JP6981335B2 - Hot metal pretreatment method - Google Patents

Description

The present invention relates to a hot metal pretreatment method.

In the hot metal dephosphorization step, an auxiliary raw material containing CaO and iron oxide is used as a refining agent. The auxiliary raw material added to the hot metal _{is mixed with SiO 2} derived from the hot metal to form slag. Further, in parallel with the dephosphorization reaction, iron oxide in the slag reacts with carbon in the hot metal to generate CO gas, and foaming (forming) of the slag occurs.

The slag forming behavior during hot metal pretreatment blowing is as follows. Initially, Si contained in the hot metal is oxidized by adding a solid oxygen source such as iron ore, sinter, and dust to generate highly viscous slag. When the oxidation of Si progresses until the hot metal [Si] concentration falls below 0.01% in the middle of blowing, the oxidation rate of carbon contained in the hot metal gradually increases, and the amount of CO gas generated increases. The generated gas accumulates as bubbles in the slag, expanding its apparent volume. When the forming is remarkable and the height of the expanded slag exceeds the furnace opening of the hot metal pretreatment reaction vessel, slag leakage called sloping occurs.

A large amount of slag having a high temperature of 1400 ° C. or higher overflowing to the outside of the container requires cleaning by heavy machinery, which not only hinders the operation but also has safety concerns, so it is essential to suppress sloping. Therefore, as described in Patent Document 1, it is known to use a forming sedative that calms forming.

Japanese Unexamined Patent Publication No. 2016-29212

By the way, by studying forming measures, it was found that the effect of suppressing forming and sloping is superior or inferior depending on the timing of adding a so-called forming sedative. When the mechanism of slag forming and sedation was investigated in detail, it was presumed that the onset of sedative effect was due to the agglutination of bubbles in the slag and the release of gas (bubble rupture) due to the generation of gas from the sedative. Therefore, in order to fully exert the sedative effect, it is necessary that some forming occurs and bubbles are accumulated in the slag at the time of adding the sedative. The present inventor examined an index for appropriately performing the injection timing of this forming sedative.

The present invention has been made in such a background, and an object of the present invention is to avoid a decrease in the operating rate due to the occurrence of sloping and to provide a cost reduction by reducing the amount of the sloping sedative used.

To solve the above problems, to measure the cumulative oxygen-flow amount during hot metal pretreatment blowing, cumulative oxygen-flow per unit is 7.0Nm ³ / t-p or more 11.0Nm in a range of less than ³ / t-p It is a hot metal pretreatment method that suppresses slag sloping, which is characterized by charging a slag forming sedative into a furnace.

The bulk density of the slag forming sedative is preferably ^{200 kg / m 3} or more and less than 4000 kg / m ^3.

Further, it is preferable that the slag forming sedative contains at least one of sodium carbonate and calcium carbonate.

According to the present invention, it is possible to avoid a decrease in the operating rate due to the occurrence of sloping and to provide a cost reduction by reducing the amount of the sloping sedative used.

It is a figure which shows the relationship between the bubble volume fraction and the slag sedation rate at the time of adding a sedative. It is a figure which shows the relationship between the cumulative acid feed amount basic unit, and the volume fraction of bubbles in a slag. It is a figure which shows the relationship between the sedative density and the sedative depth 30 seconds after putting a sedative into a furnace.

The embodiment for carrying out the invention is shown below. In the hot metal pretreatment method of the present embodiment, the cumulative acid feed amount is measured during the hot metal pretreatment blowing, and the cumulative acid feed amount basic unit is 7.0 Nm ³ / tp or more and ^{less than 11.0 Nm 3} / tp. Inject the slag forming sedative into the furnace within the range of. Therefore, it is possible to avoid a decrease in the operating rate due to the occurrence of sloping and to provide cost reduction by reducing the amount of the sloping sedative used.

Here, the background of the invention will be further described. According to the research and investigation by the test converter and the offline experiment of the actual converter, the inventors showed that the sedative rate was 0.3% per second or more when the volume fraction in the slag at the time of adding the sedative was 63% or more. It was found as shown in Fig. 1. The stagnation speed is the slag height reduction speed per second expressed as a percentage, with the distance from the height of the unformed slag to the furnace mouth as 100%. In actual machine operation, it generally takes about 30 seconds from the start of a small amount of slag overflowing from the furnace opening to the overflow of a large amount of slag and the start of falling into the furnace. If the sedation rate is 0.3% / sec or more, the slag forming height can be reduced by 10% or more in 30 seconds, so that the occurrence of sloping can be suppressed.

The inventor further stated that in the dephosphorization and blowing of the test converter and the actual converter, the cumulative amount of acid feed was VO ₂ (Nm ³ / tp: tp stands for ton-pig iron). The relationship between the bubble volume fraction Fg (volume%) in the slag was found as shown in FIG. The cumulative _{amount of acid feed basic unit VO 2} (Nm ³ / tp) is the cumulative volume of top-blown oxygen from the start of blowing to the end of blowing, and iron ore and manganese ore to be added as auxiliary raw materials. The total volume of oxygen supplied from the lower oxide converted into a gas in a standard state is divided by the weight of the hot metal in the furnace. According to FIG. 2, when the cumulative acid feed amount basic unit VO ₂ is 7.0 or more, the volume fraction of bubbles in the slag is 63% or more, and a high slag forming sedative effect can be expected.

On the other hand, if the charging is too late, the slag is formed to the vicinity of the furnace opening, and the sedative is discharged to the outside of the reaction vessel while being on the upper surface of the slag, so that the effect is not exhibited. In normal refining, a certain amount of auxiliary material is put into the furnace during blowing, and this melts to form slag. Under general conditions, the volume of unformed slag is about 5% of the volume of the converter freeboard, that is, the volume inside the converter minus the volume of the hot metal. Assuming that the slag is formed to the vicinity of the furnace mouth, the slag volume occupies 100% of the converter freeboard volume, and the volume fraction occupied by the bubbles in the slag is 100-5 = 95%. From FIG. 2, the cumulative acid feed rate basic unit at this time is 11.0 (Nm ³ / tp). From the above, it was clarified that a high slag forming sedative effect can be exhibited by adding a sedative when the cumulative acid feed rate is 7.0 or more and less than 11.0.

The bulk density of the sedative to be added is preferably ^{200 kg / m 3} or more and less than 4000 kg / m ^3. FIG. 3 shows the effect of the sedative density on the depth at which the sedative settles in the above-mentioned 30 seconds. The bulk density of the slag formed to the furnace mouth, which is the limit of sloping, that is, the minimum bulk density of the forming slag is about 200 kg / m ³ , but the bulk density of the sedative is less than ^{200 kg / m 3.} Since the buoyancy of the added sedative exceeds gravity, the sedative is placed on the surface of the forming slag and does not penetrate inside. In this case, the foaming effect of forming due to the gas generation of the sedative is smaller than that in the case where the density of the sedative is 200 kg / m ^{3 or more.}

Further, when the bulk density of the sedative is 4000 kg / m ³ or more, the settling speed of the sedative in the forming slag is extremely high, and the slag formed to the furnace mouth in 30 seconds is settled by 5 m or more. In this case, since the contact time with the slag is short, the sedative effect is small. Further, a sedative that reaches the interface between the hot metal and the slag is not preferable because it causes a phenomenon that the forming is rather promoted by the generation of gas. Therefore, the upper limit of the bulk density of the sedative is set to less than ^{4000 kg / m 3.} The bulk density of the sedative is determined by determining the volume from the buoyancy when the surface is covered with a resin film or the like and then immersed in a liquid (such as water) having a known density (Archimedes method), and the weight measured in air is used. It can be calculated using.

Paper sludge (a mixture of pulp scraps and steelmaking slag), artificial marble (a mixture of aluminum hydroxide and resin), etc. are used as the sedative to be added, but calcium carbonate such as limestone is preferably used as a gas generating substance. It is desirable to use one or more of sodium carbonate such as soda ash. Since all of these substances are industrially inexpensive and can be obtained in large quantities, it is possible to obtain the effects without significantly increasing the cost. In addition, soda ash is a name as a mineral of sodium carbonate hydrate.

Here, Table 1 shows the relationship between the cumulative amount of acid feed basic unit and the amount of slag escaped from the furnace mouth when various sedatives were added in the experimental results conducted by the present inventor.

As can be seen from Table 1, by charging the slag forming sedative into the furnace in the range where ^{the cumulative acid feed intensity is 7.0 Nm 3} / tp or more and ^{less than 11.0 Nm 3 / tp.} , The amount of slag escaped from the furnace mouth could be suppressed. Therefore, it was possible to avoid a decrease in the operating rate due to the occurrence of sloping. According to the test results of the present inventor, the sloping occurrence rate could be reduced to about one-fourth of the conventional one. In addition, the cost could be reduced by reducing the amount of sloping sedative used. According to the test results of the present inventor, the amount of the sedative used can be reduced to about one-fourth of the conventional amount by improving the efficiency of using the sedative.

Although the present invention has been described above with a focus on the embodiments, the present invention is not limited to the above embodiments and can be in various embodiments.

Claims (3)

Pretreatment of hot metal The cumulative amount of acid feed was measured during blowing, and the slag forming sedative was put into the furnace in the range where ^{the cumulative acid feed intensity was 7.0 Nm 3} / tp or more and ^{less than 11.0 Nm 3 / tp.} A hot metal pretreatment method that suppresses slag sloping, which is characterized by charging. The hot metal pretreatment method according to claim 1, wherein the bulk density of the slag forming sedative is 200 kg / m ³ or more and less than 4000 kg / m ^3. The hot metal pretreatment method according to claim 1 or 2, wherein the slag forming sedative contains at least one of sodium carbonate and calcium carbonate.

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