JP2018178191A - Method for desulfurizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for desulfurizing a molten iron solving the problem that, upon slag exhaust after desulfurizing treatment, un-exhausted slag remains in a molten iron ladle, and the slag is poured into a converter together with a molten iron, thus resulfurization is generated by oxidation refining in the converter to increase an S concentration in a molten steel after converter refining than an S concentration in the molten iron upon converter charge, i.e., the S of the slab brought into the converter has been one cause increasing S in the molten steel, thus reducing S brought into the converter and reducing S in the molten steel after refining.SOLUTION: Provided is a method for desulfurizing a molten iron where, when desulfurizing treatment to a molten iron charged in a container is performed for a plurality times, slag exhaust is performed after the first desulfurizing treatment, and slag exhaust is performed once more after the second desulfurizing treatment.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for desulfurizing hot metal in a steelmaking process.

  The hot metal discharged from the blast furnace is subjected to desulfurization as a hot metal pretreatment before dephosphorization and decarburization by a converter. Since it is desirable to minimize the residue of S in the refining process in order to produce a high quality steel, various desulfurization methods have been developed in the past to further reduce S.

  Patent Document 1 discloses a desulfurization method in which a desulfurization material is charged a plurality of times into hot metal and stirred, and a technique for adjusting the stirring power at the time of desulfurization material input to make the newly input desulfurization agent easier to contact slag. ing. Thereby, aggregation due to direct contact of the desulfurizing agent with the surface of the hot metal is avoided, and the reaction efficiency of the desulfurizing agent is improved.

Patent No. 4844679

  According to the desulfurization method of Patent Document 1, it is possible to reduce S in the hot metal, but when discharging the slag after the desulfurization treatment, slag that can not be discharged remains in the hot metal pan. Since this slag will be poured into the converter together with the molten metal, reoxidation occurs due to the oxidation refining in the converter, and the S concentration of the molten steel after the converter refinement is higher than the S concentration of the molten metal at the time of converter charging. Get higher. That is, the S of the slag brought into the converter contributed to the increase of S in the molten steel.

  This invention is made in view of the said situation, and reduces S brought in in a converter, and it aims at reducing S in molten steel after refinement.

  The present invention for solving the above problems is a desulfurization method of hot metal, and when the desulfurization treatment of hot metal in a container is performed a plurality of times, discharge is performed after the first desulfurization treatment, and after the second desulfurization treatment again It is characterized by performing exclusion.

  S brought into the converter can be reduced, and S in the molten steel after refining can be reduced.

It is a figure showing a schematic structure of a steelmaking installation concerning an embodiment of the present invention. It is a figure showing the flow of the desulfurization method of the hot metal concerning the embodiment of the present invention. It is a figure which shows S density | concentration of hot metal and slag at the time of implementing a desulfurization process only once. It is a figure which shows S density | concentration of hot metal and slag at the time of implementing desulfurization processing twice and performing discharge between 1st and 2nd desulfurization processing. It is a figure which shows the fluctuation | variation of converter input S density | concentration by the difference of the desulfurization material basic unit at the time of the 1st desulfurization processing, and the desulfurization material basic unit at the time of the 2nd desulfurization processing.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present specification and the drawings, elements having substantially the same functional configuration will be assigned the same reference numerals and redundant description will be omitted.

  In the present embodiment, desulfurization treatment of the hot metal M is performed using the steel making facility 1 shown in FIG. The flow from the blast furnace 2 to the hot metal charging to the converter 5 is generally as shown in FIG.

  First, the molten metal M discharged from the blast furnace 2 is charged into the torpedo car 3 and transported to the converter smelting facility. During this time, the first desulfurization treatment is performed on the hot metal M in the torpedo car. The method of the first desulfurization treatment is not particularly limited, and, for example, a method of injecting a desulfurization material into hot metal is employed. By this desulfurization treatment, S in the hot metal decreases and, instead, S in the slag increases. In addition, you may implement discharge (pre-discharge) before the 1st desulfurization process.

  Subsequently, the slag in the torpedo car is discharged. That is, before the molten metal M is put into the converter charging pot 4, the slag whose S concentration has risen is discharged once. Since it is difficult to discharge all slag due to the structure of the slag discharger (not shown), a certain amount of slag usually remains in the torpedo car 3 at the time of discharge. Also in the present embodiment, a certain amount of slag remains in the interior of the torpedo car 3 after slag removal. Since this slag contains S removed from the hot metal M, the S concentration is higher than that at the time of tapping.

  Next, the hot metal M in the torpedo car is put into the converter charging pot 4. At this time, the slag in the torpedo car is also poured into the converter charging pot 4 together. That is, S in the slag after the first desulfurization treatment is brought into the converter charging pot 4.

  Subsequently, the converter charging pot 4 is placed on the transport carriage and transported toward the converter 5. During this time, the second desulfurization treatment is performed on the molten metal M of the converter charging pot 4. The method of the second desulfurization treatment is not particularly limited, and, for example, a desulfurization method using KR desulfurization equipment is adopted. By the second desulfurization treatment, S in the hot metal is further reduced, and the hot metal M has an S concentration suitable for converter charging.

  Thereafter, the slag of the converter charging pot 4 is discharged. As described above, since the slag discharger (not shown) is structurally limited in slag discharge amount, a fixed amount of slag remains in the converter charging pot after the discharge. The slag includes S of slag brought in from the torpedo car 3 and S removed from the hot metal M by the second desulfurization treatment. After the slag is discharged, the molten metal M of the converter charging pot 4 is charged into the converter 5, and converter refining is started.

  In the conventional desulfurization method in which the desulfurization material is charged into the hot metal M a plurality of times, the second desulfurization treatment is started without performing the slag elimination after the first desulfurization treatment, so the waste after the second desulfurization treatment Sometimes, the slag contains two S of desulfurization treatment. Therefore, slag having a high S concentration remains in the pan after the second desulfurization and draining. On the other hand, according to the desulfurization method of the present embodiment, the first desulfurization treatment is performed because the discharge (first displacement) is performed once between the first desulfurization treatment and the second desulfurization treatment. A fixed amount of S removed from the hot metal M is discharged before starting the second desulfurization treatment. As a result, when the second discharge after the second desulfurization treatment (second discharge) is performed, the S concentration of the slag remaining in the pan is lower than when the first discharge is not performed. It becomes the concentration.

  In the present embodiment, as in the conventional case, when the molten metal M is charged from the converter charging pot 4 to the converter 5, the slag moves together with the molten metal M and S is brought into the converter, but the present embodiment Then, since the S concentration of the slag remaining in the converter charging pot 4 is lower than that in the prior art, S brought into the converter 5 also decreases as a result. This makes it possible to reduce S in the molten steel after tapping.

  In the present embodiment, although the first desulfurization treatment is performed by the torpedo car 3 and the second desulfurization treatment is performed by the converter charging pot 4, the container in which the desulfurization treatment is performed is particularly Without being limited thereto, the hot metal M may be transferred to another container to carry out the desulfurization treatment. Further, the number of times of desulfurization treatment is not limited to two, and may be more than once. In addition, multiple desulfurization treatments may be performed in the same container. However, if the desulfurization treatment is performed a plurality of times in the same container, the physical distribution will stagnate, so it is preferable to carry out in different containers. In particular, since the torpedo car 3 and the converter charging pot 4 are generally used to transport the hot metal M from the blast furnace 2 to the converter 5, the first desulfurization treatment is performed in view of suppressing the decrease in productivity. It is preferable to carry out the torpedo car 3 and to carry out the second desulfurization treatment in the converter charging pot 4.

  When the first desulfurization treatment and the second desulfurization treatment are performed, the relationship between the desulfurization agent base unit at the first desulfurization treatment and the desulfurization agent base unit at the second desulfurization treatment is 0.3. It is preferable to satisfy ≦ 0.9 of desulfurizing material basic unit at the time of first desulfurizing treatment / (desulfurizing material unit of the first desulfurizing process + desulfurizing material unit of the second desulfurizing process). Thereby, S of slag remaining in the converter charging pot 4 can be further reduced. 1 when the value of desulfurization material base unit / (desulfurization base unit at the first desulfurization processing + desulfurization base unit at the second desulfurization processing) at the time of the first desulfurization treatment is smaller than 0.3 Since the amount of slag after the second desulfurization treatment is small, it becomes difficult to carry out the exhaust operation, and there is a possibility that the exhaust can not be sufficiently carried out. As a result, a large amount of S in the slag may remain. On the other hand, when the above value is larger than 0.9, the amount of slag after the second desulfurization treatment is small, and similarly, sufficient discharge operation can not be performed, and a large amount of S in the slag may remain. The preferable lower limit value of the desulfurizing material base unit / (the desulfurizing material base unit at the first desulfurizing processing + the desulfurizing material base at the second desulfurizing processing) at the time of the first desulfurization treatment is 0.5. Further, a preferable upper limit value of the desulfurizing material base unit / (the desulfurizing material base unit during the first desulfurization processing + the desulfurizing material base unit during the second desulfurization processing) in the first desulfurization processing is 0.8.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this example. It is apparent that those skilled in the art can conceive of various changes or modifications within the scope of the technical idea described in the claims, and the technical scope of the present invention is also natural for them. It is understood to belong to

  Simulation of the desulfurization treatment was performed, and the S concentration of hot metal and slag in the process from the start of the desulfurization treatment to the slag discharge was calculated. In the present example, simulations were carried out assuming two desulfurization methods such as a desulfurization method as a comparative example of the present invention and a desulfurization method according to the present invention. The desulfurization method of the comparative example is a method in which the desulfurization treatment is performed only once, and then the waste is discharged. In the desulfurization method according to the present invention, the desulfurization treatment is performed twice in total, and the discharge is performed between the first desulfurization treatment and the second desulfurization treatment, and the discharge is performed again after the second desulfurization treatment. It is a way to do so.

The preconditions for the simulation are as follows.
Hot metal S concentration at the time of blast furnace discharge = 0.02%
Slag S concentration at blast furnace discharge = 0.30%
Amount of slag at tapping = 3.3 kg / t
Desulfurization agent input amount = 10 kg / t (in the case of the desulfurization method according to the present invention: desulfurization agent input amount at the first desulfurization treatment = 5 kg / t, desulfurization agent input amount at the second desulfurization treatment = 5 kg / t)
Residual slag after displacement = 3 kg / t
-Ln (post desulfurization hot metal S concentration / pre-desulfurization hot metal S concentration) / desulfurization agent unit unit = 0.3
Hot metal S concentration at the time of converter charging = 0.001%

  The S concentration of hot metal and slag when the desulfurization method of the comparative example is performed is shown in FIG. Moreover, S density | concentration of hot metal and slag at the time of enforcing the desulfurization method based on this invention is shown in FIG. The S concentration of slag is calculated by converting the amount of slag into the amount of molten metal, and is calculated from S in the slag and the amount of molten metal.

  As shown in FIG. 3, in the desulfurization method of the comparative example, the sum of the S concentration of the hot metal after exhausting and the S concentration of the slag became 60 ppm. On the other hand, as shown in FIG. 4, according to the desulfurization method according to the present invention, the sum of the S concentration of the hot metal after the second discharge and the S concentration of the slag became 50 ppm. In any of the desulfurization methods, there is no difference in the final S concentration of hot metal after the desulfurization treatment, but there is a difference in the S concentration of slag. This is because in the desulfurization method of the comparative example, all the S removed in the desulfurization treatment process is contained in the slag at the time of discharge, and the S concentration of the slag remaining in the pan after the discharge becomes high. is there. In addition, for example, even in the case of a desulfurization method in which a desulfurization agent is divided into two and charged into hot metal, if the waste is not carried out between the first desulfurization treatment and the second desulfurization treatment, The S concentration increases as well.

  On the other hand, in the desulfurization method according to the present invention, since the discharge is performed once between the first desulfurization treatment and the second desulfurization treatment, the slag after the discharge after the second desulfurization treatment is carried out The S concentration is relatively low. Therefore, according to the desulfurization method according to the present invention, the S concentration of the slag before converter charging can be reduced, and the S carried into the converter can be reduced.

  In the desulfurization method according to the present invention, the same simulation as in Example 1 was performed by changing the desulfurizing agent basic unit at the first desulfurization treatment and the desulfurizing agent basic unit at the second desulfurization treatment. The converter input S concentration at that time (that is, the sum of S concentration of hot metal and slag at final discharge) was calculated. The results are shown in FIG.

  As shown in FIG. 5, when the desulfurizing agent basic unit at the first desulfurization treatment was too small or too large, the reduction effect of the converter input S concentration was small. According to the results in FIG. 5, when carrying out the desulfurization treatment according to the present invention, the desulfurizing agent base unit at the time of 0.3 ≦ first desulfurization treatment / (the desulfurizing agent base unit at the first desulfurization treatment + 2 It is preferable to satisfy the desulfurizing agent basic unit at the time of the second desulfurization treatment) ≦ 0.9. Thus, the converter input S concentration can be greatly reduced. Moreover, to further reduce the converter input S concentration, the desulfurization agent base unit at the first desulfurization treatment / (the desulfurization agent base unit at the first desulfurization treatment, the desulfurization agent base unit at the second desulfurization treatment It is preferable to set the value of) to 0.5 or more and 0.8 or less.

  The present invention can be applied to the desulfurization treatment of hot metal.

1 Steelmaking facility 2 Blast furnace 3 Torpedo car 4 Converter charging pot 5 Converter M Hot metal

Claims (3)

  The desulfurization method of molten iron which performs discharge after the 1st desulfurization processing and performs discharge again after the 2nd desulfurization processing, when desulfurizing processing of the molten metal which entered the container in multiple times.   0.3 ≦≦ the first desulfurization processing rate at the first desulfurization treatment / (the desulfurization processing rate at the first desulfurization processing + the second desulfurization processing at the desulfurization process) ≦ 0.9, The hot metal desulfurization method according to claim 1, wherein the first desulfurization treatment and the second desulfurization treatment are performed. The desulfurization method of hot metal according to claim 1, wherein the first desulfurization treatment is performed by a torpedo car, and the second desulfurization treatment is performed by a converter charging pot.

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