JPS60181212A - Method for desiliconizing molten iron - Google Patents

Abstract

PURPOSE:To prevent perfectly the foaming of slag and to minimize the consumption unit of powder by feeding iron oxide gas CaO into melten iron in a prescribed with an O2 enriched gas as a carrier gas. CONSTITUTION:Powder contg. oxide and CaO is fed into molten iron with an O2 enriched gas contg. >=50vol% O2 as a carrier gas. At this time, the solid ratio (r), that is, the ratio of the amount of the powder to the amount of the O2 enriched gas is adjusted to 4-50g/Nl, and the ratio (SIGMAO2/CaO) of O2 in the O2 enriched gas and O2 in iron oxide in the powder to the amount of CaO in the powder is adjusted to 0.2-0.75Nl/g. The ratio SIGMAO2/CaO (Nl/g) is calculated by the equation (where %O2 is the vol% of O2 in the O2 enriched gas, %I, O is the wt% of iron oxide in the powder %CaO is the wt% of CaO in the powder, and %O is the wt% of O2 in the iron oxide).

Description

Detailed Description of the Invention The present invention completely eliminates the bubbling phenomenon of slag (referred to as slag foaming), minimizes the basic unit of powder used and the temperature drop during processing, and This invention relates to a desiliconization method for hot metal that can reduce oxidation loss of valuable metals.

When dephosphorizing hot metal before being subjected to decarburization refining, it is usual to carry out a desiliconization treatment in advance in order to efficiently perform the dephosphorization. More specifically, when the St concentration in the molten pig iron is 0.
It is preferable to perform a desiliconization treatment until the content is 2% or less, preferably 0.05% or less, and then dephosphorize.

In the conventional desiliconization treatment, treatment vessels such as blast furnace cast-floor troughs, torpedoes, and steel dowels are used. Various treatment methods such as
Iron oxide containing % of CaO is used. However, no matter which formulation is adopted, one of the common problems of conventional methods is slag forming. In other words, the slag foams during the desiliconization process. Conventionally, for this slag forming.

The following operational problems were always involved.

For example, when carrying out desiliconization treatment in a gutter, the desiliconizing agent introduced or projected into the gutter turns into slag in the gutter, and the desiliconization reaction also progresses, but the desiliconizing agent that has become a slag is transferred to a torpedo or ladle along with hot metal. The desiliconization reaction further progresses within this container due to the energy of this fall.

However, the slag accumulated in the vessel causes foaming, and a situation arises in which it is necessary to limit the amount of hot metal that is to be received in the vessel. usually.

Due to this slag forming, only about 70 to 80% of the intended amount of pig iron can be received in the vessel. As a result, the efficiency of transporting the hot metal is reduced and a large number of transport containers are required, and the temperature drop of the hot metal increases, resulting in a loss of thermal energy. Furthermore, in the event that slag overflows from a transport container and flows out of the container, it will take a great deal of effort and time to dispose of it afterwards, causing a major hindrance to operations. In order to prevent this from occurring, the amount of pig iron received has been further reduced in view of safety, and the amount of desiliconizing agent used has been restricted, which has become an obstacle to carrying out sufficient desiliconization treatment. are doing.

Similar problems also occur in the case of the so-called injection method, in which a desiliconizing agent is added by blowing it into hot metal in a transport container such as a tobeed. In fact, with this formulation, the flow of the slag is greater, so the degree of slag foaming is increased, and the unit consumption of the desiliconizing agent is significantly limited. Therefore, although the injection method is superior in terms of reaction efficiency, it is no exaggeration to say that prevention of slag forming is a first priority issue in order to desiliconize to the desired silicon level.

The basic cause of such problems lies in the composition of the desiliconizing agent used. In other words, in the conventional desiliconization treatment, it is necessary to ensure a sufficient oxygen source to oxidize the Si in the hot metal, and in addition, from the viewpoint of flux slag formation and slag removal. Also, Si in hot metal
oxidizing agents (e.g. iron ore, mill scale, iron sand).

High content of iron oxide (iron oxide) such as sintered ore powder
Usually, b) is mixed in an amount of about 10 to 20% at most, and the basicity (CaO/5iO2) of the treated slag is adjusted to around 1. However, in such a low basicity slag, it is not possible to separate the silicates in the slag, and the slag becomes vitrified. Therefore, CO gas generated by the reaction between the oxygen source in the slag and carbon in the hot metal or precipitated carbon contained in the slag is trapped in the slag, causing a significant bubbling phenomenon. In addition to this slag foaming, the oxygen potential on the slag side increases under such low basicity slag.

A resulfurization phenomenon was also commonly observed, and manganese, which is a valuable metal, was also oxidized, and demanganization reactions of about 70 to 120% of the amount of silicon removed were common.

These problems can basically be alleviated by increasing the CaO content in the desiliconizing agent used, but as mentioned above, with conventional formulations, the slagability deteriorates and the reactivity increases. In addition to this, the increase in CaO causes a relative decrease in oxygen sources, which reduces the oxidizing power for silicon oxidation and increases the cost of desiliconizing agents. The disadvantages such as these are greater, and in particular, the widely practiced desiliconization method in the gutter avoids increasing CaO. In addition, in the method of injection using an inert gas at a high solid-gas ratio, C
Increasing aO means that the amount of oxidizing agent for silicon oxidation is insufficient, so even if CaO is added, the amount is kept to an extremely low level.

The present invention was made with the aim of solving two or more of the various problems in conventional desilicon treatment, particularly problems such as slag forming, temperature drop during treatment, and oxidation loss of valuable metals such as manganese and iron. It is. For this purpose 1
As a result of numerous tests and studies, the inventors of the present invention found that instead of the conventional method of injecting a desiliconizing agent using an inert gas as a carrier gas, an oxygen-enriched gas was used as a carrier gas at a predetermined blending ratio. It was discovered that the aforementioned problems of conventional desiliconization methods could be completely eliminated by injecting the powder, and a completely new desiliconization treatment method for hot metal could be established. That is, the present invention is as described in the claims.

A method for desiliconizing hot metal, in which powder containing iron oxide and CaO is supplied below the surface of hot metal using oxygen-enriched gas as a carrier gas.

Oxygen concentration (%02) in oxygen-enriched gas is 40 Vo1%
that's all.

The solid-gas ratio (γ) of powder and oxygen-enriched gas is 4 to 50 g/N.
j! .

and the ratio (Σ02/Ca0) of the total amount of oxygen, which is the addition of the amount of oxygen in the oxygen-enriched gas and the amount of oxygen in iron oxide, to the blending ratio of CaO in the powder (Σ02/Ca0) is 0.2 to 0. 75N j27
g.

It is characterized by the following.

however.

(%Cab) , and in this formula.

(%02): Oxygen concentration in carrier gas (Vo1%).

(%1.0): Iron oxide blending ratio in powder (11t%)
.

(%Cab): CaO blending ratio in powder (+<1%).

(%O) Oxygen content (wt%) in iron dioxide.

γ: Ratio of powder to carrier gas (solid-gas ratio: g/Nβ).

represents.

The present invention will be explained in detail below.

The desiliconization method of the present invention is a method in which powder containing iron oxide and CaO is injected using an oxygen-enriched gas as a carrier gas, and the basic feature is that this oxygen-enriched gas is used as a carrier gas. However, at that time, the oxygen concentration in the oxygen-enriched gas (%02), the supply ratio of the oxygen-enriched gas (gear gas) and the powder (solid-air ratio), and the total amount of oxygen supplied versus CaO. At the same time, by appropriately controlling the ratio (Σ02/Cab), it is possible to completely eliminate slag forming and at the same time to achieve extremely highly efficient desiliconization. The range of this condition is illustrated below.

It is shown as in FIG. However, in FIG. 1, the oxygen concentration (%02) in the oxygen-enriched gas is shown for the case of 80 Vo1% on the 1st generation 0 front side.

The reason why each condition is regulated as described above will be clear from the various effects shown in the examples below, but the outline thereof will be explained as follows.

The present inventors conducted numerous experiments in which powder containing iron oxide and CaO was injected into hot metal using oxygen-enriched gas as a carrier gas.As a result, the range in which slag forming occurs or does not occur is Basically Σ0
We found that it can be determined by 2/CaO. That is, Ca0 with respect to the total amount of oxygen supplied to hot metal
This means that the formation behavior of forming can be understood in a unified manner based on the O ratio. According to the inventors' experiments, Σ02/C
It was found that when the aO ratio exceeds 1.0, slag foaming always occurs, and when it is less than 0.75, it does not occur at all. Moreover, this Σ02'/CaO ratio is 0.8 to 0.
At level 9, the silicon concentration before treatment (hereinafter, (%S
When the content (denoted as t) is about 0.5% or more, slag forming may occur. This is the reason why the upper limit of the Σ02/CaO ratio is set to 0.75.

11 On the other hand, when the Σ02/CaO ratio is decreased, that is, when the amount of CaO is increased relative to Σ02, the desiliconization and oxygen efficiency (hereinafter referred to as η?r; this η?r is Δ[%Si)]
/Σ02) decreased. The situation is shown in Figure 2. Σ02/C as seen in Fig. 2
η2r shows the maximum value when the aO ratio is approximately 0.5 to 0.6, and when the Σ02/CaO ratio is lower than this, the desiliconization and oxygen efficiency rapidly decreases, and the Σ02/C
When the aO ratio is lower than 0.2, the oxygen efficiency decreases to such an extent that effective desiliconization is no longer possible, so Σ02 /
The CaO ratio needs to be 0.2 or more.

Next, the reason why the solid-gas ratio (T) is set to 4 to 50 is to suppress decarburization and η? This is due to the fact that r is regulated to an optimal value. That is, if γ is small, that is, if the flow rate of the carrier gas is increased unnecessarily, the decarburization reaction will increase. The aim of desiliconization treatment of hot metal is to oxidize silicon preferentially while suppressing decarburization, but making γ too small goes against this purpose. On the other hand, γ
If the amount of powder is increased needlessly, that is, the amount of powder relative to the amount of carrier gas is increased, the amount of gas 02 necessary for the reaction will decrease, resulting in a decrease in the Σ02/CaO ratio (increasing the basicity). , η will be reduced. When (%Ca○) in the powder is 30 to 40%, the maximum γ required to give the optimum value of Σ02 /CaO ratio of 0.4 to 0.5 is set as 5.
This is why it was set to 0.

Regarding the oxygen concentration (%02) in the carrier gas, the purpose of the present invention can be achieved even with pure oxygen, but considering the prevention of erosion of the blowing nozzle and safety, the oxygen concentration in the carrier gas is not practical. For operational purposes, it is preferable to keep the voltage to 90 Vo1% or less. , and at least 40 Vo1% to obtain the effect of powder blowing with oxygen-enriched gas of the present invention.
As mentioned above, an oxygen concentration of preferably 50Vo1% or more is required. Note that when powder is injected below the surface of hot metal using such an oxygen lynching carrier gas.

Although there is a concern about the problem of erosion of the injection nozzle, it has been found that, contrary to expectations, suitable injection can be achieved even when using a refractory single tube nozzle 3. That is, r! ! The heat of reaction caused by the enriched gas is considerably offset by the latent heat of the powder and the heat taken away by sensible heat, and due to this heat taken away, even if the nozzle is made of a refractory single tube, the tip of the nozzle contains the metal content of the hot water. It was found that a hollow solidified shell was formed, which served to effectively protect the nozzle refractory. On the contrary, when the oxygen concentration in the carrier gas is lowered, an excessive amount of coagulated shells may be produced, and on the contrary, a situation may occur where effective blowing cannot be performed. Therefore, in order to carry out effective injection without erosion of refractories, it is better to maintain the oxygen concentration in this oxygen-enriched gas at a high level rather than at a low level from the viewpoint of actual operation of the method of the present invention. This is desirable.

The method of the present invention carries out powder blowing under the above-mentioned compounding conditions, but even if these compounding conditions are adopted, if this is carried out by the scene addition method or top blowing method, The present inventors4 have experimentally confirmed that the slag has poor slagability and reaction efficiency. That is, in the method of the present invention,
It is necessary to inject under this mixing condition under the hot metal scene.

Figure 3 shows the relationship between the powder consumption rate before treatment [%St) and the powder consumption rate when injected below the hot water surface according to the method of the present invention. This is the amount of powder necessary to desiliconize [%St] down to 0.05%. Also, this figure 3 shows 45% as a powder.
Using Cab-55% mill scale, solid-air ratio γ = 10
Under , (%02) is 100.80.50Vo1%
The results are shown for three levels. This is Σ
02'/CaO ratio, respectively.
．． 75.0.42.0.31.

As seen in the results in Figure 3, the powder consumption rate required to obtain a desiliconization amount of 0.4% is less than 25 kg/ton, and this powder consumption value was not achieved by the conventional method. The standard was so low that it was impossible to do so. Therefore, although the CaO content ratio seems to be high in the method of the present invention, the overall basic unit amount of powder may be significantly lower. In addition, in conventional desiliconization methods, when desiliconization reaches a level of [%St) of 0.215 to 0.15%, the desiliconization efficiency usually decreases significantly, which is not a serious problem. Although it has been difficult to desiliconize to a level lower than this, the method of the present invention can efficiently desiliconize down to [%Si] of 0.05%. This can significantly reduce the burden of subsequent dephosphorization treatment.

The structure and effects of the nine methods of the present invention will be specifically illustrated below using Examples. The processing conditions and processing results of each example are summarized in Table 1 below.

Example 1 This example is a comparative example of scene addition.

20%Ca 0-80% sintered ore desiliconizing agent 40 kg/
1 was added at once to 170 kg of hot metal at 1340°C. Then, metering gas was introduced at a flow rate of 40 N R/min through a porous brick attached to the bottom of the container to stir the bath. Approximately 3 minutes after the addition of the powder, the powder completely turned into slag and the desiliconization reaction proceeded, but after 9 minutes, a significant foaming phenomenon occurred. This thicker foam has a bath depth of 400mm.
The distance reached 250mm.

Example 2 This example is a comparative example using only oxygen gas.

5O pure oxygen gas is added from the bottom of the furnace to 170 kg of hot metal.
A desiliconization experiment was conducted by blowing Nβ/min. After pure oxygen injection, a well-flowing slag was formed on the scene. The slag started forming approximately 20 minutes after the start of blowing. The result was significant oxidation loss of manganese.

Example 3 This example is a comparative example that does not use CaO.

Mill scale was blown into 170 kg of hot metal using pure oxygen as a carrier gas from the nostle at the bottom of the furnace.

The oxygen gas flow rate is 80 Nl/min + the mill scale supply rate is 500 g/min. Significant forming occurred about 6 minutes after the start of the experiment, and the forming height reached about 300 mm with respect to the bath depth of 400 mm. Also, the oxidation loss of manganese was significant.

Example 4 This example is a comparative example in which the Σ02/CaO ratio exceeds the range of the present invention.

7 20% Ca from the furnace bottom nozzle for 170 kg of hot metal
O-80% sintered ore powder was heated to 80 Nj of pure oxygen! /
Bottom-blowing injection was performed at a blowing rate of 360 g/min using min as the carrier gas. Significant foaming occurred 12 minutes after the start of the experiment. Since the forming height exceeded 400 mm of freeboard, slag had to be removed frequently.

Example 5 This example is also a comparative example in which the Σ02/CaO ratio exceeds the range of the present invention.

25% Ca from the furnace bottom nozzle for 170 kg of hot metal
0 = 75% mill scale powder in pure oxygen 80N
Bottom blow injection was performed at a blowing rate of +450 g/m+n using β/min as a carrier gas. Significant foaming occurred 11 minutes after the start of the experiment.

Example 6 A powder consisting of 50% Ca and 0-50% mill scale was collected from a nozzle at the bottom of a vessel using 170 kg of hot metal.

80νo1%02-20 Vo1%N2 oxygen enriched gas 8ONn/min as carrier gas, 500 g/min
Bottom blow injection was performed at a blowing speed of min8.

No forming occurred. Moreover, the produced slag was in a molten state and had relatively good fluidity.

Example 7 Targeting 170 kg of hot metal, 40% from the furnace bottom nozzle
Powder consisting of Ca 0-55% mill scale-5% CaF2 was mixed with oxygen enriched gas of 80 Vo1%02-20 Vo1%N2 8ONj! /n+in was used as a carrier gas, and bottom-blown injection was performed at a blowing rate of 400 g/min. No foaming occurred at all, and a slag with low fluidity was formed.

Example 8 170 kg of hot metal was subjected to CaO from the furnace bottom nozzle.
A bottom-blowing injection was performed using pure oxygen 8ON1/min as a carrier gas. Although no foaming was observed, the generated slag was in the form of a powdery solid, and much of it adhered to the furnace wall.

Example 9 Targeting 170 kg of hot metal, 40% from the furnace bottom nozzle
19 Powder consisting of Ca 0-50% mill scale-10% CaF2, 80 Vo1%02-20 Vo1%N2
Bottom-blown injection was performed at a blowing rate of 350 g/min using 80 N l /min of oxygen-enriched gas as a carrier gas. No foaming occurred and a slag with excellent fluidity was formed.

The processing conditions and processing results of Examples 1 to 9 above are summarized in Table 1.2 In the case of the method of the present invention, there is no slag forming, and the franks consumption rate is as low as 20 to 25 kg/ton ( The desiliconization amount (Δ[%St) ) reaches approximately 0.4% under the desiliconization agent consumption (unit of desiliconization agent), and the desiliconization amount (%Si) in the hot metal after treatment reaches 0.05% or less. I know it will happen.

Furthermore, the amount of manganese removed was small, and resulfurization did not occur, but rather there was even a tendency for desulfurization, and it is clear that the desiliconization treatment can be carried out very effectively.

84- 21

[Brief explanation of the drawing]

Figure 1 shows that the oxygen concentration (%02) in the carrier gas is 80
The figure which shows the condition range of the desiliconization method of this invention showing the relationship between Σ02/CaO and solid-gas ratio γ when Vo1%. Figure 2 is a diagram showing the relationship between Σ02/CaO and desiliconization and oxygen efficiency η2r, and Figure 3 is a diagram showing the relationship between [%Si] and [%5i] before treatment.
) is a diagram illustrating the relationship between the powder consumption rate required for desiliconization to -0.05% and the pre-treatment [%Si] based on the oxygen concentration in the carrier gas. 1 day: 1 yen Figure 1 Figure 2 ΣOv/'CaO (Nl/g) Figure 3 Before treatment [ChiSi]

Claims (1)

[Claims] Solid iron oxide and Ca using oxygen-enriched gas as a carrier gas.
A method for desiliconizing hot metal in which powder containing O is supplied below the surface of the hot metal. Oxygen concentration (%02) in oxygen-enriched gas is 40 Vo1%
that's all. The solid-gas ratio (γ) of powder and oxygen-enriched gas is 4 to 50 g/N.
C Toshi. In addition, the ratio of the total oxygen amount (Σ02), which is the sum of the oxygen content in the oxygen-enriched gas and the oxygen content in iron oxide, to the blending ratio of CaO in the powder (Σ02/Cab) is 0.2 to 0.2. 0.75
Ni! /g. A method for desiliconizing hot metal characterized by: however. The ratio of Σ02/CaO (N#/g) is a quintic equation. (%02) /γ + (%1.0) 701%). (%1.0): Iron oxide blending ratio ht% in powder) 5 (
%Cab): CaO blending ratio (wt%) in powder. (%O): Oxygen content (wt%) in iron oxide. γ: Ratio of powder to oxygen-enriched gas (solid-gas ratio: g/Nβ). represents.