U.S. patent application number 10/483981 was filed with the patent office on 2004-09-02 for method for accelerating separation of granular metallic iron from slag.
Invention is credited to Tsuge, Osamu, Yoshida, Shohei.
Application Number | 20040168550 10/483981 |
Document ID | / |
Family ID | 19056630 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040168550 |
Kind Code |
A1 |
Tsuge, Osamu ; et
al. |
September 2, 2004 |
Method for accelerating separation of granular metallic iron from
slag
Abstract
The present invention is intended to provide a method for
accelerating separation of granular metallic iron as an objective
product and slag as a by-product when the granular metallic iron is
produced with reduction melting of raw-material agglomerates that
contain an iron-oxide containing material and a carbonous reducing
agent, thereby producing metallic iron of a high iron grade in
which slag is satisfactorily separated and removed. The present
invention resides in a method for accelerating separation of
granular metallic iron and slag, the method being employed to
produce the granular metallic iron with reduction melting of
raw-material agglomerates that contain an iron-oxide containing
material and a carbonous reducing agent, wherein a mixed solid of
the granular metallic iron produced with the reduction melting and
the slag produced as a by-product are quickly cooled to accelerate
separation of the granular metallic iron and the by-product slag
from each other.
Inventors: |
Tsuge, Osamu; (Kobe-shi
Hyogo, JP) ; Yoshida, Shohei; (Hyogo, JP) |
Correspondence
Address: |
Oblon Spivak McClelland
Maier & Neustadt
1940 Duke Street
Alexandria
VA
22314
US
|
Family ID: |
19056630 |
Appl. No.: |
10/483981 |
Filed: |
January 22, 2004 |
PCT Filed: |
June 17, 2002 |
PCT NO: |
PCT/JP02/05996 |
Current U.S.
Class: |
75/503 |
Current CPC
Class: |
C21B 13/0086 20130101;
C21B 2400/062 20180801; C21B 13/0046 20130101; C21B 2400/06
20180801; C21B 2400/068 20180801; C21B 13/0006 20130101; C21B 3/08
20130101; C21B 2400/072 20180801; C21B 2400/026 20180801; C21B
13/105 20130101; C21B 2400/024 20180801 |
Class at
Publication: |
075/503 |
International
Class: |
C21C 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 2001 |
JP |
2001-223266 |
Claims
1. A method for accelerating separation of granular metallic iron
and slag, the method being employed to produce the granular
metallic iron with reduction melting of raw-material agglomerates
that contain an iron-oxide containing material and a carbonous
reducing agent, wherein a mixed solid of the granular metallic iron
produced with the reduction melting and the slag produced as a
by-product are quickly cooled to accelerate separation of the
granular metallic iron and the by-product slag from each other.
2. The method according to claim 1, wherein the quick cooling is
performed using a coolant.
3. The method according to claim 1 or 2, wherein the quick cooling
is performed at a cooling rate of not less than 250.degree. C./min
in at least a part of the range from a solidifying temperature of
the granular metallic iron to 150.degree. C.
4. The method according to claim 3, wherein the quick cooling is
performed at a cooling rate of not less than 350.degree.
C./min.
5. The method according to any one of claims 1 to 4, wherein water
is employed as the coolant, the quick cooling of the granular
metallic iron is stopped until reaching 150.degree. C., and
moisture residing on and attached to the granular metallic iron is
dried.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for accelerating
separation of granular metallic iron as an objective product and
slag as a by-product when metallic iron is produced with reduction
melting of raw-material agglomerates that contain an iron-oxide
containing material and a carbonous reducing agent. More
specifically, the present invention relates to an improved method
for easily separating a mixed solid of granular metallic iron,
which is produced by supplying raw-material agglomerates to a
reduction melting furnace and reducing, melting and aggregating
iron oxides in the raw-material agglomerates, and slag, which is
produced as a by-product, into the granular metallic iron and the
slag.
BACKGROUND ART
[0002] When metallic iron of a low iron grade (in which large
amounts of slag components, such as SiO.sub.2, Al.sub.2O.sub.3 and
CaO, are contained as a veinstone component in iron ore and ash in
a carbonous material, which are used as raw materials) is supplied
as raw materials for iron melted in a steel-making furnace, e.g., a
converter or an electric furnace, many problems occur in that
operability of the electric furnace is adversely affected with an
increase of the slag amount, the iron yield is reduced because of
mixing of iron into slag, energy consumption per unit product is
increased, and productivity is lowered. Accordingly, metallic iron
of a high iron grade with a less content of slag components is
demanded as raw materials for molten iron. As a process for
producing such metallic iron of a high iron grade, it is known to
improve, for example, a direct iron-making method such as a shaft
furnace method in which metallic iron is produced by directly
reducing an iron-oxide containing material, such as iron ore and/or
iron oxides, with a carbonous material and a reducing gas, and a
method for producing metallic iron with steps of mixing a carbonous
material and powdery iron oxides into the form of agglomerates or
pellets, and reducing the mixture on a rotary hearth under heating,
as disclosed in, e.g., U.S. Pat. No. 3,443,931. By using such
improved methods, metallic iron of a high iron grade is
produced.
[0003] For example, Japanese Unexamined Patent Application
Publication No. 2000-144224 is known as an iron-making method for
obtaining high-purity metallic iron with reduction melting of
raw-material agglomerates that contain an iron-oxide containing
material, such as iron ore and/or iron oxides, and a carbonous
reducing agent such as coke. In the technology for obtaining
granular metallic iron with reduction melting of raw-material
agglomerates by using a reduction melting furnace of the moving
hearth type, as disclosed in that Publication, the iron oxides in
the raw-material agglomerates are reduced while the raw-material
agglomerates are held in a solid state. Then, metallic iron and
slag as a by-product are rendered to melt and aggregate separately.
Thereafter, by cooling the molten metallic iron and the molten slag
(with a primary cooling step in which they are cooled down to,
e.g., about 1100 to 900.degree. C.), the molten metallic iron and
the molten slag are brought into solidified states (called
respectively "granular metallic iron" and "slag granules"). After
the cooling and the solidification, the granular metallic iron and
the slag granules are discharged out of the furnace. After being
discharged, the granular metallic iron and the slag granules are
left to stand for natural cooling (secondary cooling). Further, the
granular metallic iron and the slag granules are selectively
separated from each other by any suitable separating means such
that only the granular metallic iron is employed as raw materials
for molten iron supplied to a steel-making furnace, etc.
[0004] In the above-mentioned metallic iron producing method, the
cooling is divided into a first cooling stage in which the metallic
iron and the slag are cooled for solidification to a level lower
than the solidifying point thereof, and a second cooling stage in
which the temperature is further lowered for subsequent
transportation and selection of the metallic iron.
[0005] Although the first cooling stage is performed in the
reduction melting furnace in many cases, the slag granules are
often present after the first cooling stage in such a non-separated
state.,(called a "mixed solid") that the slag granules are adhered
to the granular metallic iron. Also, in the second cooling stage in
which the granular metallic iron and the slag granules are left to
stand outside the furnace for natural cooling, the metallic iron
and the slag are not sufficiently separated from each other. For
those reasons, it has been difficult to separately collect only the
granular metallic iron at high efficiency with magnetic screening,
a sieve, etc., and to avoid a substantial amount of slag from
mixing into the granular metallic iron. Even with the metallic iron
having a high purity in itself, therefore, an amount of molten slag
generated in the steel-making furnace is increased because of the
slag components that are unavoidably mixed in the metallic iron
without being completely separated, thus resulting in adverse
effects upon operability and product quality. From those situations
in the art, there is demanded a technique capable of separating
metallic iron and slag as a by-product at high efficiency before
they are subjected to screening for separation.
[0006] In view of the above-described problems in the related art,
an object of the present invention is to provide a method for
accelerating separation of granular metallic iron as an objective
product and slag as a by-product when the granular metallic iron is
produced with reduction melting of raw-material agglomerates that
contain an iron-oxide containing material and a carbonous reducing
agent, thereby producing metallic iron of a high iron grade in
which slag is satisfactorily separated and removed.
DISCLOSURE OF THE INVENTION
[0007] The present invention having succeeded in solving the
above-described problems resides in a method for accelerating
separation of granular metallic iron and slag, the method being
employed to produce the granular metallic iron with reduction
melting of raw-material agglomerates that contain an iron-oxide
containing material and a carbonous reducing agent, wherein a mixed
solid of the granular metallic iron produced with the reduction
melting and the slag-produced as a by-product are quickly cooled to
accelerate separation of the granular metallic iron and the
by-product slag from each other. When practicing the method of the
present invention, it is recommended to quickly cool the mixed
solid using a coolant. It is also recommended that the mixed solid
be quickly cooled at a cooling rate of preferably not less than
250.degree. C./min, more preferably not less than 350.degree.
C./min, in at least a part of the range from a solidifying
temperature of the granular metallic iron to 150.degree. C. In a
preferred embodiment of the present invention, water is employed as
the coolant, the quick cooling of the metallic iron is stopped
until reaching 150.degree. C., and moisture residing on and
attached to the metallic iron is dried.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic explanatory view showing one example
of a reduction melting furnace of the circular moving hearth type
to which the present invention is applied.
[0009] FIG. 2 is a sectional view taken along the line A-A in FIG.
1.
[0010] FIG. 3 is an explanatory view showing a section of the
reduction melting furnace in the developed form as viewed in the
rotating direction of a moving hearth in FIG. 1.
[0011] FIG. 4 is a schematic explanatory view showing a manner of
cooling a mixed solid with water sprays.
[0012] FIG. 5 is a schematic explanatory view showing a manner of
cooling the mixed solid with dipping in water.
[0013] FIG. 6 is a schematic explanatory view showing a manner of
cooling the mixed solid with a nitrogen gas.
[0014] FIG. 7 is a schematic explanatory view showing a manner of
cooling a mixed solid with water.
BEST MODE FOR CARRYING OUT THE INVENTION
[0015] As a result of carrying out intensive studies to solve the
problems in the related art, the inventors have accomplished the
present invention based on the finding that, by quickly cooling a
mixed solid of granular metallic iron, which is produced with
reduction melting of raw-material agglomerates that contain an
iron-oxide containing material and a carbonous reducing agent, and
slag produced as a by-product, separation of the granular metallic
iron and the by-product slag is remarkably accelerated.
[0016] In the present invention, the raw-material agglomerates
contain an iron-oxide containing material, such as iron ore and
iron oxides or partly reduced materials thereof, and a carbonous
reducing agent, such as coke and coal. The raw-material
agglomerates may contain any suitable additive, etc. if necessary.
Also, the raw-material agglomerates are not limited in shape to a
particular one, but can be prepared in the form of pellets,
briquettes, etc. Further, the raw-material agglomerates can be
formed by any suitable method depending on the agglomerate shape.
In addition, a mixing ratio of the iron-oxide containing material
to the carbonous reducing agent is not limited to a particular
value, but can be selected to a proper value depending on the
purpose for use. The size of the raw-material agglomerates is also
not limited to a particular one.
[0017] The granular metallic iron is produced with reduction
melting of the raw-material agglomerates described above. A
practical method for the reduction melting is not limited to a
particular one, but can be carried out using: a well-known
reduction melting furnace. It is to be noted that while the present
invention will be described below in connection with, for example,
a method for producing metallic-iron using a reduction melting
furnace of the moving hearth type, the present invention is not
limited to the following description and the illustrated examples.
The present invention will be described in detail with reference to
the drawings showing a practical construction of the reduction
melting furnace.
[0018] FIGS. 1 to 3 are schematic explanatory views showing one
example of a reduction melting furnace of the moving hearth type
developed by the inventors, to which the present invention is
applied. The furnace is of a dome-shaped structure having a rotary
moving hearth in the doughnut form. Specifically, FIG. 1 is a
schematic perspective view, FIG. 2 is a sectional view taken along
the line A-A in FIG. 1, and FIG. 3 is a schematic explanatory view
showing a section of the reduction melting furnace in the developed
form as viewed in the rotating direction of the rotary hearth in
FIG. 1 for easier understanding. In the drawings, numeral 1 denotes
a rotary hearth, and 2 denotes a furnace body covering the rotary
hearth. The rotary hearth 1 is constructed such that it can be
driven by a driving device (not shown) to rotate at a proper
speed.
[0019] As a matter of course, however, the construction of the
reduction melting-furnace of the moving hearth type, to which the
present invention is applied, is not limited to the shape and
structure shown in FIGS. 1 to 3. So long as the reduction melting
furnace includes a moving hearth as a constituent element, various
reduction melting furnaces of the moving hearth-type having any
other structures, e.g., the straight grate type, can also be
effectively employed in the present invention.
[0020] A plurality of combustion burners 3 are disposed at
appropriate places in a wall surface of the furnace body 2.
Combustion heat and radiation heat generated by the combustion
burners 3 are transmitted to the raw-material agglomerates on the
rotary hearth 1 for performing heating reduction of the
raw-material agglomerates. In a preferred example of the furnace
body 2 as shown, the interior of the furnace body 2 is divided by
three partition walls K.sub.1, K.sub.2, K.sub.3 into a first zone
Z.sub.1, a second zone Z.sub.2, a third zone Z.sub.3, and a fourth
zone Z.sub.4. A raw-material supply means 4 is disposed in an
opposed relation to the rotary hearth 1 at the most upstream side
in the rotating direction of the furnace body 2, and a discharging
means 6 is provided at the most downstream side in the rotating
direction (in other words, at the side immediately upstream of the
supply means 4 because of the rotary structure).
[0021] In operation of such a reduction melting furnace, the rotary
hearth 1 is rotated at a predetermined speed, and the raw-material
agglomerates are supplied from the supply means 4 onto the rotary
hearth 1 such that a layer of the raw-material agglomerates has a
proper thickness. The raw-material agglomerates charged on the
rotary hearth 1 are subjected to combustion heat and radiation heat
generated by the combustion burners 3 while moving in the first
zone Z.sub.1. Iron oxides in the raw-material agglomerates are
reduced under heating, while maintaining a solid state, with the
aid of the carbonous material in the raw-material agglomerates and
carbon monoxide generated upon combustion of the carbonous
material. Then, the raw-material agglomerates are further reduced
under heating in the second zone Z.sub.2, whereby metallic iron is
produced with almost complete reduction of the iron oxides. The
generated metallic iron is further heated in the third zone
Z.sub.3, and hence it is carburized and melted. The thus-produced
molten metallic iron and molten slag as a by-product are present in
such a state that the molten slag lies on the molten metallic iron,
because of a difference in specific gravity between them. The
molten metallic iron and the molten slag are cooled by any suitable
cooling means C down to temperature not higher than the solidifying
point thereof in the fourth zone Z.sub.4 for solidification. The
solidified metallic iron and slag are successively discharged by
the discharging means 6. With the cooling and the solidification,
the molten metallic iron and the molten slag are mostly separated
into granular: metallic iron and slag granules, but there also
exists granular metallic iron (mixed solid) including slag adhered
to the iron because of incomplete separation. Therefore, the
granular metallic iron, the slag granules and the mixed solid are
discharged to the outside of the furnace. The mixed solid, etc.
(hereinafter "the mixed solid, etc." means not only the mixed
solid, but also the granular metallic iron and the slag granules)
discharged at that time are in a relatively high temperature state
(e.g., approximately from the solidifying temperature to
900.degree. C.).
[0022] In the present invention, the mixed solid discharged in such
a relatively high temperature state is quickly cooled to accelerate
separation of the metallic iron and the slag from each other by
utilizing a difference in shrinkage rate between the metallic iron
and the slag both contained in the mixed solid. As a result, the
mixed solid is separated into the granular metallic iron hardly
containing slag components and the slag granules (made up of slag
components, such as SiO.sub.2, Al.sub.2O.sub.3 and CaO, contained
as a veinstone component in iron ore and ash in a carbonous
material, which are used as raw materials).
[0023] In the present invention, the term "quick cooling" means
quicker cooling than in the case of leaving the mixed sold to stand
in the atmosphere for natural cooling. It is, however, particularly
recommended to quickly cool the mixed solid using a coolant, for
example, and to apply thermal impacts to the mixed solid from the
viewpoint of increasing the effect of accelerating separation of
the metallic iron and the slag from each other. Also, quick cooling
of the mixed solid at a cooling rate of not less than 250.degree.
C./min is preferred in that distortions occur in contact areas
between the metallic iron and the slag because of a sudden change
in shrinkage rate (i.e., difference in thermal expansion
coefficient) between the metallic iron and the slag both contained
in the mixed solid, whereby separation of the metallic iron and the
slag is accelerated. A more preferable cooling rate is not less
than 350.degree. C./min. The cooling rate can be calculated by
continuously measuring a temperature change of the mixed solid that
is discharged to the outside of the furnace.
[0024] The quick cooling method is not limited to a particular one,
but it is preferred to perform the quick cooling using a liquid
and/or inert gas as the coolant. The quick cooling with a liquid is
recommended because a liquid can provide a higher cooling rate and
hence a higher separation effect than inert gas. The liquid used
for the quick cooling is not limited to a particular one, and there
is no limitation as to whether any additive is added to the liquid
or not. The use of water is preferred from the viewpoints of
economy, safety and cooling efficiency. Also, there is no
particular limitation in use of inert gas, but the use of a
nitrogen gas is preferred from the viewpoints of economy and
safety.
[0025] When performing the quick cooling using water, for example,
the desired cooling rate may be obtained by spraying water to the
mixed solid while regulating the amount of the supplied water with
any suitable spraying means. As shown in FIG. 4, by way of example,
the mixed solid, etc. discharged out of the moving hearth type
furnace are transferred onto a moving means 9, such as a belt
conveyor, through a feed duct 8 for movement therewith, and water
is sprayed toward the mixed solid, etc. from spraying means 11 that
are provided in any desired number with any suitable intervals. The
sprayed water quickly cools the mixed solid, etc. and accelerates
separation of the slag and the metallic iron because of a
difference in shrinkage rate between them, whereby the granular
metallic iron and the slag granules are obtained. Alternatively,
the mixed solid, etc. may be quickly cooled at the desired cooling
rate by pooling water in a cooling tank and controlling the water
temperature with selective supply and drain of water. As shown in
FIG. 5, by way of example, the mixed solid, etc. discharged out of
the moving hearth type furnace 7 are introduced to a cooling tank
13 filled with water 12 through a feeding means 8, such as a feed
duct, for dipping in the water. After being quickly cooled down to
the predetermined temperature, the mixed solid, etc. are taken out
of the cooling tank with any suitable conveying means such as a
conveyor. The quick cooling method of dipping the mixed solid, etc.
in water is more preferable than the quick-cooling method of
spraying water because the former method can provide a higher
cooling rate, a greater difference in shrinkage rate, and hence a
higher separation rate.
[0026] When quickly cooling the mixed solid, etc. by using inert
gas such as a nitrogen gas, though not shown, the inert gas may be
directly sprayed to the mixed solid, etc., or the mixed solid, etc.
may be exposed to an atmosphere of inert gas.
[0027] Additionally, the quick cooling method is not limited to the
above-described ones, and those quick cooling methods can be
implemented in any desired combination. For example, the mixed
solid, etc. may be quickly cooled by spraying water under a
nitrogen gas atmosphere, or the mixed solid, etc. may be quickly
cooled under a nitrogen gas atmosphere after spraying water.
[0028] Further, the higher the temperature of the mixed solid, etc.
at the start of the quick cooling, the greater is the separation
effect resulting from the quick cooling. It is therefore preferable
to quickly cool the mixed solid, etc. when they are in a
high-temperature state immediately after being discharged out of
the,furnace. Because the temperature of the mixed solid, etc.
discharged out of the furnace depends on how far the mixed solid,
etc. have been cooled in the furnace, a practical temperature at
the start of the quick cooling is not limited to a particular
value. However, since the mixed solid, etc. discharged out of the
furnace are usually in a solid state, a preferable range for the
quick cooling is at least a part of the range from the solidifying
point (about 1280.degree. C.) of the metallic iron to 150.degree.
C. If the quick cooling is started from temperature lower than
150.degree. C., sufficient thermal impacts cannot be applied to the
mixed solid, etc. and the separation effect at satisfactory level
cannot be obtained in some cases.
[0029] The expression "at least a part" of the range means that the
quick cooling does not require to be continued over the entire
temperature range. For example, it is meant that when performing
the quick cooling at a cooling rate of not less than 250.degree.
C./min in at least a part of the range from the solidifying point
of the metallic iron to 150.degree. C., the mixed solid, etc. may
be left to stand for natural cooling in the other temperature range
than in a certain part of the range from the solidifying point of
the metallic iron to 150.degree. C. in which the mixed solid, etc.
are quickly cooled at a cooling rate of not less than 250.degree.
C./min. In other words, it is not meant that the quick cooling of
the mixed solid, etc.-must be continued over the entire range from
the solidifying point of the metallic iron to 150.degree. C.
Further, the quick cooling may be continued beyond the above
temperature range, and it is not meant that the quick cooling must
be stopped at the time when the temperature reaches 150.degree. C.
For example, after quickly cooling the mixed solid, etc. in the
range from the solidifying point of the metallic iron to
150.degree. C., the quick cooling may be further continued in a
temperature range lower than 150.degree. C. Anyway, the quick
cooling requires to be stopped at the time when the desired
temperature is reached.
[0030] Because the separation accelerating effect based on quick
cooling, which is employed in the present invention, is developed,
as described above, by utilizing distortion fracture at the
interface between the metallic iron and the slag attributable to
thermal impacts caused upon the quick cooling, the quick cooling
time may be selected to be very short. For example, even the quick
cooling for several seconds is sufficient to fulfill the intended
purpose. In particular, when a coolant is employed to perform the
quick cooling, the mixed solid is quickly cooled and the separation
accelerating effect is obtained at the moment when the mixed solid
is brought into contact with the coolant. For example, in the case
of dipping the mixed solid in water, the temperature of the mixed
solid is abruptly lowered at the moment when the mixed solid is
brought into contact with the water, whereupon there occurs
distortion fracture at the interface between the metallic iron and
the slag, thus resulting in separation of the metallic iron and the
slag. As a matter of course, during the period in which the mixed
solid is dipped in the water, the quick cooling of the mixed solid
is still continued, and the difference in shrinkage rate between
the metallic iron and the slag at the interface therebetween is
increased in the mixed solid that remains in a non-separated state.
Therefore, the separation accelerating effect is further enhanced
and a non-separation rate of the slag from the metallic iron is
reduced.
[0031] Furthermore, in the present invention, it is also preferable
that in addition to the use of water for the quick cooling, the
quick cooling of the metallic iron be stopped until reaching
150.degree. C., and thereafter the metallic iron be left to stand
for natural cooling. Stated otherwise, by stopping the quick
cooling (stopping contact of the mixed solid, etc. with water)
after cooling the mixed solid, etc. to 150.degree. C. using water,
and then leaving the mixed solid, etc. to stand for natural
cooling, moisture attached to the metallic iron is evaporated with
heat of the metallic iron itself. Accordingly, the metallic iron
can be dried with no need of providing any drying means such as a
drier.
[0032] In the above, the method of the present invention is
described in connection with the case of quickly cooling the mixed
solid discharged from the reduction melting furnace together with
the granular metallic iron and the slag granules. However, the
present invention is also applicable to the case of separating the
metallic iron and the slag from each other by any suitable
screening means (such as a sieve or a magnetic screening device) at
the time when the granular metallic iron, the slag granules and the
mixed solid are discharged out of the reduction melting furnace,
and then selectively taking out only the mixed solid or both of the
mixed solid and the granular metallic iron through selective
collection of the granular metallic iron, the slag granules and the
mixed solid. Thus, the method of the present invention can be
implemented regardless of the presence of the granular metallic
iron and/or the slag granules in addition to the mixed solid.
[0033] Also, by separating the metallic iron and the slag contained
in the mixed solid from each other as the granular metallic iron
and the slag granules according to the method of the present
invention, and then selectively collecting the granular metallic
iron and the slag granules by any suitable screening means (such as
a sieve or a magnetic screening device), metallic iron
raw-materials having purity of not less than about 95%, more
preferably of not less than about 98%, and containing a very small
amount of slag components can be finally obtained.
[0034] The method of the present invention will be described below
in connection with Example. It is, however, to be noted that the
following Example is not purported to limit the present invention,
and the present invention can be modified in appropriate ways based
on the purports of the present invention mentioned above and
below.
EXAMPLE
[0035] Raw-material agglomerates containing iron ore and coal were
supplied to the reduction melting furnace of the moving hearth type
shown in FIGS. 1 and 3, and then subjected to heating reduction
(temperature in the furnace: 1300.degree. C.) with combustion heat
and radiation heat generated by combustion burners while the
raw-material agglomerates were maintained in a solid state. The
raw-material agglomerates were further heated and molten under a
reducing atmosphere, thus generating a mixture of metallic iron as
an objective product and slag as a by-product. The mixture was
cooled down to 1000.degree. C. in the furnace. Granular metallic
iron, slag granules and a mixed solid all solidified with the
cooling were discharged by a discharging means provided at the
downstream side in the moving direction of a hearth. The discharged
mixed solid, etc. were introduced through a feed duct to a cooling
tank for quick cooling, to which coolants shown in Table 1 were
supplied. The cooling tank using nitrogen as the coolant is shown
in FIG. 6. The mixed solid, etc. were quickly cooled by supplying a
nitrogen gas to the cooling tank at all times (flow rate: 10
Nm.sup.3/hr) while adjusting the flow rate of the nitrogen gas so
that the cooling rate was held at 250.degree. C./min. Additionally,
the flow rate of the supplied nitrogen gas was adjusted by
exhausting the nitrogen gas through an exhaust duct 14. At the time
when the temperature of the metallic iron, etc. was lowered to room
temperature, the metallic iron, etc. were taken out of the cooling
tank as required, and a total amount of the mixed solid was
measured (see "Mass of Mixed Solid" and "Slag Non-Separation Rate"
in Table 1). In the case of the nitrogen cooling, the temperature
of the metallic iron, etc. was measured by inserting a thermocouple
in a mass of the mixed solid accumulated in the cooling tank. The
cooling tank using water as the coolant is shown in FIG. 7. Water
was pooled in the cooling tank beforehand to cool the mixed solid,
etc. introduced to the cooling tank. As a result of separately
measuring a cooling rate of the mixed solid, etc. in a water dipped
state, the cooling rate was 350.degree. C./min. At the time when
the temperature of the mixed solid, etc. was lowered to room
temperature, the mixed solid, etc. were taken out of the cooling
tank as required, and a total amount of the mixed solid was
measured. Measured results are shown in Table 1.
[0036] Further, in the case of the water cooling, the cooling rate
obtained with water dipping was separately measured. More
specifically, a thermocouple was inserted in a mass of the mixed
solid heated to 1000.degree. C. in the heating furnace, and the
cooling rate of the mixed solid was measured in a water dipped
state.
1 TABLE 1 Nitrogen Cooling Water Cooling Mass Slag Non- Mass of
Slag Non- Total of Mixed Separation Total Mixed Separation
Reduction Test No. Mass kg Solid kg Rate % Mass kg Solid kg Rate %
Ratio 1 7.40 0.70 9.5 7.47 0.15 2.0 0.21 2 6.40 0.35 5.5 6.50 0.05
0.8 0.15 3 6.00 0.15 2.5 5.40 0.01 0.2 0.08 * "Total Mass Kg" means
the mass of the mixed solid before the start of the cooling. *
"Mass of Mixed Solid kg" means the mass of the mixed solid
remaining after the cooling. * "Slag Non-Separation Rate %" = (Mass
of Mixed Solid kg)/(Total Mass kg) * "Reduction Ratio" = (Slag
Non-Separation Rate % with the water cooling)/(Slag Non-Separation
Rate % with the nitrogen cooling)
[0037] As seen from Table 1, slag can be separated and removed from
the mixed solid by employing nitrogen or water as the coolant.
Also, it is seen that the tests employing water as the coolant show
lower non-separation rates than the tests employing nitrogen as the
coolant, and hence the quick cooling means with water dipping is
more preferable quick cooling means.
COMPARATIVE EXAMPLE
[0038] Granular metallic iron was produced using the reduction
melting furnace of the moving hearth type under the same conditions
as those in Example described above. The mixed solid, etc.
discharged out of the furnace were left to stand in the atmosphere
for natural cooling to room temperature, but a very high
non-separation rate (15%) was resulted.
[0039] Industrial Applicability
[0040] According to the method of the present invention, as
described above, metallic iron and slag as components of a mixed
solid discharged out of a furnace can be separated from each other
with ease. Since the present invention provides metallic iron
raw-materials being free from slag and having high iron purity,
molten steel having stable quality can be produced with high
productivity while reducing electric power consumed by an electric
furnace per unit product, by constructing a continuous system that
utilizes the thus-provided metallic iron raw-materials as raw
materials for steel making.
* * * * *