Emission reduction device for a wood heater

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.

What is claimed is: 
     
         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.   
     
     
         2 . 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. 
     
     
         3 . 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. 
     
     
         4 . 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. 
     
     
         11 . 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   (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.   
     
     
         20 . 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.