[TECHNICAL FIELD]
[0001] The present invention relates to a method for producing pig iron.
[BACKGROUND ART]
[0002] A method of producing pig iron through charging a first layer containing an iron
ore material and a second layer containing coke alternately in a blast furnace, and
reducing and melting the iron ore material while injecting an auxiliary reductant
into the blast furnace by hot air blown from a tuyere is known. During this, the coke
serves as a heat source for melting the iron ore material, a reducing agent for the
iron ore material, a recarburizing agent for carburizing the molten iron to lower
the melting point, and a spacer for ensuring gas permeability in the blast furnace.
Due to the coke maintaining gas permeability, descent of the burden is stabilized,
and in turn, stable operation of the blast furnace is enabled.
[0003] In operation of the blast furnace, it is desirable that the proportion of the coke
is low in light of cost reduction. However, a decrease in the proportion of the coke
leads to attenuation of the above-described roles played by the coke. For example,
as a method of decreasing the proportion of the coke, in other words increasing the
proportion of the iron ore material, a blast furnace operation method of limitedly
charging reduced iron of a small grain size to a peripheral portion of the blast furnace
has been proposed (see
Japanese Unexamined Patent Application, Publication No. H11-315308). In the blast furnace operation method, it is reportedly possible to increase the
filling rate of the raw material while maintaining the roles of the coke as the heat
source, the reducing agent, the recarburizing agent, and the spacer in the central
portion of the furnace, by charging the reduced iron requiring no reduction only to
the peripheral portion of the furnace.
[PRIOR ART DOCUMENTS]
[PATENT DOCUMENTS]
[SUMMARY OF THE INVENTION]
[PROBLEMS TO BE SOLVED BY THE INVENTION]
[0005] In light of recent requirement of a decrease in CO
2 emission, a further decrease in the amount of coke used in the blast furnace operation
is demanded. In the conventional blast furnace operation method, of the roles played
by the coke, the roles as the heat source, the reducing agent, and the recarburizing
agent may be substituted by an auxiliary reductant injected from a tuyere. On the
other hand, the role as the spacer is played only by the coke. In the conventional
blast furnace operation method, the charging position of the reduced iron is limited
to the peripheral portion of the furnace. In addition, the amount of the coke used
is only relatively reduced by the charging of the reduced iron. Therefore, in the
conventional blast furnace operation method, only a limited decrease in the amount
of the coke used is possible, and the recent demand for a decrease in the CO
2 emission may not be sufficiently met.
[0006] The present invention was made in view of the foregoing circumstances, and an objective
thereof is to provide a method for producing pig iron enabling a decrease in the amount
of the coke used while maintaining stable operation of the blast furnace.
[MEANS FOR SOLVING THE PROBLEMS]
[0007] A production method of pig iron using a blast furnace with a tuyere according to
one aspect of the present invention includes: charging a first layer containing an
iron ore material and a second layer containing coke alternately in the blast furnace;
and reducing and melting the iron ore material in the charged first layer while injecting
an auxiliary reductant into the blast furnace by hot air blown from the tuyere, wherein:
an aggregate containing a reduced iron molded product obtained through compression
molding of reduced iron is blended into the first layer, the iron ore material contains
iron ore pellets as a principal material, an average basicity of the reduced iron
molded product is less than or equal to 0.5, and an average basicity of the iron ore
pellets is greater than or equal to 0.9.
[0008] In the method for producing pig iron, the first layer containing the iron ore material
contains, as an aggregate, a reduced iron molded product obtained through compression
molding of reduced iron. Since the reduced iron molded product facilitates permeation
of hot air during softening and fusing of the first layer in the melting step, the
method for producing pig iron can decrease the amount of the coke for ensuring gas
permeability. Furthermore, since the method for producing pig iron uses the reduced
iron molded product in which the average basicity is less than or equal to 0.5, the
reduced iron molded product can be obtained at relatively low cost. Moreover, since
the method for producing pig iron uses, as the principal material, the iron ore pellets
in which the average basicity is greater than or equal to 0.9, an increase in viscosity
can be inhibited when the reduced iron molded product, having the low basicity, has
melted, thereby promoting melting down. Thus, gas permeability in mainly a cohesive
zone can be improved, and furthermore, an amount of the coke used can be decreased.
Consequently, using the method for producing pig iron enables the amount of the coke
used to be decreased while maintaining stable operation of the blast furnace.
[0009] A content of the iron ore pellets in the iron ore material is preferably greater
than or equal to 50% by mass. When the content of the iron ore pellets is thus greater
than or equal to the lower limit, the gas permeability can be further improved.
[0010] The iron ore pellets are preferably self-fluxing. When the iron ore pellets are thus
self-fluxing, melting down of the reduced iron molded product is promoted, whereby
the gas permeability can be further improved.
[0011] A ratio R of a consumption of the iron ore pellets to a consumption of the reduced
iron molded product preferably satisfies the following inequality 1. When the ratio
R of the consumption of the iron ore pellets to the consumption of the reduced iron
molded product thus satisfies the following inequality 1, the effect of improving
the gas permeability due to the melting down of the reduced iron molded product can
be more certainly expressed.
[0012] In the above inequality 1: (C/S) represents an average basicity; (%SiO
2) represents a content of SiO
2 (% by mass); HBI, being in subscript, represents the reduced iron molded product;
and P represents the iron ore pellets, wherein (C/S)
Critical represents a critical basicity of the HBI.
[0013] Herein, the "principal material" as referred to means a material having the greatest
content in terms of mass. The "basicity" as referred to means a ratio of the mass
of CaO to the mass of SiO
2. It is to be noted that the "average basicity" as referred to means, in a case in
which the target mass is constituted by a plurality of granular bodies, a ratio of
a total mass of CaO to a total mass of SiO
2 in the plurality of granular bodies.
[0014] With regard to the "critical basicity", as shown in FIG. 3, when the average basicity
of the HBI is adopted as a parameter, pressure loss of a sample-packed bed is continuously
measured, and a maximum value thereof (maximum pressure loss) is plotted, the "critical
basicity" means the average basicity at which the maximum pressure loss begins to
decrease. It is to be noted that as shown in FIG. 5, for example, the sample-packed
bed can be constituted of, from the top: an upper coke layer 72a (20 mm in height);
an iron ore layer 72b (110 mm in height); and a lower coke layer 72c (40 mm in height),
using a furnace for a large-scale reduction under load test 7 in which a graphite
crucible 71 to be filled with a sample has an inner diameter of 75 mm.
[EFFECTS OF THE INVENTION]
[0015] As explained in the foregoing, the method for producing pig iron according to the
present invention enables a decrease in the amount of the coke used while maintaining
stable operation of the blast furnace.
[BRIEF DESCRIPTION OF THE DRAWINGS]
[0016]
FIG. 1 is a flow diagram illustrating the method for producing pig iron according
to an embodiment of the present invention.
FIG. 2 is a schematic view illustrating the inside of the blast furnace used in the
method for producing pig iron in FIG. 1.
FIG. 3 is a graph showing a relationship between the average basicity of the reduced
iron molded product and the maximum pressure loss.
FIG. 4 is a schematic partial enlarged view of the vicinity of an area from a cohesive
zone to a dripping zone in FIG. 2.
FIG. 5 is a schematic cross-sectional view illustrating a configuration of a furnace
for a large-scale reduction under load test used in Examples.
FIG. 6 is a graph showing a temperature profile of heating a sample-packed bed in
the Examples.
FIG. 7 is a graph showing a relationship between the temperature of the sample-packed
bed and a flow rate of gas supplied.
FIG. 8 is a graph showing results of the Examples.
[DESCRIPTION OF EMBODIMENTS]
[0017] Hereinafter, the method for producing pig iron according to each embodiment of the
present invention will be described.
[0018] The method for producing illustrated in FIG. 1 uses a blast furnace 1 illustrated
in FIG. 2, and includes a charging step S1 and a reducing/melting step S2.
Blast Furnace
[0019] The blast furnace 1 includes a tuyere 1a and a taphole 1b provided in a furnace lower
portion as illustrated in FIG. 2. Typically, a plurality of tuyeres 1a are provided.
The blast furnace 1 is a solid-gas countercurrent type shaft furnace that enables:
hot air, which is high-temperature air with high-temperature or normal-temperature
oxygen being added as needed, to be blown from the tuyere 1a into the furnace; a series
of reactions such as reduction and melting of an iron ore material 11 described later
to take place; and pig iron to be tapped from the taphole 1b. In addition, the blast
furnace 1 is equipped with a bell-armor type raw material charging device 2. The raw
material charging device 2 will be described later.
Charging Step
[0020] In the charging step S1, a first layer 10 and a second layer 20 are alternately charged
in the blast furnace 1 as illustrated in FIG. 2. In other words, the numbers of the
first layers 10 and the second layers 20 are at least two, respectively.
(First Layer)
[0021] The first layer 10 contains the iron ore material 11. Further, an aggregate 12 is
blended into the first layer 10. In addition to the iron ore material 11 and the aggregate
12, auxiliary materials such as limestone, dolomite, and silica may also be charged
into the first layer 10.
[0022] The iron ore material 11 refers to mineral ore serving as an iron raw material. In
the reducing/melting step S2, the iron ore material 11 is heated and reduced into
molten iron by the hot air blown from the tuyere 1a. In the method for producing pig
iron, the iron ore pellets are the principal material. The "iron ore pellets" are
referred to herein are made by using iron ore fine powder in an order of several tens
of µm, and by improving quality to have characteristics (for example, size, strength,
reducibility, and the like) suitable for a blast furnace. It is to be noted that in
the method for producing pig iron, the iron ore pellets preferably do not contain
sintered iron ore powder.
[0023] The lower limit of the average basicity of the iron ore pellets is 0.9, and is more
preferably 1.0, being basic, and still more preferably 1.4. When the basicity of the
iron ore pellets is less than the lower limit, the melting down of the reduced iron
molded product may be less likely to be promoted, and the gas permeability may deteriorate.
The upper limit of the average basicity of the iron ore pellets is not particularly
limited, and the average basicity of the iron ore pellets is typically less than or
equal to 2.0.
[0024] The lower limit of the content of the iron ore pellets in the iron ore material 11
is preferably 50% by mass, more preferably 90% by mass, and still more preferably
100% by mass, i.e., the iron ore material 11 is still more preferably completely constituted
by the iron ore pellets. When the content of the iron ore pellets is thus greater
than or equal to the lower limit, the gas permeability can be further improved.
[0025] The iron ore pellets are preferably self-fluxing. When the iron ore pellets are
thus self-fluxing, the melting down of the reduced iron molded product may be promoted,
whereby the gas permeability can be further improved.
[0026] It is preferred that the iron ore pellets have a porosity resulting from large open
pores having a pore size of greater than or equal to 4 µm which is greater than or
equal to 21%. When the iron ore material contain the iron ore pellets, of which the
porosity resulting from the large open pores having the pore size of greater than
or equal to 4 µm is greater than or equal to 21%, a reduction percentage of the iron
ore material can be increased, whereby the amount of the coke used can be further
decreased. As used herein, the "porosity resulting from large open pores having a
pore size of greater than or equal to 4 µm" refers to a percentage of a volume of
the large open pores having the pore size of greater than or equal to 4 µm with respect
to an apparent volume of the iron ore pellets, the percentage being calculated by
ε
0×A
+4/A [%], wherein: ε
0 [%] is an open porosity of the iron ore pellets; A [cm
3/g] is a total capacity of pores per unit weight of the iron ore pellets; and A
+4 [cm
3/g] is a total capacity of pores having a pore size of greater than or equal to 4
µm per unit weight of the iron ore pellets, each of these being measured by using
a mercury intrusion porosimeter (for example, AutoPore III 9400, manufactured by Shimadzu
Corporation). Note that an open pore refers to a pore connected to the outside of
the iron ore pellets, while a closed pore refers to a pore closed inside the iron
ore pellets.
[0027] The iron ore pellets preferably contain MgO. MgO has the effects of enhancing a slag
desulfurization ability at a hearth level, and enhancing reducibility at high temperatures.
Thus, it is considered that by making the behavior of the melting down of the iron
ore material 11 become closer to that of the reduced iron molded product, there is
an effect of promoting the melting down of the reduced iron molded product. The lower
limit of a content of the MgO in the iron ore material 11 is preferably 1% by mass,
and more preferably 1.5% by mass. On the other hand, the upper limit of the content
of the MgO is preferably 4% by mass, and more preferably 3% by mass. When the content
of the MgO is less than the lower limit, the effect of promoting the melting down
of the reduced iron molded product may not be sufficiently obtained. Conversely, when
the content of the MgO is greater than the upper limit, strength of the iron ore pellets
may deteriorate.
[0028] The iron ore material 11 may include, in addition to the iron ore pellets: sintered
iron ore, lump iron ore, carbon composite agglomerated iron ore, metal, and/or the
like. It is to be noted that in view of improving the gas permeability, a content
of the sintered iron ore in the iron ore material 11 is preferably less than or equal
to 10% by mass, and more preferably 0% by mass, i.e., the sintered iron ore is more
preferably not contained in the iron ore material 11.
[0029] It is to be noted that the reduced iron molded product contained in the aggregate
12, described later, may also serve as the iron raw material, but in the present specification,
the reduced iron molded product is not contained in the iron ore material 11.
[0030] The aggregate 12 is for improving gas permeability in a cohesive zone D described
later, whereby the hot air is permeated to the central portion of the blast furnace
1. The aggregate 12 contains a reduced iron molded product (hot briquette iron: HBI)
obtained through compression molding of reduced iron.
[0031] The HBI is obtained by molding direct reduced iron (DRI) in a hot state. The DRI
is high in porosity and has a drawback of oxidization and heat generation during marine
transportation and outdoor storage, while the HBI is low in porosity and not likely
to be re-oxidized. After serving to ensure gas permeability in the first layer 10,
the aggregate 12 functions as a metal and becomes molten iron. Since the aggregate
12 has a high metallization degree and requires no reduction, the reduction agent
is not much required for becoming the molten iron. CO
2 emission can thus be reduced. Note that the "metallization degree" refers to a proportion
[% by mass] of metallic iron with respect to the total iron content.
[0032] The upper limit of the average basicity of the reduced iron molded product is 0.5,
and more preferably 0.4. The reduced iron molded product contains, as slag components
derived from iron ore, SiO
2 and/or Al
2O
3, and the average basicity typically tends to be low. Since in the method for producing
pig iron, the reduced iron molded product having a basicity of less than or equal
to the upper limit is used, it is not necessary to prepare a high-grade reduced iron
molded product which has an increased basicity by SiO
2 and/or Al
2O
3 being eliminated, CaO being added, and/or the like. Therefore, the pig iron can be
produced at low cost. On the other hand, the lower limit of the average basicity of
the reduced iron molded product is not particularly limited, and may be 0.
[0033] A ratio R of a consumption of the iron ore pellets to a consumption of the reduced
iron molded product preferably satisfies the following inequality 1. When the ratio
R of the consumption of the iron ore pellets to the consumption of the reduced iron
molded product thus satisfies the following inequality 1, the effect of improving
the gas permeability due to the melting down of the reduced iron molded product can
be more certainly expressed.
[0034] The above inequality 1 is explained in detail below. FIG. 3 is a graph showing a
relationship between the average basicity of the HBI and the maximum pressure loss
of the packed bed in which the first layer 10 and the second layer 20 are alternately
charged. It can be understood that this maximum pressure loss being lower indicates
that the gas permeability is higher. From FIG. 3, it is revealed that when the average
basicity of the HBI is greater than a certain value, an improvement in the gas permeability
is recognized. This certain value is the critical basicity. It is considered that
in a case in which CaO being greater than or equal to this critical basicity is present,
the SiO
2 in the HBI changes into a calcium silicate melt, and the viscosity of the molten
iron generated from the HBI decreases, whereby melting down is promoted. In other
words, it can be deemed that in order to obtain the melting down-promoting effect
of the HBI, CaO being greater than or equal to the critical basicity is needed.
[0035] In FIG. 3, the CaO is provided from the HBI, but the CaO can also be provided from
the iron ore pellets. In this case, it is considered that when the CaO amount, with
respect to the SiO
2 amount in the HBI and the iron ore pellets combined, is greater than the critical
basicity, melting down of the HBI is promoted, whereby the gas permeability of the
packed bed can be enhanced.
[0036] The SiO
2 amount and the CaO amount in the HBI and the iron ore pellets combined are represented
in the following formulae 2, with the consumption of the reduced iron molded product
being represented by M
HBI [kg], and the consumption of the iron ore pellets being represented by M
P [kg].
[0037] Here, since it is considered that when, as described above, the melting down of the
HBI is promoted when CaO amount / SiO
2 amount ≥ (C/S)
Critical is satisfied, the above formulae 2 are substituted into this inequality and R=M
P/M
HBI is solved for to obtain the above inequality 1.
[0038] The lower limit of a charged rate of the reduced iron molded product is preferably
100 kg and more preferably 150 kg per 1 ton of the pig iron. When the charged rate
of the reduced iron molded product is less than the lower limit, the function of the
aggregate 12 ensuring gas permeability in the cohesive zone D in the reducing/melting
step S2 may not be sufficiently exerted. On the other hand, the charged rate of the
reduced iron molded product is defined as appropriate in such a range that the aggregate
is not excessive and does not diminish the effect of the aggregate, and the upper
limit of the charged rate of the reduced iron molded product is, for example, 700
kg per 1 ton of the pig iron.
[0039] The lower limit of a ratio of an average grain size of the reduced iron molded product
to an average grain size of the iron ore material 11 is preferably 1.3, and more preferably
1.4. As illustrated in FIG. 4, even when a part of the iron ore material 11 in the
first layer 10 is melted and moves to the lower side of the blast furnace 1 as a drip
slag 13 and the iron ore material 11 is softened and shrunk, the reduced iron molded
product having a high melting point is not softened. Blending the reduced iron molded
product, which is larger than the iron ore material 11 to at least a certain degree,
as the aggregate 12 facilitates the aggregate effect of the reduced iron molded product
to be exerted and enables suppression of layer shrinkage of the entire first layer
10. Consequently, due to the ratio of the average grain sizes being greater than or
equal to the lower limit, a channel of the hot air shown by an arrow in FIG. 4 can
be secured, whereby gas permeability in the reducing/melting step S2 can be improved.
Meanwhile, the upper limit of the ratio of the average grain sizes is preferably 10
and more preferably 5. When the ratio of the average grain sizes is greater than the
upper limit, it may be difficult to blend the reduced iron molded product uniformly
into the first layer 10, leading to an increase in segregation. It is to be noted
that the "average grain size" as referred to means a grain size in which a total mass
accounts for 50% in a grain size distribution.
[0040] The upper limit of a gas permeability resistance index of the reduced iron molded
product after a tumbler rotation test is preferably 0.1, and more preferably 0.08.
The reduced iron molded product is typically produced and used in different plants,
and subjected to transportation. Since volume can be broken and grain size distribution
can be altered during the transportation, by using the reduced iron molded product,
which ensures that the gas permeability resistance index is less than or equal to
a certain value even after the tumbler rotation test, gas permeability in the lumpy
zone E, described later, can be improved in actual blast furnace operations. On the
other hand, the lower limit of the gas permeability resistance index is not particularly
limited and may be a value close to zero, which is a theoretical limit value, but
is typically about 0.03. Note that it is only required to use the reduced iron molded
product having the gas permeability resistance index less than or equal to a predetermined
value as a characteristic, and this does not mean that the tumbler rotation test is
required in the method for producing pig iron.
[0041] As used herein, the "gas permeability resistance index after a tumbler rotation test"
of the reduced iron molded product is calculated as follows. First, the tumbler rotation
test is carried out pursuant to Iron Ores - Determination Of Tumble Strength (JIS-M8712:2000)
to obtain a grain size distribution of the reduced iron molded product through screening.
The grain size distribution is indicated with d
i [cm] being a typical grain size (median) of mesh opening used for the screening,
and w
i being a weight fraction of the reduced iron molded product belonging to the typical
grain size d
i. By using this grain size distribution, a harmonic mean diameter D
p [cm] and a granularity composition index I
sp are calculated by the following formula 3. Furthermore, by using a gravitational
conversion factor g
c [9.807 (g·cm)/(G·sec
2)], a gas permeability resistance index K is obtained by the following formula 3.
Note that rotational conditions of a tumbler in the tumbler rotation test are 24±1
rpm and 600 times.
where
where n = 0.47, C = 0.55
[0042] In addition, in a case in which the reduced iron molded product contains aluminum
oxide, the upper limit of the content of the aluminum oxide in the reduced iron molded
product is preferably 1.5% by mass and more preferably 1.3% by mass. When the content
of the aluminum oxide is greater than the upper limit, it may be difficult to ensure
gas permeability in the furnace lower portion due to increases in the melting point
and the viscosity of the slag. Consequently, by configuring the content of aluminum
oxide in the reduced iron molded product to be less than or equal to the upper limit,
an increase in the amount of the coke used can be inhibited. Note that the content
of the aluminum oxide may be 0% by mass, i.e., the reduced iron molded product may
not contain aluminum oxide, but the lower limit of the content of the aluminum oxide
is preferably 0.5% by mass. When the content of the aluminum oxide is less than the
lower limit, the reduced iron molded product becomes expensive, and the production
cost of the pig iron may be increased.
(Second Layer)
[0043] The second layer 20 contains coke 21.
[0044] The coke 21 serves: as a heat source for melting the iron ore material 11; to generate
CO gas as a reducing agent necessary for reduction of the DIR iron ore material 11;
as a recarburizing agent for carburizing the molten iron to lower the melting point;
and as a spacer for ensuring gas permeability in the blast furnace 1.
(Charging Method)
[0045] Various methods can be used as a method for alternately charging the first layer
10 and the second layer 20. The method is described herein with reference to, as an
example, the blast furnace 1 equipped with a bell-armor type raw material charging
device 2 (hereinafter, may be also merely referred to as "raw material charging device
2") illustrated in FIG. 2.
[0046] The raw material charging device 2 is provided in a furnace top portion. In other
words, the first layer 10 and the second layer 20 are charged from the furnace top.
The raw material charging device 2 includes, as illustrated in FIG. 2, a bell cup
2a, a lower bell 2b, and an armor 2c.
[0047] The bell cup 2a is where the raw material to be charged is loaded. When the first
layer 10 is charged, the raw material constituting the first layer 10 is loaded into
the bell cup 2a, and when the second layer 20 is charged, the raw material constituting
the second layer 20 is loaded into the bell cup 2a.
[0048] The lower bell 2b is in a cone shape expanding downward, and is provided inside the
bell cup 2a. The lower bell 2b is vertically movable (FIG. 2 shows an upward moved
state with a solid line, and a downward moved state with a dotted line). The lower
bell 2b is configured to seal a lower portion of the bell cup 2a when moved upward,
and to form a gap on an extended line of a lateral wall of the bell cup 2a when moved
downward.
[0049] The armor 2c is provided on a lower side with respect to the lower bell 2b, in a
furnace wall portion of the blast furnace 1. When the lower bell 2b is moved downward,
the raw material falls from the gap, while the armor 2c serves as a rebound plate
for rebounding the fallen raw material. In addition, the armor 2c is configured to
be protrudable and retractable with respect to a center (central portion) of the blast
furnace 1.
[0050] By using the raw material charging device 2, the first layer 10 can be charged as
follows. Note that the same applies to the second layer 20. In addition, the first
layer 10 and the second layer 20 are alternately charged.
[0051] First, the lower bell 2b is positioned on the upper side and the raw material of
the first layer 10 is charged into the bell cup 2a. When the lower bell 2b is positioned
on the upper side, the lower portion of the bell cup 2a is sealed, whereby the raw
material is loaded in the bell cup 2a. Note that the loaded amount is an amount of
each layer to be charged.
[0052] Next, the lower bell 2b is moved downward. As a result, a gap is generated from the
bell cup 2a, and the raw material falls through the gap in the furnace wall direction
to hit the armor 2c. The raw material that has hit and been rebounded by the armor
2c is charged into the furnace. The raw material falls while moving toward the furnace
interior due to the rebound at the armor 2c, and is accumulated while flowing from
the fallen position toward the central side of the furnace interior. Since the armor
2c is configured to be protrudable and retractable with respect to the central portion,
the fallen position of the raw material can be adjusted by protruding and retracting
the armor 2c. This adjustment enables the first layer 10 to be accumulated in a desired
shape.
Reducing/Melting Step
[0053] In the reducing/melting step S2, the iron ore material 11 in the charged first layer
10 is reduced and melted while an auxiliary reductant is injected into the blast furnace
by hot air blown from the tuyere 1a. Note that the operation of the blast furnace
is continuous, and thus the reducing/melting step S2 is carried out continuously.
On the other hand, the charging step S1 is carried out intermittently, and the first
layer 10 and the second layer 20 to be processed in the reducing/melting step S2 are
added according to the circumstances of the reduction and melting process of the first
layer 10 and the second layer 20 in the reducing/melting step S2.
[0054] FIG. 2 illustrates a state in the reducing/melting step S2. As illustrated in FIG.
2, a raceway A, which is a hollow portion in which the coke 21 whirls and is present
in an extremely sparse state, is formed in the vicinity of the tuyere 1a due to the
hot air from the tuyere 1a. In the blast furnace 1, the temperature in the raceway
A is the highest, being about 2,000 °C. A deadman B, which is a pseudo-stagnation
zone of the coke inside the blast furnace 1, is present adjacent to the raceway A.
In addition, the dripping zone C, the cohesive zone D, and the lumpy zone E are present
in an upward direction in this order from the deadman B.
[0055] The temperature in the blast furnace 1 increases from a top portion toward the raceway
A. In other words, the temperature increases in the order of the lumpy zone E, the
cohesive zone D, and the dripping zone C. For example, the temperature of the lumpy
zone E is about greater than or equal to 20 °C and less than or equal to 1,200 °C,
while the temperature of the deadman B is about greater than or equal to 1,200 °C
and less than or equal to 1,600 °C. Note that the temperature of the deadman B varies
in the radial direction, and the temperature of a central portion of the deadman B
may be lower than the temperature of the dripping zone C. In addition, by stably circulating
the hot air in the central portion in the furnace, the cohesive zone D having an inverted
V-shaped cross section is formed, whereby gas permeability and reducibility are ensured
in the furnace.
[0056] In the blast furnace 1, the iron ore material 11 is first heated and reduced in the
lumpy zone E. In the cohesive zone D, the iron ore reduced in the lumpy zone E is
softened and shrunk. The softened and shrunk iron ore falls as the drip slag, and
moves to the dripping zone C. In the reducing/melting step S2, reduction of the iron
ore material 11 proceeds principally in the lumpy zone E, while melting of the iron
ore material 11 proceeds principally in the dripping zone C. Note that in the dripping
zone C and the deadman B, direct reduction proceeds, which is a direct reaction between
the fallen liquid iron oxide FeO and carbon in the coke 21.
[0057] The aggregate 12 containing the reduced iron molded product exerts the aggregate
effect in the cohesive zone D. In other words, even in a state in which the iron ore
has been softened and shrunk, the reduced iron molded product having a high melting
point is not softened, and secures a gas permeation channel ensuring permeation of
the hot air to the central portion of the blast furnace 1.
[0058] The reduced iron molded product has a high melting point, but by a carburization
reaction from carbon monoxide in the reducing gas and/or carbon in the coke, the melting
point becomes lower, whereby the reduced iron molded product becomes molten iron in
a temperature range of about 1,500 °C in a lower portion of the cohesive zone D. Even
at this point in time, the SiO
2 of the slag components contained in the reduced iron molded product are present in
a solid state, resulting in a state of high viscosity due to a state of solid/liquid
co-presence with the molten iron from the reduced iron molded product which had melted
earlier, whereby the melting down stagnates. Here, in a case of the reduced iron molded
product having high basicity, the CaO reacts with the SiO
2 to form a calcium silicate melt, thereby resolving the solid/liquid co-presence and
thus promoting the melting down. Also in the case of the reduced iron molded product
having low basicity, i.e., containing SiO
2 in a high amount, the SiO
2 supplied from the reduced iron molded product reacts with the CaO supplied from the
iron ore pellets having a high basicity, i.e., containing CaO in a high amount, to
generate a calcium silicate melt, thereby resolving the solid/liquid co-presence and
promoting the melting down of the reduced iron molded product.
[0059] The molten iron F obtained by melting the reduced iron is accumulated on a hearth
portion, and a molten slag G is accumulated on the molten iron F. The molten iron
F and the molten slag G can be tapped from the taphole 1b.
[0060] The auxiliary reductant to be injected from the tuyere 1a is exemplified by: finely
pulverized coal obtained by finely pulverizing coal to have a grain size of about
50 µm; heavy oil; natural gas; and the like. The auxiliary reductant serves as a heat
source, a reduction agent, and a recarburizing agent. In other words, of the roles
played by the coke 21, the roles other than that of the spacer are substituted by
the auxiliary reductant.
Advantages
[0061] In the method for producing pig iron, the first layer 10 containing the iron ore
material 11 contains, as an aggregate 12, the reduced iron molded product obtained
through compression molding of reduced iron. Since the reduced iron molded product
facilitates permeation of hot air during softening and fusing of the first layer 10
in the reducing/melting step S2, the method for producing pig iron can decrease the
amount of the coke for ensuring gas permeability. Furthermore, since the method for
producing pig iron uses the reduced iron molded product in which the average basicity
is less than or equal to 0.5, the reduced iron molded product can be obtained at relatively
low cost. Moreover, since the method for producing pig iron uses, as the principal
material, the iron ore pellets in which the average basicity is greater than or equal
to 0.9, an increase in viscosity can be inhibited when the reduced iron molded product,
having the low basicity, has melted, thereby promoting melting down. Thus, gas permeability
in mainly the cohesive zone D can be improved, and furthermore, the amount of the
coke used can be decreased. Consequently, using the method for producing pig iron
enables the amount of the coke used to be decreased while maintaining stable operation
of the blast furnace 1.
Other Embodiments
[0062] The present invention is not in any way limited to the above-described embodiments.
[0063] In the above-described embodiment, the case was described in which it was assumed
that the iron ore material of all of the first layers charged contains the iron ore
pellets as the principal material, the average basicity of the reduced iron molded
product is less than or equal to 0.5, and the average basicity of the iron ore pellets
is greater than or equal to 0.9; however, the present invention also includes a configuration
in which the iron ore material of at least one of the first layers contains the iron
ore pellets as a principal material, the average basicity of the reduced iron molded
product is less than or equal to 0.5, and the average basicity of the iron ore pellets
is greater than or equal to 0.9. However, of total first layers, the first layer having
the above-described configuration preferably account for greater than or equal to
90%, more preferably account for greater than or equal to 95%, and still more preferably
account for 100%, i.e., it is still more preferable that the all layers of the first
layers have the above-described configuration.
[0064] In the above-described embodiment, the case was described in which the method for
producing pig iron of the present invention includes only the charging step and the
reducing/melting step; however, the method for producing pig iron may include other
step(s).
[0065] For example, the method for producing pig iron may include a step of charging, into
the central portion of the blast furnace, a mixture of coke and a reduced iron molded
product. In this case, in the reduced iron molded product in the mixture, it is preferred
that a proportion of the reduced iron molded product having a grain size of greater
than or equal to 5 mm is greater than or equal to 90% by mass, and a content of the
reduced iron molded product in the mixture is less than or equal to 75% by mass. When
hot air reaches the central portion of the blast furnace, the hot air goes up in the
central portion. By thus including, in the central portion, the reduced iron molded
product of a large grain size at a content being less than or equal to the upper limit,
the sensible heat can be effectively used without disturbing the flow of the hot air.
Consequently, a further decrease in the amount of the coke used is enabled. Here,
the "central portion" of the blast furnace refers to a region at a distance of less
than or equal to 0.2 Z from the center, Z being a radius of a furnace throat portion.
[0066] Furthermore, the method for producing pig iron may include a step of finely pulverizing
powder derived from the reduced iron molded product and coal. In this case, it is
preferred that the fine powder obtained by the fine pulverizing step is included as
the auxiliary reductant. A part of the reduced iron molded product is pulverized into
powder due to a conveying process and the like. Such powder lowers gas permeability
in the blast furnace, and is not appropriate for use in the first layer. In addition,
the powder has a large specific surface area, and is thus re-oxidized into iron oxide.
Injecting the auxiliary reductant containing the iron oxide from the tuyere enables
improvement of gas permeability. Consequently, by finely pulverizing powder derived
from the reduced iron molded product together with coal and using fine powder obtained
by finely pulverizing the powder and the coal as the auxiliary reductant to be injected
from the tuyere, the reduced iron molded product can be effectively used and gas permeability
in the blast furnace can be improved.
[0067] Although the case of employing the bell-armor type as the charging step according
to the above-described embodiment has been described, other types may also be employed.
The other types include a bell-less type. With the bell-less type, charging can be
carried out by using a swivel chute and adjusting the angle thereof.
[EXAMPLES]
[0068] Hereinafter, the embodiments of the present invention will be explained in detail
by way of Examples; however, the present invention is not limited to these Examples.
[0069] An effect of the basicity of the iron ore pellets on gas permeability was studied
by conducting a large-scale reduction under load test simulating the peripheral portion
of the blast furnace.
[0070] FIG. 5 illustrates a furnace for a large-scale reduction under load test 7 used in
this experiment. A graphite crucible 71 to be filled with a sample was configured
to have an inner diameter of 75 mm. A sample-packed bed 72 was constituted of, from
the top, an upper coke layer 72a (20 mm in height), an iron ore layer 72b (110 mm
in height), and a lower coke layer 72c (40 mm in height). The iron ore layer 72b corresponds
to the first layer 10 of the present invention, and the upper coke layer 72a and the
lower coke layer 72c correspond to the second layer 20.
[0071] The iron ore layer 72b was configured with a mixture of the reduced iron molded product
(HBI) and the iron ore material. It is to be noted that in the iron ore layer 72b,
the total iron content (T. Fe) was configured to be constant.
[0072] Chemical characteristics of the HBI used are shown in Table 1. The average basicity
of the HBI was 0.46. A charged rate of the HBI was 250 kg per 1 ton of pig iron.
Table 1
Contents |
Metallization Degree |
Basicity CIS |
T. Fe [% by mass] |
FeO [% by mass] |
M.Fe [% by mass] |
SiO2 [% by mass] |
CaO [% by mass] |
Al2O3 [% by mass] |
MgO [% by mass] |
[% by mass] |
(-) |
92.02 |
4.66 |
85.50 |
1.97 |
0.91 |
0.80 |
0.05 |
92.9 |
0.46 |
[0073] As the iron ore material, the following three types were prepared: (1) iron ore pellets
having an average basicity of 0.04 (SiO
2 content: 5.44% by mass; MgO content: 0.54% by mass); (2) iron ore pellets having
an average basicity of 1.20 (SiO
2 content: 4.23% by mass; MgO content: 2.11% by mass; and (3) self-fluxing sintered
iron ore having an average basicity of 2.10 (SiO
2 content: 5.40% by mass; MgO content: 1.00% by mass).
[0074] While heating each sample-packed bed 72 using the iron ore materials of the above-described
(1) to (3) with a temperature profile shown in FIG. 6 by using an electric furnace
73, gas (reducing gas) of a composition shown in FIG. 7 was supplied thereto. The
gas was supplied from a gas supply pipe 74 provided in a lower portion of the furnace
for a large-scale reduction under load test 7, and discharged from a gas discharge
pipe 75 provided in an upper portion. A total feed rate of the gas was 40 NL/min,
and temperature control was carried out by two thermocouples 76. In addition, a load
applied to the sample-packed bed 72 was 1 kgf/cm
2. The load was applied by applying a weight of a weight 78 via a loading rod 77.
[0075] A pressure loss of the sample-packed bed 72 was continuously measured under the above-described
conditions, and a time-integrated value (S value) of the pressure loss was calculated.
The S value can be used as an indicator for evaluating softening and melting behavior
of the iron ore layer 72b, and it is considered that the S value being lower indicates
higher gas permeability. The results are shown in FIG. 8.
[0076] From the results of FIG. 8, the S values are in the order of: the iron ore pellets
having the average basicity of 1.20, the iron ore pellets having the average basicity
of 0.04, and the self-fluxing sintered iron ore having the average basicity of 2.10,
whereby it is revealed that by using the iron ore pellets having the average basicity
of greater than or equal to 0.9 as the iron ore material, the gas permeability is
improved.
[0077] The average basicity (being CaO amount/SiO
2 amount) determined from the CaO amount and the SiO
2 amount calculated based on the above-described formulae 2 was: (1) 0.10 in the case
of using the iron ore pellets having the average basicity of 0.04; and (2) 1.13 in
the case of using the iron ore pellets having the average basicity of 1.20. The critical
basicity of the HBI used was 0.88, and it can be deemed that by setting the basicity
determined from the CaO amount and the SiO
2 amount calculated based on the above-described formulae 2 to greater than or equal
to the critical basicity of the HBI, i.e., by satisfying the above-described inequality
1, the gas permeability is improved.
[INDUSTRIAL APPLICABILITY]
[0078] Using the method for producing pig iron according to the present invention enables
a decrease in the amount of the coke used while maintaining stable operation of the
blast furnace.
[Explanation of the Reference Symbols]
[0079]
1 Blast furnace
1a Tuyere
1b Taphole
2 Raw material charging device
2a Bell cup
2b Lower bell
2c Armor
10 First layer
11 Iron ore material
12 Aggregate
13 Drip slag
20 Second layer
21 Coke
7 Furnace for large-scale reduction under load test
71 Graphite crucible
72 Sample-packed bed
72a Upper coke layer
72b Iron ore layer
72c Lower coke layer
73 Electric furnace
74 Gas supply pipe
75 Gas discharge pipe
76 Thermocouple
77 Loading rod
78 Weight
A Raceway
B Deadman
C Dripping zone
D Cohesive zone
E Lumpy zone
F Molten iron
G Molten slag