U.S. patent application number 13/142368 was filed with the patent office on 2011-11-03 for method for producing granular iron.
This patent application is currently assigned to KABUSHIKI KAISHA KOBE SEIKO SHO. Invention is credited to Shuzo Ito, Shoichi Kikuchi, Takeshi Sugiyama, Osamu Tsuge.
Application Number | 20110265603 13/142368 |
Document ID | / |
Family ID | 42355876 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110265603 |
Kind Code |
A1 |
Sugiyama; Takeshi ; et
al. |
November 3, 2011 |
METHOD FOR PRODUCING GRANULAR IRON
Abstract
A method for producing granular iron comprising: charging
agglomerates formed from a raw material mixture containing an iron
oxide-containing substance and a carbonaceous reducing agent onto a
carbonaceous material spread on a hearth of a furnace; and heating
the agglomerates to thereby reduce and melt iron oxides in the
agglomerates, wherein the temperature of the agglomerates in the
furnace is set in a range between 1200.degree. C. and 1500.degree.
C.; the oxygen partial pressure in atmospheric gas under which the
agglomerates are heated is set to 2.0.times.10.sup.-13 atm or more
at standard state; and the linear speed of the atmospheric gas in
the furnace is set to 4.5 cm/second or more.
Inventors: |
Sugiyama; Takeshi; (Hyogo,
JP) ; Ito; Shuzo; (Hyogo, JP) ; Tsuge;
Osamu; (Hyogo, JP) ; Kikuchi; Shoichi; (Hyogo,
JP) |
Assignee: |
KABUSHIKI KAISHA KOBE SEIKO
SHO
HYOGO
JP
|
Family ID: |
42355876 |
Appl. No.: |
13/142368 |
Filed: |
January 15, 2010 |
PCT Filed: |
January 15, 2010 |
PCT NO: |
PCT/JP10/50373 |
371 Date: |
June 27, 2011 |
Current U.S.
Class: |
75/331 |
Current CPC
Class: |
C21B 13/0073 20130101;
C21B 13/105 20130101; Y02P 10/136 20151101; Y02P 10/134 20151101;
C21B 13/0046 20130101 |
Class at
Publication: |
75/331 |
International
Class: |
B22F 9/20 20060101
B22F009/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 23, 2009 |
JP |
2009-013378 |
Claims
1. A method for producing granular iron, comprising: charging an
agglomerate formed from a raw material mixture comprising an iron
oxide comprising substance and a carbonaceous reducing agent onto a
carbonaceous material spread on a hearth of a furnace; and heating
the agglomerate to thereby reduce and melt at least one iron oxide
in the agglomerate, wherein a temperature of the agglomerate in the
furnace is in a range between 1200.degree. C. and 1500.degree. C.,
an oxygen partial pressure in atmospheric gas under which the
agglomerate is heated is to 2.0.times.10.sup.-13 atm or more at
standard state, and a linear speed of the atmospheric gas in the
furnace is 4.5 cm/second or more.
2. The method of claim 1, wherein a composition of the raw material
mixture is adjusted so that a percentage of an amount of fixed
carbon comprised in the carbonaceous reducing agent is in a range
between 98 mass % and 102 mass % with respect to an amount of fixed
carbon needed to reduce the at least one iron oxide.
3. The method of claim 1, wherein a composition of the raw material
mixture is adjusted so that a basicity of slag subgenerated in
reducing the at least one iron oxide is in a range between 1.0 and
1.6.
4. The method of claim 1, wherein a percentage of an amount of
fixed carbon comprised in the carbonaceous reducing agent is in a
range between 98 mass % and 100 mass % with respect to an amount of
fixed carbon needed to reduce the at least one iron oxide.
5. The method of claim 1, wherein the linear speed of the
atmospheric gas is 5.4 cm/second or less (including 0 cm/second)
until the at least one iron oxide begins to melt, and the linear
speed of the atmospheric gas is 4.5 cm/second or more after the at
least one iron oxide begins to melt.
6. The method of claim 1, wherein a percentage of an amount of
fixed carbon comprised in the carbonaceous material which is spread
on the hearth is in a range between 2 mass % and 5 mass % with
respect to an amount of fixed carbon needed to reduce the at least
one iron oxide, and a maximum particle size of the carbonaceous
material is 2 mm or less.
7. The method of claim 1, wherein the agglomerate size (maximum
diameter) is 50 mm or smaller.
8. The method of claim 1, wherein the agglomerate size (maximum
diameter) is 5 mm or larger.
9. The method of claim 7, wherein the agglomerate size (maximum
diameter) is 5 mm or larger.
10. The method of claim 1, wherein the temperature of the
agglomerate in the furnace is in a range between 1250.degree. C.
and 1500.degree. C.
11. The method of claim 1, wherein the temperature of the
agglomerate in the furnace is in a range between 1200.degree. C.
and 1450.degree. C.
12. The method of claim 1, wherein the temperature of the
agglomerate in the furnace is in a range between 1250.degree. C.
and 1450.degree. C.
13. The method of claim 1, wherein the oxygen partial pressure of
the atmospheric gas under which the agglomerate is heated is
2.8.times.10.sup.-13 atm or more at standard state.
14. The method of claim 1, wherein the oxygen partial pressure of
the atmospheric gas under which the agglomerate is heated is
4.8.times.10.sup.-13 atm or less at standard state.
15. The method of claim 1, wherein the oxygen partial pressure of
the atmospheric gas under which the agglomerate is heated is
4.0.times.10.sup.-13 atm or less at standard state.
16. The method of claim 13, wherein the oxygen partial pressure of
the atmospheric gas under which the agglomerate is heated is
4.8.times.10.sup.-13 atm or less at standard state.
17. The method of claim 13, wherein the oxygen partial pressure of
the atmospheric gas under which the agglomerate is heated is
4.0.times.10.sup.-13 atm or less at standard state.
18. The method of claim 1, wherein the linear speed of the
atmospheric gas in the furnace is 5 cm/second or more.
19. The method of claim 1, wherein the linear speed of the
atmospheric gas in the furnace is 13.5 cm/second or less.
20. The method of claim 1, wherein the linear speed of the
atmospheric gas in the furnace is 9 cm/second or less.
Description
TECHNICAL FIELD
[0001] This invention relates to a method for producing granular
iron by: charging agglomerates formed from a raw material mixture,
which contains an iron oxide-containing substance and a
carbonaceous reducing agent, onto a carbonaceous material spread on
a hearth of a furnace; and heating the agglomerates to thereby
reduce and melt iron oxides in the agglomerates.
BACKGROUND ART
[0002] The direct reduced iron producing method has been developed
for making granular metallic iron from a raw material mixture which
contains an iron oxide source such as iron ore or iron oxide
(hereinafter referred to as iron oxide-containing substance) and a
carbonaceous reducing agent. With this producing method, the
granular metallic iron is made by: charging the raw material
mixture onto a hearth of a heating furnace; heating the raw
material mixture with the heat transferred by gas from burners in
the furnace or radiant heat to thereby reduce iron oxides in the
raw material mixture by the carbonaceous reducing agent into
reduced iron, carburize and melt the reduced iron, followed by
coalesce it to granules while separating it from subgenerated slag;
and then cooling and solidifying it. This producing method has been
the subject of considerable practical research of late, because it
requires no large-scale facility such as a blast furnace, and
because it affords greater flexibility in terms of resources such
as not requiring coke. However, the producing method has various
problems to be solved in order to be applied on an industrial
scale, including stability of operation, safety, cost, quality of
the granular iron (product), and so forth.
[0003] Since the granular iron made by the above-mentioned direct
reduced iron producing method is sent to an existing steelmaking
facility (such as an electric furnace or a converter) and is used
as an iron source, it preferably has a low content of impurity
elements. The carbon content of the granular iron is preferably as
high as possible, without excessive range, in order to increase its
applicability as an iron source.
[0004] In an effort to improve the quality of granular iron, the
present applicant has proposed a granular iron having a high Fe
purity of 94 mass % or more and a carbon content adjusted to
between 1.0 and 4.5 mass % in Japanese Unexamined Patent
Application Publication No. 2002-339009 (Patent Document 1). This
granular iron is further adjusted to have a sulfur content of 0.20
mass % or less, a silicon content of 0.02 to 0.5 mass and a
manganese content of less than 0.3 mass %. However, adjusting the
phosphorus content of the granular iron is not disclosed in Patent
Document 1. The reason for this is as follows: since the behavior
of phosphorus in the reduction process of iron oxide is already
clear from the chemical reaction mechanism in blast furnace, it is
recognized that almost all phosphorus sourced from a material to be
reduced (that is, raw material) remains in a reduced product (that
is, metallic iron) under reductive atmosphere and that the
phosphorus does not move into subgenerated slag, and thus it is
also recognized that the phosphorus content in the raw material has
to be decreased, and/or that the granular iron made by the
producing method disclosed in Patent Document 1 has to be subjected
to a further dephosphorization, in order to reduce the phosphorus
content of the granular iron.
[0005] In recent years, the grade of iron ore has tended to be on
the decline, and the amount of phosphorus contained in mined iron
ore is on the rise. Therefore, in the future it will be
increasingly difficult to procure raw materials with a low
phosphorus content. However, a further dephosphorization subjected
to the granular iron made by the producing method disclosed in
Patent Document 1 for reducing its phosphorus content leads to
higher cost.
DISCLOSURE OF THE INVENTION
[0006] The present invention is developed based on the
above-mentioned background, and has an object to provide a method
for producing granular iron having a low phosphorus content by:
charging agglomerates formed from a raw material mixture containing
an iron oxide-containing substance and a carbonaceous reducing
agent onto a carbonaceous material spread on a hearth of a furnace;
and heating the agglomerates to thereby reduce and melt iron oxides
in the agglomerates.
[0007] One aspect of the present invention is directed to a method
for producing granular iron comprising: charging agglomerates
formed from a raw material mixture containing an iron
oxide-containing substance and a carbonaceous reducing agent onto a
carbonaceous material spread on a hearth of a furnace; and heating
the agglomerates to thereby reduce and melt iron oxides in the
agglomerates, wherein the temperature of the agglomerates in the
furnace is set in a range between 1200.degree. C. and 1500.degree.
C.; the oxygen partial pressure in atmospheric gas under which the
agglomerates are heated is set to 2.0.times.10.sup.13 atm or more
at standard state; and the linear speed of the atmospheric gas in
the furnace is set to 4.5 cm/second or more.
[0008] The object, features, aspects and advantages of the present
invention will become clearer through reference to the following
detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a graph showing the relation between the
dephosphorization ratio and the gas linear speed under different
oxygen partial pressures.
[0010] FIG. 2 is a graph showing the relation between the
dephosphorization ratio and the gas linear speed.
[0011] FIG. 3 is a graph showing the relation between the
dephosphorization ratio and the oxygen partial pressure.
[0012] FIG. 4 is a graph showing the relation between the
dephosphorization ratio and the discharging time.
[0013] FIG. 5 is a graph showing the relation between the
dephosphorization ratio and the amount of fixed carbon contained in
the carbonaceous reducing agent blended to the raw material
mixture.
BEST MODE FOR CARRYING OUT THE INVENTION
[0014] The metallurgical process of producing granular iron by:
charging agglomerates formed from a raw material mixture containing
an iron oxide-containing substance and a carbonaceous reducing
agent onto a carbonaceous material spread on a hearth of a furnace;
and heating the agglomerates to thereby reduce and melt iron oxides
in the agglomerates is usually carried out under reductive
atmosphere. The reason for this is as follows: when the process is
performed under oxidative atmosphere, the reduction of the iron
oxides contained in the agglomerates comes to a standstill during
the heating of the agglomerates, and reduced iron cannot be
obtained at a high yield. On the other hand, when the process is
performed under reductive atmosphere, reduction of the iron oxides
proceeds well. However, almost none of the phosphorus contained in
the reduced iron move to slag subgenerated in the reduction, and
still remain in the granular iron made by melting the reduced iron
due to this melting under reductive atmosphere. As a result,
granular iron with a high phosphorus content is obtained. To lower
the phosphorus content of granular iron, the obtained granular iron
is required to be supplied to an electric furnace, for example, and
subjected to a further dephosphorization.
[0015] During reducing and melting the above-mentioned agglomerates
at a high temperature between 1200 and 1500.degree. C., the
carbonaceous reducing agent causes reductive gas to spew out of the
interior of the agglomerates while the iron oxides in the
agglomerates are being reduced, in contrast, almost no reductive
gas is generated after the reduction of the iron oxides are almost
over and the reduced iron melts and separates to granular iron and
subgenerated slag. Accordingly, the inventors considered that the
composition of the granular iron during the period in which the
reduced iron melts and separates to granular iron and subgenerated
slag is greatly influenced by the composition of its atmospheric
gas. In view of this, the inventors conducted diligent study in the
vision that the suitable control of the atmospheric gas under which
the reduced iron melts and separates to granular iron and
subgenerated slag can adjust the composition of the granular iron.
As a result, the inventors found that
[0016] (I) charging the agglomerates onto a carbonaceous material
spread on a hearth of a furnace and then heating the agglomerate of
which temperature is to be in a range between 1200.degree. C. and
1500.degree. C.,
[0017] (II) setting the oxygen partial pressure in atmospheric gas
under which the agglomerates are heated to 2.0.times.10.sup.-13 atm
or more at standard state, and
[0018] (III) setting the linear speed of the atmospheric gas in the
furnace to 4.5 cm/second or more make the phosphorus contained in
the reduced iron move to slag subgenerated in the reduction while
the reduced iron is melting. The inventors also found that granular
iron with a low phosphorus content can be produced based on this
knowledge, and thus accomplished the present invention.
[0019] The present invention will now be described in terms of the
procedure of producing granular iron.
[0020] (I) Agglomerates are formed by agglomerating a raw material
mixture that contains a carbonaceous reducing agent and an iron
oxide-containing substance.
[0021] The above-mentioned iron oxide-containing substance can be,
for example, iron ore, iron sand, nonferrous smelting slag, and so
forth. The above-mentioned carbonaceous reducing agent can be, for
example, a carbon-containing substance, more specifically, coal,
coke, or the like.
[0022] Other components can also be added to the above-mentioned
raw material mixture, such as a binder, an MgO supplying substance,
or a CaO supplying substance. Binders can be, for example,
polysaccharides (such as wheat gluten and other starches). MgO
supplying substances can be, for example, MgO powder,
magnesium-containing substances extracted from natural ore,
seawater, or the like, and magnesium carbonate (MgCO.sub.3). CaO
supplying substances can be, for example, burnt lime (CaO) and
limestone (whose main component is CaCO.sub.3).
[0023] There are no particular limitations on the shape of the
agglomerates. For example, it can be in the form of a pellet or a
briquette. Nor are there any particular limitations on the size of
the agglomerates. In terms of operations, the agglomerate size
(maximum diameter) is preferably 50 mm or smaller, and it is
preferably about 5 mm or larger. This is because too large
agglomerate size decreases heat transfer to the lower part of the
pellet and results in poor productivity, additionally decreasing
agglomerating efficiency. Therefore, the agglomerate size is
preferably 50 mm or less.
[0024] Carbonaceous material is spread on the hearth in advance in
order to reduce the agglomerates. This is because the carbonaceous
material serves as a carbon supply source when not enough carbon is
contained in the agglomerates, and also acts to protect the
hearth.
[0025] It is recommended that the carbonaceous material that is
spread on the hearth have a maximum particle size of 2 mm or less.
Using a carbonaceous material with a maximum particle size of 2 mm
or less, can suppress that molten slag runs down into the gaps in
the carbonaceous material. As a result, this prevents the molten
slag from reaching the surface of the hearth and corroding the
hearth. The lower limit to the maximum particle size of the
carbonaceous material is preferably about 0.5 mm, for example.
Using a carbonaceous material in which lower limit to the maximum
particle size is about 0.5 mm can suppress that the agglomerates
sink into the carbonaceous material layer. As a result, this
prevents a drop in heating rate and a decrease in productivity.
Spreading the carbonaceous material on the hearth is preferably in
a thickness of about 1 to 5 mm, for example.
[0026] Then, the agglomerates that have been prepared are charged
to a hearth on which the carbonaceous material spreads and heated
so that the temperature of the agglomerates becomes between 1200
and 1500.degree. C., thereby the iron oxides in the raw material
mixture are reduced and melted. The temperature of the agglomerates
is preferably 1250.degree. C. or more. Setting the temperature to
1250.degree. C. or more shortens the melting time of the granular
iron and slag, and also accelerates the separation of the slag from
the granular iron, allowing granular iron with a higher iron purity
to be obtained. On the other hand, the temperature of the
agglomerates is preferably 1450.degree. C. or less. Setting the
temperature to 1450.degree. C. or less does not require the heating
furnace to be a complicated structure, and can suppress a decrease
in thermal efficiency. From the standpoints of the heating furnace
structure and energy use, the targeted metallic iron nuggets are
preferably produced at lower temperature. When burners are used as
the heating means in the furnace, the temperature of the
agglomerates can be adjusted by controlling the combustion
conditions of these burners. There are no particular limitations on
the type of furnace used in the present invention, for example, a
heating furnace or a moving hearth furnace can be used. A rotary
hearth furnace can be used, for example, as a moving hearth
furnace.
[0027] (II and III) The oxygen partial pressure in atmospheric gas
under which the agglomerates are heated is set to
2.0.times.10.sup.-13 atm or more at standard state, and that the
linear speed of this gas is set to 4.5 cm/second or more. As a
result of various experiments, the inventors found the followings:
when the reduced iron is melted under a slightly oxidative
atmosphere, the phosphorus contained in the reduced iron is
oxidized, and this phosphorus moves to the slag, and this decreases
the phosphorus content of the granular iron. More specifically,
when the oxygen partial pressure of the atmospheric gas is less
than 2.0.times.10.sup.-13 atm, or when the gas linear speed is less
than 4.5 cm/second, the dephosphorization of the granular iron
cannot be accelerated, since not enough oxidative gas is contained
in the atmospheric gas near the surface of the agglomerates.
Therefore, the oxygen partial pressure of the atmospheric gas under
which the agglomerates are heated is set to 2.0.times.10.sup.-13
atm or more at standard state, and the gas linear speed is set to
4.5 cm/second or more.
[0028] The oxygen partial pressure of the atmospheric gas is
preferably 2.8.times.10.sup.-13 atm or more at standard state. The
higher is the oxygen partial pressure, the more the
dephosphorization of the granular iron is accelerated. However,
excessively high oxygen partial pressure causes the granular iron
to be re-oxidized, and this decreases the iron purity
(metallization ratio). Therefore, the oxygen partial pressure is
preferably 4.8.times.10.sup.-13 atm or less at standard state, and
more preferably 4.0.times.10.sup.-13 atm or less at standard
state.
[0029] The linear speed of the atmospheric gas in the furnace is
preferably 5 cm/second or more. The higher is the gas linear speed,
the more the dephosphorization of the granular iron is accelerated.
However, excessively high gas linear speed causes the granular iron
to be re-oxidized, and this decreases the iron yield. Therefore,
the gas linear speed is preferably 13.5 cm/second or less, and more
preferably 9 cm/second or less.
[0030] The phrase "atmospheric gas under which the agglomerates are
heated" means the atmospheric gas near the surface of the
agglomerates. The phrase "near the surface of the agglomerates"
means the area up to a height of 50 mm from the surface of the
agglomerates. Since the oxygen partial pressure and the linear
speed of the atmospheric gas in the furnace are often different at
the bottom portion of the furnace (near the hearth) and the top
portion of the furnace (near the roof), the above-mentioned oxygen
partial pressure and gas linear speed are specified for the
atmospheric gas near the surface of the agglomerates, which affect
the redox reaction of the agglomerates.
[0031] The oxygen partial pressure of the atmospheric gas under
which the agglomerates are heated can be calculated by taking a
sample of the atmospheric gas near the surface of the agglomerates,
and analyzing the gas composition. The linear speed of the
atmospheric gas can be measured with a pitot tube or the like.
[0032] The oxygen partial pressure of the atmospheric gas can be
controlled, for example, by: adjusting the amount of oxygen fed to
the burners; adjusting the amount of fuel fed to the burners or the
air ratio, etc.; or adjusting the injection of reductive gas. The
linear speed of the atmospheric gas can be controlled, for example,
by: adjusting the amount of gas fed to the burners; adjusting the
injection angle of the burners; or varying the roof height.
[0033] The oxygen partial pressure and the linear speed of the
atmospheric gas are adjusted so as to be within the above-mentioned
ranges at latest from the point when the melting of the reduced
iron begins. This is because the composition of the granular iron
is actually affected by the atmospheric gas composition more during
melting than during solid reduction.
[0034] Preferably, the linear speed of the atmospheric gas, under
which the agglomerates are heated, is controlled to 5.4 cm/second
or less (including 0 cm/second) until the iron oxides, which are
contained in the raw material mixture, begins to melt; and the
linear speed of the atmospheric gas, under which the agglomerates
are heated, is controlled to 4.5 cm/second or more, once the iron
oxides begins to melt. In the period before the iron oxides begins
to melt, the reduction reaction is very actively occurring within
the agglomerates, this causes a difficult change in the composition
of the atmospheric gas near the surface of the agglomerates or
inside the agglomerates, even if the composition of the atmospheric
gas in the furnace is changed. Meanwhile, as the solid reduction
nears completion, melting of iron begins due to the beginning of
carburization in iron and the decrease of the melting point of the
resulting iron. When the iron begins to melt, almost no gas is
generated from the agglomerates, and thus the composition of the
iron is greatly affected by the composition of the atmospheric gas.
Therefore, the linear speed of the atmospheric gas under which the
agglomerates are heated is preferably controlled to suitable levels
up in the period before the iron oxides begins to melt and after
the melting begins respectively. Incidentally, the oxygen partial
pressure of the atmospheric gas in the period before the iron
oxides contained in the raw material mixture begins to melt is
preferably 2.8.times.10.sup.-13 atm or less.
[0035] Thus, in the present invention, it is preferable to control
the oxygen partial pressure and the linear speed of the atmospheric
gas at the time until the iron oxides begins to melt and after the
melting begins, for example, when a moving hearth furnace is used
as the heating furnace, partitions can be suspended from the
furnace roof so that the inside of the furnace is divided into a
plurality of zones, and the oxygen partial pressure and the linear
speed of the atmospheric gas is controlled for each of these
zones.
[0036] As discussed above, suitable controlling of the oxygen
partial pressure and the linear speed of the atmospheric gas in the
period of reducing and melting can proceed the dephosphorization of
the granular iron more effectively, and can produce granular iron
with a lower phosphorus content than reducing and melting just
under reductive atmosphere.
[0037] In the present invention, it is preferred to adjust the
percentage of the amount of fixed carbon contained in the
carbonaceous reducing agent blended to the raw material mixture to
be in a range between 98 mass % and 102 mass % with respect to the
amount of fixed carbon needed to reduce the iron oxides contained
in the iron oxide-containing substance. The reason for this is as
follows: when the percentage of the amount of fixed carbon
contained in the carbonaceous reducing agent is less than 98 mass %
with respect to the amount of fixed carbon needed to reduce the
iron oxides, this makes lack of carbon, and leads an inadequate
reduction of the iron oxides, even though reductive gas (CO gas)
rises up from the carbonaceous material spread on the hearth, as
discussed below. The required percentage of the amount of fixed
carbon contained in the carbonaceous reducing agent is preferably
98 mass % or more, and more preferably 98.5 mass % or more, with
respect to the amount of fixed carbon needed to reduce the iron
oxides. However, when the amount of fixed carbon contained in the
carbonaceous reducing agent is excessively large, the reductive gas
(CO gas) still continues to rise up from the agglomerates by
reacting with the atmospheric gas even after the reduction is
finished. This decreases the oxygen partial pressure in melting the
reduced iron, as discussed below, and thus makes the
dephosphorization ratio of the reduced iron be lower. Therefore,
the required percentage of the amount of fixed carbon contained in
the carbonaceous reducing agent is preferably 102 mass % or less,
and more preferably 101 mass % or less, with respect to the amount
of fixed carbon needed to reduce the iron oxides.
[0038] In the present invention, it is especially recommended that
the amount of fixed carbon contained in the carbonaceous reducing
agent be adjusted somewhat on the low side with respect to the
amount of fixed carbon needed to reduce the iron oxides. The reason
for this is as follows: the unreduced portions of the iron oxides
are reduced by the carbonaceous material spread on the hearth,
since the agglomerates are on the carbonaceous material in the
present invention, although an insufficient amount of fixed carbon
contained in the carbonaceous reducing agent seems to cause
inadequate reduction of the granular iron.
[0039] Specifically, the iron oxides (FeO.sub.x) contained in the
agglomerates are reduced by the carbon (C) contained in the
carbonaceous reducing agent and by the carbonaceous material spread
on the hearth, according to the reduction reactions in the
following formulas (1) and (2), to form granular iron.
FeO.sub.x+xCO.fwdarw.Fe+xCO.sub.2 (1)
FeO.sub.x+xC.fwdarw.Fe+xCO (2)
[0040] As a result of various experiments, the inventors found that
the reduction reaction proceeds in the proportions indicated by the
following formula (3) when a moles of the FeO.sub.x of Formula (1)
react, and when b moles of the FeO.sub.x of Formula (2) react. That
is, Formula (3) indicates the number of oxygen atoms reduced by one
carbon atom. In the reduction of FeO.sub.x the inventors estimate
that about 38% of the total occurs by direct reduction by carbon
(C), and about 72% of the total occurs by indirect reduction by
reducing gas (CO gas).
1.0.ltoreq.1+a/(a+b).ltoreq.1.5 (3)
[0041] Therefore, even though the amount of carbon, which is
calculated as one carbon atom needed to reduce one oxygen atom
contained in iron oxide, is slightly on the low side (for example,
by blending carbonaceous reducing agent a little less into the raw
material mixture), iron oxides in agglomerates are still adequately
reduced.
[0042] Also, adjusting the amount of fixed carbon contained in the
carbonaceous reducing agent on the lower side with respect to the
amount of fixed carbon needed to reduce the iron oxides causes to
form more iron oxides (FeO) contained in subgenerated slag in the
reduction, and drives the dephosphorization reaction faster in
melting the reduced iron. Therefore, the percentage of the amount
of fixed carbon contained in the carbonaceous reducing agent is
more preferably 100 mass % or less with respect to the amount of
fixed carbon needed to reduce the iron oxides.
[0043] The amount of fixed carbon needed to reduce the iron oxide
may be calculated from the composition of the raw material
mixture.
[0044] The granular iron is required to be carburized so that it
contains about 3 mass % carbon in order to decrease the melting
point of the granular iron during separating the melted granular
iron from the slag. However, when the amount of fixed carbon
contained in the carbonaceous reducing agent blended to the raw
material mixture is set to be slightly insufficient with respect to
the amount of fixed carbon needed to reduce the iron oxides, the
granular iron does not contain enough fixed carbon, and this
results that the granular iron cannot be melted. Accordingly,
spreading a carbonaceous material on the hearth and setting the
amount of fixed carbon contained in this carbonaceous material to
be in excess over the amount of fixed carbon needed to reduce the
iron oxides increase the amount of fixed carbon supplied to the
granular iron, and this can make the molten granular iron be
separated from the slag.
[0045] The percentage of the amount of fixed carbon contained in
the carbonaceous material that is spread on the hearth is
preferably adjusted to within a range between 2 mass % and 5 mass %
with respect to the amount of fixed carbon needed to reduce the
iron oxides. There are no particular limitations on the type of
carbonaceous material that is spread on the hearth, for example,
the carbon-containing material used as the above-mentioned
carbonaceous reducing agent can be used.
[0046] In the present invention, the above-mentioned agglomerates
is also preferred to adjust the composition of the raw material
mixture so that the basicity of slag subgenerated in reducing the
iron oxides is in a range between 1.0 and 1.6. The reason for this
is as follows: when the slag basicity is less than 1.0, the
dephosphorization reaction in melting the reduced iron does not
proceed and thus the phosphorus content of the granular iron cannot
be reduced. Therefore, the basicity is preferably 1.3 or more, and
more preferably 1.4 or more. However, too high slag basicity causes
too high melting point of the slag, and the resulting slag does not
melt when the reduced iron is melted, making it difficult to
separate the granular iron from the slag. As a result, the slag
ends up being mixed in the granular iron, and this degrades in
quality of the granular iron. Therefore, the basicity is preferably
1.6 or less.
[0047] The basicity of slag is the value [(CaO)/(SiO.sub.2)]
calculated from the CaO content and the SiO.sub.2 content in the
slag.
EXAMPLES
[0048] The present invention will now be described in further
detail through examples. These examples are not intended to limit
the present invention, various modifications are possible without
departing from the scope of the invention described above and
below, and these modifications are included in the technical scope
of the present invention.
[0049] In the examples, each agglomerates were made from raw
material mixtures each containing a carbonaceous reducing agent and
an iron oxide-containing substance, and then, each granular irons
were made by: charging each agglomerates onto a carbonaceous
material spread on a hearth of a heating furnace; and heating the
agglomerates to thereby reduce and melt the iron oxides in the
agglomerates in a laboratory. The compositions of the agglomerates
and the conditions of reduction and melting were varied.
Specifically, as follows.
[0050] Two kinds of iron oxide-containing substance were used: iron
ore (n) with a low phosphorus content; and iron ore (hpb) with a
high phosphorus content. Table 1 below shows the compositions of
the iron ore (n) and the iron ore (hpb). Two kinds of carbonaceous
reducing agent were also used: coal (p) with a low phosphorus
content; and coal (b) with a high phosphorus content. Table 2 below
shows the compositions of the coal (p) and the coal (b).
[0051] The iron ore each shown in Table 1 and the coal each shown
in Table 2 were blended with additives, and then, each pelletized
agglomerates (test material) with particle sizes of 18 to 20 mm
were produced. The blended additives were wheat gluten that was
added as a binder, MgO, CaO, etc. Table 3 below shows the blending
ratio of each test materials (percentages of weight values).
[0052] Table 3 shows the target values for the percentage of the
amount of fixed carbon contained in the carbonaceous reducing agent
blended to the raw material mixture with respect to the amount of
fixed carbon needed to reduce the iron oxides. Table 3 also shows
the target values for the basicity of slag subgenerated during
reduction.
[0053] Table 4 below shows the compositions of the test materials.
In Table 4, test material (1) is pellets with a low phosphorus
content, and test materials (2) to (5) are pellets with a high
phosphorus content.
[0054] Each granular irons were produced by: charging each test
materials shown in Table 4 into the furnace of which hearth was
spread with a carbonaceous material; heating them to thereby reduce
and melt the iron oxides in the raw material mixture; and
discharging products to a cooling zone at the point when the
granular iron and slag had completely separated. The number of
samples of each test materials charged into the furnace was 30. 130
g of smokeless coal with a maximum particle size of 2 mm or less
was spread over the hearth as a carbonaceous material. Extra
carbonaceous material was spread around the edges to protect the
hearth.
[0055] The test materials charged into the furnace were heated with
a heater provided to the furnace, so that the temperature of the
test materials would reach 1450.degree. C.
[0056] Inside the furnace, the linear speed of the atmospheric gas
under which the test materials were heated (the linear speed of the
atmospheric gas near the test materials) was controlled to be in a
range between 1.35 and 20.27 cm/second, and the oxygen partial
pressure of the atmospheric gas under which the test materials were
heated (the oxygen partial pressure of the atmospheric gas near the
test materials) was controlled to be in a range between 0 and
5.057.times.10.sup.-13 atm. Tables 5 and 6 below show the gas
linear speeds and oxygen partial pressures. The gas linear speeds
were the value at standard state.
[0057] The gas linear speeds were calculated from the amount of gas
supplied and the cross sectional area at the sample placement
portion inside the furnace. The oxygen partial pressures were
calculated by the following procedure.
[0058] The following formula (4) expresses a carbon combustion
reaction, and the standard generation free energy .DELTA.F in this
reaction is expressed by the following formula (5).
C(graphite)+O.sub.2 (g)=CO.sub.2 (g) (4)
.DELTA.F=-94640+0.05.times.T (cal/mol) (5)
[0059] Meanwhile, the standard generation free energy .DELTA.F of
this reaction is expressed by the following formula (6), using the
partial pressure P.sub.CO2 of the atmospheric gas accounted for by
carbon dioxide gas, and the partial pressure P.sub.O2 of the
atmospheric gas accounted for by oxygen gas.
.DELTA.F=-RT.times.log(P.sub.CO2/P.sub.O2) (6)
[0060] The absolute temperature of 1450.degree. C. is:
1450(.degree. C.)+273=1723(K),
therefore the relation between the carbon dioxide partial pressure
and the oxygen partial pressure in the atmospheric gas at
1450.degree. C. is found as follows from the above formulas (5) and
(6).
-94640+0.05.times.1723=-4.575.times.1723.times.log(P.sub.CO2/P.sub.O2)
log(P.sub.CO2/P.sub.O2)=11.995
P.sub.CO2/P.sub.O2=9.887.times.10.sup.11
[0061] Here, the partial pressure of the atmospheric gas accounted
for by carbon dioxide gas is measured, for example, when
P.sub.CO2=0.5 is measured, then
P.sub.O2=5.0571.times.10.sup.-13
is obtained as the partial pressure of the atmospheric gas
accounted for by oxygen gas.
[0062] Tables 5 and 6 show the compositions of the resulting
granular irons, and the compositions of the subgenerated slags when
granular irons were produced. Of the compositions of the granular
irons shown in Tables 5 and 6, each amount of iron is the value
calculated by subtracting the amount of alloy elements and
impurities from the total (100 mass %).
[0063] In Table 6, No. 30 is the result of discharging the granular
iron one minute before the point at which the separation of slag
and granular iron was complete, and No. 31 is the result of
discharging the granular iron from the furnace after waiting for
three minutes from the point at which the separation of slag and
granular iron was complete. In Tables 5 and 6, everything other
than Nos. 30 and 31 is the result of discharging the granular iron
from the furnace at the point when one minute had elapsed from the
point at which the separation of slag and granular iron was
complete.
[0064] The center temperatures of the test materials were measured
and found to be: approximately 1300.degree. C. at the point one
minute before the separation of slag and granular iron was complete
(No. 30); approximately 1400.degree. C. at the point when one
minute had elapsed since the completion of the separation of slag
and granular iron; and approximately 1450.degree. C. at a point
three minutes after the completion of the separation of slag and
granular iron (No. 31).
[0065] Also, the CO.sub.2 gas proportion near the test materials
was substantially constant from the point one minute before the
completion of the separation of slag and granular iron, up to the
point three minutes after the completion of the separation of slag
and granular iron. Meanwhile, some CO gas was noted to rise up from
the test material at a point one minute before the completion of
the separation of slag and granular iron, but no CO gas was seen to
rise up from the test material once the separation of slag and
granular iron was partially completed.
[0066] The dephosphorization ratio was calculated from the
composition of the granular iron and the composition of the test
material by the following formula.
Dephosphorization ratio (%)=[1-(amount of phosphorus contained in
the resulting granular iron/total amount of iron contained in the
resulting granular iron)/(amount of phosphorus contained in test
material/total amount of iron contained in test
material)].times.100
[0067] FIG. 1 shows the relation between the dephosphorization
ratio and the gas linear speed under different oxygen partial
pressures, based on the data in Tables 4 and 5. In FIG. 1, the mark
.diamond. indicates the result at an oxygen partial pressure of 0
atm, the mark .tangle-solidup. indicates the result at an oxygen
partial pressure of 1.011.times.10.sup.-13 atm, the mark x
indicates the result at an oxygen partial pressure of
1.517.times.10.sup.-13 atm, the mark O indicates the result at an
oxygen partial pressure of 3.034.times.10.sup.-13 atm, and the mark
.box-solid. indicates the result at an oxygen partial pressure of
5.057.times.10.sup.-13 atm.
[0068] As is clear from FIG. 1, when the atmospheric gas contains
oxygen, the higher is the linear speed of the atmospheric gas under
which the test material is heated, the higher is the
dephosphorization ratio. For example, with test material 3, which
had a gas linear speed of 5.41/sec, it can be seen that the
dephosphorization ratio rises when the oxygen partial pressure of
the atmospheric gas is increased from 1.517.times.10.sup.-13 atm to
3.034.times.10.sup.-13 atm, and that with a given test material and
at a given gas linear speed, the dephosphorization ratio rises when
the oxygen partial pressure of the atmospheric gas is increased.
When the oxygen partial pressure of the atmospheric gas is 0 atm
(that is, under a nitrogen gas atmosphere), the dephosphorization
is not affected by the gas linear speed. When the gas linear speed
is less than cm/second, the result for dephosphorization ratio is
reversed from that when the oxygen partial pressure of the
atmospheric gas is 1.517.times.10.sup.-13 atm, but these are
considered to be affected by sample variance or phosphorus analysis
error.
[0069] Based on the above results, increasing the gas linear speed
and the oxygen partial pressure of the atmospheric gas to the
specified values or higher is an effective way to raise the
dephosphorization ratio.
[0070] FIG. 2 shows the relation between the dephosphorization
ratio and the gas linear speed in Nos. 24, 25 and 32, out of the
results in Table 6 when the oxygen partial pressure was
3.034.times.10.sup.-13 atm. A comparison of FIG. 2 with FIG. 1
reveals that even though the amount of phosphorus contained in the
test material changes, at the condition that the oxygen partial
pressure is constant, the dephosphorization ratio rises along with
the gas linear speed. Although not shown in the drawings, the same
thing can be understood from Nos. 2, 4 and 6, for example.
[0071] FIG. 3 shows the relation between the dephosphorization
ratio and the oxygen partial pressure in Nos. 25, 27, 28 and 29,
out of the results in Table 6 when the gas linear speed was 5.41
cm/second. As is clear from FIG. 3, when the gas linear speed is
constant, the dephosphorization ratio rises along with the oxygen
partial pressure. Also, when the oxygen partial pressure is
1.517.times.10.sup.-13 atm, it can be seen that there is almost no
change in the dephosphorization ratio. Although not shown in the
drawings, it can be understood from Nos. 3, 4 and 5, for example,
that when the gas linear speed is constant, the dephosphorization
ratio rises along with the oxygen partial pressure.
[0072] FIG. 4 shows the relation between the dephosphorization
ratio and the time discharging granular iron in Nos. 25, 30 and 31,
out of the results in Table 6 when the oxygen partial pressure was
3.034.times.10.sup.-13 atm and the gas linear speed was 5.41
cm/second. FIG. 4 shows the dephosphorization ratio of variation
compared with the variation of the time discharging the granular
iron which was separated from the slag out of the furnace from the
clock time when the slag and granular iron had been completely
separated was set 0 minute, after the reduced irons were melted. As
is clear from FIG. 4, the dephosphorization ratio drops when
heating is continued after the slag and granular iron have been
separated.
[0073] The highest dephosphorization ratio in FIG. 4 is when the
discharging time is "-1 minute," and this "-1 minute" means that
the granular iron was discharged from the furnace before the
granular and slag were separated, which is a condition that cannot
be employed in actual practice.
[0074] FIG. 5 shows the relation between the dephosphorization
ratio and the amount of fixed carbon contained in the carbonaceous
reducing agent blended to the raw material mixture for Nos. 21, 22
and 25, out of the results shown in Table 6. As is clear from FIG.
5, the dephosphorization ratio is advantageously higher when the
amount of fixed carbon contained in the carbonaceous reducing agent
blended to the raw material mixture is set on the low side with
respect to the amount of fixed carbon needed to reduce the iron
oxides.
[0075] On the other hand, it can be seen that there is a further
drop in the dephosphorization ratio when the percentage of the
amount of fixed carbon contained in the carbonaceous reducing agent
blended to the raw material mixture is over 102 mass % with respect
to the amount of fixed carbon needed to reduce the iron oxides.
This is considered to be attributable to the fact that since a
large amount of reductive gas rises up even in the process of
melting the reduced iron, the effect of increasing the gas linear
speed is lost.
[0076] As is clear from the results for No. 22, even though the
amount of fixed carbon contained in the carbonaceous reducing agent
blended to the raw material mixture is set on the low side with
respect to the amount of fixed carbon needed to reduce the iron
oxides contained in the test material, adjusting the amount of
carbon contained in the carbonaceous material spread on the hearth
to be in a range between 2 and 5 mass % with respect to the amount
of fixed carbon needed to reduce the iron oxides causes stable
reduction of the iron oxides remaining after dephosphorization has
proceeded by the carbonaceous material spread on the hearth.
TABLE-US-00001 TABLE 1 COMPOSITION (mass %) IRON TOTAL ORE AMOUNT
TYPE OF IRON FeO SiO.sub.2 CaO Al.sub.2O.sub.3 MgO S P (n) 67.64
29.13 4.85 0.44 0.23 0.47 0.004 0.018 (hpb) 62.97 0.47 3.25 0.04
2.08 0.04 0.030 0.13
TABLE-US-00002 TABLE 2 COMPOSITION (mass %) TOTAL TOTAL TOTAL
AMOUNT VOLATILE ASH FIXED AMOUNT AMOUNT OF PHOSPHORUS COAL TYPE
CONTENT CONTENT CARBON OF SULFUR OF CARBON (CALCULATED VALUE) (p)
16.79 4.64 78.57 0.595 86.46 0.00243 COMPOSITION OF ASH CONTENT
(mass %) Fe.sub.2O.sub.3 SiO.sub.2 CaO Al.sub.2O.sub.3 MgO
TiO.sub.2 P.sub.2O.sub.5 15.75 43.55 3.98 27.03 1.85 1.67 0.12
COMPOSITION (mass %) TOTAL TOTAL TOTAL AMOUNT VOLATILE ASH FIXED
AMOUNT AMOUNT OF PHOSPHORUS COAL TYPE CONTENT CONTENT CARBON OF
SULFUR OF CARBON (CALCULATED VALUE) (b) 14.03 4.75 81.22 0.458
83.31 0.03254 COMPOSITION OF ASH CONTENT (mass %) Fe.sub.2O.sub.3
SiO.sub.2 CaO Al.sub.2O.sub.3 MgO TiO.sub.2 P.sub.2O.sub.5 4.26
57.25 2.16 23.93 0.59 0.87 1.57
TABLE-US-00003 TABLE 4 COMPOSITION (mass %) TOTAL TOTAL TEST AMOUNT
OF MOUNT OF MATERIAL CARBON IRON SiO.sub.2 Al.sub.2O.sub.3 CaO MgO
F P S (1) 15.62 48.60 4.01 0.48 5.96 0.97 0.35 0.017 0.104 (2)
15.90 46.01 2.92 1.67 4.17 0.87 0.36 0.100 0.094 (3) 15.89 46.63
3.31 1.75 4.11 0.80 0.32 0.099 0.094 (4) 14.32 47.29 2.98 1.72 4.20
0.87 0.36 0.100 0.087 (5) 16.14 46.55 3.41 1.72 4.31 0.84 0.36
0.094 0.133
TABLE-US-00004 TABLE 5 OXYGEN DEPHOSPHORI- GAS LINEAR PARTIAL
COMPOSITION OF COMPOSITION ZATION TEST SPEED PRESSURE .times.
GRANULAR IRON (mass %) OF SLAG (mass %) RATIO No. MATERIAL (cm/sec)
10.sup.-13(atm) C P S Fe FeO P S BASICITY (%) 1 (1) 20.27 5.057 2.9
0.005 0.134 96.92 4.96 0.110 0.244 1.47 85.25 2 (1) 20.27 3.034
3.04 0.007 0.12 96.77 2.84 0.099 0.313 1.53 79.32 3 (1) 9.01 5.057
3.18 0.014 0.114 96.64 1.9 0.068 0.379 1.52 58.59 4 (1) 9.01 3.034
3 0.018 0.091 96.83 0.98 0.037 0.486 1.43 46.86 5 (1) 9.01 1.011
3.49 0.027 0.038 96.39 0.27 0.011 0.712 1.54 19.92 6 (1) 5.41 3.034
3.23 0.023 0.056 96.63 0.45 0.020 0.589 1.43 31.95 7 (1) 1.35 1.011
3.64 0.031 0.028 96.21 0.24 0.007 0.762 1.57 7.89 8 (1) 20.27 5.057
2.15 0.005 0.164 97.65 6.83 0.086 0.292 1.41 85.36 9 (1) 20.27
3.034 2.53 0.005 0.155 97.28 3.5 0.090 0.317 1.47 85.31 10 (1) 9.01
3.034 2.65 0.019 0.111 97.19 0.72 0.032 0.501 1.44 44.11 11 (1)
5.41 3.034 2.97 0.024 0.079 96.89 0.43 0.014 0.668 1.42 29.18
TABLE-US-00005 TABLE 6 OXYGEN DEPHOSPHORI- GAS LINEAR PARTIAL
COMPOSITION OF COMPOSITION ZATION TEST SPEED PRESSURE .times.
GRANULAR IRON (mass %) OF SLAG (mass %) RATIO No. MATERIAL (cm/sec)
10.sup.-13(atm) C P S Fe FeO P S BASICITY (%) 21 (2) 5.41 3.034
3.00 0.16 0.089 96.72 0.17 0.180 0.336 1.52 23.89 22 (4) 5.41 3.034
2.90 0.07 0.121 96.88 3.94 0.640 0.198 1.50 64.85 23 (5) 5.41 3.034
2.66 0.14 0.110 97.06 0.46 0.240 0.453 1.62 28.57 24 (3) 1.35 3.034
2.96 0.16 0.073 96.78 0.47 0.136 0.378 1.47 22.13 25 (3) 5.41 3.034
2.87 0.14 0.113 96.85 0.42 0.150 0.514 1.61 31.91 26 (3) 20.27
3.034 2.91 0.15 0.103 96.81 0.81 0.250 0.292 0.68 27.02 27 (3) 5.41
1.517 2.62 0.16 0.081 97.11 0.54 0.181 0.367 1.48 22.39 28 (3) 5.41
0 2.78 0.16 0.063 96.95 0.44 0.110 0.487 1.49 22.27 29 (3) 5.41
5.057 2.79 0.11 0.109 96.96 2.16 0.390 0.225 1.48 46.56 30 (3) 5.41
3.034 1.79 0.13 0.091 97.86 1.41 0.300 0.312 1.49 37.43 31 (3) 5.41
3.034 3.29 0.15 0.111 96.42 0.80 0.200 0.237 1.47 26.72 32 (3) 9.01
3.034 2.69 0.11 0.113 97.06 2.82 0.510 0.223 1.48 46.62 33 (5) 5.41
3.034 2.82 0.14 0.113 96.88 0.48 0.140 0.554 1.61 28.44
[0077] As described above, one aspect of the present invention is a
method for producing granular iron comprising: charging
agglomerates formed from a raw material mixture containing an iron
oxide-containing substance and a carbonaceous reducing agent onto a
carbonaceous material spread on a hearth of a furnace; and heating
the agglomerates to thereby reduce and melt iron oxides in the
agglomerates, wherein the temperature of the agglomerates in the
furnace is set in a range between 1200.degree. C. and 1500.degree.
C.; the oxygen partial pressure in atmospheric gas under which the
agglomerates are heated is set to 2.0.times.10.sup.-13 atm or more
at standard state; and the linear speed of the atmospheric gas in
the furnace is set to 4.5 cm/second or more.
[0078] According to the present invention, since the reduced
agglomerates are melted in a state in which the oxygen partial
pressure of the atmospheric gas and the gas linear speed and are
controlled to the above-mentioned conditions, the phosphorus
contained in the reduced iron can be moved to the subgenerated slag
during reduction. As a result, the granular iron made by melting
the reduced iron contains less phosphorus.
[0079] In the above-mentioned method for producing granular iron,
it is preferable that the composition of the raw material mixture
is adjusted so that the percentage of the amount of fixed carbon
contained in the carbonaceous reducing agent is in a range between
98 mass % and 102 mass % with respect to the amount of fixed carbon
needed to reduce the iron oxides. This causes the reduction of iron
oxides to proceed more actively and the granular iron with lower
phosphorus content to be produced.
[0080] In the above-mentioned method for producing granular iron,
it is preferable that the composition of the raw material mixture
is adjusted so that the basicity of slag subgenerated in reducing
the iron oxides is in a range between 1.0 and 1.6. This causes the
dephosphorization reaction to proceed faster and the granular iron
with lower phosphorus content to be produced.
[0081] In the above-mentioned method for producing granular iron,
it is preferable that the percentage of the amount of fixed carbon
contained in the carbonaceous reducing agent is in a range between
98 mass % and 100 mass % with respect to the amount of fixed carbon
needed to reduce the iron oxides. This causes the amount of fixed
carbon contained in the carbonaceous reducing agent to be on the
low side with respect to the amount of fixed carbon needed to
reduce the iron oxides, and thus more iron oxides (FeO) contained
in the subgenerated slag during reduction to be produced. As a
result, this accelerates the dephosphorization reaction during the
melting of the reduced iron, therefore, the dephosphorization ratio
of the reduced iron can be further increased.
[0082] In the above-mentioned method for producing granular iron,
it is preferable that the linear speed of the atmospheric gas is
set to 5.4 cm/second or less (including 0 cm/second) until the iron
oxides begins to melt; and the linear speed of the atmospheric gas
is set to 4.5 cm/second or more after the iron oxides begins to
melt. Adjusting the linear speed of the atmospheric gas under which
the agglomerates are heated, both until the iron oxides begins to
melt and after the melting has begun, allows the reduction reaction
to proceed actively in the agglomerates up until the melting of the
iron oxide begins, and allows the melting of the iron to proceed
stably after melting has begun.
[0083] In the above-mentioned method for producing granular iron,
it is preferable that the percentage of the amount of fixed carbon
contained in the carbonaceous material which is spread on the
hearth is set in a range between 2 mass % and 5 mass % with respect
to the amount of fixed carbon needed to reduce the iron oxides; and
the maximum particle size of the carbonaceous material is set to 2
mm or less. This increases the amount of fixed carbon supplied to
the granular iron, allows the molten granular iron to separate from
slag, and also prevents the molten slag from running down into the
crevices in the carbonaceous material and corroding the hearth.
INDUSTRIAL APPLICABILITY
[0084] Granular iron with a low phosphorus content can be made
stably by using the method of the present invention for producing
granular iron.
* * * * *