JP7684573B2 - High temperature property estimation method, computer program, and blast furnace operation method - Google Patents

Description

The present invention relates to a method for estimating the high-temperature properties of ore raw materials or ore layers.

In recent years, there has been an increasing demand to reduce the reducing agent rate in the blast furnace process in order to reduce _CO2 emissions. For this reason, technological development has been promoted to improve the reducibility of raw ore materials such as sintered ore and pellets, and to control the distribution of raw ore and coke (charge distribution) in the blast furnace, thereby improving the reduction efficiency and reducing the reducing agent rate.

In addition, from the perspective of reducing the production costs of molten iron, it is desirable to reduce the amount of coke used, which is the main reducing agent in the blast furnace process, as much as possible, and technological development has been carried out to reduce the amount of coke required to produce 1 ton of molten iron (coke ratio) by, for example, injecting a large amount of pulverized coal through the tuyeres.

As the ore raw materials charged into a blast furnace descend inside the furnace, they are heated and reduced, eventually melting and dripping down. As the ore raw materials change from solid to liquid, the ore softens and the ore particles fuse together to form a fused ore layer, which significantly reduces the air permeability inside the blast furnace. The area inside the blast furnace where the fused ore layer exists is generally called the fusion zone.

In the cohesive zone, the reducing gas in the furnace hardly flows to the ore cohesive layer, and the reducing gas is biased toward the coke layer. In a method in which the ore raw material and coke are charged alternately from the top of the blast furnace, in order to ensure a gas flow path to the coke layer in the cohesive zone, it is necessary to set the amount of coke per charging charge to a certain amount or more. On the other hand, under conditions in which the amount of coke per charging charge is set to a certain amount or more, the amount of ore per charging charge increases as the coke rate decreases, and the thickness of the ore layer increases.

When the reducing gas moves from the bottom to the top of the ore layer, the reducing gas, CO gas and _H2 gas, are consumed as the reduction reaction in the ore layer by the reducing gas progresses, so the reducing power decreases toward the top of the ore layer. As a result, the reduction rate decreases toward the top of the ore layer. As described above, when the thickness of the ore layer increases, the reduction rate in the upper part of the ore layer is promoted, resulting in a decrease in the reduction rate of the entire ore layer.

In order to reduce the pressure loss in the cohesive zone under the condition of minimizing the amount of coke relative to the amount of ore (coke ratio), it is necessary to establish operating techniques that reduce the pressure loss in the cohesive zone by controlling the shape of the cohesive zone or reducing its width.

From the above viewpoints, quantitative evaluation of the reducibility and permeability of the ore layer up to the cohesive zone is extremely important, and conventionally, the "fusion start temperature Ts [°C]" and the "reduction ratio at the start of fusion Rs [%]" have been used as indices for evaluating the high-temperature properties of raw ore materials (hereinafter referred to as "high-temperature property evaluation indices"). The fusion start temperature Ts and the reduction ratio at the start of fusion Rs are defined as the temperature and reduction ratio, respectively, at which the pressure drop is 200 _mmH2O under the standard test conditions shown in Non-Patent Document 1 using a specified test device.

Hosoya, et al., Development of a method for evaluating the softening and melting properties of sintered ore, Iron and Steel Institute of Japan, February 1, 1997, Vol. 83 (1997), pp. 97-102 Yasuda et al., Formulation of the shrinkage rate during the softening process of sintered ore, Iron and Steel Institute of Japan, August 1, 2019, Vol. 105 (2019), pp. 785-792 Yasuda et al., Changes in packing structure during softening of sintered ore layers, CAMP-ISIJ, The Iron and Steel Institute of Japan, March 20, 2019, Vol. 32 (2019), p. 13 Usui et al., Kinetics of gaseous reduction of agglomerates (part 1) Reaction model of gaseous reduction of agglomerates, Iron and Steel, The Iron and Steel Institute of Japan, June 1, 1994, Vol. 80 (1994), pp. 431-439 Takaya et al., Kinetic Analysis of Gasification Reaction of Metallurgical Coke with CO2 and H2O, Iron and Steel, Iron and Steel Institute of Japan, April 1, 1989, Vol. 75 (1989), pp. 594-601 Sugiyama et al., Air Permeability Resistance of Welded Packed Beds, Iron and Steel, The Iron and Steel Institute of Japan, November 1, 1980, Vol. 66 (1980), pp. 1908-1917 Ichikawa et al., Evaluation of Air Permeability Resistance of Softened Sintered Ore Layer Considering Liquid Phase Formation, Iron and Steel, Iron and Steel Institute of Japan, 2014, Vol. 100 (2014), pp. 270-276

The fusion start temperature Ts and reduction rate Rs at the start of fusion can be measured using a specified test device, but this measurement takes about four hours. In addition, preparation of the sample and test device and cooling of the furnace also take time, so only one sample can be measured per day, limiting the number of samples that can be evaluated.

On the other hand, the inventors have proposed a method for estimating the shrinkage rate of the ore layer in the cohesive zone (Non-Patent Document 2) and a method for estimating the change in pressure loss due to shrinkage from the initial porosity and shrinkage rate of the ore layer (Non-Patent Document 3).

Next, in a blast furnace, "1. Ore filling state," "2. Temperature," "3. Reducing gas (composition, flow rate)," "4. Load on the ore layer," etc. vary depending on the position in the furnace and the operating conditions, and affect the high-temperature properties of the ore layer. For example, the ore filling state varies depending on the thickness of the charging layer, the mixed charging of various ore raw materials, and the particle size distribution of each ore raw material. The temperature distribution in a blast furnace varies depending on the heat flow ratio and the reactivity of the coke. The composition and flow rate of the reducing gas vary depending on the pulverized coal ratio and the amount of pig iron produced. The load on the ore layer varies greatly depending on the furnace volume. Therefore, in order to discuss the high-temperature properties of the ore layer in a blast furnace, it is preferable to focus on the fusion start temperature Ts and the reduction rate at the start of fusion Rs under conditions that take into account the effects of one or more of the parameters 1 to 4 mentioned above, but this point has not been considered until now.

The object of the present invention is to estimate the pressure loss of an ore layer (a packed layer of raw ore ore ore layer in a blast furnace) caused by softening and shrinking of the raw ore, and to derive a high-temperature property evaluation index of the ore layer without performing a test for measuring the above-mentioned high-temperature property evaluation index. Here, the high-temperature property evaluation index includes a fusion start temperature Ts and a reduction ratio at the start of fusion Rs, and a fusion start temperature (hereinafter referred to as Ts ^* [°C]) and a reduction ratio at the start of fusion (hereinafter referred to as Rs ^* [%]) under a predetermined condition (when the pressure loss reaches a predetermined value).

The first invention of the present application is a high-temperature property estimation method for estimating a high-temperature property evaluation index of a raw ore packed bed based on the pressure loss of the raw ore packed bed due to softening and shrinkage of the raw ore. Here, the reduction rate of the raw ore is calculated based on the temperature of the raw ore packed bed and the conditions of the reducing gas supplied to the raw ore packed bed. Then, the contraction rate of the raw ore packed bed is calculated based on the temperature of the raw ore packed bed, the load applied to the raw ore packed bed, and the reduction rate of the raw ore, and the pressure loss of the raw ore packed bed is calculated based on the contraction rate. The high-temperature property evaluation index is the reduction rate at the start of fusion, which is the reduction rate of the raw ore when the calculated pressure loss reaches a predetermined value, or the fusion start temperature, which is the temperature of the raw ore packed bed when the calculated pressure loss reaches a predetermined value.

The shrinkage rate of the ore raw material packed bed is calculated based on the mass of the ore raw material, the initial volume and initial layer thickness of the ore raw material packed bed, the temperature distribution and load distribution in the high-temperature property test, and the reduction rate of the ore raw material. The pressure loss of the ore raw material packed bed is calculated based on the shrinkage rate of the ore raw material packed bed, the particle size of the ore raw material, the initial porosity of the ore raw material packed bed, and the viscosity, density, and superficial flow velocity of the reducing gas in the high-temperature property test. The initial in the above-mentioned initial volume, initial layer thickness, and initial porosity refers to the state before the ore raw material softens and shrinks.

The second invention of the present application is a high-temperature property estimation method for estimating a high-temperature property evaluation index of an ore layer based on the pressure loss of the ore layer associated with the softening and shrinkage of the ore raw material in a blast furnace. Here, the reduction rate of the ore raw material is calculated based on the temperature of the ore layer and the conditions of the reducing gas supplied to the ore layer. Then, the contraction rate of the ore layer is calculated based on the temperature of the ore layer, the load applied to the ore layer, and the reduction rate of the ore raw material, and the pressure loss of the ore layer is calculated based on the contraction rate. The high-temperature property evaluation index is the reduction rate at the start of fusion, which is the reduction rate of the ore raw material when the calculated pressure loss reaches a predetermined value, or the fusion start temperature, which is the temperature of the ore layer when the calculated pressure loss reaches a predetermined value.

The contraction rate of the ore layer is calculated based on the mass of each raw material constituting the ore layer, the initial volume and initial layer thickness of the ore layer, the temperature distribution and load distribution along the path along which the ore layer descends in the furnace, and the reduction rate of the ore layer. The pressure loss of the ore layer is calculated based on the contraction rate of the ore layer, the particle size of each raw material constituting the ore layer, the initial porosity of the ore layer, and the viscosity, density, and superficial flow velocity of the reducing gas in the furnace.

The reduction rate can be estimated by reduction reaction rate analysis. A computer program can be configured to cause a computer to execute the processing in the high-temperature property estimation method of the first or second invention of the present application.

The third invention of the present application is a method for operating a blast furnace, which operates the blast furnace based on the high-temperature property evaluation index estimated by the high-temperature property estimation method of the second invention of the present application. The blast furnace operation based on the high-temperature property evaluation index is an operation performed to adjust the pig iron production amount based on the high-temperature property evaluation index. In this blast furnace operation, for example, when it is difficult to adjust the weighted average value described later, the pig iron production amount is reduced. Here, the reduction degree at the start of fusion is specified by the weighted average value of the reduction degrees at the start of fusion of multiple types of ore raw materials forming the ore layer and the residence time in the furnace.
Then, at least one of the weighted average value and the residence time in the furnace is adjusted so that the reduction rate at the start of fusion is equal to or greater than the lower limit. The weighted average value is represented by the following formula (I).

In the above formula (I), i is the type of raw ore, Rs _i is the reduction rate [%] of the type i of raw ore at the start of fusion, and M _i R is the blending ratio [mass %] of the type i of raw ore to all types of raw ore.

The reduction rate at the start of fusion can be expressed by the following formula (II):

In the above formula (II), Rs ^* is the reduction rate at the start of fusion [-], _Rsav is the weighted average value [%], γ is the coefficient [%/h], _tres is the residence time in the furnace [h], and _tres,0 is the reference time for the residence time in the furnace [h].

In the fourth invention of the present application, the method of operating a blast furnace includes adjusting at least one of the weighted average value Rs _av and the residence time in the blast furnace t _res , which define the reduction degree at the start of fusion, so that the reduction degree at the start of fusion of the ore layer formed in the blast furnace is equal to or higher than a lower limit value. The reduction degree at the start of fusion is represented by the following formula (III), and is the reduction degree of the ore layer formed in the blast furnace when the pressure drop of the ore layer reaches a predetermined value.

In the above formula (III), Rs ^* is the reduction rate at the start of fusion [-], _Rsav is the weighted average value [%], γ is the coefficient [%/h], _tres is the residence time in the furnace [h], and _tres,0 is the reference time for residence time in the furnace [h]. In the above formula (IV), i is the type of ore raw material, _Rsi is the reduction rate at the start of fusion of the ore raw material of type i [%], and _MiR is the blending ratio of the ore raw material of type i to all types of ore raw materials [mass%].

According to the present invention, it is possible to derive the high-temperature property evaluation indexes (fusion start temperature and reduction rate at the start of fusion) of the ore raw material without conducting tests to measure the high-temperature property evaluation indexes.

FIG. 2 is a diagram illustrating a mathematical model used in deriving the high-temperature property evaluation index of the ore layer. 1 is a flowchart showing a process for deriving high-temperature property evaluation indexes (fusion start temperature Ts ^* and fusion start reduction rate Rs ^* ) of an ore layer. FIG. 1 is a diagram showing the relationship between the shrinkage rate and temperature of an ore layer. FIG. 1 is a diagram for explaining an outline of an image analysis method using X-ray CT images. FIG. 1 is a diagram showing an example of the correlation between the coke ratio CR, the productivity _P0 , and the weighted average value Rs _av. FIG. 1 is a diagram showing the temperature rise pattern (relationship between temperature and time) in a high-temperature property test. FIG. 1 is a diagram showing a load pattern (relationship between temperature and load) in a high temperature property test. FIG. 1 is a diagram showing reducing gas conditions ( _H2 concentration 0%) for high temperature property tests. FIG. 1 is a diagram showing the reducing gas conditions ( _H2 concentration 10%) of the high temperature property test. FIG. 1 is a diagram showing the reducing gas conditions ( _H2 concentration 15%) of the high temperature property test. FIG. 1 is a diagram showing the relationship between the shrinkage rate and porosity of a sintered ore layer. FIG. 2 is a graph showing the relationship between the shrinkage rate of a sintered ore layer and the apparent particle size. FIG. 1 is a diagram showing the effect of _H2 concentration (0%) in the reducing gas on the average reduction rate of the ore layer. FIG. 1 shows the effect of _H2 concentration (10%) in the reducing gas on the average reduction rate of the ore layer. FIG. 1 shows the effect of _H2 concentration (15%) in the reducing gas on the average reduction rate of the ore layer. FIG. 1 is a diagram showing the effect of _H2 concentration (0%) in the reducing gas on the shrinkage rate of the ore layer. FIG. 1 is a diagram showing the effect of _H2 concentration (10%) in the reducing gas on the shrinkage rate of the ore layer. FIG. 1 is a diagram showing the effect of _H2 concentration (15%) in the reducing gas on the shrinkage rate of the ore layer. FIG. 1 is a diagram showing the effect of _H2 concentration (0%) in the reducing gas on the pressure drop of the ore layer. FIG. 1 is a diagram showing the effect of _H2 concentration (10%) in the reducing gas on the pressure drop of the ore layer. FIG. 1 is a diagram showing the effect of _H2 concentration (15%) in the reducing gas on the pressure drop of the ore layer. FIG. 1 is a diagram showing experimental and calculated values of the fusion start temperature Ts ^* for each _H2 concentration. FIG. 1 is a diagram showing experimental and calculated values of the reduction rate Rs ^* at the start of fusion for each _H2 concentration. FIG. 2 shows the composition of the reducing gas as a function of temperature. FIG. 13 is a diagram showing gas flow velocity according to Bosch gas flow rate (conditions 1 to 3). FIG. 1 is a diagram showing a temperature rise pattern (relationship between temperature and time) according to the residence time in the furnace (conditions 1 to 3). FIG. 1 is a diagram showing the behavior of the reduction rate (relationship between the reduction rate and the temperature) according to the residence time in the furnace (conditions 1 to 3). FIG. 1 is a diagram showing the behavior of pressure loss (the relationship between pressure loss and temperature) depending on the residence time in the furnace (conditions 1 to 3). FIG. 1 is a diagram showing the relationship between the residence time in the furnace and the reduction rate Rs ^* at the start of fusion. FIG. 13 is a diagram showing the relationship between the weighted average value Rs _av and the reduction rate Rs ^* at the start of fusion depending on the coke rate, and the lower limit value Rs ^* _min . FIG. 13 is a diagram showing changes in the weighted average value Rs _av and the productivity P ₀ associated with the blending design of the ore raw material, and changes in the weighted average value Rs _av and the productivity P ₀ associated with the design of the productivity P ₀ . FIG. 13 is a diagram showing the relationship between the weighted average value Rs _av and the reduction rate Rs ^* at the start of fusion according to the pressure loss in the lower part of the furnace, and the lower limit value Rs ^* _min .

First Embodiment
In this specification, the term "ore raw material" refers to lump ore, sinter, pellets, carbon-containing agglomerated ore, and other agglomerated ores, and the term "ore raw material packed bed" refers to a layer consisting of only one type of ore raw material. The term "ore layer" refers to a layer formed in a furnace and containing at least one of the ore raw materials, and may contain coke, ferro-coke, or auxiliary materials. The term "ore layer" is a concept that includes the ore raw material packed bed. In the furnace, the ore layer and the coke layer are formed alternately in the furnace height direction.

In this specification, the "high temperature properties" refer to the reduction rate, contraction rate, and temperature dependence of pressure loss of the ore raw material or the ore layer. The "high temperature property evaluation index" refers to an index determined from the high temperature properties, specifically, the fusion start temperatures Ts, Ts ^* , and the fusion start reduction rates Rs, Rs ^* .

The fusion start temperature Ts and the reduction ratio at the start of fusion Rs are defined as the temperature and reduction ratio at which the ore raw material softens and shrinks and the pressure loss of the ore raw material packed bed rises to a predetermined value in a predetermined high-temperature property test using a single type of ore raw material with a particle size within a predetermined range, and are used as high-temperature property evaluation indexes for the ore raw material. That is, the fusion start temperature Ts and the reduction ratio at the start of fusion Rs are high-temperature property evaluation indexes obtained in a high-temperature property test using a single type of ore raw material. Here, the predetermined value of pressure loss can be, for example, 200 _mmH2O .

The fusion start temperature Ts ^* and the reduction rate at the start of fusion Rs ^* are defined as the temperature and reduction rate at which the ore raw material contained in the ore layer softens and shrinks, and the pressure loss of the ore layer rises to a predetermined value, respectively, and are used as high-temperature property evaluation indexes of the ore layer. That is, the fusion start temperature Ts ^* and the reduction rate at the start of fusion Rs ^* are high-temperature property evaluation indexes targeted at the ore layer in an actual blast furnace. Here, the predetermined value of the pressure loss can be, for example, 50 kPa/m. The fusion start temperature Ts ^* and the reduction rate at the start of fusion Rs ^* may be used as high-temperature property evaluation indexes for the entire ore layer, or may be used as a distribution within the ore layer.

Hereinafter, as one embodiment of the present invention, a method for deriving the fusion start temperature Ts ^* of the ore layer and the fusion start reduction rate Rs ^* will be described.

(Outline of derivation of fusion start temperature Ts ^* and fusion start reduction rate Rs ^* )
As described above, the fusion start temperature Ts ^* and the reduction ratio Rs ^* at the start of fusion are the temperature and reduction ratio at the time when the ore raw material contained in the ore layer softens and shrinks, and the pressure loss of the ore layer rises to a predetermined value. In order to derive the fusion start temperature Ts ^* and the reduction ratio Rs ^* at the start of fusion, it is necessary to predict "1. Reduction behavior of the ore raw material", "2. Contraction behavior of the ore layer", and "3. Increase in pressure loss associated with contraction of the ore layer". The reduction behavior of the ore raw material is the change over time of the reduction ratio, which will be described later, the contraction behavior of the ore layer is the change over time of the contraction ratio, which will be described later, and the increase in pressure loss associated with contraction of the ore layer is the change over time of the pressure loss, which will be described later. In this embodiment, as shown in FIG. 1 , focusing on one layer of ore layer, in a predetermined mathematical model, the change in temperature over time in the process of the ore layer descending inside the blast furnace, the change in pressure, composition and flow rate of the reducing gas over time, and the change in load (vertical stress) applied to the ore layer over time are used as input conditions, and the reduction rate of the ore raw material contained in the ore layer, the contraction rate of the ore layer, and the pressure loss occurring in the ore layer are calculated (output).

As a specific calculation method, as shown in FIG. 2, first, the initial conditions (temperature, reducing gas, and load) are input into the mathematical model (step S101), and the reduction rate of the ore layer (step S102), the contraction rate of the ore layer (step S103), and the pressure loss of the ore layer (step S104) are calculated. Details of steps S102 to S104 will be described later.

Next, it is determined whether the pressure loss calculated in step S104 has reached a predetermined value (step S105), and if the pressure loss has not reached the predetermined value, the conditions (temperature, reducing gas, and load) after a predetermined time interval Δt (e.g., 5 seconds) have elapsed are input to the mathematical model (step S106). The input conditions here are conditions according to the position of the ore layer (height inside the furnace) when the ore layer descends inside the furnace during the time interval Δt.

After inputting the conditions (temperature, reducing gas, and load) after the time interval Δt (for example, 5 seconds) has elapsed into the mathematical model, the reduction rate of the ore layer (step S102), the contraction rate of the ore layer (step S103), and the pressure loss of the ore layer (step S104) are calculated again. Then, the processes from step S106 to step S104 are repeated until the pressure loss calculated in step S104 reaches a predetermined value. When the pressure loss reaches the predetermined value, the fusion start temperature Ts ^* and the reduction rate Rs ^* at the start of fusion are specified (step S107). Here, the fusion start temperature Ts ^* is the temperature (input condition of step S106) when the pressure loss that has reached the predetermined value is calculated, and the reduction rate Rs ^* at the start of fusion is the reduction rate (calculated value of step S102) when the pressure loss that has reached the predetermined value is calculated.

(Calculation of reduction rate of ore layer; step S102)
In step S102 (calculation of reduction rate) shown in FIG. 2, the reduction rate distribution in the ore layer and the composition change of the reducing gas when reducing gas (CO, CO ₂ , H ₂ , H ₂ O, N ₂ ) is blown in from the bottom of the ore layer are calculated by analyzing one-dimensional unsteady reaction rates (reduction reaction rate of the ore raw material and gasification reaction rate of the coke).

The reduction reaction rate of the ore raw material is based on a three-interface unreacted core model, and details including the reduction reaction rate equation are described, for example, in Non-Patent Document 4. Here, a reduction test is separately performed on an ore raw material having a similar chemical composition to the ore raw material used in the model calculation, and the reaction rate parameters included in the reduction reaction rate equation can be adjusted so that the results of this reduction test can be reproduced. Details of the coke gasification reaction rate equation are described, for example, in Non-Patent Document 5. Here, a gasification reaction test is separately performed on a coke having a similar chemical composition to the coke used in the model calculation, and the reaction rate parameters included in the gasification reaction rate equation can be adjusted so that the results of this gasification reaction test can be reproduced.

When calculating the reduction rate of an ore layer, the mixing state and particle size distribution of the raw materials (various ore raw materials, coke, ferro-coke, and auxiliary raw materials) contained in the ore layer can be taken into consideration when grasping the reduction rate distribution within the ore layer. Specifically, the ore layer is divided into a predetermined number of calculation cells (e.g., calculation cells with a height of 1 mm) in the furnace height direction, and the volume ratio and particle size of each raw material contained in the ore layer are set in each calculation cell. The initial porosity is the porosity of the ore layer before it softens and shrinks, and can be set for each calculation cell.

The reducing gas injected from the bottom of the ore layer is assumed to flow at a flow rate according to the volumetric proportion of each raw material contained in the ore layer, and the change in reducing gas concentration due to the reduction reaction and gasification reaction in each phase is solved. The ore layer heating conditions and the temperature dependence of the pressure, composition, and flow rate of the reducing gas (mixed gas) in the reduction reaction rate analysis can be set appropriately to simulate the conditions during actual blast furnace operation, that is, to match the conditions along the path along which the ore layer descends.

The method for determining the reduction rate distribution in the ore layer is not limited to one-dimensional unsteady reaction rate analysis, and may be, for example, two-dimensional or three-dimensional unsteady reaction rate analysis. The method for determining the reduction reaction rate of the raw ore material is not limited to the three-interface unreacted core model, and may be, for example, a multi-stage reaction zone model or a grain model. Furthermore, in one-dimensional unsteady reaction rate analysis or three-interface unreacted core model, chemical reaction rate equations disclosed in publicly known documents may be used as appropriate instead of the above-mentioned reaction rate equations (reduction reaction rate equation and gasification reaction rate equation).

In order to accurately calculate the shrinkage rate of the ore layer, it is preferable to divide the ore layer into a predetermined number of calculation cells and grasp the reduction rate distribution in the furnace height direction, as described above. However, it is also possible to calculate the reduction rate of the entire ore layer (so-called average reduction rate) by setting the volume ratio and particle size of each raw material in the entire ore layer (one layer of the ore layer) without dividing the ore layer into a predetermined number of calculation cells. In this case, there is an advantage that it is easy to compare with the results of existing high-temperature property tests.

(Calculation of shrinkage rate of ore layer; step S103)
In step S103 shown in Fig. 2, the shrinkage rate of the ore layer is calculated by integrating the shrinkage speed of the ore layer with respect to time. The shrinkage speed of the ore layer can be derived by dividing it into two temperature ranges in which the governing factors of the shrinkage behavior of the ore layer are different from each other. This will be specifically described below.

Figure 3 shows the relationship between the shrinkage rate of the ore layer and the temperature. In Figure 3, the shrinkage rate shows a maximum value at the boundary temperature. In the first temperature region that is lower than the boundary temperature, and in the second temperature region that is higher than the boundary temperature, the shrinkage rate is lower than the maximum value. Therefore, the shrinkage rate of the ore layer can be derived in each of the first temperature region and the second temperature region.

In the first temperature region, the shrinkage rate of the ore layer can be derived based on the following equations (1) and (2).

In the above formula (1), the left side is the shrinkage rate [s ^-1 ] of the i-th calculation cell, Sr _i is the average shrinkage rate [-] of the entire i-th calculation cell, t is time [s], W is the load [Pa] applied to the ore layer, and η is the apparent softening viscosity [Pa·s] of the ore raw material contained in the ore layer. The apparent softening viscosity η is obtained from the above formula (2). In the above formula (2), η ₀ is a constant [Pa·s], c ₁ is a coefficient [K], and T is the temperature [K] of the ore layer. The apparent softening viscosity η is obtained, for example, by a load-softening test, and the constant η ₀ and the coefficient c ₁ are obtained from the apparent softening viscosity η using the above formula (2).

In the first temperature region, the shrinkage rate of the ore layer (dSri/dt) is proportional to the load W applied to the ore layer and inversely proportional to the apparent softening viscosity η (shrinkage resistance of the raw ore). As can be seen from the above formulas (1) and (2), the shrinkage rate of the ore layer in the first temperature region is calculated from the load W applied to the ore layer and the temperature T of the ore layer (i.e., the input conditions in S101 and S106 shown in FIG. 2).

In the second temperature region, the shrinkage rate of the ore layer can be derived based on the following equations (3) to (6).

In the above formula (3), the left side is the shrinkage rate [s ^-1 ] of the i-th calculation cell, Sr _i is the overall average shrinkage rate [-] of the i-th calculation cell, t is time [s], β is a coefficient [-], M _SP is the mass of the ore raw material [kg], V _{0. SP} is the volume of the ore layer before shrinkage (initial volume) [m ³ ], and V _liq is the volume of the molten liquid per 1 kg of the ore raw material [m ³ /kg].

The volume V _liq of the molten liquid is calculated by the above formula (4). In the above formula (4), c ₂ is a coefficient [m ³ /(kg·K)], c ₃ and c ₄ are coefficients [m ³ /kg], T is the temperature of the ore layer [K], and R _i is the reduction rate [-] of the i-th calculation cell. The coefficients c ₂ , c ₃ , and c ₄ can be calculated in advance for each type of ore raw material by thermodynamic equilibrium calculation (e.g., Factsage) based on the composition of the ore raw material.

The coefficient β shown in the above formula (3) is obtained by the above formula (5). In the above formula (5), _c5 and _c6 are coefficients [-], and _XFe is the volume fraction of metallic iron [-]. The volume fraction of metallic iron _XFe is obtained by the above formula (6). In the above formula (6), _VFe is the volume of metallic iron [ ^m3 ], _V0.SP is the volume of the ore layer before shrinkage [ ^m3 ], and _Sri is the overall average shrinkage rate [-] of the i-th calculation cell. The coefficients _c5 and _c6 can be obtained in advance by a high-temperature property evaluation test.

As can be seen from the above formula (3), in the second temperature region, the shrinkage rate of the ore layer (dSr _i /dt) is proportional to the generation rate of the molten liquid (dV _liq /dt). Moreover, the coefficient β decreases with an increase in the volume fraction X _Fe of metallic iron in the ore layer. In the second temperature region, the shrinkage promotion effect due to the generation of the molten liquid and the shrinkage inhibition effect due to the generated metallic iron are the main controlling factors that determine the shrinkage rate of the ore layer. As can be seen from the above formulas (3) to (6), the shrinkage rate of the ore layer in the second temperature region is calculated from the temperature T of the ore layer and the reduction rate R _i , and the reduction rate R _i calculated in step S102 shown in FIG. 2 is used as the reduction rate.

The constant _η0 and the coefficients _c1 to _c6 are determined based on the properties of the ore raw material, such as the composition and pore structure. The constant _η0 and the coefficients _c1 to _c6 do not change unless the type of ore raw material is changed, and do not change due to changes in the ore raw material filling conditions or the reducing gas conditions. In addition, when multiple types of ore raw materials are mixed in the ore layer, the shrinkage rate of the entire ore layer can be obtained by determining the shrinkage rate for each type of ore raw material and taking a weighted average based on the volume ratio of each ore raw material in the ore layer.

The shrinkage rate of the ore layer is expressed as a value obtained by integrating the shrinkage rate of the ore layer derived by the above formulas (1) to (6) over time. The average shrinkage rate Sr of the entire ore layer is calculated by the following formula (7). In the following formula (7), L ₀ is the initial layer thickness [m] of the ore layer, and L _i is the layer thickness [m] of the i-th (i = 1 to n) calculation cell. The initial layer thickness L ₀ is the layer thickness of the ore layer before the ore layer softens and shrinks. The layer thickness L _i is calculated by the following formula (8). In the following formula (8), L _0,i is the initial layer thickness [m] of the i-th calculation cell, and Sr _i is the average shrinkage rate [-] of the i-th calculation cell.

When the reduction rate distribution in the furnace height direction in the ore layer is obtained in step S102 shown in FIG. 2, the contraction rate distribution in the furnace height direction in the ore layer can be obtained in step S103 shown in FIG. 2. On the other hand, when the average reduction rate of the entire ore layer is obtained in step S102 shown in FIG. 2, the contraction rate of the entire ore layer can be obtained in step S103 shown in FIG. 2.

(Calculation of pressure loss in ore layer; step S104)
The pressure drop of the ore layer can be calculated using the average shrinkage rate Sr of the entire ore layer obtained in step S103 shown in Fig. 2. Specifically, the pressure drop of the ore layer can be calculated by the following formula (9). The following formula (9) is the Ergun formula used to calculate the pressure drop.

In the above formula (9), ΔP/ΔL is the pressure loss of the ore layer [Pa/m], ε is the porosity of the ore layer [-], d is the particle size [m] of each raw material contained in the ore layer, and φ is the shape factor [-] of each raw material contained in the ore layer. The value φd obtained by multiplying the shape factor φ and the particle size d indicates the effective diameter of each raw material. μ is the viscosity of the reducing gas [Pa·s], U is the superficial flow velocity of the reducing gas [m/s], and ρ is the density of the reducing gas [kg/m ³ ]. Note that the formula for calculating the pressure loss is not limited to the above formula (9), and any known formula can be appropriately adopted.

The porosity ε shown in the above formula (9) can be calculated using the following formula (10).

In the above formula (10), ε ₀ is the initial porosity [-], α is the coefficient [-], and Sr is the shrinkage rate [-] of the ore layer. The coefficient α is a value indicating the amount of volume reduction of voids relative to the amount of volume reduction of the ore layer when the ore layer shrinks, and depends on the amount of closed pores and softening and melting properties of the raw ore. Note that the voids here refer to voids that directly contribute to the air flow resistance of the ore layer in the flow of reducing gas, and do not include, for example, closed pores inside the raw ore particles.

As shown in the above formula (9), the pressure loss ΔP/ΔL can be expressed as a function of the porosity ε, and as shown in the above formula (10), the porosity ε can be expressed as a function of the shrinkage rate Sr. Therefore, if the shrinkage rate Sr is derived, the pressure loss ΔP/ΔL can be calculated from the above formulas (9) and (10).

When the shrinkage rate distribution in the furnace height direction in the ore layer is obtained in step S103 shown in FIG. 2, the distribution of pressure loss ΔP/ΔL in the furnace height direction in the ore layer can be obtained in step S104 shown in FIG. 2. On the other hand, when the shrinkage rate of the entire ore layer is obtained in step S103 shown in FIG. 2, the pressure loss ΔP/ΔL of the entire ore layer can be obtained in step S104 shown in FIG. 2.

The coefficient α shown in the above formula (10) can be determined based on the analysis results of X-ray CT images of the ore raw material (e.g., sintered ore) or the ore layer. Note that the method for determining the coefficient α is not limited to the method using the analysis of X-ray CT images.

Figure 4 shows an overview of an image analysis method using X-ray CT images. A crucible 100 is filled with raw ore 101, and a mixed layer 102 and a coke layer 103 are stacked above and below the raw ore, respectively. By performing X-ray CT photography, a horizontal cross-sectional image 104a of the crucible 100 is obtained, and the area from which this cross-sectional image 104a is obtained is an area AA (referred to as an area to be analyzed) where only the raw ore 101 exists.

In the analysis area AA, a predetermined number of cross-sectional images 104a are extracted at equally spaced positions in the height direction of the crucible 100, and each cross-sectional image 104a is used to determine the porosity and apparent particle size. First, the cross-sectional image 104a is binarized to generate a binarized image 104b, and two extracted images 104c and 104d are generated by performing a masking process on the binarized image 104b. The extracted image 104c is an image in which only the particles of the raw ore material are extracted from the binarized image 104b, and the extracted image 104d is an image in which the internal space of the crucible 100 is extracted from the binarized image 104b.

For the extracted images 104c and 104d, the number of pixels in the black parts, the number of pixels in the white parts, and the number of pixels surrounding the white parts are counted, and the porosity of the ore raw material layer is calculated based on the following formula (11).

In the above formula (11), ε is the void ratio [-], S _Void is the number of pixels [pixels] of the void region, S _A is the number of pixels [pixels] of the region located outside the crucible 100, and S _B is the number of pixels [pixels] of the region located inside the crucible 100.

By performing the above-mentioned image analysis on multiple ore raw material layers with different shrinkage rates Sr, the porosity ε is determined for each ore raw material layer, and the coefficient α that satisfies the above formula (10) is determined based on this porosity ε. This makes it possible to define the relationship (linear function) between the coefficient α and the shrinkage rate Sr. By deriving the shrinkage rate Sr as described above, the coefficient α can be determined based on the relationship (linear function) between the coefficient α and the shrinkage rate Sr. Note that when the porosity ε is determined simply, the coefficient α may be set to a fixed value according to the type of ore raw material.

In the above explanation, the porosity ε shown in the above formula (9) is defined as a function of the shrinkage rate Sr (the above formula (10)). In addition, the particle size d shown in the above formula (9) can also be defined as a function of the shrinkage rate Sr. In this case, the above-mentioned image analysis is performed to determine the apparent particle size dc of the particles for each of the multiple ore raw material layers with different shrinkage rates Sr. This allows the correlation between the shrinkage rate Sr and the particle size dc to be determined, and by using this correlation, the particle size d shown in the above formula (9) can be determined based on the shrinkage rate Sr derived as described above.

The particle size dc can be calculated using the following formulas (12) to (14).

In the above formulas (12) to (14), dc is the apparent particle size [m], S _Solid is the area of the region where the particle exists [m ² ], and L _Solid is the peripheral length of the particle [m]. D is the inner diameter [m] of the crucible 100, S' _Solid is the number of pixels [pixels] of the region where the particle exists, and S _B is the number of pixels [pixels] described in the above formula (11). L' _Solid is the number of pixels [pixels] constituting the periphery of the particle, and L ₀ is the number of pixels [pixels] constituting the periphery of the crucible 100.

The method for calculating pressure loss is not limited to the above method. For example, in the pressure loss calculation formula disclosed in Non-Patent Document 6, the coefficient of the inertia term can be defined as a function of the contraction rate, and the pressure loss can be calculated based on the contraction rate. In addition, the pressure loss can be calculated using the pressure loss calculation formula (including the contraction rate Sr) disclosed in Non-Patent Document 7.

(Identification of high temperature property evaluation index; step S107)
In step S107 shown in FIG. 2, the reduction rate calculated in step S102 and the pressure loss calculated in step S104 are used to determine the fusion start temperature Ts ^* and the fusion start reduction rate Rs ^* , which are the high-temperature property evaluation indexes of the ore layer.

As described above, the fusion start temperature Ts ^* and the reduction ratio at the start of fusion Rs ^* respectively indicate the temperature and the reduction ratio when the ore raw material contained in the ore layer softens and shrinks, causing the pressure loss of the ore layer to rise to a predetermined value. Therefore, the temperature (input condition) when the pressure loss calculated in step S104 indicates the predetermined value is the fusion start temperature Ts ^* . In addition, the reduction ratio (the reduction ratio calculated in step S102) when the pressure loss calculated in step S104 indicates the predetermined value is the reduction ratio at the start of fusion Rs ^* . The predetermined value of the pressure loss described above can be, for example, 50 kPa/m.

In this embodiment, a method for deriving the fusion start temperature Ts ^* and the reduction rate at the start of fusion Rs ^* , which are the high-temperature property evaluation indexes of the ore layer, has been described, but the method can also be applied to deriving the fusion start temperature Ts and the reduction rate at the start of fusion Rs, which are the high-temperature property evaluation indexes of the ore raw material. When deriving the fusion start temperature Ts and the reduction rate at the start of fusion Rs, the ore layer is set as a raw material ore packed bed consisting of only one type of raw material ore, and the input conditions shown in Figure 1 are set as the test conditions for the high-temperature property test (for example, the predetermined test conditions described in Non-Patent Document 1).

In the test conditions described in Non-Patent Document 1, the lower furnace is heated at a rate of 10 ° C./min, and after reaching 1700 ° C., it is maintained at this temperature. For the upper furnace, the heating rate is 10 ° C./min up to 1000 ° C., and the heating rate is 5 ° C./min above 1000 ° C. For the reducing gas, N ₂ is introduced up to 800 ° C., and reducing gas (CO2 9.4 vol% - H ₂ 3.6 vol% - N ₂ 67.0 vol%) is introduced above 800 ° C. The flow rate of the reducing gas is constant at 34 Nl/min, and the standard superficial velocity is 10 cm/s. As a load, 0.098 MPa is applied above 800 ° C. Note that the test conditions for the high temperature property test are not limited to those described in Non-Patent Document 1, and may be appropriately set according to the operating conditions of the blast furnace to be tested.

Specifically, in step S102 (calculation of reduction rate) shown in FIG. 2, a reduction reaction rate analysis can be performed on the ore raw material packed bed based on the temperature rise pattern and reducing gas conditions of the above-mentioned test conditions. Here, the reduction rate is calculated as the reduction rate distribution in the height direction of the ore raw material packed bed or the reduction rate (average reduction rate) of the entire ore raw material packed bed.

In step S103 (calculation of shrinkage rate) shown in FIG. 2, the shrinkage rate of the ore raw material packed bed can be derived based on the temperature rise pattern (heat rise rate according to temperature) and load pattern (load applied according to temperature) of the test conditions described above. Here, when the reduction rate distribution in the bed height direction of the ore raw material packed bed is obtained, the shrinkage rate distribution in the bed height direction of the ore raw material packed bed can be obtained. In addition, when the reduction rate (average reduction rate) of the entire ore raw material packed bed is obtained, the shrinkage rate (average shrinkage rate) of the entire ore raw material packed bed can be obtained.

In step S104 (calculation of pressure loss) shown in FIG. 2, the pressure loss of the ore raw material packed bed can be derived based on the reducing gas conditions of the test conditions described above. Here, φd in the above formula (9) is the effective diameter of the ore raw material, and the coefficient α in the above formula (10) can be obtained by performing X-ray CT image analysis on the ore raw material packed bed. On the other hand, when the shrinkage rate distribution in the bed height direction of the ore raw material packed bed is obtained, the pressure loss distribution in the bed height direction of the ore raw material packed bed can be obtained. In addition, when the shrinkage rate (average shrinkage rate) of the entire ore raw material packed bed is obtained, the pressure loss (average pressure loss) of the entire ore raw material packed bed can be obtained.

In step S107 (identification of high temperature property evaluation index) shown in Fig. 2, the temperature (heating pattern of test conditions) at which the pressure loss obtained in step S104 shows a predetermined value is identified as the fusion start temperature Ts. In addition, the average reduction ratio (obtained in the first step) at which the pressure loss obtained in step S104 shows a predetermined value is determined as the fusion start reduction ratio Rs. The predetermined pressure loss can be, for example, 200 _mmH2O .

According to the embodiment, by using the above-described mathematical model, it is possible to derive the fusion start temperature Ts ^* and the reduction rate Rs ^* at the start of fusion, or to derive the fusion start temperature Ts and the reduction rate Rs at the start of fusion, without performing a test to measure the high-temperature property evaluation index.

The processes (so-called functions) described in FIG. 2 can be realized by a program. Specifically, computer programs prepared in advance to realize each function are stored in an auxiliary storage device, and a control unit such as a CPU reads the programs stored in the auxiliary storage device into a main storage device, and the control unit executes the programs read into the main storage device, thereby operating each function. Each function can be operated by a single control device, or by multiple control devices connected to each other.

The above-mentioned program can also be provided to a computer in a state in which it is recorded on a computer-readable recording medium. Examples of recording media include optical disks such as CD-ROMs, phase-change optical disks such as DVD-ROMs, magneto-optical disks such as MO (Magnet Optical) and MD (Mini Disk), magnetic disks such as floppy (registered trademark) disks and removable hard disks, and memory cards such as Compact Flash (registered trademark), Smart Media, SD memory cards, and memory sticks. Also included as recording media are hardware devices such as integrated circuits (IC chips, etc.) that are specially designed and configured for the purposes of the present invention.

Second Embodiment
If the reduction ratio Rs ^* at the start of fusion is derived as described in the first embodiment, the blast furnace can be operated based on this reduction ratio Rs ^* at the start of fusion. Specifically, the reduction ratio Rs ^* at the start of fusion is compared with a lower limit value Rs ^* _min described later, and the blast furnace can be operated so that the reduction ratio Rs ^* at the start of fusion is equal to or greater than the lower limit value Rs ^* _min , thereby enabling stable operation of the blast furnace.

First, it was found that the reduction ratio Rs ^* at the start of fusion was correlated with the weighted average value Rs _av of the reduction ratios Rs at the start of fusion of a plurality of types of ore raw materials and the residence time in the furnace t _res . That is, the reduction ratio Rs ^* at the start of fusion can be expressed as a function of the weighted average value Rs _av and the residence time in the furnace t _res as shown in the following formula (15). According to the following formula (15), the reduction ratio Rs ^* at the start of fusion can be derived based on the weighted average value Rs _av and the residence time in the furnace t _res .

In the above formula (15), Rs ^* is the reduction rate at the start of fusion [-], _Rsav is the weighted average value [%], γ is the coefficient [%/h], _tres is the residence time in the furnace [h], and tres _,0 is the reference time for the residence time in the furnace [h]. The reference time _tres,0 can be set arbitrarily, for example, to 8.0 [h].

The coefficient γ indicates the degree of influence of the residence time t _res in the furnace on the reduction rate Rs ^* at the start of fusion, and can be determined from the correlation between the reduction rate Rs ^* at the start of fusion and the residence time t _res in the furnace. Specifically, the correlation between the reduction rate Rs ^* at the start of fusion and the residence time t _res in the furnace can be expressed as a linear function, and the slope (positive value) of this linear function is the coefficient γ. For example, as described later, the coefficient γ can be set to 2.76 [%/h].

The weighted average value Rs _av shown in the above formula (15) is expressed by the following formula (16).

In the above formula (16), Rs _av is the weighted average value [%], i is the type of ore raw material, Rs _i is the reduction rate at the start of fusion of the ore raw material of type i [%], and M _i R is the blending ratio of the ore raw material of type i to all types of ore raw materials [mass %].

As can be seen from the above formula (16), the weighted average value Rs _av can be adjusted by changing the blending ratio M _i R and the reduction ratio Rs _i at the start of fusion. The blending ratio M _i R can be changed by changing the blending amount of each ore raw material. The reduction ratio Rs _i at the start of fusion can be changed by changing the type of ore raw material. By designing the blending of the ore raw materials based on this point, the weighted average value Rs _av after the blending design can be grasped.

The residence time in the furnace t _res shown in the above formula (15) is expressed by the following formula (17).

In the above equation (17), t _res is the residence time in the furnace [h], P ₀ is the productivity [t/d/m ³ ], OR is the ore ratio [kg/t], CR is the coke ratio [kg/t], ρ _оre is the apparent density of the ore layer [kg/m ³ ], ε _оre is the porosity of the ore layer [-], ρ _coke is the apparent density of the coke layer [kg/m ³ ], and ε _coke is the porosity of the coke layer [-].

According to the above formula (15), by adjusting either one of the weighted average value Rs _av and the residence time in the furnace t _res , or by adjusting both the weighted average value Rs _av and the residence time in the furnace t _res , the reduction rate Rs ^* at the start of fusion can be adjusted, and the reduction rate Rs ^* at the start of fusion can be set to the lower limit value Rs ^* _min or more. By adjusting both the weighted average value Rs _av and the residence time in _{the furnace t res , it} is possible to deal with cases where the reduction rate Rs ^* at the start of fusion cannot be sufficiently adjusted to be the lower limit value Rs ^* _min or more by simply adjusting one of the weighted average value Rs _av and the residence time in the furnace t _res . For example, when the weighted average value Rs av alone cannot be adjusted, the residence time in the furnace t res can also be adjusted, and when the residence time in the furnace t _res alone cannot be adjusted, the weighted average value Rs _av can also be adjusted. According to the above formula (16), the weighted average value Rs _av can be adjusted by designing the blending ratio of a plurality of types of raw ore materials.

As shown in the above formula (17), the residence time in the furnace t _res depends on the productivity P ₀ , the ore ratio OR, the coke ratio CR, the apparent densities ρ _оre and ρ _coke of the ore layer and the coke layer, and the porosities ε _оre and ε _coke of the ore layer and the coke layer, but considering actual blast furnace operation, the parameters that are easy to adjust are the productivity P ₀ and the coke ratio CR. Therefore, the residence time in the furnace t _res can be adjusted by adjusting at least one of the productivity P ₀ and the coke ratio CR.

In this embodiment, the reduction rate Rs _i at the start of fusion and the blending ratio M _i R are set for each type of raw ore, but there are multiple brands of raw ore such as lump ore and pellets, and even if the type of raw ore is the same (lump ore or pellets), the reduction rate Rs at the start of fusion may differ between different brands. Therefore, in the blending design of this embodiment, when multiple brands of raw ore are used as at least one type of raw ore among lump ore and pellets, it is preferable to use the reduction rate Rs at the start of fusion and the blending ratio MR set for each brand as the reduction rate Rs at the start of fusion and the blending ratio MR of the raw ore of that type.

Specifically, for example, in the case where sinter, lump ore, and pellets are used as the ore raw material, and lump ore of brand a and lump ore of brand b are used as the lump ores, the reduction ratio Rs at the start of fusion and the blending ratio MR set for the lump ore of brand a and the lump ore of brand b respectively become the reduction ratio Rs _i at the start of fusion and the blending ratio M _i R in the above formula (16). That is, the subscript i shown in the above formula (16) is defined not only to distinguish the type of ore raw material, but also to distinguish multiple brands belonging to one type.

For example, when sinter, lump ore, and pellets are used as the ore raw material, and when pellets of brand a and pellets of brand b are used as the pellets, the reduction ratio Rs at the start of fusion and the blending ratio MR set for the pellets of brand a and the pellets of brand b, respectively, become the reduction ratio Rs _i at the start of fusion and the blending ratio M _i R in the above formula (16). That is, the subscript i shown in the above formula (16) is defined not only to distinguish the type of ore raw material, but also to distinguish multiple brands belonging to one type.

The brands include those named after the place of origin (mine) of the ore raw material or the manufacturer's company. The blending ratio MR set for each brand is the mass ratio of each brand of ore raw material to 100% mass of all types and brands (by type), and is not the mass ratio of each brand of lump ore to all brands of lump ore (i.e., the mass ratio of each brand of lump ore to 100% mass of lump ore) or the mass ratio of each brand of pellets to all brands of pellets (i.e., the mass ratio of each brand of pellets to 100% mass of pellets).

Similarly, there are multiple sintered ores with different sintering raw materials and/or firing conditions, and the reduction rate Rs at the start of fusion may differ between sintered ores with different sintering raw materials and/or firing conditions. When the sintering raw materials are different, the components or particle size of the sintering raw materials themselves may be different, or the blending ratio of the sintering raw materials may be different. When the sintering raw materials are different, for example, the components of the sintered ore will be different, and the reduction rate Rs at the start of fusion may be different. On the other hand, an example of a firing condition is the fuel ratio. When the firing conditions are different, the pore structure of the sintered ore will be different, and the reduction rate Rs at the start of fusion may be different.

For this reason, in the blending design method of this embodiment, when a plurality of sintered ores with different sintering raw materials and/or firing conditions are used as the fusion start reduction rate Rs and blending ratio M _i R shown in the above _formula (16), it is preferable to use the fusion start reduction rate Rs and blending ratio MR set for each sintered ore with different sintering raw materials and/or firing conditions, respectively. In addition, the blending ratio MR set for each sintered ore with different sintering raw materials and/or firing conditions is the mass ratio of each sintered ore with different sintering raw materials and firing conditions to 100 mass% of all types of ore raw materials, and is not the mass ratio of each sintered ore with different sintering raw materials and firing conditions to all sintered ores with different sintering raw materials and firing conditions.

(Lower limit Rs ^* _min )
The lower limit Rs ^* _min is determined based on at least one parameter of the coke ratio CR and the pressure loss (airflow resistance) in the lower part of the furnace. The pressure loss in the lower part of the furnace can be calculated in step S104 shown in FIG. 2.

First, a method for determining the lower limit value Rs ^* _min from the coke ratio CR will be described.

If the correlation between the reduction ratio Rs ^* at the start of fusion and the coke ratio CR is determined in advance, the reduction ratio Rs ^* at the start of fusion corresponding to the coke ratio CR (target value) can be determined as the lower limit Rs ^* _min by specifying the target value of the coke ratio CR. The correlation between the reduction ratio Rs ^* at the start of fusion and the coke ratio CR can be determined by the method described below.

In a coordinate system with the reduction rate Rs ^* at the start of fusion and the coke ratio CR as the coordinate axes, the operation performance of the blast furnace is plotted, and a region where the operation performance of the blast furnace when stable operation is performed (hereinafter referred to as the "stable operation region") is plotted, and a region where the operation performance of the blast furnace when stable operation is not performed (hereinafter referred to as the "unstable operation region") is plotted is identified. Then, the boundary line dividing the stable operation region and the unstable operation region can be defined as the correlation between the reduction rate Rs ^* at the start of fusion and the coke ratio CR. The "division" here does not mean that the stable operation region and the unstable operation region are strictly divided, but it is sufficient if it can roughly divide the stable operation region and the unstable operation region.

The boundary line between the stable operation region and the unstable operation region can be created, for example, by the following procedure. Among the operational records in which stable operation was performed, the operational record having the lowest coke ratio CR is extracted for each reduction ratio Rs ^* at the start of fusion. Next, an approximation formula is created based on the extracted operational record and the reduction ratio Rs ^* at the start of fusion, and this is used as the boundary line.

On the other hand, if the correlation between the coke rate CR, the productivity _P0 , and the weighted average value Rs _av is obtained in advance, the combination of the productivity _P0 and the weighted average value Rs _av corresponding to the coke rate CR (target value) can be specified by determining the coke rate CR (target value) as described above. As the correlation between the coke rate CR, the productivity _P0 , and the weighted average value Rs _av , for example, the correlation shown in FIG. 5 is used. Each curve shown in FIG. 5 shows the relationship between the productivity _P0 and the weighted average value Rs _av for each coke rate CR. When specifying a combination of the productivity _P0 and the weighted average value Rs _av corresponding to the coke rate CR (target value), it is sufficient to specify the combination of the productivity _P0 and the weighted average value Rs _av so that it is included in the region located below the curve of the coke rate CR (target value) in FIG. 5. This makes it possible to adjust the residence time in the furnace t _res as described above.

Next, a method for determining the lower limit value Rs ^* _min from the pressure loss in the lower part of the furnace will be described.

If the correlation between the reduction ratio Rs ^* at the start of fusion and the pressure loss in the lower furnace is determined in advance, the reduction ratio Rs ^* at the start of fusion corresponding to the pressure loss in the lower furnace (target value) can be determined as the lower limit Rs ^* _min by specifying the target value of the pressure loss in the lower furnace. The correlation between the reduction ratio Rs ^* at the start of fusion and the pressure loss in the lower furnace can be determined by the method described below.

In a coordinate system with the reduction rate at the start of fusion Rs ^* and the pressure loss in the lower furnace as the coordinate axes, the operation record of the blast furnace is plotted, and the stable operation region and the unstable operation region are identified as described above. Then, the boundary line dividing the stable operation region and the unstable operation region can be defined as the correlation between the reduction rate at the start of fusion Rs ^* and the pressure loss in the lower furnace.

The boundary between the stable operation region and the unstable operation region can be created, for example, by the following procedure. Among the operation records in which stable operation was performed, the operation record having the smallest value of the pressure loss in the lower furnace is extracted for each reduction rate at the start of fusion Rs ^* . Next, an approximation formula is created based on the extracted operation record and the reduction rate at the start of fusion Rs ^* , and this is used as the boundary line. In addition, since it is not necessary to strictly divide the stable operation region and the unstable operation region as described above, it is not necessary to specify the stable operation region as the region in which all operation records in which stable operation was performed are plotted. In roughly dividing the stable operation region and the unstable operation region, for example, the region in which 90% or more of all operation records in which stable operation was performed are plotted can be regarded as the stable operation region.

Example 1
In order to verify the validity of the mathematical model in the first embodiment, the experimental values obtained by the high-temperature property test and the calculated values obtained by the model were compared for the reduction, layer shrinkage, and pressure drop increase behavior during the softening process of the sintered ore.

(High temperature property test conditions)
120g of coke and 1272g of sintered ore were packed into a crucible with an inner diameter of 72mm. The temperature pattern was set as shown in Figure 6 under all test conditions to simulate a reaction in a blast furnace. As shown in Figure 7, the load on the packed bed was 36kPa under all conditions at 200-800°C, and 98kPa in the region above 950°C where softening and fusion are expected. The reducing gas conditions were set in three patterns shown in Figures 8A to 8C. Although the concentrations of CO and _H2 differed under each reducing gas condition, the CO/ _CO2 ratio and the total gas flow rate (30NL/min) were the same for all tests.

(calculation conditions)
The coke layer and sintered ore layer in the crucible were used as the calculation domain. The calculation domain was divided so that the initial height of the calculation cell was 1 mm. The input conditions were the same as the sample filling method, temperature, load, and reducing gas conditions as the high-temperature property test conditions described above. The constants required to derive the shrinkage behavior of the ore raw material layer (the above formulas (2), (4), and (5)) vary depending on the type of ore raw material, and are approximately in the following value range.
η ₀ =6×10 ⁻¹⁷ to 3×10 ³ [Pa・s]
c ₁ = 2×10 ⁴ to 8×10 ⁴ [K]
c ₂ =5×10 ⁻⁸ to 1×10 ⁻⁶ [m ³ /(kg・K)]
c ₃ = -1×10 ^-4 ~ 0 [m ³ /kg]
c ₄ = -6×10 ^-5 to -1×10 ^-3 [m ³ /kg]
c ₅ =-40 ~ 0 [-]
c ₆ =0.8 to 20 [-]

The initial porosity of the sintered ore layer was set to 0.40 based on the results of analysis of X-ray CT images. The rate parameters of the coke gasification reaction were determined by first conducting a gasification reaction experiment using only coke, and fitting the exhaust gas composition and coke reaction rate to the actual measured values. The method for setting the reaction rate parameters of the reduction reaction and gasification reaction will be described later.

Figure 9 shows the relationship between the shrinkage rate and porosity of the sintered ore layer, based on the results of analysis of X-ray CT images of sintered ore. In Figure 9, the circles indicate actual measured values based on the results of analysis of X-ray CT images, and the solid lines indicate calculated values using the above formulas (9) and (10). Here, the coefficient α shown in the above formula (10) is expressed as a function of the shrinkage rate Sr, as shown in the following formulas (18) to (19).

The value of coefficient α decreased with an increase in the shrinkage rate Sr. This is thought to be because in the early stages of the softening process of the sintered ore, the voids in the sintered ore layer decrease preferentially in response to the shrinkage of the sintered ore layer, and in the later stages when the generation of molten liquid becomes noticeable, the rate at which the pores in the sintered ore decrease increases.

Figure 10 shows the relationship between the shrinkage rate of the sintered ore layer and the apparent grain size. In Figure 10, the circles indicate the actual measured values based on the analysis results of the X-ray CT images, and the solid lines indicate the calculated values according to the following formula (20).

In the above formula (20), the value obtained by dividing the particle diameter (φd) ₀ before softening and shrinking by the square root of (1-Sr) corresponds to the apparent particle diameter taking into account the crushing of sintered ore particles due to the shrinkage of the sintered ore layer. In addition, a coefficient (1+7.2Sr ³ ) was multiplied so that the actual measured value of the apparent particle diameter can be reproduced. This coefficient represents the effect of the increase in the apparent particle diameter caused by the fusion of sintered ore particles.

(Comparison of calculated and experimental values)
The effect of the H ₂ concentration in the reducing gas on the reduction rate (average reduction rate) of the entire sintered ore layer is shown in Figures 11 to 13, the effect of the H ₂ concentration in the reducing gas on the contraction rate of the entire sintered ore layer is shown in Figures 14 to 16, and the effect of the H ₂ concentration in the reducing gas on the pressure drop of the entire sintered ore layer is shown in Figures 17 to 19. In Figures 11 to 13, the reaction rate parameters of the reduction reaction by CO and H ₂ , and the reaction rate parameters of the gasification reaction and gas shift reaction of coke by CO ₂ and H ₂ O were fitted so that the average reduction rate (calculated value) coincided with the average reduction rate (experimental value).

As shown in Figures 14 to 16, the calculated values for the shrinkage rate of the sintered ore layer were almost consistent with the experimental values, confirming the validity of the mathematical model. Also, as shown in Figures 17 to 19, the calculated values for the pressure loss of the sintered ore layer were almost consistent with the experimental values, confirming the validity of the mathematical model. As the _H2 concentration in the reducing gas increased (0% → 10% → 15%), the reduction rate increased, the shrinkage of the sintered ore layer was suppressed, and the pressure loss in the sintered ore layer decreased. The suppression of the shrinkage of the sintered ore layer is considered to be mainly due to the increase in the metallic iron ratio _XFe (above formula (6)) in the sintered ore layer due to the increase in the reduction rate.

Fig. 20 shows experimental and calculated values for the fusion start temperature Ts ^* at each _H2 concentration (0, 10, 15%), and Fig. 21 shows experimental and calculated values for the fusion start reduction rate Rs ^* at each _H2 concentration (0, 10, 15%). Although there is a slight deviation between the experimental and calculated values for the fusion start temperature Ts ^* and the fusion start reduction rate Rs ^* , the tendency that the fusion start temperature Ts* and the fusion start reduction rate ^{Rs *} increase with increasing _H2 concentration is shown, and it can be understood that this method has accuracy as a method for deriving a high temperature property evaluation index.

Example 2
The effect of the residence time t _res in the furnace on the reduction ratio Rs ^* at the start of fusion was evaluated. Here, assuming that the bosh gas consumption rate (the amount of bosh gas supplied per amount of pig iron) is constant, the effect of the residence time t _res in the furnace on the reduction ratio Rs ^* at the start of fusion can be evaluated by changing the heating rate and the gas flow rate according to the change in the residence time t _res in the furnace. As the residence time t _res in the furnace increases, the heating rate and the gas flow rate decrease.

In this example, the bosh gas consumption rate was kept constant, and the bosh gas flow rate and the residence time in the furnace t _res were varied as shown in Table 1 below to determine the reduction rate Rs ^* at the start of fusion.

Only sintered ore was used as the ore raw material, the apparent density of the sintered ore layer was 3450 kg/m ³ , the particle size of the sintered ore particles was 20 mm, and the porosity of the sintered ore layer was 40%. As for the composition of the reducing gas, CO/(CO+CO ₂ ) was changed according to the temperature as shown in FIG. 22 under all of the conditions 1 to 3 shown in Table 1 above. In FIG. 22, the solid line indicates the set value, the dotted line indicates the CO composition at Fe-FeO equilibrium, FeO-Fe ₃ O ₄ equilibrium, and Fe-Fe ₃ O ₄ equilibrium, and the dashed line indicates the equilibrium line of the Boudouard reaction. In this example, an actual blast furnace is assumed, and as shown by the solid line in FIG. 22, the conditions are set such that the CO partial pressure rises at 1100°C or higher, deviates from the Fe-FeO equilibrium line, and CO/(CO+CO ₂ ) shifts to the stable region side of the Fe phase.

Regardless of the temperature, the N ₂ concentration in the reducing gas was set to 54%, and the sum of the CO concentration and the CO ₂ concentration was set to 46%. The gas flow rate of the reducing gas was set as shown in FIG. 23, which was the value obtained by dividing the bosh gas flow rate shown in Table 1 above by the cross-sectional area of the blast furnace belly. The heating pattern was set as shown in FIG. 24, in which the residence time in the furnace t _res was lengthened with the decrease in the bosh gas flow rate so that the bosh gas consumption rate was constant. Here, the heating rate was set assuming that when the residence time in the furnace t _res was 8.0 h, it took 6.0 h to reach 1600 ° C. The load (vertical stress) applied to the sintered ore layer was 36 kPa in the temperature range of 200 to 800 ° C. and 98 kPa in the temperature range of 800 ° C. or higher in all of the conditions 1 to 3 shown in Table 1 above.

Under the above conditions, the reduction rate and pressure loss of the sintered ore layer were obtained. FIG. 25 shows the temperature dependency of the reduction rate of the sintered ore layer, and FIG. 26 shows the temperature dependency of the pressure loss of the sintered ore layer. As shown in FIG. 25, in the temperature range of 1200° C. or more, the reduction rate tends to increase as the residence time in the furnace t _res increases in the order of conditions 1, 2, and 3 shown in Table 1. On the other hand, as shown in FIG. 26, the pressure loss occurring in the sintered ore layer decreased as the residence time in the furnace t _res increases in the order of conditions 1, 2, and 3 shown in Table 1. The temperature difference between conditions 1 and 3 when the pressure loss of the sintered ore layer reached 50 kPa/m was 15° C. That is, the fusion start temperature Ts ^* increased by 15° C. as the residence time in the furnace t _res increased from 8.0 (condition 1) to 9.5 (condition 3).

In this example, the reduction ratio at the start of fusion Rs ^* was defined as the reduction ratio at the time when the pressure loss of the sintered ore layer was 50 kPa/m. Figure 27 shows the relationship between the reduction ratio at the start of fusion Rs ^* and the residence time in the furnace t _res (conditions 1 to 3). According to Figure 27, the reduction ratio at the start of fusion Rs ^* increased by 2.76% in response to an increase in the residence time in the furnace t _res of 1 h. The results shown in Figure 27 mean that the reduction ratio at the start of fusion Rs ^* increases by lengthening the reduction time before the softening and fusion of the sintered ore.

According to this embodiment, the above formula (15) is expressed as the following formula (23): As shown in the following formula (23), the coefficient γ shown in the above formula (15) is 2.76, and the reference time t _res,0 shown in the above formula (15) is 8.0 h.

Fig. 28 shows the relationship between the weighted average value (weighted average value of the reduction ratio Rs at the start of fusion) Rs _av , the reduction ratio Rs ^* at the start of fusion, and the coke ratio CR during a given operation period of blast furnace A. As shown in Fig. 28, it can be seen that the weighted average value Rs _av does not change significantly from about 69% regardless of the coke ratio CR. On the other hand, the reduction ratio Rs ^* at the start of fusion changes significantly within the range of 68 to 73%, and it can be seen that the coke ratio CR decreases as the reduction ratio Rs ^* at the start of fusion increases.

The above-mentioned lower limit value Rs ^* _min can be determined based on the relationship between the reduction ratio Rs ^* at the start of fusion and the coke ratio CR shown in Fig. 28. For example, as shown by the solid line in Fig. 28, the lower limit value Rs ^* _min can be determined according to the coke ratio CR. In the example shown in Fig. 28, the lower limit value Rs ^* _min during operation at a coke ratio CR of 280 kg/t is 70%. Here, when the coke ratio CR is increased by 10 kg/t, the lower limit value Rs ^* _min needs to be reduced by 4%, and when the coke ratio CR is decreased by 10 kg/t, the lower limit value Rs ^* _min needs to be increased by 4%.

On the other hand, in the blast furnace B, the blending of the ore raw materials was adjusted so that the reduction ratio Rs ^* at the start of fusion was equal to or greater than the lower limit Rs ^* _min when the coke ratio CR was lowered. In the blast furnace C, the operating conditions (production rate) were adjusted so that the reduction ratio Rs ^* at the start of fusion was equal to or greater than the lower limit Rs ^* _min when the coke ratio CR was lowered. Table 2 below shows the coke ratio CR, production rate _P0 , residence time in the furnace tres, weighted average value _Rsav , reduction ratio Rs ^* at the start of fusion, and lower limit Rs ^* _min before and after the above-mentioned adjustment in each of the blast furnaces B and _C.

In the blast furnace B, the weighted average value Rs _av was increased so that the reduction ratio Rs ^* at the start of fusion when the coke ratio CR was reduced exceeded the lower limit Rs ^* _min . Specifically, the blending ratio M _i R of sintered ore with a high reduction ratio Rs _i at the start of fusion was increased. On the other hand, in the blast furnace C, the productivity was reduced so that the reduction ratio Rs ^* at the start of fusion when the coke ratio CR was reduced exceeded the lower limit Rs ^* _min . As shown in Table 2 above, in both the blast furnaces B and C, the reduction ratio Rs ^* at the start of fusion could be made equal to or greater than the lower limit Rs ^* _min . FIG. 29 shows the changes in the weighted average value Rs _av and the productivity P ₀ before and after the above-mentioned adjustment in the blast furnaces B and C.

FIG. 30 shows the relationship between the weighted average value (weighted average value of the reduction rate Rs at the start of fusion) Rs _av , the reduction rate ^Rs at the start of fusion, and the pressure loss in the lower furnace during a given operation period of the blast furnace A. As shown in FIG. 30, it can be seen that the weighted average value Rs _av does not change significantly from about 68 to 69% regardless of the pressure loss in the lower furnace. On the other hand, the reduction rate Rs ^* at the start of fusion changes significantly within the range of 68 to 74%, and it can be seen that the pressure loss in the lower furnace decreases with the increase in the reduction rate Rs ^* at the start of fusion. Based on the relationship between the reduction rate Rs ^* at the start of fusion and the pressure loss in the lower furnace shown in FIG. 30, the lower limit value Rs ^* _min described above can be determined. For example, as shown by the solid line in FIG. 30, the lower limit value Rs ^* _min can be determined according to the pressure loss in the lower furnace.

100: crucible, 101: raw ore, 102: mixed layer, 103: coke layer, 104a: cross-sectional image, 104b: binarized image, 104c, 104d: extracted images, AA: analysis target area

Claims (9)

A method for estimating high-temperature properties of a packed bed of raw ore, comprising the steps of: deriving a high-temperature property evaluation index of the packed bed of raw ore based on a pressure loss in the packed bed of raw ore caused by softening and shrinkage of the raw ore;
Calculating a reduction rate of the ore raw material based on a temperature of the ore raw material packed bed and a condition of a reducing gas supplied to the ore raw material packed bed;
Calculating a contraction rate of the ore raw material packed bed based on the temperature, the load applied to the ore raw material packed bed, and the reduction rate;
Calculating a pressure drop of the raw ore packed bed based on the shrinkage rate;
The high temperature property evaluation index is a fusion start reduction rate, which is the reduction rate of the ore raw material when the calculated pressure drop reaches a predetermined value, or a fusion start temperature, which is the temperature of the ore raw material packed bed when the calculated pressure drop reaches a predetermined value. The shrinkage rate of the ore raw material packed bed is calculated based on the mass of the ore raw material, the initial volume and initial layer thickness of the ore raw material packed bed, the temperature distribution and load distribution of the high temperature property test, and the reduction rate of the ore raw material,
2. The high temperature property estimation method according to claim 1, wherein the pressure drop of the raw ore packed bed is calculated based on a shrinkage rate of the raw ore packed bed, a particle size of the raw ore, an initial porosity of the raw ore packed bed, and a viscosity, density and superficial flow velocity of a reducing gas in a high temperature property test. A method for estimating high-temperature properties of an ore layer, the method comprising the steps of: deriving an evaluation index for high-temperature properties of an ore layer based on a pressure loss of the ore layer caused by softening and shrinkage of an ore raw material in a blast furnace;
Calculating a reduction rate of the ore raw material based on a temperature of the ore layer and a condition of a reducing gas supplied to the ore layer;
Calculating a contraction rate of the ore layer based on the temperature, the load applied to the ore layer, and the reduction rate;
Calculating a pressure drop in the ore layer based on the shrinkage rate;
The high temperature property evaluation index is a fusion start reduction rate, which is the reduction rate of the ore raw material when the calculated pressure drop reaches a predetermined value, or a fusion start temperature, which is the temperature of the ore layer when the calculated pressure drop reaches a predetermined value. The contraction rate of the ore layer is calculated based on the mass of each raw material constituting the ore layer, the initial volume and initial layer thickness of the ore layer, the temperature distribution and load distribution along a path along which the ore layer descends in the furnace, and the reduction rate of the ore layer;
4. The high-temperature property estimating method according to claim 3, wherein the pressure drop of the ore layer is calculated based on a shrinkage rate of the ore layer, a particle size of each raw material constituting the ore layer, an initial porosity of the ore layer, and a viscosity, density, and superficial flow velocity of a reducing gas in a furnace. The high-temperature property estimation method according to any one of claims 1 to 4, characterized in that the reduction rate is derived by reduction reaction rate analysis. A computer program for causing a computer to execute the processing in the high-temperature property estimation method according to any one of claims 1 to 5. A method for operating a blast furnace based on the high temperature property evaluation index derived by the high temperature property estimation method according to claim 3 or 4,
The reduction degree at the start of fusion is determined by a weighted average value of reduction degrees at the start of fusion of the plurality of types of the ore raw materials forming the ore layer and a residence time in a furnace,
At least one of the weighted average value and the residence time in the furnace is adjusted so that the reduction rate at the start of fusion is equal to or greater than a lower limit value;
The method for operating a blast furnace, wherein the weighted average value is represented by the following formula (I).
In the above formula (I), i is the type of the ore raw material, Rs _i is the reduction rate [%] of the type i of the ore raw material at the start of fusion, and M _i R is the blending ratio [mass %] of the type i of the ore raw material to all types of the ore raw materials. The method for operating a blast furnace according to claim 7, characterized in that the reduction rate at the start of fusion is represented by the following formula (II).
In the above formula (II), Rs ^* is the reduction rate at the start of fusion [-], Rs _av is the weighted average value [%], γ is a coefficient [% / h], t _res is the residence time in the furnace [h], and t _res,0 is the reference time [h] of the residence time in the furnace. A method for operating a blast furnace, comprising adjusting at least one of a weighted average value Rs av and a residence time in the blast furnace t _res expressed by the following formula (III) so that a reduction rate at the start of fusion, which is a reduction rate of the ore layer when a pressure drop of the ore layer formed in the _blast furnace reaches a predetermined value, is equal to or higher than a lower limit value.
In the above formula (III), Rs ^* is the reduction rate at the start of fusion [-], Rs _av is the weighted average value [%], γ is a coefficient [% / h], t _res is the residence time in the furnace [h], and t _res,0 is the reference time of the residence time in the furnace [h];
In the above formula (IV), i is the type of the ore raw material, Rs _i is the reduction rate [%] of the type i of the ore raw material at the start of fusion, and M _i R is the blending ratio [mass %] of the type i of the ore raw material to all types of the ore raw materials.