C^H
DESCRIPTION
FURNACE WALL STRUCTURE OF MOLTEN METAL VESSEL AND METHOD
FOR CONSTRUCTING FURNACE WALL OF MOLTEN METAL VESSEL
TECHNICAL FIELD
[0001]
The present invention relates to a furnace wall structure of a molten metal vessel
(for example, a converter, a molten iron ladle, a molten steel ladle, an electric furnace, or
the like), and to a method for constructing a furnace wall of a molten metal vessel.
BACKGROUND ART
[0002]
A converter, which is a molten metal vessel, is used in a high-temperature
environment because oxygen blowing is performed therein. This prevents a refractory
used for a furnace wall of the converter from being repaired frequently. Therefore, the
refractory requires high durability (erosion resistance, wear resistance, and spalling
resistance). Typically, the refractory has a thickness of approximately 900 mm. In
general, a magnesia carbon brick (MgO-C brick) is used as the refractory. The magnesia
carbon brick is excellent in fire resistance at high temperatures because of contained
magnesia, and maintains a given thermal conductivity because of contained carbon. In
addition, the magnesia carbon brick has excellent characteristics including spalling
resistance even if the furnace wall is thick.
[0003]
However, after a predetermined number of times of decarbonizing treatments, the
refractory of the furnace wall wears out to have a thinner remaining thickness, which
limits the life of the furnace wall. As a result, it is necessary to suspend the operation of
the converter and to repair the fiimace by arranging a new refractory. Therefore, to
improve the productivity of the converter, it is important to increase the life of the furnace
wall. Consequently, technical examinations into the expansion of the life of the furnace
wall have been carried out. For example. Patent Document 1 discloses a magnesia
carbon brick to which boron is added, and Patent Document 2 discloses a magnesia carbon
brick to which nickel is added. In these techniques, a magnesia carbon brick is
strengthened by an additive to improve wear resistance and spalling resistance.
CITATION LIST
Patent Document
[0004]
Patent Document 1: Japanese Unexamined Patent Application, First Publication
No. 2000-327403
Patent Document 2: Japanese Unexamined Patent Application, First Publication
No. 2006-21972
Disclosure of the Invention
Problems to be Solved by the Invention
[0005]
However, the techniques of Patent Documents 1 and 2 are indeed effective in the
extension of the life of the refractory of the converter to a certain degree. But in an
environment of use of the converter, especially in an environment where a temperature
change (temperature gradient) is larger in the thickness direction of the flimace wall, there
is a difference in thermal expansion in the refractory when seen in the thickness direction
of the furnace wall, which results in spall damage (spalling) in the refractory. Therefore,
the refractory has a limited extensible life, and a further life extension is desired. Also in
the case where there is a large change in temperature in the converter due to the operating
ratio or the like of the converter, spall damage from a thermal shock is likely to be caused,
which prevents the life of the refractory from being sufficiently extended.
[0006]
The present invention has been achieved in view of the above circumstances, and
has an object to provide a fiimace wall structure of a molten metal vessel and a method for
w
constructing a furnace wall of a molten metal vessel that makes it possible to extend the
life of a refractory even in an environment of use where spall damage is caused, and even
in a situation where, with a large temperature change in the molten metal vessel, spall
damage is likely to be caused.
Means for Solving the Problem
[0007]
(1) As a result of repetition of dedicated researches to solve the above problems and
achieve the above object, the inventors have come to adopt the following.
An aspect of the present invention is a furnace wall structure of a molten metal
vessel that is provided with a furnace wall lined with a magnesia carbon refractory,
including: a shell; a permanent refractory lined on an interior surface of the shell; a heat
insulation material lined on an interior surface of the permanent refractory; and the
magnesia carbon refractory lined on an interior surface of the heat insulation material,
wherein in a case that a thickness of the furnace wall except the shell when the furnace
wall is seen in a vertical cross-sectional view is set to be T mm in millimeter unit, the heat
insulation material with a thermal conductivity of not less than 0.01 W/(m*K) and not
more than 0.15 W/(m»K) in a range of 25°C to 300°C, with a mehing point of not less than
1000°C and not more than 1400°C, and with a thickness of not less than 2 mm and not
more than 10 mm is arranged in a range in a thickness direction between a position not
less than 0.75xT (mm) and not more than 0.92xT from an interior surface of the magnesia
carbon refractory toward the shell.
[0008]
(2) In the furnace wall structure of a molten metal vessel as described above in (1), the
magnesia carbon refractory may have a carbon content of not less than 0.5 mass% and not
more than 15 mass%.
[0009]
(3) Another aspect of the present invention is a method for constructing a furnace wall of a
molten metal vessel that is provided with a furnace wall lined with a magnesia carbon
refractory; including the steps of: lining a permanent refractory on an interior surface of a
^ ^ 9
shell; lining a heat insulation material on an interior surface of the permanent refractory;
and lining the magnesia carbon refractory on an interior surface of the heat insulation
material, wherein, in the process of lining the heat insulation material, in a case that a
thickness of the fiimace wall except the shell when the fiimace wall is seen in a vertical
cross-sectional view is set to be T mm in millimeter unit, the heat insulation material with
a thermal conductivity of not less than 0.01 W/(m»K) and not more than 0.15 W/(m»K) in
a range of 25°C to 300°C, with a mehing point of not less than 1000°C and not more than
1400°C, and with a thickness of not less than 2 mm and not more than 10 mm is arranged
in a range in a thickness direction between a position not less than 0.75xT (mm) and not
more than 0.92xT from an interior surface of the magnesia carbon refractory toward the
shell.
[0010]
(4) In the method for constructing a furnace wall of a molten metal vessel as described
above in (3), the molten metal vessel may be a converter, and an operating ratio of the
converter may be more than 0% and not more than 70%.
[0011]
(5) In the method for constructing a furnace wall of a molten metal vessel as described
above in (3) or (4), the magnesia carbon refractory may have a carbon content of not less
than 0.5 mass% and not more than 15 mass%.
EFFECTS OF THE INVENTION
[0012]
According to the aspect as described above in (1) or (3), a heat insulation material
with a thermal conductivity of 0.01 to 0.15 W/(m»K) is arranged at a position in the range
in the thickness direction between 0.75xT to 0.92xT from the operating surface of the
furnace wall and is also arranged on the back surface side of the magnesia carbon
refractory. Therefore, it is possible to make small the temperature gradient in the
magnesia carbon refractory in the thickness direction of the furnace wall. This can make
small the difference in thermal expansion of the magnesia carbon refractory in the
thickness direction of the furnace wall. Consequently, it is possible to relieve the spall
damage resulting from this.
Furthermore, as a heat insulation material, one with a melting point of 1000 to
1400°C and a thickness of 2 to 10 mm is used. Therefore, in the case where the
refractory becomes thin in the terminal stage of the life of the magnesia carbon refractory,
it is possible to melt the heat insulation material by the heat transmitted via the magnesia
carbon refractory. This can produce a gap in the region which the heat insulation
material occupied, and can allow the thermally-expanding magnesia carbon refractory to ,
move toward the shell. Consequently, it is possible to decrease the stress developed on
the operating surface side of the molten metal vessel, and hence, to suppress the spall
damage and the flaking-off of the magnesia carbon refractory to the operating surface side
of the molten metal vessel.
Therefore, even in an environment of use where spall damage is caused and in a
situation where, with a large temperature change in the molten metal vessel, spall damage
is likely to be caused, it is possible to make the damage of the magnesia carbon refractory
not the damage based on spall damage but the damage based on erosion or wear. This
makes it possible to improve the accuracy of the determination of the end of life, and to
extend the life of the magnesia carbon refractory to be used for the furnace wall.
[0013]
In the case of (2) and (5), the magnesia carbon refractory has a carbon content of
not less than 0.5 mass% and not more than 15 mass%. Therefore, it is possible to
decrease carbon content, which is likely to be oxidized and lost, more than the
conventional case. This makes it possible to improve an erosion resistance of the
magnesia carbon refractory more than that in the conventional case. This is because,
with the arrangement of the heat insulation material on the shell side of the magnesia
carbon brick, the temperature gradient in the magnesia carbon brick can be made smaller
in the thickness direction of the furnace wall, and as a result, unlike the conventional case,
it is not necessary to increase a carbon content which has a function of improving the
thermal conductivity of the magnesia carbon brick.
•
[0014]
In the case of (4), if the molten metal vessel is a converter and the converter has
an operating ratio of more than 0% and not more than 70%, the effect of the present
invention is more significant. A decrease in the operating ratio of the converter
represents that the period of time, in which the converter is not in use, is extended.
Namely, the converter having an operating ratio of more than 0% and not more than 70%
results in a situation where, with a large temperature change in the converter, the spall
damage by heat shock is likely to be caused in the magnesia carbon refractory. Therefore,
the effect of the present invention is more significant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
FIG. 1 is a vertical cross-sectional view showing a part of a furnace wall structure
of a molten metal vessel according to a first embodiment of the present invention.
FIG. 2A is a graph showing how the presence and absence of a heat insulation
material affect an erosion rate of a refractory when a converter has an operating ratio of
not more than 70%.
FIG. 2B is a graph showing how the presence and absence of a heat insulation
material affect an erosion rate of a refractory when a converter has an operating ratio of
more than 70%.
FIG. 3 is a general view of the molten metal vessel according to the first
embodiment of the present invention.
Embodiments of the Invention
[0016]
Hereunder is a description of a furnace wall structure of a molten metal vessel
and a method for constructing a furnace wall of a molten metal vessel according to an
embodiment of the present invention, with reference to the drawings.
As shown in FIG. 3, a converter (an example of molten metal vessel) of the
»
present embodiment is a piece of equipment in a steel works or the like. It is a furnace
dedicated to refining a metal such as iron and copper. An exterior portion of the
converter is made of steel. An interior portion thereof is lined with firebricks that are
resistant to high heat and shock. The converter has a shape of a barrel or a pear. A
shaft is attached thereto, which allows the converter to freely rotate back and forth. In
use, the converter is tilted when the molten iron is poured or the molten steel is removed.
On the other hand, it is in its upright position at the time of refining.
As shovm in FIG. 1, a furnace wall structure of a molten metal vessel according
to the present embodiment is a furnace wall structure of a converter (furnace) 12 including
a furnace wall 11 lined with magnesia carbon bricks (an example of magnesia carbon
refractory) 10. A heat insulation material 14 is arranged on a back surface 13 side of the
magnesia carbon bricks (MgO-C bricks) 10, to thereby extend the life of the magnesia
carbon bricks 10. The back surface 13 side of the magnesia carbon bricks 10 is an
exterior side of the furnace. In other words, it is a side opposite to an interior side of the
furnace, which is an operating surface 15 side of the furnace wall 11, namely, a molten
steel contact surface (a molten metal contact surface) side of the magnesia carbon bricks
10. This structure will be described in detail below.
[0017]
Causes of damage to the magnesia carbon brick used in the furnace wall
refractory of the converter are typically divided into erosion, wear, oxidation, and spall
damage. Erosion (damage) such as erosion, wear, and oxidation is steadily produced,
and its erosion rate is comparatively stable. On the other hand, as for spall damage,
heavy erosion (damage) is caused at one time, and the damage is occurred irregularly.
In the actual environment of use, the magnesia carbon brick is damaged due to a
combination of the aforementioned factors. Of these factors, the rate of the spall damage
is often determined by the environment of use.
The spall damage is a phenomenon in which the surface of the furnace wall
refi-actory is caused to peel due to a crack or fracture generated when an excessive heat
shock or temperature gradient is applied to the furnace wall refractory. Compared with
^ 8
the other damage factors, the spall damage results in a larger damage thickness per
occurrence, and hence, has a greater influence on the life of the converter. Furthermore,
in the spall damage, damage significantly advances at a time. This makes it difficult to
determine the end of the life of the converter. This sometimes has an adverse effect on
the production planning of the converter.
[0018]
In the material design of the magnesia carbon brick, when the amount of
magnesia is increased for improving corrosion resistance a thermal conductivity is
decreased and spalling resistance is worsen. On the other hand, use of more carbon for
improving spalling resistance lowers the composition ratio of magnesia, which worsens
corrosion resistance. In this manner, the corrosion resistance and the spalling resistance
run counter to each other.
Here, in the case of using low-carbonaceous (low carbon content: for example,
not more than 15 mass%) magnesia carbon bricks for the furnace wall with an aim of
improving corrosion resistance, the thermal conductivity of the bricks is lower and the
temperature gradient in the longitudinal direction (in the thickness direction of the furnace
wall) is larger compared with those of high-carbonaceous (high carbon amount: for
example, more than 15 mass%) magnesia carbon bricks.
[0019]
As a result, there is a difference in thermal expansion in a structure of the
magnesia carbon brick in the longitudinal direction. This is likely to generate a crack
along the longitudinal direction or the width direction (the circumferential direction of the
fiimace wall), leading to spall damage due to a temperature difference. Furthermore, if
there is a large temperature change on the molten steel contact surface side of the
magnesia carbon brick, a fracture due to a heat shock resulting from the temperature
change is added, thus promoting the spall damage.
Typically, in the case where damage to the brick is caused mainly by the spall
damage, not only the erosion rate of the brick is higher (the speed with which the
remaining thickness of the brick decreases is higher), but also it is more difficult to
H^L
determine the end of life of the brick, compared with the case where damage to the brick is
caused mainly by the erosion. Typically, it is often determined that the life of the
converter reaches its end at the time when the damage to the furnace wall refractory
advances to expose the permanent refractory. After the life of the converter reaches its
end, it is required to renew the furnace wall refractory. However, the renewal of the
furnace wall refractory requires a long period of preparation. Consequently, it is
necessary to predict when the end of life comes with high accuracy (end determination).
Furthermore, an abrupt arrival of the end prevents the scheduled production. Also in this
point, it is necessary to predict the end with high accuracy.
The end determination here signifies that, for example, the erosion rate of the
furnace wall refractory (for example, in mm/ch; thickness of eroded refractory mm per
charge production) is measured to predict the end time (the number of producible charges
until the end of life).
[0020]
In the present embodiment, the heat insulation material 14 is arranged in the
furnace wall 11 of the converter 12, as described above. Namely, on an interior surface
of a shell 16 of the fiimace wall 11 of the converter 12, a multitude of rectangular
parallelepiped (or cubic) magnesia bricks 17 (a type of permanent refractory) are lined to
cover the entire surface. On the surfaces of the magnesia bricks 17 (inner surface of the
converter), the heat insulation material 14 is attached to cover the entire surface.
Furthermore, a multitude of rectangular parallelepiped (or cubic) magnesia carbon bricks
10 are lined on the magnesia bricks 17 via the heat insulation material 14. In this manner,
the magnesia bricks 17 and the magnesia carbon bricks 10 are arranged on both sides of
the fiimace wall 11 in the thickness direction with the heat insulation material 14
therebetween. Namely, adjacent to the surface on the shell 16 side of the heat insulation
material 14 (on the exterior side), the magnesia bricks 17 are arranged. On the other
hand, adjacent to the operating surface 15 side (on the interior side) of the heat insulation
material 14, the magnesia carbon bricks 10 are arranged.
q0021]
«
10
The magnesia brick 17 is a permanent refractory provided with corrosion
resistance. Its dimension in the thickness direction of the furnace wall 11 is, for example,
approximately 50 to 250 mm. So long as it is provided with corrosion resistance, the
material for the permanent refractory is not limited to the aforementioned magnesia, but
for example, alumina, magnesia alumina spinel, silica, or the like may be used. As the
refractory, bricks may be used, or monolithic refractory may be used. The magnesia
carbon brick 10 is a wear brick that is obtained as follows. A carbonaceous raw material
is added to a magnesia aggregate and a metal powder or metal compound is added thereto,
as necessary. Furthermore, a binding agent for forming a carbon bond such as a phenol
resin, pitch, or tar is added thereto. After kneaded, the mixture is sequentially subjected
to a molding treatment and a heat treatment, to thereby form a wear brick. The length of
the wear brick in the width direction of the furnace wall 11 is, for example, approximately
600 to 1000 mm. Here, the wear brick signifies a refractory that is to be in contact with
the molten metal.
[0022]
As a magnesia source used for manufacturing the magnesia carbon bricks 10, for
example one or more selected from the group consisting of electrically fused magnesia,
sea water magnesia, and natural magnesia, and the like may be used. However, the
source is not limited only to these. To avoid a decrease in corrosion resistance by the
contained impurities, it is preferable that the brick have high purity. For example, it is
preferable that the purity of not less than 95 mass% be ensured.
As a carbon-based source used for manufacturing the magnesia carbon bricks 10,
for example one or more selected from the group consisting of natural squamous graphite,
earthy graphite, artificial graphite, pitch powder, mesophase carbon, anthracite, carbon
black, and the like may be used. However, the source is not limited to these.
[0023]
The heat insulation material 14 may be made of, for example, ceramic mainly
based on glass, silica, alumina, or the like, or may be made of a material such as
microporous ceramic. With these components, it is possible to decrease the thermal -
/•Mk 11
conductivity. It is preferable that the heat insulation material 14 have a SiOj (silica)
content of 40 to 70 mass %. Si02 may be made of microparticles with a diameter of, for
example, approximately 5 to 30 nm. The component of the balance is not specified, and
may be made of Ti02 (titania), ZrSi04, AI2O3 (alumina), or the like. It is preferable that
the heat insulation material has a shape of a sheet (plate) with a uniform thickness.
The heat insulation material 14 has: a thermal conductivity of not less than
0.01 W/(m«K) and not more than 0.15W/(m'K) in a range of a normal temperature (25°C)
to 300°C; a melting point of not less than 1000°C and not more than 1400°C; a thickness
of not less than 2 mm and not more than 10 mm. In addition, when the thickness of the
furnace wall 11 without the shell 16 is set to be T, the heat insulation material 14 is
installed at a width position not less than 0.75xT and not more than 0.92xT from the
operating surface 15 of the furnace wall 11 and also at a position of the back surface 13 of
the magnesia carbon bricks 10. The operating surface 15 when the furnace wall
refractories of the furnace wall 11 were laid is positioned of "OxT", and a shell contact
surface 18 (an interior surface of the shell 16) of the magnesia bricks 17 is positioned at
"IxT".
[0024]
If the heat insulation material 14 has a thermal conductivity of more than
0.15W/(m«K), the thermal conductivity is so high that the heat insulating capability of the
heat insulation material 14 decreases. This causes the magnesia carbon brick 10 to exert
less of the effect of suppressing spall damage. For the reason as described above, the
lower the thermal conductivity of the heat insulation material 14 is, the better the effect of
suppressing the spall damage works. However, because the lowest value of the thermal
conductivities of the heat insulation materials that are present in the world at this time is
0.01 W/(m»K), this value is adopted as the lowest value. From above, the thermal
conductivity of the heat insulation material 14 is determined to be not less than
0.01W/(m»K) and not more than 0.15W/(m»K). The upper limit of the thermal
conductivity of the heat insulation material 14 is preferably 0.12W/(m»K), and more
preferably 0.1 OW/(m*K).
m 12
[0025]
If the melting point of the heat insulation material 14 is more than 1400°C, the
melting point is so high that the heat insulation material 14 cannot melt in the erosion
process of the magnesia carbon brick 10. Therefore, it is not possible to produce a gap
on the back surface 13 side of the magnesia carbon bricks 10 (the exterior side).
This prevents the magnesia carbon bricks 10, which are expanded by heat to push
and press each other, from moving toward the shell 16. Accordingly, the stress
developed on the operating surface 15 side of the magnesia carbon brick 10 rises, resulting
in spall damage or flaking-off of the magnesia carbon brick 10 to the operating surface 15
side.
On the other hand, the lower limit of the melting point of the heat insulation
material commonly employed in a molten metal vessel, such as a converter, which is used
in a high-temperature environment, is typically 1000°C. Therefore, this value is used as
the lowest value for the heat insulation material 14.
From above, the melting point of the heat insulation material 14 is determined to
be not less than 1000°C and not more than 1400°C. However, the lower limit is
preferably 1100°C, and more preferably 1200°C.
[0026]
If the heat insulation material 14 has a thickness of less than 2 mm, the heat
insulation material 14 is too thin. Therefore, when the heat insulation material 14 mehs
in the erosion process of the magnesia carbon bricks 10, it is not possible to form a gap
with a target inner width on the back surface 13 side of the magnesia carbon bricks 10.
This prevents the exertion of the capability of relieving the stress developed on the
operating surface 15 side. As a result, the magnesia carbon bricks 10 flakes off to the
operating surface 15 side.
On the other hand, if the heat insulation material 14 has a thickness of more than
10 mm, the heat insulation material 14 is too thick. Therefore, when the heat insulation
material 14 melts in the erosion process of the magnesia carbon bricks 10, a large gap is
formed on the back surface 13 side of the magnesia carbon bricks 10. As a result, the
^ii 13
magnesia carbon bricks 10 flakes off to the operating surface 15 side.
From above, the thickness of the heat insulation material 14 is determined to be
not less than 2 mm and not more than 10 mm. However, the upper limit is preferably 7
mm, and more preferably 5 mm.
[0027]
If the installation position of the heat insulation material 14 is at a thickness
position less than 0.75 xT from the position of the operating surface 15 when the furnace
wall 11 was built (at the position of the mohen steel contact surface of the magnesia
carbon bricks 10), the installation position of the heat insulation material 14 is so close to
the operating surface 15 that the heat insulation material 14 melts early. Therefore, the
effect obtained by use of the heat insulation material 14 does not last for a long time.
Furthermore, in this case, the magnesia carbon bricks 10 are so short (thin) with respect to
the magnesia bricks 17 in the thickness direction of the furnace wall 11 that it is not
possible for the magnesia carbon bricks 10 to sufficiently exert their performance.
On the other hand, if the installation position of the heat insulation material 14 is
at a thickness position more than 0.92 xT from the position of the operating surface 15 of
the furnace wall 11, the installation position of the heat insulation material 14 is so close
to the shell 16 that, when the heat insulation capability of the heat insulation material 14 is
lost in the erosion process of the magnesia carbon bricks 10, there may be a trouble such
as a red heat of the shell 16.
From above, the installation position of the heat insulation material 14 is
determined to be at a width position not less than 0.75 xT and not more than 0.92 xT from
the operating surface 15 of the furnace wall 11, and also at the position of the back surface
13 of the magnesia carbon brick 10. However, the lower limit value is set preferably to
the position of 0.80x7, and more preferably to the position of 0.85xT. The exact
installation position of the heat insulation material 14 in the above description is
established with reference to the position at half of the thickness of the heat insulation
material 14.
[0028] -
14
As described above, with the heat insulation material 14 being installed at an
appropriate position in the furnace wall 11, it is possible to set the carbon content of the
magnesia carbon brick 10 within the range of not less than 0.5 mass% and not more than
15 mass %, which is lower than that of the conventional case. To make small the
temperature gradient of the magnesia carbon brick 10 in the longitudinal direction, the
conventional techniques have a tendency to make the carbon content, which has a fiinction
of improving the thermal conductivity, more than 15 mass% and not more than 50 mass%.
However, in the present embodiment, the heat insulation material 14 is arranged on the
shell 16 side of the magnesia carbon bricks 10. Therefore, irrespective of the amount of
carbon blended in the magnesia carbon brick 10, it is possible to make small the
temperature gradient in the longitudinal direction, and to make the carbon content of the
magnesia carbon brick 10 not more than 15 mass%, which is less than that of the
conventional case. The carbon content of the magnesia carbon brick 10 may be a
conventional one (more than 15 mass%). In this case, an improvement is made possible
in the erosion resistance due to a decrease in the amount of carbon that is likely to be
oxidized and lost.
[0029]
On the other hand, the lower limit value of the carbon content is determined to be
0.5 mass% because a binder (for example, a phenol resin) that is blended at the time of
fabricating the magnesia carbon brick 10 remains as a carbon residue in the brick, and
hence, is not completely removable. Namely, because the value corresponding to this
remaining amount is 0.5 mass%, this value is set as the lower limit value of the carbon
content.
From above, the carbon content of the magnesia carbon brick 10 is determined to
• be not less than 0.5 mass% and not more than 15 mass%. To further improve the erosion
resistance of the magnesia carbon brick 10, the upper limit value is preferably determined
tobel3mass%.
It is preferable that the heat insulation material 14 be installed over the whole of
the fiimace wall (the whole of the wall surface on the interior side) of the converter.
4 15
However, the heat insulation material 14 may be partially installed only on a region where
especially spall damage is likely to be caused (for example, on the side of steel tapping).
[0030]
Subsequently, a method for constructing a furnace wall of a molten metal vessel
according to the present embodiment will be described with reference to FIG. 1.
Firstly, a muhitude of rectangular parallelepiped magnesia bricks 17 are lined on
an interior-side inner wall surface 16a of the shell 16 via a joint, leaving no space
therebetween.
Next, on an interior-side surface 17a of the lined magnesia bricks 17, a plurality
of sheet-like heat insulation materials 14 are sticked so as to leave no space between the
adjacent heat insulation materials 14. Then, a multitude of rectangular parallelepiped
magnesia carbon bricks 10 are lined, leaving no space therebetween, on an interior-side
surface 14a of the heat insulation materials 14 that have been sticked to the interior-side
surface 17a of the magnesia bricks 17. At this time, the lining is made so that the
longitudinal direction of the magnesia carbon bricks 10 coincides with the thickness
direction of the furnace wall 11 (the radial direction of the converter 12).
[0031]
The heat insulation material 14 is installed at a position in the thickness direction
not less than 0.75xT and not more than 0.92xT from the operating surface 15 of the
furnace wall 11, and also on the back surface 13 of the magnesia carbon brick 10 in a
width range of not less than 2 mm and not more than 10 mm. The position of the heat
insulation material 14 in the furnace wall 11 in the thickness direction when it is installed
is set by adjusting the ratio of the length of the magnesia brick 17 in its thickness direction
and the length of the magnesia carbon brick 10 in the thickness direction of the furnace
wall 11.
Here, as the magnesia carbon brick 10, a conventional brick with a carbon content
of more than 15 mass% may be used. However, with the installation of the heat
insulation material 14 in the furnace wall 11, it is possible to use bricks with a carbon
content of not less than 0.5 mass% and not more thar> 15 mass%5 which is lower than that
4 16
of the conventional case. As a result, an improvement is made possible in the erosion
resistance due to a decrease in the amount of carbon that is likely to be oxidized and lost.
[0032]
As for the converter 12 as an installation target of the heat insulation material 14,
its operational conditions and the like are not particularly limited. However, with the
converter 12 with an operating ratio of more than 0 and not more than 70%, it is possible
to obtain the effects of the present embodiment more significantly.
The operating ratio of the converter 12 is found with the following formula (1).
Operating ratio (%) of converter 12 = average time for steel making (min/ch) x
number of production charges (ch/month)/calendar time (min/month) x 100 • • • (1)
The time for steel making is a period of time per charge (charge is sometimes
referred to as heat) required to manufacture steel. To be more specific, it is a total time
from an injection of scrap to a discharge of slag through charging of molten iron, blowing,
and tapping. An average value of the total time is used as the average time for steel
making (minutes per unit of charge) in the above formula (1).
[0033]
If the operating ratio of the converter 12 is more than 70%, the operating ratio of
the converter 12 is so high that the temperature change in the converter 12 is small. To
further enhance the effects of the present embodiment, the upper limit value of the
operating ratio of the converter 12 is preferably 70%), and more preferably 60%.
On the other hand, from the aforementioned reason, with the lowering of the
operating ratio of the converter 12, the temperature change in the converter 12 is larger,
which makes the effects of the present embodiment more prominent. Therefore,
although determined to be more than 0%, the lower limit value of the operating ratio of the
converter 12 may be not less than 30%) as a typical value.
In this case, even in an environment of use where spall damage is caused, and
even in a situation where, with a large temperature change in the molten metal vessel,
spall damage is likely to be caused, it is possible to extend the life of the magnesia carbon
brick 10 as a refractory. . '• - ~
j f l 17
EXAMPLES
[0034]
Next is a description of Examples carried out to verify the operational effect of
the present embodiment.
Here, researches have been conducted on actual devices, namely, a converter A
with a furnace wall structure in which the heat insulation material 14 is installed and a
converter B with a furnace wall structure in which the heat insulation material 14 is not
installed.
To be more specific, in the converter A, the furnace wall structure in which the
heat insulation material 14 was installed was made of: magnesian permanent bricks
(thickness: 65 to 230 mm) as the magnesia bricks 17; a heat insulation material 14; and
magnesian carbonaceous wear bricks (thickness: 720 to 990 mm) as the magnesia carbon
bricks 10. These three types of constituent elements were provided in this order on an
interior side of a shell 16 of a converter 12. What is shown as a result of this is Examples
1 to 5 and Comparative Examples 1 to 6.
On the other hand, in the converter B, the furnace wall structure in which the heat
insulation material 14 was not installed was made of: magnesian permanent bricks
(thickness: 114 mm); and magnesian carbonaceous wear bricks (thickness: 900 mm).
These two types of constituent elements were provided in this order on an interior side of
the shell 16. What is shown as a result of this is Comparative Examples 7 and 8.
[0035]
For the heat insulation material 14, "Porextherm WDS (registered trademark)"
manufactured by Porextherm Dammstoffe GmbH was used. Its material is a
microporous molded body mainly based on fumed silica. The heat insulation material 14
is a sheet-like material 1000 mm long x 500 mm wide (thickness is one selected from the
four types of 1, 2, 10, and 12 mm). In use, a plurality of heat insulation materials 14
were sticked to the permanent bricks. In addition, the heat insulation materials 14 were
arranged so that no space was left between the adjacent heat insulation materials 14.-
^
18
Furthermore, for the magnesian carbonaceous wear bricks, ones with a carbon
content of 13 mass% were used. In the converter A, the magnesian carbonaceous wear
bricks were installed on the surface of the heat insulation material 14. On the other hand,
in the converter B, the magnesian carbonaceous wear bricks were installed on the surface
of the permanent bricks.
Table 1 shows the conditions of the researches on the actual devices, the obtained
shell temperatures, and the results of the life of the furnace walls. The details of
Examples 1 to 5. and Comparative Examples 1 to 8 in Table 1 will be described later.
[0036]
Table 1
[0037]
"Shell temperature when furnace is shut down" in Table 1 is a temperature of the
exterior surface of the shell 16 at the location where the wear brick is most damaged and
becomes thin or the location where the permanent brick is exposed. The erosion rate is a
damage thickness of the wear brick per charge (ch).
Here, if the shell temperature when the furnace is shut down is not less than
550°C, it is determined to be "fail". This is because, if the shell temperature when the
furnace is at rest is too high, there is a possibility of leading to a trouble such as a red heat
ofthe shell 16.
The erosion rate is divided into the average damage thickness per charge for 1 to
500 charges, which is in the first half period of use (first half of operation), and the
average damage thickness per charge for 2500 to 3000 charges, which is in the second half
period of use (second half of operation). In the erosion rate, not less than 0.30
(mm/charge) is determined to be "fail" regardless the period of use is for the first half or
the second half, from the viewpoint of life extension based on the past data.
[0038]
Firstly, the results of changing the installation position ofthe heat insulation
material 14 will be described by use of Examples 1 and 2 and Comparative Examples 1
and 2.
3 ^H 19
Examples 1 and 2 are results of setting the installation position of the heat
insulation material 14 within the appropriate range (0.75xT to 0.92xT) while Comparative
Examples 1 and 2 are results of setting the installation position of the heat insulation
material 14 outside the appropriate range.
The other conditions for the heat insulation material 14, namely, the thermal
conductivity (0.02 (W/(m»K))), the melting point (1400°C), and the thickness (2 mm)
were set within their respective, appropriate ranges. The operating ratio of the converter
A was standardized at not more than 70%.
[0039]
As is clear from the resuhs of Examples 1 and 2, it has been verified that with the
installation position of the heat insulation material 14 being set between the lower limit
(0.75xT) and upper limit (0.92xT) which is the appropriate range, it was possible to
extend the life of the wear brick in the first half and second half of the period of use
without an abnormal rise in temperature of the shell.
On the other hand, in Comparative Example 1, the installation position of the heat
insulation material 14 was so close to the operating surface 15 of the furnace wall 11
(0.73xT) that the heat insulation material 14 melted at an early stage, leading to an
exposure of the permanent brick. Therefore, it was necessary to shut down the furnace at
an early stage. Consequently, it was not possible to extend the life of the wear brick. In
Comparative Example 2, the installation position of the heat insulation material 14 was so
close to the shell 16 (0.95 xT) that when the heat insulating function of the heat insulation
material 14 was lost in the erosion process of the wear brick, the temperature of the shell
might rise and there is concern to a trouble such as a red heat of the shell 16.
[0040]
Next, the results of changing the thermal conductivity of the heat insulation
material 14 will be described by use of Examples 2 and 3 and Comparative Example 3.
Examples 2 and 3 are results of setting the thermal conductivity of the heat
insulation material 14 within the appropriate range (0.01 to 0.15 (W/(m»K))) while
Comparative Example 3 is a result of setting the thermal conductivity of the heat
4 20
insulation material 14 outside the appropriate range.
The other conditions of the heat insulation material 14, namely, the installation
position in the thickness direction of the fiimace wall (0.92xT), the melting point
(1400°C), and the thickness (2 mm) were set within their respective, appropriate ranges.
The operating ratio of the converter A was standardized at not more than 70%.
[0041]
As is clear from the results of Examples 2 and 3, it has been verified that with the
setting of the thermal conductivity of the heat insulation material 14 within the appropriate
range (Example 2: 0.02 (W/(m»K)), Example 3: 0.15 (W/(m»K))), it was possible to
extend the life of the wear brick in the first half and second half of the period of use.
On the other hand, in Comparative Example 3, the thermal conductivity was so
high (0.20 (W/(m'K))) that in the first half of the period of use, the heat insulating
capability of the heat insulation material 14 is decreased and the effect of the wear brick
on suppressing spall damage become small. Therefore, it was not possible to extend the
life of the wear brick. In the second half of the period of use, when the heat insulation
material 14 melted in the erosion process of the wear brick, it was possible to form a gap
with a target inner width on the back surface side of the wear brick. With the gap, the
stress developed on the operating surface 15 was allowed to be relieved. Therefore, it
was possible to prevent the wear brick to flake off to the operating surface 15 side.
However, because the erosion rate of the wear brick was high in the first half of the period
of use, it was not possible to extend the life of the wear brick over the whole period of use.
[0042]
Next, the results of changing the melting point of the heat insulation material 14
will be described by use of Example 2 and Comparative Example 4.
Example 2 is a result of setting the melting point of the heat insulation material
14 within the appropriate range (1000 to 1400°C) while Comparative Example 4 is a result
of setting the melting point of the heat insulation material 14 outside the appropriate
range;
The other conditions of the heat insulation material 14, namely, the installation
t 21
position (0.92xT), the thermal conductivity (0.02 (W/(m»K))), and the thickness (2 mm)
were set within their respective, appropriate ranges. The operating ratio of the converter
A was standardized at not more than 70%.
As is clear from Example 2, it has been verified that with the melting point of the
heat insulation material 14 being set within the appropriate range (1400°C), it was
possible to extend the life of the wear brick in the first half and second half of the period
of use.
On the other hand, the reason for the wear brick flaking off to the operating
surface 15 side in Comparative Example 4 was conceivably as follows. The melting
point of the heat insulation material 14 was so high (1500°C) that it was not possible to
melt the heat insulation material 14 in the erosion process of the wear brick and to produce
a gap on the back surface side of the wear brick. As a result, it was not possible to
relieve the stress developed on the operating surface 15 of the wear brick. Consequently,
the thermally expanding wear brick was not allowed to move toward the shell 16, and
hence, flaked off to the operating surface 15 side. Therefore, it was not possible to
extend the life of the wear brick.
[0043]
Next, the results of changing the thickness of the heat insulation material 14 will
be described by use of Examples 2 and 4 and Comparative Examples 5 and 6.
Examples 2 and 4 are results of setting the thickness of the heat insulation
material 14 within the appropriate range (2 to 10 mm) while Comparative Examples 5 and
6 are results of setting the thickness of the heat insulation material 14 outside the
appropriate range.
The other conditions of the heat insulation material 14, namely, the installation
position (0.92 xT), the thermal conductivity (0.02 (W/(m»K))), and the melting point
(1400°C) were set within their respective, appropriate ranges. The operating ratio of the
converter A was standardized at not more than 70%.
[0044]
As is clear from Examples 2 and 4^ it has been verified that with the thickness of
22
the heat insulation material 14 being set between the lower limit (2 mm) and upper limit
(10 mm), it was possible to extend the life of the wear brick in the first half and second
half of the period of use.
On the other hand, in Comparative Example 5, the heat insulation material 14 was
too thin (1 mm). Therefore, the inner width of the gap formed when the heat insulation
material 14 melted in the erosion process of the wear brick was so narrow that it was not
possible to relieve the stress developed on the operating surface 15 side. This resulted in
the flaking off of the wear brick to the operating surface 15 side. In Comparative
Example 6, the heat insulation material 14 was too thick (12 mm). Therefore, the inner
width of the gap produced when the heat insulation material 14 melted was so wide that
the structure of the wear brick became loose. As a result, the wear brick flaked off to the
operating surface 15 side. Consequently, in Comparative Examples 5 and 6, it was not
possible to extend the life of the wear brick.
[0045]
Lastly, the results of changing the operating ratio of the converter 12 verified by
use of the converters A in Examples 2 and 5 in which the heat insulation material 14 was
installed and by the converters B in Comparative Examples 7 and 8 in which the heat
insulation material 14 was not installed will be described with reference to Table 1 and
FIGS. 2A and 2B.
In Examples 2 and 5, the conditions of the heat insulation material 14, namely,
the installation position in the thickness direction of the furnace wall (0.92xT), the thermal
conductivity (0.02 (W/(m»K))), the melting point (1400°C), and the thickness (2 mm)
were set within their respective, appropriate ranges. Example 2 is a result of the case
where the operating ratio of the converter A was not more than 70% while Example 5 is a
result of the case where the operating ratio of the converter A is more than 70%.
On the other hand, in Comparative Examples 7 and 8, the heat insulation material
14 was not installed. Comparative Example 7 is a result in the case where the operating
ratio of the converter 12 was not more than 70% while Comparative Example 8 was a
result of the case where the operating ratio of the converter 12 was above, 70%. In
^
23
Comparative Examples 7 and 8, it was not possible to extend the life of the wear brick
because the heat insulation material 14 was not used.
[0046]
If the operating ratios of the converters A and B shown in FIG. 2 A are more than
0% and not more than 70%, namely, the operating ratios of the converters A and B are low,
then the temperature change in the converters 12 is large. Therefore, in the case where
the heat insulation material 14 was installed, the erosion rate of the wear brick was not less
than 0.1 (mm/charge) (namely, first half: 0.1 (mm/charge); second half :0.19 (mm/charge)).
That is, in both of the first half and second half of the period of use, the erosion rate was
more favorable than that of the case where the heat insulation material 14 was not installed.
Therefore, in the case where the heat insulation material 14 was installed, the effect of
extending the life of the wear brick by the heat insulation material 14 was significant.
On the other hand, if the operating ratios of the converters A and B shown in FIG.
2B are more than 70%, namely, if the operating ratios of the converters 12 are high, then
the temperature change in the converters 12 small. Therefore, in the case where the heat
insulation material 14 was installed, the erosion rate of the wear brick was more favorable
than that of the case where the heat insulation material 14 was not installed, in both of the
first half and second half of the period of use. However, as for the first half of the period
of use, the degree of improvement in erosion rate was smaller than that of the case where
the operating ratio of the converter was low (0.06 (mm/charge)).
Accordingly, it was found that the effect of installing the heat insulation material
14 is more significant when the operating ratio of the converter 12 is low.
[0047]
From above, it has been verified that by use of the furnace wall structure of a
molten metal vessel and a method for constructing a furnace wall of a molten metal vessel
according to the present embodiment, it is possible to extend the life of a refractory even
in an environment of use where spall damage is likely to be caused, and even in a situation
where, with a large temperature change in the molten metal vessel, spall damage is likely
to be caused.
24
[0048]
As described above, the present invention has been described with reference to an
embodiment, the present invention is not limited to the structures shown in the
embodiment, but includes other embodiments and modifications conceivable within what
is described in the appended claims. For example, the case where a part or all the
embodiments and modifications are combined to form a fiimace wall structure of a molten
metal vessel and a method for constructing a furnace wall of a molten metal vessel
according to the present invention is included in the scope of rights of the present
invention.
Furthermore, while the converter 12 as a molten metal vessel has been described
in the embodiment, the application is not limited only to this. The present invention may
be applied to other molten metal vessels, for example a molten iron ladle, molten steel
ladle, electric furnace, and the like.
INDUSTRIAL APPLICABILITY
[0049]
According to the present invention, it is possible to provide a furnace wall
structure of a molten metal vessel and a method for constructing a furnace wall of a
molten metal vessel that makes it possible to extend the life of a refractory even in an
environment of use where spall damage is caused, and even in a situation where, with a
large temperature change in the molten metal vessel, spall damage is likely to be caused.
Brief Description of the Reference Symbols
[0050]
10: magnesia carbon brick (magnesia carbon refractory)
11: furnace wall
12: converter (molten metal vessel)
13: back surface
14-: heat insulation material -
¥ 25
15: operating surface
16: shell
17: magnesia brick
18: shell contact surface
TABLE 1
EXAMPLE 1
EXAMPLE 2
EXAMPLE 3
EXAMPLE 4
EXAMPLE 5
COMPARATIVE
EXAMPLE 1
COMPARATIVE
EXAMPLE 2
COMPARATIVE
EXAMPLE 3
COMPARATIVE
EXAMPLE 4
COMPARATIVE
EXAMPLE 5
COMPARATIVE
EXAMPLE 6
COMPARATIVE
EXAMPLE 7
COMPARATIVE
EXAMPLE 8
HEAT INSULATION MATERIAL
INSTALLATION
POSITION
(XT)
0.75
0.92
0.92
0.92
0.92
0.73
0.95
0.92
0.92
0.92
0.92
-
-
THERMAL
CONDUCTIVITY
(WAm-K))
0.02
0.02
0.15
0.02
0.02
0.02
0.02
0.20
0.02
0.02
0.02
-
-
MELTING
POINT
(°C)
1400
1400
1400
1400
1400
1400
1400
1400
1500
1400
1400
-
-
THICKNESS
(mm)
2
2
2
10
2
2
2
2
2
1
12
-
-
OPERATING
RATIO OF
CONVERTER
(%)
< 70
< 70
< 70
< 70
> 70
< 70
< 70
< 70
< 70
< 70
< 70
< 70
> 70
SHELL
TEMPERATURE
WHEN
FURNACE IS
SHUT DOWN
CO
450
470
480
460
470
430
610
470
430
500
450
520
450
EROSION RATE
(mm/ch)
FIRST HALF
(1 TO 500 ch)
0.25
0.26
0.27
0.26
0.24
0.23
0.27
0.30
0.25
0.28
0.25
0.36
0.30
SECOND HALF
(2500 TO 3000 ch)
0.23
0.23
0.24
0.24
0.22
EARLY FURNACE
SHUTDOWN
0.25
0.25
0.40
(WITH FLAKING OFF)
0.40
(WITH FLAKING OFF)
0.43
(WITH FLAKING OFF)
0.42
(WITH FLAKING OFF)
0.39
(WITH FLAKING OFF)
^

^. 10^^^ .,,
CLAIMS
1. A furnace wall structure of a molten metal vessel that is provided with a furnace
wall lined with a magnesia carbon refractory, the furnace wall structure comprising:
a shell; a permanent refractory lined on an interior surface of the shell; a heat
insulation material lined on an interior surface of the permanent refractory; and the
magnesia carbon refractory lined on an interior surface of the heat insulation material,
wherein in a case that a thickness of the furnace wall except the shell when the
fiimace wall is seen in a vertical cross-sectional view is set to be T mm in millimeter unit,
the heat insulation material with a thermal conductivity of not less than 0.01
W/(m«K) and not more than 0.15 W/(m»K) in a range of 25°C to 300°C, with a melting
point of not less than 1000°C and not more than 1400°C, and with a thickness of not less
than 2 mm and not more than 10 mm is arranged
in a range in a thickness direction between a position not less than 0.75 xT (mm)
and not more than 0.92xT from an interior surface of the magnesia carbon refractory
toward the shell.
2. The fiimace wall structure of a molten metal vessel according to claim 1,
wherein the magnesia carbon refractory has a carbon content of not less than 0.5
mass% and not more than 15 mass%.
3. A method for constructing a furnace wall of a molten metal vessel that is
provided with a furnace wall lined with a magnesia carbon refractory, the method
comprising:
lining a permanent refractory on an interior surface of a shell;
lining a heat insulation material on an interior surface of the permanent
refractory; and
lining the magnesia carbon refractory on an interior surface of the heat insulation
material.
^:IIGW;AV » I *»
wherein, in the process of linmg the heat insulation material, in a case that a
thickness of the furnace wall except the shell when the furnace wall is seen in a vertical
cross-sectional view is set to be T mm in millimeter unit,
the heat insulation material with a thermal conductivity of not less than 0.01
W/(m»K) and not more than 0.15 W/(m«K) in a range of 25°C to 300°C, with a melting
point of not less than 1000°C and not more than 1400°C, and with a thickness of not less
than 2 mm and not more than 10 mm is arranged
in a range in a thickness direction between a position not less than 0.75 xT (mm)
and not more than 0.92xT from an interior surface of the magnesia carbon refractory
toward the shell.
4. The method for constructing a furnace wall of a mohen metal vessel according to
claim 3,
wherein the molten metal vessel is a converter, and an operating ratio of the
converter has is more than 0% and not more than 70%.
5. The method for constructing a furnace wall of a molten metal vessel according to
claim 3 or 4,
wherein the magnesia carbon refractory has a carbon content of not less than 0.5
mass% and not more than 15 mass%.