JP2001064715A - Desulfurizing agent for molten iron and using method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute excellent desulfurization at a low cost by including MgO, Al and CaO in a desulfurizing agent. SOLUTION: The addition of the desulfurizing agent containing MgO, Al and CaO can be executed before charging molten iron into a molten iron vessel or after charging the molten iron into the vessel. In the case of adding this agent before charging the molten iron, the molten iron and desulfurizing agent are stirred with the energy at the dropping time of the molten iron when the molten iron is received, and further, it is desirable to execute the gas stirring or mechanical stirring after receiving the molten iron. In the case of adding the desulfurizing agent after receiving the molten iron in the vessel, the gas stirring or the mechanical stirring is executed. In the composition of the desulfurizing agent, wt. ratio (MgO/CaO) is desirable to be 0.5-0.9. As the MgO source, electro-melting MgO product, waste MgO-C brick material, etc., can be used. As the Al source, metallic Al, Fe-Al alloy, etc., can be used. These raw materials can simultaneously or separately be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a desulfurizing agent for hot metal which is less expensive than the desulfurization method with Mg and which can obtain the [S] concentration in the hot metal after desulfurization comparable to the desulfurization method with Mg. And a method for desulfurizing hot metal.

[0002]

2. Description of the Related Art Desulfurization of hot metal is roughly classified into a mechanical stirring method in which a desulfurizing agent is added and a blowing stirring method in which a desulfurizing agent is blown.

The mechanical stirring method in which a desulfurizing agent is added is a method in which a stirring blade coated with a refractory is immersed in hot metal and rotated to mix and stir the hot metal and the desulfurizing agent to perform hot metal desulfurization treatment. .

In the method of blowing and stirring a desulfurizing agent, a lance covered with a refractory is immersed in hot metal, the desulfurizing agent is transported by a carrier gas, and the desulfurizing agent is blown into the hot metal from a nozzle provided near the tip of the lance. It is.

[0005] The desulfurizing agent to be used is usually a desulfurizing agent containing CaO, and CaO in the desulfurizing agent reacts with [S] in the hot metal as follows to perform the desulfurizing treatment of the hot metal. be able to. (CaO) + [S] = (CaS) + [O] (): In slag, []: In hot metal, respectively.

However, CaO has a melting point of about 2600 ° C., and at a hot metal temperature of 1300 ° C. to 1500 ° C., the desulfurizing agent containing only CaO is mostly solid, so that the desulfurization reaction rate cannot be increased. Was.

In order to avoid this problem, a method has been proposed in which metallic Mg is added to hot metal and hot metal desulfurization is performed by a reaction of [Mg] + [S] = (MgS). Metallic Mg has a melting point of 650 ° C. and a boiling point of 1107 ° C., and can be easily liquefied or vaporized even at the aforementioned hot metal temperature, exists as molten Mg or Mg bubbles in the hot metal, and increases the desulfurization reaction rate. Can be.

This Mg-added desulfurization method has a higher desulfurization rate than the technique using only CaO, and can reduce [S] in hot metal in a short time with a small amount of desulfurizing agent. Therefore,
The problem of lowering the hot metal temperature during processing is also small.

[0009]

However, since the metallic Mg used in the Mg-added desulfurization method is expensive, there is a problem that the processing cost is increased. An object of the present invention is to provide a desulfurizing agent for hot metal that is less expensive than the desulfurization method with Mg and that can obtain the [S] concentration in the hot metal after desulfurization treatment comparable to the desulfurization method with Mg, and desulfurization of hot metal. It is to provide a method.

[0010]

The present inventors have obtained the following findings. (A) As a desulfurizing agent, a desulfurizing agent composed of a mixture of MgO particles (melting point: 2800 ° C.) and Al particles was prepared by briquetting. This desulfurizing agent reduces the MgO content with metallic Al,
gO + 2Al = 3Mg + Al ₂ O ₃
The purpose is to generate steam artificially and perform desulfurization treatment using the generated Mg steam.

[0011] While stirring the hot metal accommodated in the ladle with nitrogen gas blown from a stirring injection lance,
This briquette was added from above the hot metal and a desulfurization treatment test was performed. As a result, the [S] concentration in the hot metal was 250 ppm
To 35 ppm.

On the other hand, a hot metal sample at the end of the desulfurization treatment was collected, and the composition of suspended inclusions was examined by an electron microscope. As a result, MgO.Al ₂ O ₃ was present on the outer periphery of the MgO particles. From the presence of MgO.Al ₂ O ₃ , it can be assumed that the actual reaction occurs according to the following reaction formula.

4MgO + 2Al = 3Mg (gas) + MgO.Al ₂ O ₃ (solid) (1) Mg (gas) + S = MgS (solid) (2) That is, in the above formula (1), MgO is reduced to Al,
The desulfurization reaction shown in the above (2) can be expected at the beginning due to the generation of Mg vapor.

However, around the MgO particles, MgO.Al
_Since a reaction product of ₂ O ₃ (solid) was formed, it was found that the desulfurization reaction was suppressed.

FIG. 1 is a conceptual diagram schematically showing a desulfurization reaction when a desulfurizing agent in which Al is mixed with MgO alone is used.

The melting point of MgO.Al ₂ O ₃ is 2135 ° C.
It is much higher than the hot metal temperature of 1400 ° C. for performing the desulfurization treatment, and the activity of MgO · Al ₂ O ₃ is
It is lower than MgO, and the reduction reaction by Al does not proceed.

Further, the Al particles are formed of MgO.Al ₂
To react with MgO inside O ₃ , solid M
Al needs to diffuse in gO.Al ₂ O ₃ , and Mg
It can be estimated that the reduction reaction between O particles and Al particles is also extremely slow.

(B) As a result of studying a mixture of MgO and Al ₂ O ₃ and an oxide species forming a low melting point compound,
O has been found to be suitable. That is, MgO, A
A test was performed using a desulfurizing agent to which CaO was added to the mixture of l ₂ O ₃ , a hot metal sample at the end of the desulfurization treatment was collected, and the composition of the suspended inclusions was investigated with an electron microscope.

As a result, the CaO-M
gO-Al ₂ O ₃ or _{CaO-MgO-Al 2 O 3} -
CaS was present. It has also been found that these desulfurization reaction products have a low melting point of about 1400 ° C.

From the above, it can be estimated that the reaction of desulfurization with CaO is constituted by the following reaction formulas (1) and (2). 4MgO + 2Al + CaO = 3Mg (gas) + CaO-
MgO—Al ₂ O ₃ (liquid) (1) Mg (gas) + S = MgS (solid) (2) As shown in the above formula (1), the addition of CaO results in a low melting point CaO—MgO—Al ₂ O ₃ Is generated. At the hot metal temperature at the time of hot metal desulfurization, the hot metal is liquid, and therefore easily flows out from the surface of the MgO particles, and a new surface of the MgO particles is likely to appear.

Therefore, the desulfurization reaction represented by the above formula (2) is
A new surface of MgO grains appears and can proceed continuously.
FIG. 2 is a conceptual diagram schematically showing a desulfurization reaction when a desulfurizing agent in which Al and CaO are mixed is used for MgO alone.

As shown in FIG. 1, a ternary system of CaO—MgO—Al ₂ O ₃ formed outside the MgO grains, or M
The quaternary low melting point compound (liquid) containing gS is Mg
It flows out from the surface of the O particles, a new surface of the MgO particles appears, and the desulfurization reaction proceeds again.

(C) Next, the weight ratio of MgO to CaO (MgO / C
aO) was changed, and the weight ratio (MgO / Ca) was determined.
The relationship between O) and the [S] concentration after the hot metal desulfurization treatment was investigated. [S] concentration before desulfurization treatment was fixed at 250 ppm.

FIG. 3 shows the weight ratio of the desulfurizing agent (MgO / Ca).
It is a graph which shows the relationship between O) and the [S] density | concentration in the hot metal after a desulfurization process. As shown in the figure, the weight ratio (MgO / C
When aO) is in the range of 0.5 to 9, the [S] concentration in the hot metal can be suppressed to a low concentration of 20 ppm or less.

The present invention has been made based on the above findings, and the gist is as follows. (1) A desulfurizing agent for hot metal containing MgO, Al and CaO. (2) The composition of the desulfurizing agent is a weight ratio (MgO / CaO),
The desulfurizing agent for hot metal according to the above (1), which is 0.5 to 9.0. (3) The hot metal desulfurizing agent according to the above (1) or (2),
A method for desulfurizing hot metal, comprising adding the hot metal into a hot metal container and stirring the desulfurizing agent and hot metal.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, desulfurization treatment is performed on hot metal carried from a blast furnace as it is or after performing hot metal treatment such as desiliconization and dephosphorization. The desulfurization treatment is carried out in a topped car for transporting hot metal, or in a hot metal container lined with bricks such as ladles or irregular refractories.

The addition of the desulfurizing agent containing MgO, Al and CaO may be performed before the hot metal is put in the hot metal container or after the hot metal is accommodated in the hot metal container. Furthermore, before adding the hot metal, it may be partially added into the hot metal container, and after storing the hot metal, the remaining portion may be added.

When adding a desulfurizing agent before adding hot metal,
The hot metal and the desulfurizing agent are stirred by energy at the time of falling of the hot metal when receiving the hot metal. It is desirable to further perform gas stirring or mechanical stirring after receiving the iron. When adding a desulfurizing agent to hot metal in the hot metal container after hot metal reception, gas stirring or mechanical stirring is performed.

The gas stirring includes a method in which an injection lance is immersed in hot metal and a powdery desulfurizing agent is injected into the hot metal using a carrier gas such as nitrogen gas or argon gas. In this case, the carrier gas plays the role of gas agitation, but the injection and the gas agitation or mechanical agitation may be used in combination to promote the desulfurization effect.

The MgO used is a fused MgO product, MgO
-C brick waste material can be used. Al is metal Al, F
An e-Al alloy or the like can be used. As CaO, quicklime, dolomite, or the like can be used.

The above raw materials may be added simultaneously or separately. Other components are Al ₂ O ₃ , N
a ₂ O or the like may be contained. The reason is that it acts as a low melting point accelerator.

[0032] SiO ₂ is not preferable because it deteriorates desulfurization. The particle size when the powder is blown into the hot metal using an injection lance is preferably from 20 to 1000 μm.

The reason is that if it is less than 20 μm, the lance may be clogged, and if it exceeds 1000 μm, the cross-sectional area of the reaction interface becomes small and there is a possibility that desulfurization may deteriorate.

When the desulfurizing agent is added to the hot metal container before the hot metal is charged, a massive or briquetted desulfurizing agent is desirable.

When a desulfurizing agent is added to hot metal in the hot metal container after receiving the hot metal, the desulfurizing agent may be a bulky or briquetted desulfurizing agent or a powdery desulfurizing agent.

[0036]

[Example] Hot metal ([S] concentration: 200) from a blast furnace
~ 300 ppm) was poured into a 250 ton topped car.
The topped car containing the hot metal was transported to a hot metal desulfurizer, and the hot metal in the topped car was discharged to a 250 ton ladle containing 5 kg / ton of desulfurizing agent (average particle size: 2 mm). After that, the impeller (diameter 1.3)
5 m, 4 blades) were immersed in the hot metal. The immersion depth at this time was 1.5 m. With impeller immersion, 120
Desulfurization treatment was performed for 10 minutes while rotating at a rotation speed of rpm.
After the desulfurization treatment, the rotation of the impeller was stopped, and the impeller was pulled up from the hot metal. Table 1 shows the test results.

[0037]

[Table 1]

The desulfurizing agent cost is as follows: The relative value was based on the desulfurizing agent cost under the condition of 1. Also, N
o. In the comparative example using the metal Mg of No. 10, the metal Mg was added by a wire.

As shown in Table 1, the desulfurizing agent was CaO alone,
Alternatively, in the comparative example of the mixture of CaO and Al, the [S] concentration after the treatment decreased only to 27 ppm. On the other hand, the desulfurizing agent of the present invention, in which MgO, Al and CaO are mixed, has a No. 1 content of 8 to 21 ppm. It decreased to the same level as the desulfurizing agent for metallic Mg of No. 10. Further, it was also found that the cost of the example of the present invention was extremely low as compared with the case of using metallic Mg.

[0040]

According to the present invention, it is possible to obtain the [S] concentration in the hot metal after desulfurization treatment which is less expensive than the Mg-added desulfurization method and comparable to the Mg-added desulfurization method.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram schematically showing a desulfurization reaction when a desulfurizing agent in which Al is mixed with MgO alone is used.

FIG. 2 is a conceptual diagram schematically showing a desulfurization reaction when a desulfurizing agent obtained by mixing Al and CaO is used for MgO alone.

FIG. 3 is a graph showing the relationship between the weight ratio of desulfurizing agent (MgO / CaO) and the [S] concentration in hot metal after desulfurization treatment.

Claims (3)

[Claims] 1. A desulfurizing agent for hot metal containing MgO, Al and CaO. 2. The composition of a desulfurizing agent having a weight ratio (MgO / Ca)
The desulfurizing agent for hot metal according to claim 1, wherein O) is 0.5 to 9.0. 3. A method for desulfurizing hot metal, comprising adding the hot metal desulfurizing agent according to claim 1 or 2 to a hot metal container and stirring the hot metal and the desulfurizing agent.