JP3700458B2 - Low Si hot metal manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing low Si hot metal. Specifically, scrap, reduced iron, or a high basic substance is preferentially charged to the furnace wall side of the blast furnace, and the air permeability and liquid permeability of the furnace core part. Is a technique for stably producing a low Si hot metal without hindering the above.
[0002]
[Prior art]
FIG. 5 schematically shows the state in the blast furnace. In the blast furnace, raw materials such as iron ore (coal ore, sintered ore, pellets, etc.) and secondary raw material limestone, etc., and coke 2 are charged alternately from the top of the furnace, A layered packed layer of coke is formed. These ores 1 or coke 2 charged alternately are called one charge ore or one charge coke, respectively. Each charge ore may be charged into the furnace in one charge, or one charge ore may be divided into two or more charges. Each of the divided ore charges is called a batch. Similarly, one charge of ore or one charge of coke may be divided and charged in batches. By blowing hot air or oxygen-enriched air from the tuyere 10 installed below the furnace into the packed bed formed in the furnace, the coke is burned to generate high-temperature reducing gas, During the ascending of the packed bed, the ore is reduced and the molten pig iron and slag are dripped onto the hearth 8, and this is discharged out of the furnace through the spout 11 opened in the hearth 8. As a result, molten pig iron is produced.
[0003]
In order to operate this blast furnace stably, it is necessary to properly control the flow of high-temperature gas in the furnace, to optimize the temperature distribution of the packed bed in the furnace, and to stably raise the temperature, reduce, and melt. is there. In conventional research, if the gas flow at the center of the furnace is increased compared to the furnace wall, the raw material that forms the packed bed in the furnace falls stably, and the temperature rise, reduction, and melting are performed stably. I understand. If the gas flow increases on the furnace wall side, the gas flow tends to be uneven in the circumferential direction, and as a result, the component of the molten iron slag discharged from the outlets 11 provided in two or four in the circumferential direction. It tends to be an unstable operation that varies.
[0004]
In such an unstable operation, it is necessary to supply sufficient heat even in a location where gas permeability is relatively poor to prevent quality deterioration such as a decrease in hot metal temperature, so that the entire blast furnace is supplied into the furnace. The amount of heat must be increased. As a result, the reduction reaction of SiO ₂ proceeds in the blast furnace, causing a problem that Si in the hot metal rises. When the hot metal Si is high, it is necessary to increase the amount of flux added in the hot metal preliminary treatment or smelting treatment as a subsequent process, which is disadvantageous in terms of cost. Therefore, in order to stabilize the quality of the hot metal, it is necessary to stabilize the operation by stabilizing the gas flow distribution in the furnace.
[0005]
The most basic means of performing an operation that increases the gas flow in the furnace center is to control the particle size of the raw material charged into the furnace, to charge the raw material into the furnace central part, By charging fine raw materials into the wall, the gas ventilation resistance in the furnace center is made smaller than that in the furnace wall. That is, it is an important operating means for stable operation to make the particle size distribution of the raw material forming the packed bed in the furnace appropriate when the raw material is charged into the furnace.
[0006]
As one of means for charging the raw material, a bellless charging device is known in which charging is performed via a charging chute 3 from a hopper (not shown) installed at the top of the furnace. This is to spread the raw material into the furnace by changing the tilt angle at each swirl number while turning the charging chute 3 by a predetermined swirl number and charging it into the furnace in one raw material charging. In addition, the raw material is disposed at an arbitrary position of the packed bed by charging while sequentially changing the angle (tilt angle θ) formed with the vertically lower side of the charging chute 3. This change in tilt angle can be changed arbitrarily in principle, but since it is a facility with a scale in which dozens of tons of raw material is charged during a dozen turns of the charging chute, Changing the tilt angle suddenly to a larger or smaller value on the way is not only a heavy load in terms of equipment, but also the landing point in the furnace of the raw material charged during the change of the tilt angle There is a problem that is difficult to control. For this reason, the tilt angle is usually changed in one direction such as gradually decreasing or increasing with time.
[0007]
In order to achieve an appropriate raw material particle size distribution in the blast furnace with the bell-less charging device, it is preferable that the raw material discharged from the hopper at the top of the furnace can change in particle size over time. In general, when powder particles are introduced into the hopper from above, a mountain is formed with the top of the raw material landing point, but there is a small particle size near the top of the mountain. There is a coarser particle at the base of the part. Therefore, when discharging from the lower discharge port after that, the ridges having the smaller particle diameter are discharged, and finally the hopper wall having the larger particle diameter is discharged. Conventionally, the charging chute is moved in a so-called “ forward tilting direction” in which the turning chute is turned while gradually changing the tilting angle of the charging chute from a large angle to a small angle. At the same time, the shape of the material deposition surface in the furnace is made to be a mortar shape that is high at the furnace wall and low at the center of the furnace, so that after the material lands in the furnace, Expected to roll to the furnace center. Moreover, in this mortar-shaped raw material deposition surface shape, since the thickness of the packed layer in the furnace center is thinner than that in the furnace wall, the effect of increasing the gas flow in the furnace center can also be expected.
[0008]
By the way, in the blast furnace 4, a method of preferentially charging and operating a high basic substance on the furnace wall side of a technique for producing low Si hot metal (Si concentration in the hot metal is 0.2 wt% or less). There is. For example, JP-A-8-311511 discloses that the basicity distribution of the blast furnace charge is high in a region (furnace wall portion) larger than the dimensionless radius of the furnace 0.7 ± 0.1, and low in the center. In addition, the amount of coke charged into the central portion is increased to maintain the core core air permeability and liquid permeability at a high level, thereby stably producing low Si hot metal. In this technique, SiO gas generated by the following reaction is transferred into the hot metal in the high temperature region in front of the tuyere 13 shown in FIG. 5, but the basicity of the melt passing through the high temperature region is increased, and the activity of SiO ₂ is increased. This is based on suppressing the generation of SiO gas.
[0009]
SiO ₂ + C (in coke) → SiO (gas) + CO (gas)
SiO + C (in hot metal) → Si (in hot metal) + CO (gas)
Japanese Patent Laid-Open No. 63-137110 proposes a technique for producing low Si hot metal by adding metallic iron such as iron scrap and reduced iron to a blast furnace charge and adjusting the amount of the metallic iron. . In this technique, when the heat flow ratio, which is the ratio of the heat capacity of solid particles and gas, is increased in the blast furnace 4, the fusion zone 6 shown in FIG. This is based on the reduced opportunity for contact with SiO gas.
[0010]
Using the techniques described in Japanese Patent Laid-Open Nos. 8-311511 and 63-137110, the core of the furnace (referred to as dead man 9 where coke is deposited in a cone shape, see FIG. 5). Inactivation (a state of poor ventilation and liquid flow) can be prevented to some extent, and a low Si hot metal can be produced. However, it has been considered that there is still room for improvement in order to reliably produce low-Si hot metal because of the unstable operation.
[0011]
[Problems to be solved by the invention]
In view of such circumstances, the present invention can reliably reduce the Si concentration in hot metal to 0.2% by weight or less even when a large amount of highly basic material, iron scrap, reduced iron, etc. is used in a blast furnace, and stable operation. It aims at providing the manufacturing method of the low Si hot metal which can do.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the inventor earnestly reconsidered the conventional technique. As a result, it has been found that in the conventional method of charging while changing the charging chute in the forward tilt direction, the charged material may not surely enter the predetermined region. That is, as described above, in the method in which the charging chute is changed in the forward tilt direction and the raw material deposition surface in the furnace is formed in a mortar shape, the relatively coarse raw material moves to the furnace center after the raw material has landed in the furnace. Due to the rolling effect, the particle size of the raw material in the furnace center was made relatively large, but at the same time, there was a possibility that a highly basic substance charged into the furnace wall would flow into the furnace center. In other words, in the conventional charging method, the charge filling surface is lowered toward the center of the furnace (usually, the repose angle has a gradient of about 30 °). Therefore, in the technique described in JP-A-8-311511, a part of the high basicity substance (iron ore having a high CaO content, limestone, dolomite, etc.) charged to the periphery may roll on the inclined surface, or It flows down and fills the central part, and the highly basic substance is not deposited around the furnace, and the air permeability and liquid permeability of the furnace core are not improved.
[0013]
On the other hand, in the technique described in Japanese Patent Application Laid-Open No. 63-137110, the position of the fusion zone 6 is lowered on average over the entire radial direction of the furnace. It was not shortened and it was thought that Si absorption to the hot metal in the region was not suppressed. Therefore, the inventor further studied the countermeasures for these problems and embodied the results in the present invention.
[0014]
That is, the present invention is a low blast furnace in which at least the ore out of the raw materials composed of ore and coke is charged by tilting from the furnace center to the furnace wall while turning the charging chute provided at the top of the furnace. In the method for producing Si hot metal, one charged portion of the ore is divided into two or more batches, and one divided batch is made into a batch mixed with a high CaO-containing material, and the batch is moved in the furnace radial direction. A method for producing a low Si hot metal, characterized in that it is charged into a furnace wall portion divided into two regions of a furnace center portion and a furnace wall portion. At that time, the highly basic substance is preferably limestone and / or dolomite.
[0015]
Furthermore, the present invention is a blast furnace in which at least ore is charged by tilting in the furnace wall direction from the furnace center while turning the charging chute provided at the top of the raw material consisting of ore and coke. In the method for producing low Si hot metal, one charged portion of the ore is divided into two or more batches, and all or a part of one divided batch is made of metallic iron, and the batch is moved in the furnace radial direction. A method for producing a low Si hot metal, characterized in that it is charged into a furnace wall portion divided into two regions of a furnace center portion and a furnace wall portion. In that case, it is preferable that the metallic iron is iron scrap and / or reduced iron. In addition, the central part may be a region having a dimensionless radius of 0.6 ± 0.2 from the furnace center.
[0016]
In the present invention, when alternately charging iron ore 1 (including iron ore, sintered ore, and other ironmaking ore) and coke 2 into a blast furnace 4 equipped with a bell-less charging device, Since the tilt is changed so as to go from the center of the furnace 4 to the periphery, the tilt toward the center which has conventionally occurred on the packed bed surface is eliminated. As a result, it is possible to completely prevent one part of the material charged in the peripheral part or the surface layer from entering the central part of the furnace 4. In addition, generation of SiO gas in the high temperature region before the tuyere 10 and absorption of the gas into the hot metal are surely suppressed as compared with the prior art, and a low Si hot metal can be obtained stably.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
FIG. 1 (a) schematically shows the accumulation state of ore in the furnace when the ore 1 is charged with the tilt angle changed in the conventional forward tilt direction. Here, the ore accumulation state for each turn of the charging chute 3 is shown. Since ore is charged from the furnace wall side, the ore charged on the slope of the coke 2 deposition surface flows into the furnace center along the slope. Therefore, the raw material charged at a certain number of turns accumulates over a wide range from the dropping point to the furnace center. On the other hand, as shown in FIG. 1B, when the ore 1 is charged in the reverse tilt direction as will be described later in the present invention, as shown in FIG. The coke charged by turning forms a mountain at the point of fall and accumulates in a much narrower area than when charged in the forward tilt direction. As a result, the raw material can be charged to the dropping position of the charged material with very high accuracy. In FIG. 1, the coke collectively shows the accumulation shape for one charge.
[0019]
In the present invention, this phenomenon is used to divide the ore charge into two or more batches, and the one batch is a batch mixed with a high CaO-containing material, or a batch mixed with metallic iron, By charging this batch into the furnace wall, it becomes possible to concentrate the high CaO-containing substance on the furnace wall.
[0020]
FIG. 2 shows the state of deposition in the furnace when the ore charge is divided into two batches, and one ore batch (mixed batch) 1a is mixed with a high CaO-containing material or metallic iron. After charging a normal ore batch (non-mixed batch) 1b not mixed with high CaO-containing material or metallic iron into the furnace center of the furnace, ore batch 1a mixed with high CaO-containing material or metallic iron is the furnace wall I am charging. In this way, the ore batch is divided and the high CaO material or metallic iron is charged into the ordinary ore batch 1b charged into the furnace center so that the high CaO containing material or metallic iron is not mixed, and the high CaO content is not mixed. Since the ore batch 1a charged with the ore charged with the material or metallic iron is charged in the reverse tilt direction into the furnace wall, the high CaO-containing material or metallic iron does not flow into the furnace center. Therefore, even if the amount of small coke used is increased, high CaO-containing substances are mixed into the furnace center, and the gas flow in the furnace center is not suppressed, and SiO in the high temperature region before the tuyere Generation of gas and absorption of the gas into the hot metal can be suppressed.
[0021]
In the present invention, limestone, dolomite, iron ore having a high CaO content, or the like is used as the highly basic substance to be mixed with the iron ore 1. Furthermore, in this case, it is preferable that the basicity of the entire product charged in the peripheral portion is 1.8 to 3.0. If it is less than 1.8, the effect of reducing the generation amount of SiO gas is small, and if it exceeds 3.0, the basicity of slag is too high when it becomes slag later, and it adversely affects the stable operation of the blast furnace 4. is there. When mixing iron scrap, it is preferable to adjust its size in advance to about 3 to 200 mm. If it is too large, normal filling becomes difficult, and if it is too small, the air permeability is deteriorated. As the reduced iron, it is preferable to use the iron ore 1 preliminarily reduced by another device. This is because it can be obtained at low cost by using the exhaust gas obtained in the steelworks. In addition, iron scrap distributed in the market, iron scrap generated in the steelworks, and the like can be suitably used.
[0022]
In addition, the size of the area of the center part and the peripheral part of the furnace 4 described above varies depending on the capacity of the blast furnace 4. However, the purpose of the present invention is to increase the gas flow in the furnace (centered flow orientation) to achieve stable operation, so that the dimensionless radius of the center (distance from the center / furnace port) A preferable range is 0.6 ± 0.2 in terms of (radius). If it is less than 0.4, a clear central flow distribution of gas cannot be obtained, and if it exceeds 0.8, the effect of preferentially charging a high basic substance or iron scrap into the periphery cannot be fully exhibited. This is because the Si concentration in the hot metal does not stably become 0.15% by weight or less.
[0023]
【Example】
(Example 1)
The method according to the present invention and the conventional method were applied to the operation of a 5000 m ³ class blast furnace equipped with a bell-less charging device at different periods. The amount of pig iron produced in the operation is 9000 t / d to 11000 t / d, and the operating conditions are as follows: air flow 6500 Nm ³ / min, furnace top pressure 260 kPa, coke ratio 450 kg / t, pulverized coal ratio 70 kg / t was the standard.
[0024]
Moreover, as a charging thing, it is the block blast furnace coke in which the coke 2 adjusted the average particle diameter to 50 mm, and the iron ore 1 is a sintered ore, iron ore, etc. with a particle size of about 15-25 mm. As the highly basic substance, limestone and dolomite adjusted to a particle size of 5 to 20 mm were used. The charge per charge is 35 tons for coke 2 and 110 tons for iron ore 1.
[0025]
The iron ore was divided into two batches, and the batch charged first (O1 batch) was 65 tons, and the batch charged later (O2 batch) was 45 tons. O2 batch includes limestone and dolomite, basicity in O2 batch ore (CaO wt% / SiO ₂ weight%) was adjusted to 2.0.
[0026]
First, as Comparative Example 1, both the O1 batch and the O2 batch were charged and operated while changing the charging chute from the furnace wall to the furnace center. The turning speed was appropriately changed based on 8 rpm. The O1 batch was charged so as to be deposited on almost the entire surface in the furnace radial direction. Thereafter, the O2 batch was charged so as to land at a position corresponding to a dimensionless radius of 0.5 to 1 from the furnace center axis in the furnace radial direction by reducing the tilt angle by 1 degree per turn from the initial 60 °. .
[0027]
Thereafter, the charging according to the present invention was performed, and the operation of Example 1 was performed. The amounts and components of the O1 and O2 batches were the same, and the tilting direction of the charging chute was changed from the furnace center to the furnace wall. The O1 batch was charged so as to be deposited almost over the entire surface in the furnace radial direction as in Comparative Example 1. Thereafter, increasing by 1 ° per pivot O2 batch from tilt angle 45 °, it was charged so as to land the furnace mandrel at the furnace radial direction to a position corresponding to the dimensionless radius 0.5-1 .
[0028]
During the operation period, the brewing was performed many times. As shown in FIG. 3, the Si concentration in the hot metal was lower when the present invention was applied than when the conventional method was applied. In addition, according to the present invention, there was little disruption of the slag balance at the hearth and smooth operation was achieved, whereas in the conventional method, there was a situation where the amount of blast was forced to be reduced over a long period of time. there were. The ventilation resistance F2 in FIG. 3 is an index defined by [(air blowing pressure kg / cm ² ) ² − (furnace top pressure kg / cm ² ) ² ] / (furnace gas amount Nm ³ / min) ^1.7 , By applying the present invention, the ventilation resistance is low and stable.
(Example 2)
Under the same operating conditions as in Example 1, an operation was performed in which iron scrap and reduced iron were charged into the furnace periphery. The charge is a massive blast furnace coke in which coke 2 is sized to an average particle size of 50 mm, and iron ore 1 is sintered ore and iron ore having a particle size of about 15 to 25 mm. The iron scrap was generated in iron making and had an average size of 50 mm in length, 30 mm in width and 20 mm in thickness, and reduced iron having a particle size of 10 to 25 mm was used as the reduced iron. These amounts are 0.1 ton and 0.1 ton per ton of iron ore, respectively. The amount of coke per charge is 35 tons, and the amount of ore is 120 tons including iron scrap reduced iron.
[0029]
First, as Comparative Example 2, an operation was performed in which one charge of 120 tons of ore including 100 tons of ore, 10 tons of iron scrap, and 10 tons of reduced iron was charged into the furnace in a single charge. While changing the charging chute from the furnace wall portion toward the furnace center portion, the charging chute was charged so as to be deposited almost entirely in the furnace radial direction. The turning speed was appropriately changed based on 8 rpm.
[0030]
After that, the operation according to the present invention in a form different from that of Example 1 was performed to obtain Example 2. In Example 2, the iron ore was divided into two batches, the batch charged first (O1 batch) was 60 tons, and the batch charged later (O2 batch) was 60 tons. The O2 batch was a batch containing 10 tons of iron scrap and 10 tons of reduced iron.
[0031]
In both O2 and O2 batches, the tilting direction of the charging chute was changed from the furnace center to the furnace wall. The O1 batch was charged so as to be deposited on almost the entire surface in the furnace radial direction. Thereafter, the O2 batch was charged from the tilt angle of 45 ° by 1 ° for each turn so as to land from the furnace center axis to a position corresponding to a dimensionless radius of 0.5 to 1 in the furnace radial direction.
[0032]
As shown in FIG. 4, the average Si concentration in the hot metal was 0.20% by weight when the present invention was applied, and when the conventional method was applied, as shown in FIG. It was 0.24% by weight. That is, according to the present invention, the Si concentration in the hot metal can be reduced stably and reliably. In addition, according to the present invention, there was little disruption of the slag balance at the hearth and smooth operation was achieved, whereas in the conventional method, there was a situation where the amount of blast was forced to be reduced over a long period of time. there were.
[0033]
【The invention's effect】
As described above, according to the present invention, the furnace wall portion can be reliably charged with a high CaO-containing material, metallic iron or the like, and a more stable low Si hot metal can be produced than before.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic diagram showing a packed bed deposition shape in a furnace when coke is charged into a blast furnace, where (a) shows a conventional forward tilt method and (b) shows a reverse tilt method.
FIG. 2 is a view showing a surface deposition shape of a packed bed in a furnace according to the present invention.
FIG. 3 is a diagram showing a change with time of Si concentration in hot metal obtained by the operation of the method of Example 1 and Comparative Example 1 of the present invention.
FIG. 4 is a diagram showing a change with time of Si concentration in hot metal obtained by the operation of the method of Example 2 and Comparative Example 2 of the present invention.
FIG. 5 is a diagram showing an internal state of a general blast furnace.
[Explanation of symbols]
1 Iron ore 1a Mixed batch 1b Non-mixed batch 2 Coke (Lump coke)
3 Revolving chute 4 Blast furnace (furnace)
5 Mixture (Iron ore mixed with highly basic substances)
6 Softening zone (cohesive zone)
7 Shaft part 8 hearth 9 hearth (dead man)
10 Feather 11 Depot 12 Furnace Wall 13 Blast Furnace Centerline

Claims (2)

A method for producing low Si hot metal in a blast furnace in which at least ore is tilted in the direction of the furnace wall from the center of the furnace while turning the charging chute provided at the top of the ore and coke. 1, one charge of the ore is divided into two or more batches, and one divided batch is made into a batch mixed with a high CaO-containing material, and the batch is formed in the furnace center in the furnace radial direction, A method for producing a low Si hot metal, which is charged into a furnace wall portion divided into two regions of the wall portion. A method for producing low Si hot metal in a blast furnace in which at least ore is tilted in the direction of the furnace wall from the center of the furnace while turning the charging chute provided at the top of the ore and coke. 1, one charge of the ore is divided into two or more batches, and the whole or a part of one divided batch is made of metal iron, and the batch is placed in the furnace radial direction inside the furnace in the center of the furnace, the furnace wall A method for producing a low Si hot metal, which is charged into a furnace wall portion divided into two regions.

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