JP6164151B2 - Method for refining molten iron using a converter-type refining furnace - Google Patents

Description

The present invention relates to a method for refining molten iron using a converter-type refining furnace, and in particular, proposes a refining method performed in consideration of the use of slag in a generating furnace for land use without adversely affecting refining. .
In refining in the converter, the hot metal is decarburized to form molten steel, but it is not only difficult to distinguish between hot metal and molten steel in the middle of refining, but also complicated, so in the following explanation, And molten steel are collectively called “molten iron”. However, when the distinction between hot metal and molten steel is clear, it is indicated as hot metal or molten steel.

  In general, prior to decarburizing and refining the hot metal in a converter-type refining furnace, a hot metal pretreatment for removing silicon and phosphorus in the hot metal in advance is performed. The hot metal pretreatment is carried out for the purpose of reducing the amount of flux used for refining, increasing the purity of molten steel, preventing manganese from overoxidation during converter operation, or reducing the amount of slag. Various methods including these processes have been proposed.

By the way, at the time of the hot metal preliminary treatment, refining slag is generated in the furnace, but when this refining slag, for example, converter slag is used for various purposes, it is included in the slag depending on the use. It is necessary to prevent elution of fluorine and the like. Therefore, in the conventional hot metal preliminary treatment, a method of refining without using fluorite (CaF ₂ ), which is a fluorine source used for the purpose of increasing the dephosphorization reaction efficiency, has been studied. In recent years, the steel industry has been required to reduce greenhouse gas emissions. For this reason, the steel industry is studying a refining method that reduces the usage rate of blast furnace hot metal, which requires a large amount of energy to reduce iron oxide, while increasing the usage rate of cold iron sources such as iron scrap. Under such a background, it can be seen that the hot metal preliminary treatment in recent years tends to increase the usage ratio of the cold iron source while improving the refining method.

  By the way, the recent hot metal pretreatment method for desiliconization and dephosphorization of hot metal is performed by adding a refining agent (medium melting material) such as quick lime to the hot metal and adding a solid oxygen source such as gaseous oxygen or iron oxide. In this method, silicon and phosphorus in the hot metal are removed in the slag. As refining furnaces for pre-treatment of the hot metal, in addition to conveyor refining furnaces such as torpedo cars and blast furnace pots, converter type refining furnaces (smelting furnaces) are used, but in order to use a large amount of scrap It is advantageous to use a converter type refining furnace having a large furnace volume.

  In Patent Document 1, in a refining method for a converter that uses a converter to perform desiliconization treatment and dephosphorization treatment, after intermediate removal after desiliconization treatment, dephosphorization is performed using the same converter. A method of performing processing is disclosed. In this method, a method of controlling the slag composition to suppress the dephosphorization after desiliconization and facilitate the subsequent dephosphorization process is proposed.

  Further, Patent Document 2 discloses a hot metal preparatory process in which desiliconization treatment is performed using a converter type refining furnace, and after dewatering and discharging, the desiliconized hot metal is returned to the reaction refining furnace again to perform dephosphorization treatment. A processing method is disclosed. In this hot metal pretreatment method, the silicon concentration in the hot metal after desiliconization treatment, the basicity of slag, and the iron oxide concentration are optimized, so that dephosphorization can be efficiently carried out without using fluorite, and desiliconization. This is a method of melting scrap during processing and / or dephosphorization processing.

    In Patent Document 3, when performing desiliconization and dephosphorization of hot metal using a converter-type refining furnace, first, the hot metal discharged from the blast furnace is charged into the converter-type refining furnace. Next, the intermediate waste treatment is performed to leave a part of the slag after the hot metal and desiliconization treatment in the smelting furnace, and subsequently to the hot metal after desiliconization that is left in the smelting furnace. After the dephosphorization treatment, most of the slag remains in the converter type refining furnace, and then at least untreated hot metal is charged into the refining furnace containing the slag after the dephosphorization treatment. Thus, a method of performing a silicon removal treatment is disclosed.

JP 2001-271113 A JP 2002-129221 A JP2012-8811

Any of the techniques disclosed in these patent documents is a method of performing desiliconization treatment prior to hot metal dephosphorization treatment and discharging the desiliconization slag after this treatment in advance. In these techniques, the desiliconization treatment usually adjusts the basicity of the slag (the weight ratio of the CaO component to the SiO ₂ component in the slag) to about 1.5 or less without using much lime. . This is because slag having a basicity of 1.5 or less is free from problems such as hydration and expansion, and the pH of the elution water can be kept low, so that it becomes a slag suitable for use in land applications. .

  However, since such desiliconized slag has a high viscosity, it is known to cause a slag forming phenomenon that is expanded by CO gas generated by the reaction between hot metal and oxygen during the desiliconization process. If the slag forming occurs excessively, slag will be ejected from the furnace port of the converter-type smelting furnace during blowing, or the slag will overflow from the pot containing the slag when desiliconized slag is discharged. Sometimes.

  In addition, when the slag solidified after forming and the gas is not completely removed, the slag becomes porous and has a low density. Therefore, from the viewpoint of utilizing this slag for land use such as roadbed materials, the use of the slag is limited because the strength of the slag is inferior.

  Accordingly, an object of the present invention is to refine molten iron using a converter type vessel that is also effective for making the smelting slag generated during the refining treatment of hot metal or the like suitable for various uses, for example, land use. To propose a method.

  As a result of diligent research aiming at the development of a technology that solves the above-described problems of the prior art, the inventors have found that in a method of refining hot metal typically using a converter-type refining furnace, By making the density of the slag produced in the above or more appropriate value, the density of the slag discharged after blowing can be kept high, and by using this, the slag is used for land applications such as roadbed materials I found it to be suitable for.

That is, the method for refining molten iron using the converter type vessel according to the present invention developed to achieve the above-mentioned object is performed during the desiliconization process when the molten iron refining process is performed using the converter type refining furnace. the density of the desiliconization processed slag said transfer furnace type smelting furnace wherein refining furnace by changing the generation rate of CO gas generated in adjusting the density of the outside of the furnace discharge the slag after refining process completion 0 A method for refining molten iron with a converter-type refining furnace, characterized in that the amount is ³ g / cm ³ or more .

In the method for refining molten iron by the converter type refining furnace according to the above configuration of the present invention,
(1) The CO gas generation rate generated in the converter-type refining furnace is determined by measuring or estimating the slag height in the furnace during the desiliconization process, and from the top blowing lance according to the obtained slag height. Changing at least one of the supply amount of the gaseous oxygen source, the lance height of the top blowing lance, and the stirring gas supply amount from the bottom blowing tuyere,
(2) refining process of the molten iron, the molten iron was tapped from the blast furnace and charged into a converter type smelting furnace performs the desiliconization treatment and then, as it is part of the slag after hot metal and desiliconization treatment The intermediate waste that remains in the smelting furnace is treated, and subsequently, the lime-based medium is added to the hot metal and slag after the desiliconization process that remains in the smelting furnace, and oxygen is blown away. After the dephosphorization treatment, a part or all of the slag is left in the smelting furnace, and after the dephosphorization process, at least in the smelting furnace containing a part or all of the slag. The uncharged hot metal is charged and the next charge is desiliconized.
It can be considered as a more preferable solution.

  According to the present invention related to the above-described configuration, it is possible to obtain a slag having a suitable density as a slag for land use such as a roadbed material from a refining slag generated in a refining furnace such as a converter, It will be possible to manufacture reliably without hindering refining. In particular, the present invention can provide a technique that is effective when using desiliconized slag that is subjected to intermediate waste after desiliconization processing of slag such as roadbed material.

It is sectional drawing which shows the example of the converter-type refining furnace which can blow an upper bottom. It is explanatory drawing of the process of a converter type refining furnace.

  The present invention is a method for refining molten iron using a converter-type refining furnace (hereinafter mainly described in the example of “converter”). For the implementation of this method, it is preferable to use, for example, a converter 1 capable of blowing the upper and lower bottoms as shown in FIG. In the case of the converter 1, the top blowing refining is performed by blowing oxygen gas 8 from the tip of the top blowing lance 2 that can be moved up and down toward the hot metal 5 in the furnace. Here, industrial oxygen is used as the oxygen gas 8. Further, bottom blowing refining is performed using a bottom blowing tuyere 3 provided at the bottom of the converter 1. As the bottom blowing gas 9, it is common to use a gas containing oxygen gas or an inert gas such as Ar gas or nitrogen gas. In addition, the bottom 5 gas is stirred into the hot metal 5 by blowing the bottom blowing gas into the hot metal. It may be a gas having a function of strengthening the iron and promoting the melting of the cold iron source, or a gas having a function of blowing a solvent in the molten iron together with the carrier gas. In addition, the code | symbol 4 in a figure is the tap for discharging hot metal 5 after refining.

  In refining a converter, an oxygen source is first supplied to the hot metal contained in the furnace. As a result, components other than C such as Si, Mn, P, and Ti in the hot metal are oxidized into oxides. Also, slag layer on hot metal bath surface with reaction products such as quick lime and calcined dolomite, iron ore, mill scale, manganese ore, coke and alloy iron (Fe-Mn, Fe-Si etc.) added as an auxiliary material Form.

  What is characteristic in the present invention is that the density of the refining slag generated in the converter is adjusted. The reason is that, as described above, this slag is used as a road base material. For that purpose, it is necessary to make the slag discharged | emitted by a slag accommodation pan into a high density thing. In preliminary experiments conducted by the inventors, it has been found that the greater the density of slag in the converter during blowing, the greater the density of slag discharged into the slag containing pan. The slag density is obtained by dividing the slag weight by the volume.

  The slag density in the converter during blowing can be determined as follows. Here, the weight of the slag is the sum of the auxiliary materials charged into the converter before and during the blowing and the oxides produced by oxidizing the components in the hot metal during the blowing. Can be obtained. On the other hand, the volume of slag can be obtained by measuring the height of slag during blowing. Since slag exists on the molten iron, if the height of the molten iron at the time of blowing is known, it can be obtained from the height of the slag in consideration of the wall shape in the converter.

  The height of the slag also depends on the gas flow rate flowing into the slag during the refining process. The gas flowing into the slag includes a stirring gas from the bottom blowing tuyere and a gaseous oxygen source and a solid oxygen source supplied into the furnace and a CO gas generated by the reaction of carbon in the molten iron. In ordinary converter refining, since the former is small compared to the latter, the influence on the slag height is rather governed by the CO gas generation rate in the furnace.

  In general, the slag expands when the gas in the furnace flows into the slag, which is called a slag forming phenomenon. Therefore, the degree of slag forming can be changed by changing the CO gas generation rate, and by extension, the slag height can be adjusted by controlling the CO gas generation rate. In this way, the density of the furnace slag can be adjusted.

  In addition, the height of the in-furnace slag during blowing can use a known method such as a direct measurement using a sub lance or a non-contact measurement such as a microwave method.

  As described above, the density adjustment of the refining slag generated in the furnace can be performed by controlling (changing) the CO gas generation rate as described above. However, the CO gas generation rate can be controlled from the top blowing lance. The CO gas generation rate can be adjusted by changing one or more of the supply flow rate of the gaseous oxygen source, the lance height of the top blowing lance, and the supply flow rate of the stirring gas from the bottom blowing tuyere. And adjusting the density of the slag to a desired value. Here, the lance height of the upper blowing lance is the distance from the lower end of the upper blowing lance to the hot metal bath surface in a stationary state.

  According to a preliminary experiment by the inventors using a converter, increasing the acid feed rate from the top blowing lance or increasing the lance height from the top blowing lance increases the CO gas generation rate, while bottom blowing. It was found that the CO gas generation rate decreased by increasing the stirring gas flow rate from the tuyere. Any of these operations is a method of changing the generation rate of CO gas by changing the rate at which the oxygen source supplied into the furnace reacts with the carbon in the hot metal.

  For the generation rate of CO gas in the furnace, for example, as described in JP 2012-8811 A, a gas sampling probe for collecting the exhaust gas generated in the flue is installed, and the CO gas concentration is analyzed. You can go and evaluate. The density of the slag generated in the furnace is not uniquely determined because it depends on the physical properties such as slag viscosity and surface tension, the temperature of the hot metal, the volume and shape of the furnace, but it is desirable In consideration of these factors, the control is performed through the control of the CO gas generation rate.

  The control of the generation rate of CO gas in the furnace and the accompanying control of the density of slag in the furnace are not limited to during the desiliconization process, but can also be performed based on the same concept during the dephosphorization process. .

In the present invention, the density of slag at the end of blowing is set to 0.3 g / cm ³ or more by the above-described blowing control. If it is such a density, the density of the slag discharged to the slag containing pan after the end of blowing will maintain a density of about 0.25 g / cm ³ or more necessary for use in land areas such as roadbed materials. Can do. And when calculating | requiring slag of higher density, it is also considered to perform the process of sprinkling and cooling the discharged slag.

However, it is necessary to cause a certain amount of slag foaming in the furnace in order to sufficiently discharge slag after the end of blowing. For that purpose, it is preferable that the density of the in-furnace slag at the end of blowing is 1.0 g / cm ³ or less. When the density of the slag in the furnace is larger than this value, the slag fluidity is lowered and it becomes difficult to discharge the slag, and the slag remains excessively in the furnace and hinders the next charge blowing.

  Below, an example of the hot metal preliminary processing method using the converter 1 is shown. In the figure, (A) is hot metal charging, (B) is desiliconization treatment, (C) is intermediate waste treatment, (D) is dephosphorization treatment, and (E) is hot water treatment.

(1) First, the hot metal charging step (A) will be described.
In this step (A), the converter 1 is charged while the slag 7 after the dephosphorization treatment (hereinafter simply referred to as “post-dephosphorization slag”) 7 generated in the previous hot metal preliminary treatment remains in the converter 1. New hot metal (untreated) 11 is charged from the pan, or the new hot metal 11 is charged after the cold iron source 12 such as iron scrap is charged before the new hot metal 11 is charged. As the cold iron source 12 to be charged in advance, iron scrap such as direct reduced iron or cold iron may be used as a main component in addition to iron scrap stipulated in the “Iron Scrap Inspection Standard” of the Japan Iron Source Association. .
Here, the slag 7 after the previous dephosphorization treatment to be left in the smelting furnace 1 in preparation for the next smelting is the slag density adjusted as described above. It is used for the purpose of adjusting the slag basicity at the time of silicon treatment. The basicity (mass% CaO / mass% SiO ₂ ) (hereinafter simply referred to as “basicity”) of the slag after the dephosphorization treatment is 1.2 or more, preferably 1.4 or more. The reason is that if the basicity of the slag 7 after the dephosphorization treatment at the end of the previous dephosphorization treatment is less than 1.2, even if this slag remains, it is insufficient for adjusting the basicity in the desiliconization treatment, This is because it is necessary to add a large amount of lime-based medium. Although there is no particular limitation on the upper limit of the basicity of the slag after the dephosphorization treatment, the basicity of the slag in the normal hot metal dephosphorization treatment is about 3.0 or less, so it is necessary to further increase the basicity. Absent.

  The slag after dephosphorization treatment (last time) 7 to be left in the furnace requires 30 mass% or more of the amount of slag generated during the last dephosphorization treatment of hot metal in order to effectively adjust the basicity. More preferably, the amount is 60 mass% or more. In the present invention, if the total amount of slag remaining in the furnace after dephosphorization is used for desiliconization of new hot metal, the basicity adjustment in the desiliconization is more effective. Become. In addition, if such a method is continuously performed, the hot metal pretreatment slag discharged becomes homogeneous only with the slag after desiliconization treatment, and slag is not mixed after the dephosphorization treatment with high basicity. There is no problem of expansion of slag or elution of alkali due to the reaction. Therefore, the method of the present invention is extremely effective for increasing the use of slag.

The slag 7 after the dephosphorization treatment has a relatively high basicity and a low temperature (about 1350 ° C. or less), and therefore has low fluidity. Therefore, even if a cold iron source is charged on the slag after the dephosphorization treatment, the cold iron source is not caught in the slag and the dissolution is not delayed, so that the so-called decarburized slag remains in the furnace. Thus, inefficient operation in terms of heat balance and mass balance, such as adding a large amount of coolant and solidifying, is eliminated. In addition, the slag 7 after the dephosphorization treatment has a small density (≦ 3.0 g / cm ³ ) due to the above characteristics, and is rich in solid phase and low in fluidity, so that a large amount of fine metallic iron is contained in the tissue. Even after the slag is pulverized and magnetically separated, it contains about 10 mass% or more of metallic iron. Conventionally, this slag was discharged out of the system, but according to the present invention, after this dephosphorization treatment, the slag can be carried over to the next charge, so most of the metallic iron in the slag after this dephosphorization treatment can be carried out. There is also an effect of reducing iron loss by collecting it in the hot metal.

  In addition, since the fluidity | liquidity is comparatively high about the slag 10 at the time of completion | finish of a desiliconization process (henceforth "the slag after a desiliconization process"), the metal iron content in this slag is easy to coarsen. Accordingly, such slag has a small amount of metallic iron that remains in the slag without being recovered after the slag crushing and magnetic separation processes. Therefore, in the method of the present invention, iron loss into the slag can be reduced throughout the hot metal pretreatment.

(2) Next, the desiliconization process (B) shown in FIG. 2 (B) will be described.
This step (B) is a process of desiliconization by raising the converter 1 and supplying the oxygen gas 8 to the hot metal 5 in the furnace via the top blowing lance 2. In this desiliconization treatment, the silicon source 15 accommodated in the hopper 13 and the lime-based medium 16 accommodated in the hopper 14 are charged into the converter 1 via a chute, and the carbon material or the heat source Similarly, iron oxide or the like serving as a silicon source or an oxygen source is charged. As an oxygen source for the desiliconization treatment, it is preferable to use only oxygen gas 8 without using iron oxide having a large endotherm from the viewpoint of dissolving a large amount of cold iron source 12.

In this silicon removal treatment, silicon contained in the molten iron 5 or silicon contained in the silicon source 15 and the cold iron source 12 and transferred to the molten iron by dissolution reacts with the oxygen source (Si + O ₂ → SiO ₂ ). Desiliconization helps increase the reaction efficiency in the subsequent dephosphorization treatment. Oxidation heat is generated during the desiliconization reaction, and the hot metal temperature is raised by the oxidation heat, and the dissolution of the cold iron source 12 in the hot metal is promoted.

  The composition of the slag at this desiliconization stage takes into consideration the amount of slag 7 after the previous dephosphorization process previously left in the furnace, the estimated value of the composition, and the amount of silicon dioxide produced by the above reaction. To be determined. First, the basicity of the slag during the silicon removal treatment is adjusted to 0.8 or more and 1.5 or less. The reason is that when the slag basicity during the desiliconization treatment is less than 0.8, depending on the molten iron Si concentration, a phenomenon of rephosphorization is observed due to a decrease in the dephosphorization ability of the slag 7 after the dephosphorization treatment. . On the other hand, if the slag basicity is greater than 1.5, the solid phase ratio increases due to the increase of undenitrated CaO, so that the fluidity of the slag 7 is deteriorated after dephosphorization treatment, and this slag cannot be discharged. Cases arise. The upper limit of preferable slag basicity is about 1.2.

  Then, the basicity of the slag at the end of the desiliconization process is adjusted to be 0.5 or more and 1.5 or less. If the basicity of the slag at this stage (the slag after desiliconization treatment) is less than 0.5, the phosphorus concentration in the hot metal is increased by recovering phosphorus from the slag 7 after the previous dephosphorization treatment left in the furnace, This is because the dephosphorization load in the subsequent process becomes large and becomes inefficient. Therefore, the basicity of the slag after the desiliconization treatment at the end of the desiliconization treatment is 0.5 or more, preferably 0.8 or more. Also, if the slag basicity at this stage is higher than 1.5, the fluidity of the slag will be reduced, so the amount of waste during the next intermediate waste will be reduced or the amount of waste will be difficult to control. Therefore, the slag basicity at the end of the desiliconization treatment is 1.5 or less, preferably 1.2 or less. In addition, in order to adjust the basicity, steelmaking slag selected from decarburized slag, dephosphorized slag, ladle slag, and the like can be used as a medium material in addition to lime-based medium materials such as quick lime, limestone, and dolomite.

As described above, the density of the desiliconized slag when the desiliconization process is finished is adjusted to about 0.3 to 1.0 g / cm ³ by controlling the CO gas generation rate described above. After the intermediate waste to be described later, the waste slag is a preferable material as a slag for materialization.

  Next, the hot metal temperature at the end of the desiliconization treatment is adjusted to 1240 ° C. or higher and 1400 ° C. or lower, preferably 1260 ° C. or higher and 1350 ° C. or lower. The reason is that when the temperature is higher than 1400 ° C., dephosphorization is caused from the dephosphorization slag remaining in the furnace, resulting in an increase in the phosphorus concentration in the hot metal, and the dephosphorization load in the subsequent process becomes large, which is not efficient. In addition, it is necessary to increase the concentration of magnesia in the slag in order to prevent the lining magnesia carbon bricks from being worn, which increases costs. On the other hand, when the hot metal temperature is less than 1240 ° C., the fluidity of the slag is lowered, and there is a problem that the amount of waste during the next intermediate waste is reduced or the control of the amount of waste becomes difficult. In addition, the scrap melting rate is reduced.

  Further, the hot metal temperature at this stage is also necessary for efficient dephosphorization in the next dephosphorization step. For example, if the hot metal temperature at the end of the desiliconization treatment is set to 1350 ° C. or less, it can be expected that the coolant such as iron ore added for temperature adjustment in the dephosphorization treatment is greatly reduced. In the case where the desiliconization process and the dephosphorization process are continuously performed in the same refining furnace, it is difficult to charge the scrap before the dephosphorization process in terms of working time. In addition, the cold iron source that can be charged from the furnace during processing is expensive, sized, or limited in quantity such as bullion generated in the steelworks. In addition, it is difficult to use a large amount of cold iron source due to restrictions on the number of secondary raw materials using the furnace charging device. In short, the coolant conventionally used in the dephosphorization process is limited to iron oxide such as iron ore, and it is normal that an inexpensive cold iron source such as scrap cannot be fully utilized.

  Generally, in the refining in the desiliconization treatment stage, it is relatively easy to increase the amount of scrap used, and thereby the hot metal temperature after the desiliconization treatment can be reduced to 1350 ° C. or less. As a result, the amount of iron oxide used in the dephosphorization process can be greatly reduced. As a result, it is possible to reduce a large endothermic component due to the decomposition reaction of iron oxide, and to distribute the amount corresponding to the amount of heat to melting the cold iron source in the desiliconization process. If the temperature after desiliconization decreases, the scrap may remain undissolved, but the undissolved scrap is held in the furnace together with the hot metal and can be dissolved until the next dephosphorization process. It is. That is, for the cold iron source, there is no operational problem as long as the dissolution is completed by the end of the dephosphorization treatment.

  In addition, the additive includes silicon that becomes the oxide (silicon that exists in an oxidizable form and silicon that is not an oxide. Silicon that is not an oxide includes iron silicide, metal silicon, silicon carbide, and silicon nitride. Alternatively, it refers to those contained as other silicides, but typical additives include, in addition to ferrosilicon, powders containing about 60 mass% of silicon carbide formed into briquettes (hereinafter referred to as silicon carbide briquettes), etc. Can give.

  As an analysis method of silicon that is not an oxide in the additive, in addition to the analysis method of ferrosilicon described in JIS G 1312, total silicon analysis, acid-soluble silicon analysis, total carbon analysis, total oxygen analysis, total nitrogen analysis It can be estimated by combining a thermal mass analysis, a carbon analysis by a combustion method with an adjusted temperature history, an analysis of other contained elements, a compound analysis by an X-ray diffraction method, and the like.

  As the silicon source to be added, ferrosilicon is typically used, but inexpensive silicon carbide briquettes mainly composed of silicon carbide, waste refractories mainly composed of silicon carbide, and the like can also be used. In addition, it is not necessary to rely only on this silicon source as a heat source, and other heat sources such as carbon materials may be used in combination as long as productivity does not decrease. It is desirable to add the carbonaceous material by predicting the amount of decarburization so that the carbon concentration in the hot metal at the end of the desiliconization treatment is 3.3 mass% or more. This is because if it is less than 3.3 mass%, the heat source is insufficient in the subsequent dephosphorization and decarburization processes, and the carburization rate on the surface of the cold iron source such as scrap is reduced, resulting in a decrease in the dissolution rate.

  In addition, there is a carbon source as an additive. As this carbon source, the above-mentioned silicon carbide is used in addition to a carbon material such as coke or earthy graphite. In addition, auxiliary materials such as quick lime, light-burned dolomite, and magnesia clinker are used as the solvent material. In addition, slag such as dephosphorization slag, decarburization slag and ladle slag is also used as a source of calcium oxide or magnesium oxide. In addition, as an example of an inexpensive auxiliary material, calcium or magnesium carbonate or hydroxide can be used. However, since these have a large endotherm, it is desirable to distinguish them from other solvent materials. .

In order to improve the exhaustability of the slag 10 after the silicon removal treatment, it is effective to cause the refining slag 6 in the converter 1 to be appropriately formed. Therefore, in order to obtain a stable rejection rate in the next exhausting step, it is preferable to supply oxygen in a stoichiometric amount or more necessary for oxidizing the silicon in the hot metal and the added silicon source. Intensity of oxygen supplied to molten iron during desiliconization treatment, the amount stoichiometrically required for desiliconization to 2 Nm 3 / ^t or more, preferably it is preferable that the amount added over 4 Nm 3 / ^t. The silicon concentration in the hot metal at the end of the desiliconization treatment is 0.2 mass% or less, preferably 0.1 mass% or less, more preferably 0.05 mass% or less. This makes it possible to maintain the forming state even when exhausting after the silicon removal treatment, to maintain good exhaustability, and to suppress dephosphorization from the slag to the molten iron.

According to the inventors' research, oxygen blowing for desiliconization treatment has a top blowing acid rate of 1 to 2 Nm ³ / min · t and a bottom blowing gas blowing rate of 0.02 to 0.2 Nm ³ / min. -It has been confirmed that the above-mentioned effect can be obtained at about t. In this oxygen blowing, in order to adjust the slag density described above, the above-mentioned acid feeding rate and blowing rate are adjusted in relation to the adjustment of the top blowing lance height and the amount of the bottom blowing stirring gas supply. It is necessary to adjust within the range.

  The control of the silicon concentration is performed in combination with the control of the slag basicity and the control of the hot metal temperature described above. By such control, the lime content in the slag after dephosphorization is effective without dephosphorization even if the desiliconization of hot metal is performed while leaving the entire amount of slag after dephosphorization in the previous treatment in the furnace. It can be used for. In the present invention, in addition to the control of the silicon concentration, the slag basicity, and the control of the hot metal temperature, the slag density adjustment to be generated is combined and the slag after the dephosphorization treatment in the previous treatment is left in the furnace. The phosphoric acid concentration in the slag is increased, which promotes slag forming. In particular, phosphoric acid in the slag has an effect of lowering the surface tension of the slag, and promotes the reaction with the hot metal and the dispersion of fine bubbles. Therefore, a relatively low iron oxide concentration such that (T.Fe) is about 10 mass%. In this case, appropriate slag forming is maintained and the slag is effectively removed from the slag.

(3) Next, the intermediate waste process (C) shown in FIG.
In the hot metal pretreatment method according to the present invention, a high-density, low-base, which is excellent as a material-use application material, is produced at the time of the desiliconization process by providing an exhaust process after the desiliconization process described above. After the desiliconization process, the intermediate slag is discharged to discharge the slag from the converter 1. In addition, the removal of the slag 10 after the desiliconization treatment is also effective for reducing the amount of lime-based solvent used for adjusting to the appropriate slag basicity in the dephosphorization treatment that is the next step. is there. In addition, in the case of the hot metal pretreatment method according to the present invention in which desiliconization of new hot metal is performed while a large amount of slag after dephosphorization generated in the previous hot metal pretreatment remains in the furnace, the slag is changed to hot metal. Therefore, the concentration of phosphoric acid in the desiliconized slag becomes higher than in the prior art. Therefore, if a large amount of desiliconized slag remains, the amount of phosphoric acid in the furnace slag in the next dephosphorization process will be excessive and the dephosphorization effect will be reduced, which is important in preventing this. .

  In the hot metal pretreatment method described above, in the case where the processes of steps (A) to (C) described above are repeatedly performed continuously, phosphoric acid is accumulated in the furnace if the slag is insufficiently discharged after the desiliconization process. It is necessary to be careful as it advances. If the amount of phosphoric acid in the furnace slag increases too much in the dephosphorization stage, the dephosphorization reaction efficiency decreases due to an increase in the phosphoric acid concentration in the slag, and the phosphorus concentration in the hot metal after the treatment increases, This is because the amount of lime-based medium necessary for the reaction increases.

  Therefore, in the present invention, the removal rate of slag after desiliconization treatment (%) = (discharge slag mass%) × 100 / (in-furnace slag mass% at the end of desiliconization treatment)) is preferably at least 40%, preferably 60% or more. The reason is that when the rejection rate is less than 40%, the amount of the lime-based solvent used in the dephosphorization process in the next step increases as described above, and when the amount of slag increases, slag forming occurs. This is because slag jetting from the furnace port occurs during the dephosphorization process, resulting in an operational failure due to slag jetting. When the slag forming has subsided, the slag removal rate is reduced, and therefore it is preferable that the time from the end of the desiliconization process to the start of the tilting of the furnace body for the removal is preferably within 4 minutes. .

  If the basicity of the slag after desiliconization treatment required in the stage of the evacuation process is less than 0.5, the slag viscosity becomes high, and a good evacuation rate cannot be ensured. On the other hand, if the basicity of the slag after the desiliconization process exceeds 1.5, solid phase slag is generated, the fluidity of the slag is lowered, and the rejection rate is lowered. Therefore, from the viewpoint of securing the slag evacuation property and evacuation rate, it is sufficient to set the basicity of the slag to about 0.5 to 1.5, but the recovery from the slag in the desiliconization process is sufficient. The basicity of the slag is preferably adjusted to a range of 0.8 to 1.2 in consideration of prevention, reduction of the amount of lime-based medium and slag density control.

  The slag forming is a phenomenon necessary for controlling the density of the slag as described above, but (T.Fe) in the slag, that is, iron oxide and hot metal, or suspended in the slag in the intermediate waste process. Since it progresses also by the fine CO bubble produced | generated by reaction with the granular iron containing carbon which becomes turbid, adjustment of T and Fe also has influence in addition to the oxygen blowing. When an appropriate (T.Fe) concentration range for inducing such a reaction was verified, when (T.Fe) <5 mass%, slag forming for the necessary density adjustment was insufficient. Therefore, the driving force at the time of discharging the slag is reduced due to the tilting of the converter, and the discharging is insufficient. On the other hand, in the case of (T.Fe)> 25 mass%, the generation of CO bubbles in the fluent drastically progressed and the bumping phenomenon was confirmed, so the slag discharge operation was forced to be interrupted. Therefore, the appropriate range of (T.Fe) in the slag at the end of desiliconization, that is, in the process of intermediate waste, is determined as (T.Fe) = 5 to 25 mass% in consideration of the slag density.

  Further, in the treatment of this evacuation step, if the temperature of the slag after desiliconization is low (less than 1260 ° C.), the slag viscosity increases due to the generation of solid slag and the viscosity of the liquid phase slag increases. This causes a decline in the rejection rate. Therefore, the cold iron source intensity is adjusted according to the initial conditions of the hot metal used, and at least one of the heat source addition amount and oxygen intensity of silicon carbide, ferrosilicon, etc. By setting the hot metal temperature to 1260 ° C. or higher, the slag temperature is also set to 1260 ° C. or higher.

  However, if most of the generated slag is removed after the desiliconization treatment, hatching of the lime-based medium added newly in the dephosphorization treatment in the next step is delayed, which becomes an inhibiting factor for the dephosphorization reaction. On the other hand, hatching can be promoted by adding fluorite. However, as described above, the use of the slag is restricted, and the use of the slag is hindered. There is also a method of promoting hatching by adding iron oxide such as iron ore, but this method has a large heat loss due to decomposition endothermic reaction of iron oxide, and the amount of heat available for melting of the cold iron source is reduced. So it's not a good idea.

  Therefore, in order to promote the hatching of the lime-based medium without using fluorite or iron oxide in the dephosphorization treatment stage, an appropriate amount of the post-desiliconization slag having a preferable composition, temperature and density is placed in the furnace. It is also effective to promote the hatching by using silicon dioxide or iron oxide in the slag. In addition, when discharging slag after desiliconization treatment, it is 4 to 20 kg / h by adjusting the tilt angle of the furnace body while maintaining a preferable removal rate of desiliconization slag of 40% or more, preferably 60% or more. After the desiliconization treatment of t, the slag is discharged so as to remain in the furnace. Accordingly, the dephosphorization reaction can be efficiently promoted without using iron oxide in the dephosphorization treatment stage. Therefore, it is possible to indirectly use the amount corresponding to the heat of reaction due to the decomposition endotherm of iron oxide as heat for melting the cold iron source in the desiliconization process. In this regard, if the residual amount of slag after desiliconization is less than 4 kg / t, it is necessary to use iron oxide for promoting the hatching of the lime-based solvent in the next dephosphorization step. On the other hand, when this exceeds 20 kg / t, there is a problem that the amount of lime-based medium is increased or the dephosphorization operation is hindered.

(4) Next, the dephosphorization process (D) shown in FIG. 2 (D) will be described.
After the intermediate waste disposal step (C), the lime-based medium 16 is added to the hot metal remaining in the same converter 1 and oxygen blowing is performed as an oxygen source, so that the slag density is adjusted. While the hot metal is dephosphorized. In order to reduce heat loss, it is preferable to use only the oxygen gas 8 from the top blowing lance 2 as the oxygen source used in this dephosphorization process. Phosphorus in the hot metal is oxidized by oxygen in the supplied oxygen source to become phosphorus oxide (P ₂ O ₅ ), and this phosphorus oxide is stably added to the slag generated by the hatching of the lime-based solvent 16. It is taken in and hot metal dephosphorization proceeds. In order to advance the dephosphorization reaction efficiently, the lime-based solvent 16 is added so that the basicity of the slag after the dephosphorization treatment (the slag 7 after the dephosphorization treatment of the current charge) is 1.2 to 3.0. In addition, the dephosphorization treatment is performed so that the hot metal temperature after the completion of the dephosphorization treatment is 1280 ° C. or higher and 1360 ° C. or lower by acid feeding.

  When the slag basicity of the slag 7 after the dephosphorization treatment generated during the dephosphorization treatment is less than 1.2 or the hot metal temperature is higher than 1360 ° C., the dephosphorization ability of the slag is lowered, and the phosphorus concentration in the hot metal after the treatment is sufficient. There are cases where it cannot be reduced. On the other hand, when the slag basicity exceeds 3.0, it becomes difficult to hatch the lime-based medium, and the cost of the lime-based medium increases, and even if the hot metal temperature is less than 1280 ° C., the lime-based medium is also hatched. Becomes difficult, and the amount of heat during the decarburization process in the subsequent process is insufficient. And in order to fully secure the calorie | heat amount in the decarburization process stage in a post process, while the hot metal temperature after completion | finish of a dephosphorization process shall be 1280 degreeC or more and 1360 degrees C or less, and the carbon concentration in the hot metal at the time of completion | finish of a dephosphorization process It is desirable to adjust the amount of oxygen used and / or the amount of carbon added in the desiliconization process and the dephosphorization process so as to be 2.8 mass% or more. This also works effectively in adjusting the slag density.

  In refining as described above, there are cases where the Si concentration, P concentration, and temperature in the hot metal change and the hot metal temperature after desiliconization is low, or the hot metal P concentration is high and the dephosphorization load is high. Arise. In this case, in order to promote dissolution of lime in the dephosphorization step, it is effective to spray a lime source such as powdered lime or calcium carbonate onto the bath surface from the top blowing lance with oxygen gas or inert gas. In the region where the top-blown oxygen is irradiated on the bath surface, direct decarburization reaction and iron oxidation occur, resulting in a high temperature of about 2000 ° C. By adding a powdery lime source to the region , Melting is promoted.

In the above-mentioned hot metal preliminary treatment method, since SiO ₂ -containing slag that contributes to melting of lime is discharged after desiliconization treatment, early dissolution by projection of a powdery lime source is effective. Further, in this method, the melting heat of the cold iron source is promoted by utilizing the oxidation heat of Si in the hot metal. Therefore, it is preferable to operate at a higher temperature with respect to the dissolution rate of scrap in the hot metal. However, high temperatures are rather disadvantageous for rephosphorization and dephosphorization during desiliconization. Therefore, in the present invention, powdered iron oxide is simultaneously blown into the region where the above blown oxygen is injected, so that only the reaction region is locally cooled by the decomposition reaction (endothermic reaction) of iron oxide, and the macro In particular, it is possible to suppress dephosphorization or rephosphorization under conditions where the temperature is high. Here, as an auxiliary material containing lime and calcium carbonate, not only the single substances but also reused materials such as slag generated during converter decarburization blowing may be used. In addition, iron oxide may be used not only as a simple substance such as iron ore but also as a recycled material such as a rolling scale, sintered ore powder, and dust collection dust.

(5) Next, the brewing step (E) shown in FIG.
In this step (E), when the phosphorus concentration in the hot metal is lowered to a predetermined value through the dephosphorization step, the converter 1 is tilted to the side where the outlet is installed, The hot metal inside is poured out into a hot metal holding refining furnace (not shown). The predetermined phosphorus concentration is preferably 0.030 mass% or less.

As described above, by the molten iron refining method using the converter type refining furnace according to the present invention, for example, in the hot metal pretreatment method using a converter, At least a part of the dephosphorized post-treatment slag that remains is left undischarged, new hot metal is charged into it, desiliconization treatment is performed, and this is continuously discharged and used in the intermediate exhaust process. It becomes processing. Therefore, most of the slag discharged from the converter, especially the intermediate waste slag after the desiliconization process, has a density of 0.3 to 1.0 g / cm ³ by controlling the CO gas generation rate. . In addition, in the case of slag after dephosphorization treatment with a relatively high basicity, there is a risk of expansion due to elution of alkali or hydration reaction, which may be restricted when slag is used for land use. Therefore, a method in which no slag is discharged after dephosphorization processing, that is, in the case of discharging only desiliconization slag, can be said to be a high value-added slag processing method because such a problem does not occur.

Example 1
Using a converter having a capacity of 300 tons as shown in FIG. 1, refining was performed mainly for hot metal pretreatment. In this preliminary treatment, oxygen gas was blown from the top blowing lance toward the bath surface (molten metal), and nitrogen gas for stirring was blown into the molten iron from the bottom blowing tuyere provided at the bottom of the furnace body. A cold iron source was first charged into the converter, and then hot metal was charged into the furnace. Thereafter, desiliconization treatment was started by blowing up oxygen. After the desiliconization treatment, the furnace body was quickly tilted and the slag was removed after the desiliconization treatment. The amount of slag formed from the auxiliary raw materials charged during blowing and the oxides of Si and Mn in the hot metal during blowing was adjusted to 6 tons.

  Blowing is performed by adjusting the supply flow rate of gaseous oxygen from the top blowing lance and the lance height of the top blowing lance, changing the slag height during blowing, and changing the slag volume and slag density. It was. The wall shape in the furnace was measured in advance so that the volume could be converted from the slag height. The slag height was measured using microwaves.

Table 1 shows the operating conditions and results of Examples (Invention Examples 1 to 3) that are suitable for the present invention and Examples (Comparative Examples 1 and 2) that are not suitable for the present invention. Example 1 of the present invention in which the density of slag discharged at the end of desiliconization blowing was set to 0.3 g / cm ³ or more by adjusting the CO gas generation rate by changing the top blowing acid rate and the lance height In ˜3, the density of the desiliconized slag after cooling discharged outside the furnace was 2.5 to 3.3 g / cm ³ , and the target for use in roadbed materials could be achieved.

On the other hand, in Comparative Examples 1 and 2, the CO gas generation rate was large and the slag density at the end of desiliconization blowing was low, so the density of desiliconized slag after cooling discharged outside the furnace was 2.2-2. It became 0 g / cm ³ or less, and it was found that the slag was not suitable as a roadbed material.

(Example 2)
Using a converter with a capacity of 300 tons as shown in FIG. Oxygen for refining is blown into the hot metal from the top blowing lance against 300 tons of hot metal accommodated in the converter, and nitrogen gas for stirring is blown into the hot metal from the bottom blowing tuyeres provided at the bottom of the furnace. Pretreatment was performed. As the CaO-based solvent, quick lime (CaO) was used for both the desiliconization treatment and the dephosphorization treatment.

  In this hot metal preliminary treatment, as shown in FIG. 2, the pre-charged dephosphorization slag is left in the furnace, the hot metal is charged into the converter type refining furnace, and oxygen gas is supplied from the top blowing lance to remove it. Then, 60 mass% of the desiliconized slag was removed in the exhausting step after the desiliconization treatment, and then oxygen gas was continuously supplied from the top blowing lance to perform the dephosphorization treatment of the hot metal. After the dephosphorization treatment, the precharge dephosphorization slag was completely left in the furnace, and the next charge desiliconization treatment step was performed.

  Pre-charge residual slag (dephosphorization-treated slag), secondary raw materials introduced during blowing, and slag formed by oxidizing Si and Mn in hot metal during blowing The amount of was adjusted to 12 tons.

  During desiliconization treatment, blowing is performed by adjusting the flow rate of gaseous oxygen from the top blowing lance and the lance height of the top blowing lance, and at the same time as controlling the CO gas derivation speed, changing the height of the slag during blowing. The volume of slag was adjusted. The wall shape in the furnace was measured in advance so that the volume could be converted from the slag height. The slag height was measured using microwaves.

Table 2 shows the operation conditions and the results of the examples (Invention Examples 11 to 13) that are suitable for the present invention and the examples that are not suitable (Comparative Examples 11 and 12). In Invention Examples 11 to 13 in which the density of slag discharged at the end of desiliconization blowing was 0.3 g / cm ³ or more, the density of desiliconized slag after cooling discharged outside the furnace was 2.5 g / cm 2. becomes cm ³ or more, it was possible to achieve the goal for use in roadbeds.
In Comparative Examples 11 and 12, the CO gas generation rate was large and the slag density at the end of blowing was low, so the density of the desiliconized slag after cooling discharged outside the furnace was 2.5 g / cm ³ or less. It was.

  The hot metal preliminary treatment technology according to the present invention is mainly useful as a technology that is suitably used as a roadbed material, etc., after the refining discharged slag by the converter type refining vessel, but it is a full-scale application applicable to other refining vessels. As the hot metal treatment technology exhibits excellent effects, the scope of application of the technology is large.

DESCRIPTION OF SYMBOLS 1 Converter 2 Top blowing lance 3 Bottom blowing lance 4 Outlet 5 Hot metal 6 Refined slag 7 Slag 8 after dephosphorization processing Oxygen gas 9 Bottom blowing gas 10 Slag 11 after desiliconization processing New hot metal 12 Cold iron source 13 Hopper 14 Hopper 15 Silicon source 16 Lime-based solvent

Claims (3)

When performing refining treatment of molten iron using a converter-type refining furnace, desiliconization treatment in the refining furnace is performed by changing the generation rate of CO gas generated in the converter-type refining furnace during the desiliconization process. adjust the density of the rear slag, molten iron method refining by the converter type refining furnace in which the density of the outside of the furnace discharge the slag after refining process end is characterized in that so that the 0.3 g / cm ³ or more. The CO gas generation rate generated in the converter type refining furnace is determined by measuring or estimating the slag height in the furnace during the desiliconization process, and depending on the obtained slag height, the gaseous oxygen source from the top blowing lance 2. The adjustment according to claim 1, wherein the adjustment is made by changing at least one of the supply amount of the gas, the lance height of the top blowing lance, and the stirring gas supply amount from the bottom blowing tuyere. A method for refining molten iron in a furnace-type refining furnace. Refining treatment of the molten iron, the molten iron was tapped from the blast furnace and charged into a converter type smelting furnace performs the desiliconization treatment, then it the smelting furnace a part of the slag after hot metal and desiliconization treatment The intermediate waste that remains in the smelting furnace is then treated, and subsequently, the lime-based medium is added to the hot metal and slag after the desiliconization treatment that is left in the smelting furnace, and oxygen is blown into the molten iron. A dephosphorization process is performed, and a part or all of the slag is left in the smelting furnace after the dephosphorization process, and then at least untreated in the smelting furnace in which a part or all of the slag is accommodated after the dephosphorization process. Molten method of refining by the converter type refining furnace according to claim 1 or 2 charged with molten iron, characterized that you perform desiliconization treatment follows the charge.

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