JPH0255485B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for efficiently dephosphorizing molten metal. In recent years, there has been active development of a process in which preliminary dephosphorization and desulfurization are performed at the hot metal stage before charging into the converter, and only decarburization is performed in the converter, thereby reducing the overall processing cost. However, all of the conventional preliminary dephosphorization treatments lead to a drastic drop in the hot metal temperature, and decarburization progresses more than necessary, worsening the cost balance of the entire process, and the optimal method is still unknown. Not developed. Recently, a dephosphorization method has been proposed in which a dephosphorizing agent such as quicklime is added to hot metal to ensure the oxygen efficiency of dephosphorization. There is a method of injecting the molten metal with solid oxygen (simply referred to as solid oxygen), but even if efficient dephosphorization is achieved in this case, as mentioned above, a large drop in temperature of the molten metal due to excessive decarburization and addition of solid oxygen cannot be avoided. , the amount of exhaust gas and heat value of the exhaust gas increase during processing,
Due to the associated increase in exhaust gas treatment equipment costs and decrease in carbon content, the hot metal blending ratio is restricted due to the lack of heat source during converter blowing, and as a result, the supply and demand balance of hot metal and molten steel is drastically disrupted. Many problems are occurring at the same time, including a decrease in the amount of exhaust gas from recovery converters. The present inventors have conducted various experiments and studies on various previously proposed dephosphorization methods that have the above-mentioned problems, and have found that the ratio of gaseous oxygen to solid oxygen has a large effect on the amount of decarburization and the amount of temperature drop of the molten metal. I found out what I was doing. Therefore, we conducted further experiments and used the double tube shown in Figure 1 to release N ₂ and dephosphorizing agent (CaO+) from the outer tube.
When CaF ₂ ) and solid oxygen (mill scale or sintered ore) were injected, dephosphorization progressed while decarburization was suppressed, and when gaseous oxygen was injected, decarburization was accelerated. This means that the reaction at the flash point is gaseous oxygen.
The main effect is to promote the slag formation of CaO, and gaseous oxygen has been shown to have an extremely large effect in promoting the dephosphorization reaction by lowering the flash point temperature through melting and suppressing the decarburization reaction. In addition, simultaneous injection of gaseous oxygen and solid oxygen skillfully mixes the effects of both to locally lower the temperature of the molten metal near the fire point, but reduces the temperature drop of the entire molten metal to the point that it has virtually no effect. I also understood that. These facts indicate that if the temperature at the fire point falls, the dephosphorization reaction of 2 P + 3 CaO + 5 FeO = 3 CaO・P ₂ O ₅ + 5 Fe will be thermodynamically promoted, and the decarburization reaction of C + O = CO will be promoted. It means to suppress. Figure 2 shows the results, where a indicates the amount of temperature drop in hot metal during dephosphorization when the solid acid ratio used during dephosphorization was changed, and when the solid acid ratio exceeds 80 (%), the temperature decreases. The amount of drop is 120 (℃) or more, and when taking into account the variation in hot metal temperature, the hot metal temperature drops to a range that inhibits the smooth flow of hot metal in the hot metal transport vessel and dephosphorization reaction vessel. In addition, b indicates the amount of decarburization during dephosphorization when the solid acid ratio is changed, and the solid acid ratio is 50 (%).
The amount of decarburization increases rapidly. Therefore, it has been found that preliminary dephosphorization of hot metal can be carried out most effectively at low cost and without significantly affecting the production flow by injecting a solid acid ratio in the range of 50 to 80 (%). Therefore, the present inventors further continued experiments to find an appropriate solid-gas-acid ratio based on the amounts of phosphorization and decarburization at each time, and obtained important findings shown in FIG. 3. The diagram is
The results of the above experiments show that in the early stage when the amount of dephosphorization required at the time of treatment is large, the solid acid ratio is set at 50 to 80 (%), although it changes depending on the hot metal temperature, Si content in the hot metal, etc. 65-100 (%) at the final stage when the amount of dephosphorization required is decreasing and dephosphorization is performed while suppressing decarburization.
The intermediate between the two is the result of dephosphorization by blowing together with a dephosphorizing agent at 50 to 100 (%). As is evident in the figure, the dephosphorization rate is 93 (%) and the target phosphorus level is 0.0008.
(%), but the amount of decarburization is only 0.30
(%). This is because as dephosphorization progresses, the decarburization ability increases, and the degree of suppression of decarburization was sufficiently strengthened. The present invention was made based on the above knowledge, and its gist is that quicklime and solid oxygen are blown into hot metal along with an inert gas through the outer pipe of a double pipe, and gaseous oxygen is blown into hot metal from the inner pipe. When dephosphorizing the hot metal, the ratio of solid oxygen to the total of gaseous oxygen and solid oxygen is set at 50-80% at the beginning of the oxygen supply period and at 50-80% at the middle stage.
This is a hot metal dephosphorization method characterized by blowing 100%, 65 to 100% for unseasoned metal, and at least blowing at a higher ratio for unseasoned metal than for middle stage. Examples of the present invention will be described below. Example Hot metal containing the following components (%) was dephosphorized in a refining pot under the conditions shown in Table 1. C4.5~4.8, Si0.05~0.5, Mn0.2~0.5, P0.10~
0.12, S0.02~0.04

[Table] In Table 1 above, total oxygen amount (Nm ³ /t)
is the value in terms of gaseous oxygen, and the solid oxygen is mill scale or/and iron ore or/and sintered ore, and the dephosphorization additive is quicklime or/and fluorite or/and soda ash. Using the pulverized mixture, make an inverted T as shown in Figure 1.
It was blown into the refining pot through a double pipe lance.
Test Nos. 1 to 10 are comparative examples, and Test Nos. 11 and 12 are experimental examples of the present invention. As is clear from Table 1, the solid acid ratio
In blowing tests No. 4 to 7, which were set in the range of 50 to 80 (%), the decarburization amount was 0.30 to 0.48 (%) and the solid acid ratio was 50 (%).
The temperature drop is extremely small compared to the smaller test Nos. 1 to 3, and the temperature drop is 23 to 122 (℃), compared to the test Nos. 8 to 9 where the solid acid ratio is higher than 80 (%). small. In addition, in test Nos. 10, 11, and 12, the solid acid ratio was kept constant throughout the oxygen supply period (No. 10),
This is a comparison of cases where the initial temperature is low and the final stage is high (Nos. 11 and 12), and the latter is clearly more advantageous than the former in both decarburization and temperature drop. Although the above example shows the case of blowing into the refining pot using a double pipe lance, the effects of the present invention can be achieved even when gaseous oxygen, solid oxygen, quicklime, and other additives are simultaneously blown into the refining pot from a single pipe lance. It is exactly the same, and instead of a refining pot, it may be a pig iron mixer or a refining vessel of other shapes. According to the present invention described above, when dephosphorizing the molten metal by simultaneously blowing quicklime, gas, and solid oxygen into the molten metal, the ratio of solid oxygen to the total of gaseous oxygen and solid oxygen is adjusted at least at the initial stage of the oxygen supply period. teeth,
Since the above ratio is 50 to 80 (%), 65 to 100 (%) in the final stage, and 50 to 100 (%) in the middle stage, the temperature of the molten metal can be optimally controlled without changing the dephosphorization efficiency, and Since it becomes possible to minimize the amount of coal, various production constraints, energy losses, and increases in equipment costs can be eliminated, and great economic effects can be obtained.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams of the present invention, and the first
The figure is a schematic diagram of dephosphorizing agent injection using a double-pipe inverted T-shaped lance, Figure 2 is a graph showing the relationship between solid acid ratio, hot metal temperature drop, and amount of decarburization, and Figure 3 is a graph showing the solid acid ratio. It is a graph showing the dephosphorization and decarburization status when changing at the initial, middle, and final stages of blowing. 1...Refining pot, 2...Double pipe inverted T-shaped lance,
3...Inner pipe, 4...Outer pipe, 5...Flash point, 6...Hot metal.

Claims (1)

[Claims] 1. When dephosphorizing the hot metal by blowing solid oxides mainly composed of quicklime and iron oxide together with an inert gas through the outer pipe of a double pipe, and blowing gaseous oxygen into the hot metal from the inner pipe, the gaseous oxygen The ratio of the amount of oxygen contained in the solid oxide to the total amount of oxygen contained in the solid oxide is 50-80% at the beginning of the oxygen supply period and 50-100% during the middle period.
%, unseasoned iron is 65 to 100%, and at least the unseasoned metal is blown at a higher ratio than the middle stage.