Patent Application
20050053515
The present invention generally relates to an air cleaner unit and to an air quality system for providing cleansed air to an interior air space. The present invention also relates to methods for removing a pollutant from an air stream via an air cleaner unit or an air quality system.
There is increasing interest in supplying clean, pollution-free air to interior air spaces, such as onboard commercial aircraft. To provide cleansed air to an interior air space, such as an aircraft cabin, it may be desirable to remove pollutants such as dust or other particulates, as well as volatile- or semi-volatile organic compounds (VOCs, SVOCs) from an air stream to be fed to the interior air space. It may further be desirable to remove, or inactivate (kill), microorganisms (e.g., various bacteria), and viruses, which may be human pathogens. In the case of a vehicle, such as an aircraft, such objectives must be accomplished by an air quality system within the constraints of weight and size of the system, as well as pressure drop across the system.
Conventional commercial aircraft feed air (e.g., bleed air from a gas turbine engine) to an environmental control system (ECS), and thence via one or more high efficiency particulate (HEPA) filters to an interior air space, e.g., cabin or flight deck of the aircraft. The ECS conditions the air it receives in terms of pressure, temperature, and humidity, but does not remove particulates or pollutants such as VOCs. Although HEPA filters of prior art air circulatory systems remove some particulates, they do not remove gaseous or molecular pollutants such as VOCs or SVOCs.
U.S. Pat. No. 6,358,374 B1 to Obee et al., discloses the use of an adsorbent bed to collect VOC pollutants. The apparatus is thermally cycled to periodically desorb the pollutants by heating the adsorbent bed. Movable doors within the apparatus act as valves to change the flow path of an air stream containing desorbed pollutants, such that the desorbed pollutants are cycled through a photocatalytic air purifier. The apparatus of Obee et al. is taken off-line during heating and regenerating the adsorbent bed, and is therefore periodically out of service.
Mitsubishi Paper Mills Limited markets a commercial product (Radit™) that comprises an adsorbent and a photocatalytic agent. The adsorbent and photocatalytic agent are co-impregnated on a single support of cardboard or paper, such that the support has dual functionality. Pollutants are adsorbed by the adsorbent on the support, and the adsorbed pollutant is oxidized via a photocatalytic agent, on the same support. Locating both adsorbent and photocatalytic agent on the same support has a number of disadvantages. For example, certain adsorbents may be damaged and inactivated by exposure to the UV light used for oxidizing pollutants via the photocatalytic agent. In addition, the cardboard or paper support may also be damaged by exposure to the UV light. Such damage to the support may result in the loss of impregnated adsorbent and/or photocatalytic agent over time.
Additionally, placing both adsorbent and photocatalytic agent on the same support limits the loading of each since they compete with each other for locations on the support. Furthermore, putting the adsorbent and the photocatalytic agent on the same support means that both are in powder form, which limits the adsorbent capacity for unit volume and weight as compared with self-supporting woven or pleated adsorbent media. Still further, putting adsorbent and photocatalytic agent on the same support limits flexibility in configuring an air quality system for different situations or environments.
As can be seen, there is a need for an air cleaner unit that can be used continuously over an extended period of time without the need to regenerate a bed of adsorbent. There is a further need for an air cleaner unit that may be operated at a substantially constant temperature from about 15 to 30° C., i.e., does not require thermal cycling or a heating step. There is another need for an air cleaner unit that does not require moving parts to change the flow path of an air stream, but which instead provides a single flow path for an air stream. There is a still further need for an effective air cleaner unit that includes a photocatalytic support material that is not damaged by exposure to UV light. There is an additional need for an air cleaner unit in which an adsorbent unit is physically separated from a photocatalytic oxidation unit, such that an adsorbent material of the adsorbent unit is not damaged by UV light from the photocatalytic oxidation unit.
There is a further need for an air quality system for an aircraft that not only removes particulates, but also inactivates viruses, bacteria, and other microorganisms, as well as removing pollutants such as VOCs. The present invention provides such air cleaner units, air quality systems, and methods, as will be described in enabling detail hereinbelow.
In one aspect of the present invention, there is provided an air quality system for removing a pollutant from an air stream, the air quality system including an interior air space, and at least one air cleaner unit in communication with the interior air space, wherein the at least one air cleaner unit provides a single flow path for the air stream. The at least one air cleaner unit comprises a first photocatalytic oxidation unit and a first adsorbent unit, and the first photocatalytic oxidation unit is located upstream or downstream from the first adsorbent unit.
In another aspect of the present invention, there is provided an air quality system for an aircraft, including an interior air space including a cabin, a lower plenum, and an upper plenum; a mix manifold for distributing air to the interior air space; a lower recirculation system in communication with the mix manifold; an upper recirculation system in communication with the lower recirculation system; at least one air intake unit in communication with the mix manifold; and a plurality of air cleaner units in communication with the interior air space. Each of the plurality of air cleaner units includes at least one photocatalytic oxidation unit and at least one adsorbent unit, wherein the at least one photocatalytic oxidation unit is located upstream or downstream from the at least one adsorbent unit.
In still another aspect of the present invention, there is provided a vehicle, including an air quality system. The air quality system includes at least one air cleaner unit and an interior air space. The at least one air cleaner unit is in communication with the interior air space, wherein the at least one air cleaner unit comprises a first photocatalytic oxidation unit, a first adsorbent unit, and a second adsorbent unit, the first photocatalytic oxidation unit is located downstream from the first adsorbent unit, and the second adsorbent unit is located downstream from the first photocatalytic oxidation unit.
In yet another aspect of the present invention, there is provided an air cleaner unit for removing a pollutant from an air stream, the air cleaner unit including a housing; a first photocatalytic oxidation unit arranged within the housing; and a first adsorbent unit arranged parallel to the first photocatalytic oxidation unit in the housing, wherein the housing defines a single flow path for the air stream.
In a further aspect of the present invention, there is provided an air cleaner unit for removing a pollutant from an air stream, the air cleaner unit including a first adsorbent unit; a first photocatalytic oxidation unit located downstream from the first adsorbent unit; a second adsorbent unit located downstream from the first photocatalytic oxidation unit; and a housing. The first adsorbent unit, the first photocatalytic oxidation unit, and the second adsorbent unit are arranged parallel to each other within the housing, wherein the housing defines a single flow path for the air stream. The first adsorbent unit, the first photocatalytic oxidation unit, and the second adsorbent unit are arranged orthogonal to the air stream, wherein the first photocatalytic oxidation unit comprises a plurality of photocatalytic panels and a plurality of UV lamps so disposed as to illuminate the photocatalytic panels, each of the plurality of photocatalytic panels including a photocatalytic support and a photocatalytic agent disposed on the photocatalytic support.
In an additional aspect of the present invention, there is provided a method for removing a pollutant from an air stream, the method including providing at least one air cleaner unit, the air cleaner unit including a first adsorbent unit, a first photocatalytic oxidation unit, and a second adsorbent unit, wherein the first photocatalytic oxidation unit is located downstream from the first adsorbent unit and the second adsorbent unit is located downstream from the first photocatalytic oxidation unit; passing the air stream through the first adsorbent unit, the first adsorbent unit including a first adsorbent material having a first isotherm curve for adsorption of the pollutant; thereafter, passing the air stream through the first photocatalytic oxidation unit; and thereafter, passing the air stream through the second adsorbent unit, the second adsorbent unit including a second adsorbent material having a second isotherm curve for adsorption of the pollutant.
In another aspect of the present invention, there is provided a method for making an air cleaner unit for removing pollutants from an air stream, the method including providing a first photocatalytic oxidation unit; providing a first adsorbent unit; providing a housing for accommodating the first photocatalytic oxidation unit and the first adsorbent unit; arranging the first adsorbent unit in the housing; and arranging the first photocatalytic oxidation unit in the housing such that the first photocatalytic oxidation unit is located downstream or upstream from the first adsorbent unit, wherein the housing is adapted for providing a single flow path for passage of the air stream through the first photocatalytic oxidation unit and the first adsorbent unit.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
FIGS. 2A-C are block diagrams, each schematically representing an air quality system, according to the invention;
FIGS. 6A-C schematically represent various configurations of an air cleaner unit, according to the invention;
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
The present invention provides an air quality system and method for removing pollutants from an air stream, and for providing cleansed air to an interior air space, such as a cabin or flight deck of an aircraft. As an example, the present invention may be used to provide cleansed air to the interior air space(s) of a commercial aircraft. An air quality system and method of the invention may also be applicable to other vehicles, or to buildings, in which it is desired, or required, to remove pollutants from an interior air space, or from an air stream to be delivered to the interior air space.
Air provided to an interior air space of an aircraft may contain VOCs or other pollutants at levels well above the threshold level at which they can be detected by the human olfactory system. Such pollutants may originate from within the aircraft (e.g., the cabin), or from outside the aircraft (e.g., ground vehicle exhaust gases), and may be discharged into the interior air space of the aircraft as pulses of fluctuating concentration.
In prior art air distribution systems of conventional commercial aircraft, HEPA filters do not remove pollutants, such as VOCs, or potentially harmful microorganisms and viruses.
In contrast to the prior art, air quality systems of the invention combine a particulate filter (e.g., HEPA filter), together with at least one discrete adsorbent unit and at least one discrete photocatalytic oxidation unit, to not only remove particulates from an air stream, but also to remove pollutants such as VOCs, and to remove or inactivate pathogenic microorganisms, and the like. Each of the at least one adsorbent unit and the at least one photocatalytic oxidation unit of the invention may be a discrete unit which is physically separated from other units or components of the system. As used herein, the term VOC (volatile organic compound) may include semi-volatile organic compounds (SVOCs).
Furthermore, and unlike the prior art, air cleaner units of the present invention can be used continuously over an extended period of time, for example, for a period of several years, without the need to regenerate an adsorbent material or adsorbent unit of such air cleaner units. Still further, air cleaner units of the present invention can be operated at a substantially constant temperature, e.g., at or close to ambient temperature, such as in the range of from about 15 to 30° C. In addition, air cleaner units of the present invention do not require moving parts to change the flow path of an air stream, but instead may provide a single flow path for an air stream from which a pollutant is to be removed. Further, and still in contrast to the prior art, air cleaner units of the invention include a photocatalytic support material that is not damaged by exposure to ultraviolet (UV) light.
First recirculation system 60a may be coupled to one or more additional recirculation systems via a second set of ducts 32b. Such one or more additional recirculation systems are represented in
Again with reference to
Air quality system 120 may include a plurality of air cleaner units, which for convenience may be designated as air cleaner unit(s) A-G in
It should be understood that air quality system 120 need not include all of air cleaner unit(s) 140a-g, but instead various embodiments of air quality system 120 may include one, or a combination of two or more, air cleaner unit(s) 140a-g. Each of air cleaner unit(s) 140a-g may comprise one or more photocatalytic oxidation (PCO) units (e.g., PCO units 446a,b,
Air quality system 120 may further include one or more air intake units 112, e.g., for the intake of air from outside an aircraft cabin. As an example, air intakes units 112 may be in the form of ducts leading from gas turbine engine(s) of the aircraft for carrying bleed air from the engines towards an environmental control system (ECS) 114. Such outside air may be directed as an air stream to air cleaner unit(s) 140a. Closed arrows indicate the direction of the air stream, or the direction of air flow, within air quality system 120. Air flowing from air cleaner unit(s) 140a may be passed to ECS 114. (ECS of aircraft are well known in the art. Briefly, the ECS of an aircraft controls the pressure, temperature and humidity of air received by the ECS.) A stream of air may be fed from ECS 114 to a mix manifold 116, and thence to an interior air space, which typically includes a cabin of the aircraft. It is apparent from
Mix manifold 116 may be located downstream from air cleaner unit(s) 140d. Air quality system 120 may further include a first recirculation system 160a. Mix manifold 116, together with air cleaner unit(s) 140b and 140d, may be arranged within first recirculation system 160a. First recirculation system 160a may recirculate air within an interior air space (e.g.,
Air quality system 120 may still further include a flight deck 130. Air cleaner unit(s) 140c may be arranged between flight deck 130 and ECS 114, to provide cleansed air to flight deck 130. Air quality system 120 may still further include a second recirculation system 160b. First and second recirculation systems 160a,b may each comprise a series of ducts, together with one or more fans coupled to the ducts for drawing air into the ducts. In a commercial aircraft, first and second recirculation systems 160a,b may be housed within the lower plenum and upper plenum, respectively (see, e.g.,
Air cleaner unit(s) 140e may be arranged between first recirculation system 160a and cabin 132. Cabin 132 may be in communication with second recirculation system 160b. Air cleaner unit(s) 140g, 140f may be arranged within second recirculation system 160b. Cabin 132 may be coupled to air cleaner unit(s) 140g, 140f via cabin supply lines 121a and 121b, respectively, through which air passed from air cleaner unit(s) 140g, 140f may be delivered to cabin 132. Each of air cleaner units 140a-g can be adapted for removing pollutants from an air stream passed therethrough, such that a supply of cleansed air may be delivered to flight deck 130 and/or cabin 132.
Cabin 232 may include a plurality of zones, for example, first, second, third, and fourth zones 232a-d, respectively. Cabin 232 may be in communication with upper plenum 280a and lower plenum 280b via one or more vents (not shown). Such vents are well known in the art.
Air quality system 220 may further include one or more air cleaner units, for example, air cleaner units 240a-g. Each of air cleaner units 240a-g can be adapted for removing one or more pollutants from the air stream.
Each of air cleaner units 240a-g may comprise a single air cleaner unit or a plurality of air cleaner units in the form of a battery of air cleaner units. Typically, each member of a battery of air cleaner units may perform an equivalent function, and may occupy an equivalent location, within air quality system 220. As an example, air cleaner units 240a may comprise a pair of air cleaner units located downstream from air intake units 212a-b, and upstream from an ECS (not shown in
Air received by air cleaner units 240b from lower plenum 280b may be combined with air emanating from air intake units 212a-b, and passed to mix manifold 216. Air en route to mix manifold 216 may be passed through air cleaner unit 240d, which is located upstream from mix manifold 216. Air may then be distributed from mix manifold 216 via ducts 221 towards first, second, third, and fourth zones 232a-d, respectively, of cabin 232. Such air distributed from mix manifold 216 may be passed through air cleaner units 240e. Air received from upper plenum 280a, and passing through air cleaner units 240f, may be cleansed before being mixed with air emanating from mix manifold 216. Thereafter, the mixed air may be passed to cabin supply lines 221′. Air passing through cabin supply lines 221′ may be passed through air cleaner units 240g before being discharged into cabin 232.
Air cleaner units 240a-g may each comprise one or more PCO units in combination with one or more adsorbent units, as described hereinbelow, e.g., with reference to FIGS. 5, 6A-C. The one or more PCO units and one or more adsorbent units may be arranged within ducts 221, such that ducts 221 may provide a housing for the one or more PCO units and one or more adsorbent units. In alternative embodiments, one or more of air cleaner units 240a-g may have a separate housing, which may be coupled to ducts 221.
It is to be understood that
Air cleaner unit 340 may further include a housing 348. Particulate filter 342, adsorbent unit 344, and PCO unit 346 may be arranged parallel, or substantially parallel, to each other, and orthogonal, or substantially orthogonal, to the direction of air steam 341, within housing 348. As an example, housing 348 may comprise a duct for the passage of air within a vehicle, such as an aircraft, or building. At least in the vicinity of adsorbent unit 344 and PCO unit 346, housing 348 may be linear or follow a straight line Housing 348 may be adapted for the unidirectional passage of air stream 341. Particulate filter 342, adsorbent unit 344, and PCO unit 346 may each extend to the entire perimeter of housing 348.
Housing 348 may provide only a single flow path for air stream 341 throughout the entire extent, or length, of air cleaner unit 340. Air cleaner unit 340 does not require the use of moving parts, such as doors or valves, for redirecting the flow of an air stream 341 through components of air cleaner unit 340. Consequently, air stream 341 may follow only a single flow path, and the flow of air in air stream 341 may be unidirectional. Similarly, operation of air cleaner unit 340 does not require the taking of one or more components of air cleaner unit 340 off-line, e.g., for regeneration of adsorbent unit 344. Instead, air cleaner unit 340 has the advantage of being adapted to provide a continuous supply of cleansed air to an interior space.
In
Each adsorbent unit 344 may include an adsorbent material capable of adsorbing one or more pollutants, such as a volatile- or semi-volatile organic carbon (VOC, SVOC), or a gas, such as ammonia, methane, carbon monoxide, hydrogen sulfide, and the like. VOCs, such as various hydrocarbons, aldehydes, aromatics, toluene, etc., are well known in the art as pollutants within interior air spaces. Such VOC's may be odorous and create an uncomfortable environment for passengers and crew. Various pollutants may be of biological origin, may be derived from ingested materials, may be emitted from chemical processes, or may be discharged from motors or engines in the vicinity of an interior air space. An adsorbent material of adsorbent unit(s) 344 may comprise, for example, various forms of activated carbon, silica gel, or a zeolite. In general, such adsorbents are well known in the art.
According to one aspect of the invention, an adsorbent material of adsorbent unit(s) 344 may comprise a fine porosity adsorbent having a plurality of macropores, each of the plurality of macropores in communication with at least one micropore. Each micropore may have a diameter in the range of from about 5 to 10 Å. Typically, at least about 30% of the micropores may have a diameter in the range of from about 5 to 10 Å, and usually at least about 50% of the micropores may have a diameter in the range of from about 5 to 10 Å.
Each PCO unit 346 may include one or more photocatalytic (PC) panels in combination with one or more UV sources (e.g., a UV lamp or other source of ultra-violet radiation), as described below in connection with, for example, FIGS. 7A-C. Each PCO unit 346 may photocatalytically destroy or remove, e.g., via oxidation to carbon dioxide and water, a pollutant such as a VOC from air stream 341. Thus, PCO unit(s) 346 may act in concert with adsorbent unit(s) 344 to remove one or more pollutants from air stream 341, as is described fully hereinbelow. In addition, PCO unit(s) 346 may destroy biological agents, e.g., viruses, bacteria, and other air-borne microorganisms, as well as pollen, fungal spores, or other allergens. Bacteria and viruses may be inactivated by exposure to UV radiation from the UV source alone, or by exposure to the UV source while in the presence of a PC agent of each PC panel. Such viruses, bacteria, and other microorganisms may include human pathogens.
FIGS. 6A-C schematically represent different configurations for an air cleaner unit, according to various embodiments of the invention. Air cleaner units 440, 440′, and 440″ shown in
Air cleaner unit 440 may further include a first adsorbent unit 444a and a first PCO unit 446a arranged within housing 448. First adsorbent unit 444a and first PCO unit 446a may be arranged substantially parallel to each other and substantially parallel to particulate filter 442. First adsorbent unit 444a may be located upstream from first PCO unit 446a and may be located downstream from particulate filter 442.
With reference to
With reference to
Air cleaner units of the invention, e.g., air cleaner units 440′, 440″, having a first adsorbent material upstream from first PCO unit 444a, when combined with a second adsorbent material located downstream from first PCO unit 444a, may provide unique characteristics and advantages to such air cleaner units 440′, 440″.
While not being bound by theory, the advantages associated with using particular combinations or sequences of adsorbent units and PCO units may be better understood by considering the thermodynamics behind the adsorption process. When an adsorbent material is in contact with a given concentration of pollutant (adsorbate), an equilibrium is established between adsorbed and vapor phase concentrations of pollutant, wherein the equilibrium is a property of the adsorbent and adsorbate. When the pollutant concentration increases, the quantity of pollutant adsorbed will also increase. However, when the vapor phase concentration of the pollutant subsequently decreases, a portion of the sorbed pollutant will tend to desorb. This situation may apply, for example to a first adsorbent unit located upstream from any other adsorbent unit or PCO unit of an air cleaner unit. Pollutant desorbed from the first adsorbent unit may be removed by a first PCO unit downstream from the first (upstream) adsorbent unit. In this way, any desorbed pollutant may be prevented from being discharged into an interior air space.
For example, a pulse in pollutant concentration in an air stream entering an air cleaner unit of the invention will adsorb onto a first adsorbent unit. The higher pollutant concentration in the air stream thermodynamically translates into a higher adsorption capacity for the adsorbent of the first adsorbent unit. Consequently, the PCO unit downstream from the first adsorbent unit may be spared from receiving an unmanageably high pulse or concentration of the pollutant. After the pulse of pollutant has passed, the equilibrium of the adsorbent of the first adsorbent unit is restored by desorption of the pollutant which was adsorbed during the pulse. Such pollutant desorbed by the first adsorbent unit passes to the downstream PCO unit where it may be destroyed by oxidation. The first adsorbent unit thus serves to store a pulse of elevated pollutant concentration, and subsequently meters the pollutant (via equilibrium-driven desorption) to the PCO unit at a manageable rate. The capacity of the first adsorbent unit is not consumed, since the extra adsorbent sites used to adsorb the pulse of pollutant do so reversibly.
The operation of air cleaner units of the invention may be further improved by including at least one additional adsorbent unit, e.g., a second adsorbent unit, downstream from the at least a first PCO unit. As observed hereinabove, a second adsorbent unit may include a second adsorbent material having adsorption properties different from those of a first adsorbent material of a first adsorbent unit, e.g., the first and second adsorbent materials may have a different isotherm curve. For an adsorbent unit which is located downstream from all PCO units of a given air cleaner unit of the invention, an adsorbent material having a relatively steep isotherm curve may be used. This is because adsorbent materials having steeper isotherm curves will tend to desorb pollutants only very slowly, or adsorb pollutants irreversibly, thereby preventing or minimizing the release of such pollutants. The quantity of adsorbent needed for the second adsorbent unit may be much less than would otherwise be required in the absence of an upstream PCO unit, since the PCO unit consumes most of the impurity. In some embodiments, the second adsorbent unit may function as a “guard bed,” by preventing pollutant which would otherwise escape the system from doing so. The second adsorbent unit may also function to remove any partially oxidized pollutant degradation products, which might result from incomplete oxidation of pollutant by the PCO unit.
For an adsorbent which is placed upstream from one or more PCO units, an adsorbent material having a less steep isotherm curve may be used. An adsorbent material which is “weaker” (i.e., has a less steep isotherm curve for a particular pollutant), will tend to desorb the pollutant as the pollutant concentration decreases from a transiently higher concentration, or pulse, of the pollutant. In this way, the “weaker” adsorbent material will tend to act as a “buffer,” thereby variation in pollutant concentration reaching downstream PCO units and other adsorbent units is minimized. Examples of adsorbent materials having a relatively steep isotherm curve, and which may be used in a second or downstream adsorbent unit, include certain forms of carbon and zeolites. Examples of adsorbent materials having a less steep isotherm curve, and which may be used in a first or upstream adsorbent unit, include silica gel and some carbon materials.
Isotherm curves, which show the distribution of adsorbate (e.g., a pollutant to be adsorbed) between the adsorbed phase (adsorbed on an adsorbent material) and the vapor phase at equilibrium, are well known in the art (see, for example, Encyclopedia of Separations Technologies (D. M. Ruthven ed.), Adsorption Equilibrium Data Handbook (Valenzuela & Meyers, 1998); Carbon Adsorption Isotherms for Toxic Organics (Dobbs & Cohen, 1980), which are incorporated herein by reference).
Selecting an appropriate adsorbent material for an adsorbent unit of the invention may be, at least to some extent, a matter of design choice. The choice of adsorbent material may depend on, for example, the operating conditions of an air filter unit of which the adsorbent unit is a part, as well as on the nature of other components of the air filter unit, e.g., the nature of the PCO unit(s). For example, if during operation, it is expected that there will frequently be a relatively high concentration (e.g., >10 ppm) of pollutant for a relatively extended period (e.g., >15 minutes), followed by an extended period (e.g., >15 minutes) of no load, an adsorbent having a relatively large pore capacity (e.g., >1000 m2/g) and broad porosity (e.g., having pore diameters in the range of from about 6 to 600 Å) may be useful. However, for the removal of pollutants present at generally low concentration (e.g., <10 ppm) with periodic spikes (<15 minutes), adsorbents having a relatively high surface area (e.g., having a surface area >1000 m2/g, usually from about 1000-2500 m2/g, and often from about 1500-2500 m2/g) and having fine porosity (e.g., having micropores in the range of about 5-10 Å in diameter) may be preferred. Such fine porosity adsorbents may have a plurality of micropores with at least about 30% of the micropores having a diameter in the range of about 5-10 Å, and usually having at least about 50% of the micropores in the 5-10 Å diameter range. While not being bound by theory, micropores in the 5-10 Å diameter range may allow condensation of the pollutant within the micropores at the low partial pressures associated with low concentrations (e.g., <10 ppm) of pollutant (see, for example, R. T. Liu, Ph.D., Use of Activated Carbon Adsorbers in HVAC Applications; 6th Indoor Air Quality Conference—IAQ 93 (Operating and Maintaining Buildings for Health, Comfort, and Productivity), held November, 1993, Philadelphia, Pa.; Published: Atlanta, Ga.: ASHRAE; ISBN: 1883413133).
Adsorbent materials having a relatively high surface area and fine porosity, and which may be useful in practicing the present invention, may be carbon based (e.g., various activated carbon materials), or may be comprised of inorganic materials. Specific examples of adsorbent carbon materials are presented in Examples 4 and 5 hereinbelow. Apart from the characteristics of adsorbents which are directly related to the capacity and kinetics of pollutant adsorption, certain forms of adsorbent materials, such as activated carbon fibers or activated carbon fabrics (e.g., Kynol™ 5092-15, American Kynol, Pleasantville, N.Y.), may also offer benefits for configuration of adsorbent units, e.g., due to the structural features or mechanical properties of the adsorbent material.
PCO unit 546 may include a first PC panel 550a, a first UV source 552a, a second PC panel 550b, and a second UV source 552. PCO unit 546 may further include a housing 548. Housing 548 may comprise a duct or a portion of a duct. As an example, housing 548 may comprise a metal or a UV-resistant plastic material. First PC panel 550a, first UV source 552a, second PC panel 550b, and second UV source 552 may be arranged sequentially within housing 548 such that first and second UV sources 552a,b alternate with first and second PC panels 550a,b. In some embodiments, PCO unit 546 may include additional numbers of PC panels and additional numbers of UV sources. For example, PCO unit 546 may include up to six (6), or up to 10 or more PC panels, together with the same, or a similar, number of UV sources. The invention is not limited by the number of PC panels or by the number of UV sources.
It will be understood by those skilled in the art that conversion of pollutants at any point on a given PCO panel will be influenced by the light intensity incident on that point, such that conversions will be higher at points on the panel which are closer to a UV lamp. Air passing through a first PCO panel will have an opportunity to mix before it reaches a second PCO panel located downstream from the first PCO panel. Such mixing is beneficial, since a portion of air which may have passed through a region of the first PCO panel which was less-well illuminated may subsequently pass through a region of the second PCO panel which is better illuminated. Mixing will also occur in the spaces between the PCO units and the adsorbent units. This beneficial mixing cannot occur in prior-art designs where the adsorbent and photocatalytic material are co-located on the same structure.
Step 602 may involve passing an air stream through a HEPA filter, or other particulate filter, to remove at least a portion of particulate materials from the air stream. Such an air stream may be generated by recirculating air from an interior air space, e.g., via one or more fans, or by directing a source of outside air through one or more ducts, or by a combination of the above.
After step 602, step 604 may involve passing the air stream through a first adsorbent unit. In one embodiment, the first adsorbent unit includes a first adsorbent material that is adapted to adsorb and desorb a pollutant according to the relative concentrations of unadsorbed pollutant (e.g., in the vapor phase) and adsorbed pollutant (adsorbed by the adsorbent material). According to one aspect of the invention, the first adsorbent unit may serve as a “buffer” to minimize variations in concentration of pollutant in the air stream flowing downstream from the first adsorbent unit during changes in concentration of the pollutant upstream from the first adsorbent unit. The first adsorbent unit may include an adsorbent material such as a silica gel or an activated carbon in an adsorbent bed, or may include a carbon fabric adsorbent, or a carbon-coated ceramic monolith, or a solid carbon monolith, or the like. According to one aspect of the invention, the first adsorbent unit may include a fine porosity adsorbent material containing a plurality of micropores having diameters in the range of from about 5 to 10 Å. Typically, at least about 30% of the micropores may have a diameter in the range of from about 5 to 10 Å, and usually at least about 50% of the micropores may have a diameter in the range of from about 5 to 10 Å.
After step 604, step 606 may involve passing the air stream through a first PCO unit. The first PCO unit may include one or more PC panels and one or more UV sources, for example, as described hereinabove with reference to FIGS. 7A-C. The first PCO unit is adapted for photocatalytically destroying one or more pollutants in the air stream passed from the first adsorbent unit, including one or more pollutants desorbed from the first adsorbent unit, e.g., in response to a decrease in the concentration of the pollutant in the air stream reaching the first adsorbent unit.
After step 606, step 608 may involve passing the air stream through at least a second adsorbent unit. In one embodiment, the second adsorbent unit includes a second adsorbent material that is adapted to strongly, or irreversibly, adsorb a pollutant from the air stream reaching the second adsorbent unit. That is to say, the second adsorbent material may be adapted not to desorb a pollutant when the concentration of that pollutant in the vapor phase (e.g., the air stream entering the second adsorbent unit) decreases. According to one aspect of the invention, the second adsorbent unit may serve as a “trap” to indefinitely sequester the pollutant. The second adsorbent unit may include an adsorbent material such as an activated carbon, a zeolite, or the like. Impregnated adsorbents, such as an impregnated salt or cation may also be used.
As referred to hereinabove, the second adsorbent unit may be characterized as having a second adsorbent material which has a relatively steep isotherm curve, while the first adsorbent unit may be characterized as having a first adsorbent material which has a less steep isotherm curve. The total number of adsorbent units, or the nature of each of the adsorbent units, may be selected such that the adsorbent units as a whole will not be exhausted, and will not need replacement, until after a pre-defined extended period of operation. The adsorbent units and PCO unit(s) of the invention may be operated for a period of several years without maintenance.
After step 608, step 610 may involve passing the air stream through at least a second PCO unit. Second PCO unit may have characteristics and elements as described hereinabove, e.g., with reference to step 606. Because the air stream reaching the second PCO unit has already been cleansed by upstream PCO and adsorbent units, step 610 may be considered a “polishing” step. In contrast to the prior art, each of steps 602 through 610 may be performed at ambient temperature, or at a temperature close to ambient, e.g., in the range of from about 15 to 30° C.
Step 704 may involve providing a housing. The housing provided in step 704 may house the one or more adsorbent units and the one or PCO units, and may further provide only a single flow path for the passage of an air stream through the one or more adsorbent units and the one or PCO units of the air cleaner unit. Optional step 706 may involve arranging a HEPA filter within the housing. Alternatively, in situations where a particulate filter is located upstream from the air cleaner unit, the HEPA filter may be omitted from the air cleaner unit, and step 706 may be omitted from the method of
Step 708 may involve arranging the one or more adsorbent units and the one or more PCO units within the housing, such that the one or more adsorbent units and the one or more PCO units are arranged in a particular sequence with respect to each other and with respect to the HEPA filter. Typically, the HEPA filter is arranged within the housing such that the HEPA filter is upstream from both the one or more adsorbent units and the one or more PCO units. Some possible sequences for arranging the one or more adsorbent units and the one or more PCO units with respect to each other are described hereinabove, e.g., with reference to FIGS. 6A-C. Other possible sequences for arranging the one or more adsorbent units and the one or more PCO units with respect to each other are also within the scope of the invention.
A PCO unit comprising two parallel PC panels was constructed. Each PC panel was 20×24 inches in cross section, and the two PC panels were spaced five inches apart. The panels were coated with photocatalyst as described in commonly assigned U.S. patent application Ser. No. 10/345,022, filed Jan. 14, 2003, the disclosure of which is incorporated by reference herein in its entirety. Two 36 W UV lamps were positioned midway between the two PC panels. An air stream containing acetaldehyde (inlet concentrations in the range of 0.147 to 0.331 ppmw) was passed through the PCO unit. The air temperature of the air stream was in the range of 79-85° F., and the relative humidity was in the range of 35-48%.
Sampling ports were arranged so as to allow sampling of the air stream at both the inlet and the outlet of the PCO unit. The air so sampled was pumped to the injection port of a gas chromatograph for analysis of acetaldehyde concentration. Samples were taken from the outlet both when the ultraviolet lamps were turned on and when they were turned off. Table 2 shows average values of several measurements for each condition. The % removal of acetaldehyde via photocatalytic oxidation was calculated by comparing the “lights OFF” and “lights ON” conditions. The results are shown in Table 2. The percentage removal of acetaldehyde from the air stream by the PCO unit was higher when the flow rate of the air stream was lower.
A PCO unit comprising five parallel PC panels was constructed. Each panel was 20×24 inches in cross section, and the PC panels were spaced three inches apart. Two 36 W UV lamps were mounted between each successive pair of PC panels for a total of eight UV lamps. An air stream contaminated with low concentrations of acetaldehyde was passed through the PCO unit. The air temperature was 85° F., and the relative humidity was 21%. Air was sampled and analyzed by gas chromatography, essentially as described in Example 1. Table 3 reports average values of several measurements for each condition. The % removal of acetaldehyde from the air stream was calculated by comparing the “lights OFF” and “lights ON” conditions.
Higher concentrations of acetaldehyde in the air stream generally correspond to lower percent removal of acetaldehyde. Comparing the results in Table 3 with those in Table 2 of Example 1, the PCO unit having five PC panels provides higher percentage removal of acetaldehyde as compared with the PCO unit having two PC panels.
It is apparent from
0.8826 g of activated carbon fiber adsorbent (ACF1300 obtained from Carbon Resources, Huntington Beach, Calif.), in the form of five 3.0 cm diameter discs, was degassed overnight under 28″ vacuum at 230° C. prior to placement in a 3.0 cm diameter gas phase reactor. A sample containing 529 ppm toluene in nitrogen feed gas (Scott Specialty Gas, Plumsteadville, Pa.) was blended with compressed nitrogen to create a 2 ppm toluene gas feed. Under bypass conditions, the feed was analyzed with a zNnose™ Model 4100 Gas Chromatograph (Electronic Sensor Technology, Newbury Park, Calif.) to calibrate the instrument to 2 ppm. Initially, samples were taken every six minutes for analysis by the zNose™ sensor to evaluate the adsorption capacity of the carbon adsorbent being tested. As shown in
0.8473 g of carbon adsorbent (Kynol™ activated carbon fabric ACC-5092-15, obtained from American Kynol, Pleasantville, N.Y.), in the form of five 3.0 cm diameter discs, was degassed overnight under 28″ vacuum at 230° C. prior to placement in a 3.0 cm diameter gas phase reactor. A sample of 529 ppm toluene in nitrogen feed gas (Scott Specialty Gas, Plumsteadville, Pa.) was blended with compressed nitrogen to create a 2 ppm toluene gas feed. Under bypass conditions, the feed was analyzed with a zNnose™ Model 4100 Gas Chromatograph (Electronic Sensor Technology, Newbury Park, Calif.) to calibrate the instrument to 2 ppm. Initially, samples were taken every six minutes for analysis by the zNose™ sensor to evaluate the adsorption capacity of the carbon adsorbent being tested. As shown in
Following the adsorption of toluene by the adsorbent as described above, a desorption curve was obtained by passing a stream of toluene-free nitrogen gas through the adsorbent, and analyzing the effluent with the zNose™ analyzer. The kinetics of toluene desorption are shown in
Using the data obtained as described above, the rates of adsorption and desorption of toluene were obtained and defined for the carbon adsorbent Kynol 5092-15 over the course of the adsorption/desorption cycle, as shown in
Although certain embodiments of the invention have been described primarily with respect to supplying cleansed air to an interior space of an aircraft, the invention may be equally applicable to other vehicles, buildings, etc.
It should be understood, of course, that the foregoing relates to embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
