JP2013136831A - Method of preliminary treatment for molten iron in converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform preliminary treatment efficiently by adjusting a composition of a slag into a composition capable of performing intermediate slag-off treatment, and further controlling a concentration of silicon in a molten iron at intermediate slag-off into 0.20 mass% or less when the molten iron is preliminary treated by using a converter for performing desiliconizing treatment, intermediate slag-off treatment and dephosphorizing treatment, in this order.SOLUTION: When the molten iron 16 is preliminary treated in the converter 1 by desiliconizing treating, slag discharging and then dephosphorizing treating during desiliconizing treatment, an FeO concentration of the slag is estimated based on the unclear amount of oxygen found by oxygen balance, and comparing with the shift of the estimated FeO concentration, one or more out of an oxygen gas flow amount from a top-blowing lance 2, the lance height thereof and agitating a gas flow amount from a bottom-blowing tuyere 3 are adjusted. By this adjustment, by the time of passing nine minutes from the start of desiliconizing treatment, the FeO concentration of the slag is adjusted into a range of 3.0-30 mass%, and then at least a part of the slag is discharged from the converter, and after discharging the slag, the supply of the oxygen gas from the top-blowing lance is resumed to perform dephosphorizing treatment.

Description

  The present invention relates to a hot metal pretreatment method using a converter, and more particularly to a pretreatment method for efficiently desiliconizing and dephosphorizing hot metal that has not been previously desiliconized.

  In recent years, hot metal pretreatment methods (desiliconization treatment, dephosphorization treatment, desulfurization treatment) have been developed, and the concentration of phosphorus and sulfur in the hot metal charged into the converter has reached a level that does not require further removal. The steelmaking refining process, which mainly uses only decarburization refining in the converter, is being completed. The desiliconization process and the dephosphorization process are reactions in which silicon or phosphorus in the hot metal is oxidized and removed by oxygen in an oxygen source (oxygen gas or iron oxide) supplied to the hot metal, and the desulfurization process is a desulfurization process such as CaO. This is a reaction in which sulfur in the molten iron reacts to remove sulfur.

In particular, in the dephosphorization treatment, as shown in the following formula (1), the phosphorus oxide (P ₂ O ₅ ) produced by oxidizing phosphorus in the hot metal with oxygen in the oxygen source is dephosphorized. It is carried out by fixing with a CaO-containing substance added as an agent.

However, in the formula (1), [P] and [Fe] indicate components in the hot metal, and (FeO), (CaO) and (3CaO · P ₂ O ₅ ) indicate components in the slag. That is, phosphorus (= P) in the hot metal is oxidized by FeO, and P ₂ O ₅ produced by this oxidation reaction reacts with CaO and is absorbed by the slag produced by the hatching of the CaO-containing material. is there.

That is, in the dephosphorization treatment, the basicity of slag (= (mass% CaO) / (mass% SiO ₂ ) is used in order to absorb the generated phosphor oxide (P ₂ O ₅ ) with slag from the viewpoint of dephosphorization equilibrium. )) Must be secured above a predetermined value. Conventionally, it is generally said that the basicity of slag needs to be controlled within a range of 1.5 to 3.0 in order to promote the dephosphorization reaction.

By the way, the hot metal discharged from the blast furnace contains about 0.3 to 0.4 mass% of silicon. When an oxygen source is supplied to the hot metal, the silicon in the hot metal is thermodynamically oxidized preferentially over the phosphorus in the hot metal, so when the silicon concentration in the hot metal before dephosphorization is high, In other words, when the amount of SiO ₂ generated in the dephosphorization process is large, not only the amount of CaO-containing material used to secure the basicity of slag to a predetermined value is increased, but also the amount of slag generated is increased. , Increase manufacturing costs.

Therefore, in order to solve the above-mentioned problem, when refining the hot metal that has not been desiliconized using a converter, and dephosphorizing subsequent to this desiliconization, refining is temporarily stopped after desiliconization. In order to reduce the amount of slag in the furnace and secure the basicity, the slag mainly composed of SiO ₂ generated by the desiliconization process is discharged from the converter (referred to as “intermediate waste”). A technique for reducing the CaO-containing material used in the dephosphorization process has been proposed (see, for example, Patent Document 1).

  As described above, in order to efficiently perform the dephosphorization treatment, it is effective to control the basicity of the slag to a predetermined value. Therefore, as in Patent Document 1, when desiliconization treatment, intermediate waste removal, and dephosphorization treatment are continuously performed in one converter, the CaO-containing material used in the dephosphorization treatment is reduced, and the dephosphorization is performed. In order to ensure the basicity of the slag in the treatment at a predetermined value, it is necessary to control the silicon concentration in the hot metal at the end of the desiliconization treatment to a certain specific range.

  In response to this problem, Patent Document 2 proposes that it is optimal to perform intermediate waste after the silicon concentration in the hot metal becomes 0.20 mass% or less. This is because when the silicon concentration in the hot metal at the end of the desiliconization process is higher than 0.20% by mass, the amount of CaO-containing material necessary to adjust the basicity of the slag to 2.0 becomes too much, and the cost It is because it becomes disadvantageous. On the other hand, when the silicon concentration in the hot metal is lower than 0.03% by mass, the desiliconization efficiency is lowered. Therefore, it is preferable to perform the intermediate waste when the silicon concentration in the hot metal is 0.03% by mass or more.

As described above, when intermediate removal is performed after the desiliconization process, it is necessary to correctly determine the end point of the desiliconization process. However, the oxygen gas supplied during the desiliconization process is a desiliconization reaction (Si + 2O → SiO _2). ) And also reacts with carbon in the hot metal (C + O → CO). Solid oxygen sources such as iron ore also contribute to the decarburization reaction in addition to the desiliconization reaction. Therefore, the silicon concentration in the hot metal can be estimated only from the amount of oxygen source supplied during the desiliconization process. Therefore, it is difficult to determine the end point of the desiliconization process.

  On the other hand, Patent Document 3 analyzes the composition of exhaust gas discharged from the furnace when desiliconizing hot metal using a converter, and the nitrogen gas concentration in the exhaust gas is 30 to 60% by volume. It is disclosed that the silicon concentration in the hot metal can be controlled in the vicinity of 0.2% by mass by terminating the desiliconization process at a time point within the range. However, Patent Document 3 merely controls the silicon concentration at the end of the desiliconization process, and does not consider the fluidity of the slag at the time of intermediate discharge, depending on the properties of the slag. There is a possibility that it cannot be rejected only by tilting.

  Patent Document 4 has been proposed as a technique for detecting the forming and hatching status of slag in the converter. However, Patent Document 4 is only required to detect the forming and hatching status of slag. There is no disclosure whatsoever is suppressed or how hatching is promoted.

On the other hand, in the dephosphorization treatment, a solvent such as CaF ₂ , Na ₂ CO ₃ , or CaCl ₂ is used to promote the hatching of the CaO-containing material added as the dephosphorization refining agent and further promote the dephosphorization reaction. Has been used.

  In recent years, steelmaking slag has been recycled for use as roadbed materials, landfill materials, or CaO sources in steelmaking refining processes. The existence of is a problem. This is because fluorine, sodium, and the like in the converter slag are eluted by rainwater and groundwater, which may adversely affect the environment and the human body. Therefore, recently, for the purpose of environmental harmony, establishment of a technique for efficiently performing dephosphorization of hot metal without using a fluorine compound or a sodium compound as a solvent is required.

Moreover, in the dephosphorization treatment of hot metal, it is necessary to use the action of FeO in addition to fluorine and sodium in order to promote the hatching of the CaO-containing material, and research for this purpose is also underway. . At the same time, it is also important in the dephosphorization treatment of hot metal to control the ratio between the amount of SiO ₂ produced and the rate of introduction of the CaO-containing material, which is an important factor in determining the slag properties.

  Patent Document 5 has been proposed as an example of a conventional technique for controlling the amount of FeO in slag by oxidation refining (dephosphorization treatment, decarburization refining) of hot metal in a converter. In Patent Document 5, the transition of the amount of FeO in the slag targeted for each steel type is set by referring to the past results before the start of oxygen blowing, and the results from refining, the amount of acid sent, the input auxiliary material information, and the exhaust gas information Sequentially calculate the amount of FeO, so that the calculated actual FeO amount approaches the transition of the target FeO amount, one or more of the oxygen supply speed of the top blowing lance, the lance height, and the bottom blowing gas flow rate Techniques for controlling are disclosed. However, Patent Document 5 does not clarify the relationship between the transition of the amount of FeO in the slag and the dephosphorization reaction.

  As another example of controlling the amount of FeO in the slag, Patent Document 6 discloses a high-carbon ultra-low phosphorus steel melting method using two converters of a dephosphorization furnace and a decarburization furnace. The amount of FeO produced in the furnace is determined based on the accumulated oxygen amount obtained by sequentially calculating the oxygen balance from the exhaust gas composition and flow rate, oxygen gas flow rate, auxiliary material input amount and hot metal component during blowing. In accordance with the estimated FeO amount, at least one of the top blowing lance height, the oxygen gas flow rate, and the bottom blowing gas flow rate is adjusted, and the phosphorus concentration in the hot metal after the treatment is 0.015. A technique for reducing the mass to less than or equal to mass% is disclosed. However, Patent Document 6 does not describe the basicity of slag, which is an important indicator for operation in hot metal dephosphorization.

  Further, as a technique for dephosphorizing hot metal without using a fluorine compound, Patent Document 7 discloses that when performing desilicon dephosphorization of hot metal, a fine powder CaO source having a particle size of 1 mm or less is sprayed together with top blowing oxygen. When the silicon concentration in the hot metal is 0.2% by mass or more, in addition to the fine CaO source having a particle size of 1 mm or less, the removal method with a particle size of 5 mm or more is used. Anthrax (converter slag) was added upwardly, the slag basicity after dephosphorization was set to 1.8 to 2.2, and the slag basicity 2 minutes after the start of treatment was 1.0 to 1.4, and the treatment was started. A technique has been proposed in which the slag basicity after 5 minutes is 1.4 to 1.8.

However, Patent Document 7 does not sequentially monitor and control the amount of FeO produced that directly affects the hatching rate of the CaO-containing material, but the ratio of the mass of the CaO-containing material to be introduced and the mass of SiO _{2 to be} produced is determined. It only prescribes.

Japanese Patent Laid-Open No. 10-152714 Japanese Patent Laid-Open No. 11-323420 JP 2003-277819 A JP-A-5-255726 JP-A 61-159520 JP 2006-206930 A JP 2010-150574 A

  The present invention has been made in view of the above circumstances, and its object is to use a single converter to desiliconize hot metal that has not been desiliconized in advance, and to remove intermediate waste after this desiliconization treatment. And then dephosphorizing to pre-treat the hot metal, and by controlling the refining during the desiliconization process, the slag composition can be reduced to a composition that allows intermediate waste removal within a predetermined time of the desiliconization process. In addition, the concentration of silicon in the hot metal at the time of intermediate waste can be controlled to 0.20% by mass or less, productivity can be improved, and excess CaO can be obtained in the dephosphorization treatment after intermediate waste. It is an object of the present invention to provide a hot metal pretreatment method in a converter that can avoid the introduction of a contained material.

The gist of the present invention for solving the above problems is as follows.
[1] Oxygen gas was supplied from the top blowing lance and stirring gas was blown from the bottom blowing tuyere to desiliconize the molten iron that had not been previously desiliconized in the converter, and then produced by desiliconization. The slag is discharged from the converter. After the slag is discharged, the dephosphorization process is followed by the pretreatment of the hot metal. During the desiliconization process, the oxygen gas flow rate from the top blowing lance, the composition of the exhaust gas during refining, the exhaust gas The FeO concentration in the slag in the furnace is estimated based on the unknown oxygen amount obtained by sequentially calculating the oxygen balance from the flow rate of the raw material, the input amount of the auxiliary material, and the hot metal component, and the above is compared with the transition of the estimated FeO concentration. Adjust at least one of the oxygen gas flow rate from the blowing lance, the lance height of the top blowing lance, and the stirring gas flow rate from the bottom blowing tuyere. Or By the time when 9 minutes have elapsed, the FeO concentration of the in-furnace slag is adjusted to the range of 3.0 to 30% by mass, and then the supply of oxygen gas from the upper blowing lance is temporarily interrupted to at least the in-furnace slag. A method for pre-treating hot metal in a converter, wherein a part of the molten iron is discharged from the converter and, after discharging the slag in the furnace, the supply of oxygen gas from the top blowing lance is resumed to perform the dephosphorization process.
[2] The process according to [1], wherein the FeO concentration of the in-furnace slag is adjusted to a range of 3.0 to 30% by mass by 7 minutes from the start of the desiliconization treatment. Pretreatment method of hot metal in the furnace.
[3] During desiliconization refining, when the silicon concentration in the hot metal is 0.30% by mass or more, the oxygen gas flow rate from the top blowing lance, the lance height of the top blowing lance, for stirring from the bottom blowing tuyere The oxygen gas flow rate from the top blowing lance is selected from among the three gas flow rates to adjust the oxygen gas flow rate from the top blowing lance, while the silicon concentration in the hot metal is less than 0.30 mass%. The hot metal in the converter according to [1] or [2] above, wherein the lance height of the upper blowing lance is adjusted by selecting the lance height of the upper blowing lance among the three types. Pre-processing method.
[4] In the dephosphorization treatment, the particle size is adjusted so that the ratio of the CaO concentration to the FeO concentration in the slag ((mass% CaO) / (mass% FeO)) is in the range of 0.4 to 5.5. The above-mentioned [1] to [3], wherein a CaO-containing substance of 1 mm or less is sprayed and added to the hot metal together with oxygen gas through the upper blowing lance according to the amount of FeO generated in the furnace. A hot metal pretreatment method for a converter according to any one of the preceding claims.
[5] In the desiliconization treatment, a CaO-containing material having a particle size of 1 mm or less is used in a furnace so that the basicity of slag ((mass% CaO) / (mass% SiO ₂ )) is 0.8 to 1.2. In accordance with the amount of SiO ₂ produced in the steel, it is sprayed and added to the hot metal together with oxygen gas through the top blowing lance, and in the dephosphorization treatment, the basicity of slag ((mass% CaO) / (mass% SiO ₂ )) Within a range of 1.0 to 1.8, a CaO-containing material having a particle size of 1 mm or less is combined with oxygen gas via the top blowing lance according to the amount of SiO ₂ produced in the furnace. The hot metal pretreatment method for a converter according to any one of [1] to [4] above, wherein the hot metal is sprayed and added.

  According to the present invention, hot metal desiliconization treatment in a converter equipped with top blowing oxygen gas and stirring bottom blowing inert gas, intermediate waste after this desiliconization treatment, hot metal dephosphorization after this intermediate waste treatment In the hot metal pretreatment, the FeO concentration in the furnace slag is estimated, and the oxygen gas flow rate from the top blowing lance, the lance height of the top blowing lance, At least one of the stirring gas flow rates from the tuyere is adjusted, and by this adjustment, the FeO concentration of the in-furnace slag is 3 to 30 mass by the time when a predetermined time elapses from the start of the desiliconization treatment. Therefore, the silicon concentration in the hot metal at the end of the desiliconization process, that is, at the time of intermediate waste can be stably controlled to 0.20% by mass or less. Adjusted to a possible composition In addition, in the dephosphorization process after the intermediate waste, it is possible to avoid the introduction of an excessive CaO-containing material, and at the same time, it is possible to efficiently perform from the start of the desiliconization process to the end of the dephosphorization process, thereby improving productivity. Is achieved.

It is a schematic sectional drawing of the converter equipment used when implementing this invention. It is a figure which shows the relationship between the FeO density | concentration in slag at the time of intermediate waste, and the silicon concentration in hot metal after intermediate waste. The effect of the ratio between the CaO concentration and the FeO concentration in the slag after dephosphorization ((mass% CaO) / (mass% FeO)) on the phosphorus concentration in the hot metal after the dephosphorization treatment is as follows. FIG. In addition condition 2, it is a figure which shows the residual amount of the non-denitrified CaO in slag at the time of intermediate | middle discharge when changing the slag basicity at the time of a desiliconization process in the range of 0.5-2.0. . It is a figure which shows the relationship between the slag basicity at the time of changing the slag basicity at the time of a dephosphorization process in the range of 0.5-2.5 in addition condition 2, and the phosphorus concentration in the hot metal after a dephosphorization process. . It is a figure which shows the influence of the acid delivery speed | rate and the lance height which has on the FeO density | concentration in slag in the time of 7 minutes having passed since the time of the siliconization process disclosure. It is a figure which shows the example of transition of the FeO density | concentration in slag in a desiliconization process by contrast with the example of this invention, and a comparative example.

  Hereinafter, the present invention will be specifically described. First, a converter facility to which the present invention is applied will be described. FIG. 1 is a schematic cross-sectional view of an example of converter equipment used in carrying out the present invention.

In FIG. 1, an upper blowing lance 2 is inserted into the converter main body 1 containing the molten iron 16 from above, and oxygen gas is blown from the upper blowing lance 2 onto the molten iron 16. The bottom blowing gas for stirring made of an inert gas such as Ar gas or nitrogen gas is blown from the plurality of bottom blowing tuyere 3 arranged at the bottom, and the hot metal 16 and the slag 17 are stirred. Treatment and dephosphorization treatment are performed. Further, the oxygen gas supply flow path to the top blowing lance 2 branches before being connected to the top blowing lance 2 and CaO-containing substances such as quick lime (CaO), limestone (CaCO ₃ ), and calcined dolomite (MgO—CaO). The oxygen gas passing through the dispenser 18 is connected again to the oxygen gas supply flow path, and the CaO-containing substance 19 accommodated in the dispenser 18 uses the oxygen gas as a carrier gas. It is configured to be sprayed and added (projected) to the hot metal 16 through the top blowing lance 2. That is, it is configured such that oxygen blowing can be performed by projecting an arbitrary amount of CaO-containing material 19 onto the hot metal 16 during an arbitrary period of oxygen blowing. The CaO-containing material 19 functions to adjust the basicity of the generated slag 17 in the desiliconization process, and functions as a dephosphorization refining agent that absorbs the generated phosphorus oxide (P ₂ O ₅ ) in the dephosphorization process. By the desiliconization process and the dephosphorization process of the hot metal 16, exhaust gas containing CO gas is generated from the furnace.

  A flue 4 is installed above the converter main body 1, and a primary dust collector 8, a secondary dust collector 9, an exhaust gas flow meter 11, and an induction blower 12 are installed in this order in the subsequent stage of the flue 4. This exhaust gas treatment facility is a non-combustion exhaust gas treatment facility (also referred to as an “OG exhaust gas recovery facility”) that cools and removes CO gas in the exhaust gas and collects it in an unburned state. Then, a three-way valve, a chimney, a recovery valve, a gas holder, and the like are further arranged on the downstream side of the induction blower 12, but are omitted in FIG. A PA damper 10 is installed in the PA venturi installed as the secondary dust collector 9, and the furnace pressure of the converter main body 1 is controlled by adjusting the opening of the PA damper 10. That is, the exhaust gas generated inside the converter main body 1 by the desiliconization process and the dephosphorization process is sucked by the induction blower 12 driven by an electric motor (not shown) while the flow rate is controlled by the PA damper 10, and the gas holder It has come to be collected. When the CO gas concentration in the exhaust gas is low, it is not recovered by the gas holder, but is burned at the tip of the chimney and then released to the atmosphere.

  The side of the flue 4 connected to the furnace port of the converter body 1 is called a skirt 5 and has a structure that can move up and down. When collecting exhaust gas, the skirt 5 and the converter body In principle, it is in close contact with the furnace port 1. Further, in the flue 4, calcined lime and calcined dolomite as the CaO-containing material 19, and iron ore, mill scale, manganese ore, coke, graphite and iron alloys (Fe—Mn, Fe—Si, etc.) An auxiliary raw material charging device including a hopper (also referred to as “furnace hopper”) 6 and a charging chute 7 for charging and adding the raw material to the converter main body 1 is installed. The slag 17 is formed by quick lime, calcined dolomite, iron ore, mill scale, or the like that is charged into the furnace from the auxiliary material charging device.

The flue 4 is provided with a gas sampling probe 13 for collecting exhaust gas generated inside the converter main body 1 by desiliconization and dephosphorization, and the exhaust gas collected by the gas sampling probe 13 is analyzed by gas analysis. The gas analyzer 14 sends the CO gas concentration, CO ₂ gas concentration, hydrogen gas concentration, and oxygen gas concentration in the exhaust gas. The difference between these total values and 100% by mass is determined as nitrogen gas. In this case, when Ar gas is blown as the bottom blowing gas for stirring from the bottom blowing tuyere 3, the nitrogen gas concentration is obtained by further subtracting the Ar gas concentration. The measured exhaust gas composition is transmitted to the arithmetic device 15. Further, the arithmetic unit 15 includes a flow rate of oxygen gas supplied from the top blowing lance 2 into the furnace, an input amount of the auxiliary material input by the auxiliary material input device, and an exhaust gas measured by the exhaust gas flow meter 11. Flow rate is being transmitted.

  The arithmetic unit 15 sequentially calculates the oxygen balance during the desiliconization process, estimates the FeO concentration of the slag 17 in the furnace based on the unknown oxygen amount obtained from the calculated oxygen balance, and changes in the estimated FeO concentration Is a device for displaying. Hereinafter, a method for estimating the FeO concentration of the slag 17 and a method for displaying the transition of the estimated value by the arithmetic device 15 will be described.

  First, the arithmetic unit 15 sequentially calculates the unknown oxygen amount online during refining using the following equation (2).

In equation (2), ΔW _O2 is the unknown oxygen amount (Nm ³ / molten metal t) from the start of oxygen blowing to time ti (seconds), and A is the oxygen gas flow rate (Nm) from the top blowing lance 2 ³ / molten metal t), B is the flow rate of oxygen gas in the feed auxiliary material (Nm ³ / molten metal t), C is the flow rate of oxygen gas in the entrained air at the converter furnace port (Nm ³ / molten metal t), D Is the CO gas flow rate (Nm ³ / molten metal t) in the exhaust gas, E is the CO ₂ gas flow rate (Nm ³ / molten metal t) in the exhaust gas, F is the hot metal component, specifically silicon, manganese in the molten metal , The flow rate of oxygen gas consumed for oxidation of phosphorus (Nm ³ / molten metal t), G is the flow rate of oxygen gas in exhaust gas (Nm ³ / molten metal t), t is the time (seconds), and the subscript i of the time is This is the i-th calculation from the start of blowing. Here, the unknown oxygen amount (ΔW _O2 ) is the difference between the amount of oxygen supplied into the furnace and the amount of oxygen discharged outside the furnace, and means the amount of oxygen accumulated as oxide in the furnace. doing.

In addition, the model formula created based on the actual value calculated | required previously during the desiliconization process shall be utilized for the change of a hot metal component (Si, Mn, P). That is, the chemical composition of the hot metal 16 before the desiliconization process obtained by chemical analysis is set as an initial value, and the concentration transitions of Si, Mn, and P during the desiliconization process are set based on the actual values. Further, the oxygen gas flow rate (B) in the input auxiliary material is obtained by converting oxygen supplied into the furnace by the iron oxide form auxiliary material into oxygen gas. For example, the iron oxide form auxiliary material is iron ore. In the case of the sintered ore, “B (Nm ³ / molten metal t) = sintered ore amount (kg / molten metal t) × 0.15”, and in the case of iron ore, “B (Nm ³ / molten metal) t) = iron ore input (kg / molten metal t) × 0.20 ”. That is, the oxygen gas flow rate (B) can be determined from the oxygen content in the iron oxide auxiliary material and the amount added. The oxygen gas flow rate (C) in the entrained air can be obtained from the nitrogen gas concentration in the exhaust gas. That is, when the bottom blowing gas for stirring is not nitrogen gas, the oxygen gas flow rate (C) may be set to 1/4 of the nitrogen gas flow rate (Nm ³ / molten metal t) in the exhaust gas. In the case of nitrogen gas, the value obtained by subtracting the stirring nitrogen gas flow rate from the nitrogen gas flow rate in the exhaust gas is taken as the nitrogen gas flow rate in the air, and the oxygen gas flow rate (C) may be obtained from this nitrogen gas flow rate.

Next, the arithmetic unit 15 uses the following equation (3) based on the unknown oxygen amount (ΔW _O2 ) obtained as described above, and then in the furnace by the time when ti time has elapsed from the start of oxygen blowing. The amount of produced FeO is estimated.

However, in the formula (3), FeO _i is the amount of FeO (kg / molten iron t) generated in the furnace from the start of oxygen blowing until ti time has elapsed. The expression (3) is derived from the idea that “the unknown oxygen amount (ΔW _O2 ) is all used for the generation of FeO”.

  On the other hand, the mass of the slag 17 during refining can be obtained from the following equation (4).

However, in the equation (4), Ws _i is the amount of slag in the furnace (kg / molten metal t) when ti time has elapsed from the start of oxygen blowing, and T.CaO _i is ti from the start of oxygen blowing. The amount of CaO (kg / mol t) in the auxiliary raw material added until the time has elapsed and T.SiO _2i is the SiO ₂ in the auxiliary raw material added up to the point of time ti after the start of oxygen blowing. The total value of the amount (kg / molten metal t) and the amount of SiO ₂ (kg / molten metal t) generated by the oxidation of silicon in the molten metal, T.MgO _i, is measured by the time when ti time has elapsed from the start of oxygen blowing. The amount of MgO in the added auxiliary material (kg / molten metal t) and T.Al ₂ O _3i are the amount of Al ₂ O ₃ in the added auxiliary material until ti time has elapsed since the start of oxygen blowing ( kg / molten metal t), and T.MnO _i is the Mn in the auxiliary raw material introduced until ti time has elapsed from the start of oxygen blowing. The total value of the amount of O (kg / molten metal t) and the amount of MnO (kg / molten metal t) generated by oxidation of manganese in the molten metal, T.P ₂ O _5i is from the start of oxygen blowing until the time point ti has elapsed. is the sum of P ₂ O ₅ content in the secondary material is introduced as (kg / hot metal t), P ₂ O ₅ amount generated by the oxidation of phosphorus in the molten iron and (kg / hot metal t) to.

In calculating T.SiO _2i , regarding the amount of SiO ₂ (kg / molten metal t) generated by the oxidation of silicon in the hot metal before the lapse of ti time from the start of oxygen blowing, the following (5) Calculated by the formula.

However, in the formula (5), k _SiO2 is a reaction rate constant determined by each converter equipment, and InputO ₂ is the amount of oxygen blown up (Nm ³ / molten iron t).

The arithmetic unit 15 uses the following equation (6) from FeO _i obtained from the equation (3) and Ws _i obtained from the equation (4), and at the time when ti time has elapsed from the start of oxygen blowing. The FeO concentration of the slag 17 is calculated. However, in the formula (6), (mass% FeO) _i is the FeO concentration (mass%) of the slag 17 when ti time has elapsed from the start of oxygen blowing.

That is, the arithmetic unit 15 calculates the oxygen balance from the input oxygen gas flow rate from the top blowing lance 2, the composition of the exhaust gas during refining, the exhaust gas flow rate, the auxiliary material input amount and the hot metal components (Si, Mn, P). sequentially obtains a calculation to unknown amount of oxygen ([Delta] W _O2), based on the unknown amount of oxygen calculated ([Delta] W _O2) estimates the FeO concentration of the slag 17 in the furnace, the estimated value by displaying each time, The transition of the estimated FeO concentration is displayed.

  In order to confirm the accuracy of the estimated value of the FeO concentration in the slag by the arithmetic unit 15, the slag 17 is sampled during the desiliconization process and after the desiliconization process is completed, the chemical analysis value of the sampled slag 17, and the FeO concentration by the arithmetic unit 15 As a result of comparison with the estimated value, both agreed with accuracy within ± 5%.

  The converter equipment to which the present invention is applied is configured in this way.

  Using this converter equipment, the composition of the slag 17 is adjusted to a composition capable of intermediate waste removal within a predetermined time of the desiliconization process, and at the same time, the silicon concentration in the hot metal at the time of intermediate waste is 0.20% by mass or less. For the purpose of controlling, the hot metal 16 is subjected to a pretreatment test including desiliconization, intermediate waste, and dephosphorization, and the FeO concentration of the slag 17 during the intermediate waste and the silicon concentration of the hot metal 16 after the intermediate waste. Was investigated.

In the desiliconization treatment, oxygen gas is supplied from the top blowing lance 2 as an oxygen source, iron oxide (iron ore) is supplied from the auxiliary raw material charging device, and the basicity of the slag 17 (= (mass% CaO)). / (Mass% SiO ₂ )) is adjusted by supplying a CaO-containing substance 19 having a particle size of 1 mm or less from the top blowing lance 2 or by supplying superlime from an auxiliary raw material charging device. The FeO concentration in the slag in the silicon treatment was calculated by the above equation (6). The intermediate waste was tilted until the converter main body 1 became almost horizontal, and the slag 17 was discharged from the furnace port of the converter main body 1 to the outside of the furnace. In the dephosphorization treatment, oxygen gas is supplied from the top blowing lance 2 as an oxygen source, iron oxide (iron ore) is supplied from the auxiliary raw material charging device, and a particle diameter of 1 mm or less is supplied from the top blowing lance 2. The CaO-containing material 19 was supplied, or quick lime was supplied from the auxiliary material charging device.

  In the test, quick lime was used as the CaO-containing substance 19, and the following two levels were carried out as quick lime addition conditions. That is, in the desiliconization process and the dephosphorization process, when the entire amount of the CaO-containing material 19 to be used is supplied from the auxiliary raw material charging device (addition condition 1), the entire amount of the CaO-containing material 19 to be used is the top blow lance 2 In the case of supplying by spraying (addition condition 2), two levels were set.

In the test operation of the addition condition 1 and the addition condition 2, the basicity ((mass% CaO) / (mass% SiO ₂ )) of the slag 17 is 0.50 to 2.0 during the desiliconization process. During the phosphorus treatment, the quick lime supply conditions were set so that the basicity of slag 17 ((mass% CaO) / (mass% SiO ₂ )) was 0.50 to 2.5. Here, T.SiO _2i (kg / molten metal t) in the desiliconization treatment is the amount of SiO ₂ in the auxiliary material (kg / molten metal t) introduced from the start of desiliconization oxygen blowing until ti time has elapsed. And the total amount of SiO ₂ generated by oxidation of silicon in the hot metal (kg / hot metal t) calculated by the equation (5). In addition, T.SiO _2i (kg / molten metal t) in the dephosphorization treatment is the amount of SiO ₂ (kg / molten metal t) in the slag remaining in the furnace after intermediate waste, and the ti time from the start of dephosphorization blowing. elapsed SiO ₂ content in the auxiliary raw material which is introduced by the time the a (kg / hot metal t), and (5) is calculated by the formula, SiO ₂ amount generated by the oxidation of silicon in the molten iron (kg / hot metal t) The total value was used.

  Table 1 shows the operating conditions of the desiliconization treatment and the dephosphorization treatment, and Table 2 shows the change (average value) of the chemical composition of the hot metal in all the test operations.

  FIG. 2 shows the results of investigating the relationship between the FeO concentration in the slag at the time of intermediate waste and the silicon concentration in the hot metal after the intermediate waste in the addition conditions 1 and 2. As shown in FIG. 2, when the FeO concentration in the slag at the time of intermediate waste was less than 1.0% by mass, a test in which the silicon concentration in the hot metal after the intermediate waste became 0.20% by mass or more occurred. On the other hand, when the FeO concentration in the slag at the time of intermediate waste was 3.0% by mass or more, no test was performed in which the silicon concentration in the hot metal after intermediate waste was 0.20% by mass or more. FIG. 2 also shows a test in which the slag 17 could not be discharged even when the converter main body 1 was tilted. When the FeO concentration in the slag during the intermediate discharge was less than 3.0% by mass, It has been found that even when the silicon concentration in the hot metal after the slag is 0.20% by mass or less, the slag 17 has poor fluidity and a test in which the slag 17 cannot be evacuated occurs.

  Therefore, in order to adjust the composition of the slag 17 to a composition capable of intermediate waste and at the same time to control the silicon concentration in the hot metal at the time of intermediate waste to 0.20% by mass or less, the FeO concentration of the slag 17 is 3. It was found that it was necessary to perform intermediate evacuation when 0% by mass or more was secured. On the other hand, when the FeO concentration in the slag is 30% by mass or more, the iron yield is deteriorated and the treatment time is extended. Therefore, it is necessary to eliminate the intermediate when the FeO concentration in the slag is 30% by mass or less. The present inventors have confirmed from decarburization refining in a converter.

  In addition, if the timing of the intermediate waste treatment varies, the refining time of the desiliconization treatment and the dephosphorization treatment will vary. Therefore, from the viewpoint of improving productivity, the intermediate waste treatment is performed after a certain time has elapsed from the start of the desiliconization treatment. It is preferable to hesitate. Specifically, it is preferable to perform intermediate evacuation when 7 minutes have elapsed since the start of the desiliconization process, or when at least 9 minutes have elapsed.

  FIG. 3 shows the ratio of the CaO concentration in the slag after the dephosphorization treatment to the FeO concentration in the molten iron after the dephosphorization treatment in the addition conditions 1 and 2 ((mass% CaO) / ( The results of investigating the influence of mass% FeO)) are shown in comparison between addition condition 1 and addition condition 2. As shown in FIG. 3, when quick lime is supplied from the auxiliary raw material charging device (addition condition 1), the value of the above ratio ((mass% CaO) / (mass% FeO)) is not significantly affected. The phosphorus concentration in the hot metal after dephosphorization was higher than 0.040% by mass. On the other hand, when quick lime is sprayed and added from the top blowing lance 2 (addition condition 2), the addition condition is obtained under the same ratio ((mass% CaO) / (mass% FeO)). Compared with 1, the phosphorus concentration in the hot metal after the dephosphorization treatment was lowered.

  In particular, in the addition condition 2, the ratio of CaO concentration to FeO concentration in slag ((mass% CaO) / (mass% FeO)) is set within a range of 0.4 to 5.5, so that dephosphorization treatment is performed. It has been confirmed that the phosphorus concentration in the hot metal after that decreases to 0.030% by mass or less. This is because when the above ratio ((mass% CaO) / (mass% FeO)) is less than 0.4, the supply rate of quick lime is small and the phosphorus absorption capacity of slag is low, so the dephosphorization reaction is not promoted, On the other hand, when the above ratio ((mass% CaO) / (mass% FeO)) exceeds 5.5, the amount of CaO is larger than the amount of FeO, and quick lime is reduced. This is because the dephosphorization ability of the slag 17 is low, so that the dephosphorylation reaction is not promoted and the phosphorus concentration in the hot metal at the end of the dephosphorization is difficult to decrease.

  That is, in the dephosphorization treatment, the CaO-containing material 19 is sprayed and added from the top blowing lance 2, and the ratio of CaO concentration to FeO concentration in the slag ((mass% CaO) / (mass% FeO)) is 0. By controlling the addition amount of the CaO-containing material 19 from the top blowing lance 2 so as to be within the range of 4 to 5.5, the dephosphorization reaction of the hot metal 16 is promoted, and the dephosphorization treatment is stably performed in a short time. I found what I could do.

  Moreover, in addition condition 2, when the slag basicity at the time of a desiliconization process was changed in the range of 0.5-2.0 in addition condition 2, undeciduous CaO which remains in slag at the time of intermediate discharge | emission is shown. The result of investigating the concentration is shown. As shown in FIG. 4, when the slag basicity during the desiliconization treatment is smaller than 0.8, rephosphorusing due to a decrease in the dephosphorization ability of the slag 17 is observed, while the slag basicity is larger than 1.2. As a result, it was found that due to the increase in the solid phase ratio due to the increase in the undehydrated CaO, the fluidity of the slag 17 was deteriorated, and a test in which the slag 17 could not be discharged occurred.

  The present inventors have confirmed that the amount of slag remaining in the furnace after the intermediate waste is about 40% by mass before the intermediate waste. Based on this knowledge, the slag component at the start of dephosphorization is estimated, and in addition condition 2, the slag basicity at the time of dephosphorization treatment is changed in the range of 0.5 to 2.5, and the slag basicity and dephosphorization treatment are changed. The relationship with the phosphorus concentration in the hot metal was investigated. The survey results are shown in FIG.

  As shown in FIG. 5, it was confirmed that the dephosphorization treatment was efficiently performed by adjusting the slag basicity during the dephosphorization treatment to a range of 1.0 to 1.8. This is because if the slag basicity during the dephosphorization treatment is less than 1.0, the dephosphorization reaction of the slag 17 is not promoted, and the slag basicity during the dephosphorization treatment is more than 1.8. Is too large, the dephosphorization reaction is not promoted because the CaO-containing material 19 is difficult to hatch. On the other hand, if the slag basicity is larger than 1.8, the undehydrated CaO in the slag increases, which is disadvantageous from the viewpoint of recycling the slag 17.

The present invention has been made based on these findings. The pretreatment method of the hot metal 16 according to the present invention supplies oxygen gas from the top blowing lance 2 and blows stirring gas from the bottom blowing tuyere 3 in advance. The hot metal 16 that has not been desiliconized is desiliconized in the converter, and then the slag 17 generated by the desiliconization process is discharged from the converter. After the slag 17 is discharged, the hot metal 16 is subsequently dephosphorized. Is pretreated, the FeO concentration in the in-furnace slag is estimated based on the unknown oxygen amount (ΔW _O2 ) obtained from the equation (2), and the upper blow lance 2 is compared with the transition of the estimated FeO concentration. At least one of the oxygen gas flow rate, the lance height of the top blowing lance 2 and the stirring gas flow rate from the bottom blowing tuyere 3 is adjusted. 9 minutes have passed By the time point, the FeO concentration of the slag 17 in the furnace is adjusted to a range of 3.0 to 30% by mass, and then the converter body 1 is tilted to discharge the slag 17 in the furnace, The dephosphorization process is performed by restarting the supply of oxygen gas from the top blowing lance 2.

  In the above test, in the desiliconization process and the dephosphorization process, either the entire amount of the CaO-containing material 19 to be used is supplied from the top blowing lance 2 or added from the auxiliary raw material charging device. Although the method is used, the top blowing addition of the CaO-containing material 19 from the top blowing lance 2 and the top addition of the CaO-containing material 19 from the auxiliary raw material charging device may be used in combination. Then, the addition method may be different between the desiliconization process and the dephosphorization process, for example, by adding the auxiliary material from the auxiliary raw material charging device and by adding the upper spraying from the upper blowing lance 2 in the dephosphorization process.

  Increasing the flow rate of oxygen gas from the top blowing lance 2 results in so-called “hard blow”, and the supplied oxygen gas is not only used for reaction with silicon and carbon in the hot metal, but also reduces the production of FeO. Since the stirring between the slag 17 and the slag 17 becomes strong, the reaction between the hot metal 16 and the slag 17 occurs and the FeO of the slag 17 is reduced, whereby the FeO of the slag 17 is maintained without decreasing or increasing. Conversely, when the flow rate of the oxygen gas from the top blowing lance 2 is lowered, so-called “soft blow” occurs, and the reaction between the supplied oxygen gas and the molten iron itself (iron) occurs, and the FeO concentration in the slag increases.

  If the lance height of the top blow lance 2 (distance between the lance tip and the hot metal surface in the furnace at rest) is reduced, hard blow occurs, and the FeO concentration of the slag 17 does not decrease or increase for the above reasons. Maintained. Conversely, when the lance height of the upper blow lance 2 is increased, soft blow occurs and the FeO concentration in the slag increases.

  Further, if the stirring gas flow rate from the bottom blowing tuyere 3 is increased, the stirring of the hot metal 16 and the slag 17 becomes stronger, so that the reaction of the hot metal 16 and the slag 17 occurs and the FeO of the slag 17 is reduced, The FeO of the slag 17 is maintained without decreasing or increasing. On the contrary, if the stirring gas flow rate is decreased, the stirring of the hot metal 16 and the slag 17 becomes weak, so the reaction between the hot metal 16 and the slag 17 is suppressed, and the FeO of the slag 17 increases.

  Thus, by changing any one of the oxygen gas flow rate from the top blowing lance 2, the lance height of the top blowing lance 2, and the stirring gas flow rate from the bottom blowing tuyere 3, the FeO concentration of the slag 17 is changed. Therefore, in the present invention, the FeO concentration in the slag is sequentially estimated using the arithmetic unit 15 during the desiliconization process, and from the transition of the estimated value of the FeO concentration in the slag, for example, from the start of blowing When it is predicted that the estimated value of FeO concentration in the slag after 7 minutes will be less than 3.0 mass%, the lance height of the top blowing lance 2 is reduced to reduce the oxygen gas flow rate from the top blowing lance 2. Increase the FeO concentration in the slag by increasing at least one of increasing the stirring gas flow rate from the bottom blowing tuyere 3 and increasing the FeO concentration in the slag, for example, 7 minutes after the start of blowing Preparing an estimate of FeO concentration above 3.0 wt%.

  On the contrary, when the estimated value of the FeO concentration in the slag is predicted to exceed 30% by mass, for example, when 7 minutes have elapsed from the start of blowing, the top blowing is increased by increasing the oxygen gas flow rate from the top blowing lance 2. At least one of reducing the lance height of the lance 2 and increasing the stirring gas flow rate from the bottom blowing tuyere 3 to reduce the FeO concentration in the slag, The estimated value of the FeO concentration in the slag after 7 minutes is adjusted to 30% by mass or less.

Furthermore, the inventors investigated the generation behavior of the FeO concentration in the slag. Specifically, as the base conditions, the average value of the acid feed rate (= oxygen gas supply flow rate) from the top blowing lance 2 until 7 minutes have passed since the start of the desiliconization process is 40000 Nm ³ / hr, The average value of the lance height from the start of the process until 7 minutes elapses is set to 2.0 m, and the average value of the bottom blow flow rate from the start of the desiliconization process until 7 minutes elapses is set to 600 Nm ³ / hr, With respect to this base condition, the acid feed rate and lance height from the top blowing lance 2 were changed, and the influence of the acid feed rate and lance height on the formation of FeO was investigated.

In FIG. 6, with respect to the base conditions, the average value of the lance height and the average value of the bottom blowing flow rate from the start of the desiliconization process to the time when 7 minutes have passed are not changed, and 7 Increase / decrease of the estimated value of FeO concentration in the slag at the time when 7 minutes have elapsed from the start of the desiliconization process when the average value of the acid feed rate up to the point when minutes elapses is increased by 5000 Nm ³ / hr ( (ΔFeO concentration) is shown (● mark).

  Further, in FIG. 6, the average value of the acid feed rate and the average value of the bottom blowing flow rate from the start of the desiliconization process to the point when 7 minutes elapses are not changed and the desiliconization process is started. The amount of increase / decrease of the estimated value of FeO concentration in slag at the time when 7 minutes have elapsed from the start of desiliconization treatment relative to the base condition (ΔFeO concentration) ) (Marked with □).

  As shown in FIG. 6, the estimated value of the FeO concentration in the slag at the time when 7 minutes have elapsed from the start of the desiliconization treatment is greatly influenced by the silicon concentration in the hot metal, and the silicon concentration in the hot metal is less than 0.30 mass%. In some cases, it was found that soft blowing with an increase in lance height was effective in increasing the FeO concentration in the slag at the time when 7 minutes had elapsed from the start of the desiliconization process. On the other hand, when the silicon concentration in the hot metal is 0.30% by mass or more, it is possible to increase the acid delivery rate more than the effect of soft blow, and supply oxygen more than the oxygen consumed for desiliconization. It was found that this was effective in increasing the FeO concentration in the slag when 7 minutes passed from the start of the silicidation treatment.

  In other words, the FeO concentration in the slag is adjusted by adjusting one of the three types of oxygen gas flow rate from the top blowing lance 2, lance height of the top blowing lance 2, and stirring gas flow rate from the bottom blowing tuyere 3. In particular, when the silicon concentration in the molten iron is 0.30% by mass or more, the acid feeding rate is higher than that at that time. On the other hand, the silicon concentration in the molten iron is 0.30% by mass. It was found that the FeO concentration in the slag increases efficiently by increasing the lance height at the stage of less than% at the lance height at that time. Note that the ranges shown in Table 1 are sufficient for the fluctuation range of the oxygen gas flow rate, the lance height, and the bottom blown gas flow rate from the top blowing lance 2, but there is no problem even if they are changed outside the range shown in Table 1. .

  Thus, according to the present invention, the FeO concentration in the slag in the furnace is reduced in the pretreatment of the hot metal consisting of desiliconization treatment in the converter, intermediate waste after the desiliconization treatment, and dephosphorization treatment after the intermediate waste. Estimate and adjust the operating conditions in light of the estimated transition of FeO concentration, and the FeO concentration of the slag in the furnace is in the range of 3 to 30% by mass until 7 to 9 minutes have passed since the start of the desiliconization process. Therefore, the silicon concentration in the hot metal during intermediate waste can be stably controlled to 0.20% by mass or less, and the slag composition can be adjusted to a composition capable of intermediate waste, As a result, in the dephosphorization process after intermediate waste, it is possible to avoid the introduction of an excessive CaO-containing substance, and at the same time, it is possible to efficiently perform from the start of the desiliconization process to the end of the dephosphorization process. Improvement is achieved.

  Using the converter equipment shown in FIG. 1, the hot metal pretreatment according to the present invention (Invention Example A, Invention Example B) and the pretreatment by the conventional method in which the FeO concentration in the slag is not adjusted during the desiliconization process ( Comparative Example C and Comparative Example D) were each carried out 20 charges. The target value of the phosphorus concentration in the hot metal at the end of the dephosphorization treatment was 0.030% by mass.

  In Invention Example A, quick lime having a particle size of 1 mm or less is supplied as a CaO-containing material from the top blowing lance from the start of desiliconization blowing, and the ratio of CaO concentration to FeO concentration in slag during desiliconization treatment (( (Mass% CaO) / (mass% FeO)) is in the range of 0.4 to 5.5, and the basicity of the slag is 0.8 to 1.2. The supply amount was adjusted. During this desiliconization process, the FeO concentration in the slag is sequentially estimated, and the estimated FeO concentration in the slag is adjusted by adjusting at least one of the acid feed rate from the top blowing lance, the lance height, and the stirring gas flow rate. Was adjusted to 3.0 to 30% by mass when 7 minutes had elapsed from the start of the desiliconization treatment, and intermediate evacuation was performed when 7 minutes had elapsed. Thereafter, quick lime having a particle size of 1 mm or less is supplied from the top blowing lance as a CaO-containing material from the start of dephosphorization so that the basicity of the slag during the dephosphorization treatment is within the range of 1.0 to 1.8. In addition, dephosphorization blowing was continued while adjusting the amount of quicklime supplied from the top blowing lance.

  In Invention Example B, quick lime having a particle size of 1 mm or less is supplied from the top blowing lance as a CaO-containing material from the start of desiliconization blowing, and the ratio of CaO concentration to FeO concentration in slag during desiliconization treatment (( (Mass% CaO) / (mass% FeO)) is in the range of 0.4 to 5.5, and the basicity of the slag is 0.8 to 1.2. The supply amount was adjusted. During this desiliconization process, the FeO concentration in the slag is estimated sequentially. If the silicon concentration in the hot metal is less than 0.30% by mass, the lance height is adjusted. If the silicon concentration in the hot metal is 0.30% by mass or more Adjusted the acid feed rate from the top blowing lance, adjusted the FeO concentration in the estimated slag to be 3.0-30% by mass when 7 minutes passed from the start of the desiliconization treatment, and 7 minutes passed. An intermediate evacuation was performed at that time. Thereafter, quick lime having a particle size of 1 mm or less is supplied from the top blowing lance as a CaO-containing material from the start of dephosphorization so that the basicity of the slag during the dephosphorization treatment is within the range of 1.0 to 1.8. In addition, dephosphorization blowing was continued while adjusting the amount of quicklime supplied from the top blowing lance.

  In FIG. 7, transition of FeO density | concentration in slag until it performs intermediate waste in this invention example A, this invention example B, the comparative example C, and the comparative example D is shown. In Comparative Example C, the intermediate evacuation was attempted before the FeO concentration in the slag reached 3.0% by mass, but the slag fluidity was poor and could not be eliminated. In Comparative Example D, the FeO concentration in the slag reached 3.0% by mass and could be rejected. However, since the FeO concentration in the slag was not controlled, the timing of the rejection was at the start of the desiliconization process. It was the time when 10 minutes passed.

  Table 3 shows the average values of the operation results in the examples of the present invention and the comparative examples. In addition, the “exhaust execution rate” shown in Table 3 indicates the ratio of charges that have been able to exclude part or all of the slag during intermediate rejection. Moreover, the comparative examples shown in Table 3 include Comparative Example C and Comparative Example D.

  As shown in Table 3, in Invention Example A, the waste discharge rate is 100%, and the silicon concentration in the hot metal after the intermediate waste can be reduced to 0.20% by mass or less. In the dephosphorization treatment, the generation of undeoxidized CaO in the slag is prevented, and the quick lime for basicity compensation can be reduced. As a result, the total amount of quick lime used is reduced, and further, the exhausting rate is 100. Therefore, the phosphorus concentration after the intermediate draining did not occur, and the phosphorus concentration after the dephosphorization treatment was stabilized at a low level. Moreover, intermediate waste was performed when 7 minutes passed from the start of the desiliconization process, and the average processing time from the start of the desiliconization process to the end of the dephosphorization process was shortened.

  In Invention Example B, compared with Invention Example A, FeO production up to intermediate waste was promoted, so that the phosphorus concentration in the hot metal after intermediate waste was reduced, and the phosphorus concentration after dephosphorization treatment was reduced to this value. Compared with Invention Example A, it could be further stabilized.

DESCRIPTION OF SYMBOLS 1 Converter main body 2 Top blowing lance 3 Bottom blowing tuyere 4 Flue 5 Skirt 6 Hopper 7 Input chute 8 Primary dust collector 9 Secondary dust collector 10 PA damper 11 Exhaust gas flow meter 12 Induction blower 13 Gas sampling probe 14 Gas analyzer 15 Calculation Equipment 16 Hot metal 17 Slag 18 Dispenser 19 CaO-containing material

Claims (5)

Oxygen gas is supplied from the top blowing lance and stirring gas is blown from the bottom blowing tuyere to desiliconize the hot metal that has not been previously desiliconized in the converter, and then the slag produced by the desiliconization process is converted. After discharging from the furnace and discharging the slag, the dephosphorizing process is followed by the hot metal pretreatment.
Based on the unknown oxygen amount obtained by sequentially calculating the oxygen balance from the flow rate of oxygen gas from the top blowing lance, the composition of the exhaust gas during refining, the flow rate of the exhaust gas, the amount of auxiliary material input, and the hot metal component during the desiliconization process Estimate the FeO concentration in the furnace slag,
In light of the transition of the estimated FeO concentration, at least one of three types of oxygen gas flow rate from the top blowing lance, lance height of the top blowing lance, and stirring gas flow rate from the bottom blowing tuyere is selected. By adjusting, by this adjustment, the FeO concentration of the slag in the furnace is adjusted to a range of 3.0 to 30% by mass by the time when 9 minutes elapse from the start of the desiliconization treatment
Thereafter, the supply of oxygen gas from the top blowing lance is temporarily interrupted, and at least a part of the furnace slag is discharged from the converter. After the furnace slag is discharged, the supply of oxygen gas from the top blowing lance is resumed. A pretreatment method for hot metal in a converter, characterized in that dephosphorization is performed.   2. The molten iron in the converter according to claim 1, wherein the FeO concentration of the in-furnace slag is adjusted to a range of 3.0 to 30% by mass by 7 minutes from the start of the desiliconization process. Pre-processing method.   During desiliconization refining, when the silicon concentration in the hot metal is 0.30% by mass or more, the oxygen gas flow rate from the top blowing lance, the lance height of the top blowing lance, and the stirring gas flow rate from the bottom blowing tuyere Of the three types, the oxygen gas flow rate from the top blowing lance is selected to adjust the oxygen gas flow rate from the top blowing lance, while the silicon concentration in the hot metal is less than 0.30% by mass, the 3 The method for pre-treating hot metal in a converter according to claim 1 or 2, wherein the lance height of the upper blowing lance is adjusted by selecting the lance height of the upper blowing lance among the seeds.   In the dephosphorization treatment, the particle diameter is 1 mm or less so that the ratio of CaO concentration to FeO concentration in slag ((mass% CaO) / (mass% FeO)) is in the range of 0.4 to 5.5. The CaO-containing material is sprayed and added to the hot metal together with oxygen gas through the top blowing lance according to the amount of FeO generated in the furnace. A hot metal pretreatment method in the converter described in the above. In the desiliconization treatment, a CaO-containing substance having a particle size of 1 mm or less is generated in the furnace so that the basicity of slag ((mass% CaO) / (mass% SiO ₂ )) is 0.8 to 1.2. Depending on the amount of SiO ₂ to be added, it is sprayed and added to the hot metal together with oxygen gas through the upper blowing lance, and in the dephosphorization treatment, the basicity of slag ((mass% CaO) / (mass% SiO ₂ )) A CaO-containing material having a particle diameter of 1 mm or less is sprayed on the hot metal together with oxygen gas through the top blowing lance according to the amount of SiO ₂ produced in the furnace so that it falls within the range of 1.0 to 1.8. The hot metal pretreatment method for a converter according to any one of claims 1 to 4, wherein the hot metal is preliminarily added.

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