JP7082320B2 - Dephosphorization method of hot metal - Google Patents

Description

The present invention relates to a method for pretreating hot metal before blowing the hot metal in a converter. In particular, the hot metal efficiently dephosphorizes the hot metal without using a halide such as fluorite as a refining agent (flux). It is related to the dephosphorization treatment method.

The hot metal from the blast furnace contains a large amount of impurities such as silicon, phosphorus, and sulfur. Therefore, in recent years, when the hot metal is oxygen-blown in a converter to make molten steel, it has been used as a pre-process for oxygen blowing from the viewpoint of reducing the load in the converter, reducing the amount of steelmaking slag generated, and reducing the steelmaking cost. , So-called "hot metal pretreatment", in which hot metal is desiliconized, dephosphorized, and desulfurized, is actively performed. This hot metal pretreatment is performed while the hot metal ejected from the blast furnace is present in the hot metal iron or tilting pig iron, or after being housed in a converter, hot metal pot, or torpedo wagon, lime-based flux, oxidizing agent, and soda. This is done by blowing a refining agent such as an ash-based flux into the hot metal using oxygen, nitrogen gas, or the like as the carrier gas. As a result, oxides (SiO ₂ and P ₂ O ₅ ) produced by oxidizing silicon (Si) and phosphorus (P) in the hot metal and sulfides produced by the reaction of sulfur (S) with the refining agent (Sulfur) (SiO 2 and P 2 O 5). CaS and Na 2S) _are absorbed into the slag and removed.

Among such hot metal pretreatments, in the dephosphorization treatment, an oxidizing agent is put into the hot metal in the refining vessel to _convert phosphorus into an oxide P2 _O5 , which is incorporated into the slag generated in the upper part of the hot metal of the hot metal. Therefore, dephosphorization is performed. However, since the oxide of phosphorus is acidic, the basicity of the slag (top slag) formed on the upper part of the hot metal (the mass ratio of CaO and SiO ₂ is the mass ratio, and thereafter, "C / S". The lime-based flux was blown so that (also referred to as) was 2.0 or more.

However, when the basicity C / S of the slag is high, the melting temperature of the slag is high. Therefore, when the hot metal temperature is lowered during the pretreatment, the viscosity of the slag is increased and the CaO blown into the hot metal Slagging becomes insufficient, and the efficiency of CaO dephosphorization utilization decreases. Therefore, when trying to sufficiently perform hot metal dephosphorization, an excessive amount of lime-based flux is added, which not only increases the amount of slag, but also increases the cost of the refining agent and the cost of slag processing. was there. In addition, the hot metal temperature after the dephosphorization treatment was further lowered.

Therefore, in the dephosphorization treatment aiming at extremely low phosphorus, a halide such as fluorite (CaF ₂ ) is added to promote the slagging of CaO and reduce the amount of flux, and slag having a low melting point is formed. Techniques for promoting flux slag and ensuring dephosphorization capacity have been widely used.

However, in recent years, slag has been effectively used as a raw material for civil engineering, building materials, etc., but the addition of fluorite increases the concentration of fluorine (F) in the slag produced, so that fluorine elution, etc. However, there is a problem that it cannot be used in places where it is environmentally regulated, and it is desired to develop a dephosphorization treatment technique using slag that does not contain fluorite. Further, the fluorine in the slag also promotes the melting of the refractory material of the container used for the hot metal pretreatment, which is not desirable from the viewpoint of extending the life of the pretreatment equipment. Furthermore, it is desirable not to use fluorite in terms of refining agent cost.

Therefore, a dephosphorization technique that does not add a halide such as fluorite has been proposed. For example, in Patent Document 1, iron oxide and fresh lime are blown as refining agents in the hot metal pretreatment, and the basicity C / S of slag is maintained at a relatively high level of 2.0 to 2.5, and the Si concentration of the hot metal is maintained. Preliminary hot metal without fluorite, which is operated while maintaining the basicity C / S of slag in the range of 2.0 to 2.5 while performing desiliconization to reduce the amount to 0.03% by mass or less. A processing method has been proposed.

Japanese Unexamined Patent Publication No. 63-223114

However, the technique of Patent Document 1 has a problem that when the hot metal temperature is low, the slag in the refining container being processed solidifies and causes poor slag, or the slag slag removal property deteriorates. be. That is, at the end of the hot metal treatment in which dephosphorization is promoted by the addition of an oxidizing agent, the hot metal temperature may drop to 1260 ° C. or lower. Since the rate decreases, there is a problem that the slag solidifies and the fluidity deteriorates, the slag discharge property during the hot metal treatment deteriorates, and stable operation is hindered.

ここで、Ｌ_Ｐ＝Ｐの分配比＝（％Ｐ）／［％Ｐ］
（％Ｐ）＝スラグ中のＰ濃度（質量％）
［％Ｐ］＝溶銑中のＰ濃度（質量％）
（％Ｔ．Ｆｅ）＝スラグ中のトータル鉄濃度（質量％）
（％ＣａＯ）＝スラグ中のＣａＯ濃度（質量％）
Ｔ：溶銑の絶対温度（Ｋ）
この（２）式から、定性的には、スラグ中のＣａＯ濃度が高い、すなわち、塩基度Ｃ／Ｓが高いほど、また、溶銑温度Ｔが低いほど、燐分配比Ｌ_Ｐが大きくなり、溶銑とスラグ間の平衡Ｐ濃度が低下する（脱燐が進行する）ことがわかる。 By the way, the dephosphorization ability of slag is represented by the P distribution ratio LP (= (% _P ) / [% P]), which is the mass ratio of the P concentration in the slag to the P concentration in the hot metal, and this P distribution ratio. There are many reports on the formula for estimating _LP , but the formula of Health expressed by the following formula (2) is well known.
Record

Here, L _P = distribution ratio of P = (% P) / [% P]
(% P) = P concentration in slag (mass%)
[% P] = P concentration in hot metal (mass%)
(% T.Fe) = total iron concentration in slag (% by mass)
(% CaO) = CaO concentration in slag (% by mass)
T: Absolute temperature of hot metal (K)
From this equation (2), qualitatively, the higher the CaO concentration in the slag, that is, the higher the basicity C / _S , and the lower the hot metal temperature T, the larger the phosphorus distribution ratio LP, and the hot metal. It can be seen that the equilibrium P concentration between the slag and the slag decreases (dephosphorization progresses).

As described above, when the CaO concentration in the slag increases, the melting point of the slag increases, so that the liquid phase ratio of the slag decreases and the slag property decreases at the end of the dephosphorization treatment when the hot metal temperature decreases. , The dephosphorization ability is lowered, and the slag is solidified to deteriorate the slag scavenging property. However, in the conventional hot metal pretreatment technique, the slag composition that achieves both slag dephosphorylation ability and slag slag slag slaging property is not specifically specified.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to suppress a slagging defect and efficiently remove the halide without using a halide such as fluorite as a refining agent. The purpose is to propose a method for dephosphorizing hot metal that can be phosphorused and can be operated stably.

In order to achieve the above-mentioned problems, the inventors have conducted extensive research on the operating conditions for dephosphorizing the hot metal with an oxidizing agent. As a result, by adjusting the slag basicity at the end of the dephosphorization treatment to an appropriate range according to the hot metal temperature at the end of the dephosphorization treatment and at the same time using an oxidizing agent in which the average particle size is controlled within the appropriate range, the above-mentioned problems can be solved. We have found that we can solve the problem, and have developed the present invention.

That is, the present invention is a method for dephosphorizing the hot metal by blowing a refining agent containing a lime-based flux and an oxidizing agent into the hot metal contained in the refining container, wherein the hot metal has an average particle size of 40 to 100 μm. In use, the hot metal temperature at the end of the dephosphorization treatment is set to 1260 ° C. or lower, and the above-mentioned lime-based flux is blown into the hot metal when the hot metal temperature is 1260 ° C. or higher, and the basicity of the slag at the end of the dephosphorization treatment is performed. In relation to the hot metal temperature T at the end of the dephosphorization treatment, B is the following equation (1);
(8.01 × ^10-5 × T ² −0.1899 × T + 113.95) × 0.71 ≦ B ≦ 8.01 × ^10-5 × T ² −0.1899 × T + 113.95 ... (1) )
A method for dephosphorizing hot metal without using a halide, which is characterized by controlling so as to satisfy the above conditions. Here, the average particle size refers to the median particle size, and the particle size distribution can be measured by sieving analysis using an automatic sieving machine. In a graph plotted with the mass percentage (%) of the amount passed through the mesh of each particle size on the vertical axis and the particle size on the horizontal axis of the logarithmic scale by sieve analysis, read the particle size corresponding to the mass percentage of 50%. The median particle size. As the sieve mesh used for the sieve analysis, those specified in JIS Z8801 or the like may be used, but the mesh size is not limited to this. The basicity is the mass ratio of CaO to SiO ₂ in the slag.

The method for dephosphorizing the hot metal of the present invention is characterized in that the lime-based flux is blown into the hot metal when the hot metal temperature is 1260 ° C. or higher.

Further, the oxidizing agent used in the method for dephosphorizing hot metal of the present invention is characterized by containing CaO in the range of 10 to 20% by mass.

Further, the smelting container in the method for dephosphorizing hot metal of the present invention is characterized by being a transport container for a torpedo wagon.

According to the present invention, the slag basicity B at the end of the dephosphorization treatment is controlled within an appropriate range according to the hot metal temperature T at the end of the dephosphorization treatment, and the average particle size of the oxidizing agent is optimized. Even when the temperature drops, it is possible to efficiently perform the dephosphorization treatment of the hot metal without using a halide such as fluorite.

It is a schematic diagram which shows an example of the hot metal pretreatment equipment using a torpedo wagon. It is a schematic diagram which shows the state which the transport container of a torpedo wagon is tilted and discharged in the hot metal pretreatment facility of FIG. It is a graph which shows the influence of the hot metal temperature T and the slag basicity B at the end of dephosphorization treatment on the P concentration in hot metal after dephosphorization treatment. 6 is a graph showing the effect of the average particle size of the oxidizing agent on the P concentration in the hot metal after the dephosphorization treatment.

The hot metal dephosphorization treatment method of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing an example of a hot metal pretreatment facility that uses a transport container of a torpedo wagon as a refining container. The torpedo wagon 1 accommodates the hot metal 3 from the blast furnace in the transport container 2 and transports it to the steelmaking factory in the next process. It may be one that has been subjected to desiliconization treatment such as desiliconization of the cast bed to reduce it.

When the hot metal dephosphorization treatment is performed using the transport container 2 of the torpedo wagon 1 as a refining container, first, the torpedo wagon 1 is transported to a pretreatment facility, and the transport container 2 is transferred to the pretreatment facility, as shown in FIG. Tilt the container 2 to an angle at which the slag 4 is discharged from the furnace port 5 and at an angle at which the hot metal 3 is not discharged. The transport container 2 may be tilted before being transported to the pretreatment equipment. Since the carriage of the torpedo wagon has a drive unit capable of tilting the transport container as shown in FIG. 2, it can be used particularly preferably.

Then, as shown in FIG. 1, the dephosphorization treatment carries a refining agent containing an oxidizing agent 7 and / or a lime-based flux 8 in the hot metal 3 from the hearth 5 of the transport container 2 via the injection lance 6. This is performed by blowing the gas 9 over a predetermined time. As for the dephosphorization reaction at this time, the reaction (transition reaction) caused by the refining agent blown into the hot metal during floating is considered to be more dominant than the reaction between the slag and the metal (permanent reaction). The Si and P in the hot metal 3 are oxidized by an oxidizing agent during levitation to become SiO ₂ , P ₂ O ₅ , levy and migrate into the top slag 4 (also simply referred to as “slag”) to desiliconize. , Dephosphorized. Since the slag 4 produced on the hot metal contains a large amount of SiO ₂ and P ₂ O ₅ , as shown in FIG. 2, the transport container 2 is tilted to remove the slag 4 while dephosphorizing. In succession.

Here, as the oxidizing agent 7 contained in the refining agent, sinter, dust collected dust generated in a steel mill, sludge, or the like can be preferably used. Further, from the viewpoint of enabling the dephosphorization treatment only by adding the oxidizing agent 7, it is preferable that CaO is contained in the range of 10 to 20% by mass. When the CaO content is less than 10% by mass, when the Si concentration in the hot metal is high (for example, when it is 0.6% by mass or more), a large amount of SiO ₂ is generated prior to dephosphorization, so that the slag base is used. When the degree B is controlled so as to satisfy the equation (1), the amount of lime-based flux used may increase and the temperature of the hot metal may decrease significantly, so that the phosphorus concentration in the hot metal after the dephosphorization treatment is extremely low. It will be disadvantageous if you do. On the other hand, when CaO exceeds 20% by mass, when the Si concentration in the hot metal is low (for example, when it is 0.2% by mass or less), the supply amount of CaO becomes excessive and the slag basicity B becomes (1). When controlling so as to satisfy the formula, it may be disadvantageous when the phosphorus concentration in the hot metal after the dephosphorization treatment is set to extremely low phosphorus. It is preferably in the range of 14 to 18% by mass. Further, as the lime-based flux 8, burnt lime powder, steelmaking slag, or the like can be preferably used.

In order to investigate the effects of the slag basicity C / S and the hot metal temperature T at the end of the dephosphorization treatment on the P concentration in the hot metal after the dephosphorization treatment, the inventors have described the above-mentioned transport container for the torpedo wagon. Was used as a refining container for dephosphorization of hot metal. At this time, the amount of hot metal contained in the transport container of the torpedo wagon is 400 tons, and the dephosphorization treatment conditions are changed as shown in Table 1, and the hot metal temperature T, slag basicity B, and slag at the end of the dephosphorization treatment are changed. The presence or absence of solidification and the P concentration in the hot metal after the dephosphorization treatment were investigated, and the results are also shown in Table 1. The refining agent blown into the hot metal during the dephosphorization treatment was an oxidizing agent 7 and a lime-based flux when the hot metal temperature was 1260 ° C. or higher, and only an oxidizing agent when the hot metal temperature was lower than 1260 ° C.

FIG. 3 is a graph showing the effects of the hot metal temperature T and the slag basicity B at the end of the dephosphorization treatment on the P concentration in the hot metal after the dephosphorization treatment, in which the P concentration exceeds 0.010% by mass. Are indicated by x or Δ, and those with 0.010% by mass or less are indicated by ◯. From this figure, the slag basicity B at the end of the dephosphorization treatment is the following equation (1) in relation to the hot metal temperature T;
(8.01 × ^10-5 × T ² −0.1899 × T + 113.95) × 0.71 ≦ B ≦ 8.01 × ^10-5 × T ² −0.1899 × T + 113.95 ・ ・ ・ (1) )
It can be seen that the P concentration in the hot metal after the dephosphorization treatment is 0.010% by mass or less within the range specified in 1.

The reason for this is that when the slag basicity B is high and it deviates from the right side of Eq. Is considered to be. On the other hand, when the slag basicity B is low and deviates from the left side of the equation (1), solidification of the slag is not observed, but it is considered that the dephosphorization ability is lowered due to the decrease in the slag basicity due to the lack of CaO. Be done. Therefore, in the present invention, the slag basicity B at the end of the dephosphorization treatment is adjusted so as to satisfy the above equation (1) in relation to the hot metal temperature T after dephosphorization.

However, as can be seen from FIG. 3, even when the slag basicity B at the end of the dephosphorization treatment satisfies the above equation (1) in relation to the hot metal temperature T at the end of the dephosphorization treatment, the dephosphorization treatment is performed. There is a case (indicated by Δ in FIG. 3) in which the P concentration in the subsequent hot metal does not become 0.010% by mass or less. Therefore, as a result of investigating the cause, it became clear that the average particle size of the oxidizing agent 7 added as the dephosphorizing agent had a great influence.

FIG. 4 shows the relationship between the average particle size of the oxidizing agent and the P concentration in the hot metal after the decarburization treatment in the case where the formula (1) is satisfied. From this figure, in order to reduce the P concentration in the hot metal after the dephosphorization treatment to 0.010% by mass or less, the hot metal temperature T and the slag basicity B at the end of the dephosphorization treatment satisfy the above equation (1). In addition, it was found that it is necessary to use an oxidizing agent having an average particle size of 100 μm or less. The reason for this is that when the average particle size of the oxidant is larger than 100 μm, the reaction boundary area with the metal becomes smaller, the transition reaction when the oxidant floats in the hot metal, and the slagging property are lowered. It is thought that this is to be done. However, in order to increase the reaction area of the oxidant, it is preferable that the average particle size of the oxidant is small, but if it is less than 40 μm, it is not preferable because the transport system is likely to be clogged when transported by the carrier gas. Therefore, in the present invention, the average particle size of the oxidizing agent is in the range of 40 to 100 μm. It is preferably in the range of 40 to 80 μm. Here, the average particle size is the median particle size.

Here, a method of adjusting the hot metal temperature T and the slag basicity B at the end of the dephosphorization treatment so as to satisfy the above-mentioned equation (1) will be described.
First, the hot metal temperature T at the end of the dephosphorization treatment is necessary to measure the hot metal temperature, Si concentration and P concentration before or during the pretreatment, and to achieve the target Si concentration and P concentration. It is estimated from the heat balance based _on the amount of the oxidant added and the decomposition heat absorption reaction of FeO and Fe ₂ O3 contained in the oxidant. This temperature is called the "estimated final hot metal temperature". Further, the amount of the oxidizing agent added at that time is estimated from the amount of oxygen required for the oxidation reaction of Si and the amount of oxygen required for the oxidation reaction of P.

Next, the slag basicity is adjusted so that the slag basicity B at the end of the dephosphorization treatment satisfies the equation (1) according to the estimated final hot metal temperature obtained as described above. Here, the adjustment of the slag basicity can be performed by CaO contained in the oxidizing agent 7 added as a refining agent, but mainly by adding the lime-based flux 8.

However, this lime-based flux 8 is preferably added while the hot metal temperature is 1260 ° C. or higher. When the hot metal temperature is lowered to less than 1260 ° C., the lime-based flux 8 having a high melting point because the CaO content is higher than that of the oxidizing agent 7 is not sufficiently slag-solidified, and slag solidification is likely to occur. This is because the efficiency of dephosphorization utilization will decrease. Therefore, when the dephosphorization treatment is continuously performed at a temperature of less than 1260 ° C., it is preferable to inject only an oxidizing agent containing 10 to 20% by mass of CaO. As a result, even if the hot metal temperature becomes a low temperature of less than 1260 ° C., the dephosphorization treatment can be performed without causing solidification of the slag. The temperature at which the blowing of the lime-based flux is stopped is preferably 1270 ° C. or higher.

Of course, the estimated final hot metal temperature may be changed by measuring the hot metal temperature during the dephosphorization treatment. The slag basicity may be adjusted by actually measuring the slag basicity and the hot metal temperature during the dephosphorization treatment, but the estimated slag amount in the transport container, the hot metal component, the amount of the slag-forming agent added, and the oxidation The basicity and hot metal temperature may be estimated from the substance balance and the heat balance based on the amount of the agent added and the amount of slag discharged.

According to the present invention described above, even when the hot metal temperature at the end of the desulfurization treatment is lowered to less than 1260, there is no slag solidification due to slag solidification and the CaO concentration in the slag is not insufficient, and the hot metal is removed. The phosphorus treatment can be stably carried out.

Same as the above-mentioned experiment to investigate the effect of the temperature at which the lime-based flux is stopped from being blown into the hot metal (the temperature at which the lime-based flux is stopped) and the CaO content of the oxidizing agent on the P concentration in the hot metal after dephosphorization. As described above, a dephosphorization treatment experiment of hot metal was conducted using the transport container of the torpedo wagon as a refining container. At this time, the amount of hot metal contained in the transport container of the torpedo wagon is 400 tons, and the dephosphorization treatment conditions are changed as shown in Table 2, and the hot metal temperature T, slag basicity B, and slag at the end of the dephosphorization treatment are changed. The presence or absence of solidification and the P concentration in the hot metal after the completion of the dephosphorization treatment were investigated. The relationship between the slag basicity B and the hot metal temperature T at the end of the dephosphorization treatment was all under the condition of satisfying the equation (1), and the oxidizing agent used had an average particle size of 40 to 100 μm.

The above experimental results are also shown in Table 2. From this result, when the hot metal temperature (blowing stop temperature) when the blowing of the lime-based flux into the hot metal is stopped is lower than 1260 ° C., it seems that it is slightly solidified in the slag after the dephosphorization treatment is completed. (The degree of solidification of this slag is indicated by "slight" in Table 2), but the P concentration in the hot metal after dephosphorization treatment is up to 0.010% by mass or less. It turned out that it can be reduced. Further, even when an oxidizing agent having a CaO content outside the range of 10 to 20% by mass was used, it sometimes seemed to be slightly solidified in the slag after the dephosphorization treatment was completed (degree of this slag solidification). (Shown as "slight" in Table 2), it was also found that the P concentration in the hot metal after the dephosphorization treatment can be reduced to 0.010% by mass or less.

As described above, the slag basicity B and the hot metal temperature T at the end of the dephosphorization treatment are conditions that satisfy the above-mentioned equation (1), and an oxidant having an average particle size of 40 to 100 μm is used. It was confirmed that the dephosphorization treatment can be stably performed and the P concentration in the hot metal after the dephosphorization treatment can be more reliably reduced to 0.010% by mass or less.

1: Torpedo wagon (refining container)
2: Transport container (refining container)
3: Hot metal 4: Slag (top slag)
5: Furnace mouth 6: Injection lance 7: Oxidizing agent 8: Lime-based flux 9: Carrier gas

Claims (3)

In a method of dephosphorizing the hot metal by blowing a refining agent containing a lime-based flux and an oxidizing agent into the hot metal contained in the refining container.
As the oxidizing agent, one having an average particle size of 40 to 100 μm is used.
The hot metal temperature at the end of the dephosphorization treatment was set to 1260 ° C. or lower, and the above-mentioned lime-based flux was blown into the hot metal when the hot metal temperature was 1260 ° C. or higher.
A halide is used, characterized in that the basicity B (-) of the slag at the end of the dephosphorization treatment satisfies the following equation (1) in relation to the hot metal temperature T (° C.) at the end of the dephosphorylation treatment. How to dephosphorize not hot metal. Here, the average particle size means the median particle size, and the basicity means the mass ratio of CaO to SiO ₂ in the slag.
Note (8.01 x ^10-5 x T ^2-0.1899 x T + 113.95) x 0.71 ≤ B ≤ 8.01 x ^10-5 x T ^2-0.1899 x T + 113.95 ... ( 1) The method for dephosphorizing hot metal according to claim 1, wherein the oxidizing agent contains CaO in the range of 10 to 20% by mass. The method for dephosphorizing hot metal according to claim 1 or 2 , wherein the smelting container is a transport container for a torpedo wagon.

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