JP2019189893A - Method for desulfurizing molten iron - Google Patents

Abstract

To desulfurize molten iron in a mechanical stirring method using a desulfurizing agent containing CaO as a main component, an alumina source having no or extremely little fluorine is used instead of aluminum dross for lowering the melting point of CaO, and the desulfurizing treatment is carried out without using a fluorine raw material.SOLUTION: In the method for desulfurizing molten iron according to the present invention, molten iron 3 is desulfurized by a mechanical stirring method. In the desulfurizing treatment, quick lime and a raw material containing alumina having 0.05-9 mass% of metallic Al are added to molten iron, and the molten iron is desulfurized without using a fluorine raw material. As the raw material containing alumina, it is preferable to use one or more kinds of a band shale, slag floating on molten steel in a tundish for continuous casting, and a waste flame resistant to AlOgenerated in an iron mill.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for desulfurizing hot metal by a mechanical stirring type desulfurization method using a desulfurization agent containing CaO (calcium oxide) as a main component and not containing fluorine.

  Since sulfur in steel significantly deteriorates the mechanical properties of the steel material, desulfurization is performed at a hot metal stage with high desulfurization reaction efficiency for the purpose of reducing the sulfur content in the steel. This desulfurization treatment is performed using a gas agitation method by blowing an inert gas such as argon gas, or a mechanical agitation method using an impeller (also called “rotary blade” or “rotary blade”). In general, the method is performed by adding. In particular, since a high desulfurization efficiency can be obtained even when an inexpensive desulfurization agent mainly composed of CaO is used, in recent years, a mechanical stirring type desulfurization method using an impeller has become mainstream. Note that a mechanical stirring type desulfurization method using an impeller is referred to as a mechanical stirring type desulfurization method. In addition, quick lime is generally used as a raw material for CaO serving as a desulfurizing agent.

In the mechanical stirring desulfurization method using CaO as a desulfurization agent, since the desulfurization reaction does not proceed unless CaO is hatched, conventionally calcium fluoride (CaF ₂ ; also called fluorite) having a function of lowering the melting point of CaO has been used. It has been widely used (see, for example, Patent Document 1).

  However, since the elution of fluorine from the generated slag after desulfurization treatment (referred to as “desulfurization slag”) has an adverse effect on the environment, soil environmental standards have been set for the amount of elution of fluorine from desulfurization slag. There is a need for a desulfurization method that does not use calcium fluoride, and many proposals have been made.

For example, Patent Document 2 discloses a desulfurization agent containing iron oxide, CaO, Al ₂ O ₃ and metal aluminum (hereinafter referred to as “metal Al”). 0.5 to 20% by mass of Fe, and metallic Al There has been proposed a desulfurization agent for molten steel containing 0.2 times or more of Fe and containing iron oxide, metal Al, CaO, and Al ₂ O ₃ within a predetermined range.

Patent Document 3 discloses a desulfurization agent containing CaO, SiO ₂ and metal Al, wherein the mass ratio of CaO / SiO ₂ is 1.5 to 3.5, and metal Al is the sum of CaO and SiO ₂ . A hot metal desulfurization agent having a mass of 3 to 15% by mass has been proposed.

In Patent Document 4, by mass ratio, with respect to CaO1, Al ₂ O ₃ min is 0.30 to 0.80, Na ₂ O content is 0.04 to 0.35, and SiO ₂ content is 0.05 to 0. .30, with MgO content from 0.05 to 0.44, further, to MgO1, with Na ₂ O content from 0.50 to 3.00, and, by _{mass%, CaO, Al 2 O 3} , Na 2 There has been proposed a hot metal desulfurization agent in which the total of O, SiO ₂ and MgO is 90% or more and the balance is an inevitable impurity.

The desulfurization agents proposed in Patent Documents 2 to 4 are obtained by reacting CaO with Al ₂ O ₃ produced by oxidation of added Al ₂ O ₃ or metal Al, thereby producing a low melting point CaO—Al ₂ O. _This is a technique of generating _three compounds and hatching CaO. Moreover, the desulfurization reaction of hot metal is a reduction reaction, and the desulfurization reaction is accelerated as the oxygen potential of the atmosphere is lowered. The metal Al in the desulfurizing agent plays the role, and even when the metal Al is not contained in the desulfurizing agent, the metal Al is generally added during the desulfurization treatment of the hot metal.

JP-A-56-142833 JP 2004-204307 A JP 2000-313911 A JP 2012-82513 A

As described above, when the hot metal is desulfurized with a desulfurizing agent mainly composed of CaO without using calcium fluoride, a raw material containing Al ₂ O ₃ (referred to as “alumina source”) or a metal Al is generally used.

By the way, as an alumina source containing both Al ₂ O ₃ and metal Al, aluminum dross generated as a by-product when aluminum metal such as aluminum sash, gates, fences, ladders, etc. Also known as “aluminum”. Since Almidros has a low unit price per pure metal Al, aluminum dross is widely used as an alumina source containing metal Al in hot metal desulfurization. However, when calcium fluoride is not used as a desulfurization agent, in order to lower the melting point of CaO with Al ₂ O _3, it is necessary to input a large amount of aluminum dross during the desulfurization treatment of hot metal.

  Calcium fluoride is used when aluminum metal is regenerated and dissolved, and therefore aluminum dross contains fluorine. That is, if a large amount of aluminum dross is used during the desulfurization treatment of hot metal, the amount of fluorine eluted from the desulfurization slag may exceed the soil environment standard.

That is, in order to lower the melting point of CaO with Al ₂ O ₃ and to keep the amount of fluorine eluted from the desulfurized slag within the soil environmental standard value, it is necessary to secure aluminum dross with a low fluorine concentration. Depending on the amount of dross supplied, it was difficult to efficiently desulfurize hot metal at a low production cost.

  The present invention has been made in view of the above circumstances, and the object thereof is to lower the melting point of CaO when desulfurizing hot metal by a mechanical stirring type desulfurization method using a desulfurization agent mainly composed of CaO. Instead of alumidos, an alumina source that does not contain fluorine or has a very low fluorine content is used, and no fluorine raw material is used. An object of the present invention is to provide a hot metal desulfurization method that does not exceed the above.

The gist of the present invention for solving the above problems is as follows.
[1] In a hot metal desulfurization method in which hot metal is desulfurized by a mechanical stirring desulfurization method, an alumina-containing raw material containing 0.05 to 9% by mass of metal Al and quick lime are added to the hot metal, and a fluorine raw material is used. A method for desulfurizing hot metal, characterized in that the hot metal is desulfurized.
[2] The hot metal desulfurization method according to [1], wherein a mixture obtained by mixing the alumina-containing raw material and the quicklime in advance is added to the hot metal.
[3] The alumina-containing raw material is one or more of band shale, slag floating on the molten steel in the continuous casting tundish, and Al ₂ O ₃ -containing waste refractory generated at the steelworks The hot metal desulfurization treatment method according to the above [1] or [2], wherein the hot metal is desulfurized.

  According to the present invention, instead of aluminum dross responsible for lowering the melting point of CaO, an alumina-containing raw material containing 0.05 to 9% by mass of metal Al is used in the generation process. In addition, since the hot metal is desulfurized without using a fluorine raw material, it is possible to stably suppress the elution amount of fluorine from the desulfurized slag to less than the soil environmental standard. Moreover, since the alumina-containing raw material containing 0.05 to 9% by mass of metal Al does not use fluorine in the generation process, even if the amount used is increased, the pickup of fluorine from the alumina-containing raw material does not occur, Furthermore, since the alumina-containing raw material can be used in a large amount, for example, band shale, which is a refractory raw material, the supply amount of the alumina-containing raw material affects the stability of hot metal desulfurization treatment. The problem is avoided.

It is a schematic sectional side view of the mechanical stirring desulfurization apparatus used when implementing the hot metal desulfurization processing method according to the present invention. It is a figure which shows the relationship between the sulfur content of the hot metal before a desulfurization process, and the utilization efficiency of CaO in the desulfurization agent after a desulfurization process. It is a figure which shows the investigation result of the elution amount of the fluorine from desulfurization slag. It is a figure which shows the relationship between the basic unit of a desulfurization agent, and desulfurization amount (DELTA) S when the alumina source of a desulfurization agent is changed.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic side sectional view of a mechanical stirring desulfurization apparatus used when carrying out the hot metal desulfurization method according to the present invention. In FIG. 1, a ladle type hot metal ladle is used as a processing container for containing hot metal. An example using is shown. As for the shape of the processing vessel, since ladle is swirled and stirred by a mechanical stirring type desulfurization apparatus, a ladle type processing vessel having a circular horizontal cross section as shown in FIG. 1 is optimal. It can also be used in cars. Hereinafter, an example in which a hot metal ladle is used as the processing container will be described.

The hot metal 3 discharged from the blast furnace is received by the hot metal ladle 2 mounted on the carriage 1, and the received hot metal 3 is conveyed to a mechanical stirring desulfurization apparatus. When the hot metal ladle 2 is received by a kneading vehicle, it is desirable to transfer the hot metal 3 to a ladle type processing container prior to the desulfurization process. The hot metal 3 to be subjected to the desulfurization treatment according to the present invention may be any component, and for example, desiliconization treatment or dephosphorization treatment may be performed in advance. The desiliconization process is a process for removing mainly silicon (Si) in the hot metal by adding an oxygen source such as oxygen gas or iron ore to the hot metal 3 prior to the dephosphorization process in order to efficiently perform the dephosphorization process. In the dephosphorization treatment, an oxygen source such as oxygen gas or iron ore is added to the hot metal 3 and quick lime is added as a dephosphorization flux for absorbing the generated P ₂ O _5. In this process, phosphorus (P) in the hot metal is removed.

  As shown in FIG. 1, the mechanical stirring type desulfurization apparatus includes a refractory impeller 4 for immersing and burying in a hot metal 3 accommodated in a hot metal ladle 2 and rotating to stir the hot metal 3. The impeller 4 is configured to move up and down in a substantially vertical direction by an elevating device (not shown) and to turn around a shaft 4a as a rotating shaft by a rotating device (not shown).

  The mechanical stirring type desulfurization apparatus includes a chute 5 for charging a powder or granular desulfurization agent 6 to the bath surface of the hot metal 3 accommodated in the hot metal pan 2. Above the chute 5, a plurality of hoppers (not shown) that contain raw materials such as a desulfurizing agent 6, quicklime, alumina-containing raw material, metal Al, Al dross, carbonaceous material, and heat insulating agent are provided. Each accommodated raw material can be independently supplied into the hot metal ladle 2 through the chute 5 at an arbitrary timing.

In the hot metal desulfurization method according to the present invention, an alumina-containing raw material containing 0.05 to 9% by mass of metal Al is used as the alumina source of the desulfurizing agent, quick lime (CaO pure content: 90% by mass or more), metal An alumina-containing raw material containing 0.05 to 9% by mass of Al is used as the desulfurizing agent 6. An alumina-containing raw material containing 0.05 to 9% by mass of metal Al (hereinafter simply referred to as “alumina-containing raw material”) used as the desulfurizing agent 6 floats on the molten steel in the band shale and the tundish for continuous casting. it is preferred to have the slag, it is one or more of Al ₂ O ₃ containing waste refractory generated in steelworks.

Band shale is a mineral mainly composed of diaspor (β-Al ₂ O ₃ .H ₂ O), and is produced in Japan, but is a mineral with a large output in China and the Korean Peninsula. In addition, slag floating on the molten steel in the continuous casting tundish means that the molten steel deoxidized with metal Al is cast in the tundish, which is a relay container from the ladle to the mold when casting with a continuous casting machine. The slag generated in the above (hereinafter referred to as “slag in the tundish”). Also, the waste refractories containing Al ₂ O ₃ generated at steelworks include used tundish work bricks for continuous casting, refractories for immersion lances such as ladle refining, work bricks for hot metal ladle and molten steel pan The refractory material of the nozzle part or the plate part of the sliding nozzle for a molten steel pan can be used. Table 1 shows an example of component analysis values of the band shale and the tundish slag, and the component range of the Al ₂ O ₃ -containing waste refractory.

Band shale is a mineral containing at least 0.05% by mass to 7% by mass of metal Al and having Al ₂ O ₃ as a main component, and the tundish slag is 0.05% by mass to 9% by mass. The slag contains the following metal Al, the main component is Al ₂ O _3, and CaO, SiO ₂ , and MgO. The Al ₂ O ₃ -containing waste refractory is a used refractory containing 0.05% by mass or more and 9% by mass or less of metal Al and containing at least 10% by mass of Al ₂ O ₃ . Among these alumina-containing raw materials, the fluorine content is the highest in Al ₂ O ₃ -containing waste refractories, but it is still 0.50% by mass or less.

In this invention, when using quicklime and an alumina containing raw material as the desulfurization agent 6, quicklime and an alumina containing raw material are mixed beforehand, this mixture is accommodated in a hopper, it cuts out from a hopper, The chute 5 is passed through. The hot metal lime and the alumina-containing raw material may be stored in separate hoppers, and a fixed amount may be cut out from each hopper and simultaneously fed through the chute 5. Good. The quicklime and alumina-containing raw material used as the desulfurizing agent 6 has a particle size of preferably 1.0 mm or less, more preferably 0.05 mm or less, since the desulfurization reaction is promoted as the particle size decreases. To do. However, since the waste refractory containing Al ₂ O ₃ has various sizes and shapes, it may require a large amount of cost for pre-fractionation and refining by crushing, so the upper limit of particle size is 13.0 mm or less. May be relaxed.

Quick lime and a mass ratio of Al ₂ O ₃ in the desulfurization agent 6 so that the mass ratio (mass% Al ₂ O ₃ / (mass% Al ₂ O ₃ + mass% CaO)) is in the range of 0.05 to 0.30. It is preferable to adjust the mixing amount or blending amount of the alumina-containing raw material. When the mass ratio of Al ₂ O ₃ is less than 0.05, there is little influence of the melting point of CaO due to Al ₂ O ₃ and the hatching of CaO is not sufficient, while the mass ratio of Al ₂ O ₃ is 0.30. This is because the mass ratio of CaO in the desulfurization agent, that is, the activity of CaO is lowered, and desulfurization of the hot metal 3 is inhibited.

  Further, an exhaust duct (not shown) connected to a dust collector (not shown) is provided above the hot metal ladle 2 so that gas and dust generated during the desulfurization process are discharged. .

  The position of the carriage 1 on which the hot metal ladle 2 is mounted is adjusted so that the position of the impeller 4 is substantially at the center of the hot metal ladle 2, and then the impeller 4 is lowered and immersed in the hot metal 3. If the impeller 4 is immersed in the hot metal 3, the impeller 4 starts to turn and the speed is increased to a predetermined rotational speed. When the rotation speed of the impeller 4 reaches a predetermined rotation speed, the desulfurization agent 6 prepared by mixing quick lime and the alumina-containing raw material in advance via the chute 5 or the quick lime and the alumina-containing raw material are respectively quantified. The desulfurizing agent 6 produced by cutting is put into the hot metal bath surface through the chute 5. The hot metal 3 stirred by the impeller 4 entrains the introduced desulfurizing agent 6, and the desulfurization reaction (CaO + [S] → (CaS) + [O]) of the sulfur (S) in the hot metal with CaO in the desulfurizing agent is performed. The hot metal 3 is desulfurized by the mechanical stirring desulfurization method. Here, [S] represents sulfur in the hot metal, (CaS) represents CaS in the slag, and [O] represents oxygen in the hot metal.

  Even after the introduction of the predetermined amount of the desulfurizing agent 6 is completed, if the impeller 4 is swung to continue the desulfurization process and the stirring is performed for a predetermined time, the rotation speed of the impeller 4 is decreased and stopped. If the turning of the impeller 4 is stopped, the impeller 4 is raised and waited above the hot metal ladle 2. The generated desulfurization slag (not shown) floats and covers the hot metal surface, and the desulfurization process of the hot metal 3 is completed in a stationary state. After the desulfurization treatment is completed, the generated desulfurization slag is discharged from the hot metal ladle 2 and conveyed to the next refining process.

  From the start to the end of the desulfurization treatment, fluorine raw materials such as calcium fluoride are not used as a refining agent including the desulfurization agent. Here, the fluorine raw material is calcium fluoride, sodium fluoride, potassium fluoride, magnesium fluoride or the like, and is a compound of fluorine and an alkali metal, and a compound of fluorine, an alkaline earth metal and magnesium. .

  As described above, according to the present invention, instead of aluminum dross responsible for lowering the melting point of CaO, an alumina-containing raw material containing 0.05 to 9% by mass of metal Al in the generation process is used. Since the hot metal 3 is added to the hot metal 3 and the hot metal 3 is desulfurized without using a fluorine raw material, it is possible to stably suppress the amount of fluorine eluted from the desulfurized slag to less than the soil environment standard.

  In addition, since the alumina-containing raw material containing 0.05 to 9% by mass of metal does not use fluorine in the generation process, the alumina whose fluorine content is 0.50% by mass or less even if the amount used is increased. The amount of fluorine pick-up from the contained material is low, and the amount of generated alumina, such as band shale, which is a refractory material, can be used as the alumina-containing material. The problem that the stability of the desulfurization treatment is affected is avoided.

  In addition, this invention is not limited to said description range, A various change is possible. For example, although the ladle type hot metal ladle 2 is used as the refining container in the above description, the present invention can be implemented in the same manner as in a kneading vehicle.

  Using the mechanical stirring desulfurization apparatus shown in FIG. 1, aluminum dross, tundish inner slag, and band shale having a particle size of 1.0 mm or less are used as the alumina source, and these are respectively converted to quick lime (CaO pure; 93% by mass) to obtain a desulfurization agent, and a hot metal desulfurization treatment test was conducted. In this desulfurization treatment test, a fluorine raw material such as calcium fluoride was not used.

In all tests, the target value of the mass ratio of Al ₂ O ₃ in the desulfurization agent (mass% Al ₂ O ₃ / (mass% Al ₂ O ₃ + mass% CaO)) was set to 0.20, and quicklime and aluminum dross The amount of slag in the tundish and the band shale were adjusted. Tundish slag and bands shale used was a chemical composition shown in Table 1, aluminum dross used was 25% by weight content of the metal Al, with the content of Al ₂ O ₃ is 55 wt%, the fluorine Is aluminum dross containing 2.40% by mass.

Table 2 shows the mass ratio of _Al 2 _{O 3} calculated from component analysis value of the desulfurization slag recovered after desulfurization treatment _(mass% Al _{2 O} 3 / (mass% _Al 2 _{O 3} + wt% CaO)).

  FIG. 2 shows the relationship between the sulfur content of the hot metal before the desulfurization treatment and the utilization efficiency of CaO in the desulfurization agent after the desulfurization treatment. Here, the utilization efficiency of CaO in the desulfurizing agent means that the sulfur in the desulfurized hot metal reacts with CaO in the desulfurizing agent to become CaS, and that CaO added as a desulfurizing agent has a mass of CaS produced. It is a mass ratio (percentage) to mass. As shown in FIG. 2, the utilization efficiency of CaO in the desulfurizing agent was the same regardless of the type of alumina source.

  In the test using tundish slag and band shale as the alumina source, the elution amount of fluorine from the desulfurized slag was investigated. The survey results are shown in FIG. As is apparent from FIG. 3, in the test using tundish slag and band shale as the alumina source, the amount of fluorine eluted from the desulfurized slag satisfies the soil environmental standard (0.8 mg / L or less). It was. Note that the input fluorine amount on the horizontal axis in FIG. 3 is the product of the desulfurizing agent basic unit (kg / molten iron-t) and the desulfurizing agent fluorine mass ratio (= mass% / 100).

Moreover, using the mechanical stirring type desulfurization apparatus shown in FIG. 1, as an alumina source, Al ₂ O ₃ -containing waste refractory having a particle size of 5.0 mm or less, and Al having a particle size of more than 5.0 mm and 13.0 mm A test was conducted to compare the desulfurization reaction efficiency when using ₂ O ₃ -containing waste refractories and using aluminum dross having a particle size of 1.0 mm or less as the alumina source. In the test, the Al ₂ O ₃ -containing waste refractory and aluminum dross were each preliminarily mixed with quick lime (CaO pure content: 93% by mass) to obtain a desulfurization agent. Moreover, it tested without using fluorine raw materials, such as a calcium fluoride.

Also in this test, the target value of the mass ratio of Al ₂ O ₃ in the desulfurization agent (mass% Al ₂ O ₃ / (mass% Al ₂ O ₃ + mass% CaO)) is set to 0.20, and the blending amount of each raw material Adjusted. The used Al ₂ O ₃ -containing waste refractory is an alumina refractory having a metal Al content of 6% by mass, an Al ₂ O ₃ content of 85% by mass, and a fluorine content of 0.20% by mass, The aluminum dross used is an aluminum dross containing 25% by mass of metal Al, 55% by mass of Al ₂ O ₃ and 2.40% by mass of fluorine, as described above.

In FIG. 4, the abscissa represents the desulfurization unit, and the ordinate represents the desulfurization amount ΔS, that is, the difference between the sulfur concentration in the hot metal before the desulfurization treatment and the sulfur concentration in the hot metal after the desulfurization treatment. And the desulfurization amount ΔS. As shown in FIG. 4, as an alumina source, in the case of using the case of using the aluminum dross and Al ₂ O ₃ containing waste refractories, a difference in the desulfurization amount ΔS is not, the Al ₂ O ₃ containing waste refractories It was confirmed that it could be used as an alumina source for the desulfurization agent.

Although changing the grain size of the _Al 2 _{O 3} containing waste _{refractories,} a difference in the desulfurization amount ΔS by the particle size of the Al 2 _{O 3} containing waste refractories is not observed, the _Al 2 _{O 3} containing waste refractories If the particle size was 13.0 mm or less, it was confirmed that desulfurization treatment was possible while maintaining high desulfurization efficiency.

1 cart 2 hot metal ladle 3 hot metal 4 impeller 5 chute 6 desulfurizing agent

Claims (3)

  In the hot metal desulfurization treatment method in which hot metal is desulfurized by a mechanical stirring type desulfurization method, an alumina-containing raw material containing 0.05 to 9% by mass of metal Al and quick lime are added to the hot metal, and the hot metal is not used. A desulfurization treatment method for hot metal, characterized by desulfurization treatment.   2. The hot metal desulfurization method according to claim 1, wherein a mixture obtained by previously mixing the alumina-containing raw material and the quicklime is added to the hot metal. The alumina-containing raw material is one or more of band shale, slag floating on the molten steel in the tundish for continuous casting, and Al ₂ O ₃ -containing waste refractory generated at a steelworks The hot metal desulfurization treatment method according to claim 1 or 2, characterized in that:

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