JP2013151725A - Desulfurization treatment method for molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of increasing reaction efficiency of a desulfurizing reagent by efficiently suppressing aggregation of the desulfurizing reagent, using quicklime having a small particle size as the desulfurizing reagent in a desulfurization treatment of molten iron using a mechanical stirring process, without requiring equipment such as powder production equipment and powder transport/supply equipment.SOLUTION: A desulfurizing reagent, obtained by blending ≥2% to <40% of soda ash to quicklime in a mass ratio with respect to the quick lime and having a maximum particle diameter of <5 mm, is added onto molten iron before starting desulfurization treatment or within 1 minute after starting the desulfurization treatment and further, a substance which generates gas by contacting with the molten iron is added onto the molten iron after completion of the addition of the desulfurizing agent and before 50% of the desulfurization treatment time elapses.

Description

  The present invention relates to a technique for efficiently performing desulfurization treatment of hot metal.

In order to meet the demand for mass production of high-grade steel in recent years, development of a hot metal predesulfurization method capable of producing low-sulfur steel at a lower cost is strongly desired.
As a conventional desulfurization treatment method, a powder blowing method, a mechanical stirring method, and the like are well known, but in recent years, a mechanical stirring method is widely used because a desulfurization refining agent can be used more efficiently.

  As the desulfurizing agent to be used, quick lime is common. However, the melting point of CaO, which is the main component, is as high as about 2500 ° C., hardly melts in the range of the normal hot metal desulfurization temperature of 1300 to 1400 ° C., and the desulfurizing agent reacts with the hot metal in a solid state. Since the desulfurizing agent is a solid, the reaction rate is smaller than that of the liquid, and the reaction efficiency of the desulfurizing agent in the treatment is low. Therefore, in order to increase the reaction efficiency, it is common to use a desulfurization agent having a small particle size (for example, a maximum particle size of 5 mm or less) and to increase the reaction interface area as much as possible.

  However, when quick lime is used as a desulfurizing agent, CaO is difficult to wet with molten iron, so even if the particle size is reduced, the desulfurizing agent is aggregated during the treatment, and the reaction interface area is reduced. In addition, unreacted CaO remains in the agglomerated desulfurizing agent, which is an inhibiting factor for improving the desulfurizing agent reaction efficiency. Further, since the aggregation of the desulfurizing agent is further deteriorated by the mixing of blast furnace slag carried over from the blast furnace, the desulfurizing agent is usually forced to be removed before the desulfurization treatment. This situation is the same with respect to the fact that the slag after the hot metal preliminary desiliconization treatment or preliminary dephosphorization treatment must be removed before the desulfurization treatment in order to improve the desulfurization agent reaction efficiency.

  In this hot metal desulfurization method using the mechanical stirring method, one of the solutions to the problem of increasing the reaction efficiency of the desulfurizing agent is a method of using a halide such as fluorite acting as a melting accelerator together with the desulfurizing agent. There is. However, since the use of halides such as fluorite is not desirable from the viewpoint of protecting the global environment when using desulfurized slag as a material, it is rarely used at present.

  As another solution, Patent Document 1 collects desulfurized soot generated by hot metal desulfurization using a mechanical stirring method, sprays water, and then pulverizes the desulfurized agent aggregated using a heavy machine, thereby unreacted. There has been proposed a method for putting quicklime on the surface and reusing it. While this method is effective from the viewpoint of effective utilization of unreacted quicklime, it cannot suppress the desulfurization agent aggregation in the hot metal desulfurization treatment, and therefore cannot improve the desulfurization efficiency. Moreover, the equipment for crushing is required and the economic burden is large.

  Moreover, in patent document 2, a CaO type | system | group desulfurization agent is mixed with a carbonaceous particle before a process, and the thing with a carbonaceous particle thinly adhering to the CaO particle surface is used as a desulfurization agent. A method of improving the wettability of the hot metal and suppressing the aggregation of the desulfurizing agent has been proposed. According to this method, the effect of suppressing aggregation of the desulfurizing agent can be obtained, but mixing of CaO and carbonaceous particles is necessary in the desulfurizing agent manufacturing process, and the process is complicated and the manufacturing cost increases.

  Further, in Patent Document 3, fine CaO-based desulfurization agent is added by spraying on the hot metal bath surface through an upper spray lance, and before, simultaneously with, or after the addition, Describes a hot metal desulfurization method in which a gas generating substance is added. However, in this method, since the desulfurizing agent is sprayed through the top blowing lance, equipment for handling powder having a particle size of 500 μm or less is required. Further, regarding the relationship between the addition timing of the desulfurizing agent and the addition timing of the gas generating substance, substantially nothing is mentioned.

JP 2007-107102 A JP 2008-31537 A JP 2005-179690 A

  Thus, in the past, in order to increase the efficiency of the desulfurizing agent reaction, it was necessary to pre-treat the desulfurizing agent or make it into a powder form. Therefore, a simple and highly efficient desulfurization method has been demanded.

  The object of the present invention is to meet such conventional demands by using quick lime with a small particle size as a desulfurizing agent in the desulfurization treatment of hot metal using a mechanical stirring method, to powder production and powder conveyance and supply facilities. Is to provide a method for efficiently suppressing the agglomeration of the desulfurizing agent and increasing the desulfurizing agent reaction efficiency.

  According to the present invention, the amount of unreacted desulfurizing agent can be reduced, and the desulfurizing agent cost in the hot metal desulfurization treatment and the time required for the entire desulfurization process including the time required for the removal before the desulfurization treatment can be greatly reduced.

As a result of examining the operating conditions for suppressing desulfurization agent aggregation in the mechanical stirring type hot metal desulfurization method, the present inventors have obtained the following knowledge.
When using fine lime (CaO mass ≥ 90%) and soda ash (Na ₂ CO ₃ mass ≥ 99%) with a maximum particle size ≤ 5 mm as desulfurizing agents, hot metal is treated at a hot metal treatment temperature like soda ash or limestone. When a substance that generates gas by causing chemical reaction or thermal decomposition reaction by touching is put on the hot metal during the desulfurization treatment after the addition of the desulfurization agent is completed, desulfurization agent aggregation is suppressed and the amount of unreacted CaO is reduced. As a result, the desulfurization agent reaction efficiency is improved.

  As a desulfurization agent aggregation suppression mechanism, a gas generating material such as soda ash charged on the hot metal during the desulfurization process after the addition of the desulfurizing agent is entrained in the slag or hot metal to generate gas, and the generated gas This is considered to be because the desulfurized slag is agitated by this to separate the agglomerated desulfurizing agent. By this gas stirring and separating action, the unreacted CaO region inside the agglomerated desulfurizing agent appears at the interface with the hot metal and contributes to the desulfurization reaction, so that the desulfurization reaction efficiency is improved.

The present invention is as follows.
(1) When desulfurizing the hot metal using a mechanical stirring method, after removing the slag on the hot metal before the start of the desulfurization treatment, mix the soda ash with a mass ratio of 2% or more and less than 40% to the quick lime. A desulfurizing agent having a maximum particle size of less than 5 mm,
Add the gas to the hot metal before the start of the desulfurization treatment or within 1 minute after the start of the desulfurization treatment, and after the addition of the desulfurizing agent is completed and before 50% of the desulfurization time has elapsed, the gas is brought into contact with the hot metal. A method for desulfurizing hot metal, which comprises adding a generated substance onto the hot metal.

  (2) The hot metal desulfurization treatment method according to (1) above, wherein the hot metal upper slag removal prior to the start of the desulfurization treatment is omitted.

  According to the present invention, after the hot metal desulfurization treatment is started by rotating the hot metal stirring blade (impeller) and after the addition of the desulfurizing agent to the hot metal is completed, the hot metal is impregnated in the slag or hot metal. Therefore, a high desulfurization rate can be stably obtained as compared with the conventional case only by introducing a substance that generates gas into the hot metal.

  Therefore, it is not necessary to pre-treat or powder the desulfurizing agent, and it is possible to perform a simple and highly efficient desulfurization process without the need to provide a powder supply facility such as a top blowing lance. it can.

  Furthermore, when it is desired to increase the desulfurization efficiency, the time required for the total desulfurization process including the time required for denitrification can be greatly increased by omitting the denitrification before the start of the desulfurization process while utilizing the above-described features of the present invention. It can be shortened.

It is a graph which shows the relationship of S density | concentration (mass%) in hot metal before and after each desulfurization process of this invention example 1, this invention example 2, and a conventional example and a comparative example. The effect of improving the desulfurization rate exerted by the soda ash charging time (elapsed time from the start of the desulfurization process) during the desulfurization process in the present invention example 1 and the present invention example 2, the conventional example and the comparative example in which soda ash is not charged during the desulfurization process It is a graph shown by contrast.

  First, the hot metal discharged from the blast furnace or the hot metal pre-desiliconized or pre-dephosphorized hot metal (hereinafter simply referred to as “hot metal”) is transferred to the hot metal ladle, and the slag on the hot metal in the hot metal ladle is removed. After that, the hot metal is swirled and stirred by a mechanical stirring method using an impeller and the desulfurization process is started.

As the desulfurization agent, quick lime (CaO ≧ 90%) is mixed with soda ash (Na ₂ CO ₃ ≧ 99%) of less than 40% of its mass, and the maximum particle size is 5 mm or less. Before the desulfurization treatment is started by swirling the hot metal or in the initial stage of the treatment (within 1 minute from the start of swirl stirring), the entire amount is charged. This is because this desulfurizing agent is desired to contribute to the desulfurization reaction over the entire treatment period during the hot metal stirring.

  After the desulfurization agent has been charged onto the hot metal, the gas is exposed to the hot metal such as soda ash or limestone until 50% of the total treatment time has passed since the desulfurization process was started by turning the stirring blade. Put the generated material on the hot metal.

  This gas generating substance charging timing may be after the initial desulfurizing agent charging is completed, but the charging is performed until 30% or more of the scheduled processing time has elapsed and 50% of the desulfurizing processing time has elapsed. Is more effective.

It is not necessary to use a so-called top blowing lance or the like as the desulfurizing agent and gas generating substance charging means. For example, the desulfurizing agent and the gas generating substance may simply be dropped from the upper part of the container onto the hot metal or slag.
The removal of the blast furnace slag that has flowed into the hot metal ladle before the treatment is basically carried out to obtain a higher desulfurization rate, but if priority is given to shortening the time required for the desulfurization process, the removal is omitted. Reduce the time required for the entire desulfurization process, including the time required for removal before desulfurization.

  Here, the desulfurization rate is the ratio of the desulfurized sulfur concentration to the sulfur concentration in the hot metal before the desulfurization treatment.

Examples of the present invention will be described in comparison with conventional examples and comparative examples.
As a common implementation condition, hot metal 280-330 t discharged from the blast furnace was poured into a hot metal ladle and subjected to mechanical stirring type desulfurization treatment. For stirring, a stirring blade having four blades having a height of 500 mm and a width of 350 mm was used, and the hot metal components before treatment were [C] = 4.2 to 4.8% by mass, [Si] = 0. 30 to 0.60 mass%, [Mn] = 0.20 to 0.35 mass%, [P] = 0.100 to 0.120 mass%, [S] = 0.020 to 0.030 mass% The hot metal temperature before treatment was 1380 to 1430 ° C. The rotation speed of the stirring blade during the treatment was 120 rpm, and the desulfurization treatment time from the start of rotation to the end of rotation was 16 minutes.

  The amount of desulfurizing agent input is 5 kg per ton of hot metal fine lime having a maximum particle size of 5 mm or less, and the total amount of soda ash that is input as the initial input desulfurizing agent and the soda ash that is input as the gas generant is then calculated. Except for some examples, the unit was unified at 0.4 kg per ton of hot metal. The initial desulfurization agent and the gas generating material are both fine particles with a maximum particle size of 5 mm or less, and were introduced by dropping them onto the hot metal through a supply pipe extending directly from the bunker installed above the desulfurization equipment to the hot metal. .

Individual processing conditions and processing results are summarized in Table 1.
In Table 1, test no. 1 to 11 is Example 1 of the present invention, after removing the blast furnace slag brought into the hot metal ladle before the desulfurization treatment, and then adding a desulfurization agent containing soda ash to quick lime before starting the desulfurization treatment, Thereafter, soda ash was added during the desulfurization treatment.

  Among these, test No. No. 10 reduces the blending amount of soda ash in the desulfurizing agent to be introduced before the start of treatment to 0.1 kg per ton of hot metal (2% based on quick lime). 11 is also an example of 1.8 kg (36% with respect to quicklime).

Test No. Examples 12 to 16 are Example 2 of the present invention, in which the removal of the blast furnace slag brought into the hot metal ladle before the desulfurization treatment was omitted under the same conditions as Example 1 of the present invention.
Test No. Although 17-21 is a prior art example, after removing the blast furnace slag brought into the hot metal ladle before desulfurization processing, the desulfurization agent which mix | blended soda ash with quick lime is injected | thrown-in, In this example, the gas generating substance is not charged during the subsequent desulfurization treatment.

  Test No. 22 to 25 are comparative examples, omitting the removal of the blast furnace slag brought into the hot metal ladle before the desulfurization treatment, and adding a desulfurization agent containing soda ash to quick lime before starting the desulfurization treatment. In this example, the gas generating substance is not charged during the subsequent desulfurization treatment.

The results of Table 1 are collectively shown in FIG. 1 and FIG.
FIG. 1 is a graph showing the relationship between the S concentration in hot metal before and after the desulfurization treatment. As can be seen from this, when the present invention example 1 is compared with the conventional example at the same quick lime unit, soda ash blending ratio and treatment time, In Example 1 of the present invention, the value of S concentration in the hot metal after the desulfurization treatment was low, and all were 0.0010% by mass or less. Further, in the present invention example 2 in which the removal of the blast furnace slag was omitted, the value of the S concentration in the hot metal after the desulfurization treatment was higher than that in the present invention example 1 and the conventional example. In comparison, the value of the S concentration in the hot metal after the desulfurization treatment was low.

  FIG. 2 is a graph showing the desulfurization rate improvement effect exerted by the soda ash charging time during the desulfurization process (the elapsed time from the start of the desulfurization process). It can be seen that when the ash was added, the desulfurization rate was improved as compared with the conventional example and the comparative example in which soda ash was not added during the desulfurization treatment. This desulfurization rate improvement effect was particularly high at the time of 5 minutes after the start of the treatment (31% of the desulfurization treatment time has elapsed), so that 30% or more of the desulfurization treatment time has passed within the range of the conditions investigated this time. It can be said that charging at the time is preferable. In addition, this charging time has been confirmed until 7 minutes have elapsed since the start of the treatment (44% of the desulfurization treatment time has elapsed), and this soda ash charging effect is to promote the utilization of unreacted CaO by dispersing desulfurized slag during the treatment. For this reason, it is considered that this charging time is preferably until the point when 50% of the desulfurization treatment time has elapsed.

  In addition, in the present invention example 1, as a result of changing the blending amount of soda ash in the desulfurizing agent to be added before the start of treatment in the range of 2% to 36% with respect to quick lime, the desulfurization rate is also applied to the S concentration in the hot metal after the treatment. Even the effect of the change could not be confirmed.

  From these results, it was confirmed that when soda ash was introduced during the desulfurization treatment after the desulfurization agent was added, the desulfurization agent reaction efficiency was improved regardless of whether or not the desulfurization treatment was performed. Also, if the denitrification before desulfurization is omitted, the desulfurization agent reaction efficiency will be lower than when denitrification is performed, but even in this case, soda ash is not removed during the desulfurization process after the desulfurization agent is added. It was confirmed that the decrease in the reaction efficiency of the desulfurizing agent can be recovered to some extent by adding it. Therefore, if priority is to be given to the desulfurization efficiency even at the expense of the desulfurization agent reaction efficiency, the desulfurization process can be performed by omitting the desulfurization before starting the desulfurization process and introducing soda ash during the desulfurization process. It was found that the total desulfurization treatment efficiency can be improved.

Claims (2)

  When desulfurizing the hot metal using a mechanical stirring method, after removing the slag on the hot metal before the start of the desulfurization treatment, the lime is mixed with soda ash having a mass ratio of 2% or more and less than 40% to quick lime. The desulfurizing agent having a maximum particle size of less than 5 mm is added to the hot metal before the start of the desulfurization treatment or within 1 minute after the start of the desulfurization treatment, and after the addition of the desulfurization agent is completed, A method for desulfurizing hot metal, wherein a substance that generates gas upon contact with hot metal is added to the hot metal before 50% has elapsed.   The hot metal desulfurization method according to claim 1, wherein the hot metal upper slag removal prior to the start of the desulfurization treatment is omitted.

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