Catalytic stove

A catalytic stove comprised of a housing having a fuel-burning chamber and an effluent chamber. The effluent chamber is separated from the fuel-burning chamber by a common wall. The wall is at the top of the fuel burning chamber and is inclined to form a cathedral or domed chamber ceiling. Air inlet ports are located in the fuel burning chamber and draft air is introduced to burning fuel at substantially the same rate from each port. The effluent from the fuel flows to a catalyst in the top of the fuel burning chamber. The effluent flows substantially directly from the fuel to the catalyst without undersirable eddying thereby preventing the effluent from cooling and condensing into creosotic droplets. The catalyst assists in burning an increased percentage of the flue gases. An air diffuser is provided contiguous to the catalyst and provides an air mix with the effluent from the burning fuel to further facilitate oxidation in the catalyst.

BACKGROUND OF THE INVENTION 
This invention pertains to the art of fuel-burning devices and, more 
particularly, to a fuel-burning device including an oxidation catalyst. 
The invention is particularly applicable to woodburning stoves. The 
invention can be readily used in other fuel burning appliances in which an 
oxidation catalyst is employed, particularly in other solid fuel 
appliances. 
Conventional woodburning stoves, fireboxes or fireplaces do not burn all 
the combustible substances of a conventional fuel such as wood. The smoke 
and gas effluent of a wood fire normally contains creosotes and 
substantial quantities of oxidizable substances such as combustible gases. 
Such gases can condense and become attached to a flue passageway during 
the emission of the effluent to the environment. Continued condensation 
and attachment may result in a particularly undesirable fire hazard in a 
flue or chimney, substantially hampering the efficiency of the burning 
device, and polluting the atmosphere. 
In a wood burning operation, at a temperature of 250.degree. F., oxidizable 
effluent gases are completely fogged (condensed droplets) while at 
450.degree. F. the effluent is 70-80% gas with the remainder comprising 
condensed droplets. Since the condensed droplets will not oxidize in a 
catalyst, an effluent reheating method or element has been necessary to 
raise the temperature of the effluent such that the condensed droplets 
would again become gaseous. Alternatively, the effluent was kept extremely 
hot, often by overfiring the stove. 
Oxidation catalysts have been employed in combination with other fuel 
burning or incinerator devices for combusting smoke, creosotic flue gases 
and other objectionable components in the effluent. In order to promote 
such combustion, some prior art devices have employed various methods to 
reheat creosotic gases which have condensed to droplets during travel from 
the burning fuel to the catalyst. 
In other catalytic woodburning stoves found in the prior art, it has been 
necessary to operate the stove at a temperature higher than was desirable 
for residential operation, in order to operate the catalyst device without 
reheating the effluent. Such stoves would often consume six or more pounds 
of wood per hour in order to prevent some of the effluent from cooling to 
a temperature near 250.degree. F. and condensing as it passed from the 
woodburning flame to the catalyst. Substantial eddying of effluent along 
the stove top and side walls would cause the effluent to cool. To prevent 
such cooling an undesirably high temperature had to be maintained so that 
the effluent would contain predominantly gases as opposed to condensed 
creosote droplets. 
The present invention contemplates a new and improved device which 
overcomes all of the above referred to problems. It provides a new 
catalytic stove which is simple in design, economical to manufacture and 
adaptable for use in residential environment. It is easy to install, and 
it operates at a temperature which is not undesirably hot, unsafe, or 
wasteful of energy. The present invention provides improved catalytic 
oxidation of effluent from a burning fuel. 
The present invention combines a unique catalytic dome with a uniquely 
controlled and directed air flow. It typically lowers fuel useage from an 
objectionable six or more pounds per hour (a burning rate higher than 
normally encountered in homes) to a heretofore unobtainable two pounds per 
hour (a rate commonly desired in homes). This economy greatly expands the 
operating range of a catalytic woodburning stove. 
BRIEF SUMMARY OF THE INVENTION 
The present invention is a fuel-burning apparatus or stove comprised of a 
housing containing a fuel-burning chamber. The stove has means in the 
chamber for supporting the fuel which is to be burned. Access means are 
provided so that fuel may be easily placed in the stove. The stove also 
has a flue port which allows the products of combustion to leave the 
housing. The stove contains a fuel-burning chamber top wall which has a 
generally centrally-disposed port through which effluent may move to the 
flue port. A catalyst device is located contiguous to the port in the 
chamber top for catalytic burning of effluent flue gases. Air inlet 
openings into the fuel-burning chamber allow an equal velocity draft air 
to enter both sides of the stove. 
The air inlet ports are disposed contiguous to the fuel substance. They are 
in communication with an air passageway which has a selectively 
controllable air opening to the environment of the stove. The selectively 
controllable air opening includes a thermostatically controllable air 
opening closure device. 
The stove is designed so that effluent emitted by burning fuel remains in a 
substantially gaseous state in the fuel burning chamber and then is 
eliminated by the catalyst before the effluent leaves the housing. 
The top wall port of the fuel chamber is located above an intersection of 
the top wall and the side walls of the fuel chamber. The top wall of the 
fuel chamber is domed. 
In accordance with a more limited aspect of the present invention, the top 
wall of the fuel-burning chamber includes a selectively operable baffle 
and baffle opening disposed for communication with the flue port. 
In accordance with yet another aspect of the present invention, an air 
diffuser is disposed contiguous to the catalyst device and includes an air 
passageway communicating the air diffuser with an air inlet port. The 
diffuser is located between the catalyst and the means for supporting the 
fuel and the diffuser enhances oxidation of effluent gases. 
One benefit obtained by use of the present invention is that oxidizable 
elements are substantially eliminated from the stove effluent. 
Another benefit is that overfiring or the use of secondary heating methods 
are unnecessary in order to provide an effluent which is substantially gas 
as opposed to condensed droplets. 
Yet another benefit is that catalytic action will take place at stove 
outputs low enough to be comfortable to room occupants. In addition to 
better comfort, significant energy savings will develop from elimination 
of overfiring. 
Other benefits and advantages for the new catalytic stove will become 
apparent to those skilled in the art upon a reading and understanding of 
this specification.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings wherein the showings are for purposes of 
illustrating the preferred embodiment of the invention only and not for 
purposes of limiting same, the figures show a fuel-burning apparatus 
comprising a catalytic stove 10 preferably employed for heating a personal 
residence. 
More specifically, and with reference to FIGS. 1 and 2, stove 10 includes a 
housing 12 having a generally box-like overall configuration. The housing 
12 includes a top wall 14, a bottom wall 16, a front side wall 18, a back 
side wall 20, a first end side wall 22 and a second end side wall 24. The 
stove 10 may be spaced apart from a support surface with support legs 26. 
A fuel-burning chamber 30 is included in housing 10 for receiving fuel 
such as wood logs 32. Conventional means are provided for supporting the 
fuel substance for burning in the chamber 30 and may comprise a bottom 
wall 16 of housing 10 or a conventional support grate (not shown). Access 
to the fuel-burning chamber 30 is provided through conventional doors 34 
in front side wall 18. The doors may swing open or close and lock. A flue 
port 36 is provided in housing top wall 14 to provide for egress of 
effluent from the housing. Disposed intermediate of the top wall 14 and 
bottom wall 16 is a fuel-burning chamber top wall 40 depending from side 
walls 18, 20, 22 and 24. The top wall of the fuel chamber has a generally 
centrally-disposed port 42 for effluent communication to flue port 36 
through an effluent chamber 44. Port 42 is preferably located above the 
intersection joints 46 of the top wall of the fuel-burning chamber and the 
side walls such that the top wall 40 is inclined to comprise a cathedral 
or domed chamber type ceiling for fuel-burning chamber 30. The 
fuel-burning chamber top wall 40 preferably comprises four trapezoidally 
configured sheets joined to a fuel-burning chamber top wall port plate 48 
which includes the chamber port 42 (FIG. 3). 
A catalyst device 56 is located contiguous to the fuel-burning chamber top 
wall port 42 for catalytic burning of effluent flue gases. The catalyst 
device 56 preferably comprises a honeycomb configuration constructed of 
platinum coated or palladium coated honeycomb or screen elements. 
Suspended just above catalyst 56 is a catalyst cap member 57. This catalyst 
cap can be a plate or it can be formed of insulation such as fire brick or 
other suitable insulating material. The plate acts to raise the 
temperature of the top part of the stove, i.e., effluent chamber 44, thus 
enhancing the combustion efficiency of the catalyst. The plate also acts 
to protect the top of the stove itself from excess heat coming from the 
catalyst. The net effect of the plate acting in concert with the 
insulation 59 around the catalyst is to create what substantially is a 
secondary combustion chamber. 
Air inlet ports 60 and 62 to the fuel-burning chamber 30 are preferably 
provided contiguous to the fuel substance. Air inlet ports 60 and 62 are 
communicable with an air passageaway 64 extending along at least the 
bottom wall 16 and having a selectively controllable air opening 66 
exposed to the environment of stove 10. Preferably the selectively 
controllable air opening 66 includes a thermostatically controllable air 
opening closure device 68 for controlling the amount of air which may be 
drawn into chamber 30 through ports 60 and 62 and opening 66. Ports 60 and 
62 are positioned such that the air drawn into chamber 30 through ports 60 
and 62 is introduced into the chamber at the same velocity. The ports are 
positioned substantially opposite each other and are provided with 
suitable deflectors 63. 
It should be understood that a plurality of opposed inlet ports may be used 
but they should be positioned and sized so that substantially the same 
amount of air from each port is directed toward the approximate center of 
the fuel being burned. In this way, the air from each of the ports will 
have a tendency to collide and turn upward toward the catalyst. It is not 
a departure from the spirit of this invention if several smaller ports on 
one side of the fuel are opposed to a larger port on the other side of the 
fuel as long as the net effect is to direct substantially equal and 
opposite air flows to the center of the fire. 
With particular reference to FIGS. 3 and 4, a selectively operable baffle 
70 and baffle opening 72 are included in the fuel-burning chamber top wall 
40 to provide an alternate egress port for effluent from the fuel-burning 
chamber 30. Preferably, baffle 70 comprises a swinging door which is 
operable with an operating handle 74 for swinging the baffle 70 about its 
hinges 76. In operation, baffle 70 is opened during igniting of the fuel 
supply 32 and initial heatup of the stove 10. It is normally kept open 
until the catalyst device 56 becomes operable to oxidize effluent gases. 
The baffle is preferably also opened before the stove door is opened. 
For purposes of providing a separate air inflow near the catalyst device 56 
to facilitate oxidation of effluent gases in the catalyst device 56, an 
air diffuser 82 is located contiguous to the catalyst device 56 
intermediate of the device and the bottom wall 16 of housing 12. A 
diffuser inlet port 84 (FIG. 2) provides air to the diffuser through a 
diffuser air passageway 86, which preferably extends along the second end 
side wall 24 and the fuel-burning chamber top wall 40 to the diffuser 82. 
With particular reference to FIGS. 5, 6 and 7, it is seen that the diffuser 
comprises an outer ring 88 and a plurality of radially extending inner 
tubes 90. Both the ring 88 and the tubes 90 include a plurality of air 
bores 92 through which air may pass for mixture with the effluent of the 
fuel-burning chamber 30 for better oxidation in the catalyst device 56. 
The air bores 92 of the inner tubes 90 are directed towards the catalyst 
56 and the air bores 92 of the outer ring 88 are directed radially inward 
to facilitate better mixing with the rising effluent. 
It should be realized that the air diffuser may take a number of different 
forms. For example, it could be comprised simply of a square or round 
plate containing a number of holes. The plate is placed at the outlet end 
of the secondary air supply. If the diffuser is in the form of a plate, it 
may be placed either above or below the secondary air tube. In any event, 
the plate or diffuser does several things: (a) it creates turbulence and 
hence mixing of the flue gases with secondary air; (b) it becomes hot, in 
part from radiation from the catalyst, and this heat, in turn, greatly 
assists in additionally heating the fuel gas and secondary air mixture 
before they enter the catalyst. Typically, fire box gases at 
400.degree.-450.degree. F. are raised to about 850.degree. F. The plate 
also tends to block about one-half of the catalyst's radiation from 
reaching the wood in the fire box. This substantially prevents the wood 
from excessively burning anaerobically. 
OPERATION 
With particular attention to FIGS. 2 and 4, the improved operating 
characteristics of the new catalytic stove will be specifically discussed. 
Cooling of effluent to form condensed creosotic droplets in conventional 
stove designs is at least partly caused by eddying of effluent from a 
burning fuel within the fuel-burning chamber prior to egress of the 
effluent from the stove. Upon cooling, the effluent becomes a fog of 
condensed creosotic droplets which is an obnoxious waste product to the 
environment and causes a dangerous creosote buildup in the flue pipe. In 
order for the catalyst device in prior art stove designs to be operable, 
it was necessary to burn the fuel at an excessively high rate to raise the 
temperature such that even though eddying was substantial, the effluent 
would not cool to a level where it would substantially be comprised of 
condensed creosotic droplets. Often this required the use of six or more 
pounds of wood per hour. 
The present invention provides a stove design which substantially reduces 
eddying of effluent and thereby substantially reduces cooling of the 
effluent between the time it is emitted from the burning fuel and the time 
it reaches the catalyst. The catalyst operates at a fuel use rate of about 
two pounds of wood per hour. This extremely efficient operation is 
achieved by combining an appropriately shaped catalytic dome with properly 
directed air inlet ports which supply a substantially uniform air flow 
into the fuel. 
Air inlet ports 60 and 62 in fuel-burning chamber 30 are disposed such that 
air jets will be drawn in through the ports 60 and 62 towards the burning 
fuel in an equal balance at substantially the same velocity for 
participation in the oxidation of the fuel. Effluent from the burning fuel 
is channeled along the side walls 18, 20, 22 and 24 and the top wall 40 to 
the catalyst device 56 in a manner which substantially avoids eddying at 
the fuel-burning chamber side walls. Eddying is avoided because of the 
smooth and generally straightforward flow along the side walls and because 
of the incline of the fuel-burning chamber top wall 40. Since eddying is 
minimized, cooling is minimized. The effluent is thus in a substantially 
gaseous state when it reaches the catalyst device 56, even when the fuel 
is burned at the relatively low burn rates which are desirable in personal 
residences. 
In one embodiment of the invention, the air flow through air inlet ports 60 
and 62 is selectively controllable at a single air opening 66 by 
selectively controlling the area of the opening 66 with an air opening 
control member 68. In the preferred embodiment of the invention, the air 
opening control member 68 is automatically controlled with a thermostat 
which senses the temperature of the stove fuel-burning chamber 30. The 
control automatically opens or closes the air opening 66 for regulating 
air flow thereby raising or lowering the temperature of the fuel-burning 
chamber 30. 
After the effluent has reached the catalyst 56, and oxidizable gases in the 
effluent have been oxidized in the catalyst device, the effluent is 
directed to the flue port 36 through the effluent chamber 44 for egress 
from the stove 10. 
In the preferred embodiment of the invention, the air diffuser 82 operates 
to mix secondary air drawn in through the diffuser air inlet port 84 with 
the effluent prior to the effluent's encounter with the catalyst device 
56. This facilitates oxidation of the oxidizable flue gases in the 
catalyst device 56. It should be noted that this secondary air supply is 
pre-heated due to the location of the diffuser air passageway 86. Upon 
leaving the burning fuel 32, the effluent is normally substantially devoid 
of oxygen and the addition of air with the effluent provides the 
additional necessary oxygen for oxidation. 
The invention has been described with reference to the preferred 
embodiment. Obviously, modifications and alterations will occur to others 
upon the reading and understanding of the specification. It is my 
intention to include all such modifications and alterations insofar as 
they come within the scope of the appended claims or the equivalents 
thereof.