U.S. patent application number 11/666830 was filed with the patent office on 2007-12-27 for process for producing molten iron and apparatus therefor.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho ( Kobe Steel ltd.). Invention is credited to Kiminori Hajika, Takao Harada, Toshiyuki Kurakake, Tsuyoshi Mimura, Hidetoshi Tanaka, Tadashi Yaso.
Application Number | 20070295165 11/666830 |
Document ID | / |
Family ID | 36227848 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070295165 |
Kind Code |
A1 |
Tanaka; Hidetoshi ; et
al. |
December 27, 2007 |
Process for Producing Molten Iron and Apparatus Therefor
Abstract
A bedding carbonaceous material is charged onto a hearth of a
rotary hearth furnace, carbonaceous-material containing pellets
containing powdery iron ore and powdery coal are placed on the
bedding carbonaceous material, and the hearth is caused to pass
inside the rotary hearth furnace to heat and reduce the
carbonaceous-material containing pellets to solid reduced iron and
to heat and dry the bedding carbonaceous material by distillation
into char. Subsequently, the solid reduced iron and the char are
charged into an iron-melting furnace without being substantially
cooled, and an oxygen gas is blown into the iron-melting furnace to
melt the solid reduced iron, thereby obtaining molten iron. At
least a part of an exhaust gas from the iron-melting furnace is
used as a fuel gas for the rotary hearth furnace after being cooled
and having dust removed.
Inventors: |
Tanaka; Hidetoshi; (Hyogo,
JP) ; Mimura; Tsuyoshi; (Hyogo, JP) ; Harada;
Takao; (Hyogo, JP) ; Hajika; Kiminori; (Hyogo,
JP) ; Yaso; Tadashi; (Hyogo, JP) ; Kurakake;
Toshiyuki; (Hyogo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho (
Kobe Steel ltd.)
10-26, Wakinohama-cho 2-chome, Chuo-ku
Kobe-shi
JP
651-8585
|
Family ID: |
36227848 |
Appl. No.: |
11/666830 |
Filed: |
October 26, 2005 |
PCT Filed: |
October 26, 2005 |
PCT NO: |
PCT/JP05/19701 |
371 Date: |
April 30, 2007 |
Current U.S.
Class: |
75/484 ;
266/177 |
Current CPC
Class: |
C22B 1/245 20130101;
Y02P 10/134 20151101; C21B 2100/66 20170501; C21B 13/0086 20130101;
C21B 13/143 20130101; C21B 13/0066 20130101; Y02P 10/136 20151101;
Y02P 10/216 20151101; C21B 13/105 20130101; C21B 2100/44 20170501;
C22B 5/10 20130101; Y02P 10/20 20151101 |
Class at
Publication: |
075/484 ;
266/177 |
International
Class: |
C21B 13/10 20060101
C21B013/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2004 |
JP |
2004-316532 |
Feb 18, 2005 |
JP |
2005-042716 |
Claims
1: A molten iron producing method for producing molten iron using a
molten iron production process constructed by combining a moving
hearth type reducing furnace and an iron-melting furnace,
comprising the steps (1) to (4): (1) reducing furnace charging step
of charging a bedding carbonaceous material onto a hearth of the
moving hearth type reducing furnace and placing
carbonaceous-material composite agglomerates containing a powdery
iron oxide source and a powdery carbonaceous reducing agent on the
bedding carbonaceous material; (2) reduction step of moving the
hearth inside the moving hearth type reducing furnace, thereby
heating and reducing the carbonaceous-material composite
agglomerates to solid reduced iron and heating and drying the
bedding carbonaceous material by distillation into char; (3)
melting furnace charging step of charging the solid reduced iron
and the char into the iron-melting furnace without being
substantially cooled; and (4) melting step of blowing an
oxygen-containing gas into the iron-melting furnace to melt the
solid reduced iron into the molten iron.
2: A molten iron producing method according to claim 1, wherein the
carbonaceous-material composite agglomerates are heated and reduced
to the solid reduced iron having a metallization degree of 92% or
higher in the step (2).
3: A molten iron producing method according to claim 1, wherein the
following step (5) is provided after the step (4): (5) exhaust gas
circulating step of using at least a part of an exhaust gas from
the iron-melting furnace as a fuel gas for the moving hearth type
reducing furnace.
4: A molten iron producing method according to claim 1, wherein the
carbon content of the solid reduced iron is 10 mass % or lower in
the step (2).
5: A molten iron producing method according to claim 1, wherein the
melting is performed on the condition of a secondary combustion
ratio of 40% or lower in the step (4).
6: A molten iron producing method according to claim 1, wherein the
thickness of the bedding carbonaceous material charged onto the
hearth is 1 to 10 mm.
7: A molten iron producing method according to claim 1, wherein the
average particle diameter of the bedding carbonaceous material is 1
to 5 mm.
8: A molten iron producing method according to claim 1, wherein the
Giesler's maximum fluidity MF of the bedding carbonaceous material
satisfies a relationship of log MF equal or lower than 2.
9: A molten iron producing method according to claim 1, wherein the
volatile content of the bedding carbonaceous material is 10 mass %
or higher by dry weight.
10: A molten iron producing method according to claim 1, wherein
the volatile content of the bedding carbonaceous material is 50
mass % or lower by dry weight.
11: A molten iron producing method according to claim 1, wherein
another carbonaceous material is additionally charged into the
iron-melting furnace in the step (3).
12: A molten iron producing method according to claim 1, wherein
the average volatile matter content of all the carbonaceous
materials charged into the iron-melting furnace is 15 mass % or
lower by dry weight with the carbon contained in the solid reduced
iron excluded.
13: A molten iron producing method according to claim 1, wherein
the following step (6) is provided between the steps (2) and (3):
(6) hot-molding step of molding the solid reduced iron and the char
without being substantially cooled.
14: A molten iron producing method according to claim 1, wherein
the temperatures of the solid reduced iron and the char are
500.degree. C. to 1100.degree. C. in the step (3).
15: A molten iron producing method according to claim 1, wherein
the following steps (7) to (9) are provided instead of the step
(3): (7) hot-classifying step of classifying the solid reduced iron
and the char into coarse particles and fine particles without being
substantially cooled after taking the solid reduced iron and the
char together from the moving hearth type reducing furnace, (8)
coarse particle charging step of gravitationally charging the
coarse particles into the iron-melting furnace, and (9) fine
particles injection step of charging the fine particles into the
iron-melting furnace by injection.
16: A molten iron producing method according to claim 15, wherein
the temperature of the coarse particles is 500.degree. C. to
100.degree. C. in the step (8).
17: A molten iron producing method according to claim 1, wherein
the solid reduced iron and the char are charged into the
iron-melting furnace from above without being substantially cooled
in the step (3).
18: A molten iron producing method according to claim 17, wherein
the char is charged into the iron-melting furnace together with the
solid reduced iron and/or auxiliary raw material and other charged
materials in the step (3).
19: A molten iron producing method according to claim 17, wherein
the char and the solid reduced iron are discharged from the moving
hearth type reducing furnace, stored in a container, conveyed from
the container to a hopper disposed above the iron-melting furnace
and consequently charged into the iron-melting furnace without
being substantially cooled by being intermittently dispensed from
the hopper in the step (3).
20: A molten iron producing method according to claim 17, wherein
the char and the solid reduced iron are discharged from the moving
hearth type reducing furnace, temporarily stored in a hopper
disposed above the iron-melting furnace and consequently charged
into the iron-melting furnace without being substantially cooled by
being intermittently dispensed from the hopper in the step (3).
21: A molten iron producing method according to claim 17, wherein a
rate of blowing the oxygen-containing gas into the iron-melting
furnace is reduced at the time of charging the char in the step
(3).
22: A molten iron producing method according to claim 21, wherein
the rate of blowing the oxygen-containing gas into the iron-melting
furnace at the time of charging the char is 80% or less of the one
when the char is not charged.
23: A molten iron producing method according to claim 21, wherein a
plurality of lances are provided to blow the oxygen-containing gas,
and the blowing rate from some of the lances is reduced or the
blowing therefrom is stopped.
24: A molten iron producing apparatus constructed by combining a
moving hearth type reducing furnace and an iron-melting furnace,
comprising the following means (1) to (5): (1) bedding carbonaceous
material charging means for charging a bedding carbonaceous
material onto a hearth of the moving hearth type reducing furnace;
(2) raw material charging means for placing carbonaceous-material
composite agglomerates containing a powdery iron oxide source and a
powdery carbonaceous reducing agent on the bedding carbonaceous
material; (3) heating means for heating and reducing the
carbonaceous-material composite agglomerates to solid reduced iron
and heating and drying the bedding carbonaceous material by
distillation into char while the hearth is moved inside the moving
hearth type reducing furnace; (4) melting furnace charging means
for charging the solid reduced iron and the char into the
iron-melting furnace from above without being substantially cooled,
at least the char being intermittently charged; and (5) oxygen
blowing means for blowing an oxygen-containing gas into the
iron-melting furnace to melt the solid reduced iron into the molten
iron.
25: A molten iron producing apparatus constructed by combining a
moving hearth type reducing furnace and an iron-melting furnace,
comprising the following means (1) to (6): (1) bedding carbonaceous
material charging means for charging a bedding carbonaceous
material onto a hearth of the moving hearth type reducing furnace;
(2) raw material charging means for placing carbonaceous-material
composite agglomerates containing a powdery iron oxide source and a
powdery carbonaceous reducing agent on the bedding carbonaceous
material; (3) heating means for heating and reducing the
carbonaceous-material composite agglomerates into solid reduced
iron and heating and drying the bedding carbonaceous material by
distillation while the heat is moved inside the moving hearth type
reducing furnace; (4) reduced iron containing means for containing
the solid reduced iron and the char discharged from the moving
hearth type reducing furnace without being substantially cooled;
(5) reduced iron storing means disposed above the iron-melting
furnace for temporarily storing the solid reduced iron and the char
conveyed from the reduced iron containing means and including
intermittent dispensing means for intermittently dispensing and
charging the solid reduced iron and the char into the iron-melting
furnace without being substantially cooled; and (6) oxygen blowing
means for blowing an oxygen-containing gas into the iron-melting
furnace to melt the solid reduced iron into the molten iron.
26: A molten iron producing apparatus constructed by combining a
moving hearth type reducing furnace and an iron-melting furnace,
comprising the following means (1) to (5): (1) bedding carbonaceous
material charging means for charging a bedding carbonaceous
material onto a hearth of the moving hearth type reducing furnace;
(2) raw material charging means for placing carbonaceous-material
composite agglomerates containing a powdery iron oxide source and a
powdery carbonaceous reducing agent on the bedding carbonaceous
material; (3) heating means for heating and reducing the
carbonaceous-material composite agglomerates into solid reduced
iron and heating and drying the bedding carbonaceous material by
distillation while the heat is moved inside the moving hearth type
reducing furnace; (4) reduced iron storing means for temporarily
storing the solid reduced iron and the char discharged from the
moving hearth type reducing furnace, the reduced iron storing means
including intermittent dispensing means for intermittently
dispensing and charging the solid reduced iron and the char into
the iron-melting furnace without being substantially cooled; and
(5) oxygen blowing means for blowing an oxygen-containing gas into
the iron-melting furnace to melt the solid reduced iron into the
molten iron.
27: A molten iron producing apparatus according to claim 24,
wherein a baffle plate for suppressing the scattering of the char
into an exhaust gas is provided between a charging portion for the
char and a discharging portion for discharging the exhaust gas from
the iron-melting furnace at a ceiling portion of the iron-melting
furnace.
28: A molten iron producing apparatus according to claim 24,
wherein guiding means for guiding the char to the outer surface of
molten metal in the iron-melting furnace is provided at the
charging portion for the char.
29: A molten iron producing apparatus according to claim 25,
wherein a baffle plate for suppressing the scattering of the char
into an exhaust gas is provided between a charging portion for the
char and a discharging portion for discharging the exhaust gas from
the iron-melting furnace at a ceiling portion of the iron-melting
furnace.
30: A molten iron producing apparatus according to claim 26,
wherein a baffle plate for suppressing the scattering of the char
into an exhaust gas is provided between a charging portion for the
char and a discharging portion for discharging the exhaust gas from
the iron-melting furnace at a ceiling portion of the iron-melting
furnace.
31: A molten iron producing apparatus according to claim 25,
wherein guiding means for guiding the char to the outer surface of
molten metal in the iron-melting furnace is provided at the
charging portion for the char.
32: A molten iron producing apparatus according to claim 26,
wherein guiding means for guiding the char to the outer surface of
molten metal in the iron-melting furnace is provided at the
charging portion for the char.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and an apparatus
for producing molten iron and particularly to an improved method
for efficiently producing molten iron having a high iron purity by
heating and reducing an iron oxide source such as iron ore together
with a carbonaceous reducing agent such as coal in a molten iron
production process constructed by combining a moving hearth type
reducing furnace and an iron melting furnace.
BACKGROUND TECHNOLOGY
[0002] The inventors of the present invention developed a molten
iron production method for, in a molten iron production process in
which a rotary hearth furnace (moving hearth type reduction
furnace) and a melting furnace (iron-melting furnace) are coupled,
obtaining molten iron by feeding solid reduced iron to a melting
furnace after heating and reducing a compact containing iron oxide
and a carbonaceous reducing agent to the solid reduced iron having
a metallization degree of 60% or higher in a rotary hearth furnace,
and melting the solid reduced iron while controlling the secondary
combustion ratio in the melting furnace to be 40% or lower by
burning a carbonaceous material fed as a fuel with oxygen to melt
the solid reduced iron. They also indicated that a part of or all
of the carbonaceous material fed as the fuel into the melting
furnace could be fed as a bedding carbonaceous material onto the
hearth of the rotary hearth furnace (see Japanese Unexamined Patent
Publication No. 2004-176170).
[0003] However, only qualitative actions and effects were indicated
concerning the method using the bedding carbonaceous material, and
specific operating conditions for further reducing the fuel
specific consumption while stabilizing the operations of the rotary
hearth furnace and the melting furnace were still uncertain. Thus,
there was a room for improvement.
[0004] On the other hand, the inventors of the present invention
also proposed a method for, in a process for producing metallic
iron by feeding a raw material containing an iron-oxide containing
substance and a carbonaceous reducing agent after laying a powdery
bedding carbonaceous material for atmospheric adjustment on the
hearth of the rotary hearth furnace, and heating the raw material
in the furnace to reduce and melt the raw material, recycling the
bedding carbonaceous material-discharged from the rotary hearth
furnace to be used again in the rotary hearth furnace, thereby
preventing such a phenomenon that the powdery bedding carbonaceous
material is caked into a cracker-shaped material (see Japanese
Unexamined Patent Publication No. 2003-213312).
[0005] However, the above process includes no melting furnace and
produces the metallic iron only using the rotary hearth furnace,
and physical and chemical properties required for the bedding
carbonaceous material, the recycling conditions of the bedding
carbonaceous material and the like cannot be applied as they are to
the molten iron production process disclosed in the former prior
art document in which the rotary hearth furnace and the melting
furnace are coupled.
SUMMARY OF THE INVENTION
[0006] Accordingly, an object of the present invention is to
provide a molten iron producing method which can further reduce the
fuel specific consumption while stabilizing the operations of a
moving hearth type reducing furnace and an iron-melting furnace in
a molten iron production process constructed by combining the
moving hearth type reducing furnace and the iron-melting furnace,
and a suitable molten iron producing apparatus.
[0007] The present invention is directed to a molten iron producing
method for producing molten iron using a molten iron production
process constructed by combining a moving hearth type reducing
furnace and an iron-melting furnace, comprising the following steps
(1) to (4):
[0008] (1) reducing furnace charging step of charging a bedding
carbonaceous material onto a hearth of the moving hearth type
reducing furnace and placing carbonaceous-material composite
agglomerates containing a powdery iron oxide source and a powdery
carbonaceous reducing agent on the bedding carbonaceous
material,
[0009] (2) reduction step of moving the hearth inside the moving
hearth type reducing furnace, thereby heating and reducing the
carbonaceous-material composite agglomerates to solid reduced iron
and heating and drying the bedding carbonaceous material by
distillation into char,
[0010] (3) melting furnace charging step of charging the solid
reduced iron and the char into the iron-melting furnace without
being substantially cooled, and
[0011] (4) melting step of blowing an oxygen-containing gas into
the iron-melting furnace to melt the solid reduced iron into the
molten iron.
[0012] According to the present invention, the hearth can be more
securely protected by using the bedding carbonaceous material to
avoid troubles such as the peeling of the hearth. Therefore, the
moving hearth type reducing furnace can be continuously operated
over a longer period of time. Further, since the char after
devolatization contains no volatile content, the damage of the
refractory by the combustion of the volatile content in the
iron-melting furnace can be prevented, thereby extending the lift
of the refractory of the iron-melting furnace. Further, the
reoxidation of the solid reduced iron in the moving hearth type
reducing furnace can be prevented by using the bedding carbonaceous
material, whereby a high metallization degree of, e.g. 92% or
higher, can be achieved and the carbonaceous material consumption
in the iron-melting furnace can be considerably reduced.
[0013] As a result, the specific fuel consumption can be further
reduced while the operations of the moving hearth type reducing
furnace and the iron-melting furnace are more stabilized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a flow diagram of a molten iron production process
showing one embodiment of the invention,
[0015] FIGS. 2A and 2B are sections diagrammatically showing a
state near a hearth of a rotary hearth furnace,
[0016] FIGS. 3A and 3B are graphs showing relationships between the
thickness of a bedding carbonaceous material and the metallization
degree of solid reduced iron,
[0017] FIG. 4 is a graph showing relationships between the carbon
content and the crushing strength of the solid reduced iron,
[0018] FIG. 5 is a flow diagram showing one embodiment of a batch
charging method according to the invention,
[0019] FIGS. 6A and 6B are sections showing a state of a gas flow
in the iron-melting furnace according to the invention, wherein
FIG. 6A shows a basic construction and FIG. 6B shows an example in
which a baffle plate is disposed,
[0020] FIGS. 7A and 7B are sections showing a state of a gas flow
in the iron-melting furnace according to the invention, wherein
FIG. 7A shows an example in which a guide plate is disposed and
FIG. 7B shows an example in which a guide duct is disposed,
[0021] FIG. 8 is a graph showing a particle size distribution of
solid particles, and
[0022] FIG. 9 is a graph showing a relationship between an oxygen
gas blowing rate and the scattering rate of solid particles.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0023] Hereinafter, the present invention is described in detail
with reference to the drawings showing one embodiment thereof.
First Embodiment
[0024] FIG. 1 is a flow diagram of a molten iron production process
showing one embodiment of the present invention, wherein this
molten iron production process is constructed by coupling a rotary
hearth furnace 14 as a moving hearth type reducing furnace and an
iron-melting furnace 16.
[0025] Iron ore "a" as an iron oxide source and coal b as a
carbonaceous reducing agent are, if necessary, separately crushed
into particles having diameters of approximately below 1 mm. The
thus obtained powdery iron ore A as a powdery iron oxide source and
powdery coal B as a powdery carbonaceous reducing agent are mixed
at a specified ratio, a suitable amount of binder and/or a suitable
amount of moisture are added if necessary (further, all or a part
of an auxiliary raw material I as a slag forming agent to be added
in the iron-melting furnace 16 may be added here), and these are
mixed by a mixer 8. Thereafter, the mixed compound is granulated to
have a particle diameter of about 6 to 20 mm in a granulator 11,
thereby obtaining carbonaceous-material containing pellets D as
carbonaceous-material composite agglomerates. It should be noted
that a volatile content of the coal (carbonaceous reducing agent) b
is desirably 30 mass % or lower because the carbonaceous-material
containing pellets D are likely to burst upon being heated in the
rotary hearth furnace 14 if the volatile content is excessively
high.
[0026] The carbonaceous-material containing pellets D are
preferably dried in a drier 13 until the moisture content thereof
becomes 1 mass % or lower in order to prevent the bursting in the
rotary hearth furnace 14.
[0027] (1) Reducing Furnace Charging Step
[0028] Subsequently, for example, coal as a bedding carbonaceous
material E is charged onto a hearth 32 of the rotary hearth furnace
14 to have a specified thickness as diagrammatically shown in FIG.
2A, and the carbonaceous-material containing pellets D are placed
on this bedding carbonaceous material E to have the thickness of
two layers or less.
[0029] As a means for charging the bedding carbonaceous material E
onto the hearth 32 in this way (bedding charging means) can be used
a means for quantitatively dispensing the bedding carbonaceous
material E, for example, from an intermediate hopper disposed above
the rotary hearth furnace 14 and feeding the dispensed bedding
carbonaceous material onto the hearth 32 via a charging pipe, and
dispersing the fed bedding carbonaceous material E along the width
direction of the hearth 32 by means of a dispersion screw. As a
means for placing the carbonaceous-material containing pellets D on
this bedding carbonaceous material E (raw-material charging method)
can be used a means having a construction similar to the bedding
charging means, including an intermediate hopper, a charging pipe
and a dispersion screw and disposed downstream from the bedding
charging means with respect to a moving direction of the hearth
32.
[0030] The thickness of the bedding carbonaceous material E charged
onto the hearth 32 is preferably 1 to 10 mm. If this thickness is
below 1 mm, it is difficult to securely cover the entire outer
surface of the hearth 32 and a reoxidation preventing effect may
become insufficient. On the other hand, if this thickness exceeds
10 mm, an effect of heating the carbonaceous-material containing
pellets D from their bottom surfaces via the outer surface of the
hearth 32 is reduced and an amount of the carbonaceous material
charged into the iron-melting furnace 16 becomes excessive,
resulting in a higher possibility of increasing the fuel specific
consumption. The thickness of the bedding carbonaceous material E
is more preferably 2 to 5 mm.
[0031] The average particle diameter of the bedding carbonaceous
material E is preferably 1 to 5 mm. If the average particle
diameter is below 1 mm, the bedding carbonaceous material is likely
to disperse upon being changed into the rotary hearth furnace 14
and the iron-melting furnace 16, thereby reducing a carbonaceous
material yield. On the other hand, if the average particle diameter
exceeds 5 mm, it is approximate to the upper limit of the
preferable thickness of the bedding carbonaceous material E and it
becomes difficult to lay the bedding carbonaceous material E at a
uniform thickness. In addition, clearances between the carbonaceous
particles become larger and the carbonaceous-material containing
pellets D enter these clearances. Thus, it becomes difficult to
uniformly bed the carbonaceous-material containing pellets D on the
layer of the bedding carbonaceous material E, thereby increasing a
possibility of leading to reductions in productivity and
metallization degree. The average particle diameter of the bedding
carbonaceous material D is more preferably 2 to 4 mm.
[0032] The crushed coal b may be sieved using a specified particle
diameter (sieve mesh of, e.g. 1 mm) as a criteria, and the powdery
material below the sieve may be used as the powdery carbonaceous
reducing agent B and the one above the sieve may be used as the
bedding carbonaceous material E.
[0033] The Giesler's maximum fluidity MF of the bedding
carbonaceous material E preferably satisfies a relationship: log
MF.ltoreq.2. If log MF exceeds 2, the carbonaceous particles are
excessively softened and molten upon being heated in the rotary
hearth furnace 14 and deposit is likely to be formed on the hearth
32. The Giesler's maximum fluidity MF more preferably satisfies a
relationship: log MF.ltoreq.1.
[0034] The volatile content of the bedding carbonaceous material E
is preferably 10 mass % or higher by dry weight. This is because
coal such as anthracite coal having less volatile content has a
high apparent density due to its dense structure and is likely to
burst to be powdered despite its less volatile content.
[0035] The volatile content of the bedding carbonaceous material E
is preferably 50 mass % or lower, more preferably 40 mass % or less
by dry weight. The volatile content in the bedding carbonaceous
material E is almost completely devolatized upon being heated in
the rotary hearth furnace 14, and can be used as a fuel gas in the
rotary hearth furnace 14. However, if the volatile content is
excessive, more combustible gas than necessary is produced from the
bedding carbonaceous material at an initial stage of reduction in
the rotary hearth furnace 14 and the unconsumed combustible gas is
discharged while of 6 min., more preferably 8 min. This causes the
carbonaceous-material containing pellets D to be heated in the
rotary hearth furnace 14, whereby the iron oxide in the
carbonaceous-material containing pellets D is reduced by the
carbonaceous reducing agent to be metallized, thereby becoming
solid reduced iron F. The metallization degree of the thus obtained
solid reduced iron F is 92% or higher, and the carbon content
thereof is preferably 10 mass % or lower, more preferably 5 mass %
or lower. On the other hand, the bedding carbonaceous material E is
heated in the rotary hearth furnace 14 to have the volatile content
thereof devolatized (dried by distillation), thereby becoming char
G. The devolatized volatile content is burnt in the rotary hearth
furnace 14 to be effectively used as a fuel. As a means (heating
means) for heating the carbonaceous-material containing pellets D
and the bedding carbonaceous material E can be used, for example, a
plurality of burners (not shown) disposed at an upper part of the
side wall of the rotary hearth furnace 14.
[0036] If the atmospheric temperature is 1350.degree. C. or higher,
the carbonaceous-material containing pellets D are molten on the
hearth 32 to be separated into iron components and slag components.
Since the carbonaceous-material containing pellets D are difficult
to discharge from the rotary hearth furnace 14 while being molten,
they are discharged after being cooled and solidified in the rotary
hearth furnace 14. The solid reduced remaining in the exhaust gas
from the rotary hearth furnace 14, which leads to a reduced energy
efficiency. Further, if the volatile content is excessive, the
carbonaceous material becomes lighter due to the devolatization of
the volatile content caused by heating and is likely to scatter
upon being discharged from the rotary hearth furnace 14, thereby
leading to a reduced carbonaceous material yield. The bedding
carbonaceous material E is desirably dried before being charged
into the rotary hearth furnace 14. A carbonaceous material whose
volatile content is about 50 mass % or higher like brown coal is
dried, it becomes porous and easier to ignite and, therefore, is
difficult to handle.
[0037] It is not necessary to use only one kind of bedding
carbonaceous material having the above preferable amount of the
volatile content, and two or more kinds of carbonaceous materials
having different amounts of volatile contents may be used by being
suitably mixed. Carbonaceous materials already heat-treated in a
separate process such as coke powder or petroleum coke may be used
as the one to be mixed.
[0038] (2) Reduction Step
[0039] The carbonaceous-material containing pellets D and the
bedding carbonaceous material E placed in layers on the hearth 32
in this way are caused to pass inside the rotary hearth furnace 14
heated at an atmospheric temperature of 1100.degree. C. to
1450.degree. C., more preferably 1250.degree. C. to 1450.degree. C.
for a residence time iron F in this case is a mixture of powdery
iron and solid slag. However, it is not preferable from a viewpoint
of the productivity and the energy efficiency of the entire process
to cool and solidify the pellets D molten in the rotary hearth
furnace 14 and melt again in the iron-melting furnace 16.
Accordingly, in order to further improve the productivity and the
energy efficiency of the entire process, it is desirable to
discharge the carbonaceous-material containing pellets D from the
rotary hearth furnace 14 before being molten on the hearth and melt
them in the iron-melting furnace 16 while improving the
productivity in the rotary hearth furnace 14 by setting the
atmospheric temperature at 1350.degree. C. or higher during the
reduction in the rotary hearth furnace 14.
[0040] In order to prevent the molten iron and the molten slag from
damaging a hearth refractory in the case that the
carbonaceous-material containing pellets D should be molten on the
hearth 32, it is also effective to provide a layer of a
carbonaceous material P for hearth protection, which is a fine
carbonaceous material for preventing the permeation of the molten
material between the hearth 32 and the bedding carbonaceous
material E or a carbonaceous material P for hearth protection
containing fine carbonaceous material as shown in FIG. 2B.
[0041] The metallization degree of the solid reduced iron F is set
at 92% or higher and the carbon content thereof is preferably set
at 10 mass % or lower, more preferably at 5 mass % or lower for the
following reasons.
[0042] First, the reasons for setting the metallization degree at
92% or higher are given. Specifically, the higher the metallization
degree of the solid reduced iron F, the less carbon amount is
necessary to metallize iron oxide (FeO, etc.) remaining in the
solid reduced iron F in the iron-melting furnace 16, wherefore the
entire carbonaceous material consumption in the iron-melting
furnace 16 can be reduced. Thus, it is desirable to maximally
increase the metallization degree. However, if the
carbonaceous-material containing pellets are reduced by the rotary
hearth furnace without using the bedding carbonaceous material, the
solid reduced iron is reoxidized by the oxidizing atmosphere in the
rotary hearth furnace. Thus, it has been conventionally very
difficult to stably obtain a metallization degree of 90% or higher
as shown in FIG. 3A. Contrary to this, if the bedding carbonaceous
material E is used, oxidizing gas components CO.sub.2 and H.sub.2O
in the oxidizing atmosphere are modified into reducing gas
components through reactions: CO.sub.2+C.fwdarw.2CO and
H.sub.2O+C.fwdarw.H.sub.2+CO by the char G produced from the
bedding carbonaceous material E, with the result that the
reoxidation of the solid reduced iron F is either suppressed or
prevented. Thus, a metallization degree of 92% or higher can be
easily obtained as shown in FIG. 3B, and a metallization degree of
94% or higher can also be attained depending on the operation
conditions. Therefore, the metallization degree of the solid
reduced iron F is set at 92% or higher. The more preferable
metallization degree of the solid reduced iron F is 94% or
higher.
[0043] Next, reasons for setting the carbon content preferably at
10 mass % or lower, more preferably at 5 mass % or lower are given.
Specifically, if the carbon content in the solid reduced iron F is
high, it covers a carbon amount necessary to metallize iron oxide
(FeO, etc.) remaining in the solid reduced iron F and the remaining
carbon amount is used to carburize the molten iron obtained by
melting the solid reduced iron. Thus, a higher carbon content is
preferable from a viewpoint of the carbonaceous material
consumption in the iron-melting furnace 16. However, the higher the
carbon content (remaining carbon amount), the smaller the crushing
strength of the solid reduced iron F as shown in FIG. 4. Thus, the
solid reduced iron is easier to powder at the time of being
discharged from the rotary hearth furnace 14 and being charged into
the iron-melting furnace, thereby increasing a dust loss.
Accordingly, a lower carbon content is preferable from a viewpoint
of an iron yield and a carbon yield. Therefore, the upper limit of
the carbon content of the solid reduced iron F is set at a maximum
value within such a range that crushing strength is not excessively
reduced. This upper limit is preferably 10 mass % or lower, more
preferably 5 mass % or lower. The preferable lower limit of the
carbon content of the solid reduced iron F is about 1.5 mass %
which is necessary to metallize iron oxide (FeO, etc.) remaining in
the solid reduced iron F if the metallization degree is 92%.
[0044] If liquid coal is used as the powdery carbonaceous reducing
agent B to be contained into the carbonaceous-material containing
pellets D, the carbon content can be increased to as high as about
10 mass % while maintaining the strength of the solid reduced iron
F. However, since the liquid coal is not abound and generally
expensive, it is desirable to use coal having no fluidity and
employ a production method for reducing the carbon content in the
solid reduced iron F to 5 mass % or lower.
[0045] Such metallization degree and carbon content of the solid
reduced iron F can be obtained by suitably adjusting the mixing
ratio of the iron ore (iron oxide source) "a" and the coal
(carbonaceous reducing agent) b in the carbonaceous-material
containing pellets D, the thickness and the average particle
diameter of the bedding carbonaceous material E, the atmospheric
temperature of the rotary hearth furnace 14, the residence time of
the carbonaceous-material containing pellets D in the rotary hearth
furnace 14, and other factors.
[0046] (3) Melting Furnace Charging Step
[0047] The solid reduced iron F and the char G thus obtained are
preferably taken out of the rotary hearth furnace 14 and
intermittently charged into the iron-melting furnace 16 while being
hot (in other words, while being at high temperature or without
being substantially cooled) As one example of such a melting
furnace charging means, the following hopper and containers may be
used.
[0048] Specifically, as shown in FIG. 5, the solid reduced iron F
and the char G are taken out together by means of a discharge screw
101 disposed at the exit of the rotary hearth furnace 14 and
contained into a container 102 as a reduced iron containing means.
When the container 102 becomes full, it is switched over to another
empty container 102' and the container 102 is turned upside down by
an unillustrated turning machine after a slide gate valve 103
disposed atop the full container 102 is closed, and is conveyed to
a position above a hopper 106 as a reduced iron storing means
disposed above the iron-melting furnace 16 by a carriage 104 and a
crane 105. Here, the slide gate valve 103 is opened to transfer the
solid reduced iron F and the char G in the container 102 to the
hopper 106 to temporarily store them. At least the container 102
and the hopper 106 are coated with refractory because they charge
the solid reduced iron F and the char G into the iron-melting
furnace 16 while they are hot (in other words, being at high
temperature or without being substantially cooled). The solid
reduced iron F and the char G are intermittently dispensed together
(without being separated) by opening and closing a slide gate valve
107 as an intermittent dispensing means disposed at the bottom of
the hopper 106, and are charged into the iron-melting furnace 16 by
dropping, taking advantage of gravity, via a charging pipe 108
(such intermittent charging method is referred to as a "batch
charging method", whereas a continuous charging method normally
employed is referred to as a "continuous charging method"). In
order to avoid the reoxidation of the solid reduced iron F and the
combustion of the char G upon separating the container 102 from the
rotary hearth furnace 14 or upon transferring the content of the
container 102 to the hopper 106, at least the container 102 and the
hopper 106 are so constructed as to be purgeable by an inert gas
such as a nitrogen gas. It should be noted that the solid reduced
iron F and the char G are preferably charged in such a manner as
not to touch the inner wall surface of the iron-melting furnace
16.
[0049] Another carbonaceous material H (hereinafter referred to as
"additional carbonaceous material") to be added if the carbonaceous
material consumption necessary in the iron-melting furnace 16
cannot be covered only by the auxiliary raw material I as the slag
forming agent, the carbon content in the solid reduced iron F and
the char G and the like (hereinafter referred to as "auxiliary raw
material and other charged materials) is added in the iron-melting
furnace 16 by a system different from the one for the solid reduced
iron F and the char G. Since the solid reduced iron F, the char G,
the auxiliary raw material and other charged materials adhere and
deposit upon touching the inner wall surface of the iron-melting
furnace 16, they are preferably charged in such a manner as not to
touch the inner wall surface of the iron-melting furnace 16.
[0050] By charging the solid reduced iron F and the char G while
being hot (being at high temperature or without being substantially
cooled) in this way, solid sensible heat can be effectively
recovered and the carbonaceous material consumption of the
iron-melting furnace 16 can be reduced.
[0051] Further, by intermittently dispensing the solid reduced iron
F and the char G and letting them drop in a mass into the
iron-melting furnace 16 within a short period of time, a scattering
rate of dust of the char G into an exhaust gas M can be reduced,
wherefore the carbonaceous material yield in the entire process can
be improved.
[0052] Specifically, if the solid particles made up of the solid
reduced iron F and the char G are continuously charged as solid
reduced iron has been conventionally continuously charged, there is
a high probability that they separately drop because a solid mass
feed rate per unit time is small. Thus, the char particles being
lightweight and having small particle diameters are likely to get
scattered into the exhaust gas by the flow of the gas produced from
molten metal. Contrary to this, if the solid reduced iron F and the
char G are intermittently charged together, the particles of the
char G drop as aggregates together with other solid particles
heavier and larger in particle diameter than the char because the
solid mass feed rate per unit time is large. Thus, gas around the
aggregates is caused to flow downward. As a result, the particles
of the char G likely to scatter as single particles drop along the
downward flow of the gas, wherefore the char particles prevail
against the flow of the gas produced from the molten metal and
added into the molten metal with a good yield without being
scattered.
[0053] It is recommended to intermittently dispense the solid
particles (solid reduced iron F and char G) (charge into the
iron-melting furnace 16) at a frequency of 1 to 10 min., more
preferably 2 to 5 min for the following reasons. Specifically, if
the charging frequency is excessively increased, it becomes
difficult to obtain the scatter preventing effect because the solid
mass feed rate per unit time does not become sufficiently large. In
addition, equipment troubles are likely to occur because the slide
gate valve 107 is frequently opened and closed. On the other hand,
if the charging frequency is excessively lessened, the scatter
preventing effect is saturated. In addition, since a large amount
of the solid reduced iron F and the char G are added at once, there
arise problems that the iron-melting furnace 16 becomes difficult
to control due to its large thermal fluctuation; the effect of
recovering the solid sensible heat is reduced due to the
temperature decreases of the solid reduced iron F and the char G
upon being charged into the iron-melting furnace 16; and the
capacity of the hopper 106 needs to be increased to thereby
increase the plant cost.
[0054] The solid reduced iron F and the char G upon being charged
into the iron-melting furnace 16 without being substantially cooled
are made to have temperatures at which the solid reduced iron F and
the char G discharged from the intermediate hoppers can be charged
into the furnace 16 without causing thermal loads to the furnace 16
when being charged into the furnace 16, specifically 500.degree. C.
to 1100.degree. C.
[0055] For the following reasons, it is preferable that the
temperatures of the solid reduced iron F and the char G upon being
charged into the iron-melting furnace 16 are 500.degree. C. to
1100.degree. C. If the temperatures are below 500.degree. C., the
effect of recovering the solid sensible heat is small. On the other
hand, if the temperatures are above, 1100.degree. C., the heat
resistance of the discharge screw and the like become problematic
and operation troubles are likely to occur.
[0056] If the carbonaceous material consumption necessary in the
iron-melting furnace cannot be covered only by the carbon content
of the solid reduced iron F and the char G, the additional
carbonaceous material H may be additionally charged into the
iron-melting furnace 16 as described above.
[0057] The average volatile matter content in all the carbonaceous
material to be charged into the iron-melting furnace 16 (excluding
carbon contained in the solid reduced iron F) is preferably 15 mass
% or lower by dry weight. In the case of charging the additional
carbonaceous material H, it is desirable to choose the kind of coal
such that an average volatile matter content which is a weighted
average of the volatile content of the additional carbonaceous
material H and that of the char G (normally about 0 mass %) is 15
mass % by dry weight. If the average volatile matter content
exceeds 15 mass %, gas-phase temperature excessively increases due
to the combustion of the volatile content in the iron-melting
furnace 16, thereby increasing a risk of damaging the
refractory.
[0058] (4) Melting Step
[0059] The solid reduced iron F is molten to separate slag L by
blowing an oxygen gas J as an oxygen-containing gas into the
iron-melting furnace 16 by means of a plurality of lances as an
oxygen blowing means to burn the carbonaceous material (char G,
additional carbonaceous material H), whereby molten iron K can be
obtained. It should be noted that the iron-melting furnace 16 may
be of the inclining type or of the fixed type.
[0060] In this melting step, it is preferable to perform the
melting on the condition of a secondary combustion ratio of 40%. If
the secondary combustion ratio exceeds 40%, the effect of reducing
the carbonaceous material consumption can be hardly confirmed when
the metallization degree of the solid reduced iron F is 92% or
higher. In addition, the gas-phase temperature excessively
increases to increase a risk of damaging the refractory, thereby
increasing loads on the iron-melting furnace 16. A more preferable
range of the secondary combustion ratio is 10 to 40% at which the
carbonaceous material consumption is sufficiently low, and a even
more preferable range thereof is 15 to 30% at which the loads on
the iron-melting furnace 16 are further reduced.
[0061] (5) Melting-Furnace Exhaust Gas Circulating Step
[0062] Since the exhaust gas (melting-furnace exhaust gas) M in the
iron-melting furnace 16 contains high concentrations of CO and
H.sub.2 components, it is desirable to feed at least a part of the
exhaust gas M to the rotary hearth furnace 14 after cooling it and
removing dust therefrom in a gas cooling/dust removing apparatus 24
and to use the exhaust gas as a fuel gas for the rotary hearth
furnace 14 by adding an external fuel N if necessary.
[0063] As described above, according to the first embodiment, the
hearth 32 is securely protected by using the bedding carbonaceous
material E, thereby avoiding troubles such as the peeling of the
hearth, with the result that the rotary hearth furnace 14 can be
continuously operated over a long period of time. Further, the
volatile content that is devolatized when the bedding carbonaceous
material E is heated in the rotary hearth furnace 14 is effectively
used as the fuel gas for the rotary hearth furnace together with at
least a part of the exhaust gas, wherefore the fuel consumption of
the rotary hearth furnace 14 can be reduced. Since the char G after
the devolatization contains no volatile content, a damage of the
refractory caused by the combustion of the volatile content in the
iron-melting furnace 16 can be prevented, thereby extending the
life of the refractory of the iron-melting furnace 16. Further, the
reoxidation of the solid reduced iron F in the rotary hearth
furnace 14 can be prevented by using the bedding carbonaceous
material E, thereby achieving a high metallization degree of 92% or
higher to considerably reduce the carbonaceous material consumption
in the iron-melting furnace 16. The entire process including the
reduction and the melting can be made into an energetically
self-contained process by adjusting the metallization degree of the
solid reduced iron F, the consumed amount of the bedding
carbonaceous material, and the amount of the volatile content of
the bedding carbonaceous material E to conform the total heat
quantity of the exhaust gas produced from the iron-melting furnace
16 to the heat quantity necessary and sufficient in the rotary
hearth furnace 14. Further, the rate of scattering fine particles
of the char G and the like into the exhaust gas can be reduced to
improve the carbonaceous material yield in the entire process by
intermittently dispensing the solid reduced iron F and the char G
and letting them drop in a mass into the iron-melting furnace 16
from above within a short period of time.
Second Embodiment
[0064] The following step (6) may be provided between the reduction
step (the above step (2)) and the melting furnace charging step
(the above step (3)).
[0065] (6) Step of Hot-Forming the Solid Reduced Iron F and the
Char G Together while they are Hot
[0066] Specifically, the solid reduced iron F and the char G may be
dispensed together, for example, from the hopper 106 while being
hot, and pressure-formed into hot briquetted iron (HBI) by a hot
forming machine, and this HBI may be dropped and charged into the
iron-melting furnace 16 at a temperature of, e.g. 500 to
1100.degree. C. without being cooled.
[0067] This prevents the fine particles from scattering at the time
of being charged into the iron-melting furnace 16, and an amount of
dust in the exhaust gas from the iron-melting furnace 16 can be
considerably reduced. Therefore, an iron yield and a carbon yield
can be considerably improved.
[0068] Since the purpose of forming here is to eliminate fine
particles, the shape of the compacts is not limited to that of a
briquette and the compacts may be plate-shaped aggregates or
aggregates having irregular shapes. The compacts need not be strong
unless they become fine particles again due to a handling impact
until the charging into the iron-melting furnace 16.
Third Embodiment
[0069] The following steps (7) to (9) may be provided instead of
the melting furnace charging step (the above step (3)).
[0070] (7) Hot-classifying step of classifying the solid reduced
iron F and the char G into coarse particles and fine particles
while they are hot or without being substantially cooled after the
solid reduced iron F and the char G are taken together out of the
rotary hearth furnace 14.
[0071] (8) Coarse particle charging step of gravitationally
charging coarse particles into the iron-melting furnace 16
[0072] (9) Fine particle injection step of charging the fine
particles into the iron-melting furnace 16 by injection
[0073] Specifically, facilities having the following construction
may be employed. A screen having sieve meshes of about 2 to 5 mm is
provided at a portion of the rotary hearth furnace 14 where the
solid reduced iron F and the char G are discharged, and the solid
reduced iron F and the char G are sieved while being hot, wherein
course particles above the sieve and fine particles below the sieve
are temporarily stored in separate intermediate hoppers. The coarse
particles are charged into the iron-melting furnace 16 from above
at a temperature of, e.g. 500.degree. C. to 1100.degree. C. by the
gravitational drop. On the other hand, the fine particles are blown
into the molten iron in the iron-melting furnace 16 and/or the
molten slag formed on the molten iron via an injection lance and a
tuyere provided at the furnace side of the iron-melting furnace 16
and/or at the bottom of the furnace using an inert gas such as
N.sub.2 as a carrier gas.
[0074] Since this causes the fine particles to be trapped in the
molten iron and/or the molten slag, the scattering of the fine
particles can be prevented at the time of charging into the
iron-melting furnace 16 and the amount of dust in the exhaust gas
from the iron-melting furnace 16 can be considerably reduced
similar to the second embodiment. Therefore, an iron yield and a
carbon yield can be considerably improved.
Fourth Embodiment
[0075] The aforementioned melting step (4) is preferably performed
as follows. Specifically, it is preferable to reduce a blowing rate
of the oxygen gas (total blowing rate from a plurality of lances)
at the time of charging the solid reduced iron F and the char G
into the iron-melting furnace 16. This can reduce an amount of gas
produced from the molten metal and further reduce the scattering
amount of the char G.
[0076] In order to securely reduce the scattering amount of the
char G, it is desirable to set the blowing rate (total amount) of
the oxygen gas at the time of charging the solid reduced iron F and
the char G at 80% or lower, more preferably 60% or lower of the
blowing rate (total amount) of the oxygen gas when the solid
reduced iron F and the char G are not charged. However, the blowing
rate is desirably 30% or higher since the combustion in the furnace
may stop if the blowing rate is excessively reduced.
[0077] In this case, out of the plurality of lances, the oxygen
blowing rate(s), for example, from some (one or a plurality of)
lance(s) disposed near the position where the solid reduced iron F
and the char G are charged may be preferentially reduced or
stopped. This enables a local and considerable reduction of the
amount of the gas produced from the molten metal near the position
where the solid reduced iron F and the char G are charged.
Therefore, the scattering amount of the char G can be even more
reduced.
[0078] Further, it is preferable to dispose a baffle plate 114
between a reduced iron charging opening 112, which is a charging
portion for the solid reduced iron F and the char G, and an exhaust
gas discharging opening 113, which is a discharging portion for the
exhaust gas (melting-furnace exhaust gas) from the iron-melting
furnace 16 at a ceiling portion 111 of the iron-melting furnace 16
as shown in FIG. 6B. If no baffle plate 114 is disposed, the char G
is likely to be discharged together with the melting-furnace
exhaust gas M along the gas flow taking a shortcut from the reduced
iron charging opening 112 to the exhaust gas discharging opening
113 along the ceiling portion 111 as shown in FIG. 6A. Contrary to
this, if the baffle plate 114 is disposed, the gas flow from the
reduced iron charging opening 112 along the ceiling portion 111 has
its course diverted downward by the baffle plate 114 as shown in
FIG. 6B. Thus, the char G carried by this gas flow can more
easily-reach the outer surface of the molten metal by the downward
flow, thereby effectively suppressing the scattering of the char G
into the melting-furnace exhaust gas M.
[0079] In this melting step as well, the melting is preferably
performed on the condition of a secondary combustion ratio of 40%
or lower. A more preferable range of the secondary combustion ratio
is 10 to 40% at which the carbonaceous material consumption is
sufficiently low, and an even more preferable range thereof is 15
to 30% at which the loads on the iron-melting furnace 16 are
further reduced.
[Modifications]
[0080] Although the solid reduced iron and the char are
intermittently charged into the iron-melting furnace together in
the foregoing embodiments, they may be classified into the solid
reduced iron and the char by a screen or the like while being hot
after being taken out from the rotary hearth furnace and may be
separately charged into the iron-melting furnace. In this case, it
does not matter whether the solid reduced iron is charged
continuously or intermittently, but the char is intermittently
charged. However, it is more preferable to charge the char together
with the solid reduced iron as in the first embodiment rather than
to separately charge the char since the solid mass feed rate per
unit time is larger in the former case and the scattering of the
char can be more securely prevented.
[0081] Although the auxiliary raw material and the other charged
materials are added into the iron-melting furnace by the system
different from the one for the solid reduced iron and the char in
the above example, they may be charged by the same system. In the
case of classifying the solid reduced iron and the char and
separately charging them into the iron-melting furnace, the
auxiliary raw material and the other charged materials may be added
to the char and charged together by the same system. It is more
preferable to charge the char together with the auxiliary raw
material and the other charged materials since the solid mass feed
rate per unit time becomes larger and the scattering of the char
can be more securely prevented.
[0082] Although the solid reduced iron F and the char G are charged
using the container and the hopper both provided with the slide
gate valve according to the illustrated batch charging method, the
container may be dispensed with and the solid reduced iron F and
the char G taken out from the rotary hearth furnace may be directly
charged into the hopper provided with the slide gate valve and the
solid reduced iron F and the char G may be intermittently dispensed
by opening and closing the slide gate valve if the rotary hearth
furnace and the iron-melting furnace can be installed proximate to
each other.
[0083] In the above example, a reduction in the oxygen gas blowing
rate at the time of charging the solid reduced iron and the char
into the iron-melting furnace is accomplished by providing the
iron-melting furnace with a plurality of lances and reducing or
stopping the oxygen blowing rate from all or some of the lances.
However, the iron-melting furnace may be provided with only one
lance and the oxygen blowing rate from this lance may be
reduced.
[0084] Although the baffle plate is disposed at the ceiling portion
of the iron-melting furnace in the above example, guiding means 115
such as a guide plate 115' or a guide duct 115'' may be disposed at
the reduced iron charging opening 112 as shown in FIGS. 7A and 7B
instead of or in addition to the baffle plate. The downward flow of
the solid in the iron-melting furnace 16 can be ensured by these
guiding means 115 to make it easier for the char G to reach the
outer surface of the molten metal. This can prevent the char G from
being trapped in the gas flow along the ceiling portion 111 and
being discharged together with the melting-furnace exhaust gas
M.
[0085] Although the iron ore is used as the iron oxide source in
the above example, blast furnace dust, mill oxide and the like
containing iron oxide may be concomitantly used. Further, matters
containing nonferrous metals and their oxides together with iron
oxide such as dust and slag discharged from a metal refinery may
also be used.
[0086] Although coal is used as the carbonaceous reducing agent,
the bedding carbonaceous material and the additional carbonaceous
material in the above example, cokes, oil cokes, charcoals, wood
chips, waste plastics, old tires and the like may also be used.
[0087] Although the carbonaceous-material containing pellets are
used as carbonaceous-material composite agglomerates and granulated
by the granulator in the above example, carbonaceous-material
containing briquettes may be used instead of the
carbonaceous-material containing pellets and may be molded by
compression by a compression molding machine. In this case,
depending on the kind of the binder, moisture may not be added and
rather dried raw material may be used at the time of molding. Since
the strength of the carbonaceous-material containing briquettes can
be improved to suppress the bursting at the time of heating by
increasing the compressive force of the compression molding
machine, even a carbonaceous material containing a volatile content
of 30 mass % or higher can also be used as the carbonaceous
material to be contained.
[0088] Although a combination of the charging pipe and the
dispersion screw are used as the means for feeding the bedding
carbonaceous material to the hearth in the above example, the
bedding carbonaceous material may be dispersed on the hearth by a
vibratory feeder.
[0089] Although the oxygen gas is used as the oxygen-containing gas
in the above example, high-temperature air or oxygen-enriched
high-temperature air may be used.
[0090] Although the rotary hearth furnace is used as the moving
furnace type reducing furnace in the above example, a linear
furnace may be used.
[0091] Although the carbonaceous material as the energy source for
the iron-melting furnace is burnt with the oxygen-containing gas in
the above example, an electric energy may be used.
[0092] Although the screen is used as the classifying means in the
hot-classifying step in the above example, means for classifying
the particles based on differences in travel caused by the particle
size by letting them drop from a slant surface to a free space or
means for classifying the particles by the fluid beds may also be
used.
EXAMPLE-1
[0093] Test operations were conducted on conditions shown in
TABLE-2 for a case where the bedding carbonaceous material was used
(Inventive Examples 1, 2) and for a case where no bedding
carbonaceous material was used (Comparative Example 1), using iron
ire and coal having chemical compositions shown in TABLE-1 with
respect to the flow diagram of the process shown in FIG. 1, and
operation results written also in TABLE-2 were obtained. Here,
Inventive Example 1 was an example where only the char derived from
the bedding carbonaceous material is charged into the iron-melting
furnace without using the additional carbonaceous material at all;
Inventive Example 2 is an example where the additional carbonaceous
material was charged into the iron-melting furnace in addition to
the char derived from the bedding carbonaceous material; and
Comparative Example 1 is an example where all the carbonaceous
materials (excluding carbon contained in the solid reduced iron) to
be charged into the iron-melting furnace were directly charged into
the iron-melting furnace without via the rotary hearth furnace. As
a reference, items of the total coal consumptions of the rotary
hearth furnace and the iron-melting furnace shown in the column of
the operation results of TABLE-2 are shown in TABLE-3. In this test
operations, the iron ore was crushed into particles of smaller than
1 mm; and the coal had its particle size adjusted by a combination
of operations of sieving and crushing and the coal particles having
particle diameters of smaller than 1 mm was used as the
carbonaceous reducing agent, those having particle diameters of 1
to 5 mm (average particle diameter: 2.2 mm) as the carbonaceous
material and those having particle diameters of larger than 5 mm as
the additional carbonaceous material in any of Inventive Examples
1, 2 and Comparative Example 1. A range of the particle diameters
of the carbonaceous-material containing pellets D was set to be 6
to 20 mm, and the number of layers of the carbonaceous-material
containing pellets D to be placed on the hearth was set at 0.9
layer on the average. TABLE-US-00001 TABLE 1 T.Fe FeO SiO.sub.2
Al.sub.2O.sub.3 CaO IRON ORE 67.2 26.9 5.7 0.4 0.1 Fixed Carbon
Volatile Ash logMF COAL 74.0 15.9 10.1 0.0
[0094] TABLE-US-00002 TABLE 2 OPERATION RESULTS Average Volatile
Total Coal Matter Consumption Content of of Rotary OPERATION
CONDITIONS Charges Hearth Rotary Hearth Furnace Iron-Melting into
Furnace Thickness of Residence Furnace Solid Reduced Iron Iron- and
Iron Bedding Time of Secondary Carbon Melting Melting Carbonaceous
Atm. Temp. pellets Combustion Metallization Content Furnace Furnace
material (mm) (.degree. C.) (min) Ratio (%) Degree (%) (mass %)
(mass %) (kg/thm) INVETIVE 4 1350 8 15 95 4.0 <1 648 EXAMPLE 1
INVENTIVE 1.3 1350 8 14 95 4.0 11.9 685 EXAMPLE 2 COMPARATIVE --
1350 8 10 85 4.0 15.9 835 EXAMPLE 1
[0095] TABLE-US-00003 TABLE 3 (unit: kg/thm) ADDITIONAL
CARBONACEOUS MATERIAL CARBONACEOUS BEDDING AMOUNT OR DIRECTLY
MATERIAL CARBONACEOUS CHARGED CARBONACEOUS AMOUNT IN PELLETS
MATERIAL AMOUNT MATERIAL AMOUNT TOTAL COAL CONSUMPTION INVENTIVE
EXA. 1 425 223 0 648 INVENTIVE EXA. 2 425 74 186 685 COMPARATIVE
EXA. 1 425 0 410 835
[0096] As shown in TABLE-2, as compared to Comparative Example 1 in
which no carbonaceous material was used, the metallization degree
of the solid reduced iron increased from 85% (below 90%) to 95%
(above 92%) and the total coal consumptions of the rotary hearth
furnace and the iron-melting furnace could be reduced by 150 kg to
187 kg per ton of the molten iron.
[0097] Although the rotary hearth furnace needs to be regularly
stopped operating in order to scrape off the deposit on the outer
surface of the hearth for the protection of the hearth of the
rotary hearth furnace in Comparative Example 1, the formation of
the deposit on the outer surface of the hearth was hardly confirmed
in Inventive Examples 1, 2 and the rotary hearth furnace needed not
be stopped for such a purpose.
[0098] Further, as compared to Comparative Example 1, the average
volatile matter content of the carbonaceous material (char+addition
carbonaceous material) to be charged into the iron-melting furnace
could be reduced from 15.9 mass % (above 15 mass %) to 1.9 mass %
or below 1 mass % (below 15 mass %); an apparent reduction in the
temperature of the upper iron coating of the iron-melting furnace
was recognized; and the effect of reducing the heat load was
recognized.
EXAMPLE 2
1: Effect Brought about by the Reduced Oxygen Gas Blowing Rate at
the Time of Charging Solid Particles
[0099] First, in order to confirm the effect brought about by the
reduced oxygen gas blowing rate at the time of charging the solid
particles (solid reduced iron and char), a mathematical model
simulating the iron-melting furnace (including neither the baffle
plate nor the guiding means) having the construction shown in FIG.
6A was prepared, and a simulation calculation was carried out to
predict the scattering rate of the solid particles into the exhaust
gas.
(Calculation Conditions)
[0100] Dimensions of the iron-melting furnace: inner diameter=2.0 m
(constant along height direction), free board height 2.0 m [0101]
Inner diameter of the reduced iron charging opening: 0.4 m [0102]
Inner diameter of the exhaust gas discharging opening: 0.8 m [0103]
Apparent density of the solid particles: 1.4 g/cm.sup.3 (see note
below). [0104] Particle size distribution of the solid particles:
FIG. 8 (see note below) [0105] Charging rate of the solid
particles: 300 kg/h (at the time of continuous charging) [0106]
oxygen blowing rate: 800 Nm.sup.3/h (normal operation=period during
which no solid particle is charged) [0107] Melting-furnace exhaust
gas amount: 1700 Nm.sup.3/h [0108] Melting-furnace exhaust gas
temperature: 1650.degree. C. [0109] Amount of gas produced per unit
cross section of the outer surface of the molten metal is assumed
to be constant (Notes)
[0110] Although the scattering rate of the solid particles changes
depending on their apparent density and particle size distribution,
the apparent density of the solid particles was set to be 1.4
g/cm.sup.3 and the particle size distribution thereof was set to be
one shown in FIG. 8 in this simulation calculation.
[0111] In the case of charging the solid reduced iron and the char
together, the mass ratio of the solid reduced iron to the char
forming the solid particles is about 90:10 to 80:20; the apparent
density of the solid reduced iron is 2 to 3 g/cm.sup.3 and that of
the char is about 1.0 g/cm.sup.3; and the solid particles are
assumed to contain about 4 mass % of the particles having diameters
of 1 mm or shorter.
(Calculation Results)
[0112] For the case of continuously charging the solid particles, a
simulation calculation was conducted by successively reducing the
oxygen gas blowing rate from 100% to 30% with the oxygen gas
blowing rate during the normal operation set at 100%. The
calculation results are shown in FIG. 9. It can be confirmed from
FIG. 9 that the scattering rate of the solid particles was reduced
to 30.3% or lower by reducing the oxygen gas blowing rate to 80% or
lower although it was 41.7% at the oxygen gas blowing rate of 100%,
i.e. improved by 10% or more. Here, the scattering rate of the
solid particles is a value expressing a ratio (%) of the mass of
the solid particles scattered into the exhaust gas to the total
mass of the solid particles charged into the iron-melting
furnace.
2: Effect Brought about by the Batch Charging Method
[0113] Since it was difficult to confirm the influence of the batch
charging by the simulation calculation, a cold model of the
iron-melting furnace corresponding to the above mathematical model
was fabricated and the above influence was confirmed by a model
experiment.
[0114] The model experiment was carried out by variously changing
the charging frequency of the solid particles and the oxygen gas
blowing rate for the case of intermittently charging the solid
particles based on the case of continuously charging the solid
particles. The experiment results are shown in TABLE-4. As is clear
from TABLE-4, it was confirmed that the scattering rate of the
solid particles was reduced from 33.4% to 20.1 to 22.3% even
without reducing the oxygen gas blowing rate by intermittently
charging the solid particles at regular time intervals and was
further reduced to 8.6 to 8.9% by reducing the oxygen gas blowing
rate simultaneously with the intermittent charging. TABLE-US-00004
TABLE 4 CHARGING METHOD CONTINUOUS BATCH CHARGING FREQUENCY Every
Every Every Every -- 2 min. 5 min. 2 min. 5 min. O.sub.2 GAS 100%
100% 100% 50% 50% BLOWING RATE SCATTERING 33.4% 22.3% 20.1% 8.9%
8.6% RATE
EXAMPLE 3
[0115] Test operations were conducted on conditions shown in
TABLE-5 for a case where the solid reduced iron and the char were
intermittently charged every 5 min. (Inventive Examples 3, 4) and
for a case where the solid reduced iron and the char were
continuously charged (Comparative Example 2), using iron ire and
coal having chemical compositions shown in TABLE-1 and using the
bedding carbonaceous material in the rotary hearth furnace. In any
of Inventive Examples 3, 4 and Comparative Example 2, the solid
reduced iron and the char were charged together into the
iron-melting furnace, but the auxiliary raw material and the
additional carbonaceous material were charged by a system different
from the one for the solid reduced iron and the char. Further,
neither the baffle plate nor the guiding means was provided in the
iron-melting furnace. The operation results are written in TABLE-5.
As shown in TABLE-5, the operation conditions of the rotary hearth
furnace and the secondary combustion ratio of the iron-melting
furnace were the same in Inventive Examples 3, 4 and Comparative
Example 2, but the operation could be carried out by only charging
the char derived from the bedding carbonaceous material into the
iron-melting furnace without using the additional carbonaceous
material at all in Inventive Examples 3, 4, but the additional
carbonaceous material needed to be charged in addition to the char
in Comparative Example. As a reference, items of the total coal
consumptions of the rotary hearth furnace and the iron-melting
furnace shown in the columns of the operation results of TABLE-5
are shown in TABLE-6. In these test operations, the iron ore was
crushed into particles of smaller than 1 mm; and the coal had its
particle size adjusted by a combination of operations of sieving
and crushing and the coal particles having particle diameters of
smaller than 1 mm was used as the carbonaceous reducing agent,
those having particle diameters of 1 to 5 mm (average particle
diameter: 2.2 mm) as the carbonaceous material and those having
particle diameters of larger than 5 mm as the additional
carbonaceous material in any of Inventive Examples 3, 4 and
Comparative Example 2. A range of the particle diameters of the
carbonaceous-material containing pellets D was set to be 6 to 20
mm, and the number of layers of the carbonaceous-material
containing pellets D to be placed on the hearth was set at 0.9
layer on the average. TABLE-US-00005 TABLE 5 OPERATION RESULTS
Total Coal OPERATION CONDITIONS Consumption Rotary Hearth Furnace
Carbon Content of Rotary Thickness Residence Iron-Melting Furnace
Solid Reduced in Exhaust Hearth of Bedding Time 2nd. Iron Gas Dust
from Furnace and Carb. Atm. of Comb. Solid Reduced Metal. Carbon
Iron-Melting Iron-Melting Material Temp. Pellets Ratio Iron &
Char Degree Content Furnace Furnace (mm) (.degree. C.) (min) (%)
Charging Method (%) (mass %) (kg/thm) (kg/thm) INVETIVE 4 1350 8 15
Batch: Every 95 4.0 13 648 EXAMPLE 3 5 min. O.sub.2 Blowing Rate:
50%*.sup.1 INVENTIVE 4 1350 8 15 Batch: Every 95 4.0 33 675 EXAMPLE
4 5 min. O.sub.2 Blowing Rate: 100%*.sup.2 COMPARATIVE 4 1350 8 15
Continuous 95 4.0 50 697 EXAMPLE 2 *.sup.1The O.sub.2 blowing rate
is set at 50% in the period of 30 seconds after starting charging
of solid particles. *.sup.2The O.sub.2 blowing rate is maintained
at 100% at the time of charging solid particles.
[0116] TABLE-US-00006 TABLE 6 (unit: kg/thm) CARBONACEOUS BEDDING
ADDITIONAL MATERIAL CARBONACEOUS CARBONACEOUS MATERIAL AMOUNT IN
PELLETS MATERIAL AMOUNT AMOUNT TOTAL COAL CONSUMPTION INVENTIVE
EXA. 3 425 223 0 648 INVENTIVE EXA. 4 425 223 27 675 COMPARATIVE
425 223 49 697 EXA. 2
[0117] As shown in TABLE-5, as compared with Comparative Example 2
employing the continuous charging method, the effect of improving a
carbonaceous material yield could be confirmed in Inventive Example
4 employing the batch charging method according to which the oxygen
blowing rate was not reduced at the time of charging the solid
particles. In Inventive Example 3 employing the batch charging
method according to which the oxygen blowing rate was reduced at
the time of charging the solid particles, the carbon content
contained in the dust in the exhaust gas from the iron-melting
furnace was reduced from 50 kg to 13 kg per ton of the molten iron,
thereby considerably improving the carbonaceous material yield.
Further, as shown in TABLE-6, the total coal consumption of the
rotary hearth furnace and the iron-melting furnace could be reduced
by 49 kg per ton of the molten iron by making the use of the
additional carbonaceous material unnecessary.
[0118] As described above, the inventive method for producing
molten iron using the molten iron producing process constructed by
combining the moving hearth type reducing furnace and the
iron-melting furnace is characterized by comprising the following
steps (1) to (4):
[0119] (1) Reducing furnace charging step of charging the bedding
carbonaceous material onto the hearth of the moving hearth type
reducing furnace and placing the carbonaceous-material composite
agglomerates containing the powdery iron oxide source and the
powdery carbonaceous reducing agent on the bedding carbonaceous
material;
[0120] (2) Reduction step of moving the hearth inside the moving
hearth type reducing furnace to heat and reduce the
carbonaceous-material composite agglomerates to the solid reduced
iron and heating and drying the carbonaceous material by
distillation into char;
[0121] (3) Melting-furnace charging step of charging the solid
reduced iron and the char into the iron-melting furnace while they
are hot or without being substantially cooled; and
[0122] (4) Melting step of blowing the oxygen-containing gas into
the iron-melting furnace to melt the solid reduced iron, thereby
obtaining the molten iron.
[0123] According to this method, the hearth can be more securely
protected by using the bedding carbonaceous material to avoid
troubles of the peeling of the hearth, therefore the moving hearth
type reducing furnace can be continuously operated for a longer
period of time. Since the devolatized char has no volatile content,
the damage of the refractory by the combustion of the volatile
content in the iron-melting furnace can be prevented, thereby
extending the life of the refractory of the iron-melting furnace.
Further, the reoxidation of the solid reduced iron in the moving
hearth type reducing furnace is prevented by using the bedding
carbonaceous material to achieve a high metallization degree,
therefore the carbonaceous material consumption in the iron-melting
furnace can be considerably reduced. As a result, the carbonaceous
material consumption can be further reduced while the operations of
the moving hearth type reducing furnace and the iron-melting
furnace can be more stabilized.
[0124] Further, according to the inventive method, a high
metallization degree of 92% or above can be achieved.
[0125] According to the inventive method, at least a part of the
exhaust gas from the iron-melting furnace can be used as a fuel gas
for the moving hearth type reducing furnace. By doing this, the
volatile content devolatized upon heating the bedding carbonaceous
material in the moving hearth type reducing furnace is effectively
used as the fuel for the moving hearth type reducing furnace
together with at least a part of the exhaust gas from the
iron-melting furnace, thereby reducing the fuel consumption of the
moving hearth type reducing furnace.
[0126] Further, according to the inventive method, another
carbonaceous material can be additionally charged into the
iron-melting furnace in the above step (3). By doing so, the case
where the carbonaceous material consumption required by the
iron-melting furnace cannot be covered only by the carbon content
in the solid reduced iron F and the char G can also be coped
with.
[0127] Furthermore, according to the inventive method, the
hot-molding step of molding the solid reduced iron and the char
while they are hot may be provided between the above steps (2) and
(3). By doing so, the scattering of the fine particles at the time
of charging into the iron-melting furnace can be prevented and the
amount of dust in the exhaust gas from the iron-melting furnace can
be considerably reduced. Therefore, the iron yield and the carbon
yield can be considerably improved.
[0128] Further, the inventive method may comprise the following
steps (7) to (9) instead of the above step (3):
[0129] (7) Hot-classifying step of classifying the solid reduced
iron and the char into coarse and fine particles while they are hot
or without being substantially cooled after taking them together
out of the moving hearth type reducing furnace;
[0130] (8) Coarse particle charging step of gravitationally
charging the coarse particles into the iron-melting furnace;
and
[0131] (9) Fine particle injection step of charging the fine
particles into the iron-melting furnace by injection.
[0132] Since the fine particles are trapped in the molten iron
and/or the molten slag by these steps, the scattering of the fine
particles at the time of charging into the iron-melting furnace can
be prevented and the amount of dust in the exhaust gas from the
iron-melting furnace can be considerably reduced. Therefore, the
iron yield and the carbon yield can be considerably improved.
[0133] In the step (3) of the inventive method, the solid reduced
iron and the char may be charged into the iron-melting furnace from
above while being hot. By doing so, the scattering rate of the fine
particles of the char and the like into the exhaust gas can be
reduced, therefore the carbonaceous material yield can be improved
in the entire process.
[0134] The method for charging the solid reduced iron and the char
into the iron-melting furnace from above while they are hot may be
a method according to which the char and the solid reduced iron are
discharged from the moving hearth type reducing furnace, stored in
the container, conveyed to the hopper disposed above the
iron-melting furnace from the container and consequently charged
into the iron-melting furnace while being hot by being
intermittently dispensed from the hopper or a method according to
which the char and the solid reduced iron are discharged from the
moving hearth type reducing furnace, stored in the hopper and
consequently charged into the iron-melting furnace while being hot
by being intermittently dispensed from the hopper.
* * * * *