WO2015134804A1

WO2015134804A1 - Emission reduction device for a wood heater

Info

Publication number: WO2015134804A1
Application number: PCT/US2015/019055
Authority: WO
Inventors: Lance Carl Grace; Tyler Mainord Grace
Original assignee: Lance Carl Grace; Tyler Mainord Grace
Priority date: 2014-03-05
Filing date: 2015-03-05
Publication date: 2015-09-11
Also published as: CA2941234A1; US20150253006A1

Abstract

An inventive apparatus for reducing emissions from a wood heater comprises (i) two or more volumes of a porous, catalyst-coated medium and (ii) one or more holders for the catalyst-coated medium. The one or more holders are structurally arranged to hold the volumes of the catalyst-coated medium in a specified spatial arrangement within an exhaust flue of the wood heater. The catalytic media are sized and shaped so that, in that specified spatial arrangement, the volumes obstruct substantially all straight-line paths from a combustion chamber of the wood heater through the exhaust flue past the volumes of the catalyst-coated medium. In the specified spatial arrangement, the volumes also leave unobstructed at least one tortuous exhaust gas flow path from the combustion chamber through the exhaust flue around and past the volumes of the catalyst-coated medium.

Description

EMISSION REDUCTION DEVICE FOR A WOOD HEATER

PRIORITY CLAIM

[0001] This application claims priority based on U.S. provisional App. No.

5 61 /948,095 filed 05 MARCH 2014 in the names of Lance Carl Grace and Tyler Mainord Grace entitled "Wood Stove Retrofit Emission Control Device", said provisional application being hereby incorporated by reference as if fully set forth herein.

i o FIELD OF THE INVENTION

[0002] The field of the present invention relates to wood heaters. In particular, apparatus and methods are described herein for reducing emissions from a wood heater.

SUMMARY

[0003] An inventive apparatus for reducing emissions from a wood heater comprises (i) two or more volumes (i.e., pieces) of a porous, catalyst-coated medium and (ii) one or more holders for the catalyst-coated medium. The one or more holders are structurally arranged to hold the volumes of the catalyst-coated medium in a specified spatial arrangement within an exhaust flue of the wood heater. The catalytic media are sized and shaped so that, in that specified spatial arrangement, the volumes obstruct substantially all straight-line paths from a combustion chamber of the wood heater through the exhaust flue past the volumes of the catalyst-coated medium. In the specified spatial arrangement, the volumes also leave unobstructed at least one tortuous exhaust gas flow path from the combustion chamber through the exhaust flue around and past the volumes of the catalyst-coated medium.

[0004] An inventive method for reducing emissions from a wood heater using the inventive apparatus comprises directing exhaust gas from the combustion chamber of the wood heater through the exhaust flue of the wood heater past the two or more volumes of the porous, catalyst-coated medium.

[0005] An inventive method for reducing emissions from a wood heater comprises installing in the exhaust flue of the wood heater the two or more volumes of the porous, catalyst-coated medium and the one or more holders of the inventive apparatus. The inventive apparatus can be retrofitted into the exhaust flue of a preexisting and previously installed wood heater.

[0006] Objects and advantages pertaining to reducing emissions from wood heaters may become apparent upon referring to the example embodiments illustrated in the drawings and disclosed in the following written description or appended claims.

[0007] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figs. 1 A and 1 B illustrate schematically a wood heater and an inventive emission reduction apparatus according to the present disclosure.

[0009] Figs. 2 and 3 are schematic cross sectional views of examples of an

inventive emission reduction apparatus on a wood heater.

[0010] Figs. 4 and 5 illustrate schematically straight-line and tortuous flow paths, respectively, through an example of an inventive emission reduction apparatus.

[0011] Figs. 6A and 6B illustrate schematically disk- and ring-shaped volumes, respectively, of a porous, catalyst-coated medium.

[0012] The embodiments depicted are shown only schematically: all features may not be shown in full detail or in proper proportion, certain features or structures may be exaggerated relative to others for clarity, and the drawings should not be regarded as being to scale. The embodiments shown are only examples: they should not be construed as limiting the scope of the present disclosure or appended claims.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] For purposes of the present disclosure and appended claims, the term "wood heater" means, as defined in Title 40 of the Code of Federal Regulations (CFR) at Chapter I, Subchapter C, Part 60, Subpart AAA, §60.531 : "an enclosed, wood burning appliance capable of and intended for space heating or domestic water heating that meets all of the following criteria: (1 ) An air-to-fuel ratio in the combustion chamber averaging less than 35-to-1 as determined by the test procedure prescribed in §60.534 performed at an accredited laboratory; (2) A usable firebox volume of less than 0.57 cubic meters (20 cubic feet); (3) A minimum burn rate of less than 5 kg/hr (1 1 Ib/hr) as determined by the test procedure prescribed in §60.534 performed at an accredited laboratory; and (4) A maximum weight of 800 kg (1 ,760 lb). In determining the weight of an appliance for these purposes, fixtures and devices that are normally sold separately, such as flue pipe, chimney, and masonry components that are not an integral part of the appliance or heat distribution ducting, shall not be included." The term "wood stove," if appearing anywhere herein, shall be deemed equivalent to "wood heater."

[0014] An inventive emission reduction device 100 according to the present disclosure (Figs. 1 A, 1 B, and 2-5) can be installed in the exhaust flue 40 of a preexisting, previously installed wood heater 10 or of a new wood heater 10.

Installation and use with a previously installed wood heater 10, i.e., via a retrofit, can be particularly effective for economical reduction of wood heater emissions, since the entire heater need not be replaced. The cost reduction of such a retrofit versus a new wood heater makes adoption of the inventive reduced-emission wood heater technology more likely. The inventive emission reduction device 100 is installed in or as part of an exhaust flue of the wood heater 10, so that exhaust gases from the combustion chamber 20 of the wood heater are directed through or past a set of two or more pieces of a porous, catalyst-coated medium 102.

Although typically placed directly on the exhaust outlet 30 from the combustion chamber 20, the emission reduction device 100 typically is not considered as a part of the wood heater 10, but rather it should considered as a portion of the exhaust system 40 of the wood heater 10.

[0015] During periods of operation when exhaust gas passing through the exhaust flue 40 exceeds a light-off temperature for the given catalytic material and enough oxygen is available in the exhaust stream, the catalyst-coated medium 102 converts the organic particulates and species gas pollution substantially completely into water vapor and carbon dioxide. At exhaust gas temperatures below the catalyst light-off temperature, the catalyst-coated medium 102 acts as a particulate filter to capture and retain organic particulates {e.g., soot particles) or products of incomplete combustion. When the exhaust gas temperature later exceeds the catalyst light-off temperature and enough oxygen is available in the exhaust stream, the retained organic particulates or products of incomplete combustion are converted into water vapor and carbon dioxide. As with any catalytic device that enables substantially complete combustion, decomposition of organic particulates and products of incomplete combustion into water and carbon dioxide is

exothermic, so that additional thermal energy is released by the wood heater, potentially increasing its efficiency.

[0016] Spatial arrangement of the porous, catalyst-coated medium 102 is such that, even if the medium becomes temporarily totally blocked or clogged with retained organic particulates or products of incomplete combustion, exhaust gas from the wood heater can continue to flow through the exhaust flue 40 past the medium. The inventive emission reduction device 100, and its constituent catalyst- coated medium 200, can remain in place throughout all phases of the fuel burn in the wood heater 10.

[0017] That arrangement is desirable, because, unlike previous catalytic devices for wood heaters, no action is required on the part of the user. During an earlier, start-up phase of a fire or a later, cool-down phase {e.g., just prior to the fire going out), lower temperatures and lower exhaust flow can lead to clogging of the catalytic medium. Conventional devices therefore are typically arranged to be removed from the exhaust flow path during start-up (by moving or bypassing the catalytic medium), and then replaced in the exhaust flow path by the user after the wood heater reaches a sufficiently high operating temperature. There is no suitable mechanism to ensure that the emission reduction device is used properly, or even used at all. In contrast, the inventive emission reduction device 100 is always in place and yet enables the wood heater to function properly, whether at low or high operating temperatures. In other words, it is a passive device, and in its simplest configurations requires neither electrical power nor a mechanical or electrical control system.

[0018] An inventive apparatus 100 for reducing emissions from a wood heater 10 comprises (i) two or more volumes (i.e., pieces) of a porous, catalyst-coated medium (collectively 102; individual volumes 102a, 102b, etc.), and (ii) one or more holders 104 for the volumes of the catalyst-coated medium 102. The volumes of the catalyst-coated medium 102 are also referred to herein as the catalytic media 102. The one or more holders 104 are structurally arranged to hold the volumes of the catalyst-coated medium 102 in a specified spatial arrangement within an exhaust flue 40 of the wood heater 10. The catalytic media 102 are sized and shaped so that, in that specified spatial arrangement, the volumes obstruct substantially all straight-line paths 98 from a combustion chamber 20 of the wood heater through the exhaust flue 40 past the volumes of the catalyst-coated medium 102. In the specified spatial arrangement, the catalytic media 102 also leave unobstructed at least one tortuous exhaust gas flow path 99 from the combustion chamber 20 through the exhaust flue 40 around and past the volumes of the catalyst-coated medium 102.

[0019] In some example embodiments, the porous, catalyst-coated medium 102 comprises a regular or irregular, three-dimensional latticework of ceramic material forming an open-celled structure (depicted schematically in Figs 6A and 6B; open- celled structure omitted from the other Figures so as not to clutter the drawings). The open-cell structure provides a relatively high ratio of surface area to volume, and that surface area is coated with a catalytic material effective to catalyze conversion of organic particulates or products of incomplete combustion to water and carbon dioxide. The catalytic material in some examples includes one or more metals (e.g., a transition metal such as nickel, palladium, or platinum) or one or more metal oxides (e.g., alumina or a zeolite). Specific examples of suitable catalytic media are disclosed in, inter alia:

- U.S. Pub. No. 2001 /0029004 entitled "Apparatus for improving air quality" published 10/1 1 /2001 in the names of Sparling et al;

- U. S. Pat. No. 6,237,587 entitled "Woodburning fireplace exhaust catalytic cleaner" issued 05/29/2001 in the names of Sparling et al; - U.S. Pat. No. 8,622,054 entitled "Methods and systems for reducing combustion emissions" issued 01 /07/2014 in the names of Grace et al; and

- PCT Pub. No. WO 2012/027512 entitled "Enhanced emission control for outdoor wood-fired boilers" published 03/01 /2012 in the names of Grace et al.

Any suitable porous, catalyst-coated medium 102 can be employed, including any of those disclosed in the references listed above, each of which is hereby incorporated by reference as if fully set forth herein. Among significant

characteristics of such media relevant to the inventive emission reduction device are: (i) a porous structure that presents little or no restriction of fluid flow; (ii) a three dimensional latticework that results in turbulent flow of fluid through the medium; (iii) large ratio of surface area to volume, on both microscopic and macroscopic levels; and (iv) resistance to flame-induced damage. In some examples the catalyst-coated medium includes a catalytic material with a light-off temperature greater than about 350° F; in some of those examples the catalyst-coated medium includes a catalytic material with a light-off temperature greater than about 500° F.

[0020] The catalytic media 102 are sized and shaped to fit within the exhaust flue (or a housing) but do not fill the entire cross-sectional area of the exhaust flue 40 (or housing 1 10). The unfilled portions of the flue cross section allow an

unobstructed exhaust flow path 99 even if the catalytic media 102 are blocked or clogged. The catalytic media 102 are arranged so that the respective unfilled portions of the flue cross section do not align vertically from one volume to the next, so as to obstruct substantially all straight-line paths 98 from the combustion chamber 20 through the exhaust flue 40 past the catalytic media 102. The sizes, shapes, and specified arrangement of the catalytic media 102 achieve a number of goals. By obstructing substantially all straight-line paths 98 from the combustion chamber 20 through the exhaust flue 40 past the catalytic media 102, the exhaust gas will tend to flow through those media under high-temperature operating conditions, i.e., above the light-off temperature, when the porous, open-celled structure of the catalytic media 102 is not clogged by retained particulates or combustion products and therefore allows nearly free flow of the exhaust gas therethrough (Fig. 4). Flow of the exhaust gas through the volumes of the porous, open-celled structure of the catalyst-coated medium 102 enhances the effect of the catalytic material to complete the combustion of material in the exhaust gas. By providing an alternative, tortuous flow path 99 around and past the volumes of the catalytic medium 1 02 (Fig. 5), exhaust gas can continue to flow out of the combustion chamber and through the flue even if the catalytic medium becomes clogged by retained particulates or combustion products, as may occur under low- temperature conditions (i.e., below the light-off temperature) that are common during start-up and cool-down portions of a burn cycle. Those retained materials can be burned off during a subsequent period of high-temperature operation (during the same burn cycle or a subsequent burn cycle). The device is therefore self-cleaning

[0021 ] The tortuous exhaust flow path 99 can therefore provide several advantages. First, during low-flow and low-temperature phases of the fire, when clogging or blockage of the catalyst-coated medium 1 02 is possible, such as during the initial start-up or just before the fire goes out, a sufficient path remains through which exhaust gas can flow up through the emission reduction device 1 00 and the exhaust flue 40 (e.g., a stove pipe or chimney). Second, during phases of the fire with medium flows and medium temperature levels, the tortuous path 99 can enable the catalyst to reach more quickly the light-off temperature or to remain above the light-off temperature and maintain its catalytic effect. Third, during high- flow and high-temperature phases of the fire, the exhaust gas flows directly through all volumes of the catalyst-coated medium 1 02 with little pressure restriction to the flow.

[0022] In one example embodiment, the two or more volumes of the catalyst- coated medium comprise upper and lower disk-shaped volumes 1 02a and 1 02c and a ring-shaped volume 1 02b (as in Figs. 2-5, 6A, and 6B). In this example the specified arrangement of the catalytic media 1 02 comprises (i) the lower disk- shaped volume 1 02c being positioned below and separated by a vertical gap from the ring-shaped volume 1 02b, (ii) the upper disk-shaped volume 1 02a being positioned above and separated by a vertical gap from the ring-shaped volume 1 02b; (iii) the upper and lower disk-shaped volumes 1 02a/1 02c being sized so as to form an annular portion of the tortuous exhaust gas flow path 99 within the exhaust flue 40 (or housing 1 1 0) ; and (iv) the ring-shaped volume 1 02b being sized so as to confine the tortuous exhaust gas flow path 99 to an axial passage through the ring-shaped volume 1 02b. A high-temperature gasket, comprising any suitable material, can be employed to form at least a partial seal between the periphery of the ring-shaped volume 1 02b and the inner surface of the exhaust flue 40 or housing 1 1 0, and can also serve as one of the holders 1 04. The tortuous exhaust gas flow path 99 (Fig. 5) includes (i) upward flow through a lower annular passage around the periphery of the lower disk-shaped volume 1 02c, (ii) inward flow between the lower disk-shaped volume 1 02c and the ring-shaped volume 1 02b,

(iii) upward flow through the axial passage of the ring-shaped volume 1 02b,

(iv) outward flow between the ring-shaped volume 1 02b and the upper disk-shaped volume 1 02a, and (v) upward flow through an upper annular passage around the periphery of the upper disk-shaped volume 1 02a. The cross-sectional areas of the annular and axial passages can be made roughly similar to each other (e.g., within a factor of two or three). Similarly, the vertical gap between the ring-shaped volume 1 02b and the disk-shaped volumes 1 02a/1 02c can be chosen so that inward and outward flow areas at the edges of the disk-shaped volumes 1 02a/1 02c are roughly similar to the areas of the annular and axial passages {e.g., within a factor of two or three).

[0023] In one specific example (Fig. 2) : the inner diameter of the (typically cylindrical) exhaust flue 40 or housing 1 1 0 is about 6 inches (a standard size for flue pipe) ; the diameters of the upper and lower disk-shaped volumes 1 02a/1 02c are both about 5 inches; the outer diameter of the ring-shaped volume 1 02b is about 6 inches and its inner diameter is about 3 inches; all three volumes

1 02a/1 02b/1 02c are about 1 inch thick; and the vertical gaps between the disk- shaped volumes 1 02a/1 02c and the ring-shaped volume 1 02b between them are both about 0.5 inches. In another specific example (Figs. 3-5) : the inner diameter of the (typically cylindrical) housing 1 1 0 is about 8 inches (expanded relative to a standard flue pipe, a standard upper exhaust opening of the wood heater, or the inner diameter of a secondary air inlet chamber 1 05a, if present) ; the diameters of the upper and lower disk-shaped volumes 1 02a/1 02c are both about 5¾ inches; the outer diameter of the ring-shaped volume 1 02b is about 8 inches and its inner diameter is about 5 inches; all three volumes 1 02a/102b/1 02c are about 1 inch thick; and the vertical gaps between the disk-shaped volumes 1 02a/1 02c and the ring-shaped volume 1 02b between them are both about 1 inch. If needed or desired, additional disk- and ring-shaped volumes of the catalyst-coated medium can be employed in an alternating sequence to provide additional catalytic capacity.

[0024] Myriad other numbers, sizes, shapes, and spatial arrangement can be employed for the catalytic media 102. Some examples can include a set of circular disks with an offset portion removed {e.g., an angular sector, a circular segment, a smaller offset circle), with each disk rotated so its missing portion does not align with the missing portions of adjacent disks. Arranging such a set of disks in a vertical stack with gaps between them can yield a spiral or serpentine exhaust gas flow path 99.

[0025] The one or more holders 104 can be formed in any suitable way and structurally arranged to hold the volumes of the catalyst-coated medium 102 in the specified arrangement within the exhaust flue 40 or housing 1 10. The catalyst coated medium holder(s) 104 can be fabricated from a variety of substantially rigid, non-combustible materials including but not limited to: one or more metal or metal alloys such stainless steel, steel, titanium, and so on; one or more ceramic materials; or one or more composite materials such as a continuous fiber ceramic composite (CFCC). In some examples, two identical or mirror-image members make up the holder and can be attached to each other either by screws, nuts and bolts, rivets, welds, or other suitable fasteners. In other examples, five or more smaller members pieces are used to hold the catalytic media in the specified arrangement. In the disks-and-ring example described above, the gasket that can be employed to seal around the periphery of the ring-shaped volume 102b can also act as a holder 104 by securing the ring-shaped volume 102b to the inner surface of the housing 1 10 or exhaust flue 40; additional holders 104 connect the disk- shaped volumes 102a/102c to the ring-shaped volume 102b. In still other examples, the two or more volumes of the catalyst-coat medium themselves can also act as the one or more holders. In such as example, the catalytic media 102 can be fabricated with structural features (such as posts, tabs, slots, holes, and so forth) that enable them to be fitted together to form the specified arrangement. In many examples, the one or more holders 104 typically are attached to or otherwise engage an inner surface of the exhaust flue 40 or a dedicated housing 1 10 to hold the catalytic media in place, and can in some instances be formed as part of the exhaust flue 40 or housing 1 10 {e.g., as an inward-extending flange or rim within the flue or housing on which the catalytic media might rest).

[0026] In instances when the inventive emission reduction device 100 is installed as part of a new wood heater installation, it can be desirable to mount the holder(s) 104 and the catalytic media 102 directly within a lower end of the exhaust flue 40, just outside the combustion chamber 20 of the wood heater. In a retrofit

installation, when the inventive emission reduction device 100 is installed in the exhaust flue 40 of a pre-existing, previously installed wood heater 10, it can be advantageous to arrange the catalytic media 102 and holder(s) 104 in a separate, dedicated housing 1 10. Such a housing 1 10 often would take the form of a short length of flue pipe similar to that of the exhaust flue 40. Any suitable materials can be employed to form the housing 1 10, including those disclosed above for forming the one or more holders 104. A housing 1 10 can also be employed in an inventive emission reduction device that is part of a new wood heater installation. [0027] In some examples, the housing 1 10 can be sized to fit within the exhaust flue 40; in such an arrangement the housing 1 10 should substantially block flow of exhaust gas around the housing 100 within the flue 40, so that substantially all of the exhaust gas flows through the housing 1 10 and the emission control device 100. In other examples, the housing 1 10 can be arranged to be incorporated as a segment of the exhaust flue 40; in such an arrangement the housing 1 10 is adapted at its lower end to connect to the exhaust outlet 30 of the combustion chamber 20 and at its upper end to form a connection with the rest of the exhaust flue 40. In some instance an adapter ring 106 or 107 of some sort might be needed to mate the upper or lower end of the housing 1 10 to the exhaust outlet 30 of the combustion chamber 20 or to the exhaust flue 40, respectively.

[0028] In many use environments, heat generated by the catalyzed combustion reactions occurring within the volumes of the catalyst-coated medium 102 is more than sufficient to maintain the catalytic material above the light-off temperature. In that instance, excess heat thus produced can be advantageously radiated into the ambient surroundings of the wood heater 10 and exhaust flue 40 as additional heat output of the wood heater 10, thereby increasing the overall heating efficiency of the wood heater. In other use environments, an insulated housing 1 10 {e.g., a segment of insulated, double-walled flue pipe) can be employed to retain heat within the housing 1 10 to maintain the catalytic media 102 above the light-off temperature longer than might otherwise occur without such insulation. In still other use environments, one or more heating elements can be employed to heat the catalytic media 102 to remain above the light-off temperature, e.g., using a suitable temperature sensor and control mechanism.

[0029] In a wood heater, once the fuel is loaded and lit and the fuel door 12 is closed, combustion air enters through a set of combustion air inlets 14 suitably arranged about the combustion chamber 20 to allow ambient air to enter. Those combustion air inlets 14 are often arranged so as to enable adjustment of the amount of air that reaches the fire, to control the fire's intensity. One source of pollution from wood heaters is that, upon leaving the combustion chamber 20 and entering the exhaust flue 40, sufficient oxygen may not remain to allow complete combustion in the exhaust flue of those organic particulates or products of incomplete combustion that remain entrained in the exhaust gas. Without sufficient oxygen, even the presence of a catalytic medium will not allow complete

combustion of combustible material in the exhaust gas. In the inventive emission reduction device 100, a secondary air inlet tube 105 can be provided to enable additional ambient air (including oxygen) to be drawn into the exhaust gas and pass with the exhaust gas past the volumes of the catalyst-coated medium 102. Such an air inlet tube 105 has an open inner end arranged to be held within the exhaust flue 40 below the volumes of the catalyst-coated medium 102, i.e., between the combustion chamber 20 and the catalytic media 102. In Fig. 2 the open, inner end is shown as a simple tube ending within the emission reduction device 100 {e.g., in the lower end of the housing 1 10, if present). In Figs. 3-5 the open inner end of the air inlet tube 105 terminates in an annular chamber or manifold 105a arranged around the lower end of the emission reduction device 100 (or housing 1 10, if present), which has secondary air inlet orifices 105b connecting the chamber 105a to the interior of the emission reduction device 100.

[0030] An open outer end of the air inlet tube 105 is positioned outside the combustion chamber 20, at a level below a level of the combustion air inlets 14 into the combustion chamber 20, so as to draw ambient air (from around the wood heater 10 or from a different indoor or outdoor space) through the air inlet tube 105 into the exhaust flue 40 during operation of the wood heater 10. In some examples, the air inlet tube 105 can be routed along an inside or outside surface of the combustion chamber 20 so as to heat ambient air drawn into the air inlet tube 105 during operation. In some examples, a fan or blower can be employed to increase the flow of ambient air through the tube 105 into the exhaust flue 40; such a fan or blower can be coupled to a controller and one or more sensors in or on the wood heater 10, the exhaust flue 40, or the inlet tube 105 {e.g., temperature sensor, carbon monoxide sensor, airflow sensor , or other sensor). In some examples, the air inlet tube 105 can be shaped and arranged at its open inner end so as to employ the Venturi effect or other aerodynamic effect to facilitate air flow through the inlet tube. The open inner end of the air inlet tube 105 (and any manifold 105a that might be present) can be held in place by one of the one or more holders 104, by mounting in or on the housing 1 10 (if present), by mounting in or on the exhaust flue 40, or by mounting in the combustion chamber 20 at the lower end of the exhaust flue 40 (i.e., at the exhaust opening 30).

[0031] An inventive method for reducing emissions from a wood heater comprises directing exhaust gas from the combustion chamber 20 of the wood heater 10 through the inventive emission reduction device 100 disclosed above, i.e., through the exhaust flue 40 of the wood heater past the two or more volumes of the porous, catalyst-coated medium 102 that are arranged as disclosed above. As noted above, at catalyst temperatures below a light-off temperature, the porous, catalyst- coated medium 102 can act as a particle filter to trap and retain organic

particulates and products of incomplete combustion entrained in the exhaust gas. Even if the catalytic media 102 are completely clogged under those conditions, the tortuous exhaust gas flow path 99 enables the exhaust gas to flow through the exhaust flue 40 around and past the volumes of the catalyst-coated medium 102. At catalyst temperatures above the light-off temperature, the exhaust gas flows through the volumes of the catalyst-coated medium 102 with only negligible resistance to flow. Particulates or combustion products retained by the catalytic media during a cooler phase of a fire (e.g., at start-up, or shortly before going out) can be removed by combustion during another, hotter phase of that fire or of a subsequent fire.

[0032] Another inventive method for reducing emissions from a wood heater 10 comprises installing in the exhaust flue 40 of the wood heater 10 the inventive emission reduction device 100 disclosed above, i.e., the two or more volumes of the porous, catalyst-coated medium 102 and the one or more holders 104, arranged as disclosed above. The inventive emission reduction device 100 can be installed as part of a new wood heater 10. Perhaps even more advantageously, the inventive emission reduction device 100 can be retrofitted into the exhaust flue 40 of a pre-existing and previously installed wood heater 10.

[0033] In addition to the preceding, the following examples fall within the scope of the present disclosure or appended claims:

[0034] Example 1 . An apparatus for reducing emissions from a wood heater, the apparatus comprising two or more volumes of a porous, catalyst-coated medium and one or more holders, wherein: (a) the one or more holders are structurally arranged to hold the volumes of the catalyst-coated medium in a specified spatial arrangement within an exhaust flue of the wood heater; and (b) the volumes of the catalyst-coated medium are sized and shaped so as to (i) obstruct, when held by the one or more holders in the specified spatial arrangement, substantially all straight-line paths from a combustion chamber of the wood heater through the exhaust flue past the volumes of the catalyst-coated medium, and (ii) leave unobstructed, when held by the one or more holders in the specified spatial arrangement, at least one tortuous exhaust gas flow path from the combustion chamber through the exhaust flue around and past the volumes of the catalyst- coated medium.

[0035] Example 2. The apparatus of Example 1 further comprising an air inlet tube with an open inner end arranged to be held by one or more of the one or more holders in communication with the exhaust flue between the combustion chamber and the volumes of the catalyst-coated medium, wherein an open outer end of the air inlet tube is positioned outside the combustion chamber, at a level below a level of one or more combustion air inlets into the combustion chamber, so as to draw ambient air through the air inlet tube into the exhaust flue during operation of the wood heater. [0036] Example 3. The apparatus of Example 2 wherein the air inlet tube is routed along an inside or outside surface of the combustion chamber so as to heat the ambient air drawn into the air inlet tube during operation of the wood heater. [0037] Example 4. The apparatus of any one of Examples 1 through 3 further comprising a housing containing the one or more holders and the volumes of the catalyst-coated medium, wherein the housing is sized and shaped so as to fit within the exhaust flue.

[0038] Example 5. The apparatus of any one of Examples 1 through 3 further comprising a housing containing the one or more holders and the volumes of the catalyst-coated medium, wherein the housing is structurally arranged so as to be incorporated as a segment of the exhaust flue.

[0039] Example 6. The apparatus of Example 5 further comprising an adapter member structurally arranged so as to mate a lower end of the housing to an upper exhaust opening of the wood heater or to mate an upper end of the housing to the exhaust flue.

[0040] Example 7. The apparatus of any one of Examples 4 through 6 further comprising an air inlet tube held by the housing so that an open inner end of the air inlet tube is in communication with the exhaust flue between the combustion chamber and the volumes of the catalyst-coated medium, wherein an open outer end of the air inlet tube is positioned outside the combustion chamber, at a level below a level of one or more combustion air inlets into the combustion chamber, so as to draw ambient air through the air inlet tube into the exhaust flue during operation of the wood heater.

[0041] Example 8. The apparatus of any one of Examples 1 through 3 further comprising a segment of the exhaust flue, wherein the one or more holders and the volumes of the catalyst-coated material are mounted within the segment of the exhaust flue.

[0042] Example 9. The apparatus of any one of Examples 1 through 8 wherein the one or more holders are formed of the porous, catalyst-coated medium.

[0043] Example 10. The apparatus of any one of Examples 1 through 9 wherein the porous, catalyst-coated medium comprises a regular or irregular, three- dimensional latticework of ceramic material forming an open-celled structure coated with a catalytic material effective to catalyze conversion of organic particulates or products of incomplete combustion to water and carbon dioxide. [0044] Example 1 1 . The apparatus of any one of Examples 1 through 10 wherein the porous, catalyst-coated medium is coated with a catalytic material that includes one or more metals or one or more metal oxides.

[0045] Example 12. The apparatus of any one of Examples 1 through 1 1 wherein the porous, catalyst-coated medium includes a catalytic material with a light-off temperature greater than about 350° F.

[0046] Example 13. The apparatus of any one of Examples 1 through 12 wherein the porous, catalyst-coated medium includes a catalytic material with a light-off temperature greater than about 500° F.

[0047] Example 14. The apparatus of any one of Examples 1 through 13 wherein the two or more volumes of the catalyst-coated medium comprise upper and lower disk-shaped volumes and a ring-shaped volume, and the specified arrangement comprises (i) the lower disk-shaped volume being positioned below and separated by a vertical gap from the ring-shaped volume, (ii) the upper disk-shaped volume being positioned above and separated by a vertical gap from the ring-shaped volume; (iii) the upper and lower disk-shaped volumes being sized so as to form an annular portion of the tortuous exhaust gas flow path within the exhaust flue; and (iv) the ring-shaped volume being sized so as to confine the tortuous exhaust gas flow path to an axial passage through the ring-shaped volume.

[0048] Example 15. The apparatus of any one of Examples 1 through 14 further comprising an insulator disposed around a segment of the exhaust flue containing the volumes of the catalyst-coated material.

[0049] Example 16. The apparatus of any one of Examples 1 through 14 wherein a segment of the exhaust flue containing the volumes of the catalyst-coated material is structurally arranged so as to radiate heat into an ambient volume surrounding the wood heater.

[0050] Example 17. A method for reducing emissions from a wood heater using the apparatus of any one of Examples 1 through 16, the method comprising directing exhaust gas from the combustion chamber of the wood heater through the exhaust flue of the wood heater past the two or more volumes of the porous, catalyst-coated medium. [0051] Example 18. The method of Example 17 wherein: (i) at catalyst

temperatures below a light-off temperature, the porous, catalyst-coated medium acts as a particle filter to trap and retain organic particulates and products of incomplete combustion entrained in the exhaust gas, and the tortuous exhaust gas flow path enables the exhaust gas to flow through the exhaust flue around and past the volumes of the catalyst-coated medium even if the catalyst-coated medium is clogged with the retained organic particulates or products of incomplete

combustion; and (ii) at catalyst temperatures above the light-off temperature, the exhaust gas flows through the volumes of the catalyst-coated medium.

[0052] Example 19. A method for reducing emissions from a wood heater, the method comprising installing in the exhaust flue of the wood heater the two or more volumes of the porous, catalyst-coated medium and the one or more holders of the apparatus of any one of Examples 1 through 16.

[0053] Example 20. The method of Example 19 wherein the wood heater is a pre- existing and previously installed wood heater and the volumes of the catalyst- coated medium and the holder are retrofitted into the exhaust flue of the preexisting and previously installed wood heater.

[0054] It is intended that equivalents of the disclosed example embodiments and methods shall fall within the scope of the present disclosure or appended claims. It is intended that the disclosed example embodiments and methods, and

equivalents thereof, may be modified while remaining within the scope of the present disclosure or appended claims.

[0055] In the foregoing Detailed Description, various features may be grouped together in several example embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that any claimed embodiment requires more features than are expressly recited in the corresponding claim. Rather, as the appended claims reflect, inventive subject matter may lie in less than all features of a single disclosed example embodiment. Thus, the appended claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate disclosed embodiment. However, the present disclosure shall also be construed as implicitly disclosing any embodiment having any suitable set of one or more disclosed or claimed features (i.e., a set of features that are neither incompatible nor mutually exclusive) that appear in the present disclosure or the appended claims, including those sets that may not be explicitly disclosed herein. In addition, for purposes of disclosure, each of the appended dependent claims shall be construed as if written in multiple dependent form and dependent upon all preceding claims with which it is not inconsistent. It should be further noted that the scope of the appended claims does not necessarily encompass the whole of the subject matter disclosed herein.

[0056] For purposes of the present disclosure and appended claims, the conjunction "or" is to be construed inclusively (e.g., "a dog or a cat" would be interpreted as "a dog, or a cat, or both"; e.g., "a dog, a cat, or a mouse" would be interpreted as "a dog, or a cat, or a mouse, or any two, or all three"), unless: (i) it is explicitly stated otherwise, e.g., by use of "either... or," "only one of," or similar language; or (ii) two or more of the listed alternatives are mutually exclusive within the particular context, in which case "or" would encompass only those

combinations involving non-mutually-exclusive alternatives. For purposes of the present disclosure and appended claims, the words "comprising," "including," "having," and variants thereof, wherever they appear, shall be construed as open ended terminology, with the same meaning as if the phrase "at least" were appended after each instance thereof, unless explicitly stated otherwise.

[0057] In the appended claims, if the provisions of 35 USC § 1 12(f) are desired to be invoked in an apparatus claim, then the word "means" will appear in that apparatus claim. If those provisions are desired to be invoked in a method claim, the words "a step for" will appear in that method claim. Conversely, if the words "means" or "a step for" do not appear in a claim, then the provisions of 35 USC § 1 12(f) are not intended to be invoked for that claim.

[0058] If any one or more disclosures are incorporated herein by reference and such incorporated disclosures conflict in part or whole with, or differ in scope from, the present disclosure, then to the extent of conflict, broader disclosure, or broader definition of terms, the present disclosure controls. If such incorporated

disclosures conflict in part or whole with one another, then to the extent of conflict, the later-dated disclosure controls. [0059] The Abstract is provided as required as an aid to those searching for specific subject matter within the patent literature. However, the Abstract is not intended to imply that any elements, features, or limitations recited therein are necessarily encompassed by any particular claim. The scope of subject matter encompassed by each claim shall be determined by the recitation of only that claim.

Claims

What is claimed is:

An apparatus for reducing emissions from a wood heater, the apparatus comprising two or more volumes of a porous, catalyst-coated medium and one or more holders, wherein:

(a) the one or more holders are structurally arranged to hold the volumes of the catalyst-coated medium in a specified spatial arrangement within an exhaust flue of the wood heater; and

(b) the volumes of the catalyst-coated medium are sized and shaped so as to (i) obstruct, when held by the one or more holders in the specified spatial arrangement, substantially all straight-line paths from a combustion chamber of the wood heater through the exhaust flue past the volumes of the catalyst-coated medium, and (ii) leave unobstructed, when held by the one or more holders in the specified spatial arrangement, at least one tortuous exhaust gas flow path from the combustion chamber through the exhaust flue around and past the volumes of the catalyst-coated medium.

The apparatus of Claim 1 further comprising an air inlet tube with an open inner end arranged to be held by one or more of the one or more holders in communication with the exhaust flue between the combustion chamber and the volumes of the catalyst-coated medium, wherein an open outer end of the air inlet tube is positioned outside the combustion chamber, at a level below a level of one or more combustion air inlets into the combustion chamber, so as to draw ambient air through the air inlet tube into the exhaust flue during operation of the wood heater.

The apparatus of Claim 2 wherein the air inlet tube is routed along an inside or outside surface of the combustion chamber so as to heat the ambient air drawn into the air inlet tube during operation of the wood heater.

The apparatus of Claim 1 further comprising a housing containing the one or more holders and the volumes of the catalyst-coated medium, wherein the housing is sized and shaped so as to fit within the exhaust flue.

5. The apparatus of Claim 1 further comprising a housing containing the one or more holders and the volumes of the catalyst-coated medium, wherein the housing is structurally arranged so as to be incorporated as a segment of the exhaust flue.

6. The apparatus of Claim 5 further comprising an adapter member structurally arranged so as to mate a lower end of the housing to an upper exhaust opening of the wood heater or to mate an upper end of the housing to the exhaust flue.

7. The apparatus of Claim 5 further comprising an air inlet tube held by the

housing so that an open inner end of the air inlet tube is in communication with the exhaust flue between the combustion chamber and the volumes of the catalyst-coated medium, wherein an open outer end of the air inlet tube is positioned outside the combustion chamber, at a level below a level of one or more combustion air inlets into the combustion chamber, so as to draw ambient air through the air inlet tube into the exhaust flue during operation of the wood heater.

8. The apparatus of Claim 1 further comprising a segment of the exhaust flue, wherein the one or more holders and the volumes of the catalyst-coated material are mounted within the segment of the exhaust flue.

9. The apparatus of Claim 1 wherein the one or more holders are formed of the porous, catalyst-coated medium.

10. The apparatus of Claim 1 wherein the porous, catalyst-coated medium

comprises a regular or irregular, three-dimensional latticework of ceramic material forming an open-celled structure coated with a catalytic material effective to catalyze conversion of organic particulates or products of incomplete combustion to water and carbon dioxide.

1 1 . The apparatus of Claim 1 wherein the porous, catalyst-coated medium is coated with a catalytic material that includes one or more metals or one or more metal oxides.

12. The apparatus of Claim 1 wherein the porous, catalyst-coated medium includes a catalytic material with a light-off temperature greater than about 350° F.

13. The apparatus of Claim 1 wherein the porous, catalyst-coated medium

includes a catalytic material with a light-off temperature greater than about 500° F.

14. The apparatus of Claim 1 wherein:

(c) the two or more volumes of the catalyst-coated medium comprise upper and lower disk-shaped volumes and a ring-shaped volume; and

(d) the specified arrangement comprises (i) the lower disk-shaped volume being positioned below and separated by a vertical gap from the ring- shaped volume, (ii) the upper disk-shaped volume being positioned above and separated by a vertical gap from the ring-shaped volume; (iii) the upper and lower disk-shaped volumes being sized so as to form an annular portion of the tortuous exhaust gas flow path within the exhaust flue; and (iv) the ring-shaped volume being sized so as to confine the tortuous exhaust gas flow path to an axial passage through the ring- shaped volume.

15. The apparatus of Claim 1 further comprising an insulator disposed around a segment of the exhaust flue containing the volumes of the catalyst-coated material.

16. The apparatus of Claim 1 wherein a segment of the exhaust flue containing the volumes of the catalyst-coated material is structurally arranged so as to radiate heat into an ambient volume surrounding the wood heater.

17. A method for reducing emissions from a wood heater, the method comprising directing exhaust gas from a combustion chamber of the wood heater through an exhaust flue of the wood heater past two or more volumes of a porous, catalyst-coated medium, wherein:

(a) one or more holders are structurally arranged to hold the volumes of the catalyst-coated medium in a specified spatial arrangement within the exhaust flue; and (b) the volumes of the catalyst-coated medium are sized and shaped so as to (i) obstruct, when held by the one or more holders in the specified spatial arrangement, substantially all straight-line paths from the combustion chamber through the exhaust flue past the volumes of the catalyst-coated medium, and (ii) leave unobstructed, when held by the one or more holders in the specified spatial arrangement, at least one tortuous exhaust gas flow path from the combustion chamber through the exhaust flue around and past the volumes of the catalyst-coated medium.

18. The method of Claim 17 wherein:

(c) at catalyst temperatures below a light-off temperature, the porous,

catalyst-coated medium acts as a particle filter to trap and retain organic particulates and products of incomplete combustion entrained in the exhaust gas, and the tortuous exhaust gas flow path enables the exhaust gas to flow through the exhaust flue around and past the volumes of the catalyst-coated medium even if the catalyst-coated medium is clogged with the retained organic particulates or products of incomplete combustion; and

(d) at catalyst temperatures above the light-off temperature, the exhaust gas flows through the volumes of the catalyst-coated medium.

19. A method for reducing emissions from a wood heater, the method comprising installing in an exhaust flue of the wood heater two or more volumes of a porous, catalyst-coated medium and one or more holders, wherein:

(a) the one or more holders are structurally arranged to hold the volumes of the catalyst-coated medium in a specified spatial arrangement within the exhaust flue; and

The method of Claim 19 wherein the wood heater is a pre-existing and previously installed wood heater and the volumes of the catalyst-coated medium and the holder are retrofitted into the exhaust flue of the pre-existing and previously installed wood heater.