JP2000073113A - Desiliconizing method of molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desiliconizing method of a molten iron in which no losses are made in the slag forming, carbon and manganese, silicon in the molten iron can be efficiently oxidized and removed to a value as low as possible, preferably <=0.20%, and the quantity of slag generation is reduced. SOLUTION: A desiliconizing method of a molten iron comprises a first process in which a desiliconizing agent (a substance containing oxygen and a substance containing calcium oxide) is added to the molten iron containing silicon so that the alkalinity of the treated slag is below 0.8, and the quantity of silicon in the molten iron is >=0.20%, and a second process in which the slag generated in the first process is separated and removed, and the desiliconizing agent is added to the molten iron, the alkalinity of the treated slag is >=0.8 to <=2.0, and the quantity of silicon in the molten iron is below 0.20%. More preferably, the slag generated in the second process is reused for the desiliconizing agent in the first process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a desiliconization method for oxidizing and removing silicon in molten iron.

[0002]

2. Description of the Related Art Molten iron produced in a blast furnace or the like contains about 0.3% of silicon. Since silicon is an element that is more easily oxidized than carbon and phosphorus, which are other elements in molten iron, carbon and phosphorus can be oxidized and removed only after silicon is oxidized and removed from molten iron. In addition, silicon oxide generated by oxidizing and removing silicon increases the amount of slag generated, and also acts as an inhibitor of dephosphorization. Therefore, the amount of calcium oxide used to promote dephosphorization also increases, resulting in the generation of dephosphorized slag. There is a problem of increasing the amount. Although dephosphorized slag can be partially used for roadbed materials, etc., a large amount is discarded in landfills, etc., and reducing its generation is an important issue.

[0003] As a countermeasure, desiliconization is widely used as a pre-process of dephosphorization and decarburization of molten iron. In the desiliconization treatment of molten iron, an oxygen source for oxidizing and removing silicon, lime for adjusting the composition of desiliconized slag, and the like are appropriately added to the molten iron, and the mixture is stirred and the reaction proceeds. As the oxygen-containing substance, sinter, iron ore, mill scale, oxygen gas and the like are generally used.

[0004] As a method of adding a desiliconizing agent, a method of adding the molten iron in a tapping gutter of a blast furnace (Japanese Patent Application Laid-Open No. 56-217), a method of adding a molten iron in a transfer container (Japanese Patent Application Laid-Open No. 55-115913), A method of injecting and adding desiliconization flux while covering the molten iron with dephosphorization flux in a furnace for desiliconization and dephosphorization (Japanese Patent Laid-Open No. 62-109911) is disclosed.

[0005] In order to reduce the amount of slag generated in the dephosphorization treatment, silicon in the molten iron is reduced to a value as low as possible, preferably 0.20% or less, ideally 0.10% in the preceding desiliconization treatment.
% Must be oxidized to a value of not more than%. When silicon is oxidized and removed to a low concentration, the oxidation reaction of carbon and manganese in the molten iron that proceeds simultaneously cannot be ignored,
Various problems arise. In other words, intensified slag forming, loss of carbon and manganese (the carbon and manganese to be secured in the molten iron are transferred to the gas phase and slag), and desiliconization reaction efficiency (contributes to desiliconization of the added oxygen source) (A ratio of the oxygen source to be used) decreases. When the efficiency of the desiliconization reaction decreases, the amount of the desiliconizing agent required to obtain a certain amount of desiliconization (silicon concentration before the treatment-silicon concentration after the treatment) increases, and unreacted iron oxide increases. This also increases the amount of desiliconized slag.

There is a method of introducing lime to suppress slag forming. This is because lime increases the basicity of the slag and lowers the surface tension of the molten slag, thereby shortening the life of bubbles and suppressing forming. However, when lime is excessively added, the amount of calcium oxide that does not contribute to the desiliconization reaction increases, so that the amount of slag also increases.

In the desiliconization methods disclosed in the above publications, no consideration is given to suppression of the amount of desiliconized slag.
In addition, appropriate treatment conditions in a low silicon region where the amount of silicon in the molten iron is 0.20% or less have not been clarified.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the slag forming and the loss of carbon and manganese in the desiliconization of molten iron without reducing the efficiency of the desiliconization reaction. Another object of the present invention is to provide a method for efficiently oxidizing and removing silicon to a value as low as possible and reducing the amount of slag generated.

[0009]

SUMMARY OF THE INVENTION Silicon in molten iron is reduced to 0.
When oxidizing and removing to a low concentration of less than 20%, ideally 0.10% or less, the oxidation reaction of carbon and manganese in molten iron, which is a competitive reaction, cannot be ignored. As a result, there were problems such as intensified slag forming, increased loss of carbon and manganese, and decreased efficiency of desiliconization reaction. It can be suppressed by introducing lime as a forming countermeasure, but there is a new problem of increasing the amount of slag, so it was necessary to further clarify the conditions for solving these problems.

In order to efficiently oxidize and remove silicon to a low concentration, it is necessary to reduce the activity of the reaction product silicon oxide as much as possible. When the activity of silicon oxide is high, a reduction reaction of silicon oxide, which is a reverse reaction of desiliconization, tends to occur, and the desiliconization reaction does not proceed. Since silicon oxide is an acidic oxide, the activity of silicon oxide can be reduced by adding a basic oxide such as calcium oxide to increase the basicity of slag.

[0011] Based on this idea, various desiliconization treatment conditions capable of efficiently removing silicon by oxidation, suppressing slag forming, and suppressing loss of oxidation of carbon and manganese in a low silicon region of less than 0.20% were examined. As a result, they have found that these can be achieved by setting the slag basicity to 0.8 or more.

On the other hand, if the basicity of slag increases, the amount of slag during the desiliconization increases proportionately, which causes a problem that the cost required for disposal and reuse thereof increases. Further studies were conducted.

The inventors have noticed that when the target silicon concentration is high, there is not much forming and the slag amount does not increase so much. In a region of 0.20% or more during desiliconization, the slag basicity is 0.8%. I got the idea that it is not necessary to do this. In order to reduce the activity of silicon oxide in slag only in the low silicon region of 0.20% or less, if the slag basicity is set to 0.8 or more, efficient oxidization removal of silicon and slag forming are performed. It was conceived that both suppression of oxidization loss of carbon and manganese and suppression of increase in slag amount at the time of desiliconization treatment can be achieved.

Based on this idea, the desiliconization process in which the target of the silicon concentration after the process is less than 0.20% is a two-stage process, and the first stage is a process of high silicon and low basicity. Thereafter, a method of temporarily suspending the desiliconization treatment, removing the slag, and performing a low-silicon, high-basicity treatment in the second stage was conceived.

In the first-stage desiliconization treatment, since the basicity is low and the amount of lime added can be reduced, the amount of slag generated can be reduced. In the second step, since the silicon concentration is low, by setting the slag basicity to 0.8 or more,
It becomes possible to suppress the forming, the loss of oxidation of carbon and manganese, and the efficient desiliconization.

The inventors have paid attention to the fact that the slag generated in the second-stage treatment has a high concentration of calcium oxide and a low concentration of silicon oxide, so that the concentration of unreacted iron oxide is high.
That is, since the silicon concentration in the molten iron is high in the first step (hereinafter referred to as the first step), the reducing power of iron oxide is strong, and the second step (hereinafter referred to as the second step) in the first step. Since the efficient desiliconization treatment is possible even at a lower basicity, the slag generated in the second step can be recovered and reused in the first step to effectively utilize or reduce and recover the desiliconized slag. With this in mind, the present invention has been completed.

The gist of the present invention resides in the following (1) and (2). (1) An oxygen-containing substance and a calcium oxide-containing substance are added to molten iron containing silicon, and the concentration ratio of calcium oxide and silicon oxide in the treated slag is defined as (weight% CaO) / (weight% SiO ₂ ). A slag having a basicity of less than 0.8 to oxidize and remove silicon in the molten iron to a concentration of 0.20% by weight or more; and separating and removing the slag generated in the first step from the molten iron. After that, an oxygen-containing substance and a calcium oxide-containing substance are added to the molten iron to generate a slag having the basicity of 0.8 or more and 2.0 or less, and to reduce silicon in the molten iron to a concentration of less than 0.20%. A second step of oxidizing and removing the molten iron up to the second step.

(2) The method for desiliconizing molten iron according to the above (1), wherein the slag generated in the second step is used as the oxygen-containing substance and the calcium oxide-containing substance in the first step.

Here, the oxygen-containing substance is a gas containing oxygen, that is, oxygen containing an appropriate amount of pure oxygen or an inert gas, or a substance containing iron oxide, that is, iron ore, sinter, sand iron, mill scale, iron making, or the like. A substance containing steelmaking dust and manganese oxide, that is, manganese ore, etc., is collectively referred to.
The calcium oxide-containing substance refers to quicklime, limestone and the like.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first step of the present invention, an oxygen-containing substance and a calcium oxide-containing substance are added to molten iron containing silicon. Oxygen-containing substances include iron oxides such as iron ore, sinter, iron sand, mill scale, various steelmaking dusts,
Alternatively, an oxide of manganese reacts with silicon in the molten iron to form silicon oxide, and iron or manganese itself becomes a useful substance in the molten iron. Alternatively, these oxygen-containing substances are substances that form slag with the added calcium oxide-containing substance. Oxygen gas (or oxygen-containing gas) may be used as the oxygen-containing substance. Calcium oxide-containing substances include quicklime, limestone and the like.

At the same time as the addition of the oxygen-containing substance, an appropriate amount of the calcium oxide-containing substance is added, and the base defined by the concentration ratio of calcium oxide and silicon oxide in the slag after treatment (% by weight CaO) / (% by weight SiO 2) Adjust to produce a slag with a degree value less than 0.8. As described above, the silicon in the molten iron is oxidized and removed until the concentration becomes 0.20% or more. Here, “until the concentration becomes 0.20% or more” may be 0.20% or a slightly higher value, or the target silicon amount or slag generation amount of the molten iron after the second step treatment. In consideration of the above, a value considerably higher than 0.20% (for example, about 0.25%) may be used.

The reason why the content of silicon in the molten iron after the treatment in the first step is specified to be 0.20% or more is that the silicon is desiliconized to a silicon concentration of less than 0.20% under the low basicity slag in the first step. This is because, if the process proceeds, a stable and efficient desiliconization process becomes impossible due to a decrease in the efficiency of removing silicon by oxidation, an overflow of the slag from the processing vessel due to intensified slag forming, an increase in the oxidation loss of carbon and manganese, and the like.
Preferably it is 0.20 to 0.23%.

The reason that the value of the slag basicity after the treatment in the first step is less than 0.8 is that the value of the slag basicity is 0.8 when the content of silicon in the molten iron during the treatment is 0.20% or more.
Even if it is less than the above, the desiliconization reaction can proceed sufficiently efficiently, and the degree of slag forming and oxidation loss of carbon and manganese can be suppressed to an allowable range. Rather, setting the value of the slag basicity to 0.8 or more under the condition of the silicon concentration unnecessarily increases the amount of the calcium oxide-containing material, which is disadvantageous in terms of cost and increases the amount of slag generated. It is because. Preferably it is 0.7 or less. Although the lower limit is not particularly limited, a practical range in consideration of forming suppression is about 0.4.

The reason why the value of the slag basicity after the treatment in the second step is 0.8 or more and 2.0 or less is that if the value is less than 0.8, the silicon in the molten iron after the treatment is reduced to less than 0.20%. Under such conditions, it becomes impossible to efficiently promote the desiliconization reaction, resulting in intensified slag forming and increased oxidation loss of carbon and manganese.

If the value of the slag basicity in the second step exceeds 2.0, the amount of addition of the calcium oxide-containing substance is unnecessarily increased and the fluidity of the slag is reduced, which is disadvantageous in terms of cost. Slag generation increases. In consideration of cost and slag recycling described below, the preferred range of the slag basicity in the second step is 1.0 to 1.8,
More preferably, it is 1.2 to 1.6.

The desiliconized slag generated in the second step is desirably recycled as the desiliconized slag in the first step. That is, calcium oxide contained in the slag at a high concentration is effectively used as a slag basicity adjuster in the first step, and valuable metal oxides such as iron oxide and manganese oxide contained in the slag are converted into silicon. This is because the molten iron of the first step having a high reducing power can be reduced and recovered, and the amount of slag generated in the entire desiliconization treatment can be reduced.

When this recycling is performed, if the basicity of the recycled slag is less than 0.8, the effect of the slag basicity adjusting agent in the first step becomes insufficient, and the merits of recycling cannot be obtained. The slag basicity after the second step needs to be 0.8 or more.

In both the first step and the second step, it is desirable to stir molten iron and slag in order to increase the reaction rate. Stirring is performed by a conventional method, but it is preferable to select a place (process) suitable for stirring. For example, as the first step, there are a method utilizing the flow of molten iron in a tapping gutter of a blast furnace, and a method utilizing a stirring action when flowing into a receiving vessel in a blast furnace. As a place and a method of the treatment in the first step and the second step, a method in which an oxygen-containing substance and a calcium oxide-containing substance are blown together with a carrier gas into a molten iron carrying container (a torpedo car or a ladle), and a mechanical method using a immersion rotary impeller or the like There are stirring methods and the like. The stirring method in the first step and the second step may be the same method or different methods.

Particularly, in the second step of the present invention, a mechanical method is preferred for the method of stirring the molten iron. The reason is that the large stirring effect and the promotion of the desiliconization reaction by promoting the mass transfer of silicon in the molten iron can be promoted, and the use of gas for stirring does not require slag forming. This is because it is an appropriate method.

The method of adding the desiliconizing agent used in the above treatment is not particularly limited, and any method such as a powder injection method, an upward addition method, and a spraying method can be used.

[0031]

EXAMPLES (Example 1) sinter powder from above the molten iron flowing in the trough of a blast furnace (FeO: 8 wt%, Fe ₂ O _3: 73 wt%, CaO: 9 containing wt%) the process 8.0 kg per target ton of molten iron and 1.0 kg of quicklime were added and dropped together with the molten iron into a torpedo car (a molten iron transporting vessel) to allow the desiliconization reaction of the first step to proceed (hereinafter, the added amount per ton of molten iron) And the amount of slag generated per ton of molten iron is simply expressed as “kg / t”). The stirring of the molten iron in the torpedo car was performed only by the falling of the molten iron.

The average silicon concentration in the molten iron to be processed flowing in the gutter of the blast furnace was 0.35% by weight. The silicon concentration in the molten iron in the torpedo car after the desiliconization treatment is 0.2
1% by weight, slag basicity was 0.6.

After the first step, the torpedo car was tilted and the slag in the torpedo car was removed by a mechanical slag removing device.

In the second step, 7.0 kg / t of the sintered ore powder was added to the molten iron remaining in the torpedo car by an injection method using an immersion lance, and 2.5 kg / t of lump lime was added from above. By adding t, the desiliconization reaction was allowed to proceed.

After completion of the desiliconization treatment in the second step, the silicon concentration in the molten iron in the torpedo car was 0.10% by weight, and the slag basicity after the treatment was 1.4. The above processing is referred to as Example 1 of the present invention, and Table 1 shows the processing contents.

[0036]

[Table 1]

As a comparison with the inventive example 1, comparative examples 1, 2, 3, and 4 were carried out.

Comparative Example 1 is an example in which the slag basicity after the first step is higher than that of Example 1 of the present invention. As the first step, the same sintered ore powder as described above was added to the molten iron in the gutter of the blast furnace at 8.0 kg / kg.
At the same time, quick lime was added 2.5 kg / t upward and dropped together with the molten iron into a torpedo car to advance the desiliconization reaction. The average silicon concentration in the molten iron in the blast furnace gutter was 0.35% by weight. After the completion of the desiliconization treatment, the silicon concentration in the molten iron in the torpedo car is 0.22% by weight, and the slag basicity is 1.3.
Met.

In the second step of Comparative Example 1, sintered ore powder and quicklime were added under the same conditions and in the same manner as in the second step of Inventive Example 1. The silicon concentration in the molten iron after the treatment is 0.10% by weight,
The slag basicity after the treatment was 1.4.

As shown in Table 1, the slag forming was suppressed in the first step of Comparative Example 1 because the slag basicity was high, but the slag amount was 2.2 kg / kg compared to Example 1 of the present invention. t increased.

Comparative Example 2 is an example in which the slag basicity after the treatment in the second step is reduced as compared with Example 1 of the present invention. First
As a process, the above sintered ore powder was added to the molten iron in the gutter of the blast furnace at 8.0 k
g / t and quick lime were added in an amount of 1.0 kg / t and dropped together with the molten iron into a torpedo car to advance the desiliconization reaction. Average silicon concentration in molten iron in blast furnace gutter is 0.35% by weight
Met. After the completion of the desiliconization treatment, the silicon concentration in the molten iron in the torpedo car is 0.21% by weight, and the slag basicity is 0.1%.
It was 6.

After the first step, the torpedo car was tilted and slag was removed by a mechanical slag removing device. Then
To the molten iron in the torpedo car, the same sintered ore powder as described above was injected into the molten iron at a rate of 7 kg / t and lump lime at a rate of 0.3 kg.
The desiliconization reaction was allowed to proceed by addition from above kg / t.

The silicon concentration in the molten iron in the torpedo car after the completion of the second step desiliconization treatment is 0.12% by weight, and the desiliconization amount (silicon concentration before treatment-silicon concentration after treatment) is smaller than in Example 1. The slag basicity after the treatment decreased to 0.5.

As shown in Table 1, in Comparative Example 2, since the slag basicity was low, the amount of slag was reduced by 2.5 kg / t as compared with Example 1 of the present invention, but slag forming was intensified.

Comparative Example 3 is an example in which the slag basicity after the second step is increased to 2.0 or more as compared with Example 1 of the present invention.
As the first step of desiliconization, 8.0 kg / t of the above-mentioned sintered ore and 1.0 kg / t of quicklime are added to the molten iron in the blast furnace gutter, and the resultant is dropped together with the molten iron into a torpedo car to allow the desiliconization reaction to proceed. Was. The average silicon concentration in the molten iron in the blast furnace gutter was 0.35% by weight. The silicon concentration in the molten iron after the completion of the desiliconization treatment was 0.21% by weight, and the slag basicity was 0.6. After the end of the desiliconization treatment in the first step, the torpedo car was tilted and slag was removed by a mechanical slag removal device. Next, as the second step, 7.0 kg / t of the above-mentioned sintered ore powder and 4.0 kg / t of massive quicklime were added to the molten iron in the torpedo car by injection from above,
The desiliconization reaction was allowed to proceed.

The silicon concentration in the molten iron in the torpedo car after the second step was 0.12% by weight, and the amount of desiliconization (silicon concentration before treatment−silicon concentration after treatment) was smaller than that of Example 1 of the present invention, Slag basicity rose to 2.5. In Comparative Example 3, the fluidity of the treated slag was lower than that in Example 1 due to the excessive increase in basicity.

As shown in Table 1, since the slag basicity was high in Comparative Example 3, the slag amount was increased by 2.1 kg / t as compared with Example 1 of the present invention, and the slag forming was almost equivalent.

Comparative Example 4 is an example in which the desiliconization treatment was performed only in a single step. In Comparative Example 4, no treatment was performed in the gutter of the blast furnace, and 15.0 kg / t of sintered ore powder and 6.0 kg / t of massive quicklime were added to molten iron in the torpedo car by injection, and degassing was performed. The silicon reaction was allowed to proceed. The silicon concentration in the molten iron in the torpedo car after the treatment was 0.11% by weight, and the slag basicity after the treatment was 1.4.

In Table 1, a single desiliconization treatment is shown as the first step. In Comparative Example 4, a large amount of the desiliconization agent was added under the condition that the slag basicity was high. The slag forming was increased by 4.0 kg / t from the sum of the first step and the second step.

Example 2 The recycling of the slag generated in the second step was tested as follows. As a first step of the first step, 8.0 kg / t of the same sintered ore powder as in Example 1 was added to molten iron having a silicon concentration of 0.35% by weight in a torpedo car by injection, and 1.0 kg of massive quicklime was added.
/ T was added from above to advance the desiliconization reaction. First
The silicon concentration in the molten iron in the torpedo car after the process was 0.21% by weight, and the slag basicity after the treatment was 0.6.

After the first desiliconization treatment in the first step, the torpedo car was tilted and slag in the torpedo car was removed by a mechanical slag removing device. As the second step of desiliconization in the molten iron in the torpedo car, 7.0 kg / t of the same sintered ore powder as in Example 1 was added by injection, and 2.5 kg / t of massive quicklime was added from above, The desiliconization reaction was allowed to proceed.

The silicon concentration in the molten iron in the torpedo car after the second step was 0.10% by weight, and the slag basicity after the treatment was 1.4. The slag was collected and recycled for the next silicon removal treatment of molten iron flowing in the blast furnace gutter.

As the second step of the first step, 5.5 kg of the above-mentioned sintered ore was added to the molten iron flowing in the gutter of the blast furnace by upward addition.
At time t, 4.0 kg / t of the recovered slag was added and dropped together with the molten iron into a torpedo car to advance the desiliconization reaction. The average silicon concentration in the molten iron in the blast furnace gutter was 0.35% by weight. After the completion of the desiliconization treatment, the silicon concentration in the molten iron in the torpedo car was 0.20% by weight, and the slag basicity was 0.6.

Thereafter, as in the second and subsequent times, five treatments were carried out in the same manner as in the second time, by using the recovered slag from the previous second step in the first step. The average of the processing conditions of the second to fifth times is referred to as Invention Example 2. The degree of forming in the first step and the second step of Inventive Example 2 was equivalent to that of Inventive Example 1.

As shown in Table 2, in Example 2 of the present invention, part of the slag in the second step was recycled and used for the next desiliconization treatment.
It decreased by 3.4 kg / t from the sum of the step and the second step.

[0056]

[Table 2]

Example 3 The following test was conducted to investigate the desiliconization efficiency by the stirring method. In the first step, 8.0 kg / t of sintered ore powder is added to molten iron having a silicon concentration of 0.35% by weight in a torpedo car by injection, and lump of quicklime is added from above 1.0 kg / t to remove silicon. The reaction was allowed to proceed. The silicon concentration in the molten iron in the torpedo car after the first step was 0.21% by weight, and the slag basicity after the treatment was 0.6.

After the first step, the torpedo car is tilted,
The molten iron and slag were transferred to a hot metal pot, and the slag in the hot metal pot was removed by a mechanical slag removing device.

In the second step, 7.0 kg / t of sintered ore powder and 2.5 kg / t of lump lime are added to the molten iron in the hot metal ladle, and the impeller is immersed in the molten iron and rotated. The desiliconization reaction was allowed to proceed while the mixture was stirred. The silicon concentration in the molten iron in the hot metal ladle after the second step was 0.08% by weight, and the slag basicity after the treatment was 1.3. This is described as Invention Example 3.

Table 3 shows Examples 1 and 3 of the present invention. As shown in Table 3, Example 3 of the present invention in which the second step was performed by a mechanical stirring method was Example 1 of the present invention in which sinter ore powder was added by powder injection and limestone was just introduced from above.
The amount of desiliconization could be further increased with the same amount of desiliconization agent.

[0061]

[Table 3]

[0062]

According to the present invention, it is possible to improve the efficiency of desiliconization to a low silicon region having a silicon concentration of 0.2% or less, reduce the forming, and reduce the loss of carbon and manganese in the pretreatment of molten iron before steelmaking refining. In addition, the amount of generated slag can be significantly reduced.

Claims (2)

[Claims] 1. An oxygen-containing substance and a calcium oxide-containing substance are added to molten iron containing silicon, and the concentration ratio of calcium oxide and silicon oxide in the treated slag (weight% Ca
O) / (wt% SiO ₂ ) has a basicity of 0.8
Less than 0.20 of silicon in the molten iron
A first step of oxidizing and removing to a concentration of not less than% by weight;
After separating and removing the slag generated in the process from the molten iron, an oxygen-containing substance and a calcium oxide-containing substance are added to the molten iron,
A second step of producing a slag having a basicity of 0.8 or more and 2.0 or less and oxidizing and removing silicon in the molten iron to a concentration of less than 0.20%. Method. 2. The method according to claim 1, wherein the slag generated in the second step is used as the oxygen-containing substance and the calcium oxide-containing substance in the first step.