Method for operating blast furnace

Abstract

A method for operating a blast furnace according to an aspect of the present disclosure is a method for operating a blast furnace in which an iron raw material containing reduced iron is charged into the blast furnace, the method including: an acquisition process of acquiring in advance an ηCO distribution in a reference operation in which no reduced iron is contained in the iron raw material to be charged; a high ηCO region identification process of defining, as an average ηCO, an average value of ηCO in the ηCO distribution or an ηCO calculated from a top gas, and identifying in advance a high ηCO region in which a relative ηCO, obtained by dividing the ηCO in the ηCO distribution by the average ηCO, is 1.0 or more; and a charging process of charging 75% by mass or more of the reduced iron into the high ηCO region.

Description

Blast furnace operation method

[0001] The present invention relates to a method for operating a blast furnace in which iron raw materials including reduced iron are charged into the furnace. This application claims priority based on Japanese Patent Application No. 2024-001753, filed on January 10, 2024, the contents of which are incorporated herein by reference.

[0002] Iron raw materials and coke as a reducing agent and fuel are alternately charged into the blast furnace from the top. Tuyere holes are formed at the bottom of the blast furnace, and hot air is blown through these holes, and auxiliary fuel such as pulverized coal is also blown into the furnace.

[0003] Patent Document 1 describes a technique of charging reduced iron or the like into a position where the ratio Lc / Dc, which is the ratio of the coke layer thickness Lc to the average coke particle diameter Dc, is 2 or less (a thin region of the coke layer, the thickness of which is equal to or less than two coke particles).

[0004] In Patent Document 2, the gas composition distribution in the furnace radial direction at the furnace top is measured, and ηCO (CO ２ % / (CO%+CO ２ %)) is 0.57 or more, a technology is disclosed in which reduced iron or the like is charged via a sub-hopper into the region.

[0005] Patent No. 6358231 Patent No. 6769507

[0006] Takatani et al. , ISIJ International, VOL. 39 (1999), pp. 155-2 2.

[0007] The charging positions of reduced iron and the like in Patent Documents 1 and 2 are both in a region where ηCO is high (region where reduction load is high).

[0008] However, the method of Patent Document 1 requires identifying areas where the coke layer is thin, which is difficult to identify.

[0009] In addition, in the method of Patent Document 2, the range in the furnace diameter direction where reduced iron and the like are charged is small, so it is necessary to prepare a sub-hopper. ２ % / (CO%+CO ２%)) is 0.57 or more, and therefore versatility is low. Furthermore, there is also a problem in that the upper limit of the charging amount of reduced iron, etc. is low.

[0010] The gist of the present disclosure is as follows.

[0011] (1) A method for operating a blast furnace according to one aspect of the present disclosure is a method for charging iron raw materials containing reduced iron into the furnace, the method comprising: a step of acquiring in advance an ηCO distribution for standard operation in which the charged iron raw materials do not contain reduced iron; a step of identifying a high ηCO region in advance in which a relative ηCO region, obtained by dividing the ηCO in the ηCO distribution by the average ηCO, is 1.0 or greater; and a step of charging 75 mass% or more of the reduced iron into the high ηCO region. (2) Preferably, in the method for operating a blast furnace described in (1) above, the high ηCO region identifying step acquires a relative ηCO distribution, which is a distribution of relative ηCO obtained by dividing the ηCO in the ηCO distribution by the average ηCO, and identifies the high ηCO region based on the relative ηCO distribution. (3) Preferably, in the method for operating a blast furnace described in (1) or (2) above, the blast furnace has a charging hopper for charging the reduced iron, and the charging hopper is a dual-purpose charging hopper for charging the reduced iron and iron raw materials other than the reduced iron. (4) Preferably, in the method for operating a blast furnace described in any one of (1) to (3) above, when the iron raw materials are taken as 100 mass%, the proportion of reduced iron contained in the iron raw materials is 0.5 mass% or more and 50 mass% or less. (5) Preferably, in the method for operating a blast furnace described in any one of (1) to (4) above, in the charging step, 80 mass% or more of the reduced iron is charged into the high ηCO region. (6) Preferably, in the blast furnace operation method described in any one of (1) to (5) above, in the high ηCO region identification step, a region in which the relative ηCO is 1.2 or more is regarded as the high ηCO region.

[0012] According to the present invention, it is possible to identify high ηCO regions and deposit reduced iron intensively in these regions, thereby more effectively reducing the reducing agent ratio (RAR).

[0013] 1 is a ηCO distribution obtained using a blast furnace mathematical model. 2 is a relative ηCO distribution obtained by replacing ηCO in the ηCO distribution of FIG. 1 with relative ηCO. 3 is a bar graph showing the reducing agent ratio (RAR) for each reduced iron charging position. 4 is a scatter diagram showing the relationship between the reduced iron mixing ratio in the high ηCO region and the reducing agent ratio (RAR). 5 is a ηCO distribution and a relative ηCO distribution obtained in an actual furnace.

[0014] The method for operating a blast furnace according to the present invention is a method for charging iron raw materials including reduced iron into a furnace, and includes an obtaining step, a high ηCO region identifying step, and a charging step. Each step will be described below.

[0015] >Regarding the Acquisition Step< The acquisition step is a step of acquiring in advance the ηCO distribution for a standard operation. The standard operation is an operation in which the charged iron raw material does not contain reduced iron, and refers to an operation during the period from the time the charging conditions are last changed to the time reduced iron is charged. Note that when the charging conditions are changed, the conditions in the furnace fluctuate immediately thereafter, but eventually stabilize. In the acquisition step, it is preferable to acquire in advance the ηCO distribution when the conditions in the furnace are stable. More preferably, in the acquisition step, the ηCO distribution at a time as close as possible to the time reduced iron is charged is acquired.

[0016] ηCO is the ratio of CO and CO ２ and is calculated by the following formula: ηCO = CO ２ % / (CO%+CO ２ %)

[0017] CO ２ There is no particular limitation on the method for measuring CO %, CO %, etc. ２ %, and CO % can be measured.

[0018] The reduced iron preferably has a metallic iron content of 70 mass % or more. The metallic iron content is the relative proportion of metallic iron in the total iron content of the reduced iron. Metallic iron is iron that is not bound to oxygen or does not exist as pyrite.

[0019] The reduced iron may be iron scrap, pig iron, reduced iron pellets, reduced iron briquettes, etc. The pig iron is cold pig iron cast into a lump weighing about 10 to 30 kg for easy handling.

[0020] The iron raw materials (excluding reduced iron) are one or more of sinter, lump ore, pellets, etc., and these may contain auxiliary materials (e.g., limestone, silica, serpentine, etc.). It is desirable that the standard operation is stable operation. Stable operation refers to an operating state in which the gas flow in the furnace and the burden packing bed's load drop and temperature distribution are properly controlled. For example, an operating state in which all of the following conditions are met is considered stable operation: - There is no uneven flow of gas flow in the furnace, and gas is supplied relatively uniformly to the packing bed, or there is little fluctuation in the gas flow. - There is little fluctuation in the load drop of the burden packing bed (e.g., load drop stagnation and slippage). - Heat is supplied to the furnace in the right amount, or there is little temperature fluctuation.

[0021] The ηCO distribution can be obtained by analyzing the gas composition measured by the upper probe of the blast furnace. A plurality of probes (e.g., upper probe, middle probe, and lower probe) extending into the furnace are installed in the shaft of the blast furnace, and the probe located closest to the furnace top is the upper probe. The number of measurement points by the upper probe is generally about 7 to 15. The ηCO distribution is a graph showing the distribution of ηCO in the radial direction of the furnace.

[0022] The ηCO distribution may be obtained by providing the operational parameters of the reference operation to a blast furnace mathematical model (see Non-Patent Document 1) and analyzing the model. That is, the ηCO distribution may be obtained based on the measurement results of an upper probe of an actual blast furnace, or may be obtained based on a blast furnace mathematical model.

[0023] Unless otherwise specified, the blast furnace mathematical model described below refers to the blast furnace mathematical model of Non-Patent Document 1.

[0024] The blast furnace mathematical model divides the internal area of ​​the blast furnace into multiple small areas, and performs calculations by substituting preset blast furnace operating conditions and raw material properties for each small area into formulas for material balance, momentum balance, and energy balance. This allows the solids (ore raw materials, etc.) and furnace gases (CO gas, H ２ This is a mathematical model that calculates state variables such as the reduction reaction rate with the furnace (e.g., gas), the gas flow in the furnace, the gas temperature in the furnace, the gas composition in the furnace, and ηCO, and comprehensively simulates the state inside the furnace.

[0025] >High ηCO Region Identifying Step< The high ηCO region identifying step is a step of identifying in advance a high ηCO region where the relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO is 1.0 or more.

[0026] The average η may be the average value of η in the η distribution (hereinafter also referred to as "distribution average η"), or may be η calculated from the top gas (hereinafter also referred to as "top gas η"). The distribution average η may be the arithmetic mean value of η at each furnace diameter position measured with an upper probe, or may be the median. Since the top gas is gas collected at the top of the furnace, the top gas η is uniquely determined. The distribution average η and the top gas η are approximately the same value. Therefore, the relative η calculated from the distribution average η and the relative η calculated from the top gas η are approximately the same value.

[0027] The furnace top gas ηCO may be obtained by analyzing the furnace top gas of an actual blast furnace, or may be obtained based on the analysis results of a blast furnace mathematical model.

[0028] Furthermore, according to the results of studies by the present inventors, the average value of η in the η distribution is often about 50%. Therefore, in the high η region identification step, the average η in the η distribution may be considered to be 50%. In this case, it is not necessary to measure and calculate the distribution average η and the top gas η.

[0029] In the high ηCO region identification step, a region where the relative ηCO is 1.1 or more is considered to be a high ηCO region. On the other hand, the region considered to be a high ηCO region may be a region where the relative ηCO is 1.1 or more, a region where the relative ηCO is 1.2 or more, or a region where the relative ηCO is 1.3 or more.

[0030] According to the findings of the present inventors, the high ηCO region usually exists continuously. However, the high ηCO region may exist discontinuously. In this case, reduced iron may be charged into each of the plurality of discontinuous high ηCO regions.

[0031] >Charging Step< The charging step is a step in which 75 mass % or more of the reduced iron is charged into the high ηCO region. That is, when the reduced iron contained in the iron raw material layer is taken as 100 mass %, 75 mass % or more of the reduced iron is charged into the high ηCO region. The charged amount of reduced iron is preferably 77 mass % or more, 80 mass % or more, 82 mass % or more, or 85 mass % or more.

[0032] In this embodiment, the high ηCO region is identified based on the average ηCO (in other words, the furnace diameter position where the relative ηCO is 1.0 is used as the boundary), so the high ηCO region can be defined over a relatively wide range. Therefore, this method is more versatile than the method of Patent Document 2, in which the position where reduced iron is charged (the furnace diameter region where the ηCO is 57% or more) is narrow or cannot be identified. The furnace diameter region where the ηCO is 57% or more described in Patent Document 2 often does not exist within the furnace. Therefore, the operating method of Patent Document 2 often cannot be implemented. On the other hand, the furnace diameter position where the relative ηCO is 1.0 always exists within the furnace in principle. The blast furnace operating method according to this embodiment can be applied to various charge distributions.

[0033] Furthermore, in the operation illustrated in FIG. 1 described later, it is difficult to identify a furnace diameter region where ηCO is 57% or more, and therefore, in the method of Patent Document 2, it is difficult to identify the position where reduced iron is charged.

[0034] By charging 75% or more by mass of the reduced iron contained in the iron raw material layer into the high ηCO region, the reduced iron can be concentrated and deposited in the region with a high reduction load, thereby reducing the reducing agent ratio (RAR). The "iron raw material layer" refers to the ore layer located between coke layers. This ore layer may be formed in one dump or multiple dumps. While the reduced iron may be concentrated and charged in a specific portion of the high ηCO region, there is a risk that the gas flow may change due to a local increase in permeability at the charging position, resulting in unstable operation. Therefore, it is desirable to charge the reduced iron throughout the high ηCO region. It is more desirable to charge the reduced iron uniformly throughout the high ηCO region.

[0035] A raw material charging method for achieving this iron raw material layer can be explored using a model experimental device simulating a blast furnace or a numerical simulation model such as DEM (Discrete Element Method). In such an experimental device, iron raw materials are charged into the furnace while changing the arrangement of reduced iron in the charging hopper, to form an iron raw material layer. After the iron raw material layer is formed, a raw material charging method for achieving the above-mentioned layer structure can be explored by evaluating the distribution of reduced iron in the iron raw material layer. In the numerical simulation model, the processing performed in the above-mentioned experimental device is simulated by information processing using software.

[0036] The charging hopper can store reduced iron and iron raw materials other than reduced iron. In other words, since the high ηCO region can be specified over a relatively wide range, reduced iron and iron raw materials other than reduced iron can be charged into the furnace from the same charging hopper (in other words, a dual-purpose charging hopper). Therefore, there is no need to provide a sub-hopper dedicated to reduced iron, as described in Patent Document 2.

[0037] When the iron raw materials (including reduced iron) forming the iron raw material layer are taken as 100 mass%, the proportion of reduced iron is preferably 0.5 mass% or more and 50 mass% or less. The proportion of reduced iron relative to the iron raw materials may be 0.8 mass% or more, 1.0 mass% or more, or 3 mass% or more. The proportion of reduced iron relative to the iron raw materials may be 40 mass% or less, 35 mass% or less, or 30 mass% or less. If the amount of reduced iron is excessively small, the effect of reducing the reducing agent ratio (RAR) cannot be fully exerted. If the amount of reduced iron is excessively large, the amount of oxygen to be reduced decreases, resulting in a decrease in reducing gas in terms of operational design, which has disadvantages such as making it impossible to maintain the furnace top gas temperature.

[0038] The present inventors obtained the above-mentioned knowledge regarding the appropriate charging position of reduced iron from the analysis results of a blast furnace mathematical model. That is, using the blast furnace mathematical model, they evaluated the effect of the charging position of reduced iron in the furnace radial direction on the reducing agent ratio (RAR).

[0039] First, the furnace volume is 4,500 m ３ Using a large blast furnace A of about 100 mm in size as the analysis target, the parameters of the blast furnace mathematical model were fitted so as to reproduce the operational specifications during a stable operation period when reduced iron was not being used (in other words, the operational specifications for standard operation) and the measured values ​​of the upper probe. The ηCO distribution in the furnace radial direction at the position of the upper probe at this time (corresponding to the ηCO distribution obtained in the acquisition step) is shown in Figure 1.

[0040] The broken line η (50.3%) in the figure is the average η (top gas η) calculated based on the gas composition of the top gas. As described above, the average η may be the distribution average η calculated based on the measurement results of the upper probe.

[0041] Figure 2 shows the relative ηCO distribution in which ηCO in the ηCO distribution in Figure 1 is replaced with relative ηCO. The relative ηCO was calculated by dividing ηCO in the ηCO distribution by the average ηCO. It can be seen that both ηCO and relative ηCO are low in the center of the furnace and near the furnace wall.

[0042] In the center of the furnace and near the furnace walls, the weight ratio of the ore raw material to the coke (O / C) is low in order to ensure good ventilation inside the furnace, and the ηCO is generally also low. The analysis results in Figure 1 agree with this.

[0043] The high ηCO region was defined as a region where the relative ηCO was 1.0 or higher, and the effect of the reduced iron charging position was analyzed using a blast furnace mathematical model. In the illustrated example, the high ηCO region, defined in terms of the dimensionless radius of the furnace diameter, is 0.38 to 0.89. Each charging condition is represented by a Roman numeral (I to XV). The metallic iron content of the reduced iron was 96 mass% and the particle size was 42 mm. 10 mass% of the iron raw materials during standard operation was replaced with reduced iron (i.e., iron raw materials other than reduced iron: reduced iron = 90 mass%: 10 mass%), and the effect of the reduced iron charging position in the furnace radial direction on the reducing agent ratio (RAR) was evaluated. The amount of reduced iron charged (mass%) at each furnace radial position under each charging condition I to XV is shown in Tables 1 to 4. The furnace radial position is indicated by the dimensionless radius of the furnace diameter.

[0044]

[0045]

[0046]

[0047]

[0048] The O / C distribution in the radial direction of the furnace was constant under all charging conditions. The ore (O) was defined as the sum of the weights of reduced iron and other iron raw materials. Under charging condition II, the amount charged toward the center of the furnace was greater than that in the high ηCO region, while under charging condition XI, the amount charged toward the wall of the furnace was greater than that in the high ηCO region. The blast rate and oxygen enrichment rate were kept constant, and only the PC injection rate was adjusted to maintain a constant molten iron temperature. The reducing agent ratios (RAR) were compared.

[0049] The effect of the reduced iron charging conditions on the reducing agent rate (RAR) is shown in Figure 3. The reducing agent rate (RAR) significantly worsened when the reduced iron was concentrated near the furnace center (charging condition II) and when it was concentrated near the furnace wall (charging condition XI). This is because the reduced iron charging conditions ηCO and ηH ２This is due to the deterioration of the reducing agent ratio (RAR). From these results, it can be said that it is undesirable to concentrate reduced iron in the furnace center or near the furnace wall where the O / C ratio is low. Furthermore, charging conditions XII, XIII, and XIV also showed a significant deterioration in the reducing agent ratio (RAR), similar to charging condition II.

[0050] The reduced iron mixing ratio in the high ηCO region (the proportion of reduced iron placed in the high ηCO region when the total amount of reduced iron is taken as 100 mass%) and the reducing agent ratio (RAR) for each charging condition are shown in Table 5 and Fig. 4. Fig. 4 is a scatter plot of the data shown in Table 5, with the reduced iron mixing ratio in the high ηCO region on the horizontal axis and the reducing agent ratio (RAR) on the vertical axis. The reduced iron mixing ratio is the proportion of the amount of reduced iron charged in the high ηCO region to the total amount of reduced iron charged into the furnace when iron raw materials containing reduced iron are charged into the furnace. A reducing agent ratio of 442.0 kg / t or less was judged to be acceptable.

[0051]

[0052] Under charging conditions II, XI, XII, XIII, and XIV, where the reducing agent ratio (RAR) deteriorated, the proportion of reduced iron mixed in the high ηCO region was found to be low. Furthermore, the RAR tended to decrease as the amount of reduced iron mixed in the high ηCO region increased. These analysis results revealed that the RAR significantly increased when the proportion of reduced iron mixed in the high ηCO region fell below 75 mass%.

[0053] EXAMPLES The present invention will be described in detail with reference to examples.

[0054] Furnace capacity 4000m ３ In the large blast furnace B described above, during a certain period (hereinafter also referred to as the operation period) when operation without reduced iron (i.e., standard operation) was stable, the η distribution in the furnace radial direction was obtained by gas analysis using an upper probe, and the η distribution in the top gas was measured by gas analysis at the furnace top, and the relative η distribution was calculated. The results are shown in Figure 5.

[0055] From the relative η distribution, the region of 0.33 to 0.94 in the dimensionless furnace radius (i.e., the region where the relative η is 1.0 or more) was defined as the high η region. Note that the period for identifying the high η region is arbitrary, but it is more preferable to specify it as a period during which stable operation is taking place. The stable operation will not be described again.

[0056] While the charging conditions of the iron raw material and coke during operation were not changed, 10 mass% of the iron raw material was replaced with reduced iron with a metallic iron content of 96%. In the example, the reduced iron was intended to be charged relatively uniformly in a specified high ηCO region. In the comparative example, the reduced iron was intended to be concentrated near the furnace wall.

[0057] From the results of preliminary simulation studies, the mixed proportions of reduced iron in the high ηCO region in the example and the comparative example were 84 mass% and 73 mass%, respectively. Table 6 shows a comparison of the main blast furnace operation parameters between the example and the comparative example.

[0058]

[0059] It can be seen that there is no significant difference in the amount of hot metal tapped and the temperature of hot metal between the Example and the Comparative Example. ２ It was confirmed that the reducing agent ratio (RAR) could be lowered due to the improved reduction efficiency.

Claims

1. A method for operating a blast furnace in which an iron raw material containing reduced iron is charged into a furnace, the method comprising: an acquisition step of previously acquiring an ηCO distribution in a reference operation in which the charged iron raw material does not contain reduced iron; a high ηCO region specifying step of defining an average value of ηCO in the ηCO distribution, or ηCO calculated from top gas as average ηCO, and previously specifying a high ηCO region where relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO is 1.0 or more; and a charging step of charging 75% by mass or more of the reduced iron into the high ηCO region. A method for operating a blast furnace, characterized by the above.

2. In the high ηCO region specifying step, a relative ηCO distribution, which is a distribution of relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO, is acquired, and the high ηCO region is specified based on the relative ηCO distribution. The method for operating a blast furnace according to claim 1, characterized by the above.

3. The blast furnace has a charging hopper for charging the reduced iron, and the charging hopper is a combined charging hopper for charging the reduced iron and iron raw materials other than the reduced iron. The method for operating a blast furnace according to claim 1 or 2, characterized by the above.

4. When the iron raw material is 100% by mass, the ratio of reduced iron contained in the iron raw material is 0.5% by mass or more and 50% by mass or less. The method for operating a blast furnace according to claim 1 or 2, characterized by the above.

5. In the charging step, 80% by mass or more of the reduced iron is charged into the high ηCO region. The method for operating a blast furnace according to claim 1 or 2, characterized by the above.

6. In the high ηCO region specifying step, a region where the relative ηCO is 1.2 or more is regarded as the high ηCO region. The method for operating a blast furnace according to claim 1 or 2, characterized by the above.