Blast furnace operation methods

Abstract

This invention provides a method for operating a blast furnace that enables stable operation even when ferrocoke is used as a raw material. [Solution] This is a method of operating a blast furnace in which a coke layer and an ore layer are alternately formed inside the blast furnace, and ferro-coke is mixed with the ore layer and charged. The method of operating the blast furnace includes a first batch charging step in which a first batch of the ore layer is charged towards the center of the blast furnace, and a second batch charging step in which a second batch of the ore layer containing more ferro-coke than the first batch is charged towards the wall of the blast furnace. In the first batch charging step, the first batch is charged so that its top is located closer to the wall than the center of the blast furnace. In the second batch charging step, the second batch is charged so that its top is located closer to the wall than the top of the first batch.

Description

Technical Field

[0001] The present invention relates to an operating method for a blast furnace using ferrocoke as a raw material for the blast furnace.

Background Art

[0002] As a method for promoting the reduction reaction in the operation of a blast furnace and reducing the ratio of reducing agents, there is a technique of using ferrocoke, which is a composite lump product obtained by previously pulverizing, mixing, molding, and carbonizing coal and iron ore, and carbonizing the internal iron ore into metallic iron and the coal into coke.

[0003] For example, Patent Document 1 discloses an operating method for a blast furnace using ferrocoke, coke, and iron ore, which are formed into lumps by heating a raw material mainly composed of coal and iron ore as a raw material for the blast furnace.

[0004] Ferrocoke is characterized by having higher reactivity with CO2 gas than conventional metallurgical coke (hereinafter referred to as "chamber furnace coke" for distinction from ferrocoke) produced by carbonizing coal in a coke oven or the like. The following formula (a) can be said to be a reaction for regenerating CO2 generated in the reduction of iron ore shown in the following formula (b) into CO gas having reducing power. CO2 + C → 2CO ···(a) FeO + CO → Fe + CO2 ···(b)

[0005] Therefore, if the reaction of the above formula (a) occurs promptly in a region where the CO2 gas concentration is increased by the reaction of the above formula (b), the CO2 gas is regenerated into CO gas having reducing power, and the reduction of iron ore is promoted.

[0006] Therefore, when ferrocoke is used as a raw material for a blast furnace, measures are taken to maintain the permeability of the lower part of the blast furnace. For example, Patent Document 2 discloses a blast furnace operation method in which a coke layer and an ore layer are formed inside the blast furnace, characterized in that the ore layer is divided into multiple batches of ore layers, ferrocoke is mixed into at least one of the multiple batches of ore layer, and ferrocoke is not mixed into at least one other batch of ore layer. Patent Document 3 also discloses a blast furnace operation method in which iron ore raw material, ferrocoke, and metallic iron raw material are charged from the top of the furnace. Patent Document 4 discloses a method for using low-strength ferrocoke by adjusting the reducibility of the ore according to the reactivity of the ferrocoke and causing the ferrocoke to react and disappear before reaching the lower part of the furnace. Patent Document 5 discloses a method for preventing ferrocoke from remaining in the lower part of the furnace and preventing deterioration of the aeration and liquid permeability of the lower part of the furnace by defining the particle size, iron content, and usage range of ferrocoke. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2006-28594 [Patent Document 2] Japanese Patent Publication No. 2012-172167 [Patent Document 3] Japanese Patent Publication No. 2008-57005 [Patent Document 4] Japanese Patent Publication No. 2017-61727 [Patent Document 5] Japanese Patent Publication No. 2011-149090 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the method described in Patent Document 1, the unburned pulverized coal powder and the powder generated from ferrocoke significantly worsen the permeability at the bottom of the blast furnace, which may make it impossible to maintain stable blast furnace operation.

[0009] In the method described in Patent Document 2, ferrocoke is mixed into the batch with the largest ore layer thickness ratio. However, when ferrocoke is mixed into the batch on the furnace center side, the ferrocoke segregated in the center flows into the furnace core, hindering the permeability and permeability of the lower part of the furnace, which can cause serious operational problems such as deterioration of slag.

[0010] In the method described in Patent Document 3, metallic iron raw materials such as scrap are charged into the blast furnace along with ferrocoke. Because scrap has sharp edges, there is a risk of damaging or breaking the belt conveyor that transports the raw materials in the blast furnace.

[0011] Therefore, using a skip system that transports blast furnace raw materials using metal skip cars could potentially prevent damage to the belt conveyor. However, the skip system has limitations in the raw material charging capacity of the blast furnace and is not suitable for large blast furnaces.

[0012] Furthermore, in addition to these transportability issues, scrap differs significantly from other blast furnace raw materials and ferrocoke in terms of size, density, and shape. Therefore, there is a risk of separation from ferrocoke due to segregation when the scrap is placed in the hopper at the top of the furnace or when it is charged into the blast furnace. As a result, there is a problem in ensuring sufficient permeability.

[0013] The method described in Patent Document 4 aims to cause ferrocoke to react and disappear before reaching the bottom of the furnace by combining it with highly reducible ore. However, near the center of the blast furnace, the basic principle is to arrange more coke and less ore to ensure gas flow. As a result, the amount of reduction reaction is small relative to the gas volume, and the CO2 concentration is low. Consequently, ferrocoke descends to the bottom of the furnace without reacting and disappears, flowing into the furnace core. This can hinder the permeability and fluid flow in the lower part of the furnace, potentially causing serious operational problems such as deterioration of slag production.

[0014] The method described in Patent Document 5 involves using ferrocoke at a ratio of 30 mass% to 50 mass% of coke, which allows for operation without hindering the aeration and liquid permeability of the lower part of the furnace. However, as the amount of ferrocoke used increases, the temperature of the heat storage zone drops significantly, reducing the reduction rate of the sintered ore. This can prevent the sintered ore from effectively utilizing the increased CO gas generated by the increased amount of ferrocoke used, potentially reducing the effect of reducing the reducing agent ratio. Furthermore, ferrocoke mixed towards the center of the furnace flows into the core without being removed by the reaction for the reasons mentioned above, hindering the aeration and liquid permeability of the lower part of the furnace and potentially causing serious operational problems such as deterioration of slag production.

[0015] This invention has been made in view of the above circumstances, and aims to provide a method for operating a blast furnace that enables stable operation even when ferrocoke is used as a raw material for the blast furnace. [Means for solving the problem]

[0016] To solve the above problems, the present invention has the following features. [1] A method for operating a blast furnace, comprising alternately forming coke layers and ore layers inside the blast furnace, and mixing ferrocoke into the ore layers before charging, The process includes a first batch charging step in which the first batch is charged into the central side of the ore layer, The process includes a second batch charging step in which a second batch of the ore layer, which contains more ferrocoke than the first batch, is charged to the wall side of the blast furnace. In the first batch charging process, the first batch is charged such that its top is located closer to the wall than the center of the blast furnace. A method for operating a blast furnace, wherein in the second batch charging process, the second batch is charged such that the top of the second batch is located closer to the wall than the top of the first batch. [2] The usage ratio of the ferrocoke in the ore layer is set to 15 mass% or more of the coke. The first batch and the second batch contain ore raw materials, In the method for operating a blast furnace according to [1], the ore raw material of the second batch is an ore raw material having a higher reducibility than the ore raw material of the first batch.

Advantages of the Invention

[0017] According to the method for operating a blast furnace of the present invention, in the first batch charging step, the first batch is charged so that the top of the first batch is located closer to the wall side than the center of the blast furnace. Also, in the second batch charging step, the second batch, which contains more ferrocoke than the first batch, is charged so that the top of the second batch is located closer to the wall side than the top of the first batch. Thereby, ferrocoke can be unevenly distributed on the wall side rather than the center side of the blast furnace. Therefore, it is possible to prevent the inflow of ferrocoke and powdery substances derived from ferrocoke into the center side and the hearth of the blast furnace, and to make the air permeability in the blast furnace appropriate. As a result, the operation of the blast furnace can be carried out stably.

Brief Description of the Drawings

[0018] [Figure 1] It is a treatment flow of a method for operating a blast furnace. [Figure 2] It is an explanatory diagram showing a mode in which an ore layer is formed by the first batch charging step and the second batch charging step in FIG. 1.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 shows a treatment flow of a method for operating a blast furnace. The method for operating a blast furnace forms a coke layer and an ore layer alternately in the blast furnace and charges the raw materials of the blast furnace.

[0020] As shown in FIG. 1, in the method for operating a blast furnace, among the raw materials of the blast furnace, the raw materials of the coke layer are charged into the blast furnace, and the coke layer charging step is executed (step S01).

[0021] In step S01, the coke layer charging process, for example, the raw materials for the coke layer are charged using a swirling chute. The coke layer is charged in such a way that it forms layers from the furnace wall side to the center side of the blast furnace, and is particularly thicker towards the center.

[0022] Next, the ore layer mixed with ferrocoke is charged. Specifically, the first batch charging process is performed, in which the first batch of raw materials from the ore layer is charged towards the center of the blast furnace (step S02).

[0023] In the first batch charging process of step S02, the raw materials for the first batch are charged using a rotating chute. The first batch is charged by adjusting the tilt angle of the rotating chute so that its peak is formed on the wall side from the center of the blast furnace.

[0024] The first batch contains ore raw materials. The ore raw materials of the first batch are not particularly limited, but may include, for example, sintered ore, lump ore, pellets, and reduced iron. Small lumps of coke may also be mixed into the first batch. Furthermore, the first batch has a lower ferrocoke content than the second batch. It is preferable that ferrocoke is not intentionally added to the first batch.

[0025] Next, a second batch charging process is performed in which the second batch of raw materials from the ore layer is charged to the wall side of the blast furnace (step S03).

[0026] In the second batch charging process of step S03, for example, the raw materials for the second batch are charged using a swivel chute. The second batch is charged by adjusting the tilt angle of the swivel chute so that it is charged closer to the wall than the apex of the first batch. Therefore, the apex of the second batch is formed outside the apex position of the first batch.

[0027] The second batch contains ore raw materials. The ore raw materials of the second batch are not particularly limited, but may include, for example, sintered ore, lump ore, pellets, and reduced iron. Small lumps of coke may also be mixed into the second batch. Furthermore, the second batch has a higher ferrocoke content than the first batch. It is preferable that ferrocoke is intentionally added to the second batch.

[0028] Furthermore, it is desirable that 80% by mass or more of ferrocoke be added to the second batch, preferably 90% by mass or more, and more preferably 100% by mass be added.

[0029] When the proportion of ferro-coke used in the ore layer is set to 15 mass% or more of the coke, the reduction ratio can be further reduced by making the reducing properties of the ore raw materials in the second batch higher than those of the first batch. In this case, it is desirable that the ore raw materials in the first batch include more raw materials with lower reducibility than those in the second batch; for example, it is desirable that lump ore, which is less reducible than sintered ore, be included in greater proportions than in the second batch. Conversely, it is desirable that the ore raw materials in the second batch include more raw materials with higher reducibility than those in the first batch; for example, it is desirable that sintered ore or pellets, which are more reducible than lump ore, be included in greater proportions than in the first batch.

[0030] Figure 2 shows the configuration of the ore layer formed by the first batch charging process in step S02 and the second batch charging process in step S03 of Figure 1. As shown in Figure 2, the blast furnace raw materials are charged into the blast furnace 100 via a swirling chute 50 installed at the top of the blast furnace 100. The charged raw materials are heated by the furnace gas as they descend to the bottom of the furnace. Subsequently, the ore is softened and melted in the fusion zone 60 and discharged outside the furnace as molten iron 70. Even after the ore melts, coke remains as a solid, and most of it is burned and consumed at the tuyeres 80. On the other hand, some of the coke charged to the center of the blast furnace does not reach the tuyeres 80 and forms the furnace core 90. Since the coke in the furnace core 90 is not consumed at the tuyeres 80, it remains in the blast furnace for a long period of time. Therefore, maintaining good permeability of the furnace core 90 is important for stable blast furnace operation.

[0031] In the example shown in Figure 2, an ore layer 40 is formed on top of a coke layer 30, which is the blast furnace raw material 20.

[0032] The ore layer 40 includes a first batch 41 and a second batch 42. The top P1 of the first batch 41 is located on the wall 11 side of the center C of the blast furnace 100. The first batch 41 has an inclined surface 41a that slopes from the top P1 of the first batch 41 to the center C of the blast furnace 100.

[0033] The top P2 of the second batch 42 is located closer to the wall 11 than the top P1 of the first batch 41. The second batch 42 has an inclined surface 42a that slopes from the top P2 of the second batch 42 to the wall 11 of the blast furnace 100. In the example shown in Figure 2, ferrocoke 43 is added only to the second batch 42.

[0034] Here, let R be the radius of the blast furnace 100. Let r1 be the distance from the center C of the blast furnace 100 to the top P1 of the first batch 41 in the radial direction of the blast furnace 100. Let r2 be the distance from the center C of the blast furnace 100 to the top P2 of the second batch 42 in the radial direction of the blast furnace 100. Note that in this embodiment, radius R will be described as the inner diameter of the blast furnace 100.

[0035] The relationship between radius R and distance r1 is such that the value of r1 / R is between 0.4 and 0.7, and preferably between 0.5 and 0.6.

[0036] The relationship between radius R and distance r2 should be such that the value of (r2 / R)-(r1 / R) is 0.2 or greater. That is, in the second batch loading process of step S03 in Figure 1, the second batch is loaded in such a way that the tilt angle θ of the rotating chute 50 is greater than when the first batch is loaded to the apex position in the loading process of step S02.

[0037] In this way, by performing the first batch charging process and the second batch charging process, the ore of the second batch on the wall portion 11 side of the blast furnace 100 can be charged in a way that prevents it from flowing into the center C side of the blast furnace 100.

[0038] Specifically, in the example shown in Figure 2, the region from the top P1 of the first batch 41 to the center C of the blast furnace 100 is not covered by the second batch 42. The surface layer of the region from the top P1 of the first batch 41 to the center C of the blast furnace 100 is composed almost entirely of the first batch 41. In other words, the amount of the second batch 42 decreases sharply towards the center C of the blast furnace 100, with the top P1 of the first batch 41 as the boundary.

[0039] In other words, the amount of powdery material derived from ferrocoke in the first batch 41, located on the central C side of the blast furnace 100, can be reduced compared to the second batch, thereby improving the permeability on the central C side of the blast furnace 100. This effect becomes even more pronounced, especially by increasing the ferrocoke content in the second batch 42 compared to the first batch 41.

[0040] Furthermore, it is known that the raw materials charged to the central C side flow into the furnace core 90 of the blast furnace 100. While the ore melts into a liquid in the lower part of the furnace, ferrocoke, being mainly composed of carbon, exists as a solid in the lower part of the furnace. In particular, if powdery material derived from ferrocoke flows into the furnace core, it obstructs the ventilation of the lower part of the furnace, making it difficult to continue stable operation.

[0041] In this invention, by forming a first batch 41 and a second batch 42 in the ore layer 40, the ferrocoke 43 can be unevenly distributed towards the wall portion 11 of the blast furnace 100. Therefore, the inflow of powdery material derived from ferrocoke into the furnace core can be prevented, the permeability of the blast furnace 100 can be improved, and the reducing agent ratio can be reduced. This makes it possible to achieve stable operation.

[0042] Here, if the ferrocoke content in the second batch is higher than that of the first batch, the localized ratio of ferrocoke to ore raw material will be higher compared to when it is evenly distributed between both batches. Therefore, when using more than a certain amount of ferrocoke, the temperature of the heat storage zone will drop significantly, which may reduce the reduction rate of the ore and prevent the reducing agent ratio from decreasing sufficiently.

[0043] In the blast furnace operation method of the present invention, for example, when the usage ratio of ferrocoke is 15 mass% or more of coke, by using a material with higher reducibility as the ore raw material for the second batch than the ore raw material for the first batch, the decrease in the reduction rate of the ore can be suppressed and the reducing agent ratio can be sufficiently reduced.

[0044] Furthermore, in the blast furnace 100, so-called heat loss occurs due to heat dissipation from its walls 11 and other parts. Ferrocoke absorbs heat through chemical reactions in the blast furnace 100. By unevenly distributing the ferrocoke 43 towards the walls 11 of the blast furnace 100, the heat absorption by the ferrocoke 43 lowers the temperature of the furnace walls, thereby reducing heat dissipation from the walls 11. This makes it possible to improve the energy efficiency of the blast furnace 100 and reduce the reducing agent ratio.

[0045] In the embodiments described above, the first batch and the second batch were described as being formed as a single layer. However, as long as the above-mentioned relationship of particle size and the relationship of apex P1 and P2 in the first batch and the second batch are maintained, the first batch and the second batch may be composed of multiple layers. [Examples]

[0046] To confirm the effects of the present invention, a volume of 5000 m³ was used. 3 Operational tests were conducted at the blast furnace. The sizes of each raw material used were those typically used in operations. While there are no particular limitations on the size or shape of the ferrocoke, the ferrocoke used in the test was a mixture of coal and iron raw materials, with an iron content of 30 mass%, and was stored in an ellipsoidal cup measuring 30mm x 25mm x 18mm (length x width x height) for 6cm. 3 The molded product, shaped to size, was then carbonized in a carbonization furnace at a maximum temperature of 850°C.

[0047] The reducing agent ratio and permeability were evaluated using a conventional example without ferro-coke, an inventive example using ferro-coke, and a comparative example. In all cases, the ore layers were charged into the blast furnace in the order of a first batch and then a second batch. The tilt angle of the swivel chute was adjusted so that the peak position of the first batch was r1 / R = 0.58 and the peak position of the second batch was r2 / R = 0.81 when charging.

[0048] In Invention Example 1, 30 kg / tp of ferrocoke was used, and ferrocoke was mixed and charged only in the second batch. In Invention Example 2, 60 kg / tp of ferrocoke was used, and ferrocoke was mixed and charged only in the second batch. Note that the unit kg / tp used in the ferrocoke unit consumption, coke ratio, pulverized coal ratio, etc. in this application represents the mass in kg of the relevant substance when producing 1 ton of molten iron.

[0049] In Invention Example 3, ferrocoke was mixed and charged only in the second batch at a rate of 60 kg / tp. The first batch of Invention Example 3 mainly contained lump ore, which is less reducible than in other examples, while the second batch mainly contained sintered ore, which is more reducible.

[0050] In Comparative Example 1, 30 kg / tp of ferrocoke was used, and in the first and second batches, the ferrocoke was mixed and charged so that the ratio of ferrocoke per unit of ore was equal. In Comparative Example 2, 60 kg / tp of ferrocoke was used, and in the first and second batches, the ferrocoke was mixed and charged so that the ratio of ferrocoke per unit of ore was equal.

[0051] In Conventional Example 1, Invention Examples 1-3, and Comparative Examples 1-2, the raw materials were blended so that the average reducibility (RI) of the ore (listed in Table 1 as the average RI of the first batch and the average RI of the second batch) was 62 for both the first and second batches, except for Invention Example 3. For Invention Example 3, a large amount of lump ore with low reducibility was blended in the first batch, and a large amount of sintered ore with high reducibility was blended in the second batch, resulting in an average RI of 60 for the first batch and an average RI of 65 for the second batch. Table 1 shows the operating conditions and operating results.

[0052] Furthermore, when evaluating breathability, k = (PB 2 -PT 2 ) / VB 1.7 The airflow resistance index (k), obtained by the following formula, was used. Here, PB is the airflow pressure (g / cm²). 2 ), PT is the furnace top pressure (g / cm²). 2 ), VB is the airflow rate (Nm 3 This represents / min).

[0053] [Table 1]

[0054] In Invention Example 1, the air permeability resistance did not increase compared to Conventional Example 1, while the reducing agent ratio decreased by 10 kg / tp.

[0055] In Invention Example 2, the air permeability resistance did not increase compared to Conventional Example 1, while the reducing agent ratio decreased by 15 kg / tp.

[0056] In Invention Example 3, the reducing agent ratio decreased by 20 kg / tp without an increase in air permeability resistance compared to Conventional Example 1. In Invention Example 3, a greater effect was obtained than in Invention Example 2 by incorporating a highly reducible raw material into the second batch.

[0057] In Comparative Example 1, the airflow resistance increased compared to Conventional Example 1, resulting in a decrease in the pig iron production ratio and making stable operation difficult. Furthermore, although the reducing agent ratio in Comparative Example 1 was lower than that of Conventional Example 1, it was not sufficient compared to that of Invention Example 1.

[0058] In Comparative Example 2, the airflow resistance increased compared to Conventional Example 1, resulting in a lower tapping ratio and making stable operation difficult. Furthermore, the reducing agent ratio in Comparative Example 2 was the same as in Conventional Example 1. In Comparative Example 2, it was necessary to increase the coke ratio to ensure proper airflow.

[0059] Based on the results described above, in Invention Examples 1 to 3, to which the present invention was applied, the permeability resistance did not increase compared to Conventional Example 1, and the reducing agent ratio was sufficiently reduced compared to Conventional Example 1. As a result, it became possible to operate the blast furnace stably. [Explanation of symbols]

[0060] 100 blast furnace 11 Wall 12 Bottom 13. Detention Unit 20 Blast furnace raw material 30 Coke layer 40 Ore layer 41. Batch 1 41a Inclined surface of the first batch 42. Second batch 42a Inclined surface of the second batch 43 Ferrocoke C Blast Furnace Center P1 Top of the first batch P2 Top of the second batch R: Radius of the blast furnace r1 Distance from the center of the blast furnace to the top of the first batch r2 Distance from the center of the blast furnace to the top of the second batch

Claims

1. A method for operating a blast furnace, comprising alternately forming coke layers and ore layers inside the blast furnace, and mixing ferrocoke into the ore layers before charging, The process includes a first batch charging step in which the first batch is charged into the central side of the ore layer, The process includes a second batch charging step in which a second batch containing the ferrocoke from the ore layer is charged to the wall side of the blast furnace, In the first batch charging process, the first batch is charged such that its top is located closer to the wall than the center of the blast furnace, and it has an inclined surface that slopes from its top to the center of the blast furnace. A method for operating a blast furnace, wherein in the second batch charging step, the second batch is charged such that the top of the second batch is located closer to the wall than the top of the first batch.

2. The usage ratio of the ferrocoke in the ore layer is set to 15 mass% or more of the coke. The first batch and the second batch each contain ore raw materials. The method for operating a blast furnace according to claim 1, wherein the ore raw material used in the second batch is an ore raw material that is more reducible than the ore raw material used in the first batch.

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