KR102142198B1 - Desulfurizing agent, method for desulfurizing molten iron and method for producing molten iron - Google Patents

Abstract

Providing a method for desulfurizing molten iron and a method for manufacturing molten iron, which has excellent desulfurization efficiency and can reduce the cost of desulfurization treatment.
As a desulfurizing agent used for desulfurization of molten iron, it contains quicklime with a total pore volume of 0.1 ml/g or more, which is the sum of the volumes of pores having a pore diameter of 0.5 μm or more and 10 μm or less.

Description

Desulfurization agent, molten metal desulfurization method and manufacturing method of molten iron {DESULFURIZING AGENT, METHOD FOR DESULFURIZING MOLTEN IRON AND METHOD FOR PRODUCING MOLTEN IRON}

The present invention relates to a desulfurizing agent, a method for desulfurizing molten iron and a method for manufacturing molten iron.

The molten iron drawn out from the blast furnace usually contains a high concentration of sulfur (S), which adversely affects the quality of the steel. For this reason, in the steelmaking process, various molten iron pretreatments and molten steel desulfurization are performed depending on the required quality. Among these, as the outboard desulfurization of molten iron (also referred to as "melting-out desulfurization"), desulfurization is carried out by adding a desulfurizing agent to an injecting desulfurization method in which desulfurization is carried out by blowing a desulfurizing agent into the molten iron or by stirring blades. Methods such as mechanical stirring desulfurization are known. In addition, in such a molten iron desulfurization method, a desulfurization agent mainly containing inexpensive quicklime as a refining agent is often used in any method, and the desulfurization reaction proceeds according to the reaction formula shown in the formula (1).

CaO + S → CaS + O ... (1)

In this desulfurization treatment, a method of using a solvent such as fluorspar (CaF ₂ ) or an alumina-based solvent (媒溶劑) is known for the purpose of improving the reaction efficiency by promoting slag formation of quicklime. For example, 95 wt% CaO-5 wt% CaF ₂ is widely used as a desulfurizing agent in which a solvent is mixed. However, since these solvents are generally expensive, increasing the blending ratio of the solvents in the desulfurizing agent leads to an increase in the cost of the desulfurizing agent. In addition, when the compounding rate of the solvent in the desulfurizing agent is increased, the CaO concentration in the desulfurizing agent decreases, so that the reaction efficiency of the desulfurizing agent decreases. On the other hand, a combination of a desulfurizing agent of a calcium-based or soda-based desulfurizing agent with a higher mixing ratio of a solvent, or by adding CaCO ₃ to a de-sulfurizing agent of a quick-liming main having an increased mixing ratio of a solvent (for example, Patent Document 1) , There is a method to improve the reaction efficiency of the desulfurizing agent. However, in view of the recent concern that fluoride has an impact on the environment, a desulfurizing agent without fluorspar is desired. For this reason, there is a demand for a desulfurizing agent having a high desulfurization efficiency without using fluorite or a technique for improving the desulfurization ability of quicklime itself.

As a desulfurizing agent that does not use quicklime or fluorspar, for example, calcium carbide-based and soda-based desulfurizing agents have been put into practical use, but both have advantages and disadvantages. Calcium carbide-based desulfurization agents have strong desulfurization capabilities, but there are problems such as acetylene gas generation in the post-treatment of slag generated by desulfurization treatment. In addition, calcium-carbide desulfurization agents are difficult to handle because they are not only expensive, but also dangerous. Although a soda-based desulfurizing agent is relatively inexpensive, it is highly alkaline, and thus has a great effect on refractory materials such as furnaces and containers. In addition, since the soda-based desulfurizing agent contains Na in the exhaust gas, its removal treatment is required. In addition, since the soda-based desulfurizing agent has a high Na ₂ O content in the slag, there are restrictions on reuse of it in cement or the like. For this reason, it cannot be said that it is a preferable desulfurizing agent like fluorine from the influence on the environment. Further, as a desulfurization method using a desulfurizing agent other than calcium carbide-based and soda-based, a method using metal Mg as a desulfurizing agent is also well known. The metal Mg easily reacts with S in the molten iron to form MgS, but since the boiling point is low at 1100°C, it is vigorously vaporized in the molten iron at 1250°C to 1500°C, and there is a risk of scattering the molten iron. In addition, in the desulfurization treatment using the metal Mg, the generated Mg vapors are dissipated into the atmosphere without sufficiently contributing to the desulfurization reaction, so the efficiency is poor. Furthermore, since the metal Mg is very expensive, it leads to an increase in the cost of the desulfurization treatment.

As a technique for improving the desulfurization ability of quicklime itself, a countermeasure for improving the desulfurization efficiency of the desulfurizing agent has been made in terms of lime properties. For example, Patent Documents 2 and 3 disclose a method of controlling density, specific surface area, pore size, and the like as lime properties in molten metal desulfurization by injection desulfurization. According to Patent Documents 2 and 3, by controlling such lime properties, it is possible to control (slow down) the rate of desulfurization agent blowing into the molten iron, and to accelerate the reaction between the molten iron and the desulfurizing agent. However, in Patent Documents 2 and 3, the injection desulfurization method is targeted as the method of desulfurization of molten iron, and it is not an optimum lime property in the mechanical stirring desulfurization method. In addition, in Patent Document 2, the particle size of the desulfurizing agent to be targeted is as small as 200 µm or less. In the case of using such a fine desulfurizing agent, it becomes easy to secure the reaction interface area, but in the mechanical stirring desulfurization method, it is important to use a desulfurizing agent having a large particle diameter from the viewpoint of securing the addition yield, and such a particle size There is no description of how to secure the reaction interfacial area using a large desulfurizing agent.

In the mechanically stirred desulfurization method, the powdered desulfurizing agent added to the bath surface of the molten iron usually flows into the molten iron, and the desulfurizing agent and S in the molten iron react. As described above, in the case of the method of adding the desulfurizing agent to the bath surface in the upper direction (also referred to as the upper addition method), the aggregation of the desulfurizing agent proceeds, so that the reaction interface area becomes small, so that the desulfurization efficiency is lowered. In this upper addition method, the slag after desulfurization treatment becomes agglomerated particles of several millimeters to several tens of millimeters. On the other hand, as a method of improving the reaction efficiency in a mechanically stirred desulfurization method, a method (also called a projection method) of projecting a powdered desulfurizing agent onto a bath surface is known. In the projection method, since the aggregation of the desulfurizing agent at the time of being carried into the molten iron is suppressed compared to the upper addition method, the actual reaction interface area becomes large, and the desulfurization ability can be improved. However, even in such a projection method, since the aggregation of the projected desulfurizing agent still proceeds, the reaction interfacial area of the desulfurizing agent itself was not sufficiently utilized.

Regarding this problem in the projection method, Patent Documents 4 and 5 disclose a method of projecting a desulfurizing agent using a carrier gas. In Patent Documents 4 and 5, aggregation of the desulfurizing agent can be suppressed by promoting the penetration of the desulfurizing agent into the molten iron by using a carrier gas. However, in the projection method described in Patent Documents 4 and 5, since the properties of quicklime are not considered at all, a technique for further improving the desulfurization efficiency of quicklime from the viewpoint of lime properties is required.

Japanese Patent Application Publication No. Hei 8-268717 Japanese Patent Publication No. 5101988 Japanese Patent Application Publication No. 62-56509 Japanese Patent Publication No. 5045031 Japanese Patent Publication No. 5195737

Then, this invention was made|formed in view of the said subject, and it aims at providing the desulfurization agent, molten iron desulfurization method, and manufacturing method of molten iron which are excellent in desulfurization efficiency, and can reduce the cost of desulfurization treatment.

According to an aspect of the present invention, as a desulfurizing agent used for desulfurization of molten iron, a desulfurizing agent characterized by containing quicklime having a total pore volume of 0.1 ml/g or more, which is the sum of the volumes of pores having a pore diameter of 0.5 µm or more and 10 µm or less. Is provided.

According to one aspect of the present invention, when the molten iron is desulfurized with a mechanically stirred desulfurization apparatus, the total pore volume, which is the sum of the volumes of the pores having a pore diameter of 0.5 μm or more and 10 μm or less, is 0.1 ml/g or more, and an average particle diameter A molten metal desulfurization method is provided, characterized in that a desulfurizing agent containing a powdery quicklime having a size of 210 µm or more and 500 µm or less is used.

According to one aspect of the present invention, there is provided a method for manufacturing molten iron, characterized in that the molten iron desulfurization method is used.

According to one aspect of the present invention, there is provided a desulfurizing agent, a molten iron desulfurization method, and a manufacturing method of molten iron which are excellent in desulfurization efficiency and can reduce the cost of desulfurization treatment.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the mechanical stirring-type molten iron desulfurization apparatus which concerns on one Embodiment of this invention.
Fig. 2 is a graph showing the relationship between the total pore volume of quicklime and the desulfurization rate in the first test.
3 is a graph showing the relationship between the average particle diameter of quicklime and the desulfurization rate in the first test.
4 is a graph showing the relationship between the flow rate in the horizontal direction of the bath surface and the desulfurization rate in the second test.

In the following detailed description, many specific details are set forth in order to provide a thorough understanding of embodiments of the invention. However, it will be apparent that one or more embodiments may be practiced without these specific details. In addition, well-known structures and devices are shown in schematic view in order to simplify the drawings.

First, the description of how the present inventors have reached the present invention will be described. The present inventors conducted a polite study on the effect of desulfurization efficiency due to each characteristic from the viewpoint of the characteristics (mainly lime properties) of the desulfurizing agent in the mechanically stirred desulfurization method. As a result, it was found that, among various characteristics such as specific surface area and activity, the effect of pore size distribution and particle size of quicklime was large, and in particular, the total pore volume of pores having a pore diameter range of 0.5 μm or more and 10 μm or less greatly affected Came out. The mechanically stirred desulfurization apparatus (1) used in the first test in Fig. 1, and the conditions of the apparatus and the test method in which the first test was performed are shown in Table 1, respectively.

As shown in FIG. 1, the mechanically stirred desulfurization apparatus 1 is a refining apparatus for desulfurizing the molten iron 3 accommodated in the molten iron ladle 2. The molten iron ladle 2 is placed on the cart 4 and is disposed at the processing position. In the first test, the ladle diameter of the molten iron ladle 2 was 4 m, the weight of the molten iron 3 was 300 t/ch, and the temperature of the molten iron 3 was 1280°C or higher and 1330°C or lower. , S concentration ([S]) of the molten iron 3 before desulfurization treatment was set to 0.025 wt% or more and 0.035 wt% or less. Moreover, ch (charge) is a unit indicating the number of desulfurization treatments performed for each molten iron ladle 2 by the mechanically stirred desulfurization apparatus 1, and 300 t/ch is a molten iron processed in one desulfurization treatment. It shows that the weight of (3) (the weight of the molten iron 3 accommodated in the molten iron ladle 2) is 300 t.

The mechanical stirring desulfurization device 1 includes a stirring blade (impeller) 5, a projection means 6, and an upper addition means 7. The stirring blade 5 is a stirrer made of a refractory material, and the upper end of the vertical direction (up and down with respect to the ground in Fig. 1) is connected to an axis, and four blades projecting in a direction perpendicular to the central axis centered on this axis. Have Further, on the upper end side of the shaft of the stirring blade 5, it is connected to a rotating device or a lifting device not shown. The stirring blade 5 rotates about the axis by receiving the rotation drive from the rotating device. In addition, the stirring blade 5 is configured to be able to elevate in the vertical direction by the elevating operation of the elevating device. In the first test, the diameter of the stirring blade 5 was 1.45 m, and the stirring blade 5 was rotated at a rotation speed of 130 rpm to perform desulfurization treatment. The projection means 6 has a hopper 8, a rotary feeder 9, and a lance 10. A desulfurizing agent is contained in the hopper 8. The rotary feeder 9 cuts the desulfurizing agent contained in the hopper 8 at a predetermined cutout speed, and supplies it to the lance 10. The lance 10 is a lance of 65A, and is disposed extending above the bath surface of the molten iron 3 in the vertical direction. The lance 10 sprays the desulfurizing agent cut out from the rotary feeder 9 with nitrogen, which is a carrier gas supplied from a carrier gas supply device (not shown), to inject the desulfurizing agent onto the bath surface of the molten iron 3. The upper addition means 7 has a hopper 11, a rotary feeder 12, and an input chute 13. A desulfurizing agent is contained in the hopper 11. The rotary feeder 12 cuts the desulfurizing agent contained in the hopper 11 at a predetermined cutout speed, and supplies it to the input chute 13. The lower end of the pouring chute 13 is disposed above the bath surface of the molten iron 3, and the desulfurizing agent supplied from the rotary feeder 12 is freely dropped from the front end to be injected into the bath surface of the molten iron 3. In the first test, a desulfurization treatment was performed by adding a desulfurizing agent to the molten iron 3 by either the projection method using the projection means 6 or the upper method using the upper addition means 7. Moreover, when desulfurization treatment was performed by the projection method, the flow rate of nitrogen gas was set to 0 Nm ³ /min to 7 Nm ³ /min, and a desulfurizing agent was added at a rate of 200 kg/min. On the other hand, when desulfurization treatment was performed by the upper addition method, a desulfurizing agent was added at a rate of 1000 kg/min.

In addition, in the first test, the desulfurizing agent was used only as a powdery quicklime, and desulfurization treatment was performed without adding any additives other than those inevitably contained in the quicklime. Desulfurization agent) was added. Then, in order to investigate the relationship between the total pore volume of quicklime and the desulfurization rate (the ratio of the amount of change in the S concentration before and after treatment to the S concentration before treatment), and the relationship between the particle size and desulfurization rate of quicklime, Desulfurization treatment was performed under the conditions of changing the pore volume or the particle size of quicklime, respectively.

The total pore volume of quicklime is calculated from the measured pore diameter distribution. The method of measuring the pore diameter distribution is as follows. First, as a pre-treatment, the quicklime was dried at 120°C for 4 hours and constant temperature. Subsequently, using Autopore IV9520 manufactured by Micromerities, a pore distribution having a pore diameter of about 0.0036 μm to 200 μm of dried quicklime was determined by mercury intrusion, and a cumulative pore volume curve was calculated. Then, the total pore volume of pores having a diameter of 0.5 µm to 10 µm was determined from the calculated cumulative pore volume curve. The pore diameter was calculated using Washburn's equation ((2) equation). In the formula (2), P denotes pressure, D denotes pore diameter, σ denotes the surface tension of mercury (=480 dynes/cm), and θ denotes the contact angle (= 140 degrees) between mercury and the sample.

P × D = -4 × σ × cosθ ... (2)

In addition, the particle size is an average particle size, and a predetermined average particle size is obtained by sifting a desulfurizing agent. The method for measuring the average particle diameter of the desulfurizing agent is as follows. First, 500 g of desulfurizing agent is collected at the time of shipment from the manufacturer or when stacked on the hopper 8. Subsequently, the collected desulfurizing agent is 45 µm or less, 45 µm to 75 µm, 75 µm to 100 µm, 100 µm to 125 µm, 125 µm to 150 µm, 150 µm to 300 µm, 300 µm to 500 µm, and 500 µm to Sieve was carried out in 9 steps of 1000 µm and 1000 µm or more. And the average particle diameter was computed by calculating with the weight ratio of Formula (3) about the sieve desulfurizing agent. In the formula (3), D _a is the average particle diameter (mm), d _i is the average particle diameter (median value of the sieve's eye) in each particle size range (mm), and w _i is the desulfurizing agent on each sieve. It represents the weight (kg).

[Equation 1]

As a result of the first test, Fig. 2 shows the relationship between the total pore volume and the desulfurization rate, which are the sum of the volumes of the pores having a pore diameter of 0.5 µm or more and 10 µm or less when the projection method or the upper addition method is used. Moreover, in the conditions shown in FIG. 2, the particle size of the desulfurizing agent was 1 mm or less. As shown in Fig. 2, in any case of the projection method and the upper addition method, the total pore volume with a pore diameter of 0.5 µm or more and 10 µm or less becomes 0.1 ml/g or more, which significantly increases the desulfurization rate, and is 80%. It was confirmed that the above high desulfurization rate was obtained. Moreover, it was confirmed that the improvement value of the desulfurization rate became large by using the projection method in comparison with the upper side addition method.

Next, Fig. 3 shows the relationship between the average particle diameter of the desulfurizing agent and the desulfurization rate when the projection method or the upper addition method is used. Moreover, in the conditions shown in FIG. 3, the total pore volume of pore size of 0.5 µm or more and 10 µm or less was set to 0.2 ml/g. As shown in FIG. 3, it was confirmed that the desulfurization rate increased remarkably in a range in which the average particle diameter of the desulfurizing agent was 210 µm or more and 500 µm or less. And in the said range, it was confirmed that the desulfurization rate further increased by the average particle diameter of the desulfurizing agent being 230 µm or more. Moreover, it was confirmed that the improvement value of the desulfurization rate became large by using the projection method in comparison with the upper side addition method.

Here, at least one of an upper addition method and a projection method is generally used as a method for adding a desulfurizing agent in a mechanically stirred desulfurization method. In the case of such an addition method, unlike the injection desulfurization method in which the added desulfurizing agent completely penetrates the molten iron, it becomes difficult to add a small diameter desulfurizing agent in the molten iron in a good yield. For this reason, in the mechanically stirred desulfurization method, the particle size of the desulfurizing agent to be added becomes important for improving the yield. In general, when a desulfurizing agent having a small particle size is used, and the desulfurizing agent can infiltrate the molten iron, it is advantageous for improving the desulfurization reaction efficiency in that it becomes possible to secure a reaction interface area with the molten iron. However, since the desulfurizing agent having a small particle size becomes smaller in diameter, it becomes more difficult to infiltrate into the molten iron, and thus the possibility that it is not contributed to the reaction increases even when added. On the other hand, when the particle size of the desulfurizing agent to be added is increased, the penetration into the molten iron is advantageous and the yield is improved, but the reaction interface area decreases, which is disadvantageous from the viewpoint of the desulfurization reaction. For this reason, in order to promote the reaction while securing the yield to the molten iron, it is important to ensure that the appropriate particle diameter of the desulfurizing agent is increased and that the reaction efficiency is increased.

On the other hand, from the results of the first test, the present inventors believe that the presence of pores having a pore diameter of 0.5 µm or more and 10 µm or less is important for improving the desulfurization efficiency in a mechanically stirred desulfurization method using quicklime as a desulfurizing agent. It was found that it is important to use a desulfurizing agent having a total pore volume of 0.1 ml/g or more. Further, it has been found that by using the desulfurizing agent having an average particle diameter of 210 µm or more and 500 µm or less, an appropriate particle diameter for improving yield when added to molten iron can be secured. Thus, the desulfurization efficiency can be further improved by controlling the average particle diameter in addition to the pores. And when using the desulfurizing agent of this condition in a mechanical stirring type desulfurization method, it turned out that the method of adding the desulfurizing agent to the molten iron|metal 3 is a projection method, and higher desulfurization rate is obtained compared with the upper addition method. From the results of this first test, the following phenomena are considered. At the temperature at which the molten iron desulfurization is performed, the quicklime is solid, and when the quicklime added to the bath surface of the molten iron 3 has the pore size, the molten iron 3 penetrates into the pores on the surface of the quicklime, thereby physically chartering the molten iron 3 ) And quick-lime wettability is improved. Thereby, it is thought that the penetration into the molten iron|metal 3 of quicklime is promoted and the desulfurization efficiency is improved. Further, similar properties and properties of quicklime are shown in references 2 and 3, but in the case of references 2 and 3, they differ from the addition of a desulfurizing agent to the bath surface of the molten iron 3 in mechanically stirred desulfurization. The principle is completely different from the above-described phenomenon. Therefore, the desulfurizing agent found by the present inventors cannot be derived from the average pore diameters described in Cited References 2 and 3.

Next, the present inventors conducted a desulfurization treatment under various stirring conditions as a second test in order to investigate the effect of stirring conditions on the desulfurization rate in the projection method. In the second test, the desulfurizing agent was used only as a powdery quicklime in the same manner as in the first test, and the total pore volume with a pore diameter of 0.5 µm or more and 10 µm or less was 0.1 ml/g or more and a particle diameter of 2 mm or less was used. Moreover, the addition amount of the desulfurizing agent was set to a constant amount of 5 kg/t, and desulfurization treatment was performed without adding any additives inevitably contained in the lime. In addition, in the second test, desulfurization treatment was performed using the mechanically stirred desulfurization apparatus 1 shown in FIG. 1. In addition, in the second test, when adding the desulfurizing agent, only the projection means 6 was used, and the conditions for adding the desulfurizing agent were the same as in the first test. Then, in the second test, the effect of these stirring conditions on the desulfurization rate was investigated by changing the bath surface position of the molten iron 3 for spraying the desulfurizing agent and the number of revolutions of the stirring blade 5.

The stirring conditions resulted in different desulfurization rates due to the difference in the rotational speed of the stirring blade 5 and the spraying position of the desulfurizing agent. They were in the horizontal direction of the bath surface of the molten iron 3 at the position where the desulfurizing agent was injected. I could arrange it at a flow rate. Here, the flow velocity in the horizontal direction is the flow velocity in the horizontal tangential direction of swirl flow generated by mechanical agitation at a position where the desulfurizing agent is sprayed on the bath surface of the molten iron 3.

As a result of the second test, Fig. 4 shows the relationship between the flow rate in the horizontal direction of the bath surface and the desulfurization rate. As shown in FIG. 4, when the flow rate in the horizontal direction of the bath surface at the position where the desulfurizing agent was injected was 1.1 m/s or more and 11.9 m/s or less, it was confirmed that the desulfurization reaction was further promoted. When the desulfurizing agent is sprayed together with the carrier gas on the bath surface of the molten iron 3, it is considered that the speed of the molten iron 3 is also an important factor as conditions for the quick lime of the solid to invade the molten iron 3. When the horizontal flow velocity of the bath surface at the location where the desulfurizing agent is injected is slower than 1.1 m/s, the desulfurizing agent added in the molten iron 3 does not move into the vortex created by the stirring blade 5, and immediately rises to the bath surface. Discard, the reaction between the desulfurizing agent and the molten iron 3 is not promoted. On the other hand, when the horizontal flow velocity of the bath surface at the position where the desulfurizing agent is sprayed is faster than 11.9 m/s, the vertical velocity of the desulfurizing agent is pushed against the horizontal velocity of the molten iron 3, so that some desulfurizing agents are scattered. This was observed. From this, when the flow velocity in the horizontal direction of the bath surface at the position where the powdered desulfurizing agent is injected is 1.1 m/s or more and 11.5 m/s or less, the effect of adjusting the pore diameter capacity is exhibited, and the desulfurizing agent in the molten iron 3 is more efficiently exhibited. It is thought that it was possible to let it come in.

In addition, in the series of tests described above, only the quick lime that satisfies the conditions of the pore volume or particle size was tested as a quick stone member, but some of the quick lime that does not satisfy the conditions of the pore volume or particle size was mixed and partially mixed. It may be used as a desulfurizing agent. In this case, the effect according to the mixing rate of quicklime that satisfies the conditions of the pore diameter capacity of the present invention is obtained.

<Desulfurization agent, molten iron desulfurization method and manufacturing method of molten iron>

Next, the desulfurization agent, molten iron desulfurization method, and manufacturing method of molten iron based on the above-mentioned knowledge will be described. In this embodiment, the desulfurization treatment of the molten iron|metal 3 is performed using the mechanical stirring desulfurization apparatus 1 shown in FIG. 1 similarly to the said 1st and 2nd test. In addition, the mechanical stirring desulfurization device 1 is a lid (not shown) that covers the upper opening of the molten iron ladle 2, or an exhaust duct formed in this lid and connected to an exhaust device (not shown) (not shown) Have Gas or dust generated during the desulfurization treatment is discharged to the exhaust device through this exhaust duct.

In the molten iron desulfurization method according to the present embodiment, first, the molten iron ladle 2 in which the molten iron 3 is accommodated is loaded onto the bogie 4, and the stirring blade 5 has a predetermined position with respect to the molten iron ladle 2 The cart 4 moves until it becomes. Subsequently, the stirring blade 5 is lowered by the lifting device, so that the stirring blade 5 is immersed in the molten iron 3. Then, while being immersed in the molten iron 3, the stirring blade 5 is rotated by a rotating device, and the number of revolutions increases until it reaches a predetermined number of revolutions. At this time, the generated gas or dust is discharged from the exhaust duct by the exhaust device. Then, after the stirring blade 5 reaches the normal rotational speed, a desulfurizing agent is added to the molten iron 3 by the projection means 6 or the upper addition means 7.

The desulfurizing agent is a quicklime having a total pore volume of 0.1 ml/g or more, and an average particle diameter of 210 µm or more and 500 µm or less, which is the sum of the volumes of pores having a pore diameter of 0.5 µm or more and 10 µm or less. Moreover, it is preferable to set the minimum value of the particle size of quicklime to 40 micrometers or more in consideration of scattering at the time of addition. Further, the quicklime may be calcined by any furnace, such as a kiln furnace, a Merz furnace, or a Beckenbach furnace. When the projection means 6 is used, the desulfurization agent cut out by the rotary feeder 9 is blown from the lance 10 into the bath surface of the molten iron 3 with carrier gas such as nitrogen, thereby allowing the molten iron 3 ). At this time, it is preferable to blow a desulfurizing agent at a position where the flow velocity in the horizontal direction of the bath surface of the molten iron 3 is 1.1 m/s or more and 11.9 m/s or less. The position where the flow velocity of the bath surface becomes the above range is calculated in advance from the stirring conditions such as the number of revolutions of the stirring blade 5 and the injection position of the desulfurizing agent. On the other hand, when the upper addition means 7 is used, the desulfurizing agent cut by the rotary feeder 9 is added upward to the bath surface of the molten iron 3 through the input chute 13.

After the desulfurizing agent is added, stirring of the molten iron 3 by the stirring blade 5 is performed until a predetermined time has elapsed. Thereafter, the number of revolutions decreases until the rotation of the stirring blade 5 is stopped by the rotating device, and after the rotation is stopped, the stirring blade 5 is raised by the lifting device. Subsequently, the slag generated by the desulfurization treatment is floated, covering the bath surface of the molten iron 3, and in a stopped state, the desulfurization treatment is terminated. Thereby, molten iron 3 of a desired S concentration is produced.

<Modification>

The present invention has been described above with reference to specific embodiments, but it is not intended to limit the invention by these descriptions. By referring to the description of the present invention, it is apparent to those skilled in the art that various embodiments of the disclosed embodiments together with other embodiments of the present invention are apparent. Therefore, the claims should be interpreted to cover all of these modifications or embodiments included in the scope and gist of the present invention.

For example, in the above embodiment, it is said that only deliming agent is used with quick lime having a total pore volume of 0.5 µm or more and 10 µm or less and 0.1 ml/g or more and an average particle diameter of 210 µm or more and 500 µm or less. It is not limited to this example. For example, the desulfurizing agent may be a mixture of quicklime in which the total pore volume and particle diameter are within the above range, and quicklime in which the total pore volume and particle diameter are outside the above range. In addition, a solvent such as alumina may be added to the desulfurizing agent in addition to quicklime in which the total pore volume and particle diameter are within the above range. In this case, the desulfurization ability of the quicklime is improved as compared with the quicklime in which the quicklime falls outside the above range, so that even if the amount of the solvent added is small, equal or higher desulfurization efficiency can be obtained. Further, the desulfurizing agent according to the present invention does not contain a solvent having at least one elution element among fluorine, sodium and potassium.

Moreover, in the said embodiment, when desulfurization processing was performed, it was set as the structure which only a desulfurizing agent is used as a refiner, but this invention is not limited to such an example. For example, as a refining agent that further accelerates the desulfurization reaction, a deoxidizing agent such as powder of aluminum dross containing metal Al or metal Al may be added. In this case, the deoxidizing agent may be accommodated in a hopper different from the desulfurizing agent, and after being cut out from the hopper, it may be added to the molten iron 3 through the input chute 13. Further, for example, a solvent such as fluorite or soda ash may be added as a refining agent. In this case, the solvent may be added in a mixed state with the desulfurizing agent in advance, accommodated in a hopper different from the desulfurizing agent, cut out from the hopper, and then added to the molten iron 3 through the input chute 13.

In the above-described embodiment, although one lance 10 is formed in the projection means 6, the present invention is not limited to this example. For example, two or more lances 10 may be formed.

In the above-described embodiment, the desulfurizing agent is configured to be used in a mechanically stirred hot-metal desulfurization method, but the present invention is not limited to these examples. As a desulfurizing agent, when using quicklime with a total pore volume of 0.1 ml/g or more, which is the sum of the volumes of pores having a pore diameter of 0.5 µm or more and 10 µm or less, as shown in Fig. 2, the desulfurization rate is increased by increasing the reaction interface area. Significantly increases. This effect is effective not only in the mechanical stirring type desulfurization method, but also in other desulfurization methods for desulfurizing molten iron, such as, for example, injection desulfurization. For this reason, the desulfurizing agent according to the present invention may be used in a method of desulfurization treatment other than the mechanically stirred hot-metal desulfurization method.

<Effects of the embodiment>

(1) The desulfurizing agent according to an aspect of the present invention is a desulfurizing agent used for desulfurization of molten iron, and contains quicklime with a total pore volume of 0.1 ml/g or more, which is the sum of the volumes of pores having a pore diameter of 0.5 µm or more and 10 µm or less. .

According to the configuration of (1) above, by setting the total pore volume of quicklime in the above range, the desulfurization efficiency by quicklime can be improved. Thereby, it becomes possible to improve the production efficiency by shortening the desulfurization treatment time, reducing the temperature loss and reducing the processing cost, and reducing the amount of dust and slag generated due to the desulfurization treatment. In addition, the cost of the refining agent can be reduced and handling becomes easy as compared to other desulfurizing agents other than CaO systems having high reaction efficiency. And it can be applied to both addition means of the upper side addition method and the projection method in a mechanical stirring desulfurization method.

(2) In the structure of the above (1), quicklime is a powder having an average particle diameter of 210 µm or more and 500 µm or less, and is used in a mechanically stirred molten iron desulfurization method.

According to the configuration of (2) above, by setting the average particle diameter of quicklime in the above range, the desulfurization efficiency by quicklime can be further improved. In addition, by using a desulfurizing agent in a mechanically stirred molten iron desulfurization method, the effect of improving the desulfurization efficiency by quicklime of the above constitution can be obtained more effectively.

(3) In the structure of the above (2), quicklime has an average particle diameter of 230 µm or more and 500 µm or less.

According to the structure of (3) above, compared with the structure of (2) above, desulfurization efficiency can be further improved.

(4) In the structure of any one of (1) to (3) above, substantially no at least one of fluorine, potassium and sodium is contained. Here, the state in which at least one element among fluorine, potassium, and sodium is substantially free means that at least one element is not contained by intentional addition, except for inevitable incorporation of trace amounts.

According to the structure of (4) above, the use amount of the expensive solvent is reduced, and the cost of the refining agent in the desulfurization treatment can be reduced. In addition, since it does not contain a component that is concerned about the environment, such as fluorine, slag after desulfurization treatment can be effectively utilized. And, since it does not contain sodium, it is unnecessary to remove Na from the exhaust gas, and the cost of refractory can be reduced. In addition, the cost of the refining agent can be reduced and handling becomes easy as compared to other desulfurizing agents other than CaO systems having high reaction efficiency.

(5) In any one of said (1)-(3), it consists only of quicklime. Moreover, in addition to CaO, the desulfurizing agent may contain a component which is inevitably contained in quicklime.

According to the configuration of (5) above, since no desulfurizing agent other than a solvent or a CaO system is used, the cost of the refining agent can be significantly reduced. In addition, since it does not contain a solvent having an eluting element such as sodium or potassium, the amount of the expensive solvent is reduced, and the cost of the refining agent in the desulfurization treatment can be reduced. In addition, since it does not contain a component that is concerned about the environmental impact, such as fluorine, slag after desulfurization treatment can be effectively utilized. In addition, since it does not contain sodium, it is unnecessary to remove Na from the exhaust gas, and the cost of refractory can be reduced.

(6) The molten metal desulfurization method according to an aspect of the present invention is the sum of the volumes of pores having a pore diameter of 0.5 µm or more and 10 µm or less when desulfurizing molten iron (3) with a mechanically stirred desulfurization apparatus (1). A desulfurizing agent containing powdered quicklime having a total pore volume of 0.1 ml/g or more and an average particle diameter of 210 µm to 500 µm is used.

According to the configuration of (6), the same effects as those of (1) and (2) can be obtained.

(7) In the structure of the above (6), the quicklime has an average particle diameter of 230 µm or more and 500 µm or less.

According to the configuration of (7) above, the same effects as those of (3) can be obtained.

(8) In the configuration of the above (6) or (7), the mechanically stirred desulfurization device (1) includes a stirring blade (5) for stirring the molten iron (3) and a molten iron (3) from above the molten iron (3). ) Is provided on the bath surface of the upper spray lance 10 for spraying a desulfurizing agent with a carrier gas, and when the desulfurization treatment of the molten iron 3 is carried out, the molten iron is stirred using the stirring blade 5, and the molten iron 3 In this stirred state, a desulfurizing agent is sprayed onto the bath surface using the upper spray lance 10.

According to the configuration of (8) above, the effect of improving the desulfurization efficiency of quicklime can be made greater than that of the case where a desulfurizing agent is added using the upper side addition method.

(9) In the configuration of the above (8), when the desulfurizing agent is sprayed onto the bath surface, the flow velocity in the horizontal direction of the bath surface at the position where the desulfurizing agent is sprayed is set to 1.1 m/s or more and 11.5 m/s or less.

According to the configuration of (9) above, in the case where a desulfurizing agent is added by a projection method, the desulfurization efficiency can be further improved.

(10) The method for producing molten iron according to one aspect of the present invention uses the molten metal desulfurization method described in any one of (6) to (9) above.

According to the configuration of (10) above, the same effects as those of (6) to (9) can be obtained.

Example 1

Next, an embodiment implemented by the present inventors will be described. In Example 1, the desulfurization treatment of the molten iron 3 was performed using the molten metal desulfurization method which concerns on the said embodiment using the mechanical stirring desulfurization apparatus 1 shown in FIG.

In Example 1, after being discharged from the blast furnace, the molten iron 3 subjected to the desulfurization treatment was subjected to two stages of desalination treatment in the blast furnace casting bottom and the molten iron ladle serving as the molten iron container. . The composition of the molten iron 3 before the desulfurization treatment is [Si] = 0.05 wt% to 0.10 wt%, [C] = 4.3 wt% to 4.6 wt%, [Mn] = 0.22 wt% to 0.41 wt by prior desulfurization. %, [P] = 0.10 wt% to 0.13 wt%, and [S] = 0.025 wt% to 0.035 wt%. The temperature of the molten iron 3 before the desulfurization treatment was 1280°C to 1330°C.

In addition, in Example 1, desulfurization treatment was performed under a plurality of conditions using a desulfurizing agent in which the total pore volume, particle diameter, and ratio of quicklime were changed within the scope of the above embodiment. In addition, in Example 1, the addition amount of the desulfurizing agent was a constant amount of 5 kg/t, and when adding the desulfurizing agent, either the projection method by the projection means 6 or the upper addition method by the upper addition means 7 Desulfurization treatment was performed under a plurality of conditions using the method described above. The conditions for adding the desulfurizing agent and stirring conditions were the same as those in the first test shown in Table 1. Moreover, in all the addition methods of a desulfurizing agent, the position of the bath surface to which a desulfurizing agent is added was made into the same position. Then, the desulfurization efficiency was evaluated by calculating the desulfurization rate from the S concentration of the molten iron 3 measured before and after the desulfurization treatment.

Further, in Example 1, as a comparative example, desulfurization was performed in the same manner as in Example, by performing desulfurization treatment under conditions using injection desulfurization, the sum of the total pore volume of quicklime, and the average particle diameter different from the range of the above embodiment. Efficiency was evaluated.

Table 2 shows the evaluation results of the test level and desulfurization efficiency in Example 1. In Table 2, the ratio (%) of quicklime represents the ratio of quicklime in which the pore diameter is 0.5 µm or more and 10 µm or less, and the particle diameter is 2 mm or less among the quicklime that is a desulfurizing agent. In Table 2, the total pore volume of 0.5 to 10 µm (ml/g) represents the total pore volume which is the sum of the volumes of pores having a pore diameter of 0.5 µm or more and 10 µm or less. Moreover, the average pore diameter of the quicklime used was 0.1 micrometer-0.3 micrometer.

As shown in Table 2, in Examples 1-1 to 1-17 in which the characteristics of quicklime, which is a desulfurizing agent, were the conditions of the above embodiment, a high desulfurization rate of 75% or more was obtained regardless of the difference in the method of adding the desulfurizing agent. Confirmed. Moreover, the tendency for the desulfurization rate to become higher was confirmed in the condition using the projection method of Examples 1-9 to 1-15 than the condition using the upper addition method of Examples 1-1 to 1-8.

On the other hand, in Comparative Examples 1-1 to 1-12, in which either the sum of the total pore volume or the particle diameter is different from the conditions in the above embodiment, the desulfurization rate becomes 70% or less, and is compared with Examples 1-1 to 1-17. Therefore, it was confirmed to be low.

Example 2

Next, in Example 2, when the method for adding the desulfurizing agent was a projection method, the effect on the desulfurization efficiency under stirring conditions was investigated. In Example 2, a desulfurizing agent was added using a projection method in the same manner as in Examples 1-1 to 1-15, and the desulfurization treatment was performed under a plurality of conditions in which the sum of the total pore volume of the quicklime serving as the desulfurizing agent, the particle size, and the stirring conditions were changed. Was conducted. Table 3 shows the evaluation results of the test level and desulfurization efficiency in Example 2. In addition, the difference in stirring conditions, which is a difference between the rotational speed of the stirring blade 5 and the injection position of the desulfurizing agent, was summarized by the horizontal flow velocity of the bath surface of the molten iron 3 calculated from each condition.

As shown in Table 3, Examples 2-3 to 2-9, in which the flow velocity in the horizontal direction of the bath surface of the molten iron 3 at the position where the desulfurizing agent was injected is in the range of 1.1 m/s or more and 11.5 m/s or less, It was confirmed that in the conditions of 2-15 to 2-19, the desulfurization rate was 97% or more, and higher compared to other conditions.

1: Mechanical stirring desulfurization device
2: charter ladle
3: charter boat
4: Balance
5: stirring blade
6: Projection means
7: Upper side addition means
8: hopper
9: rotary feeder
10: Lance
11: hopper
12: rotary feeder
13: input chute

Claims (12)

Desulfurization agent used for desulfurization of molten iron,
The total pore volume, which is the sum of the volumes of the pores having a pore diameter of 0.5 µm or more and 10 µm or less, contains quicklime of 0.1 ml/g or more,
The quicklime is a powder having an average particle diameter of 210 μm or more and 500 μm or less,
A desulfurizing agent characterized in that it is used in a mechanical stirring type molten iron desulfurization method. delete According to claim 1,
The quicklime, the desulfurization agent, characterized in that the average particle diameter of 230 ㎛ to 500 ㎛. The method of claim 1 or 3,
A desulfurizing agent characterized in that it is substantially free of at least one of fluorine, potassium and sodium. The method of claim 1 or 3,
A desulfurizing agent comprising only the quicklime. When desulfurizing molten iron with a mechanically stirred desulfurization device,
Characterized in that a desulfurizing agent containing a powdery quicklime having a total pore volume of 0.1 ml/g or more and an average particle diameter of 210 µm or more and 500 µm or less is used, which is the sum of the volumes of pores having a pore diameter of 0.5 µm or more and 10 µm or less. Method for desulfurization of molten iron. The method of claim 6,
The quicklime, molten iron desulfurization method, characterized in that the average particle diameter of 230 ㎛ or more and 500 ㎛ or less. The method of claim 6,
The mechanically stirred desulfurization device includes a stirring blade for stirring the molten iron and an upper spray lance for spraying the desulfurizing agent with a carrier gas on the bath surface of the molten iron from above the molten iron,
In the desulfurization treatment of the molten iron,
Stir the molten iron using the stirring blade,
The molten iron desulfurization method, characterized in that the molten iron is sprayed to the bath surface using the upper spray lance while the molten iron is stirred. The method of claim 7,
The mechanically stirred desulfurization device includes a stirring blade for stirring the molten iron and an upper spray lance for spraying the desulfurizing agent with a carrier gas on the bath surface of the molten iron from above the molten iron,
In the desulfurization treatment of the molten iron,
Stir the molten iron using the stirring blade,
The molten iron desulfurization method, characterized in that the molten iron is sprayed to the bath surface using the upper spray lance while the molten iron is stirred. The method of claim 8,
When the desulfurizing agent is sprayed on the bath surface, the flow rate in the horizontal direction of the bath surface at the position where the desulfurizing agent is sprayed is 1.1 m/s or more and 11.5 m/s or less. The method of claim 9,
When the desulfurizing agent is sprayed on the bath surface, the flow rate in the horizontal direction of the bath surface at the position where the desulfurizing agent is sprayed is 1.1 m/s or more and 11.5 m/s or less. A method for manufacturing molten iron, characterized in that the method for desulfurizing the molten iron according to any one of claims 6 to 11 is used.

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