ozone, and VOC, can be present indoors either from transporting of poor outdoor air quality or from indoor sources, such as furnaces, insulation, furniture, paints, etc. In manufacturing facilities, poor indoor air quality can also result from plant operations and recirculating air systems. In residential buildings, excess high CO levels have been found from incomplete combustion in furnaces, and from transport through electrical conduits of high CO that is generated from short circuited outdoor electrical cables. In outdoor applications, leaks from valves or equipment relating to processes carrying noxious compounds are important to be treated in order that repair of the leaks are not hampered.
Currently, there are limited devices commercially available for treating localized air. None of these devices, however, are portable for treating local areas. Adsorbents such as carbon cartridges may be used to trap odorous compounds. However, these cartridges can adsorb limited types of VOC compounds and need to be replaced periodically. Catalytic devices are also used for removing these compounds. However, because catalyst activities are in general too low at ambient temperature for VOC oxidation, most applications will require to heat the catalyst to higher temperatures to facilitate air cleanup. The resulting treated gas temperatures are often too high for the air to be released directly into a room or other localized environment and may require a stack or directing means to discard the hot air. With this constraint, most catalyst devices are not portable and typically are mounted in larger and non-portable air recirculation systems. Catalyzing heat transfer surfaces that have significant air movement to clean up room air has also been mentioned. This approach is not very effective for two reasons: 1): the surface temperature is relative low and catalyst is only effective to treat limited VOC compounds, 2) the device is not portable. With these inherent constraints, there are yet commercial devices that have been accepted to be very effective for localized air treatment.
A practical device for localized air treatment will require the device to be capable of abating most odorous and toxic gas compounds. The device also needs to be portable so that it can be easily moved to treat problem areas. For example, to abate odors from freshly painted areas, the device can be moved to treat that area only. For persons working in odorous or high pollutant-containing areas, the device can be used to remove unpleasant odors around the neighborhood of individuals without the need of treating the whole room air. For furnaces that leak CO or other VOC species, the device can be located in that local area to quickly destroy these compounds. For meeting these needs, the device needs to be lightweight, and provide air circulation with the treated air being discharged into the room or localized area to displace untreated air. In doing so, the temperature of the treated air needs to be controlled in a comfortable temperature range (e.g. less than 120 F.) so as not to substantially increase the ambient temperature.
U.S. Pat. No. 4,852,468 discloses a ventilated work station for removing toxic fumes generated during sculpting of fingernails. However, this apparatus does not treat (destroy) the toxic fumes and only draws the fumes away from the work station.
U.S. Pat. No. 5,366,128 discloses a portable apparatus for removing fumes and vapors from the work area of a nail technician. However, as with U.S. Pat. No. 4,852,468, the disclosed apparatus only draws the fumes away from an area and does not destroy the fumes.
U.S. Pat. No. 5,547,640 discloses a high temperature air purifier for incinerating volatile organic contaminants and airborne particulates. An optional oxidation catalyst may be placed on the cup wall and the walls of the air passages near the hot end to speed up initial warm-up and combustion at lower temperatures, but it is stated that pure thermal oxidation is fast enough at temperature above 1600 degree F. Such a device, however, would not meet the strict design criteria of the present invention in having a portable, highly thermal efficient pollutant abatement device.
Applicants provide an advance over the prior art in providing a portable and highly thermal efficient rotary regenerative catalytic oxidizer for abating indoor pollutants or pollutants localized to a specific area (e.g., fugitive emissions whether indoors or outdoors). The advantages of which are herein below described.
SUMMARY OF THE INVENTION
The present invention provides a portable pollutant abatement apparatus for removal of indoor pollutants or localized pollutants such as volatile organic compounds (VOCs).
One embodiment of the invention provides a portable pollutant abatement apparatus for removal of pollutants and odorous compounds such as volatile organic compounds from ambient air present in a localized environment comprising:
an inlet for receiving the ambient air and directing the air to a fully or partially catalyzed rotary, heat regenerative device;
the rotary device comprising electrical heating means and means to recover heat from the air after catalytic oxidation and before the oxidized air is returned to the ambient air; and
an outlet for directing the oxidized air from the rotary device to the ambient air.
In another embodiment, we have quite unexpectedly found that in order to achieve the highest VOC destruction efficiency, surfaces that are only partially coated with a catalyst composition have a higher VOC destruction efficiency than surfaces that have been fully coated with catalyst.
The method of the present invention provides directing the air to be treated to the rotary regenerative oxidizer, for heating and catalytic oxidation therein. The air stream then flows through a transfer chamber which oxidizes the pollutants in the stream and thereafter flows through an output portion of the rotary oxidizer and vented.
Another embodiment also operates in steady state and comprises a stationary fully or partially catalyzed heat regenerative bed, and, a one-piece rotary element that continuously rotates the air flow entering and exiting the bed, thereby alternating the various gas flows through the system.
If desired, the present invention may accommodate a purge stream which redirects cleansed exhaust air or other air back through the regenerative bed, thereby removing trapped contaminants.
An advantage for achieving high thermal efficiency is that the cleaned stream can be readily discharged without the need of a stack, thereby making the device portable and compact for handling small streams.
As used herein, the term air is intended to include both the ambient “outside” air and the ambient “inside” air of enclosed structures such as buildings. Therefore, the present invention contemplates treating indoor air, wherein the treated air exiting from the rotary device of the present invention is exhausted or vented to the air (“indoor”) of the building. In application to “outside” air treatment, the present invention is ideally suited for treating so called fugitive emissions that may be localized to the extent the emissions have been emanating, for example, from a leaky valve or piping connection whether outside or inside of a building.
REFERENCES:
patent: 4418046 (1983-11-01), Izumo et al.
patent: 4678643 (1987-07-01), Fetzere
patent: 4834962 (1989-05-01
Chen James M.
Fu James C.
Nguyen Pascaline H.
Steger John J.
Doerrler William
Engelhard Corporation
Miller Stephen I.
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