CATALYTIC OZONE CONVERTER

Abstract: An improved catalytic converter (10) is provided particularly for use in reducing the ozone content of an air flow stream supplied to an aircraft environmental control system (12) for cabin pressurization and/or air-conditioning. The catalytic converter (10) comprises one or more plate-fin elements (32) coated with a selected catalyst (40) and arranged within a housing (20) in a generally cylindrical concentric ring or spiral wrap configuration. The plate-fin element (132) or elements (32) define an axial succession of fin rows (38) wherein the fins of each row are offset relative to the fins of each adjacent row.

Description: CATALYTI C OZONE CONVERTER BACKGROUND O F THE INVENTION This invention relates generally to improvements in catalytic converters, particularly of the type used in combination with an aircraft cabin environmental control system to reduce or eliminate ozone in conditioned air supplied to an aircraft cabin space- Environmental control systems for aircraft are generally known in the art for supplying pressurized and conditioned air to an aircraft cabin space. In such systems, a bleed air flow obtained from an engine compressor stage is often used as a source of fresh air for supply to the aircraft cabin space at a selected temperature, pressure, and relative humidity. In some cases, the engine bleed air is supplemented by a flow of fresh outside air. Environmental control systems of this type are provided to enhance the comfort of flight crew and passengers within the aircraft, especially in the course of relatively high altitude flight operations. Modern jet aircraft are typically designed for fuel-efficient operation - at relatively high altitudes on the order of 25,000 feet or more above sea level. At such altitudes, the ozone content in ambient air is relatively high. As a result, the air flow stream supplied to the aircraft environmental control system exhibits a substantial ozone content. Ozone is widely recognized as an air pollutant, and can cause lung and eye irritation, headaches, fatigue and/or breathing discomfort in humans. Catalytic converter devices have been used in aircraft applications to reduce or eliminate undesirable ozone in an air flow stream supplied to the aircraft cabin space by converting the ozone to oxygen. Such converters typically include a catalyst bed exposed to the air flow stream for purposes of decomposing ozone to oxygen. Such converters have unfortunately been relatively large in terms of size and weight in order to achieve the reguisite mass transfer between the gaseous air flow stream and the solid catalyst. The present invention relates to an improved catalytic ozone converter of compact size and lightweight construction, while providing ' highly efficient ozone decomposition with relatively minimal converter pressure drop. DISCLOSURE OF THE INVENTION In accordance with the invention, an improved catalytic converter is provided for reducing the ozone content of an air flow stream supplied to an aircraft cabin space for purposes of cabin pressurization and/or air-conditioning. The catalytic converter comprises -one or more plate-fin elements coated with a selected catalyst and retained within a housing preferably in a generally cylindrical configuration. The plate-fin element or elements define a large plurality of fins arranged in an axial succession of .offset or staggered fin rows to obtain relatively high mass transfer between the air flow stream and the catalyst for purposes of ozone decomposition, with reduced or minimal pressure drop. In the preferred form of the invention, a plurality of plate-fin elements of lightweight metal substrate material such as aluminum are formed as by stamping to define the axial succession of fin rows. Each fin row includes a regular pattern of corrugated fins, preferably having a generally rectangular profile, with the fins of each row being laterally offset or staggered relative to the fins of each adjacent row. The plate-fin elements are wrapped in a relatively tight cylindrical configuration, with a preferred form including a plurality of generally concentric plate- fin rings. The resultant cylindrical plate-fin core is mounted as by brazing within the converter housing with each fin row having a generally annular configuration. Alternately, a single plate-fin element in a spiral wrap configuration may be used to define the converter core for installation into the housing. In either case, the core provides the substrate for subsequent application of the catalyst coating to the plate-fin structure, such as by application of a catalyst- containing wash coat. The air flow stream obtained, for example, as a bleed air flow from an engine compressor stage, is passed through the converter housing for intimate mass transfer with the catalyst coating on the plate-fin elements. In this regard, the offset fin rows provide for rapid transport of ozone molecules from the air flow stream to the catalyst surface with minimal disturbance of the air flow. This results in a relatively high mass transfer rate of ozone to the catalyst and a relatively low pressure drop in air flow stream. At the catalyst surface, the ozone rapidly decomposess to oxygen. Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principals of the invention. BRIEF DES CRIPTION O F THE DRAWINGS The accompanying drawings illustrate the invention. In such drawings: FIGURE 1 is a schematic diagram illustrating use of a catalytic ozone converter of the present invention for reducing the ozone content in an air flow stream supplied to an aircraft cabin space; FIGURE 2 is an enlarged fragmented exploded perspective view illustrating one preferred form of the catalytic ozone converter embodying the novel features of the invention; FIGURE 3 is an enlarged fragmented perspective view illustrating a plate-fin element having a succession of offset fin rows for use in the catalytic converter of the present invention; FIGURE 4 is an enlarged fragmented sectional view illustrating a portion of the catalytic converter, depicting a plurality of plate- fin elements corresponding generally with FIG. 3 wrapped in concentric cylindrical array; and FIGURE 5 is an enlarged fragmented perspective view illustrating an alternative preferred form of the invention, with a single plate fin element wrapped in a spiral array. BEST MODE FOR CARRY I NG OUT THE I NVENT I ON As shown in ,the exemplary drawings, an improved catalytic ozone converter referred to generally by the reference numeral 10 is provided for use in combination with an environmental control syste 12 ( FIGURE 1) for pressurization and/or conditioning of air supplied to an aircraft cabin space 14. The catalytic converter 10 comprises a relatively lightweight and compact converter device for reducing the ozone content of an air flow stream supplied to the environmental control system 12 for cabin pressurization and/or conditioning purposes. As shown generally in FIGURE 1, the catalytic ozone converter 10 of the present invention is mounted in-line along an air flow conduit or duct 16 through which an air flow stream passes to the aircraft environmental control system 12. FIG. 1 illustrates the air flow stream in the form of bleed air obtained typically from a compressor stage of a gas turbine aircraft engine (not shown) , although use of compressed ram air and/or a combination of engine bleed and ram air are known in the art. The environmental control system typically comprises an air cycle machine such as a turbocompressor in combination with appropriate heat exchanger and water extraction devices and the like to provide a conditioned and suitably pressurized flow through a distribution conduit 18 to the aircraft cabin space 14. The catalytic ozone converter 10 is provided to reduce the ozone content in the air flow stream used for environmental cabin space control, wherein the natural ozone content present in the bleed and/or ambient ram air often exceeds acceptable limits especially in the course of relatively high altitude flight operations. As shown in FIG. 2 the catalytic converter 10 comprises a housing 20 of generally circular cross sectional shape having . inlet and outlet flanges 22 and 24 adapted for in-line connection by means of circumferential clamps 25 along the length of the air flow conduit 16 at a location upstream from the environmental control system 12. A preferred construction for the housing 20 includes a diametrically expanding inflow segment 26 for converting air flow stream velocity to increased pressure head. The expanding inflow segment 26 merges smoothly with a cylindrical segment 28 within which a converter core 30 is mounted, as will be described in more detail. The cylindrical segment 28 of the housing 20 merges in turn with a tapered outflow segment of rapidly reducing diametric size for reconverting pressure head to velocity. The converter core 30 comprises a plurality of plate-fin elements 32 mounted within the cylindrical segment 23 of the housing 20 to define a multitude of small flow paths. The plate-fin elements 32 are arranged in a tightly packed cylindrical configuration, as a plurality of generally concentric annular rings. In this regard, the center of the cylindrical space defined by the housing 20 may be occupied by a small diameter support tube 34 having a short plate-fin element strip 32' received therein, or the support tube may be capped. Each plate-fin element 32 is constructed from a relatively lightweight metal substrate material such as aluminum which can be shaped as by stamping to define raised fins 36. As shown in FIG. 3 , the fins 36 are arranged in an axial succession of adjacent rows 38, with the - fins 36 preferably having a corrugated configuration of generally rectangular profile. Importantly, the fins 36 of each row 38 are laterally staggered or offset relative to the fins 36 at the adjacent leading and trailing sides thereof. Each plate fin element -32 carries a coating 40 of a selected catalyst material of a type known in the art for ozone decomposition, such as a catalyst including platinum and a base metal. Such catalyst materials are referenced, for example, in U.S . Patents 4, 405, 507 ; 4,206, 083 ; and 4, 173 ,549. The plate fin elements 32 are arranged in the cylindrical configuration in generally concentric 5 rows, as previously described, for installation within the cylindrical segment 28 of the converter housing 20. In one preferred configuration, the cylindrical housing segment 28 has a diametric size on the order of eleven inches, and each plate-fin 10 element 32 is formed to define a fin height of about 0.25 inch, in combination with a fin row pattern of approximately ten rows 38 per inch axial length. With this construction, a converter core 30 defined by a snugly packed array of concentric plate-fin ! 5 elements 32 having an axial length of about three inches has been shown to provide highly efficient ozone decomposition in an aircraft environmental control system application. However, it will be understood that alternate configurations may be used, 0 such as alternate plate-fin element profiles of triangular, waved or slotted shape, mounted within a core housing which can be cylindrical, rectangular, or other suitable shape. As shown .in FIGS . 3 and 4, the cylindrically 5 packed plate-fin elements arranges the fin rows 38 in an annular shape, with the fins 36 of adjacent rows being offset relative to each other. This construction provides a large plurality of small flow paths extending axially through the converter core. 0 At each offset, the flow encounters the leading edge of the next row of fins, thereby achieving intimate mass transfer between the incoming air flow stream and the catalyst coating 40. This efficient decomposition and removal of ozone from the flow 5 stream is accomplished with relatively minimal pressure drop across the converter core. Thus, substantial air inflow rates can be maintained without exceeding ozone content or pressure drop limits. FIGURE 5 illustrates one alternative preferred form of the invention, wherein the converter core is constructed from a single plate-fin element 132 having the offset rows 38 of coated fins 36, as previously described. FIGURE 5 illustrates the plate-fin element 132 wrapped upon itself in a spiral configuration to form the generally cylindrical converter core retained within the cylindrical segment 28 of the tubular converter housing 20. The improved catalytic ozone converter 10 of the present invention thus provides a lightweight and compact device for reducing and/or removing ozone from an air flow stream for aircraft cabin pressurization and/or air-conditioning purposes. The converter 10 provides highly efficient ozone conversion in a device with minimal pressure drop and minimal weight. A variety of modifications and improvements to the catalytic ozone converter 10 of the present invention will be apparent to those skilled in the art. Accordingly, no limitation on the invention is intended by way of the foregoing description and accompanying drawings, except as set forth in the appended claims.

Claims: WHAT IS CLAIMED IS: 1. A catalytic ozone converter (10), comprising: a housing (20) adapted for axial flow through- passage cf an ozone-containing air flow stream; and a converrer core (30) mounted within said housing (20), said converter core (30) including at least one plate-fin element (32) defining a plurality of fins (36) arranged in an axial succession of rows (38) , with the fins of each row being offset with respect to the fins of each adjacent row; characterized in that said at least one plate-fin element (32) has an ozone decomposition catalyst (40) thereon. 2. The catalytic ozone converter (10) of claim 1 wherein said housing (20) has a generally circular cross sectional shape, and further wherein said converter core (30) has a generally cylindrical shape. 3. The catalytic ozone converter (10), of claim 2 wherein said ar least one plate-fin element (32) comprises a plurality of plate-fin elements arranged in a packed configuration of substantially concentric rings. 4. The catalytic ozone converter (10) of claim 2 wherein said at lease one plate-fin element (32) comprises a unitary p_-ate-fin element (132) wrapped upon itself in a spiral configuration. 5. A catalytic ozone converter (10) of claim 1 wherein said at least one plate fin element (32) is formed from a lightweight metal stamping, said catalyst (40) being applied to said stamping. 6. For use in combination with an aircraft environmental control system (12) for receiving an ozone- containing air flow stream used for environmental control of an aircraft cabin space (14) a catalytic ozone converter (10) , comprising: a housing (20) having open inlet and outlet ends (22, 24) to permit axial flow-through passage of the ozone- containing air flow stream; and a converter core (30) mounted within said housing (20) , said converter core including at least one plate-fit element (32) defining a plurality of fins arranged in an axial succession of rows (38) with the fins of each row being offset with respect to the fins of each adjacent row; characterized in that said at lest one plate-fin element has an ozone decomposition catalyst (40) thereon. 7. The catalytic ozone converter (10) of claim 6 wherein said housing (20) has a generally circular cross sectional shape, and further wherein said converter core 3C: has a generally cylindrical shape. 8. The catalytic ozone converter (10) of claim 7 wherein said at least one plate-fin element (32) comprises a plurality of plate-fin elements arranged in a packed configuration of substantially concentric rights. 9. The catalytic ozone converter (10) of claim 7 wherein said at lease one plate-fin element (32) comprises a unitary plate-fin element (132) wrapped upon itself in a spiral configuration. 10. The catalytic ozone converter (10) of claim 6 wherein said at least one plate fin element (32) is formed from a lightweight metal stamping, said catalyst being applied to said stamping as a coating (40) .

Inventors: DEVIN SEAN MICHAEL, RUDER JOSEPH M, DEVIN, SEAN, MICHAEL, RUDER, JOSEPH, M.
Applicants: ALLIED SIGNAL INC, ALLIED-SIGNAL INC.
Application year: 1993
Main classification: B01D53
IPC codes: B01D53, B01J35