DESCRIPTION
UNFIRED CARBON-CONTAINING AGGLOMERATE FOR BLAST FURNACES AND PRODUCTION METHOD THEREFOR
TECHNICAL FIELD
[0001]
The present invention relates to unfired carbon-containing agglomerates (cold-bonded carbon composite agglomerates) for blast furnaces, and particularly the present invention relates to cold-bonded carbon composite agglomerates (iron ore agglomerates) which are capable of lowering the melting point of a slag at a lower part of a blast furnace so as to reduce a reducing agent rate in the blast furnace.
The present application claims priority on Japanese Patent Application No. 2009-191966, filed on August 21, 2009, the content of which is incorporated herein by reference.
BACKGROUND ART
[0002]
Conventionally, various kinds of iron-containing dusts and carbon-containing dusts which are collected from various dust collectors in ironworks are blended, a cement-based hydraulic binder is added thereto, and the mixture is kneaded and molded to manufacture cold-bonded agglomerates having diameters in a range of 8 to 16 mm which are used as a raw material for a blast furnace.
[0003]
As a method for manufacturing cold-bonded carbon composite agglomerates, a
method has been known in which iron-making dust is granulated in pellets and the pellets are then cured and hardened. In the process in which the iron-making dust is granulated in the pellets, the particle size distribution of the dust is adjusted within an appropriate range, then a binder such as burnt lime, cement, or the like and 5 to 15% of water are added thereto, and the mixture is granulated by a disc pelletizer or the like to obtain the pellets.
[0004]
In the process of manufacturing such cold-bonded carbon composite agglomerates, it has been required to increase the carbon content (T. C) in the cold-bonded carbon composite agglomerates for the purpose of reducing the reducing agent rate in a blast furnace operation.
[0005]
For example, according to Patent Document 1, an iron oxide-containing raw material and a carbon-based carbon material (carbonaceous material) are blended, a binder is added thereto, and the mixture is kneaded, molded, and cured to manufacture cold-bonded carbon composite agglomerates. The cold-bonded carbon composite agglomerates contains carbon, and the carbon content is 80 to 120% of the theoretical carbon amount required for reducing iron oxide included in the iron oxide-containing raw material to obtain metal iron. In addition, the binder is selected such that the crushing strength at normal temperature becomes 7850 kN/m2 or more, and then kneading, molding, and curing are performed. Since a reduction reaction occurs due to carbon mixed in the iron oxide within the cold-bonded carbon composite agglomerates, it is possible to improve the reduction rate.
[0006]
However, according to this manufacturing method, the carbon content is limited
to secure the strength, and it is not possible to achieve a sufficient effect of reducing the reducing agent rate in the blast furnace. In the case where a large amount of these cold-bonded carbon composite agglomerates are used in the blast furnace in order to sufficiently achieve the effect that the reducing agent rate is reduced, a heat absorption amount due to a dehydration reaction of the binder in the blast furnace becomes large. Thus, there is a disadvantage in that a low-temperature thermal reserve zone is formed, which promotes disintegration of sintered ores (iron ore sinter) during reduction.
In addition, since large amounts of burnt lime and CaO-based cement are used as the binder, the CaO content in the cold-bonded carbon composite agglomerates becomes large. Therefore, the viscosity of a melt generated from the cold-bonded carbon composite agglomerates becomes excessively high in the course of the reaction. This inhibits aggregation and dripping of the formed metal. Due to the above reasons, there is a disadvantage in that air permeability and liquid permeability of the lower part of the blast furnace are degraded.
[0007]
For example, if the cold-bonded carbon composite agglomerates are melted and dripped at low temperatures, the cold-bonded carbon composite agglomerates are melted in an early stage in a vertical furnace and easily flow down in the gaps of raw materials filled in the furnace. In such a case, a contact period with cokes becomes longer. As a result, it is possible to promote a reduction reaction of fine iron ores within the cold-bonded carbon composite agglomerates and a carburizing reaction of generated iron.
[0008]
According to Patent Document 2, attention has been focused on the fact that even when SiO2 and Al2O3 are concentrated in the surface of fine iron ores, it is possible to lower the melting temperature of the fine iron ores by coating the iron ores with CaCO3.
Then, based on the point of this focus, cold-bonded carbon composite agglomerates in which fine iron ores and flux are combined via coals have been proposed.
[0009]
Here, Patent Document 2 discloses carbon composite agglomerates which contain 23.3 to 24.6% by mass of coals, and the carbon content of the coals is generally about 70%, and the remainder consists of ash and volatile matter. Accordingly, the carbon content in the carbon composite agglomerates corresponds to 16 to 17% by mass.
[0010]
On the other hand, many reports have been proposed concerning a relationship between dripping properties and the constituents of the sintered ores.
For example, Non-Patent Document 1 reports that a dripping temperature of the sintered ores varies in a non-linear manner with respect to a ratio of CaO/SiO2, that the dripping temperature reaches to the lowest value at the ratio of CaO/SiO2 is around 1.0, and that the dripping temperature is lowered when a MgO content is increased.
[0011]
In addition, Non-Patent Document 2 reports that the airflow resistance at high temperatures is lowered in the case where 2% of MgO is added to cement-bonded pellets containing 7% of carbon.
[0012]
As described above, it has been known that the ratio of CaO/SiO2 and the MgO content as gangue mineral compositions are optimized in order to enhance metal dripping properties of the sintered ores and dust pallets having a carbon content of less than 10%. However, it have not been known about a metal dripping property of carbon composite agglomerates having a high carbon content (18 to 25% by mass) whose reduction behavior is completely different and adequate conditions of a slag melting point in the lower part of
the furnace which determines the metal dripping property.
[0013]
Thus, the present inventors examined reduction properties of carbon composite agglomerates (total C content of 20%, total Fe content of 40%, 11% of CaO, 6% of SiO, 2.5% of A12O3, and 0.5% of MgO) with a high carbon content. FIG. 8 shows relationships between temperature and reduction rates for conventional sintered ores (total Fe content of 58.5%, 8% of FeO, 10% of CaO, 5% of SiO2,1.7% of Al2O3, and 1.0% of MgO) and carbon composite agglomerates having a high carbon content. Referring to FIG. 8, it can be understood that the reduction progresses significantly in a low temperature area in the carbon composite agglomerates as compared with the conventional sintered ore. This is an important feature of the carbon composite agglomerates having a high carbon content.
[0014]
Next, a variation in a slag melting point (CaO-SiO2-AhOs-MgO-FeO) due to a progress of the reduction was simulated by a computer with the use of the reduction rate in FIG. 8 which was obtained from a result of the above reduction test. Here, the slag melting point was calculated from the reduction rate on the assumption that all unreduced iron was present as FeO among iron constituents in the sintered ores and the carbon composite agglomerates. The results are shown in FIG. 9. Here, the melting point means the temperature at which all constituents become liquid phases, and the melt is still generated even at a temperature of the melting point or lower. However, since the melt amount becomes smaller when the melting point is higher, the melting point represents the melt amount in an indirect manner.
[0015]
Referring to FIG. 9, the slag melting point of the sintered ores is substantially
equal to the sample temperature in a range of 1200 to 1400°C, and it is considered that a large amount of a melt is generated in this temperature region. On the other hand, the slag melting point of the carbon composite agglomerates significantly rises from about 900°C and reaches 1600°C or higher. Accordingly, it is considered that a reduction proceeds in a state in which the melt amount is extremely small in the carbon composite agglomerates having a high carbon content. For this reason, a solid phase is constantly present; and therefore, aggregation of the metal is inhibited, which results in degradation of dripping. Among the above five component system (CaO-SiO2-Al2O3-MgO-FeO), the influence of FeO on the melting point is extremely large in the carbon composite agglomerates having a high carbon content, and the reduction rapidly proceeds at low temperatures. The result shown in FIG. 9 is a phenomenon unique to the carbon composite agglomerates having a high carbon content.
[0016]
As described above, the reduction of the carbon composite agglomerates having a high carbon content significantly proceeds in a low temperature region as compared with the sintered ore, and the reduction proceeds in a state in which the melt amount is extremely small. Therefore, knowledge about the dripping properties in the reduction progress of the sintered ores reduction cannot be applied directly to the case of the carbon composite agglomerates with high carbon content.
[0017]
If the slag melting point is high when the carbon composite agglomerates are used in the blast furnace, a lower surface of a cohesive zone is lowered, and a lower dripping zone area is narrowed. In addition, slag hold-up amounts in a dripping zone and a deadman are increased. Specifically, the melt does not flow smoothly in the dripping zone and the deadman (zone in which metals and slags are separated due to the specific
gravities and flow down into a hearth), and the melt remains in a gap part (flow path). For this reason, gas flow becomes one-sided, and uniform gas heating cannot be attained. Therefore, a less-heated part is locally generated, and it becomes difficult to operate with stable air permeability in the furnace part.
PRIOR ART DOCUMENT Patent Document
[0018]
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2003-342646
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2005-325412 Non-Patent Document
[0019]
Non-Patent Document 1: ISIJ International 44 (2004), p. 2057
Non-Patent Document 2: Iron and Steel, 70 (1984), p. 825
DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
[0020]
According to the present invention, constituent conditions of the carbon composite agglomerates having an optimal slag melting point for the use in the blast furnace are specified. Then, based on the research results, the present invention aims to provide cold-bonded carbon composite agglomerates which enable to reduce a reducing agent rate in a blast furnace by lowering a slag melting point, and a method for
manufacturing the same.
Means for Solving the Problems
[0021]
The present inventors found that it was possible to reduce a slag melting point in a lower part of a furnace by setting a ratio of CaO/SiO2 as gangue mineral constituents in the carbon composite agglomerates to be in a specific range (1.0 to 2.0) and found cold-bonded carbon composite agglomerates capable of achieving an excellent metal dripping property. The inventors also found that it is preferable to adjust blending amounts of an iron ores having a high SiO2 content and a MgO-containing fluxing material, as will be described later, in order to set the ratio of CaO/SiO2 as gangue mineral constituents in the cold-bonded carbon composite agglomerates to be in a range of 1.0 to 2.0.
[0022]
Cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment of the present invention is manufactured by mixing and kneading iron-containing raw materials, carbon-containing raw materials, and a binder, molding a kneaded substance to obtain a molded body, and then curing the molded body, wherein a carbon content (T. C) is in a range of 18 to 25% by mass, and a ratio of CaO/SiO2 between a CaO content (% by mass) and a SiO2 content (% by mass) as gangue mineral constituents is in a range of 1.0 to 2.0.
In the cold-bonded carbon composite agglomerates for blast furnaces according to the embodiment of the present invention, a gangue amount ((CaO + SiO2 + Al2O3 + MgO)/(100 - carbon content (T. C))) represented by the CaO content (% by mass), the SiO2 content (% by mass), an Al2O3 content (% by mass), a MgO content (% by mass),
and the carbon content (T. C) (% by mass) in the cold-bonded carbon composite agglomerates may be in a range of 0.25 or less, and the MgO content may be in a range of 0.5% by mass or more.
A content of the binder may be in a range of 5 to 10% by mass.
[0023]
A method for manufacturing cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment of the present invention includes: forming a molded body by mixing and kneading iron-containing raw materials, carbon-containing raw materials, and a binder and molding a kneaded substance to obtain the molded body; and obtaining cold-bonded carbon composite agglomerates by subsequently curing the molded body, wherein one or more blending conditions selected from a group consisting of an iron ore brand and a binder blending amount are adjusted in the forming of the molded body such that a carbon content (T. C) becomes in a range of 18 to 25% by mass and a ratio of CaO/SiO2 between a CaO content (% by mass) and a SiO2 content (% by mass) as gangue mineral constituents becomes in a range of 1.0 to 2.0 in the cold-bonded carbon composite agglomerates.
In the method for manufacturing cold-bonded carbon composite agglomerates for blast furnaces according to the embodiment of the present invention, the blending condition may be adjusted in the forming of the molded body such that a gangue amount ((CaO + SiO2 + A12O3 + MgO)/(100 - carbon content (T. C))) represented by the CaO content (% by mass), the SiO2 content (% by mass), an Al2O3 content (% by mass), a MgO content (% by mass), and the carbon content (T. C) (% by mass) becomes in a range of 0.25 or less, and the MgO content becomes in a range of 0.5% by mass or more in the cold-bonded carbon composite agglomerates.
A binder blending amount may be adjusted within a range of 5 to 10% by mass.
In the forming of the molded body, either one or both of fluxing material and iron ores having a high SiO2 content may be further blended, and the fluxing material may be selected from the group consisting of silica stone, serpentine, peridotite, dolomite, nickel slag, magnesite, and brucite, and the blending amounts of the fluxing material and the iron ores having a high SiO2 content may be adjusted such that the carbon content (T. C) becomes in a range of 18 to 25% by mass and the ratio of CaO/SiO2 between the CaO content and the SiO2 content becomes in a range of 1.0 to 2.0 in the cold-bonded carbon composite agglomerates.
Effects of the Invention
[0024]
The cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment of the present invention contains a sufficient carbon content in order to enhance not only a reduced rate of the cold-bonded carbon composite agglomerates but also reduced rates of main iron-containing raw materials for blast furnaces such as sintered ores and the like. Moreover, it is possible to suppress the slag melting point to be lower in an operation of the blast furnace as compared with a conventional case and achieve an excellent property of slag formed during reduction (metal dripping property).
Therefore, it is possible to realize satisfactory air permeability in the lower part of the furnace in the operation of the blast furnace if the cold-bonded carbon composite agglomerates according to the embodiment of the present invention are used as a part of the iron-containing raw materials for the blast furnace. In addition, it is possible to greatly reduce the reducing agent rate (cokes ratio).
[0025]
Since a non-sintering (non-firing) process is applied to the method for
manufacturing the cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment of the present invention, it is possible to save energy and reduce CO2 as compared with a sintering (firing) process. In addition, it is possible to recycle dusts generated in the iron-making process as iron-containing raw materials and carbon materials (carbonaceous material) by a relatively inexpensive and simple method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026]
FIG. 1 is diagram showing a relationship between a binder (cement) blending amount (and a ratio of CaO/SiO2) and cold crushing strength.
FIG. 2 is a diagram showing relationships between a ratio of CaO/SiO2 and slag melting points of sintered ores and cold-bonded carbon composite agglomerates in the case where a MgO content is 1.5%.
FIG. 3 is a diagram showing relationships between a MgO content and slag melting points of sintered ores and cold-bonded carbon composite agglomerates in the case where a ratio of CaO/SiO2 is 1.5.
FIG. 4 is a diagram showing relationship between a ratio of CaO/SiO2 and metal dripping rates of cold-bonded carbon composite agglomerates and sintered ore.
FIG. 5 is a diagram showing relationships between a MgO content and metal dripping rates of cold-bonded carbon composite agglomerates and sintered ore.
FIG. 6 is a diagram showing relationships between a gangue amount (CaO+SiO2+MgO+Al2O3) / (100-T.C) and a metal dripping rate.
FIG. 7 is a diagram showing a relationship between a carbon content (T. C) and a metal dripping rate of cold-bonded carbon composite agglomerates.
FIG. 8 is a diagram showing relationships between a temperature and reduction
rates of conventional sintered ores and cold-bonded carbon composite agglomerates having a high carbon content.
FIG. 9 is a diagram showing relationships between a temperature and calculated values of slag melting points of conventional sintered ores and cold-bonded carbon composite agglomerates with high carbon content.
BEST MODE FOR CARRYING OUT THE INVENTION
[0027]
Cold-bonded carbon composite agglomerates for blast furnaces according to the present embodiment is manufactured by a method in which iron-containing raw materials, carbon-containing raw materials, and a binder are mixed and kneaded, a kneaded substance is molded to obtain a molded body, and the molded body is then cured. The carbon content (T. C) is in a range of 18 to 25% by mass, and a ratio of CaO/SiO2 of the gangue mineral constituents is in a range of 1.0 to 2.0. Thereby, an optimal slag melting point for use in the blast furnace can be obtained.
[0028]
In the embodiment, the carbon content (T. C) of the cold-bonded carbon composite agglomerates is in a range of 18 to 25% by mass, and preferably in a range of 20 to 23% by mass.
In the case where the carbon content is less than 18%, an effect of reducing the reducing agent rate is lowered even if the amount of the gangue mineral constituents are adjusted. In the case where the carbon content exceeds 25% by mass, it is not possible to maintain the minimum cold crushing strength necessary to be used for the blast furnace.
[0029]
The ratio of CaO/SiO2 (also referred to as a basicity) between a CaO content (%
by mass) and a SiO content (% by mass) as gangue mineral constituents of the cold-bonded carbon composite agglomerates is in a range of 1.0 to 2.0, and preferably in a range of 1.4 to 1.7.
By setting the ratio of CaO/SiO2 to a small value within a range of 1.0 to 2.0, it is possible to enhance the metal dripping rate. In the case where the ratio of CaO/SiO2 exceeds 2.0, the metal dripping rate becomes less than 50%. In the case where the ratio of CaO/SiO2 is less than 1.0, an effect that the metal dripping rate is enhanced is saturated.
[0030]
In this embodiment, the gangue amount is preferably in a range of 0.25 or less, and more preferably in a range of 0.22 to 0.25. Here, the gangue amount is a value calculated by the following equation.
Gangue amount = (CaO + SiO2 + Al2O3 + MgO)/(100 - carbon content (T. C))
Here, CaO, SiO2, Al2O3, and MgO in the equation respectively represent a CaO content (% by mass), a SiO2 content (% by mass), an Al2O3 content (% by mass), and a MgO content (% by mass) in the cold-bonded carbon composite agglomerates.
By setting the gangue amount to be in a range of 0.25 or less, it is possible to reduce the slag amount and further enhance the dripping property.
[0031]
The MgO content is preferably in a range of 0.5% by mass or more, and more preferably in a range of 0.6 to 2.0% by mass. Thereby, the melting point of a low FeO slag (slag having a low FeO content) is lowered by MgO, and it is possible to further enhance the metal dripping property.
[0032]
The method for manufacturing cold-bonded carbon composite agglomerates for blast furnaces according to the present embodiment includes: a step of forming a molded
body in which iron-containing raw materials, carbon-containing raw materials, and a binder are mixed and kneaded, and a kneaded substance is molded to obtain the molded body; and a step of subsequently curing the molded body to obtain cold-bonded carbon composite agglomerates. In the forming of the molded body, either one or both of ore brand and a binder blending amount are adjusted such that a carbon content (T. C) of the cold-bonded carbon composite agglomerates becomes in a range of 18 to 25% by mass and a ratio of CaO/SiO2 between a CaO content (% by mass) and a SiO2 content (% by mass) as gangue mineral constituents is in a range of 1.0 to 2.0.
[0033]
As the iron-containing raw materials used in this embodiment, a sinter dust generated in an iron-making process, an iron-containing dust such as a blast furnace dust, a pellet feed having smaller particle sizes than those of the fine iron ores for sintering, fine iron ores produced by fracturing and/or granulating fine iron ores for sintering are exemplified.
The contents of iron and gangue mineral constituents such as SiO2 and the like are completely different depending on the ore brand to be used. Accordingly, it is possible to adjust a ratio of CaO/SiO2 by selecting the ore brand to be used. Particularly, the ratio of CaO/SiO2 is greatly influenced by a blending amount of iron ores having a high SiO2 content.
As the ore brand used in the embodiment, Indian High Siliceous, Robe River, Yandicoogina, Rio Doce (Itabira), Marra Mamba, and the like are exemplified.
[0034]
As the carbon-containing raw materials used in the embodiment, a blast furnace primary dust, a coke dust, fine cokes, anthracite, and the like are exemplified.
[0035]
As the binder used in the embodiment, an aging binder including fine powder containing granulated blast furnace slag as a main constituent and an alkali stimulant, which is generally used, burnt lime, portland cement, bentonite, and the like are exemplified. The blending amount (additive amount) of the binder can be appropriately determined in consideration of other blending conditions and the like. In the case where the blending amount of the binder is excessively small, it is difficult to sufficiently maintain a cold rolling strength of the cold-bonded carbon composite agglomerates. In addition, in the case where the blending amount of the binder is excessively large, the slag amount in the cold-bonded carbon composite agglomerates is increased, and the air permeability of the lower part of a furnace becomes unstable. Thereby, it is not possible to stably obtain an effect of reducing the reducing agent rate.
[0036]
Thus, the cold strength of the cold-bonded carbon composite agglomerates in which a ratio of CaO/SiO2 was varied by adjusting the binder blending amount was examined. The obtained results are shown in Table 1 and FIG. 1.
[0037]
Table 1
(Table Removed)
[0038]
The cold strength was lowered as the binder (cement) blending amount was decreased (CaO/SiO2 was lowered). In addition, in the case where the ratio of CaO/SiO2 was less than 1.0 (the binder (cement) blending amount was less than 5% by mass), it was difficult to maintain the cold crushing strength of 100 kg/cm2. In the case where the cold crushing strength of the cold-bonded carbon composite agglomerates becomes less than 100 kg/cm2, a change of the cold-bonded carbon composite agglomerates into powder may occur in some cases during transportation and charge into the blast furnace. In order to maintain the cold crushing strength at equal to or more than 100 kg/cm2, the binder (cement) blending amount is preferably set to be in a range of 5% by mass or more. In addition, in the case where the binder (cement) blending amount exceeds 10% by mass, an increase in the gangue amount may occur in some cases. For this reason, the binder (cement) blending amount is preferably set to be in a range of 10% by mass or less. Accordingly, it is preferable that the binder blending amount be in a range of 5 to 10% by mass.
[0039]
Here, free water is taken into hydrates in the carbon composite agglomerates agglomerates due to a hydration reaction of the cement during the curing from among the manufacturing processes including mixing, kneading, molding, and curing. Although the total blending amount of the raw materials is slightly varied over the manufacturing processes for the above reason, the variation amount is extremely small, and it is possible to consider that the total blending amount is hardly changed. Therefore, for example, the binder blending amount is substantially the same as the binder content in the manufactured cold-bonded carbon composite agglomerates. The same is true for the other constituents, and the blending amounts thereof during the manufacturing processes are substantially the same as the contents in the cold-bonded carbon composite agglomerates.
Accordingly, the binder content in the cold-bonded carbon composite agglomerates of the embodiment is preferably in a range of 5 to 10% by mass; and thereby, it is possible to achieve the cold crushing strength of 100 kg/cm2 or more as described above.
[0040]
In the embodiment, it is preferable that fluxing materials and iron ores having a high SiO2 content are further blended. Thereby, it is possible to more precisely adjust the constituent contents. Particularly, it is possible to adjust the ratio of CaO/SiO2 regardless of the binder amount.
As the fluxing materials, silica stone containing SiO2 as a main constituent, serpentine containing MgO as a main constituent, peridotite, dolomite, nickel slag, magnesite, brucite, and the like are exemplified. In addition, the iron ores having a high SiO2 content is ores having a SiO2 content of 3.5% by mass or more.
[0041]
Generally, when chemical constituents of the target cold-bonded carbon composite agglomerates are defined, the blending amounts of the fluxing materials and the iron ores having a high SiO2 content are automatically determined. Accordingly, the blending amounts of the fluxing materials and the iron ores having a high SiO2 content are not particularly limited and appropriately determined in accordance with the chemical constituents of the cold-bonded carbon composite agglomerates.
[0042]
Next, a method of adjusting the ratio of CaO/SiO2, the MgO content, and the gangue amount will be described in more detail.
The ratio of CaO/SiO2 is determined in accordance with the CaO amount and the SiO2 amount contained in the raw materials to be blended.
[0043]
CaO is contained mainly in the binder, a blast furnace primary dust used as a carbon-containing raw material, a sinter dust, a converter dust, and the like used as iron-containing raw materials, and it is possible to adjust the CaO content by appropriately adjusting the blending amounts thereof. However, in the case where a cement-based binder having a high CaO content is used as a binder, it is necessary to reduce the binder blending amount itself in order to adjust the CaO content such that the ratio of CaO/SiO2 becomes in a range of 1.0 to 2.0. Therefore, it is necessary to consider whether or not sufficient cold crushing strength can be obtained.
[0044]
SiO2 and MgO are mainly contained in the binder, a blast furnace primary dust used as the carbon-containing raw material, a sinter dust used as the iron-containing raw material, ash contained in carbon-based materials, and the like.
In the present embodiment, it is possible to achieve a certain effect regardless of an addition state of SiO2 (a state of raw materials containing SiO2) if the ratio of CaO/SiO2 in the cold-bonded carbon composite agglomerates is in a range of 1.0 to 2.0. In relation to MgO as well, it is also possible to achieve a certain effect regardless of an addition state of MgO (a state of raw materials containing MgO) if the MgO content is in a range of 0.5 % by mass or more.
In the case where the ratio of CaO/SiO2 is reduced or the MgO content is set to be in a range of 0.5% by mass or more in a positive manner, it is preferable to blend fluxing materials such as silica stone, serpentine, peridotite, dolomite, nickel slag, magnesite, brucite, and the like and iron ores having a high SiO2 content. Thereby, it is possible to adjust the ratio of CaO/SiO2 and the MgO content regardless of the binder amount as described above. However, if large amounts of the fluxing materials and the iron ores
having a high SiO2 content are blended, the gangue amount is increased. Therefore, it is preferable to adjust the ratio of CaO/SiO2 and the MgO content such that the gangue amount becomes in a range of 0.25 or less.
[0045]
In the present embodiment, ranges for the carbon content (T. C), the ratio of CaO/SiO2, the gangue amount, and the MgO content are defined as described above. Experimental results showing criticalities of the ranges will be shown below.
The reduction rates at 1400°C of the sintered ores and the cold-bonded carbon composite agglomerates, in which the ratio of CaO/SiO2 is 1.5 and the MgO content is 1.5% were measured. Then, FeO concentrations in the slags were calculated from the obtained reduction rates on the assumption that all unreduced irons were present as FeO in the slags. As a result, it was found that the FeO concentration in the slag was 34% in the case where the sintered ores was used while the FeO concentration was 2% in the case where the cold-bonded carbon composite agglomerates were used. By utilizing the FeO concentrations, a relationship between the slag melting point and either one of the ratio of CaO/SiO2 or the MgO content was examined for the sintered ores and the cold-bonded carbon composite agglomerates. Here, the slag melting points (CaO-SiO2-Al2O3-MgO-FeO) were obtained from a computer simulation.
[0046]
FIG. 2 shows relationships between the ratio of CaO/SiO2 and the slag melting point in the case where the MgO content is 1.5%. FIG. 3 shows relationships between the MgO content and the slag melting point in the case where the ratio of CaO/SiO2 is 1.5.
As can be understood from FIG.2, degrees of influences of the ratio of CaO/SiO2 on the slag melting point are different in the sintered ores and the cold-bonded carbon composite agglomerates. This is caused by a difference in the reduction rates (namely,
the FeO concentrations in the slag) at high temperatures. Specifically, in the sintered ore, the slag melting point is lowered by 278°C in the case where the ratio of CaO/SiO2 is decreased by 1.0. On the other hand, in the cold-bonded carbon composite agglomerates, the slag melting point is lowered by 620°C in the case where the ratio of CaO/SiO2 is decreased by 1.0. Therefore, the influence of the ratio of CaO/SiO2 in the cold-bonded carbon composite agglomerates is twice as large as the influence of the ratio of CaO/SiO2 in the sintered ore;.
[0047]
In the cold-bonded carbon composite agglomerates, the reduction rate at low temperatures is high. In the case where the cold-bonded carbon composite agglomerates having a high carbon content are used, a reduction is rapidly performed in the upper part of the blast furnace as compared with the case where the fired agglomerates having a lower carbon content are used. Therefore, an amount of an unreduced iron constituent (FeO amount) remaining in the slag which is reduced in the upper part and moves to the lower part becomes small. If the FeO amount in the slag is decreased, the slag melting point is raised. As described above, the slag melting point also depends on a basicity (CaO/SiO2). For this reason, it is considered that the slag melting point is greatly varied due to the basicity in the cold-bonded carbon composite agglomerates. In addition, it is considered that the slag melting point becomes extremely high if the basicity in the fired carbon composite agglomerates is high.
[0048]
Referring to FIG. 3, in the sintered ore, the slag melting point is lowered by 50°C in the case where the MgO content is increased by 1.0%. On the other hand, in the cold-bonded carbon composite agglomerates, the slag melting point is lowered by 22°C in
the case where the MgO content is increased by 1.0%. Therefore, the influence of the MgO content in the cold-bonded carbon composite agglomerates is about half of the influence of the MgO content in the sintered ore.
[0049]
However, in a precise sense, a dripping behavior does depend not only on the slag melting point but also on the slag amount and other physical properties of the slag (viscosity, wettability with metal, and the like). . Therefore, the dripping behavior is a complicated phenomenon and is not completely understood even at present. However, it is obvious that a constituent condition for lowering the slag melting point to promote the metal dripping in the sintered ores is different from that in the cold-bonded carbon composite agglomerates.
[0050]
Thus, the dripping properties of the cold-bonded carbon composite agglomerates containing various gangue mineral constituents were examined by an apparatus of softening-melting test under load.
Iron-containing raw materials and carbon-containing raw materials were fractured, and mixed with a binder and fluxing materials, then the mixture was kneaded to obtain a kneaded substance. Then, the kneaded substance was molded, and a molded body was cured for a predetermined period to manufacture the cold-bonded carbon composite agglomerates. The carbon content T. C (total carbon) of the cold-bonded carbon composite agglomerates was set to 20% by mass. In addition, the blending ratios of the iron-containing raw materials and the fluxing materials were adjusted such that the ratio of CaO/SiO2 and the MgO content became predetermined values. The blending amount of the binder (cement) was set to 10% by mass.
Specifically, the gangue amount ((CaO + SiO2 + Al2O3 + MgO)/(100 - carbon
content (T. C))) was set to a constant value of 0.22, the MgO content was set to a constant value of 0.9% by mass, and the blending amounts of the portland cement and the silica stone fine powder were adjusted such that a ratio of CaO/SiO2 became a predetermined value in a range of 0.5 to 2.5. As described above, the cold-bonded carbon composite agglomerates in which the ratios of CaO/SiO2 of the gangue mineral constituents were different from each other within a range of 0.5 to 2.5 were produced.
In addition, the cold-bonded carbon composite agglomerates in which the ratio of CaO/SiO2 was a constant value of 2.0 and the MgO contents were various values were produced.
[0051]
At first, a softening-melting test under load was performed on the cold-bonded carbon composite agglomerates in which the ratio of CaO/SiO2 of the gangue mineral constituents was different from each other within a range from 0.5 to 2.5.
On the assumption of actual usage of the blast furnace, the cold-bonded carbon composite agglomerates were mixed at a ratio of 10% with an ordinary sintered ores (CaO/SiO2 =1.8). In a stage at which heating was performed up to 1600°C and a reduction was conducted, the amount (ratio) of metal dripped from a crucible was measured. Then, the metal dripping rate (%) defined by the following formula was calculated. Metal dripping rate (%) = dripped metal amount/(total amount of charged Fe x 0.95) x 100
In addition, the metal dripping rate was also measured in the same manner for a sample consisting of only the sintered ores as well. In the case where the metal dripping rate of the sintered ores becomes less than 50%, the lower surface of a cohesive zone is lowered, and the lower dripping zone area is narrowed. Therefore, air permeability in the lower part is degraded, and it becomes difficult to perform stable operations.
The obtained results are shown in Table 2 and FIG. 4. [0052]
Table 2
(Table Removed)
[0053]
As can be understood from FIG. 4, in the case where the ratio of CaO/SiO2 of the cold-bonded carbon composite agglomerates is higher, the metal dripping rate is decreased. Particularly, in the case where the ratio of CaO/SiO2 of the cold-bonded carbon composite agglomerates exceeds 2.0, it becomes difficult to maintain the metal dripping rate of 50%. Since indirect reduction proceeds from a low temperature region by using the cold-bonded carbon composite agglomerates, the FeO content in the slag which is present along with metal in a cohesive layer is decreased, and the slag melting point is raised. Generally, an iron melt generated by reduction captures carbon of cokes when falling down to the lower part of the blast furnace, and the carbon content is increased (carburization of metal produced by reduction). It can be considered that aggregation of iron melts after the carburization of metal produced by reduction is prevented due to the increase in the slag melting point; and thereby, the result shown in FIG. 4 is obtained. In the case where the ratio of CaO/SiO2 is less than 1.0, the slag dripping rate is less than 50% regardless of the
fact that the melting point of coexisting slag was sufficiently low. This is because the ratio of SiO2 as a network former is increased; and thereby, the viscosity of the coexisting slag is raised, and the aggregation of the metals is inhibited.
In addition, FIG. 4 also shows a measurement result representing a relationship between the ratio of CaO/SiO2 and the metal dripping rate of the sintered ores having the MgO content of 1.5%. Even in the sintered ore, a tendency can be observed in which the metal dripping rate is decreased as the ratio of CaO/SiO2 is raised. However, the variation is gradual. It is possible to confirm even from the result in FIG. 4 that constituent conditions to be fulfilled for achieving an excellent metal dripping property in the cold-bonded carbon composite agglomerates are different from that in the sintered ore.
As described above, it is necessary that the ratio of CaO/SiO2 be in a range of 1.0 to 2.0 in order to enhance the metal dripping rate. The ratio of CaO/SiO2 is preferably in a range of 1.4 to 1.7; and thereby, it is possible to achieve the metal dripping rate of more than 60%.
[0054]
The softening-melting test under load was performed in the same manner on the cold-bonded carbon composite agglomerates in which the ratio of CaO/SiO2 was 2.0, and the MgO contents were various values. Then, a relationship between the MgO content and the metal dripping rate in the case where the cold-bonded carbon composite agglomerates were mixed at a ratio of 10% with the sintered ores was examined. The obtained results are shown in Table 3 and FIG. 5.
[0055]
Table 3
(Table Removed)
[0056]
As cam be understood from FIG. 5, it is effective to raise the MgO content in the cold-bonded carbon composite agglomerates in order to enhance the metal dripping rate. From the variation in the metal dripping rate in the case where the cold-bonded carbon composite agglomerates having a ratio of CaO/SiO2 of 2.0 is mixed at a ratio of 10% with the sintered ore, it is understood that the metal dripping rate of 50% can be maintained in the case where the MgO content is 0.5% by mass or more. As the MgO content is higher, the metal dripping rate is raised. However, the effect is saturated from about the MgO content of 2.0%. This is because the melting point of the aforementioned low FeO slag (slag having a low FeO content) is lowered due to MgO, and it is possible to more effectively achieve the effect due to MgO under a condition that the ratio of CaO/SiO2 is higher.
Accordingly, it is preferable that the MgO content is in a range of 0.5% by mass or more. The upper limit thereof is not particularly set.
[0057]
In addition, FIG. 5 also shows a measurement result representing a relationship
between the MgO content and the metal dripping rate (%) of the sintered ores in which the ratio of CaO/SiO2 is 2.0. Even in the sintered ore, the tendency can be observed in which the metal dripping rate is raised as the MgO content is raised. However, the variation (influence) is greater than that of the cold-bonded carbon composite agglomerates. It can be confirmed even from the result in FIG. 5 that the constituent conditions to be fulfilled for achieving an excellent metal dripping property in the cold-bonded carbon composite agglomerates are different from those in the sintered ore.
[0058]
In addition, the amount of coexisting slag (gangue amount + unreduced FeO amount) is also an important factor to be fulfilled for achieving the dripping property. Therefore, cold-bonded carbon composite agglomerates were produced in which the ratio of CaO/SiO2 was 1.5, the MgO content was 1.0%, and the gangue amounts were different. Then, the metal dripping rates were measured, and the dripping properties were examined.
As described above, the gangue amounts were calculated by the following equation:
Gangue amount = (CaO + SiO2 + Al2O3 + MgO)/(100 - carbon content (T. C)).
The obtained results are shown in Table 4 and FIG. 6.
[0059]
Table 4
(Table Removed)
[0060]
As described above, the FeO concentration in the slag is already lowered to 2% in a relatively low temperature part; and therefore, the influence of the FeO concentration is small. As a result, regardless of the slag amount, a satisfactory metal dripping property is observed in the case where the gangue amount is 0.25 or less. It is considered that the physical properties of the slag such as a solid phase ratio, viscosity, wettability with metal, and the like are more dominant factors rather than the slag amount, with respect to the metal dripping properties in the case where the gangue amount is in a range of 0.25 or less. However, in the case where the gangue amount exceeded 0.25, the influence of the slag amount cannot be ignored, and the dripping properties are degraded. Moreover, in the case of the gangue amount in this level (more than 0.25), a hearth slag amount is significantly increased when a large amount of cold-bonded carbon composite agglomerates is used in the blast furnace, and slag tapping becomes unstable, which causes a variation in air blow.
Based on the above results, it is preferable that the constituents of the cold-bonded carbon composite agglomerates are adjusted such that the gangue amount ((CaO + SiO2 + MgO + Al2O3)/(100 - TC)) becomes in a range of 0.25 or less.
[0061]
Moreover, an influence of the carbon content (T. C) in the cold-bonded carbon composite agglomerates on the metal dripping rate was examined.
The cold-bonded carbon composite agglomerates were produced by adjusting the blending ratios of raw materials such that the MgO content was constant at 1.0% by mass, the gangue amount was constant at 0.22, the ratio of CaO/SiO2 was 0.5,1.0, 1.5, 2.0, or 2.5, and the carbon content (T. C) was 10, 15, 18, 25, or 30% by mass.
The metal dripping amount (ratio) was measured in the same manner as in the aforementioned method. The obtained results are shown in FIG. 7.
[0062]
Table 5
(Table Removed)
[0063]
Based on the results in FIG. 7, it can be understood that the metal dripping rate is lowered as the carbon content (T. C) is increased. This is because the concentration of FeO in the slag which is present along with metal is decreased as the carbon content (T. C) is increased as described above.
As described above, it is necessary that the metal dripping rate be 50% or more in order to realize a stable operation in the blast furnace. With regard to the case where the ratio of CaO/SiO2 is in a range of 1.0 to 2.0, it can be understood that the metal dripping rate of 50% or more can be achieved when the carbon content (T. C) is in a range of 25% by mass or less. Therefore, it is necessary to set an upper limit of the carbon content (T.
C) to 25% by mass.
[0064]
Although the blending amounts of the constituents and the gangue mineral of the cold-bonded carbon composite agglomerates are adjusted within predetermined ranges, molding methods, shapes, and physical structures (holes, porosities, and the like) are not limited according to the embodiment. It is possible to apply various configurations of cold-bonded carbon composite agglomerates for blast furnaces such as pellets, briquettes, and the like. In addition, various molding methods such as extrusion molding and the like can be applied, and the same effects can be obtained.
[0065]
In the blast furnace, a charged substance moves from the upper part to the lower part, and reduction gas moves from the lower part to the upper part. Thereby, thermal exchange and reaction proceed. Therefore, the blast furnace is a countercurrent reactor. Generally, in sequential operations of the blast furnace, there were cases where reduction fores of the reduction gas was lost in the upper layer of the ore layers and reduction did not sufficiently proceed. Particularly, fired agglomerates do not contain carbons; and therefore, the fired agglomerates do not have a self-reduction ability. As a result, in the case of using the fired agglomerates, the fired agglomerates are not sufficiently reduced in the upper part of the ore layers. In the case where the fired agglomerates move to the lower part of the blast furnace in a state in which the reduction is not completed, reduction occurs in the dripping zone and the deadman of the blast furnace, which results in direct reduction. In such a case, there are problems in that burden on the blast furnace is increased and air permeability is degraded.
On the other hand, if the cold-bonded carbon composite agglomerates of the present embodiment are used, it is possible to greatly enhance the reduction efficiency
particularly in the upper layer of the ore layers since the cold-bonded carbon composite agglomerates of the present embodiment are present along with the iron ores in the blast furnace.
However, with regard to the cold-bonded carbon composite agglomerates having a high carbon content, the basicity (CaO/SiO2), in particular, has a great influence on the slag melting point as described above (FIG. 2). According to the present embodiment, the cirbon content (T. C) and the ratio of CaO/SiO2 are defined based on the aforementioned research results of the inventors. Thereby, a satisfactory metal dripping property is achieved. Therefore, the slag hold-up amounts in the dripping zone and the deadman are decreased, and satisfactory air permeability can be secured.
Moreover, the cold-bonded carbon composite agglomerates of the present embodiment are present along with the iron ores in the blast furnace as described above; and thereby, in particular, it is possible to greatly enhance the reduction efficiency in the upper layer of the ore layers. Since it is possible to greatly enhance the reduction efficiency in the upper layer of the ore layers in which the reduction is difficult to proceed, the reduction efficiency in the entire blast furnace is greatly enhanced. Therefore, it is possible to reduce a larger amount of reduction materials than the amount of cokes which is the same as the excess carbon amount in the cold-bonded carbon composite agglomerates of the present embodiment.
EXAMPLES
[0066]
Fine powdered iron-containing raw materials (fired dust and iron ores) were prepared as the iron-containing raw materials, and carbon materials (carbonaceous materials) (coke dust, coke powder, and blast furnace primary dust) were prepared as the
carbon-containing raw materials. In addition, cement (high early strength portland cement) was prepared as the binder. Moreover, fluxing materials having high SiO2 contents were also used in some examples.
The blending amounts of the raw materials were adjusted such that the blending ratio of the cement (high early strength portland cement) was in a range of 4 to 9% by mass and the blending ratios of the carbon materials (carbonaceous material) and the fine powdered iron-containing raw materials became various values. These raw materials were mixed with water and the mixture was kneaded by an Eirich mixer. The obtained kneaded substance was granulated (molded or shaped) by a Pan pelletizer; and thereby, raw pellets were obtained. Then, the raw pellets were cured in the sun for two weeks; and thereby, the cold-bonded carbon composite agglomerates were produced. Here, the water amount in the raw pellets was adjusted to be in a range of 10 to 14% by mass in accordance with the amount of the blended cement.
[0067]
With regard to the obtained cold-bonded carbon composite agglomerates, the cold crushing strength was measured by the following method based on JISM8718. A compressive load was applied onto one sample at a prescribed pressurizing speed, and a load value when the sample broke was measured. A load value (kg/cm2) per unit cross-sectional area was obtained. Then, an average value of 100 samples was calculated and used as a strength index.
By the aforementioned method, a slag melting point and a metal dripping rate of the cold-bonded carbon composite agglomerates were measured.
In addition, operations of the blast furnace were performed while 50 kg/tp of the cold-bonded carbon composite agglomerates were used as a part of raw materials in the blast furnace having an effective volume of 5500 m3. Then, an upper K value, a lower K
value, a blowing pressure fluctuation, and a reducing agent rate in the operations of the blast furnace were measured, and average values of operation results for about one month were obtained. The results are shown in Table 6. [0068]

Table 6
(Table Removed)
[0069]
Referring to Table 6, in Example 1, the contents of constituents were suitably adjusted, and the ratio of CaO/SiO2 was set to 2.0, and the MgO content was set to 0.6%, and the gangue amount was set to 0.22. In the use in the blast furnace, air permeability in the lower part of the furnace was enhanced, and the reducing agent rate was lowered to 470 kg/tp. Therefore, an effect due to the usage of the cold-bonded carbon composite agglomerates having a high carbon content was exhibited.
[0070]
In Example 2, the fluxing materials having high SiO2 contents were blended to raise the SiO2 content, and the ratio of CaO/SiO2 was further lowered to 1.0. Since the ratio of CaO/SiO2 and the MgO content were in a proper range in Example 2, the slag melting point could be lowered. However, since the gangue amount was increased up to 0.28, the metal dripping property became relatively low, and the reducing agent rate was not significantly lowered.
[0071]
In Example 3, the binder amount was lowered to 4% in order to reduce the gangue amount. Since the contents of chemical constituents were proper, the metal dripping rate was enhanced. However, since the binder amount was small, the cold crushing strength was insufficient at 85 kg/cm2. Therefore, the amount of powder in the furnace was increased when used in the blast furnace; and thereby, the air permeability in the upper part was degraded, and the reducing agent rate was at a slightly high level.
[0072]
In example 4, the contents of chemical constituents were adjusted by blending the fluxing materials without decreasing the binder amount. As a result, it was possible to produce the cold-bonded carbon composite agglomerates having a satisfactory metal
dripping property without deteriorating the cold crushing strength. When used in the blast furnace, the reducing agent rate was lowered to the maximum extent.
[0073]
In Example 5, the ratio of CaO/SiO2 and the gangue amount were in the ranges prescribed according to the present embodiment (CaO/SiO2: 1.0 to 2.0, gangue amount: 0.25 or less); however, the MgO content was set to be 0.4% which was low. Therefore, the metal dripping rate remained at 52%, and the reducing agent rate was reduced; however, the effect of reducing the reducing agent rate was small.
[0074]
On the other hand, in Comparative Example 1, cold-bonded carbon composite agglomerates were produced in which the carbon content (T. C) was 17% by mass that was low, the ratio of CaO/SiO2 was 1.9 that was low, and the MgO content was 1.0% that was high. Since the carbon content (T. C) was low, the slag melting point was sufficiently low, and there was no problem in the dripping property. However, when used in the blast furnace, it was difficult to lower the reducing agent rate because the carbon content was low.
[0075]
In Comparative Example 2, cold-bonded carbon composite agglomerates were produced in which the carbon content (T. C) was raised up to 20% and the ratio of CaO/SiO2 was raised up to 2.2. Since the reduction rate at low temperatures was enhanced, the slag melting point was significantly raised. Moreover, since the ratio of CaO/SiO2 was more than 2.0, the metal dripping property was lowered. However, when used in the blast furnace, the air permeability in the lower part of the furnace was degraded, and a variation in air pressure was remarkably increased. Thereby, the operations became unstable. Therefore, it was not possible to sufficiently obtain the
effect due to the high carbon content, and the reducing agent rate remained at a level of 500 kg/tp.
[0076]
In Comparative Example 3, cold-bonded carbon composite agglomerates were produced which had a high carbon content of 30% that was more than the upper limit of 25% by mass of the prescribed range in the embodiment. Since the contents of the other constituents were in appropriate ranges, the dripping rate was enhanced to 65%. However, the cold strength was 60 kg/cm2 which was low, and it was not possible to obtain a minimum strength necessary for the use in the blast furnace. Therefore, a powder charging amount into the blast furnace was increased, and it became difficult to operate stably for a long period.
[0077]
As described above, it can be understood that the metal dripping property is satisfactory and the reducing agent rate when using in the blast furnace can be lowered in the case where the carbon content (T. C) is set to be in a range of 18 to 25% by mass and the ratio of CaO/SiO2 is set to be in a range of 1.0 to 2.0 in the cold-bonded carbon composite agglomerates. Particularly, in the case where the gangue amount (CaO + SiO1 + Al2O3 + MgO)/(100 - carbon content (T. C)) is in a range of 0.25 or less and the MgO content is in a range of 0.5% by mass or more, the effects can be remarkably observed. In addition, in the case where such constituent adjustment is performed by the addition of the fluxing materials and the binder blending amount is set to be in a range of 5 to 10%, it is also possible to maintain the cold crushing strength.
INDUSTRIAL APPLICABILITY [0078]

The cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment of the present invention has a carbon content sufficient to enhance not only the reduced rate of the cold-bonded carbon composite agglomerates but also the reduced rate of the main iron-containing raw materials for blast furnaces such as sintered ores and the like. Moreover, it is possible to suppress the slag melting point to be lower as compared with a conventional case in the operations of the blast furnace, and an excellent property of slag formed during reduction (metal dripping property).
Therefore, if the cold-bonded carbon composite agglomerates according to an embodiment of the present invention are used as a part of the iron-containing raw materials for the blast furnaces, it is possible to realize satisfactory air permeability in the lower part of the furnace in the operations of the blast furnace, and the reducing agent rate (coke rate) can be greatly reduced.
[0079]
In the method for manufacturing cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment of the present invention, a non-firing process is applied; and therefore, it is possible to save energy and reduce CO2 as compared with a firing process. In addition, it is possible to recycle dust generated in the iron-making process as iron-containing raw materials and carbon materials (carbonaceous material) by a relatively inexpensive and simple method.
Therefore, the embodiment of the present invention can preferably be applied to a technical field relating to the carbon composite agglomerates used in the blast furnaces.

CLAIMS
1. Cold-bonded carbon composite agglomerates for blast furnaces which is
manufactured by mixing and kneading iron-containing raw materials, carbon-containing
raw materials, and a binder, molding a kneaded substance to obtain a molded body, and
then curing the molded body,
wherein a carbon content (T. C) is in a range of 18 to 25% by mass, and a ratio of CaO/SiO2 between a CaO content (% by mass) and a SiO2 content (% by mass) as gangue mineral constituents is in a range of 1.0 to 2.0.
2. The cold-bonded carbon composite agglomerates for blast furnaces according to
Claim 1,
wherein a gangue amount ((CaO + SiO2 + Al2O3 + MgO)/(100 - carbon content (T. C))) represented by the CaO content (% by mass), the SiO2 content (% by mass), an Al2O3 content (% by mass), a MgO content (% by mass), and the carbon content (T. C) (% by mass) in the cold-bonded carbon composite agglomerates is in a range of 0.25 or less, and
the MgO content is in a range of 0.5% by mass or more.
3. The cold-bonded carbon composite agglomerates for blast furnaces according to
Claim 1,
wherein a content of the binder is in a range of 5 to 10% by mass.
4. A method for manufacturing cold-bonded carbon composite agglomerates for blast
furnaces, the method comprising:
forming a molded body by mixing and kneading iron-containing raw materials, carbon-containing raw materials, and a binder and molding a kneaded substance to obtain the molded body; and
obtaining cold-bonded carbon composite agglomerates by subsequently curing the molded body,
wherein one or more blending conditions selected from a group consisting of an iron ore brand and a binder blending amount are adjusted in the forming of the molded body such that a carbon content (T. C) becomes in a range of 18 to 25% by mass and a ratio of CaO/SiO2 between a CaO content (% by mass) and a SiO2 content (% by mass) as gangue mineral constituents becomes in a range of 1.0 to 2.0 in the cold-bonded carbon composite agglomerates.
5. The method for manufacturing cold-bonded carbon composite agglomerates for blast
furnaces according to Claim 4,
wherein the blending condition is adjusted in the forming of the molded body such that a gangue amount ((CaO + SiO2 + Al2O3 + MgO)/(100 - carbon content (T. C))) represented by the CaO content (% by mass), the SiO2 content (% by mass), an Al2O3 content (% by mass), a MgO content (% by mass), and the carbon content (T. C) (% by mass) becomes in a range of 0.25 or less, and the MgO content becomes in a range of 0.5% by mass or more in the cold-bonded carbon composite agglomerates.
6. The method for manufacturing cold-bonded carbon composite agglomerates for blast
furnaces according to Claim 4,
wherein a binder blending amount is adjusted within a range of 5 to 10% by mass.
7. The method for manufacturing cold-bonded carbon composite agglomerates for blast furnaces according to Claim 4,
wherein in the forming of the molded body, either one or both of fluxing material and iron ores having a high SiO2 content are further blended, and the fluxing material is selected from the group consisting of silica stone, serpentine, peridotite, dolomite, nickel slag, magnesite, and brucite, and
the blending amounts of the fluxing material and the iron ores having a high SiO2 content are adjusted such that the carbon content (T. C) becomes in a range of 18 to 25% by mass and the ratio CaO/SiO2 between the CaO content and the SiO2 content becomes in a range of 1.0 to 2.0 in the cold-bonded carbon composite agglomerates.