Abstract:
Systems, apparatus, and methods for the catalytic removal of at least one pollutant from an air stream via a catalytic precooler arranged in series with at least one augmentative catalytic device. The augmentative catalytic device may be located upstream or downstream from the catalytic precooler. The augmentative catalytic device may be integrated with the catalytic precooler, thereby eliminating the need for a separate housing and minimizing weight. Alternatively, the augmentative catalytic device may be disposed within a separate housing, thereby facilitating access for maintenance and decreasing direct maintenance costs.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to an environmental control system, and more particularly, to an augmented catalytic heat exchanger system and method for removing one or more pollutants from an air stream.  
         [0002]     Commercial aircraft feed bleed air from a gas turbine engine to an environmental control system (ECS) and thence 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 to provide for the comfort of flight crew and passengers.  
         [0003]     Modern jet (gas turbine engine) aircraft are typically designed for fuel-efficient operation at relatively high altitudes of 25,000 feet or more where the atmospheric ozone content is relatively high. The ozone concentration may depend on a number of factors, such as the altitude, geographic location, time of year, etc. The ozone concentration in the atmosphere is typically in the range of from about 0.2 to 2.0 ppm. The upper limit permitted by FAA regulations for the ozone concentration in cabin air of commercial aircraft is 0.1 ppm. Excessive levels of ozone can cause a number of medical problems, including lung and eye irritation, headaches, fatigue, and breathing discomfort.  
         [0004]     In the prior art, vehicular environmental control systems have used a catalytic converter for the removal of ozone, wherein the catalytic converter is a stand-alone device, thereby adding weight to the ECS. Adding weight to the ECS may be a major disadvantage, particularly in the case of aircraft. A stand-alone catalytic converter may also cause an undesirable pressure drop across the system. Furthermore, due to the relatively low surface area of conventional catalytic converters, the maintenance period is relatively short, and direct maintenance costs are consequently relatively high.  
         [0005]     U.S. Pat. No. 5,151,022 to Emerson et al. discloses an ECS for a vehicle for removing nuclear, biological, and chemical warfare agents from air, wherein the ECS includes a primary heat exchanger and a catalytic converter as a separate device.  
         [0006]     U.S. Pat. No. 4,665,973 to Limberg et al., discloses an ECS including a catalytic heat exchanger for the removal of ozone. However, Limberg et al. does not disclose an ancillary or augmentative catalytic device to be used in conjunction with the catalytic heat exchanger. Consequently, due to the relatively low catalytic conversion efficiency, for example about 60%, of a stand-alone catalytic heat exchanger, the ECS of Limberg et al. may fail to meet FAA regulations on ozone concentration in cabin air, or may require frequent maintenance to boost the catalytic conversion efficiency to a point sufficient to meet such FAA regulations.  
         [0007]      FIG. 1A  schematically represents, in side view, a portion of an ECS  10  for a vehicle (not shown), including a primary heat exchanger  12  and a stand-alone catalytic converter  14 , according to the prior art. An air stream  18  may be passed through primary heat exchanger  12 , which cools the air but does not remove ozone from air stream  18 , and thence, via a conduit  16 , to catalytic converter  14 , which removes one or more pollutants from air stream  18 . In the case of a commercial aircraft, primary heat exchanger  12  and catalytic converter  14  may have a weight of about 44 Kg and 5.8 Kg, respectively.  
         [0008]      FIG. 1B  schematically represents, in side view, a portion of an ECS  10 ′ for a vehicle (not shown), including a stand-alone catalytic primary heat exchanger  12 ′, also according to the prior art. An air stream  18  may be passed through catalytic primary heat exchanger  12 ,′ which both cools the air and catalytically removes one or more pollutants.  
         [0009]     A disadvantage with the prior art system of  FIG. 1A  is that the combined weight of primary heat exchanger  12  and catalytic converter  14  greatly exceed that of a catalytic heat exchanger (e.g., catalytic heat exchanger  12 ′ of  FIG. 1B ). A further disadvantage with the prior art system of  FIG. 1A  is that the catalytic efficiency, e.g., the ozone conversion efficiency, may decrease over a relatively short operation period, such that extensive maintenance of catalytic converter  14  is required within a period of from about 9,000 to 22,000 hours.  
         [0010]     A disadvantage of catalytic heat exchanger  12 ′ of  FIG. 1B  is that the catalytic efficiency, e.g., the ozone conversion efficiency, may be considerably less that that of the prior art system of  FIG. 1A .  
         [0011]     As can be seen, there is a need for an ECS including a catalytic primary heat exchanger or catalytic precooler, which exhibits catalytic activity for the destruction of ozone, in combination with an ancillary or augmentative catalytic device also for the destruction of ozone, wherein the weight of the augmentative catalytic device is less than that of prior art stand-alone catalytic converters. Because the augmentative catalytic device may be smaller in size than a stand-alone catalytic converter, any pressure drop within the system may be mitigated.  
         [0012]     There is also a need for a catalytic heat exchanger system having a catalytic precooler in series with an augmentative catalytic device, wherein each of the catalytic precooler and the augmentative catalytic device are adapted for ozone removal from an air stream, and wherein the total weight of the catalytic heat exchanger system is less than the combined weight of a non-catalytic precooler and a stand-alone catalytic converter of the prior art.  
         [0013]     There is a further need for a catalytic heat exchanger system having a catalytic precooler in series with an augmentative catalytic device, wherein the overall ozone conversion efficiency of the catalytic heat exchanger system is at least about 85% after 30,000 hours of operation, and wherein the direct maintenance cost for the catalytic heat exchanger and ancillary catalytic device is less than that of prior art stand-alone catalytic converters.  
       SUMMARY OF THE INVENTION  
       [0014]     In one aspect of the present invention, there is provided catalytic heat exchanger system, for removing at least one pollutant from an air stream, comprising a first housing, a catalytic precooler disposed within the first housing, and an augmentative catalytic device disposed in series with the catalytic precooler. Each of the catalytic precooler and the augmentative catalytic device is adapted for passage of an air stream therethrough, and each of the catalytic precooler and the augmentative catalytic device is adapted for removal of the pollutant from the air stream.  
         [0015]     In another aspect of the present invention, there is provided a catalytic heat exchanger system comprising a first housing, a catalytic precooler disposed within the first housing, a second housing, and an augmentative catalytic device disposed within the second housing. The augmentative catalytic device is disposed in series with the catalytic precooler, each of the catalytic precooler and the augmentative catalytic device is adapted for passage of an airstream therethrough, and each of the catalytic precooler and the augmentative catalytic device is independently capable of catalytic ozone conversion.  
         [0016]     In still another aspect of the present invention, there is provided a catalytic heat exchanger system, for the removal of at least one pollutant from an air stream, comprising a first housing, a catalytic precooler disposed within the first housing, wherein the catalytic precooler comprises a plurality of hot pass passages arranged longitudinally within the first housing, a first catalyst support disposed within the plurality of hot pass passages, and at least one catalyst disposed on or within the first catalyst support. The catalytic heat exchanger system may further comprise an augmentative catalytic device disposed in series with the catalytic precooler, wherein the augmentative catalytic device comprises a plurality of channels, and a second catalyst support disposed within the plurality of channels, the at least one catalyst disposed on or within the second catalyst support, and the at least one catalyst adapted for catalytic ozone conversion. The augmentative catalytic device may have a circular configuration, such as a spiral configuration or a concentric ring configuration. The plurality of channels may be straight channels or off-set channels, and the catalytic precooler and the augmentative catalytic device may have a combined ozone conversion efficiency of at least about 85% after operation of the catalytic heat exchanger system for a period of about 30,000 hours.  
         [0017]     In yet another aspect of the present invention, there is provided an environmental control system, for providing conditioned air to a cabin of a vehicle, comprising a catalytic heat exchanger system adapted for removing at least one pollutant from an air stream, and the catalytic heat exchanger system further adapted for cooling the air stream. The catalytic heat exchanger system may further comprise at least one duct coupled to the catalytic heat exchanger system for providing the air stream to the catalytic heat exchanger system from a compressed air source. The catalytic heat exchanger system may comprise a catalytic precooler disposed within a first housing, and an augmentative catalytic device disposed in series with the catalytic precooler.  
         [0018]     In a further aspect of the present invention, there is provided a vehicle comprising at least one environmental control system for providing conditioned air to a cabin of the vehicle, and at least one compressed air source for providing an air stream to the at least one environmental control system, wherein the environmental control system comprises a catalytic heat exchanger system adapted for cooling the air stream and for catalytically removing at least one pollutant from the air stream. The catalytic heat exchanger system may comprise a catalytic precooler disposed within a first housing, and an augmentative catalytic device disposed in series with the catalytic precooler, wherein each of the catalytic precooler and the augmentative catalytic device is independently capable of catalytic ozone conversion.  
         [0019]     In still a further aspect of the present invention, there is provided a method for providing cleansed air to a cabin of a vehicle, the method comprising providing an airstream from a compressor, passing the airstream through a first catalytic device, and thereafter passing the airstream through a second catalytic device, wherein the second catalytic device is arranged in series with the first catalytic device, and wherein each of the first catalytic device and the second catalytic device is independently capable of catalytic ozone conversion.  
         [0020]     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1A  schematically represents, in side view, a portion of an environmental control system for a vehicle, including a primary heat exchanger coupled to a stand-alone catalytic converter, according to the prior art;  
         [0022]      FIG. 1B  schematically represents, in side view, a portion of an environmental control system for a vehicle, including a stand-alone catalytic primary heat exchanger, also according to the prior art;  
         [0023]      FIG. 2  is a block diagram schematically representing a vehicle including a catalytic heat exchanger system, according to one embodiment of the invention;  
         [0024]     FIGS.  3 A-B are block diagrams, each schematically representing a catalytic heat exchanger system, according to two alternative embodiments of the invention;  
         [0025]     FIGS.  4 A-B each schematically represent, in longitudinal sectional view, a catalytic heat exchanger system having a catalytic precooler and an augmentative catalytic device within a single housing, according to two alternative embodiments of the invention;  
         [0026]     FIGS.  5 A-B each schematically represent, in longitudinal sectional view, a catalytic heat exchanger system having a catalytic precooler and an augmentative catalytic device within separate housings, according to two alternative embodiments of the invention;  
         [0027]     FIGS.  6 A-B are a longitudinal sectional view and a transverse sectional view, respectively, schematically representing a catalytic precooler, according to one embodiment of the invention;  
         [0028]      FIG. 6C  is a transverse sectional view schematically representing a hot pass passage of the catalytic precooler of FIGS.  6 A-B, according to the invention;  
         [0029]      FIG. 7  is a perspective view schematically representing a plate-fin precooler, according to another embodiment of the invention;  
         [0030]      FIG. 8A  is a perspective view schematically representing a plurality of straight passages for a plate-fin catalytic device, according to one embodiment of the invention;  
         [0031]      FIG. 8B  is a perspective view schematically representing a plurality of off-set passages for a plate-fin catalytic device, according to another embodiment of the invention;  
         [0032]      FIG. 9A  is a side view schematically representing an augmentative catalytic device adapted for catalytic ozone removal, according to one embodiment of the invention;  
         [0033]      FIGS. 9B and 9C  are axial views schematically representing the augmentative catalytic device of  FIG. 9A , according to two alternative embodiments of the invention;  
         [0034]      FIG. 9D  is an enlarged axial view of the augmentative catalytic device of  FIG. 9A  showing a plate-fin configuration, according to one embodiment of the invention;  
         [0035]      FIG. 9E  is an enlarged sectional view of a portion of a fin of the augmentative catalytic device of  FIG. 9A , including a catalyst support disposed on the fin, according to one embodiment of the invention; and  
         [0036]      FIG. 10  schematically represents a series of steps involved in a method for providing cleansed air to a cabin of a vehicle, according to another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     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.  
         [0038]     Broadly, the present invention provides apparatus, systems, and methods for removing at least one pollutant from an air stream, and for providing cleansed air to an interior air space. As an example, the present invention may be used to remove ozone from an air stream provided by a compressor of a vehicle, and for providing cleansed air to an interior air space of the vehicle, such as a cabin or flight deck of a commercial aircraft. The cleansed air may be provided by passing the air stream through a catalytic heat exchanger system of an environmental control system (ECS) of the present invention. The air stream may be derived, for example, from engine bleed air (i.e., air provided by the compressor of a gas turbine engine), or from a dedicated ambient air compressor.  
         [0039]     An air stream to be supplied to an interior air space of an aircraft may contain various pollutants, such as ozone, VOCs, or carbon monoxide, and the like. Ozone may be present in the air stream at levels well above the maximum level (presently 0.1 ppm) permitted by the FAA. In the case of an air stream derived from an air intake unit of an aircraft, the ozone concentration may typically be in the range of from about 0.2 to 2.0 ppm, depending on factors such as geographic location, the time of year, and the altitude.  
         [0040]     Environmental control systems of the prior art have used either a non-catalytic primary heat exchanger in combination with a separate, stand-alone catalytic converter, or a catalytic primary heat exchanger alone (i.e., in the absence of a catalytic converter per se), for the removal of pollutants from air.  
         [0041]     In contrast to the prior art, apparatus and systems of the present invention solve the problems associated with prior art apparatus and systems by providing a catalytic heat exchanger system which incorporates a catalytic precooler or primary heat exchanger in combination with an augmentative catalytic device, wherein both the catalytic precooler and the augmentative catalytic device are independently adapted for removal from air of a pollutant, such as ozone, whereby the maintenance period may be extended to at least about 30,000 hours of operation, while maintaining an ozone conversion efficiency of at least about 85%.  
         [0042]      FIG. 2  is a block diagram schematically representing a vehicle  100  including a compressed air source  104  and an ECS  110 , according to one embodiment of the invention. As an example, vehicle  100  may comprise a commercial aircraft, and ECS  110  may provide conditioned air to the cabin of vehicle  100 . Alternatively, vehicle  100  may comprise a land vehicle. Compressed air source  104  may provide an air stream  18  (see, e.g.,  FIGS. 4A-5B ) to ECS  110 . Compressed air source  104  may comprise a compressor of a gas turbine engine or a dedicated air compressor (neither of which are shown).  
         [0043]     Again with reference to  FIG. 2 , ECS  110  may include a catalytic heat exchanger system  120 . Catalytic heat exchanger system  120  may comprise a catalytic precooler or primary heat exchanger  140  coupled to an augmentative catalytic device  150 . Both catalytic precooler  140  and augmentative catalytic device  150  may be adapted for the passage of air stream  18  therethrough. Catalytic precooler  140  and augmentative catalytic device  150  may be coupled to each other in series. The flow rate of air stream  18  may typically be in the range of from about 20 to 400 pounds of air per minute, and usually from about 150 to 350 pounds per minute.  
         [0044]     Each of catalytic precooler  140  and augmentative catalytic device  150  may be adapted for the independent catalytic decomposition of ozone (or ozone conversion), that is to say, both catalytic precooler  140  and augmentative catalytic device  150  may catalytically decompose ozone independently of each other. Typically, ozone may be catalytically converted to molecular oxygen via catalytic heat exchanger system  120 .  
         [0045]     Each of catalytic precooler  140  and augmentative catalytic device  150  may have an initial ozone conversion efficiency of at least about 80%. The initial ozone conversion efficiency may be considered to be a typical ozone conversion efficiency when catalytic heat exchanger system  120  is first used. The ozone conversion efficiency of both catalytic precooler  140  and augmentative catalytic device  150  typically decreases over time, and specifically following operation of catalytic heat exchanger system  120 , e.g., during flight of an aircraft. However, each of catalytic precooler  140  and augmentative catalytic device  150  may typically have a second ozone conversion efficiency of at least about 60% after a period of operation of catalytic heat exchanger system  120  of about 30,000 hours, wherein the second ozone conversion efficiency maybe considered to be an ozone conversion efficiency after operation of catalytic heat exchanger system  120  for a defined period of time, in this instance 30,000 hours.  
         [0046]     In the case of a commercial aircraft, augmentative catalytic device  150  may have a weight typically in the range of from about 2.0 Kg to 4.0 Kg, and usually from about 2.5 Kg to 4.0 Kg. Catalytic precooler  140  may have a weight similar to that of primary heat exchanger  12  (see  FIG. 1A ), for example, about 44 to 45 Kg.  
         [0047]     ECS  110  may further include one or more secondary or tertiary heat exchangers, dehumidifiers, water traps, condensers, and/or additional elements, for example, as described in U.S. Pat. No. 4,655,973, the disclosure of which is incorporated by reference herein in its entirety.  
         [0048]     FIGS.  3 A-B are block diagrams, each schematically representing a catalytic heat exchanger system, according to two alternative embodiments of the invention. Thus,  FIG. 3A  shows a catalytic heat exchanger system  120  including a first housing  130 , wherein both catalytic precooler  140  and augmentative catalytic device  150  are disposed within first housing  130 . In the embodiment of  FIG. 3A , augmentative catalytic device  150  may be located either upstream or downstream from catalytic precooler  140 .  
         [0049]      FIG. 3B  shows a catalytic heat exchanger system  120 ′ including first housing  130  and a second housing  132 , wherein catalytic precooler  140  is disposed within first housing  130 , while augmentative catalytic device  150  is disposed within second housing  132 . In the embodiment of  FIG. 3B , augmentative catalytic device  150  may be located either upstream or downstream from catalytic precooler  140 .  
         [0050]     FIGS.  4 A-B each schematically represent a catalytic heat exchanger system  120   a,    120   b  respectively, as seen in longitudinal sectional view, having catalytic precooler  140  and augmentative catalytic device  150  within a single (first) housing  130 , according to two alternative embodiments of the invention. By accommodating both catalytic precooler  140  and augmentative catalytic device  150  within a single housing  130 , considerable weight savings may be achieved.  
         [0051]     In the embodiment of  FIG. 4A , catalytic heat exchanger system  120   a  includes augmentative catalytic device  150  located upstream from catalytic precooler  140 . In contrast, catalytic heat exchanger system  120   b  of  FIG. 4B  includes augmentative catalytic device  150  located downstream from catalytic precooler  140 . At least one duct  134  may be coupled to catalytic heat exchanger system  120   a,  e.g:, for providing air stream  18  to first housing  130  from compressed air source  104  (see, e.g.,  FIG. 2 ). In FIGS.  4 A-B the direction of flow of airstream  18  is indicated by the arrow.  
         [0052]     With further reference to FIGS.  4 A-B, catalytic heat exchanger system  120   a,    120   b,  catalytic precooler  140 , and augmentative catalytic device  150  may have those characteristics and elements as described hereinabove, e.g., with reference to FIGS.  2 ,  3 A-B. First housing  130  may be coupled to other elements of ECS  110  (see  FIG. 2 ) via the at least one duct  134 .  
         [0053]     In the case of an air stream  18  which may be provided from bleed air from the compressor of a gas turbine engine, the temperature of air stream  18  upstream of catalytic precooler  140  may typically be in the range of from about 400 to 1000° F., and usually from about 600 to 800° F.; while the temperature of air stream  18  downstream of catalytic precooler  140  may typically be in the range of from about 200 to 450° F., and usually from about 300 to 400° F.  
         [0054]     In the case of catalytic heat exchanger system  120   a  ( FIG. 4A ) augmentative catalytic device  150  may include a catalyst, or catalyst mixture, suited to a relatively high temperature of air stream  18  at a location upstream from catalytic precooler  140 . In general, overall ozone conversion efficiency may be greater when augmentative catalytic device  150  is upstream from catalytic precooler  140  due to the higher air temperature. In contrast, in the case of catalytic heat exchanger system  120   b  ( FIG. 4B ) augmentative catalytic device  150  may include a catalyst, or catalyst mixture, suited to a relatively low temperature of air stream  18  at a location downstream from catalytic precooler  140 . Further, in situations where contamination of augmentative catalytic device  150  may be anticipated as a potential problem, the downstream location shown in  FIG. 4B  may be selected.  
         [0055]     FIGS.  5 A-B each schematically represent a catalytic heat exchanger system  120 ′ a,    120 ′ b,  respectively, as seen in longitudinal sectional view, according to two alternative embodiments of the invention. In catalytic heat exchanger system  120 ′ a  of  FIG. 5A , catalytic precooler  140  and augmentative catalytic device  150  may be housed within a first housing  130  and a second housing  132 , respectively, wherein augmentative catalytic device  150  and second housing  132  may be located downstream from catalytic precooler  140  and first housing  130 .  
         [0056]     In catalytic heat exchanger system  120 ′ b  of  FIG. 5B , catalytic precooler  140  and augmentative catalytic device  150  may be again housed within a first housing  130  and a second housing  132 , respectively. However, in the embodiment of  FIG. 5B , augmentative catalytic device  150  and second housing  132  may be located upstream from catalytic precooler  140  and first housing  130 . The temperature of air stream  18  may vary according to an upstream or downstream location with respect to catalytic precooler  140 , generally as described hereinabove with reference to FIGS.  4 A-B. By locating augmentative catalytic device  150  either upstream or downstream from catalytic precooler  140 , a temperature of air stream  18  best suited to the catalytic activity exhibited by augmentative catalytic device  150  may be selected.  
         [0057]      FIG. 6A  is a longitudinal sectional view of a catalytic precooler  140  comprising a plurality of hot pass passages  142 , according to one embodiment of the invention, wherein each of hot pass passages  142  may be in the form of a cylinder arranged longitudinally within first housing  130 . The direction of flow of air stream  18  is indicated by the arrow as being parallel to hot pass passages  142 . Each of the plurality of hot pass passages  142  may comprise a ceramic, such as cordierite (magnesium aluminum silicate); or a metal such as steel, aluminum, an aluminum alloy, titanium, or a titanium alloy, and the like. In alternative embodiments, catalytic precooler  140  may have a crossflow plate-fin configuration or structure (see, e.g.,  FIG. 7 ).  
         [0058]      FIG. 6B  is a transverse sectional view of catalytic precooler  140 , for example, as seen along the lines  6 B- 6 B of  FIG. 6A . Only three layers or rows of hot pass passages  142  are shown in  FIG. 6B  for the sake of clarity. In practice, hot pass passages  142  may be distributed both vertically and horizontally throughout first housing  130 . The direction of flow of cold fluid  19 , may be in a direction substantially orthogonal to the longitudinal axis of first housing  130 , as indicated in  FIG. 6B  by the arrow.  
         [0059]      FIG. 6C  is an enlarged transverse sectional view of a hot pass passage  142  of catalytic precooler  140  of FIGS.  6 A-B, according to the invention. Hot pass passage  142  may include a hot pass passage inner surface  142   a.  A first catalyst support  148  may be disposed on hot pass passage inner surface  142   a.  First catalyst support  148  may be porous, and may comprise, for example, a refractory metal oxide, such as alumina, titania, manganese dioxide, or cobalt oxide, each with or without the addition of silica. At least one catalyst (not shown) may be disposed on or within first catalyst support  148 .  
         [0060]     Typically, the at least one catalyst may have catalytic activity for removing or decomposing at least one pollutant from air stream  18 . Examples of pollutants that may be removed from air stream  18  by the at least one catalyst include ozone, various volatile organic hydrocarbons (VOCs), carbon monoxide, and the like. The at least one catalyst may comprise, as an example, a precious metal, a transition metal, or their metal oxides, or mixtures thereof. Examples of catalysts that may be disposed on or within first catalyst support  148 , and which may be capable of removing at least one pollutant from air stream  18  include Pd, Pt, Au, Ag, Ir, Rh, Ni, Co, Mn, Cu, Fe, either in metal or oxide form, or mixtures thereof. In general, catalyst compositions for removal of ozone or other pollutants from air are well known in the art.  
         [0061]      FIG. 7  is a perspective view of a portion of a catalytic precooler  140 ′ of plate-fin construction, according to another embodiment of the invention. Catalytic precooler  140 ′ may include a plurality of parallel plates  144 , and a plurality of fins  146   a,    146   b  disposed between each pair of plates  144 . A first plurality of fins  146   a  disposed between a first pair of plates  144  may define a plurality of hot pass passages  142 . A second plurality of fins  146   b  disposed between a second pair of plates  144  may define a plurality of cold pass passages  143 , wherein hot pass passages  142  are substantially orthogonal to cold pass passages  143 . This structure for catalytic precooler  140 ′ may be referred to as a crossflow plate-fin configuration. According to one embodiment of the invention, a first catalyst support  148  may be disposed on the surface of hot pass passages  142 , wherein first catalyst support  148  may have at least one catalyst thereon or therewithin, for example, as described with reference to  FIG. 6C .  
         [0062]      FIG. 8A  is a perspective view schematically representing a plurality of hot pass passages  142  for a plate-fin catalytic device, according to one embodiment of the invention, wherein the plate-fin catalytic device may be a catalytic precooler  140 . Hot pass passages  142  may be defined by a plurality of fins  146   a.  In the embodiment of  FIG. 8A , each hot pass passage  142  may be in the form of a straight, or plane, passage.  
         [0063]      FIG. 8B  is a perspective view schematically representing a plurality of hot pass passages  142 ′ for a plate-fin catalytic device, such as catalytic precooler  140 , according to another embodiment of the invention. Hot pass passages  142 ′ may be defined by a plurality of off-set fins  146   a,  such that hot pass passages  142 ′ may be similarly off-set. By off-setting hot pass passages  142 ′ turbulence of air passing therethrough may be increased. Augmentative catalytic device  150  (see, e.g., FIGS.  9 A-D) may also have a plate-fin configuration analogous to that shown in  FIG. 8A  or  FIG. 8B .  
         [0064]     A first catalyst support  148 , having at least one catalyst disposed thereon or therein, may be disposed on the surfaces of hot pass passages  142 ,  142 ′, essentially as described hereinabove (e.g., with respect to  FIGS. 6C, 7 ). Plates  144  (see, e.g.,  FIG. 7 ) are omitted from FIGS.  8 A-B for the sake of clarity.  
         [0065]      FIG. 9A  is a side view schematically representing an augmentative catalytic device  150   a,    150   b  adapted for independent catalytic removal of ozone from an air stream, according to one embodiment of the invention. Augmentative catalytic device  150   a,    150   b  may include axial surface  151 .  
         [0066]      FIG. 9B  is an axial view of augmentative catalytic device  150   a  of  FIG. 9A . Augmentative catalytic device  150   a  may be of plate-fin construction (see, e.g., FIGS.  7 ,  8 A-B). Augmentative catalytic device  150   a  may be essentially circular and may have a spiral plate-fin configuration. A single plate-fin layer, for example, comprising a plane metal sheet (or plate  154  (see FIG.  9 D)) disposed in contact with a corrugated metal sheet (forming fins  156 ) may be rolled up to form the spiral configuration of augmentative catalytic device  150   a.    
         [0067]      FIG. 9C  is an axial view of augmentative catalytic device  150   b  of  FIG. 9A , according to an alternative embodiment of the invention. Augmentative catalytic device  150   b  may have similar characteristics and features as described for augmentative catalytic device  150   a,  with reference to  FIG. 9B . However, augmentative catalytic device  150   b  may have a concentric ring configuration of plate-fin construction, instead of the spiral configuration of augmentative catalytic device  150   a.  A concentric ring configuration may be formed by coupling a plurality of concentric rings, each concentric ring being of plate-fin construction, to form the configuration of augmentative catalytic device  150   b    
         [0068]      FIG. 9D  is an enlarged axial view of a portion (labeled  150 ′) of augmentative catalytic device  150   a,    150   b  of  FIGS. 9B, 9C , respectively, showing fins  156  disposed between plates  154  to define a plurality of channels  152 . Fins  156  and plates  154  may each comprise a metal such as stainless steel or aluminum. Channels  152  may be present at a cell density typically in the range of from about 350 to 700 cells per square inch (cpsi) of axial surface  151  of augmentative catalytic devices  150   a,    150   b,  usually from about 400 to 600 cpsi, and often from about 350 to 550 cpsi. Channels  152  may be arranged longitudinally within augmentative catalytic device  150   a,    150   b.  Channels  152  within augmentative catalytic device  150   a,  or within augmentative catalytic device  150   b,  may be either straight channels, analogous to straight passages  142   a  ( FIG. 8A ), or off-set channels, analogous to off-set passages  142   b  ( FIG. 8B ). The plurality of channels  152  may jointly define a plate-fin substrate for a second catalyst support  158  (see  FIG. 9E ).  
         [0069]      FIG. 9E  is an enlarged sectional view of a portion of a fin  156  of augmentative catalytic device  150   a,    150   b,  showing second catalyst support  158  disposed on fin  156 . At least one catalyst may be disposed on or within second catalyst support  158 . Second catalyst support  158  may comprise a material such as alumina, titania, manganese dioxide, or cobalt oxide, each with or without the addition of silica. Second catalyst support  158  of augmentative catalytic device  150   a,    150   b  may be the same as first catalyst support  148 , or may be different from first catalyst support  148 , of catalytic precooler  140  (see  FIG. 6C ).  
         [0070]     The at least one catalyst disposed on or within second catalyst support  158  may comprise Pd, Pt, Au, Ag, Ir, Rh, Ni, Co, Mn, Cu, Fe, or mixtures thereof. The at least one catalyst disposed on or within second catalyst support  158  may be the same as, or different from, the at least one catalyst disposed on or within first catalyst support  148 .  
         [0071]      FIG. 10  schematically represents a series of steps involved in a method  200  for providing cleansed air to a cabin of a vehicle, according to another embodiment of the invention. The vehicle may be powered by at least one gas turbine engine. The vehicle may be a land vehicle, such as a tank for military operations, or a commercial aircraft, such as a wide-body passenger aircraft. The air provided to the cabin may be cleansed by the removal of at least one pollutant, such as ozone, from a stream of air supplied to a catalytic heat exchanger system of an ECS of the vehicle.  
         [0072]     Step  202  of method  200  may involve providing an air stream via one or more ducts to an inlet of the catalytic heat exchanger system. The air stream may be provided by a compressor, which may be the compressor of at least one gas turbine engine, or a dedicated air compressor.  
         [0073]     Step  204  may involve passing the air stream through a first catalytic device. The first catalytic device may be a catalytic precooler or an augmentative catalytic device. The catalytic precooler and augmentative catalytic device may have those features, elements, and characteristics as described hereinabove, e.g., with reference to  FIGS. 2-9E . Thus, the first catalytic device may be adapted for the removal of at least one pollutant, e.g., ozone, from the air stream.  
         [0074]     Step  206  may involve, after step  204 , passing the air stream through a second catalytic device. The second catalytic device may be a catalytic precooler or an augmentative catalytic device, as described hereinabove. The second catalytic device may be located downstream from the first catalytic device.  
         [0075]     Method  200  may provide an ozone conversion efficiency of at least about 85% after operation, i.e., after performing steps  204  and  206 , for a period of at least about 30,000 hours, in the absence of any maintenance or cleaning of either the first or the second catalytic device.  
         [0076]     Although the invention has been described, inter alia, with respect to ozone removal in an aircraft, the invention may also be applicable to the removal of other pollutants from air, and to land vehicles, as well as the removal of pollutants from air to be supplied to interior air spaces of buildings, and the like.  
         [0077]     It should be understood, of course, that the foregoing relates to exemplary 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.