Note: Descriptions are shown in the official language in which they were submitted.
Albertsen-Vanr woestine 5-9 Omnibus
1~7~~
SOLID FUEL BURNING STOVE AND CATAL~TIC 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 sufrer from three
significant drawbacks. First, woocl burning stoves represent a
severe fire hazard since the wood fuel therefore contains volatible
substances which are normaliy 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 co~ustion
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 aforementioned 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 combustion.
.
.,
~178~32
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 fuel efficiency and utiliæation is increased.
- These and other objects of the present invention are achieved
by the modification of a stove to include a ~atalytic 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 either 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 ~s 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.
Moreover, while various catalytic converter means might be
acceptable in any of the foregoing embodiments for removing the
aforementioned volatiles 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
ar.d volume, thereof, are critical. For example, in typical automotive
~ 17803~
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 ~olume, V (in cubic inches), of
the catalytic converter means, when expressed as a function of the
cell density, N (in cells per square inch) ~hereof, 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
NVX4
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 the 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
- 3 -
. . .
803~
for the 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.
Thus in this specification there is provided a solid fuel
burning stove which comprises a combustion 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 fuels is sufficiently high to sustain
the catalytic oxidation of the volatibles contained in solid fuels,
said stove further comprising means for admitting air for com-
bustion to said chamber, including a door on said combustion
chamber moveable between open and closed positions relative to a
first opening in said chamber and a second opening in said combus-
tion chamber adjacent the bottom thereof, the combustion chamberhaving therein two further openings for exhausting combustion
gases from said chamber to the exterior thereof, and means for
selectively closing the other of said two further openings, said
converter being positioned so that, when said other opening is
closed, all said gases from said combustion chamber are caused to
pass through said converter.
In another aspect the present invention provides a solid
fuel burning stove, which comprises a combustion 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 fuels is sufficiently high to
~'17~303Z
sustain the catalytic oxidation of the volatibles contained in
solid fuels, wherein the catalytic converter means has a honey-
comb structure situated for the exhaust to normally pass
through it to the flue and the stove includes an exhaust bypass
means for allowing at least a portion of the exhaust to bypass
the porous catalytic structure, said stove comprising means for
admitting air for combustion to said chamber, including a door
on said combustion chamber moveable between open and closed
positions relative to a first opening in said chamber and a
second opening in said combus~ion chamber adjacent the bottom
thereof, the combustion chamber having therein two further
openings for exhausting combustion gases from said chamber to the
exterior thereof, means for selectively closing one of said
two further openings, and said converter being positioned to
communicate with the other of said two further openings so
that, when said one opening is closed, all said gases from said
combustion chamber are caused to pass through said 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;
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1178032
FIG. 4A is. an 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
bracket 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
~.~
".
~ 30
. .
~ 4b -
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1 1~8032
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 16, 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 rrom the combustion chamber 12. In
-- 5 --
~178Q3Z
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, ~his position is no greater than 6 inches from the
combustion chamber. The aforementioned insulation 18 is provided to
ensure that at least some of the heat liberated from fuel being
combusted in the combustion 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 a 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 meanslmay 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 flrst 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
- 6 -
I ~7803~
28 ar 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 additional 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 different 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.
:
-- 7 --
:~17~3032
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 catalytic 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 common 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 combustion 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
-- 8
- I 178032
is located within the primary combustion c~amber. The ins~lation
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 environment.
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. The primary combustion chamber 12 is pre-
fer~bly insulated to provide sufficient heat for light 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
_ g _
~ . ,
:
117~032
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 the 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
10 shown in FIG. 7 also includes a bypass passageway 40 controlled
by a bypass damper 42 rotatabie about an axis 44 whereby combustion
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
~srformance, i.e., prevention of creosote accumulation as well
-- 10 -- , . -
1 178~2
a~ ~or 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-
i 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 conGiderable
unburned material passes through the flue. Specifically, 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 5q. in. Catalytic performance of
a number of cells may be determined from Table I:
Table I
PerformanceVolumeDiameter LenqthDensity
V (in3) D (in) L (in)~l (cells/in2)
Optimum 150 5.66 6 16
Acceptable lS0 5.66 6 9
O Acceptable 75 5.66 3 25
Marginal 7S 5.66 3 16
Marginal 50 5.66 2 25
Unacceptable 75 5.66 3 9
From the foregoing data it has been hypothesized 'hat
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, ~hould be at least:
V = -6720.23/~2 + 25;4.85/N + 14.84
... _ . ,, . . , . .. _ , . _ . ., , .. . . . . .. . _ . . . . . , _ .. .. ..
.
1 17~0~2
For acceptable performance, Volume, V, of the conver-
ter, expressed as a function of cell density, ~, should be at
least:
V = -4458.33/N2 + 1957.5/N + 3.83
For marginal performance, Volume, V, of the converter,
expressed as a function of cell den.~ity, ~, should be at least:
V _ _3333.33/~2 + 1537.50/N - 14.17
Moreover, even if a particular catalytic converter
means has optimum, acceptable or marginal performance as defined
O above, it has been determined that the converter means must
additionaily exhibit a suitable pressure drop accross it for
adequate stove operation, since, as cell density is increated
to improve catalytic performance, the pres~ure 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:
11 4 (X + T)
~P = m -- 28 . 4L 2
p 7rD X
where:
~p = pressure drop
~!0 m = mass flow rate of gases
= gas viscosity
ps gas density
L = converter length
D s converter diameter
X = inside cell dimension
T s wall thickness
This form can be modi'ied to give:
L
.P = m --56.8 4
P NVX
_ 12 _
ll780321
where:
L = converter length
N = cell density
V = converter volume
X = inside cell dimension
All the terms which are constant can be moved to the left side of
the equation and accordingly:
QPp = 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 thanor 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 the 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:
1 1~8032
Table II
K L (-in) N (cells/in )V (in ) X (in)
2.40 3 9 75 0O273
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.
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1 1780'~2
The fire box 110 has in the center of its front wall 113
a large 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 edgesr respecti~ely, 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,
10 support the doors 124 and 125 so that 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
20 124 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
~ ~78032
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
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l 178032
plate 146 is swung from its closed, ,f~ull line position to its
open or broken line position as- shown in ~i~g. 10~ wherein the
upper ed~e o~ plate 146 comes to rest against the support plate
151. ObViously whenever the door 125 is closed, it xeengages
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 plate 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 lla.
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 foxmed 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 illustr~ted),
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 1&4. The forward,
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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 rearwàrdly
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
latter 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
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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 part 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
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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 two, 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.
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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. Tne 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 2C3
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
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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.
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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 edge 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.
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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.
~ owever, it has been found that when a converter 182 of
the type disclosed herein is employed, additional and more
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I 1~803~
compl ~ 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 conv~rter,
when, operative will clean the glass of any deposits through high
intensity radiant heat.
From the foregoing it will be apparent that the present
invention provides a relatively simple and inexpensive means for
effecting substantially 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
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 fuelsl including coal provided
the usual cautions are taken to prevent the escape of noxious fumes.
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