KR102260982B1 - Method dephosphorization and molten steel recovery during converter double slag operation - Google Patents

Abstract

The present invention relates to a method for improving double slag dephosphorization with steel manufacturing byproducts. More specifically, the present invention relates to a method for increasing a molten steel recovery rate by reducing the molten iron loss into the slag and performing an efficient dephosphorization in accordance with the early slag formation by using SCBall instead of quicklime for a certain ratio in the dephosphorization process in a double slag work during a steel manufacture process using a steel converter. In accordance with the present invention, lime is collected from nature, and is used for substituting quicklime processed at a high temperature, and the SCBall, a steel manufacturing byproduct, is used for reducing damage to nature. In addition, the use of fossil fuel, the main cause for global warming, is reduced, and the slag formation rate of quicklime is also increased during the dephosphorization process through reusing wastes, thereby having an excellent effect for protecting the environment. At the same time, the loss of molten iron generated in a furnace, which is discharged to the slag in the steel converter process, is reduced, and the efficiency of the steel manufacture process using the steel converter is increased.

Description

Efficient dephosphorization and molten steel recovery during converter double slag operation

The present invention relates to a method for improving double slag dephosphorization using a steelmaking by-product, and more particularly, phosphorus (Phosphorus) in a double slag dephosphorization process that removes silicon, phosphorus, and sulfur, which are impure elements, from molten iron tapped from a blast furnace. The purpose of the present invention is to provide a technology for removing and using steel by-products to increase the recovery rate of molten iron, and by rapidly cooling and spheroidizing converter decarburized slag during the steelmaking process and using it as a slag preparation material in the double slag dephosphorization process, It relates to a method for improving double slag dephosphorization using steelmaking by-products to minimize it.

As a conventionally known technique, a molten steel manufacturing method (Application No. 10-2003-0062234) is disclosed, but the technique compensates for heat loss by directly injecting ladle slag in a hot state into LF, and It is an invention that is characterized by reducing slag treatment cost or recycling valuable components contained in ladle slag by tapping molten steel in a converter while leaving ladle slag. 2002-0061709) mainly aims to recover valuable metals by using converter slag as a direct dephosphorization agent in performing pre-treatment dephosphorization.

In addition, an invention (application No. 10-2008-7020316) whose gist is the addition of alumina or titanium dioxide to control the slag composition and temperature within an appropriate range and to reduce the amount of slag generated during the molten iron pretreatment dephosphorization operation is known. The low-melting solvent composition (Application No. 10-2001-0047900) with slag soothing effect and dephosphorization ability for converter refining has a low melting point with excellent dephosphorization ability while retaining slag soothing effect during blowing in the converter refining process. In composing the mae solvent, it is prepared as pellets by mixing limestone with a particle size of 0.1 to 1.0 mm to provide slag calming effect and iron oxide with a particle size of 0.1 to 1.0 mm to provide dephosphorization ability and low melting point. , characterized in that it comprises a melting point of 1,100 ~ 1,300 ℃.

When the molten iron pretreatment process according to the conventional method is performed through the above process, when the molten iron extracted from the blast furnace arrives at the pretreatment process, sintered ore and quicklime are first put into the upper part, and the sintered ore reacts with the silicon in the molten iron After forming silica (SiO ₂ , hereinafter silica), it reacts with quicklime to form a complex low-melting oxide, so there is a problem in that the dissolution rate of the initial quicklime is slow and the reaction time is increased.

In addition, although it is a common method to additionally add fluorite to improve the quicklime dissolution rate, fluorite has a problem in that it dissipates fluorine gas into the atmosphere or increases fluorine content in the cooling water system, thereby causing environmental pollution.

In addition, various solvents were used to promote dissolution of quicklime or to develop a separate flux that does not contain fluorine, but the technology commercialized so far is limited to general work, and pretreatment dephosphorization work is based on fluorite. You just have to put in the mordant. In a situation in which the introduction of the pretreatment dephosphorization process for the purpose of reducing the amount of slag for the purpose of increasing the demand for high-grade steel and eco-friendly work is expanding compared to the past, the development of a mordant agent that can replace such fluorite is required first.

KR 10-2003-0062234 (2003. 09. 05.) KR 10-2002-0061709 (2002. 10. 10.) KR 10-2008-7020316 (2007. 02. 26.) KR 10-2001-0047900 (2001. 08. 09.)

Quicklime used in the dephosphorization process is a steel-making auxiliary material obtained by extracting limestone from nature and subjecting it to high-temperature heat treatment. A lot of natural damage occurs during the limestone extraction process, and a large amount of carbon dioxide is emitted by using coke, a fossil fuel, during the high-temperature heat treatment process. do. In addition, when quicklime is used as a slag preparation material, molten iron is inevitably oxidized and escapes into a large amount of slag, resulting in a large loss of iron source.

The present invention was devised to solve the above problems, and the problem to be solved in the present invention is to reprocess converter decarburization slag generated as a by-product in the steelmaking process so that it can be used in the dephosphorization process, and then put it in to dephosphorize double slag. Its purpose is to enable eco-friendly operation by reducing the absolute amount of auxiliary materials inputted as a dephosphorization agent by directly acting as a dephosphorization material and increasing the steelmaking efficiency by preventing the iron source from being lost to slag.

In addition, the present invention rapidly cools the high-temperature liquid converter slag through high-pressure and high-speed gas injection through Steel Compound Ball (hereinafter referred to as SC Ball) processed from converter slag, which is a kind of steelmaking by-product. The purpose is to maintain a certain size without being hydrated because it does not react with moisture in the air even if stored for a long time in the air.

The method for improving double slag dephosphorization using steelmaking by-products according to the present invention for achieving the above object suppresses the use of quicklime, which is a raw material for natural damage, and reduces the amount of molten iron escaping into slag, phosphorus concentration compared to dephosphorization slag It is characterized in that it provides an efficient double slag dephosphorization process by rapidly cooling and spheroidizing small decarburized slag to replace quicklime.

In addition, the SCBall of the present invention controls the composition of the slag so that the slag does not contain Free CaO by rapidly cooling the high-temperature liquid-phase converter decarburization slag with a low phosphorus concentration and high iron content compared to the dephosphorization slag through high-pressure and high-speed gas injection. characterized.

According to the present invention, natural damage is reduced by using SCBall, a by-product of steelmaking, by replacing quicklime that is extracted from nature and treated at high temperature, reducing the use of fossil fuels, the main culprit of global warming, and recycling waste to Tallinn city. It has an excellent effect on environmental protection by increasing the quicklime rate, and at the same time, it is effective in increasing the efficiency of the steelmaking converter process by reducing the loss of molten iron produced in the blast furnace as slag in the converter process.

1 is a graph relating to the mixing ratio of quicklime and SCBall according to the present invention.
Figure 2 is a graph of the loss of molten iron according to the mixing ratio of quicklime and SCBall according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Recently, the quality of iron ore has decreased and the phosphorus content of molten iron has increased, but as the demand for high-grade steel increases, it is necessary to make low phosphorus steel in the converter operation, so the double slag method reaches 70% of the converter operation.

However, in the existing double slag operation, the primary dephosphorization process operation method is to try dephosphorization by injecting 10 tons of quicklime, and as a result, 20 tons of dephosphorization slag is generated. After excluding all the generated dephosphorization slag, decarburization operation is continued. However, the composition of dephosphorization slag is shown in Table 1.

<Composition of Tallinn Slag> division T.Fe CaO SiO ₂ Al ₂ O ₃ MgO MnO P ₂ O ₅ basicity Content (wt%) 18.1 32.2 18.2 1.59 6.05 2.93 6.77 1.76

For pre-treatment dephosphorization, the molten iron drawn from the blast furnace is transported in a torpedo car, a transport container, and is re-picked to the charging ladle, which is a reaction vessel, for pre-treatment dephosphorization in the steelmaking process and is represented as a dephosphorization furnace. It is charged to the pre-treatment dephosphorization facility. For pretreatment dephosphorization, quicklime, sintered ore and flux are put in the upper part of the molten iron, and dephosphorization is performed by mechanical stirring or gas injection.

Looking at the above process in more detail, in order to form slag, first, desiliconization (Si + O ₂ = SiO ₂ ) and dephosphorization (C + ½O ₂ = CO, 2P + 5/2O) through primary and secondary oxidation reactions ₂ = P ₂ O ₅ ) is carried out, and slag is formed through a chemical reaction of quicklime, sintered ore, and flux through a method such as stirring or gas blowing.

The reaction formula of this _{dephosphorization reaction is 5Fe 2} O ₃ + 6P = 10Fe + 3P ₂ O ₅ and P ₂ O ₅ + 3CaO + Ca ₃ (PO ₄ ) ₂ .

At this time, it is a common method to add fluorite in addition to the conventional method to improve the quicklime dissolution rate, but it is desirable to suppress fluorite as much as possible because it causes environmental pollution by dissipating fluorine gas into the atmosphere or increasing the fluorine component in the cooling water system.

On the other hand, in the prior art, a method for controlling the melting point of slag formed during operation is used in order to solve the problem of reaction efficiency between slag-molten iron without distinguishing between a general process of simultaneously performing dephosphorization and decarburization and a double slag process.

According to the prior invention, the amount of Steel Compound Ball (hereinafter referred to as SC Ball) is determined by the molten iron component and the amount of molten iron, and the method for determining the amount of input is to input the amount necessary to limit the value _{of CaO/SiO 2 to 2.2 or more and 5.5 or less.} , More preferably, CaO / SiO ₂ It is the best condition to control 2.5 or more and 4.0 or less.

That is, when the CaO / SiO ₂ value is 2.2 or less, the dissolution rate of quicklime increases but the dephosphorization efficiency is lowered, and when it has a value of 5.5 or more, the slag melting point is too high to achieve the original goal of the present invention, so CaO / SiO _{The value of 2} should be limited to 2.2~5.5.

Here, the calculation of the input amount of SCBall can be calculated through the following equation.

<Calculation formula for input amount of SCBall>

W _CaO : Quicklime input weight (kg)

W _HM : molten dose (ton)

V _ratio : target basicity (CaO/SiO ₂ )

wt%(i) _SC : Content of i component in SCBall

W _SC : SCBall input weight (kg)

However, the calculation of the amount of quicklime input as above is not appropriate for the double slag dephosphorization process. That is, in the general converter process, the end point basicity must be set to 2.5-4 so that dephosphorization, desiliconization, and decarburization can proceed smoothly in sequence or at the same time. In the double slag dephosphorization process, the goal is only basic dephosphorization, and then a more precise decarburization process This is because, first, a large amount of dephosphorization must be performed by increasing the quicklime dissolution rate, and the final phosphorus concentration in molten steel is adjusted in the decarburization process. That is, in the double slag dephosphorization process, it is preferable to set the target basicity to 1.5 to 2.5.

SCBall is composed of an amorphous state in which general slag is rapidly cooled and spheroidized, and is mainly a calcium ferrite state (CaO-Fe ₂ O ₃ ) complex oxide with a body-centered cubic structure. As a result, it forms a melting point at 1,100℃ and melts before quicklime around quicklime, which has a melting point of 2,400℃, to induce early melting of quicklime. It is characterized by

However, the phosphorus content (P ₂ O ₅ ) of the general slag of the decarburization end point is 1.73 wt%, but the phosphorus content of the dephosphorization end point slag of the double slag process is 6.77 wt%, and the phosphorus inclusion range of SCBall has a margin of 5 wt%. That is, in the general process, SCBall only serves to promote the product of quicklime, but in the double slag dephosphorization process, SCBall has the ability to directly dephosphorize. Through the above characteristics, it can be said that the use of SCBall in the dephosphorization process of double slag shows a lot of difference from the general process. Therefore, in the present invention, it is intended to use the decarburized slag as a dephosphorization material by using the difference in the phosphorus concentration of the slag.

In the double slag dephosphorization process, it is appropriate to control the amount of slag to 20 tons based on 300 tons of molten iron. Currently, most of the 10 tons of quicklime are used to form 20 tons of slag. As a result, the composition of the dephosphorization slag is as shown in Table 1 above.

According to the slag composition in Table 1, 20 tons of slag is formed in the dephosphorization process based on a 300-ton molten iron converter, and 6.77 wt% of phosphorus (P ₂ O ₅ ) is contained in the slag, so the total amount of dephosphorization of 20 tons is 1.35 tons. .

On the other hand, the decarburization endpoint slag has the composition shown in Table 2, and the composition of SCBall to be used in the present invention is also shown in Table 2.

division T.Fe CaO SiO ₂ Al ₂ O ₃ MgO MnO P ₂ O ₅ basicity Content (wt%) 21.0 42.2 10.2 2.17 8.53 2.43 1.73 4

According to Table 2, SCBall _{contains 1.73 wt% of phosphorus (P 2} O ₅ ), and when used in the double slag dephosphorization process, has a dephosphorization ability of 5 wt% compared to the phosphorus concentration of 6.77 wt% of the dephosphorization end point slag. Therefore, when quicklime and SCBall are used in the dephosphorization process, the amount used is determined as follows. It is assumed that 1 ton of quicklime is composed of 2 ton of slag, assuming a recovery rate of 60%.

<Calculation formula for quicklime and SCBall usage>

( 2 · X · 6.77 ) + ( Y · 5 ) = 135 ----- Formula (1)

Y = - 2.68 X + 27

X = - Y/2.68 + 10

X is the amount of quicklime used (kg), 6.77 is the quicklime dephosphorization capacity

Y is SCBall usage (kg), 5 is SCBall dephosphorization capacity

where 0 < X < 10 0 < Y < 27,

20 < 2·X + Y < 27 --------------------------- Formula (2)

On the other hand, as for the basicity, SCBall has a basicity of 4 (CaO/SiO ₂ ), but when used in the dephosphorization process, desiliconization also occurs. Through desiliconization, SiO ₂ is additionally absorbed, and the SiO ₂ content is originally 10.2wt%. is increased to 18.2 wt%, and accordingly the basicity is _{lowered to 2.3 (CaO/SiO 2} , 42/18). Accordingly, the above-mentioned target base also falls within the range of 1.5-2.5.

In addition, looking at the molten iron that escapes to the slag during the dephosphorization process, since 18wt% of iron is contained in the slag at the end of the dephosphorization, the total iron loss of the 20-ton slag will be 3.6 tons. However, when using SCBall, since SCBall already contains 21 wt% of iron, about 3 wt% of iron is rather recovered as molten iron during the dephosphorization process. When this is calculated, the amount of molten iron loss (Z) is as follows (Calculation Equation 3).

Z = 2 · X · 18 + (-) Y · 3 ------------ Formula (3)

However, X and Y are numbers that satisfy the formula ( 2 · X · 6.77 ) + ( Y · 5 ) = 135

X is the amount of quicklime used (kg), 18 is the amount of quicklime slag iron loss (wt%)

Y is SCBall usage (kg), 3 is SCBall slag iron source recovery amount (wt%)

Therefore, it will be said that the most efficient operation method is to determine the amount of use that minimizes the above formula (3) under the conditions of the formulas (1) and (2). Therefore, if SCBall is used instead of 2.68 tons per 1 ton of quicklime and the capacity of the converter is taken into account, the total amount of slag is 20~25 tons, but considering the target basicity and target slag composition, the amount of quicklime used is 3~8 tons, and the amount of SCBall used is 3~8 tons. 5-14 tons of silver is preferable.

below. Examples will be described.

In the pretreatment process for performing dephosphorization according to the present invention, a certain amount of SCBall of the components shown in Table 3 was added to make the total amount of slag 23 tons, and the result of improved dephosphorization efficiency was obtained, and the results are shown in Table 4 indicated.

division T.Fe CaO SiO ₂ Al ₂ O ₃ MgO MnO TiO ₂ P ₂ O ₅ SCBall (wt%) 21.0 42.2 10.2 2.17 8.53 2.43 0.35 1.73

division T.Fe SiO ₂ CaO P ₂ O ₅ basicity Dragon Boat (P)
(wt%) After treatment (P)
(wt%) Usage (kg) quicklime SCBall Example 18.28 18.49 31.97 6.76 1.72 0.099 0.025 5000 13600 18.51 18.98 31.40 6.73 1.65 0.104 0.022 5000 13600 18.41 17.85 32.54 6.65 1.82 0.103 0.027 6000 11920 18.85 17.93 32.01 6.67 1.78 0.104 0.020 6000 11920 18.09 16.95 33.23 6.24 1.96 0.101 0.030 7000 8320 17.91 16.74 33.53 6.32 2.00 0.110 0.022 7000 8320 17.49 15.02 34.29 6.18 2.28 0.098 0.025 8000 5560 17.79 15.57 34.71 6.16 2.22 0.100 0.019 8000 5560

Through this experiment, the appropriate composition of quicklime and SCBall to improve dephosphorization efficiency was confirmed.

According to this embodiment of the present invention, quicklime and sintered ore used as auxiliary materials in the prior art were separately input, and slag dissolution during dephosphorization was not easy depending on the _{SiO 2 generation rate generated by oxidation of silicon during molten iron.} , when dephosphorization operation is performed according to the above composition, SCBall is melted at a low temperature of 1,100° C. to promote the recycling of quicklime, and SCBall itself acts as a dephosphorization function, thereby achieving very good dephosphorization efficiency.

The technique presented in the present invention solves the problem of slag dissolution, improves the dephosphorization reaction efficiency of the double slag process, and reduces the use of quicklime as much as possible and increases the use of SCBall in order to prevent the loss of molten iron to slag. It can be, and the mixing ratio of SCBall considered in the present invention can be solved through the above-mentioned formula in consideration of the amount of auxiliary raw materials input during operation.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (4)

In the method for improving double slag dephosphorization using steelmaking by-products,
It is characterized in that the amount of quicklime and SCBall (Steel Compound Ball) is calculated through the following formulas (Equation 1 and Equation 2) to determine the input amount and mixing ratio, and then added to the molten iron during dephosphorization,
The input amount of the SC Ball is,
When input according to the molten iron component and the amount of molten iron, the basicity is controlled to be 1.5 to 2.5 in order to control the slag composition,
The amount of molten iron loss is minimized through the following formula (Calculation Equation 3),
The SC Ball,
Total iron powder (T.Fe) 21.0 wt%, calcium oxide (CaO) 42.2 wt%, silicon dioxide (SiO ₂ ) 10.2 wt%, aluminum oxide (Al ₂ O ₃ ) 2.17 wt%, magnesium oxide (MgO) 8.53 wt% , Manganese oxide (MnO) 2.43wt%, phosphorus (P ₂ O ₅ ) Double slag dephosphorization improvement method using steelmaking by-products, characterized in that the content is 1.73wt%.

Quicklime and SCBall usage formula
( 2 · X · 6.77 ) + ( Y · 5 ) = 135 ----- Formula (1)
Y = - 2.68 X + 27
X = - Y/2.68 + 10
X is the amount of quicklime used (kg), 6.77 is the quicklime dephosphorization capacity
Y is SCBall usage (kg), 5 is SCBall dephosphorization capacity
where 0 < X < 10 0 < Y < 27,
20 < 2·X + Y < 27 --------------------------- Formula (2)

Calculation formula for loss of molten iron (Z)
Z = 2 · X · 18 + (- Y · 3) ------------ Formula (3)
However, X and Y are numbers that satisfy the formula ( 2 · X · 6.77 ) + ( Y · 5 ) = 135
X is the amount of quicklime used (kg), 18 is the amount of quicklime slag iron loss (wt%)
Y is SCBall usage (kg), 3 is SCBall slag iron source recovery amount (wt%) delete delete delete

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