Note: Descriptions are shown in the official language in which they were submitted.
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A wall structure for use in a furnace or the similar and a method for its
construction
The present invention concerns a wall structure for use in a furnace or the
similar, for
example a furnace for calcination of carbon bodies. The invention also
concerns a
method for constructing such a wall structure. The invention relates in
particular, but
not exclusively, to walls or partition walls with internal flue gas ducts,
i.e. flue walls.
Furnaces for calcination of carbon blocks to be used in the production of
aluminium
in accordance with the Hall-Heroult process may be designed with several
sections
arranged in two parallel rows. Such furnaces have a combustion cycle which is
moved in relation to the sections as the carbon material is calcinated. The
sections
are mutually and successively linked by ducts which conduct hot combustion gas
or
flue gas through the furnace structure. Each section can be divided into
several
smaller pits by means of flue walls or cassette walls. These flue walls are
provided
with several flue gas ducts, through which hot gas is conducted in order to be
able to
transfer heat efficiently to objects placed in the sections so that the
calcination
process becomes as homogeneous as possible. One problem with such furnaces, in
which the flue walls may extend for several metres both vertically and
horizontally, is
that the walls lose their parallelism over time as a consequence of
heating/cooling
cycles with large temperature differences. In the worst cases, bowing and
creep can
cause problems running the furnace in a satisfactory manner. This is on
account of
leakage and burn-off or problems inserting/removing objects as a consequence
of
large geometrical deviations in the pits.
CH 258544 shows a furnace in which a partition wall may comprise flue gas
ducts
(fig. 3). In this solution, an attempt is made to absorb longitudinal changes
in the
partition wall as a consequence of thermal heating/cooling in vertical joints
between
each brick, while the wall ends are fixed in place. One problem which will
arise over
time when using this principle for expansion/contraction is that particles
from material
placed in the furnace may be deposited in the joints and prevent the intended
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expansion fully or partially. If the wall has a certain clearance between
where it is
fixed and the rest of the structure of the furnace, this clearance will
gradually be
used up as the partition wall is extended permanently as a consequence of the
stated mechanism. Over time, therefore, a structure of this type may bow and
lose its parallelism. Further problems which may arise are that bricks may be
crushed fully or partially if the necessary expansion is not permitted after a
given
number of thermal cycles. A subsequent collapse of brick work may thus occur,
which will give rise to expensive repair work and put the furnace fully or
partially
out of operation for a period of time.
The above problems can be fully or partially avoided with aspects of the
present
invention. In accordance with an embodiment of the present invention, the
necessary expansion/contraction of the wall in its longitudinal direction as a
consequence of thermal cycles will be compensated for at at least one end of
the
wall, while the bricks are mutually locked to each other. Walls in accordance
with
an embodiment of the present invention have proved to be very stable over
repeated temperature cycles and the costs related to restoration of brickwork
and
possible stoppages of the furnace can thus be reduced considerably.
According to one aspect of the present invention, there is provided a wall
structure
for use in a furnace for calcination of carbon blocks, where the wall
structure is
exposed to cyclic thermal loads, the wall structure consisting of bricks of
refractory
material in several courses and comprising internal flue gas ducts, wherein
the
wall structure is able to compensate for longitudinal changes as a consequence
of
the cyclic thermal loads, which longitudinal changes are absorbed by a
connection
at at least one end of the wall structure, wherein the bricks in adjacent
courses are
offset in relation to each other and at least two of them comprise contact
elements
interacting with complementary contact elements of the bricks in the adjacent
course, wherein the contact elements being raised ends and recesses of the
ends
of the flue gas ducts respectively arranged in the bricks.
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The present invention will be described in further detail in the following by
means
of examples and figures, where:
Fig. I shows, in sections from above, details concerning the fixing of one end
of a
partition wall in relation to adjacent brickwork,
Fig. 2 shows, in sections from above, two parallel partition walls fixed at
their ends
to adjacent brickwork,
Fig. 3 shows a detail of the fixing of the ends of the partition walls,
Fig. 4 shows a detail of the end of the partition wall,
Fig. 5 shows another detail of the end of the partition wall,
Fig. 6 shows a detail of the structure of the partition wall.
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Figure 1 shows, in sections from above, brickwork 1, which may be a head wall
in a
furnace which may be built up from a row of individual bricks. The brickwork
shown in
the figure is adapted for the fixing of partition walls 3', 3", 3"', 3"" (only
four are
partially shown in the figure). The connection 2 between the partition wall 3'
and the
brickwork 1 is shown in an enlarged section in the lower part of the figure.
This
section shows an end brick 4 in the partition wall 3', a wedge brick 6 and an
anchor
brick 5 which constitutes part of the brickwork 1 and is permanently fixed to
it. The
wedge brick 6 may expediently have a rectangular cross-section and have side
surfaces 10, 10' which interact with the respective surfaces 8, 9 and 8', 9'
of the end
brick and anchor brick. The anchor brick 5 and end brick 4 are mutually
movable and
expansion of the partition wall of which the end brick is a part is permitted
via the
expansion joint 7 between the end surface 14 of the wedge brick and the
surface 11
of the end brick. Contraction, which may occur in the wall structure, can be
compensated for in that the end brick 4 is permitted to move away from the
anchor
brick 5 while the connection via the wedge brick 6 is maintained. In an
alternative
embodiment, the connection may consist of only two elements, i.e. without the
wedge
brick, in that a shape equivalent to the wedge brick is made as an integral
part of
either the anchor brick or end brick. The size of the expansion joint 7 is
adjusted
according to experience, depending on the brick material, operating conditions
with
the application in question or other conditions. The same will apply to the
longitudinal
contact in the connection 2 with regard to contraction of the wall structure.
It is expedient for the interacting surfaces in the connection 2 to run along
the full
vertical extent of the partition wall, i.e. all courses of bricks in the
partition wall and
equivalent courses in the brickwork are designed in the way shown in the
figure. One
advantage of such a design is that variations in the length of the wall
structure,
including in its vertical direction, can be absorbed in the connection 2.
In the example shown in the figure, the adjacent surfaces 13, 12 on the anchor
brick
and end brick 4 respectively are designed with chamfor so that the surfaces
create
a V-shape. The aim of such a V-shape is that particle material which may lie
against
the partition wall and which consequently may be pressed in against the
connection
can be drained out of this area in connection with an expansion (extension) of
the
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partition wall. It is also advantageous for the surfaces to have a V-shape
during
emptying/cleaning of the section. The angle between the surfaces may
expediently
be 300 or more. The size of this angle will, among other things, depend on the
material to be drained away and the surface pressure for which the surfaces
are
designed. Moreover, the connection 2 will comprise surfaces which form a seal
to the
extent that no problems will arise with the penetration of material into the
connection
during a contraction-related movement of the end brick 4.
Figure 2 shows, in sections from above, two parallel partition walls 114, 115
which
are fixed at their ends to adjacent brickwork 101, 102. In this embodiment,
the
connections are designed so that the anchor bricks 103, 104, 105, 106 are
shaped in
such a way that the wedge brick forms an integral part of the anchor brick.
The
anchor bricks thus interact directly with the adjacent end bricks 107, 108,
109, 110.
The figure shows that the pattern for bricks in the course in partition wall
114 is
different from that in partition wall 115 with regard to the design of the
bricks. In the
first partition wall, end brick 107 has one flue gas duct 111, while end brick
108 in
partition wall 115 has two flue gas ducts 112, 113. An equivalent arrangement
is
shown at the other ends of the partition walls. Moreover, brick 116 with flue
gas ducts
118, 119 in partition wall 114 has the same design as brick 117 with flue gas
ducts
120, 121 in partition wall 115, but the horizontal position in the respective
walls is
different.
By laying alternating courses equivalent to that shown in the section of
partition wall
114 and that shown in the section of partition wall 115 over each other when
building
up the partition walls, the bricks will be anchored to each other via courses
of bricks
above and below each other by means of interacting contact elements, among
other
things by means of the design of the flue gas ducts. This will be illustrated
in further
detail in figures 4-6.
Figure 3 shows details of the fixing of the ends of the partition walls, more
precisely
an expedient design of an anchor brick. The upper part of the figure shows, in
perspective, the lower side of a brick 150, while the lower part of the figure
shows, in
perspective, the upper side of an equivalent brick 150'. The bricks' external
shapes
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correspond to that shown in earlier figures, but figure 3 also shows
interacting
elements which are designed to ensure mutual retention between the different
courses of anchor bricks. In the example shown, anchor brick 150 is provided
with
rotationally symmetrical recesses 151 which interact with the rotationally
symmetrical
bosses 151' in anchor brick 150'. It is expedient for the interacting elements
to have a
semi-spherical shape or rounded cone shape. However, other geometrical shapes
may also be used. As the figure also shows, the bricks' protruding parts 153,
153'
(equivalent to the integral wedge brick in 6 in figure 1) are provided with
interacting
elements 152, 152'. In the embodiment shown, the element 152 consists of a
rotationally symmetrical recess, while the equivalent element 152' consists of
a
rotationally symmetrical protrusion. It is expedient for these elements to
have a
mainly cylindrical shape. A structure of anchor bricks as shown here will
produce
stable brickwork in which forces which may arise locally in, for example, one
or more
bricks, can be distributed partially to bricks in courses above and below.
This will be
particularly favourable for the protruding parts of the bricks, where, for
example,
forces which arise on the protruding part 153 on brick 150 can be distributed
to the
underlying brick 150' via interacting elements 152, 152' and, in equivalent
fashion, to
any brick above (not shown).
Figure 4 shows a brick equivalent to brick 107 as shown in figure 2. The upper
part of
the figure shows the brick from above. The lower part of the figure shows the
brick in
a section from the side. The figure shows the flue gas duct 111, which, at its
top, has
a raised end 200 and, at its lower part, has a recess 201. The raised end 200
is
adapted to an equivalent recess in a brick designed to be placed on brick 107,
while
the recess 201 is designed to fit on a raised part of an underlying brick (not
shown).
The raised ends and recesses will contribute to the flue gas duct having a
sealed
connection between the courses and they will contribute to a good mutual
anchoring
of the bricks. Moreover, the brick 107 may be provided with transverse tongue
202,
202' at its top and equivalent transverse recesses 203 at its bottom for
further
stabilisation of the brick.
Figure 5 shows a brick equivalent to brick 108 in figure 2. The upper part of
the figure
shows the brick from above and the lower part of the figure shows the brick in
a
section from the side. The figure shows flue gas ducts 112, 113, which, at
their top,
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have raised ends 250, 251 and, at their lower parts, have recesses 252, 253.
The
raised ends 250, 251 are adapted to equivalent recesses in one or two bricks
designed to be placed on brick 108, while the recesses 252, 253 are designed
to fit
on raised parts of one or two underlying bricks (not shown). The raised ends
and
recesses will contribute to the flue gas ducts having a sealed connection
between the
courses and they will contribute to a good mutual anchoring of the bricks. As
in the
previous figure, the brick 108 may be provided with transverse tongues 254,
254' at
its top and equivalent transverse recesses 255 at its bottom for further
stabilisation of
the brick.
Figure 6 shows a brick equivalent to brick 116 in figure 2. The upper part of
the figure
shows the brick from above and the lower part of the figure shows the brick in
a
section from the side. The figure shows flue gas ducts 118, 119, which, at
their top,
have raised ends 300, 301 and, at their lower parts, have recesses 302, 303.
The
raised ends 300, 301 are adapted to equivalent recesses in one or two bricks
designed to be placed on brick 116, while the recesses 302, 303 are designed
to fit
on raised parts of one or two underlying bricks (not shown). The raised ends
and
recesses will contribute to the flue gas ducts having a sealed connection
between the
courses and they will contribute to a good mutual anchoring of the bricks.
However, it
may be necessary to use mortar or a sealing compound for further stabilisation
of the
connections between the bricks.
Although the examples show partition walls with flue gas ducts, equivalent
advantages and principles to those in the present invention may also be
exploited for
wall structures without ducts running through them, where the structure is
exposed to
large thermal loads in another way. This may, for example, be the case for
wall
structures installed inside a furnace chamber in order to divide the chamber.
In the embodiments shown, the contact elements are designed so that
protrusions
are arranged on the top of the bricks, while recesses are arranged on the
bottom of
the bricks. However, it would also lie within the framework of the present
invention if
the protrusions were arranged on the bottom and the recesses on the top or
possibly
if a combination of these were used.
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In accordance with the present invention, the movements which arise in the
wall
structure are mainly absorbed at at least one end, which may be fixed against
other
brickwork in a furnace. A certain relative movement must also be permitted
between
the wall structure and its underlying structure, for example a fixed floor
structure.
