blast furnace for iron production

Abstract

A blast furnace for ironmaking, wherein iron ore is at least partially reduced by a reducing gas injected into the stack of the blast furnace in the injection zone, the blast furnace comprises an inner wall and an outer wall in contact with the material charged into the blast furnace, the inner wall in the injection zone comprises local inward expansions, and the injection of the reducing gas is performed under the inward expansions.

Description

Technology Field

[0001] The present invention relates to a blast furnace for ironmaking and a process for injecting reducing gas into the blast furnace. Background Technology

[0002] In a blast furnace, the conversion of iron-containing charges (sintered material, pellets, and iron ore) into cast iron or hot metal is typically carried out by the reduction of iron oxides by reducing gases (particularly containing CO, H2, and N2) formed by the combustion of coke in a blower located at the bottom of the blast furnace, into which air preheated to a temperature of 1000°C to 1300°C, known as a hot blast, is injected.

[0003] To improve productivity and reduce costs, auxiliary fuels such as crushed coal, fuel oil, natural gas, or other fuels combined with oxygen concentration of hot air are injected through the air inlet.

[0004] The gas recovered from the upper part of the blast furnace is called top gas and consists mainly of CO, CO2, H2, and N2 in proportions of 20-28%v, 17-25%v, 1-5%v, and 48-55%v, respectively. Although this gas is partially used as fuel in other plants such as power plants, the blast furnace remains a significant producer of CO2.

[0005] Given the significant increase in atmospheric CO2 concentration since the beginning of the last century and the resulting greenhouse effect, it is essential to reduce CO2 emissions on a large scale, and therefore especially in blast furnaces.

[0006] To this end, over the past 50 years, the consumption of reducing agents in blast furnaces has been reduced by half, and currently, in blast furnaces with a conventional configuration, the carbon consumption has reached a lower limit connected to the laws of thermodynamics.

[0007] One known method for further reducing CO2 emissions is to reintroduce top gas, purified to CO2 and rich in CO, into the blast furnace, which is known as a TGRBF (Top-Gas Recycling Blast Furnaces). Thus, the use of CO-rich gas as a reducing agent can reduce coke consumption and consequently CO2 emissions. Such injection can be carried out at two levels in the reducing zone of the blast furnace, for example, at the traditional tuyere level, replacing hot air in the lower part of the blast furnace stack.

[0008] However, this so-called shaft injection of reducing gas must not interfere with the operation of the steelmaking process and must not impair its productivity.

[0009] A blast furnace is needed that reduces environmental impact while maintaining the same or improved level of productivity compared to conventional blast furnaces.

[0010] This problem is solved by a blast furnace according to the present invention, wherein iron ore is at least partially reduced by a reducing gas injected into the stack of the blast furnace in an injection zone, the blast furnace comprises an inner wall and an outer wall in contact with the material charged into the blast furnace, the inner wall in the injection zone comprises local inward expansions, and the injection of the reducing gas is performed under the inward expansions.

[0011] The blast furnace of the present invention may also include the following optional features, which are considered individually or according to all possible technical combinations:

[0012] - The enlargements have a width (W) of 50 to 250 mm, and

[0013] - The injection of reducing gas is performed near the area below the expansion section, and

[0014] - The injection of reducing gas is performed at a distance (L) below the enlargements that is less than or equal to the width (W) of the enlargement, and

[0015] - Local inward enlargement is performed by adding a protrusion to the inner wall, and

[0016] - The inner wall is made of staves that come into contact with the material charged into the blast furnace, and local inward expansions are made using staves with a trapezoidal cross-section, and

[0017] - The reducing gas is injected by an injection device capable of injecting the gas downward, and

[0018] - Reducing gas is injected by an injection device capable of injecting gas at an angle (α) where plane X perpendicular to the inner wall of the blast furnace is 15° to 30°, and

[0019] - The blast furnace has a working height (H), and the injection of reducing gas is performed starting from the level of the air outlet at a height of 20% to 70% of the working height (H), and

[0020] - The blast furnace has a working height (H), and the injection of reducing gas is performed starting from the level of the blower and at a height of 30% to 60% of the working height (H).

[0021] The present invention also relates to a method of ironmaking carried out in a blast furnace according to previous embodiments, wherein the injection of reducing gas is performed at a speed of 75 m / s to 200 m / s.

[0022] The steelmaking method may also include the following optional features, which are considered individually or according to all possible technical combinations:

[0023] - Reducing gas includes a portion of the top gas discharged from the blast furnace during the steelmaking process, and

[0024] - Reducing gas is injected at a temperature of 850℃ to 1200℃, and

[0025] - The reducing gas preferably contains 65%v to 75%v of carbon monoxide CO, 8%v to 15%v of hydrogen H2, and 1%v to 5%v of carbon dioxide CO2, with the remainder being mainly nitrogen N2. Brief explanation of the drawing

[0026] Other features and advantages of the present invention will become apparent from the description given below, which is non-limiting and illustrated with reference to the accompanying drawings. Figure 1 shows a side view of a blast furnace in which a reducing gas is injected in the reducing zone. Figure 2 shows a top view of the blast furnace of Figure 1. FIG. 3 illustrates a shaft furnace according to one embodiment of the present invention. Figure 4 shows a DEM-CFD simulation of the inside of the shaft furnace according to the present invention according to a change in the reduction gas injection position. Figure 5 shows a DEM-CFD simulation of the inside of the shaft furnace according to the present invention according to a change in the reduction gas injection angle. Specific details for implementing the invention

[0027] In the drawings, the elements are exemplary and cannot be depicted in scale.

[0028] FIG. 1 is a side view of a blast furnace according to the present invention. The blast furnace (1) comprises, starting from the top, a throat (11) where materials are loaded and gas is discharged, a stack (also called a shaft) (12), a belly (13), a bosh (14), and a hearth (15). The loaded materials are mainly iron-containing materials such as sintered material, pellets, or iron ore, and carbon-containing materials such as coke. The injection of hot air required for carbon combustion and the subsequent reduction of iron is carried out by a blower port (16) located between the bosh (14) and the hearth (15). From a structural perspective, the blast furnace has an outer wall, or shell (2), which is covered by a refractory lining and boards (3) that form an inner wall (5) inside the blast furnace, as shown in FIG. 3. In order to reduce the consumption of coke, which is the primary carbon source for iron reduction, it was considered to inject reducing gas into the blast furnace in addition to hot air. This injection of reducing gas is performed within the stack of the blast furnace, primarily in the lower part of the stack (12), for example, just above the belly (13). In a preferred embodiment, the injection of reducing gas is performed at a distance of 20% to 70%, preferably 30% to 60%, of the working height (H) of the furnace from the level of the classic tuyeres. The working height (H) of the blast furnace is the distance between the level of hot air injection through the classic tuyeres and the zero level of the charge, as shown in FIG. 1.

[0029] Injection is performed through several injection outlets (4) around the perimeter of the furnace, as shown in FIG. 2, which is a plan view of the blast furnace (1) at the injection level of the reducing gas. In a preferred embodiment, there are as many injection outlets as there are boards forming the inner wall (5). 200 to 700 Nm per ton of high-temperature metal in the blast furnace 3 A reducing gas is injected.

[0030] FIG. 3 illustrates an injection outlet (4) of a furnace according to an embodiment of the present invention. In this embodiment, the board (3) is provided with a protrusion (6) that forms a local enlargement of the inner wall (5), and the injection outlet (4) is located below this local enlargement. While the protrusion is one embodiment of the local enlargement, other methods may be considered, such as an implementation of a board having a trapezoidal shape, in which the lower part of the board is larger than its upper part and the injection outlet is located below the lower part. The local enlargement signifies a local increase in the width of the inner wall. Performing injection below the local enlargement can create a cavity, which is a region free of material, which protects the injection area from the movement of material within the furnace and thus improves the durability of the injection device. Furthermore, since the material does not come into close proximity to the injection outlet, clogging of the injection device is avoided. In a preferred embodiment, this width (W) is configured to be 50 to 250 mm to provide a cavity of sufficient size to protect the injection outlet. The injection outlet is located at a distance (L) from the enlargement. In a preferred embodiment, this distance (L) is closest to 0 and is primarily inferior to the width (W) of the expansion section. As a width, this parameter allows for controlling the size of the formed cavity. The gas injection outlet (4) is designed so that the reducing gas is injected at an angle (α) having a plane (P) perpendicular to the inner wall at the location of the expansion section. In a preferred embodiment, the angle (α) is 0 to 30°. This specific range increases the depth to which the reducing gas penetrates into the furnace, thereby improving contact with the internal load. If it exceeds 30°, a larger amount of gas is cooled upon contact with the inner wall, and the expected reduction effect cannot be obtained.

[0031] When a steelmaking process is performed in a shaft furnace according to the present invention, it is preferable that the reducing gas be injected at a speed of 75 to 200 m / s to have a cavity size sufficient to protect the injection device. In the range of 120-200 m / s, the cavity size does not increase further, and above 200 m / s, the cavity is not controlled and may impair the good distribution of the burden due to the formation of mixed layers of coke and iron-containing materials, and thus impair the productivity of the steelmaking process.

[0032] In a preferred embodiment, the reducing gas introduced into the blast furnace is the top gas discharged from the blast furnace that is gas-treated to remove dust and obtain a suitable composition, pressure, and temperature. This reducing gas preferably contains 65%v to 75%v of carbon monoxide (CO), 8%v to 15%v of hydrogen (H2), and 1%v to 5%v of carbon dioxide (CO2), with the remainder being mainly nitrogen (N2). It is preferably injected at a temperature of 850 to 1200°C.

[0033] FIG. 4 shows the results of a DEM-CFD (Discrete Element Method and Computational Fluid Dynamics) simulation of mass transfer within a blast furnace according to the present invention, depending on the reduction gas injection location in relation to the expansion section. In FIG. 4A, when gas is injected near a local inward expansion section, the distance L can be considered to be 0. In FIG. 4B, the distance L is 200 mm, and in FIG. 4C, the distance L is 400 mm. In the simulation, the expansion section width is constant in all figures and is the same at 200 mm, the reduction gas velocity is also constant and is the same at 120 m / s, and the injection angle (α) is fixed at 30°. Through the simulation, it can be seen that the cavity becomes smaller as the distance from the expansion section increases. There is even no cavity formation at 400 mm. Therefore, in this specific configuration, it is a preferred embodiment to have an injection section located at 0 to 200 mm.

[0034] Figure 5 shows the results of a CFD simulation of gas injected into a blast furnace according to the present invention as a function of the injection angle (α). In Figures 5A, 5B, 5C, 5D, and 5E, the angle (α) is 0°, 15°, 30°, 45°, and 60°, respectively. In the simulation, the width of the expansion section is constant at 200 mm in all figures, the reducing gas velocity is also constant at 120 m / s, and the injection was performed near the expansion section (L=0 mm). The reducing gas is represented by a square, where a darker square indicates a larger amount. From the simulation, it can be observed that starting from an angle of 15°, more gas penetrates deeper into the load charged into the blast furnace. However, when the angle is higher than 30°, the gas tends to flow toward the inner wall of the cooling furnace and will not come into contact with the load.

[0035] According to the blast furnace of the present invention, by efficiently injecting reducing gas, it is possible to reduce the inflow burden of the blast furnace and suppress coke consumption and CO2 emissions without lowering the productivity of the blast furnace.

Claims

Claim 1 A blast furnace for ironmaking (1), wherein iron ore is at least partially reduced by a reducing gas injected into a stack (12) of the blast furnace in an injection zone, the blast furnace (1) comprises an inner wall (5) and an outer wall (2) in contact with a material charged into the blast furnace, wherein in the injection zone the inner wall (5) comprises local inward expansions (6), wherein the injection of the reducing gas is performed below the inward expansions, wherein the reducing gas is injected by an injection device (4) designed to inject gas downward, wherein the expansions (6) have a width (W) of 50 to 250 mm, and wherein the reducing gas is injected by the injection device designed to inject gas at an angle (α) of 15° to 30° with respect to a plane X perpendicular to the inner wall (5) of the blast furnace. Claim 2 A blast furnace for ironmaking, wherein the injection of the reducing gas is performed near the area below the enlargement sections (6) in claim 1. Claim 3 A blast furnace for ironmaking according to claim 1, wherein the injection of the reducing gas is performed at a distance (L) below the enlargements that is less than or equal to the width (W) of the enlargements. Claim 4 A blast furnace for ironmaking, wherein the local inward enlargements are formed by adding protrusions (6) to the inner wall (5) in the first paragraph. Claim 5 A blast furnace for ironmaking according to claim 1, wherein the inner wall (5) is made of staves (3) that come into contact with the material charged into the blast furnace, and the local inward expansions (6) are made using staves (3) having a trapezoidal cross-section. Claim 6 delete Claim 7 delete Claim 8 A blast furnace for ironmaking according to claim 1, wherein the blast furnace has a working height (H), and the injection of the reducing gas is performed starting from the level of the blower (16) at a height of 20% to 70% of the working height (H). Claim 9 A blast furnace for ironmaking according to claim 1, wherein the blast furnace has a working height (H), and the injection of the reducing gas is performed starting from the level of the blower (16) at a height of 30% to 60% of the working height (H). Claim 10 A steelmaking method performed in a blast furnace according to any one of claims 1 to 5, 8 and 9, wherein the injection of reducing gas is performed at a speed of 75 m / s to 200 m / s. Claim 11 A method of ironmaking according to claim 10, wherein the reducing gas comprises a portion of the upper gas discharged from the blast furnace during the ironmaking process. Claim 12 A steelmaking method according to claim 10, wherein a reducing gas is injected at a temperature of 850°C to 1200°C. Claim 13 In claim 10, a steelmaking method wherein the reducing gas has the following composition: 65%v ≤ CO ≤ 75%v 8%v ≤ H2 ≤ 15%v 1%v ≤ CO2 ≤ 5%v remainder N2. Claim 14 delete

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