Wood burning stove

Abstract

Disclosed herein is an improved wood burning stove having a combustion chamber and a flue for removing exhaust from the chamber wherein the improvement comprises the addition of a catalytic converter means for oxidizing oxidizable species in the exhaust. In one embodiment, the catalytic converter means is situated in a flue immediately adjacent the combustion chamber. In another embodiment, the catalytic converter means is situated in the combustion chamber itself. In addition the nature and structure of a catalytic converter means have been determined for marginal acceptable and optimum performance with adequate pressure drop thereacross.

What is claimed is: .[. 
     
       1.  In a woodburning stove of the type having: a combustion chamber, and   a flue for removing exhaust from said chamber, the improvement comprising: a catalytic converter means for oxidizing oxidizable species in said exhaust, said catalytic converter means comprising a honeycomb structure having a plurality of mutually parallel catalytic cells, each having a flow length oriented in the direction of the flow of said exhaust, and a volume (V) in cubic inches expressed as a function of the cell density (N) of said cells in cells per square inch in a direction perpendicular to said flow being at least:.]. ##EQU9##  .[.     
     
     
       2.  The stove of claim 1 wherein said catalytic converter means is situated in said flue immediately adjacent said chamber..]. .[.3. The stove of claim 1 wherein said flue communicates with said combustion chamber at an exit port and wherein said catalytic converter means is situated in said chamber at said exit port..]. .[.4. The stove of claim 1 wherein said catalytic converter is situated in said combustion chamber..]. .[.5. The stove of claim 1 further comprising: a heat exchange chamber in communication with said flue, and   an opening interconnecting said combustion and heat exchange chambers, said   
     
     
        catalytic converter means being situated adjacent said opening..]. .[.6. 
     
     
        The stove of claim 1 wherein said oxidizable species is creosote..]. 7. .[.The stove of claim 1 wherein said volume in cubic inches is at least:.]. .Iadd.In a woodburning stove of the type having: a combustion chamber, and a flue for removing exhaust from said chamber, the improvement comprising: a catalytic converter means for oxidizing oxidizable species in said exhaust, said catalytic converter means comprising a honeycomb structure having a plurality of mutually parallel catalytic cells, each having a flow length oriented in the direction of the flow of said exhaust, and a volume (V) in cubic inches expressed as a function of the cell density (N) of said cells in cells per square inch in a direction perpendicular to said flow being at least: .Iaddend. ##EQU10## 
     
     
         8. The stove of claim .[.1.]. .Iadd.7 .Iaddend.wherein said volume in cubic inches is at least: ##EQU11## 
     
     
         9. The stove of claim .[.1.]. .Iadd.7 .Iaddend.wherein said volume in cubic inches is at least: ##EQU12## 
     
     
         .[.10.  The stove of claim 1 wherein the cell density is substantially 
     
     
        less than 200 cells/square inch..]. .[.11.  The stove of claim 1 wherein the cell density is in the range of about 9-100 cells/square inch..]. 
     
     
        .[.  .  The stove of claim 1 wherein the cell density is in the range of 
     
     
        about 9-50 cells/square inch..]. 13. The stove of .[.claim 1.]. .Iadd.any of claims 7-9, 19-20 or 24 .Iaddend.wherein the cell density is in the 
     
     
        range of 9-25 cells/square inch. 14. The .[.stoves.]. .Iadd.stove .Iaddend.of .[.claim 1, 7, 8 or 9.]. .Iadd.claims 7-9, 19-20 or 24 .Iaddend.wherein the square of the length of said cells divided by the product of the cell density times the converter volume times the fourth 
     
     
        power of the insides dimension of one of said cells is less than 5. 15. The .[.stoves.]. .Iadd.stove.]..Iaddend.of .[.claim 1, 7, 8, or 9.]. .Iadd.any of claims 7-9, 19-20 or 24 .Iaddend.wherein the square of the length of said cells divided by the product of the cell density times the converter volume times the fourth power of the inside dimension of one of 
     
     
        said cells is less than 7. 16. The .[.stoves.]. .Iadd.stove .Iaddend.of .[.claim 1, 7, 8 or 9.]. .Iadd.any of claims 7-9, 19-20 or 24 .Iaddend.wherein the square of the length of said cells divided by the product of the cell density times the converter volume times the fourth power of the inside dimension of one of said cells is less than 10. 
     
     
        .Iadd. 7.  The stove of claim 7 wherein said volume in cubic inches is less than: ##EQU13## 
     
     
        .Iaddend. .Iadd.18.  The stove of claim 8 wherein said volume in cubic inches is less than: ##EQU14## 
     
     
        .Iaddend. .Iadd.19.  In a woodburning stove of the type having: a combustion chamber, and a flue for removing exhaust gas from said chamber, the improvement comprising: a ceramic catalytic converter for oxidizing oxidizable species in said exhaust, located in said woodburning stove, at a location wherein the temperature produced by heat liberated from fuel being combusted in said combustion chamber is sufficiently high to light off and sustain the catalytic oxidation of the volatiles in the exhaust, free of any external source of heat other than heat liberated from fuel being combusted in said   
     
     
        combustion chamber. .Iaddend. .Iadd.20.  The stove of claim 19 in which said catalytic converter comprises: a plurality of catalytic cells each having a length oriented in the   
     
     
        direction of the flow of said exhaust. .Iaddend. .Iadd.21.  The stove of claim 19 or 20 in which said converter's resistance to flow is such that the pressure drop across the converter does not prevent combustion in the 
     
     
        stove. .Iaddend. .Iadd.22.  In a woodburning stove of the type having a combustion chamber and, a flue for removing exhaust from said chamber, the improvement comprising:   catalytic converter means for oxidizing oxidizable species in said exhaust, said catalytic converter means having a volume of at least about 50 cubic inches and a cell density of at least about 9 cells per square inch.   
     
     
        .Iaddend. .Iadd.23.  The stove of claims 7-9, 19-20 or 22 in which, said catalytic converter means is located within said stove at a location wherein the temperature produced by heat liberated from fuel being combusted in said combustion chamber is sufficiently high to light off and sustain the catalytic oxidation of the volatiles in the exhaust. .Iaddend. .Iadd.24. The stove of claim 25 in which said converter means comprises: a plurality of catalytic cells, each having a length oriented in the   
     
     
        direction of the flow of said exhaust. .Iaddend. .Iadd.25.  The stove of claim 23 in which the resistance to flow of said converter means is such that the pressure drop across the converter means does not prevent combustion in the stove. .Iaddend. .Iadd.26. The stove of claim 23, wherein said catalytic converter means is located in said combustion chamber. .Iaddend. .Iadd.27. The stove of claim 23, wherein said catalytic 
     
     
        converter means is located in said flue. .Iaddend. .Iadd.28.  A woodburning stove, comprising: a combustion chamber adapted for the burning of wood fuel to produce heat and exhaust;   a flue communicating with said combustion chamber for removing exhaust therefrom; and   catalytic converter means for oxidizing oxidizable species in said exhaust, said catalytic converter means comprising a honeycomb structure having a multiplicity of mutually parallel catalytic cells for allowing exhaust from said combustion chamber to pass through said catalytic converter, said catalytic converter means having means for preventing creosote accumulation in said catalytic converter means and said flue during combustion of wood in said combustion chamber. .Iaddend. .Iadd.29. The stove of claim 28, wherein said catalytic converter means further comprises:   means for preventing discharge of detectable amounts of unoxidized residue into said flue. .Iaddend. .Iadd.30. The stove of any of claims 7, 19, 22 or 30 wherein said catalytic converter means comprises:   a ceramic monolith having an alumina washcoat applied thereto and coated with a catalyst consisting essentially of precious metal selected from the group consisting of palladium, platinum, and palladium-platinum alloys.   
     
     
        .Iaddend. .Iadd.31.  The stove of claim 30, wherein said catalytic converter means is coated with 13 to 57 grams per cubic foot of said precious metal. .Iaddend. .Iadd.32. The stove of claims 7, 19, 22 or 28, further comprising: a plurality of walls defining said combustion chamber therebetween, heat of combustion from said combustion chamber being transferred through said walls to heat the surrounding air; and an air inlet port penetrating one of said walls for supplying air to said combustion chamber. .Iaddend. .Iadd.33. The stove of claim 32, further comprising:   insulation means surrounding said combustion chamber for causing a portion of the heat liberated in said combustion chamber to heat the exhaust in said flue sufficiently to light off said catalytic converter, the balance of the heat liberated in said combustion chamber being transferred through said walls. .Iaddend. .Iadd.34. The stove of claim 32, further comprising:   a grate disposed within said combustion chamber and adapted to support wood   
     
     
        for combustion thereon. .Iaddend. .Iadd.35.  The stove of claim 34, further comprising: an ash pan for collecting ash which falls through said grate; and   a door built into one of said walls having means for allowing wood to be loaded on said grate and means for allowing said ash pan to be inserted into and removed from said combustion chamber. .Iaddend.