JP7082321B2 - Dephosphorization method of hot metal - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention is a technique for efficiently dephosphorizing hot metal without using fluorite as a refining agent (flux) when removing phosphorus contained in hot metal.

Hot metal contains a large amount of impurities such as silicon, phosphorus, and sulfur, and in the refining process of steel materials, it is removed from the viewpoint of reducing the load in the converter, reducing the amount of steelmaking slag generated, and reducing the steelmaking cost. As a pre-process for charcoal treatment, so-called hot metal pretreatment, in which hot metal is desiliconized, dephosphorized, and desulfurized, is actively performed. In this hot metal pretreatment, the hot metal ejected from the blast furnace is used as a refining agent for lime-based flux and oxidation while it is present in the hot metal iron and the pouring iron, or after it is stored in the converter, hot metal pot, and torpedo wagon. It is carried out by blowing an agent and / or a soda ash-based flux or the like into a hot metal using oxygen or nitrogen as a carrier gas. Specifically, it oxidizes silicon (Si) and phosphorus (P) in hot metal and absorbs the generated oxides (SiO ₂ and P ₂ O ₅ ) into the slag, or absorbs sulfides (CaS and Na ₂ ). It is performed by absorbing S) into slag.

Among such hot metal pretreatments, especially when dephosphorization is performed, an oxidizing agent is added to the hot metal to remove phosphorus as an oxide into the slag. However, since the phosphorus oxide is acidic, it has been conventionally used. In many cases, a lime-based flux was blown so that the basicity of the formed slag (the mass ratio of CaO and SiO ₂ and abbreviated as C / S) was as high as 2.0 or more. However, slag with high basicity has a high melting temperature, and if the hot metal temperature drops during the hot metal pretreatment, the viscosity of the slag becomes high, so that the slag that has been blown in is insufficiently slagged and the dephosphorization utilization efficiency is low. There was a tendency to become. Therefore, if the hot metal is dephosphorized to the extremely low P concentration range, the refining agent will be used excessively, which not only increases the amount of slag but also increases the refining cost and the slag processing cost. 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, in order to promote the slagging of CaO and reduce the amount of flux, a halide such as fluorite (CaF ₂ ) is added to dephosphorize and melt the slag. The method of maintaining a high dephosphorization rate up to the extremely low phosphorus region has been adopted. However, the addition of a halide such as fluorite will increase the fluorine (F) content and the like in the formed slag. In recent years, slag has come to be effectively used as a raw material for civil engineering and building materials, but as social interest in environmental problems increases, its use in applications where the elution of fluorine is a problem is restricted. Therefore, there is a demand for operations that do not use halides such as fluorite. Further, since halogens such as fluorine in the slag have an effect of accelerating the melting of the refractory of the container used for the pretreatment, it is preferable not to use a halide from the viewpoint of extending the life of the pretreatment equipment. Furthermore, it is desirable not to use fluorite from the viewpoint of refining agent cost. Therefore, various methods for increasing both the dephosphorization capacity of slag and the melting rate (slagging rate) have been proposed.

For example, Patent Document 1 discloses a technique for dephosphorizing hot metal without using fluorite. The technology keeps the basicity C / S in the slag relatively high at 2.0 to 2.5 in advance from before the start of operation, reduces the Si concentration in the hot metal to 0.03% by mass or less, and even after that. The slag basicity C / S is always maintained in the range of 2.0 to 2.5 for operation.

Japanese Unexamined Patent Publication No. 63-223114

However, the conventional technique still has the following problems to be solved.
The technique described in Patent Document 1 has a problem that when the hot metal temperature is low, the slag during the treatment is deteriorated, the slag in the smelting furnace is solidified, and the slag is poorly formed. That is, in the final stage of treatment in which dephosphorization is promoted by an oxidizing agent, the hot metal temperature may drop to 1260 ° C. or lower. Impairs liquidity. As a result, the slag during the dephosphorization treatment deteriorated, the slag solidified, and in turn, poor slag formation often occurred, and the operation was unstable.

The oxidative dephosphorization reaction is represented by the following chemical formula 1. In the formula (a), [P] represents phosphorus dissolved in molten iron, (FeO) represents iron oxide in slag, and (P ₂ O ₅ ) represents phosphorus oxide in slag.

The Gibbs free energy ^ΔGO and the equilibrium constant K _P of this dephosphorylation reaction are expressed by the following mathematical formula 1. In the formula (1), T is, for example, the molten iron temperature [K] at the end of the dephosphorization treatment, _ai is the activity of the chemical substance i, and R is the gas constant (8.314 m ² · kg · s ⁻ . ² · K ^-1 · mol ^-1 ).

There are many reports on the equilibrium formula of the dephosphorization reaction, but the phosphorus distribution estimation formula by Hairy is expressed by the following formula 2 with the phosphorus distribution ratio LP = (mass% _P ) / [mass% P]. In the formula (2), (mass% X) represents the mass percentage of the substance X in the slag, and [mass% M] represents the mass percentage of the substance M in the molten iron. 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 treatment temperature, the larger the phosphorus distribution ratio LP, and the equilibrium de- _P concentration in the hot metal. You can see that is going down. On the other hand, it is known that as the CaO concentration in the slag increases, the melting point of the slag rises, the liquid phase ratio decreases in the dephosphorization treatment temperature range, and the slag slag is inferior. In addition, the decrease in the liquid phase ratio of slag causes a phenomenon called slag solidification, in which it becomes difficult to remove the slag from the torpedo wagon. So far, the slag composition that achieves both the above-mentioned high slag dephosphorylation ability and easy slag slag slag slaging property has not been specifically specified.

The present invention has been made in view of the above circumstances, and an object thereof is to dephosphorize the hot metal without using a halide such as fluorite, and to perform a low P concentration hot metal (for example, P concentration 0. (010% by mass or less) is an industrially stable method for melting, specifically, the hot metal temperature and slag basicity are controlled, the fluidity of the slag is not impaired, fluorite failure is suppressed, and efficient removal is performed. It is an object of the present invention to provide a method for dephosphorizing hot metal that can be phosphorused and can be operated stably.

The present invention developed to solve the above problems and realize the above object is as shown in the following gist structure. That is, the present invention is a method in which a refining agent containing a lime-based flux and an oxidizing agent (excluding halides) is blown into the hot metal held in the refining container to dephosphorize the hot metal, and the temperature at the end of the treatment is 1200 ° C. The temperature should be in the range of 1260 ° C. or lower , and the basicity of the slag at the end of the treatment should be adjusted to the range of 1.0 or more and 1.8 or less . Here, the basicity of the slag is the mass ratio of CaO and SiO ₂ . We propose a method for dephosphorizing hot metal, which is characterized by the above.

Regarding the method for dephosphorizing the hot metal according to the present invention,
a. The oxidizing agent contains CaO in the range of 10% by mass or more and 20% by mass or less, SiO ₂ in the range of 5% by mass or more and 10% by mass or less, and CaO / SiO ₂ in the mass ratio of 1.2 or more. Being in the range of 2.2 or less,
b. The refining container is a torpedo wagon,
Etc. may be a more preferable solution.

As described above, according to the present invention, a slag-free refining agent such as fluorite is used to control the hot metal temperature and slag basicity at the end of the treatment, and to remove slag during the dephosphorization treatment. It is possible to maintain the phosphorus capacity and promote slag slag at the same time, and it is possible to industrially and stably smelt the hot metal P concentration to 0.010% by mass or less.

It is a schematic diagram which shows the hot metal pretreatment equipment used for one Embodiment of this invention. FIG. 3 is a schematic cross-sectional view taken along the line AA'showing a state in which the torpedo wagon used in the above embodiment is tilted and continuously discharged. It is a graph which shows the influence which the hot metal temperature and the slag basicity C / S at the end of a treatment have on the P concentration after a treatment.

An embodiment embodying the present invention will be described with reference to the attached drawings. FIG. 1 is a schematic view showing a hot metal pretreatment facility used in one embodiment of the present invention. A case where the method of the present invention is carried out by using a torpedo wagon 1 as a transport container as a refining container will be described. FIG. 2 is a schematic cross-sectional view taken along the line AA'showing a state in which the torpedo wagon 1 is tilted and continuously discharged.

The hot metal 2 taken out from the blast furnace is housed in the container 10 of the torpedo wagon 1. The hot metal 2 may be previously subjected to a desiliconization treatment such as desiliconization of the cast bed. After the torpedo wagon is transported to the pretreatment equipment or before being transported, the container 10 of the torpedo wagon 2 is tilted at a predetermined angle. As shown in FIG. 2, the angle at which the container 10 is tilted is an angle at which the slag 3 is discharged from the furnace opening of the container 10 and an angle at which the hot metal 2 is not discharged.

In the method for dephosphorizing hot metal according to the present invention, as shown in FIG. 1, the container 10 of the hot metal wheel 1 is used as a refining container, the injection lance 4 is immersed in the hot metal 2 from the furnace port 100, and the refining agent is used in the carrier gas 7. It is transported and blown over a predetermined time. As a result, Si and P in the hot metal 2 are oxidized and transferred to the slag 3, and the hot metal is desiliconized and dephosphorized. In particular, in the dephosphorization reaction in the low phosphorus region, it is considered that the transient reaction of the injected dephosphorizing agent becomes dominant over the interfacial reaction of slag-metal. That is, the top slag present on the hot metal plays a role of retaining the P once captured by the dephosphorizing agent (that is, does not cause the return P from the slag to the hot metal).

As the refining agent, an oxidizing agent 6 is used, and a lime-based flux 5 is added as needed. As the oxidizing agent 6, sinter, dust collected in the steelworks, sludge generated in the steelworks, and the like can be preferably used. Further, CaO is contained in the range of 10% by mass or more and 20% by mass or less, SiO ₂ is contained in the range of 5% by mass or more and 10% by mass or less, and CaO / SiO ₂ is 1.2 or more and 2.2 by mass ratio. It is preferably in the following range. Further, as the lime-based flux 5, burnt lime powder, steelmaking slag and the like can be preferably used.

In the present invention, the Si concentration [mass%] and the P concentration [mass%] of the hot metal 2 before or during the pretreatment are analyzed, and the temperature [° C.] of the hot metal is also measured, and after the target pretreatment. Obtain the amount of oxygen [Nm ³ ] required for processing to the Si concentration and P concentration of the hot metal. Here, the obtained oxygen amount is referred to as an estimated required oxygen amount [Nm ³ ], and the estimated required oxygen amount [Nm ³ ] is an empirical dephosphorylation oxygen efficiency [%] under various conditions of the pretreatment equipment used. It may be obtained by using. Using the obtained estimated required oxygen amount [Nm ³ ], the hot metal temperature [° C.] after the treatment is estimated. Here, the obtained hot metal temperature is referred to as an estimated final hot metal temperature. The estimated final hot metal temperature was based on the required amount of the oxidizing agent added and the decomposition heat absorption reaction of FeO and Fe ₂ O ₃ contained in the oxidizing agent, depending on the hot metal Si concentration and the P concentration after the target pretreatment. Estimated from the heat balance.

Then, the slag basicity after the treatment is adjusted. First, the supply amounts of CaO and SiO ₂ contained in the oxidizing agent are estimated from the required amount of the oxidizing agent determined above. Further, the supply amount of SiO ₂ as an oxide of Si in the hot metal can be estimated from the hot metal Si concentration before the treatment and the Si concentration after the target treatment. As a result, the basicity C / S of the treated slag is estimated. If the post-treatment slag basicity C / S estimated above is lower than 1.0 , a lime-based flux 5 is added to adjust the slag basicity to 1.0 or higher. On the other hand, when the estimated post-treatment slag basicity C / S is higher than 1.8 , sludge or the like having a relatively low CaO content can be used as the oxidizing agent 6 or oxygen gas can be used after the treatment. Adjust so that the slag basicity C / S is 1.8 or less . In the conventional dephosphorization treatment under conditions where the slag basicity exceeds 1.8, the dephosphorization rate has dropped sharply in a low temperature region such as 1260 ° C. or lower, but in the present invention, the dephosphorization rate has dropped sharply. By adjusting the post-treatment slag basicity C / S to the range of 1.0 to 1.8, it was found that dephosphorization proceeds even at a low temperature such as 1260 ° C. or lower.

Of course, the selection of the oxidant type, the selection of oxygen gas and lime-based flux 5, and the amount of the oxidant 6 added can be determined by analyzing the Si concentration and P concentration of the hot metal during the treatment and measuring the hot metal temperature. , May be adjusted each time.

FIG. 3 is a graph showing the effects of the post-treatment hot metal temperature and the post-treatment slag basicity on the P concentration of the post-treatment hot metal. In FIG. 3, the treated hot metal P concentration of 0.004% by mass or less is plotted with a circle, the amount of more than 0.004% by mass of 0.010% by mass or less is plotted with a triangle, and the value of more than 0.010% by mass is ×. Plotted with marks. As is clear from FIG. 3, the post-treatment hot metal temperature is within the range of 1180 ° C. or higher and lower than 1300 ° C., and the post-treatment slag basicity is within the range of 0.7 or higher and 2.1 or lower. It is possible to melt hot metal having a low P concentration of 0.010% by mass or less. Further, as is clear from FIG. 3, the hot metal temperature after the treatment is set within the range of 1200 ° C. or higher and 1260 ° C. or lower, and the post-treatment slag basicity is set within the range of 1.0 or higher and 1.8 ° C. or lower. It is possible to melt hot metal having an extremely low P concentration of 0.004% by mass or less. On the other hand, when the hot metal temperature after the treatment is less than 1180 ° C., or when the basicity of the slag after the treatment exceeds 2.1, the melting point of the slag is higher than the hot metal temperature, and the slag is not sufficiently slagged. After the treatment, the hot metal P concentration may exceed 0.010% by mass. Further, when the hot metal temperature is 1300 ° C. or higher, the slag dephosphorization ability is lowered due to the high temperature, or when the slag basicity after the treatment is less than 0.7, the CaO concentration in the slag is too low. As a result, the dephosphorization ability of the slag becomes insufficient, and the hot metal P concentration after the treatment exceeds 0.010% by mass.

As described above, according to the present invention, even when the final hot metal temperature is low, the hot metal dephosphorization treatment can be stably carried out without slag solidification resulting in poor slag or insufficient CaO concentration in the slag. Became.

A torpedo wagon 1 was used as a refining container, and 400 tons of hot metal 2 was accommodated. In the equipment configuration shown in FIG. 1, with the container of the torpedo wagon shown in FIG. 2 tilted, nitrogen gas or oxygen gas is used as the carrier gas, and a refining agent mixed with a lime-based flux and an oxidizing agent is injected from the injection lance. It was blown into the hot metal. At this time, the oxidizing agent used was a sintered ore containing 11% by mass of CaO and 6% by mass of SiO ₂ (mass ratio of CaO to SiO ₂ was 1.83). In the treatment end determination, the estimated required oxygen amount is calculated on the assumption that the target Si concentration is 0.02% by mass and the P concentration is 0.010% by mass, and the estimated required oxygen amount is determined by an oxidizing agent or a carrier gas. Until the supply was finished. As a result, the processing time was in the range of 80 minutes or more and 100 minutes or less. Table 1 shows various processing conditions and results. For these examples, the hot metal 2 was pretreated by using the hot metal wheel 1 as the hot metal transport container in the same manner as in the above embodiment. Processing No. 1-5 satisfy the conditions of the post-treatment slag basicity C / S and the hot metal temperature of the present invention . Processing No. In 6-26, the post-treatment slag basicity C / S or hot metal temperature is outside the range of the present invention.

Processing No. In 1 to 5, the hot metal temperature at the end of the treatment was set to the range of 1200 to 1260 ° C., and the slag basicity was adjusted to the range of 1.0 to 1.8 according to the method of the present invention. As a result, the hot metal P concentration after the treatment was 0.004% by mass or less. Processing No. In 6-9, the Si before the treatment was low, and the hot metal temperature after the treatment was in the range of 1180 ° C. or higher and 1200 ° C. or lower. Processing No. The temperature after treatment of 10 to 14 was in the range of 1270 to 1290 ° C. Processing No. In Nos. 15 to 18, the amount of CaO flux added was small, and the slag basicity after the treatment was in the range of 0.7 to 0.9. Processing No. In 19 to 22, the amount of CaO flux added was large, and the slag basicity after treatment was in the range of 1.9 to 2.1. As a result, the processing No. In 6 to 22, the P concentration after the treatment was in the range of 0.005 to 0.010% by mass.
Processing No. In 23-25, the post-treatment slag basicity or the hot metal temperature was out of the invention range, so that the post-treatment P concentration exceeded 0.010% by mass.

According to the present invention, it is applicable not only to the above-exemplified torpedo wagon but also to a method of blowing a dephosphorizing agent into a refining container to dephosphorize the hot metal. According to the present invention, it is possible to melt a hot metal having an extremely low P concentration that reduces the dephosphorization treatment in the subsequent steps.

1 Torpedo wagon (refining container)
10 Container 100 Furnace 2 Hot metal 3 Slag 4 Injection lance 5 Lime-based flux 6 Oxidizing agent 7 Carrier gas

Claims (3)

In a method of dephosphorizing the hot metal by blowing a refining agent (excluding halides) containing lime-based flux and an oxidizing agent into the hot metal held in the smelting container, the temperature at the end of the treatment is in the range of 1200 ° C. or higher and 1260 ° C. or lower . The basicity of the slag at the end of the treatment is adjusted to a range of 1.0 or more and 1.8 or less . Here, the basicity of the slag is the mass ratio of CaO and SiO ₂ . Dephosphorization method. The oxidizing agent contains CaO in the range of 10% by mass or more and 20% by mass or less, SiO ₂ in the range of 5% by mass or more and 10% by mass or less, and CaO / SiO ₂ in the mass ratio of 1.2 or more. 2.2 The method for dephosphorizing hot metal according to claim 1, which is in the range of 2.2 or less. The method for dephosphorizing hot metal according to claim 1 or 2, wherein the smelting container is a torpedo wagon.

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