JP4765722B2 - Blast furnace start-up operation method - Google Patents

Description

The present invention, among the rest wind blast, the raw material level is lowered than usual (hereinafter, referred to as reduced scale.) Relates to blast furnace commissioning operation method of rest Kazego in the state.

  In the blast furnace, ore, which is an iron source, and coke, which is a reducing material (hereinafter collectively referred to as raw materials), are charged alternately in layers from the top of the furnace, and the air heated from the tuyere at the bottom of the furnace Blow. In actual operation, there are various operation forms such as blowing pulverized coal together with air heated from the tuyere, but the raw material charged from the top of the furnace gradually descends (this is also referred to as unloading). On the other hand, the basic principle is to operate continuously in countercurrent by the rise of the gas in the furnace blown from the tuyere.

  However, there is a case where the operation is temporarily suspended for the purpose of repairing the main body facilities and incidental facilities (this is called “resting wind”). Since the temperature in the blast furnace decreases during such a pause, it is extremely important to recover the reduced temperature in the blast furnace in a short period of time and restore it to the normal operating state when resuming air blowing after the pause. Become. In general, the hot metal temperature is used as an index related to the temperature in the blast furnace before and after resting.

  In blast furnace rest wind, for example, when repairing a part where raw materials exist in normal operation, the rest wind may be performed after the scale is reduced. Reduction is an operation to lower the position of the raw material charging surface by setting the amount of raw material charged from the top of the furnace to be less than or equal to the amount of unloading in the blast furnace, but the rest time is the same. However, when the scale is reduced, the temperature of the hot metal temperature decreases greatly during the start-up operation, and the frequency of the phenomenon that the load does not drop during the start-up (hereinafter referred to as shelf hanging) increases. If these occur, the return to the steady operating state is delayed, and the amount of production cut at startup becomes large. Conventionally, operations such as increasing the coke ratio have been implemented.

For example, in Patent Document 1, in a blast furnace in which pulverized coal blowing operation is performed, a furnace state defect or unstable phenomenon such as slip, shelf hanging, blow-through, etc., which occurs immediately after resuming air blowing after resting, is eliminated, and by resuming air blowing An operation method for enabling smooth start-up in a short time is disclosed. The method disclosed in Patent Document 1 reduces the amount of pulverized coal blown from the tuyere, preferably at least 5 hours before entering the resting wind, and increases the amount of coke charged from the top of the furnace, It is controlled to increase the heat flow ratio when the wind is off.
Japanese Patent Laid-Open No. 9-256011

Further, in Patent Document 2, the furnace interior entry level is reduced from the stock line to a height of 0.3 to 0.5 times the distance from the tuyere while continuing the raw material charging, The raw material charging is stopped at the bottom, the raw material charging amount is adjusted to 0.8 to 1.5 m / hr while the raw material charging is continued, and the tuyere of hot air or oxygen-enriched hot air is used. The ratio of the pressure loss amount ΔP from the current level to the current reduction level and the pressure WS at the tuyere due to the charge is adjusted so that it is less than the predetermined value for preventing blow-by that has been previously determined from past operation results. Techniques for adjustment are disclosed. The purpose of this technology is to avoid unstable phenomena such as outgassing when shifting to a reduced scale wind, and to enter the wind smoothly.
JP 2001-73014 A

  However, the technique disclosed in Patent Document 1 has no application in reduced wind pauses, and cannot eliminate the unstable phenomenon that occurs particularly by reducing the scale. In addition, even the technique disclosed in Patent Document 2 cannot solve the unstable furnace state phenomenon when the wind is not started.

  The problem to be solved by the present invention is that the conventional technique cannot solve the instability phenomenon that occurs when the scale is reduced and the instability phenomenon of the furnace condition at the time of start-up of the resting wind.

The blast furnace start- up operation method of the present invention is
In order to eliminate the unstable furnace condition in the blast furnace start-up operation after the reduced wind break,
When resting the blast furnace after reducing the scale,
The reduction is performed at a reduction speed of 1.0 to 2.0 m / hr,
The most important feature is that the set coke ratio CR (kg / pt) when the blast furnace enters resting wind is set within the following range.
2.5 × h + 440 <CR <6 × h + 410
However, h (= breeze time (hr)) ≧ 16

And
In order to prevent shelves from being raised and the tuyeres from being damaged during startup,
In the blast furnace start- up operation after a reduced wind break,
The main feature is that the raw material to be backfilled at a reduced scale is charged so as to have a coke ratio in the range of +50 to +100 kg / pt with respect to the set coke ratio CR defined in the above range. .

  According to the present invention, in the start-up operation of reduced scale off-air, it is possible to eliminate the unstable phenomenon of the furnace condition and realize a smooth start-up operation and to achieve a production plan.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings.
In blast furnace operation, a decrease in hot metal temperature leads to a trouble with ironing and a delay in returning to normal specifications, so it is important to suppress the decrease in hot metal temperature as much as possible.

  However, in the blast furnace rest wind, the hot metal temperature at the start of the rest wind decreases with respect to the hot metal temperature before entering the rest wind, and as shown in FIG. 1, the difference becomes larger as the rest time becomes longer. Become. Furthermore, in the resting wind accompanied by reduction, the degree becomes larger as shown in FIG.

The mechanism by which the hot metal temperature is further lowered during a rest with a reduced scale as compared with a rest without a reduced scale will be described below.
FIG. 2 (a) shows the temperature distribution in the blast furnace. The temperature of the raw material charged from the top of the furnace rises quickly and reaches about 1000 ° C. Thereafter, the temperature is maintained for a while (thermal preservation zone), and when the raw material reaches a fusion zone where the raw material starts to melt, the temperature is raised again, and the temperature becomes 1200 ° C. or higher. The pig iron dripped in the cohesive zone is further heated when passing through the coke packed bed, reaches 1500 ° C. or higher, and is discharged from the tap outlet.

Even if the transition to resting wind occurs, the level of the cohesive zone at the time of resting wind is maintained at the normal operating level, and the decrease in hot metal temperature before and after the resting wind is the heat dissipation during the resting wind. It is mainly due to.
On the other hand, when the scale is reduced to shift to resting wind, the hot metal temperature at the start of the resting wind is further reduced.

This phenomenon will be described below.
In the scaled down wind, the raw material charging is usually continued several hours before the off wind, and the charging level is lowered. At this time, when the reduction speed is slow, the reduction rate of the raw material charging speed is small, so the heat flow ratio (ratio of the heat capacity of the charging raw material and the rising gas) is almost the same as before the reduction. Further, since the amount of ore to be reduced must be ensured, as shown in FIG. 2 (b), the level of the cohesive zone at the time of resting is lowered as much as the charging level is lowered. As a result, when the resting wind is started up, the heating after dropping of the cohesive zone is insufficient, and the hot metal temperature is further reduced.

  By the way, as a means for suppressing the decrease in the level of the cohesive zone during the transition to the reduced wind break, there is a method of increasing the scale reduction speed to enter the wind break. Increasing the reduction speed means lowering the raw material charging speed, so the amount of ore to be reduced and dissolved decreases, and the heat capacity of the gas relatively increases (decrease in heat flow ratio). Therefore, the effect of raising the cohesive zone is generated, and the lowering of the previous cohesive zone level is suppressed. However, an extreme decrease in the heat flow ratio causes an excessive increase in the furnace top gas temperature, and is limited to a range that can be withstood by the furnace top equipment and the like.

FIG. 3 shows a change in the hot metal temperature drop when the reduction speed is changed.
It can be seen that when the reduction speed is increased to 1.0 m / hr or more, the decrease in the hot metal temperature before and after entering the resting wind is reduced. However, if the reduction speed exceeds 2.0 m / hr, the furnace top gas temperature at the time of reduction rises to 400 ° C. or more and affects the furnace top equipment, so the reduction speed is 1.0 m / hr. It is desirable to set it as the range below 2.0m / hr above.

  However, when the scale down speed is increased and the scaled down wind is entered, there is an increase in the frequency of occurrence of instability of the furnace condition (= shelf hanging phenomenon) in which the unloading of the charge is stagnant during the start-up process. It was seen. Shelf hanging deteriorates the melt-off characteristics of the cohesive zone in the blast furnace, or generates a highly breathable area in the packed bed, etc., and balances the lift of the blower and the lowering of the raw material. Is a phenomenon of stagnation. Once shelf hanging occurs, it is necessary to reduce the air flow and release the balance (shelf dropping), leading to a reduction in blast furnace operation.

  As described above, when the scaled down wind is started up, if the scale-down speed is increased, the frequency of the shelf suspension increases, and the lack of ore reduction is considered. Although the decrease in the cohesive zone level is suppressed by increasing the reduction speed, as a result, as shown in FIG. 4, the region until the ore charged at the start-up is reduced and melted down becomes narrower, It is thought that due to insufficient reduction of ore, the pressure loss of the cohesive zone itself increases, causing shelf hanging.

  As a means for solving this shortage of ore reduction, it is possible to increase the coke ratio of the raw material to be charged. However, an excessive increase in the coke ratio increases the Si concentration in the hot metal at the time of start-up. As a result, the fluidity of the hot metal in the furnace deteriorates, and the tuyere is damaged due to poor liquid permeability before the tuyere. Cause things. From this, it is considered that there is an appropriate charging coke ratio for the reduced wind time, reduced level, and the like. FIG. 5 shows the results of the rest time and the coke ratio set at rest.

  As described above, when the coke ratio set at the time of resting with respect to the resting time is too low, the hot metal temperature is lowered at the time of start-up. On the other hand, if the coke ratio set at the time of resting is too high, the Si concentration in the hot metal rises excessively and causes damage to the tuyere.

From these facts, it is understood that there is an appropriate value for the coke ratio CR (kg / pt) set at the time of resting, and this appropriate value can be expressed by the following equation. In the following equation, the resting time h (hr) is normally targeted for resting of 16 hours or more in order to carry out the construction of blowing the furnace opening in the reduced scale operation.
2.5 × h + 440 <CR <6 × h + 410

That is, the blast furnace start- up operation method of the present invention is
When resting the blast furnace after reducing the scale,
The reduction is performed at a reduction speed of 1.0 to 2.0 m / hr,
In addition, the set coke ratio CR (kg / pt) when the blast furnace enters resting air is set within the range of the above formula.

And , during the reduced downtime, from experience, the coke ratio when the raw material level is backfilled to the normal operation level at the start of the downtime is +50 to +100 kg relative to the coke ratio at the reduced downtime. / when charging in the range of pt, it is the bridging generation and tuyere breakage frequency is minimized at the time of start-up (see Fig. 6).

Examples of the present invention are shown below.
Table 1 below shows the results of scaled off-air operation when the scale was reduced by 6 to 13 m from the normal operating raw material level and rested for 30 to 45 hours.

  From Table 1, it can be seen that when the reduction speed is increased, a drop in the hot metal temperature at the start-up can be suppressed, but the shelf hanging phenomenon becomes remarkable. On the other hand, it can be seen that if the coke ratio for backfilling is set appropriately at the time of start-up as in the example of the present invention, the occurrence of shelf hanging and tuyere damage can be suppressed.

  The present invention is not limited to the above example, and it goes without saying that the embodiment may be appropriately changed within the scope of the technical idea described in each claim.

It is a figure which shows the hot metal temperature fall at the time of a rest wind. (A) is a figure which shows the temperature distribution in a furnace at the time of a normal operation, (b) is a figure which shows the temperature distribution in a furnace after transfering to a reduced scale rest wind. It is a figure which shows the hot metal temperature fall inhibitory effect at the time of raising a reduction speed. It is a figure which shows the reduction | restoration delay of an ore at the time of maintaining a cohesive zone level and performing start-up operation. It is the figure which showed the result of having tested variously the range of the appropriate setting coke ratio with respect to a rest time with A blast furnace (2700m < ³ >). It is the figure which showed the result of having variously tested the effect which made the coke of a backfill up with respect to a base, and was optimized in the reduced-scale rest wind start-up with A blast furnace (2700m < ³ >).

Claims (1)

When resting the blast furnace after reducing the scale,
The reduction is performed at a reduction speed of 1.0 to 2.0 m / hr,
And the blast furnace startup operation after reduction scale rest air set in a range of the following expression set coke ratio CR (kg / pt) when the blast furnace enters the rest wind,
Blast furnace start- up operation characterized by charging raw material to be backfilled in a reduced scale to a coke ratio in the range of +50 to +100 kg / pt with respect to the set coke ratio CR defined by the following formula Method.
2.5 × h + 440 <CR <6 × h + 410
However, h (= breeze time (hr)) ≧ 16

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