Blast furnace operation method

Abstract

We propose a method for smoothly injecting pulverized coal into a blast furnace from the tuyere without causing blockage in the piping. [Solution] This is a method of operation in which the adhesion of one or more types of pulverized coal injected into the blast furnace tuyeres is appropriately controlled, as determined by both the mass fraction of pulverized coal with a particle size below a set value and the component ratio (Al2O3 / SiO2). By adopting this method, it is possible to reliably prevent pulverized coal from adhering to the inside of the pipes and blocking the pipes, and it becomes possible to stably inject pulverized coal into the blast furnace from the tuyeres.

Description

[Technical Field]

[0001] The present invention relates to a blast furnace operation method for injecting pulverized coal into a blast furnace, and in particular to a blast furnace operation method for smoothly injecting pulverized coal into the blast furnace through a tuyere without the pulverized coal adhering to the inside of the piping and causing blockage of the piping. [Background technology]

[0002] In blast furnace operation, iron ore, the main source of iron, is fed into the furnace from the top, along with coke, which acts as a reducing agent.In recent years, a technology has become popular in which pulverized coal is instead of coke as a reducing agent.Pulverized coal is air-transported through piping and injected into the blast furnace through the tuyere, where it is combusted before the tuyere to promote the generation of CO gas, contributing to the effective reduction of iron ore (pulverized coal injection technology).

[0003] The coke must be produced using expensive caking coal, but the coal used for the pulverized coal injection is relatively inexpensive steam coal. Therefore, in recent years, efforts have been made to reduce the cost of hot metal by using pulverized coal to reduce the amount of coke used.

[0004] Since coke is charged from the top of the furnace, it takes about eight hours to reach the tuyere at the bottom of the furnace. On the other hand, pulverized coal supplied to the furnace from the tuyere reaches the front of the tuyere immediately, burns, and raises furnace heat in a short time. Therefore, by injecting pulverized coal from the tuyere, it is possible to achieve immediate furnace heat maintenance.

[0005] Conventionally, to improve the combustibility of pulverized coal at the tuyere tip, a method has been known in which the particle size of the pulverized coal is reduced and the specific surface area is increased, thereby increasing the contact area with oxygen. However, if the particle size of the pulverized coal is reduced too much, the pulverized coal is more likely to adhere to the inside of the pipe during airflow transport. If the amount of adhesion increases, the pipe will eventually become clogged, resulting in a decrease in the amount of pulverized coal injected into the blast furnace. Furthermore, this pulverized coal is injected from multiple tuyere pipes located around the circumferential direction of the blast furnace. If several of the pulverized coal transport pipes become clogged, a deviation in the circumferential direction of the gas flow in the blast furnace will occur, causing furnace malfunctions such as blow-by.

[0006] To avoid this phenomenon, a method has been proposed in which the particle size distribution of pulverized coal is measured to evaluate the transportability of the pulverized coal, and the coal crushing force is adjusted using the deviation between the measured value and a target value. It has been proposed that the proportion of particles with a particle size of 44 μm or less is preferably 45 to 50 mass%, and the proportion of particles with a particle size of 74 μm or more is preferably 40 mass% or less (i.e., the proportion of particles with a particle size of less than 74 μm is 60 mass% or more). This technology is a method of suppressing adhesion to the inside of a pipe while maintaining the combustibility of the pulverized coal by controlling the particle size of the pulverized coal in this way (Patent Document 1). In addition, conventionally, the interparticle adhesive force of the pulverized coal to be injected was measured in advance, and the value of the interparticle adhesive force was 3.26 × 10 -7 A method of operating a blast furnace has also been proposed in which pulverized coal of N or less is injected into the furnace through tuyere (Patent Document 2).

[0007] It is also known that the adhesiveness of pulverized coal generally differs depending on the chemical form of the minerals present in each brand of coal. 27 Al or 27 Another known method involves measuring the nuclear magnetic resonance spectrum of Si, classifying the chemical forms of inorganic minerals present in the coal, the main components of which are Al and Si, based on the measured spectrum, and evaluating the transportability of the coal based on this classification (Patent Document 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2013-43998 A [Patent Document 2] JP 2016-113664 A [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-207817 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the method disclosed in Patent Document 1, which only controls the particle size of pulverized coal, sometimes fails to prevent pipe clogging when the brand of coal being injected is changed. Also, the method disclosed in Patent Document 2 reduces the inter-particle adhesive force to 3.26 × 10 -7 It is necessary to use pulverized coal of N or less. However, in blast furnaces, multiple brands of pulverized coal may be mixed and injected, and it is necessary to measure the interparticle adhesive force in advance according to the mixing ratio of each pulverized coal brand. However, since there are countless coal mixing patterns and the interparticle adhesive force is also affected by particle size, it is difficult to measure the interparticle adhesive force in advance every time and use the measured value as a process control index. Furthermore, while the method disclosed in Patent Document 3 makes it possible to evaluate the transportability of pulverized coal for each coal brand, it does not mention how to operate a blast furnace when both the coal particle size and brand change.

[0010] Therefore, the present invention aims to propose a technology for solving the above-mentioned problems of the conventional technology. That is, the present invention is a method for appropriately managing the adhesion of one or more types of pulverized coal injected through the tuyere of a blast furnace, which is obtained from both the particle size (mass proportion of -44 μm) and the component ratio (Al2O3 / SiO2). By adopting such a method, it is possible to reliably prevent the pulverized coal from adhering to the inside of the pipe and clogging the pipe, and it becomes possible to stably inject the pulverized coal into the blast furnace through the tuyere. [Means for solving the problem]

[0011] That is, the inventors conducted various tests and research to solve the above-mentioned problems of each of the conventional technologies. As a result, they concluded that it is effective to evaluate not only the particle size (particle size) of the pulverized coal injected into the blast furnace, but also the adhesion characteristics of the pulverized coal, and in particular, to evaluate the adhesion strength of pulverized coal of different coal brands. That is, they found that when pulverized coal with a measured adhesion strength of 1.5 kPa or less is used in addition to the particle size (particle size), clogging of the piping by the pulverized coal injected into the blast furnace is at a level that does not cause problems.

[0012] Thus, in the present invention, it was concluded that it is effective to use pulverized coal whose particle size and components have been adjusted so that the adhesive force value of the pulverized coal is 1.5 kPa or less.

[0013] The present invention is a method developed based on the above findings, and the gist of the present invention is as follows.

[0014] That is, the present invention proposes a method for operating a blast furnace in which one or more types of pulverized coal are injected into the blast furnace from tuyere ports via piping, characterized in that the adhesiveness of the pulverized coal is controlled based on the mass proportion (A) of the particle size of the pulverized coal that is equal to or less than a set value and the component ratio (B) of Al2O3 / SiO2 contained in the pulverized coal.

[0015] The present invention also provides a. The control of the adhesion of pulverized coal is performed by setting the mass ratio (A) to the mass ratio of pulverized coal having a particle size of 44 μm or less, and setting the mass ratio (A) to 1.76 × 10 -2 The adhesive force value defined as × (A) + 1.18 × (B) is 1.5 kPa or less (where A is the mass fraction of pulverized coal with a particle size of 44 μm or less, and B is the Al2O3 / SiO2 component ratio contained in the pulverized coal). b. The pulverized coal injected into the blast furnace from the tuyere has a mass ratio (A) of 44 μm or less in particle size (A) of {(1.5-1.18B) × 10} 2} / 1.76 or less (where B is the Al2O3 / SiO2 component ratio contained in the pulverized coal), c. The pulverized coal injected into the blast furnace from the tuyere has a mass ratio of particle size of 44 μm or less (A) < {(1.5-1.18B) × 10 2} / 1.76 (where B is the Al2O3 / SiO2 component ratio contained in the fine powder), is believed to be a more preferred embodiment. [Effects of the Invention]

[0016] According to the present invention relating to the above-mentioned summary configuration, in a blast furnace operation method in which one or more types of pulverized coal are injected into a blast furnace through a tuyere, by appropriately controlling the particle size (mass proportion of -44 μm) and chemical composition (Al2O3 / SiO2) of the pulverized coal and using one or more types of pulverized coal with desirable adhesive properties, it becomes possible to prevent the pulverized coal from adhering to the inside of the transportation pipe or clogging the inside of the pipe, and to stably inject the pulverized coal into the blast furnace through the tuyere. Furthermore, according to the method of the present invention, if the particle size and chemical composition are known in advance, it becomes possible to evaluate the adhesiveness of the pulverized coal and perform desirable blast furnace operation without the need for special measurements. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic diagram illustrating the injection of pulverized coal into a blast furnace. [Figure 2] 1 is a graph showing the relationship between particle size and adhesive force for each brand of pulverized coal. [Figure 3] FIG. 1 shows SEM images of low-adhesive pulverized coal A and high-adhesive pulverized coal E, and the results of component analysis by EDS analysis. [Figure 4] 1 is a graph showing the relationship between the particle size and components of pulverized coal and adhesive force. [Figure 5] 1 is a graph showing an approximation formula obtained by regression analysis of pulverized coal adhesive force. [Figure 6] 1 is a graph showing the relationship between calculated adhesive force and pressure inside the pulverized coal injection tank in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Fig. 1 is a schematic diagram showing how pulverized coal pneumatically transported by air or other gas is injected into a blast furnace through tuyere 2. Reference numeral 3 in the figure indicates a pipe for supplying the pulverized coal from an injection tank to tuyere 2 via a distributor 5. Reference numeral 4 in the figure indicates how deposits 4 accumulate in the pipe 3, causing an increase in injection pressure.

[0019] According to the findings of the inventors, when pulverized coal is injected from tuyere 2 in a blast furnace operation method, it is important to appropriately control the adhesiveness of the pulverized coal, which is determined from the mass fraction (A) of particles with a particle size of 44 μm or less and the Al2O3 / SiO2 component ratio (B) contained in the pulverized coal. By appropriately controlling the adhesiveness of the pulverized coal in this way, it becomes possible to effectively prevent the pulverized coal from adhering to the inside of the pipes and clogging of the pipes, and it becomes possible to stably inject the pulverized coal from the tuyere into the blast furnace.

[0020] In other words, when the mass fraction of the pulverized coal to be injected into the blast furnace 1 having a particle size of 44 μm or less is defined as (A) and the Al2O3 / SiO2 component ratio of this fine powder is defined as (B), it was found that it is preferable to appropriately control these two numerical values.

[0021] More specifically, the relationship between the mass fraction (A) of particles with a particle size of 44 μm or less and the Al2O3 / SiO2 component ratio (B) is expressed by the following formula: 1.76 × 10 -2 By injecting one or more types of pulverized coal that satisfy × (A) + 1.18 × (B) ≦ 1.5 into the blast furnace from the tuyere 2, the pulverized coal can be stably injected into the blast furnace from the tuyere.

[0022] Based on the above findings, the inventors attempted to evaluate the adhesiveness of pulverized coal by measuring the adhesive force of pulverized coal powder layers with different particle sizes and coal brands. The adhesive force was determined by a method in which a shear strength test was conducted multiple times while changing the applied normal stress, in which a normal stress was applied to the pulverized coal powder layer with a load rod, causing the load rod to shear, and measuring the shear strength. The shear stress when the normal stress was zero was calculated by extrapolation, and this extrapolated value was defined as the adhesive force of the powder layer.

[0023] Figure 2 shows the relationship between the mass percentage of pulverized coal particles with a particle size of 44 μm or less and adhesive force, obtained by conducting tests in which each coal brand (A to F) was pulverized under a number of pulverization conditions. In this test, the mass percentage of particles with a particle size of 44 μm or less was determined by measuring the particle size of the pulverized coal using a dynamic image analysis particle sizer, but other particle sizes, such as a laser diffraction particle sizer or a dynamic light scattering particle sizer, can also be used. Table 1 below shows the component values ​​of each brand of pulverized coal used. Furthermore, the relational expression for the Al2O3 / SiO2 component ratio was derived by setting the fine particle size of pulverized coal to 44 μm or less, but the upper limit of the fine particle size of pulverized coal may be appropriately set as a control index.

[0024] [Table 1]

[0025] Next, Figure 2 shows that for pulverized coal of the same brand, the adhesive force (kPa) increases as the mass fraction of particles with a particle size of 44 μm or less increases. However, it was also found that for pulverized coal of different brands, the adhesive force differs significantly even if the mass fraction of particles with a particle size of 44 μm or less is approximately the same.

[0026] The inventors attributed this phenomenon to differences in the clay mineral content of pulverized coal depending on the brand. Specifically, the main inorganic compound in coal is SiO2, and clay minerals are substances represented by the chemical formula Al2Si2O5(OH)4. Therefore, the inventors conducted SEM observations of the cross sections of coal particles of low-adhesive pulverized coal A and high-adhesive pulverized coal E. Figure 3 shows SEM images of low-adhesive pulverized coal A and high-adhesive pulverized coal E. Almost no mineral compounds were observed in the coal particles of low-adhesive pulverized coal A. On the other hand, it was found that the coal particles of high-adhesive pulverized coal E contained large amounts of Si and Al oxides. These Si and Al oxides are clay minerals contained in the coal and are thought to be the cause of adhesion.

[0027] Next, the inventors attempted to analyze the adhesiveness of each coal brand based on the ratio of Al2O3, which is abundant in clay minerals, to SiO2, the main component of non-clay minerals. Figure 4 shows the relationship between adhesive strength and the mass fraction of pulverized coal with a particle size of 44 μm or less when stratified with Al2O3 / SiO2 < 0.4, Al2O3 / SiO2 = 0.4-0.6, and Al2O3 / SiO2 > 0.6. As shown in Figure 4, the higher the Al2O3 / SiO2 ratio, the higher the adhesive strength, even when the mass fraction of particles with a particle size of 44 μm or less is the same. This is presumably because the higher the Al2O3 / SiO2 ratio, the higher the clay mineral content in the coal, which makes it easier for pulverized coal to agglomerate due to the clay minerals, thereby increasing adhesive strength.

[0028] Next, Figure 5 shows the results of a regression analysis of adhesive strength, with the mass fraction of particles with a particle size of 44 μm or less and the Al2O3 / SiO2 component ratio contained in pulverized coal as explanatory variables. It can be seen that the adhesive strength of pulverized coal depends on the mass fraction (A) of particles with a particle size of 44 μm or less and the Al2O3 / SiO2 component ratio (B) contained in pulverized coal, as shown in the following formula (1). (Adhesion strength of pulverized coal [kPa]) = 1.76 × 10 -2 ×(A)+1.18×(B) ···(1)

[0029] When the adhesive force shown in formula (1) is 1.5 kPa or less, clogging of the pneumatic transport pipe for pulverized coal injected into the blast furnace is within a range where it is not a problem. Therefore, based on formula (1), it can be seen that the preferable range of the mass fraction (A) of particles with a particle size of 44 μm or less is as shown in formula (2). TIFF2026044253000003.tif21166Here, B is the component ratio Al2O3 / SiO2 in the pulverized coal.

[0030] As described above, in the blast furnace operation method according to the present invention, the adhesion of pulverized coal injected into the blast furnace is achieved when the mass fraction (A) of particles with a particle size of 44 μm or less and the component ratio (B) satisfy the above formula (2), i.e., {(1.5-1.18B)×10 2} / 1.76 or less (where B is the component ratio Al2O3 / SiO2 in the pulverized coal), adhesion of pulverized coal to the inside of the pipes and blockage of the pipes can be effectively suppressed, and it has been found that pulverized coal can be stably injected into the blast furnace from the tuyere. [Example]

[0031] In blast furnace operation with a pulverized coal injection rate of 180 to 210 kg / ton of hot metal, the particle size (mass fraction of -44 μm) and composition value (Al2O3 / SiO2) of the pulverized coal to be injected were measured, and the adhesive force was calculated from the measured values ​​using equation (1). The relationship between the adhesive force and the pressure inside the injection tank during the pulverized coal injection period was investigated. As a result, when pulverized coal adhered to the inside of the injection pipe, the injection pipe became clogged and the pressure inside the injection tank rose. In addition, there is a management upper limit for the pressure inside the injection tank, and if this limit is exceeded, it indicated that the pulverized coal injection pipe had become clogged. 6 is a graph showing the results of an example of the present invention and a comparative example (each showing one result per day). As shown in this figure, within the operating range compatible with the method of the present invention, the pressure inside the pulverized coal injection tank is below the upper limit, indicating that adhesion of pulverized coal to the piping is at a level that does not pose a problem in operation.

[0032] In contrast, in the case of the blast furnace operation of the comparative example, there were occasional days when the pressure inside the pulverized coal injection tank exceeded the upper limit value, indicating that the injection piping was being blocked due to adhesion of pulverized coal to the piping. [Industrial Applicability]

[0033] The pulverized coal processing technology used in the blast furnace operation method according to the present invention can also be used as a pulverized coal transport technology to metallurgical furnaces, heating furnaces, and other facilities that use pulverized coal. In particular, it is useful as a transport technology that utilizes the relationship between the required particle size and viscosity components when evaluating and examining adhesion to the inside of a transport pipe. [Explanation of symbols]

[0034] 1 blast furnace 2 Tuyere 3 Piping 4. Adhesion 5 Distributor

Claims

【Request Item 1】 In a blast furnace operation method in which one or more types of pulverized coal are injected into a blast furnace from a tuyere through a pipe, the mass ratio (A) of the particle size of the pulverized coal being equal to or less than a set value and the Al contained in the pulverized coal are ２ O ３ / SiO ２ and the value of the component ratio (B) of the blast furnace. 【Request Item 2】 The adhesion of the pulverized coal is controlled by setting the mass ratio (A) to a mass ratio of pulverized coal having a particle size of 44 μm or less, and setting the mass ratio (A) to 1.76×10 －２ 2. The method for operating a blast furnace according to claim 1, wherein the adhesive force defined as (A) + 1.18 × (B) is 1.5 kPa or less, where A is the mass fraction of the pulverized coal having a particle size of 44 μm or less, and B is the Al content of the pulverized coal. ２ O ３ / SiO ２ is the component ratio. 【Request Item 3】 The pulverized coal injected into the blast furnace from the tuyere has a mass ratio (A) of 44 μm or less in particle size (A) of {(1.5−1.18B)×10} ２ 3. The method for operating a blast furnace according to claim 1, wherein B is Al contained in the pulverized coal. ２ O ３ / SiO ２ is the component ratio. 【Request Item 4】 The pulverized coal injected into the blast furnace from the tuyere has a mass ratio of particle diameter of 44 μm or less (A) < {(1.5 - 1.18B) × 10 ２ 4. The method for operating a blast furnace according to claim 3, wherein the mixing ratio of the pulverized coals of a plurality of brands is adjusted so as to satisfy the following relationship: B is the Al contained in the fine powder. ２ O ３ / SiO ２ is the component ratio.

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