JP2003213313A - Method for desulfurizing molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a desulfurizing method of the molten iron with which high desulfurizing ratio can be achieved by promoting entrapment of desulfurizing agent into molten iron, by adding the desulfurizing agent into a vessel including the molten iron and by mechanical stirring using an impeller. <P>SOLUTION: In the method for applying the desulfurizing treatment by adding the desulfurizing agent into the molten iron in the vessel and stirring, it is desirable to add the desulfurizing agent in which CaO concentration in the desulfurized slag after this treatment, is ≥40 mass%, and the shape having ≥70% slag mass-ratio after this treatment, appears granular-state whose size is 3 to 20 mmϕ diameter expresed in terms of the sphere and specific gravity is ≥3.5, and further, the component is adjusted so that the liquid phase ratio at the treating temperature becomes 5 to 30%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hot metal desulfurization method capable of stably ensuring a high desulfurization rate.

[0002]

As a method for desulfurizing and refining hot metal, a desulfurizing and refining agent is added to the hot metal in a vessel and then stirred by blowing gas or mechanically to accelerate refining, or desulfurizing and refining with gas blown into the hot metal. A method of adding a chemical agent to perform refining is known. Among these, in the method of performing desulfurization refining by mechanically stirring the hot metal in the container, the desulfurization refining agent is added to the hot metal in the container, and the impeller equipped with the rotary blade at the tip of the rotating shaft is immersed in the hot metal. Then, the hot metal is stirred by rotating the impeller at a high speed. The desulfurization refining agent is present on the surface of the hot metal because it has a smaller specific gravity than that of the hot metal. Since the hot metal forms a rotating flow in the container as the impeller rotates, a depression is created in the center of the hot metal surface, and the desulfurization refining agent concentrates in this depression, and then the rotating blades of the impeller cause It is thought that the desulfurization and refining reaction proceeds until it is forcibly invaded into the hot metal and resurfaced by being repelled.

From such a point of view, the shape of the rotary vane which is advantageous for winding up the desulfurizing agent (for example, Japanese Patent Laid-Open No. 2000-24791).
No. 0) or a technique relating to the setting of the relative positional relationship between the rotary blades and the hot metal surface (for example, JP 2001-247910 A).
Japanese patent publication). But these technologies
Only disclosing the technology for making the inclusion of desulfurization slag advantageous, in view of the fact that the present inventors have obtained that the situation of the inclusion of slag greatly changes depending on the composition of the slag or the properties of the slag. However, these technologies alone do not provide sufficient conditions for obtaining high desulfurization ability.

On the other hand, as for the desulfurizing agent used for the desulfurization of molten pig iron out of the furnace, an inexpensive desulfurizing agent containing CaO as a main component is widely used because CaO is a component having an extremely high desulfurizing ability. There is. Further, a technique of utilizing a desulfurization reaction via Mg gas generated by adding metallic Mg is also disclosed. Specifically, the reaction represented by the formula (1) is used. Mg (gas) + [S] = MgS (1) Further, a method of obtaining this Mg gas having a desulfurizing effect in the middle of the treatment by coexisting a reducing agent of MgO and Al, for example, the reaction of the formula (2) is also disclosed. ing. 3MgO + 2Al = 3Mg (gas) + Al ₂ O ₃ (2)

However, the disclosed technology relating to the desulfurizing agent used for the desulfurization treatment of these hot metals lacks the viewpoint of the difficulty of being rolled into the hot metal, and only discusses the desulfurizing ability of the desulfurizing agent alone, Another viewpoint, which is extremely important in the case of only the desulfurization process by mechanical stirring using an impeller, was lacking. Therefore, even if a desulfurizing agent having a high desulfurizing ability is used alone, depending on its composition, in the desulfurization process by mechanical stirring using an impeller, the inclusion of the desulfurizing agent becomes insufficient in the first place due to insufficient incorporation into the hot metal. In some cases, the high desulfurization ability to be exhibited cannot be exhibited.

As described above, the prior art lacks the viewpoint that the behavior of the desulfurized slag being wound into the hot metal by the impeller changes depending on the composition of the slag and the properties of the slag. However, in the process of hot metal desulfurization by mechanical agitation using an impeller, even if the same impeller and the same agitation method are used, the slag entrainment situation changes greatly depending on the composition and properties of the slag,
There was an urgent need to find the conditions on the slag side that are advantageous for slag inclusion.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and specifies the conditions on the slag side where a desulfurizing agent is effectively wound into hot metal in mechanical stirring using an impeller, Therefore, the present invention provides a technique for stably producing an extremely high desulfurization rate.

[0008]

Means for Solving the Problems The present inventors have obtained the following findings as a result of earnest studies for achieving the above-mentioned object. That is, the hot metal desulfurization method in which the desulfurizing agent is effectively wound into the hot metal in the mechanical stirring using the impeller and the desulfurization reaction is caused extremely stably is as follows. (1) In a method of performing desulfurization treatment by adding a desulfurizing agent to hot metal in a hot metal container and stirring, the CaO concentration in the desulfurized slag after the treatment is 40% by mass or more, and the amount of the slag after the treatment. 70% or more of the shape has a sphere equivalent diameter of 3 mm
A method for desulfurizing hot metal, which is characterized by exhibiting a grain size of φ or more and 20 mmφ or less and having a specific gravity of 3.5 or more. (2) In a method of performing desulfurization treatment by adding a desulfurization agent to hot metal in a hot metal container and stirring, a desulfurization agent having a liquid phase ratio of 5% to 30% at a treatment temperature is used as the desulfurization agent to be added. A method for desulfurizing hot metal, characterized in that it is added.

[0009]

DETAILED DESCRIPTION OF THE INVENTION As a result of earnest research, the following has been found regarding the relationship between the degree of difficulty of winding desulfurized slag and the size of a desulfurizing agent. That is, when the size of the desulfurization agent is small, the impeller causes a large resistance immediately after the desulfurization slag jumps into the hot metal and has a large specific surface area.Furthermore, the repelling force given by the impeller is not effectively transmitted. The invasion distance to the hot metal becomes shorter and the staying time becomes shorter. As the size of the desulfurization slag increases, the resistance from the hot metal decreases due to the decrease in the specific surface area, and the force from the impeller is effectively transmitted to the desulfurization slag particles, and the penetration distance into the hot metal becomes longer. As the size of the desulfurization slag particles further increases, the penetration distance becomes longer, but the total surface area of the entire desulfurization agent used for the desulfurization reaction becomes smaller, and the desulfurization rate decreases. Therefore, there is an appropriate size in which the desulfurized slag is effectively rolled up in the hot metal.

In addition to the size of the desulfurized slag particles, the specific gravity also becomes important. The specific gravity referred to here is the bulk specific gravity of the granular desulfurization slag particles. If the specific gravity is too small, regardless of the size, the buoyancy given to the hot metal prevails and the penetration distance to the hot metal cannot be increased, so the specific gravity must be a certain value or more. come.

The inventors conducted a desulfurization experiment by mechanical stirring with a desulfurizing agent having various particle diameters and specific gravities using a test furnace having a melt weight of 1 ton. In order for desulfurization slag to be effectively wound into the hot metal and to cause the desulfurization reaction to occur very stably, the shape of the desulfurization slag after treatment should be 3 mmφ in terms of spherical equivalent diameter.
It has been found that it is necessary that the ratio of the total amount of slag to be 70% or more is that which has a granular shape with a size of 20 mmφ or less and a specific gravity of 3.5 or more.

As the desulfurizing agent in which the desulfurizing agent is effectively wound into the hot metal in the mechanical stirring using the impeller, a slag containing 40% or more of CaO is formed in advance so that the size and the specific gravity satisfy the above conditions. However, the method described below can be used to automatically obtain it by the granulation effect at the beginning of the mechanical stirring by the impeller. That is, as the desulfurizing agent to be added, the liquid phase rate at the processing temperature is 5% to 30%.
% Is to add a desulfurizing agent. Here, the treatment temperature refers to the pre-treatment temperature or the hot metal temperature at the start of the treatment, since the granulating action is mainly performed at the start of the treatment.

As described above, in the hot metal desulfurization process by mechanical stirring using an impeller, since the hot metal forms a rotary flow in the container as the impeller rotates, a depression is formed at the center of the hot metal surface and desulfurization occurs. Refining agent concentrates in this depression. At this stage, granulation according to the tumbling granulation theory occurs due to the presence of an appropriate amount of liquid in the high-melting-point solid desulfurizing agent mainly composed of CaO. In granulation based on the tumbling granulation theory, by adding an appropriate amount of water to a small-diameter solid powder and then rolling it, the solid powder is bound by the capillary suction force generated between the voids between the solid powder and the water. In the case of mechanical stirring with an impeller, it is the solid part of the CaO-based desulfurization agent to which solid powder is added, and the water content is the same as that obtained by melting the desulfurization agent itself. It is considered to be equivalent to the hot metal of the part. In fact, when observing the inside of the slag particles after the treatment when the desulfurization agent having a liquid phase ratio of 5% to 30% at the treatment temperature was observed, it was thought that the liquid phase was such that the space between the CaO powders was filled. The texture was observed, and at the same time, the iron was also incorporated. Thus, the slag particles containing base iron have a large specific gravity, and a specific gravity of 3.5 or more can be easily obtained, so that the slag particles are easily rolled into the hot metal by mechanical stirring.

[0014]

Example 1 A test smelting furnace capable of melting 0.75 tons of hot metal was subjected to a desulfurization test using a 1 / 7-similar model of desulfurization treatment in an actual hot metal ladle shown below. With mechanical stirring in the desulfurization process of the actual hot metal ladle, the diameter of the blade is 1415 mm for 250 tons of hot metal contained in the hot metal ladle.
Mechanical agitation is performed using a refractory-coated impeller for stirring having a four-blade structure having a length of 855 mm. At this time, the diameter of the rotating shaft is 600 mm. In the stirring impeller used at this time, the upper root radius is 300 mm, the lower root radius is 600 mm, the angle θ is 14 degrees, and no bulging portion is used. Further, the number of rotations was adjusted so that the ratio of the depth of the upper end of the impeller to the depth of the recessed portion of the hot metal surface during stirring was 0.7. In the desulfurization test using a 0.75 ton test melting furnace in this example, a hot metal ladle and an impeller for stirring, which have a shape quite similar to the desulfurization treatment in the above-mentioned actual machine and which is 1/7 in size, are used. I was there. Further, the number of revolutions and the immersion depth of the stirring impeller were adjusted so that the ratio of the upper end depth of the impeller to the depth of the hot metal surface concave portion during stirring was 0.7.

In the desulfurization test in the test melting furnace in this example, CaO powder and iron powder were mixed in a predetermined ratio in advance, compression-molded, and lightly crushed, and then classified and sized. Used as a desulfurizing agent. In the test, the density of the desulfurization agent particles was changed by changing the mixing ratio of CaO powder and iron powder while selecting the size of the classified desulfurization agent particles, and the S concentration in the hot metal before and after the desulfurization treatment for 12 minutes was changed. The suitability of the added desulfurizing agent was judged from the change. Here, the desulfurization rate is expressed as (before treatment [% S] -after treatment [% S]) / before treatment [% S]
X100, the desulfurization rate of 70% or more was regarded as "good desulfurization rate", and the adequacy of the added desulfurization agent was judged.

In FIG. 1, the specific gravity of the desulfurizing agent was changed from a desulfurizing agent having a specific gravity of 3.2 to 100% by mass of CaO to a desulfurizing agent having a mixing ratio of CaO having a specific gravity of 5.9 of 29% by mass, and at the same time, desulfurization was performed. The results of the desulfurization test when the agent size was changed from 1 mmφ to 40 mmφ are shown. The amount of desulfurizing agent used was 5.25 kg (ratio of 7 kg to 1 ton of hot metal)
Fixed to. That is, the larger the size of the desulfurizing agent, the smaller the total number of desulfurizing agent particles and the total surface area of the desulfurizing agent particles. The processing temperature is 1350 ° C ±
It was kept constant at 10 ° C. The desulfurizing agent was added all at once from above the hot metal container before the stirring treatment, and stirring was started immediately after the addition.
The particle size of the slag particles after the treatment was almost the same as the particle size of the desulfurizing agent particles at the time of addition.

From FIG. 1, regardless of the specific gravity of any slag particles, the desulfurization rate increases with an increase in the particle size of desulfurizing agent particles up to 10 mm mmφ, and conversely decreases as the particle size further increases. Further, when the slag grain size was the same, the desulfurization rate increased until the slag grain specific gravity reached 4.0, and conversely decreased when it exceeded. As a result, in the range where the desulfurization rate of 70% or more is obtained, the shape of the desulfurizing agent after the treatment is granular having a sphere-equivalent diameter of 3 mmφ or more and 20 mmφ or less, and a specific gravity of 3.0 or more. It was confirmed that it was 5.5 or less.

In this test, the specific gravity of slag particles was 5.
The condition of 5 or less is 4 as the CaO concentration in the slag.
It is 0 mass% or more, and the fact that a sufficient desulfurization rate cannot be obtained under the condition that the slag specific gravity exceeds 5.5 corresponds to that the CaO concentration falls below 40 mass% in that range.
This is because, when trying to contain a component having a higher specific gravity than CaO in order to increase the slag specific gravity, if the CaO content is not set to 40% by mass or more, the entrainment can be sufficiently caused, It shows that the high desulfurization ability of CaO cannot be fully exhibited.

Therefore, from this test, Ca in the slag particles was
It was confirmed that the O content was 40% by mass or more as a necessary condition. CaO with a larger specific gravity than iron powder
When mixed with slag to form slag particles, the upper limit of the specific gravity can be set higher than 5.5, but it is clear that the CaO content must be 40% by mass or more in that case as well. Is. Furthermore, the upper limit of the specific gravity of the slag particles should be lower than that of the hot metal, regardless of what is mixed. This is because when the specific gravity of the slag particles is higher than that of the hot metal, the slag particles settle or are suspended in the hot metal and are not easily separated.

(Example 2) Using the actual desulfurization equipment of 250 tons of treated hot metal and stirring conditions shown in Example 1, CaO powder having an average diameter of 100 μmφ was mixed with various additives shown in Table 1 for desulfurization agent. The desulfurization test was conducted. The amount of desulfurization agent added was constant at 7 kg per ton of hot metal, the temperature was between 1300 ° C. and 1400 ° C., and the treatment time was 12 minutes. In addition, Mg which is an additive other than CaO
O, Al ₂ O ₃ , SiO ₂ , and CaF ₂ are powders each having an average particle size of 100 μmφ, and C according to the compounding ratio shown in Table 1.
It was physically mixed with aO powder in advance with a mixer. The mixed powder thus prepared was added as a desulfurizing agent from above the hot metal ladle, and immediately after the addition, stirring was performed by an impeller.

Table 1 shows the desulfurization rate obtained as a result of the test, the treatment temperature, the liquid phase rate of the desulfurizing agent used, the average particle diameter of the slag particles after the treatment, and the number of particles having a particle diameter of 3 mmφ or more and 20 mmφ or less. The ratio, the average specific gravity of the slag particles, and the composition of the treated slag particles are shown. Among these, as for the desulfurization rate, as in Example 1, those having a desulfurization rate of 70% or more were “good desulfurization rate”.
The suitability of the added desulfurization agent was judged as. After the treatment, in most cases, the treated hot metal was in the form of granules, and the particle size and the specific gravity were measured as follows. First, 50 slag particles are arbitrarily sampled, and the volume and mass of each are measured. The diameter of a sphere having the same volume can be obtained by using the actual measurement value of the volume, and this was obtained as the sphere equivalent diameter. The specific gravity was calculated by the formula of (mass: gram) / (volume: cubic cm). The slag composition after treatment is the same as slag particles 5
Zero slag particles were sampled, made into a powder form in a mortar without distinguishing individual slag particles, and the iron content was separated by magnetic separation, and the mass% of the iron content was first determined. Furthermore, for the remaining slag powder, the CaO content concentration was determined by chemical analysis. Here, after resin embedding and polishing in advance, the composition analysis of individual slag particles was performed by SEM / EDX analysis. It was confirmed that the composition was the same as the composition in the slag particles. Further, the liquid phase rate was calculated and evaluated by the following method.

In order to obtain the liquid phase ratio of the mixture of oxide and fluoride at high temperature, it is necessary to calculate the equilibrium state of the liquid phase and the solid phase of the multi-component system. Here, reference document 1
(Yamada et al., Molten salt and high temperature chemistry, Vol 41, N
o. 2, 1998) at page 107. An equilibrium calculation between the liquid phase and the solid phase of the above mixture of oxide and fluoride was performed using the calculation method shown in FIG. Here, standard free energy values and activity values of liquid phase and solid phase components are required as data to be input to the equilibrium calculation program. This internal standard free energy value is given in Reference 2 (H. Gaye
and J. Welfringer: Proceedings of "2 ^nd Internatio
nal Symposium on Metallurgical Slags andFluxes ",
Warrendale, PAMet. Soc. Of AIME, Ed. By HAFine
and DR Gaskell, 1984, 357) were used as they were. The activity value was handled as follows. That is, all solid phases were assumed to be pure oxides (or fluorides) or oxide compounds, and the activity value of the component oxides (or fluorides) was fixed at 1. Also, the component activity in the liquid phase is 1 of Reference 1
The free energy of mixing was first obtained by the equation (4) on page 02, and the activity value was derived by using the equation (7) on page 103. In addition, various interaction parameter values (physical property values) in the equation (4) are described in Reference Document 3 (H. Gaye, et.al.:Procee
^{dings of "4 th International Conference on} Molten
Slags and Fluxes ", 1992, Sendai, ISIJ), the value of Table 2 on page 108 was used as it was.

By the above method, the quantitative ratio of the liquid phase at the treatment temperature, the equilibrium precipitation amount of the solid phase and the type of the precipitated solid phase can be obtained by inputting the treatment temperature and the desulfurizing agent composition. The liquid phase rate shown in Table 1 is obtained in this way, and is (mass of liquid phase in desulfurization) / (mass of desulfurization agent) × 1
It is defined by 00 (%).

In Table 1, Nos. 1 to 10 are examples showing that stable high desulfurization ability was obtained by the method of the present invention. In both cases, the liquid phase ratio of the added desulfurization agent at the treatment temperature is in the range of 5% to 30%, but at this time, the size of the treated slag particles is 70% from 3 mmφ to 20 mmφ.
The specific gravity is 3.5 or more by being included in the above range and further containing the base iron in the slag particles. The CaO concentration of the treated slag particles containing base iron was 40% by mass or more. That is, in the desulfurization treatment in which mechanical stirring is performed by a stirring impeller in a hot metal container, the composition of the desulfurizing agent to be added has a liquid phase ratio of 5% or more at a treatment temperature of 3% or more.
It was confirmed that by adjusting the content to be in the range of 0% or less, the size and the specific gravity are easily rolled up in the hot metal due to the rolling granulation action during the stirring process, and thus a stable high desulfurization ability can be obtained. did it.

No. 11 to No. 16 are comparative examples when the liquid phase ratio is lower than 5% or exceeds 30%. When it is lower than 5%, the granulation is insufficient and the slag particles are Small diameter,
Furthermore, the increase in specific gravity due to the incorporation of base iron during granulation was also insufficient, and entrainment into the hot metal did not occur effectively, so high desulfurization capacity was not obtained. Also, the liquid phase rate is 30%
On the contrary, if it exceeds, the slag particles will grow too large,
It can be seen that the high desulfurization ability could not be obtained because the total surface area of the slag particles became small.

No. 17 and No. 18 are adjusted so that the liquid phase ratio of the added desulfurizing agent is in the range of 5% or more and 30% or less, and the granulation is performed properly, but the slag particles are C in
A comparative example in which a high desulfurization rate was not obtained because the aO concentration was lower than 40 mass% is shown.

[0027]

[Table 1]

[0028]

According to the method of hot metal desulfurization in the mechanical stirring process using the impeller according to the present invention, by adjusting the size and the specific gravity of the desulfurized slag, the inclusion of the added slag into the hot metal is promoted and stable. It is possible to obtain high desulfurization ability.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a desulfurization agent particle size and specific gravity and a desulfurization rate.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Anjo             1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel shares             Company Kimitsu Works (72) Inventor Masahiro Toki             1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel shares             Company Kimitsu Works F-term (reference) 4K014 AA02 AB03 AC08 AD00

Claims (2)

[Claims] 1. A method of performing desulfurization treatment by adding a desulfurizing agent to hot metal in a hot metal container and stirring, wherein the CaO concentration in the desulfurized slag after the treatment is 40% by mass or more,
In addition, 70% or more of the amount ratio of the treated slag is in the form of particles having a sphere-equivalent diameter of 3 mmφ or more and 20 mmφ or less, and the specific gravity is 3.5 or more. Desulfurization method. 2. A method of performing desulfurization treatment by adding a desulfurization agent to hot metal in a hot metal container and stirring the mixture, wherein the desulfurization agent has a liquid phase ratio of 5% to 30% at a processing temperature. A method for desulfurizing hot metal, which comprises adding an agent.