DESCRIPTION
UNFIRED CARBON-CONTAINING AGGLOMERATE AND PRODUCTION METHOD THEREFOR
TECHNICAL FIELD
[0001]
The present invention relates to unfired carbon-containing agglomerates (cold-bonded carbon composite agglomerates) for blast furnaces which are produced by mixing and molding iron-containing raw materials and carbon-containing raw materials and then curing a molded body. Particularly, the present invention relates to cold-bonded carbon composite agglomerates (iron ore agglomerates) having a carbon content (T. C) in a range of 18 to 25% by mass and a porosity in a range of 20 to 30%.
The present application claims priority on Japanese Patent Application No. 2009-192273, 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 and briquettes which have 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, with regard to the cold-bonded carbon composite agglomerates of Patent Document 1, 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 the cold-bonded carbon composite agglomerates of Patent Document 1 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. Thereby, a low-temperature thermal reserve zone is formed. There is a disadvantage in that disintegration of sintered ores (iron ore sinter) during reduction is facilitated by the low-temperature thermal reserve zone.
[0007]
In Patent Document 2, an attention is paid to a fact that particle sizes and carbon contents of carbon materials (carbonaceous materials) greatly affect hot strength in a reduction temperature area as well as cold strength of the cold-bonded carbon composite agglomerates. From the point of view, Patent Document 2 proposes a method for manufacturing cold-bonded carbon composite agglomerates for blast furnaces having a cold crushing strength of 50 kg/cm2 or more. This manufacturing method includes: adding a hydraulic binder to iron-containing raw material fine powder which contains 40% by mass or more of iron and carbon material (carbonaceous material) fine powder which contains 10% by mass or more of carbon; mixing the mixture while a water content is adjusted; and granulating. In the manufacturing method, the particle sizes of all the raw materials are set to 2 mm or less, the blending ratio of the carbon material (carbonaceous material) fine powder is adjusted such that the contained carbon ratio (T. C) in all of the raw materials becomes in a range of 15 to 25% by mass, and the median size of the carbon material (carbonaceous material) fine powder is set to be in a range of 100 to
150 µm.
[0008]
As described above, with regard to the cold-bonded carbon composite agglomerates for blast furnaces, enhancement of the carbon content, enhancement of the reduction rate, and enhancement of cold strength and hot strength (which affect a disintegration degree in the furnace) have been issues.
[0009]
In addition, the cold-bonded agglomerates for blast furnaces require an appropriate water content in granulating and molding processes. Moreover, since the strength of the cement-based binder is developed by a hydration reaction, the amount of combined water (crystallization water) is larger than those in the other raw materials; and therefore, there is a disadvantage in that an bursting property in the blast furnace is poor.
[0010]
On the other hand, converter dust generated in ironworks is collected by a non-combustion type gas processing apparatus and the converter dust as iron raw materials is mixed with carbon powder, and pellets are produced. The pellets are partially reduced into reduced iron in a reduction furnace with rotary hearth and are reused. The converter dust to be collected contains a large amount of water and has a poor handling property and a poor mixing property with other powders. Therefore, the converter dust is dried and then is used. However, metal iron having a large specific surface area is contained in a fine powder state in the converter dust, and there is a problem in that the metal iron reacts with air and generates heat due to oxidization in the case where the converter dust is excessively dried.
[0011]
Patent Document 3 discloses a method for recycling converter dust. The method
includes: mixing powder containing iron oxide and powder containing carbon into the converter dust which is collected by a non-combustion type dust collector of converter gas; adjusting a water content of the mixture to 17 to 27% by mass; molding the mixture to produce a molded body having a porosity of 40 to 54%; and reducing the molded body by a reduction furnace with rotary hearth. According to this method, heat generation due to oxidization of metal iron is prevented, and a satisfactory reduction rate can also be obtained.
[0012]
According to this method, there is an effect of preventing the heat generation due to oxidization when the molded body is reduced in the reduction furnace with rotary hearth. Therefore, this method does not directly help the enhancement of the bursting property in a blast furnace which has different operating conditions such as an operating temperature and the like.
[0013]
In addition, Patent Document 4 discloses a method for reducing iron oxide by using a reduction furnace with rotary hearth. This method includes: placing a molded body containing metal oxide and carbon on a moving hearth; and heating the molded body by a heat from combustion gas of an upper part to perform firing reduction. In the method, a porosity of the molded body containing ferric oxide is adjusted to a specific value. By adjusting the porosity of the molded body to the specific value, volume expansion generated in reduction of the iron oxide from hematite to magnetite is absorbed by air holes. Therefore, stable reduction with less disintegration can be realized.
[0014]
This method is also effective for preventing disintegration during the reduction of the molded body in the reduction furnace with rotary hearth. However, this method does
not directly help prevention of disintegration in a blast furnace which has different operating conditions such as an operating temperature, a reduction pattern, and the like.
[0015]
In order to improve disintegration resistance with respect to bursting due to water vapor, disintegration during reduction (disintegration due to reduction, reduction disintegration), and the like, a reducibility of iron oxide in the cold-bonded carbon composite agglomerates, cold crushing strength, and hot crushing strength so as to provide cold-bonded carbon composite agglomerates for blast furnaces capable of performing efficient blast furnace operations, it is necessary to maintain the carbon content in the carbon composite agglomerates for blast furnaces at a constant level and set a structural morphology in detail for the porosity.
[0016]
However, if the porosity is high, gasification of the carbonaceous materials and a reduction rate of the iron oxide are promoted while the cold strength and hot strength are degraded. In addition, if the porosity is excessively low, there is a problem in that the disintegration in the furnace such as bursting due to water vapor, disintegration during reduction, and the like become more noticeable.
PRIOR ART DOCUMENT Patent Document
[0017]
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2003-342646
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2008-95177
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2003-82418
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2003-89813
DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
[0018]
The present invention aims to specify the porosity and the carbon content of carbon composite agglomerates which are suitable for efficient blast furnace operations; and thereby, the present invention aims to provide cold-bonded carbon composite agglomerates for blast furnaces which make it possible to perform efficient blast furnace operations, and a method for manufacturing the same.
Means for Solving the Problems
[0019]
The present inventors have examined a porosity and a carbon content of carbon composite agglomerates for blast furnaces. As a result, the present inventors have found that it is possible to provide cold-bonded carbon composite agglomerates capable of attaining the following properties by controlling blending conditions and production conditions such that the porosity becomes in a range of 20 to 30% and the carbon content becomes in a range of 18 to 25% by mass in the cold-bonded carbon composite agglomerates.
(a) Excellent disintegration resistance with respect to bursting due to water vapor and disintegration during reduction (disintegration due to reduction, reduction disintegration)
(b) High reducibility of iron oxide in cold-bonded carbon composite agglomerates
(c) Reduction promotion for peripheral iron ores (iron-based charged substance)
The blending conditions to be controlled are particle sizes (particle size distributions) of raw materials, an amount of carbon fine powder, a blending amount of ores having a high combined water content, an amount of cement, and the like.
[0020]
Cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment 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 porosity is in a range of 20 to 30%.
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 a molded body; and obtaining cold-bonded carbon composite agglomerates by subsequently curing the molded body, wherein in the forming of the molded body, one or more blending conditions selected from a group consisting of a water content in the raw materials, a particle size of the raw materials, an amount of fine cokes, a blending amount of ores having a high combined water content, and a binder blending amount are adjusted such that a carbon content (T. C) becomes in a range of 18 to 25% by mass and a porosity becomes in a range of 20 to 30% in the cold-bonded carbon composite agglomerates.
Effects of the Invention [0021]
The cold-bonded carbon composite agglomerates for blast furnaces according to an embodiment of the present invention has sufficient carbon content in order to enhance not only a reduction rate of the cold-bonded carbon composite agglomerates but also reduction rates of main iron-containing raw materials for blast furnaces such as sintered ores (iron ore sinter) and the like. Moreover, the cold crushing strength of 100 kg/cm2 or more which is required for raw materials for blast furnaces is maintained, and hot strength in a reduction temperature region is superior to that of a conventional iron ore agglomerates.
Therefore, it is possible to suppress disintegration of the cold-bonded carbon composite agglomerates such as bursting due to water vapor, disintegration during reduction, and the like in the blast furnace operations. In addition, it is possible to greatly reduce the reducing agent rate (cokes ratio) during the blast furnace operations. As a result, efficient blast furnace operations can be realized.
[0022]
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 materials) by a relatively inexpensive and simple method. .
BRIEF DESCRIPTION OF THE DRAWINGS [0023] FIG. 1 is a diagram showing relationships between porosities and disintegration
degrees during reduction of cold-bonded carbon composite agglomerates.
FIG. 2 is a diagram showing relationships between porosities and bursting properties of cold-bonded carbon composite agglomerates.
FIG. 3 is a diagram showing a relationship between a disintegration degree during reduction and an upper K value of cold-bonded carbon composite agglomerates.
FIG. 4 is a diagram showing relationships between carbon contents (T. C) and bursting properties of cold-bonded carbon composite agglomerates.
FIG. 5 is a diagram showing a relationship between an bursting property and an upper K value of cold-bonded carbon composite agglomerates.
FIG. 6 is a diagram showing relationships between porosities and cold crushing strengths of cold-bonded carbon composite agglomerates with different carbon contents.
FIG. 7 is a diagram showing relationships between porosities and reducing agent rates in a BIS furnace of cold-bonded carbon composite agglomerates with different carbon contents.
FIG. 8 is a diagram showing relationships between porosities and the reduction rates at 1000°C of cold-bonded carbon composite agglomerates with different carbon contents.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024]
The cold-bonded carbon composite agglomerates for blast furnaces of the present embodiment is produced 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 the porosity is in a range of
20 to 30%. Thereby, it is possible to suppress disintegration of the cold-bonded carbon composite agglomerates such as bursting due to water vapor, disintegration during reduction, and the like in blast furnace operations and the reducing agent rate in a blast furnace can also be reduced.
[0025]
In this embodiment, the carbon content (T. C) of the cold-bonded carbon composite agglomerates is set to be in a range of 18 to 25% by mass.
As will be described later in Examples, in the case where the carbon content (T. C) exceeds 25% by mass, it is not possible to maintain the minimum cold crushing strength which is necessary for use in a blast furnace (FIG. 6). In addition, an bursting property becomes noticeable, and it becomes impossible to perform stable operations in an actual blast furnace (FIGS. 4 and 5).
In the case where the carbon content (T. C) is less than 18% by mass, an effect of enhancing the reduction rate becomes small (FIGS. 7 and 8). Therefore, it is not possible to obtain the effect of improving blast furnace operations.
The carbon content (T. C) of the cold-bonded carbon composite agglomerates is preferably in a range of 20 to 23% by mass, and more preferably in a range of 22 to 23% by mass.
[0026]
In this embodiment, the porosity of the cold-bonded carbon composite agglomerates is set to be in a range of 20 to 30%.
As will be described later in Examples, in the case where the porosity is less than 20%, the effect of enhancing the reduction rate is limited (FIGS. 7 and 8). In addition, the disintegration degree in the blast furnace is increased and there may be cases where the disintegration degree exceeds the upper limit required for the raw materials used in the
blast furnace (FIG. 1).
In the case where the porosity exceeds 30%, the effect of enhancing the reduction rate is saturated (FIGS. 7 and 8). In addition, the cold crushing strength is lowered, and it becomes impossible to keep the minimum cold crushing strength which is necessary for use in the blast furnace (FIG 6).
The porosity of the cold-bonded carbon composite agglomerates is preferably in a range of 23 to 27%, and more preferably in a range of 24 to 26%.
[0027]
The method for manufacturing the 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. In the forming of the molded body, one or more blending conditions selected from a group consisting of a water content in the raw materials, a particle size of the raw materials, an amount of fine cokes (fine powdered cokes), a blending amount of ores having a high combined water content, and a binder blending amount are adjusted such that the carbon content (T. C) becomes in a range of 18 to 25% by mass and the porosity becomes in a range of 20 to 30% in the cold-bonded carbon composite agglomerates.
[0028]
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 fired dust obtained by firing oil-containing sludge, a fine iron ores such as pellet feed or the like having smaller particle sizes than those of powdered iron ore for sintering, ores having a high combined water content which contains a large amount of combined water (crystallization
water), and the like are exemplified.
[0029]
As the carbon-containing raw materials used in the embodiment, a blast furnace primary dust, a coke dust, fine cokes, anthracite are exemplified.
[0030]
In the embodiment, "water content in raw materials" is also referred to as free water and means a water content included in raw materials in a raw molded body after molding (before curing). By increasing the water content in the raw materials, it is possible to increase the porosity. However, if the water content in the raw materials is excessively high, the disintegration degree (bursting property) becomes higher. Therefore, it is preferable to adjust the water content in the raw materials within a range of 8 to 15%.
[0031]
In the embodiment, the particle size of the raw materials means a weighted average value of mass median sizes d50 of the iron-containing raw materials and the carbon-containing raw materials to be used. By reducing the particle size of the raw materials, it is possible to decrease the porosity. However, in the case where the particle size of the raw materials are excessively small, the disintegration degree (bursting property) becomes higher, and problems such as adhesion at the time of production and the like occur. Therefore, it is preferable to adjust the weighted average value of the mass median sizes d50 within a range of 10 o 50 µm.
[0032]
In the embodiment, the fine cokes mean fine-powdered cokes having a mass median size d50 of 100 µm or less. By increasing the amount of the fine cokes as the carbon-containing raw materials, it is possible to increase the porosity. However, if the
amount of fine cokes is excessively small, a problem occurs in that the disintegration degree (bursting property) becomes higher. Therefore, it is preferable to adjust the amount of fine cokes within a range of 10 to 30%.
[0033]
In the embodiment, the ores having a high combined water content mean ores which contain 5% or more of combined water (crystallization water) such as Robe River, Yandicoogina, Marra Mamba, or the like. By increasing the amount of the ores having a high combined water content, it is possible to increase the porosity of the cold-bonded carbon composite agglomerates. However, if the amount of ores having a high combined water content is excessively large, the disintegration degree (bursting property) becomes higher. Therefore, it is preferable to adjust the blending amount of the ores having a high combined water content within a range of 5 to 20%.
[0034]
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 furnace part becomes unstable. Thereby, it is not possible to stably obtain an effect of reducing the reducing agent rate. From the above viewpoints, a particularly preferable range of the binder blending amount is in a range of 5 to 19% by
mass.
[0035]
In the step of forming the molded body, the iron-containing raw materials and the carbon-containing raw materials cut out from a raw material hopper are loaded and mixed with a binder such as cement or the like in a wet ball mill, a Lodige mixer, or the like. Thereafter, water is added, and then, the mixture is kneaded. The kneaded substance of the raw materials obtained after sufficient kneading is molded by a Pan pelletizer, a briquette machine, or the like. Then, in the step of curing the molded body, the molded body is cured in the sum for several days until strength necessary for handling appears in a primary curing yard. Thereafter, the molded body is cured in the sun in a secondary curing yard to sufficiently allow the strength due to the binder such as cement or the like to appear. Thereby, the cold-bonded carbon composite agglomerates for blast furnaces are produced. Then, the cold-bonded carbon composite agglomerates for blast furnace are supplied to and used in the blast furnace.
[0036]
In the present embodiment, it is possible to set the carbon content (T. C) to be in a range of 18 to 25% by mass and set the porosity to be in a range of 20 to 30% of the cold-bonded carbon composite agglomerates by adjusting the production processes (pellets, briquettes) and blending conditions (a water content in raw materials, a particle size of raw materials, an amount of fine cokes, a blending amount of ores having a high combined water content, and a binder blending amount). Particularly, it is possible to do so by adjusting one or more blending conditions selected from a group consisting of a water content in raw materials, a particle size of raw materials, an amount of fine cokes, a blending amount of ores having a high combined water content, and a binder blending amount.
Although a pellet molded body is more porous than a briquette molded body, any one of them may be selected depending on the conditions of raw materials.
As described above, the larger the cement blending amount (binder blending amount) is, the finer the cold-bonded carbon composite agglomerates becomes. If either one of the water content in raw materials, the amount of carbon fine powder (amount of fine cokes), or the blending amount of ores having a high combined water content increases, the porosity increases. However, it is preferable to appropriately adjust them in consideration of molding yield, adhesion at the time of production, and constituents of products.
[0037]
Although carbon in the cold-bonded carbon composite agglomerates of the present embodiment reduces iron oxide in the cold-bonded carbon composite agglomerates, excess carbon further reduces iron ores in the peripheral in the blast furnace. Accordingly, it is possible to enhance the reduction rate (FIGS. 7 and 8).
In sequential operations of the blast furnace, CO gas (reduction gas) reduces iron ores while rising from a lower layer to an upper layer in the blast furnace. However, in the case where the blast furnace was operated only with the use of cokes as a reduction material, reduction force of the reduction gas is weakened in the upper layer part of the ore layers, and there were cases where reduction of ores did not sufficiently proceed.
On the other hand, when 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 due to the presence of the cold-bonded carbon composite agglomerates of the present embodiment along with the iron ores in the blast furnace. 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 of 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 (FIG. 7).
In addition, since the reduction efficiency of the entire blast furnace can be greatly enhanced, it is possible to reduce the reducing agent rate in relation to the blast furnace operations, which also includes pulverized coal injected through a tuyere. Since the reducing agent rate can be reduced, it is also possible to reduce the amount of C02 generated in the iron-making process and to thereby reduce environmental burden.
EXAMPLES
[0038]
Hereinafter, description will be given of embodiments of the present invention based on specific Examples. These are only embodiments, and the present invention is not limited thereto. (Example 1) (Production of cold-bonded carbon composite agglomerates)
Iron-containing raw materials, carbon-containing raw materials, and a binder were used, and mixing, addition of water, kneading, molding (granulating) were performed while adjusting the blending amounts of raw materials, a particle size, and a water content as shown in Table 1 to produce cold-bonded carbon composite agglomerates.
With regard to the obtained cold-bonded carbon composite agglomerates, porosities were measured by a water method (based on JIS K2151) in which water displacement was performed to measure an apparent specific gravity.
[0039]
Table 1
(Table Removed)
[0040]
Table 1 shows specific types of the used iron-containing raw materials, the types
of carbon-containing raw material, the water contents in raw materials, the particle sizes of the raw materials (average values), the types and the blending amounts of the ores including combined water (crystallization water), the types and the blending amounts of the binders, the carbon contents and the porosities of the obtained cold-bonded carbon composite agglomerates.
[0041]
It was found that the cold-bonded carbon composite agglomerates of the embodiment could be produced by adjusting the water content in raw materials, the particle size of raw materials, the blending amount of ores having a high combined water content, and the binder amount within the range shown in Table 1.
Here, it is not necessary to limit the granulation equipment, and any granulation equipment with functions of kneading raw materials, adding water, granulating, and sieving a molded body is applicable and a kneading machine, a granulator, and the like are not particularly limited.
[0042] (Example 2) (Influence of porosity)
Cold-bonded carbon composite agglomerates having different porosities were prepared to examine the influence of porosity on a disintegration phenomenon of the cold-bonded carbon composite agglomerates in the furnace.
The iron-containing raw materials and the carbon-containing raw materials which were the same as those in Example 1 were fractured and mixed with cement (binder). The mixture was kneaded, and a kneaded substance was molded. The obtained molded body was cured for a predetermined period to produce cold-bonded carbon composite agglomerates having a carbon content (T. C) of 15% by mass or 25% by mass.
Here, the blending amounts of the iron-containing raw materials and the carbon-containing raw materials were set to constant values, and the molding pressure for compression molding and the cement amount were adjusted to produce cold-bonded carbon composite agglomerates having a porosity of 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%. In addition, by finely adjusting the brand of the carbon-containing raw materials in accordance with the change in the blending amount of cement, the carbon content (T. C) was made to be constant at 15% by mass or 25% by mass.
[0043]
A disintegration property (disintegration property during reduction) was evaluated by the following method in which a test for disintegration during reduction (JIS M8720) was applied. The temperature of a 500 g sample was raised in N2 and maintained at 550°C in reduction gas containing 30% of CO for a predetermined period. At this time, a reduction time at 550°C was set to 1 minute, 10 minutes, 30 minutes, or 60 minutes; and thereby, samples for measurement were produced. Then, rotation impact of 900 rotations was given to the sample for measurement in a rotation test machine. The ratio of particles having sizes of 2.8 mm or less in the sample for measurement after applying the rotation impact (disintegration degree (-2.8 mm%)) was measured, and the disintegration property during reduction was evaluated based on the disintegration degree (-2.8 mm%). The results for the cold-bonded carbon composite agglomerates having the carbon content (T. C) of 25% by mass are shown in Table 2 and FIG. 1. Here, the disintegration degree (-2.8 mm%) measured by applying the test for disintegration during reduction will also be referred to as the disintegration degree during reduction in this specification.
[0044]
Table 2
(Table Removed)
[0045]
In addition, the bursting property in the blast furnace, which is the biggest weakness of the cold-bonded agglomerates, was also evaluated.
The bursting property was measured by the following method with reference to a test method of decrepitation of iron ores (ISO 8371: Iron ore-Determination of description index). 500 g of a sample was rapidly heated up to the maximum temperature of 700°C in N2. At this time, in order to examine the influence of heating speed (temperature rising speed), the heating speed was set to 5°C/minute, 50°C/minute, 500°C/minute, or 1000°C/minute; and thereby, samples for measurement were produced. Then, the ratio of particles having sizes of 6.3 mm or less in the sample for measurement (disintegration degree (-6.3 mm%)) was measured, and the disintegration degree was evaluated as the bursting property. The results for the cold-bonded carbon composite agglomerates having the carbon content (T. C) of 15% by mass are shown in Table 3 and FIG. 2.
[0046]
Table 3
(Table Removed)
[0047]
In general, a disintegration phenomenon caused by gas generation due to evaporation and gasification of contained water and combined water (crystallization water) (derived from iron ores and cement) is called bursting. In addition, a disintegration phenomenon caused by gap generation, volume expansion, and internal stress which occur in connection with the reduction is called disintegration during reduction. In the present specification, the inventors aim to define conditions by considering the disintegration degree in the furnace regardless of the causes of the phenomena; and therefore, "disintegration" may be used for both in some cases in the following description.
[0048]
Referring to FIG. 1, it can be understood that the reduction time has a great influence while the disintegration degree is tend to be lowered as the porosity is increased. The disintegration during reduction is caused by volume expansion and internal stress at the time of reduction from hematite to magnetite, and the most active disintegration is observed around 550°C. For this reason, it has been known that the disintegration during reduction depends on residence time around 550°C. That is, in the reduction at
temperatures of 550°C or more, the disintegration is diminished in fact. Therefore, the residence time at 550°C as well as the porosity affect the disintegration during reduction. In the reduction furnace with rotary hearth, the temperature rising speed is 1000°C/minute which is high, and the residence time at 550°C is about 1 minute. Therefore, the disintegration during reduction is small in scale. On the other hand, in the blast furnace, the residence time at 550°C is in a range of 10 minutes (center part) to 60 minutes (peripheral part); and therefore, there is a problem that the disintegration during reduction rate becomes higher.
[0049] (Example 3) (Allowable Range of Disintegration Degree During Reduction)
In order to perform stable operations in a real blast furnace, it is necessary to set an upper K value to be in a range of 0.4 or less in general. From the upper limit of the upper K value, an allowable range of the disintegration degree during reduction of the cold-bonded carbon composite agglomerates was examined.
The blending amounts of raw materials were adjusted such that the carbon content (T. C) became 25% by mass, and cold-bonded carbon composite agglomerates having different porosities were produced in the same manner as in Example 2.
The disintegration degrees (-2.8 mm%) were measured in the same manner as in the evaluation method for the disintegration property during reduction in Example 2.
[0050]
In addition, in order to evaluate air permeability of a shaft part during the use of the blast furnace, the upper K values were measured by the following method. In a blast furnace having an internal volume of 4500 m3, various types of cold-bonded carbon
composite agglomerates having different porosities (namely, disintegration degrees) were used to perform short period tests. Cold-bonded carbon composite agglomerates at a content of 10 % by weight of the total content of iron-based charged substances were mixed and charged into an ore layer. According to operation specifications for the blast furnace under base conditions, the reducing agent rate was 480 kg/tp, and a weight ratio between ores and cokes was 5.0. An airflow resistance value (upper K value) in the upper part of the shaft was calculated from a measurement value of a pressure probe installed on a furnace wall. The obtained results are shown in Table 4 and FIG. 3. [0051]
Table 4
(Table Removed)
[0052]
FIG. 3 shows a relationship between the disintegration degree and the upper K value of the cold-bonded carbon composite agglomerates. As described above, in order to perform stable operations in the actual blast furnace, it is necessary to set the upper K value to be in a range of 0.4 or less. From the relationship between the disintegration degree (disintegration degree during reduction) and the upper K value of the cold-bonded carbon composite agglomerates shown in FIG. 3, it can be understood that with regard to the cold-bonded carbon composite agglomerates having the carbon content of 25% by weight, the upper K value is raised to over 0.4 and it becomes difficult to perform stable

operations when the disintegration degree (disintegration degree during reduction) exceeds 40%. Therefore, it is important to lower the disintegration degree (disintegration degree during reduction) to 40% or less for the cold-bonded carbon composite agglomerates having the carbon content of 25% by weight.
[0053]
Referring to FIG. 1, the disintegration degrees are relatively low values in the case where the porosities are in a range of 20% or more. On the other hand, the disintegration degrees during reduction are bordered at 20% and suddenly increased when the porosities are in a range of 20% or more. Particularly, this tendency is noticeable in the case where the reduction time is 30 minutes or more. On the other hand, in the case where the porosity is set to in a range of 20% or more, it is possible to suppress the disintegration degree (disintegration degree during reduction) to 40% or less even in the case where the reduction time is 60 minutes. This is considered to be because the internal stress caused by the volume expansion of the cold-bonded carbon composite agglomerates is dispersed due to air holes when the porosity is increased and thereby the disintegration during reduction is considered to be suppressed. Accordingly, in order to solve the problem of the disintegration (disintegration during reduction) of the cold-bonded carbon composite agglomerates for blast furnaces, it is necessary to set the reduction time to be as short as possible and set the porosity to be in a range of 20% or more.
[0054]
Referring to FIG. 2, the disintegration (bursting property) tends to be reduced as the porosity is increased; however, the influence of the temperature rising speed is noticeable. This is considered to be because the generation amount and the discharge amount of water vapor are not balanced within the sample per time as the temperature
rising speed is higher and thereby internal pressure is increased. In the reduction furnace with rotary hearth, the temperature rising speed is 1000°C/minute which is high, and the cold-bonded carbon composite agglomerates easily explodes. On the other hand, the temperature rising speed in the blast furnace is in a range of 5°C/minute (peripheral part) to 50°C (center part). Therefore, with reference to FIG. 2, it is possible to consider that the problem of disintegration (bursting property) does not occur when the cold-bonded carbon composite agglomerates having the carbon content of 15% by mass are used in the blast furnace.
[0055] (Example 4) (Influence of carbon content)
Next, the influence of the carbon content (T. C) of cold-bonded carbon composite agglomerates was examined.
The cold-bonded carbon composite agglomerates having different carbon contents (T. C) and porosities were prepared to examine the influence of the carbon content (T. C) on the disintegration (bursting property).
In the same manner as in the method for Example 2 other than that the blending amounts of the iron-containing raw materials and the carbon-containing raw materials, molding pressure for compression molding, and the cement amount were adjusted, cold-bonded carbon composite agglomerates were produced in which the carbon content (T. C) was 15% by mass, 18% by mass, 25% by mass, or 30% by mass and the porosity was 10%, 20%, 30%, or 40%.
In the same manner as in the evaluation method for the bursting property in Example 2 other than that the heating speed (temperature rising speed) was set to 50°C/minute, the disintegration degrees (-6.3 mm%) were measured to evaluate the
bursting properties. Here, the heating speed of 50°C/minute is the most severe temperature rising condition in the blast furnace. The obtained results are shown in Table 5 and FIG. 4. [0056]
Table 5
(Table Removed)
[0057]
As shown in FIG. 4, it can be understood that the disintegration due to bursting is increased as the carbon content (T. C) in the cold-bonded carbon composite agglomerates is increased. This is considered to be because a matrix strength of the cold-bonded carbon composite agglomerates is lowered as the carbon content (T. C) is increased and thereby resistance against the pressure of internally generated gas is lowered. Therefore, it is necessary to consider the bursting property in the case where the carbon content (T. C) is in a range of 18% by mass or more as in the embodiment.
[0058] (Example 5) (Allowable Range of Bursting Property)
As described above, it is necessary to set the upper K value to be in a range of 0.4 or less in order to perform stable operations in the actual blast furnace. From the upper limit of the upper K value, the allowable range for the bursting property of the cold-bonded carbon composite agglomerates was examined.
In the same manner as in the method for Example 2 other than that the blending
amounts of the iron-containing raw materials and the carbon-containing raw materials, molding pressure for compression molding, and the cement amount were adjusted, cold-bonded carbon composite agglomerates were produced in which the carbon content (T. C) was 20% by mass and the porosities were various values.
In the same manner as in the evaluation method for the bursting property in Example 2 other than that the heating speed (temperature rising speed) was set to 50°C/minute, the disintegration degrees (-6.3 mm%) were measured to evaluate the bursting properties.
The upper K values were measured in the same manner as in Example 3 with the use of the cold-bonded carbon composite agglomerates at a content of 10% by mass of the total content of iron-based charged substances. The obtained results are shown in Table 6 and FIG. 5.
[0059]
Table 6
(Table Removed)
[0060]
FIG. 5 shows a relationship between the bursting property and the upper K value of the cold-bonded carbon composite agglomerates having the carbon content (T. C) of 20 % by mass. From FIG. 5, the influence of the bursting property on the air permeability of the blast furnace was examined in the case where the cold-bonded carbon composite agglomerates was used at a content of 10 % by mass of the total content of iron-based charged substances in the blast furnace.
From the relationship between the bursting property and the upper K value of the cold-bonded carbon composite agglomerates used in the blast furnace shown in Fig 5, it can be understood that the upper K value is raised to over 0.4 and it becomes difficult to perform stable operations when the bursting property exceeds 30%. Accordingly, it is important to lower the bursting property to 30% or less.
[0061]
In Examples 2 and 3, it can be understood From FIG. 2 that the bursting property becomes more unnoticeable as the porosity becomes higher. In addition, it can also be understood from FIG. 1 that it is necessary to set the porosity to be in a range of 20% or more. Referring to FIG. 4, it can be understood that the bursting property becomes 30% or less in the case where the carbon content (T. C) is in a range of 25% by mass or less in the cold-bonded carbon composite agglomerates having the porosity of 20% or more. Accordingly, it can be understood that it is necessary to set the carbon content (T. C) to be in a range of 25% by mass or less.
[0062] (Example 6)
(Cold Crushing Strength, Reduction Rate at 1000°C and Reducing agent rate in BIS Furnace)
In the same manner as in the method for Example 2 other than that the blending amounts of the iron-containing raw materials and the carbon-containing raw materials, molding pressure for compression molding, and the cement amount were adjusted, cold-bonded carbon composite agglomerates were produced in which the carbon content (T. C) was 15% by mass, 18% by mass, 25% by mass, or 26% by mass and the porosity was 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%.
[0063]
For the charged raw materials for the blast furnaces, strength to tolerate handling until charge into a blast furnace such as transport, granulating, and the like. As an index of such strength, cold crushing strength of the cold-bonded carbon composite agglomerates was measured in this example.
[0064]
The cold crushing strength was measured as follows based on JIS M8718 "iron ore pellet crushing strength test method". Compression burden was loaded on one sample at a prescribed pressure pan speed, a load value when the sample broke was measured, and an average value of 100 samples was evaluated as the cold crushing strength. The obtained results are shown in Table 7 and FIG. 6.
[0065]
Table 7
(Table Removed)
[0066]
FIG. 6 shows a relationship between the porosity and the cold crushing strength of the cold-bonded carbon composite agglomerates.
Referring to FIG. 6, it can be understood that the cold crushing strength does not depend on the carbon content and is determined substantially depending on a difference in porosities in the case where the carbon contents (18% by mass, 25% by mass) are in the carbon content range according to the embodiment. With regard to both of the carbon
composite agglomerates having the above-described carbon contents, in the case where the porosities were in a range of 30% or more, it was difficult to maintain 100 kg/cm2 which is the lower limit of the cold crushing strength necessary for use in the blast furnace. Accordingly, it is necessary that the porosity be set to be in a range of 30% or less from the viewpoint of the cold crushing strength.
[0067]
With regard to the cold-bonded carbon composite agglomerates having the carbon content of 26% by mass (which exceeds the upper limit of 25% by mass of the range prescribed in the embodiment), the cold crushing strength is less than 100 kg/cm2 (the lower limit for the use in the blast furnace) when the porosity is 20% or more. Accordingly, it is necessary that the carbon content is set to be in a range of 25% by mass or less. If the amount of blended cokes is excessively large, the amount of binder which penetrates into the openings in the cokes is increased. Accordingly, it is considered that it becomes difficult to obtain the strength in an efficient manner by the binder in the case where the carbon content exceeds 25% by mass.
[0068]
Next, for the obtained cold-bonded carbon composite agglomerates, the reducing agent rate in a BIS furnace and the reduction rate at 1000°C were measured as follows based on a property evaluation test method at the time of use in the blast furnace (BIS furnace: see Iron and Steel, 72 (1984), 1529).
Cold-bonded carbon composite agglomerates at a content of 10% by mass of the total content of iron-based charged substances were uniformly mixed into the ore layers and charged into the BIS furnace so as to form a layer structure with a coke layer. The BIS furnace is a test apparatus for simulating a countercurrent reaction of a shaft part in the blast furnace, and the BIS furnace includes a reaction pipe into which sintered ores
(iron ore sinter) and cokes are charged in a layer structure and a vertical movement type electric furnace. The charge amount was adjusted such that a weight ratio between iron oxide and carbon became 5.0. Gas having a Bosch gas amount and a composition corresponding to an operation, in which the reducing agent rate was 480 kg/tp and a blowing rate of fine powdered carbon (pulverized coal) was 150 kg/tp, was supplied to the BIS furnace to perform reduction of ores.
Shaft efficiency and temperature of thermal reserve zone in the BIS furnace were measured, and balance of heat and material was calculated based on the measured values. The reducing agent rate in the BIS furnace was obtained based on the balance of heat and material.
Moreover, after the reduction of ores by the BIS furnace was completed, sintered ores and cold-bonded carbon composite agglomerates at a position of 1000°C were collected. Then, chemical analysis was performed on the collected sintered ores and the cold-bonded carbon composite agglomerates, and the reduction rate at 1000°C was obtained from the analysis values. Here, the reduction rate at 1000°C represents a reduction property of the total iron-based charged substances including the charged cold-bonded carbon composite agglomerates.
The obtained results are shown in Tables 8 and 9 and FIGS. 7 and 8.
[0069]
Table 8
(Table Removed)
[0070]
Table 9
(Table Removed)
[0071]
FIGS. 7 and 8 respectively show the reducing agent rate and the reduction rate at 1000°C in the BIS furnace in the case where the cold-bonded carbon composite agglomerates at a content of 10% by weight of the total content of the iron-based charged substances were uniformly mixed into the ore layers. Referring to FIGS. 7 and 8, it can be understood that the reduction rate at 1000°C is increased while the reducing agent rate is lowered as the carbon content becomes higher. When the carbon content is 15%, the reduction rate at 1000°C is remarkably lowered, and the efficiency of the blast furnace operations is lowered. Accordingly, the lower limit of the carbon content (T. C) is set to

18%.
[0072]
In addition, the reduction rate at 1000°C is enhanced as the porosity is increased. Even in the cold-bonded carbon composite agglomerates having the carbon content (T. C) of 18% by mass, the reduction rate reaches 75% and the reducing agent rate reaches 470 kg/tp when the porosity is 20%. However, in the case where the porosity is less than 20%, an effect of enhancing the reduction rate at 1000°C and reducing the reducing agent rate is limited, and substantially the same result is obtained as that in a case without the cold-bonded carbon composite agglomerates. In addition, it was found that the effect of enhancing the reduction rate at 1000°C and reducing the reducing agent rate was saturated in the case where the porosity exceeds 30%. Therefore, it can be understood that the porosity may be set to be in a range of 20% or more to 30% or less for the carbon composite agglomerates having the carbon content (T. C) of 18% by mass and 25% by mass.
[0073]
From the above results, it can be understood that cold-bonded carbon composite agglomerates in which the carbon content (T. C) is in a range of 18 to 25 % by mass and the porosity is in a range of 20 to 30% may be used in order to most efficiently exhibit the effects of the disintegration degree, the bursting property, the cold crushing strength, the reduction rate, and the reducing agent rate in the blast furnace operations.
[0074]
Here, free water is taken into hydrates in the carbon composite agglomerates due to a hydration reaction of the cement during the curing from among the manufacturing processes including mixing, kneading, molding, and curing. Therefore, the total blending amount of the raw materials is slightly varied over the manufacturing processes
for the above reason; however, the variation amount is extremely small, and it is possible to consider the total blending amount to be 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.
INDUSTRIAL APPLICABILITY
[0075]
The cold-bonded carbon composite agglomerates 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 in the use in the blast furnace. Moreover, the cold crushing strength 100 kg/cm2 or more is maintained which is required as raw materials for blast furnaces, and superior hot strength is obtained in the reduction temperature range as compared with a conventional case. Therefore, it is possible to greatly reduce the reducing agent rate (cokes rate) in operations of the blast furnaces.
[0076]
Furthermore, according to the method for manufacturing cold-bonded carbon composite agglomerates according to an embodiment of the present invention, 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 materials) 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 porosity is in a range of 20 to 30%.
2. 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 a molded body; and
obtaining cold-bonded carbon composite agglomerates by subsequently curing the molded body,
wherein in the forming of the molded body, one or more blending conditions selected from a group consisting of a water content in the raw materials, a particle size of the raw materials, an amount of fine cokes, a blending amount of ores having a high combined water content, and a binder blending amount are adjusted such that a carbon content (T. C) becomes in a range of 18 to 25% by mass and a porosity becomes in a range of 20 to 30% in the cold-bonded carbon composite agglomerates.