Note: Descriptions are shown in the official language in which they were submitted.
This relates to improvements in solid fuel devices
particularly wood burning -furnaces.
Background of the Invention
It has been recognized that a serious problem with
wood burning furnaces is the effects o-f incomplete combustion.
Incomplete combustion results in the emission o-f pollutants,
the deposition of the products of the incomplete combustion
on the various elements within the furnace and in failure to
achieve peak ef-ficiency. A number of proposals have been made
to reduce the level of uncombusted materials given off by
solid fuel burning devices including the use of secondary
combustion chambers.
It has been discovered that by passing the flue gases
containing the products of incomplete combustion through a
tunnel the walls of which have been rendered incandescent by
the passage of hot flue gases therethrough, a substantial
increase in the pyrolysis of the flue gases occurs, thereby
resulting in reduction of the level of uncombusted materials in
the gases.
The device contemplated for carrying out this method
utilized a straight -tunnel having relatively thick walls
composed of refractory material and connecting a combustion
chamber to a heat exchanger base portion~ Because the tunnel
; could not be less than a certain minirnum length in order to
provide aclequate dwell time to complete pyrolysis, there resulted
a furnace which was relatively large because o-f the necessary
separation of these two chambers to accommodate the connecting
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tunnel. Such a device was also hea~y due to the relati~ely
thick walls of the tunnel.
Brief Summary of Invention
In apparatus according to the present invention,
there is provided a tunnel which is positioned in the base of
the heat exchange chamber. Such positioning of the tunnel
reduces the spacing be-tween the combustion chamber and the base
of heat exchange chamber thereby reducing dimensions, amounts
i of materials and weight of the furnace. Moreover by positioning
the tunnel in the base of the heat exchange chamber the heat
exchanger located directly above receives heat not only -from
the gases passing through it but it also receives radiant
energy directly from the tunnel walls.
The tunnel according to the invention has a foldecl
construction which serves effectively to lengthen it to permit
adequate dwell time by the gases, while at the same time
reducing its overall length in the direction of the tunnel
axis. This folded construction also causes the heated flue
gases to impinge on the outsides of the tunnel walls thereby
reducing the time required to bring the tunnel up to temperature
; during start-up.
It is a further feature of this invention that a
single air source is used for providing air for effecting a
draft and for providing air to the combustion chamber. Improved
efficiency is achieved by preheating the air fed to the
combustion chamber by passing it through a stainless steel
conduit passing through the heat exchanger chamber prlor to
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introduction into the combustion chamber.
In accordance wi-th the present lnvention there is prov-
ided apparatus for burning solid materials comprising a combustion
chamber; a fuel chamber communicating with the combustion chamber;
a heat exchange chamber situated laterally o~ the combustion cham-
ber, the heat exchange chamber including a heat exchange means; a
tunnel connecting the combustion chamber to the heat exchange
chamber, the tunnel being adapted to conduct flue gases from the
combustion chamber to the heat exchange chamber, the tunnel inclu-
ding walls having inside and outside surEaces, at least one of thewalls being adapted to transmit energy by radiation from the out-
side surface thereof to the heat exchange means.
In accordance with another aspect of the invention there
is provided apparatus for burning solid materials comprising a
combustion chamber; a fuel chamber situated above the combustion
chamber and communicating therewith by way of an opening in the
top of the combustion chamber; a heat exchange chamber situa~ed
laterally of the combustion chamber, the heat exchange chamber
including a heat exchange means; a tunnel connecting the combustion
chamber to the heat exchange chamber, the tunnel being adapted to
conduct flue gases from the combustion chamber to the heat exchange
chamber t the tunnel being adapted to cause secondary combustion in
the gases during passage therethrough, the tunnel including walls
having inside and outside surfaces, at least a portion of the pas-
sage being situated in the combustion chamber; at least one wall
being adapted to transmit energy by radiation from the outside
thereof to the heat exchange means.
This invention is particularly suitable for use in wood
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burning furnaces however the principle is applicable to achieve
a greater degree of combustion in other devices for burning
solids, such as incinerators.
In drawings which illustrate embodiments of the
invention,
Figure 1 is a side view partly in sections of a furnace
incorporating a refractory ba~e and tunnel in accordance with the
present invention,
Figure 2 is a plane view of the refractory base and
tunnel in accordance with the present invention,
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Figure 3 is a section of the line AA o-f Figure 2.
Figure 4 is a perspective view of the upper portion
of the tunnel shown in the previous Figures.
Referring to Figure 1 there is illustrated a furnace
having fuel chamber 14. The steel walls of the fuel chamber
are surrounded by water contained in tank 13. The contact of
the water with the outside walls of the fuel chamber serves
to prevent the fuel chamber from becoming so hot as to cause
combustion of the wood therein. The hinged cover 10 is
adapted to open to permit access to the fuel chamber 14 for
loading wood therein. A mechanical linkage 30 connects the
fuel chamber cover 10 to the air source 15.- A ball valve (not
shown) in the air source 15 is operated by the linkage 30 and
serves to cut off charge air to the furnace when the fuel
chamber cover 10 is opened. Elimination of charge air when
the cover 10 is opened prevents the discharge of sparks and
- smoke through the upper opening of the fuel chamber 14.
As combustion of the wood takes place in the combustion
i~ chamber 3, unburned wood from the supply in the wood chamber is
continuously fed downward to the combustion chamber 3 by gravity.
Combustion chamber 3 is situated below the fuel
chamber 14 and in direct communication with it. The combustion
chamber 3 is supplied with air for combustion by air source
15 via air supply pipe 17. The air supply pipe 17 is composed
of stainless steel and is adapted to withstand high temperatures
while at the same time conducting heat from the outside to the
air passing through it.
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As will be seen from Figures 2 and 3, pipe 17 is
located in the centre of the heat exchanger base aboYe the
tunnel. Thus the pipe 17 is subjected to the high temperature
atmosphere of the heat exchanger chamber which causes heating
of the air being fed through the pipe 17 to the combustion
chamber.
~ eferring to Figures 2 and 3, the walls of the
combustion chamber 3 are composed of castable refractory
material and are lined with an insulating refractory material.
The comhustion chamber 3 is connected to the tunnel 10 via
opening 9 in the wall ~. The main part of the tunnel 10 is
bounded by sloping 100r 20, vertical walls 7 and 8 and
sloping top wall 5. The top and vertical walls of the tunnel
are composed of castable refractory material and are preEormed
as a unit. The top ~all 5 extends beyond the vertical walls 7
and 8 both laterally and in the direction o:E travel of the
gases to effectively extend the tunnel. The top wall 5 is
tapered by edges 11 and 12 at the gas exit end of the tunnel.
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B ~ ==~G~ngc~s ~1 ~rc located in the heat exchanger
chamber above the tunnel and consist of vertically oriented
tubes 21 through which the flue gases pass upwardly. The outside
walls of the tubes 21 are surrounded by water and are adapted
to conduct heat from the flue gases to the water. A forced
draft inducer 16 which is fed by air from air source 15 assists
movement of the 1ue gases through chimney 18.
In operation, fuel chamber 1~ is loaded with wood which
is fed by gravity into the combustion chamber 3. Air -from the
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air source 15 is fed via pipe 17 through the heat exchange
chamber where it is heated, to the orifice of pipe 17 in the
combustion chamber to provide the necessary oxygen for combustion
oE the wood. The air is injected at a pressure of between 3
and 14 inches of water depending on the desired output, in the
direction opposite to the direction of movement of the exiting
gases. By injecting the air in such direction-the necessary
turbulence and high temperatures are produced to allow combustion
to proceed at a very high rate. The movement of the injected
air also serves to remove the ash from the combustion area,
exposing the surface of the wood to the combustion process.
Since the period during which the combustion gases
driven off from the burning wood remain in the combustion
chamber is not sufficient to produce complete combustion
thereof, the gases moving out of the combustion chamber 3
through opening 9 in wall ~ and into tunnel 10 may carry with
them a substantial quantity oE gaseous materials in relation to
which complete combustion has not taken place. After a period
of start up of the furnacel the hot gases passing through the
tunnel 10 cause it to become incandescent. As gases continue
to move through the tunnel 10, the high temperatures caused
by the incandescent state of the tunnel produce additional
combustion of uncombusted materials. The walls and the floor
of the tunnel are maintained in an incandescent state by the
gases passing through and the combustion that is taking place,
in the tunnel. The degree of combustion which takes place in
the tunnel is a function of the temperature oE the entering
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gases, the temperature of the tunnel and the dwell time of the
gases in the tunnel. The latter is a function of the pressure
differential across the length of the tunnel and the tunnel
dimensions. It has been found that satisfactory results are
achieved using a heat exchange chamber base twelve inches wide
in the direction of the tunnel axis and with tunnel temperatures
in the range 1300 to 1800F and combustion chamber temperatures
in the range of 1300 to 21Q0F. The effective tunnel length
will of course be greater than twelve inches (the width of
the cham~er base) by reason of the folded tunnel construction
of the present invention.
As the gases move through the tunnel 10 and reach
the end thereof they are no longer confined by walls 7 and 8,
and tend to move laterally outward and upward. This movement
causes the hot flue gases to contact the outside o-f side walls
7 and 8 and to some degree the outside to top wall 5. As a
result, heat is transferred to the outsides of these walls. 'This
serves to assist a more rapid heating of the tunnel walls to
operating temperatures during start up. I'he incandescent
2Q state of the tunnel walls produces appreciable radiation of
energy to the heat exchanger thus aiding the transferred
energy to heat exchanger and the heating of the surrounding
water.
After emerging from heat exchanger base chamber 6
the gases move upwardly through heat exchanger tubes 21 where
heat from the gases is transferred via the walls of the tubes
21, to water stored in the surrounding tank. The heated water
may be used for various purposes.
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Movement of the gases up through chimney 18 is
assisted by means draft device 16 to which air i5 supplied by
alr source
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