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 ferrocoke is mixed into the ore layer and charged into the furnace. The method of operating a blast furnace includes a calculation step of calculating the ratio of ferrocoke and pulverized coal according to an appropriate range of powder index calculated based on the amount of powder generated from the ferrocoke in the lower part of the blast furnace and the amount of unburned pulverized coal in the lower part of the blast furnace, and a charging step of charging the blast furnace raw materials into the blast furnace with the calculated ratio of ferrocoke and pulverized coal.

Description

[Technical Field]

[0001] This invention relates to a method for operating a blast furnace using ferrocoke as a raw material. [Background technology]

[0002] One method to promote the reduction reaction during blast furnace operation and lower the reducing agent ratio is to use ferrocoke, a composite agglomerate in which coal and iron ore are pre-crushed, mixed, and molded, and then carbonized to convert the internal iron ore into metallic iron and the coal into coke.

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

[0004] Coke is pulverized due to reaction degradation within the blast furnace and abrasion during loading. Furthermore, ferro-coke, due to its high reactivity, tends to pulverize more easily after reaction than metallurgical coke. This pulverized material affects the permeability within the blast furnace, and consequently, impacts the stable operation of the blast furnace.

[0005] 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 method of operating a blast furnace in which iron ore raw material, ferrocoke, and metallic iron raw material are charged from the top of the furnace.

[0006] Incidentally, pulverized coal has lower material costs than coke, which is produced from lumpy coal. For this reason, costs are reduced by blowing large amounts of pulverized coal into blast furnaces. However, increasing the amount of pulverized coal blown into the blast furnace increases the amount of unburned powder remaining at the tuyeres. This unburned powder causes poor ventilation at the bottom of the blast furnace, an increase in the furnace body's heat load, and increased fluctuations in load drop due to the periphery of the blast furnace gas. Therefore, these problems are expected to become more pronounced when using ferrocoke and pulverized coal as raw materials for blast furnaces.

[0007] Therefore, Patent Document 3 describes changing the hot reactivity (CRI) of the coke charged from the top of the furnace according to the amount of pulverized coal blown in. Furthermore, Patent Document 4 describes suppressing coke pulverization by controlling the reducibility index (RI) of the sintered ore and the slag ratio within an appropriate range. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2006-28594 [Patent Document 2] Japanese Patent Publication No. 2008-57005 [Patent Document 3] Japanese Patent Application Publication No. 9-170008 [Patent Document 4] Japanese Patent Publication No. 2005-272968 [Overview of the project] [Problems that the invention aims to solve]

[0009] 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.

[0010] In the method described in Patent Document 2, 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] In the method described in Patent Document 3, since ferrocoke is far more reactive than coke, there is a problem in that it is significantly pulverized due to reaction degradation before it reaches the raceway of the blast furnace.

[0014] The method described in Patent Document 4 suppresses the pulverization of coke, but it also pulverizes ferrocoke, causing the pulverized ferrocoke to descend to the bottom of the blast furnace. In other words, there is room for improvement in addressing the above-mentioned problem caused by the pulverization of ferrocoke.

[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 in which a coke layer and an ore layer are alternately formed in the blast furnace, and ferrocoke is mixed with the ore layer and charged, comprising: A calculating step of calculating the unit consumption of ferrocoke, the post-reaction strength of ferrocoke, and the pulverized coal ratio so that the amount of powder generated from the ferrocoke at the lower part of the blast furnace and the powder amount index calculated based on the amount of unburned powder of pulverized coal at the lower part of the blast furnace fall within an appropriate range; A charging step of charging raw materials of the blast furnace into the blast furnace with the calculated unit consumption of ferrocoke, the post-reaction strength of ferrocoke, and the pulverized coal ratio. A method for operating a blast furnace. [2] The method for operating a blast furnace according to [1], wherein in the calculating step, the powder amount index is calculated using the following formula (1). Powder amount index (kg / t-p) = Unit consumption of ferrocoke (kg / t-p) × [Concentration of carbon in ferrocoke] (mass%) / 100 × (1.0 - Post-reaction strength of ferrocoke / 100) + Coefficient (α) × Pulverized coal ratio (kg / t-p) ··· (1) [3] The method for operating a blast furnace according to [2], wherein in the calculating step, the powder amount index is set to 55 kg / t-p or less.

Effect of the Invention

[0017] According to the method for operating a blast furnace of the present invention, there are a calculating step of calculating the unit consumption of ferrocoke, the post-reaction strength of ferrocoke, and the pulverized coal ratio so that the powder amount index falls within an appropriate range, and a charging step of charging raw materials of the blast furnace into the blast furnace with the calculated unit consumption of ferrocoke, the post-reaction strength of ferrocoke, and the pulverized coal ratio. Therefore, the amount of powder at the lower part of the blast furnace can be made to be within an appropriate range. As a result, it becomes possible to perform stable operation of the blast furnace.

Brief Description of the Drawings

[0018] [Figure 1] It is a treatment flow of the method for operating a blast furnace. [Figure 2]This graph shows the relationship between the ferrocoke consumption per unit and the required post-reaction strength in Test Example 1. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows the treatment flow of the blast furnace operation method. As shown in Figure 1, the blast furnace operation method is performed in which a calculation process is carried out to calculate the ferrocoke unit cost, the post-reaction strength of the ferrocoke, and the pulverized coal ratio so that the powder amount index, which is calculated based on the amount of powder generated from ferrocoke in the lower part of the blast furnace and the amount of unburned pulverized coal in the lower part of the blast furnace, is within an appropriate range (step S01).

[0020] The powder content index is determined, for example, by adding up the amount of powder generated from ferrocoke in the lower part of the blast furnace and the amount of unburned pulverized coal. The amount of powder generated from ferrocoke in the lower part of the blast furnace can be determined, for example, by the following formula (a). Note that the unit kg / tp used in the ferrocoke unit consumption, coke ratio, pulverized coal ratio, amount of ferrocoke powder, amount of unburned pulverized coal, powder content index, etc. in this application represents the mass in kg of the relevant substance when producing 1 ton of molten iron. Ferrocoke unit cost (kg / tp) × [carbon concentration in ferrocoke] (mass%) / 100 × (1.0 - post-reaction strength / 100) ... (a)

[0021] The powdery material at the bottom of the blast furnace can be considered to be mostly derived from carbon. Therefore, in equation (a), the ferro-coke intensity is multiplied by the carbon concentration in the ferro-coke. The ferro-coke intensity is the mass of ferro-coke per ton of molten iron.

[0022] The carbon concentration in ferrocoke can be measured by the industrial analysis method described in JIS M8812. While not particularly limited, ferrocoke can be formed by mixing coal and iron raw materials, for example, with an iron raw material content of 30 mass%. Furthermore, while not particularly limited, the size of ferrocoke is typically 0.5 to 25 cm. 3 Preferably, it should have a size of 5-8 cm. 3 It is considered more preferable to have this shape. The shape of the ferrocoke is not particularly limited, but for example, an ellipsoid shape can be used, and the size can be adjusted according to the cup size of the molding machine, for example, 6 cm. 3 In this case, it is molded using an ellipsoidal cup with dimensions of 30mm x 25mm x 18mm (length x width x height).

[0023] The general method for measuring the post-reaction strength (CSR) of coke is specified in ISO 18894 and defined as follows: 200 g of coke, adjusted to a particle size of 19-22.4 mm, is reacted at 1100°C for 2 hours while flowing 100% CO2 gas at 5 L / min. After the reaction, the coke is processed at 600 rotations in a Type I drum tester, and the mass yield of the coke sieved onto a 9.5 mm sieve is defined as the CSR. However, ferrocoke is more reactive than general coke, making evaluation difficult under similar conditions. Therefore, the reaction temperature and time were changed, and the post-reaction strength of ferrocoke (hereinafter also simply referred to as post-reaction strength) was determined as the mass ratio on a 9.5 mm sieve after reacting at 1000°C in a CO2 atmosphere for 60 minutes, and then rotating at 20 rpm for 600 rotations in a Type I drum tester. The mass ratio is determined by (mass of ferrocoke remaining on the sieve after the test) / (mass of ferrocoke after the reaction).

[0024] The inventors have found that by measuring the post-reaction strength of ferrocoke under the above conditions, the reaction state and the amount of powdered material when ferrocoke reaches the bottom of the blast furnace can be reproduced with greater accuracy.

[0025] Here, the post-reaction strength can be adjusted by changing the ore ratio in the ferrocoke, or, as with conventional metallurgical coke, by changing the properties of the coal used in the blend, such as the average maximum reflectance (Ro) or maximum fluidity (MF) of the vitrinite.

[0026] However, post-reaction strength is generally negatively correlated with reactivity. Therefore, in order to maintain the effectiveness of ferrocoke, it is preferable to set the upper limit of post-reaction strength to around 70. Also, since post-reaction strength is generally correlated with cold strength, it is preferable to set the lower limit to around 30 in order to prevent pulverization at the top of the blast furnace.

[0027] Based on the above, the post-reaction strength is preferably adjusted to between 30 and 70, more preferably to 40 or higher, and more preferably to 50 or higher. This is because a higher post-reaction strength leads to more stable blast furnace permeability, allowing for stable operation over a wider range of pulverized coal ratios.

[0028] The amount of unburned pulverized coal at the bottom of the blast furnace can be determined, for example, by the following formula (b). Coefficient (α) × Pulverized coal ratio (kg / tp) (b)

[0029] Pulverized coal is coal that has been crushed, dried, and then adjusted to a predetermined particle size. In other words, pulverized coal contains carbon. The pulverized coal ratio is the mass (kg) of pulverized coal per ton of molten iron.

[0030] The coefficient (α) can be calculated based on the carbon concentration in the pulverized coal and the combustion rate of the pulverized coal. For example, if the carbon concentration in the pulverized coal is 80 (mass%) and the combustion rate of the pulverized coal is 70 (mass%), the coefficient (α) can be calculated as follows. Coefficient (α) = 80 / 100 × (1 - 70 / 100) = 0.24

[0031] Furthermore, the carbon concentration in pulverized coal can be measured by the industrial analysis method described in JIS M8812. The combustion rate of pulverized coal can also be calculated, for example, by collecting unburned powder from a pulverized coal combustion site and analyzing its components.

[0032] The coefficient (α) should preferably be set within the range of 0.20 to 0.28. If the coefficient (α) is greater than 0.28, the amount of unburned powder represented by equation (b) increases, making it difficult for blast furnaces with a high pulverized coal ratio to accept powder derived from ferrocoke. Therefore, it is desirable to improve the combustibility of the pulverized coal so that the coefficient (α) is 0.28 or less. While a smaller coefficient (α) is better, it is difficult to set it below 0.20 due to constraints on the carbon concentration and combustion rate of the pulverized coal. In this embodiment, an example in which the coefficient (α) is set to 0.24 will be described.

[0033] The flour quantity index is calculated by adding the values ​​from equations (a) and (b) above, and then using the following equation (c). Powder content index (kg / tp) = Unit cost of ferrocoke (kg / tp) × [Concentration of carbon in ferrocoke] (mass%) / 100 × (1.0 - Post-reaction strength of ferrocoke / 100) + coefficient (α) × pulverized coal ratio (kg / tp) ... (c)

[0034] In the calculation process of step S01, the unit consumption of ferrocoke, the post-reaction strength of ferrocoke, and the pulverized coal ratio are calculated so that the powder quantity index is within an appropriate range.

[0035] The appropriate range for the powder quantity index is a numerical value that represents the amount of powdery material that can be allowed in the lower part of the blast furnace. The appropriate range for the powder quantity index is calculated based on, for example, the volume of the blast furnace and the carbon consumption reaction limit in the blast furnace. The carbon consumption reaction in the blast furnace is mainly represented by equations (2), (3), and (4), and is collectively called the solution loss reaction. C + CO2 → 2CO ···(2) C + H2O → CO + H2 ... (3) C + FeO → CO + Fe ... (4)

[0036] The amount of carbon consumed by the solution loss reaction in a blast furnace can be easily determined by the difference between the amount of carbon in the CO and CO2 contained in the top gas and the amount of carbon in the CO generated at the tuyeres, and it is known to be approximately 80-100 kg / tp. The carbon consumed by the solution loss reaction includes unburned pulverized coal powder, powdery material derived from ferrocoke, as well as powdery material derived from coke, lumps of ferrocoke, and lumps of coke. The inventors have found that by keeping the powder index, which is expressed as the total amount of unburned pulverized coal powder and powdery material derived from ferrocoke, below an appropriate range, these are consumed by the solution loss reaction and do not cause aeration obstruction.

[0037] The appropriate range for the powder quantity index is generally set to 55 kg / tp or less, and more preferably to 50 kg / tp or less. From the viewpoint of blast furnace permeability, a smaller powder quantity index is desirable, but if it is too small, the range in which operation is possible will be limited. Therefore, a realistic lower limit is to set the appropriate range to a value of around 45 kg / tp. In this embodiment, the appropriate range for the powder quantity index will be described as 55 or less.

[0038] For example, in the calculation process, the pulverized coal ratio may be adjusted so that the powder quantity index falls within an appropriate range, depending on the ferrocoke unit cost and the post-reaction strength.

[0039] For example, in the calculation process, the ferrocoke unit cost may be adjusted so that the powder quantity index falls within an appropriate range, depending on the pulverized coal ratio and the post-reaction strength.

[0040] For example, in the calculation process, the post-reaction strength may be adjusted so that the powder content index falls within an appropriate range, depending on the pulverized coal ratio and the ferrocoke unit consumption.

[0041] Figure 2 shows, as an example, the results of calculating the post-reaction strength required for the powder content index to be within the appropriate range, based on the pulverized coal ratio and ferro-coke intensity. Here, the coefficient (α) is set to 0.24, and the appropriate range is 55 kg / tp or less. Calculations were performed for three cases: pulverized coal ratios of 150, 180, and 210 kg / tp.

[0042] Furthermore, in the calculation process of step S01, the post-reaction strength should be adjusted to be between 30 and 70, as described above.

[0043] Finally, the charging process is carried out in which the blast furnace raw materials are charged into the blast furnace according to the ferrocoke unit cost, the post-reaction strength of the ferrocoke, and the pulverized coal ratio calculated in step S01 (step S02).

[0044] In the charging process of step S02, ferrocoke is charged into the blast furnace along with other blast furnace materials using a charging device located at the top of the blast furnace, based on the ferrocoke unit cost, the post-reaction strength of the ferrocoke, and the pulverized coal ratio calculated in the calculation process of step S01.

[0045] The blast furnace operation method of the present invention includes a calculation step of calculating the ferrocoke unit consumption, the post-reaction strength of ferrocoke, and the pulverized coal ratio so that the powder quantity index is within an appropriate range, and a charging step of charging the blast furnace raw materials into the blast furnace with the calculated ferrocoke unit consumption, post-reaction strength of ferrocoke, and pulverized coal ratio. Therefore, the amount of powdery material in the lower part of the blast furnace can be kept within an appropriate range. This makes it possible to operate the blast furnace stably. [Examples]

[0046] To confirm the effects of the present invention, a volume of 5000 m³ was used. 3 An operational test was conducted in the blast furnace. The ferrocoke used in the test was prepared by mixing coal and iron raw materials so that the iron raw material ratio was 30 mass%, and measuring 6 cm in an ellipsoidal cup with dimensions of 30 mm x 25 mm x 18 mm. 3The molded product formed into a size was carbonized in a carbonization furnace at a maximum temperature of 850°C. The carbon concentration in the ferrocoke was 62% by mass. The carbon concentration in the ferrocoke was measured according to the industrial analysis method described in JIS M8812.

[0047] Using a conventional example that does not use ferrocoke, an inventive example that uses ferrocoke, and a comparative example, the reduction material ratio and air permeability were evaluated. By changing the ferrocoke unit, strength after reaction, and pulverized coal ratio, they were evaluated as Test Examples 1 to 3. Tables 1 to 3 show the operating conditions and evaluation results of Test Examples 1 to 3. The appropriate range of the powder amount index was set to 55 or less. Also, the coefficient (α) was set to 0.24. The above formula (c) was used to calculate the powder amount index.

[0048] In the evaluation of air permeability, the air permeability index (k) obtained by k = (P [[ID={9}]] B 2 -P T 2 ) / V B 1.7 was used. Here, in this formula, P B is the blowing pressure (g / cm 2 ), P T is the top pressure of the furnace (g / cm 2 ), and V B is the blowing volume (Nm 3 / min).

[0049]

Table 1

[0050]

Table 2

[0051]

Table 3

[0052] In Test Example 1, an example of operation with a pulverized coal ratio of 150 kg / tp was designated as Conventional Example 1, and examples using ferro-coke were designated as Inventive Example 1 and Comparative Example 1, and the operational results were compared for these. In Comparative Example 1, the ferro-coke unit consumption was set to 45 kg / tp, and ferro-coke with a post-reaction strength of 27 was used. Although the reducing agent ratio was 10 kg / tp lower than in Conventional Example 1, the air permeability resistance index of Comparative Example 1 was higher than in Conventional Example 1, and the pig tapping ratio also decreased, making stable operation impossible. The powder content index of Comparative Example 1 was 56.4. Therefore, in Inventive Example 1, while keeping the amount of ferro-coke used and the pulverized coal ratio the same as in Comparative Example 1, the ferro-coke with a post-reaction strength of 36 was changed so that the powder content index was 55 or less, thereby reducing the coke ratio and lowering the reducing agent ratio by 15 kg / tp compared to Conventional Example 1. Furthermore, the air permeability resistance index of Invention Example 1 was made equivalent to that of Conventional Example 1, and stable operation was maintained.

[0053] In Test Example 2, an example of operation with a pulverized coal ratio of 190 kg / tp was designated as Conventional Example 2, and examples using ferro-coke were designated as Inventive Example 2 and Comparative Example 2, and the operational results were compared for these. In Comparative Example 2, when the pulverized coal ratio was maintained at the same level as Conventional Example 2, and 30 kg / tp of ferro-coke with a post-reaction strength of 43 was used, the aeration resistance increased, the pig tapping ratio decreased, and stable operation could not be continued. The powder content index for Comparative Example 2 was 56.2. Therefore, in Inventive Example 2, while using 30 kg / tp of ferro-coke with a post-reaction strength of 43 was the same as in Comparative Example 2, the pulverized coal ratio was reduced so that the powder content index was 55 or less. As a result, the reducing agent ratio could be reduced by 10 kg / tp while maintaining the same aeration resistance compared to Conventional Example 2, and stable operation was maintained.

[0054] In Test Example 3, an example of operation with a pulverized coal ratio of 210 kg / tp was designated as Conventional Example 3, and examples using ferro-coke were designated as Inventive Example 3 and Comparative Example 3, and the operational results were compared for these. In Comparative Example 3, the pulverized coal ratio was the same as in the Conventional Example, and ferro-coke with a post-reaction strength of 56 was used at a unit consumption of 20 kg / tp. Compared to Conventional Example 3, the aeration resistance increased, the pig tapping ratio decreased, and stable operation could not be maintained. The powder content index for Comparative Example 3 was 55.9. Therefore, in Inventive Example 3, the pulverized coal ratio was the same as in the Conventional Example, and the use of ferro-coke with a post-reaction strength of 56 was not changed. However, the ferro-coke unit consumption was reduced to 15 kg / tp so that the powder content index was 55 or less. As a result, the aeration resistance remained the same as in Conventional Example 3, the reducing agent ratio could be reduced by 5 kg / tp, and stable operation was maintained.

[0055] Based on the above, it can be seen that in Invention Examples 1 to 3, stable operation was achieved by operating in a manner that satisfies the conditions determined by the present invention. The above results demonstrate the effectiveness of the present invention.

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, A calculation process for calculating the unit consumption of ferrocoke, the post-reaction strength of ferrocoke, and the pulverized coal ratio, such that the amount of powder generated from the ferrocoke in the lower part of the blast furnace and the amount of unburned pulverized coal in the lower part of the blast furnace are within an appropriate range. A method for operating a blast furnace, comprising: a charging step of charging the blast furnace with blast furnace raw materials at the calculated unit consumption of ferrocoke, the post-reaction strength of ferrocoke, and the pulverized coal ratio.

2. The method for operating a blast furnace according to claim 1, wherein in the calculation step, the powder quantity index is calculated using the following formula (1). Powder content index (kg / t-p) = Unit cost of ferrocoke (kg / t-p) × [Concentration of carbon in ferrocoke] (mass%) / 100 × (1.0 - Post-reaction strength of ferrocoke / 100) + coefficient (α) × pulverized coal ratio (kg / t-p) ... (1)

3. The method for operating a blast furnace according to claim 2, wherein in the calculation step, the powder quantity index is 55 kg / t-p or less.

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