KR101366720B1 - Method of desulfurization of molten iron - Google Patents

Abstract

Desulfurization method of hot metal using the mechanical stirring type desulfurization apparatus provided with the stirring blade WHEREIN: The lime system desulfurization agent whose particle diameter is 30-400 micrometers on the bath surface of the molten iron stirred by the stirring blade. By carrying out the desulfurization treatment by carrying out the desulfurization treatment with the gas for conveyance through a top lance, the desulfurization agent can be added with a high addition yield, and the aggregation of the added desulfurization agent can be prevented, accordingly It enables stable and high efficiency desulfurization.

Description

Desulfurization method of molten iron {METHOD OF DESULFURIZATION OF MOLTEN IRON}

This invention uses a mechanical stirring desulfurization apparatus provided with a stirring blade, and a squeezing lance to a hot metal (molten iron) and a bath surface being stirred by the stirring blade. The present invention relates to a method for desulfurization of a molten iron by spraying a desulfurization agent through a top lance.

With the recent increase in the production of low-sulfur steel, efficient desulfurization treatment in the molten iron phase has become essential. As for the desulfurization treatment of molten iron, a method using a solid desulfurization agent such as lime (CaO) has conventionally been common. For example, a CaO based desulfurization agent is blown into a molten iron container, such as a topedo car or a hot metal ladle, using a blowing injection lance. Inject the desulfurization method or immersion stirring blade (also called "impeller") into the molten iron in the molten iron conveying vessel, and add the lime-based desulfurizing agent at the same time while stirring the molten iron by the rotating stirring blade (top addition / addition from A mechanical stirring desulfurization method has been performed.

In the desulfurization reaction using the lime-based desulfurization agent, increasing the reaction interfacial area is effective for the efficiency of the desulfurization reaction. Therefore, when the size in diameter of the desulfurization agent to be added is refined, the desulfurization reaction efficiency is improved. do. However, in the mechanical stirring type desulfurization method in a practical machine, a method of supplying a desulfurizing agent from a hopper and adding a desulfurizing agent into the processing container from an inlet provided above the processing container such as a molten iron ladle is generally used. to be. When the fine-grain desulfurization agent is added in this manner, the desulfurization agent to be scattered and the desulfurization agent which fly up to the air stream increase, and the addition yield of the desulfurization agent decreases, and eventually, an efficient desulfurization treatment is not obtained.

In order to solve this problem, Patent Literature 1 discloses a desulfurization agent on a bath surface of a molten iron that is stirred by a stirring blade in a method for desulfurization of a molten iron using a mechanical stirring type desulfurization apparatus through a deodorizing lance. A method of performing desulfurization treatment by blasting with carrier gas) has been proposed. According to the patent document 1, since the desulfurization agent of the fine granules excellent in reactivity is added upstream with a conveying gas, the scattering at the time of addition becomes small, and the addition yield of a desulfurization agent improves. In addition, the fine grain desulfurization agent has a large reaction system area, and therefore, the desulfurization reaction is promoted and the desulfurization rate can be remarkably improved. Moreover, in patent document 1, with respect to the horizontal distance R from the center of a stirring blade to the injection position of a desulfurization agent, from a viewpoint of smoothly scattering the desulfurization agent absorbed in molten iron | metal,

d / 3 ≤ R ≤ d / 2 + 1/3 × (D-d)

(2) Formula: However, it is said that it is preferable that D is the inner diameter (diameter) of the process container which accommodates molten iron | metal, and d is the diameter of the stirring blade (circuit)-[0020].

Japanese Laid-Open Patent Publication 2005-179690

In order to improve the desulfurization reaction efficiency per unit mass of the desulfurization agent, the substantial increase in the reaction system area is important. In patent document 1, in order to avoid the aggregation of the desulfurizing agent which becomes a problem when adding a desulfurizing agent from the upper side of a process container, and to increase a substantial reaction system area, a powdery desulfurizing agent is conveyed using a deodorizing lance. It is sprayed on the molten iron bath surface with gas. Here, the aggregation is a phenomenon in which the added powdery desulfurization agent is spherically grown in the molten iron or on the molten iron after addition, and grows spherically. In order to substantially increase the reaction system area, it is necessary to suppress the aggregation. In order to suppress agglomeration and to reduce agglomeration diameter, the method of adding a finer desulfurization agent can be considered. On the other hand, even in the case of injection addition from the upper lance, there is a problem that the addition yield deteriorates if the desulfurizing agent is too finely refined.

From this point of view, if Patent Document 1 is verified, Patent Document 1 does not define the particle size of the desulfurization agent, and therefore, it is possible to stably obtain a desulfurization treatment that prevents aggregation of the desulfurization agent added while adding the desulfurization agent in a high addition yield. It is hard to say that it is difficult.

In the molten iron preliminary treatment step, the molten iron may be subjected to desiliconization treatment and dephosphorization treatment before the molten iron is subjected to desulfurization treatment. In this case, the desulfurization treatment is carried out after removing the slag produced by the previous process of desulfurization or dephosphorization, but the slag of the previous process is not completely removed, and the slag of the previous process is inevitably mixed. The mixing amount fluctuates. Since both the desulfurization treatment and the dephosphorization treatment are refining using an oxidation reaction, the mixed slag has a high oxidation degree. This mixed slag is incorporated in the molten iron when the molten iron is stirred by the stirring blade, and is reduced by the carbon in the molten iron. This phenomenon is a phenomenon equivalent to the addition of oxygen to the molten iron, and thus adversely affects the desulfurization reaction which is a refining refinement. That is, the desulfurization reaction is inhibited by the mixed slag. This phenomenon has a greater effect in the injection addition by the deodorizing lance than the method of adding the desulfurization agent by the addition of the desulfurization agent. This is because the mixing slag and the desulfurizing agent (upper flux) are aggregated on the bath surface by the lettuce addition method, and the mixing slag is not directly wound onto the molten iron and the desulfurization reaction is hardly inhibited by the mixing slag. This is because there are few desulfurization agents (additional flux) present on the molten iron surface, and the mixed slag is often wound up as it is.

This invention is made | formed in view of the said situation, The objective is using the mechanical stirring type desulfurization apparatus provided with the stirring blade, and spray-desulfurizing agent is added to the molten iron bath surface stirring by the stirring blade through a deodorizing lance. Thus, in the desulfurization treatment of molten iron, it is possible to add a desulfurization agent in a high addition yield, and at the same time, it is possible to prevent aggregation of the added desulfurizing agent, thereby providing a molten iron desulfurization method which can stably desulfurize with high efficiency. It is.

In the desulfurization method of molten iron according to the first invention for solving the above problems, in the desulfurization method of molten iron using a mechanical stirring type desulfurization apparatus, the particle diameter is 30 to 400㎛ on the bath surface of the molten iron stirred by the stirring blades The phosphorus lime desulfurization agent is added to the desulfurization treatment with a gas for transport via a deodorization lance.

In the molten iron desulfurization method according to the second aspect of the present invention, in the first aspect, the upper lance is disposed vertically downward, the inner wall radius of the processing vessel housing the molten iron is D, the radius of the stirring blade is R, the processing vessel. When the horizontal distance from the center of to the center of the upper lance is A, the radius R of the stirring blade satisfies the relationship of the following formula (1) with respect to the inner wall radius D of the processing vessel. The horizontal distance A is within a range that satisfies the relationship of the following formula (2) with respect to the inner wall radius D and the radius R of the stirring blade.

R? (1/2) x D... (One)

R ≦ A ≦ (1/2) × D... (2)

However, in formulas (1) and (2), D is the inner wall radius (m) of the processing vessel housing the molten iron, R is the radius of the stirring blade (m), and A is from the center of the processing vessel to the top lance center. Is the horizontal distance in m.

In the desulfurization method of molten iron according to the third invention, after the desulfurization slag generated in the desulfurization treatment by the lime-based desulfurization agent, which has been collected in advance, is added to the bath surface of the molten iron, The molten iron is stirred, and then the desulfurization agent is added thereto.

According to the present invention, since the lime-based desulfurizing agent having a particle size in the range of 30 to 400 µm is sprayed and added from the upper lance, fine powder which is easy to scatter is not contained, and scattering during spraying is prevented. In addition, since the large particle having a small reaction system area is not contained, and the aggregation of the added desulfurization agent is prevented, the desulfurization reaction system area is increased, and the desulfurization treatment at high efficiency can be stably realized. As a result, a reduction in the amount of desulfurization agent consumed, a reduction in the amount of generated slag, and the like are achieved, which brings industrially beneficial effects.

1 is a schematic view of a mechanical stirring desulfurization apparatus used in the present invention.
FIG. 2 is a diagram showing the relationship between the particle size (horizontal axis: mm) and the scattering ratio (vertical axis:%) of the lime-based desulfurization agent.
3 is a graph showing the relationship between the particle diameter (mm axis) of the lime-based desulfurization agent and the average diameter (mm axis: mm) of the desulfurization slag.
4 is a graph showing the relationship between the particle size (horizontal axis: mm) of lime-based desulfurization agent and the sulfur concentration (vertical axis: mass%) in molten iron after treatment.

(Mode for carrying out the invention)

Hereinafter, the present invention will be described in detail.

MEANS TO SOLVE THE PROBLEM In order to confirm the optimal particle size range of the desulfurization agent to add in the desulfurization process of molten iron which uses a mechanical stirring type desulfurization apparatus by carrying out a fresh addition of a lime system desulfurization agent with a conveying gas via a deodorization lance, The desulfurization test of molten iron | metal was performed by changing the particle size of the desulfurization agent in various ways using the mechanical stirring type desulfurization apparatus of a practical machine. 1, the schematic of the mechanical stirring type desulfurization apparatus used in the desulfurization test is shown.

In FIG. 1, the molten iron ladle 2 which accommodates the molten iron 3 taken out from the blast furnace is mounted in the carrying truck / carrier 1, and is attached to a mechanical stirring desulfurization apparatus. It is brought in. The mechanical stirring desulfurization apparatus is provided with a refractory stirring blade 4 for immersing and burying in the molten iron 3 contained in the molten iron ladle 2 and turning to stir the molten iron 3. The stirring blade 4 is moved up and down substantially in the vertical direction by an elevating device (not shown), and is rotated by the rotating device (not shown) with the shaft 4a as the rotating shaft. In addition, the mechanical stirring type desulfurization apparatus is provided with a deodorizing lance 5 for adding the lime-based desulfurization agent 7 to the molten iron 3 contained in the molten iron ladle 2. The upper lance 5 is connected to a supply unit comprising a dispenser 8 containing a powdered lime-based desulfurization agent 7 and a supply device 9 for quantitatively supplying the dispenser 8. From the top lance 5, the lime-based desulfurization agent 7 in powder form can be supplied together with the carrier gas 10 at an arbitrary timing. As the carrier gas 10, a reducing gas, an inert gas, or a non-oxidizing gas is used. In addition, above the molten iron ladle 2, a dust hood 6 covering the molten iron ladle 2 is provided, and is being processed through an exhaust duct (not shown) attached to the dust collecting hood 6. Exhaust gas or dust is sucked into the dust collector (not shown). In the case of this desulfurization apparatus, the shaft 4a and the uptake lance 5 of the stirring blade 4 are provided so that the up-and-down movement can penetrate the dust collection hood 6.

In the desulfurization test, CaO-20 mass% Al ₂ O ₃ having a particle diameter of 10 to 1000 μm was used as the lime desulfurization agent 7, and the scattering behavior of the lime desulfurization agent 7 and the diameter of the desulfurization slag after the treatment. And desulfurization behavior. Table 1 shows the desulfurization treatment conditions. In addition, the particle size of the desulfurizing agent in the present invention is defined by sieving, and as long as the diameter passes through the sieve, even if the longer diameter is fusiform than the sieve hole size. It is defined as smaller than the hole dimension of the sieve branch. In addition, in the desulfurization test which changes the particle size of this desulfurization agent, what adjusted particle size to the average particle diameter +/- 10% was used as the lime-based desulfurization agent (7) to be used.

ship chartering mass 300 tons Temperature 1280 ~ 1320 ℃

Chemical composition C 4.2 mass% Si 0.02 mass% P 0.10 mass% Mn 0.2 mass% S 0.03 mass%
Desulfurization Furtherance CaO-20 mass% Al ₂ O ₃ Particle size 10 ~ 1000㎛ Addition amount 7 kg / molten iron tone Treatment vessel inner diameter 4m
Stirring Stirring blade diameter 1.45m Revolutions 120 rpm time 15 minutes

The molten iron ladle 2 which accommodated 300 tons of molten iron 3 of 1280-1320 degreeC was mounted in the trolley | bogie 1, and a molten iron ladle so that the position of the stirring blade 4 may be substantially center of a molten iron ladle 2; The position of the trolley | bogie 1 which mounted (2) was adjusted, and then the stirring blade 4 was lowered and immersed in the molten iron | metal 3. When the stirring blade 4 was immersed in the molten iron 3, turning of the stirring blade 4 was started and the speed was raised to predetermined rotation speed (120 rpm). When the rotation speed of the stirring blade 4 reaches predetermined rotation speed, the supply apparatus 9 is started, and the lime-based desulfurization agent 7 accommodated in the dispenser 8 is bathed in the molten iron 3 with gas for conveyance. Spraying was carried out from the top lance 5 toward the side to desulfurize. In this desulfurization test, the installation position of the upper lance 5 is the upper lance 5 of the inner wall radius of the molten iron ladle 2, which is a processing container, from the center of the molten iron ladle 2. If the horizontal distance from the center of the surface to A (m) is A (m), the distance A becomes (1/2) × D, and the tip of the top lance 5 is removed from the stop surface of the molten iron 3 in the molten iron ladle. The distance to the head (called the lance height) was set at 1.0 m. Also, the distance A was larger than the radius R of the impeller. And the uptake lance 5 was arrange | positioned perpendicularly downward in this position, and nitrogen gas was used as gas for conveyance.

When the addition of the predetermined amount (7 kg / melt tone) of lime-based desulfurization agent 7 was completed, and stirring for a predetermined time (15 minutes) was performed, the rotation of the stirring blade 4 was stopped. When the rotation of the stirring blade 4 stopped, the stirring blade 4 was raised and it was made to stand above the molten iron ladle 2. As shown in FIG. The generated desulfurization slag floats and covers the molten iron surface, and the desulfurization treatment of the molten iron 3 ends in the stopped state.

After the end of the desulfurization treatment, a sample was taken from the molten iron 3 to investigate the sulfur content of the molten iron, and 10 kg of the desulfurized slag suspended on the molten iron was collected, and the average diameter of the desulfurized slag was determined according to the particle size distribution measurement. Calculated. In addition, the amount of lime-based desulfurization agent 7 captured by the filter of the dust collector during the desulfurization treatment was measured, and the ratio (percentage) to the amount of the desulfurization agent added was evaluated as a scatter ratio. In addition, the particle diameter of the desulfurization slag is defined by the sieve separation, similar to the particle diameter of the desulfurization agent described above, and the hole of the sieve branch as long as it passes through the sieve, even if the long diameter is fusiform larger than the hole dimension of the sieve branch. It is defined as smaller than the dimension. In addition, the method of measuring the average particle diameter of desulfurization slag is based on the method described in P8-P12 of "The powder engineering general book, Vol. 1, the basic physical properties of powder, a horseshoe: The powder industry association, the issuer: Nikkan Kogyo Shimbun." The weighting average particle diameter was measured by making reference r (any of 0 (number), 1 (length), 2 (area), and 3 (volume)) as 1 (namely, the reference | standard of a distribution as length).

In Fig. 2, the relationship between the particle diameter (horizontal axis: mm) and the scattering rate (the vertical axis:%) of the lime system desulfurization agent is shown in Fig. 3, and the relationship between the particle diameter of the lime system desulfurization agent and the average diameter (vertical axis: mm) of the desulfurization slag. Indicates. As is clear from Figs. 2 and 3, when the particle size of the desulfurizing agent is less than 30 µm, the scattering rate rises rapidly, reaching 80% or more. On the other hand, the larger the particle diameter of the desulfurization agent is, the larger the average diameter of the desulfurization slag is. However, in the range where the particle size of the desulfurization agent is 400 µm or less, the average diameter of the desulfurization slag is not so large. In the range where the particle size of the desulfurizing agent exceeds 400 µm, the scattering ratio is low, but the average diameter of the desulfurizing slag becomes large, and an increase in the reaction system area cannot be expected.

4 shows the relationship between the particle size of the lime-based desulfurizing agent and the sulfur concentration (vertical axis: mass%) in the molten iron after the treatment. As expected from the scattering ratio and the average diameter of the desulfurization slag, the particle size of the lime-based desulfurization agent 7 was found to be in the range of 30 to 400 µm, whereby stable desulfurization treatment to the low sulfur steel region was possible. In addition, the desulfurization agent particle diameter of the horizontal axis of FIGS. 2-4 has shown the average particle diameter of the desulfurization agent which adjusted the particle size to the range of average particle diameter +/- 10%.

This invention was made based on the said test, In the desulfurization method of molten iron using a mechanical stirring type desulfurization apparatus, the lime-based desulfurization agent whose particle diameter is 30-400 micrometers on the bath surface of the molten iron stirred by the stirring blade, The desulfurization treatment is carried out by adding freshly together with the carrier gas through the deodorizing lance.

Moreover, the test which changed the installation position in the radial direction of the molten iron ladle 2 of the upper lance 5 was also performed using the lime-based desulfurization agent 7 in the range whose particle diameter is 30-400 micrometers. In this case, when the radius of the stirring blade 4 is set to R (m), the stirring blade radius R is equal to or less than 1/2 of the inner wall radius D of the molten iron ladle 2 (R ≦ (1/2) × The upper lance 5 was vertically downward, and the lance height was constant at 1.0 m. The position of the stirring blade 4 was installed in the substantially center position of the molten iron ladle 2. As shown in FIG.

As a result, the horizontal distance A from the center of the molten iron ladle 2 to the center of the uptake lance 5 is defined as the inner wall of the molten iron ladle 2 from the outer circumferential position of the stirring vane 4, that is, the stirring vane radius R. When the radius D is in the range up to 1/2 (R ≦ A ≦ (1/2) × D), the average value of sulfur concentration in the molten iron after desulfurization is 0.0007% by mass (range: 0.0006 to 0.0015) Mass%), the scattering ratio of the desulfurization agent was 5 to 10%, the particle diameter of the desulfurization slag was 5 to 10 mm, and stable and satisfactory results were obtained.

When the installation position of the upper lance 5 is the center side of the molten iron ladle 2 (less than the outer peripheral position of the stirring blade 4 from the center of a molten iron ladle, 0 <= A <R) rather than this suitable range, an addition position In the vicinity, a large lump of desulfurization agent was formed, the particle size of the desulfurization slag became excessive, and the desulfurization agent adhered to the shaft 4a of the stirring blade 4, and the desulfurization reaction deteriorated. On the other hand, when it is outside from the suitable range ((1/2) x D <A≤D), the scattering ratio of the desulfurization agent increases as the outer side becomes larger, and the particle size of the desulfurization slag increases.

This forms a range in which the flow in the bath surface and the bath is downward in the vertical direction due to the vortex formed by the stirring blade 4, and the desulfurization agent 7 is wound up in the bath by adding the desulfurization agent 7 to this range. And desulfurization reaction advances. If too close to the center of the molten iron ladle 2, the desulfurization agent 7 accumulates in the part of hot metal which rotates at the same speed with impeller. This is because, in the case of passing through the outside, the bath surface and the flow in the bath are vertically upward, and it takes time to be taken up in the bath, and scattering and aggregation progress therebetween.

That is, under the condition that the stirring blade radius R is in the range which satisfy | fills the relationship of following formula (1) with respect to the inner wall radius D of the molten iron ladle 2, the uptake lance 5 is arrange | positioned in a perpendicular downward direction. When it did, it turned out that high desulfurization rate is obtained when setting the installation position of the upper lance 5 to the range which satisfy | fills the relationship of following formula (2).

R? (1/2) x D... (One)

R ≦ A ≦ (1/2) × D... (2)

However, in formulas (1) and (2), D is the inner wall radius (m) of the processing vessel housing the molten iron, R is the radius of the stirring blade (m), and A is from the center of the processing vessel to the top lance center. Is the horizontal distance in m.

In operation, it is preferable to manage the scattering ratio of a desulfurization agent to 40% or less and desulfurization slag in the range of 14 mm or less of particle diameters by the said conditions etc., respectively. In addition, it is not essential to position the stirring blade 4 (and rotating shaft) in the center of a processing container, and even if it makes it eccentric, there is no problem in stirring.

In addition, what is necessary is just to determine the size of a stirring blade and a processing container according to the target molten iron | metal processing amount (generally 250-350 tons) and the grade of stirring required. As a reference, R is preferably D / 3 or more from the viewpoint of stirring.

Reducing gas, inert gas, or non-oxidizing gas is used as the conveying gas when the lime-based desulfurization agent 7 is blown in from the upper lance 5. Hydrocarbon gas etc. are mentioned as reducible gas, Argon gas etc. are mentioned as inert gas, Nitrogen gas etc. are mentioned as non-oxidizing gas. Since the desulfurization reaction of molten iron is a reduction reaction, a reducing gas is most suitable as a carrier gas in said gas. That is, conveyance by a reducing gas is advantageous compared with other gases, since the partial pressure of oxygen at the reaction interface is lowered to promote the desulfurization reaction. In particular, low oxygen partial pressure at the ideal molten iron-desulfurizer interface is realized under conditions where the fine powdery desulfurization agent penetrates the molten iron.

As the lime-based desulfurization agent 7, any substance can be used as long as it contains lime (CaO) as a main component, or in other words, contains 50 mass% or more of CaO. Specifically, even if burned lime, limestone or the like is used alone, Al ₂ O ₃ or CaF ₂ or the like is mixed as the agent which promote melting, and further, Dromite (CaO-MgO) (dolomite) and the like can also be used as the lime-based desulfurization agent (7). However, for example, when the ratio of Al ₂ O ₃ is increased with a CaO-Al ₂ O ₃ system (residual impurity of 5% by mass or less) by increasing the ratio of Al ₂ O ₃ , the amount of liquid phase is increased. It is not a matter of promoting aggregation and leading to a decrease in the area of the reaction system. That is, in the CaO-Al ₂ O ₃ desulfurizing agent, it was found by the investigation that a proper area is present in the proportion of Al ₂ O _3. Here, the metal Al to be added (for example, included in the case of using aluminum lime as a raw material) is regarded as an active ingredient of the Al ₂ O ₃ source of the CaO-Al ₂ O ₃ quality lime-based desulfurization agent.

In this invention, it is preferable to collect the desulfurization slag which generate | occur | produced in the desulfurization process using the lime-based desulfurization agent previously performed before the said desulfurization process. Then, the recovered desulfurized slag is added onto the molten iron of the molten iron ladle 2 before the start of stirring of the molten iron 3 by the stirring blade 4, and the molten iron 3 is stirred by the stirring blade 4. The added desulfurized slag is wound up in molten iron or the desulfurized slag recovered is added to molten iron 3 which is stirred by the stirring blade 4, and the added desulfurized slag is wound up in molten iron. Thereafter, the addition of the lime-based desulfurization agent 7 from the top lance 5 may be started. The reason for starting the addition of the lime-based desulfurization agent 7 from the intake lance 5 after the desulfurization slag is wound into the molten iron is that the powdery lime desulfurization agent 7 added from the intake lance 5 is efficiently in the molten iron. To intrude. That is, the added desulfurization slag exists on the molten iron bath surface for a while even when the molten iron 3 is in the stirring state by the stirring blade 4, and in this state, the molten iron of the desulfurizing agent from the intake lance 5 ( This is because it prevents intrusion into 3). Although the time required before the added recovery slag is wound into the molten iron is different depending on the equipment and the operating conditions, it can be easily confirmed by visual observation or the like.

It is common for the molten iron drawn out from the furnace to be first subjected to desulfurization treatment and / or dephosphorization treatment. After the desulfurization treatment and / or the dephosphorization treatment, the slag containing iron oxide generated in the treatment step is discharged, but it is difficult to completely discharge the slag from the receiving container, and the slag containing iron oxide remains. That is, slag containing iron oxide remains in the molten iron ladle 2 before starting desulfurization treatment.

In addition, even when the desulfurization treatment process is the first process, furnace slag or desiliconization slag generated at blast furnace runner flows into the molten iron ladle 2 and is transferred to the desulfurization treatment process. In this case, the components in the slag transferred to the desulfurization treatment process, that is, the iron oxide contained in the desulfurization agent and the dephosphorization agent, or SiO ₂ contained in the desulfurization slag, the dephosphorization slag, the furnace slag, adversely affect the desulfurization reaction.

That is, iron oxide is disadvantageous to the desulfurization reaction which is a reduction reaction, and SiO ₂ coexists with CaO, which is a main component of the desulfurization agent, thereby causing a decrease in basicity of the reaction site and desulfurization ability.

In this case, the desulfurized slag recovered in advance is added into the molten iron ladle prior to the addition of the lime-based desulfurization agent 7 to the molten iron 3, and the iron oxide-containing slag remaining by stirring the added desulfurized slag with the molten iron 3 or The SiO ₂ containing slag is mixed with the added desulfurization slag, and desulfurized slag adheres to the surface of the iron oxide containing slag or the SiO ₂ containing slag, so as to be covered with the desulfurized slag. In this form, even when wound in the molten iron, the outer periphery is surrounded by a high melting point desulfurization slag, so that the iron oxide-containing slag or SiO ₂ -containing slag does not directly contact the molten iron 3 and contains iron oxide-containing slag and SiO _2. The adverse effect of slag on the desulfurization reaction is prevented.

In other words, by adding the desulfurized slag recovered in advance, supply of oxygen to the molten iron 3 from the remaining iron oxide-containing slag is prevented, or the basic deterioration of the reaction site due to the remaining SiO ₂ -containing slag is prevented. It is possible to prevent the desulfurization reaction, which is a reduction reaction, from being inhibited by the remaining slag.

In particular, when the desulfurization agent is projected on the bath surface by the upper lance 5, the effect of adding the desulfurization slag becomes more remarkable.

In addition, the present inventors added the desulfurization slag which was collect | recovered beforehand in the molten iron ladle before stirring start of the molten iron 3 by the stirring blade 4, when a desulfurization process is performed after a desulfurization process, and an iron oxide concentration is high. high, and the SiO ₂ as the main component, that is around, and make sure that the desulfurization slag of CaO as a main component is generated.

As described above, according to the present invention, since the lime-based desulfurizing agent 7 having a particle size within the range of 30 to 400 µm is sprayed and added from the upper lance 5, scattering during spraying is prevented, Agglomeration of the added desulfurization agent is prevented, the area of the desulfurization reaction system increases, and desulfurization treatment at high efficiency is realized stably.

[Example]

Example 1

FIG using mechanical agitation type desulfurizing apparatus shown in FIG. 1, and as a desulfurizing agent to accounting analysis using CaO-20 wt% Al ₂ O ₃ (desulfurizing agent amount: 7㎏ / ton molten iron), it represents the result of the desulfurization treatment of molten iron. Nitrogen gas was used as a gas for conveyance of a lime type desulfurization agent. The used stirring blade has four blades, and a blade has no inclination. The position of the stirring blades was almost centered on the molten iron ladle.

As the operating conditions, the particle size of the lime-based desulfurization agent is in the range of 20 μm or less (Comparative Example 1), in the range of 500 to 1000 μm (Comparative Example 2), in the range of 200 to 400 μm (Invention Example 1), and 30 to 100. It is set as four levels of the range of micrometers (Invention Examples 2-5), In Comparative Examples 1 and 2 and Inventive Examples 1 and 2, the installation positions of the intake lances are arranged in a range satisfying the above formula (2), The effect of the desulfurization agent particle size on the desulfurization reaction was investigated. In Examples 3 and 4 of the present invention, the upsetting lance was installed in a range not satisfying the above formula (2), and the influence of the installation position of the upsetting lance on the desulfurization reaction was investigated. In addition, in Example 5 of this invention, the installation position of a top lance was installed in the range which satisfy | fills said Formula (2), and the desulfurization slag collect | recovered beforehand was added on molten iron before rotation of the stirring blade. The other operating conditions except the particle size of the lime-based desulfurization agent and the installation position of the deodorizing lance were in accordance with Table 1. Both tests were also performed 100 charge (ch). Operating conditions and results are shown in Table 2.

Desulfurizing
Particle size
(탆) Desulfurization Slag
Recycle amount
(Ton / ch) Upright lance
location
(Distance A) Average S concentration of molten iron (mass%)
After processing
Chartered
S concentration
(mass%) After processing
S <0.003
Mass%
ratio(%) Desulfurization
Before treatment Desulfurization
After processing Comparative Example 1 ≤20 0 R≤A≤D / 2 0.029 0.0039 0.0080 20 Comparative Example 2 500-1000 0 R≤A≤D / 2 0.028 0.0048 0.0110 11 Inventive Example 1 200-400 0 R≤A≤D / 2 0.030 0.0009 0.0020 100 Inventive Example 2 30-100 0 R≤A≤D / 2 0.029 0.0017 0.0034 90 Inventive Example 3 30-100 0 0≤A <R 0.031 0.0022 0.0050 80 Inventive Example 4 30-100 0 D / 2 <A≤D 0.031 0.0023 0.0052 77 EXPERIMENT 5 30-100 1.0 R≤A≤D / 2 0.031 0.0007 0.0015 100

D: inner wall radius of the molten iron ladle, R: radius of the stirring blade, A: distance from the center of the molten iron ladle to the center of the upsetting lance

As shown in Table 2, compared with the comparative example 1 and the comparative example 2, in this invention example 1 and this invention example 2, the average sulfur concentration of the molten iron | metal after desulfurization process fell. In addition, when the present invention example 3 and the present invention example 4 in which the installation position of the intake lance is outside the suitable range, and the invention example 2 in which the installation position of the intake lance are suitable, the desulfurization efficiency in Example 2 of the invention ( The desulfurization efficiency was found to be high. In addition, in Example 5 of the present invention in which the desulfurized slag was recycled, it was confirmed that the average sulfur concentration of the molten iron after the desulfurization treatment was further lowered and the deviation was smaller.

[Example 2]

In the said patent document 1, from the viewpoint of dispersion | distribution to the molten iron | metal of a desulfurization agent, the installation position of a bad smell lance is examined. Therefore, in order to confirm the relationship with the suitable upper lance installation position in this invention, the desulfurization process was performed on various conditions shown in Table 3. Operating conditions other than those shown in Table 3 were the same as in Example 1. Both tests were also 100 charged.

In Examples 6 to 9 of the present invention, d / 3 ≤ R ≤ d / 2 + 1/3 x (Dd), in which the position of the upsetting lance is suitable in Patent Literature 1 ((2R) / 3 ≤ A when represented by a symbol of the present invention). ≤ R + (1/3) × (2D-2R), and the right side satisfies (2D) / 3 + R / 3), but R ≤ A ≤ (1/2) × D for which the present invention is suitable It is not satisfactory. In Examples 6 to 9 of the present invention, the desulfurization efficiency was improved as compared with Comparative Example 3, which is a conventional additive method, but the desulfurization efficiency was further improved in Inventive Example 10 and Inventive Example 11, which are suitable ranges of the present invention. have. That is, as shown in the ratio which becomes the highest S concentration and S <0.003 mass% after a process, in this invention example 10 and this invention example 11, it is implement | achieving low sulfide by very small deviation.

[Example 3]

Under various conditions shown in Table 4, the desulfurization treatment was performed, and the results obtained were also shown in Table 4 together. Operating conditions other than those shown in Table 4 were the same as in Example 1. Here, in Examples 12-16 of Table 4, after the recycled desulfurization slag (recovery slag) was thrown in advance, the influence of the stirring time from the top lance to the start of the desulfurization agent addition was confirmed. In Examples 17 to 22 of the present invention, the influence of the Al ₂ O ₃ mixing amount in the CaO-Al ₂ O ₃ -based desulfurization agent was confirmed. In Examples 23 and 24 of the present invention, the influence of the carrier gas of the desulfurization agent was confirmed. .

In the desulfurization apparatus used in this example, it was confirmed that it took about 1 minute before the added desulfurization slag (recovery slag) was wound into the molten iron, but in Examples 12 to 16 of the present invention, the stirring time was set to 2 minutes and 3 minutes. In Example 15 and Example 16, the desulfurization efficiency was particularly good. Moreover, although the desulfurization efficiency fell in Examples 13 and 14 of this invention which stirred more than 4 minutes, it is thought that this is because the time after desulfurization agent addition cannot be fully secured in the same stirring time. Therefore, the stirring time of 3 minutes or less was especially suitable in this mechanical stirring type desulfurization apparatus.

In addition, in the mechanical stirring type desulfurization apparatus used in the present Example from Examples 17 to 22 of the present invention, the Al ₂ O ₃ mixed amount in the CaO-Al ₂ O ₃ desulfurization agent was 10 to 30% (weight to the total amount of the desulfurization agent). %) Was found to be particularly suitable. In addition, from the present invention example 23 and the present invention example 24, it was confirmed that when the reducing gas (propane gas (hydrocarbon-based gas) of the present invention example 24) was used as the carrier gas, the desulfurization efficiency was further improved.

In addition, although it was confirmed that the effect of the present invention can be obtained without any problem in the known desulfurization agent and the carrier gas other than those used in the above-mentioned examples, it is preferable to use a CaO-Al ₂ O ₃ based desulfurization agent as the desulfurization agent. Was advantageous.

According to the present invention, the desulfurization treatment at high efficiency, that is, the treatment such that S after desulfurization treatment is, for example, 0.003 mass%, can be stably realized by suppressing the variation of the result. As a result, a reduction in the amount of desulfurization agent consumed, a reduction in the amount of generated slag accompanying it, and the like are achieved, resulting in an industrially beneficial effect.

1: carrying truck / carrier
2: molten iron ladle (processing container)
3: molten iron
4: stirring blade
4a: axis of rotating wing
5: top lance
6: dust collecting hood
7: lime desulfurization agent
8: dispenser
9: feeder
10: carrier gas
A: horizontal distance from the center of the processing vessel to the center of the upper lance
R: radius of stirring blade
D: inner wall radius of treatment vessel

Claims (3)

In the desulfurization method of hot metal using a mechanical stirring type desulfurization apparatus, a lime-based desulfurization agent having a particle size of 30 to 400 µm is placed on a bath surface of a molten iron stirred by a stirring blade. The upper lance is subjected to a deodorizing treatment with a gas to be conveyed through a top lance, and the deodorizing lance is disposed downward in the vertical direction, the inner wall radius of the processing vessel housing the molten iron is D, and the radius of the stirring blade is R, the treatment. When the horizontal distance from the center of the vessel to the center of the intake lance is A, the radius R of the stirring blade satisfies the relationship of the following formula (1) with respect to the inner wall radius D of the processing vessel. And the horizontal distance (A) is within the range in which the horizontal distance (A) satisfies the relationship of the following formula (2) with respect to the inner wall radius (D) and the radius (R) of the stirring blade.
R? (1/2) x D... (One)
R ≦ A ≦ (1/2) × D... (2)
However, in formulas (1) and (2), D is the inner wall radius (m) of the processing vessel housing the molten iron, R is the radius of the stirring blade (m), and A is from the center of the processing vessel to the top lance center. Is the horizontal distance in m. delete The method of claim 1,
The desulfurization method of molten iron which adds the desulfurization slag produced | generated by the desulfurization process with the lime system desulfurization agent previously collected on the bath surface of the said molten iron, and then stirs the molten iron with the said stirring blade, and adds the said desulfurization agent after that.

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