EP3327150A1

EP3327150A1 - Desulfurizing agent, method for desulfurizing molten iron and method for producing molten iron

Info

Publication number: EP3327150A1
Application number: EP16830368.3A
Authority: EP
Inventors: Yoshie Nakai; Naoki Kikuchi; Hideya Masaki; Akira Ichikawa; Hiroharu Ido; Yuji Miki
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2015-07-24
Filing date: 2016-07-15
Publication date: 2018-05-30
Anticipated expiration: 2036-07-15
Also published as: EP3327150A4; TWI616402B; JPWO2017018263A1; KR102142198B1; CN107849623A; WO2017018263A1; JP6156598B2; CN107849623B; TW201714828A; EP3327150B1; BR112018001331B1; KR20180016593A; BR112018001331A2

Abstract

To provide a method for desulfurizing hot metal and a method for producing hot metal, which have excellent desulfurization efficiency and are capable of reducing the cost necessary for desulfurization treatment. A desulfurization flux used for hot metal desulfurization comprising quicklime in which a total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more.

Description

Technical Field

The present invention relates to a desulfurization flux, a method for hot metal desulfurization, and a method for producing hot metal.

Background Art

Generally, hot metal tapped from a blast furnace contains sulfur (S) that has a negative influence on the quality of steel at high concentration. Therefore, in a steel making step, various hot metal preliminary treatment and molten steel desulfurization are performed in accordance with required quality. Among these, as out of a furnace desulfurization of hot metal (also referred to as "hot metal desulfurization"), an injection desulfurizing method in which desulfurization is performed by injecting a desulfurization flux into hot metal, a mechanical-stirring type desulfurizing method in which desulfurization is performed by adding a desulfurization flux to hot metal stirred by a stirring blade, and the like are known. In addition, in such a method for desulfurizing hot metal, in any method, a desulfurization flux consisting primarily of inexpensive quicklime as a refining agent is highly used, and a desulfurizing reaction proceeds in accordance with a reaction formula indicated by formula (1).

CaO+S→CaS+O··· (1)
In such desulfurization treatment, for the purpose of improving reaction efficiency by acceleration of slag formation of quicklime, a method using a flux such as fluorite (CaF₂) and an alumina-based flux, is known. For example, as a desulfurization flux in which a flux is mixed, 95 wt% CaO-5 wt% CaF₂ is widely used. However, such a flux is generally expensive, and thus, increasing of a blending ratio of the flux in the desulfurization flux leads to an increase in cost necessary for the desulfurization flux. In addition, when increasing the blending ratio of the flux in the desulfurization flux, the CaO concentration in the desulfurization flux is decreased, and thus, a decline in the reaction efficiency of the desulfurization flux is a concern. In this context, there is a method in which the reaction efficiency of a desulfurization flux is improved by using a desulfurization flux consisting primarily of quicklime, in which the blending ratio of a flux is increased, in combination with a calcium carbide-based or soda-based desulfurization flux, or adding CaCO₃ to a desulfurization flux consisting primarily of quicklime, in which the blending ratio of a flux is increased (for example, PTL 1). However, in view of the recent situation where the influence of fluorine on environment is a concern, a desulfurization flux not using fluorite is desired. Therefore, a desulfurization flux having high desulfurization efficiency without using fluorite and a technology for improving desulfurization ability of quicklime itself are required.
As a desulfurization flux not using quicklime or fluorite, for example, calcium carbide-based and soda-based desulfurization flux are in practical use, but both desulfurization flux have advantages and disadvantages. The calcium carbide-based desulfurization flux has strong desulfurization ability, but there is a problem in that acetylene gas is generated in posttreatment of slag generated by desulfurization treatment. In addition, since the calcium carbide-based desulfurization flux is expensive, and furthermore, is a hazardous material, handling is difficult. The soda-based desulfurization flux is relatively inexpensive, but is highly alkalic, and thus, has a large influence on refractories, such as a furnace and a vessel. In addition, the soda-based desulfurization flux contains Na in exhaust gas, and thus, removal treatment thereof is necessary. Furthermore, the soda-based desulfurization flux has high Na₂O content in slag, and thus, recycling for cement or the like is limited. Therefore, it cannot be said that the calcium carbide-based and soda-based desulfurization flux are desirable desulfurization flux in view of the influence on environment, as in fluorine. Furthermore, as a desulfurizing method using a desulfurization flux other than the calcium carbide-based and soda-based desulfurization flux, a method using metal Mg as a desulfurization flux is well known. Metal Mg easily reacts with S in hot metal to generate MgS, but violently vaporizes in hot metal at 1250°C to 1500°C because of having a low boiling point of 1100°C, and is at risk of spattering the hot metal. In addition, in desulfurization treatment using metal Mg, since generated Mg vapor is diffused into the air without sufficiently contributing to a desulfurizing reaction, the efficiency is poor. Furthermore, metal Mg is extremely expensive, thereby leading to an increase in cost necessary for the desulfurization treatment.
As a technology for improving desulfurization ability of quicklime itself, an effort to improve desulfurization efficiency of a desulfurization flux from the viewpoints of lime properties is made. For example, a method for controlling a density, a specific surface area, a pore diameter volume as lime properties, in hot metal desulfurization by an injection desulfurizing method is disclosed in PTL 2, 3. According to PTL 2, 3, by controlling these lime properties, a floating-up speed of a desulfurization flux injected into hot metal can be controlled (lowered), and a reaction of the hot metal and the desulfurization flux can be accelerated. However, in PTL 2, 3, the injection desulfurizing method is targeted as a method of hot metal desulfurization, and the lime properties are not optimum in a mechanical-stirring type desulfurizing method. Furthermore, in PTL 2, the particle diameter of the targeted desulfurization flux is small, 200 µm or less. When using the foregoing fine desulfurization flux, it becomes easy to ensure a reaction interface area, but in the mechanical-stirring type desulfurizing method, it is important to use a desulfurization flux having a large particle diameter from the viewpoints of ensuring an addition yield, and a method for ensuring a reaction interface area using such a desulfurization flux having a large particle diameter is not described at all.
In the mechanical-stirring type desulfurizing method, generally, a powdery desulfurization flux added to a bath surface of hot metal is involved in the hot metal, and the desulfurization flux reacts with S in the hot metal. In this manner, in the case of a method for top-adding the desulfurization flux to the bath surface (also referred to as top-adding method), aggregation of the desulfurization flux proceeds, so that a reaction interface area becomes small, and a decrease in desulfurization efficiency was a problem. In the foregoing top-adding method, slag after desulfurization treatment becomes aggregated particles having a size of a few millimeters to a few tens of millimeters . In contrast, as a method for improving reaction efficiency in the mechanical-stirring type desulfurizing method, a method for blasting a powdery desulfurization flux on a bath surface (also referred to as powder blasting method) is known. In the powder blasting method, since aggregation of the desulfurization flux when being involved in hot metal is suppressed compared to the top-adding method, a practical reaction interface area becomes large, and the desulfurization ability can be improved. However, also in the foregoing powder blasting method, the aggregation of the blasted desulfurization flux still proceeds, and thus, the reaction interface area of the desulfurization flux itself could not be sufficiently used.
For this problem in the powder blasting method, a method of blasting a desulfurization flux using carrier gas is disclosed in PTL 4, 5. In PTL 4, 5, penetration of the desulfurization flux itself into hot metal is accelerated by using the carrier gas, so that aggregation of the desulfurization flux can be suppressed. However, since the properties of quicklime are not considered at all in the powder blasting method described in PTL 4, 5, a technology for further improving desulfurization efficiency of quicklime from the viewpoints of lime properties is required.

Citation List

Patent Literature

PTL 1: JP H8-268717 A
PTL 2: JP 5101988 B2
PTL 3: JP S62-56509 A
PTL 4: JP 5045031 B2
PTL 5: JP 5195737 B2

Summary of Invention

Technical Problem

The present invention was made in view of the above-described problems, and it is an object of the present invention to provide a desulfurization flux, a method for desulfurizing hot metal, and a method for producing hot metal, which have excellent desulfurization efficiency and are capable of reducing the cost necessary for desulfurization treatment.

Solution to Problem

According to one mode of the present invention, a desulfurization flux used for hot metal desulfurization, comprising: quicklime in which a total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more is provided.
According to one mode of the present invention, a method for desulfurizing hot metal, in which, when performing desulfurization treatment of hot metal in a mechanical-stirring type desulfurization device, a desulfurization flux containing powdery quicklime in which a total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more and an average particle diameter is from 210 µm to 500 µm is used is provided.
According to one mode of the present invention, a method for producing hot metal using the above-described method for desulfurizing hot metal is provided.

Advantageous Effects of Invention

According to one mode of the present invention, a desulfurization flux, a method for desulfurizing hot metal, and a method for producing hot metal, which have excellent desulfurization efficiency and are capable of reducing the cost necessary for desulfurization treatment, are provided.

Brief Description of Drawings

FIG. 1 is a schematic diagram illustrating a mechanical-stirring type hot metal desulfurization device according to one embodiment of the present invention;
FIG. 2 is a graph illustrating a relationship of a total pore volume of quicklime and a desulfurization rate in a first test;
FIG. 3 is a graph illustrating a relationship of an average particle diameter of quicklime and the desulfurization rate in the first test; and
FIG. 4 is a graph illustrating a relationship of a flow rate of a bath surface in a horizontal direction and a desulfurization rate in a second test.

Description of Embodiments

In the following detailed description, a number of specific details will be described for providing complete understanding of embodiments of the present invention. However, it is clear that one or more embodiments are practicable without such specific details. In addition, well-known structures and devices are illustrated by diagrams for simplifying the drawings.

First, how the present inventors made the present invention will be described. From the viewpoints of characteristics of a desulfurization flux (mainly, lime properties), the present inventors conducted extensive studies on the influence of the respective characteristics on desulfurization efficiency in a mechanical-stirring type desulfurizing method. Accordingly, it was found that, among various characteristics, such as a specific surface area and the degree of activity, pore diameter distribution and a particle diameter of quicklime have a profound influence, and in particular, a total pore volume of pores whose pore diameter range is from 0.5 µm to 10 µm has a profound influence. FIG. 1 illustrates a mechanical-stirring type desulfurization device 1 used in a first test, and Table 1 indicates conditions of devices and test methods by which the first test was conducted.

[Table 1]

Hot metal Conditions		Weight	300	t/ch
		Hot metal transfer Ladle Diameter	4	m
		Temperature	1280-1330	°C
		Before Treatment [S]	0.025-0.035	wt%
Desulfurization flux Conditions		Type	CaO
		Granularity	0.1-10	mm
		Additive Amount (CaO)	5	kgt
Stirring Conditions		Number of Blades	4
		Blade Diameter	1.45	m
		Rotation Speed of Blades	130	rpm
		Stirring Time
	15	min
Adding Conditions	Top-Adding Method	Addition Rate of Desulfurization Flux	1000	kg/min
	Powder Blasting Method	Lance Diameter	65A
		Addition Rate of Desulfurization Flux	200	kg/min
		Flow Rate of Nitrogen Gas	0-7	Nm³/min

As illustrated in FIG. 1, the mechanical-stirring type desulfurization device 1 is a refining device that performs desulfurization treatment of hot metal 3 stored in a hot metal transfer ladle 2. The hot metal transfer ladle 2 is arranged at a treatment position with being placed on a wagon 4. In the first test, the ladle diameter of the hot metal transfer ladle 2 was set to be 4 m, the weight of the hot metal 3 was set to be 300 t/ch, the temperature of the hot metal 3 was set to be from 1280°C to 1330°C, and the S concentration of the hot metal 3 before the desulfurization treatment ([S]) was set to be from 0.025 wt% to 0.035 wt%. It is to be noted that ch (charge) is a unit indicating the number of times of the desulfurization treatment performed for each hot metal transfer ladle 2 by the mechanical-stirring type desulfurization device 1, and 300 t/ch indicates that the weight of the hot metal 3 to be treated in one desulfurization treatment (the weight of the hot metal 3 stored in the hot metal transfer ladle 2) is 300 t.
The mechanical-stirring type desulfurization device 1 includes a stirring blade (impeller) 5, a powder blasting means 6, and a top-adding means 7. The stirring blade 5 is a refractory stirrer, is connected to a shaft at the upper end in a vertical direction (an up-and-down direction with respect to the plane of paper of FIG. 1), and has four blades that project in a direction perpendicular to a central shaft centered at the shaft. In addition, the upper end side of the shaft of the stirring blade 5 is connected to a rotating device and/or an elevating device, which is not illustrated. When the shaft receives rotary drive from the rotating device, the stirring blade 5 rotates around the shaft. In addition, the stirring blade 5 is configured to be capable of elevating in the vertical direction by elevating operation of the elevating device. In the first test, the desulfurization treatment was performed by setting the diameter of the stirring blade 5 to be 1.45 m and rotating the stirring blade 5 at a rotation speed of 130 rpm. The powder blasting means 6 has a hopper 8, a rotary feeder 9, and a lance 10. The hopper 8 stores a desulfurization flux. The rotary feeder 9 cuts out the desulfurization flux stored in the hopper 8 at a predetermined cutout speed, and supplies the desulfurization flux to the lance 10. The lance 10 is a 65A lance, and is arranged above a bath surface of the hot metal 3 so as to extend in the vertical direction. The lance 10 jets the desulfurization flux cut out from the rotary feeder 9 together with nitrogen that is carrier gas supplied from a carrier gas supplying device, which is not illustrated, so that the desulfurization flux is sprayed on the bath surface of the hot metal 3. The top-adding means 7 has a hopper 11, a rotary feeder 12, and an injecting chute 13. The hopper 11 stores a desulfurization flux. The rotary feeder 12 cuts out the desulfurization flux stored in the hopper 11 at a predetermined cutout speed, and supplies the desulfurization flux to the injecting chute 13. The injecting chute 13 is arranged such that the lower end is above the bath surface of the hot metal 3, and makes the desulfurization flux supplied from the rotary feeder 12 free-fall from the end, so that the desulfurization flux is injected into the bath surface of the hot metal 3. In the first test, the desulfurization treatment was performed by adding the desulfurization flux to the hot metal 3 by either adding method of a powder blasting method using the powder blasting means 6 or a top-adding method using the top-adding means 7. It is to be noted that, when performing the desulfurization treatment by the powder blasting method, the flow rate of the nitrogen gas was set to be 0 Nm³/min to 7 Nm³/min, and the desulfurization flux was added at an addition rate of 200 kg/min. On the other hand, when performing the desulfurization treatment by the top-adding method, the desulfurization flux was added at an addition rate of 1000 kg/min.
In addition, in the first test, only powdery quicklime was used as the desulfurization flux, the desulfurization treatment was performed without adding an additive agent other than a component inevitably contained in quicklime, and 5 kg/t (the additive amount per 1 ton of the hot metal) of the desulfurization flux was added by the powder blasting method or the top-adding method. Furthermore, in order to search a relationship of a total pore volume of quicklime and a desulfurization rate (a ratio of the amount of change of the S concentration before and after the treatment with respect to the S concentration before the treatment) and a relationship of a particle diameter of quicklime and the desulfurization rate, the desulfurization treatment was performed under the conditions where the total pore volume of quicklime or the particle diameter of quicklime is changed.
The total pore volume of quicklime is calculated from pore diameter distribution to be measured. A method for measuring the pore diameter distribution is as follows. First, quicklime was dried at a constant temperature of 120°C for 4 hours as pretreatment. Next, pore distribution in which the pore diameter of the dried quicklime is about from 0.0036 µm to 200 µm was obtained by the mercury intrusion technique using AutoPore IV 9520 manufactured by Micromeritics Instrument Corp., and a cumulative pore volume curve was calculated. Furthermore, the total pore volume of pores having a diameter of from 0.5 µm to 10 µm was obtained from the calculated cumulative pore volume curve. The pore diameter was calculated using Washburn's equation (equation (2)). It is to be noted that, in equation (2), P, D, σ, and θ indicate a pressure, the pore diameter, surface tension of mercury (=480 dynes/cm), and a contact angle of mercury with a sample (=140 degrees), respectively. $P \times D = - 4 \times σ \times cosθ$
Furthermore, the particle diameter is an average particle diameter, and a predetermined average particle diameter was obtained by screening the desulfurization flux. A method for measuring the average particle diameter of the desulfurization flux is as follows. First, 500 g of the desulfurization flux is collected during shipping from a manufacturer or during loading up the hopper 8. Next, the collected desulfurization flux was screened into 9 steps, 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, 500 µm to 1000 µm, and 1000 µm or more. Furthermore, for the screened desulfurization flux, the average particle diameter was calculated by calculation with a weight ratio of equation (3). It is to be noted that, in equation (3), D_a indicates the average particle diameter (mm), d_i indicates an average particle diameter in each of particle diameter ranges (screen mesh medium value) (mm), and w_i indicates a weight of the desulfurization flux on each screen (kg).
[Equation 1] $D_{o} = \frac{\sum_{i} (w_{i})}{\sum_{i} (w_{i} / d_{i})}$
As the result of the first test, a relationship of the total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm and the desulfurization rate when using the powder blasting method or the top-adding method is illustrated in FIG. 2. It is to be noted that, under the conditions illustrated in FIG. 2, the particle diameter of the desulfurization flux was set to be 1 mm or less. As illustrated in FIG. 2, it was confirmed that, in either case of the powder blasting method or the top-adding method, when the total pore volume of pores having a pore diameter of from 0.5 µm to 10 µm becomes 0.1 mL/g or more, the desulfurization rate is significantly increased, and a high desulfurization rate of 80% or more can be obtained. In addition, it was confirmed that improvable value of the desulfurization rate becomes larger by using the powder blasting method compared to the top-adding method.
Next, a relationship of the average particle diameter of the desulfurization flux and the desulfurization rate when using the powder blasting method or the top-adding method is illustrated in FIG. 3. It is to be noted that, under the conditions illustrated in FIG. 3, the total pore volume of pores having a pore diameter of from 0.5 µm to 10 µm was set to be 0.2 mL/g. As illustrated in FIG. 3, it could be confirmed that the desulfurization rate is significantly increased in a range where the average particle diameter of the desulfurization flux is from 210 µm to 500 µm. Furthermore, it could be confirmed that, in the above-described range, when the average particle diameter of the desulfurization flux becomes 230 µm or more, the desulfurization rate is more increased. In addition, it was confirmed that room for improvement of the desulfurization rate becomes larger by using the powder blasting method compared to the top-adding method.
Here, as the adding method of the desulfurization flux in the mechanical-stirring type desulfurizing method, at least one of the top-adding method and the powder blasting method is generally used. In the case of the foregoing adding method, it becomes difficult to add a desulfurization flux having a small diameter into hot metal in good yield unlike an injection desulfurizing method in which all of an added desulfurization flux penetrates into hot metal. Therefore, in the mechanical-stirring type desulfurizing method, in order to improve the yield, the particle diameter of the desulfurization flux to be added is important. Generally, when a desulfurization flux having a small particle diameter is used and the desulfurization flux can penetrate into hot metal, a reaction interface area with the hot metal can be ensured, and there is an advantage for improving desulfurizing reaction efficiency. However, the desulfurization flux having a small particle diameter becomes more difficult to penetrate into the hot metal as the diameter becomes smaller, and thus, increases the probability of not contributing to the reaction even when being added. In contrast, when the particle diameter of the desulfurization flux to be added is made large, there is an advantage for the penetration into the hot metal to improve the yield, but the reaction interface area is decreased, and there is a disadvantage from the viewpoints of the desulfurizing reaction. Therefore, in order to accelerate the reaction while ensuring the yield for the hot metal, it is important to achieve a balance between ensuring of an appropriate particle diameter of the desulfurization flux and increasing of the reaction efficiency.
In this context, from the result of the first test, the present inventors found that, in order to improve the desulfurization efficiency in the mechanical-stirring type desulfurizing method using quicklime as the desulfurization flux, existence of pores having a pore diameter of from 0.5 µm to 10 µm is important, and it is important to use the desulfurization flux in which the total pore volume of the pores is 0.1 mL/g or more. Furthermore, it was found that, as the desulfurization flux, by using one having an average particle diameter of from 210 µm to 500 µm, an appropriate particle diameter for improving the yield during addition to the hot metal can be ensured. In this manner, by controlling the average particle diameter in addition to the pores, the desulfurization efficiency can be more improved. Furthermore, it was found that, when the desulfurization flux under the conditions is used in the mechanical-stirring type desulfurizing method, a higher desulfurization rate can be obtained by using the powder blasting method as the adding method of the desulfurization flux to the hot metal 3, compared to the top-adding method. The following phenomenon is considered from these results of the first test. Quicklime is solid at a temperature where hot metal desulfurization is performed, and when quicklime added to the bath surface of the hot metal 3 has the above-described pore diameter size, the hot metal 3 penetrates into the pores of the surface of quicklime, so that wettability of the hot metal 3 and quicklime is physically improved. Accordingly, it is considered that the penetration of quicklime into the hot metal 3 is accelerated, and the desulfurization efficiency is improved. It is to be noted that, although similar properties and characteristics of quicklime are indicated in cited literature 2, 3, the cases of cited literature 2, 3 are different from the addition of the desulfurization flux to the bath surface of the hot metal 3 in mechanical-stirring type desulfurization, and thus, are completely different in principle from the above-described phenomenon. Therefore, the above-described desulfurization flux that the present inventors found cannot be conceived from the average pore diameter described in cited literature 2, 3.
Next, in order to search an influence of stirring conditions on the desulfurization rate in the powder blasting method, the present inventors performed the desulfurization treatment under various stirring conditions as a second test. In the second test, in the same manner as the first test, only powdery quicklime was used as the desulfurization flux, and quicklime in which the total pore volume of pores having a pore diameter of from 0. 5 µm to 10 µm is 0.1 mL/g or more and the particle diameter is 2 mm or less was used. It is to be noted that the additive amount of the desulfurization flux was the constant amount, 5 kg/t, and the desulfurization treatment was performed without adding an additive agent other than a component inevitably contained in quicklime. In addition, in the second test, the desulfurization treatment was performed using the mechanical-stirring type desulfurization device 1 illustrated in FIG. 1. It is to be noted that, in the second test, only the powder blasting means 6 was used when adding the desulfurization flux, and the adding conditions of the desulfurization flux were made the same as those of the first test. Furthermore, in the second test, by changing the position of the bath surface of the hot metal 3 on which the desulfurization flux is sprayed and the rotation speed of the stirring blade 5, the influence of these stirring conditions on the desulfurization rate was searched.
Differences in the rotation speed of the stirring blade 5 and the spraying position of the desulfurization flux, as the stirring conditions, result in different desulfurization rates, and they could be organized with a flow rate of the bath surface of the hot metal 3 at the position on which the desulfurization flux is sprayed in a horizontal direction. Here, the flow rate in the horizontal direction is a flow rate of a swirling flow generated from mechanical stirring at a position where the desulfurization flux is sprayed on the bath surface of the hot metal 3 in a horizontal tangent direction.
As the result of the second test, a relationship of the flow rate of the bath surface in the horizontal direction and the desulfurization rate is illustrated in FIG. 4. As illustrated in FIG. 4, it could be confirmed that, when the flow rate of the bath surface at the position on which the desulfurization flux is sprayed in the horizontal direction is from 1.1 m/s to 11.9 m/s, the desulfurizing reaction is more accelerated. When the desulfurization flux is sprayed on the bath surface of the hot metal 3 together with the carrier gas, it is considered that the rate on the side of the hot metal 3 is also an important element as conditions of solid quicklime to penetrate into the hot metal 3. When the flow rate of the bath surface at the position on which the desulfurization flux is sprayed in the horizontal direction is slower than 1.1 m/s, the desulfurization flux added into the hot metal 3 cannot move into the swirl generated by the stirring blade 5, and floats to the bath surface immediately, so that the reaction of the desulfurization flux and the hot metal 3 is not accelerated. In contrast, when the flow rate of the bath surface at the position on which the desulfurization flux is sprayed in the horizontal direction is faster than 11.9 m/s, a rate of the desulfurization flux in the vertical direction was overwhelmed by the rate of the hot metal 3 in the horizontal direction, and a part of the desulfurization flux spattered was observed. Therefore, it is considered that, when the flow rate of the bath surface at the position on which the powdery desulfurization flux is sprayed in the horizontal direction is from 1.1 m/s to 11.5 m/s, the effect obtained by adjusting a pore diameter volume is exerted, and the desulfurization flux can be incorporated into the hot metal 3 more efficiently.
It is to be noted that, in the above-described series of tests, experiments were conducted using only quicklime that satisfies the above-described conditions of the pore volume and the particle diameter as a quicklime source, but the desulfurization flux may be obtained by partially mixing quicklime that does not satisfy these conditions of the pore volume and the particle diameter. In this case, an effect in accordance with a mixing rate of quicklime that satisfies the conditions of the pore diameter volume of the present invention is obtained.

Next, a desulfurization flux, a method for desulfurizing hot metal, and a method for producing hot metal according to one embodiment of the present invention based on the above-described finding will be described. In the present embodiment, the desulfurization treatment of the hot metal 3 is performed using the mechanical-stirring type desulfurization device 1 illustrated in FIG. 1 in the same manner as the above-described first and second tests. It is to be noted that the mechanical-stirring type desulfurization device 1 has a cover (not illustrated) that covers an upper opening part of the hot metal transfer ladle 2, and an exhaust duct (not illustrated) that is provided on the cover and is connected to an exhaust device (not illustrated). Gas and dust generated during the desulfurization treatment are discharged to the exhaust device through the exhaust duct.
In the method for desulfurizing hot metal according to the present embodiment, first, the hot metal transfer ladle 2 in which the hot metal 3 is stored is placed on the wagon 4, and the wagon 4 is moved until the stirring blade 5 is located at a predetermined position with respect to the hot metal transfer ladle 2. Next, the stirring blade 5 is descended by the elevating device, so that the stirring blade 5 is immersed in the hot metal 3. Then, the stirring blade 5 rotates by the rotating device with the immersion in the hot metal 3, and the rotation speed is increased to a predetermined rotation speed simultaneously. At this time, generated gas and dust are discharged from the exhaust duct by the exhaust device. Furthermore, after the stirring blade 5 reaches a stationary rotation speed, the desulfurization flux is added to the hot metal 3 by the powder blasting means 6 or the top-adding means 7.
The desulfurization flux is quicklime in which the total pore volume defined as the sum of the volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more and the average particle diameter is from 210 µm to 500 µm. It is to be noted that, preferably, the minimum value of the particle diameter of quicklime is 40 µm or more, in consideration of spattering during the addition or the like. In addition, quicklime may be fired in any furnace, such as a kiln furnace, a Maerz furnace, and a Beckenbach furnace. When the powder blasting means 6 is used, the desulfurization flux cut out by the rotary feeder 9 is injected from the lance 10 into the bath surface of the hot metal 3 together with the carrier gas, such as nitrogen, thereby the desulfurization flux is added to the hot metal 3. At this time, preferably, the desulfurization flux is injected to a position where the flow rate of the bath surface of the hot metal 3 in the horizontal direction is from 1.1 m/s to 11.9 m/s. The position where the flow rate of the bath surface is in the above-described range is calculated in advance from the stirring conditions, such as the rotation speed of the stirring blade 5 and the spraying position of the desulfurization flux. In contrast, when the top-adding means 7 is used, the desulfurization flux cut out by the rotary feeder 9 is top-added to the bath surface of the hot metal 3 through the injecting chute 13.
After the desulfurization flux is added, stirring of the hot metal 3 by the stirring blade 5 is performed until predetermined time passes. After that, the rotation speed is decreased 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 ascended by the elevating device. Next, slag generated by the desulfurization treatment floats to cover the bath surface of the hot metal 3, and becomes a rest state, so that the desulfurization treatment is completed. Accordingly, the hot metal 3 having a desired S concentration is produced.

Although the present invention has been described above with reference to the specific embodiment, it is not intended to limit the invention by the description. By referring to the description of the present invention, various modified examples of the disclosed embodiment and other embodiments of the present invention are apparent to those skilled in the art. Therefore, it should be understood that claims cover these modified examples or embodiments included in the scope and spirit of the present invention.
For example, in the above-described embodiment, only quicklime in which the total pore volume of pores having a pore diameter of from 0. 5 µm to 10 µm is 0.1 mL/g or more and the average particle diameter is from 210 µm to 500 µm is used as the desulfurization flux, but the present invention is not limited to the foregoing example. For example, the desulfurization flux may be a mixture of quicklime in which the total pore volume and the particle diameter are in the above-described ranges and quicklime in which the total pore volume and the particle diameter are out of the above-described ranges. In addition, an alumina-based flux or the like may be added to the desulfurization flux in addition to quicklime in which the total pore volume and the particle diameter are in the above-described ranges. In this case, the desulfurization ability of quicklime is improved compared to quicklime out of the above-described ranges, and thus, equivalent or higher desulfurization efficiency can be obtained even when the additive amount of the flux is small. It is to be noted that the desulfurization flux according to the present invention does not contain a flux having at least one elution element of fluorine, sodium, and potassium.
In addition, the above-described embodiment is configured such that, when performing the desulfurization treatment, only the desulfurization flux is used as a refining agent, but the present invention is not limited to the foregoing example. For example, as a refining agent for further accelerating the desulfurizing reaction, a deoxidizing agent, such as aluminum dross powder containing metal Al, and metal Al, may be added. In this case, the deoxidizing agent is stored in a hopper different from that of the desulfurization flux, and after being cut out from the hopper, may be added to the hot metal 3 through the injecting chute 13. In addition, for example, as a refining agent, a flux such as fluorite and soda ash, may be added. In this case, the flux may be added after being mixed with the desulfurization flux, or the flux is stored in a hopper different from that of the desulfurization flux, and after being cut out from the hopper, may be added to the hot metal 3 through the injecting chute 13.
Furthermore, the above-described embodiment is configured such that one lance 10 is provided in the powder blasting means 6, but the present invention is not limited to the foregoing example. For example, two or more lances 10 may be provided.
Furthermore, the above-described embodiment is configured such that the desulfurization flux is used in the mechanical-stirring type hot metal desulfurizing method, but the present invention is not limited to the foregoing example. When quicklime in which the total pore volume defined as the sum of the volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more is used as the desulfurization flux, as illustrated in FIG. 2, the desulfurization rate is significantly increased as the reaction interface area is increased. The effect is effective in not only the mechanical-stirring type hot metal desulfurizing method but also another desulfurizing method for performing desulfurization treatment of hot metal, such as an injection desulfurizing method. Therefore, the desulfurization flux according to the present invention may be used in a method of desulfurization treatment other than the mechanical-stirring type hot metal desulfurizing method.

(1) The desulfurization flux according to one mode of the present invention is a desulfurization flux used for hot metal desulfurization, comprising: quicklime in which a total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more.
According to the configuration of the above (1), by making the total pore volume of quicklime be in the above-descried range, the desulfurization efficiency by quicklime can be improved. Accordingly, improvement in production efficiency due to shortening of desulfurization treatment time, a reduction in temperature loss and a reduction in treatment cost, and a reduction in the amount of generation of dust and slag generated by desulfurization treatment become possible. In addition, cost of a refining agent can be more reduced and handling becomes easier compared to a desulfurization flux other than a CaO-based desulfurization flux having high reaction efficiency. Furthermore, the desulfurization flux can be applied to both adding means of the top-adding method and the powder blasting method in the mechanical-stirring type desulfurizing method.
(2) In the configuration of the above (1), the quicklime is powdery quicklime having an average particle diameter of from 210 µm to 500 µm, and is used in a mechanical-stirring type hot metal desulfurizing method.
According to the configuration of the above (2), by making the average particle diameter of quicklime be in the above-descried range, the desulfurization efficiency by quicklime can be more improved. In addition, by using the desulfurization flux in the mechanical-stirring type hot metal desulfurizing method, the improving effect of the desulfurization efficiency by quicklime having the above-described configuration can be obtained more effectively.
(3) In the configuration of the above (2), the quicklime has the average particle diameter of from 230 µm to 500 µm.
According to the configuration of the above (3), the desulfurization efficiency can be more improved compared to the configuration of the above (2).
(4) In any of the configurations of the above (1) to (3), the desulfurization flux does not substantially contain at least one of fluorine, sodium, and potassium. Here, a state where at least one element of fluorine, sodium, and potassium is not substantially contained means that at least one element in the above elements is not contained by intentional addition except inevitable incorporation of a minor component.
According to the configuration of the above (4), the amount of used of an expensive flux is reduced, and cost of a refining agent in desulfurization treatment can be reduced. In addition, since a component for which the influence on environment is a concern, such as fluorine, is not contained, slag after the desulfurization treatment can be effectively used. Furthermore, since sodium is not contained, Na removal treatment from exhaust gas is not necessary, and cost for refractories can be reduced. Furthermore, cost of a refining agent can be more reduced and handling becomes easier compared to a desulfurization flux other than a CaO-based desulfurization flux having high reaction efficiency.
(5) In any of the configurations of the above (1) to (3), the desulfurization flux is containing only the quicklime. It is to be noted that a component inevitably contained in quicklime may be contained in addition to CaO.
According to the configuration of the above (5), since a flux and a desulfurization flux other than a CaO-based desulfurization flux are not used, cost of a refining agent can be drastically reduced. In addition, since a flux having an elution element, such as sodium and potassium, is not contained, the amount of used of an expensive flux is reduced, and the cost of a refining agent in desulfurization treatment can be reduced. Furthermore, since a component for which the influence on environment is a concern, such as fluorine, is not contained, slag after the desulfurization treatment can be effectively used. Furthermore, since sodium is not contained, Na removal treatment from exhaust gas is not necessary, and cost for refractories can be reduced.
(6) In the method for desulfurizing hot metal according to one mode of the present invention, when performing desulfurization treatment of hot metal 3 in a mechanical-stirring type desulfurization device 1, a desulfurization flux containing powdery quicklime in which a total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more and an average particle diameter is from 210 µm to 500 µm is used.
According to the configuration of the above (6), the same effect as that of the configurations of the above (1) and (2) can be obtained.
(7) In the configuration of the above (6), the quicklime has the average particle diameter of from 230 µm to 500 µm.
According to the configuration of the above (7), the same effect as that of the configuration of the above (3) can be obtained.
(8) In the configuration of the above (6) or (7), the mechanical-stirring type desulfurization device 1 indludes a stirring blade 5 configured stir the hot metal 3, and a top lance 10 configured to spray the desulfurization flux on a bath surface of the hot metal 3 together with carrier gas from above the hot metal 3, and, when performing the desulfurization treatment of the hot metal 3, the hot metal is stirred using the stirring blade 5, and the desulfurization flux is sprayed on the bath surface using the top lance 10 with the hot metal 3 being stirred.
According to the configuration of the above (8), the improving effect of the desulfurization efficiency of quicklime can be more increased compared to when the desulfurization flux is added using the top-adding method.
(9) In the configuration of the above (8), when the desulfurization flux is sprayed on the bath surface, a flow rate of the bath surface at a position on which the desulfurization flux is sprayed in a horizontal direction is from 1.1 m/s to 11.5 m/s.
According to the configuration of the above (9), when the desulfurization flux is added by the powder blasting method, the desulfurization efficiency can be further improved.
(10) The method for producing hot metal according to one mode of the present invention uses the method for desulfurizing hot metal according to any of the configurations of the above (6) to (9).

According to the configuration of the above (10), the same effect as that of the configurations of the above (6) to (9) can be obtained.

Example 1

Next, Examples conducted by the present inventors will be described. In Example 1, the desulfurization treatment of the hot metal 3 was performed using the mechanical-stirring type desulfurization device 1 illustrated in FIG. 1, using the method for desulfurizing hot metal according to the above-described embodiment.
In Example 1, as the hot metal 3 for which the desulfurization treatment is to be performed, hot metal for which, after being tapped from a blast furnace, two-step desiliconization treatment in a blast furnace casthouse and a hot metal transfer ladle that is a hot metal receiving vessel had been performed was used. The composition of the hot metal 3 before the desulfurization treatment was, by the advance desiliconization treatment, [Si]=0.05 wt% to 0.10 wt%, [C] =4.3 wt% to 4.6 wt%, [Mn]=0.22 wt% to 0.41 wt%, [P]=0.10 wt% to 0.13 wt%, and [S]=0.025 wt% to 0.035 wt%. The temperature of the hot metal 3 before the desulfurization treatment was 1280°C to 1330°C.
In addition, in Example 1, the desulfurization treatment was performed under multiple conditions using desulfurization flux in which the total pore volume, the particle diameter, and the ratio of quicklime were changed in the range of the above-described embodiment. Furthermore, in Example 1, the additive amount of the desulfurization flux was the constant amount, 5 kg/t, and the desulfurization treatment was performed under multiple conditions in which either method of the powder blasting method by the powder blasting means 6 or the top-adding method by the top-adding means 7 was used when adding the desulfurization flux. The adding conditions and the stirring conditions of the desulfurization flux were made the same as those of the first test indicated in Table 1. It is to be noted that, in either adding method of the desulfurization flux, the position of the bath surface to which the desulfurization flux is added was made the same. The desulfurization efficiency was evaluated by calculating the desulfurization rate from the S concentration of the hot metal 3 measured before and after the desulfurization treatment.
Furthermore, in Example 1, as comparative examples, the desulfurization treatment was performed under a condition using an injection desulfurizing method and under a condition in which the sum of the total pore volume and the average particle diameter of quicklime were different from those in the range of the above-described embodiment, and the desulfurization efficiency was evaluated in the same manner as the examples.
Table 2 indicates an evaluation result of a test level and desulfurization efficiency in Example 1. In Table 2, the ratio (%) of quicklime indicates a ratio of quicklime having a pore diameter of from 0.5 µm to 10 µm and a particle diameter of 2 mm or less in quicklime that is the desulfurization flux. In addition, in Table 2, 0.5-10 µm total pore volume (mL/g) indicates the total pore volume defined as the sum of the volumes of pores having a pore diameter of from 0.5 µm to 10 µm. It is to be noted that the average pore diameter of used quicklime was 0.1 µm to 0.3 µm.
As indicated in Table 2, it was confirmed that, in Examples 1-1 to 1-17 in which the characteristics of quicklime that is the desulfurization flux are the conditions of the above-described embodiment, a high desulfurization rate of 75% or more can be obtained despite the difference in the adding method of the desulfurization flux. In addition, it was confirmed that the desulfurization rate tends to be more increased under the conditions using the powder blasting method of Examples 1-9 to 1-15 compared to the conditions using the top-adding method of Examples 1-1 to 1-8.
In contrast, it was confirmed that, 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 of the above-described embodiment, the desulfurization rate is 70% or less, and is lower compared to that of Examples 1-1 to 1-17.

Example 2

Next, in Example 2, when using the powder blasting method as the adding method of the desulfurization flux, the influence of the stirring conditions on the desulfurization efficiency was searched. In Example 2, the desulfurization flux was added using the powder blasting method in the same manner as Examples 1-1 to 1-15, and the desulfurization treatment was performed under multiple conditions in which the sum of the total pore volume, the particle diameter, and the stirring conditions of quicklime that is the desulfurization flux were changed. Table 3 indicates an evaluation result of a test level and desulfurization efficiency in Example 2. It is to be noted that the differences in the stirring conditions, which are the differences in the rotation speed of the stirring blade 5, the spraying position of the desulfurization flux, and the like, were organized with the flow rate of the bath surface of the hot metal 3 in the horizontal direction, which was calculated from each condition.
As indicated in Table 3, it was confirmed that, under the conditions of Examples 2-3 to 2-9 and 2-15 to 2-19, in which the flow rate of the bath surface of the hot metal 3 at the position on which the desulfurization flux is sprayed in the horizontal direction is in the range of from 1.1 m/s to 11.5 m/s, the desulfurization rate is 97% or more, and is higher compared to other conditions.

Reference Signs List

1: mechanical-stirring type desulfurization device
2: hot metal transfer ladle
3: hot metal
4: wagon
5: stirring blade
6: powder blasting means
7: top-adding means
8: hopper
9: rotary feeder
10: lance
11: hopper
12: rotary feeder
13: injecting chute

Claims

A desulfurization flux used for hot metal desulfurization, comprising:
quicklime in which a total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more.
The desulfurization flux according to claim 1, wherein the quicklime is powdery quicklime having an average particle diameter of from 210 µm to 500 µm, and is used in a mechanical-stirring type hot metal desulfurizing method.
The desulfurization flux according to claim 2, wherein the quicklime has the average particle diameter of from 230 µm to 500 µm.
The desulfurization flux according to any one of claims 1 to 3, not substantially containing at least one of fluorine, sodium, and potassium.
The desulfurization flux according to any one of claims 1 to 3, containing only the quicklime.
A method for desulfurizing hot metal, wherein,
when performing desulfurization treatment of hot metal in a mechanical-stirring type desulfurization device, a desulfurization flux containing powdery quicklime in which a total pore volume defined as a sum of volumes of pores having a pore diameter of from 0.5 µm to 10 µm is 0.1 mL/g or more and an average particle diameter is from 210 µm to 500 µm is used.
The method for desulfurizing hot metal according to claim 6, wherein
the quicklime has the average particle diameter of from 230 µm to 500 µm.
The method for desulfurizing hot metal according to claim 6 or 7, wherein
the mechanical-stirring type desulfurization device includes a stirring blade configured to stir the hot metal, and a top lance configured to spray the desulfurization flux on a bath surface of the hot metal together with carrier gas from above the hot metal, and,
when performing the desulfurization treatment of the hot metal, the hot metal is stirred using the stirring blade, and the desulfurization flux is sprayed on the bath surface using the top lance with the hot metal being stirred.
The method for desulfurizing hot metal according to claim 8, wherein,
when the desulfurization flux is sprayed on the bath surface, a flow rate of the bath surface at a position on which the desulfurization flux is sprayed in a horizontal direction is from 1.1 m/s to 11.5 m/s.
A method for producing hot metal using the method for desulfurizing hot metal according to any one of claims 6 to 9.