JPH055115A - Method for pre-treating molten iron - Google Patents

Abstract

PURPOSE:To restrain the development of slopping and to execute desiliconizing and dephosphorizing treatments at the same time by changing a blending ratio of desiliconizing agent, i.e., raising CaO ratio and lowering mill scale ratio, at the time of executing pre-treatment to molten iron in a vessel of torpedo car. CONSTITUTION:At the time of executing the pre-treatment to the molten iron ion the vessel of torpedo car 3, by blending 30-40% CaO, 3-10% CaF2 and 50-65% oxidizing agent of mill scale, etc., the pre-treatment is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for blending raw materials for a desiliconizing agent and a method for operating desiliconization / dephosphorization, particularly when performing hot metal pretreatment in a torpedo car container.

[0002]

2. Description of the Related Art In a conventional hot metal pretreatment method, as shown in FIG. 5, the desilvering treatment 4 and the dephosphorization / desulfurization treatments 9 and 11 are clearly separated and independent in equipment and treatment process. In particular, in the case of de-silting, (I) de-silvering in a blast furnace casting floor and (II) de-silvering in the container of the torpedo car 3 are typical processes. There are different container processes such as 16, and various combinations of processes.

Here, the system with the lowest equipment cost for a small amount of treatment is the method (II), and in a factory that already has a torpedo car desulfurization facility, a desilvering and dephosphorization facility is required by modifying the injection tank and injection lance. Can be modified to

The treatment method is simple, and when the hot metal 13 is injected into the torpedo car 3, blast furnace slag exists on it.
Therefore, through the injection lance 6, gaseous oxygen
The actual state is that hot metal pretreatment is performed by blowing an oxidizing agent such as mill scale and a flux of CaO, CaF ₂ or the like into the hot metal using a carrier gas.

[0005]

As described above, conventionally, in the injection of oxygen and flux by the injection lance in the container such as a torpedo car, the injection and the swinging and forming of the hot metal and slag cause the outside of the torpedo car. A phenomenon that erupts occurs and this is called sloping.

This sloping causes not only hot metal loss, but also slag hot metal adhesion to the torpedo car, deposition on the railroad track, and in the worst case, an inoperability of the torpedo car. As a result, slag and hot metal removal and cleaning work occurs, which impedes production.

In order to solve such a problem, the present invention considers the following causes of sloping and provides the most efficient simultaneous desilvering / dephosphorization treatment method.

[0008]

[Means for Solving the Problems] As a way of thinking about the occurrence of slopping, slopping is caused by slag forming, and when the forming height exceeds the height of the freeboard in the torpedo car, slopping occurs.

The forming height is determined by the balance between the bubble generation rate and the bubble disappearance rate.

The bubbling rate depends on the flow rate of gas passing through the slag layer, and is mainly determined by the CO gas generation rate. The defoaming rate depends on the bubble life and is mainly determined by the slag composition.

[0011]

[Table 1]

The effect of the molten metal level on the slopping occurrence rate is that the sloping frequency increases when the molten metal level becomes high and the freeboard becomes small, while when the molten metal level becomes low, sloping does not occur. From this, it is estimated that the expansion rate of slag foaming, which is considered to be the main cause of sloping, has both a continuous distribution and an upper limit value. Therefore, within a certain range of operating conditions, it is possible to reliably reduce the sloping occurrence rate by expanding the freeboard. Also, if enough freeboards are secured, it is possible to operate with zero sloping rate. However, in general, securing an excessively wide freeboard tends to increase equipment costs and decrease productivity, so it seems that it is not a good idea to seek a solution for sloping suppression measures only for freeboard expansion. ..

The effect of processing temperature on the sloping rate is shown in FIG. The sloping frequency increases significantly when the processing temperature is high. The reason for this can be considered as follows.

When the processing temperature is high, other elements shown below are also inclined to the sloping inducing side in many cases.
Therefore, a clear correlation is observed between the sloping occurrence rate and the processing temperature. In the hot metal pretreatment process where it is desired to secure a heat source, the treatment temperature cannot be intentionally lowered, so it is not directly linked to the suppression measure, but the treatment temperature seems to be useful for the most efficient treatment conditions.

[0015]

[Table 2]

FIG. 2 (b) compares the temperature drop ΔTsi during the desilvering process between the conventional method and the method of the present invention, but the method of the present invention is the most effective as a measure for suppressing the occurrence of sloping. It is clear that the conditions are selected.

The most important factor to consider further is the slag composition.

FIG. 3 shows the relationship between the phenomenon of sloping and the slag composition.

Basicity CaO / SiO ₂ is 0.7 or more (T
-Sloping does not occur in the region where Fe%) is 10% or less. It is clear that the conventional method tends to cause sloping because many of them are out of this region.

In the method of the present invention, as a method for controlling the slag composition within this region, the method of mixing the raw materials for the silica removing agent is changed.

CaO 25 → 30% or more and 40% or less, C
aF ₂ 0 → 3% or more and 10% or less, mill scale 75
→ 65% or less and 50% or more, and the slag composition during treatment is high basicity CaO / SiO ₂ > 1, (T · Fe%) <10%
In addition, the operating condition is such that the oxygen supply rate is further reduced and the CO gas generation rate is minimized. Since this blending ratio approximates to the original dephosphorization agent, the dephosphorization reaction also progresses as the temperature during treatment decreases.
Sloping is less likely to occur.

[0022]

EXAMPLES Table 3 shows examples of the results of the conventional method (II), and Table 2 shows examples of the present invention.

Table 3 shows [Si] 0.50% [P] 0.08
Hot metal having a content of 0% [S] of 0.020% at 1420 ° C., CaO of 10.2 kg / t, and mill scale of 29.8.
Desulfurization was performed with a mixed powder of kg / t and an injection gas oxygen of 2.2 Nm ³ / t, and [Si] 0.20%, [P]
0.080%, [S] 0.020% 14
20 ° C. hot metal was obtained.

Thereafter, as shown in the processing method in FIG. 1, de- [P] [S] processing is performed, and [Si] 0.02%, [P]
13 with 0.015% and [S] 0.005% 13
The hot metal of 04 degreeC was obtained.

However, as shown in FIG. 6, there was no temperature drop during the de-Si [Si] treatment, but sloping occurred, and the process was interrupted at the stage of 40 kg / t injection of the desiliconized material, and the process was terminated to shift to the slag processing. ..

Table 4 shows [Si] 0.50%, [P] 0.0
1412 ° C with 80%, [S] 0.020%
Powder of CaO 16 kg / t, CaF ₂ 3 kg / t, mill scale 36 kg / t and 2.2 Nm ³ / t
Injection of oxygen gas to remove [Si] 0.15%, [P] 0.050 without generating sloping at all.
%, [S] 0.020%, and 1372 ° C. hot metal was obtained.

[0027]

[Table 3]

[0028]

[Table 4]

[Si] 0.02% [P] 0.015% [S] is then determined by the processing method and temperature transition shown in FIGS.
Hot metal having a content of 0.005% at 1296 ° C. was obtained without any sloping during the dephosphorization treatment.

In FIG. 1, 1 is a blast furnace, 2 is a casting floor trough, and 3
Is a torpedo car, 4 is a silica removal treatment, 5 is a silica removal agent, 6 is an injection lance, 7 is gaseous oxygen, 8 is waste sludge treatment,
9 is a dephosphorization treatment, 10 is a dephosphorization agent, 11 is a desulfurization treatment, 1
2 is a desulfurizing agent, 13 is hot metal, 14 is a hot metal ladle, 15 is a decarburizing treatment, and 16 is an upper-bottom blowing converter.

[0031]

As described above, the composition of the slag composition during treatment is changed to a high basicity and a low oxygen supply rate by changing the composition of the desulfurizing agent in the conventional desilvering treatment to increase the CaO ratio and decrease the mill scale ratio. As an operating condition, the occurrence of sloping is suppressed, and the light dephosphorization reaction proceeds at the same time as the desilvering treatment to reduce the load of full-scale dephosphorization treatment after slag, and the hot metal pretreatment facility is established by the torpedo car system alone. Can be made

According to the present invention, it is an object of the present invention to provide an industrially advantageous technique capable of achieving a large reduction in equipment cost, stable operation, and economic effects.

[Brief description of drawings]

FIG. 1 is a diagram showing a hot metal pretreatment method according to the present invention.

FIG. 2A is a diagram showing a relationship between a sloping occurrence phenomenon and a processing temperature. (B) is the temperature drop during the silica removal treatment according to the conventional method and the present invention.
The figure which shows Tsi.

FIG. 3 is a diagram showing a relationship between a sloping phenomenon and a slag composition.

FIG. 4 is a diagram showing an example of temperature change and sloping suppression during hot metal pretreatment according to the present invention.

FIG. 5 is a diagram showing a conventional hot metal pretreatment method.

FIG. 6 is a diagram showing an example of temperature change and sloping occurrence during hot metal pretreatment by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Blast furnace 2 ... Casting basin 3 ... Torpedo car 4 ... Desulfurization treatment 5 ... Desulfurization agent 6 ... Injection lance 7 ... Gaseous oxygen 8 ... Waste treatment 9 ... Dephosphorization treatment 10 ... Desulfurization agent 11 ... Desulfurization treatment 12 ... Desulfurizing agent 13 ... hot metal 14 ... hot metal pot 15 decarburization 16 ... top-bottom blowing converter

Claims (1)

Claims: 1. When performing hot metal desiliconization in a container such as a torpedo car, CaO is 30 to 40% and CaF ₂ is 3-1.
0%, oxidizer such as mill scale is added to 50-65%, and the slag composition during treatment is CaO / SiO ₂ > 1, (TF
e%) <10%, and further reduce the oxygen supply rate,
A pretreatment method for hot metal, characterized in that the dephosphorization reaction is simultaneously advanced with the temperature decrease during the treatment to make it possible to suppress the sloping by making the operating conditions to minimize the CO gas generation rate.