JP2004300507A - Method for restraining foaming of slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely restrain the foaming of slag in a reaction vessel at a low cost in a desiliconizing process, dephosphorizing process and converter decarburizing process in molten iron. <P>SOLUTION: When the desiliconizing treatment or the dephosphorizing treatment is applied to molten iron, a formed material composed of a mixture of plastics and fine granular iron powder obtained as the iron-making dust, is continuously added into the generated slag and the foaming of the generated slag is restrained by reducing the iron oxide in the slag with the plastics in the formed material. Further, after completing the decarburizing refining performed by top-blowing or bottom-blowing oxygen to the molten iron in a converter 24, the above formed material 4 is added into the slag 23 in the converter and the foaming of the slag in the converter is restrained by reducing the iron oxide in the slag with the plastics in the formed material in the slag so that the total Fe concentration in the slag becomes ≤ 18 mass%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention suppresses the bubbling (“forming”) phenomenon of slag in a reaction vessel, which is formed by generated gas generated in association with refining in a pretreatment process of hot metal and a converter decarburization refining process of hot metal. It is about the method.
[0002]
[Prior art]
In recent years, in a steel mill consisting of an integrated pig steel process, hot metal discharged from a blast furnace is subjected to a pretreatment consisting of desulfurization, desiliconization, and dephosphorization before being refined in a converter. In the furnace, an operation mode of only decarburizing and raising the temperature using low-phosphorized and low-sulfurized pretreated hot metal is becoming mainstream. Here, the desiliconization treatment is accompanied by a desiliconization reaction at the time of the dephosphorization treatment, and the desiliconization reaction inhibits the dephosphorization reaction. Before the process, the silicon in the hot metal is removed in advance. Therefore, if the efficiency of the dephosphorization treatment is not pursued, the dephosphorization treatment may be directly performed without performing the desiliconization treatment.
[0003]
In desiliconization treatment and dephosphorization process of molten iron, blowing oxygen source such as oxygen gas or iron oxide to molten iron or insufflation, although performing desiliconization and dephosphorization by oxidation, high containing SiO ₂ in a large amount Due to the formation of the viscous slag, the forming of the slag is extremely intense, and this is the biggest bottleneck in the desiliconization and dephosphorization. That is, the hot metal pretreatment is often performed in a hot metal transfer vessel such as a hot metal ladle or a torpedo car, and in the hot metal transfer vessel, the freeboard is smaller than that of a refining furnace such as a converter. The slag easily overflows from the hot metal transport container, so that the pretreatment must be interrupted, or the operation rate must be reduced due to the operation of removing the slag that has been jetted out.
[0004]
Further, in the converter operation, since the dephosphorization reaction is not required by applying the hot metal pretreatment, the amount of slag can be significantly reduced, and slag forming has been improved as compared with the conventional method. However, in order to prevent the splash of iron splash and the rise of nitrogen concentration in the molten steel during oxygen blowing, a cover slag covering the surface of the molten metal is necessary. Is done. When formed slag is formed, it is necessary to wait for tapping until the slag is calmed down.On the other hand, in recent converter operations that do not require dephosphorization, the number of converters in operation is reduced, and The mission of the middle converter is to increase the operating rate and improve the productivity, and therefore it is extremely important to quickly calm down the slag forming and to make it ready for tapping.
[0005]
Therefore, conventionally, various sedatives have been proposed for calming such slag forming. For example, Patent Literature 1 discloses one or more selected from stable industrial waste, incinerated ash or aluminum ash of combustible waste containing 5 mass% or more of recovered pulp material or papermaking sludge and the remainder being pulverized. A foaming slag sedative consisting of a mixture of the following has been proposed. Patent Document 2 discloses that a mixture of one or more of coal, limestone, plastic, and paper sludge with fine iron powder is used as a main raw material, and the main raw material is pulverized, and a binder is added thereto and mixed. Then, a briquette-like forming slag sedative having an apparent specific gravity in the range of 2 to 5 which is formed by compression and then molding has been proposed. Patent Literature 3 proposes a solid forming foam slag quenching agent obtained by mixing a combustible substance, metallic aluminum, and a CO gas generating substance, and then compression-molding the mixture.
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. Hei 7-145417
[Patent Document 2]
JP-A-9-217107
[Patent Document 3]
JP 2000-160223 A
[Problems to be solved by the invention]
However, the operation mode differs between the hot metal pretreatment and the converter refining as described above, and the timing and the amount of addition of the sedative as described above are naturally different. It has not been. As a result, the slag was insufficiently calmed or excessively calmed. Although sedatives of various compositions have been proposed as described above, it has been unclear what composition is suitable for a sedative capable of slag slag reliably and inexpensively. As described in Patent Document 3, a sedative to which expensive metallic aluminum is added is not practical even if the sedative effect is remarkable.
[0010]
The present invention has been made in view of the above circumstances, and its purpose is to remove slag in a reaction vessel in a hot metal desiliconization process and a dephosphorization process, and a hot metal converter decarburization refining process. An object of the present invention is to provide a specific method capable of reliably and inexpensively suppressing forming.
[0011]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above problems. The results of the study are described below.
[0012]
The slag is formed by retaining the gas generated during the refining in the slag. Therefore, forming is less likely to occur in a slag having a lower viscosity. However, the composition of the slag is preferably a predetermined composition corresponding to each refining, and changing the composition of the slag to suppress forming was not considered.
[0013]
Conventionally, in order to calm the formed slag, the forming slag is degassed and shrunk by destroying or piercing the forming slag, thereby lowering the surface level of the slag. In other words, by forming a hole in the forming slag by the fall of the sedative itself, by applying a physical force to the forming slag, such as stirring and breaking the forming slag, by the combustion gas generated by the combustion and decomposition of the sedative, The forming slag was calming down.
[0014]
Although such a physical suppression method is sufficiently effective in suppressing slag forming, the present inventors have found that it is effective to reduce the amount of gas itself that forms slag.
[0015]
This gas is partly due to the CO gas generated by the reaction between the oxygen source such as top-blown oxygen or bottom-blown oxygen and the carbon in the molten metal, but the iron oxide in the slag and the carbon in the molten metal react with each other. The generated CO gas was found to be the most responsible for slag forming. In the converter decarburization refining, it is clear from the fact that slag forming is formed even after the end of the acid supply. Therefore, it was found that reducing iron oxide in the slag by reducing the slag was effective in preventing forming. That is, since the iron oxide in the slag is reduced, the gas generated by the reaction between the iron oxide in the slag and the carbon in the molten metal is reduced.
[0016]
Plastics containing carbon and hydrogen as main components generate not only carbon as a reducing agent but also highly reducing hydrogen gas when heated, and thus effectively act as a slag reducing agent. Furthermore, plastic is inexpensive as compared with a metal-based deoxidizing agent such as Al. In particular, by using waste plastic, not only cost but also effective use of industrial waste can be achieved.
[0017]
In the case of converter decarburization of hot metal, the total Fe concentration in slag at the end of refining is usually about 20 to 30 mass%. It has been found that by reducing this slag to reduce the total Fe concentration in the slag to 18 mass% or less, desirably to 15 mass% or less, slag forming can be stably suppressed. The total Fe concentration in the slag is the total value of iron in all iron oxides (FeO, Fe ₂ O _3, etc.) in the slag. On the other hand, in the case of desiliconization and dephosphorization of hot metal, slag is continuously formed by the addition of an oxygen source. It was found that slag forming could be suppressed.
[0018]
However, when powdery, granular, film-like, or flake-shaped plastic is subjected to compression molding or extrusion molding, the apparent density of a single plastic molded body is at most about 500 kg / m ³ . The true density of the molten slag is about 3000 kg / m ³ , and the apparent density at the time of forming is about 300 to 600 kg / m ^3, depending on the state of forming. Therefore, a molded article made of only plastic cannot settle in the formed slag, and cannot efficiently reduce the slag even if the plastic is decomposed to generate carbon and hydrogen gas. Therefore, in order to increase the apparent density of the compact, fine iron powder such as converter OG dust, which is ironmaking dust, is used for density adjustment. In this case, judging from the apparent density of the forming slag, it is sufficient that the apparent density of the molded body composed of the plastic and the fine iron powder is 700 kg / m ³ or more.
[0019]
In particular, the converter OG dust contains 70 to 90 mass% of metallic iron as a pure component and has a high true density, so it is optimal as a density adjuster and can be obtained in powder form. It can be used without any modification. Furthermore, since the content of iron oxide is small, there is an advantage that when added to slag, the iron oxide concentration in slag is not increased. In the present invention, since it is necessary to reduce the iron oxide in the slag by plastic, mixing the iron oxide in the compact added to calm the slag is based on the degree of oxidation of the slag, that is, the iron oxide concentration. Is increased, which is not preferable from this viewpoint.
[0020]
The present invention has been made based on the above-described examination results, and the method for suppressing slag forming according to the first invention is directed to a method of blowing a stirring gas or a slag-making agent into hot metal in a reaction vessel to stir the hot metal. When adding oxygen source or solid oxygen source and subjecting hot metal to desiliconization or dephosphorization, molding consisting of a mixture of plastics mainly composed of carbon and hydrogen and fine iron powder obtained as ironmaking dust The body is continuously added to the slag produced by the addition of the oxygen source, and the iron oxide in the slag is reduced by the plastic in the molded body, thereby being produced by a desiliconization treatment or a dephosphorization treatment. It is characterized in that slag forming is suppressed.
[0021]
The slag forming suppression method according to the second invention, after the decarburization refining performed by blowing or bottom blowing oxygen to the hot metal in the converter, a plastic mainly composed of carbon and hydrogen, A compact made of a mixture with fine iron powder obtained as iron-making dust is added to slag in a converter, and iron oxide in the slag is added to the compact so that the total Fe concentration in the slag becomes 18 mass% or less. The slag forming in the converter is suppressed by reducing with plastic.
[0022]
A slag forming suppression method according to a third invention is characterized in that, in the first or second invention, the fine iron powder obtained as the ironmaking dust is converter OG dust.
[0023]
A slag forming suppression method according to a fourth invention is characterized in that, in any one of the first to third inventions, the apparent density of the single molded body is 700 kg / m ³ or more.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, a first embodiment will be described. Drawing 1 is a figure showing an example of a 1st embodiment of the present invention, and is a schematic diagram of desiliconization processing equipment of molten iron used when performing desiliconization processing concerning the present invention.
[0025]
In FIG. 1, a ladle-type hot metal ladle 6 containing hot metal 2 tapped from a blast furnace (not shown) is mounted on a bogie 7 and carried into the desiliconization treatment facility 1. The desiliconization treatment equipment 1 is provided with an upper blowing lance 8 and a blowing lance 9, and the upper blowing lance 8 and the blowing lance 9 have a structure capable of moving up and down in the hot metal pot 6. From the upper blowing lance 8, a gaseous oxygen source such as industrial pure oxygen is blown to the hot metal 2 as a desiliconizing agent.
[0026]
The blowing lance 9 is connected to the storage tank 10 and the storage tank 11, and supplies the solid oxygen source 3 stored in the storage tank 10 and the quicklime 5 stored in the storage tank 11 with an inert gas such as nitrogen or Ar. It can be added by blowing into the hot metal 2 as a carrier gas. The solid oxygen source 3 is added as a desiliconizing agent, and iron oxide such as iron ore or mill scale may be used. The quicklime 5 is a flux for adjusting the basicity (CaO / SiO ₂ ) of the slag 16 generated by the desiliconization reaction. In this case, another flux may be mixed with the quicklime 5, or another flux may be used instead of the quicklime 5. The solid oxygen source 3 in the storage tank 10 and the quick lime 5 in the storage tank 11 can be blown by controlling the amount and time of addition independently from each other. Alternatively, only the inert gas such as Ar or Ar may be blown to stir the hot metal 2.
[0027]
The desiliconization treatment facility 1 is further provided with a raw material supply facility comprising hoppers 12 and 13, a raw material conveyor 14 and a chute 15, and the hopper 12 accommodates the solid oxygen source 3 and the hopper 12. A molded body (hereinafter, referred to as “sedative 4”) made of a mixture of plastic mainly composed of carbon and hydrogen and fine iron powder obtained as iron-making dust is accommodated in 13. Using this raw material supply equipment, the solid oxygen source 3 in the hopper 12 and the sedative 4 in the hopper 13 can be placed in the hot metal pot 6 and added. Note that a flux such as quicklime 5 may be placed in the hot metal pot 6 and added thereto. However, since the hot metal 2 is stirred by the buoyancy of the flux, from the viewpoint of stirring the hot metal 2, as described above, the quicklime is used. The flux such as 5 is preferably added by blowing.
[0028]
Using the desiliconization treatment equipment 1 having such a configuration, the desiliconization treatment method according to the present invention is performed as follows.
[0029]
That is, the blowing lance 9 is immersed in the hot metal 2 and a gaseous oxygen source is continuously supplied from the upper blowing lance 8 as a desiliconizing agent while stirring the hot metal 2 by blowing an inert gas such as nitrogen or Ar as a stirring gas. The solid oxygen source 3 is continuously or intermittently added using a blowing lance 9 or a raw material supply facility, or both are used. At this time, a flux such as quicklime 5 may be added to adjust the basicity of the slag 16 to be generated.
[0030]
By adding gaseous oxygen source or a solid oxygen source 3, silicon in hot metal 2 is oxidized to SiO _2, a high SiO ₂ concentration slag 16 are formed. As the slag 16 is formed, the sedative 4 is continuously added onto the slag 16 until the end of the desiliconization treatment.
The addition amount of the sedative 4 depends on the amount of the slag 16 to be produced. However, since ₂ to 3 kg of SiO ₂ is produced per ton of hot metal by the desiliconization treatment, the plastic content is about 1/10 of that, That is, it is sufficient to add about 0.2 to 0.3 kg of a plastic content per 1 ton of hot metal.
[0031]
Part of the added solid oxygen source 3 and part of the iron oxide formed by the addition of the oxygen source are mixed with the slag 16 and the iron oxide concentration in the slag 16 increases. By adding 4, the iron oxide in the slag 16 is reduced, so that the amount of CO gas generated by the reaction between the iron oxide in the slag 16 and the carbon in the hot metal 2 is reduced, and the slag 16 is formed. Is suppressed.
[0032]
As described above, the converter OG dust is preferably used as the iron-making dust constituting the tranquilizer 4, while the plastic mainly composed of carbon and hydrogen is preferably waste plastic.
[0033]
In this case, the plastic containing carbon and hydrogen as main components is not particularly limited as long as it is a plastic classified as an engineering plastic such as polypropylene, polyethylene, polystyrene, and polyvinyl acetylene. Includes waste and defective products generated during the manufacture and processing of plastics, and plastics that are wastes generated as so-called garbage generated from ordinary households. Due to their nature, foreign substances other than plastics (metals, paper, other inorganic and organic substances) Contains plastics adhered or mixed. A mixture of waste plastic and product plastic may be used.
[0034]
Plastic content sedatives 4 is not particularly limited, when a small plastic content, since it is necessary to add large amounts of sedatives 4, single 700 kg / m ³ or more sedatives 4 It is preferable to ensure the apparent density of and the plastic content is 20 mass% or more.
[0035]
By performing the desiliconization treatment on the hot metal 2 in this manner, the forming of the slag 16 can be suppressed stably, and the ejection of the slag 16 from the hot metal pot 6 can be prevented. As a result, not only can the operation rate of the desiliconization treatment facility 1 be increased, but also operational safety is ensured.
[0036]
Although the above description has been made with reference to the example of the desiliconization treatment of the hot metal 2, the present invention can be applied to the dephosphorization treatment of the hot metal 2. The dephosphorization treatment of the hot metal 2 is also performed using the same equipment as the desiliconization treatment equipment 1 shown in FIG. 1 while adding a gaseous oxygen source and a fixed oxygen source, and refining while placing or blowing the quicklime. However, in the case of the dephosphorization treatment, the quicklime 5 is used as a dephosphorization flux, reacts with the phosphor oxide generated by the dephosphorization reaction to fix phosphorus in the slag 16 and to form the base of the generated slag 16. It is for adjusting the degree. Therefore, the refining method is the same as in the desiliconization process, although the amount of quicklime 5 added is greater than in the desiliconization process. Then, also in the dephosphorization treatment, the silicon in the hot metal 2 is oxidized and transferred to the slag 16. Therefore, also in the case of the dephosphorization treatment, if the slag 16 is formed by the addition of the gaseous oxygen source or the solid oxygen source, the sedative 4 is continuously added to the slag 16 until the end of the dephosphorization treatment. The addition amount of the sedative 4 may be in accordance with the desiliconization treatment.
[0037]
Next, a second embodiment will be described. Drawing 2 is a figure showing an example of a 2nd embodiment of the present invention, and is a schematic diagram of converter equipment used when performing converter decarburization refining concerning the present invention.
[0038]
In FIG. 2, a converter equipment 21 has a converter main body 24 for decarburizing and refining hot metal therein to produce molten steel 22, and an upper blowing lance 27 for supplying industrial pure oxygen to the converter main body 24. A hood 28 that covers the furnace opening of the converter main body 24 and introduces gas generated from the converter main body 24 into a dust collector (not shown), a hopper 29 that contains the tranquilizer 4, and is connected to the hopper 29. And a chute 31 for supplying the sedative 4 into the converter main body 24, which penetrates the converter 28. Between the hopper 29 and the chute 31, there is provided a cutting device 30 for adjusting the amount of the sedative 4 added, and the converter body 24 is provided with a stirring gas such as nitrogen or Ar at the bottom thereof. A plurality of bottom blowing tuyeres 26 for blowing are provided, and a tapping port 25 for tapping molten steel 22 is provided at an upper portion of the side wall.
[0039]
Into the converter main body 24, hot metal from a blast furnace is charged, and if necessary, a flux such as quicklime and an alloying element addition source such as Mn ore are charged and stirred from the bottom blowing tuyere 26. While blowing the working gas, industrial pure oxygen is blown from the top blowing lance 27 to carry out the decarburization and refining of the hot metal. The supplied oxygen reacts with the carbon in the hot metal to decarbonize the carbon in the hot metal. The furnace temperature rises with the start of the decarburization refining, and the slag 23 is formed in the converter main body 24 by melting the residual slag adhered during the previous treatment and the added quicklime. The total Fe concentration in the slag 23 increases with the progress of the decarburization refining.
[0040]
When the carbon concentration in the molten steel 22 decreases to a predetermined value of 0.03 to 0.08 mass% by the supply of industrial pure oxygen from the upper blowing lance 27, the supply of oxygen from the upper blowing lance 27 is stopped, Next, the tranquilizer 4 in the hopper 29 is charged into the converter main body 24 via the chute 31. The same sedative 4 is used as that used in the above-mentioned desiliconization treatment. However, the size may be changed.
[0041]
In this case, the amount of the sedative agent 4 to be added is such that the iron oxide in the slag 23 is reduced by the plastic in the sedative agent 4 and The addition amount is determined so that the Fe concentration is 18 mass% or less, desirably 15 mass% or less. The amount of slag 23 can be determined by the amount of quicklime added. Since the Fe concentration can be empirically determined from the carbon concentration in the molten steel 22 at the end of the decarburization refining, the amount of the sedative 4 to be added may be determined based on these. Since the reduction yield of the plastic varies depending on the apparent density and size of the sedative 4 and the method of addition, it is preferable to investigate each condition in advance and determine the amount to be added based on the results. However, since the reduction yield can be secured at least 50%, if the reduction yield is calculated as 50%, the total. The Fe concentration can be reduced to the predetermined value or less.
[0042]
By performing the decarburization refining of the hot metal by the converter equipment 21 in this way, the forming of the slag 23 can be stably suppressed, and the slag 23 can be prevented from being ejected from the converter main body 24. As a result, the calming waiting time of the slag 23 is greatly reduced, and not only can the operation rate of the converter equipment 21 be increased, but it is not necessary to remove the slag deposited directly below the converter main body 24, Stable converter operation can be performed.
[0043]
【The invention's effect】
According to the present invention, it is possible to reliably and inexpensively suppress the forming of slag in the reaction vessel, in the desiliconization process and dephosphorization process of the hot metal, and in the converter decarburization refining process of the hot metal, As a result, not only can the operation rate of the equipment for these treatments be increased, but also the operational safety is ensured, and industrially beneficial effects are brought about.
[Brief description of the drawings]
FIG. 1 is a view showing an example of a first embodiment of the present invention, and is a schematic view of a hot metal desiliconization treatment facility used when performing a desiliconization treatment according to the present invention.
FIG. 2 is a view showing an example of a second embodiment of the present invention, and is a schematic view of converter equipment used when performing converter decarburization refining according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Desiliconization processing equipment 2 Hot metal 3 Solid oxygen source 4 Calming agent 5 Quicklime 6 Hot metal pot 7 Dolly 7
8 Top blowing lance 9 Blowing lance 16 Slag 21 Converter equipment 22 Molten steel 23 Slag 24 Converter body 27 Top blowing lance 28 Hood

Claims (4)

When a gaseous oxygen source or a solid oxygen source is added to the hot metal in the reaction vessel while agitating gas or a slag-making agent is blown into the hot metal to stir the hot metal, and when the hot metal is subjected to desiliconization or dephosphorization, carbon And a plastic mainly composed of hydrogen, and a compact formed of a mixture of fine iron powder obtained as iron-making dust, continuously added to the slag generated by the addition of the oxygen source, to reduce the iron oxide in the slag A method for suppressing slag forming, characterized by suppressing forming of slag generated by desiliconization treatment or dephosphorization treatment by reducing with a plastic in the molded article. After the decarburization smelting performed by blowing or bottom blowing oxygen on the hot metal in the converter, it is composed of a mixture of plastic mainly composed of carbon and hydrogen and fine iron powder obtained as ironmaking dust. The compact is added to the slag in the converter, and the iron oxide in the slag is reduced by the plastic in the compact so that the total Fe concentration in the slag is 18 mass% or less. A method for suppressing slag forming, characterized by suppressing forming of slag. The slag forming suppression method according to claim 1 or 2, wherein the fine iron powder obtained as the ironmaking dust is converter OG dust. The apparent density of the molded body itself is characterized in that it is 700 kg / m ³ or more, slag methods of forming suppressed according to any one of claims 1 to 3.

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