KR920000700B1 - The coating method of slag - Google Patents

Abstract

The slag coating method for protecting the furnace wall is characterized by remaining the converter furnace slag 15-50 kg per molten steel 1 ton in the furnace, lowering the temperature of slag, adding dolomite 4.4-4.7 kg for magnesia (MgO) and limestone 2- 20 kg to the furnace with molten steel, and then swing the converter furnace by 1-6 times. The important factors are controlling the quantity of dolomite and a number of swings in the optimum conditions.

Description

Slag Coating Method for Protection of Furnace Wall

1 is a change in composition of slag during the drilling.

2 is a process drawing of the conventional method and the present invention.

3 is a graph showing the relationship between dolomite use and (MgO) leaching amount from the furnace wall.

4 is a comparison of the delineation effect of the conventional method and the present invention.

The present invention relates to a method of coating the slag on the furnace wall of the converter for protecting the furnace wall of the converter, and more particularly to a method of coating only a part of the converter blown end slag on the inner wall of the converter for the furnace wall protection of the converter. The erosion factors of the refractory material constituting the furnace body are generally melted by the reaction with slag during the drilling, mechanical wear caused by the collision with the charging material, thermal spalling due to fluctuation of the furnace temperature, and the flow of the contents of the furnace. And erosion due to scattering. Conventional methods for extending furnace life span are to reduce the dissolution of refractory containing (MgO) as a main component by maintaining the high concentration of slag (MgO) during refining and to spray and attach irregular refractory to locally eroded furnace walls. Or refractory by slag coating the furnace wall by tilting the furnace body before and after after increasing the viscosity of the slag.

Maintaining high slag (MgO) concentration during blowing is for the following reasons. The rate at which (MgO), which constitutes the refractory body, elutes into slag is expressed by the following general formula.

The left term of this equation indicates the change in the concentration of MgO in time and is an indicator of the erosion rate of the refractory. K in the right port is a constant depending on slag amount and fluidity, (% MgO) sat is the saturation concentration of (MgO) in slag, and (% MgO) is the (MgO) concentration in slag. Refractories are eluted when the concentration of (MgO) in the slag is lower than the saturation concentration from Eq. (1), but when the concentration is the same as the saturation concentration, the erosion rate becomes zero (0). It can be seen that.

Therefore, in order to reduce the erosion of the refractory by slag, it is necessary to operate under the conditions where saturation concentration of slag (MgO) is low, or to maintain the high concentration of slag (MgO). To reduce the (MgO) saturation concentration in the slag, it is necessary to keep the slag temperature low, the basicity high, and the (% FeO) low, and arbitrary adjustments are limited in view of the metallurgical refining effect or workability. Therefore, a method of maintaining high concentration of (MgO) in slag by adding dolomite containing a large amount of (MgO) or by using some residual slag of the termination point of slag after the start of the blow, is widely used.

When dolomite is added during the blowing, the slag formation rate is faster than the dissolution rate of the dolomite, and thus, in the early stage of the blowing, the furnace refractory is inevitably eluted in parallel with the dolomite goods. Therefore, in order to secure and maintain slag with high (MgO) concentration even in the early stage of blowing, there has been reported a method of using some slag of the front heat.

FIG. 1 schematically shows the change in slag composition from the start of blow to the end when the slag is retained and utilized during normal operation. In the general operation, the slag composition starts from (I) and moves to (II) according to the (SiO ₂ ) generation and quicklime goods by the oxidation of [Si] in molten iron. ) Is increased and the blowing ends at the position of (III). On the other hand, when the slag is retained and used, it begins to be blown at ①, similar to the final slag composition of the previous heat, and moves to the composition ② with the formation of (SiO ₂ ). Return to composition. As such, when slag is used and applied, the slag's high base can be maintained throughout the pretreatment process from start to finish.If dolomite is added with the start of the treatment, the concentration of (MgO) in the slag Since it is kept high, refractory erosion by slag during blowing can be effectively suppressed.

As described above, converter refractory erosion has many factors such as mechanical wear during raw material loading, erosion due to flow of furnace contents, and thermal spalling, in addition to chemical dissolution by slag. In addition to reducing the erosion of the furnace, there is a need for an active method of growing and repairing the furnace walls by slag coating or spraying of irregular refractory materials. However, the method of fostering and repairing the amorphous refractory by spraying it on the necessary part is not only expensive, but also takes a long time to repair, thereby lowering the productivity. Therefore, the slag coating method for refractory by fixing the converter slag after tapping to the furnace wall in a cheap and efficient manner is widely used. In this method, the slag is fixed on the furnace wall and refractory by forcibly cooling the hot end slag to increase the viscosity and then tilting the furnace body forward and backward.

The disadvantage of this method is that slag coating can be applied to the furnace walls of the charging side and the tapping side as the furnace body is tilted before and after, but the trunnion side does not come into contact with the slag, so the spray method should be used in parallel. In addition, since the amount of slag is relatively high, the amount of coolant (Dolomite) consumed to lower the slag temperature is high, and if the remaining slag is not excluded after coating, excessive slag amount during the drilling results in weak workability such as slopeing. Therefore, after slag coating, the remaining slag should be excluded, and the added dolomite is simply used to cool the slag, and in order to maintain high MgO concentration, it is inevitable that the dolomite is added immediately after the start of the drilling.

It is an object of the present invention to exclude a part of the blowing end slag and to do with the dolomite, if necessary, with quicklime to improve the slag cooling effect by improving the slag cooling effect and without remaining slag after coating. It is intended to provide a method of coating slag for protecting the furnace walls of converters that reduces the use of auxiliary materials (Dolomite) as well as extending the service life of the raw materials.

EMBODIMENT OF THE INVENTION Hereinafter, the structure of this invention is demonstrated.

In the present invention, after leaving the converter slag in 15-50Kg furnace per ton of molten steel, the furnace body is established, and the slag temperature is added by putting dolomite and quicklime 5-20Kg corresponding to 4.4-4.7Kg (MgO) per ton of molten steel. It relates to a slag coating method for protecting the furnace wall, characterized in that the slag is coated on the furnace wall of the converter by tilting the furnace body 1-6 times after lowering the furnace.

In the present invention, the slag is coated on the furnace wall, and the remaining slag is not excluded, so that dolomite input used as a reconstituting agent during the blowing is omitted, unlike when applying the conventional slag coating method.

The amount of dolomite corresponding to 4.4-4.7Kg (MgO) per tonne of molten steel is usually 12-l8Kg per tonne of molten steel. 2 shows an operation process diagram for comparison between the conventional method and the present invention.

The reason for the numerical limitation will be described below.

If the amount of slag residue is too small, it is difficult to expect sufficient slag coating effect, and if too much slag is generated, the slag is ejected to the outside of the furnace during the blow, so the slag residue is preferably 15-50 kg per ton of molten iron. Dolomite is added to utilize (MgO) contained in the dolomite, and it is preferable to add the amount of dolomite equivalent to 4.4-4.7Kg of (MgO) per ton of molten steel based on the amount of (MgO). This is because when the amount of dolomite (that is, MgO) is added is insufficient, the wall protection effect is insufficient. When the amount of dolomite is added, the slag viscosity is lowered and the refining function of the slag is inhibited.

That is, when (MgO) in the range of 4.4-4.7Kg per ton of molten iron is added, the amount of (MgO) elution from the furnace wall is close to zero, indicating that the effect of furnace protection is excellent.

The quicklime is added to cool the slag when the slag fluidity is good enough that the coating of slag is insufficient even though dolomite is added, and the amount cannot be set to an accurate standard, and the slag is added to the furnace wall according to the slag situation after the dolomite is added. It is sufficient if the amount can be sufficiently attached, particularly about 5-20kg.

Of course, quicklime does not need to be added when the condition is such that slag can be sufficiently attached to the furnace wall due to dolomite addition. As in the case of injecting quicklime, the number of tilting of the furnace should be inclined until the slag is sufficiently coated on the furnace wall. If the number of tilting is small, the coating efficiency is insufficient. -6 times is preferred.

Hereinafter, the present invention will be described in detail through examples.

Example 1

Dolomite was added to the (MgO) source unit of Table 1 to the slag residual amount per ton of molten steel as shown in Table 1 by using a composite blower having a capacity of 300 tons. And the amount of quicklime added and the number of furnace body tilt was properly adjusted, and after the experiment several times for each condition (MgO) elution was measured and the average value is shown in Table 1 below.

TABLE 1

As shown in Table 1, Example (ad) of the present invention showed less (MgO) elution amount than Comparative Example (1-3), which is the Example (ad) of Comparative Example (1) in the protection effect of the furnace wall. Better than -3).

Example 2

Slag per ton of molten steel is maintained within the range of 15-50Kg by using a composite blower with a capacity of 300 tons. After the mixture was added in the range of 18Kg, if necessary, quicklime was added 5-20Kg per ton of molten steel, and the slag was coated on the furnace wall 1-6 times before and after depending on the slag property, and the main material was charged and charged. After the start of the burial, the quicklime needed for refining was added in consideration of the quicklime input during slag coating, and dolomite was not added.

In the conventional method of FIG. 3, as in the slag coating method of FIG. 2, the slag part is attached to the furnace wall by hardening the furnace body to which 4-5 tons are added for slag cooling in the state of remaining slag after tapping. After the rest of the slag was excluded. In addition, 20-30Kg of dolomite was used per ton of molten steel by adding 3-5 tons of dolomite to reduce furnace wall erosion, that is, (MgO) leaching by maintaining a high concentration of (MgO) in the slag with the start of blowing. The correlation between the (MgO) elution from the furnace wall and the dolomite use after the blowing was shown in FIG. The (MgO) elution from the furnace wall calculates the amount of (MgO) contained in the slag from the slag amount obtained from the mass balance and the (MgO) concentration at the blowing point, and calculates the ash rate of the dolomite supplied into the furnace. Assuming the same, it means the remainder except for the amount of (MgO) dissolved from dolomite and the amount of (MgO) contained in residual slag. In FIG. 3, when the amount of (MgO) elution is positive, (MgO) is eluted from the furnace wall, and when it is negative (-), when the amount attached to the furnace wall is larger than the amount eluted from the furnace wall. Therefore, it means effective for protecting the wall.

Therefore, in order to maintain the (MgO) elution amount in the negative value, when coated according to the conventional method, it is necessary to use 27Kg / ton-steel dolomite corresponding to (MgO) of about 9Kg or more per ton of molten steel. In the case of coating according to the operation process chart, it can be seen that the same effect can be obtained by using dolomite of 15Kg / ton-steel, which is equivalent to (MgO) of about 4.5Kg per ton of molten steel of the present invention.

On the other hand, the adverse effects on the refining effect of recycling the endpoint slag containing a large amount of impurities were examined. As an example, the results of the Tallinn reaction are shown in FIG. 4 is a comparison between the measured distribution ratio and the theoretically calculated distribution ratio. The measured value and the calculated value are expressed by the following equation.

It can be seen from the drawings that the present invention, which retains and utilizes slag, exhibits a slightly higher phosphorus ratio than the conventional method, and the dephosphorylation effect is improved.

As described above, since the present invention has a relatively small amount of slag, the amount of sensible heat contained in the slag is reduced, so that the use of the same amount of coolant provides excellent cooling effect, thereby ensuring high viscosity slag, improving slag coating efficiency, and coating slag. By using only some of the starting point slag, there is no adverse effect on the refining effect, and the use of raw materials (Dolomite) can be greatly reduced. In the present invention, quantitative evaluation is difficult, but in the existing operation, when some molten steel remains in the furnace after tapping, the remaining molten steel flows out during the exclusion, mixed with the slag and solidified, so that the slag treatment was difficult. Since the remaining molten steel does not flow out, the slag treatment is not only easy, but also the iron yield is increased, which has a remarkable effect on extending the service life of the body, reducing the consumption of secondary raw materials, improving the error rate and improving workability.

Claims (1)

After the tapping, 15-50Kg converter slag per ton of molten steel is left in the furnace, and the furnace body is established.Then, dolomite and 5-20Kg of quicklime equivalent to 4.4-4.7Kg (MgO) per ton of molten steel are added to the slag temperature. The slag coating method for the furnace wall protection of the converter, characterized in that the slag is coated on the furnace wall of the converter by tilting the furnace body 1-6 times after falling.

Images