JP5983492B2 - Hot metal pretreatment method - Google Patents

Description

  The present invention relates to a hot metal pretreatment method in which a hot metal desiliconization process and a dephosphorization process are continuously performed using a single converter-type refining furnace with an intermediate waste gas removal step interposed therebetween.

  In recent years, there has been a strong demand for reducing greenhouse gas emissions. In the iron and steel industry, when hot metal dephosphorization and decarburization refining are performed in the converter, A method of reducing the energy required for steel product production by blending a cold iron source such as iron scrap with the hot metal of this type has been carried out. Unlike iron oxide such as iron ore charged into the blast furnace, this does not require reducing the cold iron source, which is metallic iron, rather than refining pig iron discharged from the blast furnace to produce molten steel. This is because molten steel can be produced with low energy consumption and low greenhouse gas emissions. Moreover, by adding a cold iron source to the hot metal manufactured in the blast furnace and melting the molten steel, molten steel exceeding the amount of molten iron manufactured in the blast furnace can be melted, and the production amount of molten steel can be increased.

  In recent years, since it is advantageous in terms of cost and quality, dephosphorization treatment (also referred to as “preliminary dephosphorization treatment”) is performed as a preliminary treatment for hot metal before decarburization refining in a converter. A refining method for removing phosphorus in hot metal has been performed. This is because the dephosphorization reaction proceeds more thermodynamically as the refining temperature is lower, that is, the dephosphorization reaction proceeds more easily in the hot metal stage than in the molten steel stage, and the dephosphorization refining can be performed with a small refining agent. Based on what can be done.

In general, in the hot metal pretreatment, first, a solid oxygen source such as iron oxide is added to the hot metal to perform desiliconization treatment, slag generated by this desiliconization treatment is removed, and if necessary, the hot metal is further separated. After transferring to a refining vessel, a dephosphorizing agent (medium solvent) and a dephosphorizing agent (oxygen source such as oxygen gas) are added to carry out a dephosphorization process. Usually, a CaO-based solvent such as quick lime is used as a dephosphorizing refining agent for this dephosphorization treatment, and a solid oxygen source (such as iron oxide) or a gaseous oxygen source (such as oxygen gas) is used as an oxygen source as a dephosphorizing agent. Used. In addition, torpedo cars, ladles (blast furnace pots and charging pots), converter-type refining furnaces, and the like are used as the refining containers for performing the pretreatment. Although dephosphorization may be performed immediately without desiliconization, silicon (Si) has a stronger affinity for oxygen (O) than phosphorus (P), and therefore silicon is more likely than phosphorus in hot metal. Since this is preferentially oxidized, desiliconization reaction (Si + 2O → SiO ₂ ) is dominant in the initial refining process of dephosphorization in this case (this period is also called “desiliconization period”). The dephosphorization reaction (2P + 5O → P ₂ O ₅ ) proceeds from the point in time when the amount of silicon is reduced to some extent.

  The hot metal that has been subjected to the dephosphorization treatment by the above method is almost free from the oxidation of silicon, which is a heat source, and carbon (C) is also oxidized (C + O → CO), so that the carbon concentration is 1.5 compared to that at the start. Since there is no thermal allowance for melting cold iron sources such as iron scrap, it is not possible to add cold iron sources in the decarburization and refining process in the dephosphorized hot metal converter. The problem has arisen. For this reason, when it is necessary to increase the production of molten steel, the dephosphorization treatment as a preliminary treatment is abandoned and the dephosphorization and decarburization refining are simultaneously performed in the converter, and the operation is returned to the conventional converter blowing. May be performed.

  However, by performing the dephosphorization process, not only can cost reduction and quality improvement of the steel material be achieved, but also the amount of slag generation can be reduced. After dephosphorization treatment, only decarburization refining is performed in the converter, and at the same time, the blending ratio of cold iron sources such as iron scrap is increased, and more molten steel is produced from the molten iron per unit mass produced in the blast furnace. It is desirable to manufacture.

  In order to dissolve many cold iron sources in hot metal, it is necessary to effectively utilize the heat of combustion of carbon and silicon in the hot metal as a heat source for melting the cold iron source. The converter-type smelting furnace has a large empty space in the furnace and can strongly stir the hot metal, and can increase the oxygen gas supply flow rate, so the combustion heat of carbon and silicon in the hot metal is used. It is advantageous as a refining vessel for dissolving a cold iron source in hot metal. Therefore, the heat of combustion of silicon in the hot metal resulting from the desiliconization treatment is effectively utilized, and the amount of heat required for hatching the dephosphorization refining agent is reduced by reducing the amount of dephosphorization refining agent used for the dephosphorization treatment. Furthermore, with the aim of increasing the thermal margin of the hot metal by suppressing the heat release from the hot metal by continuing the desiliconization process and the dephosphorization process, Several hot metal pretreatment methods have been proposed in which the desiliconization process and the dephosphorization process are continuously performed with an intermediate evacuation process in between.

For example, Patent Document 1 discloses using a converter-type smelting furnace having a means for injecting powder and / or gas into the hot metal from the bottom of the furnace and a means for blowing oxygen gas into the hot metal from the top of the furnace. desiliconization of, in performing the dephosphorization process, first, as the desiliconization treatment at the end of the slag basicity ([wt% CaO] / [wt% SiO _2]) is in the range of 0.3 to 1.3 After the desiliconization process is performed by adjusting the supply amount of the CaO-based medium solvent, the furnace is tilted to discharge the slag generated in the furnace from the furnace port, and then the dephosphorization process is performed. A hot metal refining method has been proposed.

Japanese Patent Laid-Open No. 10-152714

  However, the above prior art has the following problems.

In the desiliconization treatment in which the silicon in the hot metal is removed by oxidation, the basicity of slag ([mass% CaO] / [mass% SiO ₂ ]) is reduced by the generated SiO ₂ . Such a low basicity slag has a low thermodynamic dephosphorization ability, and if phosphorus is present in the slag, the phosphorus in the slag shifts to hot metal and the so-called “rephosphorus reaction” occurs. To do. That is, the phosphorus concentration in the hot metal is increased by the recovery reaction.

In Patent Document 1, hot metal desiliconization treatment and dephosphorization treatment are alternately performed using one converter-type refining furnace. When performing desiliconization treatment, the furnace is pre-charged with dephosphorization treatment. In many cases, part of the generated dephosphorization slag remains attached to the furnace wall or the like. When the desiliconization process of the next charge is started with the dephosphorization slag remaining, the remaining dephosphorization slag reacts with the low basicity slag generated as the desiliconization reaction proceeds, that is, the low basicity. As a result, the basicity is lowered by the slag, and the phosphorus (P ₂ O ₅ ) contained in the dephosphorized slag is transferred to the molten iron. When the hot metal desiliconization and dephosphorization processes are alternately performed using one converter-type smelting furnace, the pre-charge dephosphorization slag remains actively in the furnace for the purpose of heat recovery and iron source recovery. In this case, the amount of recovered phosphorus is further increased.

  If the phosphorus concentration in the hot metal is increased by dephosphorization during the desiliconization process, the amount of dephosphorizing agent (CaO-based solvent) used in the subsequent dephosphorization process must be increased, and efficient dephosphorization. Processing cannot be performed. Patent document 1 does not consider this problem at all.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to perform hot metal desiliconization treatment and dephosphorization treatment using a single converter-type refining furnace with an intermediate waste removal step in between. In the continuous hot metal pretreatment method, the dephosphorization reaction is prevented during the desiliconization process and during the exhaust process, and the dephosphorization process can be performed sufficiently from the cost and quality aspects. Is to provide a preliminary processing method.

The gist of the present invention for solving the above problems is as follows.
[1] A desiliconization process for desiliconizing the hot metal by supplying an oxygen source from an upper blow lance to the hot metal in the converter-type refining furnace, and at least a part of the slag generated in the desiliconization process. An exhausting process for exhausting from the furnace type refining furnace, and after the exhausting process, a hot metal left by adding a CaO-based medium solvent into the converter type refining furnace and supplying an oxygen source from the top blowing lance A dephosphorization process for dephosphorizing the hot metal, and the basicity of the slag in the furnace so that the composition of the slag in the furnace in the desiliconization process does not reach the SiO ₂ saturation region. ([Mass% CaO] / [mass% SiO ₂ ]) is adjusted in accordance with the hot metal temperature and the iron oxide concentration in the slag, and the hot metal pretreatment method.
[2] After the dephosphorization process, the hot metal is discharged from the converter-type smelting furnace, and then the molten iron is left in a state where all or most of the slag generated in the dephosphorization process remains in the converter-type smelting furnace. The hot metal pretreatment method according to [1], wherein the hot metal charged in the converter-type refining furnace is subjected to desiliconization treatment.
In [3] the desiliconization step, and adjusting the basicity of the furnace slag after desiliconizing treatment ([mass% CaO] / [wt% SiO _2]) to 0.8 or more, the [1] or the hot metal pretreatment method according to [2].
[4] In the desiliconization process, the temperature of the in-furnace slag after the desiliconization process is adjusted to 1280 ° C. or higher and 1380 ° C. or lower, and any one of [1] to [3] above The hot metal pretreatment method according to claim 1.
[5] In the desiliconization treatment step, the sum of the total iron content and the manganese oxide content of the in-furnace slag after the desiliconization treatment is adjusted to 10% by mass or more and 30% by mass or less. The hot metal pretreatment method according to any one of [1] to [4].
In [6] the desiliconization step, and adjusting the basicity of the furnace slag during desiliconization treatment ([mass% CaO] / [wt% SiO _2]) to 0.8 or more, the [1] The hot metal pretreatment method according to any one of [5] above.
[7] Any one of [2] to [6] above, wherein slag in an amount of 50% by mass or more of the slag produced in the dephosphorization process is left in a converter type refining furnace. The hot metal pretreatment method according to Item.

According to the present invention, when the desiliconization treatment step and the dephosphorization treatment step are alternately performed using the same converter-type refining furnace, with the intermediate removal step interposed, in the desiliconization treatment step, composition to avoid the saturation region of the SiO _2, in accordance with the molten iron temperature and the slag Zhongtie oxide concentration, since adjusting the basicity of the furnace slag ([wt% CaO] / [wt% SiO _2]), Even if the pre-charged dephosphorization slag remains in the furnace, the dephosphorization reaction from the remaining dephosphorization slag to the molten iron is prevented, and a small amount of CaO-based solvent is sufficient in the next dephosphorization process. It is possible to perform the dephosphorization process, that is, to perform a sufficient dephosphorization process in terms of cost and quality.

It is a schematic sectional drawing of the converter type refining furnace used when enforcing the hot metal preliminary processing method concerning the present invention. It is the schematic which shows the hot metal pre-processing method which concerns on this invention in order of a process. CaO, illustrates a portion of isothermal cross section at 1300 ° C. for 3 component phase diagram of the SiO _2, FeO.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of a converter type refining furnace used when carrying out the hot metal pretreatment method according to the present invention, and FIG. 2 is a schematic view showing the hot metal pretreatment method according to the present invention in the order of steps. . In addition, FIG. 1 is a figure which shows the desiliconization process process of FIG. 2- (B).

  In the hot metal preliminary treatment method according to the present invention, a converter-type refining furnace 1 capable of top bottom blowing as shown in FIG. 1 is used. The top blowing is performed by supplying an oxygen-containing gas toward the hot metal 5 as an oxygen source from the tip of the top blowing lance 2 via the top blowing lance 2 that can move up and down inside the converter type refining furnace 1. As the oxygen-containing gas, oxygen gas, oxygen-enriched air, air, or a mixed gas of oxygen gas and inert gas can be used. FIG. 1 shows an example in which oxygen gas 8 is used as the oxygen-containing gas. Here, the oxygen gas 8 is industrial pure oxygen. The bottom blowing is performed through a bottom blowing tuyere 3 provided at the bottom of the converter type refining furnace 1. The bottom blowing gas 9 may be a gas containing oxygen gas or only an inert gas such as Ar gas or nitrogen gas, but by blowing into the hot metal, the stirring of the hot metal 5 is strengthened to dissolve the cold iron source. In addition to having the function of promoting, the bottom blowing tuyere 3 may have a function of blowing the iron making agent into the molten iron together with the transfer gas.

  In the present invention, two or more converter-type refining furnaces 1 are used for refining the hot metal 5, and at least one of these converter-type refining furnaces 1 is used for the hot metal pretreatment according to the present invention, and the rest At least one group is used for decarburization refining of the hot metal 5 subjected to the hot metal pretreatment according to the present invention. That is, the pretreatment is performed in the converter type refining furnace 1 for hot metal pretreatment, and then the hot metal 5 is transferred to the converter type refining furnace 1 for decarburization refining and decarburization treatment is performed.

  In the pretreatment method of the hot metal 5 according to the present invention, as shown in FIG. 2- (A), the charging pot 10 is placed in the converter-type refining furnace 1 in which the cold iron source 7 such as iron scrap is previously charged. Then, the hot metal 5 is charged.

Next, oxygen gas or iron oxide is supplied as an oxygen source to the hot metal 5 in the converter type refining furnace, and desiliconization processing is performed as shown in FIG. Silicon contained in the hot metal 5 reacts with oxygen in the oxygen source (Si + 2O → SiO ₂ ), and the desiliconization process proceeds. The hot metal temperature rises due to the oxidation heat of silicon by this desiliconization reaction, and the dissolution of the cold iron source 7 in the hot metal is promoted. Before the desiliconization treatment and / or during the desiliconization treatment, the basicity of the slag 6 ([mass% CaO] / [mass% SiO ₂ ]) (hereinafter simply indicated as “basicity”) as necessary. In addition, a CaO-based solvent is added to the converter-type refining furnace 1. The slag 6 generated in the desiliconization process is also called “desiliconization slag”.

  As an oxygen source for the silicon removal treatment, only the oxygen gas 8 from the top blowing lance 2 may be used, or iron oxide (not shown) may be used in combination with the oxygen gas 8. In order to form the slag 6 having the target basicity during the desiliconization process performed in a short time, it is effective to use iron oxide having a function of promoting the hatching of the CaO-based solvent. From the viewpoint of dissolving a large amount of cold iron source 7 which is one of the objects of the present invention, it is not preferable to use iron oxide that absorbs heat during heating and decomposition. Therefore, iron oxide is used as an oxygen source. This is preferably avoided as much as possible. Moreover, since the converter-type smelting furnace 1 is used as a smelting vessel, strong stirring is possible, and even when desiliconization treatment is performed using only oxygen gas 8, a sufficiently basic slag 6 is formed. Can be made.

After this desiliconization treatment step, as shown in FIG. 2- (C), an exhausting step is provided to convert the low basicity slag 6 generated in the desiliconization treatment and containing a large amount of SiO ₂ into a converter type refining process. Discharge from the furnace port of the furnace 1.

  After the exhausting step, the hot metal 5 remaining in the converter type refining furnace is supplied with a CaO-based solvent and an oxygen source, and the hot metal 5 is dephosphorized as shown in FIG. In the dephosphorization process, the basicity of the slag in the furnace is adjusted to a range of 1.5 to 3.5. The oxygen source used in this dephosphorization process is mainly composed of the oxygen gas 8 from the top blowing lance 2 as in the desiliconization process, but a part of iron oxide may be used. The present invention aims to dissolve a large amount of the cold iron source 7, and it is preferable to avoid the use of iron oxide that absorbs heat during heating and decomposition as an oxygen source as much as possible.

  As the CaO-based medium solvent used in the dephosphorization treatment, quick lime, calcium carbonate, or the like can be used. However, it is not limited to these, What contains 50 mass% or more of CaO, and also contains other components, such as a fluorine and an alumina as needed, can be used as a CaO type | system | group solvent solvent at the time of a dephosphorization process. . As a method for adding the CaO-based medium solvent, granular and lump-shaped ones can be charged from a hopper on the furnace, and powdery ones can be charged through an upper blowing lance 2 or the like.

Phosphorus in the hot metal is oxidized to oxygen in the supplied oxygen source to become phosphorus oxide (P ₂ O ₅ ), which is formed by the incubation of the CaO-based solvent and functions as a dephosphorizing refining agent. Incorporated into the slag as a stable compound of 3CaO · P ₂ O ₅ , the dephosphorization reaction of the hot metal 5 proceeds.

  When the dephosphorization reaction proceeds and the phosphorus concentration in the hot metal is lowered to a predetermined value, the dephosphorization process is finished, and the converter-type refining furnace 1 is provided with a tap 4 as shown in FIG. The hot metal 5 in the converter type refining furnace is discharged to a hot metal holding container (not shown) through the hot water outlet 4 (a hot water discharge step). The slag generated in the dephosphorization process is also called “dephosphorization slag”. Hereinafter, the slag generated in the dephosphorization process is referred to as dephosphorization slag.

  After discharging the hot water, without discharging the dephosphorization slag in the furnace, the converter type refining furnace 1 may be charged with the cold iron source 7 and the hot metal 5 to start the next charge desiliconization process. In addition, after the dephosphorization slag in the furnace is discharged, the cold iron source 7 and the hot metal 5 may be charged to start the next charge desiliconization process. When all or most of the dephosphorization slag formed in the furnace is left in the furnace and desiliconization treatment for the next charge is started, the amount of heat and iron content of the dephosphorization slag of the previous charge is depleted. It can be recovered in the treatment, and the CaO content in the dephosphorization slag of the previous charge can be used as a CaO source in the desiliconization treatment of the next charge, reducing the amount of CaO-based solvent used during the desiliconization treatment can do.

In the present invention, when performing desiliconization treatment and dephosphorization treatment on the hot metal 5 in this way, the dephosphorization reaction from the dephosphorization slag remaining in the furnace to the hot metal 5 does not occur in the desiliconization treatment step. In addition, the basicity ([mass% CaO] / [mass% SiO ₂ ]) of the slag 6 generated during the desiliconization treatment (hereinafter referred to as “desiliconized slag 6”) is appropriately adjusted.

It is known that phosphorus in the dephosphorized slag is often present as a solid solution of 2CaO · SiO ₂ and 3CaO · P ₂ O ₅ . Therefore, in order to prevent the dephosphorization reaction, when the dephosphorization slag and the low basicity desiliconization slag 6 are reacted, the solid solution is prevented from dissolving in the desiliconization slag 6 after the reaction. do it. As a result of intensive studies, the inventors have adjusted the composition of the desiliconized slag 6 so that the basicity of the desiliconized slag 6 after the desiliconization treatment does not reach the SiO ₂ saturation region on the phase diagram. It has been found that the recovery reaction can be substantially prevented.

The main components of the desiliconized slag 6 can be regarded as three components of CaO, SiO ₂ , and FeO. FIG. 3 shows a part of an isothermal sectional view at 1300 ° C. of the three component phase diagram. In FIG. 3, the SiO ₂ saturated region at 1300 ° C. is represented as a “shaded part” range. Basicity of dephosphorization slag SiO ₂ high basicity side than the saturation region, i.e., is a high CaO concentration side, SiO ₂ is produced with the progress of the desiliconizing reaction, and the SiO ₂ and dephosphorization slag Reacts, the composition of the desiliconized slag 6 in the furnace moves to the high SiO ₂ side. In the present invention, the composition of the desiliconized slag 6 is adjusted so that the composition of the desiliconized slag 6 does not reach the SiO ₂ saturation region even if it moves to the high SiO ₂ side.

The composition on the boundary line of the SiO ₂ saturated region depends on the FeO concentration in the slag, that is, the iron oxide concentration. FIG. 3 shows the composition on the boundary line at different FeO concentrations of 10 mass% and 20 mass%. When the FeO concentration in the slag is 10% by mass, the SiO ₂ saturation region is reached when the basicity of the desiliconized slag 6 is 0.7 or less, and when the FeO concentration in the slag is 20% by mass, the desiliconized slag is obtained. When the basicity of 6 is 0.5 or less, the SiO ₂ saturation region is reached. The FeO concentration in the slag is determined by the blowing conditions during the desiliconization process (such as acid flow rate and bottom blowing gas flow rate), but the composition on the boundary line depends on the FeO concentration in the slag expected from the blowing conditions. What is necessary is just to set the target basicity of desiliconization slag 6 appropriately so that it may not be exceeded.

Further, the SiO ₂ saturation region changes depending on the temperature of the desiliconized slag 6. In general, the higher the temperature, the smaller the SiO ₂ saturation region and the larger the temperature. Therefore, at the target temperature during the desiliconization process, the composition on the boundary line of the SiO ₂ saturation region of the ternary phase diagram of CaO, SiO ₂ , and FeO may be confirmed, and the target basicity of the desiliconization slag 6 may be set. .

Considering that the normal desiliconization treatment condition is that the hot metal temperature is about 1300 ° C. and the FeO concentration in the desiliconization slag is about 10 to 20%, the desiliconization slag 6 after the desiliconization treatment is practically used. By setting the basicity to 0.8 or more, the recovery reaction is suppressed. In order to more reliably execute the above idea, the composition of the desiliconized slag 6 does not reach the SiO ₂ saturation region throughout the entire period of the desiliconization process, that is, the basicity of the desiliconized slag 6 is 0.8 or more. You may adjust to. In addition, what is necessary is just to consider that the temperature of the desiliconization slag 6 is equivalent to the temperature of the hot metal 5.

  Based on this concept, the hot metal before desiliconization treatment with a phosphorus concentration of about 0.10 to 0.15% by mass in a normal blast furnace is in contact with desiliconized slag containing phosphorus derived from the precharge. Even in this case, it is possible to advantageously perform the dephosphorization treatment step after the draining without causing the recovery reaction.

In the present invention, the iron oxide in the desiliconized slag is regarded as FeO and is interpreted on the phase diagram. Fe ₂ O ₃ is also present in iron oxide, but in steelmaking slag including desiliconized slag 6, the main component of iron oxide is FeO, and there is no problem even if it is handled as FeO substantially. In addition, other slag components such as MgO and Al ₂ O ₃ are present in steelmaking slag, but these effects may be taken into account using phase diagram calculation software or the like.

The basicity ([mass% CaO] / [mass% SiO ₂ ]) of the desiliconized slag 6 can be calculated based on the following formula (1).
Basicity = [(furnace residual amount of CaO (kg / molten pig iron -t)) + (addition amount of CaO in the desiliconization treatment (kg / molten pig iron -t))] ÷ [(furnace residual SiO ₂ amount (kg / molten pig iron -t)) + (Amount of SiO ₂ produced by desiliconization treatment (kg / mol -t))] ... (1)
Note that the amount of SiO ₂ produced in the desiliconization treatment can be calculated from the change in the Si concentration in the hot metal before and after the desiliconization treatment.

  In the present invention, in order to adjust the basicity of the desiliconization slag 6, before the desiliconization treatment and / or during the desiliconization treatment, a CaO-based solvent is introduced into the furnace as required according to the formula (1). Added. The CaO-based solvent includes quick lime, calcium carbonate, dolomite, converter slag (slag generated by decarburization refining in the converter), slag in the ladle (slag present on the molten steel in the ladle, In addition, a converter slag mixed at the time of steel production and a deoxidation product such as alumina added with a slag modifier such as quicklime can be used.

In the desiliconization process, the furnace temperature is as low as about 1250 to 1350 ° C., and a large amount of SiO ₂ is generated in a short time of several minutes. Therefore, rephosphorization is efficiently suppressed with a small addition amount of CaO-based solvent. In order to do this, it is preferable to use a CaO-based medium solvent that has a low melting point and easily hatches and has a high CaO content. Specifically, a CaO-based solvent having a liquid phase ratio of 25% by volume or more at 1300 ° C. is desirable. Examples of such a CaO-based solvent include basicity ([mass% CaO] / [mass% SiO ₂ ]) is ₂ to 4.5, and a steelmaking slag having a sum of Fe ₂ O ₃ content and Al ₂ O ₃ content of 10% by mass or more can be mentioned.

  As a method for adding the CaO-based medium solvent, granular and lump-shaped ones can be charged from a hopper on the furnace, and powdery ones can be charged via an upper blowing lance 2 or the like. The CaO-based solvent may be added after the desiliconization process is started, but in order to sufficiently hatch the desiliconized slag 6 during the desiliconization process, the CaO-based solvent is introduced into the furnace in advance. You may keep it. When the pre-charge dephosphorization slag is actively left in the furnace, it may not be necessary to add a CaO-based solvent if the silicon concentration of the hot metal 5 used in the desiliconization process is low. In order to reduce the amount of CaO-based solvent used, the amount of dephosphorization slag remaining in the furnace is preferably 50% by mass or more.

In the pretreatment method of the hot metal 5 according to the present invention, after the desiliconization process is completed, the low-basic desiliconization slag 6 containing a large amount of SiO ₂ in the furnace is discharged from the converter type refining furnace 1. From the viewpoint of exhaustability, the basicity of the desiliconized slag 6 to be discharged is preferably 1.5 or less, and the temperature of the desiliconized slag 6 is preferably 1280 ° C. or higher. This ensures the fluidity of the desiliconized slag 6, and has good evacuation property and evacuation rate (exhaust rate (mass%) = (exhaust slag mass) × 100 / [(generated in the desiliconization process). This is to obtain (slag mass) + (residual slag mass of the previous charge)]). From the viewpoint of reducing the addition amount of the CaO-based solvent, it is desirable to further reduce the basicity within a range in which the composition of the desiliconized slag 6 does not reach the SiO ₂ saturation region. Hereinafter, it is more preferable to set it to 1.0 or less.

  When the basicity of the desiliconized slag 6 exceeds 1.5, the solid phase slag is generated, so that the slag fluidity is lowered, and even if the temperature of the desiliconized slag 6 is lower than 1280 ° C., the solid phase slag is similarly produced. Since the decrease in slag fluidity due to the increase in the viscosity and the increase in the viscosity of the liquid phase slag itself occur, the fluidity of the desiliconized slag 6 becomes low and it becomes difficult to discharge. In order to prevent this, depending on the initial conditions of the hot metal 5 to be used, for example, even if the silicon removal process proceeds and the silicon concentration in the hot metal is less than 0.05% by mass, the temperature of the silicon removal slag 6 However, in this case, it is necessary to further supply oxygen gas to advance the decarburization reaction to increase the slag temperature and to perform the exhausting process. More preferable conditions for the removal are that the basicity of the desiliconized slag 6 is 1.0 or less and the temperature of the desiliconized slag 6 is 1320 ° C. or more.

  On the other hand, if the temperature of the desiliconization slag 6 is too high, dephosphorization from the desiliconization slag may occur even if the basicity of the desiliconization slag 6 is adjusted to 0.8 or more. The hot metal temperature is preferably 1380 ° C. or lower.

From the viewpoint of practically suppressing the dephosphorization reaction from the desiliconized slag after the desiliconization treatment, the total iron (T.Fe) content and the manganese oxide (MnO) content of the furnace slag after the desiliconization treatment Is preferably adjusted to 10 mass% or more and 30 mass% or less. Here, the total iron content means the concentration of iron contained in the iron oxide (FeO, Fe ₂ O ₃ ) in the slag. Both iron oxide and manganese oxide in the slag can be an oxidizing source that oxidizes phosphorus in the hot metal. Therefore, under conditions where the slag basicity after the desiliconization treatment is 0.8 to 1.5, If the sum of the total iron content and the manganese oxide content is 10% by mass or more, the dephosphorization reaction can be practically suppressed. In addition, when the sum of the total iron content and the manganese oxide content in the slag exceeds 30% by mass, the CaO concentration necessary for stabilizing the phosphorus that has migrated into the slag decreases, and valuable. Loss of metal components (Mn, Fe) increases, and slag forming and slopping are difficult to control in operation.

  The sum of the total iron content and manganese oxide content in desiliconized slag (= [mass% T. Fe] + [mass% MnO]) is the supply rate of the top blown oxygen gas and the feed rate of the bottom blown gas It is controlled by adjusting at least one of the dynamic pressure at the bath surface position of the top blowing gas and the supply rate of iron oxide and manganese oxide.

  In the present invention, the removal rate of the desiliconized slag 6 in the removal process ensures 30% by mass or more. This is because it is necessary to adjust the basicity of the dephosphorization slag to 1.5 to 3.5 in order to advance the dephosphorization reaction in the subsequent dephosphorization process, and when the rejection rate is less than 30% by mass, Not only will the amount of CaO-based solvent to be added in the dephosphorization process increased, but the amount of slag in the dephosphorization process will increase, and slag forming during the dephosphorization process will not be suppressed, and a converter type refining furnace This is because an operational trouble due to slag leakage from the furnace port 1 occurs.

  In addition, in order to avoid a high cost compared to the average unit of quick lime from conventional hot metal pretreatment to converter decarburization refining, and to secure the minimum amount of residual slag required for dephosphorization In this case, it is preferable that the rejection rate is 50% by mass or more and 80% by mass or less. That is, in order to suppress the total amount of CaO-based medium solvent consumed from the pretreatment of the hot metal 5 to the decarburization and refining, it is preferable to increase the waste rate to 50% by mass or more. On the other hand, if the generated desiliconized slag 6 exceeds 80% by mass, the hatching of the CaO-based solvent newly added in the next dephosphorization treatment step is impaired, and the dephosphorization reaction is inhibited. Therefore, the rejection rate is preferably 80% by mass or less.

As described above, according to the present invention, the desiliconization process is performed when the desiliconization process and the dephosphorization process are alternately performed by using the same converter-type refining furnace 1 with the intermediate desorption process interposed therebetween. In the process, the basicity ([mass% CaO] / [mass% SiO ₂ ]) of the desiliconized slag 6 is adjusted so that the composition of the desiliconized slag 6 does not become the SiO ₂ saturation region. Even if phosphorus slag remains in the furnace, the dephosphorization reaction from the remaining dephosphorization slag to the hot metal 5 is prevented, and the dephosphorization process is sufficient with a small amount of CaO-based solvent used in the next dephosphorization process. Is realized.

  Further, in the present invention, since the hot metal 5 is desiliconized in the converter-type refining furnace 1, the furnace volume is sufficient, and a large amount of gaseous oxygen source can be converted into the hot metal 5 in a short time without using iron oxide. The combustion heat of silicon is not expended on the heat of decomposition of iron oxide, and this heat of combustion can be used to dissolve the cold iron source 7. Since the dephosphorization process is continuously performed after the silicidation process, it is possible to utilize the heat released by the transfer of the refining vessel as the heat for melting the cold iron source.

  In addition, this invention is not limited to the range of the said description, A various change is possible. For example, in the desiliconization process and the dephosphorization process, a device having a heat application function (secondary combustion promoting lance, fuel supply type lance) may be used in order to more advantageously apply heat to the hot metal 5. May be.

  The hot metal preliminary treatment was performed using a converter-type refining furnace having a capacity of 300 tons as shown in FIG. Oxygen for refining is blown to the hot metal from the top blowing lance against 300 tons of hot metal contained in the converter-type refining furnace, and nitrogen gas for stirring is introduced into the hot metal from the bottom blowing tuyeres provided at the bottom of the furnace. Pretreatment was performed by blowing. As the CaO-based solvent, quick lime (CaO) was used for both the desiliconization treatment and the dephosphorization treatment.

  As shown in FIG. 2, the hot metal preliminary treatment is performed by introducing hot metal into a converter-type refining furnace, adding quick lime, supplying oxygen gas from an upper blowing lance, and performing a desiliconization process. A part of the slag was discharged, and after adding quick lime, oxygen gas was subsequently supplied from the top blowing lance to dephosphorize the hot metal. After the dephosphorization treatment, the dephosphorization slag was completely discharged except for the amount adhering to the furnace, and the next charge desiliconization treatment step was performed. The hot metal to be used in the desiliconization process is adjusted to a temperature of 1300 ° C. and a phosphorus concentration of 0.10% by mass, and the desiliconization slag rejection rate in the exhaust process after the desiliconization process is adjusted to 50% by mass. did. The target value of the phosphorus concentration in the hot metal after the dephosphorization treatment was set to 0.030% by mass or less.

  In this preliminary treatment method, in the present invention example 1 and the present invention example 2, the amount of quicklime added according to the formula (1) is adjusted so that the basicity of the desiliconized slag in the desiliconization process is 0.8 or more. In addition, quick lime was added so that the basicity of the dephosphorization slag was 2.0 in the dephosphorization process. On the other hand, in the comparative example 1 and the comparative example 2, the addition amount of quicklime was adjusted so that the basicity of the desiliconization slag in a desiliconization process might be less than 0.8. However, in Comparative Example 1 and Comparative Example 2, in the dephosphorization treatment step, the total amount of quicklime added in the desiliconization treatment step and the dephosphorization treatment step is the same as that of Invention Example 1 and Invention Example 2, respectively. The amount of quicklime added was increased.

  The silicon concentration of the hot metal used in the desiliconization process, the amount of quicklime added during the desiliconization process, the basicity of the desiliconized slag collected after the desiliconization process, the total iron content and the manganese oxide content in the desiliconized slag Table 1 shows the temperature of desiliconized slag (= [mass% T. Fe] + [mass% MnO]). Further, Table 1 shows the quick lime addition amount in the dephosphorization treatment step after the waste removal step, the concentration of phosphorus in hot metal after the dephosphorization treatment, and the total quick lime addition amount in the desiliconization treatment step and the dephosphorization treatment step. .

  In the present invention example 1 and comparative example 1 in which the silicon concentration of the hot metal provided in the desiliconization treatment process is the same, and in the present invention example 2 and comparative example 2, the preliminary treatment is performed so that the total amount of quicklime is the same. In the present invention examples 1 and 2 in which the basicity of the desiliconization slag during and after the desiliconization treatment is 0.8 or more, the phosphorus concentration of the hot metal after the dephosphorization treatment is a target of 0.030% by mass. It became the following. On the other hand, in Comparative Examples 1 and 2 in which the basicity of the desiliconized slag during and after the desiliconization treatment is less than 0.8, the phosphorus concentration of the hot metal after the dephosphorization treatment is the target of 0.030% by mass. In the decarburization and refining in the converter performed in the post-process after the pretreatment, an excess of quick lime was required to remove phosphorus.

  The hot metal preliminary treatment was performed using the converter type refining furnace used in Example 1. In this hot metal preliminary treatment, the dephosphorization slag of the pre-charge was left in the furnace, and the removal rate of the desiliconization slag in the removal process after the desiliconization treatment was adjusted to 60% by mass. The hot metal preliminary treatment was performed under the same conditions as in Example 1. The residual rate (= 100-exhaust rate) of the dephosphorization slag of the precharge was changed in the range of 30 to 100% by mass. The temperature of the hot metal used in the desiliconization process was adjusted to 1300 ° C. and the phosphorus concentration to 0.10% by mass, and the target value of the phosphorus concentration of the hot metal after the dephosphorization process was set to 0.030% by mass or less.

  In Example 3 of the present invention, the silicon concentration of the hot metal used for the desiliconization process is 0.30% by mass, and the basicity of the desiliconization slag can be ensured to be 0.8 only by the dephosphorization slag of the remaining precharge. The desiliconization treatment was carried out without adding quick lime. In Invention Examples 4 to 8, the amount of quicklime was adjusted so that the basicity of the desiliconized slag in the desiliconization process was 0.8 or more. On the other hand, in Comparative Examples 3 and 4, as a result of performing the desiliconization treatment without adding quick lime, the basicity of the desiliconization slag in the desiliconization treatment step was less than 0.8.

  Further, in the inventive examples 9 to 11, the desiliconization treatment was performed by adding quick lime, but the inventive example 9 is the sum of the total iron content and the manganese oxide content of the desiliconized slag (= [mass % T.Fe] + [mass% MnO]) is 10 mass% or less, Example 10 of the present invention has a desiliconization slag temperature of 1380 ° C. or more, Example 11 of the present invention is the total iron content of manganese and the manganese It is a result when the sum with oxide content is 30 mass% or more.

  Residual rate of dephosphorization slag in pre-charge in furnace, silicon concentration of hot metal used in desiliconization process of charge, amount of quick lime added during desiliconization process, basicity of desiliconized slag collected after desiliconization process Table 2 shows the sum of the total iron content and the manganese oxide content in the desiliconized slag and the temperature of the desiliconized slag. In addition, the amount of quicklime added in the dephosphorization process after the discharge process of the charge, the concentration of phosphorus in hot metal after the dephosphorization process, and the total amount of quicklime added in the desiliconization process and the dephosphorization process are also shown. It is shown in 2.

  Example 4 of the present invention and Comparative Example 3 in which the silicon concentration of the hot metal used in the desiliconization treatment step was the same 0.40% by mass, and the entire amount of dephosphorization slag was left in the furnace to perform the desiliconization treatment of the next charge. In the present invention example 4 in which the basicity of the desiliconized slag after the desiliconization treatment is 0.8 or more, the hot metal phosphorous concentration after the dephosphorization treatment became a target of 0.030% by mass or less. On the other hand, in Comparative Example 3 in which the basicity of the desiliconized slag after the desiliconization treatment is less than 0.8, the total amount of quicklime is greater than that of the present invention example 4, but after the dephosphorization treatment. The phosphorus concentration in the hot metal exceeds the target of 0.030% by mass, and in the decarburization and refining in the converter performed in the post-process after the pretreatment, an excess of quick lime is required to remove phosphorus. did.

  In the inventive examples 3 to 8 where the dephosphorization slag was left in the furnace after the dephosphorization treatment and the desiliconization treatment of the next charge was performed, the dephosphorization slag was not actively left in the furnace. Compared with the present invention examples 1 and 2, the hot metal having the target phosphorus concentration could be obtained with the same or less total amount of quicklime added.

  Further, in Example 9 of the present invention, since the sum of the total iron content and the manganese oxide content of the desiliconized slag does not reach 10% by mass, it is not possible to perform exhaustion in the middle sufficiently, In the present invention example 10, the temperature of the desiliconized slag exceeds 1380 ° C., and in the present invention example 9 and the present invention example 10, the amount of quicklime added to suppress the dephosphorization in the desiliconization process is the present invention example 3. Increased compared to ~ 8.

  In Invention Example 11, the sum of the total iron content and the manganese oxide content of the desiliconized slag exceeds 30% by mass, and it is difficult to control the slopping during the desiliconization process. The company was forced to cease productivity and reduce productivity by extending operating hours. Moreover, the CaO density | concentration in slag reduces because the sum of the total iron content and manganese oxide content of desiliconization slag is low, and the amount of quicklime used in the dephosphorization process is also Examples 3-8 of the present invention. Increased in comparison.

  In Comparative Example 4, although the total amount of quicklime added was 12.5 kg / molten metal-t, the molten iron concentration after the dephosphorization treatment significantly exceeded the target value.

DESCRIPTION OF SYMBOLS 1 Converter type refining furnace 2 Top blowing lance 3 Bottom blowing tuyere 4 Outlet 5 Hot metal 6 Slag 7 Cold iron source 8 Oxygen gas 9 Bottom blowing gas 10 Charging pan

Claims (4)

A desiliconization treatment step of desiliconizing the hot metal by supplying an oxygen source from the top blow lance to the hot metal in the converter type refining furnace, and at least a part of the slag generated in the desiliconization treatment step An exhausting process for exhausting from the furnace, and after the exhausting process, a CaO-based solvent is added to the converter type refining furnace, and an oxygen source is supplied from the top blowing lance to dephosphorize the molten iron remaining. A dephosphorization treatment step to treat, a hot metal pretreatment method comprising:
Said have you to desiliconization treatment step, as the composition of the in-furnace slag throughout the entire period of desiliconization work not saturation region of the SiO _2, CaO-based media solvent to the converter type refining furnace in the desiliconization treatment with adjusting basicity of furnace slag ([mass% CaO] / [wt% SiO _2]) to 0.8 or more by adding,
The temperature of the in-furnace slag after desiliconization treatment is adjusted to 1280 ° C. or more and 1380 ° C. or less, and the basicity ([mass% CaO] / [mass% SiO ₂ ]) of the in-furnace slag after desiliconization treatment is 0 .8 to 1.2
The fluidity of the in-furnace slag is secured by adjusting the temperature and basicity ([mass% CaO] / [mass% SiO ₂ ]) of the in-furnace slag after the desiliconization treatment , The rejection rate (rejection rate (mass%) = (exhaust slag mass) x 100 / [(slag mass generated in the desiliconization process) + (residual slag mass of the previous charge)]) is 50 mass% or more and 80 mass % Hot metal pretreatment method, characterized by being in the range of not more than% . After the dephosphorization step, the hot metal is discharged from the converter type refining furnace, and then, the slag in an amount of 50% by mass or more of the slag generated in the dephosphorization step is left in the converter type refining furnace. The hot metal pretreatment method according to claim 1, wherein the hot metal is charged in step 1 and desiliconization is performed on the hot metal charged in the converter type refining furnace. 3. The hot metal preliminary treatment method according to claim 2, wherein the entire amount of slag generated in the dephosphorization process is left in a converter type refining furnace. The sum of the total iron content and the manganese oxide content of the in-furnace slag after the desiliconization treatment is adjusted to 10 mass% or more and 30 mass% or less in the desiliconization treatment step. The hot metal pretreatment method according to any one of claims 3 to 3 .

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