JP4533293B2 - Converter discharge method - Google Patents

Description

  The present invention relates to a converter discharge method.

  In steel refining, hot metal preliminary treatment is widely performed in which dephosphorization treatment and decarburization treatment are divided and dephosphorization treatment is performed on molten iron before decarburization. Hot metal pretreatment methods are broadly divided into methods that use transport containers such as torpedo cars and pans, and methods that use converters. Methods that use converters are different in terms of processing speed, heat tolerance, etc. In recent years, the hot metal pretreatment has become the mainstream in recent years.

  Separation and removal of slag after hot metal pretreatment, that is, waste, is an important step in terms of preventing dephosphorization and reducing secondary materials in the decarburization process. 1) A method in which the converter is rolled over while leaving the molten iron in the converter, and only the upper slag is discharged (for example, see Patent Document 1). 2) Molten iron from the outlet of the converter. There is a method (for example, refer to Patent Document 2) in which the hot water is discharged into another container and then discharged.

  When there is no surplus in the number of converters and dephosphorization and decarburization are carried out continuously in the same converter, the former method (= the method of eliminating only the upper slag) is the latter method (= Compared with the method of draining molten iron once), there is no need for draining or recharging, and there is less complexity of the draining work, so the productivity of the converter is not reduced, and there is no heat dissipation loss due to transfer of containers such as tapping hot water Therefore, there is an advantage such as high heat tolerance, but on the other hand, it is difficult to efficiently discharge only slag while suppressing the outflow of molten iron, and there is a large amount of slag remaining in the furnace without being discharged That is, there is a problem that the rejection rate is low.

  Here, the waste rate is the weight ratio of waste slag out of the slag generated during the preliminary dephosphorization process.

  Therefore, various proposals have been made as an efficient method for exhausting only the upper slag. For example, gas is blown from a plurality of tuyere provided on the furnace belly and the bottom of the furnace to remove the slag. A method of moving to the furnace port side to exhaust (for example, see Patent Document 1), a method of blowing in oxidizing gas to promote slag foaming (= slag foaming) (for example, Patent Document 3, Etc.) have been proposed.

  However, in these methods, it is necessary to modify the converter to install tuyere in the furnace, and in the converter where refractory erosion has progressed, the slag position changes due to the change in the internal volume, and the tuyere There are problems that the position deviates from the optimum position, and that it is necessary to constantly inject gas in order to prevent the tuyere clogging during blowing, which increases unnecessary gas costs.

  Moreover, although the method (for example, refer patent document 4) which selectively eliminates only slag using an electromagnetic force is proposed, it is a capital investment cost, and is inferior at high temperature and intense vibration. There are problems such as increased maintenance costs in the environment.

  In addition, a method of scraping the molten iron upper layer slag with a scraper equipped with a scraper plate called dragger (for example, see Patent Document 5), which is used as a method for draining from torpedo cars and pans, is applied to the converter. However, considering the capacity of the converter, the facility becomes too large and it is not realistic.

  As described above, the method of discharging only the upper slag while leaving the molten iron in the converter is easier to work, more productive, and more heat-resistant than the method of discharging after hot water is discharged. On the other hand, it is difficult to separate molten iron and slag, that is, in terms of the rejection rate.

  Furthermore, although it is more productive than the method of draining once the hot water has been drained, it usually takes several minutes to drain, especially when aiming for a high drainage rate. Tend to be longer. Thus, there is a need for an efficient method capable of rapid waste removal in order to further improve productivity.

Japanese Patent No. 2558292 Japanese Patent No. 1761646 JP 05-279721 A JP 05-247514 A JP 59-13009

  The present invention is a method in which the converter is turned over while the molten iron remains in the converter, and the slag in the upper layer of the molten iron is discharged. The purpose is to provide an exclusion method.

  The present invention is characterized in that the tilting speed of the converter is set within an appropriate range in a method of rolling over the converter while leaving the molten iron in the converter and discharging the slag of the upper layer of the molten iron. . Furthermore, when discharging at a tilting speed within an appropriate range, the waste is discharged into a waste pan having an appropriate effective capacity.

  That is, the gist of the present invention is as follows.

(1) In the method in which the molten iron is left in the converter, the converter is rolled over and the formed slag on the upper layer of the molten iron is discharged from the furnace port, and the tilt angle reaches at least θ ₁ ° from θ ₀ °. The average tilting speed up to 20 ° / min and the average tilting speed from reaching θ ₁ ° to θ ₂ ° is set to 6.6 ° / min or less. Method.

Here, θ ₀ ° is the tilt angle at which the slag starts to flow out from the furnace port, θ ₂ ° is the maximum tilt angle at the time of evacuation, and θ ₁ ° is defined by equation (1).
θ ₁ = 0.6 × (θ ₂ −θ ₀ ) + θ ₀ (1)

  By enabling waste with a high waste rate, the amount of by-products used and the amount of slag that is a by-product are reduced. In addition, the productivity of the converter is improved by enabling rapid discharge.

  The best mode for carrying out the present invention will be described below.

  While the molten iron is left in the converter, the converter is overturned to discharge the upper slag of the molten iron. There was a phenomenon in which molten iron flowed out together with the slag at the end of the evacuation, and it was difficult to improve the evacuation rate and expedite the evacuation.

  Therefore, as a result of intensive studies aimed at improving the rejection rate by suppressing the outflow of molten iron and speeding up the rejection, the present inventor has found the mechanism of the following phenomenon. .

  That is, since the viscosity of the slag is as high as several tens of times that of the molten iron, the shearing force when the slag flows out is large, and the molten iron is dragged by the shearing force and flows out together with the slag.

  Therefore, in order to suppress the outflow of molten iron, it is necessary to reduce the flow rate at the time of slag outflow and reduce the shearing force. However, reducing the flow rate of slag outflow reduces the evacuation speed. None other than the speeding up of exclusion.

  However, on the other hand, it has also been found that by appropriately adjusting the tilting speed of the converter, it is possible to achieve both an improvement in the rejection rate and a quicker rejection.

  FIG. 1 shows a schematic diagram of the evacuation situation. In the initial stage of evacuation, since the tilt angle is small, the slag thickness is sufficiently thick and the shearing force of the slag outflow applied to the molten iron surface is small. Therefore, at the initial stage of evacuation, the molten iron does not easily flow out even if the tilting speed is high.

  On the other hand, as the tilt angle increases toward the final stage of evacuation, the slag thickness gradually decreases, and the slag outflow shearing force on the molten iron surface gradually increases. Therefore, it is necessary to reduce the shearing force applied to the molten iron and reduce the outflow of the molten iron by reducing the tilting speed at the end of the elimination period.

  In this way, the iron is tilted at a high speed in the early stage of slagging, and at the end of spilling, the tilting speed is reduced, that is, the tilting speed of the converter is adjusted according to the slaughtering stage, thereby preventing the molten iron from flowing out. While suppressing, it becomes possible to perform rapid evacuation and to improve both the evacuation rate and expedite evacuation.

  In addition, since the tilting is performed at a high speed in the early stage of waste, there is an advantage that the waste can be made more efficient by using the forming (= foaming) of the hot metal pretreatment slag. Under the conditions such as the temperature and composition of the hot metal pretreatment slag, the slag has a high viscosity and is easily formed, so the slag is easily formed by the CO gas generated by the decarburization reaction during blowing.

  By forming, the bulk volume of the slag increases 10 to 20 times, but the slag thickness increases and the evacuation becomes easy. However, since the generation of CO gas is less during the slag than during blowing, the forming gradually subsides during the slag and the bulk volume of the slag is reduced.

  Therefore, in order to increase the efficiency of waste disposal using forming, it is desirable to tilt at high speed in the early stage of waste removal where the bulk volume of the slag is sufficiently large due to forming.

For tilting speed, the average inclining speed until the tilt angle reaches at least theta ₁ ° from theta ₀ °, and 20 ° / min or more, and an average tilt speed from theta ₁ ° until it reaches the theta ₂ °, It is desirable to make it smaller than the average tilt speed from θ ₀ ° to θ ₁ °.

Here, θ ₀ ° is the tilt angle at which the slag starts to flow out from the furnace port, θ ₂ ° is the maximum tilt angle at the time of evacuation, and θ ₁ ° is defined by equation (1). The reference for the tilt angle is a tilt angle of 0 ° when the furnace is upright.
θ ₁ = 0.6 × (θ ₂ −θ ₀ ) + θ ₀ (1)

Furthermore, the average tilt speed is expressed by the following equation (2), where T _θn−θm is the time from when the tilt angle reaches θ _m ° until it reaches θ _n °.
Average tilt speed = (θ _n −θ _m ) / T _θn−θm (2)

For this reason, if the average inclining speed until the tilt angle reaches at least theta ₁ ° from theta ₀ ° is less than 20 ° / min, the tilting speed is slow, resulting in calm the forming in the furnace during which This means that the bulk volume of slag is reduced and a sufficient rejection rate cannot be obtained.

  Here, the sufficient rejection rate varies depending on the conditions of operation and steel type, but is usually about 70%. If this rejection rate is exceeded, phosphorus to be discharged out of the system is discharged together with slag. be able to.

  When the rejection rate is less than about 70%, a dephosphorization load is applied even during the decarburization process that is performed after the dephosphorization process, so that the amount of secondary materials used increases, components deviate due to dephosphorization, etc. The problem is likely to occur. However, depending on the steel type, it may be desirable to further increase the rejection rate.

  In addition, from the standpoint of further increasing the rejection rate, it is desirable that the average tilt speed is high, but in reality, if the average tilt speed is too high, slag that flows out of the furnace port will flow into the operating floor in front of the furnace. Because of the problem, it is usually considered that the upper limit is about 120 ° / min.

On the other hand, it is possible to reject with an average tilt speed of 20 ° / min or more up to a tilt angle exceeding θ ₁ °, and from the aspect of increasing the rejection rate, tilting at a high speed to a tilt angle as large as possible is possible. In reality, however, when tilting at a high speed until the end of discharge, the phenomenon that molten iron flows out with slag occurs and the yield decreases, so the tilting angle is the average tilting speed from θ ₀ °. The upper limit of the tilt angle at which the angle can be set to 20 ° / min or more is desirably the tilt angle represented by the expression (3).

However, even in this case, it is necessary to make the average tilt speed from θ ₁ ° to θ ₂ ° smaller than the average tilt speed from θ ₀ ° to θ ₁ °.
0.9 × (θ ₂ −θ ₀ ) + θ ₀ (3)

Here, in order to realize the above tilt pattern, values of the tilt angle θ ₀ ° at which the slag starts to flow out of the furnace port and the maximum tilt angle θ ₂ ° at the time of discharge are required, but θ ₀ ° The approximate value can be estimated from the furnace volume during tilting and the amount of molten iron and slag in the furnace calculated from the refractory profile in the furnace, and the exact value is simply calculated from the furnace slag. The tilt angle that flows out may be recorded.

On the other hand, for θ ₂ °, it is possible to predict the tilt angle at which the molten iron flows out when tilted quasi-statically from the furnace volume during tilting and the amount of molten iron in the furnace calculated from the refractory profile in the furnace. Although it is possible, the tilt angle at which the molten iron actually flows out is affected by the immediately preceding tilt speed. Therefore, it is necessary to change the tilt speed in advance to determine θ ₂ °.

Furthermore, theta ₀ ° and theta ₂ °, in order to change from time to time in accordance with the charging amount of the furnace shape and the molten iron and slag, such erosion condition of furnace refractories, theta ₀ ° and theta ₂ ° from those conditions It is more desirable to be able to predict.

  In actual tilting, it is realistic to set a tilting pattern in advance so as to satisfy the above tilting pattern, and tilt according to the pattern. Further, the tilt pattern control may be a control that switches the tilt speed stepwise or a control that switches the tilt speed continuously.

  On the other hand, when discharging slag that has become bulky due to forming when evacuating with high efficiency using forming, to prevent slag from overflowing from the basin pan, A pot is required.

The present inventor has studied the capacity of the slag pan that realizes the above tilt pattern and does not overflow from the slag pan, taking into account the slag calming speed and tilt pattern, and 0 per 1 ton of molten iron in the converter. It has been found that it is desirable to secure an effective capacity of .11 m ³ or more.

  Here, the effective capacity is the capacity of the pan excluding the volume, such as slag that has been charged in the pan in advance to prevent the slag from sticking to the wall of the pan, that is, the capacity that can actually be drained.

The reason for this is that when the effective capacity per 1 ton of molten iron in the converter is less than 0.11 m ³ , if the tilting is performed at a high speed in the initial stage of discharging, the formed slag is settled in the discharging pot. Since it exceeds the capacity of the slag pan, it can tilt at high speed only at the initial stage of spilling in order to prevent overflow from the slag pan, and thereafter the tilting speed must be reduced. That is.

  Accordingly, during this time, the forming in the furnace is settled and the bulk volume of the slag is reduced, so that a sufficient removal rate cannot be obtained and rapid removal cannot be performed.

On the other hand, if the capacity of the pan is too large, there is an extra equipment cost and there is an upper limit on the tilting speed due to restrictions such as the outflow of molten iron and slag flowing into the operation floor. It is not necessary that the effective capacity per 1 ton of molten iron in the converter of the waste pan is more than 0.20 m ³ .

  The exclusion test by the exclusion method of the present invention will be described.

  The test was conducted in a 370 t converter. After charging scrap and hot metal, preliminarily dephosphorizing the hot metal by adding a faux lime or silica stone or other slagging agent to a specified basicity and slag amount according to the amount of Si in the hot metal. It was.

  After dephosphorization, the converter was turned over and slag was discharged from the furnace port. At that time, the pattern of the tilting speed, the effective capacity of the waste pan, etc. were changed, and the waste time and the waste rate were evaluated. Here, the rejection rate was obtained by mass balance calculation and slag weighing based on the composition of slag.

The tilt angle θ _{0 at} which the slag starts to flow out of the furnace port is 60 °, and the determination of the maximum tilt angle at the time of discharge is the time when the skilled operator determines that the molten iron will flow out if tilted further. However, the maximum tilt angle θ ₂ was 84 ° at all levels.

  Table 1 shows the test level and test results, and FIG. 2 shows the tilt speed pattern (relationship between time and tilt angle) in the example. The tilt pattern was manually controlled to be a predetermined pattern.

Levels 1 and 2 are comparative examples in which the pattern of tilting speed is outside the scope of the present invention, levels 3 to 6 are examples of the present invention in which the pattern of tilting speed is within the scope of the present invention, and level 4 -6 is an invention example in which the pattern of the tilting speed is within the range of the present invention, and the effective capacity of the slag pan per 1 ton of molten iron is within the desired range (0.11 m ³ or more).

  As shown in Table 1, compared to comparative examples (levels 1 and 2) in which the tilt speed pattern is outside the scope of the present invention, examples in which the tilt speed pattern is within the scope of the present invention (levels 3 to 6). In this case, the rejection rate is as high as 70% or more, the rejection time is shortened, and the rejection rate per unit time is improved.

  In particular, at the level where the effective capacity of the sewage pan is large (levels 4 to 6), the slag does not overflow and can be tilted at a high speed up to a large tilting angle. As a result, the spillage rate greatly exceeds the target 70%. At the same time, the excretion time was sufficiently shortened compared to the comparative example.

It is a figure which shows a rejection situation typically. (A) shows the evacuation situation at the beginning of evacuation, and (b) shows the evacuation situation at the end of evacuation. It is a figure which shows the pattern (relationship of time and a tilt angle) of the tilt speed in an Example.

Explanation of symbols

1 Tilt angle 2 Slag 3 Molten iron

Claims (1)

In the method where the molten iron is left in the converter, the converter is rolled over, and the formed slag of the upper layer of the molten iron is discharged from the furnace port, the average until the tilt angle reaches at least θ ₁ ° from θ ₀ ° A converter evacuation method, characterized in that the tilting speed is 20 ° / min or more and the average tilting speed from θ ₁ ° to θ ₂ ° is 6.6 ° / min or less .
Here, θ ₀ ° is the tilt angle at which the slag starts to flow out from the furnace port, θ ₂ ° is the maximum tilt angle at the time of evacuation, and θ ₁ ° is defined by equation (1).
θ ₁ = 0.6 × (θ ₂ −θ ₀ ) + θ ₀ (1)

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