JP4779388B2 - How to remove hot metal - Google Patents

Description

  The present invention proposes a dephosphorization method for hot metal, particularly a method for improving the reaction efficiency of the dephosphorizing agent and increasing the accuracy of low phosphorus dephosphorization.

In recent years, hot metal smelted in a blast furnace is generally subjected to dephosphorization in a hot metal pretreatment vessel such as a converter, ladle or toppedor as pretreatment for decarburization and refining.
In such hot metal dephosphorization treatment, hot metal discharged from a blast furnace and an auxiliary material containing a dephosphorizing agent are put into the pretreatment vessel, and then oxygen gas is blown over the hot metal in the pretreatment vessel. By this, the phosphorus in the hot metal is oxidized, and at the same time, the phosphorous oxide generated at this time is transferred into the slag, thereby removing the phosphorus in the hot metal. In particular, the dephosphorization process using a refining vessel such as a converter has an advantage that the dephosphorization process can be performed more quickly than the dephosphorization process using a ladle or a topy doker.

For example, in a method of dephosphorizing hot metal using a converter, oxygen gas is mainly blown from an upper blowing lance and a dephosphorizing agent or the like is put into the furnace. In such treatment, it is known that a dephosphorization reaction as shown in the following formula (2) proceeds between hot metal and slag. In this treatment, a solvent such as CaF ₂ , NaCO _3, or CaCl ₂ is also added in order to promote the dephosphorization reaction, that is, to promote the dephosphorization reaction due to the melting of CaO in the slag.
2 [P] +5 (FeO) +3 (CaO) → 3 (CaO · P ₂ O ₅ ) +5 [Fe] (2)

  By the way, in recent years, slag has been recycled for use as roadbed material or landfill material. Accordingly, the converter slag is problematic due to the presence of fluorine (F), sodium (Na), and the like contained therein. The reason is that it is considered that F, Na and the like are eluted by rainwater and groundwater and may adversely affect the environment and the human body. Therefore, in recent dephosphorization treatment, hot metal dephosphorization is performed without using a solvent such as fluorine (F), sodium (Na), or chlorine (Cl) as the auxiliary material for the purpose of environmental harmony. Measures are being considered.

However, the hot metal dephosphorization technique using a dephosphorizing agent that does not contain a solvent agent such as F or Na needs to hatch CaO in the lime-based dephosphorizing agent. For that purpose, it is effective to effectively use the action of FeO in the slag. As for such dephosphorization technology, as disclosed in the documents exemplified as Patent Document 1, Patent Document 2, and Patent Document 3, the oxygen balance is determined from the exhaust gas composition, flow rate, oxygen gas flow rate, auxiliary material input amount, and the like. To calculate the amount of accumulated oxygen, control this amount of accumulated oxygen, and adjust the amount of oxygen at the time of blowing, etc., so that (% T. Fe) in the slag and the blowing stopper P (hereinafter, [% P] is abbreviated as _f ).
Japanese Patent Laid-Open No. 2-19413 JP-A-1-242711 JP 2002-275519 A

In general, the dephosphorization process is advantageously performed in a low temperature hot metal stage in terms of equilibrium, and in particular, without using a solvent containing F, Na, or Cl, the hot metal is removed in a hot metal pretreatment vessel such as a converter. In order to perform phosphorus, it is considered effective to promote the hatching of CaO with FeO as shown in the above formula (2).
However, in the hot metal stage, FeO in the slag and hot metal are in a non-equilibrium state, and this state changes depending on the hot metal temperature, oxygen gas blowing conditions, bottom blowing gas blowing conditions, etc. It is very difficult. In addition, the excessive amount of FeO causes deterioration of dephosphorization, occurrence of slopping, deterioration of yield, etc. due to dilution of the CaO concentration of the slag. Therefore, it is necessary to appropriately control the amount of FeO during blowing.

  The converter blowing technologies disclosed in the above-mentioned Patent Documents 1, 2, and 3 are mainly decarburized blowing, and in this case, FeO is close to equilibrium as the C content decreases due to decarburization. It is generated stably. However, in the blowing for hot metal dephosphorization, it is necessary to prioritize the dephosphorization process while suppressing the progress of decarburization. Therefore, in such a method, it is necessary to generate FeO in a non-equilibrium state, and it is required to control the amount of FeO immediately after the start of blowing. In this respect, the converter blowing method described in Patent Document 1 uses the measurement of [mass% C] by the intermediate sub lance and the amount of accumulated oxygen in the slag from the time of using the intermediate sub lance to the blowing (T. Fe). It only discloses a method for controlling the above. Further, the converter blowing control method described in Patent Document 2 calculates the amount of accumulated oxygen from the time when 30 to 70% has elapsed from the start of blowing.

  However, in the converter, in the method of dephosphorizing the hot metal with a dephosphorizing agent not containing a solvent such as F, Na, or Cl, in order to promote the dephosphorization reaction, immediately after the start of blowing. During the entire blowing process, it is necessary to control the hatching of CaO with FeO, the suppression of slopping, and the improvement of Fe yield. It was still insufficient. In addition, in the method described in Patent Document 3, although dephosphorization is performed without using fluorite, there is a problem that it takes time to dephosphorize to the target phosphorus concentration as compared with the case of using fluorite. there were.

  The object of the present invention is to use a converter as a hot metal pretreatment vessel, and to use a dephosphorization agent that does not contain a solvent such as F, Na, Cl, etc., to ensure high dephosphorization reaction efficiency and to reduce the phosphatization of molten steel. The purpose is to propose a method for realizing it quickly and reliably.

  In order to solve the above problems, the present invention focuses on the action of FeO produced in slag by blowing oxygen from the top blowing lance in a method of dephosphorizing hot metal using a converter as a hot metal pretreatment container. By promoting both the hatching of the dephosphorization agent by FeO and the slag-metal reaction by the hot metal stirring based on the blowing of the stirring gas from the bottom blowing tuyere, as represented by fluorite The dephosphorization reaction was made efficient without relying on auxiliary materials containing F, Na, Cl and the like. Therefore, in the present invention, the oxygen gas supply position from the top blowing lance, the oxygen gas blowing flow rate, the agitation of the molten metal and the strength of the steel bath surface dynamic pressure, or the operation timing thereof are optimally controlled. It is.

  That is, the present invention uses a hot metal pretreatment vessel provided with an upper blowing lance and a bottom blowing tuyere, and simultaneously blows oxygen gas from the upper blowing lance and simultaneously blows stirring gas from the bottom blowing tuyere. In the method of performing dephosphorization, oxygen gas spraying from the top blowing lance to the bath surface after adding the dephosphorizing agent in the hot metal pretreatment vessel is soft blow until the dephosphorizing agent is completely hatched, After the hatching is completed, hard blow is performed, and when the FeO content in the slag generated at the time of soft blow becomes 30 mass% or more, the stirring gas flow rate from the bottom blowing tuyere is increased to between the slag and the metal. This is a hot metal dephosphorization method characterized by strengthening the stirring of the hot metal.

In the present invention, it is effective to raise the hot metal before adding the dephosphorizing agent to a temperature of 1300 ° C. or higher, and the soft blow performed until the completion of the hatching is a hard blow performed after the completion of the hatching. This is an operation for increasing the height of the upper lance relative to the time. In this soft blow operation, it is effective to relatively increase the oxygen gas flow rate. On the other hand, the hard blow performed after the completion of the hatching is an operation of relatively lowering the upper blowing lance height than the soft blow. In this hard blow operation, oxygen gas is blown over the oxygen gas to generate a hot spot (recess, hereinafter, also simply referred to as “hot spot”) on the hot metal bath surface.
In the present invention, the soft blow means that the oxygen jet does not enter from the upper blowing lance in the bath or is light, and the oxygen jet has a deep penetration depth in the bath. Those that form a hot spot and cause a refining reaction (decarburization reaction) are distinguished as hard blow. However, if the dephosphorization process can be operated to allow some decarburization, mild decarburization is possible. The oxygen gas flow rate may be increased to generate FeO until the weak hard blow side that can allow the carbon reaction is reached.

  Moreover, in this invention, when stirring between the said slag and metal with the stirring gas from a bottom blowing tuyere, when the FeO content in the slag to produce | generate is 30 mass%-50 mass%, the flow volume of the stirring gas is set. It is effective to increase.

In the present invention, the hot metal temperature before adding the dephosphorizing agent is set to about 1300 ° C. or more by adding oxygen and / or blowing an oxygen gas from an upper blowing lance. At this time, the oxygen gas is blown when the heat generating material is used and / or when [Si] being melted is used as the heat source, preferably by making the blown oxygen and the heat generating material, for example, This is effective for causing an exothermic reaction between ferrosilicon (FeSi) and Si in the hot metal. Immediately after the temperature rise of the hot metal temperature, the dephosphorizing agent is added to the furnace, and the blowing of oxygen gas by the upper blowing lance is switched to the soft blowing to perform the blowing that gives priority to the generation of FeO.

  In the present invention, the switching to the hard blow after the completion of the hatching is performed by spraying oxygen gas in the soft blow and mutual stirring of the slag and metal by the stirring gas from the bottom blowing tuyere. It is possible to reduce FeO in the slag by performing oxygen blowing with this hard blow when the dephosphorization value is reached.

Furthermore, in the present invention, when dephosphorizing hot metal using a converter, by sequentially calculating the oxygen balance from the exhaust gas composition during blowing and its flow rate, oxygen gas flow rate, auxiliary material input amount, hot metal components Based on the required amount of accumulated oxygen, the amount of FeO generated in the furnace is estimated from the following equation (1), and (FeO / CaO) during blowing is reduced to 0.5 to 3 according to the estimated amount of FeO. It is effective to add a dephosphorizing agent so that it can be maintained at .5.
FeO (kg / t) = [Amount of accumulated oxygen] (m ³ (standard state) / t) /22.4×71.85 (1)

In the present invention, the amount of dephosphorization agent is controlled so that (FeO / CaO) of the generated slag becomes 1.5 or more at the stage of at least 30% of the total amount of blown oxygen during blowing. It is effective.
This method of the present invention promotes the hatching of CaO by increasing the FeO content until the initial stage of blowing, that is, until the progress of blowing is about 30% of the total amount of blown oxygen, and at the end of blowing The purpose is to control the slag composition in the low phosphorus area of the slag, and to promote dephosphorization by sequentially adding dephosphorizing agents such as quick lime and limestone in accordance with the amount of FeO produced during blowing. I mean. This also means that the dephosphorization agent can be continuously fed depending on the amount of FeO produced. That is, these dephosphorizing agents that are sequentially added are quickly hatched by the reaction of the above formula (2) according to the amount of FeO, and promote the dephosphorization reaction. Compared with the conventional method in which the dephosphorizing agent is added all at once at the beginning of blowing, this method is gradually performed in accordance with the amount of FeO that the introduced dephosphorizing agent sequentially produces at each stage of blowing. Therefore, it is advantageous for the reaction efficiency of the dephosphorizing agent, that is, low phosphatization.

In the present invention, as the dephosphorizing agent, any one of lime-based dephosphorizing agents selected from quick lime, limestone and calcined lime, iron ore, sintered ore, and converter refining slag containing no F, Na and Cl are used. It is effective to use the above dephosphorizing agent.
Furthermore, in the present invention, the control of slag (FeO / CaO) during blowing is performed by controlling any one or more of the top blowing lance height, the top blowing oxygen gas flow rate, and the bottom blowing stirring gas flow rate. It is effective to use soft blow or hard blow.

  According to the present invention, in dephosphorization of hot metal using a hot metal pretreatment vessel such as a converter in which top blowing and bottom blowing can be used together, dephosphorization is required by shortening the hatching time and promoting the slag-metal reaction. Time can be shortened. In addition, since the present invention is a method for dephosphorization using a dephosphorization agent that does not contain F, Na, or Cl, which is a dephosphorization agent and is feared to affect the environment and the human body, there is no adverse effect on the environment. .

In addition, according to the present invention, when hot metal dephosphorization is performed by a converter, high reaction efficiency can be ensured, so that low phosphation ([% P] _f ≦ 0.020 mass%) hot metal is stably produced. Will be able to.

Next, an example of an embodiment of the present invention will be described.
FIG. 1 is a diagram showing an example of the operation timing in the dephosphorization process according to the present invention, FIG. 2 is a diagram showing the bath surface dynamic pressure during the dephosphorization process shown in FIG. 1, and FIG. It is a figure explaining the outline | summary of a phosphorus process. FIG. 3 shows a preferred embodiment of the present invention using the converter 1 as a hot metal pretreatment container, but the present invention is not limited to this example. In this example, the hot metal 2 discharged from the blast furnace is supplied into the converter 1, and in the present invention, the hot metal temperature is set to 1300 ° C. or higher by blowing oxygen gas from an upper blowing lance. Next, auxiliary materials containing a lime-based dephosphorizing agent and the like are charged into the converter 1. Basically, immediately after that, the height of the lance from the hot metal bath surface and the flow rate of the oxygen gas is adjusted from the top blowing lance 11 disposed so as to be able to move up and down above the converter 1 toward the bath surface f. On the other hand, from the bottom blowing tuyere 12 disposed at the bottom of the converter 1, the stirring gas is blown to the bottom to stir the hot metal 2 to produce FeO and at the same time Operations to promote the hatching of raw materials. As a result, the phosphorus separated from the molten iron 2 through FeO is dissolved in the slag 3 produced by the hatching of the auxiliary raw material, so that the dephosphorization process is performed. The dephosphorized hot metal is immediately decarburized and refined in the next refining process or desulfurized and then decarburized and refined.

As the dephosphorizing agent for dissolving phosphorus in the slag 3, in addition to FeSi which is a heat generating material, the auxiliary material is a lime-based dephosphorizing agent selected from quick lime, limestone and calcined lime, iron ore, sintered ore or F Any one or two or more types of converter refining slag containing no Na and Cl are used. As this dephosphorizing agent, use of a lime-based dephosphorizing agent is particularly preferred from the viewpoint of reaction efficiency and cost.
In addition, this dephosphorizing agent acts effectively in inducing a dephosphorization reaction as shown in the following formula (2) by causing a CaO content to cause a hatching reaction via FeO.
2 [P] +5 [FeO] +3 (CaO) → 3 (CaO · P ₂ O ₅ ) +5 [Fe] (2)

Hereinafter, the method for hot metal dephosphorization according to the present invention will be described with an example.
First, as shown in FIG. 1 and FIG. 2, the basic pattern of top blowing is from the initial stage of dephosphorization to the time t ₃ when hatching is complete (in FIG. 1, when the processing time is 9 minutes). up to 80%), do the soft blow and high oxygen gas flow rate by the top blowing lance, then the slag formation completion t ₃ hereinafter, to reduce the FeO produced, together with a hard blow by top lance low Operate the oxygen gas flow rate.

  The soft blow described in the present invention means that a hot spot (recess) is formed on the bath surface of the hot metal by the jet of the top blown oxygen gas by making the height of the top blow lance relatively higher than in the case of the hard blow. It means that oxygen gas is blown up to such an extent that it is not generated. On the other hand, the hard blow means that oxygen gas is blown on the hot metal bath surface to generate a hot spot (recess).

As described above, in the dephosphorization process according to the present invention, first, the dephosphorizer is added to the molten iron in the furnace (or other auxiliary materials may be added simultaneously), and then the hatching is completed from the initial stage of the dephosphorization process. to time t _3, as well as perform a soft blow with a higher top lance 11, preferably performs an operation to increase the flow rate of the oxygen gas jetted. For example, this soft blow has an upper blowing oxygen gas flow rate of 1.5 to 2.0 m ³ _N / min · t, a height from the bath surface at the lower end of the upper blowing lance 11 (hereinafter referred to as “upper blowing lance height”). This is realized by setting h to 3.0 m. The dynamic pressure (P) applied to the bath surface at this time is about 1700 Pa, as shown in FIG. 2, until the slag layer 3 forming the bath surface f is pushed and a hot spot is generated in the hot metal 2. Soft blow to the extent that does not reach.

Thus, when the soft blow operation is first performed, a large amount of oxygen is supplied to the hot metal and Fe and P in the auxiliary raw material, thereby promoting the generation of FeO. That is, this soft blow produces a lot of FeO on the surface layer of the hot metal 2 and the FeO reacts with the dephosphorizing agent CaO to form a low melting point compound such as calcium ferrite. Therefore, the high melting point CaO that does not hatch at a suitable hot metal temperature is lowered. Therefore, when the FeO generation is accelerated, CaO in slag formation (CaO _· P 2 _{O 5)} is also promoted, dephosphorization proceeds.

  The reason for soft blow at the initial stage of this dephosphorization is as follows. This is because, from the initial stage of blowing, if the bath is in a hard blow state where the dynamic pressure on the bath surface is high, the generated FeO reacts with the carbon in the hot metal and is reduced to Fe, so that the FeO concentration does not increase. That is, at the initial stage of blowing, by using soft blow, it is possible to increase the amount of FeO generated and maintain the generated FeO at a high concentration. In addition, by using soft blow that does not form a hot spot on the hot metal bath surface, it is possible to suppress the hot metal temperature rise due to combustion during decarburization and decarburization, and to maintain a hot metal temperature suitable for dephosphorization. Can do.

As described above, in the present invention, at least until slag formation completed by a soft blow, promotes the production of FeO, for subsequent slag formation completion t ₃ after end of the blow, the on The blow lance height is lowered to make a hard blow state, and the top blow oxygen gas flow rate is preferably reduced. For example, the upper blowing lance 11 is lowered until the lance height h is 1.5 m, and the upper blowing oxygen gas flow rate is lowered to 1 m ³ _N / min · t. The bath surface dynamic pressure at this time is about 2000 Pa.

In this way, at the end of the blowing, instead of the operation for promoting hatching so far, hard blow is performed, and the oxygen gas flow rate is lowered to suppress the generation of FeO. A process of reducing FeO to Fe to improve the hot metal yield is performed. The reason is that at the time of hatching completion t ₃ , the slag contains at least 30 mass% or more of FeO, and if the dephosphorization process is terminated as it is, the FeO content remains in the slag at a high concentration. It is not preferable. Therefore, at the end of blowing, hard blow is performed to recover the Fe content and improve the yield.

  The hard blow switching after the completion of hatching starts from the stage when the progress of the blowing process reaches 80%, or the dephosphorization reaction proceeds in the dephosphorization of the hot metal with a P concentration of 0.020 mass% in the hot metal. And it should just start from the stage which reached P concentration 0.030 mass%. Although FeO in the slag is reduced and recovered by the hard blow, the dephosphorization reaction proceeds at the bath interface, and the recovery of the Fe component and the dephosphorization reaction proceed simultaneously. In addition, although the blowing time is extended, the operation of recovering FeO in the slag as Fe may be performed by switching to the hard blow from the stage where the dephosphorization of the hot metal has reached a predetermined value. At that time, it is preferable to slightly increase the amount of oxygen.

In addition to such a basic pattern of oxygen gas top blowing, in the present invention, a temperature rising period (about 1 minute in FIG. 1) may be provided before top blowing by the soft blow.
The operation during the temperature rising period is preferably to introduce FeSi or the like as a heat generating material into the converter 1, and in addition to this, by supplying oxygen gas through an upper blowing lance, It is to raise the temperature. The operation is performed, for example, until the temperature h of the hot metal reaches 1300 ° C. at which the auxiliary raw material easily hatches until the temperature rising point t ₁ (FIG. 1). It is preferable that the oxygen gas flow rate be set to 2 m ³ _N / min · t, which is higher than that in the case of soft blow.

  Further, in the temperature rising process, the hot metal can be heated with [Si] in the hot metal as a heat source by setting it in a hard blow (bath surface dynamic pressure 3650 Pa) state, such as FeSi. A method using an exothermic agent together may be used. In addition, when the hot metal temperature carried in the converter 1 is sufficiently high, the treatment during the temperature rising period is unnecessary.

  In this way, by raising the temperature of the hot metal, the hatching of the dephosphorizing agent to be charged is promoted after the temperature raising operation. When charging the dephosphorizing agent, if the secondary raw material charging that produces FeO, such as sintered ore, is used together, the time required for the dephosphorizing agent to complete hatching is shortened, and thus the time required for dephosphorization is shortened. I can. In this embodiment, calcined lime and other auxiliary materials, which are dephosphorizing agents, are charged after the temperature rises, and the auxiliary materials are quickly melted.

Next, a bottom blowing pattern performed in parallel with such top blowing will be described.
In a preferred embodiment of the present invention, with respect to the bottom blowing of the stirring gas, the flow rate of the bottom blowing gas is reduced from the initial stage to the middle stage of the dephosphorization process, and the hatching completion time t is later than the temperature raising period. than ₃ from the previous strong stirring start time t ₂ until the end of the dephosphorization process, a high gas flow rate.

Specifically, bottom blowing is performed at a bottom blowing gas flow rate of 0.05 m ³ _N / min · t from the beginning to the middle of the dephosphorization process. The converter hot metal 2 is agitated by this bottom blowing, and the degree of agitation is as weak as the soft blow so that FeO produced in the slag 3 does not decrease.
That is, since the slag 3 is placed under weak stirring, the generation of FeO is promoted by the oxygen gas flow generated by the upper blowing lance. The bottom blowing gas flow rate may be the lowest flow rate at which the molten iron does not flow into the bottom blowing tuyere.

Then, after the time t ₂ when the generation of FeO progresses and it is estimated that FeO necessary for the hatching of CaO to dephosphorylate the molten iron 2 is generated, the strong stirring start time is set, for example, in the slag 3 When the FeO content of the steel becomes 30 mass% or more and 50 mass% or less, the bottom blowing gas flow rate is increased to, for example, 0.2 m ³ N / min · t and the mixture is vigorously stirred. In this way, when the necessary amount of FeO is generated, it is immediately switched to strong stirring, thereby further promoting the slag-metal reaction, thereby further reducing the processing time for dephosphorization. become able to.

Here, the strong agitation refers to agitation in which the molten iron 2 and CaO in the slag are mixed to form the slag 3. The agitation by the bottom blown gas, generally, the dephosphorization reaction because occurs at the interface between the slag and the metal, a strong agitation start time t ₂ subsequent processing, by performing strong agitation and slag and hot metal 2 is mixed well The time until the dephosphorization value of the hot metal reaches a predetermined value, that is, the dephosphorization reaction time can be shortened. Note that an inert gas such as Ar or N ₂ can be used as the bottom blowing gas for stirring.

In the present invention, the reason why the FeO content in the slag is set to 30 mass% or more is that, when the FeO content is 30 mass% or more, the hatching of CaO proceeds and the dephosphorization reaction proceeds well. This is because it is bad. Further, when the FeO content is less than 30 mass%, [P] _f ≦ 0.020 mass% cannot be stably obtained in hot metal dephosphorization.
On the other hand, if the FeO content in the slag to be generated exceeds 50 mass%, FeO becomes excessive, causing slopping, and further, the generated FeO dilutes CaO in the slag, leading to a decrease in the dephosphorization reaction. 50 mass% or less.

  Regarding the method of controlling the amount of FeO, the oxygen balance is calculated from the exhaust gas composition, flow rate, oxygen gas flow rate, etc., and the amount of accumulated oxygen is determined or controlled, or the amount of iron component oxidation reaction is determined and controlled. In addition to the above, it is also possible to use a method in which experiments are performed in advance in the converter to be used, and the amount of FeO in the slag in the process of blowing is measured by sampling. Hereinafter, a method for obtaining and controlling the amount of accumulated oxygen will be described in detail.

The basic idea of the present invention is that the converter blowing conditions are determined according to the amount of FeO in the slag during blowing, on the premise that a lime-based dephosphorizing agent not containing F, Na, or Cl is used. The amount of the lime-based dephosphorizing agent is to be controlled so that the most advantageous condition for hatching is FeO / CaO) = 0.5 to 3.5. By performing such converter hot metal dephosphorization blowing, it is possible to achieve a dephosphorization reaction with a high reaction efficiency and a low phosphorus concentration.
Therefore, a preferred embodiment of the present invention will be described, such as estimation of the amount of FeO based on the amount of accumulated oxygen, control of the amount of FeO, and control of lime-based dephosphorization agent according to the amount of FeO. In the following description, “m ³ (standard state)” is simply indicated as “m ³ _N ”.

なお、溶銑成分の変化については、予め吹錬中の実績値から作ったモデル式を利用した。 (1) Estimating the amount of FeO based on the amount of accumulated oxygen In the converter hot metal dephosphorization blowing (preferably using a top / bottom blowing converter) suitable in the present invention, input oxygen using the following equation (3) From the total amount of oxygen and the total amount of output oxygen using the following equation (4), first, the accumulated oxygen amount during blowing is calculated sequentially using the following equation (5). Then, the above formula (1) is applied based on the accumulated oxygen amount, and the amount of FeO in the furnace is estimated by calculation.
FIG. 4 is a diagram schematically showing the procedure for obtaining the amount of FeO in the furnace in an easy-to-understand manner.

In addition, about the change of hot metal component, the model formula made from the actual value during blowing was utilized beforehand.

  Further, the above formula (5) is obtained by regarding the difference between the input oxygen supplied to the hot metal and the output oxygen consumed by the reaction as accumulated oxygen. Equation (1) is derived based on the idea that the amount of accumulated oxygen is regarded as FeO.

そして、
上記（８）式により、炉口部での酸素ガス量であるＱout(％Ｏ₂)を求めることができる。 Of the above oxygen balance calculation, Qout (% O ₂ ), Qout (% CO ₂ ), and Qout (% CO) calculated from the converter exhaust gas component and flow rate are obtained as follows. First, the exhaust gas composition and flow rate during blowing are measured as needed, and the following (6), (7), and (8) equations are used to determine the exhaust gas composition and its flow rate at each time point, and by integrating these, The amounts of furnace opening CO gas, furnace opening CO ₂ gas, furnace opening O ₂ gas (oxygen that did not contribute to the reaction) are obtained. When obtaining the furnace port CO gas amount, if the bottom blown gas is CO gas, it is calculated in consideration of this.

And
From the above equation (8), Qout (% O ₂ ), which is the amount of oxygen gas at the furnace port, can be obtained.

In the calculation of the above formulas (3) to (8), assuming that the exhaust gas contains CO, CO ₂ , O ₂ , H ₂ , Ar, and the other is N ₂ , the following (9 ) To obtain the N ₂ gas concentration.
(% N ₂ ) = 100 − {(% CO) + (% CO ₂ ) + (% O ₂ ) + (% H ₂ ) + (% Ar)} (9)
However,
(% N ₂ ): N ₂ gas concentration (%)
(% CO): CO gas concentration (%),
(% CO ₂ ): CO ₂ gas concentration (%)
(% O ₂ ): O ₂ gas concentration (%)
(% H ₂ ): H ₂ gas concentration (%)
(% Ar): Ar gas concentration (%)

Then, the amount of N ₂ at the furnace port is determined using the following equations (10) to (12) in consideration of the case where the bottom blowing gas is Ar gas.

Next, a procedure for calculating the amount of combustion of the CO gas generated from the furnace by the oxygen in the air sucked for dust collection at the furnace port of the converter will be described. That is, assuming that the bottom blowing gas is N ₂ gas, the amount of N ₂ in the entrained air is obtained using the following equation (13), and N ₂ : O ₂ = 4: 1 in the entrained air. , The amount of oxygen gas in the entrained air is determined using the above equations (8) and (12) and the following equations (13) to (14).

When the oxygen in the air calculated as described above causes the CO gas from the furnace to burn completely to CO ₂ (2CO + O ₂ = 2CO ₂ ), ₂ mol of CO is consumed with respect to 1 mol of O ₂ , Since ₂ mol of CO ₂ is generated, the amounts of CO and CO ₂ gas generated in the furnace can be obtained using the following equations (15) to (16).

(2) Control of the amount of FeO Next, the amount of FeO in the furnace during blowing that can be calculated and calculated as described above, together with the height of the top blowing lance, the amount of top blowing oxygen gas or the amount of bottom blowing stirring gas By adjusting one or more of these, the amount of FeO during blowing is controlled online within an appropriate range. An example of controlling the amount of FeO will be described below, but the present invention is not limited to this exemplified method.
The experiment for controlling the amount of FeO conducted by the inventors was carried out with the blowing pattern shown in Table 2 under the experimental conditions using the hot metal shown in Table 1. The transition of each blowing pattern and the amount of FeO is shown in FIGS. FIG. 5a shows a slightly lower top blow lance height (hard blow). In this case, the amount of FeO produced is small. As a result, hatching deteriorated, dephosphorization reaction was poor, and [% P] _f was high. In FIG. 5c, since the amount of the bottom blowing gas for stirring is low, the bath stirring in the furnace becomes insufficient and FeO is excessively generated, and slopping occurs due to excessive FeO amount, and (T.Fe) in the slag. Increased and the steel yield was worsened. In FIG. 5b, compared with FIG. 5a, the top blowing lance height is increased, so-called soft blowing. As a result, sufficient FeO can be generated, and the amount of bottom blowing gas is increased to strengthen the agitation. As a result of suppressing the formation of FeO, the amount of FeO could be kept within an appropriate range.
In addition, said experiment is based on a 200t top bottom blowing converter, and bottom blowing is an example which performed inert gas blowing. That is, in addition to the estimation of the amount of FeO, the control of FeO during blowing can be performed by adjusting the amount of the top blowing oxygen gas or the bottom blowing gas in addition to the control of the top blowing lance height as described above.

(3) Control of charging of lime-based dephosphorizing agent according to the amount of FeO During blowing, an experiment was conducted in which lime-based dephosphorizing agent was sequentially charged according to the amount of FeO in the converter. Table 3 shows the blowing pattern in this experiment. The experimental results are shown in FIGS. 6a to 6c, respectively. As shown in FIG. 6a, [% P] _f ≦ 0.020% is a low value in the range of slag (FeO / CaO) max≈ (2.8 to 4.1). However, if (FeO / CaO) max = 3.5, slapping occurs, so (FeO / CaO) max = 3.5 is preferable. Therefore, in the present invention, it was determined that slag (FeO / CaO) ≦ 3.5 from the viewpoint of suppressing slopping in converter blowing. Then, as shown in FIG. 6b, when (FeO / CaO) ≦ 3.5, and (FeO / CaO) _initial = 0.5 or more in the slag, [% P] _f is stable and low. became. From the above results, it was decided to control the blowing dynamically during blowing (FeO / CaO) = 0.5 to 3.5.

Furthermore, when (FeO / CaO) in a stage exceeding 30% of the total amount of blown oxygen under the blowing conditions of slag (FeO / CaO) = 0.5 to 3.5 was investigated, FIG. As shown, it was found that when the ratio was 1.5 or more and 3.5 or less, [% P] _f was stably low. This is because the amount of FeO produced is large from the early stage of blowing, and the melting (hatching) of CaO is good.
From these results, in the present invention, the (FeO / CaO) of the slag during blowing is in the range of 0.5 to 3.5, and further in the stage where it exceeds 30% of the total amount of blown oxygen (FeO / CaO). ) Was found to be effective to control the blowing dynamically so as to be 1.5 or more.

  In addition, when the total amount of blown oxygen exceeds 30%, the amount of generated FeO increases rapidly, and when the total amount of blown oxygen reaches 50%, a sufficient amount of FeO can be secured. In the above, it is understood that it is preferable to perform the blowing control of the converter that performs the dephosphorization treatment so that (FeO / CaO) ≧ 1.5 by the stage of the total blowing oxygen amount exceeding 30% and not exceeding 50%. .

  The control of (FeO / CaO) ≧ 1.5 is carried out by adjusting the suitable amount of lime-based dephosphorizing agent based on the estimated amount of FeO generated in the furnace at each stage of blowing as described above. This is realized by dividing and feeding according to the amount. Here, the lime-based dephosphorizing agent is not only added in small amounts from the furnace, but also in powder form by spraying it into the hot metal bath from the top blowing lance, or from the bottom blowing port. Any method may be used for dividing the gas into the hot metal bath together with the gas. Note that increasing FeO to promote the dephosphorization reaction results in iron loss into the slag, and therefore FeO reduction is performed within a range that does not reduce the dephosphorylation reaction in the low phosphorus region at the end of blowing. Specifically, it is realized by reducing FeO by decreasing the amount of top-blown oxygen gas or increasing the amount of bottom-blown gas (stirring power enhancement).

  When the dephosphorization process is performed according to the present invention, according to the experience of the inventors, a hot metal having a phosphorus concentration of 0.1 mass% when charged into the converter 1 is 0.020 mass% or less in a treatment time of 12 minutes. It has been found that it can be dephosphorized to the level of low phosphorus steel. Therefore, according to the present invention, it is preferable to raise the temperature of the hot metal to a temperature at which hatching is easy, and then perform soft blow and top blow at a high oxygen gas flow rate to shorten the time for completion of hatching. It was found that by increasing the bottom blowing gas flow rate at an early stage, the time between the slag-metal reaction was shortened, and it was possible to purify extremely low phosphorus steel in a short time.

Furthermore, in the present invention, since suppressing decarburization as a soft blow from an initial dephosphorization process until slag formation completion t _3, it had no effect on the operation of the primary decarburization blowing performed after dephosphorization treatment.
Moreover, since the slag-metal reaction was promoted by strong stirring by bottom blowing and top blowing by hard blow, the ratio of the amount of lime that contributed to dephosphorization in the total amount of lime charged (dephosphorizing lime efficiency) A high value of 40 to 50% was shown. For this reason, the amount of charging lime and the amount of slag are reduced, and cost reduction and resource saving are also possible.

The result of performing blowing (invention examples 1 and 2) suitable for the method of the present invention and blowing (comparative example) by an incompatible method using a 200-t top / bottom blowing converter will be described.
a. The blowing in Invention Examples 1 and 2 was as shown in Table 1, and the blowing pattern was dynamically controlled within the range of Table 3. When (FeO / CaO) during blowing is maintained in the range of 0.5 to 3.5 (Invention Example 1), when the total amount of blown oxygen exceeds 30% (FeO / CaO) ≧ This is an example (Example 2 of the present invention) operated at 1.5.
b. The blowing in the comparative example is as shown in Table 1, and the blowing pattern is an example of operation as a constant condition. The results are shown in Table 4 and shown in FIGS. 7a to 7c.

7A is a graph of [% P] _f and frequency number in the comparative example, FIG. 7B is a graph of [% P] _f and frequency number in Example 1 of the present invention, and FIG. 7c is [% P] in Example 2 of the present invention. It is a graph of _f and frequency number. As can be seen from these figures, in the comparative example, the variation of [% P] _f was large, and the average [% P] _f = 0.023 mass%. In the inventive examples 1 and 2, the variation of [% P] _f was small, and the average [% P] _f was 0.019 mass% and 0.018 mass%, respectively, confirming the superiority of the inventive examples. Moreover, in the converter type hot metal dephosphorization method according to the present invention, decarburization at the time of dephosphorization can be kept low, which is thermally advantageous.

  INDUSTRIAL APPLICABILITY The present invention can be applied to the field of converter blowing technology, particularly the field of top-bottom blowing converter, and particularly effective as a method for performing hot metal dephosphorization using this converter. It is.

It is a figure which shows the timing of each process in the dephosphorization process of this invention. It is a figure which shows the bath surface dynamic pressure at the time of a dephosphorization process. It is a figure explaining the outline | summary of the dephosphorization process in a converter. It is a schematic diagram which shows the FeO amount calculation procedure in a furnace. It is a graph which shows transition of a blowing pattern and the amount of FeO. It is a graph for demonstrating the blowing pattern of Table 3. FIG. It is a graph which shows frequency relationship with [% P] _f of this invention method and a comparative example.

Explanation of symbols

1 Converter 11 Top blowing lance 12 Bottom blowing tuyere 2 Hot metal 3 Slag

Claims (11)

  A method of dephosphorizing hot metal by using a hot metal pretreatment vessel equipped with an upper blowing lance and a bottom blowing tuyere, and simultaneously blowing oxygen gas from the upper blowing lance and blowing a stirring gas from the bottom blowing tuyere , After adding the dephosphorizing agent in the hot metal pretreatment container, the oxygen gas is blown from the top blowing lance to the bath surface until the dephosphorizing agent is completely hatched, and after the hatching is completed, A hot metal dephosphorization method characterized by increasing the stirring gas flow rate from the bottom blowing tuyere when hard blow is performed and the FeO content in the slag produced during soft blow is 30 mass% or more.   The hot metal dephosphorization method according to claim 1, wherein the hot metal before adding the dephosphorizing agent is heated to a temperature of 1300 ° C. or higher.   3. The soft blow is to make the height of the upper blow lance higher than that of the hard blow, while the hard blow is an operation to make the height of the upper blow lance lower than that of the soft blow. Dephosphorization method for hot metal as described in 1.   4. The hot metal removal according to claim 1, wherein an oxygen gas flow rate is increased in the soft blow stage, while an oxygen gas flow rate is reduced in the hard blow stage. 5. Phosphorus method.   The stirring gas blown from the bottom blowing tuyere increases its flow rate when the FeO content in the slag is 30 mass% to 50 mass%. Of dephosphorizing hot metal.   The hot metal temperature is raised by adding a heat-generating material and / or by blowing oxygen gas from an upper blowing lance, and the dephosphorizing agent is added after the hot metal temperature is raised. The method for dephosphorizing molten iron according to any one of 1 to 5. 7. The hot metal dephosphorization method according to claim 1, wherein the switching to hard blow after the completion of hatching is performed when the phosphorus in the hot metal reaches a predetermined value . When dephosphorizing hot metal using a converter as a hot metal pretreatment vessel, the oxygen balance is obtained by sequentially calculating the oxygen balance from the exhaust gas composition and its flow rate, oxygen gas flow rate, auxiliary material input amount, and hot metal components during blowing. Based on the amount of stored oxygen, the amount of FeO produced in the furnace is estimated from the following equation (1), and (FeO / CaO) during blowing is set to 0.5 to 3. according to the estimated amount of FeO. The dephosphorization method for hot metal according to any one of claims 1 to 7, wherein a dephosphorizing agent is added so that the temperature can be maintained at 5.
FeO (kg / t) = [Amount of accumulated oxygen] (m ³ (standard state) / t) /22.4×71.85 (1)   The dephosphorization agent is controlled so that (FeO / CaO) becomes 1.5 or more at a stage where 30% of the total amount of blowing oxygen during blowing is exceeded. 9. The hot metal dephosphorization method according to any one of items 8 to 9.   As the dephosphorizing agent, one or more of lime-based dephosphorizing agent, iron ore and sintered ore selected from quick lime, limestone or converter smelting slag not containing F, Na and Cl and calcined lime is used. The hot metal dephosphorization method according to claim 1, wherein the hot metal is dephosphorized. The control of (FeO / CaO) of slag during blowing is performed based on the top blowing lance height, the top blowing oxygen gas flow rate, and the bottom blowing stirring gas flow rate. The method for dephosphorizing hot metal as described in the item.

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