JP2018172719A - Desulfurization method of molten pig iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desulfurization method of molten pig iron, which can suppress slag generation and desulfurization cost without using a fluorine source.SOLUTION: In the desulfurization method of molten pig iron, desulfurizing agents 5a and 5b containing lime and Al-based deoxidizing agents 6a and 6b having metal Al in the amount of 10 mass% or more and the balance of mainly AlOare added to perform desulfurization of a hot metal 2 including molten pig iron tapped from a blast furnace and subjected to a dephosphorization treatment. In accordance with the phosphorus concentration in the hot metal 2 before the desulfurization treatment, adjustment is made so that the amount of the Al-based deoxidizing agents to be added is increased as the phosphorus concentration decreases.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hot metal desulfurization method.

In recent years, as the demand for high-grade steel production increases, a method for producing low-sulfur steel with low sulfur concentration at low cost is strongly desired in the steelmaking process of steelworks. As a method for efficiently producing low-sulfur steel at a low cost, desulfurization treatment for removing sulfur in the hot metal is performed in the hot metal stage where the carbon concentration of the molten iron is high. As a method for such desulfurization treatment, a method using CaO, CaC ₂ , soda ash or the like as a desulfurization agent has been used for a long time. In recent years, CaO-based desulfurization agents are widely used because they are inexpensive.

  In addition, as the hot metal stage treatment (hot metal preliminary treatment), dephosphorization treatment for removing phosphorus in the hot metal into the slag is also performed. In hot metal dephosphorization, dephosphorization proceeds by supplying a CaO-based solvent and an oxygen source to the hot metal. At this time, since a large amount of oxygen source needs to be supplied to the hot metal in order to advance the dephosphorylation reaction, the oxygen potential of the hot metal and slag tends to increase as the dephosphorization reaction proceeds. In addition, in the dephosphorization process performed in a transport container such as a kneading car or a hot metal ladle, a solid oxygen source such as iron oxide is used as a main oxygen source, so the hot metal temperature tends to decrease as the dephosphorization progresses. It becomes.

For this reason, when the hot metal desulfurization treatment is performed after the dephosphorization treatment, fluorite (CaF ₂ ) has been conventionally used in order to promote the hatching of the CaO-based desulfurization agent and improve the desulfurization reaction efficiency. However, in recent years, in order to promote the use of steel slag, operations that do not use the fluorine source as much as possible have been directed, and the problem is that the desulfurization efficiency of the desulfurization agent decreases and the amount of use of the desulfurization agent increases. Yes.
In contrast, attempts have been made to improve the efficiency of the desulfurizing agent by mixing an Al-based deoxidizing agent such as Al dross powder containing metal Al with the CaO-based desulfurizing agent.

For example, Patent Document 1 proposes a desulfurization agent containing CaO as a main component, containing 5 to 20% by mass of Al dross (aluminum ash), and further blended with fluorite and carbon.
Further, Patent Document 2, CaO / SiO ₂ ratio of CaO and SiO ₂ is 1.5 to 3.5, and Al is 3% to 15 weight% of the total weight of the CaO and SiO _2, CaO, A desulfurization agent containing SiO ₂ and Al has been proposed. In Patent Document 2, SiO ₂ is a hatching accelerator for CaO, and metal Al functions as a hot metal deoxidizer for reducing the oxygen potential of hot metal.
Furthermore, Patent Document 3 proposes a CaO-Al dross-based desulfurizing agent in which the blending ratio of an Al-based deoxidizer having a metal Al content of 10% by mass or more is 7% by mass or more in terms of Al ₂ O ₃ . . It is said that metal Al not only lowers the oxygen potential of hot metal, but also has an effect on the heat generation due to the oxidation reaction of metal Al and the hatching of CaO in quicklime by Al ₂ O ₃ .

Japanese Patent Laid-Open No. 3-274217 JP 2000-313911 A JP 2010-229439 A

However, in the method disclosed in Patent Document 1, fluorite is used and fluorine (F) is contained in the generated slag. Therefore, the slag treatment is very expensive and not practical.
Further, the desulfurization agent of Patent Document 2 uses SiO ₂ as a hatching accelerator, and the hatching of CaO is promoted. However, since SiO ₂ becomes a component that inhibits the desulfurization reaction, the desulfurization reaction is delayed. There is a fear. In addition, since a considerable amount of SiO ₂ is added so that the CaO / SiO ₂ ratio is 1.5 to 3.5, the amount of desulfurization agent used increases, and the generated desulfurization slag may increase. Moreover, it cannot be applied to a small-sized facility that cannot use three or more kinds of different refining agents due to facility restrictions.

Furthermore, in the desulfurization agent of Patent Document 3, although the hatching of lime is promoted by the metal Al and Al ₂ O ₃ , excessive addition of the Al-based deoxidizer causes an increase in cost. If the amount of Al ₂ O ₃ used is excessive, the amount of liquid phase of the generated oxide will be excessive, leading to agglomeration of lime particles and reducing the reaction interface, which may adversely delay the desulfurization reaction. is there. Moreover, there exists a possibility that the desulfurization slag to generate | occur | produce may increase by the excessive addition of Al type deoxidizer. Further, for hot metal in which solid oxygen such as gaseous oxygen or iron oxide is blown for the purpose of de-Si or de-P, even if an Al-based deoxidizer is added according to Patent Document 3, the amount of metal Al is deoxidized. In some cases, the deoxidation effect could not be obtained due to the small amount necessary for the amount of the catalyst.
Therefore, the present invention has been made paying attention to the above-mentioned problems, and provides a hot metal desulfurization method capable of suppressing the amount of slag generated and the desulfurization cost without using a fluorine source such as fluorite. The purpose is to do.

According to one aspect of the present invention, the hot metal containing hot metal discharged from a blast furnace and subjected to dephosphorization treatment is mainly composed of a desulfurization agent containing quicklime and a content of metal Al of 10% by mass or more. A hot metal desulfurization method for performing desulfurization treatment by adding an Al-based deoxidizer which is Al ₂ O ₃ , wherein the phosphorus concentration is lowered according to the phosphorus concentration of the hot metal before the desulfurization treatment. Accordingly, there is provided a hot metal desulfurization method characterized by adjusting the amount of the Al-based deoxidizer to be increased.

  According to one embodiment of the present invention, there is provided a hot metal desulfurization method capable of suppressing the generation amount of slag and the desulfurization cost without using a fluorine source such as fluorite.

It is a schematic diagram which shows a hot metal desulfurization apparatus. It is a graph which shows the relationship between the phosphorus density | concentration in hot metal, and a metallic Al basic unit. It is a graph which shows the relationship between the excessive addition amount of metal Al, and desulfurization efficiency. It is a graph which shows the conditions in a formula (4)-a formula (6).

  In the following detailed description, numerous specific details are set forth, illustrating embodiments of the present invention, in order to provide a thorough understanding of the present invention. However, it will be apparent that one or more embodiments may be practiced without such specific details. In the drawings, well-known structures and devices are schematically shown for simplicity.

Hereinafter, the background of the inventors of the present invention will be described. The present inventors have studied various means for efficiently desulfurizing hot metal including hot metal after dephosphorization using a CaO-based desulfurization agent that does not contain a fluorine source such as fluorite.
In the hot metal dephosphorization process, it is allowed by the balance between the hot metal composition required for the production of the target hot metal, the hot metal temperature such as the hot metal temperature and silicon content before the treatment, and the time required in the preceding and subsequent processes. The degree of dephosphorization of the hot metal after the treatment varies greatly depending on various conditions such as the treatment time. Therefore, when the desulfurization treatment is performed after the dephosphorization treatment, the degree of oxidation of the slag after the dephosphorization treatment mixed in the hot metal and the desulfurization treatment varies depending on the degree of dephosphorization, and thus the desulfurization efficiency varies. In addition, although slag generated after dephosphorization treatment is operated so as not to bring it into desulfurization treatment as much as possible, iron yield can be reduced by reducing the amount of slag brought from dephosphorization treatment to desulfurization treatment. It will cause a decline. For this reason, the introduction of slag after the dephosphorization treatment must be allowed to some extent to the extent that a decrease in iron yield does not become a problem.

Moreover, in order to improve the desulfurization efficiency without using a fluorine source such as fluorite, it is necessary to use an Al-based deoxidizer containing metal Al. However, since the desulfurization efficiency varies due to the difference in the degree of oxidation of the hot metal and slag as described above, an excessive amount of Al-based deoxidizer containing metal Al is added to obtain a sufficient deoxidation effect by metal Al. There was a need to do. On the other hand, if an excessive amount of Al-based deoxidizer is added, the amount of liquid phase of oxide produced by Al ₂ O ₃ produced by oxidation of contained Al ₂ O ₃ or metal Al becomes excessive, and powdery In some cases, the CaO-based desulfurization agent is agglomerated and the reaction interfacial area is decreased, which may have an adverse effect on promoting desulfurization. As described above, when the desulfurization efficiency varies due to excess or deficiency of the Al-based deoxidizer, it may result in insufficient desulfurization, and it is necessary to extend the desulfurization treatment time or add a CaO-based desulfurizer, In order to avoid a decrease in productivity due to such measures, an increase in the amount of CaO-based desulfurizing agent used was caused.

<Investigation on the influence of desulfurization treatment conditions>
In order to solve such a problem, the present inventors, in the hot metal desulfurization equipment 1 having a hot metal amount of 300 t shown in FIG. And desulfurization treatment was performed under the addition conditions of an Al-based deoxidizer. Then, from the results of the desulfurization treatment, the influence of the hot metal conditions such as the phosphorus concentration of the hot metal 2 and the desulfurization treatment conditions such as the amount of added metal Al on the desulfurization efficiency was investigated.

(Desulfurization processing equipment)
The hot metal desulfurization apparatus 1 is a mechanical stirring type desulfurization apparatus that desulfurizes the hot metal 2 accommodated in the hot metal ladle 3 as a processing container. The hot metal ladle 3 is mounted on a cart 4 that can move in the left-right direction in FIG. As shown in FIG. 1, the hot metal desulfurization apparatus 1 includes a stirring blade 10, four hoppers 11 a to 11 d, two rotary feeders 12 a and 12 b, two cutting devices 13 a and 13 b, and an input chute 14. And an upper blowing lance 15.

  The stirring blade 10 is provided with a shaft portion 10a extending in the vertical direction (vertical direction in FIG. 1), and a blade made of a refractory material provided at the tip of the shaft portion 10a and projecting substantially radially about the shaft portion 10a. Part 10b. Further, the stirring blade 10 is configured such that the upper end side in the vertical direction is connected to a lifting device and a rotating device (not shown), is movable up and down in the vertical direction, and is rotatable about the shaft portion 10a.

The four hoppers 11a to 11d are containers for storing a refining agent such as a desulfurizing agent or a deoxidizing agent. The hopper 11a has a powdered desulfurizing agent 5a, the hopper 11b has a granular or powdery Al-based deoxidizing agent 6a, the hopper 11c has a powdery desulfurizing agent 5b, and the hopper 11d has a powdered Al The system deoxidizer 6b is stored. The desulfurization agents 5a and 5b are lime-based desulfurization agents mainly made of CaO, and are, for example, powder (quick lime powder) obtained by pulverizing quick lime. Further, the desulfurizing agents 5a and 5b do not contain a fluorine source such as fluorite, and are, for example, in the form of a powder having a diameter of 1 mm or less. The Al-based deoxidizers 6a and 6b are, for example, Al dross (aluminum ash, aluminum dross) containing 10% by mass or more and 50% by mass or less of metal Al and 80% by mass or more of metal Al and Al ₂ O ₃ in total. is there. Further, the Al-based deoxidizer 6a does not contain a fluorine source such as fluorite, and is, for example, a powder having a diameter of 5 mm or less or a powder having a diameter of 1 mm or less. Furthermore, the Al-based deoxidizer 6b does not contain a fluorine source such as fluorite and is, for example, in the form of a powder having a diameter of 1 mm or less.

The two rotary feeders 12a and 12b are cutting devices provided in the hoppers 11a and 11b, respectively. The two rotary feeders 12a and 12b cut out the desulfurizing agent 5a and the Al-based deoxidizing agent 6a from the hoppers 11a and 11b, respectively, and supply them to the charging chute 14.
The two cutting devices 13a and 13b are provided in the hoppers 11c and 11d, respectively. The two cutting devices 13a and 13b cut the desulfurizing agent 5b and the Al-based deoxidizing agent 6b from the hoppers 11c and 11d at a predetermined speed, respectively. The desulfurizing agent 5b and the Al-based deoxidizing agent 6b cut out from the two cutting devices 13a and 13b are supplied to the top blowing lance 15 together with a carrier gas such as nitrogen gas or Ar gas.

The charging chute 14 is arranged above the hot metal ladle 3 whose tip is disposed at the processing position, and along with the charging chute 14 the desulfurizing agent 5a and the Al-based deoxidizing agent 6a supplied from the two rotary feeders 12a and 12b. And drop it onto the bath surface of the hot metal 2 in the hot metal pan 3.
The top blowing lance 15 is a lance extending in the vertical direction, for example, and is disposed above the hot metal ladle 3 disposed at the processing position. The top blowing lance 15 sprays the desulfurizing agent 5b and the Al-based deoxidizing agent 6b cut out from the two cutting devices 13a and 13b from the nozzle formed at the lower end together with the conveying gas on the bath surface of the hot metal 2 Spray on.

In the hot metal desulfurization apparatus 1, the two rotary feeders 12a and 12b and the two cutting apparatuses 13a and 13b cut out the desulfurizing agents 5a and 5b and the Al-based deoxidizing agents 6a and 6b at arbitrary timings, respectively. It is configured to be able to. Further, whether the desulfurizing agent or the Al-based deoxidizing agent is added from the charging chute 14 or the top blowing lance 15 can be appropriately selected in consideration of the reaction efficiency and the time required for the addition.
Further, an exhaust duct port (not shown) connected to a dust collector (not shown) is provided above the hot metal desulfurization apparatus 1 so that gas and dust generated during the desulfurization process are discharged.

(Desulfurization method)
The present inventors performed a desulfurization process by the following method using such hot metal desulfurization apparatus 1.
The hot metal 2 to be desulfurized includes hot metal that has been subjected to dephosphorization. In hot metal dephosphorization, hot metal discharged from a blast furnace housed in a kneading car, oxidizer powder containing iron oxide such as sintered ore powder, and lime-based solvent solvent powder such as quick lime And processing was performed. In the dephosphorization process, phosphorus or silicon in the hot metal is removed until a predetermined concentration is reached, or until the concentration according to the hot metal conditions before the process, the supply amount of the dephosphorization agent, the processing conditions such as the processing time, etc. Removed. Next, the hot metal that had been subjected to the dephosphorization treatment was transferred from one or more kneading wheels to the hot metal ladle 3. At this time, it is sufficient that at least one of the kneading vehicles used for the transfer contains the molten iron subjected to the dephosphorization treatment. When a plurality of kneading vehicles are used, the dephosphorization treatment is performed. There may be chaotic cars that contain hot metal that is not. Further, a sample of hot metal 2 accommodated in the hot metal ladle 3 was collected and analyzed for phosphorus concentration and sulfur concentration. Since the slag flowing out from the kneading car into the hot metal ladle 3 contains iron oxide at a relatively high concentration and it is desirable to remove this slag as much as possible, the slag was then removed (also referred to as “removal”). . The stripping was performed by tilting the hot metal ladle 3 to such an extent that the hot metal 2 did not flow out and scraping the slag with a stripping plate having its tip immersed in the slag and discharging it from the upper edge of the hot metal pan. In addition, since the yield of hot metal was reduced as the amount of residual slag was reduced, the removal was completed to the extent that the hot metal surface was exposed to some extent.

In this investigation, desulfurization treatment was performed on the hot metal 2 accommodated in the hot metal ladle 3 in this way. First, the slag after the desulfurization process generated by the desulfurization process of the other hot metal was prepared in advance and added on the bath surface of the hot metal 2 accommodated in the hot metal ladle 3 using a heavy machine. This slag was intended to be reused as a desulfurizing agent, and was added at about 6 kg / t by weight per 1 ton of hot metal.
Next, the hot metal ladle 3 was mounted on the cart 4, and the position of the cart 4 was adjusted so that the position of the stirring blade 10 was approximately the center of the hot metal pan 3.
Furthermore, the stirring blade 10 was lowered while rotating at a low speed and immersed in the hot metal 2 at a predetermined depth.
Thereafter, at least a part of the desulfurization agent necessary for the desulfurization treatment set in advance was added as the desulfurization agent 5a, and the rotation speed of the stirring blade 10 was increased to a predetermined rotation speed of about 120 rpm.

Next, when the rotation speed of the stirring blade 10 reached a predetermined rotation speed, desulfurization treatment was performed by continuously stirring for a predetermined time. During this time, the remaining portion of the desulfurizing agent addition amount set as necessary is added from the desulfurizing agent 5a continuously or intermittently through the charging chute 14.
In addition, in order to promote the desulfurization reaction at the timing when the desulfurization agent 5a is initially added or in parallel with the addition of the desulfurization agent 5a, or before or after the desulfurization agent 5a is added, the Al-based deoxidizer 6a is added to the chute. 14 was added. As the Al-based deoxidizer 6a, a metal Al content of 12% by mass was used.

After the supply of the set amount of the desulfurizing agent 5a was completed, the hot metal 2 was further stirred by the stirring blade 10. And when stirring was performed for 12 to 15 minutes from the start of a process, the desulfurization process was complete | finished and the rotational speed of the stirring blade 10 was lowered | hung and stopped.
Further, when the rotation of the stirring blade 10 was stopped, the stirring blade 10 was raised and placed on standby above the hot metal ladle 3.

  In this investigation, in order to investigate the influence of the hot metal 2 component and the Al-based deoxidizer 6a on the desulfurization efficiency, the mass ratio of the Al-based deoxidizer 6a to the desulfurizer 5a is 20% by mass to 35% by mass. The desulfurization treatment was performed under the conditions changed in the range. Moreover, the addition amount (basic unit) of the desulfurization agent 5a was adjusted according to the sulfur concentration of the hot metal 2 before the desulfurization treatment and the target sulfur concentration of the hot metal 2 after the desulfurization treatment. And the sample of the hot metal 2 after a desulfurization process was extract | collected, the sulfur concentration of the hot metal 2 was measured, and the desulfurization efficiency was verified.

Here, the desulfurization efficiency η is defined by the following formula (1), and the natural logarithm of the ratio of the sulfur concentration of the hot metal 2 before and after the desulfurization treatment is defined as the sum of the desulfurization agent (desulfurization agent 5a and desulfurization agent 5b). It is the value divided by the desulfurizing agent basic unit (kg / t), which is the amount added per 1 ton of hot metal. In the formula (1), [S] _i is the sulfur concentration (mass%) before the desulfurization treatment, [S] _f is the sulfur concentration (mass%) after the desulfurization treatment, and W _CaO is the desulfurization agent used in the desulfurization treatment. This is the desulfurization agent basic unit (kg / t) of (desulfurization agent 5a and desulfurization agent 5b).
η = ln ([S] _i / [S] _f ) / W _CaO (1)

  The results of this survey are shown in FIG. In FIG. 2, the horizontal axis represents the phosphorus concentration of the hot metal 2 before the desulfurization treatment, and the vertical axis represents the metal Al basic unit (kg / t), which is the added amount per 1 ton of metal Al contained in the Al-based deoxidizer. . In FIG. 2, the circle plots show the results of the desulfurization efficiency η being as high as 0.4 or more, and the square plots show the results of the desulfurization efficiency η being as low as less than 0.4. When the desulfurization efficiency η is less than 0.4, desulfurization cannot be performed up to the target sulfur concentration, and the risk of desulfurization failure increases.

As shown in FIG. 2, it was confirmed that the desulfurization treatment in which the desulfurization efficiency η was less than 0.4 was distributed with high frequency below the broken line in the graph of FIG. This is presumably because the deoxidation effect was not sufficiently obtained and the desulfurization efficiency was lowered by reducing the amount of metal Al added to the dephosphorization conditions of the hot metal. Further, the lower limit value of the metal Al basic unit for preventing the desulfurization efficiency η from being less than 0.4 due to the small amount of metal Al added is represented by the following formula (2) from the broken line in the graph of FIG. . (2) In the _{formula, Y Al} metal Al per unit (kg / t), _{X P} is a phosphorus concentration of the molten iron 2 before desulfurization treatment (mass%).
Y _Al = 0.28−X _P /0.75 (2)

As can be seen from FIG. 2, the desulfurization efficiency η is less than 0.4 when the metal Al basic unit is lower than the formula (2) below the formula (2), that is, the phosphorus concentration before the desulfurization treatment. there is a possibility. On the other hand, in FIG. 2, a small number of desulfurization treatments in which the desulfurization efficiency η is less than 0.4 are also distributed in a range near the upper end side of the distribution of the metal Al basic unit. This is because the liquid phase amount of the oxide produced by Al ₂ O ₃ produced by oxidation of metal Al becomes excessive, the aggregation of the powdered CaO-based desulfurization agent proceeds, the reaction interface area decreases, and desulfurization This is thought to be due to an adverse effect on promotion.

Therefore, assuming that the required addition amount of metal Al in the desulfurization treatment is expressed by the equation (2), the excess addition amount E _Al (kg / t) of metal Al per 1 ton of hot metal is expressed by the following equation (3). FIG. 3 shows the relationship between the excess addition amount _EAl and the desulfurization efficiency η. In addition, if the excess addition amount E _Al of metal Al is a positive value, it indicates that the metal Al is added in excess of the required addition amount, and if it is negative, the metal Al is added less than the required addition amount. Indicates that
E _Al = Y _Al- (0.28-X _P /0.75) (3)

From Figure 3, the excess amount _{E Al} metal Al 0 kg / t or more, to the range of 0.12 kg / t, that _{is, by Y Al} and _{X P} is a range satisfying the following equation (4) It was confirmed that the desulfurization efficiency η was less than 0.4 and it was possible to suppress the occurrence of poor desulfurization.
0.28−X _P /0.75≦Y _Al ≦ 0.40−X _P /0.75 (4)
Incidentally, if the excess amount E _Al metal Al is 0.12 kg / t exceeds, by too many amount of the metal Al, lime particles are agglomerated by increasing the amount of liquid phase of the slag, the reaction interface As a result, the desulfurization efficiency may be lowered.

<Desulfurization method>
The method for desulfurizing hot metal 2 according to an embodiment of the present invention is based on the above findings. In the hot metal 2 desulfurization method according to this embodiment, the hot metal 2 is desulfurized using the mechanical stirring type hot metal desulfurization apparatus 1 shown in FIG. In addition, the structure of the hot metal desulfurization apparatus 1 is the same as the said investigation.
In the present embodiment, the dephosphorization treatment is performed on the hot metal discharged from the blast furnace, as in the above-described investigation. The hot metal 2 subjected to the desulfurization treatment contains the hot metal that has been subjected to the dephosphorization treatment and is accommodated in the hot metal ladle 3 as in the above investigation. In addition, before the desulfurization treatment, a sample of the hot metal 2 accommodated in the hot metal ladle 3 is collected and analyzed for phosphorus concentration and sulfur concentration. Further, similarly to the above-described investigation, the hot metal 2 accommodated in the hot metal ladle 3 is subjected to removal to remove slag floating on the bath surface.

  In the desulfurization treatment, first, in the same manner as in the above investigation, slag after desulfurization treatment generated in the desulfurization treatment of other hot metal is prepared in advance, and is placed on the bath surface of the hot metal 2 accommodated in the hot metal ladle 3 using a heavy machine. Add. At this time, the desulfurization ability of the used desulfurized slag is effectively utilized to suppress the amount of newly used desulfurizing agent and to circulate the used desulfurized slag for the purpose of reducing the amount of slag discharged outside the system. Reuse. However, even if the amount of slag to be recycled is increased to a certain extent, the desulfurization efficiency of reused slag gradually decreases, so the amount of newly used desulfurizing agent and the amount of slag discharged outside the system cannot be reduced much. It is not a good idea because it causes an increase in the work load for reuse and an increase in the temperature drop of the hot metal. For this reason, it is desirable that the amount of desulfurization slag to be reused be kept at the same level as the amount of desulfurization agent to be newly used, and is preferably about 4 kg / t to 8 kg / t.

Next, the hot metal ladle 3 is mounted on the cart 4, and the position of the cart 4 is adjusted so that the position of the stirring blade 10 is substantially the center of the hot metal pan 3.
Further, the stirring blade 10 is lowered while rotating at a low speed and immersed in the hot metal 2 at a predetermined depth.
Thereafter, at least a part of the desulfurization agent 5a and the desulfurization agent 5b necessary for the desulfurization treatment set in advance is added as a desulfurization agent 5a, and the rotation speed of the stirring blade 10 is set to a predetermined rotation of about 120 rpm. Raised to number.

Next, when the rotation speed of the stirring blade 10 reaches a predetermined rotation speed, the desulfurization treatment is performed by continuously stirring for a predetermined time. During this time, the remainder of the addition amount of the desulfurizing agent set as necessary is added continuously or intermittently from at least one of the desulfurizing agent 5a and the desulfurizing agent 5b via the charging chute 14 or the upper blowing lance 15. .
Further, in order to promote the desulfurization reaction at the timing of the initial stage or in parallel with the addition of the desulfurizing agents 5a and 5b, or before or after the addition of the desulfurizing agents 5a and 5b, 6 a and 6 b are added from the charging chute 14 or the upper blowing lance 15.

  The Al-based deoxidizers 6a and 6b are added according to the phosphorus concentration of the hot metal 2 before the desulfurization treatment so that the total addition amount increases as the phosphorus concentration of the hot metal 2 decreases. In this case, the total addition amount of the Al-based deoxidizers 6a and 6b is the same as the total addition amount of the pure metal Al in the Al-based deoxidizers 6a and 6b depending on the phosphorus concentration of the hot metal 2 (2) It is preferable to make it change according to the inclination of, and more preferably within the range shown by the equation (4). The Al-based deoxidizers 6a and 6b may be added by adding them from the charging chute 14 alone, by adding them from the charging chute 14 as a mixture with the desulfurizing agent 5a, or by a mixture of the desulfurizing agent 5b. The method of projecting from the top blowing lance 15 can be used alone or in combination. There are no particular restrictions on the timing of addition in the method of adding each of the Al-based deoxidizers 6a and 6b. However, the oxygen source contained in the slag in the hot metal ladle 3 or the hot metal desulfurization slag to be reused is quickly reduced for desulfurization. In order to improve efficiency, it is desirable to add a sufficient amount of Al-based deoxidizers 6a and 6b at the initial stage of the desulfurization treatment. For this reason, it is desirable to add 30 mass% or more of the total addition amount of the Al-based deoxidizer to the Al-based deoxidizer 6a, 6b by 2 minutes after the start of the desulfurization treatment, and 40 mass% or more and 80 mass%. It is more desirable to add up to%. It is desirable to add a part of the Al-based deoxidizers 6a and 6b to the middle of the desulfurization process as well as promoting the reduction and hatching of the desulfurization agents 5a and 5b added to the middle of the desulfurization process. This is to prevent excessive liquid phase slag from being generated in the initial stage and agglomeration of the desulfurizing agents 5a and 5b from proceeding. In general, a sufficient amount of the Al-based deoxidizer 6a is added alone or as a mixture with the added desulfurizer 5a by the beginning of the desulfurization treatment, and a relatively small amount of the Al-based deoxidizer is added to the middle of the desulfurization treatment. A method of projecting a mixture of 6b and the desulfurizing agent 5b from the top blowing lance 15 is desirable from the viewpoint of the efficiency of the desulfurizing agent.

After the supply of the set total amount of desulfurizing agents 5a and 5b was completed, the hot metal 2 was further stirred by the stirring blade 10. Then, the desulfurization process is completed by stirring for a predetermined time from the start of the process, and the rotational speed of the stirring blade 10 is decreased to stop.
Further, when the rotation of the stirring blade 10 is stopped, the stirring blade 10 is raised, and is put on standby above the hot metal ladle 3.
After that, when the generated slag floats to cover the hot metal surface and is in a stationary state, the hot metal ladle 3 is transported to the removal field.
Subsequently, the slag produced | generated by the desulfurization process is discharged | emitted from the hot metal ladle 3 in the same way as the inflow slag from a chaotic vehicle mentioned above, and the hot metal ladle 3 is conveyed to the following decarburization refining process.

<Modification>
Although the present invention has been described above with reference to specific embodiments, it is not intended that the present invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention will be apparent to those skilled in the art, including various modifications along with the disclosed embodiments. Therefore, it should be understood that the embodiments of the present invention described in the claims also include embodiments including these modifications described in the present specification alone or in combination.

For example, in the above embodiment, the Al-based deoxidizers 6a and 6b are added so that the metal Al basic unit increases as the phosphorus concentration of the hot metal decreases according to the slope of the equation (2), or further (4) Although it is preferable to add in the range of the metal Al basic unit according to the phosphorus concentration of the hot metal shown in the formula, the present invention is not limited to such an example. Adjustment of the addition amount of the Al-based deoxidizers 6a and 6b according to the phosphorus concentration of the hot metal 2 is based on the actual state of operation, and the total amount of the Al-based deoxidizers 6a and 6b is reduced as the phosphorus concentration of the hot metal decreases. The relative amount may be adjusted so as to increase the amount of addition, but it is preferable that the phosphorus concentration of the hot metal is adjusted so as to have the same degree of inclination as the equation (2). That is, as shown in the straight line of the following formula (5) shown in FIG. You may adjust the addition amount of Al type deoxidizer 6a, 6b according to the phosphorus density | concentration of hot metal so that a unit may be adjusted.
Y _Al = 0.30−X _P /0.75 (5)
Further, for example, according to a step-like, straight line-like, or curved-line function as shown in the following formula (6) shown in FIG. 4, the addition amount of the metal Al basic unit, that is, the Al-based deoxidizers 6 a, 6 b is set. In any case, it is preferable to add the Al-based deoxidizers 6a and 6b within the range of the metallic Al basic unit corresponding to the phosphorus concentration of the hot metal satisfying the formula (4).

  Moreover, in the said embodiment, although the phosphorus density | concentration of the hot metal used for adjustment of Al type deoxidizer was taken as the analytical value of the hot metal 2 accommodated in the hot metal ladle 3, this invention is not limited to this example. For example, the phosphorus concentration of hot metal contained in the hot metal ladle 3 may be estimated by analyzing the phosphorus concentration of the hot metal of the hot metal car and performing weighted averaging of the mixture ratio of hot metal from each of the hot metal cars. .

Furthermore, in the said embodiment, although the kneading vehicle was used in the hot metal conveyance and the dephosphorization process, this invention is not limited to this example. For example, instead of a kneading wheel, a hot metal ladle may be used as a transport container or a dephosphorization reaction container. Further, in the dephosphorization process, a converter type dephosphorization process in which oxidative refining is performed using a gaseous oxygen source or a solid oxygen source in a converter type refining furnace may be performed.
Furthermore, in the said embodiment, although the slag after the desulfurization process used by the desulfurization process of the other hot metal was added to the hot metal 2, this invention is not limited to this example. The desulfurization treatment may be performed using only a refining agent such as a desulfurization agent and an Al-based deoxidizer added in the hot metal desulfurization apparatus 1 without adding the slag after the desulfurization treatment to the hot metal 2.

  Furthermore, in the said embodiment, although it applied in the mechanical stirring type hot metal desulfurization apparatus 1, this invention is not limited to this example. For example, it is also applicable to injection-type desulfurization treatment methods in which a dipping lance is immersed in hot metal contained in a transport container such as a kneading wheel or hot metal ladle and a desulfurizing agent or an Al-based deoxidizing agent is blown from the dipping lance. can do. Also in the injection-type desulfurization treatment method, the deoxidation effect according to the dephosphorization conditions of the hot metal can be obtained and the desulfurization efficiency can be reduced by adjusting the addition amount of the Al-based deoxidizer as in the above embodiment. Can be prevented.

<Effect of embodiment>
(1) The desulfurization method for hot metal 2 according to one aspect of the present invention includes a desulfurization agent 5a, 5b containing quick lime and a metal Al containing hot metal containing hot metal discharged from a blast furnace and subjected to dephosphorization. A hot metal desulfurization method in which a desulfurization treatment is performed by adding Al-based deoxidizers 6a and 6b having a content of 10% by mass or more and the balance being mainly Al ₂ O _3. According to the phosphorus concentration, the amount of Al-based deoxidizer added is adjusted to increase as the phosphorus concentration decreases.

  According to the configuration of (1) above, the Al-based deoxidizer is added in accordance with the phosphorus concentration of the hot metal 2 as compared with the conventional desulfurization method in which the addition amount of the Al-based deoxidizer is always a constant ratio with respect to quicklime. The usage amount of 6a, 6b is changed. Thereby, according to the difference in the oxygen potential of the slag after the dephosphorization process mixed in the hot metal 2 or the hot metal ladle 3, the use amount of the Al-based deoxidizers 6a and 6b increases as the oxygen potential increases. Can be added. For this reason, even when the oxygen potential of the hot metal 2 and the slag is increased by the dephosphorization treatment, it is possible to effectively prevent an adverse effect on the desulfurization reaction. As a result, even if CaO-based desulfurization agents 5a and 5b that do not use a fluorine source are used, it is possible to prevent the desulfurization efficiency from being extremely reduced, and it is not necessary to use a desulfurization agent excessively in a proactive manner. As a result, the amount of desulfurization agent used can be reduced, and desulfurization can be performed with high desulfurization efficiency. That is, according to the configuration of (1), it is possible to suppress the occurrence of defective desulfurization without excessively increasing the amount of the desulfurizing agents 5a and 5b and the Al-based deoxidizing agents 6a and 6b. Moreover, the generation amount of slag and the desulfurization cost can be suppressed. Further, since it is not necessary to increase the use type of the refining agent, it can be easily applied to a small facility.

(2) In the above configuration (1), the phosphorus concentration of the molten iron 2 before desulfurization treatment _{X P} (wt%) of 0.03 or more, in the range of 0.15 or less, relative to the phosphorus concentration _{X P,} Al Amounts of _Al- based deoxidizers 6a and 6b so that the added amount Y _Al (kg / t) per 1 ton of molten metal contained in the system-based deoxidizers 6a and 6b satisfies the formula (4). To decide.
According to the configuration of the above (2), in addition to the effect of the configuration of the above (1), the Al-based deoxidizer 6a, which is necessary for preventing the desulfurization efficiency from being lowered according to the oxygen potential of the hot metal 2 and the slag. 6b can be added without excess or deficiency.

(3) In the configuration of the above (1) or (2), the hot metal 2 in the processing vessel (for example, hot metal ladle 3) is desulfurized while being stirred by a stirring blade.
According to the configuration of (3) above, in the mechanical stirring type hot metal desulfurization apparatus 1 similar to the above embodiment, it is possible to prevent the desulfurization efficiency from being lowered.

  Next, examples performed by the present inventors will be described. In the example, the hot metal discharged from the blast furnace was accommodated in a mixed car having a capacity of about 300 t, then transferred to a hot metal dephosphorization facility, and the molten iron stored in the mixed car was transferred to the sintered ore as in the above embodiment. The hot metal dephosphorization treatment was carried out by blowing powder of an oxidizing agent such as powder and powder of a lime-based solvent such as quick lime. The phosphorus concentration in the hot metal discharged from the blast furnace was in the range of 0.12% by mass to 0.14% by mass, and almost all the molten iron in the kneading car was treated. However, the degree of dephosphorization varies depending on the silicon concentration of the hot metal before processing, the processing time allowed depending on the stock status of hot metal, the status of the production plan of steel products, etc., and the phosphorus concentration of hot metal after processing is It became the range of 0.035 mass%-0.12 mass%.

  Subsequently, the hot metal after the dephosphorization process accommodated in the kneading car was conveyed to a steelmaking factory, and the hot metal was transferred from one or more kneading cars to a hot metal ladle having a capacity of about 300 t. And like the said embodiment, while removing a part of slag on the hot metal bath surface, the hot metal sample was extract | collected and each component density | concentrations, such as sulfur concentration and phosphorus concentration, were analyzed. Furthermore, after adding about 6 kg / t of desulfurization slag generated in the desulfurization treatment of other hot metal on the hot metal bath surface in the hot metal pan, the mechanical stirring type hot metal desulfurization shown in FIG. The hot metal ladle 3 was moved to the apparatus 1 to carry out the desulfurization treatment. The components of the hot metal 2 before the desulfurization treatment are: C: 4.0% by mass to 4.4% by mass, Si: less than 0.01% by mass to 0.10% by mass, P: 0.040% by mass to 0.120% The mass% was S: 0.025 mass% to 0.035 mass%.

  Further, in the hot metal desulfurization apparatus 1 shown in FIG. 1, the stirring blade 10 is dipped to a predetermined depth while rotating at a low speed in about 300 t of hot metal 2 accommodated in the hot metal ladle 3, and quick lime as a desulfurizing agent 5a is added per 1t of hot metal. 5 kg was added on top. And the stirring blade 10 was rotated at the rotational speed of 120 rpm, the hot metal 2 and the desulfurization agent 5a were stirred, and the desulfurization process was started. Based on the target concentration (upper limit) of the sulfur concentration of the hot metal 2 before the desulfurization treatment and the sulfur concentration after the desulfurization treatment, the additional amount of quick lime as the desulfurization agents 5a and 5b and the stirring time (desulfurization treatment time) are adjusted, After the addition of a predetermined amount of quick lime of 5 kg to 8 kg per 1 ton of hot metal, the desulfurization treatment was completed when stirring for the predetermined time was completed. After the stirring blade 10 is stopped and raised, the hot metal ladle 3 is moved to the demolition field, and the slag generated by the desulfurization treatment is discharged from the hot metal ladle, and a hot metal sample is collected and used for component analysis. The hot metal ladle was transported to the decarburization refining process.

In the desulfurization treatment, Al dross is used as the Al-based deoxidizers 6a and 6b in the same manner as in the above embodiment, and the desulfurization treatment is performed under the seven conditions of Examples 1 to 5 and Comparative Examples 1 and 2 by variously changing the addition method. did. As Al dross, in Example 5, the content of metal Al was 30% by mass, and in Examples 1-4 and Comparative Examples 1 and 2, the content of metal Al was 12% by mass. .
In Comparative Example 1, 5 kg / t of the desulfurizing agent 5a was added on top at the start of the desulfurization treatment, and then the Al-based deoxidizing agent 6a was added as a fixed amount of about 1.8 kg per 1 ton of hot metal. When an additional amount of desulfurizing agent was added, the desulfurization treatment was continued about 500 times by a method in which only the desulfurizing agent 5a was added in one or more times.

  Further, in Comparative Example 2, similarly to Comparative Example 1, after adding 5 kg / t of desulfurizing agent 5a at the start of desulfurization treatment, when adding an additional amount of desulfurizing agent, once or a plurality of times. Separately, only the desulfurizing agent 5a was added on top. Furthermore, in Comparative Example 2, every time the desulfurization agent 5a is added at the beginning of the desulfurization treatment and during the desulfurization treatment, 30% by mass of the Al-based deoxidizer 6a is added to the added desulfurization agent 5a. The desulfurization treatment was continued about 500 times.

In contrast, in Example 1, in accordance with the phosphorus concentration X _P desulfurization pretreatment hot metal 2 _(by mass%), the target value of the amount of Al-based deoxidizer 6a, an Al-based deoxidizer 6a The basic unit Y _Al (kg / t) of metal Al contained in a certain Al dross was determined so as to satisfy the formula (5). Then, similarly to Comparative Example 1, after adding 5 kg / t of quicklime at the start of the desulfurization treatment, an adjusted amount of the Al-based deoxidizer 6a was added all at once. Further, when adding an additional amount of desulfurizing agent 5a, about 500 desulfurization treatments were continuously performed by a method in which only quick lime was added in one or a plurality of times.

In Example 2, the target value of the addition amount of the Al-based deoxidizer 6a is determined so that the basic unit _YAl (kg / t) of the metal Al contained in the Al-based deoxidizer 6a satisfies the equation (6). did. Then, performed is continued desulfurization treatment of about 500 times in the same manner as in Example 1 except for adjusting the amount of addition of Al-based deoxidizer 6a stepwise in accordance with the phosphorus concentration X _P desulfurization pretreatment hot metal 2 It was.
In Example 3, immediately after adding 5 kg / t of quicklime at the start of the desulfurization treatment, the basic unit Y _Al (kg / t) of metal Al contained in the Al-based deoxidizer 6a satisfies the formula (2). Was added with an Al-based deoxidizing agent 6a whose amount was adjusted. Then, every time the additional amount of desulfurizing agent 5a was added on top, about 500 times of desulfurization treatment was continued by adding 15% by mass of Al-based deoxidizing agent 6a to the added desulfurizing agent 5a. .

In Example 4, the desulfurizing agent 5a and the Al-based deoxidizing agent 6a were added at the start of the desulfurization process in the same manner as in Example 3. Thereafter, an additional amount of desulfurizing agent and 15% by mass of an Al-based deoxidizing agent with respect to the additional amount of desulfurizing agent are respectively used as a desulfurizing agent 5b and an Al-based deoxidizing agent 6b. The desulfurization treatment was continued about 500 times by the method of spraying and adding to the hot metal 2 from the blowing lance 15.
In Example 5, desulfurization treatment was performed about 500 times in the same manner as in Example 1 except that Al dross having a metal Al content of 30% by mass was used as the Al-based deoxidizer 6a.

  In Examples 1 to 5 and Comparative Examples 1 and 2, there is a high risk of desulfurization defective charge, and the charge generation ratio at which the desulfurization efficiency η defined by the formula (1) is less than 0.4 is the case of Comparative Example 1. Table 1 shows an evaluation based on an index based on the generation ratio. In any of the examples and comparative examples, the average basic unit (addition amount per 1 ton of hot metal) of the desulfurizing agents 5a and 5b is about 6 kg / t, and the average of metal Al contained in the added Al-based deoxidizers 6a and 6b. The basic unit (added amount per 1 ton of hot metal) was about 0.22 kg / t.

  Based on the results in Table 1, the amount of Al dross as the Al-based deoxidizers 6a and 6b is adjusted to increase as the phosphorus concentration in the hot metal 2 decreases according to the phosphorus concentration in the hot metal 2 before the desulfurization treatment. In the method of the present invention, it has been confirmed that the generation of defective desulfurization charge can be suppressed without increasing the amount of desulfurization agent or Al-based deoxidizer used.

DESCRIPTION OF SYMBOLS 1 Hot metal desulfurization apparatus 10 Stirring blade 10a Shaft part 10b Blade part 11a-11d Hopper 12a, 12b Rotary feeder 13a, 13b Cutting device 14 Input chute 15 Top blowing lance 2 Hot metal 3 Hot metal ladle 4 Carriage

Claims (3)

To the hot metal containing hot metal extracted from a blast furnace and subjected to dephosphorization treatment, an Al-based desulfurization agent containing a desulfurization agent containing quicklime and a metal Al content of 10% by mass or more and the balance being mainly Al ₂ O ₃ is used. A desulfurization method for hot metal in which a desulfurization treatment is performed by adding an acid agent,
A hot metal desulfurization method comprising adjusting the amount of addition of the Al-based deoxidizer as the phosphorus concentration decreases in accordance with the phosphorus concentration of the hot metal before the desulfurization treatment. The phosphorus concentration X _{P (wt%)} of the hot metal pre-desulfurization process 0.03 or more and 0.15 or less, relative to the phosphorus concentration of the metal Al contained in the Al-based deoxidizer 2. The addition amount of the Al-based deoxidizer is determined such that the addition amount Y _Al (kg / t) per 1 ton of hot metal is in a range satisfying the following expression (4): 2. Hot metal desulfurization method.
0.28−X _P /0.75≦Y _Al ≦ 0.40−X _P /0.75 (4)   The hot metal desulfurization method according to claim 1 or 2, wherein the hot metal in the processing vessel is desulfurized while being stirred by a stirring blade.

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