Specification
METHOD OF REDUCTION PROCESSING OF STEEL-MAKING SLAG
[~echnicaFl ield of the Invention]
[OOO 11
The present invention relates to a continuous reduction processing apparatus and a
continuous reduction processing system for a steel-making slag that apply reduction
processing in the industrial scale to the steelmaking slag generated during steel making, and
recover valuable components while modifying properties of the steel-making slag so as to
conform to various applications.
[Background Art]
[0002]
During the steel making processes, a large amount of steel-making slag is generated.
Although the steel-making slag contains, for example, P and metal components such as Fe
and Mn, it also contains a large amount of CaO, which leads to expansion and collapse. This
his restricted the steel-making slag to be used as, for example, a material for roadbed or
aggregate. However, in recent years, resources have been increasingly recycled, and a large
number of methods for recovering the valuable substances from the steel-making slag has
been disclosed.
[0003]
Patent Document 1 discloses a method of processing iron and steel slag, which
includes adding iron and steel slag generated during melting and making iron and steel, to I
molten iron and steel liquid in the smelting furnace, fbrther adding heat and reducing agents,
moving Fe,. Mn, and P to the molten liquid while altering the iron and steel slag to obtain
altered slag, and then, moving Mn and P in the molten liquid into the slag. However, this I
s-l-a-g with predetermined components can be obtained, andhe-nce, results in poor working
' efficiency.
[0004]
Patent Document 2 discloses a method, which includes: supplying steel slags having
iron oxide contents of more than 5 wt% onto asteel bath having a carbon content of less than
1.5 wt%; then introducing carbon or carbon carriers to carbonize the steel bath to obtain the
steel bath having a carbon content of more than 2.0 wt%; and then performing reduction
processing.
[OOOS]
However, with the method described in Patent Document 2, the concentration of C
(hereinafter, [C)) in the molten iron is set to less than 1.5 wt% at the time of inserting the
molten slag to suppress the discharge of the large amount of gas, and the [C] is increased to
more than 2.0 wt% at the time of performing smelting reduction, thereby performing desired
reduction. Thus, a process of de-carbonization in conjunction with an increase in
temperatures and a process of addition of carbon for reduction are repeated, which results in
batch processing. As a result, working efficiency deteriorates. It should be noted that,
since the method described in Patent Document 2 increases the [C] to more than 2.0 wt% at
the time of performing the reduction processing, it is considered that this method promotes
the reduction reaction mainly through the reaction between slag and metal.
[0006]
Further, in the method described in Patent Document 2, the carbon material is used
as the heat source as well as the reducing agent, and hence, the amount of exhaust gas
increases. Thus, it is assumed that the thermal efficiency deteriorates, and the amount of
dust generated increases.
3
.- .- -. Non-Patent Document 1 discloses res.u lts .o- f reduction tests in which steel-making
slag powder, carbon material powder, and slag-modifying agent powder are inserted through a
hollow electrode into an electric fumace. However, in the reduction tests described in
on-Patent Document I, the test is performed in an electric fumace by processing the cold
steel-making slag, which has been solidified and crushed, and hence, the energy-consumption
rate is large.
[OOOS]
Further, Patent Document 3 discloses a technique of recovering valuable metals by
reducing molten slags generated during smelting of non-ferrous metals using-carbonaceous
reducing agents in an open-type direct-current electric fumace to separate it into a metal phase
and a slag phase. However, the method described in Patent Document 3 also involves a
batch process with an electric furnace using the cold slag as the target of the processing, and
hence, the energy-consumption rate is large.
[0009]
As described above, these methods of recovering valuable components from the
slags each have a problem of poor working efficiency or large energy-consumption rate.
[Related Art Documents]
[Patent Document]
[OO 1 O]
Patent Document I: Japanese Unexamined Patent Application, First Publication No.
S52-033897
Patent Document 2: Published Japanese TransIation No. 2003-520899 of the PCT
International Publication
Patent Document 3: Australia Patent No. AU-B-20553/95
[OO 1 11 .- . - . . . .- . -.
Non-Patent Docuhent 1: Scandinavian Journal of Metallurgy 2003; 32: p.7-14
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[OO 121
As described above, with the conventional method that recycles the hot steel-making
slag through batch processing, the working efficiency is poor. With the conventional
method that recycles the cold steel-making slag as resources through melting, there is a
problem of the high energy-consumption rate.
[00 131
Then, the object of the present invention is to provide, as a measure with a favorable
working efficiency and reduced energy-consumption rate, a continuous reduction processing
apparatus and a continuous reduction processing system for a steel-making slag that apply
reduction processing to the steel-making slag, and recover valuable components while
modifying properties of the steel-making slag so as to conform to various applications.
[Means for Solving the Problem]
[00 141
Considering the measure that provides favorable working efficiency and reduced
energy-consumption rate, which is the object of the present invention, it is effective to use the
' hot steel-making slag from the viewpoint of reducing the energy-consumption rate.
However, when the hot steel-making slag is charged onto the molten iron in the electric
furnace, there occurs a phenomenon (slag foaming) that the steel-making slag rapidly reacts
with the molten iron and suddenly boils, and the slag may spill over from the electric fiunace
if this phenomenon strongly occurs (overflow).
As described above, in the method described in Patent Document 2, this rapid - .
boiling phenomenon is avoided by "slowing the reaction speed by decreasing the [C] in the
molten iron." However, with this method, the working efficiency deteriorates.
[00 151
More specifically, in the present invention, a similar problem arises as a problem to
be solved, and C in the molten iron reduces FeO in the slag in a reduction furnace such as a
converter, which promotes reduction reaction through reaction between the slag and the metal.
Thus, in order to improve the ability to reduce, it is necessary to repeat de-carbonization and
carbonization, which results in deteriorated working efficiency. Accordingly,'only the
reduction of the [C] is insufficient as a countermeasure.
[00 161
In view of the facts described above, the present inventors made a keen study, and
newly.found through experiments that, during the reduction reaction in the electric funlace, a
reaction between FeO and C in the slag more predominantly occurs, rather than a reaction
between the slag and the metal. Then, it was found that, by using reduced [C] of
approximately 1.5 mass%, it is possible to perform the reduction processing of the slag
without the need of carbonizing, although the ability to reduce is slightly lower, and with this
method, it is possible to improve the working efficiency.
[0017] . .
Thus, by using the electric furnace, it is possible to suppress the slag foaming, which
suddenly occurs .at .the time of charging the molten steel-making slag, and the
above-described method can be one of the measures for preventing the slag from
overflowing.
[00 181
6
However, -th_ereies a possibility that the [C] in the molten iron is high. -.nys, a study
was also made on a method that provides favorable working efficiency while reducing the
energy-consumption rate, even if the concentration of C in the molten iron is high. Then, the
present inventors made experiments to realize a continuous reduction processing apparatus
and a continuous reduction processing system for a steel-making slag that can solve the
above-mentioned problem, by using the electric furnace.
[0019]
As a result, regarding a specific measure for preventing overflow at the time of
supplying steel-making slag, which has fluidity while hot, directly into the electric furnace, it
was discovered through experiments that, from the viewpoint of suppressing the phenomenon
of sudden boiling of the molten slag while avoiding the overflow, it is preferable to employ
the following two methods:
(a) temporarily place the steel-making slag, having fluidity while hot, in a device capable of
adjusting the amount of flow of it into the electric fiunace, and then, charge the steel-making
slag into the electric furnace while adjusting the amount of flow of it into the electric h a c e
so as not to overflow the steel-making slag in the electric furnace; and
(b) pre-form a molten slag layer, preferably an inactive molten slag layer (reduced slag layer)
serving as a buffer zone on the molten iron, and then, flow the hot steel-making slag onto the
buffer zone.
Further, it was also discovered that it is more preferable for suppressing overflow to I I
employ, in addition to the methods (a) and (b) described above:
(c) supply, in advance, a carbon material to the molten slag in an excessively suspended
manner; and 1 . I
(d) reduce .. t-he [ -C ] in the molten iron to not more than 3 mass% @rovided_thats trong
reduction is not necessary).
The present invention is made based on the above findings, and the gist thereof is as
follows.
roo221
(1) A continuous reduction apparatus for continuously reducing a steel-making slag in an
electric furnace, configured by
(i) an electric h a c e comprising an auxiliary-raw-material supplying unit for supplying an
auxiliary-raw-material including reduction agent to a molten slag layer on a molten steel
generated by reducing the steel-malting slag, a supplying portion for a hot steel-making slag,
an electrode for heating the molten slag layer, a cinder notch, and a tap hole, and
(ii) a slag supplying furnace which is connected to the electric furnace via the hot steel
making slag supplying portion and comprises a tilting unit that can adjust the supplying
amount of the hot steel-making slag to the electric'furnace.
[0023]
(2) The continuous reduction apparatus for continuously reducing a steel-making slag
according to (I), wherein the electric furnace is a fixed-type and closed-type electric fiunace.
[0024]
(3) The continuous reduction apparatus for continuously reducing a steel-making slag
according to (2),wherein the fixed-type and closed-type electric fumace is a direct-current
electric &mace.
(4) The continuous reduction apparatus for continuously reducing a steel-malting slag
I
acco-r-d ing to any one of (I) to (3), wherein the auxiliary-raw-material supplying tube is
installed in the electrode.
(5) The continuous reduction apparatus for continuously reducing a steel-making slag
according to any one of (1) to (4), wherein the slag supplying furnace is provided with an
exhaust hole for an exhaust gas generated fiom the electric furnace,
[0027]
(6) A continuous reduction system for continuously reducing a steel-making slag by
supplying a steel-making slag from a slag supplying fumace, that can be tilted and is
connected to the electric fumace, to a molten slag layer on a molten iron in the electric
fumace provided with a cinder notch and a tap hole on the furnace side wall, wherein:'
(a) the-electric power supplied to an electrode of the electric furnace is measured,
(b) an amount of the steel-making slag to be reduced is calculated based on the supplied
electric power, and then a predetermined amount of reducing agent is calculated based on the
calculated amount of the steel-making slag to be reduced;
(c) a tilting angle of the slag-supplying furnace is controlled by actuating the tilting unit such
that an amount of the steel-making slag supplied follows the amount of the steel-making slag
to be reduced, and
(d) a suppliedarnount from the auxiliary-raw-material supplying unit is controlled so as to
supply the predetermined amount of the reducing agent.
[Effects of the Invention]
According to the present invention, it is possible to modify, with a reduced
energy-consumption, the steel-making slag into a material that can be used for various
applications such as a cement raw material, a civil engineering material, and a ceramic I
products, and recover the valuable elements such as_Fg,-vln, and P into the - ...- - molten iron.
Further, it is possible to recycle Fe and Mn into the steel-making processes, and use P as a
phosphate fertilizer or-phosphoric acid material. by applying oxidation treatment.
[Brief Description of the Drawings]
[0029]
FIG. 1 shows an embodiment of a continuous reduction processing apparatus for a
steel-making slag according to the present invention.
FIG. 2 shows a comparatjve diagram illustrating changes in the "T. Fe" in the
molten slag in the electric h a c e s with or without the opening portion.
FIG. 3 shows another embodiment of a continuous reduction processing apparatus
for a steel-making slag according to the present invention.
FIG. 4 shows another embodiment of a continuous reduction processing apparatus
for a steel-making slag according to the present invention.
FIG. 5 shows an embodiment of a continuous reduction processing system
according to the present invention.
[Embodiments of the Invention]
[0030]
The present invention is based on a technical idea that the energy-consumption rate
can be lowered by performing the reduction processing during the time when the steel-making
slag is hot and has fluidity.
More specifically, the present inventors reached an idea that it is possible to utilize,
as resources, steel-making sIag generated in the steel-making processes with reduced
energy-consumption rate, by charging the steel-making slag into the electric furnace during
the time when it is hot and has fluidity to reduce the steel-making slag, recovering valuable
. - -- - .- -. [003 11 ..
1) Below, an apparatus of the present invention will be described.
COO323
The steel-making slag, to which the device of the present invention is directed, is
only necessary to be slag generated during the steel-making processes, and is not limited to
specific slag.
[0033]
In addition, it is only necessary for the hot steel-making slag to have fluidity
sufficient to continuously or intermittently flow into the electric furnace, and it is not
necessary for the hot steel-making slag to be in the completely melted state. The rate of
solid phase in the hot steel-making slag is not specifically limited. However, slag involves
fluidity sufficient to flow into the electric furnace when the rate of solid phase of the hot
steel-making slag is not more than approximately 30% at approximately 1400°C. Note that
the rate of solid phase can be calculated using a commercially available software.
[0034]
Below, the explanation is made on the basis of the drawings. FIG. 1 illustrates an
embodiment of the apparatus of the present invention which includes an electric furnace and a
slag-supplying furnace.
[0035]
The electric furnace 1 is a fixed-type and closed-type direct-current electric furnace,
and is provided with electrode 2 formed by an upper electrode 2a and a h a c e bottom
electrode 2b that are paired in the vertical direction. On the bottom portion of the electric
furnace I., the molten iron 5 is accommodated, and on the molten iron 5, there formed a layer
of the molten slag 6 including a steel-making slag 6' supplied from the slag-supplying furnace
- 9. The layer of the molten slag 6 is heated by the electrode 2.
q : ~ : ~ ~ - - g ; r ~ ~ - - % - g 7 ~ ~ & ~ - ~ ~ ~ 2 = &
On the left of the furnace ceiling 1 c of the electric furnace 1, a slag-supplying
portion 4 is provided which supplies the steel-making slag 6' having fluidity while hot from
the slag-supplying hmace 9;- Once the external air (oxygen or oxygen-containing gas)
enters the electric hrnace 1, oxidation reaction occurs on the surface of the molten slag layer
6; and the "T. Few in the molten slag layer 6 increases, which leads to a decrease in the
reduction performance.
LO0371
FIG. 2 comparatively illustrates changes with time in the "T. Fe" (mass%) in the
molten slag in the electric furnaces with or without the opening portion at the f-ace wall.
[003 81
By blowing the reducing agent (carbon material.) to subject the molten slag to
reduction processing, the "T. Few in the molten slag reduces (see the duration for "BLOWING
CARBON MATERIAL" in the drawing). However, with the opening portion at the h a c e
wall of the electric furnace, an air is suctioned and the inside of the furnace becomes an
oxidizing environment, whereby the surface of the molten slag is re-oxidized. Accordingly,
after the blowing of the reducing agent (carbon material) ends, the "T. Few in the molten slag
increases due to the re-oxidation.
[0039]
On the other hand, in the case where the opening portion is not provided at the
fumace wall of the-electric h a c e , the inside of the furnace is maintained to be the reducing
atmosphere. Thus, the re-oxidation does not occur at the surface of the molten slag 6, and
the reduction reaction of FeO advances due.to C in the molten slag and the molten iron,
whereby the "T. Fe" in the molten slag reduces, which makes it possible to maintain a
I
predetermined low stand-gd. .. Accordingly, it is preferable for the electric furnace1tg-be
formed in a closed type with which the external air does not enter.
In addition, in the slag-supplying furnace 9, an exhausting portion 13 is disposed to
the slag-supplying furnace 9 so as to configure an exhaust path of the electric-furnace exhaust
gas.
[0040]
The inside of the electric furnace 1 is a reducing atmosphere containing the primary
component fomed by CO gas generated through the reduction reaction and H2 generated
from reducing agents supplied (carbon material). If the slag-supplying furnace 9 is
configured as the exhaust path of the electric-furnace exhaust gas, the reducing atmosphere
can be maintained, thus, it is possible to prevent oxidation reaction from occurring at the
surface of the molten slag 6.
[004 11
The electric furnace 1 has a fumace side wall la provided with a cinder notch 7 that
discharges the molten slag 6 to a slag ladle (not illustrated). In addition, the electric furnace
1 has a furnace side wall 1 b disposed on the other side of the furnace side wall la of the
electric furnace 1 and provided with a tap hole 8 that is located at the level (height) lower than
the cinder notch 7 and discharges the molten iron 5 to a molten-iron trough (not illustrated).
To prevent the furnace side wall la and the furnace side wall lb from damaging by melting, it
is preferable that the cinder notch 7 and the tap hole 8 are not disposed close to each other on
the same furnace side wall, and it is only necessary that they are spaced apart in a distance
that can prevent the furnace side wall la and the furnace side wall lb from damaging by
melting.
[0042]
13 I I I
Note,t&t_the fiunace side wall la, the furnace side wall Ib, and a-h.ace ceiling lc I
are cooled by jacket or water spraying (not illustrated).
I
The electric furnace 1 may be provided with a raw-material supplying unit (not
illustrated) that suppIies iron materials such as small scrap iron and direct reduced iron (DRI)
into the electric furnace 1. The electric furnace 1 can produce the molten iron by melting
and reducing the small scrap iron, reduced iron, powder dusts, and the like.
COO441
The electric furnace 1 is provided with an auxiliary-raw-material supplying unit that
supplies reducing agents necessary for reduction, and auxiliary-raw-materials such as
modifying powder that modify properties of the molten slag. FIG. 3 shows an embodiment
of an auxiliary-raw-material supplying tube 14a disposed through the furnace ceiling lc ofthe
electric furnace 1 in a manner that the auxiliary-raw-material supplying tube 14a penetrates
the furnace ceiling lc. By supplying the auxiliary-raw-materials (for example, reducing
agents and modifying powder) from the auxiliary-raw-material supplying tube 14a into the
electric furnace, the amount of gas generated in the furnace is reduced. Hence, the
. auxiliary-raw-materials fall with the force of gravity onto the surface of the molten slag 6, and
are mixed with the molten slag 6.
1
Further, it may be possible to form the upper eIectrode 2a of the electrode 2 so as to 1
I
be a hollow electrode, and use the hollow portion as the auxiliary-raw-material supplying tube.
By using the hollow electrode, it is possible to directly blow the auxiliary-raw-materials (for I
example, reducing agent and modifying powder) into the arc spot.
[0046]
Further, the electric furnace may be provided with a lan~e-fobrl owing powders, to .- . . . - .
supply, into the electric furnace, powders (auxiliary-raw-material) that are more likely to
spatter without using a hollow portion of the hollow electrode or the auxiliary-raw-material
supplying tube. In a configuration illustrated in FIG. 4, the electric furnace 1 is provided
with the lance 14 for blowing an auxiliary-raw-material disposed through the furnace ceiling
lc in a manner that penetrates the furnace ceiling lc.
[0047]
In the continuous reduction processing apparatus as shown in FIG. 3, the
auxiliary-raw-material supplying tube 14a is disposed near the electrode 2, however, the
auxiliary-raw-material supplying tube 14a may be disposed at a position apart f-rom the
electrode 2.
In addition, the auxiliary-raw-material supplying tube 14a may be provided at the
furnace ceiling Ic of the electric furnace 1 together with a lance 14b for blowing an
auxiliary-raw-material.
[0048 J

The slag-supplying furnace 9 (see FIG. 1, FIG. 3, and FIG. 4) is configured by an
upper wall 1 1 and a bottom wall 10, and is provided with an opening portion 13a that receives
a steel-making slag 6' supplied from a slag pot (not illustrated) and a lid 13b that closes the
opening portion. On the slag-supplying furnace 9, an exhausting portion 13 may be
provided at the upper portion. It is preferable to make the bottom wall 10 of the
slag-supplying furnace 9 out of refractory lining wall, and make the upper walI 11 out of a
water-cooled refractory lining wall.
-. - . The slag-supplying furnace 9 can be tilted at a-giyen angle with the tilting axis z
being a center. Accordingly, it is possible to control the amount of inflow of the
steel-making slag 6' to the electric furnace 1 from the slag-supplying portion 4 connected to
the electric furnace 1. . . .
[OOSO]
In the case where the slag-supplying furnace 9 includes an exhausting portion 13,
via the dust collector (not illustrated), the atmosphere in the slag-supplying furnace 9 is
constantly under negative pressure. In this negative pressure state, the high temperature
exhaust gas including CO gas and H2 gas generated in the electric furnace 1 enters fiom the
slag-supplying portion 4 into the slag-supplying fumace 9, and is discharged, through the
inside of the slag-supplying furnace 9 serving as an exhaust path, from the exhausting portion
13 to the dust collector (not illustrated) via an exhausting gas duct (not illustrated);
[OOS 11
In this configuration, even if an external air enters from a gap between the
slag-supplying fumace 9 and a connecting portion of the electric furnace 1, the external air
entered flows into the inside of the slag-supplying apparatus, thus, the atmosphere in the
electric furnace 1 is constantly maintained to be a high-temperature reducing atmosphere.
On the other hand, the inside of the slag-supplying fumace 9 is maintained to be a
high-temperature reducing atmosphere as same as the inside of the electric fumace 1, thus, the
temperature of the steel-making slag 6' is maintained, and the steel-making slag 6' is not
oxidized. . . .
[0052]
The slag-supplying b a c e 9 may be provided with a nozzle 12 that blows oxygen
or oxygen-containing gas into the electric-furnace exhaust gas including CO and H2. If the
,electric-fbmace exhaust gas is burnt in the slag-supplying furnace 9, it is possible to maintain
the inside of the slag-supplying furnace 9 to behigh temperatures, and this malces it possible -,
to avoid the steel-making slag 6' From being solidified and the adhesion of the steel-making
slag 6' to the furnace walls of the slag-supplying h a c e . Furlher, it is possible to obtain
fluidity necessary for charginginto the electric furnace 1
Even when the sensible heat or combustion heat of the exhaust gas is used, there is a
case in which the temperature in the slag-supplying furnace 9 does not reach the temperature
at which the steel-making slag does not adhere to the fumace wall of the slag-supplying
fumace. For such a case, the slag-supplying furnace 9 may be provided with a burner 12a so
as to emit flame in the slag-supplying fumace 9.
Further, the slag-supplying furnace 9 may be provided with a slag modifying agent.
adding unit (not illustrated) that adds to the steel-making slag 6', a slag modifying agent for
modifying the steel-making slag 6' in the slag-supplying furnace9 . In addition, the slag
modifying agent may be charged, through the burner 12a into the slag-supplying b a c e 9 in
a molten form.
[0055]
The slag-supplying furnace 9 is provided with a tilting unit (not illustrated) that
controls the charging amount of the steel-making slag by tilting the slag-supplying furnace 9 I
with a tilting axis z being the center. I Below, explanation is made with respect to the charging of the steel-making slag 6'
into the electric fumace 1 using the slag-supplying furnace 9.
[0056]
,
First, a measure (a) wiil be described below.
(a) The steel-making slag haxmg fluidity while hot is temporarily held in a device ... . .
that can adjust the amount of inflow into the electric fumace, and then, is charged while the
amount of inflow into the electric furnace is being adjusted in a manner such that the
steel-making slag having fluidity while hot does not overflow in the electric fixnace.
(00571
An appropriate amount of the molten iron (for example, 100 to 150 tons) is
contained in advance as hot metal in the electric furnace. Then, the hot steel-making slag in
the amount that can be reduced with respect to the rate of the electric power supplied to the
electric furnace is charged fiom the slag-supplying furnace onto the molten slag on the molten
iron to continuously maintain the molten slag layer.
In the apparatus of the present invention, it is possible to freely select the mode of
. .
charging the steel-making slag into the electric fumace, by actuating the tilting unit, and
adjusting the tilting angle of the slag-supplying furnace with the tilting axis z being the center.
[0059]
h other words, using the tilting unit, the slag-supplying furnace 9 is tilted with the
tilting axis z being the center, whereby the steel-making slag 6' supplied fiom the slag pot
(not illustrated) is stored and held, and the steel-making slag 6' stored is co~tinuouslyo r
intermittently charged to the layer of the molten slag 6 on the molten iron 5 in the electric
furnace 1 while adjusting the charging amount so as not to overflow from the electric fumace
due to the foaming of the molten slag.
[0060]
It should be noted that the steel-making slag is temporarily stored and held in the
sIag-supplying h a c e . However, in the case where the amount of supply from the slag pot
is small and the. steel-making slag does not need to be temporarily stored and held in the
slag-supplying fumae, it may be.possible to fix the slag-supplying fumace at constant mgl-es
and use it as the slag runner.
[0061]
By tilting the slag-supplying furnace to charge the steelmaking slag into the electric
furnace, the high-temperature surface layer of the steel-making slag in the slag-supplying .
fumace is updated, whereby thermal efficiency to the steel-making slag remaining in the
slag-supplying fbrnace in~proves.
COO623
In the case where the steel-making slag is intermittently charged into the eIectric -
furnace, it may be possible to employ:
(i) a mode in which the steel-making slag is charged in a manner such that charging and
stopping are repeated, or I
1
!
(ii) a mode in which a predetermined amount of the steel-making slag is collectively charged I
i
at predetermined intervals of time.
[0063]
If the charging rate is too fast at the time of charging the steel-making slag into the
electric fiunace, the amount of gas generated temporarily increases, and the slag becomes in a
slag foaming state, possibly leading to an abnormal state such as spillover (overflow) from the
electric furnace. Xn such a case, it is preferable to reduce the tilting angle of the
slag-supplying furnace so as to temporarily stop charging the steel-making slag into the
electric furnace, or increase the rate at which the reducing agents are supplied.
When the steel-making slag is charged into the electric fumace, it is preferable to
detect whether the molten slag layer strongly foams (slag foaming) and abnormality such as
overflow occurs, for example, by always monitoring the inside and outside of the fumace
using a monitor came. -r a; monitoring the behavior of the hot steelimaking slag Ung a sound
meter; or monitoring the surface level of the molten slag by radiaf ng microwave. If the
results appear to exceed a threshold value, it is preferable to adjust the amount of the
steel-making slag charged into the electric furnace.
100651
To prevent the slag foaming from occurring in the molten slag and prevent the
molten slag from spilling over (overflowing) the electric furnace, there is a measure (b) as
described below, other than the measure (see the measure (a) described above) of adjusting
the amount of the steel-making slag charged from the slag-supplying h a c e . Accordingly,
the measures (a) and (b) may be used at the same time.
(b) By causing reduced slag to exist as slag located on the molten iron, it is possible
to make it function as a buffer zone. This makes it possible to dilute and lower the
concentration of FeO in the steel-rnaki.ng slag.to be charged, and reduce the possibility that
the steel-making slag and the molten iron are brought into contact with each other.
In other words, by causing the molten slag obtained after reduction processing to
exist as a buffer zone on the surface of the molten iron, it is possible to reduce the
concentration of "FeO" in this molten slag and reduce the possibility that the molten slag and
the molten iron are brought into contact with each other, which makes it possible to prevent
the molten slag from foaming. As a result, it is possible to prevent the molten slag from
overflowing from the electric furnace.
The amount of inflow of the steel-making slag into the electric furnace is basically
determined according to the amount of electric power supplied to the electrode. In other
words, the amount of inflow of the steel-making slag continuously or_intermittently charged is
calculated on the basis of the unit electric power consumption necessary for the steel-making
slag reduction processing and the amount of electric power actually supplied.
(00691
The rate of charging the steel-making slag needs to accord with the rate of electric
power supplied to the electrode in the long term, but does not need to accord with the rate of
electric power supplied to the electrode in the short term. This is because, in the case where
a predetermined amount of the steel-making slag is intermittently charged into the electric
fimace, the amount of inflow does not accord with the rate of electric power supplied to the
electrode in the short term. In this case, it may be accorded with the rate of electric power
supplied, in the long term.
[0070]
It should be noted that the electric power consumption rate necessary for the
reduction processing applied to the steel-making slag can be obtained through heat balance
calculation in which heat of reaction and heat radiation are taken into consideration.
However, the electric power consumption rate described above is an estimated value obtained
through the heat balance calculation, and hence, the error appears in a form of change in
tem&atures of the molten slag in the electric furnace.
The change in the temperatures of the molten slag can be controlled by adjusting the
electric power. supplied, the amount of inflow of the steel-making slag or the amount of
reducing agents supplied. In general, the tenlperatues in the electric furnace are controlled,
for example, such that the temperatures of the moIten iron fall in the range of 1400 to 1550°C, I and the temperatures of the molten slag fall in the range of 1500 to 1650°C. I
-. . .. As to the charging of the steel-making slag, it is o~ly_necessaryto prevent the
molten slag from overflowing. Thus, the steel-making slag may be charged into .the electric
furnace continuously or intermittently. It should be noted that, in the case where the
steel-making slag is charged intermittently, it is important to experimentally check, in
advance, that the amount of the steel-making slag set for each charge does not cause slag
foaming and the resulting overflow.
[0073]

In order to perform the reduction processing to the molten slag, located on the
molten iron, onto which the steel-making slag is charged, it is necessary to charge, in the
electric furnace, the reducing agent having an amount corresponding to the amount of the
steel-making slag charged in the electric furnace.
[0074]
The reducing agent (auxiliary-raw-material) may be supplied continuously or
intermittently from the awtiliary-raw-material supplying tube provided to the furnace lid (as
illustrated in FIG. 3). In addition, the reducing agent may be also supplied continuously or I I
intermittently from a hollow portion of a hollow electrode or a lance for blowing an
auxiliary-raw-material (see FIG. 1 and FIG. 4). At this time, it may be possible to mix the
reducing agent with at .least one material of the slag modifying agent and a raw material
containing iron.
I
I
I
[0075] .. . , I
In general, carbon materials are used as the reducing agent. As the carbon I
. 8
materials, it may be possible to use, for example, coke ash, anthracite culm, graphite powder,
dust powder containing carbon, .and fly ash. : I
- . The slag modifying agent is used mainlxfor adjusting (SiO2) or (A1203), and it is
necessary to select an appropriate material for the slag modifying agent. It is preferable for
the slag modifying agent to contain one type or two or more types selected fiom SiOz, CaO,
A1203, and MgO. Further, it may be possible to use, as the slag modifying agent, coal ash,
slag powder containing the large amount of SiOzand AI203, brick chips, aluminum dross, and
the like. It is preferable for the raw material containing iron to include one type or two or
more types selected from iron scrap, reduced iron, and powder dust.
COO771
Further, as for the method of preventing the molten slag from foaming and
overflowing fiom the electric finnace, it may be possible to use the following method in
combination.
(c) A method of suspending, in the molten slag layer, a carbon material with the excessive
amount relative to the amount necessary for the reduction processing.
[0078]
For reducing the steel-making slag, the amount of the reducing agent
(auxiliary-raw-material) supplied to the molten slag layer is necessary in the stoichiometric
equivalent amount necessary for the reduction reaction between the steel-making slag and the
reducing agent. However, in order to prevent the molten slag fiom being foaming state and
to prevent the molten slag from spilling over from the electric furnace, it is preferable that 1.1
to 1.6 times the stoichiometric amount necessary for the reduction reaction with the molten
slag is set as a predetermined amount of the reducing agent, and the reducing agent is added
to the molten slag layer for suspending, thereby preventing the slag foaming from occurring.
If the reducing agent (powder carbon) is less than 1.1 times the stoichiometric
amount, it is difficult to achieve the effect of suppressing foaming obtained as a result of theadditioli
of the reducing agent. If the reducing agent exceeds 1.6 times the stoichiometric .... -
amount, the further effect of suppressing foaming cannot be obtained.
Further,.as for.the method of preventing the molten slag from foaming and
overflowing from the electric furnace, it may be possible to use the following method in.
combination.
(d) A method of reducing the concentration of [C] in the molten iron to not more than 3
mass%.
This method is based on the experimental finding that the reduction in the
concentration [C] in the molten iron to not more than 3 mass% makes it easy to prevent the
molten slag from foaming and overflowing from the electric h a c e .
[005 11
In the apparatus of the present invention, the steel-making slag is charged into the
molten slag layer in the electric furnace from the slag-supplying furnace continuously or
intermittently, while the slag of the molten: slag layer is intermittently discharged from the
cinder notch provided on the furnace bottom side wall. Accordingly, in the electric furnace,
the reducing process of the steel-making slag can be continuously performed. Accordingly,
the processing efficiency of the steel-making slag is extremely high.
[0082]
If the thickness of the molten slag layer in the electric furnace increases and reaches .
a predetennined level, the cinder notch (reference number 7 in the drawing) is opened to
discharge the molten slag to the outside of the furnace. Further, when the interface between
the layer of the molten slag and the molten iron approaches the vicinity of the cinder notch,
the tap hole located below the cinder notch is opened to discharge the molten iron. If the
I
interface between the layer of the molten slag and the molten iron is located close to the
cinder notch, the separation p e q f p ~ cbee tween the molten slag and the molten iron
deteriorates.

The molten slag discharged from the cinder notch is subjected to a granulated and
rapid-cooling process immediately, or is received in a container to be subjected to slow
cooling, thereby obtaining a product. The molten iron discharged from the tap hole is
accommodated in a molten iron pot, and is subjected to a dephosphorization process by
supplying oxygen or iron oxide, and dephosphorization agents to the molten iron in a mixed
manner. The target phosphorus concentration after the dephosphorization is set to be almost
equal to the phosphorus concentration discharged from the blast furnace so as to be used in
the steelmaking processes.
[0084]
The molten iron after the dephosphorization is formed into mold pig iron, or is
transferred to a ladle car or molten iron pot, and then, is transported to the steelmaking
process. On the other hand, the slag generated through the dephosphorization process has
PzOs in the high concentration, and hence, is used as phosphate fertilizer or industrial
phosphoric acid material.
2) Below, a system of the present invention will be described.
With reference to FIG. 5, an embodiment of the system of the present invention will
be described based on the contiiluous reduction apparatus shown in FIG. 3.
First, the electric power supplied to the electrode of the electric furnace is set.
However, since the actual electric power supplied is apart from the set supplied electric power,
-~p-+-~:~~~~-~~-$zq-T-~-~-~=~~&--%=~~Z~ - - a -- - - - - ,-,t - - I
the amount of the actu~xd~upplied electric power is inputted to the calculating unit.1 Sa, and
based thereon, the amount of steel-making slag X to be reduced is calculated and the
predetermined amount of the reducing agent is calculated based on the calculated amount of,
the steel-making slag X to be reduced.
[008 71
It should be noted that a predetermined amount of the reducing agent is, as
mentioned above, preferably set in a range of 1.1 times to 1.6 times the stoichiometric amount
necessary for reduction reaction with the molten slag, in order to prevent the slag foaming
from occurring in the molten slag and prevent the molten slag from spilling over the electric
furnace.
Then, the amount Y of the steel-making slag charged into the electric furnace is
controlled so as to follow the calculated amount X of the steel-making slag to be reduced, as a
target value.
[OOSS]
More specifically, the amount Y of the steel-making slag charged into the electric
h a c e is calculated by measuring the change in the amount of the steel-making slag in the
slag-supplying furnace by a weight meter 3b, and then inputting the measured value to a
calculation unit 1 5b.
[0089]
The calculated amount Y of the steel-making slag charged and the amount X of the
hot steel-making slag to be reduced which is calculated based on the amount of the electric
power actually suppIied are compared by a calculation unit 15c. Then, with a control unit,
the tilting unit 3a is actuated to adjust the tilting angle of the slag-supplying furnace with the
tilting axis Z being the center such that the amount Y of the steel-making slag charged follows
the amount X- -. of t.h. e steel-making slag to be reduced, as a target value.. _-Itshould be noted
that the charging of the steel-making slag can be performed continuously or intermittently.
[0090]
When the steel-making slag is continuously charged, the arnount Y of the
steel-making slag may be controlled so as to follow the target value of the amount X of the
steel-making slag to be'reduced. The control method is not specified, but for example,
widespread PID control or the like may be used.
[009l]
On the otherhand, when the steel-making slag is intermittently charged, as same as
the case of the continuous charging, the amount Y of the steel-making slag is controlled so as
to follow the target value of the amount X of the steel-making slag to be reduced. However,
for example when a predetermined amount of the steel-making slag is collectively supplied at
predetermined intervals of time, it is possible to employ the value corresponding to the
charging rate per unit time as the amount Y of the steel-making slag charged.
[0092]
In this case, the control can be achieved by setting the amount of the steel-making
slag collectively supplied and the predetermined intervals of the time in advance, and
performing a sequence control. In such a case, it is important to confirm, in advance, the
amount of the steel~makingsl ag which does not cause the overflowing, even if the
steelmaking slag is collectively supplied.
[0093 J
In addition, a calculation unit calculates a predetermined amount of the reducing
agent based on the charging amount X of the steelmaking slag to be reduced, aid then, using
the calculated value as a target value, the supplied arnount from the auxiliary-raw-material
supplying tube is adjusted. In this case, the supplied amount is controlled by a device (not
illustgated) that controls the supplied amount fiom the auxiliary~raw-material supplying tube
14a.
[Examples]
[0094]
Next, Examples of the present invention will be described. The conditions
described in Examples are merely examples of conditions given for confirming feasibility and
effects of the present invention, and conditions related to the present invention are not limited
to these examples of condition. . The present invention may employ various conditions,
provided that they do not depart from the main points of the present invention and the object
of the present invention can be achieved.
[0095]
(Example 1)
, In the continuous reduction processing apparatus illustrated in FIG. 5, the
steel-making slag discharged from a converter in a molten state (rate of solid phase: not more
than 25%) was charged into the slag-supplying furnace, and was temporarily stored. Then,
the slag-supplying furnace was tilted once every 10 minutes to charge the steel-making slag
with approximately 8 tons for each charge into the direct-current electric hmace.
[0096]
The slag was charged into the electric fbrnace under conditions where pig iron with
approximately 130 tons was contained in the electric furnace and a molten slag layer I
subjected to reduction processing existed on the pig iron with a thickness of approximately
200 mm. Note that the reason for setting the amount of inflow of the steel-making slag to I
I
approximately 8 tons for each charge is that it has been checked, through preliminary
experiments using an actual device, that strong foaming does not occur under this condition.
.- . . -. . Further, the rate of supplying of the steel-making - slag was set to average 800 kg/min.
This rate was calculated on the basis of the electric power consumption rate that is necessary
for the reduction processing of the steel-making slag and is obtained through the method
described above in order to continuously supply electric power of approximately 30 MW as
described below.
[0098]
Coke ash was supplied from the auxiliary-raw-material supplying tube 14a into the
furnace while the electric power is being supplied. This supplying rate was set to 85 kglmin,
which corresponds to 1.5 times as fast as the stoichiometric supplying rate. Further; as for
the slag modifying agerit, fly ash: 378 kglt-slag and bauxite powder: 47 kglt-slag were
continuously supplied from the auxiliary-raw-material supplying tube 14a onto the molten
slag layer to achieve the target basicity: 1.2 and target (A1203): 12 mass%.
The temperature in the electric furnace was controlled to be molten iron
temperatures: 1450 h 5°C and slag temperatures: 1550 * 5OC. Since the electric hrnace was
not provided with any opening portion that communicates with the atmospheric air, the inside
of the furnace was maintained to be the reducing atmosphere. Table 1 shows compositions
of the molten slag and temperatures thereof.
[O 1001
[Table 11
Table 1 (Massoh)
Charged Slag
(MnO) I (MgO)
6.1 1 8.2
[T. Fel
18. 6
(P, o5
1.5
Temp..
1450°C
(M. Fe)
2 . 0
(CaO)
49.0
(S i O2
12.2 .
The electric h a c e always contacned-molten iron (C; 3.0 mass%) having the
composition show1 in Table 2 with the amount of 100 to 150 tons, and the molten slag layer
with the thickness of approximately 100 to 300 mm. For the electric furnace, the electric
power of approximately 30 MW was continuously supplied from the electrode to apply
reduction processing to the steel-making slag charged into the molten slag layer without
causing the slag foaming.
[O 1 021
[Table 21
Table 2 (Mass%)
[0 1 031
The slag of the molten slag layer was discharged once every hour with the amount
of approximately 46 tons from the cinder notch, and the molten iron was discharged once
every five hours with the amount of approximately 44 tons from the tap hole. From the
components of the discharged molten slag and the components of the discharged molten iron,
it can be found that the slags were reduced as shown in Table 3 and Table 4, and the
concentrations of P and Mn in the molten iron increased.
[0 1041
[Table 31
Table 3 (Mass%)
~ --f = = - , F ~ = * - -& 2. .@- --?-..y - - - -- -- -
- .
Compositio~i of Molten Steel
[ S 1
0.024
[Cl
3. 0
Tern p.
1450°C
C S i 1 CMnl
0.01 1 0.32
1 PI
0. 12
[Table 41
Table 4 (Mass%)
The electric power consumption rate necessary for reduction processing of the
molten slag was 607 kWh1t-slag in the case of decarbonized slag at 1450°C. On the other
hand, for the purpose of comparison, the same decarbonized slag was charged in a form of
cold powder. As a result, the electric power consumption rate was 13 14 kWh/t-slag.
[0107]
(Example 2)
C P I
1. 40
CM n.1
0. 80
Discharged Molten Steel I. [ C ]
&%$& I 3. 0
A reduction and modification process under the same conditions as those for
Example 1 except that instead of using an auxiliary-raw-material supplying tube 14a, a hollow
electrode was used for the electrode, and, the hollow portion is used as an
. Csl'
0. 038
[ s i l
0. D l
auxiliary-raw-material supplying tube for supplying the slag modifying agent and the
reducing agent.
[0 1081
Temperatures in the electric furnace were controlled so as to be molten iron
temperatures:. 1450 5OC, and slag temperatures: 1450 * 5OC. The reduction processing of
'the hot steel-making slag was continuously performed without causing the overflow of the
molten slag.
[0109]
During the reduc- t.i.. o ..n . - . p rocessing, the slag in the molten slag layer was dis.c .-h .-a r- g.e- d
once every hour with the amount of approximately 46 tons from the cinder notch, and the
molten iron was discharged once every five hours with the amount of approximately 44 tons
from the tap hole. The components of the discharged molten slag and the components of the
discharged molten iron were almost the same as those shown in Table 3 and Table 4.
[Ol lo]
In Examples 1 and 2, the steel-making slag with the amount of approximately 8 tons
was charged once every 10 minutes simultaneously. Under such charging conditions, the
reduction processing of the molten slag was continuously performed without causing the
overflow of the molten slag. Further, the rate of inflow of the steel-making slag was 800
kg/min on average.
[Oll 11
This means that, in the apparatus according to the present invention, in the case
where the steel-making slag is continuously charged at charging rates of 800 kg/min, or at
charging rates of not more than 800 kglmin, the foaming is less likely to occur, and under
these conditions, the reduction processing of the molten slag can be continuously performed
without causing the overflow of the molten slag. In other words, Examples 1 to 2, which
employ intermittent charging, are examples that demonstrate the applicability of the apparatus
according to the present invention to the continuous charging of the steel-making slag.
[0112]
(Comparative Example)
In order to reduce the steel-making slag having the components shown in Table 1,
the steel-making slag with the amount of 20 tons in a hot state was supplied at once into the
electric furnace 1 containing the molten iron having the components and temperature shown
in Table 2. After the steel-making slag is supplied into the electric furnace, the slag foaming - ,- - . . . . .
of the molten iron suddenly occurred, and hence, the operation had to be stopped.
[Industrial Applicability]
[0113] . . .
According to the present invention, since the reducing process of the hot
steel-making slag is continuously performed without break while discharging the slag
intermittently, it is possible to, with low energy-consumption rate and high efficiency, rnodie
the steel-making slag into a material that can be used for various applications such as a
cement raw material, a civil engineering material, and a ceramic product, while recovering
valuable elements such as Fe, Mn, and P into a molten iron.
[0114]
It is possible to recycle Fe and Mn into the steel-making processes, and use P as a
phosphate fertilizer or phosphoric acid material. Further, according to the present invention,
in the same electric furnace, it is possible to produce a molten iron by melting and reducing
the small scrap iron, reduced iron, powder dusts, and the like. Therefore, the present
invention is highly applicable to smelting techniques in the steel industry.
prief ~escri~tiofn t he Reference Symbols]
1 Electric furnace .
la, lb Furnace side wall
1 c Furnace ceiling
2 Electrode
2a Upper electrode
2b Furnace bottom electrode
3a Tilting unit
=======T~=g%~m-~-d-- p+--=+-+ L
...
3b Weight meter -
4 Slag-supplying portion
5 Molten iron
6 Molten slag
6' Steel-making slag
7 Cinder notch
8 Tap hole
9 Slag-supplying furnace
1 0 Bottom wall
1 1 Upper wall
12 Nozzle
12a Burner
13 Exhausting portion
13 a Opening portion
13 b Lid for closing the opening portion 13a
14 Auxiliary-raw-material supplying lance
14a Auxiliary-raw-material supplying tube
15a, 15b, 15c Calculation unit
X Amount -of steel-making slag to be reduced by a set electric power
Y Amount of steel-making slag charged to electric h a c e
Z Tilting Axis
[Designation of Document] Claims
* . . ... . -
1. A continuous reduction apparatus for continuously reducing a steel-making slag in an
electric b a c e , configured by
(i) an electric furnace comprising an auxiliary-raw-material supplying unit for supplying an
auxiliary-raw-material including reduction agent t6 a molten slag layer on a molten steel
generated by reducing the steel-making slag, a supplying portion for a hot steel-making slag,
an electrode for Eeating the molten slag layer, a cinder notch, and a tap hole, and
(ii) a slag supplying furnace which is connected to the electric furnace via the hot steel
.making slag supplying portion and comprises a tilting unit that. can adjust the supplying
amount of the hot steel-making slag to the electric furnace.
2. The continuous reduction apparatus for continuously reducing a steel-making slag
according to claim 1, wherein the electric furnace is a f~~ed-tyapned closed-type electric
fumace.
3. The continuous reduction apparatus for continuously reducing a steel-making slag
according to claim 2,wherein the fixed-type and closed-type electric furnace is a direct-current
electric furnace.
4. The continuous reduction apparatus for continuously reducing a steel-making slag
according to. any one of claims 1 to 3, wherein the auxiliary-raw-material supplying tube is
installed in the electrode.
5. The continuous reduction apparatus for continuously reducing a steel-making slag
according to any one of claims 1 to 4, wherein. . t- .h e .s- .l. ag supplying furnace is provided with an
'exhaust hole for an exhaust gas generated from the electric fiunace,
6. A continuous reductioil system for continuously reducing a steel-making slag by
supplying a steel-making slag from a slag supplying fkrnace, that can be tilted and is
connected to the electric funnace, to a molten slag layer. on a molten iron in the electric
furnace provided with a cinder notch and a tap hole on the hrnace side wall, wherein:
(a) the electric power supplied to an electrode of the electric furnace is measured,
(b) an amount of the steel-making slag to be reduced is calculated based on the supplied
electric power, and then a predetermined amount of reducing agent is calculated based on the .
calculated amount of the steel-making slag to be reduced;
(c) a tilting angle of the slag-supplying furnace is controlled by actuating the tilting unit such
that an amount of the steel-making slag supplied follows the amount of the steel-making slag
to be reduced, and
(d) a supplied amount from the auxiliary-raw-material supplying unit is controlled so as to
supply the predetermined amount of the reducing agent.