Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
7-~ 5
The pr~sent invention relates to a wood burniny Eurnace
or assembly Eor the combustion of Euel in the Eorm of slabs or
log lengths in continuous manner.
Furnaces or combustion assemblies having a combustion
chamber with a fuel feed and primary and secondary air inlet open-
ings and an ash receptable beneath the combustion chamber are well
known.
However, such known assemblies are not suitable for being
continuously fed with and the burning of wood fuel which is in the
form of slabs or log lengths in the order of approximately 1 to 1.5
metres long.
Moreover, the continuous combustion of fuel of this type
presents difficulties particularly with respect to the following:
1. The rate of feed of the fuel must be consistent with
the rate of combustion, and
2. Burning of the wood fuel along a feed pass and prior
to its introduction into the combustion chamker must be prevented.
In addition such a furnace must be capable of successful operation
and control whether the fuel be dry, or damp, or wet, and in this
regard, and when the fuel is wet or damp,environmental considerat-
ions are important and the formation and discharge of smoke and other
pollutants must be minimized as much as possible.
It is absolutely essential that these problems and diffi-
culties be overcome if one is to satisfactorily continuously operate
a wood burning assembly which is continuously fed with fuel.
The prime purpose of the present invention then is to pro-
vide a wood burning furnace or assembly which avoids the inherent
disadvantages of furnaces of this general type and which enables
the continuous combustion of fuel in the form of slabs or long
. ~ .
.
i ~ ~;47~
lengths which are Eed to a combustion chamber in continuous
manner and which inhibits combus-tion or pre-igni-tion of the fuel
during the travel along the feed path and before introduction into
the combustion chamber.
Applicant has established through experimentation that
the present assembly (depending upon the length of the feed path
and the volume of fuel) provides continuous operation for up to
10 to 12 hours with only two fillings of the assembly. In the pilot
furnace constructed and operated, the feed supply tunnel was approx-
imately four metres long having a cross-section area of approximately
.25 square metres.
During the combustion of fuel which is continuously fed
to a combustion chamber, the danger of pre-ignition and combustion
of the fuel prior to its introduction into the combustion chamber
is always present. This is particularly true in the case of dry
fuel, but the danger still exists even when the fuel is wet or damp,
inasmuch as the fuel becomes dried during its travel in the feed
tunnel as a result of heat radiating from the combustion chamber
and the resultant heating of the completed assembly. Drying of
wet or damp fuel in the feed tunnel is also increased as a result
of the spaces or gaps between the pieces of wood in the feed tunnel,
and which enable the circulation of warm drying air. To minimize
the extent of these gaps or spaces, it is preferred that at least
the bottom portion of the combustion chamber and at least an adja-
cent portion of the feed tunnel being of semi-circular cross-sec-
tion so that the fuel can become compacted as much as possible.
The more the fuel is compacted, the less is the danger of pre-
ignition or pre-combustion and the presentation of fuel pieces in
concentrated manner into the combustion chamber greatly enhances
~ .
~ 3 ~ 4 7 ~ r)
the rate of combustion.
The present invention avoids the inherent disadvantages
of the prior art arrangements and fully satisfies all requirements
for an assembly of this type by specifically providing a wood burn-
ing assembly for fuel in the form of slabs or log lengths
comprising a combustion chamber with a grate and primary
and secondary air inlet ports, and an ash receptacle beneath the
grate, and a grate closure plate slideably mounted with respect
to the grate enabling selected opening and closing thereof,
and a feed tunnel opening into the combustion chamber
and means within the feed tunnel to advance the fuel to the com-
bustion chamber
and a movable abutment plate in the combustion chamber
at a position opposite to the feed tunnel, the abutment plate being
interconnected with drive means for the means to advance the fuel
to control rate of advance of the fuel into the combustion chamber,
and means in the feed tunnel adjacent the combustion chamber to
inhibit combustion of the fuel prior to its introduction into the
combustion chamber.
The invention will now be more fully described with ref-
erence to the accompanying drawings wherein:
Figure 1 is a side sectional view of one embodiment of
the present invention;
Figure 2 is a sectional view taken along line II-II of
Figure l;
Figure 3 is a sectional view taken generally along line
III-III of Figure 1, illustrating a preferred embodiment;
Figure 4 is a side sectional view taken along line IV-IV
of Figure 3;
Figure 5 is a sectional view taken generally along line
--3--
~ lfi~7~1S
V-V oE Figure l;
Figure 6 is a side sectlonal view of a combust:ion chamber
and adjacent portion of a feed tunnel showing the arrangement of
air inlet control elements; and
Figure 7 is a side sectional view oE a preE~rre(l constrwct-
ion of the present inventive concept.
The accompanying drawings will now be discussed in detail
and wherein like reference numerals refer to like parts.
Numeral 1 indicates a feed tunnel which opens in the area
shown at 2 into a combustion chamber 9. The feed tunnel has a fill-
ing door 24, and the combustion chamber has door 3 and a grate 5 be-
neath which is positioned an ash receptacle 22.
A combustion gas discharge duct 21 is positioned above the
combustion chamber leading into a heat exchanger 25 which may be of
the air or water type. The heat exchanger 25 may be in the form of
a boiler, and due to environmental considerations a smoke and poll-
utant extractor may also be provided.
The feed tunnel 1 is provided with fuel advancing means
which may be in the form of an endless chain conveyor 20, positioned
within a safety hood 20'. The conveyor is driven by motor means
(not shown) and additionally may be provided with a crank '' for
filling purposes. The conveyor 20 carries conveyor plate 23 which
is pivotally mounted thereon for pivoting movement only in the di-
rection of arrow A as shown. The plate 23 is of a dimension which
generally fills the interior of the feed tunnel. The pivoted mount-
ing of the plate 23 enables the feed tunnel to be filled by insert-
ing fuel through door 24 and its securement against movement in a
direction opposite to arrow A enables it to advance wood fuel along
the feed tunnel during continuous operation of the conveyor 20 at
--4--
i ~ fi 4 7 ~1 r~
very slow speed. rrhe conveyor may be mountecl elther above the ~eed
tunnel as shown or beneath it, and the aclvancing mechanism may take
different forms such as a screw feed positioned in the bottom of the
tunnel to advance the wood to the combustion chamber. The conveyor
means continuously advances the wood at a very low rate of speed
dependent upon the speed of combustion of the wood within the com-
bustion chamber.
Positioned within the combustion chamber 9 opposite to
the entrance of the feed tunnel is a movable abutment plate 4 which
carries a rod 11 which extends exteriorly of the combustion chamber
to a position adjacent a limit switch 12. The abutmen plate 4 is
biased to the position shown in Figure 1 by the provision of spring
11'. Pressure against abutment plate 4 by the advancing wood pieces
moves the plate against the tension of spring 11, and the wood is
continuously advanced by the conveyor until such time as rod 11 con-
tacts limit switch 12 which is electrically interconnected with the
drive means (not shown) of the conveyor 20. Closing of the limit
switch 12 by rod 11 stops the conveyor drive, and commencement of
the conveyor drive occurs when the force of fuel against the abut-
ment plate 4 is removed (as a result of the burning of fuel) andthe rod 11 is withdrawn from the limit switch 12 under the action
of spring 11'. Interconnection between the limit switch 12 may
either be electrically as described or by the use of a Bowden cable.
Figure 2 shows that the interior of the feed tunnel may
be rectangular. However, and as shown in the preferred embodiment
of Figure 3, at least the lower portion of the combustion chamber
and the adjacent portion of the feed tunnel are of generally semi-
circular cross-section. This arrangement is also shown in Figure 5,
and from which it will be noted that the grate 5 is also of semi-
~ -5
1 ~ ~1 7 llr ~ ~
circular configura-tlcn and that khe grate ~ArS extelld irl the d:i-
rection of movement of -the fuel.
~ n a further preferred embodiment, the combustion chamber
and adjacent portion of the feed tunnel are provided with guide
members 10 with the dlstance between the oppositely positioned
guide members decreasing in the direction of advance oE the wood
fuel. The semi-circular configuration of the combustion chamber
and the provision of the guide element 10 compress the wood fuel
as much as possible within the combustion chamber providing for a
much more concentrated combustion.
Numeral 7 generally indicates various means to inhibit
pre-ignition and combustion of the fuel within the feed tunnel,
these means consisting of water sprinkler 13, dished depression
14, and at least one downwardly depending flexible skirt or feely
pivoted flap or flaps 26, all as clearly shown in Figure 4. These
elements combine to inhibit combustion of the fuel within the
tunnel in the area shown by numeral 27.
Operation of the water sprinkler 13 may suitably be con-
trolled by thermal probe 13' which controls supply valve 13''. se-
neath sprinkler 13 is provided a dished depression 14 which prefer-
ably is provided with an inclined surface 19 to guard against the
jamming of wood.
An upper covering for grate 5 is not considered to be
necessary inasmuch as the covering could become blocked by small
fragments of wood or bark. Due to the provision of inclined sur-
face 19, any accumulated fragments are simply moved ahead by the
advancing fuel into the combustion chamber.
Beneath grate 5 a movable grate closure plate 6 is pro-
vided and as shown in Figure 5, the plate 6 may have semi-circular
--6--
fi47~5
configurations.
Due to the constituent nature oE the wood fuel, and rela-
tive degree of dryness and thickness, uniform combustion of the
fuel is not possible with the result that slower burning pieces
will be advanced into the combustion chamber at a speed greater than
their degree of combustion, and without some control over the con-
veyor operation a jam of wood within the combustion chamber could
occur. Abutment plate 4 acting on limit switch 12 to stop conveyor
feed for a short time avoids this difficulty. As soon as pressure
against abutment plate 4 is removed due to combustion, the conveyor
resumes movement.
As discussed above, the guide elements 10 compact the ad-
vancing fuel as much as possible to provide a concentrated combustion
mass. In addition, however, the elements 10 act to lift the lower-
most pieces of the advancing fuel to a somewhat inclined direction
of feed so that they can advance further into the combustion chamber
before contacting abutment plate 4.
In addition to providing for a more concentrated combus-
tion, the semi-circular configuration of the combustion chamber and
at least an adjacent portion of the feed tunnel minimizes the spaces
between the fuel pieces and this has the effect of inhibiting com-
bustion of the fuel within the feed tunnel. Pre-ignition, and
pre-combustion of the fuel within the feed tunnel can be minized
by this arrangement but can never be completely eliminated. To
further inhibit this pre-combustion, the elements 7 as discussed
above are provided in the feed tunnel adjacent the combustion
chamber. The skirt or flap 26 which is freely pivotally mounted
lies against the upper pieces of wood and this minimizes the radi-
ation of heat from the combustion chamber along the feed tunnel.
-7-
`i I ~47~ 5
This skirt or flap can consist oE a Ele~xib1e skirt assembly, or a
number of small pivotally mounted metal rocls suspende~l in the Eorm
of a curtain or may consist of a number of pivotally suspended sheet
metal plates.
Since it is unavoidable that there will be spaces be-tween
the fuel pieces and through which ~ases of combustion and radiated
heat will pass, the present invention also incorporates a thermally
controlled water sprinkler 13 to extinguish any combustion which might
occur in the feed tunnel. Thermal probe 13' detects the presence of
combustion activating valve 13'' to sprinkle water on the fuel to
extinguish the fire. Once the fire is extinguished, and the tempera-
ture of probe 13' becomes reduced, valve 13'' closes. Any damping
of the wood as a result of the water sprinkling is not disadvantageous
but rather is to the contrary since the advancing wood fuel will
become more uniformly wetted resulting in a more uniform combustion
within the combustion chamber.
Dished depression 14 is provided to collect water dis-
charged from sprinkler 13. The water within the depression 14 be-
comes heated from the combustion chamber and is evaporated, which
provides a moist atmosphere within the feed tunnel which further
inhibits re-combustion.
Also of importance in obtaining optimum and continuous
efficient combustion is some provision for the control of air ad-
mitted into the assembly for the combustion process. As will be
seen in Figure 6, the assembly is provided with a primary air inlet
port 17 and a secondary air inlet port 17'. Also with respect to
Figure 6, a pivotally mounted probe arm 15 is provided and which
is movable from a vertical position to a raised position as shown
in Figure 6 as a result of being contacted by fuel logs and slabs
--8--
`~ t ~ 7~
30. The amount of air permitt~d to enter pr:imary air inlet port 17
is controlled by a damper plate 16, and both plate 16 and grate
cover plate 6 are interconnected with probe arm 15 by means of
linkages 15' shown schematically in Figure 6. The assembly as shown
in Figure 6 is fully loaded with wood 30 and the probe arm 15 is
fully elevated which fully opens damper plate 16, and grate cover
plate 6 is fully withdrawn which provides maximum admission of air
resulting in maximum combustion.
The secondary air inlet opening 17' and its related damper
may be controlled independently from the operation of damper plate
16 and grate cover plate 6.
However, as shown in Figure 6, damper plate 16 may be pro-
vided with an adjustment stop 17'' which enables precise control of
the amount of air admitted for combustion. If the feed tunnel is
only partially filled with fuel, grate cover plate 6 half-covers
grate 5, and damper plate 16 half-covers the primary air inlet
port 17 and the positioning of adjustment stop 17'' governs the
degree to which the secondary air inlet port 17' can be opened,
thus enabling precise air control.
If probe arm 15 is in a vertical position, this indicates
the absence of fuel with the result that grate 5 is closed by cover
plate 6 and primary air inlet port 17 is closed by damper plate 16
and secondary air inlet port 17' is substantially closed.
A preferred construction is illustrated in Figure 7, and
in this arrangement, the combustion chamber and adjacent portion of
feed tunnel 1 are formed as a unitary component. In this embodiment
the feed tunnel is water cooled by means of a water jacket, and the
surface 26 having the dished depression 14 therein is made of stain-
less steel.
_g_
17 ~I r~
The combustion chclmLler area o~ the assernbly silown in ~ig-
ure 7 is pre-Eerably Llned wi-th ~ire bricks 13 or other equivalen-t
material.
In Figure 7, the grate cover plate and adjustment plate
are not shown.
The arrangement as shown in Figure 7 has several a~vant-
ages. The water cooling of the feed tunnel minimizes the tempera-
ture within this area of the assembly, and -this inhibits pre-ignition
or pre-combustion. The fire brick lining within the combustion cham-
ber promotes longevity of the complete structure.
Also as shown in Figure 7, the bottom of grate 5 is posi-
tioned somewhat lower than as shown in Figure 1, and this assists
in maximum combustion. In the depression formed by the lowering
of grate 5, a layer of hot embers may form which are not disturbed
by the advancing fuel.
Within the scope of the present invention, it is possible
to replace abutment plate 4 and limit switch 12 by other suitable
arrangements associated with fuel pushing plate 23. With such an
alternative arrangement, increased resistance to fuel movement is
sensed, and the conveyor arrangement stopped until such resistance
lessens as a result of the combustion process.
With reference to Figure 1, the feed tunnel 1 could be
provided with a horizontal partition such as shown by the broken
lines 32. With this arrangement, independently operating conveyors
will be provided, and the various means discussed above to prevent
pre-ignition in the feed tunnel will be provided in each of the
compartments of the feed tunnel. With the feed tunnel divided into
upper and lower compartments, the conveyor in the upper portion
would move at a speed slower than the conveyor in the lower portion.
--10--
