JPS5925911A - Dephosphorization treatment of molten iron - Google Patents

Abstract

PURPOSE:To prevent rephosphorization and to improve dephosphorization efficiency by removing continuously the molten slag formed on a bath surface in the stage of dephosphorization at the same period when a dephosphorizing agent is blown. CONSTITUTION:The molten slag formed on a bath surface is continuously removed by using a vacuum suction type slag removing device 7 or the like at the same instant when a dephosphorizing agent is blown in the stage of blowing the dephosphorizing agent under the bath surface of molten iron 3 and dephosphorizing the molten iron. The sucked up slag is granulated by water jets or the like and is recovered. The amt. of the dephosphorizing agent to be blown is reduced by the above-mentioned method, whereby the time for the treatment is reduced. The need for slag-off after the dephosphorization is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in the preliminary dephosphorization method of bath pig iron, including reduction of auxiliary materials during converter blowing, process saving of ultra-low phosphorus copper melting, and reduction of slag generated from the steelmaking process. The present invention relates to a preliminary dephosphorization method for hot metal that aims to reduce the amount of phosphorization.

Conventionally, when performing preliminary dephosphorization of hot metal, a method has been used in which a dephosphorizing agent is added onto the surface of the hot metal bath and stirring using mechanical stirring or gas injection is used to increase reaction efficiency.

Furthermore, in recent years, powder blowing technology has been established, and a method of blowing a fine powder dephosphorizing agent under the surface of a hot metal bath using gas as a carrier medium has become popular.

In order to carry out the dephosphorization process using a controlled dephosphorizing agent, it is necessary to promote the contact and reaction between the dephosphorizing agent and the hot metal. The method of injecting the dephosphorizing agent powder below the surface of the hot metal bath is characterized by the fact that the reaction interfacial area is larger in trajectory than the conventional method of adding the dephosphorizing agent above the bath surface, and the process is carried out simultaneously. The dephosphorization reaction efficiency is high because intense mixing of the hot metal and the dephosphorizing agent can be expected due to the flowing gas. The first example of this method is
As shown in the figure. Fine powder dephosphorizing agent in a dephosphorizing agent blowing device 5 is blown into the bath pig iron 3 in the ladle through a lance 4. A similar dephosphorization process is also carried out on the hot metal inside the Torpedo car.The dephosphorizing agent uses quicklime or soda ash as an absorbent for the dephosphorization product, and as an oxygen source, -C iron ore, mill scale,
Converter dust is used, a mortar resistant agent is added, fluorite, colemanite, calcium chloride, etc. are added, and a mixture is used to achieve the optimum composition.

By such a method of injecting a dephosphorizing agent, the dephosphorizing agent unit, that is, the amount of dephosphorizing agent used per 1 ton of hot metal, varies depending on the temperature and composition of the hot metal before treatment, but is approximately 50 to 70%.
It was 9/l-bath iron.

The present inventors have conducted various studies on the reaction mechanism of hot metal dephosphorization by injecting a dephosphorizing agent, and as a result, they have found that the dephosphorization reaction is closely related to the oxygen potential at the position where the reaction is proceeding. Here, the oxygen potential is expressed as the partial pressure of gaseous oxygen in equilibrium, and is a measure of the oxidizing or reducing atmosphere.

The dephosphorization reaction of hot metal proceeds by absorbing and fixing P2O5 generated by oxidation of phosphorus in the hot metal with strong basic oxides such as CaO1N, +20, and separating it from the molten iron as slag. Therefore, an oxidizing atmosphere is advantageous for dephosphorization, and when dephosphorizing hot metal with a low carbon concentration, it is necessary to increase the oxygen potential at the dephosphorization reaction site using iron oxide or gaseous oxygen.

If the oxygen potential is expressed in PO2 (unit: atm), the oxygen potential of hot metal is PO2 = ] 0-+aa
In contrast, quicklime-based slag has PO
2: Sufficient dephosphorization cannot be achieved unless it is maintained in a highly oxidizing atmosphere of about 100-12ai (strictly speaking, slag/
Various studies have revealed that the phosphorus distribution between metals cannot be increased.

The present inventors actually measured PO2 in hot metal during blowing treatment in the conventional hot metal dephosphorization method shown in FIG. 1, and also estimated it from thermodynamic data.

What has become clear from a series of studies is that Poz near the discharge port of lance 4, indicated by 1 in Figure 1, is lo -10~
10" atm and the oxygen potential is kept high enough for the dephosphorization reaction, whereas in the part 2 in the figure where the slag and hot metal on the bath surface are in contact, PO2: 1'0
It was a low oxygen potential of ~10'' atm.

Therefore, the dephosphorizing agent injected from the lance below the surface of the hot metal bath,
Since PO2 is high in the vicinity of the lance discharge port, it immediately reacts with phosphorus in the bath pig iron, floats up as dephosphorization products such as 3CaO-P2O5, and becomes slag on the bath surface.

However, the slag on the bath surface has low PO2, and if the slag's dephosphorizing ability is relatively small, P2 is present in the slag.
It cannot be maintained at 0 s, and phosphorus migrates into the hot metal.

Figure 2 is a diagram showing changes in the phosphorus concentration in hot metal during an experiment in which the dephosphorizing agent was injected until the middle of the treatment, and then the supply of the dephosphorizing agent was stopped and only gas was injected and stirring was performed. . In this way, depending on the processing conditions, even if a dephosphorizing agent is injected under the surface of the hot metal bath and the dephosphorization reaction is progressing, slag on the bath surface and rapid phosphorusation may proceed at the same time, resulting in a decrease in dephosphorization efficiency. It was found that it was decreasing.

The applicant has also proposed a method of dephosphorizing bath pig iron in an extremely short time by injecting a large amount of lime-based flux using a bottom-blowing converter. When dephosphorizing hot metal using this bottom-blowing converter, by blowing the key/rear gas of human silk and the flux of Taihi, the dephosphorization near the hot point in the hot metal and the dephosphorization ability can be improved. Dephosphorization occurs in both steps: slag on a high bath surface and dephosphorization at the contact interface with hot metal.

In contrast, in the dephosphorization agent injection process in the hot metal pretreatment vessel, there is a limit to the amount of carrier gas blown and therefore a limit to the amount of flux supplied, so although the dephosphorization that occurs in the hot metal progresses, The difference is that the slag on the bath surface may have a high phosphorus concentration and low dephosphorizing ability, and conversely, it may rephosphorize in the hot metal, so it is known that there is room for improvement.

Based on the above findings, the present inventors have completed the present invention as a result of research on a method for improving dephosphorization efficiency and reducing the unit consumption of a dephosphorizing agent by preventing rephosphorization.

The purpose of the present invention is to provide an efficient (preliminary dephosphorization of hot metal) dephosphorization method using a simple equipment for blowing a dephosphorizing agent into a conventional ladle. This is because when the dephosphorization treatment of hot iron baths is carried out by blowing a dephosphorizing agent under the surface of the hot iron bath, the molten slag formed on the bath surface after the dephosphorization reaction is treated with the dephosphorizing agent. The present invention relates to a method for dephosphorizing hot metal, which is characterized by increasing dephosphorization efficiency by continuously removing phosphorus at the same time as blowing.

As a specific method for continuously removing slag, for example, the most suitable method is to use a vacuum suction type slag removal device that has been developed in recent years. This device utilizes the difference in specific gravity between slag and metal,
It uses vacuum suction to suck up only the slag,
The slag that has been absorbed is granulated and recovered by a water jet.

Figure 3 shows the outline of processing using this device.
3 is hot metal, 4 is lance, 5 is dephosphorizing agent injection device +M'-1
6 is a dust collection hood, and 7 is a vacuum suction type slag removal device.

Figure 6174 shows a comparison of changes in phosphorus content in the bath iron during dephosphorization between the method of the present invention and the conventional method (Figure 1). Approximately 5 minutes to dephosphorize until the phosphorus concentration in the hot metal reaches the same level (approximately 1 okg/l-bath iron as dephosphorizing agent)
You can save some money.

After conducting many experiments using the method of the present invention, we found that in order to facilitate the vacuum suction of slag, the position of the blowing lance should be eccentrically placed toward the wall from the vertical axis of the container, and the lance should be placed near the wall opposite to the lance. If a slag vacuum suction head is installed, the effect will be even greater.The gas blown in from the lance and the dephosphorizing agent will cause the hot metal bath to shake violently, and the extent of the shaking will be greater than that in the vicinity of the lance. At a more distant position, the fluctuation of the slag surface position is small, and the slag can be suctioned and removed without frequently changing the position of the vacuum suction head.

FIG. 5 is a plan view illustrating the positional relationship between the lance and the vacuum suction head. 4 is a lance, and 7 is a vacuum suction type slag removal device.

According to the present invention, the amount of dephosphorizing agent used in the past is reduced from 50 to 70 kg.
/ was a single-bath pig iron, but under the same conditions 5 to 10 kg
/ has become possible to reduce the amount of hot metal. Furthermore, the dephosphorizing agent injection time (
Since there is no need to drain the slag again after the dephosphorization process, it is possible to significantly shorten the time required for the preliminary treatment process, resulting in significant labor and energy savings.

EXAMPLE An example of implementing the present invention using a hot metal ladle will be shown in comparison with a conventional method. The apparatus used to carry out the method of the present invention is shown in FIG. 3, and the conventional method is shown in FIG.

100) Powder injection equipment into hot metal of 200k
The dephosphorizing agent was fed at a rate of g/min and blown through a lance. At the same time, the slag on the bath surface was continuously removed using a vacuum suction type slag removal device 16''.The results are shown in Table 1 in comparison with the conventional method (comparative example).

As a dephosphorizing agent, a mixed powder of 60% iron ore, 30% quicklime, and 10% rock was used, and as a carrier gas, 80% oxygen was used.
A mixed gas containing 20% nitrogen was used.

Dephosphorizing agent consumption is 1210 to 15 kg/l compared to conventional method
We were able to reduce the amount of hot iron used.

[Brief explanation of the drawing]

Fig. 2 is a vertical cross-sectional view showing a conventional hot metal dephosphorization method, and Fig. 2 shows the change over time in the phosphorus concentration in hot metal in an experiment in which a dephosphorizing agent was injected halfway through the process in the conventional method, and then only gas was injected. Figure 3 is a vertical cross-sectional view showing an embodiment of the method of the present invention;
Figure 4 is a graph showing changes in phosphorus concentration in hot metal during dephosphorization treatment, and Figure 5 is a plan view showing an embodiment of the present invention. ■...High oxygen potential region, 2...Low oxygen potential region, 3. Hot metal, 4. Blowing lance, 5.
...Powder injection, 6. Dust collection foot, 7. Vacuum suction type slag removal device. Time (now) Figure 5

Claims (1)

[Scope of Claims] 1. When dephosphorizing hot metal by blowing a dephosphorizing agent under the surface of the hot iron bath, the molten slag formed on the bath surface after the dephosphorization reaction is A hot metal dephosphorization treatment method characterized by increasing dephosphorization efficiency by continuously removing the agent at the same time as blowing the agent. 2. The method for dephosphorizing hot metal according to claim 1, wherein the dephosphorizing agent is injected at a position eccentric from the vertical axis of the hot metal holding container, and the slag is formed at an opposing eccentric position.