Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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S P E C I F I C A T I 0 N
The invention relates to a device for the col-
lection and discharge of the ash generated in wood fur-
naces, in particular in so-called stoker furnaces in which
the fuel is placed in a combustion chamber whose bottom is
cup-shaped and defined by an air permeable ring of grate
bars.
In these known wood furnaces, the combustion air
is pushed under pressure through the grate bars. The
combustion takes place in two stages. The precombustion
takes place in the cup while an a~ter-combustion or residual
combustion takes place in the combustion chamber located
above the cup. In such a combustion, the wood wastes
develop many combustible gases which burn as second stage
in the combustion chamber of a boiler while secondary air
1~ is being fed in.
The advantage of such a furnace is that it can
be shut off for hours without the embers dying. A time
switch can make certain that the furnace is turned on
briefly in certain time intervals when the shutoff periods
are too long. ~nother advantage of such wood furnaces is
that they can be installed in a great variety of modifica-
tions, or instance with a boiler.
The combustion in such furnaces is very good,
the automatic control simple and effective, and the
furnaces can be built at competitive prices.
However, one considerable disadvantage of such
furnaces is that they still generate a great amount of
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ash which collects in the stoker pan and can be removed
and transported away with difficulty only. This problem
contributes materially to such wood furnaces being limited
in their size as well as the kinds of fuel to be burned.
While bark, for instance, can be burned excellently in
the wood furnaces, its great ash content limits the
applicability of such furnaces. In continuous operation,
ash is generated by the ton when burning bark.
It is an object of the present invention to remedy
this situation and create a device for the collection and
discharye of ash wherein the flat portion of a cup-shaped
combustion chamber bottom is replaced by an ash collection
chamber bounded downwardly by a flat bearing surface for
a pusher slide frame in which is provided centrally a channel
extending transversely or diagonally and a discharge screw
rotatably mounted therein.
According to the invention, this problem is solved
in that the flat portion of the cup-shaped stoker bottom
is replaced by an ash collection chamber defined down-
wardly by a flat bearing surface for a pusher slide framein which is provided centrally a channel and a discharge
screw or similar discharge member rotatably mounted
therein. The device replaces directly the flat bottom
of the cup-shaped stoker panO When starting the wood
furnace, the space under the grate bars, i.e., the ash
collection chamber, fills with fuel. After a certain
operating period, ash forms which trickles down and grad-
ually displaces the fuel in the ash collection chamber
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upwardly. When enough ash has accumulated, the device
is started. It transports the ash collecting on the
bearing surface into the channel layer by layer by means
of the pusher slide frame, and the screw or similar
discharge member conveys the ash in the channel from
the area of the wood furnace to a collecting point or to
a removal conveyor belt or the like. The device may
operate continuously at a low fre~uency of pusher slide
frame motions, or also intermittently. It may be auto-
matically controlled as a function of the ash generated
or as a function of the fuel fed in.
Advantageous further developments are evident
from the sub-claims.
The invention is explained below in greater
detail with reference to schematic drawings depicting
one embodiment example.
Fig. 1 shows, in vertical section, the lower
part of a wood furnace of the type in ~uestion with a
device according to the invention, and
Fig. 2 a horizontal section of the combustion
chamber of the furnace per Fig. 1 with a top view of the
device according to the invention.
The wood furnace 1 has a combustion chamber 2
defined in the usual manner by refractory linings. At
its lower end the combustion chamber is bounded by a
cup-shaped stoker bottom 4. It consists in the usual
manner of a ring 5 of grate bars 6 which are slightly
inclined from vertical, determining with their lower ends
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the narrowest cross section 8 in the bottom area of the
combustion chamber under formation of gaps 7. On the
one hand, the fuel is fed through the grate bars, e.g.,
through a tube and a screw 9. On the other hand, com-
bustion air under pressure is blown into the combustionchamber through the gaps 7.
The narrowest surface area 8 of the stoker
bottom 4 is normally defined by a flat, closed bottom
section. According to the invention, this flat bottom
section, defined by the narrowest passage plane 8, is
omitted so that a free passage is formed by an ash
collection chamber 10 located underneath the stoker
pan 4. As evident from Fig. 1, the ash collection
chamber 10 expands considerably to all sides as compared
to the narrowest point 8 of the stoker pan 4. Towards
the bottom, the ash collection chamber 10 is defined by
a flat bottom surface 11 which extends across the entire
cross section of the ash collection chamber 10. Provided
in the bottom is an approximately centrally disposed
collecting channel 12 extending transversely or diametri-
cally, in which a drivable discharge member, in particular
a screw 13, 14 is rotatably mounted. Resting directly on
the flat bottom surface 11 is a pusher slide frame 20.
It is supported by a push bar 15 which protrudes through
the side wall of the ash collection chamber to the outside,
where it is connected via an articulated coupling 16 to
a drive mechanism, preferably a double-acting pressure
medium cylinder 17, capable of moving the push bar 15
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back and forth along its lengthwise direction and over
a predetermined stroke length, as indicated by the double
arrow 25. The free end 13 of the push bar is the slide
frame 20 which, in the top view per Fig. 2, has a pointed
oval contour. In the example shown, the slide frame
practically has two pushing sections 21 and 22, shaped
symmetrical to the longer ellipse axis. Each pushing
section is curved in conformity with the curvature of the
outline of the ash collection chamber 10. The contour
edge 23 facing the outside is beveled outwardly and down-
wardly in the manner of a blade while the contour edge 24,
parallel thereto and facing the inside, is steep or per-
pendicular to the bottom surface 11.
During the reciprocating motion according to
the double arrow 25, the pusher slide frame 20 is moved
back and forth accordingly, whereby it wipes over the
entire bearing surface 11. Due to these motions, the
ash lying on the bearing surface 11 is taken along about
at the level of the thickness 37 of the frame and con-
veyed into the channel 12 where th~ ash can be trans-
ported away to the outside by the screw 13, 14. This
results in the ash being discharged essentially uniformly
over the extent of the ash chamber and thus in an even
lowering of the ash column which extends through the ash
collection chamber 10 to the level of the stoker pan 4
where the first actual combustion takes place.
To prevent the fuel from falling directly into
the channel 12 when starting, the channel may be covered
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upwardly by a deflection element. In the example depicted,
a permanently installed, roof-shaped deflection element 36
extending along the channel on both sides of the push bar
15 is provided, spaced rom the channel according to the
thickness 37 of the slide frame.
As an alternative, a flat ash grate may be dis-
posed in a plane between the narrowest plane 8 o~ the
stoker pan and the bearing surface 11 of the ash collection
chamber 10. The configuration is preferably such that the
ash grate 31, 32, consisting of several sections, is mov-
able back and forth to a limited extent below the narrow-
est cross-sectional surface 8 of the stoker pan, as
indicated by the double arrow 35. Provided for this pur- ~
pose are grate guiding means 30 and a driving coupling
between the pusher slide frame 20 and the ash grate.
In the example shown, a driving lug 34 project-
ing upwardly is provided at the free end of the push bar
15. The ash grate 31, 43 has -two driver stops 32, 33
which are mutually spaced, extend perpendicular to the
axis of the wood furnace and may be designed as a frame
member projecting downwardly. During its reciprocating
motions according to arrow 25 the pusher slide frame 20
takes the grates along for a short distance shortly before
reaching each reversal point. This shaking motion assures
that the ash reliably falls through the gaps in the grates
31, 32. In this case, there is no need for a cover 36 for
the channel 12 as the fuel pieces cannot drop under the
grate plane into the ash collection chamber 10.
