Operation method of reduction furnace and method for producing reduced iron

Abstract

Provide an operation method for a reduction furnace that significantly improves operation stability. Control the ratio H2 / CO of the amount of H2 to the amount of CO of the reducing gas blown into the reduction furnace according to the average particle diameter Dp of iron oxide.

Description

Technical Field

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

Background Art

[0002] In recent years, in steelworks, against the backdrop of global environmental problems and fossil fuel depletion problems, there has been a strong demand for energy conservation. The raw material of iron is mainly iron oxide, and in a steelworks, a reduction process for reducing this iron oxide is essential. The most common reduction process worldwide is the blast furnace. In a blast furnace, coke and pulverized coal react with oxygen in hot air (air heated to about 1200°C) at the tuyere. By this reaction, CO and H2, which become reducing gases, are generated, and the iron ore in the furnace is reduced by these reducing gases. With the improvement of blast furnace operating technology in recent years, the reductant ratio (the amount of coke and pulverized coal used per ton of hot metal produced) has been reduced to about 500 kg / t, and the reductant ratio has already reached almost the lower limit. Therefore, no further significant reduction in the reductant ratio can be expected.

[0003] On the other hand, in regions where natural gas is produced, a method of producing reduced iron by a vertical reduction furnace (hereinafter also referred to as a shaft furnace) is also often used. In this method, the reduction furnace is filled with agglomerated iron ore such as sintered ore and pellets as iron oxide. Then, a reducing gas containing CO and H2 generated from natural gas is blown into the reduction furnace to reduce the iron oxide according to the following equations to produce reduced iron. Fe2O3 + 3CO → 2Fe + 3CO2 ···(i) Fe2O3 + 3H2 → 2Fe + 3H2O ···(ii)

[0004] Fig. 1 shows an example of a production process of reduced iron. In the figure, reference numeral 1 is a reduction furnace, 1a is iron oxide, 1b is reduced iron, 3 is a dust collector, 4 is a dehydration device, 5 is a natural gas supply unit, 6 is an air supply unit, and 7 is a reformer.

[0005] In this process for producing reduced iron, iron oxide is charged from the upper part of the reduction furnace and gradually lowered. Then, high-temperature reducing gas is blown in from the middle part of the reduction furnace to reduce the iron oxide. Reduced iron is discharged from the lower part of the reduction furnace. On the other hand, top gas mainly containing CO, CO2, H2, and H2O is discharged from the upper part of the reduction furnace. After dust collection and cooling, part of the top gas is fed to a reforming device as a raw material for reformed gas. In the reforming device, a reforming reaction occurs between the top gas and natural gas supplied from outside, and reformed gas mainly containing CO and H2 is generated. And this reformed gas is blown into the reduction furnace. Also, the remaining part of the top gas is used as heating fuel in the combustion chamber of the reforming device after dehydration, and is burned, for example, by oxygen in the air.

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

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the conventional manufacturing process of reduced iron as in Patent Document 1, during operation, the reaction in the reduction furnace may become unstable, leading to a decrease in productivity and an interruption in operation. Therefore, in the operation of the reduction furnace related to the manufacturing process of reduced iron, improvement of operation stability is currently required.

[0009] The present invention has been developed in view of the above situation, and an object thereof is to provide an operation method of a reduction furnace and a manufacturing method of reduced iron with significantly improved operation stability. In the present disclosure, any numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, respectively.

Means for Solving the Problems

[0010] The inventors have conducted repeated studies to solve the above problems. First, the inventors investigated the cause of the instability of the reaction in the reduction furnace in the manufacturing process of reduced iron 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 according to the above formulas (i) and (ii) (hereinafter also referred to as the reduction reaction). For this purpose, it is necessary to efficiently bring iron oxide and reducing gas into contact. That is, it is necessary to maintain good air permeability, which means the ease of flow of the reducing gas in the reduction furnace. For example, when a region with low air permeability occurs in the reduction furnace, the reducing gas becomes difficult to flow in that region. As a result, the reduction reaction stagnates and the operation becomes unstable. In addition, a large amount of oxygen remains in the produced reduced iron. (b) The air permeability varies depending on the particle size of the iron oxide filled in the reduction furnace (hereinafter also referred to as the particle size of the iron oxide). That is, depending on the particle size of the iron oxide, the amount of voids in the packed bed of iron oxide in the reduction furnace changes. And the voids in the packed bed of iron oxide in the reduction furnace serve as the flow path for the reducing gas. Therefore, the air permeability will vary depending on the particle size of the iron oxide. And due to this change in the particle size of the iron oxide (for example, the variation in the particle size of the iron oxide due to the brand or lot change of the iron ore used), in the process of producing reduced iron, it may cause the destabilization of the reduction reaction in the reduction furnace during operation (hereinafter also referred to as the operational instability of the reduction furnace).

[0011] Based on the above findings, the inventors considered that in order to prevent the operational instability of the reduction furnace, it might be effective to change the ease of flow of the reducing gas itself according to the change in the particle size of the iron oxide, and further conducted various experiments and studies. As a result, the following findings were obtained. (c) The ease of flow of the reducing gas itself can be adjusted, for example, by changing the temperature of the reducing gas blown into the reduction furnace (hereinafter also referred to as the blown-in reducing gas) (hereinafter also referred to as the temperature control of the blown-in reducing gas). However, in order to sufficiently adjust the ease of flow of the reducing gas itself, a significant change in the temperature of the blown-in reducing gas may be required. Therefore, in the temperature control of the blown-in reducing gas, it may deviate from the temperature range suitable for the reduction reaction, and instead cause the operational instability of the reduction furnace or problems in terms of the durability of the equipment.

[0012] Therefore, the inventors examined a method of changing the ease of flow of the reducing gas itself by a method other than the temperature control of the blown-in reducing gas. As a result, the following findings were obtained. (d) The ease of flow of the reducing gas itself can be adjusted by changing the ratio of the amount of H2 to the amount of CO in the blown-in reducing gas, H2 / CO (hereinafter also referred to as the H2 / CO of the blown-in reducing gas) (hereinafter also referred to as the H2 / CO control of the blown-in reducing gas). Here, the H2 / CO of the blown-in reducing gas referred to here is the volume ratio under standard conditions (which can also be said to be the flow rate ratio under standard conditions). (e) Also, in the control of the H2 / CO of the blown reduction gas, only the ratio of the reduction reaction occurring according to the above formulas (i) and (ii) changes, and the flowability of the reduction gas itself can be adjusted without causing operational instability in the reduction furnace. Therefore, the control of the H2 / CO of the blown reduction gas is extremely advantageous compared to the temperature control of the blown reduction gas.

[0013] And, based on the above findings, the inventors further conducted studies and obtained the following findings. (f) By controlling the H2 / CO of the blown reduction gas according to the average particle diameter Dp of the iron oxide filled in the reduction furnace, preferably by controlling to satisfy the following formula (1), it is possible to produce reduced iron with high operational stability regardless of the change in the particle diameter of the iron oxide. 4.0 ≦ α(H2 / CO) β ≦ 8.0 ···(1) The present invention was completed by further studies based on the above findings.

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

[0015] 1. A charging step of charging iron oxide into a reduction furnace, A blowing step of blowing a reduction gas into the reduction furnace, A reduction step of reducing the iron oxide with the reduction gas in the reduction furnace to obtain reduced iron, An operating method of a reduction furnace having: An operating method of a reduction furnace, wherein the ratio H2 / CO of the amount of H2 to the amount of CO of the reduction gas blown into the reduction furnace is controlled according to the average particle diameter Dp of the iron oxide filled into the reduction furnace.

[0016] 2. The operating method of the reduction furnace according to 1 above, wherein the ratio H2 / CO of the amount of H2 to the amount of CO of the reduction gas blown into the reduction furnace is controlled according to the average particle diameter Dp of the iron oxide filled into the reduction furnace so as to satisfy the following formula (1). 4.0 ≦ α(H2 / CO) β ≦ 8.0 ···(1) In the formula, α = 0.7155Dp + 0.2833 β = 0.0037Dp - 0.3957 It is as follows.

[0017] 3. A method for producing reduced iron by the operation method of the reduction furnace according to the above 1 or 2.

Effect of the Invention

[0018] According to the present invention, it becomes possible to produce reduced iron under high operation stability. Further, according to the present invention, it becomes possible to produce reduced iron under high operation stability regardless of the particle size of the iron oxide as a raw material, which is extremely advantageous industrially.

Brief Description of the Drawings

[0019]

Figure 1

Modes for Carrying Out the Invention

[0020] Hereinafter, an operation method of a reduction furnace according to an embodiment of the present invention will be described.

[0021] The operation method of the reduction furnace according to an embodiment of the present invention is A charging step of charging iron oxide into the reduction furnace, and An injection step of injecting reducing gas into the reduction furnace, and A reduction step of reducing the iron oxide with the reducing gas in the reduction furnace to obtain reduced iron. It has. Note that the charging step, the injection step, and the reduction step may be performed according to a conventional method, for example, in the same manner as the above-described conventional manufacturing process of reduced iron. Therefore, the description is omitted here.

[0022] And in the operation method of the reduction furnace according to an embodiment of the present invention, it is extremely important to control H2 / CO of the injected reducing gas according to the average particle size Dp of the iron oxide charged into the reduction furnace.

[0023] As described above, in the process of manufacturing reduced iron, changes in the particle size of iron oxide may cause operational instability in the reduction furnace. To prevent such operational instability in the reduction furnace caused by changes in the particle size of iron oxide, it is important to change the ease of flow of the reducing gas itself according to the change in the particle size of iron oxide. More specifically, it is important to control the H2 / CO of the blown reducing gas according to the average particle size Dp of the iron oxide filled in the reduction furnace.

[0024] In particular, it is preferable to control the H2 / CO of the blown reducing gas so as to satisfy the following formula (1) according to the average particle size Dp of the iron oxide filled in the reduction furnace. This makes it possible to manufacture reduced iron under high operational stability regardless of changes in the particle size of iron oxide. 4.0 ≤ α(H2 / CO) β ≤ 8.0 ···(1) In the formula, α = 0.7155Dp + 0.2833 β = 0.0037Dp - 0.3957 Here,

[0025] Here, the average particle size Dp of iron oxide is measured as follows, for example. Before filling the iron oxide into the reduction furnace, for example, in the transfer line of the iron oxide for filling the reduction furnace, the iron oxide is sampled. Then, the sampled iron oxide is sieved through sieves with a mesh pitch of 1 mm 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 mesh size is obtained. Then, the average particle size Dp of the iron oxide is obtained by dividing the sum of the obtained products by the total mass of the iron oxide sieved. That is, the average particle size Dp of iron oxide can be expressed as follows. Dp = (d 25 × 25 + d 24 × 24 + ··· + d1 × 1) / M In the formula, dn: the mass (kg) of the iron oxide remaining on the sieve with an nmm mesh M: the total mass (kg) of the iron oxide sieved n: the mesh size, an integer from 1 to 25 Here,

[0026] Incidentally, as described above, as the iron oxide, for example, agglomerated iron ores such as sintered ores and pellets (hereinafter also referred to as agglomerated ores, etc.) are used. Although agglomerated ores and the like may contain components other than iron oxide, the average particle size of the iron oxide here means the particle size of the particles of agglomerated ores and the like including components other than iron oxide. Further, the sampling amount of the iron oxide 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 of Dp) is preferably 8 to 12 hours. Further, from the viewpoint of timely reflecting the measurement result of the average particle size Dp of the iron oxide in the control of H2 / CO of the blown reduction gas, 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] Incidentally, the control of H2 / CO of the blown reduction gas can be carried out, for example, by supplying hydrogen gas from the outside, changing the amount of top gas used in the reforming reaction, temporarily storing the gas generated by the reforming reaction of the top gas and natural gas (mainly a gas containing CO and H2) or supplying it to another load.

[0028] Incidentally, the gas composition of the blown reduction gas is, for example, CO + H2: 95 to 100% by volume, and the balance: 0 to 5% by volume. In this range, it is preferable to control the H2 / CO of the blown reduction gas.

[0029] Further, examples of the composition of the top gas discharged from the reduction furnace include CO: 11 to 14% by volume, CO2: 9 to 11% by volume, H2: 54 to 58% by volume, H2O: 19 to 23% by volume, and the balance: 0 to 1% by volume.

[0030] The conditions other than the above are not particularly limited, and may be in accordance with conventional methods. For example, the flow rate of the blown reduction gas is preferably 1500 to 2000 Nm 3 / t. Here, Nm 3 / t is the flow rate (in terms of standard state conversion) per 1 t of production of direct reduced iron (DRI). The temperature of the blown reduction gas is preferably 850 to 1050°C. The pressure of the blown reduction gas is preferably 200 to 800 kPA.

[0031] In the operation method of the reduction furnace according to an embodiment of the present invention, in particular, it is directed to a method using a shaft furnace as a direct reduction ironmaking method. The shaft furnace has the advantages of high production efficiency, operating rate, and operation stability. Examples of the shaft furnace method include, for example, Midrex (registered trademark) and HyL (registered trademark).

[0032] Further, the method for producing reduced iron according to an embodiment of the present invention is to produce reduced iron by the above operation method of the reduction furnace. Regarding conditions other than the above, there are no particular limitations, and ordinary methods may be followed.

Examples

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

[0034] At this time, in the invention example, the average particle size Dp of the iron oxide charged into the reduction furnace was measured every 8 hours. Then, while controlling the H2 / CO of the blown reduction gas according to the measured average particle size Dp of the iron oxide, reduced iron was produced. Note that the measured average particle size Dp of the iron oxide was in the range of 9 to 15 mm. Also, the sampling amount of iron oxide per time was 10 kg. On the other hand, in the comparative example, reduced iron was produced with the initial gas composition of the blown reduction gas without controlling the H2 / CO of the blown reduction gas.

[0035] As a result, in the inventive example, stable operation was possible without interruption over the entire 30-day operation period. On the other hand, in the comparative example, the reaction in the reduction furnace became unstable during the operation period, and the operation had to be interrupted unavoidably.

[0036] (Example 2) Using the reduction iron manufacturing process shown in Fig. 1, reduction iron was manufactured under the same steady operation conditions as in Example 1. At this time, the average particle diameter Dp of the iron oxide filled into the reduction furnace was measured in the same manner as in Example 1. Also, while controlling H2 / CO of the blown reduction gas according to the measured average particle diameter Dp of the iron oxide under the conditions shown in Table 1, reduction iron was manufactured.

[0037] Then, taking into account the production amount of reduction iron during the entire operation period, the operation stability was evaluated according to the following criteria. The evaluation results are also shown in Table 1. 1 (Pass, particularly excellent): No interruption of operation, and the production amount of reduction iron is 99,000 t or more 2 (Pass, excellent): No interruption of operation, and the production amount of reduction iron is 80,000 t or more and less than 99,000 t 3 (Fail): Operation interruption

[0038]

Table 1

[0039] In both No. 1 and 2, stable operation was possible without interruption over the entire 30-day operation period. Also, in No. 1, particularly excellent operation stability was obtained.

[0040] Also, when reduction iron was manufactured under conditions where the flow rate, temperature, and pressure of the blown reduction gas during steady operation were variously changed in the ranges of 1500 - 2000 Nm 3 / t, 850 - 1050 °C, and 200 - 800 kPA, respectively, the same results as above were obtained.

Explanation of symbols

[0041] 1 Reduction furnace 1a Iron oxide 1b Reduced iron 3 Dust removal device 4 Dewatering device 5 Natural gas supply section 6 Air supply section 7 Reforming device

Claims

1. a charging step of charging the iron oxide into a reduction furnace; a blowing step of blowing a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with the reducing gas in the reduction furnace to obtain reduced iron; A method for operating a reduction furnace, comprising: The ratio of H to CO in the reducing gas injected into the reducing furnace is determined according to the average particle diameter Dp of the iron oxide charged into the reducing 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 determined 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 , further comprising controlling the amount of CO in the reduction furnace. 4.0≦α(H ２ / CO) β ≦8.0 ・・・(1) During the ceremony, α=0.7155Dp+0.2833 β=0.0037Dp-0.3957 It is.

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

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