CA1178031A

CA1178031A - Solid fuel burning stove and catalytic converter

Info

Publication number: CA1178031A
Application number: CA000374510A
Authority: CA
Inventors: Robert V. Vandewoestine
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1980-04-02
Filing date: 1981-04-02
Publication date: 1984-11-20
Also published as: EP0037281B1; DE3172190D1; EP0037281A3; EP0037281A2

Abstract

ABSTRACT OF THE DISCLOSURE

This stove is divided by a partition into a lower, combustion chamber, and an upper chamber which communicates directly with an exhaust opening in the stove. A catalytic converter is removably mounted in an opening in the partition.
A by-pass damper, which is connected to the stove door, is normally held closed over a by-pass opening in the wall of the lower chamber, when the door to the stove is closed, whereby all combustion gases from the lower chamber must pass upwardly through the converter and the secondary chamber to the exhaust opening. When the stove door is opened, the by-pass damper tilts by gravity into an open position so that combustion gases from the lower chamber pass directly to the exhaust opening rather through the upper chamber, and rather than being accidentally discharged out of the open door. The converter causes all by-products of combustion to be subjected to a secondary combustion in the converter before passing to the exhaust opening. A
fan blows air under pressure into a space formed between the stove and a surrounding heat shield thereby to distribute more heat, and to prevent overheating of the walls of the stove. Primary combustion air is admitted by a damper to the bottom of the stove, and secondary air is admitted through an opening in the stove door around the edges of two glass panes which are mounted in the door.

Description

Albertsen~VanDewoestine 5-9 Omnibus l 178031 SOLID FUEL BURNING STOVE AND CATALYTIC CONVERTER

The invention relates to stoves which burn solid fuel, such as especially coal and wood stoves having improved efficiency and safety, and further relates to catalytic converters or combustors for use in such stoves.
Due to the relative scarcity and high cost of petroleum products, wood or coal burning stoves have been increasingly em-ployed for home heating and other purposes. A reasonably air tight wood or coal burning stove is far more efficient than a home fireplace, which may result, in fact, in a net energy loss. Especially the stoves burning wood presently being utilized suffer from three significant drawbacks. First, wood burning stoves represent a severe fire hazard since the wood fuel therefore contains volatible substances which are normally not oxidized during combustion. These volatiles will burn if mixed with air at temperatures in excess of 590 C. However, the typical wood burning stove operates within a temperature range of between 230 and 370 C. At these temperatures, these volatible substances, known generally as creosote, remain unoxidized and tend to adhere to the flue pipes and are a cause of not infrequent chimney fires. Secondly, the incomplete combustion of the carbonaceous fuel in wood burning stoves leaves the unoxidized residue as a pollutant and an environmental hazard which is discharged to the atmosphere. Third, the unoxidized residue represents a loss of overall combustion efficiency. While claims have been made to efficiencies greater than 65% in some wood burning stoves, independent testing laboratories have determined that the combustion efficiency of typical wood burning stoves lies in the range of between 50 and 65%. One possible solution to the aforemen.ioned problems is to increase the combustion temperature of the typical wood burning stove by providing additional air into the combustion chamber so as to create temperatures high enough to bring about complete combustlon.

~ i`7803~1~
Variations on this technique date back to the 18th century with the Franklin stove, wherein the volatiles are mixed with additional air in the combustion chamber in order that temperatures high enough to bring about complete combustion may be obtained. These efforts have only been partially successful.
It is an object of the present invention to provide solid fuel burning stoves and catalytic converters therefor, having increased safety and efficiency, in which the unoxidized carbonaceous pollutants are minimized, and the f~el efficiency and utilization is increased.
10 - ~hese and other objects of the present invention are achieved by the modification of a stove to include a catalytic converter which reduces the reaction temperature sufficiently to remove volatile substances at the ordinary operating temperatures of the stove.
In accordance with the present invention, the catalytic converter is located either in the combustion chamber of the stove or in the flue extending therefrom but in eithex case at a location wherein the temperature produced by heat liberated from burning solid fuels is sufficiently high to sustain the catalytic oxidation of the volatiles contained in wood fuels.
In the preferred embodiment of the present invention, the catalytic converter means is situated in the flue emanating from a wood burning stove either as close as possible to or even partially within the combustion chamber of the stove.
In another embodiment of the present invention, a wood burning stove is provided with a primary combustion chamber and a secondary heat exchange chamber and with a communicating passageway therebetween.
A catalytic converter means is situated in the passageway.
In still another embodiment of the present invention, the catalytic converter means is integral with or applied directly to the walls of the combustion chamber of the wood burning stove.
~ oreover, while various catalytic converter means might be acceptable in any of the foregoing embodiments for removing the aforementioned vol~tiles from the flue gas of a wood burning stove, it has been found that the nature and structure of the catalytic monolith, that is the cell density, length, inside cell dimension ~n~ ll~P. thereo are critical~ For example, in typical automotive 1 ~78031 applications, it has been found that catalytic converters having a cell density (in a plane perpendicular to to the axial direction of cells) of 200 cells per square inch are desirable. However, in wood burning stoves, it has been found that catalytic cell densities of this magnitude may cause severe plugging and excessive back pressure, resulting in insufficient draft to operate the stove.
In wood or coal burning stoves, it has been found that the external volume of the catalytic converter means has a marked effect on catalytic performance. Specifically, it has been found that for optimum catalytic performance, the volume, V (in cubic inches), of the catalytic converter means, when expressed as a function of the cell density, N (in cells per square inch) thereof, should be at least:
2554.85/N - 6720.23/N2 + 14.84.
Additionally, it has been found that for optimum pressure drop in a wood burning stove, the catalytic converter means employed should have a predetermined ratio of its length, L (in inches) to-its density, N (in cells per square inch), volume, V (in cubic inches), and inside cell dimension, X (expressed in inches). Specifically, it has been found that:

<5 Still more specifically, it has been found that a catalytic converter means with a volume of 150 in.3, a cell density of 16 cells/in2 a length of 6 in. and an inside cell dimension of 0.21 in. is particularly preferred as to both its catalytic performance and the pressure drop t~ereacross.
A stove of the present invention advantageously includes an exhaust bypass for allowing at least a portion of ~he exhaust or combustion gases to bypass the porous catalytic structure of the converter means when such converter means causes excessive back pressure, e.g. upon plugging of the structure by creosote or upon opening the stove door. In such case, the converter means is situated " I ~78031 for ~ ~ exhaust or combustion gases to normally pass through its porous catalytic structure to the flue.
Hence, according to a further embodiment, the stove includes exhaust bypass means for allowing at least a portion of the exhaust to bypass the catalytic structure of the converter. In a preferred embodiment, the converter means is moveable to permit at least some exhaust to bypass the converter.
Further the advantageous embodiments of the converter and of the stove of this invention will be described in the following detailed description of the drawings and the appended claims.
This description is made with exemplary and non-limiting reference to a wood burning stove.
Brief Description of the Drawings FIG. 1 is a cross-sectional view of a wood burning stove employing a catalytic converter means in accordance with one embodiment of the present invention;
FIG. 2 is a detailed view of the mounting arrangement of the catalytic converter means shown in FIG. 1 in a first position;
FIG. 3 is a detailed view of the catalytic converter means shown in FIG. 2, but rotated 90;
FIG. 4A is a elevational view of a flue for a wood burning stove having alternative mounting arrangement for a catalytic converter means, than that shown in FIGS. 1-3;
FIG. 4B is an elevational view of a catalytic converter means and mounting bracket therefor for use with the flue of FIG. 4A;
FIG. 4C is a top view of the converter means and mounting brac~et shown in FIG. 4B;
FIG. 5 is a detailed view of an alternative embodiment of the mounting arrangement shown in FIG. 2-3;
FIG. 6 is a sectional view of a wood burning stove employing a catalytic converter means mounted in accordance with another embodiment of the present invention;

~ 'IG. 7 is a cross-sectional view of a wood burning stove employing a catalytic converter means mounted in accordance with a third embodiment of the present invention.
FIG. 8 is a plan view of a stove made according to one embodiment of this invention, portions of the stove being cut away and shown in section for purposes of illustration;
FIG. 9 is a front elevational view of this stove also with portions thereof cut away and shown in section for purposes of illus-tration;
FIG. 10 is a side elevational view of this stove with portions again being cut away and shown in section;
FIG. 11 is a slightly enlarged, fragmentary sectional view taken generally along the line 4-4 Fig. 2 looking in the direction of the arrows, and illustrating one manner in which dual glass windows can be mounted in the front doors of the stove; and FIG. 12 is a view similar to Fig. 11 and illustrating still another manner in which dual windows can be mounted in the stove doors.
Referring now to Fig. 1 a cross-sectional view of a typical wood burning stove modified in accordance with one embodiment of the present invention will be described. A wood burning stove is shown generally at 10. The wood burning stove 10 includes a firebox or primary combustion chamber 12 situated above an ash pan 14 and separated therefrom by means of a grate 15. Access to the primary combustion chamber 12 is by means of an entrance door or hatch shown generally at 16. Suitable insulation 18 may surround the combustion chamber 12 including the interior surface of the hatch or door 1~, although such insulation is not a requirement. A flue 20 communicates with the combustion chamber 12 by means of an exit port 22. A primary air inlet port 17 provides a source of oxygen for combustion within the primary combustion chamber 12. Wood fuel is combusted in the primary combustion chamber 12 and exhaust gases emanating therefrom pass through exit port 22 to the flue 20 and from there to the outside environment.

In accordance with one aspect of the present invention, a catalytic converter means 24 is situated internal to the flue 20 immediately adjacent to the exit port 22 from the combustion chamber 12. In 117~303~
accordance with this aspect of the present invention, the catalytic converter means 24 is situated as close as possible to the combustion chamber 12, even extending in part into the combustion chamber 12 if the configuration of the exit port 22 permits such an installation.
In any event, at most, the catalytic converter means 24 is situated at a position in the flue where converter inlet temperature are above 200C. Generally, this position is no greater than 6 inches from the combu~tion chamberO The aforementioned insulation 18 is provided to ensure that at least some of the heat liberated from fuel being combusted in the cGmbustion chamber 12 is utilized to heat the exhaust in the flue 20 sufficiently to cause light off of the converter 24 rather than being transferred through the walls of the wood burning stove 10.
The catalytic converter means 24 is preferably G ceramic honeycomb structure having a plurality of mutually parallel cells extending therethrough with a catalytic substance being applied to the walls thereof. Such catalytic converter means may be made by applying an unfired ceramic to a carrier means, corrugating the coated carrier, subsequently firing the ceramic and thereafter applying a catalyst thereto as set forth in U.S. Patent 3,112,184-Hollenbach. Alternatively, the catalytic converter means may be formed by extrusion from a suitable die means as taught in U.S.
Patent 3,790,654-Bagley.
Since the catalytic converter means 24 may operate at temperatures of between 700 to 900 C. and since internal temperatures of the converter means 24 may at times reach 1100 C., it is desirable that the flue 20 have insulation (not shown) surrounding the same in the vicinity of the catalytic converter means 24.
Alternatively, as shown in FIG. 5, it is desirable to provide the flue 20 with a shielding means comprising a first generally cylindrically shaped baffle 26 surrounding an internal cylindrical baffle 28. Cool air enters the space between the first baffle 26 and the second baffle 28 and passes in the vicinity of the catalytic con-verter means 24 and then exits in the space between the second baffle ~ I ~78031 28 ana the flue 20. Such an installation not only shields the high temperatures of the catalytic converter means 24 from persons in the vicinity thereof, but also provides an addltional source of heat transfer to the space being heated by the wood burning stove 10, thus increasing the combustion efficiency of the stove.
The mounting of the catalytic converter 24 within the flue 20 may be accomplished by situating the catalytic converter means 24 in a metal ring 30 which preferably is formed from stainless steel.
At the time the stove is loaded with new or additional fuel, and the door 16 is opened, increased air flow into its combustion chamber 12 occurs and the presence of catalytic converter means 24 may cause an excess back pressure causing smoke to improperly exhaust. In such an instance, it is necessary that the oxidation products bypass the catalytic converter means.
Accordingly, in the embodiment shown in FIG. 1, it is desirable to mount the catalytic converter means 24 for rotation as shown specifically in FIGs. 2 and 3. There it will be seen that a handle 32 is provided which projects from the flue 20. The handle 32 is connected to the mounting plate 30 which supports the catalytic converter means 24. The mounting plate 30 is rotatably mounted within the flue by means of bushings 34 and 36. Rotation of the handle 32 causes rotation of the mounting plate 30 and ultimately of the catalytic converter means 24 so as to permit combustion gases to pass through the flue 20 without passing through the catalytic converter means 24 during those periods when excess back pressure may be encountered such as when the door 16 is open. As shown in FIGS. 1-3 in order to accomodate converters of difrerent thickness or cell length, the area 31 in the flue 20 in which rotation occurs has a larger cross-sectional area than the remainder of the flue 20.
Without such an arrangement, the converter means 24 would not have sufficient clearance for rotation within the flue 20 unless its cross-sectional area were less than that of the flue.

~78()31 Referring now to FIGs. 4A-4C, another mounting arrangement from that shown in FIGs. 2 and 3 will be described. Specifically, with respect to FIG. 4A, a portion of a flue 20 is shown having an opening 62 therein. The opening 62 extends at least 180 about the periphery of the flue. Parallel tracks 64 on the internal surface of the flue 20 are provided.
As shown in FIG. 4B, a catalytic converter means 24 is provided having annular mounting brackets 66 on the top and bottom surfaces thereof, the brackets 66 preferably being formed from stainless steel. The brackets 66 are spaced so as to mate with tracks 64 such that the ~atalytic converter means 24 may be slideably engaged within the flue 20. The brackets 66 are joined to a shielding means 68 having a suitable handle 70, such that the catalytic converter means 24 may be selectively placed in the flue 20, with the shield 68 providing a closure to the opening 62. The converter means 24 may also be at least partially removed from the flue 20 when new or additional fuel is added to the combustion chamber 12, thus eliminating excess back pressure. An additional shielding means similar to that shown at 68 may also be provided which is not associated with a catalytic converter means for closing opening 62 when new or additional fuel is added to the combustion chamber so that smoke does not exit from this opening.
Referring now to FIG. 6, still another embodiment of the present invention is disclosed wherein like numerals are utilized to describe features co~mon to the embodiment shown in FIGs. 1-3.
In the embodiment shown in FIG. 6, a wood burning stove 10 is shown having a primary com~ustion chamber 12 with an ash pan 14. ~ grate 15 provides a support for the location of wood fuel to be combusted within the primary combustion chamber 12. Wood fuel is introduced within the primary combustion chamber 12 by means of a door or hatch 16. Insulation 18 may be situated within the interior of the combustion chamber 12. Moreover, in accordance with the embodiment shown in FIG. 6, a catalytic converter means 24 is provided which is located within the primary combustion chamber. The insulation 18 is provided to ensure that some of the heat liberated in the combustion chamber 12 is utilized for light off of the catalytic converter means 24. The catalytic converter means 24 is retained within a bracket 38, preferably made from stainless steel. Combustion products from the primary combustion chamber 12 exit therefrom by passing through the catalytic converter means 24 and thereafter exiting by means of the flue 20 to the external envirsnment.
In the embodiment shown in FIG. 6, a bypass passageway 40 is provided which communicates with the interior of the combustion chamber 12 of the wood burning stove 10. Access to the bypass passageway 40 is controlled by means of a bypass damper 42 which is rotatable about an axis 44 so as to allow combustion gases to bypass the catalytic converter means 24 during those periods in which an excess back pressure is expected such as when wood fuel is added to the combustion chamber 12.
Referring now to FIG. 7, still another embodiment of the present invention is disclosed, again with like numerals referring to items common to those shown in the embodiments of FIGS. 1 and 5. FIG. 7 discloses a wood burning stove 10 having a primary combustion chamber 12 wherein wood fuel is combusted. Wood fuel is placed in the primary combustion chamber 12 by means of a door or hatch (not shown ).
Communication between the primary combustion chamber 12 and the ash pan 14 is by way of a grate 15 as shown. Air for combustion enters the primary combustion chamber 12 by means of a primary air inlet 17 and by means of grate 15. 'rhe primary combustion chamber 12 is pre-ferably insulated to provide sufficient heat for llght off of the converter means 24. Unlike the embodiments shown in FIGS. 1 and 6, in addition to the provision of a primary combustion chamber 12, the embodiment shown in FIG. 7 also includes a heat exchange chamber 46 interconnected by means of an opening 48 to the primary combustion chamber 12. Situated in or adjacent to the opening 48 is a catalytic converter means 24. Combustion gases from the combustion chamber 12 _ 9 1 1~8~31 are directed by means of a flow director or vane 50 to the catalytic converter means and catalyzed combustion gases are then passed through the heat exchanger chamber 46 in the vicinity of a heat exchanger comprising a serpentine series of pipes or tubes 52.
The combustion gases are then directed to ~che flue 20 by means of a communicating passageway 54. Entrance to the communicating passageway 54 is controlled by means of a damper 56 which is rotatable about an axis 58.
Like the embodiment shown in FIG. 6, the wood burning stove lO shown in FIG. 7 also includes a bypass passageway 40 controlled by a bypass damper 42 rotatable about an axis 44 whereby co~bustion gases may be caused by bypass the catalytic converter means 24 when excess back pressure is expected such as during loading of additional fuel.
In the embodiment shown in FIG. 7, a secondary air inlet 60 is provided such that additional oxygen may be provided to the vicinity of the catalytic converter means 24 for sufficient operation thereof.
The secondary air inlet 60 preferably comprises a tube, one end of which contains apertures 61 in the vicinity of the converter means 24, and the other end terminating in the vicinity of the primary air inlet 17.
With respect to each of the embodiments shown in the foregoing figures, it has been determined that the nature and structure of the catalytic converter means 24 which is employed is important. The catalytic converter means 24 employed preferrably includes a ceramic monolith having an alumina washcoat applied thereto and coated with precious metal catalysts such as palladium, platinum or alloys of the two in amounts ranging from, for example, 13 grams per cubic foot to 57 grams per cubic foot. However, regardless of the catalysts selected or the loading thereof, the length, volume, and wall thickness of the catalytic monolith selected as well as the density of the catalytic cells employed are critical for adequate creosote removal without excessive back pressure.
Specifically, it has been determined that for adequate ?erformance, i.e., prevention of creosote accumulation as well a~7so3l a- for improvement of combustion efficiency, the volume of the converter means as well as the cell density thereof must be con-trolled. Catalytic performance may be considered optimum if no creosote accumulation is detected and if no detectable unoxi-; dized residue is discharged in the flue. Catalytic performance may, however, still be acceptable if no creosote is formed even though a small quantity of unoxidized residue may be detected.
Finally, performance may be considered marginal if most but not all creosote is eliminated from the flue even if considerable unburned material passes through the flue. Speciically, it has been determined that optimum performance may be attained with a catalytic converter means having a volume of 150 cu. in.
and a density of 16 cells per sq. in. Catalytic performance of a number of cells may be determined from Table I:
Table I
Perfor~anceVolume Diameter LengthDensity V (in3) D (in) L (in)~-~ (cells/in2) Optimum 150 5.66 6 16 Acceptable lS0 5.66 6 9 0 Acceptable 75 5.66 3 25 Marginal 75 5.66 3 16 Marginal 50 5.66 2 25 Unacceptable 75 5.66 3 9 From the foregoing data it has been hypothesized that catalytic performance is related to volume and denisty by the following relationships:
For optimum performance, Volume, V in cubic inches, of the converter, expressed as a function of cell density, ~
expressed in terms of cells per square inch, should ~e at least:
0 V = -6720.23/~2 ~ 25;4.85/~ + 14.84 . . ..

For acceptable performance, Volume, V, of the conver-ter, expressed as a function of cell density, ~, should be at least:
V = _4458.33/~2 + 1957.5/N ~ 3.83 For marginal performance, Volume, V, of the converter, expressed as a function of cell density, N, should be at least:
V = -3333.33/N2 + 1537.50/N - 14.17 ~oreover, even i~ a particular catalytic converter means has optimum, acceptable or marginal performance as defined above, it has been determined that the converter means must additionally exhibit a suitable pressure drop accross it for adequate stove operation, since, as cell density i5 increated to improve catalytic pçrformance, the pressure drop across the converter may be too great to sustain combustion in the stove.
The pressure drop through a square cell catalytic con-verter is defined as:
4 (X + T) ~P = m 28.4L 2 4 p ~D X
where:
~p = pressure drop m = mass flow rate of gases ~= g~s vis~osity P= gas density L = converter length D z converter diameter X = inside cell di.mension T z wall thickness This form can be modi~ied to sive:
L
~P = m p 56.3 4 117~31 where:
L = converter length N = cell density V = converter volume X = inside cell dimension Al] the terms which are constant can be moved to the left side of the equation and accordingly:

~Pp L
. 4 = K (constant) 56.8 m~ NVX

It has been determined that pressure drop may be con-sidered optimum where K is less than 5. In such a situation, the pressure drop across the catalytic converter means is generally not noticable. An acceptable pressure drop may still be had where K is greater than or equal to five but less than seven. In such a situation, pressure drop is noticeable, however, there are generally no adverse effects. In the situation where K is greater than or equal to seven but less than 10, a significant pressure drop occurs across the catalytic converter means and the useful-ness of a particular catalytic converter means will depend on the particular wood burning stove with which it is utilized. Finally, it is believed that when K is greater than or equal to 10 excessive pressure drop across ~he converter occurs, such that combustion may not be sustained. As may be seen from the data set forth in Table II, the following catalytic converter means were tested for pressure drop thereacross:

Table II

K L---(-in) N (cells/in )~ (in ) X (in)

2.40 3 9 75 0.273 4.80 6 9 150 0.273

3.86 3 16 75 0.210 7.71 6 16 150 0.210

4.32 2 25 50 0.165 6.48 3 25 75 0.165 Also, while the use of cellular monolithic type catalytic converters has been described above, those skilled in the art will appreciate that beds- of catalytic pellets might also be employed, the pellets being situated in a metal mesh or other perforated container. However, it should be understood that the use of a ceramic monolithic catalytic converter means is preferred.
Referring now to the drawings by numerals of reference, 110 denotes generally a stove's fire box, comprising a plane, vertical front wall 113, a pair of spaced, parallel side walls 114 and 115, which project at right angles rearwardly from the front wall 113, and a vertically disposed back wall 116, which extends transversely between the rear edges of the side walls 114 and 115, and parallel to the front wall 113. The rectangular firebox 110 is secured centrally on the upper surface of a plane, hori-zontally disposed bottom plate 117 and is closed at its upper end by a similar plate 118, which is secured adjacent its marginal edges on the fire box adjacent each of its corners on the upper ends of four, similarly shaped metal feet or legs 119, which are designed to support the bottom 117 of the fire box horizontally on the floor of a room or the like.

1 17803~

The fire box 110 has in the center of its front wall 113 a laxge rectangular opening 121 (Figs. 9 and 10), which is surrounded by a narrow flange 122 that projects laterally from the outer surface of wall 113. The opening 121 is adapted to be closed by two, rectan~ular, similarly-shaped doors 124 and 125, which are hingedly connected as at 126 and 127 to the left and right hand side edges, respectively, of the front wall 113 as shown in Fig. 9. These hinge connections 126 and 127, which are conventional and are therefore not described in detail herein~
support the doors 124 and 125 so tha~ the inner edges thereof meet and nearly engage along a vertical seam 128 (Fig. 9), when the doors are closed over the opening 121.
Doors 124 and 125 are manipulated by a pair of knobbed handles 130 and 131 (Figs. 8 and 9), the former of which is a dummy handle that is fixed at its inner end to the lower, right hand corner of door 124 as shown in Fig. 9. Handle 131 is rotatably journaled intermediate its ends in an opening 132 formed in the lower left hand corner of door 125 (Fig. 9), and projects at its inner end into the fire box 110 when the doors 124 and 125 are closed. Secured at one end to the inner end of handle 131 to project radially therefrom is a small, rectangular plate 134. A screw 135 is adjustably threaded into the outer end of plate 134 (Fig. 10) so as to have its head disposed in closely spaced, confronting relation to the stationary fire box wall 113, when the doors 124 and 125 are latched closed as shown in the drawings.
When the plate 134 and adjustable screw 135 are swung by handle 131 into their latching positions (Fig. 10), plate 134 extends downwardly in front of a horizontal plate 138, that is positioned just above and parallel to the bottom plate 117 of the fire box to form part of a liner therefor. Plate 138 is fastened t 178031 adjacent its forward edge to the front wall 113; and adjacent its rear edge it has thereon a downwardly projecting flange portion 139 (Fig. 10) which is supported on plate 117 just forwardly of wall 116. The fire box liner also includes a back plate or wall 141 (Fig. 10), which is secured along its lower edge to the rear edge of the liner plate 138, and the lower portion of which pro-jects upwardly and parallel to the rear wall 116 of the fire box.
Intermediate its ends,plate 141 is bent slightly as at 142 so that its upper portion is inclined slightly to the vertical, and away from the rear wall 116 of the fire box. This inclined, upper portion of the liner plate 141 has therein a large, rec-tangular bypass opening 143 which registers with an exhaust opening 144 that is formed in the upper end of the rear fire box .wall 116 for a purpose noted hereinafter.
Opening 143 is adapted to be closed by a large, rectangu-lar damper plate 146, which has its lower edge mounted for pivotal movement in an angle bracket 147, that is secured to the inside surface of plate 141 adjacent to the lower edge of opening 143.
Plate 146 is pivotal between the legs of a generally U-shaped bracket 148, the marginal side of which is fastened to the inside surface of the liner plate 141 adjacent opposite sides of opening 143. The back or inside surface of damper plate 146 rests upon the inner end of a push rod 150, which slides adjacent its inner end in an opening in a support plate 151, which is fastened to, and projects upwardly from, bracket 148. Adjacent its outer end rod 150 projects slidably through an opening in a stationary baffle 152 on the upper edge of wall 113, and into engagement with the inside of the door 125 when the latter is closed. With this construction, whenever the door 125 is swung to its open position, the weight of the inclined damper plate 146 urges the push rod 150 toward the left in Fig. 10 until the 1 171803~

plate 146 is swung from its closed, ~ull line position to its open or broken line position as shown in Fi~g. 10, wherein the upper edge o~ plate 146 comes to rest ayainst the support plate 151. Obviously whenever the door 125 is closed, it reengages the push rod 150 and forces it and plate 146 back to their full line positions as shown in Fig. 10, thus once again closing the bypass opening 143.
Secured on top of the fire box cover pla~te 118 substan-tially centrally thereof is a rectangular housing 155, the upper end of which is sealed by a large, flat cover plate 157 which is similar in configuration to, but slightly smaller than, plate 118.
The interior of housing 155 defines an exhaust chamber 158, which communicates through a large, rectangular opening 159 (Fig. 10), in plate 118 with the space formed in the upper end of the fire box between the bypass opening 143 and the exhaust opening 144 in wall 116.
Secured along one edge of the inside of the vertical por-tion of the liner plate 141, and projecting horizontally therefrom into the center of the fire box above and in spaced, parallel relation to the bottom plate 138 of the liner, is a rigid plate or shelf 161, which can be used to support thereon burning embers for banking a fire in the box 110 as noted hereinafter. Secured in opposite ends in the opposed side walls of the fire box, and extending transversely therebetween in a plane containing the shelf 161, is a plurality of spaced, parallel metal bars 162, which form supports for a conventional grate (not illustrated), which may be removably placed in a fire box 110 for holding kindling, fire wood, etc., in a known manner.
Removably mounted on the liner plate 138, and extending at its rear and beneath the support rods 162 and the shelf 161, is a relatively shallow, rectangular ash pan 164. The forward, .,~"

l ~ ~'8031 vertically disposed wall 165 of the pan 164 is spaced horizon-tally from the front wall 113 of the fire box, and has thereon a forwardly projecting lip or flange 166 which overlies the door latching plate 134, and which provides a handle portion for moving the pan 164 into and out of the fire box through its front doors 124 and 125. When these doors are closed (Fig. 10), the forward edge of the flange 166 is spaced slightly rearwardly from the inside surfaces of the doors to allow air for combustion to enter the combustion chamber above pan 164 from the space between plates 117 and 138, as noted hereinafter. Air from this lattex space is also permitted to enter the combustion chamber through a plurality of spaced openings 167 which are formed in the front wall 165 of the pan.
The primary source of air for supporting combustion in the fire box 110 is a rectangular opening 171 (Fig. 10), which is formed in the base plate 117 adjacent to its rear edge, and inwardly from the flange 139 on the liner plate 138. The quantity of air admitted through this opening is controlled by a damper plate 172, which is supported by a bracket 173 for sliding move-ment against the underside of plate 117. A pair of lugs 174, which project from the bottom of plate 172 adjacent to its forward end, are adjustably attached to the threaded end of a horizontal operating rod 175, which is slidably supported intermediate its ends by bracket 176 which projects from the underside plate 117.
A knob 177 on the outer end of rod 175 can be used manually to shift the damper 172 back and forth to cover or uncover the opening 171 to varying degrees, thereby to control the amount of primary combustion air that is admitted to the fire box.
; Secured intermediate its ends in a circular opening, which is formed in the fire box cover plate 118 medially of its sides and slightly to the left (Fig. 10), or forwardly of its 1 ~78031 centerline, is a steel ring or sleeve 181. Removably mounted in the bore sleeve 181 is the cylindrically-shaped catalytic converter element 182. The outside diameter of element 82 is slightly less than the inside diameter of sleeve 181 so that the element can be readily inserted into, and withdrawn from the bore of the sleeve. Element 182 is seated at its lower end on an elongate supporting pin 184, opposite ends which are removably seated in registering openings formed in the annular wall of sleeve 181 adjacent to its lower end, so that the pin 184 extends substantially diametrically across the center of the sleeve. As shown more clearly in Fig. 10, the sleeve 181 and the enclosed converter element extend at their upper ends par~ way into the exhaust chamber 158 in the housing 155, and at their lower ends extend into the upper end of the combustion chamber in the fire box 110.
Welded or otherwise secured to the inside surface of the exhaust chamber cover plate 157 to overlie the upper ends of sleeve 181 and its converter element 182 is a stainless steel plate 185. A circular opening 186 in the center of plate 185 20 registers coaxially with the sleeve 181 and element 182, and also with a circular opening 187 in the plate 157. A transparent, disc-shaped window or sight glass 188 is secured in the opening 187 to register with the center of the converter element 182, - and to provide means for observing the element during operation of the stove.
When the damper plate 146is in its closed position over the bypass opening 143 (Fig. 10), all combustion gases and the like rising from the interior of the fire box 110 must pass up-wardly through the converter element 182 before entering the exhaust chamber 158. From there the gases pass beneath a plate baffle 190, which extends downwardly from the cover plate 157 l l 7ao3l and transversely between the side walls of housing 155 so as to be positioned between the sleeve 181 and the exhaust opening 159.
Consequently, after the gases have passed through element 181 and beneath baffle 190, they pass downwardly through the opening 159 to the opening 144 in the back 116 of the opening box. This opening communicates through an exhaust duct or flue 191 with the fire box chimney (not illustrated). As shown more clearly in Fig. 10, this duct 191 is secured at its inner end around the opening 144 in plate 116, and extends intermediate its ends through a registering opening formed in the back 193 of a gener-ally U-shaped radiation shield, which surrounds the rear portion of the fire box 110 between plates 117 and 118.
This shield includes twol spaced, parallel side portions or arms 194 and 195, which project from section 193 forwardly to be disposed in spaced, parallel, overlapping relation to slightly more than the rear halves of the side walls 114 and 115 of the fire box. A conventional electric blower 196, which is mounted at the exterior of the radiation shield (Fig. 10), has its dis-charge end secured by a plate 197 over opening 198, which is formed in the back portion 193 of the shield in communication with the narrow space which is formed between the shield and the rear portion of the fire box. When the stove is in operation, the shield 193, 194, 195 and the associated blower 196 perform the functions of preventing the fire box side walls 114 and 115 from overheating, thereby obviating the need to employ a fire brick lining in the fire box, and also serving to direct heated air from the space between the shield and the fire box out of the vertical openings formed between the forward edges of the shield and the fire box, when the stove and fan 196 are in use.
Even when the fan is not in use the shield blocks direct radia-tion from the back and side walls of fire box 110 allowing the stove to be safely positioned closer to combustible walls.

-~r, ll78~131 As shown more clearly in Figs. 9 and 11, the doors 124 and 125 have therein large, central, rectangular openings 201 and 202 respectively. Each of the openings 201 and 202 is closed by a pair of spaced, parallel, vertically disposed panes 203 and 204 of medium and high temperature glass, respectively. Two of these panes are shown by way of example in Fig. 11. Since the manner in which the way the two panes are mounted in each door 124 and 125 is similar, only the construction of door 124 will be described in detail herein.
Referring now to Fig. 11, 206 denotes generally a rectangular frame which is fastened to the inside of the door 124 around its opening 201. This frame also has therethrough a rectangular opening 207 which registers with, and is similar in configuration to, the opening 201 in the door. The panes 203 and 204 are secured in frame 206 to extend transversely between the openings 201 and 207 in spaced, parallel relation to each other.
The outer pane 203 is sealingly secured by conventional gasket material along three of its edges, namely its upper edge (as at 208) and along its two side edges, against the inside of door 124 around its opening 201. Deliberately, however, the gasket material is not incorporated between the lower edge of pane 203 and the confronting surface of the frame 206, whereby an elongate, narrow opening or gap 209 is formed between the frame of 206 and the lower edge of pane 203. Pane 204, on the otherhand, has its two vertical side edges and its lower edge secured, as at 211, by gasket material against the inside surface of the frame 206 around its opening 207, so that its upper edge is spaced as at 212 slightly beneath the confronting surface of frame 206.
As a result of the manner in which panes 203 and 204 are mounted in each door 124 and 125, when the stove is in opera-- tion a secondary supply of air for combustion enters the interior of the fire box through its doors 124 and 125 by passing through the gap 209 along the bottom of the outer pane 203, as indicated by the arrows in Fig. 11, then upwardly between the panes 203 and 204, and then through the gap 212 and out of the opening 207 in frame 206 to the combustion chamber adjacent its upper end.
Assuming that the stove is in operation, primary air will also be entering the interior of the fire box at this time from beneath the liner plate 138, passing upwardly as shown by the arrows in Fig. 11 between the lip 166 on the ash pan 164 and into the combustion chamber. Also as indicated by the arrows in this figure, a portion of this primary air is free to pass to the interior of the fire box through the openings 167 in the front wall of pan 164.
The inner pane operates at a higher temperature due to reflected radiation from the outer pane. The higher temperature reduces condensation. The secondary air flow draws any flow of smoke away from the upper portion of the window. As a result of the design of the pane mountings in the doors 124 and 125, and also because of the manner in which the primary air is fed into the fire box over the forward edge 166 of the ash pan, the windows or panes 203 and 204 are, in essence, self-cleaning. For example, with incoming secondary air entering the fire box along the upper edges of doors 124 and 125, and with the primary combustion-supporting air being directed by the ash pan lip 166 vertically upwardly along the inside of the window panes 204, accumulation of ash and other foreign matter on the panes 203 and 204 is minimized. Moreover, with the secondary air entering the upper end of the combustion chamber, it supplies the necessary oxygen for supporting complete combustion of gaseous fuels in the catalytic converter which might otherwise be only partially burned because of an inadequate supply of oxygen from the primary air supply from the bottom of the fire box.

Fig. 12, which is similar to Fig. 11, illustrates a modified manner of mounting the two panes 203 and 204 in doors 124 and 125 to permit a secondary supply of air therethrough.
In this modified embodiment each of the panes 203 and 204 has its vertical side edges and its lower edg~ secured by gasket material as in 215 against the inside frame 206, thereby forming a gap 216 in the frame 206 over the upper edges of the two panes 203 and 204 in each door so that the secondary air supply enters through the doors 124 and 125 over the upper edges of the panes.
Also as in the preceding embodiment, the primary air still enters the fire box over the forward edge of the lip 166 on the ash pan 164, so that the incoming primary air tends to wash or clean the inside surfaces to the inner panes 204.
In use, handle 131 may be manipulated by rotating it counterclockwise from its position as shown in Fig. 9, thereby swinging its latching screw 135 out of registry with the bottom wall 113, and thus permitting both doors 124 and 125 to be swung open about their respective hinges 126 and 127. A conventional grate (not illustrated) can then be placed on top of supporting rods 162, together with a supply of fuel (for example wood). The damper 172 is then opened at least partially; and assuming that the converter element 182 is already in the holder 181, the fire can be started and the doors 124 and 125 once again may be closed.
As previously noted, whenever door 125 is open, the damper plate 146 swings downwardly to its broken line position in Fig. 10, thereby opening the bypass 143 so that any flame or gases in the fire box will be drawn rearwardly and outwardly through the openings 143 and 144 and the exhaust duct 191 to the associated chimney (not illustrated). This prevents any undesirable rush of flame and/or gas out of the front of the fire box, when its doors are opened during its operation.

- .

~ 17~V31 After the fire has been started and the fire box doors have been closed, door 125 strikes the rod 150 which pushes the damper plate 146 closed over the bypass opening 143, so all carbon and gases generated in the combustion chamber will there-after have to pass upwardly through the converter element 182 before entering the exhaust chamber 158. Especially in the spring and the fall, when the heating requirements of a stove of the type described are not as high, the combustion air fed to the fire box is usually quite restricted. At this point much of the combustion in the fire box is accompanied by pyrolysis, which is an incomplete combustion of fuel resulting from oxidizing without sufficient air. As a result, smoke is produced because the hot combustible gases, tars, and carbon particles are not mixing well enough with available oxygen, and the temperature in the combustion chamber of the fire box is not high enough, under this type of operation, to effect complete combustion.
However, it has been found that when a converter 182 of the type disclosed herein is employed, additional and more - 23a --~7 ~178031 com~ ~e combustion occurs in and around the converter itself.
~ The effectiveness of the converter element 182 can be monitored by observing its color through the sight glass 188. When the element is working properly, it tends to glow bright red or orange in color, indicating that secondary combustion is taking place in and around the element, thereby completely burning up combustible gases, tars and carbon particles which might otherwise be discharged as undesirable emissions to the associated stack or chimney. The relative position of the sight glass with respect to the catalytic converter is such that the catalytic converter, when, operative will clean the glass of any deposits through high intensity radiant heat.
From the foregoing it wiIl be apparent that the present invention provides a relatively simple and inexpensive means for effecting substantiall~ complete and thorough combustion of all combustible by-products of the fuel which is burned in the main combustion chamber of applicant's novel stove. By supplying combustion air from two different sources, (i.e., both from the bottom and from the top of the fire box) it is possible better to maintain the quantity of oxygen necessary to support combustion both in the main combustion chamber of the fire box, and in the vicinity of the converter element 182.
The automatically operating damper control rod 150 provides a i simple means for eliminating any undesirable flashback or discharge of flame and gas out of the front of the stove whenever its doors 124 and 125 are open.

While this invention has been described in connection with the use of the fire wood, it will be apparent that it can be used to burn any type of bio-mass fuels, including coal provided the usual cautions are taken to prevent the escape of noxious fumes.

117~031 SUPPLEMENTARY DISCLOSURE

Following on the work outlined in the original disclosure it has further been found that, for at least satisfactory performance in the smaller eommercial stoves (e.g. with firebox volumes of about 1.5 to 2 eubic feet or so~, the volume, V (in cubie inehes), of the eatalytic eonverter means (i.e. honey-comb strueture), when expressed as a function of the ~
eell density, N (in eells per square inch of transverse eross-section) of the honeycomb strueture in a direction perpendicular to exhaust flow passages through the cells should be at least:
V 1 35 ~ 400 34 - 0.013.
N N
For larger commerical stoves with firebox volumes of about 5 or so cubic feet, it has been found that perfor-mance provided by the cellular eatalytic converter means is:
1. marginally adequate where its volume is at leas*:
V 3333.33 __ 1537.50 _ 14.17;
N N
2. generally acceptable where its volume is at least:
V 4458.33 ~ 1957.5 ~ 3.83;
N N
and 3. optimum where its volume is at least:
6720.23 + 2554.85 ~ 14.84.
N N
Referring to the data set out at Table 1 it has further been found that satisfactory or acceptable performance was also obtained in a smaller stove with a 1.6 cubic foot firebox and a cellular catalytic conver-ter having a 3.5 x 4 x 3 inch external size and a cell density of 16 cells/in .

~D25 l 178031 Again in accordance with that same data it has further been found that, as minimum criteria for the present invention and for acceptable perfor-mance at least in smaller volume firebox stoves, volume, V in cubic inches, of the converter, express-ed as a function of cell density, N expressed in terms of cells per square inch, should be at.least:
V=1.35/N2 ~ 400.34/N-0.013 Thus in further aspect of the invention there is provided, in a solid fuel burning stove, of the type having:
a combustion chamber, and a flue for removing exhaust from said chamber, the improvement comprising:
a catalytic converter means as in claim 1 for oxidizing oxidizable species in said exhaust, said catalytic converter means comprising a honey comb 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:
1.35 400.34 : V = 2 + ~ 0.013.
N N
In one embodiment the volume in cubic inches of the stove is at least :
3333.33 ~ 1537.5 _ 14.17.
: N2 N
. In another embodiment the volume in cubic inches is at : least: 4458.33 1957.5 . V = ~- + + 3.83.
N N
6720 23 2554.85 V = - + + 14.84.
: ~.2 In certain embodiments the cell density of the stove is substantually less then 200 cells per square inch, preferrably in the range of about 9 to 100 cells per square inch, and most preferrably from 9 to 50 cells per square inch. Also particularly preferred is a range of 9 to 25 cells per square inch.

1 178~31 In one embodiment of such a stove 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, preferrably less than 7, most preferrably less than 5.

,~

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A solid fuel burning stove, which comprises a com-bustion chamber, and a flue for removing exhaust from said chamber, the improvement of a catalytic converter for oxidizing oxidizable species in said exhaust, located either in said combustion chamber or in said flue, at a location wherein the temperature produced by heat liberated from burning solid fuel is sufficiently high to sustain the catalytic oxidation of the volatibles contained in solid fuels.

2. A stove according to claim 1, wherein said catalytic converter is situated in the flue as close as possible to or par-tially within said combustion chamber.

3. A stove as claimed in 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. A stove as claimed in claim 3, further comprising:
a heat exchange chamber in communication with said flue; and an opening or a passageway interconnecting said combustion and heat exchange chambers, said catalytic converter being situation adjacent said opening or in said passageway, respectively.

5. A stove as claimed in claim 1, wherein said oxi-dizable species is creosote.

6. A stove as claimed in claim 1, wherein said con-verter comprises a catalytic coating of palladium, platinum, or alloy thereof.

7. A stove as claimed in claim 1, wherein said con-verter is coaxially mounted in a metal sleeve.

8. The stove of claim 1, wherein said converter com-prises a plurality of catalytic cells each having a length oriented in the direction of the flow of said exhaust and a volume (V) in cubic inches expressed as a function of the density (N) of said cells in ceIls per square inch in a direc-tion perpendicular to said flow being at least:

V = .

9. The stove of claim 1, wherein said converter com-prises a plurality of catalytic cells each having a length oriented in the direction of the fIow of said exhaust and a volume (V) in cubic inches expressed as a function of the density (N) of said cells in cells per square inch in a direc-tion perpendicular to said flow being at least:
V= .

10. The stove of claim 1, wherein said catalytic con-verter comprises a plurality of catalytic cells each having a length oriented in the direction of the flow of said exhaust and a volume (V) in cubic inches expressed as function of the density (N) of said cells in cells per square inch in a direc-tion perpendicular to said flow, said function being at least:

V = .

11. The stove of claims 8, 9 or 10, 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 5.

12. The stove of claims 8, 9 or 10, 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.

13. The stove of claims 8, 9 or 10, 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.

14. The stove of claim 8, 9 or 10, wherein the cell density is substantially less than 200 cells/square inch.

15. The stove of claim 8, 9 or 10, wherein the cell density is in the range of about 9-100 cells/square inch.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
SD16. In a solid fuel burning stove of the type having:
a combustion chamber, and a flue for removing exhaust from said chamber, the improvement comprising:
a catalytic converter means as in claim 1 for oxidizing oxidizable species in said exhaust, said catalytic converter means comprising a honey comb 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 func-tion of the cell density (N) of said cells in cells per square inch in a direction perpendicular to said flow being at least:
V = .
SD17. The stove of claim 16 wherein said catalytic conver-ter means is situated in said flue immediately adjacent said chamber.

SD18. The stove of claim 16 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.

SD19. The stove of claim 16 wherein said catalytic con-verter is situated in said combustion chamber.
SD20. The stove of claim 16 further comprising:
a head 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.

SD21. The stove of claim 16 wherein said oxidizable species is creosote.

SD22. The stove of claim 16 wherein the cell density is substantially less than 200 cells/square inch.

SD23. The stove of claim 16 wherein the cell density is in the range of about 9-100 cells/square inch.

SD24. The stove of claim 16 wherein the cell density is in the range of about 9-50 cells/square inch.

SD25. The stove of claim 16 wherein the cell density is in the range of 9-25 cells/square inch.

SD26. The stove of claim 16 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.

SD27. The stove of claim16 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.

SD28. The stove of claim 1 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.