JP4182660B2 - Blast furnace operation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a blast furnace operation method, and in particular, proposes a blast furnace operation method capable of performing stable operation even under a low coke ratio.
[0002]
[Prior art]
The operation of the blast furnace is performed by alternately charging raw materials such as iron ore and coke into the furnace to form a deposition layer mainly composed of an ore layer and a coke layer in the furnace, and a blower tuyere ( (Hereinafter referred to simply as “the tuyere”), high-temperature air is blown to burn the coke in the deposited layer and the pulverized coal blown from the tuyere, and the like in a high-temperature furnace containing a reducing gas such as CO gas. Gas is generated, and the ore is reduced and melted into hot metal and hot metal while it is discharged from the top of the furnace through the inside of the sedimentary layer (ore ore layer and coke layer) in the furnace. It is a series of work to discharge from.
[0003]
Conventionally, in such blast furnace operations, efforts have been made to reduce the production cost of pig iron, but in particular, the amount of coke required per 1 ton of hot metal (kg / t; hereinafter referred to as “coke ratio”) is reduced. Is known to be effective. Of course, since the amount of raw material (ore, etc.) required to produce 1t of hot metal is determined, in order to reduce the coke ratio, the amount of coke charged in the blast furnace is set to the amount of charged ore. It is necessary to make it relatively less. This means that it is necessary to increase the ratio of the ore layer thickness to the coke layer thickness (hereinafter abbreviated as “O / C”) in the charge deposit layer. .
[0004]
Usually, when changing the O / C, an operation of increasing the ore layer thickness without increasing the coke layer thickness (increasing ore charge per charge) is often performed. The reason for this is to maintain a coke layer thickness to ensure a distribution path of the in-furnace gas in the region where the ore starts to melt. However, as reported in “Materials and Processes” (vol. 9, p. 627-630), when the thickness of the ore layer in the blast furnace is increased, the reduction of the ore located above the ore layer is delayed. For this reason, there arises a problem that the temperature at which the pressure loss rises due to deformation and fusion of the raw material particles decreases.
[0005]
As described above, increasing the thickness of the ore layer in order to reduce the coke ratio tends to increase the pressure loss in the furnace, which may not be preferable. In particular, when the operation of injecting fuel such as pulverized coal from the tuyere instead of the coke at the top of the furnace, the amount of coke from the top of the furnace must be reduced. Larger (Coke ratio decrease). Therefore, when such an operation is performed, an increase in pressure loss in the ore layer inevitably occurred, which has been a big problem.
[0006]
In order to solve the above problem, the ore layer thickness is not changed as it is, or rather is reduced, while the coke layer thickness is reduced, thereby realizing a reduction in O / C in the furnace to achieve stable blast furnace operation. Need to do. However, in such an operation, although the amount of coke charged per charge is reduced, maintaining an appropriate coke layer thickness with the reduced amount of charged coke is a charge similar to that of a bell-less charging device. Even if a charging device with high distribution controllability is used, it is difficult. The bell-less charging device can drop coke and raw material into the furnace little by little through the swirl charging chute, and can charge and deposit a predetermined amount of coke and raw material relatively accurately, It is suitably used for forming an appropriate charging distribution in the furnace.
[0007]
As an example of controlling the blast furnace charge, in particular, the coke deposit shape at the top of the furnace, by a bell-less charging device, there is a method as disclosed in Japanese Patent Application Laid-Open No. 2000-212613. In this method, when the coke is sequentially swirled from the furnace wall part to the furnace center part, a terrace part with a substantially flat deposition surface is provided in the vicinity of the furnace wall part, and a mortar shape is formed on the center side from this terrace part. It is the method of charging so that the inclined part may be formed. At this time, when the length of the inclined portion from the inside of the furnace wall is r and the radius of the furnace port is ro, the ratio of r / ro is 0.27 or less so that the core portion of the furnace port is rough. It is important to control the coke deposition shape so that a mixed layer mainly composed of grain coke is formed. That is, according to such a method, a part of the already deposited coke deposition layer is swept toward the furnace center by the ore charged thereon, and coarse coke is collected in the core of the furnace. Mixed layers can be formed.
[0008]
In “Materials and Processes” (vol. 8, p. 1065), when the terrace length is reduced in such a coke layer deposition shape, the phenomenon of “coke collapse” in which coke is washed away by ore increases. There is a report to do.
[0009]
Japanese Patent Application Laid-Open No. 2000-212613 proposes an attempt to control the coke terrace length within an appropriate range by controlling the shape of the coke in the furnace, thereby making the inflow due to coke collapse appropriate. is doing. In this method, as described above, when the ore is charged from the furnace wall side by the swivel chute under low coke ratio operation, the result is that the lower coke is swept into the furnace center. In some cases, all the layers are washed away, and as a result, there are places where there is almost no coke layer. In such a location, the gas in the furnace hardly flows, and the temperature rise and reduction of the ore are hindered.
[0010]
Therefore, in blast furnace operation with a small coke ratio and a large O / C, it is considered desirable to make the terrace of the coke layer relatively long. In such a case, the ore charged in the terrace will not flow toward the furnace center, and the thickness of the coke layer will be less affected by the ore charging. It is.
[0011]
However, even if the charge distribution control of the blast furnace is performed based on such an idea and the operation is performed with the air flow rate and the charge distribution being constant, there is a problem that the operation sometimes becomes unstable. According to the inventors' research, this problem was found to be due to the fluctuation of the raw material particle size. That is, among raw materials, for example, ore is handled and sized so that it has an almost constant particle size before being used in the blast furnace from the base of the raw material. Whereas the particle size is almost uniform, the raw material such as sintered ore varies greatly depending on the operation of the sintering machine, the method of crushing treatment, and the like. In addition, since sintered ore is often manufactured by a sintering machine adjacent to the blast furnace and used immediately, particle size fluctuation occurs compared to other iron raw materials, although sizing and sieving are performed. There is a tendency to be easy. In order to eliminate the influence on the blast furnace operation due to the particle size of the charged raw material, it is necessary to detect the state of the fluctuation before charging the blast furnace, for example, to carry out frequent particle size analysis of the sinter. Not right. Therefore, in the past, the actual situation is that the particle size variation in the raw material is detected in advance and the charge distribution is adjusted in advance.
[0012]
[Problems to be solved by the invention]
As described above, in the conventional blast furnace operation, when the coke ratio is reduced, the thickness of the coke layer becomes thin, and the collapse of coke is inevitably caused by the charging of the ore. When the terrace length is increased, a phenomenon that the gas flow fluctuation in the furnace due to the fluctuation of the raw material particle size becomes remarkable occurs, making it difficult to reduce the coke ratio. Such a phenomenon was conspicuous when a low coke ratio operation with a coke ratio of about 350 kg / t or less was intended, and stable operation during the low coke ratio operation was difficult.
[0013]
An object of the present invention is to propose a blast furnace operating method capable of ensuring stable operation of the blast furnace while realizing such low coke ratio operation. In particular, we propose a charge distribution control method that enables stable blast furnace operation when low coke ratio operation is performed using a large amount of raw materials with large particle size fluctuations such as sintered ore.
[0014]
[Means for Solving the Problems]
As an effective method for realizing the above-mentioned object, the present invention relates to a method for controlling the structure of a blast furnace coke deposited layer using a bell-less charging apparatus and operating the blast furnace. ratio using Rutotomoni average particle diameter of Ru 12mm~18mm der raw material exceeded 60%, the deposition geometry of the coke deposited layer at the time of the low-coke ratio operation, the coke terrace length / throat radius A blast furnace operating method is proposed in which the deposition is performed such that the ratio is 0.12 to 0.3 and the coke inclination angle is 10 to 20 °.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The inventors used a full-scale model (the top of the blast furnace), charged ore on various shapes of coke deposits, and investigated the deposit shape in each case. FIG. 1 shows an outline of this experimental apparatus. This equipment conveys the charged raw material from the raw material tank 1 to the furnace top bunker 2 via the surge hopper 1 'by the belt conveyor 3, and loads it into the furnace via the swivel chute 4 that tilts and rotates at an arbitrary angle. To enter.
[0016]
The inventors investigated the relationship between the coke deposition shape and the coke layer collapse due to the charging of iron-based raw materials such as ore (hereinafter referred to as iron-based raw materials or raw materials) using this experimental apparatus. That is, by adjusting the bell-less charging pattern, the inclination angle of the coke deposit layer was variously adjusted, and then the iron-based raw material was charged on the coke deposit layer. The results are shown in FIGS. 2 (a) and 2 (b). Here, the boundary between the coke deposition layer and the iron-based material after the iron-based material was charged was determined by observing a cross section of a sample taken from the surface by injecting resin in the height direction and curing the resin. As shown in FIG. 2 (b), when the inclination angle is 30 °, the coke surface shape before charging the iron-based material and the boundary shape of the iron-based material-coke layer after charging the iron-based material are different. It can be clearly seen that the coke deposit layer has been destroyed by charging the raw materials. On the other hand, as shown in FIG. 2 (a), it has been clarified that when the inclination angle is 20 ° or less, the coke deposit layer does not collapse. In this sense, in order to prevent the collapse of the coke deposit layer, the angle (inclination angle) in the inclined portion of the coke deposit layer other than the coke terrace should be about 20 ° or less, preferably 10 ° to 20 °. I understand.
[0017]
In the following description, the coke terrace is a flat portion formed on the furnace wall side in each of the coke deposition shapes in FIG. That is, in the surface shape after the coke deposition, a flat portion having an inclination angle of 5 ° or less in the furnace radial direction was defined as a coke terrace, and the length of the coke terrace from the furnace wall inner surface was defined as the coke terrace length. The value obtained by dividing the length of the coke terrace by the radius of the furnace mouth is defined as the dimensionless coke terrace length, and the angle at the coke slope on the furnace center side of the coke terrace is from the furnace center side to the furnace wall side. It was defined as the elevation angle when viewed, and the coke inclination angle (coke deposition inclination angle).
[0018]
Next, the inventors investigated the relationship between the coke deposition shape and the gas distribution change when the raw material particle size changed. In this investigation, the turning pattern of the turning chute 4 was adjusted to form various coke deposit shapes, and raw materials such as iron ore were charged thereon. The particle size of the raw material was 2 levels. And the raw material was extract | collected in 11 places of furnace radial directions, while measuring the distance (layer thickness) from a surface layer to a coke layer, the particle size analysis of the extract | collected raw material was performed. The airflow resistance index φ at each position in the radial direction is calculated from the layer thickness and particle size distribution of the raw material (see Kawasaki Steel Technical Report vol. 6, No. 1 (1974), p. 16), and an example of the measurement result 3 and FIG.
In addition, in calculating the ventilation resistance index, in addition to the ore layer and coke layer thickness and particle size obtained in the above investigation, it is necessary to determine the blowing conditions such as the blowing rate in the blast furnace, so the internal volume Calculations were made assuming operating conditions in a 4500m class ³ blast furnace.
[0019]
FIG. 3 shows the results of the above investigation. (A) shows the case where the coke terrace length is as short as 0.12 and the coke inclination angle is 20 °. The raw material layer ventilation resistance index in the vicinity of the wall does not change much. On the other hand, FIG. 3B is an example in which the coke terrace length is increased to 0.38 and the coke inclination angle is set to 20 °, but when the average particle diameter of the raw material is decreased to 12 mm as compared with 18 mm, The ventilation resistance of the entire raw material layer is increased.
[0020]
According to the inventors' consideration of this result, in the case of FIG. 3B where the dimensionless coke terrace length is large (≧ 0.3), the coke inclination angle on the furnace center side should be a gentle inclination of 20 °. For example, the raw material charged from the bellless swirl chute 4 is deposited almost as it is at the charged position, and does not flow into the furnace center. Therefore, the ore particle size is reduced at each position in the furnace radial direction. It is thought that an increase in ventilation resistance was observed.
[0021]
On the other hand, in the case of FIG. 3A where the coke terrace length is small (≦ 0.12), when the raw material particle size is coarse, the raw material does not flow into the furnace center as in the case where the coke terrace length is large. However, as the raw material particle size becomes finer, the-part of the raw material charged in the coke terrace area of the furnace wall flows into the furnace center side due to the decrease in the angle of repose of the raw material due to the decrease in the particle size of the raw material itself. As a result, a decrease in the ore layer thickness at the furnace wall occurs, and the increase in the ventilation resistance due to the decrease in the raw material particle size is offset by the decrease in the ventilation resistance due to the decrease in the ore layer thickness. It is thought that the increase in ventilation resistance at the wall was suppressed.
[0022]
These phenomena are also observed when the coke terrace shown in FIG. 3 (c) is short and the coke inclination angle is as small as 10 °, and the average of the raw materials is obtained in the range where the coke terrace is short and the coke inclination angle is 10 to 20 °. When the particle size becomes smaller, the ore loaded on the furnace wall side flows into the furnace center side due to the change in the angle of repose of the raw material itself, and the ore layer thickness of the furnace wall part is reduced, which leads to the ventilation of the furnace wall part. It turns out that it works in the direction which suppresses the change of resistance.
[0023]
FIG. 4 summarizes the above-described phenomena in various coke deposition shapes. In this figure, the coke terrace length is plotted on the horizontal axis, and the increase in the furnace wall ventilation resistance index when the average particle size of the raw material is reduced by 6 mm (18 mm → 12 mm) is plotted on the vertical axis. When the deposition angle of coke is 10 ° to 20 ° and the dimensionless coke terrace length is 0.3 or less, even if the average particle size of the raw material changes, the increase in the ventilation resistance index at the furnace wall is very large. However, if the deposition inclination angle is reduced to 7 °, the ore is charged into a substantially flat coke surface shape, and even if the average particle size of the ore decreases, it flows into the furnace core. It hardly occurs and there is no decrease in the ore layer thickness in the furnace wall. As a result, the ventilation resistance index of the furnace wall tended to increase regardless of the dimensionless coke terrace length.
[0024]
3 and 4 show that the dimensionless coke terrace length (the value obtained by dividing the coke terrace length r from the furnace wall inner surface to the terrace shoulder by the furnace port radius R) exceeds 0.3. When the raw material particle size decreases, the ventilation resistance of the furnace wall portion increases rapidly. The reason for this is that when the raw material particle size is reduced under conditions where the coke terrace length is small, a part of the raw material deposited on the coke terrace is caused by a decrease in the angle of repose accompanying the particle size reduction of the raw material itself. Flowing to the furnace center side, the decrease in particle size and the decrease in layer thickness due to flow cancel each other, resulting in almost no change in furnace wall ventilation resistance. On the other hand, when the coke terrace length is large, the particle size of the raw material is large. Regardless of the material, the material deposited on the coke terrace hardly flows into the central portion, and the layer thickness is maintained as it is, so that the ventilation resistance increases when the particle size decreases. Furthermore, even when the coke terrace length is small, if the coke inclination angle at the furnace center is as small as 7 °, the flow of ore is suppressed. The resistance is increased.
[0025]
To summarize the above test results, in order to suppress the collapse of the coke deposit layer and the fluctuation of gas distribution when the sinter grain size is reduced, the coke deposit shape has a dimensionless coke terrace length of 0.3 or less, and the coke deposit It has been found that it is necessary to have an inclination angle of the layer of 10 ° to 20 °.
[0026]
Furthermore, in order to determine the conditions for the amount of raw material with a particle size variation such as sintered ore, pellets are used as a raw material with almost no particle size variation, and the sintered ore with a changed average particle size and an appropriate blending ratio. I changed the survey. The results are shown in FIG. It can be seen that when the ratio of sintered ore in the raw material exceeds 60% and the dimensionless coke terrace length exceeds 0.3, the ventilation resistance index of the furnace wall portion increases remarkably according to the particle size of the sintered ore. In other words, it can be seen that the method of the present invention is effective when a large amount of raw material such as sintered ore having a large particle size variation is used.
[0027]
【Example】
In this example, a low coke ratio operation was performed in a blast furnace having a bell-less charging device with an internal volume of 4500 m ³ under a condition of a sinter ratio of 78%. When reducing the coke ratio, the raw material charge per charge was kept constant, and the coke charge was reduced. The charging sequence is a two-batch charging of coke and raw material. The result of this operation is shown in FIG. Under the condition of dimensionless coke terrace length of 0.25 and coke inclination angle of 30 °, the fluctuation of the aeration in the lower part of the furnace mainly increases as the coke ratio decreases, and if the coke ratio decreases to about 350 kg / t, it is difficult to continue stable operation. Met. Next, when the dimensionless terrace length was adjusted to 0.40, the blow-through phenomenon at the furnace wall became prominent, and when the coke ratio decreased to about 350 kg / t, it was difficult to continue stable operation. Therefore, when the conditions suitable for the method of the present invention were adjusted, that is, the dimensionless terrace length was 0.3 or less and the coke inclination angle was 20 ° or less, stable operation was possible even when the coke ratio was 350 kg / less.
[0028]
【The invention's effect】
As described above, according to the present invention, stable blast furnace operation can be performed even during low coke ratio operation. In particular, even when a large amount of raw material having a large particle size fluctuation is charged, blast furnace operation with a low coke ratio can be performed stably.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of a full-scale model blast furnace charging apparatus.
FIGS. 2A and 2B are graphs showing the state of coke collapse accompanying raw material charging in a model experiment.
FIG. 3 is a graph showing the relationship between the coke terrace length and the change in the radial direction airflow resistance index when the raw material particle size changes (from 18 mm to 12 mm).
FIG. 4 is a graph showing the relationship between the coke terrace length and the change in the furnace wall ventilation resistance index when the raw material particle size is changed by a model experiment.
FIG. 5 is a graph showing the relationship between the coke terrace length and the furnace wall ventilation resistance index when the pellet ratio is changed by a model experiment.
FIG. 6 is a blast furnace operation graph of coke ratio reduction to which an embodiment of the present invention is applied.

Claims (1)

Bell-less by controlling the structure of the charging device blast furnace coke deposited layer was charged with a method of performing operation of the blast furnace, Rutotomoni average particle size sinter ratio exceeds 60% Ru 12mm~18mm der Using the raw materials, the coke deposition layer has a deposited shape when the low coke ratio operation is performed. The ratio of coke terrace length / furnace port radius is 0.12-0.3, and the coke inclination angle is 10-20 °. Blast furnace operation method characterized by depositing to become.

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