Blast furnace operation methods

Abstract

To provide a blast furnace operation method that uses reduced iron and performs high-temperature blowing at a temperature higher than the current blowing temperature of approximately 1200°C, for example, 1300°C or higher, and that can ensure a sufficient top gas temperature (for example, around 100-180°C). [Solution] A method for operating a blast furnace, comprising a charging step of charging iron raw materials containing 50% or more by mass of reduced iron and coke into the furnace, and a blowing step of blowing hot air into the blast furnace from a tuyer, wherein the blowing temperature and nitrogen enrichment rate of the hot air are controlled according to the charging ratio of reduced iron in the iron raw materials.

Description

[Technical Field] 【0001】 This invention relates to a method for operating a blast furnace. [Background technology] 【0002】 In blast furnace operation, sintered ore, pellets, lump ore, etc. (hereinafter collectively referred to as "iron raw materials"), along with coke as a reducing agent and fuel, are alternately charged into the blast furnace from the top. Hot air is also blown in from tuyeres located at the bottom of the furnace, and auxiliary fuels such as pulverized coal are blown in. The iron raw materials and coke (hereinafter collectively referred to as "charges") charged from the top of the furnace form alternating layers of ore and coke. As the charges descend, they gradually descend through the blast furnace towards the bottom, being heated and heated by the gas rising from the bottom. The iron raw materials are heated and reduced as they descend within the blast furnace, melting and separating into pig iron and slag, which then drip onto the hearth. 【0003】 Conventionally, blast furnace operating methods have been considered that involve replacing some of the iron raw materials with reduced iron such as scrap, molded iron, reduced iron pellets (DRI), and reduced iron briquettes (HBI), with the aim of lowering the reducing agent ratio (RAR) (total weight of reducing agents (coke, pulverized coal (PC), etc.) per ton of molten iron), improving the permeability of the ore layer, and improving permeability and liquid permeability by raising the temperature of the furnace core coke. 【0004】 For example, Patent Document 1 discloses a blast furnace operation method in which the amount of scrap charged from the top of the furnace to the periphery increases in accordance with the amount of pulverized coal injected and the alumina content of the sintered ore charged from the top of the furnace, and decreases the amount of scrap charged from the top of the furnace to the periphery in accordance with the amount of pulverized coal injected and the alumina content of the sintered ore charged from the top of the furnace. Furthermore, Patent Document 2 proposes a blast furnace operation method that maintains furnace permeability by replacing a portion of the iron raw materials with scrap when the reduction pulverization index (RDI) of sintered ore or the DI of coke deteriorates below standard values. Furthermore, Patent Document 3 proposes a blast furnace operation method that measures the increase in pressure loss (deterioration of permeability) associated with an increase in the amount of pulverized coal injected, and increases the amount of reduced iron charged in accordance with the increase. [Prior art documents] [Patent Documents] 【0005】 [Patent Document 1] Patent No. 3017009 [Patent Document 2] Japanese Patent Publication No. 2008-240028 [Patent Document 3] Patent No. 3589016 [Non-patent literature] 【0006】 [Non-Patent Document 1] Kouji TAKATANI, Takanobu INADA, Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace", ISIJ International, Vol.39(1999), No.1, p.15-22 [Overview of the Initiative] [Problems that the invention aims to solve] 【0007】 As described in Patent Documents 1 to 3 above, the ratio of reducing agents can be reduced by using reduced iron as part of the iron raw material. This is because the use of reduced iron can reduce the amount of heat required for reduction in the blast furnace (heat output). On the other hand, in order to reduce the heat required for reduction (heat output), from the perspective of the heat balance within the blast furnace, one possible method to reduce the amount of combustion carbon (reducing agent ratio) (heat input) is to increase the sensible heat of the blown air (heat input) by increasing the blown air temperature (performing high-temperature blowing). However, it has been found that when taking the heat balance of the blast furnace by using reduced iron and performing high-temperature air blowing, the top gas temperature may decrease to such an extent that it is below 100°C. When the top gas temperature is below 100°C, the gas flow rate at the furnace mouth decreases, making it difficult to discharge dust outside the furnace or reducing the effective reaction area inside the furnace, which may lead to operational instability. 【0008】 As a method of increasing the top gas temperature while maintaining the amount of hot metal produced and the temperature of the hot metal, for example, it is conceivable to reduce the oxygen enrichment rate (oxygen concentration) in the hot air being blown. Here, the oxygen enrichment rate is defined such that the amount of oxygen in air is 21% by volume, and for hot air, it is the ratio of the enriched oxygen. When the oxygen enrichment rate is 1.5%, it means that the ratio of oxygen in the hot air is 21 + 1.5 = 22.5% by volume. However, as a result of investigations by the present inventors, when using reduced iron and performing high-temperature air blowing, even when the oxygen enrichment rate is 0% (no oxygen enrichment), the top gas temperature may be below 100°C. It has been found that simply controlling the oxygen enrichment rate may not be sufficient to ensure an adequate top gas temperature. 【0009】 Therefore, an object of the present invention is to provide an operating method for a blast furnace that uses reduced iron and performs high-temperature air blowing at a temperature higher than the current air blowing temperature of about 1200°C, for example, 1300°C or higher, and can ensure a sufficient top gas temperature (for example, about 100 to 180°C). 【Means for Solving the Problem】 【0010】 The present inventors examined methods for ensuring a sufficient top gas temperature in an operating method for a blast furnace that uses reduced iron and performs high-temperature air blowing. As a result, it has been found that by controlling the air blowing temperature of the hot air and the nitrogen enrichment rate according to the charging ratio of reduced iron in the iron raw material, a sufficient top gas temperature can be ensured. 【0011】 The present invention has been made in view of the above findings. The gist of the present invention is as follows. [1] A charging step of charging an iron raw material containing 50 mass% or more of reduced iron and coke into a furnace, and a blowing step of blowing hot air into the blast furnace from a tuyere. A method for operating a blast furnace, comprising controlling the blowing temperature and nitrogen enrichment rate of the hot air according to the charging ratio of the reduced iron in the iron raw material. [2] When the coke ratio is 310 kg / t or less, when the ratio in mass% of the reduced iron in the total iron raw material is A, the blowing temperature is B in units of °C, and the nitrogen enrichment rate is C in volume%, the following formula (2) is satisfied. The method for operating a blast furnace according to [1]. C , -2 , , [Figure 1] , , 【0013】 , , , , , 【0012】 , , , , , , ≦ C ≦ C max (2) Here, C min , C max , α, and β are values obtained by the following formulas (3) to (6). C min = α × (B - 1200) + β - 2.5 (3) C max = α × (B - 1200) + β + 2.5 (4) α = 1.473×10 -4 × (100 - A) + 1.267×10 -2 (5) β = -0.2224×(100 - A) + 3.671 (6) [3] The method for operating a blast furnace according to [2], wherein A is 50 to 100 mass%. 【Advantages of the Invention】 【0012】 According to the present invention, it is possible to provide a method for operating a blast furnace that can ensure a sufficient top gas temperature even when using reduced iron and performing high-temperature blowing. Further, by using reduced iron, the reducing agent ratio can be reduced. 【Brief Description of the Drawings】 【0013】 [Figure 1] It is a diagram showing the relationship between the blowing temperature and the nitrogen enrichment rate when using reduced iron. [Figure 2] This figure shows the relationship between the airflow temperature and the reducing agent ratio when using reduced iron. [Figure 3] This figure shows the relationship between the blower temperature and the blast furnace carbon reduction rate when using reduced iron. [Modes for carrying out the invention] 【0014】 A method for operating a blast furnace according to one embodiment of the present invention (a method for operating a blast furnace according to this embodiment) comprises a charging step of charging iron raw materials containing 50% by mass or more of reduced iron and coke into the furnace, and a blowing step of blowing hot air into the blast furnace from a tuyeres. Each of these will be explained. Conditions that are not explained are not particularly limited; operations should be conducted under publicly known conditions. 【0015】 (Charging process) In the charging process, iron raw materials and coke are charged alternately from the top of the furnace so that they form layers. In the blast furnace operation method according to this embodiment, in order to reduce the reducing agent ratio, iron raw materials containing reduced iron are used. Examples of reduced iron include scrap, die-cast iron, reduced iron pellets (DRI), and reduced iron briquettes (HBI). Of these, die-cast iron or HBI are preferred in terms of handling ease and safety in terms of heat generation during storage. Also, since scrap may contain trump elements, it is preferable to use materials other than scrap in that respect. Furthermore, with the aim of obtaining a carbon reduction rate that exceeds the current carbon reduction rate at the current blowing temperature, it is preferable that A is 50% or more, where A is the mass percentage of reduced iron in the total iron raw material. It is more preferable that A is 60% or more. The entire iron raw material may be reduced iron (A=100%). Any known coke may be used. Here, the carbon reduction rate is the percentage reduction (by mass) in the carbon intensity introduced at the blast furnace boundary, and is calculated using the following formula. Carbon reduction rate = (Carbon intensity at standard blast furnace operation - Carbon intensity at target operation) / Carbon intensity at standard blast furnace operation × 100 Here, standard blast furnace operation refers to operation using normal raw materials and normal blowing temperature, to which the blast furnace operation method according to this embodiment is not applied. For example, the conditions listed in Table 1 can be cited as examples. 【0016】 The method of installation is not limited; any known method may be used. 【0017】 (Blowing process) In the blowing process, hot air is blown into the blast furnace from the tuyeres. Pulverized coal may also be blown in at the same time. The hot air reacts with the pulverized coal blown in with it and with the coke in the blast furnace to generate high-temperature reducing gas (mainly CO gas in this case). In other words, the hot air gasifies the coke and pulverized coal. The generated reducing gas rises within the blast furnace, heating and reducing the iron-based raw materials. The iron-based raw materials descend within the blast furnace, being heated and reduced by the reducing gas. Subsequently, the iron-based raw materials melt and drip down the furnace, further reduced by the coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% carbon by mass. The molten pig iron from the hearth is removed from the tap and used in the next steelmaking process. 【0018】 The inventors used the parameters shown in Table 1 as the basic operating conditions (normal pulverized coal operation), and simulated the blast furnace parameters using a blast furnace mathematical model when the proportion of reduced iron used in the total iron source raw materials was changed to 60% and 100%, and the blown air temperature was varied from 1200 to 2000°C. 【0019】 The following is an overview of the blast furnace mathematical model used for evaluation. Blast furnace mathematical model: The internal region of the blast furnace is divided in the height, radial, and circumferential directions to define multiple meshes (small regions), and the behavior of each mesh is simulated (see, for example, Non-Patent Document 1). Table 1 shows the parameters for conventional basic operation. In the simulation, since the range of top gas temperature controlled in normal blast furnace operation is 105°C to 180°C, the reducing agent ratio, airflow rate, and nitrogen enrichment rate were adjusted so that the tapping rate and molten iron temperature were the same as in basic operation within the range of top gas temperature between 105°C and 180°C. Furthermore, as the reducing agent ratio decreased, the PC ratio (PCR) was reduced preferentially under the condition of a constant coke ratio (CR) of 250 kg / t, followed by a reduction in the coke ratio. Nitrogen enrichment rate refers to the proportion of nitrogen enriched relative to the 79% volume of nitrogen in the air, assuming that the hot air blown in from the tuyer, including nitrogen, is air. The nitrogen enrichment rate can be expressed as follows: For example, if the nitrogen enrichment rate is 1.5 volume%, it indicates that the hot air contains 79 + 1.0 = 80.5 volume% nitrogen. On the other hand, if the nitrogen enrichment rate is -1.0 volume%, it indicates that the hot air contains 79 - 1.0 = 78.0 volume% nitrogen. In this case, since oxygen enrichment usually reduces the volume percentage of nitrogen, a nitrogen enrichment rate of -1.0 volume% is equivalent to an oxygen enrichment rate of +1.0 volume%. 【0020】 [Table 1] 【0021】 As a result of the simulation, Figure 1 shows the relationship between the airflow temperature and nitrogen enrichment rate when using reduced iron. As can be seen from Figure 1, by appropriately controlling the nitrogen enrichment rate according to the amount of reduced iron used and the blown air temperature, the furnace top gas temperature can be controlled within an appropriate range. Furthermore, Figure 2 shows the relationship between the blown air temperature and the reducing agent ratio when using reduced iron, and Figure 3 shows the relationship between the blown air temperature and the blast furnace carbon reduction rate when using reduced iron. The data used for plotting in Figures 2 and 3 is the same data as in Figure 1. As can be seen from Figures 2 and 3, increasing the blown air temperature (and nitrogen enrichment rate) can reduce the reducing agent ratio, and as a result, the carbon reduction rate in blast furnace operation can be increased. From the above results, it can be seen that although the reducing agent ratio differs depending on the detailed operating conditions, the general trend can be estimated using the following formula. RAR = 350 - 9.4 × 10 -2 ×(B-1200)-2.5×(A-60) (1) Here, RAR, B, and A represent the reducing agent ratio (kg / t), the blown air temperature (°C), and the mass percentage of reduced iron in the total iron raw material (%), respectively. 【0022】 Specifically, in the blast furnace operation method according to this embodiment, when operating in which reduced iron is used in an operation in which reduced iron is used in an operation in which reduced iron is used in an operation in which reduced iron is used in an operation in which the reducing agent ratio is estimated by formula (1), and when the furnace heat balance is adjusted by fixing one of the coke ratio and pulverized coal ratio that constitute the reducing agent ratio and adjusting the other, it is preferable that the following formula (2) is satisfied when A is the mass % of reduced iron in the total iron raw material, B is the blown air temperature in °C, and C is the nitrogen enrichment rate in volume %. 【0023】 C min ≤ C ≤ C max (2) Here, C min , C max α and β are values ​​obtained by the following equations (3) to (6). C min =α × (B - 1200) + β - 2.5 (3) C max =α × (B - 1200) + β + 2.5 (4) α = 1.473 × 10 -4 ×(100-A)+1.267×10 -2 (5) β = -0.2224 × (100 - A) + 3.671 (6) 【0024】 The reasoning behind the derivation of the above equation is explained below. As shown in Figure 1, the gradient α of the nitrogen enrichment rate with respect to the blown air temperature differs between the cases of using 100% by mass of reduced iron and 60% by mass, but the gradient is almost the same even if the furnace top gas temperature is different. Therefore, α was set as a linear function of the reduced iron utilization rate. Also, β, that is, the appropriate nitrogen enrichment rate when the blown air temperature is 1200°C (when the furnace top gas temperature is 140°C), also differs between the cases of using 100% by mass of reduced iron and 60% by mass, so β ​​was set as a linear function of the reduced iron utilization rate. Furthermore, the range of nitrogen enrichment rates that can be taken depending on the furnace top gas temperature is approximately ±2.5%, and this is incorporated into equations (3) and (4). [Examples] 【0025】 In the operation of a blast furnace in which iron raw materials and coke are charged into the furnace and hot air is blown into the furnace from tuyeres, the proportion of reduced iron A (mass%) in the total iron raw materials was set to 50-100% by mass, and the hot air blowing temperature B and nitrogen enrichment rate were changed according to the proportion of reduced iron charged. 【0026】 Specifically, using the parameters for basic operation as a base, a blast furnace mathematical model was used to set a nitrogen enrichment rate that satisfies equation (2) in the range of 1600 to 2000°C for the blower temperature B, according to the proportion of reduced iron A, so that the amount of iron produced and the molten iron temperature would be the same as during basic operation. The top gas temperature and carbon reduction rate at that time were then determined. C min ≤ C ≤ C max (2) Here, C min , C max α and β are values ​​obtained by the following equations (3) to (6). C min =α × (B - 1200) + β - 2.5 (3) C max =α × (B - 1200) + β + 2.5 (4) α = 1.473 × 10 -4 ×(100-A)+1.267×10 -2 (5) β = -0.2224 × (100 - A) + 3.671 (6) The results are shown in Table 2. 【0027】 [Table 2] 【0028】 In Table 2, CR is the coke ratio, PCR is the PC ratio, RAR is the reducing agent ratio, InputC is the carbon intensity (unit of carbon) supplied to the blast furnace with the blast furnace as the boundary, and InputΔC is the carbon reduction rate. As can be seen from Table 2, it was confirmed that a high carbon reduction rate can be obtained while ensuring a sufficient furnace top gas temperature (100-180°C) by changing the hot air blowing temperature and nitrogen enrichment rate according to the charging ratio of reduced iron, within the range of a coke ratio of 310 kg / t or less, similar to basic operation.

Claims

[Claim 1] A charging process involves charging iron raw materials containing 50% or more by mass of reduced iron and coke into the furnace. The blowing process involves blowing hot air into the blast furnace from the tuyeres, A method for operating a blast furnace having, The blowing temperature and nitrogen enrichment rate of the hot air are controlled according to the proportion of reduced iron charged into the iron raw material. A method for operating a blast furnace, characterized by the following. [Claim 2] When the coke ratio is 310 kg / t or less, and the mass percentage of the reduced iron to the total iron raw material is A, the blown air temperature is B in °C, and the nitrogen enrichment rate is C in volume percentage, the following equation (2) is satisfied: A method for operating a blast furnace according to claim 1, characterized in that... C ｍｉｎ ≦ C ≦ C ｍａｘ (2) Here, C ｍｉｎ , C ｍａｘ α and β are values ​​obtained by the following equations (3) to (6). C ｍｉｎ =α×(B-1200)+β-2.5 (3) C ｍａｘ =α×(B-1200)+β+2.5 (4) a = 1.473×10 －４ ×(100-A)+1.267×10 －２ (5) β = -0.22224×(100-A)+3.671 (6) [Claim 3] The above A is 50 to 100% by mass. The method for operating a blast furnace according to claim 2, characterized in that...

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