Method for estimating high temperature region reduction rate of sintered ore, and method for manufacturing sintered ore

Abstract

To more accurately estimate the high temperature region reduction rate of a sintered ore.SOLUTION: A method for estimating the high temperature region reduction rate of a sintered ore comprises: using a high temperature region reduction rate being the reduction rate of a sintered ore at a predetermined temperature in a high temperature region accompanying the formation of a liquid phase as a target variable; and estimating the high temperature region reduction rate of an inserted sintered ore to be estimated due to be used for a blast furnace from values of explanatory variables in a state before heating the inserted sintered ore on the basis of a relational expression obtained by deriving at least porosity, the average size of crystal grains of calcium ferrite and the alumina concentration of the calcium ferrite in a state before heating the sintered ore as explanatory variables.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for estimating the high temperature region reduction rate of sintered ore and a method for producing sintered ore using the same. [Background technology]

[0002] Currently, the main raw material for blast furnaces in Japan is sintered ore, which is made by blending iron-containing raw material powder such as iron ore, auxiliary materials, carbonaceous material, and return ore.

[0003] Sintered ore is usually produced as follows: First, iron ore or other iron-containing raw material powder, which is the main raw material, is mixed with limestone or other auxiliary materials, carbonaceous material (coke), and return ore in a predetermined ratio, and an appropriate amount of water is added, followed by granulation using a kneader or the like to produce a sintered raw material. The granulated sintered raw material is a pseudo-particle (hereinafter also referred to as "pseudo-particle") in which core particles, for example, particles with a diameter of about 1 to 5 mm, are surrounded by particles with a diameter of 0.5 mm or less, called "adherent powder."

[0004] Next, this sintering raw material is loaded onto the pallet of a downward-suction type Dwight Lloyd (DL) sintering machine (hereinafter referred to as the sintering machine) to form a packed bed, and the top surface of the packed bed is ignited with a burner. Ignition creates a combustion zone where the carbonaceous material in the upper layer of the packed bed burns. The combustion zone progresses from the top to the bottom of the packed bed by sucking air from inside the pallet from below. In the combustion zone, the heat of combustion of the carbonaceous material raises the temperature of the surrounding pseudo-particles, causing them to partially melt. The molten liquid bridges the gaps between the pseudo-particles, sintering them and producing sintered ore. The produced sintered ore is crushed and sieved to a specified particle size, and particles above a certain particle size become sintered ore, which is used as a blast furnace feedstock. Note that particles below a certain particle size (usually less than 5 mm) are recovered as return ore and reused as part of the sintering raw material.

[0005] In blast furnace operation, sintered ore and coke are stacked inside the furnace, and the sintered ore is reduced by passing a reducing gas through it to produce molten iron, which is then removed. Sintered ore accounts for approximately 70% of the raw material used in blast furnaces. To efficiently promote the reduction reaction of the iron source, it is necessary to understand the reducibility of the sintered ore beforehand. It is known that the reducibility of sintered ore is governed by its porosity and chemical composition. Porosity is related to the contact area with the reducing gas inside the blast furnace, and the greater the porosity, the greater the reducibility. While the reducibility of sintered ore is evaluated based on its chemical composition (such as the content of Al2O3 and SiO2), it is known that the reduction reaction rate varies depending on the type of minerals that make up the sintered ore, even if the chemical composition is the same, and as a result, the reducibility also varies.

[0006] The reducibility of sintered ore is often evaluated by the JIS-RI test specified in JIS_M8713 "Iron ore - Test method for reducibility." The JIS-RI test is a simple simulation test in which reduction is carried out for a specified period of time at a constant temperature of 900°C. However, a method has also been proposed for evaluating the reducibility of sintered ore using a high-temperature property measuring device that reduces sintered ore while raising its temperature to 1400°C or higher.

[0007] Patent Document 1 discloses a high-temperature load softening test device, an example of a high-temperature property measurement device. This high-temperature load softening test device involves placing lump iron ore to be used in a vertical furnace in a crucible, placing the crucible in an electric furnace, and introducing reducing gas from below the electric furnace to heat and reduce the iron ore. The electric furnaces are arranged in two tiers, one above the other, and the joint between the two electric furnaces is connected with a flange. Reducing gas is introduced from below the lower electric furnace, and the lower electric furnace is heated while empty, while the crucible containing the iron ore is placed in the upper electric furnace. The temperature of the upper electric furnace and the temperature of the iron ore in the crucible are simultaneously measured, and the power of the upper electric furnace is adjusted to maintain a predetermined temperature difference, thereby conducting a high-temperature load softening test. The device allows for the introduction of highly preheated reducing gas and thermal insulation control, enabling more accurate representation of the reduction and melting behavior of sintered ore in an actual blast furnace. In Non-Patent Document 1, the achieved reduction ratio R at 1200°C measured using this high-temperature load softening test device is1200 is used as an index of the reducibility of sintered ore in the high-temperature range. Non-Patent Document 2 also uses a similar device to measure reducibility from a different perspective. It is known that when the amount of molten liquid increases in the high-temperature range, sintered ore softens and is crushed by the load applied from above. When this state is reached, the contact area between the sintered ore and the reducing gas flowing inside the blast furnace decreases, causing significant stagnation in reduction. The softening start temperature at which sintered ore begins to soften is defined as Ts, and the reduction rate at this time as RTs. The higher the RTs, the better the blast furnace operation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 7-27623 [Non-patent literature]

[0009] [Non-Patent Document 1] Yozo Hosoya et al.: Iron and Steel, 83(1997), 97-102 [Non-patent document 2] Kenichi Higuchi et al.: ISIJ International, 44(2004), 2057-2066 Summary of the Invention [Problem to be solved by the invention]

[0010] In the JIS-RI test, reducibility is evaluated at a constant temperature of 900°C. However, in an actual blast furnace, reduction occurs as the temperature rises to 1400°C or higher. The main difference between the JIS-RI test and an actual blast furnace is whether or not molten liquid is generated in the sintered ore during reduction. In other words, in the JIS-RI test, the temperature never rises above 900°C, so no molten liquid (liquid phase) is generated. Instead, the evaluation is based on the reduction reaction between the solid (solid phase) and the reducing gas. However, in an actual blast furnace, the temperature rises to 1100°C or higher, so molten liquid is generated. The presence of molten liquid significantly affects reducibility depending on its behavior. For example, FeO produced during reduction reacts with gangue and melts as the temperature rises. Melting softens the sintered ore, reducing the porosity within the sintered ore and the proportion of voids between the sintered ore. This reduces the permeability of the reducing gas, thereby affecting reducibility. In other words, although evaluation of reducibility by the JIS-RI test has the advantage of being easy to measure, it has the problem of low reproducibility (degree of simulation) of the reduction phenomenon in an actual blast furnace.

[0011] On the other hand, test furnaces that heat sintered ore to 1400°C or higher (such as the high-temperature property measurement device mentioned above) are more expensive than the test furnaces required for JIS-RI testing, and the test furnaces themselves are considerably larger. Another issue is the length of time required for evaluation. Raising the test temperature to 1400°C or higher requires a longer cooling time for the test furnace, and while JIS-RI testing allows measurements to be performed six times a day, tests can only be performed once every one to two days. This makes them difficult to use as test furnaces for process control, and they are not currently used for process control at steelworks (manufacturing sites).

[0012] Thus, when attempting to increase the degree of simulation of the reduction phenomenon in an actual blast furnace, the test temperature must be increased to a high temperature, which increases the test load and reduces the frequency of measurements.

[0013] The present invention aims to provide a method for estimating the reduction degree of sintered ore in the high-temperature region, which is a simple method for accurately estimating the reduction degree of sintered ore in the high-temperature region, and a method for producing sintered ore using the method. Here, the high-temperature region reduction degree refers to the reduction degree of sintered ore at a predetermined temperature when reduced under conditions simulating those of a blast furnace, from room temperature to a predetermined temperature equal to or higher than the temperature at which molten liquid is produced. [Means for solving the problem]

[0014] In order to solve the above problems, according to one aspect of the present invention, the high temperature region reduction rate, which is the reduction rate of sintered ore at a predetermined temperature in the high temperature region accompanied by liquid phase generation, is used as the objective variable, and the high temperature region reduction rate of the charged sintered ore, which is the target of evaluation and is to be used in a blast furnace, is estimated from the values ​​of the explanatory variables in the state before heating of the charged sintered ore, based on a relational equation derived using at least the porosity, the average size of calcium ferrite crystal grains, and the alumina concentration of calcium ferrite in the state before heating of the sintered ore.

[0015] The above relational expression may further include, as an explanatory variable, the ratio of calcium ferrite crystal grains having a grain size of 50 μm or more and an alumina concentration of 10 mass % or more. The relational expression is preferably a multiple regression expression with explanatory variables. Furthermore, the predetermined temperature is preferably the softening start temperature of the sintered ore.

[0016] According to another aspect of the present invention, in a method for producing sintered ore, the above-mentioned method for estimating the high temperature region reduction rate of sintered ore may be used to compare a first high temperature region reduction rate, which is the high temperature region reduction rate of sintered ore produced under first production conditions, with a second high temperature region reduction rate, which is the high temperature region reduction rate of sintered ore produced under second production conditions, and the production conditions for sintered ore with the higher high temperature region reduction rate may be adopted. [Effects of the Invention]

[0017] According to the present invention, the high temperature region reduction degree can be estimated more accurately based on the porosity, the average crystal grain size of calcium ferrite, and the alumina concentration of calcium ferrite in the sintered ore before heating. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a flowchart showing an example of a method for estimating a high-temperature region reduction rate. DETAILED DESCRIPTION OF THE INVENTION

[0019] (High temperature reduction rate of sintered ore) When evaluating the reducibility of sintered ore, as described above, a high-temperature property measuring device capable of raising the temperature to a high-temperature region accompanied by liquid phase generation (hereinafter simply referred to as the high-temperature region) is used to measure the reduction degree at a predetermined temperature in the high-temperature region (high-temperature region reduction degree), and this can be used as an index representing the reducibility in the high-temperature region. However, as described above, such high-temperature property measuring devices (high-temperature load softening test devices) are not currently widely used in steelworks. The high-temperature region accompanied by liquid phase generation varies depending on the sintered ore, but is, for example, in the temperature range of 1050°C or higher and 1300°C to 1400°C.

[0020] Therefore, the inventors of the present application have searched for a method for estimating the high temperature region reduction rate without conducting a test using a high temperature property measuring device, which requires a long time.

[0021] Sinter contains multicomponent calcium ferrite (SFCA: Silico-Ferrites of Calcium Aluminum, hereinafter referred to as CF) formed during the sintering process. Multicomponent calcium ferrite is a multicomponent continuous solid solution, which is formed by the crystallization of calcium ferrite phases (2CaO·Fe2O3, CaO·Fe2O3, CaO·2Fe2O3) incorporating SiO2 and Al2O3. The presence of gangue components (SiO2, Al2O3, etc.) and iron (FeO-Fe2O3) is important for high-temperature reducibility in the high-temperature region where a melt is formed. The inventors have discovered that the average grain size of multicomponent calcium ferrite minerals containing SiO2 and Al2O3 and the composition of the multicomponent calcium ferrite, particularly the alumina concentration, determine the high-temperature reducibility of sinter.

[0022] Therefore, the inventors conceived the idea of ​​estimating the high-temperature reducibility of sintered ore from the average grain size of multi-component calcium ferrite (CF) and the alumina concentration (Al2O3 concentration) of multi-component calcium ferrite (CF). They also considered that by taking into account porosity, which is known to contribute to reducibility, in addition to these factors, reducibility could be estimated more accurately. Specifically, a relational expression was previously determined that expressed the correlation between the high-temperature reducibility of sintered ore (high-temperature region reduction rate) and three factors: the porosity of the sintered ore, the average grain size of the CF, and the alumina concentration of the CF. Then, using this relational expression as an estimation formula, the high-temperature reducibility (high-temperature region reduction rate, hereinafter simply referred to as reduction rate) of the sintered ore to be evaluated could be quickly estimated based on the measured values ​​of the porosity, the average grain size of the CF, and the alumina concentration of the CF. The method for estimating the return rate according to this embodiment will be described below.

[0023] <Summary of the method for estimating the return rate> Fig. 1 is a flowchart showing an outline of a method for estimating the reduction degree. First, an outline of the method for estimating the reduction degree will be explained based on Fig. 1, and then details of the method for measuring porosity, the average crystal grain size of CF in sintered ore, and the alumina (Al2O3) concentration of CF will be explained. The high-temperature region reduction degree is a value measured at a predetermined temperature in the high-temperature region (high-temperature region reduction degree) using a high-temperature property measuring device capable of raising the temperature to 1050°C or higher, which is a high-temperature region accompanied by liquid phase generation.

[0024] Here, the sintered ore samples used to determine the relational expression for estimating the high temperature region reduction rate (hereinafter also referred to as the estimation expression) may be obtained by collecting sintered ore from an actual sintering machine, or may be produced using a sintering pot. Since determining the estimation expression based on samples having a wide range of characteristics leads to a more accurate estimation expression, it is preferable to use both.

[0025] As shown in FIG. 1, first, for a sample of sintered ore, the average crystal grain size of CF, the alumina (Al2O3) concentration of CF, and the porosity (hereinafter, these three are also referred to as porosity, etc.) are measured. The porosity, etc. are measured at room temperature. Next, the high temperature region reduction rate is measured for samples from the same lot as the samples for which the porosity, etc. were measured (step S1).

[0026] Next, an estimation formula is constructed by multiple regression analysis from the values ​​of the average crystal grain size of CF in the sintered ore, the alumina concentration of CF, the porosity, and the high-temperature region reduction rate measured in step S1 (step S2). Specifically, the estimation formula is expressed, for example, as the following formula (1). In step S2, the high-temperature region reduction rate is set as the objective variable X, and the average crystal grain size of CF in the sintered ore, the alumina concentration of CF, and the porosity are set as explanatory variables θ1, θ2, and θ3, respectively, and the coefficient α 1~3 and constant α0.

[0027]

number

[0028] In order to maintain the accuracy of the estimation of the high-temperature region reduction degree, it is necessary to include at least the three factors mentioned above (average grain size of CF in sintered ore, alumina concentration of CF, and porosity) as explanatory variables in Equation (1), which is a multiple regression equation.

[0029] Furthermore, by using the ratio of CF with a particle size of 50 μm or more and an alumina concentration of 10 mass% or more to the total CF as an explanatory variable in addition to the three factors mentioned above, the accuracy of estimating the reduction degree in the high-temperature region can be improved. Furthermore, instead of or in addition to the above ratios, other factors, such as the average chemical components of sintered ore (alumina, silica, magnesia, FeO), or the specific surface area, the operating conditions (aggregate consumption, pallet speed, layer thickness, and the blending ratio of each ore brand), can be added as explanatory variables to Equation (1). Increasing the number of explanatory variables naturally improves the accuracy of estimating the reduction degree in the high-temperature region.

[0030] Next, the average CF grain size, CF alumina concentration, and porosity of the sintered ore to be evaluated and to be used in the blast furnace (referred to as "charged sintered ore" in the claims) are measured at room temperature (step S3). The sintered ore to be evaluated is the actual sintered ore produced in a sintering machine and to be used in the blast furnace. However, it can also be substituted with simulated sintered ore produced in a sintering pot test device to simulate the production conditions of the actual machine. The three measured values ​​in step S3 are substituted into the estimation formula (Equation (1)) constructed in step S2 to calculate the high-temperature region reduction ratio (estimated high-temperature region reduction ratio) of the sintered ore to be evaluated (step S4). The calculated estimated high-temperature region reduction ratio can be used to set the operating conditions of the sintering machine and blast furnace.

[0031] <Method for measuring porosity of sintered ore> In the method for estimating the high-temperature reduction ratio described above with reference to Figure 1, the porosity is measured for both the sample sinter used to develop the estimation equation and the sinter to be evaluated (steps S1 and S3). Various methods have been proposed for measuring the porosity of sinter, including the mercury method (JIS M8716), the water method (JIS K2151), the paraffin method (immersion in molten paraffin at 80°C), the plasticine method (clay coating method) (covering the sinter with plasticine), and the PAC method (vacuum packaging in film) (Toshitsugu Kasama et al., Iron and Steel 83 (1997) 109-114). The PAC method is particularly preferred due to its ease of measurement and high measurement accuracy.

[0032] The PAC method uses a vacuum packaging machine to immerse sinter wrapped in film in water, measure its volume, and calculate the porosity. According to the PAC method, the external shape of the sinter is determined by the balance between atmospheric pressure and the surface tension of the film, and it is said to be able to stably quantify pores up to a maximum diameter of approximately 15 mm. It is possible to count even relatively coarse pores, and to measure the total porosity, including the unevenness of the sinter surface, with high accuracy.

[0033] <Method for measuring the average size of CF in sintered ore and the alumina concentration of CF> In the method for estimating the high-temperature reduction ratio described above with reference to Figure 1, the average size of CF and the alumina concentration of CF are measured for both the sample sinter used to develop the estimation equation and the sinter to be evaluated (steps S1 and S3). The average size of CF and the alumina concentration of CF in the sinter are measured using the electron backscatter diffraction pattern (EBSD) method. In EBSD measurement, an electron beam is irradiated onto the sample, and the crystal structure and crystal orientation of the irradiated area are analyzed from the diffraction pattern of the emitted backscattered electrons. The sinter to be measured is embedded in resin, cut, polished, and carbon-coated. Electron backscatter diffraction patterns (EBSD, also known as EBSP) are then measured while the electron beam is continuously moved to analyze the crystal structure and crystal orientation. The crystal structure and crystal orientation of CF determined in advance from a known sample are used in the analysis.

[0034] The average size of CF in sintered ore is derived based on the crystal structure and crystal orientation analyzed by EBSD measurement. A continuous region with the same crystal orientation in a CF crystal structure is considered a single crystal grain (single crystal), and the distribution of CF crystal grains is obtained as a two-dimensional map of the photographed area. For each CF crystal grain (single crystal) in the photographed area, the size D is determined based on its area value Sc (which may be the perimeter, minor axis diameter, and major axis diameter) (for example, the circle-equivalent diameter A calculated using Equation (3) described below). The area-weighted average is then used as the average size of CF in that photographed area. Similar measurements are then performed on multiple photographed areas, and the area-weighted average is then used as the average size of CF in the sintered ore. On the other hand, the alumina concentration of CF is derived based on the crystal structure analyzed by EBSD measurement. Because the crystal structure of CF changes depending on the alumina concentration of CF, the alumina concentration of CF can be derived by first correlating the relationship between the crystal structure of CF and the alumina concentration of CF. The alumina concentration of a single CF crystal grain is determined as the arithmetic average of the alumina concentrations at measurement points within the grain. The procedure for determining the alumina concentration of CF in sintered ore from the alumina concentration of a single CF crystal grain is the same as the procedure for the average size described above.

[0035] <Method for measuring the ratio of crystal grains with a grain size of 50 μm or more and an alumina concentration of 10 mass% or more> Although not shown in the figure, the softening start temperature Ts and the reduction ratio RTs at that time can be estimated more accurately by using the ratio (proportion) of calcium ferrite with a particle size of 50 μm or more and an Al2O3 concentration of 10 mass% or more as an explanatory variable in the above-described method. The size D and alumina concentration of each calcium ferrite grain are already obtained from EBSD, as described above. Focusing on grains with an alumina concentration of 10 mass% or more, all grains with a size D of 50 μm or more are selected, and the sum Sn of the areas of the selected grains in the imaged region is calculated. The ratio of the sum Sn of the aforementioned areas to the total area S of calcium ferrite in the imaged region can be calculated. The principles of the EBSD method are described in "Basic Principles and Applications of EBSP Method (I)" (Suzuki Seiichi, Microscope Vol. 39, No. 2 (2004)), "Basic Principles and Applications of EBSP Method (II)" (Suzuki Seiichi, Microscope Vol. 39, No. 3 (2004)), and "Basic Principles of EBSD Method and Applications to Material Structure Analysis" (Suzuki Seiichi, Journal of the Japan Institute of Electronics Packaging Vol. 13, No. 6 (2010)), and as these can be used by referring to these documents, a detailed explanation will be omitted here.

[0036] <Method for measuring the reduction rate in the high temperature region during the estimation formula construction stage> In the method for estimating the high-temperature region reduction degree described above with reference to FIG. 1, the high-temperature region reduction degree of a sample sintered ore is measured during the development of the estimation equation (step S1). The high-temperature region reduction degree is preferably measured, for example, in a test in which a load is applied to the sintered ore under temperature-rising reduction (a temperature-rising, load-softening test). In an actual blast furnace, the sintered ore and coke are stacked and reduced with reducing gas (CO-CO gas) while the temperature is raised at a rate of 5°C to 20°C / min. The temperature-rising, load-softening test can simulate the behavior of sintered ore under temperature-rising reduction while reproducing the effect of the load from the upper charge in an actual blast furnace. It is also desirable to use the high-temperature, load-softening test apparatus described in Patent Document 1 as a high-temperature property measurement device. By introducing a highly preheated reducing gas and controlling the adiabaticity, a load-softening test can be performed that simulates the sample temperature stagnation and reduction delay caused by the large amount of heat absorption that occurs as a result of the rapid reduction of molten FeO at temperatures above 1000°C. It is possible to measure the reduction rate in the high temperature region under conditions that more precisely simulate the reduction and melting behavior of sintered ore in an actual blast furnace.

[0037] The predetermined temperature for measuring the high temperature region reduction rate can be, for example, a temperature in the range of 1100°C to 1200°C (1100°C or higher and 1200°C or lower). Preferably, the softening start temperature Ts is used. This is because the high temperature region reduction rate RTs at the softening start temperature Ts has the highest correlation with the reducing agent rate in blast furnace operation. A method for determining the softening start temperature Ts will be shown in the Examples (see paragraph 0049).

[0038] <Sintered ore manufacturing method> Next, a method for producing sintered ore using the above-described method for estimating the high-temperature region reduction degree will be described. In the method for producing sintered ore according to this embodiment, the high-temperature region reduction degree (first high-temperature region reduction degree) is estimated (calculated) in advance using the above-described estimation method for the actual sintered ore currently being charged into the blast furnace or for simulated sintered ore produced in a sinter pot test device that simulates the production conditions of the actual sintered ore. To produce sintered ore that is more suitable for blast furnace operation than the actual sintered ore currently being charged, it is necessary to change the current sintered ore production conditions (first production conditions). Here, "changing the production conditions" includes not only changing the control conditions of the sintering machine, but also changing the production conditions of the sintered ore (such as a portion of the raw material blend or the blending ratio), and changing both the control conditions of the sintering machine and the production conditions of the sintered raw material.

[0039] Therefore, a sample sinter is prepared to estimate the high-temperature region reduction rate (second high-temperature region reduction rate) under the production conditions to be changed (second production conditions). Specifically, the production conditions of the actual machine are temporarily changed to the second production conditions to produce actual sinter, or a simulated sinter that simulates the second production conditions is prepared using a sinter pot test device. The high-temperature region reduction rate (second high-temperature region reduction rate) is estimated (calculated) for the produced actual sinter or simulated sinter using the estimation method described above. Then, the first and second high-temperature region reduction rates are compared. If the second high-temperature region reduction rate is higher than the first high-temperature region reduction rate, the subsequent production conditions in the actual machine are changed from the first production conditions to the second production conditions to produce sinter. Note that the high-temperature region reduction rate may be compared using either the actual sinter or the simulated sinter, but it is preferable to evaluate one of them and manage the production conditions.

[0040] Other reasons for changes in manufacturing conditions include changes in the raw material mix or required production volume. Changes in the raw material mix occur, for example, due to changes in the source (origin) of raw materials such as iron ore, a natural resource. Naturally, changes in the raw material mix result in changes in the properties of the sintered ore. Changes in the required production volume of sintered ore are caused, for example, by production adjustments based on the required volume of the blast furnace. Sintered ore is produced by operating a sintering machine continuously over an extended period of time. To increase the production volume of sintered ore, measures are taken such as increasing the blower exhaust air volume, thickening the raw material packed bed in the sintering machine, or increasing the pallet movement speed; however, in either case, the increased firing speed changes the properties of the sintered ore.

[0041] As described above, when it becomes necessary to change the current production conditions, for example, samples (actual sintered ore or simulated sintered ore) under two production conditions (first production conditions and second production conditions) are prepared by the method described above, and the high-temperature region reduction degree is estimated. By comparing and evaluating the two estimated high-temperature region reduction degrees (first high-temperature region reduction degree and second high-temperature region reduction degree), it is possible to determine the production conditions (first production conditions or second production conditions) for sintered ore that are more suitable as a blast furnace feedstock, and to adopt these as the production conditions for sintered ore thereafter.

[0042] The method for estimating the high-temperature reduction ratio described above and the method for producing sintered ore using the estimated high-temperature reduction ratio allow for more accurate estimation of the high-temperature reduction ratio based on the porosity of the sintered ore, the average grain size of calcium ferrite in the sintered ore, and the alumina concentration of calcium ferrite in the sintered ore. By adjusting the production conditions to achieve an appropriate high-temperature reduction ratio, the reduction reaction of the iron source in the blast furnace can be efficiently promoted. The above-described method for estimating the high-temperature reduction ratio can estimate the high-temperature reduction ratio simply by measuring the average grain size of the CF crystals, the alumina (Al2O3) concentration of the CF, and the porosity of the sintered ore to be evaluated. Because it is not necessary to actually heat the sintered ore to the high-temperature range, the evaluation takes a short time and can be performed at a frequency comparable to that of the JIS-RI test. Therefore, it can be used for actual process control.

[0043] EBSD measurement is also used to measure the average grain size of calcium ferrite in sintered ore and the alumina concentration of calcium ferrite, which allows for the identification of each individual calcium ferrite grain in sintered ore, enabling the average grain size and chemical composition to be analyzed with high precision. In the above-described method for estimating the high-temperature region reduction degree and the method for producing sintered ore using the estimated high-temperature region reduction degree, a multiple regression equation obtained in one sintering machine may be applied to another sintering machine. However, by using a regression equation obtained in one sintering machine for the same sintering machine, the high-temperature region reduction degree can be estimated with higher accuracy. [Example]

[0044] Example 1 shows an example in which the relationship between the porosity of sintered ore, the average size of calcium ferrite, the alumina concentration of calcium ferrite, and the high temperature region reduction rate RTs at the softening start temperature Ts of the sintered ore was determined as a multiple regression equation.

[0045] (Preparation of sample sinter) The sample sinter used to determine the estimation formula (hereinafter referred to as sample sinter) was sinter produced using a pot test device under various conditions. The sample sinter was given a wide range of quality characteristics, with a total of 104 conditions (26 conditions x 4 conditions) created by changing the iron ore blend (26 conditions) and the charging density of the blended raw materials when charged into the sinter pot (4 conditions). The main specifications of the pot test device are shown in Table 1.

[0046] [Table 1]

[0047] (Measurement of reduction rate in high temperature region) In this example, the high-temperature load softening test apparatus described in Patent Document 1 was used to more accurately reproduce the reduction and melting behavior of sintered ore in an actual furnace by introducing highly preheated reducing gas and performing adiabatic control, and the high-temperature region reduction ratio was measured. In addition, the high-temperature region reduction ratio RTs, where a predetermined temperature is the softening start temperature Ts, was adopted as an index representing the reducibility of sintered ore in the high-temperature region.

[0048] Specifically, a high-temperature load softening test under elevated temperature reduction was performed on each of the prepared sintered ores using the high-temperature load softening test apparatus described in Patent Document 1, and the reduction ratio in the high-temperature region was measured. The sized simulated sintered ore was charged into a graphite crucible with a perforated bottom to a layer thickness of 70 mm. Coke sized to 10-15 mm was charged above and below the simulated sintered ore to a layer thickness of 20 mm. The heating rate of the lower furnace was set to the maximum furnace capacity of 10°C / min, and the heating rate of the upper furnace was set to 10°C / min up to 1000°C and 5°C / min above 1000°C, the average heating rate of a real furnace. Reducing gas was introduced above 800°C, and the gas flow rate was constant at 34 NL / min. A load of 0.098 MPa was applied above 800°C. The upper furnace was heated at the start of the experiment, and switched to adiabatic control when the melt formed in the sintered ore at around 1200°C and the pressure drop in the sample layer began to rise sharply (when softening began). Other experimental conditions were the same as those described in Non-Patent Document 1.

[0049] The softening start temperature Ts was defined as the temperature at which the sample pressure loss exceeded 2.0 kPa in the high-temperature load softening test apparatus described in Patent Document 1. The reduction rate calculated from the weight loss at this time was defined as the high-temperature region reduction rate. The reduction rate R was calculated from the weight loss ΔW, where W is the weight of the charged sintered ore, and C is the FeO concentration. FeO , Fe2O3 concentration C Fe2O3 Then, the weight loss ΔW at the softening starting temperature Ts can be calculated from the following formula (2). Ts By using this, the high temperature region reduction rate RTs can be calculated.

[0050]

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[0051] (Calcium ferrite measurement) A portion of the prepared simulated sinter was embedded in resin, cut, and polished. After carbon deposition, the polished cross section of the sinter was observed using a scanning electron microscope (SEM) and analyzed using the EBSD method to examine the distribution of the mineral phases formed on the cross section of the sinter.

[0052] In this example, the size D of the crystal grains of calcium ferrite (CF) was determined as follows. A region showing the same crystal orientation by EBSD was regarded as one crystal grain (single crystal), and the circle-equivalent diameter based on the area of ​​each crystal grain (hereinafter referred to as the circle-equivalent diameter) was determined as the crystal grain size. When the area of ​​a certain two-dimensional closed region of an indeterminate shape is Sc, the circle-equivalent diameter A can be determined by the following equation (3) using pi, where π is the circumference of the circle.

[0053]

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[0054] For each sinter, the circle-equivalent diameter A of all CF crystal grains within the SEM observation range was determined according to the above method to be the size D, and the average particle size, which was the area-weighted average (arithmetic mean), was determined to be the average size of the CF crystal grains.

[0055] In this example, the alumina (Al2O3) concentration of CF was determined as follows: Data on alumina concentration, crystal structure, and crystal orientation were obtained in advance for known multi-component calcium ferrites with different Al2O3 compositions (SFCA phase with a high SiO2 content, SFCA-I phase with a low SiO2 content). The abundance (area fraction) of each crystalline phase of CF (SFCA phase with a high SiO2 content, SFCA-I phase with a low SiO2 content) in the sample observation range (measurement range) was determined using the EBSD method, and the abundance fraction of each crystalline phase was multiplied by the alumina concentration. The sum of these values ​​was used as the alumina concentration of the CF in the sintered ore.

[0056] (Porosity measurement) In this example, the porosity was measured by the PAC method described above. Each sintered ore wrapped in a film was immersed in water, and its volume was measured to calculate the porosity.

[0057] (Test results) The above items were measured for the sample sinter before heating, and the obtained sample data (number of samples: n = 104) varied in the ranges of RTs of 58 to 78%, porosity (θ1) of 35 to 45 volume %, average CF crystal grain size (average particle size: θ2) of 5 to 130 μm, and CF alumina concentration (θ3) of 5 to 14 mass %.

[0058] Based on the test results, multiple regression analysis was performed to determine an estimation formula for RTs. The estimation formula in this example was determined as shown in formula (4). The estimation accuracy R 2 The coefficient of determination was 0.97.

[0059]

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[0060] Furthermore, when the ratio (θ4) of CF particles with a particle size (circle equivalent diameter A) of 50 μm or more and an alumina concentration of 10 mass% or more was added as an explanatory variable, the multiple regression equation of equation (5) was obtained.

[0061]

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[0062] R, which represents the estimated accuracy 2 was improved from 0.97 to 0.99 by adding θ4.

Claims

1. A multiple regression equation is derived using a high temperature region reduction rate, which is a reduction rate of sintered ore at a softening start temperature in a high temperature region accompanied by the generation of a liquid phase, as a response variable, and using at least the porosity, the average size of calcium ferrite crystal grains, and the alumina concentration of calcium ferrite in a state before heating of the sintered ore as explanatory variables, A method for estimating the high temperature region reduction rate of sintered ore, characterized in that the high temperature region reduction rate of the sintered ore to be evaluated and to be used in a blast furnace is estimated from the values ​​of the explanatory variables in the pre-heated state of the sintered ore.

2. 2. The method for estimating the high temperature region reduction degree of sintered ore according to claim 1, wherein the multiple regression equation further includes, as an explanatory variable, a ratio of crystal grains having a grain size of 50 μm or more and an alumina concentration of 10 mass% or more in the calcium ferrite crystal grains.

3. According to the method for estimating the high temperature region reduction rate of sintered ore according to claim 1 or 2, A first high temperature region reduction rate, which is a high temperature region reduction rate of the sintered ore produced under the first production conditions, is compared with a second high temperature region reduction rate, which is a high temperature region reduction rate of the sintered ore produced under the second production conditions; A method for producing sintered ore, characterized in that the production conditions for sintered ore with a higher high-temperature region reduction rate are adopted.

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