Note: Descriptions are shown in the official language in which they were submitted.
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COOLING PANEL FOR A SHAFT FURNACE, SHAFT FURNACE PROVIDED
WITH COOLING PANELS OF THIS NATURE, AND A PROCESS FOR
PRODUCING SUCH A COOLING PANEL
The invention relates firstly to a cooling panel for a shaft furnace of the
type
through which at least one vertical duct runs, the ends of which are connected
to
connection ends running transversely with respect to the plane of the cooling
panel. The
invention furthermore relates to a shaft furnace provided with a jacket, the
jacket being
provided on the inside with cooling panels of this nature. In this context,
the jacket is
understood to mean the metal casing of the furnace. Finally, the invention
relates to a
process for producing the novel cooling panels.
A standard embodiment of a shaft furnace is a blast furnace for the reduction
of
iron ore. However, shaft furnaces are frequently also used for other purposes.
Where
the following text explains the invention with reference to applications for a
blast
furnace, this description also comprises applications for other types of shaft
furnaces.
The thermal loads imposed on the wall of a blast furnace are generally
extremely
high. These thermal loads may, for example, be of the order of magnitude of
250 000 W/mz. To prevent damage to the metal casing of the furnace, it is
therefore
necessary to provide this wall with a cooling system. One of the means which
is
2 0 frequently employed for this purpose is the use of so-called cooling
panels. These are
metal panels which are attached to the inside of the steel casing, also known
as j acket or
steel jacket, at least one vertical duct running through these cooling panels.
These ducts
are then connected to connection ends which run through the jacket. That side
of the
cooling panel which faces towards the inside of the furnace may be provided
with
2 5 recesses in which refractory bricks are fitted, in order to avoid or at
least reduce direct
thermal contact between the hot furnace charge and the cooling panel. Unlined
cooling
panels are also used, however, in which case the cooling panel is cooled so
intensively
that a solidified crust is formed against them. This solidified crust consists
of slag
constituents and constituents of the charge inside the furnace.
3 0 Traditionally, cooling panels are made from cast iron. However, it has
been found
that cast iron panels can lead to problems if the refractory lining becomes
worn or if
parts of the crust break or melt off. Specifically, a sudden increase in the
thermal load
on the cooling panel, partially owing to structural changes in the material of
the cooling
panel, may give rise to deformation of the cooling panel and movements thereof
which,
3 5 especially if they are repeated a number of times, may lead to cracks and
leaks in the
water ducts. To some extent, leaks of this nature can be avoided by closing
off ducts. If
there are a number of leaks, it may be necessary to shut down the furnace and
carry out
emergency repairs.
CONFIRMATION COPY
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Previously, it has been proposed to reduce these drawbacks by casting the
cooling
panels not from cast iron but from copper. Due to the better thermal
conductivity of
copper, such a panel can tolerate higher thermal loads, while temperature
differences
within the cooling panel are lower. Consequently, this also reduces the risk
of leaks and
cracking in the cooling panel. Nevertheless, it has been found that even with
cast
copper cooling panels problems may arise in the long term, inter alia as a
result of
fatigue phenomena in the material and owing to casting defects present in cast
copper
cooling panels. In US 4,382,585, it is proposed to eliminate these drawbacks
by
producing a cooling panel not by casting copper, but rather by machining a
thick rolled
l0 or forged copper sheet. In this case, the ducts are drilled through this
sheet and in some
cases blocked again at the ends. This design has also proven to have
drawbacks.
Blocking the ends of the ducts may again lead to leakage. Also, the shape of
such
cooling panels is limited owing to the way in which they are produced. A
profiled
surface on the furnace side can only be achieved at high cost, while the
drilling of long
ducts limits the length of the cooling panels. Generally, one drawback of the
known
copper cooling panels is that the connection ends also consist of copper. In
many cases,
copper is too soft to make mechanical connections for the cooling panels.
Therefore, there is a need for a cooling panel which consists predominantly of
copper and does not have the drawbacks described. Moreover, this cooling panel
is to
2 0 be of a form which reduces the thermal loads and allows a stable crust to
form,
providing additional protection and thermal insulation for the cooling panel.
It has been found that such a cooling panel according to the invention can be
obtained if, in this cooling panel, each duct and the connection ends are
formed from a
continuous tube made from a material selected from the group consisting of low-
carbon
2 5 steel, stainless steel and an alloy which predominantly comprises Cu and
Ni with an Ni
content of > 28% by weight, and the remainder of the cooling panel consists of
copper
which is cast around this tube, the cooling panel being provided, on the side
remote
from the connection ends, with a multiplicity of horizontal ribs. Preferably
the ribs have
a length, in the width direction of the cooling panel which is smaller than
the width of
3 0 the cooling panel.
More preferably the ribs have a length in the said width direction of the
cooling
panel of <_ 50%, preferably <_ 25% of the width of the cooling panel. The
copper/nickel
alloy as described has a higher melting point than copper, with the result
that the copper
body of the cooling panel can be cast around these tubes without the tube
itself also
3 5 melting. It has proven possible to form copper-nickel alloys with a high
nickel content
into high-quality tubes which are generally used for heat-exchanger pipes
under
exacting mechanical, thermal and chemical conditions. Even if the cast copper
body
begins to exhibit pores or cracks, there will still be no leakage of water
owing to the
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high quality of the tube used. By furthermore providing the cooling panel with
ribs on
the side facing towards the furnace content, spaces are formed between these
ribs, in
which spaces a crust can form. The crust can consist of slag, ore, iron or a
mixture
thereof. Also, the crust can have been prepared by applying refractory bricks,
concrete
or masses between the ribs. If the ribs taper, that means that the heat flux
to the main
body of the cooling panel is reduced, which is of benefit to the durability of
the cooling
panel. By positioning a plurality of ribs next to one another on the cooling
panel and
making them short, it is also possible to avoid high thermal stresses in these
ribs, so
that they themselves also have a longer service life.
l0 However, according to the invention, the ribs may also be shaped such that
they
thicken towards their free ends remote from the main body of the cooling
panel. This
prevents the loosening of the crust from within the ribs, which guarantees an
extra
protection of the cooling panel.
It should be noted that US patent No. 3,853,309 has disclosed a water-cooled
blowing nozzle in which a copper/nickel tube is also cast in copper over part
of its
length. However, the use of blowing nozzles in a blast furnace in technical
terms relates
to a completely different problem from that of cooling a furnace wall with the
aid of
cooling panels.
According to the invention, an alloy which contains between 65 and 70% by
weight Ni, approx. 3% by weight Fe and < 1% of one or more of the elements Mn,
Si
and C has proven to be a particularly suitable material for the continuous
tube
according to the invention. The use of Monel, which has a composition of
approx. 28%
Cu, 68% Ni, 3% Fe, 1% Mn and low Si and/or C contents, is particularly
preferred.
An important function of the ribs is that they allow a crust to form on the
surface
2 5 of the cooling panel, and in particular they are also able to hold this
crust in place. The
latter factor is also of undoubted importance in view of the fact that the
charge which is
moving continuously down the blast furnace exerts a high frictional force on
the wall
and thus, in particular, on the crust formed. Ultimately, a large part of this
frictional
force is absorbed by the ribs, which thereby run the risk of becoming damaged.
To
3 0 ensure that these ribs are well able to withstand this frictional force,
it has proven
highly advantageous, according to the invention, to provide these ribs with
supporting
backs. These supporting backs ensure that the vertical load imposed is better
absorbed
and distributed by the cooling panel. As a result, the risk of the ribs being
deformed,
breaking off or being damaged in some other way is reduced.
3 5 In a first embodiment of these ribs with a supporting back, each of the
ribs with a
supporting back is T-shaped in cross section, parallel to the plane of the
cooling panel.
According to another embodiment, each of the ribs with supporting backs has a
cross
section in the shape of a +, parallel to the plane of the cooling panel.
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At locations where the frictional force of the falling charge may be extremely
high, it may be advisable to provide the ribs with a plurality of supporting
backs.
According to one possible embodiment according to the invention, for this
purpose the
ribs are provided with supporting backs on either side in the vicinity of
their ends.
Copper as a material for cooling panels is considerably more expensive than
cast
iron. However, owing to the much better thermal conductivity of copper than
that of
iron, it has proven possible to save considerable amounts of material through
the shape
of the cooling panel. In one possible embodiment of the cooling panel, for
this purpose
the wall is provided with undulating recesses on the side of the connection
ends, on
either side of each duct, in which recesses reinforcing walls which fill up
the recesses
are distributed over the height of the cooling panel. Despite the fact that
the cooling
panel has consequently been locally thinned, it remains sufficiently strong.
Optionally
in combination with these undulating recesses on the side of the connection
ends, it has
also proven possible, in another embodiment of the cooling panel according to
the
invention, to provide the wall on the side remote from the connection ends
with
undulating recesses on either side of each duct. This also allows considerable
amounts
of material to be saved.
In addition to the cooling panel described, the invention also relates to a
shaft
furnace provided with a jacket which on the inside is at least partially
provided with the
2 o cooling panels described above.
Finally, the invention also relates to a process for producing a cooling panel
of
one of the types described above. This process is characterized in that the
continuous
tube (or tubes) is firstly given its final shape, after which the copper for
the cooling-
panel body to be formed is cast around it at a temperature which is so close
to the
2 5 melting point of the tube material that, after the cast material has
cooled, it is attached
to the tube material. This method results in there being virtually no
resistance to the
passage of heat between the continuous tube and the surrounding copper of the
cooling
panel. In this context, it should be noted that the term copper is to be
understood as
meaning not only completely pure copper but also low alloy copper with a
composition
3 o such as that which is customarily used for the production of copper
cooling panels.
The invention will now be explained with reference to a number of diagrammatic
figures.
Fig. 1 shows a longitudinal section through a cooling panel.
Fig. 2 shows a detail of this panel on an enlarged scale.
3 5 Fig. 3 shows part of a cross section through the cooling panel shown in
Fig. 1, on
an enlarged scale.
Fig. 4 shows a perspective view illustrating the detail from Fig. 2.
Fig. 5 shows a possible configuration of ribs with supporting backs.
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Fig. 6 shows smaller ribs in larger numbers.
Fig. 7 shows ribs with additional supporting backs.
Fig. 8 shows yet another configuration of the ribs with supporting backs.
In Figs. 1 and 3, (1) denotes the steel casing of a blast furnace (the so-
called
jacket). A cast copper cooling panel body is denoted by (2), through which a
cast-in
tube (3) runs. This tube is made from Monel. The connection ends (4) and (5)
of the
continuous tube (3) project through openings in the jacket (1), through which
cooling
water from outside the furnace can circulate through the cooling panel inside
the
furnace and thus cool this panel. As can be seen from Fig. 3, it is possible
for a plurality
l0 of continuous tubes (3) to be cast into the cooling panel (2).
The space between the jacket (1) and the cooling panel may be filled up with a
casting compound (6). Attachment bolts for attaching the cooling panel to the
jacket (1)
from outside the furnace are not shown. This attachment method is of a
traditional
nature, as is customarily used in cooling panels.
Tapering ribs (7) are cast onto the furnace side of the cooling panel. These
ribs
(7) may be distributed over the surface of the panel in a pattern such as that
shown in
Fig. 5. Since the length of these ribs is limited, it will be impossible for
high thermal
stresses to build up in these ribs. A vertical frictional force which a
downwardly
moving charge may exert on the ribs can be absorbed by supporting backs (9)
(cf. Fig.
2 0 2 and Fig. 5).
Solidifying crust material (8) may collect between the ribs, and if
appropriate the
supporting backs, forming thermal insulation between the furnace content and
the
cooling panel. The shape of the ribs prevents the possibility of this crust
being torn off
again easily by the downwardly moving charge. Furthermore, the tapering form
of the
2 5 ribs limits a high thermal load on the cooling panel via the ribs. As the
crust (8)
becomes thicker, that part of the ribs which is exposed to heat will become
smaller.
If, after prolonged use of the cooling panels and/or as a result of
fluctuating
thermal loads on these panels as a result of highly divergent operating
conditions, the
cooling panels should become damaged, this damage will be limited to small
cracks
3 0 (13) in the vicinity of the outer edge of the ribs, as indicated in Fig.
4. It has been found
that damage of this nature remains limited and certainly will not propagate
into the
main body of the cooling panel. Even if damage were to arise in that area as a
result of
extreme operating conditions, this does not lead to damage to the cast-in
Monel tubes.
Fig. 3 furthermore shows how it is possible to save copper during the
35 construction of the cooling panels by making that wall (11) of the cooling
panel which
faces towards the jacket (1) undulate around the tubes (3). The strength of
the cooling
panel can be maintained by arranging reinforcing walls (12) in the recesses
formed,
distributed over the height of the cooling panel.
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In a similar way, it is also possible to make that surface (10) of the cooling
panel
which faces towards the furnace content undulating.
The ribs (7) can be made larger or smaller depending on whether it is desired
for
them to penetrate more or less deeply into the furnace. Fig. 6 shows an
embodiment in
which smaller ribs (7) with supporting backs (9) are arranged in a more
tightly packed
pattern.
If working under conditions in which it is possible to expect extremely high
frictional forces from a downwardly moving charge, it is recommended for each
rib to
be provided with a multiplicity of supporting backs. In the embodiment shown
in Fig.
7, four supporting backs (15-18) are arranged on each rib (14). This shape
provides an
additional resistance to a crust (8) which has formed being torn off.
Fig. 8 shows yet another embodiment (20) of the ribs with supporting backs.
These are in the form of upright crosses.
