JP2017206740A - Method for reducing iron ore - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing iron ore where iron ore is reduced at high efficiency, thus the optimization of a molten iron temperature, the improvement of dephosphorization efficiency and the reduction of iron loss are made possible.SOLUTION: Provided is a method for reducing iron ore in converter type molten iron preliminary treatment, including: the first step where the basicity of slag 11 in a converter 10 is controlled to 0.5 to below 1, and also, the viscosity of the slag 11 is controlled to 0.15 Pa s or lower, and iron ore is charged inside the converter 10; and the second step where lime-based raw material is charged inside the converter 10 to increase the basicity of the slag 11 into 1 to 1.5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a converter refining method in the manufacture of steel products, and more particularly to a method of reducing iron ore in a converter-type hot metal pretreatment for removing Si and removing P.

When converter-type hot metal preliminary treatment is performed, iron ore, dust, mill scale, etc. should be put into the hot metal as solid iron oxide as a coolant in order to adjust the hot metal temperature suitable for de-P (dephosphorization). Is common.
For example, Patent Document 1 introduces auxiliary raw materials such as calcined lime into a first converter charged with hot metal, and after adjusting the basicity of slag to 1 to 4, starts blowing. Iron ore was added and demetalization blowing was carried out while adjusting the hot metal temperature to 1250 to 1400 ° C. After the completion of this blowing, dephosphorized iron was removed from the first converter, A method for carrying out the main blowing by charging a converter is disclosed.
In Patent Documents 2 and 3, a solid oxygen source (iron ore, sintered ore, mill scale, etc.) for all oxygen is used to ensure the reaction interface area between the slag and the molten metal and the hot metal temperature necessary for de-P. ), The method of reducing the concentration of P in the hot metal and making the general-purpose steel reliably produced by optimizing the timing of charging the solid oxygen source.

Japanese Patent Laid-Open No. 2002-60826 JP 2011-219817 A JP 2011-211981 A

However, iron ore has a larger particle size than dust or the like, and has a composition mainly composed of Fe ₂ O ₃ , so that it takes time for dissolution and reduction. Therefore, dissolution and reduction of iron ore become insufficient, and iron loss due to insufficient cooling of the hot metal temperature, reduction in de-P efficiency, and insufficient reduction occurs.
This phenomenon is particularly noticeable when a large amount of iron ore is added and processing is performed in a short time.

  The present invention has been made in view of such circumstances, and reduces the iron ore with high efficiency to optimize the hot metal temperature, improve de-P efficiency, and reduce iron loss. The purpose is to provide.

The gist of the present invention made to solve the above problems is as follows.
(1) In the iron ore reduction method in the converter type hot metal preliminary treatment,
A first step in which the basicity of the slag in the converter is 0.5 or more and less than 1 and the viscosity of the slag is 0.15 Pa · s or less, and iron ore is charged into the converter;
And a second step of adjusting the slag basicity to 1 to 1.5 by introducing a lime-based raw material into the converter.

(2) The iron ore reduction method according to (1), wherein a part or all of the lime-based raw material is slag generated in the converter or another converter.

Since the iron ore reduction method according to the present invention has the first step of setting the basicity and viscosity of the slag in the converter within a predetermined range and putting the iron ore into the converter, the dissolution rate of the iron ore Can be improved. And since the 2nd process of raising the basicity of slag using a lime-type raw material and adjusting within a predetermined range is performed, the reduction reaction of an iron ore can be accelerated | stimulated and the FeO density | concentration in slag can be reduced.
Therefore, it is possible to reduce iron loss while reducing iron ore with high efficiency and achieving optimization of the hot metal temperature and improvement of de-P efficiency. For this reason, especially when a large amount of iron ore is added and processed in a short time, the effect of the present invention becomes more remarkable.

  Here, when using slag generated in a converter as a lime-based material, the amount of quick lime and limestone that can be used as a lime-based material, for example, can be reduced to zero, and the running cost can be reduced. And economical.

It is explanatory drawing of the reduction method of the iron ore which concerns on one embodiment of this invention. It is the graph which showed the influence which the basicity of slag has on the dissolution rate of iron ore and dust.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIG. 1, the iron ore reduction method according to one embodiment of the present invention is a hot metal pretreatment (converter type hot metal pretreatment) method using a converter 10, and slag in the converter 10. The first step of putting iron ore into the converter 10 with the iron ore charging chute 15 with the basicity and viscosity of 11 within the predetermined ranges, and the lime-based raw material into the converter 10 and the slag 11 And a second step of adjusting the basicity within a predetermined range, and is a method capable of reducing iron ore with higher efficiency than before.
This will be described in detail below.

(Preparation process)
First, the hot metal 12 is charged into the converter (upper bottom blowing converter) 10.
At this time, if necessary, iron scrap can be placed in the converter 10 in advance before the hot metal 12 is charged, or can be charged after the hot metal 12 is charged.
After the hot metal 12 is charged into the converter 10, an inert gas (for example, Ar gas (argon gas), N ₂ gas (nitrogen gas), etc.) is supplied from the bottom blowing nozzle 13 provided at the lower part of the converter 10. ) And the following steps are performed while stirring.

(First step)
Here, the basicity of the slag 11 in the converter 10 is adjusted to 0.5 or more and less than 1 and the viscosity of the slag 11 is adjusted to 0.15 Pa · s or less, and iron ore is charged into the converter 10. . The basicity of the slag 11 is represented by “{CaO concentration in slag (mass%)} / {SiO ₂ concentration in slag (mass%)}” (hereinafter simply referred to as basicity or C / S Also described). Further, the iron ore contains Fe ₂ O ₃ as a main component (for example, 70% by mass or more, and further 80% by mass or more).
The basicity of the slag 11 described above was defined based on the following test.

The test was performed by adding 50 g of a preheated sample to the slag while stirring 100 g of the slag melted in an iron crucible under an Ar gas atmosphere. This sample includes iron ore (FeO: 0.14% by mass, Fe ₂ O ₃ : 97.94% by mass) and dust (FeO: 30.78% by mass, Fe ₂ O ₃ : 55.75% by mass) for comparison. %) Was used.
Also, slag to inject sample (iron ore and dust) contains a FeO 25 wt%, the remainder consists of a SiO ₂ Metropolitan CaO, by changing the CaO and SiO ₂ ratio, a basicity of 0.6 Each was adjusted to 1.0. The slag temperature was 1350 ° C.

The slag was collected 3 minutes after the sample was charged, and the total Fe concentration T.I. Fe (mass%) and metal Fe concentration in the sample Each Fe (mass%) was analyzed, and the converted FeO concentration (mass%) was determined by the following formula.
(Converted FeO concentration) = {(T.Fe)-(M.Fe)} / 56 × 72
The rate of increase in the converted FeO concentration in slag (% / min) obtained by dividing the value obtained by subtracting the initial FeO concentration (30% by mass) from this converted FeO concentration (% by mass) by 3 minutes is taken as the dissolution rate of the sample. evaluated.

FIG. 2 shows the test results.
When iron ore was added from above to slag having a basicity of 1 or more and 2 or less (in the converter 10), dissolution of the iron ore was greatly inhibited, so the basicity of the slag was set to less than 1.
For example, as shown in FIG. 2, when the basicity (C / S) of slag was 1.0, a tendency that the dissolution rate of dust was better than that of iron ore was obtained. However, it was found that by reducing the basicity of slag to 0.6, the dissolution rate of iron ore can be increased as compared with the case where the basicity is 1.0 and can be increased to the same level as dust. .

In addition, when the basicity of slag is reduced to less than 0.5, the amount of SiO _{2 in} the slag becomes excessive and the viscosity of the slag increases. For this reason, when iron ore is added from above the slag, the iron ore becomes easy to be captured by the slag layer, and dissolution and reduction of the iron ore are hindered.
Based on the above findings, the basicity of the slag 11 is set to 0.5 or more and less than 1 (preferably, the lower limit is 0.6, the upper limit is 0.9, and further 0.8).

Moreover, the viscosity of slag was prescribed | regulated based on the following knowledge.
As described above, when the viscosity of the slag is high, when iron ore is added from above the slag, the iron ore is easily captured by the slag layer, and the reduction of the iron ore is hindered.
In order to make it difficult for iron ore to be captured by the slag layer within the above-described range of slag basicity, the viscosity of the slag 11 needs to be 0.15 Pa · s or less.

The lower limit of the viscosity is not particularly specified because the iron ore becomes difficult to be captured by the slag layer as the viscosity decreases, but considering the composition of the slag, for example, about 0.10 Pa · s It is.
The viscosity of the slag 11 is based on the composition of the slag 11 and the like. The estimated viscosity formula by Iida et al. (Takamichi Iida, 4 others, “Viscosity of Molten Slag / Glass— It can be calculated (estimated) using “accurate viscosity estimation method—”, Agne Technical Center, June 25, 2003, p.

The iron ore may be added within the above-described ranges of the basicity and viscosity of the slag 11, and specifically, the amount of SiO ₂ generated in the hot metal preliminary treatment and the converter 10 are charged. From the balance with the CaO source (for example, quicklime, limestone, recycled slag), the basicity is 0.5 or more and less than 1 and the viscosity is 0.15 Pa · s or less. Here, as a method for reducing the viscosity of the slag 11, for example, dust having a high FeO concentration (for example, 20 mass% or more, and further 25 mass% or more) in the converter 10 as compared with iron ore. It is desirable to use the charging method.

(Second step)
In the first step described above, after all of the iron ore has been charged into the converter 10, the lime-based raw material is charged into the converter 10, and the basicity of the slag 11 is made higher than the basicity in the first step. It is raised and adjusted to 1 or more and 1.5 or less (preferably 1.1 or more and less than 1.5, and further 1.2 or more and less than 1.5).
The slag 11 after the iron ore is charged has a high FeO concentration (for example, 20% by mass or more). For this reason, iron loss can be reduced by adding a lime-based raw material, adjusting the basicity within the above-described range, accelerating the reduction of FeO, and forming a slag having a reduced FeO concentration. In addition, when the basicity of slag is more than 1.5, the dissolution of the auxiliary raw material is caused, and de-P is inhibited.

Here, for the lime-based raw material, for example, quick lime, limestone, recycled slag or the like can be used in combination with one or more, but from the viewpoint of economy, recycled slag is partly or wholly part of the lime-based raw material. Is preferably used.
This recycled slag is slag generated in the past operation of the converter 10 or other converter, and has a basicity of about 3 to 4 (recycled slag described in the first step described above). The same).

In this manner, after the basicity of the slag 11 is increased to 1 or more and 1.5 or less (at the time when it is set), the slag 11 is blown by performing top blowing acid using the lance 14.
As a result, when iron ore is added into the converter 10 from above, the iron ore can be reduced with high efficiency, so that it is possible to optimize the hot metal temperature, improve de-P efficiency, and reduce iron loss. Become.

As described above, since the iron ore reduction method of the present invention is effective for the upward addition of iron ore into the converter 10, the amount of iron ore input is not particularly specified.
However, since iron ore can be reduced with high efficiency, the effect of the iron ore reduction method of the present invention is particularly remarkable when a large amount of iron ore is added and processing is performed in a short time.

Accordingly, the input amount of iron ore may be, for example, about several kg per ton of hot metal, but is preferably 15 kg or more, more preferably 30 kg or more per ton of hot metal from the viewpoint of the effect of the present invention. On the other hand, the upper limit value of the input amount is, for example, about 50 kg in consideration of actual operation.
Moreover, the treatment time (blowing time) of the hot metal preliminary treatment is, for example, 10 minutes or less (further 5 minutes or less). On the other hand, the lower limit value of the treatment time is, for example, about 2 minutes although it depends on the amount of hot metal to be treated.

(Third step)
After the above-described blowing is completed, the converter 10 is tilted, and the generated slag 11 in the furnace is discharged from the furnace port of the converter 10. And after adding quick lime newly in the converter 10, the blow blasting which carries out top blowing acid using the lance 14 is performed.
After this blowing is completed, the converter 10 is tilted, and the molten steel is discharged from the outlet 16.
In addition, the code | symbol 17 in FIG. 1 is the slag which adhered to the inner surface of the converter 10, and was solidified.

Next, examples carried out for confirming the effects of the present invention will be described.
Here, in the hot metal preliminary treatment using the converter, iron ore was charged into 400 tons of hot metal in the converter.
The Si concentration in the hot metal was 0.5% by mass, the mass of hot metal with respect to the total mass of hot metal and iron scrap (ie, HMR) was 90% by mass, and the temperature of the hot metal was about 1350 ° C.
The procedure for putting iron ore into the converter is shown below.

First, the basicity (C / S) of slag is 0.5 to 0.5 from the balance between SiO ₂ produced by performing the converter type hot metal preliminary treatment and the CaO source (quick lime, limestone, recycled slag) to be introduced. Iron ore was charged at 30 to 36 kg / ton (kg / t) at a timing in which the viscosity of the slag became 0.12 to 0.21 Pa · s in the range of 1.2. The input amount of the iron ore was determined as a target temperature at 1270 to 1320 ° C. at the temperature after the hot metal preliminary treatment according to the required amount of dephosphorization (the first step).
Next, at the timing when the amount of iron ore was completely charged, recycled slag (lime-based raw material) was added, and the basicity (C / S) of the slag was increased and adjusted to 0.9 to 1.6.
And after starting blowing by a lance, it was completed in 10 minutes or less (the above, 2nd process).
Table 1 shows the test conditions and results.

In Examples 1 to 5, the basicity and viscosity of the slag are within the appropriate ranges (basicity: 0.5 to less than 1, viscosity: 0.15 Pa · s or less) in the first step, and iron ore is placed in the converter. Are the test conditions and results when the basicity of the slag is increased in the second step to be within an appropriate range (1 to 1.5).
In this case, the melting rate of the iron ore could be improved, and the hot metal temperature after the hot metal pretreatment after blowing for 10 minutes could be lowered to the target temperature ± 10 ° C. As a result, the P concentration in the hot metal could be reduced to 37 × 10 ⁻³ mass% or less, and the FeO concentration in the slag could be reduced to 19 mass% or less.

On the other hand, in Comparative Examples 1 and 3, the basicity of the slag in the first step is out of the appropriate range (Comparative Example 1: 1.2, Comparative Example 3: 1.1). These are test conditions and results when the viscosity of the slag in the process is outside the proper range (Comparative Example 1: 0.21 Pa · s, Comparative Example 2: 0.20 Pa · s). In addition, the basicity of the slag in the 2nd process of Comparative Examples 1-3 is made into the appropriate range.
In this case, the dissolution rate of the iron ore decreased, and the hot metal temperature after the hot metal preliminary treatment could only be reduced to 25 ° C. or higher with respect to the target temperature. For this reason, the P concentration in the hot metal rose to 40 × 10 ⁻³ mass% or more, and the FeO concentration in the slag also increased to 20 mass% or more.

Comparative Examples 4 and 5 are test conditions and results when the basicity of the slag in the second step is outside the appropriate range (Comparative Example 4: 0.9, Comparative Example 5: 1.6). In addition, the basicity and viscosity of the slag in the first step are within an appropriate range.
In this case, since the basicity of the slag was less than the lower limit of the appropriate range in Comparative Example 4, the reduction of FeO could not be promoted, and the FeO concentration in the slag increased. In Comparative Example 5, the slag base Since the degree exceeded the upper limit of the appropriate range, the P concentration in the hot metal increased.

From the above, by using the iron ore reduction method of the present invention, it is possible to reduce iron ore with high efficiency, to optimize the hot metal temperature, to improve de-P efficiency, and to reduce iron loss. It could be confirmed.
In Examples 1 to 5 described above, the case where 30 to 35 kg / ton of iron ore was charged into the converter was described, but the amount of iron ore charged was within the range of several kg / ton to 50 kg / ton. However, the same tendency as the results of Examples 1 to 5 was obtained.

  As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included. For example, a case where the iron ore reduction method of the present invention is configured by combining some or all of the above-described embodiments and modifications is also included in the scope of the right of the present invention.

10: Converter, 11: Slag, 12: Hot metal, 13: Bottom blowing nozzle, 14: Lance, 15: Iron ore charging chute, 16: Steel outlet, 17: Slag

Claims (2)

In the iron ore reduction method in the converter type hot metal preliminary treatment,
A first step in which the basicity of the slag in the converter is 0.5 or more and less than 1 and the viscosity of the slag is 0.15 Pa · s or less, and iron ore is charged into the converter;
And a second step of adjusting the slag basicity to 1 to 1.5 by introducing a lime-based raw material into the converter.   2. The iron ore reduction method according to claim 1, wherein a part or all of the lime-based raw material is slag generated in the converter or another converter.

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