Blast furnace injection lance and blast furnace operation method

Abstract

To prevent an excessive rise in furnace temperature in a blast furnace operation method in which a charcoal material having a large combustion speed is blown into the blast furnace.SOLUTION: In an operation method of a blast furnace in which a blast furnace blowing lance 5 is inserted into a blow pipe, pulverized coal containing 50 mass% or more of a charcoal material having a combustion speed of 3.0 (mg / min) or higher is blown from an inner tube 51 by a carrier gas while a hydrogen-based reducing gas is blown from an outer tube 52, and the blast furnace is operated so as to satisfy the condition of X1 / X2≥0.5 where a flow rate of the hydrogen-based reducing gas is set to X1 and a flow rate of the carrier gas is set to X2. The blast furnace blowing lance has double-tube structure, and the tip opening of the inner tube is inclined by 55 degrees or more to a plane perpendicular to the axial direction of the inner tube. A distance W between the inner tube and the outer tube in the longitudinal direction is limited to a predetermined range.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a blast furnace injection lance for injecting pulverized coal or the like into a blast furnace and a method for operating a blast furnace. [Background technology]

[0002] In blast furnace operation, pig iron is produced by alternately charging layers of iron raw materials (lump ore, sintered ore, pellets, etc.) and coke (reducing agent) from the top of the furnace. Known cost-reduction methods for blast furnace operation include reducing the amount of coke charged and injecting pulverized coal through lances installed in the tuyere. Another known method of operating a blast furnace involves injecting a hydrogen-based reducing gas through the tuyere, with the aim of lowering the reducing agent rate of the blast furnace and reducing carbon dioxide emissions.

[0003] If the pulverized coal injected through the tuyere contains a high amount of volatile matter (VM), the blast pressure fluctuates, hindering stable blast furnace operation. Therefore, low-VM semi-anthracite (hereinafter referred to as "conventional coal") is typically used as the pulverized coal injected into the blast furnace. However, in recent years, resource depletion has made it difficult to secure low-VM coal. Therefore, methods of injecting modified coal (hereinafter referred to as "char") obtained by carbonization of biomass or lignite as the carbonaceous material have been investigated. However, char derived from biomass or lignite has weaker carbon bonds than conventional carbonaceous materials, making it easier to combust (i.e., has a higher combustion rate). Therefore, using the aforementioned char as the carbonaceous material for injection can shift the combustion position (combustion focus) toward the tuyere, resulting in an excessive increase in the furnace body temperature.

[0004] Patent Document 1 discloses a blast furnace injection lance having a double-tube structure in which a gaseous reducing agent is injected from an inner tube and cooling air is circulated between the outer tube and the inner tube, but does not consider the above-mentioned problems. Patent Document 2 describes a double-tube lance in which the tip of the inner tube is notched in order to prevent wear of the tuyere. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-312757 [Patent Document 2] Japanese Utility Model Application Publication No. 62-97154 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to prevent an excessive rise in furnace body temperature in a blast furnace operation method in which carbonaceous material having a high combustion rate is injected into the blast furnace. [Means for solving the problem]

[0007] In order to solve the above problems, the blast furnace injection lance of the present invention is characterized in that: (1) a blast furnace injection lance of a double-tube structure having an outer tube and an inner tube, the tip opening of the inner tube is inclined at a predetermined angle θ of 55 degrees or more with respect to a plane perpendicular to the axial direction of the inner tube, and when the distance in the longitudinal direction of the blast furnace injection lance between the most distal end of the tip opening of the inner tube and the tip opening of the outer tube is W, the distance W satisfies the following formula (1): W≦tanθ×D······································································Formula (1) where D is the diameter of the inner tube.

[0008] (2) The blast furnace injection lance described in (1) above, characterized in that the most distal end of the inner pipe is disposed at one of a protruding position on the outside of the outer pipe, a position inside the pipeline of the outer pipe, and a flush position with the tip opening of the outer pipe.

[0009] (3) The blast furnace injection lance according to (1) or (2) above, characterized in that the tip opening of the outer pipe is perpendicular to the axial direction of the inner pipe.

[0010] (4) A method for operating a blast furnace in which the blast furnace injection lance according to any one of (1) to (3) above is inserted into a blowpipe, characterized in that while injecting a hydrogen-based reducing gas from the outer tube, pulverized coal containing 50 mass % or more of carbonaceous material having a combustion rate of 3.0 (mg / min) or more is injected from the inner tube by a carrier gas, and the injection condition shown in the following formula (2) is satisfied when the flow rate of the hydrogen-based reducing gas is X1 and the flow rate of the carrier gas is X2. X1 / [Effects of the Invention]

[0011] According to the present invention, in a method for operating a blast furnace in which carbonaceous material with a high combustion rate is injected into the blast furnace, an excessive increase in the furnace body temperature can be prevented by adjusting the amount of hydrogen-based reducing gas injected and the inclination angle of the tip of the inner tube of the blast furnace injection lance. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a blast furnace. [Figure 2] FIG. 2 is an enlarged view of the tip of a blast furnace injection lance. [Figure 3] This is a test device that simulates the lower part of a blast furnace. [Figure 4] 1 is a graph showing the relationship between the tip inclination angle θ and the rate of increase in the number of carbonaceous particles. [Figure 5] 1 is a graph showing the relationship between the hydrogen-based reducing gas flow rate (X1) / carrier gas flow rate (X2) and the rate of increase in the number of carbonaceous particles. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram of a blast furnace (bell-less type blast furnace) according to this embodiment. In the blast furnace 1, iron raw materials such as sintered ore, pellets, and lump ore are used as the main raw materials, and coke, pulverized coal, and a hydrogen-based reducing gas are used as reducing agents. The iron raw materials and coke are charged alternately in layers from the top of the blast furnace 1. As a result, within the blast furnace 1, a lumpy zone, a cohesive zone where the iron raw materials melt and change from solid to liquid, and a drip zone where liquid molten iron and molten slag drip down the coke layer are formed.

[0014] The blast furnace 1 in this embodiment includes a tuyere 2, an annular pipe 3, a blowpipe 4, a blast furnace injection lance 5, and a taphole 6. The annular pipe 3 is disposed so as to surround the lower portion of the blast furnace 1. The blowpipes 4 are disposed intermittently around the annular pipe 3, and each is connected to a different tuyere 2. The blast furnace injection lance 5 passes through each blowpipe 4, and the tip of the blast furnace injection lance 5 extends into each blowpipe 4. The taphole 6 is provided to discharge molten iron accumulated at the hearth. In the above-described configuration, the blast furnace injection lance 5 injects pulverized coal and a hydrogen-based reducing gas into the blowpipe 4. The injected pulverized coal and hydrogen-based reducing gas are then blown into the blast furnace 1 through the tuyere 2 together with hot air blown from the annular pipe 3 to the blowpipe 4.

[0015] The hot air is generated, for example, in a hot air stove (not shown). The hot air stove may be, for example, a cylindrical furnace including a heat regenerator with silica bricks arranged in a lattice pattern inside. The temperature of the hot air is detected, and the amount of heat stored in the hot air stove and the amount of air supplied are controlled based on the detection results, thereby adjusting the temperature of the hot air. The equipment configuration of the blast furnace 1 described above is an example, and the present invention is not limited to these configurations. In other words, the present invention can also be applied to, for example, a bell-type blast furnace.

[0016] The pulverized coal contains 50% by mass or more of carbonaceous material with a high combustion rate, assuming the total amount of pulverized coal injected as 100% by mass. In other words, in the blast furnace operating method of this embodiment, the operating condition is to inject pulverized coal rich in carbonaceous material with a high combustion rate from the tuyere 2. The combustion rate is defined as follows: First, carbonaceous material (10 mg mass) is heated from room temperature to 1000°C at a heating rate of 900°C / min using an infrared gold image furnace (e.g., Thermo plus EV02 / TG-DTA8120 (manufactured by Rigaku Corporation)) while flowing air at a flow rate of 200 ml / min. The combustion rate (mg / min) can be calculated by dividing the mass of the carbonaceous material (10 mg) by the time from the start of heating to the end of the mass change of the carbonaceous material. The end point of the mass change of the carbonaceous material is the point at which the slope of the time-dependent change curve of the carbonaceous material mass deviates from a linear relationship.

[0017] In addition, in this specification, "carbonaceous material with a high combustion rate" refers to carbonaceous material with a combustion rate of 3.0 (mg / min) or more. Carbonaceous material with a combustion rate of 3.0 (mg / min) or more is easier to burn than conventional carbonaceous material. Char obtained by dry distillation of biomass or lignite can be used for carbonaceous material with a combustion rate of 3.0 (mg / min) or more. Examples of biomass that can be used include agricultural biomass (straw, sugarcane, rice bran, vegetation, coconut kernels, etc.), forestry biomass (papermaking waste, sawmill waste, thinned wood, firewood, etc.), livestock biomass (livestock waste), fisheries biomass (fish processing residue), and waste biomass (food waste, RDF (Refuse Derived Fuel), garden trees, construction waste, sewage sludge). There are no particular limitations on the origin of lignite. Char is a carbonaceous material that is produced when carbonaceous material is heated without softening or melting (see JIS0104, Terminology for Coal Utilization Technology).

[0018] The particle size of the pulverized coal used in this embodiment is not particularly limited, but can be set to, for example, 75 μm or less.

[0019] The configuration of the blast furnace injection lance 5 will be described in detail with reference to FIG. 2. FIG. 2 is an enlarged view of the tip of the blast furnace injection lance of this embodiment. The blast furnace injection lance 5 has a double-tube structure consisting of an inner tube 51 and an outer tube 52. Pulverized coal is injected through the inner tube 51, and a hydrogen-based reducing gas is injected through the outer tube 52 (in other words, the gap formed between the inner tube 51 and the outer tube 52). An inert gas such as nitrogen gas can be used as a carrier gas for injecting the pulverized coal. The hydrogen-based reducing gas is a reducing gas containing at least hydrogen as an element, and may be a hydrogen-containing gas such as natural gas, COG, LPG, or methane gas, or may be hydrogen gas itself.

[0020] The tip surface 51A of the inner tube 51 is formed in a notched shape and is inclined by θ (hereinafter referred to as the tip inclination angle θ) with respect to a plane perpendicular to the longitudinal axis 5a of the inner tube 51 and the outer tube 52. Details of the tip inclination angle θ will be described later. The tip surface 52A of the outer tube 52 is perpendicular to the longitudinal axis 5a and does not have a notched shape like the inner tube 51. Here, when the distance (separation distance) in the direction of the longitudinal axis 5a between the most distal end of the tip surface 51A of the inner tube 51 and the tip surface 52A of the outer tube 52 is W, the distance W must satisfy the following formula (1). W≦tanθ×D······································································Formula (1) Here, D is the diameter of the inner tube 51. Figure 2 illustrates a state in which the tip of the inner pipe 51 and the tip surface of the outer pipe 52 are flush (i.e., distance W = 0), but within the range of equation (1), the inner pipe 51 may protrude from the outer pipe 52 (see "protruding position" in Figure 2) or may be retracted inside the outer pipe 52 (see "position inside the pipe" in Figure 2).

[0021] The present inventors have discovered that an excessive rise in the furnace body temperature can be prevented by simultaneously satisfying condition A regarding the amount of hydrogen-based reducing gas injected, and conditions B and C regarding the structure of the blast furnace injection lance 5. Condition A: When the flow rate of the hydrogen-based reducing gas flowing through the outer tube 52 is X1 and the flow rate of the carrier gas flowing through the inner tube 51 is X2, X1 / X2≧0.5. Condition B: The tip inclination angle θ of the tip surface 51A of the inner pipe 51 is set to 55 degrees or more (less than 90 degrees). Condition C: W≦tanθ×D Condition C has been described above, so the description will not be repeated.

[0022] By simultaneously satisfying conditions A and B, with condition C being a prerequisite, the pulverized coal discharged from the inner pipe 51 becomes dense and less likely to come into contact with oxygen, shifting the combustion focus toward the furnace interior. This prevents an excessive increase in the furnace body temperature. Specifically, by setting the tip inclination angle θ to 55 degrees or greater, the pulverized coal particles discharged from the inner pipe 51 can be initially dispersed. Furthermore, by satisfying the injection condition of condition A, the dispersed pulverized coal particles are surrounded by the hydrogen-based reducing gas and are no longer able to disperse. Instead, they become dense, maintaining a dense state until they are injected into the furnace. In other words, the dispersed pulverized coal particles collide with the hydrogen-based reducing gas traveling straight in a ring shape and are repelled toward the center of the ring, thereby concentrating the pulverized coal particles. On the other hand, if the tip inclination angle θ is less than 55 degrees, the pulverized coal particles discharged from the inner pipe 51 do not disperse and are less likely to collide with the hydrogen-based reducing gas, preventing the above-mentioned concentrating effect from being fully realized.

[0023] Next, the present invention will be specifically described with reference to examples. (Test 1) Using a test apparatus simulating the lower part of a blast furnace (see Figure 3), the furnace body temperature change rate (%) was evaluated while varying the flow rate of the carbonaceous material used as pulverized coal and the hydrogen-based reducing gas. The furnace body temperature was measured using a temperature sensor 15 (described below). The experiment was conducted under constant reference conditions, and the temperature at which almost no change was observed on the temperature sensor 15 was defined as the furnace body temperature under the reference conditions. Next, the conditions were changed and the experiment was continued until the temperature sensor 15 readings no longer changed. The temperature at which no change occurred was measured. The difference between the two temperatures was divided by the furnace body temperature under the reference conditions to determine the furnace body temperature change rate under the changed conditions. The time required for the conditions to stabilize after the change was approximately 3 hours. In the test furnace 10 shown in Figure 3, 12 is a tuyere, 13 is a blowpipe that supplies hot air to the tuyere 12, 14 is a double-tube test furnace lance (hereinafter referred to as the test furnace double-tube lance 14), and 15 is a temperature sensor. The number of double-tube test furnace lances 14 was one.

[0024] The test furnace 10 was a vertical rectangular parallelepiped with a length of 1.2 m, a width of 1.2 m, and a height of 2.4 m, and the furnace wall had a double-layer structure with firebricks attached to the inside of the steel shell. A thermocouple was used as the temperature sensor 15, and this thermocouple was placed 600 mm above the central axis of the tuyere 12 between the furnace bricks and the steel shell.

[0025] The test furnace 10 was filled with coke with a particle size of 9 to 13 mm. The hot air temperature was set to 1200°C, and the air flow rate was 0.8 m 3 The injection rate of pulverized coal was set to 200 (kg / pig-ton), which is the typical injection rate in an actual furnace. The pulverized coal particles (75 μm or less) used were those used in actual blast furnaces.

[0026] Table 1 shows the types and properties of the carbonaceous materials used as pulverized coal in this test. Char 1 is char obtained by carbonizing lignite, and Char 2 is char obtained by carbonizing biomass (wood). Ash is ash content, and FC is fixed carbon. VM has been described above, so its explanation will not be repeated here. [Table 1]

[0027] Table 2 shows the injection ratio of each carbonaceous material injected from the double-tube lance 14 for the test furnace, the tip inclination angle θ, the flow rate ratio (X1 / X2) of the hydrogen-based reducing gas and the carrier gas, the furnace body temperature change rate, and the evaluation results. The injection ratio of each carbonaceous material is shown as a mass fraction when the total amount of pulverized coal injected in each comparative example and example is 100% by mass. The furnace body temperature change rate in each example and comparative example was calculated assuming the furnace body temperature increase rate in the reference example to be 100%. A furnace body temperature change rate of 100% or less was evaluated as "Good," and a furnace body temperature change rate of more than 100% was evaluated as "Poor." A hydrogen-containing gaseous reducing agent (H2: approximately 59%, CH3: approximately 29%, CO: approximately 6%, N2: approximately 6%, by mass%) simulating the components of coke oven gas was used as the hydrogen-based reducing gas. [Table 2] Comparing the Reference Example, Comparative Example 1, and Comparative Example 2, in which the tip inclination angle θ was standardized to 0 degrees, the furnace body temperature change rate (%) increased by reducing the content of semi-anthracite A, which has a combustion rate of less than 3.0 (mg / min), from 100% by mass to 50% by mass and replacing it with Char 1 or Char 2, which has a combustion rate of 3.0 (mg / min) or more. It is thought that the inclusion of carbonaceous material with a combustion rate of 3.0 (mg / min) or more caused the combustion focus to move near the tuyere, increasing the furnace body temperature change rate (%).

[0028] In Examples 1 to 4, the furnace body temperature change rate was approximately the same as that of the Reference Example (100%), and the evaluation was "Good." It is presumed that by satisfying Conditions A and B, the effect of concentrating the pulverized coal was realized, and the combustion focus shifted toward the furnace interior. Furthermore, comparing Examples 1 and 2 with Examples 5 and 6, it was found that even when X1 / X2 was reduced from 1.0 to 0.5, the furnace body temperature change rate (%) was maintained at approximately the same level as that of the Reference Example. Comparing Examples 5 and 6 with Comparative Examples 3 and 4, it was found that by reducing X1 / X2 from 0.5 to 0.4, the furnace body temperature change rate (%) was significantly increased compared to that of the Reference Example. It is presumed that the reduction in X1 / X2 to 0.4 reduced the effect of maintaining the pulverized coal in a concentrating state, and the combustion focus shifted toward the tuyere.

[0029] (Test 2) To investigate why setting the tip inclination angle θ above 55° improves the furnace body temperature change rate, the increase in the concentration of carbonaceous particles was measured by varying the tip inclination angle θ. The increase in the concentration of carbonaceous particles was evaluated as the increase in the number of carbonaceous particles within a given region. Specifically, a general-purpose fluid analysis software (FLUENT) was used to calculate the motion of particles injected into the blowpipe from the lance, and snapshots of the carbonaceous particles in the blowpipe at a position 100 mm from the tip of the lance toward the furnace interior were output. From the output snapshots, the number of carbonaceous particles within a circular region (equivalent to 6.25% of the cross-sectional area of ​​the blowpipe) centered on the center point of the blowpipe cross section was counted. Pulverized coal particles (particle size: 75 μm or less) injected into a real blast furnace were used as the carbonaceous particles. The flow rate ratio (X1 / X2) of the hydrogen-based reducing gas and the carrier gas was set to 1.2.

[0030] Based on the tabulation results, the increase rate (%) of the number of carbonaceous particles was calculated, with the number of carbonaceous particles in the circular region when the tip inclination angle θ was 0 degrees being set to 100%. FIG. 4 is a graph summarizing the calculation results. Referring to the same figure, the increase rate of the number of carbonaceous particles (i.e., the increase rate of the degree of concentration of carbonaceous particles) increased as the tip inclination angle θ increased. In particular, when the tip inclination angle θ was set to 55 degrees or more, the increase rate of the degree of concentration of carbonaceous particles increased significantly. In other words, it was found that the pulverized coal discharged from the blast furnace injection lance was sufficiently concentrated by setting the tip inclination angle θ to 55 degrees or more.

[0031] (Test 3) To evaluate the effect of the injection amount of hydrogen-based reducing gas on the dispersion of carbonaceous material, the flow rate of the hydrogen-based reducing gas was changed and the rate of increase in the density of carbonaceous material particles was examined. The density of carbonaceous material particles was calculated using the same method as in Test 2. The tip inclination angle θ was set to 55 degrees. The graph in Figure 5 shows the test results, and the flow rate of the hydrogen-based reducing gas is expressed as X1 / X2 (flow rate of hydrogen-based reducing gas / flow rate of pulverized coal carrier gas) described in the embodiment.

[0032] As shown in the figure, it was found that when X1 / X2 reached 0.5, the rate of increase in the density of carbonaceous particles increased sharply.

[0033] Furthermore, under the injection condition of X1 / X2 = 0.5, the increase rate of the density of the carbonaceous particles was investigated by changing the orientation of the tip surface of the inner pipe (hereinafter referred to as the cut surface) between "up," "right," "down," and "left." The results were "13.1%, "13.5%, "13.3%, and "12.9%, respectively." It was confirmed that the increase rate of the density of the carbonaceous particles hardly changed depending on the orientation of the cut surface. The orientation of the cut surface was defined as "up," "right," "down," and "left," respectively, in a clockwise direction, based on the direction in which the cut end of the cut surface faces when viewing the tuyere from inside the furnace. [Explanation of symbols]

[0034] 1: Blast furnace 2: Tuyere 3: Annular pipe 4: Blowpipe 5: Blast furnace injection lance 6: Taphole 51: Inner tube 52: Outer tube

Claims

1. A method for operating a blast furnace in which a blast furnace injection lance is inserted into a blowpipe, comprising: The blast furnace injection lance has a double-tube structure including an outer tube and an inner tube, the tip opening of the inner tube is inclined at a predetermined angle θ of 55 degrees or more with respect to a plane perpendicular to the axial direction of the inner tube, and when the distance in the longitudinal direction of the blast furnace injection lance between the most distal end of the tip opening of the inner tube and the tip opening of the outer tube is W, the distance W satisfies the following formula (1): While blowing a hydrogen-based reducing gas through the outer tube, Pulverized coal containing 50% by mass or more of a carbonaceous material having a combustion rate of 3.0 (mg / min) or more is blown into the inner tube by a carrier gas, A method for operating a blast furnace, characterized in that, when the flow rate of the hydrogen-based reducing gas is X1 and the flow rate of the carrier gas is X2, the injection condition shown in the following formula (2) is satisfied: W≦tanθ×D・・・・・・Formula (1) X1 / X2≧0.5...Formula (2) where D is the diameter of the inner tube.

2. 2. The method for operating a blast furnace according to claim 1, wherein the tip of the inner pipe is disposed at any one of a protruding position outside the outer pipe, a position inside the outer pipe within the pipeline, and a flush position with the tip opening of the outer pipe.

3. 3. The method for operating a blast furnace according to claim 1, wherein the tip opening of the outer pipe is perpendicular to the axial direction of the inner pipe.

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