JP2012017521A - Dephosphorization method of molten iron using dust - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform dephosphorization processing of molten iron while preventing the occurrence of foaming of slag without impairing dephosphorization efficiency when performing dephosphorization processing of molten iron using dusts as a smelting agent.SOLUTION: Dephosphorization processing is divided into three stages, that is, the initial stage, the middle stage, and the final stage and then performed. A plurality of dusts including blast furnace dusts is used as an initial stage smelting agent used in the initial stage, a middle stage smelting agent used in the middle stage, and a final stage smelting agent used in the final stage. In the initial smelting agent and the middle stage smelting agent, the free C concentration in the mixed dusts is set to 5.0 mass percents or less and the compounding ratio of the mixed dusts is set to 40 mass percents or less and in the final stage smelting agent, the free C concentration in the mixed dusts is set to 2.0 mass percents or less and the compounding ratio of the mixed dusts is set to less than 10 mass percents. The dephosphorization processing is performed using the initial stage smelting agent, the middle stage smelting agent, and the final stage smelting agent.

Description

  The present invention relates to a hot metal dephosphorization method using, for example, dust in which hot metal is dephosphorized using dust as a refining agent.

Conventionally, Patent Documents 1 to 4 disclose techniques for collecting dust generated during refining in a steelmaking factory and using the dust for dephosphorization of hot metal.
Patent Document 1 is a technique for recovering valuable metals such as Cr and Ni in dust by blowing AOD furnace dust collection dust into hot metal in a ladle as hot metal dephosphorization and desiliconization agents. It is disclosed that the dust is used for dephosphorization treatment.

In Patent Document 2, iron dust having a carbon content of 5 wt% or less is reacted with molten pure iron (Fe) or an iron-phosphorus (Fe—P) alloy to reduce zinc oxide in the iron dust. It is a technique for volatilizing and recovering zinc, and it is disclosed that the recovered material is used for processing.
Patent Document 3 describes a hot metal pretreatment method in which deoxidization and dephosphorization are performed by blowing an oxidizing agent from a lance immersed in hot metal in a kneading vehicle. [0033] discloses that iron-made dust is used as a solid oxygen source.

Patent Document 4 discloses a technique of using iron oxide-containing dust collection dust discharged from iron-related equipment as an oxidizing agent for hot metal desiliconization and dephosphorization.
In addition, there are techniques shown in Patent Documents 5 to 10 as techniques for dephosphorizing hot metal using a refining agent.

JP 05-320731 A Japanese Patent Laid-Open No. 11-050166 JP 2005-248219 A JP 2002-294320 A Japanese Patent Publication No. 02-055485 JP 2002-105520 A Japanese Patent Publication No. 05-014004 Japanese Patent No. 3740894 JP 07-188722 A JP 2001-234224 A

  In Patent Documents 1 to 4, although it is disclosed that dephosphorization of hot metal is performed using dust as a part of the refining agent, each of the dephosphorization processes is divided into an initial period, an intermediate period, and an end period. It is not described in detail what kind of refining agent is used corresponding to the time. Moreover, it is not described in detail how the mixing ratio of dust and other raw materials is used in the refining agent. Further, Patent Documents 1 to 4 do not discuss a refining agent for preventing slag forming that tends to occur during dephosphorization.

As shown in Patent Document 5 to Patent Document 10, there are many techniques for performing a dephosphorization process using a refining agent, but any technique shows the relationship between the refining agent and each stage of the dephosphorization process. Clearly there is no technology to prevent slag forming.
Therefore, in view of the above problems, the present invention provides a hot metal dephosphorization process while preventing the occurrence of slag forming without impairing the dephosphorization efficiency when dephosphorizing the hot metal using dust as a refining agent. It is an object of the present invention to provide a hot metal dephosphorization method using dust.

In order to achieve the above object, the present invention has taken the following measures.
That is, the technical means for solving the problem in the present invention is that when performing a dephosphorization treatment of hot metal by blowing a refining agent into the hot metal, the dephosphorization treatment is divided into an initial period, an intermediate period, and an end stage, and the refining is performed. The initial refining agent used in the initial period, the intermediate refining agent used in the middle period, and the final refining agent used in the final period, a plurality of dusts including blast furnace dust are used. The free C concentration in the mixed dust mixture is 5.0% by mass or less, and the blending ratio of the mixed dust is 40% by mass or less. For the above-mentioned final refining agent, the free C concentration in the mixed dust is 2 The blending ratio of the mixed dust is less than 10% by mass, and the dephosphorization treatment is performed using the initial refining agent, the intermediate refining agent, and the final refining agent.

  In another technical means of the present invention, when performing dephosphorization of hot metal by blowing a refining agent into the hot metal, the dephosphorization is divided into an initial stage, an intermediate stage, and an end stage, and the initial stage used in the initial stage is used. A plurality of dusts including blast furnace dust are used for the refining agent, the medium-term refining agent used in the medium term, and the final-stage refining agent used in the last term. For the initial refining agent, free C in the mixed dust mixed is used. The concentration is 5.0% by mass or less, and the mixing ratio of the mixed dust is 30% by mass or less, and for the medium-term refining agent, the free C concentration in the mixed mixed dust is 5.0% by mass or less, In addition, the mixing ratio of the mixed dust is set to 40% by mass or less. With respect to the terminal refining agent, the free C concentration in the mixed mixed dust is set to 2.0% by mass or less, and the mixing ratio of the mixed dust is 10%. Has less than the amount%, the initial refining agent lies in performing dephosphorization process using metaphase refining agent and end-stage refining agent.

  According to the present invention, when performing dephosphorization of hot metal using dust as a refining agent, dephosphorization of hot metal can be performed while preventing the formation of slag without impairing the dephosphorization efficiency.

It is a figure which shows the dephosphorization process of the hot metal by a kneading vehicle. It is the figure which showed how to obtain | require the free C density | concentration in mixed dust. It is the figure which showed the refining agent manufacturing apparatus which manufactures a refining agent. It is a flowchart which shows how to allocate a refining agent. It is the figure which showed the relationship between the amount of oxygen required for dephosphorization, and the carbon concentration in the hot metal after a dephosphorization process. It is the figure which showed the relationship between total oxygen amount and dephosphorization efficiency. It is the figure which showed the relationship between the carbon concentration [C] of hot metal after a dephosphorization process, and the metal adhesion amount after a dephosphorization process. It is the figure which showed the relationship between hot metal temperature and metal adhesion.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a view showing a state in which hot metal dephosphorization processing is performed.
As shown in FIG. 1, the hot metal dephosphorization processing method of the present invention is intended for, for example, a method in which hot metal is charged into a kneading vehicle 1 and processed in the kneading vehicle 1. Specifically, first, the hot metal 2 discharged from the blast furnace is charged into the container 3 of the kneading vehicle 1, and the kneading vehicle is moved to the dephosphorization station in order to perform the dephosphorization process in the kneading vehicle 1. In the dephosphorization station, a blowing lance 5 for blowing gaseous oxygen into the molten iron 2 is inserted into the opening 4 in the container 3 of the kneading wheel 1 and a blowing lance for blowing a refining agent or the like into the molten iron 2. 6 is inserted. Thereafter, gaseous oxygen is blown toward the molten iron 2 using the blowing lance 5 and a refining agent is blown toward the molten iron 2 using the blowing lance 6 to dephosphorize the molten iron 2. In addition, the dephosphorization processing method of this invention is not limited to the dephosphorization process by the kneading vehicle 1, If a processing facility blows in a refining agent using the powder blowing lance 6, a processing container will be limited to the kneading vehicle 1. A processing vessel such as a hot metal ladle or a converter may be used.

Hereinafter, the dephosphorization method will be described in detail.
In the hot metal dephosphorization method of the present invention, the dephosphorization treatment is divided into three stages of initial, intermediate and final stages, and a refining agent is added as appropriate at each time (initial, intermediate and final stages). The refining agent used in the initial stage is called the initial refining agent, the refining agent used in the middle period is called the middle refining agent, and the refining agent used in the last stage is called the end refining agent. A technique for dividing the dephosphorization process into three stages has conventionally existed as described in Japanese Patent Publication No. 5-14004. In addition, although each period is described in Japanese Patent Publication No. 5-14004 and Japanese Patent Publication No. 5-12406, etc., in the present invention, the silicon concentration [Si] of the hot metal is 0.10 to 0.05 mass. % Is the initial period, the period of 50 to 80% of the total processing time in the dephosphorization process (the period from the start of dephosphorization to the end of dephosphorization) is the middle period, and the remaining period is the final period. .

  A refining agent (initial refining agent, medium refining agent, and end refining agent) added to the hot metal at each time is a mixture of several types (plural) of dust, lime (burned lime), and converter slag. Blast furnace dust (dust generated in the blast furnace), steelmaking dust (dust generated when refining in a converter), pretreatment dust (dust generated during pretreatment), sintering Although there is dust (dust generated when the raw material is sintered), in the present invention, blast furnace dust is always blended in the refining agent. Each dust is collected dust collected by a dust collector installed in each process.

  Now, blast furnace dust tends to have a higher Free-C concentration (concentration of liberated carbon) than other dusts such as steelmaking dust. If a large amount of blast furnace dust is used in the refining agent to increase the Free-C concentration (referred to as free C concentration) in the refining agent, the efficiency of the dephosphorization process may be reduced. Therefore, even when blast furnace dust is used as a refining agent, it is necessary to use an amount of blast furnace dust that does not affect the dephosphorization efficiency.

Specifically, the initial refining agent for the dephosphorization treatment and the intermediate refining agent used in the middle period are the same refining agent, and the free C concentration in the mixed dust mixed with respect to the initial refining agent and the medium refining agent is 5.0 mass. The type and amount of dust are adjusted so as to be less than or equal to%.
In the initial and middle stages of the dephosphorization treatment, the desiliconization reaction mainly proceeds. However, if the free C concentration in the mixed dust is larger than 5.0% by mass even in the initial and middle stages, A large amount of CO gas is generated when it reacts with free C (in the initial refining agent and medium refining agent) and oxygen such as blown solid oxygen, and slag forming occurs. On the other hand, when the free C concentration in the mixed dust is 5.0% by mass or less, the amount of generated CO gas is small and slag forming can be suppressed.

That is, as described above, the free C concentration is increased by adding the blast furnace dust to the initial refining agent or the medium refining agent. Blast furnace dust can be used effectively by making free C density | concentration of inside into 5.0 mass% or less.
FIG. 2 shows how to obtain the free C concentration in the mixed dust when a plurality of dusts are blended. In FIG. 2, a case where two types of blast furnace dust (blast furnace dust A, blast furnace dust B) and steelmaking dust A are mixed with a hopper or the like will be described as an example.

  As shown in FIG. 2 (a), first, free C concentration in each dust (blast furnace dust A: 6.3 mass%, blast furnace dust B: 5.7 mass%, steelmaking dust A: 1.8 mass%) Is measured in advance. Then, the total dust amount (55 ton) in the mixed dust is determined from the input amount of blast furnace dust A (24 ton), the input amount of blast furnace dust B (16 ton), and the input amount of steelmaking dust A (15 ton). The free C concentration (4.9% by mass) is obtained.

  As shown in FIG. 2 (b), when the mixed dust remains, the remaining amount of the remaining dust, each input amount of new blast furnace dust A, blast furnace dust B, and steelmaking dust A, and each blast furnace dust The free C concentration in the mixed dust is obtained from the free C concentration. In addition, although FIG. 2 explains how to obtain the free C concentration when two types of blast furnace dust and steelmaking dust are mixed, the free C concentration of the mixed dust is calculated by calculating in the same manner for other dusts. Can be requested.

  As described above, the free C concentration in the mixed dust is set to 5.0% by mass or less with respect to the initial refining agent and the medium refining agent. In addition, in the present invention, the mixing ratio of the mixed dust is 40%. The mass is not more than%. The mixing ratio of the mixed dust is the ratio of the mixed dust to the total material (the ratio of the mixed dust in the refining agent). For example, the mixed dust (lime, converter slag, etc.) and mixed dust ( This is the ratio of mixed dust to the total of blast furnace dust, steelmaking dust, etc.). In the early and middle stages of the dephosphorization treatment, it is necessary to mainly blow a large amount of CaO to increase the basicity of the slag, to lower the viscosity of the slag, and to facilitate the escape of CO gas from the slag. When the blending ratio is larger than 40% by mass, not only the supply amount of CaO to be supplied is small and the basicity of the slag is difficult to increase, but also there is a large amount of FeO in the mixed dust, so that a large amount of FeO is supplied. It is. If the supply amount of CaO is small and the supply amount of FeO is large, slag forming may occur.

Therefore, in the present invention, in the initial refining agent and the medium-term refining agent, by making the blending ratio of the mixed dust 40% by mass or less, it is possible to secure the supply amount of CaO and prevent a large amount of FeO from being supplied, This suppresses slag forming.
As described above, in the initial refining agent and the medium refining agent used in the initial and middle stages of the dephosphorization treatment, the free C concentration in the mixed dust is 5.0% by mass or less, and the mixing ratio of the mixed dust is 40% by mass or less. By using the initial refining agent and the medium refining agent for the dephosphorization treatment, efficient dephosphorization treatment can be performed while suppressing slag forming.

  Now, the terminal refining agent used at the end of the dephosphorization process is different from the above-described initial refining agent and medium refining agent. That is, at the final stage of the dephosphorization process, the dephosphorization reaction is actively promoted. Under such circumstances, when a refining agent having a high free C concentration in the mixed dust is used, carbon and oxygen in the refining agent are used. May be preferentially reacted and the dephosphorization efficiency may be reduced.

  Carbon in the refining agent reacts with the hot metal to generate CO gas, but at the end of the dephosphorization process, the slag basicity may be sufficiently high, and slag foaming may occur. Is low. However, if a large amount of carbon and hot metal react violently, there is a risk that the flame will rise due to intense combustion of carbon. In particular, at the end of the dephosphorization stage, components such as P, Mn, Si, etc. in the hot metal are lower than in the initial and middle stages, so the carbon in the hot metal is preferentially burned and a flame is generated due to the combustion of carbon. It ’s easy.

Therefore, it is preferable to use a terminal refining agent having a low free C concentration in the mixed dust compared to the initial refining agent and the medium refining agent. Specifically, the free C concentration in the mixed dust is 2.0% by mass. The following problems are assumed to be difficult to occur.
In addition, at the end of the dephosphorization treatment, priority should be given to the dephosphorization reaction, and it is desirable that the free C concentration is low in the end-stage refining agent (mixed dust) as described above. From such a viewpoint, the mixing ratio of the mixed dust and the dust is set to 10% by mass or less so that the free C concentration in the end-stage refining agent does not increase.

  As described above, in the present invention, a plurality of dusts including blast furnace dust are used for the initial refining agent and the intermediate refining agent used in the initial period and the intermediate period and the final refining agent used in the final period. Moreover, regarding the initial refining agent and the medium refining agent, the free C concentration in the mixed dust mixture is 5.0 mass% or less, and the blending ratio of the mixed dust is 40 mass% or less. Furthermore, regarding the end-stage refining agent, the free C concentration in the mixed dust is set to 2.0 mass% or less, and the mixing ratio of the mixed dust is set to less than 10 mass%, and the initial refining agent, the middle-stage refining agent, and the end-stage refining agent are added. It is supposed to be used for dephosphorization.

  In the above-described embodiment, the initial refining agent and the medium refining agent are the same, but the initial refining agent and the medium refining agent may be different. In this case, in the initial refining agent, it is preferable that the free C concentration in the mixed dust is 5.0% by mass or less, and the blending ratio of the mixed dust is 30% by mass or less. Here, in the initial refining agent, since the mixing ratio is 40% or less, forming can be suppressed as described above. However, when the mixing ratio is 30% or less, FeO to be supplied decreases (in the initial refining agent, As a result, it is possible to prevent the splitting.

  In the initial stage of the dephosphorization process, the slag is hatched, and the surface of the hot metal is not sufficiently covered with the slag. When a large amount of FeO is blown in such a state that the surface of the hot metal is not covered, as shown in JP-A-2001-64713, the molten iron that is scattered by blowing FeO (blowing of a refining agent) is formed in the slag. Since it is not supplemented, spitting will occur. Therefore, by reducing the mixing ratio to 30% or less and suppressing the amount of FeO contained in the refining agent, it is possible to prevent splitting due to blowing of the refining agent. Note that when spitting occurs, the yield of the lance is shortened due to a decrease in the iron yield or the collision of the hot metal with the lance. Therefore, it is preferable not to generate the splitting as much as possible.

When such an initial refining agent is used, the medium refining agent used thereafter preferably has a free C concentration in the mixed dust of 5.0% by mass or less and a blending ratio of 40% by mass or less.
FIG. 3 shows a refining agent production apparatus 10 that produces a refining agent from several types of dust, burnt lime, converter slag, and the like. The refining agent manufacturing apparatus 10 includes a first dust tank 11 for introducing blast furnace dust, a second dust tank 12 for introducing dust other than blast furnace dust, and raw materials other than dust (for example, iron ore, lime, limestone, converter) And a plurality of raw material tanks 13 into which slag, sintered ore and the like are charged. The 1st dust tank 11, the 2nd dust tank 12, and each raw material tank 13 can adjust the speed | rate (supply speed) which discharges | emits material toward conveyance means 14, such as a belt conveyor.

Moreover, the refining agent manufacturing apparatus 10 grinds the hopper 15 that accommodates each material of the first dust tank 11, the second dust tank 12, and the plurality of raw material tanks 13, and the mixed material conveyed from the hopper 15. A crusher 16 and a plurality of storage tanks 17 for storing the pulverized mixed material for each type of refining agent are provided.
In this refining agent manufacturing apparatus 10, each material in the first dust tank 11, the second dust tank 12, and each raw material tank 13 can be transferred to the hopper 15 by the transfer means 14, and each material is mixed in the hopper 15. be able to. In the refining agent manufacturing apparatus 10, the mixed material mixed in the hopper 15 can be finely pulverized by the pulverizer 16, and the refining agent manufactured according to the type of the refining agent can be stored in the storage tank 17. It has become.

In the refining agent manufacturing apparatus 10, the materials in the first dust tank 11, the second dust tank 12, and each raw material tank 13 are supplied to the hopper 15 and the pulverizer 16, so that the above-described initial refining agent and medium-term refining agent are provided. Agent, terminal refining agent can be produced.
In carrying out the dephosphorization treatment, the amount of the refining agent used in the initial, middle and final stages is determined, for example, as described in JP-A-62-1161908. First, in the dephosphorization treatment, the ratio of gaseous oxygen (gas oxygen blown into the hot metal) and solid oxygen (solid oxygen supplied to the hot metal) is determined based on the dephosphorization concentration of the hot metal after the treatment and the treatment temperature (hot metal temperature). decide. In addition, the basicity of the slag is also defined when performing the dephosphorization treatment. In Japanese Patent Application Laid-Open No. Sho 62-161908, the basicity of slag is controlled to 5-6. However, in the present invention, there is a problem that slag adheres to the upper part of the kneading vehicle due to the melting point of the slag. There is a fear. Therefore, the total CaO is determined with the goal that the basicity of the slag is 2.2 to 2.5.

For example, as shown in Japanese Patent Application Laid-Open No. 62-161908, the total SiO _{2 in the} kneading vehicle is determined from the [Si] concentration after desiliconization and the residual de-Si slag volume remaining in the kneading vehicle, and the basicity of the slag is determined. Considering this, the basic unit of the main dephosphorizing agent (refining agent) is determined. Next, when the basic unit of the dephosphorizing agent main component (refining agent) is determined, the supplied oxygen amount is determined from the dephosphorization rate. As shown in FIG. 2 of Japanese Patent Laid-Open No. Sho 62-161908, the ratio of total oxygen blown in the dephosphorization process is as shown in the S / O ratio [solid oxygen amount / (solid oxygen amount + gaseous oxygen amount)]. There is a relationship that ΔT (pre-treatment hot metal temperature−post-treatment hot metal temperature) becomes larger on the negative side as it increases. This relationship is used to determine the solid oxygen intensity and the gaseous oxygen intensity in the supplied oxygen intensity. In Japanese Patent Laid-Open No. 62-161908, the case where one type of refining agent is used is described. However, in the present invention, since the refining agents used are different depending on the initial, middle and final stages, as shown in Table 1, slag is used. Depending on the basicity, it may be allocated to several types of refining agents so that the total amount of the required CaO basic unit and the required solid oxygen basic unit are equal. In Table 1, the necessary CaO unit is as wide as 16.9 to 19.1 (kg / tp) because the target basicity is in the range of 2.2 to 2.5.

For example, when the refining agent 1 is manufactured using the refining agent manufacturing apparatus 10 as an initial refining agent, the refining agent 2 is manufactured as a medium refining agent, and the refining agent 3 is manufactured as a terminal refining agent, how to allocate each refining agent Is as follows.
First, as shown in FIG. 4, as described above, the gaseous oxygen unit, solid oxygen unit, and CaO unit in the dephosphorization process are obtained (step 1). Next, as shown in Step 4, from the Si concentration of the hot metal before the treatment as shown in Step 2 and the CaO amount, SiO amount, and solid oxygen amount in the refining agent 1 as shown in Step 3, as shown in Step 4, The basic unit of the refining agent 1 for obtaining a Si concentration of 0.1 to 0.05% (for example, 0.1% or 0.05%) is obtained. That is, since the initial stage of the dephosphorization process is a period until the Si concentration in the hot metal reaches 0.1 to 0.05%, the basic unit of the refining agent 1 for achieving this is obtained.

  Next, as shown in step 5, after determining the basic unit of the refining agent 1, the amount of CaO and the solid oxygen basic unit necessary for the middle and final stages are obtained. As shown in Step 6, as shown in Step 7, i) Dephosphorization from the amount of CaO in the refining agent 2 and the refining agent 3, the amount of SiO, the amount of solid oxygen, the blowing speed of the refining agent 2 and the refining agent 3, etc. The basicity of the slag after the treatment is 2.2 to 2.5, ii) the refining agent 2 can be switched in the middle stage of the dephosphorization process, and iii) the calculated dephosphorization time is shortened (if possible The basic units of the refining agent 2 and the refining agent 3 are obtained.

In addition, since the amounts of the refining agent 2 and the refining agent 3 are reference values, in the actual treatment, if the refining agent 2 can be switched to 50% to 80% of the total dephosphorization time in the middle of dephosphorization, the refining is performed on the way. The switching from the agent 2 to the refining agent 3 may be changed. Moreover, the amount of oxygen required until the Si concentration in the hot metal becomes 0.1% can be obtained by, for example, the equation (1). In addition, Pi of Formula (1) is the phosphorus concentration of hot metal before a dephosphorization process, and pf is the phosphorus concentration of the hot metal after a dephosphorization process. O ₂ is the total amount of oxygen used in the dephosphorization process (excluding oxygen used in the desiliconization reaction).

  As shown in FIG. 4, by performing the operations from Step 1 to Step 7, for example, as shown in Table 2, the refining agent 1, the refining agent 2, and the refining agent 3 can be allocated. In addition, the allocation of the refining agent shown in Table 2 is 31.7 minutes for the combined treatment time for the middle and final stages, 20.0 minutes for the treatment period for the middle period, and the ratio of the treatment time for the middle period to the total dephosphorization treatment time ( (Medium treatment time / total dephosphorization treatment time) 63%, the basicity of the slag after treatment was 2.3, the Si concentration of hot metal before treatment was 0.20 mass%, and the Si concentration of hot metal after treatment was 0 It is a result when it is set to 0.01 mass%. The values shown in Table 2 show how the refining agents are allocated as an example, and the present invention is naturally not limited to this.

  Table 3 summarizes the implementation conditions.

Table 3 shows the supply rates of the initial refining agent, the medium refining agent, and the final refining agent. The amount of O ₂ (solid oxygen) contained in each refining agent shown in Table 3 can be obtained by, for example, formula (2). The compositions of the initial refining agent, the medium refining agent, and the final refining agent are as shown in Table 4.

Tables 5 to 10 show examples of the dephosphorization treatment of the hot metal dephosphorization method of the present invention based on the implementation conditions shown in Table 3 and the refining agent shown in Table 4, and the hot metal of the present invention. This is a summary of comparative examples in which dephosphorization treatment was performed by a method different from the dephosphorization method.
In the examples and comparative examples, the slag foams during the dephosphorization process. As evaluated. Note that slag forming is described in, for example, “Iron and Steel, vol. 78 No. 2 (1992), p200-208, Mota Hara, Kazuaki Kanno”.

  Further, in the examples and comparative examples, the dephosphorization efficiency is best “◎” if the value of the formula (1) is 0.14 or more, good “◯” if it is 0.18 or more, and less than 0.14. If there was a defect, it was judged as “x”. As shown in the formula (1), a large amount of total oxygen required for the dephosphorization treatment means that the dephosphorization efficiency is lowered. In other words, the dephosphorization efficiency is reduced. If it is bad, the carbon concentration [C] in the hot metal after the dephosphorization process is lowered.

That is, as shown in FIG. 5, the relationship between the amount of oxygen necessary for dephosphorization (total oxygen amount, excluding oxygen necessary for desiliconization) and the carbon concentration in the hot metal after the dephosphorization treatment is as follows. As the amount of oxygen increases (dephosphorization efficiency decreases), [C] in the hot metal after the dephosphorization treatment decreases.
Here, as shown in FIG. 6, when the relationship between the total oxygen amount and the dephosphorization efficiency is seen, the dephosphorization efficiency is less than 0.14 and the total oxygen amount is 11.5 Nm ³ / ton larger, As shown in FIG. 5, the carbon concentration [C] in the hot metal after the dephosphorization treatment is less than 4.0% by mass. If the carbon concentration [C] of the hot metal after dephosphorization is less than 4.0% by mass, the amount of metal and slag adhering to containers such as kneading vehicles tends to increase. C] is preferably 4.0% by mass or more, and the dephosphorization efficiency needs to be 0.14 or more.

  Note that the total oxygen amount shown in FIG. 5 is calculated by using the actual data in the average dephosphorization treatment in which the phosphorus concentration in the hot metal before the treatment is reduced from 0.115% to 0.023%. It summarizes the relationship with phosphorus efficiency. The temperature after dephosphorization treatment was 1285 ° C., which is the target temperature after dephosphorization treatment. Further, one point in FIG. 5 indicates an average value when 50 to 70 charges are performed for the dephosphorization process, and vertical lines indicate a value of ± 1σ. Here, as shown in FIG. 5, even when the dephosphorization efficiency is 0.14 or more, the carbon concentration after dephosphorization is less than 4.0% by mass in consideration of variations during dephosphorization. There are cases where bullion and slag adhere. However, the case where the carbon concentration is less than 4.0% by mass is only 10% to 20% of the case where the carbon concentration is less than 4.0% even when the dispersion is taken into consideration, and the metal is continuously attached to the kneading vehicle or the like. The probability is small enough, and the bullion attached during the next treatment may dissolve, so there is no significant adverse effect on the operation.

Further, when the dephosphorization efficiency is 0.18 or more, the carbon concentration [C] after the dephosphorization treatment is 4.1% on average, and the probability that the carbon concentration [C] after the treatment is less than 4.0 is Very small. Thus, the dephosphorization efficiency is 0.14 or more and preferably 0.18 or more.
In addition, when dephosphorization efficiency is bad, it is thought that dephosphorization efficiency can be improved by lowering the hot metal temperature. However, as shown in FIG. 8, when the hot metal temperature is lowered and the hot metal temperature after dephosphorization is less than 1270 ° C., the hot metal is attached to the ladle after it has been charged into the ladle (after being dispensed). There is a tendency for the amount of bullion adhesion to increase. That is, when the hot metal that is less than 1270 ° C. is discharged into the ladle and the ladle is transported, heat is dissipated while the ladle is being transported to approach the solidification temperature of the hot metal, so that the bullion attached to the ladle increases. In view of this, it is not preferable to lower the hot metal temperature in order to increase the dephosphorization efficiency.

  FIG. 7 summarizes the relationship between the carbon concentration [C] of the hot metal after the dephosphorization treatment and the adhesion amount of the metal (deposition amount of metal and slag) after the dephosphorization treatment. One point in FIG. 7 shows an average value when the dephosphorization process is performed for 20 to 70 charges. In addition, the temperature of the hot metal after the dephosphorization process at this time is a result of 1280 to 1290 ° C. As shown in FIG. 7, the amount of metal adhesion increases rapidly when the carbon concentration [C] reaches 4.0% by mass. From this point of view, the carbon concentration [C] after the dephosphorization treatment is also observed. It is necessary to perform a dephosphorization process so that it may become 4.0 mass% or more.

  In Examples and Comparative Examples, when oxygen or the like is blown through a lance, spattering occurs when the hot metal scatters, and “Yes” is present when spitting occurs, and when no spitting occurs. Evaluated as “None”. The presence or absence of spitting is judged visually or with a camera installed at the furnace port. When spitting occurred above the furnace port of the kneading car, it was determined that spitting occurred, and when spitting did not reach the furnace port of the kneading car, no spitting was set. Further, in the examples and comparative examples, during the dephosphorization process, for example, when a flame goes up from the furnace port of a chaotic vehicle, there is a flame and is evaluated as “Yes”, and when it does not rise, it is evaluated as “No” that there is no flame. did.

  Furthermore, in the Example and the comparative example, it measured about the adhesion amount of bullion and slag. Before the dephosphorization treatment and after the dephosphorization treatment, the empty weight of the kneading car (iron skin + refractory + total weight of deposits) was measured with a load cell, and the increase in weight was defined as the amount of slag and metal adhesion. . The empty weight of the kneading car was measured after the molten iron was discharged into the hot metal ladle after the dephosphorization process and the slag remaining in the kneading car was discharged. If the amount of bullion and slag attached per dephosphorization process is 1.0 ton / ch or less, the attached bullion may be dissolved in the process after the next charge or when the hot metal is discharged. It ’s never a big problem. However, when the adhesion amount of bullion and slag per dephosphorization treatment is 3.0 ton / ch or more, it is difficult to dissolve the adhered bullion and slag in normal operation. It is necessary to remove bullion and slag adhesion. In this case, there is a problem that the refractory is removed at the same time. In addition, if the amount of slag deposited per dephosphorization process exceeds 3.0 tonnes, the slag adhered to the upper side may cause the balance of the chaotic vehicle to become unstable, or the molten metal load (charge amount). There is a case where productivity is reduced due to a significant decrease in

  In Tables 5 to 10, the first dust tank and the second dust tank correspond to the refining agent manufacturing apparatus 10 shown in FIG. 3, and the blending amount of the first dust tank is the blending amount of blast furnace dust. The blending amount of the second dust tank is the blending amount of dust other than the blast furnace dust, and the blending amount other than dust is the blending amount from the raw material tank 13 (the total value of the materials discharged from each raw material tank 13). is there. The free C concentration of the first dust tank is the free C concentration of blast furnace dust discharged from the first dust tank, and the free C concentration of the second dust tank is the other C concentration discharged from the second dust tank. This is the free C concentration of dust.

  In Examples 1 to 12 and Examples i to viii, with respect to the initial refining agent and the medium refining agent, the free C concentration in the mixed dust is 5.0% by mass or less (the column of the free C concentration in the blended dust). And the mixing ratio of the mixed dust is 40% by mass or less (the column of the dust mixing ratio). Moreover, regarding the end-stage refining agent, the free C concentration in the mixed dust is 2.0 mass% or less, and the blending ratio is less than 10 mass%.

By doing so, the carbon concentration [C] in the hot metal after the dephosphorization treatment is 4.0 mass% or more, the dephosphorization efficiency can be 0.14 or more, and slag forming is prevented. I was able to. In addition, the temperature after dephosphorization treatment was 1270 ° C. or higher (post-treatment temperature column), and the slag / metal adhesion amount could be less than 1.0 ton / ch.
In Comparative Examples 13 to 16, since blast furnace dust was not used as the refining agent, the blast furnace dust had to be disposed of (dust disposal section).

In Comparative Examples 17 to 19, as a result of increasing the amount of oxygen used to reduce [P] after the dephosphorization treatment to the normal level, the carbon concentration [C] in the hot metal after the dephosphorization treatment was 4. It became less than 0 mass%. In addition, the dephosphorization efficiency was less than 0.14, and slag forming occurred in the initial or middle period.
In Comparative Examples 20 to 22, since the mixing ratio is larger than 40% in the initial refining agent or the medium refining agent, the carbon concentration [C] in the molten iron after the dephosphorization treatment is 4.0% by mass. The dephosphorization efficiency was less than 0.14, and forming occurred.

  In Comparative Examples 23 and 24, the timing of switching the refining agent to the dephosphorization end stage exceeds 80% of the total oxygen (column of the timing of switching to the dephosphorization end stage), and the middle period that should be used in the middle period It is in such a state that a refining agent is also used in the last stage. As a result, since the agent having a high free carbon concentration was used at the end of dephosphorization, the dephosphorization reaction was inhibited by free carbon, and the dephosphorization efficiency was less than 0.14, resulting in a very inefficient dephosphorization treatment. . As a result of increasing the amount of oxygen used to reduce [P] after the dephosphorization treatment to the normal level, the carbon concentration [C] in the molten iron after the dephosphorization treatment was less than 4.0% by mass. In addition, since a refining agent having a high free carbon concentration was blown in at the end of dephosphorization, there was a risk that the blown carbon reacted with oxygen to raise the flame.

  In Comparative Examples 25 and 26, the timing for switching the refining agent to the dephosphorization end stage is less than 50% of the total oxygen, and the end refining agent is used in the middle stage of the dephosphorization process. It has become. As a result, since the timing after the dephosphorization stage was early, the agent having a high oxygen content in the refining agent was used in a state where the basicity of the slag was not sufficiently increased. As a result, slag forming occurred.

  In Comparative Examples 27 and 28, since the free C concentration in the mixed dust was made higher than 2.0 mass% with the end-stage refining agent, a flame was observed during the dephosphorization treatment. In Comparative Examples 27 and 28, the amount of oxygen used was increased in order to reduce [P] after the dephosphorization treatment to the normal level, so that the carbon concentration [C] in the hot metal after the dephosphorization treatment was 4. The dephosphorization efficiency was less than 0.14, and the dephosphorization treatment was very inefficient.

In Comparative Examples 29 and 30, as a result of increasing the amount of oxygen used to reduce [P] after the dephosphorization treatment to the normal level, the carbon concentration [C] in the molten iron after the dephosphorization treatment was 4.0 mass. %. Moreover, the dephosphorization efficiency was also less than 0.14, and the dephosphorization process was very inefficient.
In Examples 31 to 35 and Examples ix to xvi, in addition to the conditions shown in Examples 1 to 12 and Examples i to viii, in the initial refining agent, the blending ratio is set to 30% by mass or less. Therefore, it was possible to prevent splitting. In Examples 36 to 38, in the initial refining agent, when the mixing ratio was 30 to 40% by mass, although slag forming could be prevented, spitting occurred.

  It should be noted that matters not explicitly disclosed in the embodiment disclosed this time, such as operating conditions and operating conditions, various parameters, dimensions, weights, volumes, and the like of a component, deviate from the range normally practiced by those skilled in the art. However, matters that can be easily assumed by those skilled in the art are employed.

DESCRIPTION OF SYMBOLS 1 Chaotic wheel 2 Hot metal 3 Container 4 Opening part 5 Spraying lance 6 Blowing lance 10 Refining agent manufacturing apparatus 11 1st dust tank 12 2nd dust tank 13 Raw material tank 14 Conveying means 15 Hopper 16 Crusher 17 Storage tank

Claims (2)

When dephosphorizing the hot metal by blowing a refining agent into the hot metal,
The dephosphorization process is divided into initial, middle and final stages, and the initial refining agent used in the initial stage, the intermediate refining agent used in the middle period and the final refining agent used in the final stage include blast furnace dust. Use multiple dusts,
Regarding the initial refining agent and the medium refining agent, the free C concentration in the mixed dust mixture is 5.0% by mass or less, and the mixing ratio of the mixed dust is 40% by mass or less.
For the terminal refining agent, the free C concentration in the mixed dust is 2.0 mass% or less, and the blending ratio of the mixed dust is less than 10 mass%,
A dephosphorization method for hot metal using dust, wherein the dephosphorization treatment is performed using the initial refining agent, the middle refining agent, and the final refining agent. When dephosphorizing the hot metal by blowing a refining agent into the hot metal,
The dephosphorization process is divided into initial, middle and final stages, and the initial refining agent used in the initial stage, the intermediate refining agent used in the middle period and the final refining agent used in the final stage include blast furnace dust. Use multiple dusts,
Regarding the initial refining agent, the free C concentration in the mixed dust mixture is 5.0 mass% or less, and the blending ratio of the mixed dust is 30 mass% or less,
For the medium-term refining agent, the free C concentration in the mixed dust mixed is 5.0 mass% or less, and the mixing ratio of the mixed dust is 40 mass% or less,
For the above-mentioned final refining agent, the free C concentration in the mixed dust mixture is 2.0 mass% or less, and the blending ratio of the mixed dust is less than 10 mass%,
A dephosphorization method for hot metal using dust, wherein the dephosphorization treatment is performed using the initial refining agent, the middle refining agent, and the final refining agent.

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