Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a baking furnace for
continuous production of elongated carbon bodies with a
substantially uniform cross section such as for example
carbon electrodes for use in electric smelting furnaces,
lining blocks, anode- and cathode elements in electrolytic
cells for production of aluminium. The elongated carbon
bodies may have any cross section, e.g. circular,
rectangular or others.
method is known for production of elongated carbon
bodies where unbaked carbonaceous electrode paste
comprising a carbon material and a carbonaceous binder
continuously is baked to a solid carbon body by charging
the unbaked electrode paste into a casing having a cross
section correspondinq to the cross section of the carbon
body to be produced, and continuously or substantially
continuously lowering the casing down through a baking
urnace to which baking furnace heat energy is supplied.
It is further known to use a perforated casing whereby
gases which evolve in the electrode paste by heating, flow
from the electrode and into the baking furnace where they
are combusted.
It has been observed that the gases which evolve during the
heating of the electrode paste and flow into the baking
furnace through the perforations in the casing, have a
tendency to condense in the upper part of the baking
furnace where the cold electrode casing containing cold
electrode paste enters into the baking furnace. This
condensate which consists of a large number of different
hydrocarbon fractions, will eventually be carbonised in the
upper paxt of the baking furnace and a layer of hard
carbonized material will slowly build up and after some
time, completely fill up the annulus between the baking fur-
nace and the electrode casing. This will have the result that
after operation of the furnace for some weeks it will not
be possible to move the casing or the eleçtrode conse~uently
relative to the baking furnace. The growth in this layer
of hard carbonized material in the upper part of the baking
furnace must therefore more or less continuously be
observed and at a certain time the baking process has to be
stopped and the baking furnace has to be dismantled in order
to remove the layer of carbonized material. During removal
of the layex of carbonized material, the baking zone in the
carbon body is cooled, whereby an inhomogeneity is produced
in the elongated carbon body.
If the baking furnace is operating in direct connection
with an electric smelting furnace for production of a
carbon electrode which is directly used in the smelting
furnace, the operation of the smelting furnace has to be
shut down during the removal of the layer of carbonized
material in the baking furnace. This will result in loss
of production from the smelting furnace and in addition
there will be a high risk of electrode breakage when the
part of the electrode containing the above mentioned in-
homogeneity enters into the smelting furnace.
It is an object of the present invention to provide a
baking furnace which prevents the build up of hard,
carbonized material in the upper part of the baking
furnace.
It is a further ob~ect of the present invention to provide
an efficient gas sealing between the electrode casing and
the upper part of the baking furnace in order to prevent
gas leakages from the baking furnace to the environment.
Accordingly, the present invention relates to a baking
furnace for continuous production of elongated carbon
bodies having a substantially uniform cross section,
wherein the baking furnace continuously or substantially
continuously is moved relatively to the carbon body with a
speed which corresponds to a preset baking speed for the
carbon body.
According to the present invention the baking furnace
comprises an outer shell made from steel and a refractory
lining arranged on the inside of the shell which defines a
combustion chamber about the carbon body which is being
produced. A cooling chamber is arranged between the upper
part of the refractory lining and the carbon body which is
being produced, the lower part of the cooling chamber
extending into the combustion chamber and the upper part of
the cooling chamber e~tending above the refractory lining
of the combustion chamber. In the lower part of the
combustion chamber there is arranged a channel for the
off-gases from the combustion chamber.
The cooling chamber preferably has internal channels for
circulation of a cooling medium. Above the cooling chamber
there is arranged a guide ring for guiding the carbon body
through the baking furnace and a gas sealing to prevent gas
leakages from the combustion chamber. The gas sealing
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preferably comprises a flexible gasket arranged between
vertically arranged lower flanges which are affixed to a
plate on the top of the cooling chamber and ver.ically
arranged upper flanges which are affixed to another plate
and where the distance between the upper and lower flanges
and thereby the tightening of the gasket against the carbon
body, can be adjusted by means of a plurality of bolts.
Further embodiments of the present invention will be
evident from the claims.
The baking furnace according to the present invention will
now be further described in connection with the drawings !
which shows a preferred embodiment of the present ',
invention.
Figure 1 shows a vertical cut through a baking furnace
according to the present invention, and;
Figure 2 shows an enlarged view oE a part of figure 1.
On figure 1 there is shown a baking furnace 1 for
production of elongated carbon bodies 2. The baking
furnace is arranged about a casing 3 for the carbon body 2.
The casing 3 has a cross section which corresponds to the
cross section of the carbon body.
Unbaked carbonaceous electrode paste 4 which consists of a
carbon material and a carbonaceous binder is charged into
the casing 3. By heating of the electrode paste 4 in the
baking furnace 1, the electrode paate is baked into a solid
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carbon body 2. The casing 3 is preferably perforated (not
shown) in order to allow gases which evolve during the
heating of the electrode paste to flow through the
perforations and into the baking furnace.
The baking furnace 1 comprises an outer shell 5 and a
refractory lining 6 defining a combustion chamber 7. The
combustion chamber 7 is heated to the necessary baking
temperature by means of at least one burner 8 for solid,
liquid or gaseous fuel. The burner or burners 8 are
preferably tangentially arranged in relation to the
combustion chamber 7. The burner 8 has supply pipes 9 and
10 for fuel and combustion air. Below the refractory
lining 6 there is arranged a channel 11 for off-gases from
the baking furnace 1. The off-gas is sucked out from the
channel 11 through an off-gas pipe 12. In the off-gas pipe
12 there is arranged a valve 13 for regulating the volume
of off-gas from the baking furnace.
The channel 11 has a central opening with a diameter
slightly greater than the diameter of the baked carbon body
2. Between the channel 11 and ,the casing 3 for the carbon
body 2 there will therefore be a slot 14. When the baking
furnace 1 is in operation, environmental air is sucked in
through the slot 14 and thereby provides a seal so that
gases from the combustion chamber 8 will not escape through
the slot 14.
In the upper part 15 of the refractory lining 6 of the
baking furnace 1, there is provided an opening for the
casing 3. This opening has a somewhat greater cross
section than the cross section of the casing 3.,,,In the
annular slot between the upper part 15 of the refractory
lining 6 and the casing 3 there is arranged a cooling
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chamber 16 for circulation of a cooling medium. The
cooling chamber 16 has supply pipe 17 and return pipe 18
for the cooling medium which preferably is water. The
cooling chamber 16 may be divided into sections and each
section may be provided with internal walls (not shown) in
order to ensure a proper flow of cooling medium through the
cooling chamber 16.
The cooling chamber 16 is arranged in such a way that its
lower end is at about the same level as the lower end of
the upper part 15 of the refractory lining 6 as shown on
figure 1. The cooling chamber 16 extends upwardly to a
level at least above the upper end of the upper part 15 of
the refractory lining 6.
The cooling chamber 16 is affixed to the outer shell 5 via
an annular plate 20 which is secured to the shell 5 by
means of bolts 21.
If the baking furnace 1 is used for baking a carbon
electrode in direct connection with an electric smelting
furnace, electric insulation 25 is preferably inserted
between the shell 5 on the baking furnace 1 and the annular
plate 20.
Above the cooling chamber 16 there is secured a guide ring
22 made from rod iron or the like. The purpose of guide
ring 22 is to guide the casing relatively to the baking
furnace. In the area above the guide ring 22 there is
arranged gas sealing means 23 for preventing gas leakages
between the casing 3 and the baking furnace 1.
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The gas sealing means 23 is shown in enlarged scale on
figure 2. The gas sealing means 23 comprises a lower
annular plate 24 which is secured to the cooling chamber
16. To the plate 24 there are affixed two annular
vertically running flanges 26 and 27. Between the flanges
26 and 27 there is provided a flexible gasket 28 made of a
material having a high melting point. The upper end of the
gasket 28 is arranged between annular vertical flanges 29
and 30 which are connected to a second annular plate 31.
The second annular plate 31 is affixed to the flange 26 by
means of a plurality of threaded bolts 32 having handles
33. By adjusting the distance between the first plate 24
and the second plate 31 by operating the handles 33, the
flexible gasket 28 is tightened or loosened. The gasket 28
can be adjusted locally about the circumference of the
casing 3 by operations of the handles 33.
In operation the baking furnace 1 is continuously or
substantially continuously moved relative to the casing 3
with a speed corresponding to the preset baking speed for
the carbon body 2. When the casing 3 with the unbaked
electrode paste 4 enters into the baking furnace 1, the
electrode paste is heated and the electrode paste then
becomes liquid whereafter the paste is baked into a solid
carbon body.
During the baking, carbonaceous gases evolve in the
electrode paste. These gases flow into the baking furnace
1 through perforations in the casing 3 and most of the
gases are immediately cumbusted by the combustion air which
is supplied to the baking furnace.
A part of the gases will, however, condense on the cooling
area 19 on the lower vertical part of the cooling chamber
16 where the temperature is kept below 400C by the cooling
medium circulating in the cooling chamber. As the
temperature in the baking chamber is in the interval
between 700 and 1300C, the part of the gases which come
into contact with the cooling area 19 will condense. The
temperature in the area of the cooling chamber 16 is,
however, so low that the conden$ed gases will not be carbon-
ized. The condensate from the gases will therefore drop down
into the combustion chamber where it will immediately be
combusted. The cooling chamber further provides that the
gas in the annulus between the casing 3 and the cooling
chamber is kept at a lower temperature. The gasket 28 is
thereby protected against high temperature exposure. The
lifetime for the gasket 28 will thereby be increased.
By the present invention a baking furnace is provided
which can be operated for lo~g periods ~
without operation difficulties due to build ups of layers
of carbonized material. Further, a very good gas seal
between the carbon body and the baking furnace is obtained,
thereby minimizing the possibility for leakage of hazardous
gases from the baking furnace to the environment.
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