Method for operating reduction furnace and method for producing reduced iron

Abstract

The present invention provides a method for operating a reduction furnace, with which operation stability is greatly improved. The ratio H2 / CO of the H2 amount to the CO amount of a reducing gas to be blown into the reduction furnace is controlled in accordance with the average particle diameter Dp of iron oxide.

Description

Method for operating a reduction furnace and method for producing reduced iron

[0001] The present invention relates to a method for operating a reduction furnace and a method for producing reduced iron.

[0002] In recent years, steelworks have been strongly required to save energy against the backdrop of global environmental issues and the depletion of fossil fuels. The raw material for iron is mainly iron oxide, and a reduction process to reduce this iron oxide is essential in steelworks. The most common reduction process that is widespread worldwide is the blast furnace. In a blast furnace, coke or pulverized coal reacts with oxygen in hot air (air heated to about 1200°C) in the tuyere. This reaction produces CO and H, which become reducing gases. ２ These reducing gases are used to reduce iron ore and other materials in the furnace. Thanks to recent improvements in blast furnace operation technology, the reducing agent rate (the amount of coke and pulverized coal used per ton of molten iron produced) has been reduced to approximately 500 kg / t, which is already at its lower limit. Therefore, a further significant reduction in the reducing agent rate cannot be expected.

[0003] Meanwhile, in areas where natural gas is produced, a method of producing reduced iron using a vertical reduction furnace (hereinafter also referred to as a shaft furnace) is also commonly used. In this method, a reduction furnace is filled with iron ore agglomerates such as sintered ore or pellets as iron oxide. Then, CO and H generated from natural gas are added to the reduction furnace. ２ A reducing gas containing Fe is blown in to reduce iron oxide in accordance with the following formula, thereby producing reduced iron: ２ O ３ +3CO→2Fe+3CO ２ ... (i) Fe ２ O ３ +3H ２ → 2Fe + 3H ２ O... (ii)

[0004] An example of a process for producing reduced iron is shown in Figure 1. In the figure, reference numeral 1 denotes a reduction furnace, 1a denotes iron oxide, 1b denotes reduced iron, 3 denotes a dust removal device, 4 denotes a dehydration device, 5 denotes a natural gas supply section, 6 denotes an air supply section, and 7 denotes a reformer.

[0005] In this process of producing reduced iron, iron oxide is charged into the top of the reduction furnace and gradually lowered. High-temperature reducing gas is blown into the furnace from the center to reduce the iron oxide. Reduced iron is discharged from the bottom of the reduction furnace. Meanwhile, gases, mainly CO and CO2, are discharged from the top of the reduction furnace. ２ , H ２ , H ２ The furnace top gas containing O is discharged. After dust collection and cooling, a portion of the furnace top gas is sent to the reformer as a raw material for reformed gas. In the reformer, a reforming reaction occurs between the furnace top gas and natural gas supplied from the outside, and mainly CO and H are produced. ２ This reducing gas is then blown into the reducing furnace. The remaining part of the furnace top gas is dehydrated and then used as heating fuel in the combustion chamber of the reformer, where it is burned, for example, with oxygen in the air.

[0006] As a technology related to such a process for producing reduced iron, for example, Patent Document 1 discloses the following: "A method for producing reduced iron by reducing iron oxide, comprising: a reduced iron producing step of reducing the iron oxide by bringing the iron oxide into contact with a reducing gas while causing it to fall from a top of a reduction furnace to reduce the iron oxide to produce reduced iron, and discharging the reduced iron from the bottom of the reduction furnace; a reformed gas producing step of extracting furnace top gas from the reduction furnace, adjusting the moisture content thereof, and performing dust removal treatment thereon to produce a process gas, and supplying at least the process gas into a reformer to produce a reformed gas containing carbon monoxide and hydrogen in the reformer; a reducing gas supplying step of supplying the produced reformed gas to the reduction furnace as the reducing gas; a cooling step of introducing a cooling gas into a cooling region set in a lower part of the reduction furnace to cool the cooling region; and a reformed gas introducing step of extracting a portion of the reformed gas and introducing it into the cooling region to increase the carbon content of the reduced iron passing through the cooling region."

[0007] JP 2017-88912 A

[0008] However, in the conventional reduced iron production process such as that described in Patent Document 1, the reaction in the reduction furnace becomes unstable during operation, which can lead to a decrease in productivity or interruption of operation. Therefore, there is currently a demand for improvement in operational stability in the operation of the reduction furnace in the reduced iron production process.

[0009] The present invention has been developed in view of the above-described current situation, and aims to provide a method for operating a reducing furnace and a method for producing reduced iron that significantly improve operational stability. Note that in this disclosure, any numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower limit and upper limit, respectively.

[0010] The inventors conducted extensive research to solve the above-mentioned problems. First, the inventors investigated the causes of instability in the reaction in a reduction furnace during the reduced iron production process and obtained the following findings: (a) In the production of reduced iron, it is important to promote the reaction between iron oxide and reducing gas (hereinafter also referred to as the reduction reaction) according to the above formulas (i) and (ii). To achieve this, it is necessary to efficiently bring the iron oxide and the reducing gas into contact with each other. That is, it is necessary to maintain good gas permeability, which refers to the ease of flow of the reducing gas within the reduction furnace. For example, if a region with low gas permeability occurs within the reduction furnace, the reducing gas will have difficulty flowing through that region. This will cause the reduction reaction to stagnate and operation to become unstable. Furthermore, a large amount of oxygen will remain in the produced reduced iron. (b) The gas permeability varies depending on the particle size of the iron oxide packed into the reduction furnace (hereinafter also referred to as the iron oxide particle size). That is, the amount of voids in the packed layer of iron oxide in the reduction furnace varies depending on the particle size of the iron oxide. The voids in the packed layer of iron oxide in the reduction furnace serve as channels for the reducing gas. Therefore, the air permeability varies depending on the particle size of the iron oxide. This change in particle size of the iron oxide (for example, fluctuation in particle size of the iron oxide due to change in the brand or lot of iron ore used) may cause instability in the reduction reaction in a reducing furnace during operation in the process of producing reduced iron (hereinafter also referred to as instability in the operation of the reducing furnace).

[0011] Based on the above findings, the inventors considered that changing the flowability of the reducing gas itself in accordance with changes in the particle size of iron oxide might be effective in preventing the operation of the reducing furnace from becoming unstable, and conducted further experiments and studies. As a result, they obtained the following findings: (c) The flowability of the reducing gas itself can be adjusted, for example, by changing the temperature of the reducing gas injected into the reducing furnace (hereinafter also referred to as "injected reducing gas") (hereinafter also referred to as "temperature control of the injected reducing gas"). However, in order to sufficiently adjust the flowability of the reducing gas itself, it may be necessary to significantly change the temperature of the injected reducing gas. Therefore, temperature control of the injected reducing gas may result in a temperature range outside the range suitable for the reduction reaction, which may instead lead to unstable operation of the reducing furnace or problems with the durability of the equipment.

[0012] Therefore, the inventors have investigated a method for changing the flowability of the reducing gas itself other than by controlling the temperature of the reducing gas being injected, and have obtained the following findings: (d) The flowability of the reducing gas itself is affected by the ratio of the amount of H to the amount of CO in the reducing gas being injected. ２ Amount ratio H ２ / CO (hereinafter, H of the blown reducing gas) ２ / CO) (hereinafter, H ２ The H 2 O 3 of the blown reducing gas mentioned here can be adjusted by the H 2 O 3 control. ２ / CO is the volume ratio under standard conditions (also referred to as the flow rate ratio under standard conditions). ２ In the H / CO control, the rate at which the reduction reactions according to the above formulas (i) and (ii) occur can be changed, and the ease of flow of the reducing gas itself can be adjusted without causing instability in the operation of the reducing furnace. ２ Controlling the amount of CO is extremely advantageous over controlling the temperature of the blown reducing gas.

[0013] Based on the above findings, the inventors further conducted research and found the following: (f) The H content of the blown reducing gas is adjusted depending on the average particle diameter Dp of the iron oxide charged into the reducing furnace. ２By controlling the ratio of α(H 2 O 3 ) to α(H 2 O 3 ), preferably by controlling the ratio of α(H 2 O 3 ) to α(H 2 O 3 ), it becomes possible to produce reduced iron with high operational stability, regardless of changes in the particle size of iron oxide. ２ / CO) β ≦8.0 (1) The present invention was completed based on the above findings and further investigations.

[0014] That is, the gist and configuration of the present invention are as follows.

[0015] 1. A method for operating a reducing furnace, comprising: a filling step of filling a reducing furnace with iron oxide; an injection step of injecting a reducing gas into the reducing furnace; and a reduction step of reducing the iron oxide with the reducing gas in the reducing furnace to obtain reduced iron, wherein the ratio of H to CO in the reducing gas injected into the reducing furnace is adjusted according to the average particle diameter Dp of the iron oxide filled into the reducing furnace. ２ Amount ratio H ２ A method for operating a reduction furnace to control CO.

[0016] 2. The ratio of H to CO in the reducing gas injected into the reducing furnace is adjusted according to the average particle diameter Dp of the iron oxide charged into the reducing furnace so as to satisfy the following formula (1): ２ Amount ratio H ２ 4.0≦α(H ２ / CO) β ≦8.0 (1) In the formula, α=0.7155Dp+0.2833 β=0.0037Dp−0.3957.

[0017] 3. A method for producing reduced iron, comprising producing reduced iron by the method for operating a reduction furnace according to 1 or 2 above.

[0018] According to the present invention, it is possible to produce reduced iron under highly stable operation. Furthermore, according to the present invention, it is possible to produce reduced iron under highly stable operation regardless of the particle size of the iron oxide used as a raw material, which is extremely advantageous from an industrial perspective.

[0019] FIG. 1 is a diagram illustrating an example of a process for producing reduced iron.

[0020] A method for operating a reducing furnace according to one embodiment of the present invention will now be described.

[0021] A method for operating a reducing furnace according to one embodiment of the present invention includes: a filling step of filling the reducing furnace with iron oxide; an injection step of injecting a reducing gas into the reducing furnace; and a reduction step of reducing the iron oxide with the reducing gas in the reducing furnace to obtain reduced iron. Note that the filling step, injection step, and reduction step may be performed in accordance with conventional methods, for example, in the same manner as in the above-described conventional reduced iron production process. Therefore, a description thereof will be omitted here.

[0022] In the method for operating a reducing furnace according to one embodiment of the present invention, the H content of the blown reducing gas is adjusted according to the average particle diameter Dp of the iron oxide charged into the reducing furnace. ２ It is extremely important to control CO.

[0023] As described above, in the process of producing reduced iron, the change in particle size of iron oxide may cause the operation of the reducing furnace to become unstable. In order to prevent the operation of the reducing furnace from becoming unstable due to the change in particle size of iron oxide, the flowability of the reducing gas itself is changed according to the change in particle size of iron oxide. More specifically, the H ２ It is important to control CO.

[0024] In particular, the H content of the blown reducing gas is adjusted to satisfy the following formula (1) according to the average particle diameter Dp of the iron oxide charged into the reducing furnace. ２ It is preferable to control the ratio of α(H 2 O 3 ) to α(H 2 O 3 ). This makes it possible to produce reduced iron with high operational stability, regardless of the change in particle size of iron oxide. ２ / CO) β ≦8.0 (1) In the formula, α=0.7155Dp+0.2833 β=0.0037Dp−0.3957.

[0025] Here, the average particle size Dp of the iron oxide is measured, for example, as follows. Before the iron oxide is charged into a reduction furnace, for example, the iron oxide is sampled on a transfer line for the iron oxide to be charged into the reduction furnace. The sampled iron oxide is then sieved through sieves with 1 mm pitch ranging from 1 mm to 25 mm in descending order of mesh size, and the product of the mass of the iron oxide remaining on each sieve and the sieve mesh size is calculated. The sum of the calculated products is then divided by the total mass of the iron oxide sieved to calculate the average particle size Dp of the iron oxide. That is, the average particle size Dp of the iron oxide can be expressed by the following formula: Dp = (d ２５ ×25+d ２４ ×24+...+d １ × 1) / M where, dn: mass (kg) of iron oxide remaining on a sieve with nmm sieve openings, M: total mass (kg) of iron oxide sieved, and n: sieve opening size, an integer from 1 to 25.

[0026] As mentioned above, the iron oxide used is, for example, agglomerated iron ore such as sinter ore or pellets (hereinafter also referred to as agglomerated ore). Agglomerated ore may contain components other than iron oxide, and the average particle size of iron oxide referred to here means the particle size of the particles themselves, such as agglomerated ore, which also contains components other than iron oxide. The amount of iron oxide sampled is preferably, for example, 5 to 10 kg. The time interval for measuring the average particle size Dp of the iron oxide (hereinafter also referred to as the measurement interval for Dp) is preferably 8 to 12 hours. The measurement results of the average particle size Dp of the iron oxide are used to calculate the H ２ From the viewpoint of timely reflection in the control of CO, the measurement interval of Dp is more preferably 10 hours or less. The particle size of the iron oxide is generally about 5 to 15 mm.

[0027] In addition, the H of the blown reducing gas ２ The control of CO / CO can be carried out by, for example, supplying hydrogen gas from the outside, changing the amount of furnace top gas used in the reforming reaction, or controlling the amount of gas (mainly CO and H) generated by the reforming reaction of the furnace top gas and natural gas. ２ This can be achieved by temporarily storing the gas (including

[0028] The gas composition of the blown reducing gas is, for example, CO + H２ : 95 to 100% by volume, balance: 0 to 5% by volume, and within this range, H ２ It is preferable to control the CO.

[0029] The composition of the furnace top gas discharged from the reduction furnace is CO: 11 to 14% by volume, CO ２ : 9 to 11 volume%, H ２ : 54 to 58% by volume, H ２ O: 19 to 23% by volume, balance: 0 to 1% by volume can be exemplified.

[0030] The conditions other than those mentioned above are not particularly limited and may be in accordance with conventional methods. For example, the flow rate of the blown reducing gas is 1500 to 2000 Nm ３ / t is preferred, where Nm ３ / t is the flow rate (standard state conversion) per ton of reduced iron (DRI) produced. The temperature of the reducing gas injected is preferably 850 to 1050° C. The pressure of the reducing gas injected is preferably 200 to 800 kPA.

[0031] The method for operating a reduction furnace according to one embodiment of the present invention is particularly directed to a method using a shaft furnace as a direct reduction ironmaking process. Shaft furnaces have the advantages of high production efficiency, availability, and operational stability. Examples of shaft furnace types include Midrex (registered trademark) and HyL (registered trademark).

[0032] In addition, a method for producing reduced iron according to one embodiment of the present invention produces reduced iron by the above-described method for operating a reduction furnace. Note that conditions other than those described above are not particularly limited and may be those according to conventional methods.

[0033] Examples are described below. (Example 1) Reduced iron was produced under the following conditions using the reduced iron production process shown in Figure 1. Note that these conditions are for steady operation. Note that here, the iron oxide was charged into the reduction furnace while sequentially changing the brand of iron ore to be used as iron oxide. Flow rate of blown reducing gas: 2000 Nm ３ / t Temperature of blown reducing gas: 850 ° C. Pressure of blown reducing gas: 200 kPa Initial gas composition (volume ratio) of blown reducing gas: H２ : CO : balance = 55 : 40 : 5 Operation period: 30 days Reduced iron production rate: 150 t / h

[0034] In this case, in the example of the present invention, the average particle diameter Dp of the iron oxide charged into the reduction furnace was measured every 8 hours. Then, the H of the blown reducing gas was adjusted according to the measured average particle diameter Dp of the iron oxide. ２ Reduced iron was produced while controlling the H / CO ratio. The average particle size Dp of the measured iron oxide was in the range of 9 to 15 mm. The amount of iron oxide sampled per run was 10 kg. On the other hand, in the comparative example, the H ２ The reduced iron was produced without controlling the amount of CO / CO and with the initial gas composition of the blown reducing gas unchanged.

[0035] As a result, in the inventive example, stable operation was possible without interruption throughout the entire operation period of 30 days, whereas in the comparative example, the reaction in the reducing furnace became unstable during the operation period, and operation was forced to be interrupted.

[0036] (Example 2) Reduced iron was produced by the reduced iron production process shown in Fig. 1 under the same steady-state operation conditions as in Example 1. In this case, the average particle size Dp of the iron oxide charged into the reduction furnace was measured in the same manner as in Example 1. In addition, under the conditions shown in Table 1, the H ２ Reduced iron was produced while controlling the concentration of CO.

[0037] The operational stability was evaluated based on the following criteria, taking into account the amount of reduced iron produced during the entire operation period. The evaluation results are also shown in Table 1. 1 (pass, particularly excellent): No interruption to operation, and an amount of reduced iron produced of 99,000 tons or more 2 (pass, excellent): No interruption to operation, and an amount of reduced iron produced of 80,000 tons or more but less than 99,000 tons 3 (fail): Operation interruption

[0038]

[0039] In both No. 1 and No. 2, stable operation was achieved without interruption throughout the entire 30-day operation period. Furthermore, No. 1 exhibited particularly excellent operational stability.

[0040] The flow rate, temperature and pressure of the blown reducing gas during steady operation are set to 1500 to 2000 Nm ３ The same results as above were obtained when reduced iron was produced under various conditions within the ranges of 1 / t, 850 to 1050°C, and 200 to 800 kPA.

[0041] REFERENCE SIGNS LIST 1 reduction furnace 1a iron oxide 1b reduced iron 3 dust removal device 4 dehydration device 5 natural gas supply section 6 air supply section 7 reformer

Claims

1. A method for operating a reduction furnace, comprising: a charging step of charging iron oxide into the reduction furnace; an injecting step of injecting a reducing gas into the reduction furnace; and a reducing step of reducing the iron oxide with the reducing gas in the reduction furnace to obtain reduced iron, the method comprising: determining a ratio of H to CO in the reducing gas injected into the reduction furnace according to an average particle diameter Dp of the iron oxide charged into the reduction furnace. ２ Quantity ratio H ２ A method for operating a reduction furnace that controls CO.

2. The ratio of H to CO in the reducing gas injected into the reducing furnace is adjusted according to the average particle diameter Dp of the iron oxide charged into the reducing furnace so as to satisfy the following formula (1): ２ Quantity ratio H ２ The method for operating a reduction furnace according to claim 1, wherein the ratio of α(H ２ / CO) β ≦8.0 (1) In the formula, α=0.7155Dp+0.2833 β=0.0037Dp-0.3957.

3. A method for producing reduced iron, comprising the steps of: producing reduced iron by the method for operating a reduction furnace according to claim 1 or 2.

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