JPH0277516A - Method for treating steelmaking slag producing at steelmaking process - Google Patents

Abstract

PURPOSE:To reduce unit consumption of a flux needing to refining by adding the prescribed quantity of flux into molten steel tapped into a ladle to execute prevention of re-phosphorization and heat holding of the molten steel and directly re-charging the ladle slag into a refining furnace after discharging the molten steel. CONSTITUTION:At the time of tapping the molten steel into the ladle from the refining furnace, the flux of lime, etc., is added at 1-10kg/t of molten steel to the molten steel in the ladle. By this method, the re-phosphorization and molten metal temp. drop are prevented. Successively, the molten steel is discharged into a casting machine from the ladle, and the remained ladle slag is directly re-charged into the refining furnace. Before re-charging this, it is desirable to avoid heat loss by bringing this ladle slag into contact with cooling material of scrap, etc., as chargable into the refining furnace and cooling. By re-charging the above ladle slag into the refining furnace, the unit consumption of the flux in the refining furnace is reduced and also by recovering the metal content in the ladle slag, the steelmaking cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for treating steelmaking slag, particularly ladle slag, and more specifically, a method for directly recharging steelmaking slag into a smelting furnace without performing regeneration treatment. This invention relates to a method for treating ladle slag.

(Prior Art) Steelmaking slag, which is inevitably generated during the steelmaking process, has conventionally been mainly disposed of on land at a high cost, or dumped at sea and used for landfill. However, recently, efforts have been made to recycle ladle slag and re-charge it into the refining furnace in order to utilize it effectively.

For example, in the refining of steel in a converter or the like, flux (solvent) is added as an auxiliary raw material for the purpose of dephosphorization and desulfurization, so that so-called refining slag is produced. In the tapping process, which is the final point of the steelmaking process, the molten steel is normally flowed into the ladle while suppressing the inflow of slag. Fluxes such as quicklime are being added again.

Japanese Patent Laid-Open No. 194107/1983 discloses a method of effectively utilizing the ladle slag produced by the steel manufacturing method in which quicklime is added as flux into the ladle during tapping. In this method, after the molten steel is discharged from the ladle, the collected ladle slag is cooled, crushed, and subjected to magnetic separation to dephosphorize and
It is recycled as an auxiliary raw material for desulfurization and added to the smelting furnace again to promote slag formation in the smelting furnace, thereby reducing the unit consumption of auxiliary raw materials.

(Problems to be Solved by the Invention) However, in the conventional method described above, the focus was on effectively reusing the ladle slag as a secondary raw material for steelmaking (for dephosphorization and desulfurization), so the ladle slag was cooled and crushed. It is then subjected to magnetic separation treatment and recycled as an auxiliary raw material. This method has the following two problems.

First, at present, the cost required for reprocessing using this method is higher than the cost required for disposing of ladle slag and for processing lime, and reuse results in an increase in cost.

Second, the dust generated during the crushing and magnetic separation process causes environmental health problems inside and outside the factory.

Here, the purpose of the present invention is to be able to recover the metal content contained in ladle slag in addition to reducing the flux consumption rate required for refining, and to solve all of the above-mentioned problems of the conventional method. The purpose is to provide a method that can be used.

(Means for Solving the Problems) The two problems in the conventional method described above arise because the ladle slag is subjected to cooling, crushing, and magnetic separation treatment for regeneration, so the present inventors have improved these steps. Based on a different idea of reusing the ladle slag as a raw material for steelmaking as a whole, rather than reusing it as an auxiliary raw material as in the conventional method, the ladle slag is directly recycled into the smelting furnace. We considered charging.

As a result of experiments in oxygen top/bottom-blown converters, it was found that by directly recharging ladle slag into the smelting furnace, the flux consumption rate in the smelting furnace was reduced, and the metal content contained in the ladle slag was recovered. It was confirmed that the steel tapping yield improved. In other words, by changing the way of thinking to using ladle slag as a raw material for steelmaking as a whole rather than as an auxiliary raw material for dephosphorization and desulfurization as in the past, it was discovered that conventional steelmaking costs could be significantly reduced by directly recharging ladle slag. .

Furthermore, when recharging the ladle slag into the smelting furnace, it is preferable to cool the slag to a certain extent due to safety and high temperature measures. The inventors have also discovered that ladle slag can be cooled in a short time while suppressing heat loss by discharging ladle slag into a slag ladle (slag ladle), and have completed the present invention.

In addition, in the method of the present invention, since the ladle slag is directly reused without being crushed, environmental hygiene problems due to dust do not occur.

The gist of the present invention is to prevent rephosphorization and keep the molten steel warm by adding 1 to 10 kg of flux per ton of molten steel into the ladle when tapping the steel from the refining furnace to the ladle. This is a method for treating steelmaking slag generated during the steelmaking process, which is characterized by directly recharging the ladle slag that remains after discharging molten steel from the ladle into the refining furnace.

According to a preferred embodiment of the invention, before the ladle slag is re-charged into the smelting furnace, it is cooled by contacting with a coolant such as scrap that can be charged into the smelting furnace.

In this way, the present invention was made possible for the first time by understanding the entire ladle slag as a raw material for steelmaking.
This method is based on a completely different concept from the conventional method, which uses slag as an auxiliary raw material. Therefore, the present invention does not require recycling treatment of ladle slag, which was essential in the conventional method, and the problems of the conventional method are also solved at the same time.

(Operation) Next, the present invention will be explained in more detail with reference to the accompanying drawings.

The 11th is a schematic explanatory diagram showing each step fat to (fl) of the method according to the present invention.

In the +a+ process, ferroalloy, deoxidizer, and flux are added to the molten steel 3 tapped from the converter 1, which is a refining furnace, into the ladle 2 at the time of tapping, to adjust the composition, prevent rephosphorization, and control the molten steel temperature. This will help prevent the decline.

This process itself is well known and can be carried out in the same manner as before.

Quicklime is preferred as the flux, but other fluxes (eg, dolomite) can also be used. The amount of flux added varies depending on the amount of refining slag that has flowed into the ladle from the converter and the deoxidization state of the wire, but for example, the amount of flux added is 10 to 30.
0 to 10 to 10 per ton of molten steel.

Next, the molten steel in the ladle is discharged to the tundish 4 in a (bl process (casting process)), and is caused to flow into a mold by a continuous casting method or an ingot forming method as shown in the figure.

At this time, the ladle slag 5 remaining in the ladle 2 is drained into a slag ladle 6 or the like in the (cl process). Then, in step +81, the ladle slag is re-charged into the refining furnace (converter) 8 from, for example, a scrap chute, and used as a raw material for steelmaking.In other words, the ladle slag is not recycled before being re-charged.

Inside the ladle, the added flux is in a pre-melt state. Ladle slag is a composite slag produced by mixing this flux with deoxidized products (AQzos, Sing, MnO, etc.) and refining slag that has flowed into the ladle.

The typical composition of ladle slag is shown below.

As is clear from this composition and the examples described below,
According to the present invention, even if ladle slag is directly re-charged into the smelting furnace without regenerating treatment, the slag promotion effect and dephosphorization and desulfurization ability are sufficiently maintained. fully contributes to the reduction.

In addition, in the method of the present invention, the ladle slag directly re-charged into the refining furnace contains metal, and this transfers into the steel, thereby improving the tapping yield. In addition, in the method of the present invention, the metal content in the slag is effectively used as a raw material for steelmaking, so the metal content in the slag can be increased by ending the discharging of the i@steel from the ladle to the tundish early. However, there is no loss of metal.

Therefore, high quality steel can be easily produced.

The amount of ladle slag to be re-charged into the smelting furnace according to the method of the present invention is preferably about 10 to 20 kg/kg.9 Normally, the entire amount of ladle slag can be returned to the smelting furnace; Depending on the amount produced or its composition, only a portion may be reinjected into the smelting furnace, and the remainder may be used for other purposes or discarded.

In this way, when ladle slag is reused in a smelting furnace, considering the cooling capacity of the slag in the smelting furnace, the higher the slag temperature at the time of recharging, the more advantageous it is, and the greater the effect of improving the steel tapping yield. . In this sense, it is preferable that the ladle slag 5 discharged into the slag ladle 6 is immediately reused in a hot slag state in the smelting furnace without being cooled.

However, if the temperature of the ladle slag is too high, there is a risk of a steam explosion during rainy weather when recharging it into the smelting furnace from the scrap chute, for example, and heat insulation measures are taken for the charging route such as the chute and the weighing machine. is also required. Therefore, in actual operation, taking these problems into consideration, it is advantageous to cool the ladle slag to a certain extent before recharging it into the smelting furnace.

The ladle slag is still in a molten state immediately after discharging the molten steel and being discharged into the slag ladle, and it takes a long time to cool it down if it is allowed to radiate heat by natural cooling. Therefore, the rotation rate of the slag pan is reduced, and the number of slag pans must be increased. Furthermore, since the slag pan is exposed to high temperatures during cooling, thermal deformation occurs in the slag pan, shortening the life of the pan and increasing costs.

Furthermore, if the ladle slag is simply cooled by heat radiation, the amount of heat lost from the slag due to temperature drop becomes a loss and is not effectively utilized.

Advantages of the present invention! According to Mr. 1m, as a slag cooling method that can minimize heat loss during cooling and shorten cooling time, it uses materials that can be charged into the smelting furnace, such as scrap, as a coolant. Cooling the ladle slag by bringing it into contact with the ladle slag, specifically,
For example, the ladle slag can be cooled by the coolant by supplying the coolant to a slag ladle in advance and discharging the slag from the ladle to the slag ladle.

In addition to scrap, cooled pig iron or iron oxide coolants such as iron ore can be used as a coolant.Normally, the temperature of ladle slag when it is discharged from the ladle is around 1400℃. , by such cooling method, the slag temperature can be reduced to about 800℃.
It is preferable to cool the slag to about 1000°C before recharging it into the smelting furnace.The cooling rate of the slag depends on the amount of coolant added to the slag pan, so the slag temperature or slag cooling time is It can be controlled by the amount of wood placed.

According to the cooling method described above, at the same time as cooling the ladle slag,
Materials used as coolant, such as scrap, can also be heated, minimizing heat loss. Therefore, when the mixture of ladle slag and coolant in the slag ladle is fed into the refining furnace as a raw material for steelmaking, the cooling capacity is reduced, so the effect of improving the yield of steel tapping is large. In addition, the cooling time of the ladle slag is significantly shortened, and the ladle slag can be directly re-charged into the smelting furnace in the shortest possible time, increasing the rotation rate of the slag ladle and extending the life of the ladle. . Furthermore, it has been found that the metal contained in the ladle slag has the effect of preventing seizure of the inner surface of the slag ladle.

To explain this cooling method with reference to FIG. 1, (as shown in the fl process, scrap 9 is placed in the slag ladle 6 in advance, and the molten ladle slag 5 is poured into the fc process). It flows in as shown. After that, similarly (dl
After the transportation process, it is re-charged into the refining furnace 8 as a steelmaking raw material in the te+ process. The empty slag pot 6 is loaded with scrap 9 again to prepare for the next slag discharge.

In this way, when cooling the ladle slag before recharging it into the smelting furnace, it is particularly advantageous to employ the cooling method described above that uses scrap etc. as a coolant, but there are other methods. It goes without saying that it is also possible to cool the ladle slag.

Next, the present invention will be explained in more detail with reference to Examples.

An example of carbon steel refining using a 250 ton oxygen top/bottom blowing converter on IJmli is shown below.

In this example, as shown in Figure 1, from the converter to the ladle? '8
When tapping steel, 5 kg/l of flux (quicklime) is added in order to prevent rephosphorization from the refined slag that has flowed into the molten steel and to prevent a drop in the temperature of the molten steel. Deoxidizer (AQ, Si alloy) 4kg
Then, after the molten steel was discharged from the ladle, the composition of the ladle slag remaining in the ladle was analyzed, and the composition was as shown in Table 2 below.

The slag remaining in the ladle was immediately transferred to a slag ladle, and without cooling, various amounts of slag were charged into the converter in the form of hot slag to perform converter blowing. At the beginning of the converter blowing process, quicklime was added as usual.

Figure 2 shows Si in hot metal based on a series of operational data for this example.
(wt%) and quicklime basic unit (kg/l, required amount of quicklime (kg) per 1 molten steel), when ladle slag is not used, when ladle slag is used, about 10 kg/l and about 20 kg/l
The results are summarized in a graph comparing the results with the addition of .

As is clear from the results in FIG. 2, by recharging the ladle slag into the converter according to the present invention, the unit consumption of quicklime, which was charged into the converter in conventional blowing, was reduced by 1. It was possible to reduce the amount of added slag by 0.3 to 0.7 kg/kg/kg.

In addition, when ladle slag was not added, it was necessary to use 1.0 kg of fluorspar on average.
When 10 kg/l of ladle slag is added according to the method of the present invention, fluorite is used! (kg/l) became zero.

The use of ladle slag made it possible to perform blowing without using fluorite.

The following Table 3 shows the conventional blowing method without adding ladle slag and the hot slag (lA
Typical examples of the amount of quicklime used, the amount of iron ore used, and the tapping yield are shown for cases in which the amount of quicklime used, the amount of iron ore used, and the steel tapping yield are shown for cases where the slag is added as cold slag (at room temperature) and blown.

It can be seen that the addition of ladle slag contributes to the yield of steel, especially when hot slag is added, the yield of steel produced increases.
In this case, the amount of iron ore used as a coolant is also increased. In this case, the ladle slag was cooled using scrap.

Table 3 Comparison of Steel Tapping Yield Molten steel tapped from a converter in the same manner as in Example 1 was processed in a ladle. After discharging the molten steel from the ladle, the remaining ladle slag 6,0 tons is drained into a ladle in which 0 to 2.0 tons of scrap has been placed in advance, and the ladle slag is heated to about 800℃.
The cooling time until reaching the temperature was measured.

Figure 3 shows the relationship between the amount of scrap deposited in the ladle and the cooling time.
It took 0 to 300 minutes, but if 2.0 tons were added, it could be cooled in about 20 minutes. That is, it can be seen that the cooling time is significantly shortened by discharging the ladle slag into a slag ladle filled with scraps. Furthermore, as is clear from the figure, the increase in the amount of contributed scrap and the shortening of the cooling time are linearly correlated, and it can be seen that the cooling time can be controlled by the amount of scrap.

Even when the ladle slag in the ladle cooled in this way was added to perform converter blowing, the same effect as shown in Example 1 was obtained, the quicklime consumption rate was almost halved, and the firefly The amount of stone used was almost zero, and the steel tapping yield was improved to the same level as in the case of cold addition shown in Table 3.

(Effects of the Invention) As described in detail above, according to the present invention, the ladle slag produced by adding fluffox can be directly reloaded into the smelting furnace as a raw material for steelmaking, without requiring the conventional and time-consuming recycling process. By using this method, it is possible to reduce the cost associated with recycling and also avoid the environmental problem of dust generation caused by pulverization during the recycling process.

In addition, by directly recharging ladle slag, in addition to reducing the unit consumption of quicklime and fluorite, the metal content in the slag is transferred to steel, and the temperature of the ladle slag to be recharged is lower than that of conventional methods. Unlike steel, it can be maintained at a high temperature, which has the economical effect of improving the tapping yield.

The advantages of the present invention! In the i aspect, the ladle slag that has been discharged is cooled by a coolant such as scrap to such an extent that there are no problems in terms of safety or equipment. Cooling by this method is
Since the slag temperature can be lowered in a short time, the rotation rate of the slag ladle can be increased and the life of the ladle can be prevented from decreasing. Furthermore, since the temperature of the scrap is raised at the same time as the ladle slag is cooled, the cooling capacity when these are reintroduced as raw materials for steelmaking is small, and the steel tapping yield is improved. Furthermore, the cooling rate and cooling temperature can be controlled depending on the amount of scrap, and the operation is easy.

[Brief explanation of the drawing]

Fig. 1 is a process diagram illustrating an example of the recharging flow of ladle slag in the method according to the present invention; Fig. 2 shows the relationship between the amount of Si in hot metal and the basic unit of quicklime without adding ladle slag. and FIG. 3 is a graph showing the relationship between the large amount of scrap used for cooling and the cooling time of ladle slag.

Claims (2)

[Claims] (1) 1 per ton of molten steel when tapping from the refining furnace to the ladle
A steelmaking process characterized by adding ~10 kg of flux into the ladle to prevent rephosphorization and to keep the molten steel warm, and then directly recharging the ladle slag that remains after discharging the molten steel from the ladle into the refining furnace. A method for treating steelmaking slag generated during the process. 2. The method according to claim 1, wherein the ladle slag is cooled by contacting with a coolant capable of being introduced into the smelting furnace before being reinjected into the smelting furnace.