Apparatus and method for refining molten metal

Abstract

To provide an apparatus and a method for refining molten metal with which in the refining of molten metal, particularly, Cr-containing molten steel, the excessive use of a reducing material can be restrained.SOLUTION: In an apparatus for refining molten metal and a method for refining molten metal, an internal shape 21 of a refining vessel 1 is measured using a profilometer 6 that irradiates the inside of the refining vessel 1 with a laser, one or more types (calculation items) of a kind, a flow rate, and a total supply amount of a refining gas 25, particularly the total oxygen supply amount, are determined using the internal shape 21 measured by the profilometer 6, particularly an area of a molten metal surface 23, and refining is performed by adjusting the calculation items according to the determination result.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus and a method for refining molten metal. [Background technology]

[0002] When refining chromium-containing steels, especially those containing 11% or more chromium such as stainless steels, a widely used decarburization refining method is the AOD method, in which oxygen gas or a mixture of oxygen gas and an inert gas is blown into molten steel contained in a refining vessel. In the AOD method, as decarburization progresses and the carbon concentration in the molten steel decreases, the chromium in the molten steel becomes more susceptible to oxidation. Therefore, to suppress the oxidation of chromium, the proportion of an inert gas such as argon gas in the blown gas is increased as the carbon concentration decreases. Furthermore, vacuum refining can be used to promote decarburization in the low carbon concentration range.

[0003] Patent Document 1 discloses a method in which oxygen gas or a mixed gas of oxygen gas and an inert gas is supplied as the blowing gas, decarburization is performed at atmospheric pressure until the [C] concentration in the molten steel falls to 0.5 mass%, and after the [C] concentration falls to this value or below, the pressure inside the vessel is reduced to 200 torr or less for decarburization. This method performs decarburization under reduced pressure from a relatively high [C] concentration and also performs decarburization using a mixed gas of oxygen gas under reduced pressure, thereby improving the decarburization rate with the same oxygen supply amount and reducing the reducing material consumption and expensive inert gas consumption.

[0004] Patent Document 2 discloses a converter refractory profile measuring device that measures the refractory profile of a converter, and is characterized in that it has a profile meter that can measure the distance to an object to be imaged within a two-dimensional imaging range, and that the profile meter can observe part or all of the inner surface shape of the refractory inside the converter furnace through the furnace throat. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-287629 [Patent Document 2] Japanese Patent Application Publication No. 2018-185253 Summary of the Invention [Problem to be solved by the invention]

[0006] Cr-containing molten steel is refined using an AOD furnace, combining atmospheric and vacuum refining. When refining a specific Cr-containing molten steel, the total oxygen gas supply required for refining is determined when the refining method of the AOD furnace is maintained constant. It has been observed that even when the same product is refined using the same method, the total oxygen gas supply required for refining decreases as the number of refining cycles (heat count, hereafter also referred to as "heat cycles") increases after the AOD furnace refractory lining is renewed (early after construction). Therefore, based on the refining performance of Cr-containing molten steel, the total oxygen gas supply amount is determined for each cycle, and refining is carried out using the determined total oxygen gas supply amount. For example, the total oxygen gas supply amount is divided into the following categories: up to 50 cycles, 51 to 100 cycles, 101 to 300 cycles, and 301 cycles and beyond, and refining is carried out using the determined total oxygen gas supply amount.

[0007] When refining was performed with the total oxygen gas supply determined using the above method, it was found that the total oxygen gas supply was excessive depending on the number of furnace runs. When the total oxygen gas supply is excessive, the excess oxygen causes excessive oxidation of Cr in the molten steel and it is absorbed into the slag, resulting in excessive use of reducing material.

[0008] An object of the present invention is to provide a molten metal refining apparatus and a molten metal refining method that can prevent excessive use of reducing agents, particularly in the refining of Cr-containing molten steel, by measuring the internal shape of the refining vessel using a profile meter. [Means for solving the problem]

[0009] That is, the gist of the present invention is as follows. [1] A refining vessel for molten metal, the inner surface of which is lined with refractory material, a device for supplying refining gas into the refining vessel, and a profile meter for measuring the internal shape of the refining vessel by irradiating a laser into the refining vessel; a calculator that determines one or more of the type, flow rate, and total supply amount of refining gas (hereinafter referred to as "calculation items") using the internal shape measured by the profile meter; a flow rate control device that adjusts the calculation items according to the calculation results obtained by the calculator; A molten metal refining apparatus comprising: [2] The apparatus for refining molten metal according to [1], characterized in that the molten metal is chromium-containing molten steel, the refining gas is oxygen gas, and the calculation item is the total supply amount of oxygen gas. [3] The molten metal refining apparatus further includes a reducing material supply device for supplying a reducing material into the refining vessel; The molten metal refining apparatus according to [2], characterized in that the computing device calculates a surface area of ​​the molten metal in the refining vessel using the internal shape measured by the profile meter, determines a total supply amount of the oxygen gas in accordance with the calculated surface area of ​​the molten metal, and determines a supply amount of the reducing material to be supplied from the reducing material supply device in accordance with the calculated total supply amount of the oxygen gas. [4] determining in advance an appropriate amount of the total supply amount of oxygen gas corresponding to the calculated molten metal surface area based on the refining result of the molten metal, and storing the determined amount in the computing device; The molten metal refining apparatus according to [3], characterized in that an appropriate supply amount of the reducing material corresponding to the total supply amount of the oxygen gas is determined in advance based on the refining results of the molten metal and then stored in the computing device.

[0010] [5] A molten metal refining vessel having a refractory-lined inner surface of the steel shell is used, refining gas is supplied into the refining vessel to perform refining, and the internal shape of the refining vessel is measured using a profile meter that irradiates a laser into the refining vessel; Using the internal shape measured by the profile meter, one or more of the type, flow rate, and total supply amount of refining gas (hereinafter referred to as "calculation items") is determined; A method for refining molten metal, characterized in that the calculation items are adjusted in accordance with the result of the determination and refining is carried out. [6] The method for refining molten metal according to [5], characterized in that the molten metal is Cr-containing molten steel, the refining gas is oxygen gas, and the calculation item is the total supply amount of oxygen gas. [7] The method for refining molten metal further comprises supplying a reducing agent into the refining vessel; The method for refining molten metal according to [6], characterized in that a surface area of ​​the molten metal in the refining vessel is calculated using the internal shape measured by the profile meter, a total supply amount of the oxygen gas is determined according to the calculated surface area of ​​the molten metal, and an amount of the reducing agent to be supplied is determined according to the calculated total supply amount of the oxygen gas. [8] determining in advance an appropriate amount of the total supply amount of the oxygen gas corresponding to the calculated molten metal surface area based on the refining results of the molten metal; The method for refining molten metal according to [7], wherein an appropriate supply amount of the reducing agent corresponding to the total supply amount of the oxygen gas is determined in advance based on the refining result of the molten metal. [Effects of the Invention]

[0011] The present invention provides a molten metal refining apparatus and a molten metal refining method that can prevent excessive use of reducing agents, particularly in the refining of Cr-containing molten steel, by measuring the internal shape of a refining vessel using a profile meter and determining refining conditions according to the molten metal surface area. [Brief explanation of the drawings]

[0012] [Figure 1] This is a front cross-sectional view of a molten metal refining equipment, where (A) shows the furnace in the early stages of construction, and (B) shows the furnace in the final stages of construction. [Figure 2] FIG. 1 is a cross-sectional plan view showing the state in which the internal shape of a refining vessel is measured using a profile meter. [Figure 3]FIG. 1 is a diagram showing the relationship between the furnace number of a refining vessel and the molten metal surface area. [Figure 4] FIG. 1 is a diagram showing the relationship between the molten metal surface area in a refining vessel and the total oxygen supply amount. [Figure 5] FIG. 4 is a diagram showing the relationship between the total oxygen supply amount and the amount of reducing agent used. [Figure 6] FIG. 10 is a diagram showing the relationship between the number of furnace runs and the total oxygen supply amount in the examples. [Figure 7] FIG. 1 is a diagram showing the relationship between the number of furnace runs and the amount of reducing material used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1, the molten metal refining apparatus of the present invention is characterized by comprising: a molten metal refining vessel 1, the inner surface of which is lined with a refractory material 3 in a shell 2; a device for supplying a refining gas 25 into the refining vessel 1; a profile meter 6 that measures the internal shape 21 of the refining vessel 1 by irradiating a laser into the refining vessel 1; a computer 11 that determines one or more of the type, flow rate, and total supply amount of the refining gas 25 (calculation parameters) using the internal shape 21 measured by the profile meter 6; and a flow control device 12 that adjusts the calculation parameters according to the calculation results obtained by the computer 11. The device for supplying the refining gas 25 can be either a bottom-blowing tuyere 4 that injects the refining gas 25 into the molten metal 22 by bottom-blowing, or a top-blowing lance 5 that injects the refining gas 25 onto the molten metal 22 from above.

[0014] The method for refining molten metal that is the subject of the present invention is characterized in that it uses a refining vessel 1 for molten metal 22 with a refractory material 3 lining the inner surface of the steel shell 2, supplies a refining gas 25 into the inside of the refining vessel 1 to perform refining, measures the internal shape 21 of the refining vessel 1 using a profile meter 6 that irradiates a laser into the refining vessel 1, determines one or more (calculation items) of the type, flow rate, and total supply amount of the refining gas 25 using the internal shape 21 measured by the profile meter 6, and performs refining by adjusting the calculation items according to the results of the determination.

[0015] The molten metal 22 can preferably be applied to Cr-containing molten steel. The refining gas 25 can preferably be applied to oxygen gas. By selecting the total supply amount of oxygen gas (hereinafter also referred to as "total oxygen supply amount") from among the above calculation items, favorable results can be obtained. Below, an example will be described in which the molten metal is Cr-containing molten steel, the refining gas is oxygen gas, and the calculation item is the total oxygen supply amount.

[0016] The present invention is suitably used in a refining apparatus and a refining method in which molten metal 22 is chromium-containing molten steel, refining gas 25 is a gas containing oxygen gas, and refining is performed by injecting the oxygen-containing gas into the chromium-containing molten steel in a refining vessel. The refining vessel 1 for the molten metal 22 has a shell 2 whose inner surface is lined with refractory material 3. An AOD furnace is suitably used as the refining vessel 1 for refining the chromium-containing molten steel. A bottom-blowing tuyeres 4 and a top-blowing lance 5 are used as devices for supplying the refining gas into the refining vessel 1. Molten steel is contained in the refining vessel 1 as the molten metal 22, and slag 23 is formed on top of the molten steel. The refining gas 25 is injected into the chromium-containing molten steel in the refining vessel through the bottom-blowing tuyeres 4.

[0017] Vacuum refining and atmospheric refining are used to refine chromium-containing molten steel. Figure 1 shows the atmospheric refining process. When vacuum refining is performed, an exhaust hood (not shown) is attached to the refining vessel 1, and the pressure inside the vessel is reduced by gas suction. Since an exhaust hood is not attached during atmospheric refining, as shown in Figure 1, gas can be injected using not only the bottom-blowing tuyere 4 but also the top-blowing lance 5.

[0018] In the present invention, a profile meter 6 is provided that irradiates a laser into the refining vessel 1 to measure the internal shape 21 of the refining vessel 1, and the internal shape 21 of the refining vessel 1 can be measured using the profile meter 6. As shown in the plan view of Figure 2, the refining vessel 1 is tilted so that the throat 7 of the refining vessel 1 faces horizontally, and the profile meter 6 is positioned in the direction in which the throat 7 faces, and a laser is irradiated from the profile meter 6 into the refining vessel, which is the field of view 26 of the profile meter, so that the internal shape 21 of the refining vessel 1 can be measured.

[0019] The refining vessel 1 for molten metal 22 has a shell 2 that is lined with a refractory 3 on the inner surface. As the number of refining cycles (number of heats) increases, the refractory 3 inside the refining vessel 1 undergoes progressive wear, and as this wear progresses, the internal volume of the refining vessel 1 that contains the molten metal 22 increases. In Figure 1, Figure 1(A) shows the state at the beginning of construction, and Figure 1(B) shows the state at the end of construction. When a certain amount of molten metal 22 is contained in the refining vessel 1, in the early stages of construction of the refractory 3 (Figure 1(A)), the internal volume based on the internal shape 21 is narrow, so the molten metal bath is deep (the position of the molten metal surface 24 is high) and the molten metal surface area is narrow. On the other hand, as the number of refining cycles increases (Fig. 1(B)), the internal shape 21 recedes toward the steel shell 2 compared to the internal shape 31 at the initial stage of construction (shown by the two-dot chain line in Fig. 1(B)). As the internal volume increases, the depth of the molten metal layer becomes shallower (the molten metal surface 24 drops compared to the molten metal surface 34 at the initial stage of construction), and the molten metal surface area increases. By using the profile meter 6, the current internal shape 21 of the refining vessel 1 can be determined, making it possible to accurately determine the molten metal surface area when a predetermined amount of molten metal is contained. Fig. 3 shows the relationship between the number of cycles since the initial stage of construction and the molten metal surface area calculated from the measurement results of the profile meter 6 when an AOD furnace is actually used to refining chromium-containing molten steel.

[0020] When the same type of Cr-containing molten steel is melted using an AOD furnace with the same refining method, as described above, it has been recognized that the total required supply of oxygen gas during refining decreases as the number of refining cycles (furnace cycles) increases after the refractory lining of the AOD furnace is renewed (at the beginning of construction).

[0021] The inventors came up with the idea that there might be some correlation between the total oxygen gas supply amount, which decreases as the number of furnace runs increases, and the molten metal surface area, which increases as the number of furnace runs increases (see FIG. 3).

[0022] When chromium-containing molten steel is refined in an AOD furnace, the decarburization process progresses and the carbon concentration in the molten steel decreases. In the final stages of the process, oxygen gas injected into the molten steel oxidizes the chromium in the molten steel to form Cr2O3 (reaction 1), which is then absorbed into the slag. Next, the Cr2O3 in the slag reacts with carbon in the metal at the slag-metal interface to form CO gas and chromium (reaction 2). This second reaction occurs at the slag-metal interface, i.e., the molten metal surface 24, which is the interface between the molten metal 22 and the slag 23. The larger the area of ​​the slag-metal interface, i.e., the molten metal surface 24, the faster the reaction rate. The faster the reaction rate, the faster the decarburization reaction of the molten steel progresses, and the lower the total oxygen gas supply required. If the total amount of oxygen gas supplied is greater than the required amount, the Cr in the molten steel will be excessively oxidized, and the amount of reducing agent required to reduce the Cr2O3 in the slag will also increase.

[0023] Based on the above idea, the relationship between the molten steel surface area based on the results measured by the profile analyzer 6 and the required total oxygen supply amount required for refining was evaluated. Figure 4 shows the relationship between the molten steel surface area measured by the profile analyzer 6 and the required total oxygen supply amount determined from refining results when refining chromium-containing molten steel in an AOD furnace. As a result, as can be seen in Figure 4, it became clear that the required total oxygen supply amount decreases as the molten steel surface area increases. Based on this result, it is possible to measure the internal shape 21 of the refining vessel 1 with the profile analyzer 6 to calculate the molten steel surface area, and then perform oxygen injection by adopting the optimum required total oxygen supply amount for that molten steel surface area.

[0024] The molten metal refining apparatus of the present invention further comprises a reducing material supply device 13 for supplying a reducing material into the refining vessel 1, and the computer 11 can determine the amount of reducing material to be supplied from the reducing material supply device 13.

[0025] Total oxygen supply volume (unit: Nm3 A linear relationship can be seen between the oxygen injection rate (kg / t) and the amount of reducing agent used (unit: kg / t) as shown in Figure 5. It has become clear that if oxygen injection is performed by adopting the optimum total oxygen supply amount based on the molten metal surface area measured by Profile Total 6, the amount of oxygen injected will not be excessive, and as a result, the amount of reducing agent used can be reduced.

[0026] By determining in advance the optimum total supply amount of oxygen gas corresponding to the calculated molten metal surface area based on the refining results of the molten metal and determining in advance the optimum supply amount of reducing agent corresponding to the total supply amount of oxygen gas based on the refining results of the molten metal, it is possible to perform oxygen injection by adopting the optimum total required oxygen supply amount based on the molten metal surface area measured by the profile meter 6, thereby preventing excessive oxygen injection and resulting in a reduction in the amount of reducing agent used. In the molten metal refining apparatus of the present invention, the optimum total supply amount of oxygen gas corresponding to the calculated molten metal surface area can be determined in advance based on the refining results of the molten metal and stored in the computer 11, and the optimum supply amount of reducing agent corresponding to the total supply amount of oxygen gas can be determined in advance based on the refining results of the molten metal and stored in the computer 11.

[0027] As mentioned at the beginning, the molten metal refining apparatus that is the subject of this invention, as shown in Figure 1, comprises a refining vessel 1 for molten metal 22, the inner surface of which is lined with refractory material 3 in the steel shell 2, a device for supplying refining gas 25 into the inside of the refining vessel 1, a profile meter 6 that measures the internal shape 21 of the refining vessel 1 by irradiating a laser into the refining vessel, a calculator 11 that determines one or more of the type, flow rate, and total supply amount of refining gas (calculation items) using the internal shape 21 measured by the profile meter 6, and a flow rate control device 12 that adjusts the calculation items according to the calculation results obtained by the calculator 11.

[0028] The method for refining molten metal that is the subject of the present invention is characterized in that it uses a refining vessel 1 for molten metal 22 with a refractory material 3 lining the inner surface of the steel shell 2, supplies a refining gas 25 into the inside of the refining vessel 1 to perform refining, measures the internal shape 21 of the refining vessel 1 using a profile meter 6 that irradiates a laser into the refining vessel 1, determines one or more (calculation items) of the type, flow rate, and total supply amount of the refining gas 25 using the internal shape 21 measured by the profile meter 6, and performs refining by adjusting the calculation items according to the results of the determination.

[0029] As described above, the molten metal 22 is preferably Cr-containing molten steel.

[0030] As mentioned above, oxygen gas can be preferably used as the refining gas 25. Furthermore, the refining gas 25 can be selected from a mixture of oxygen gas and an inert gas such as Ar gas or nitrogen gas, in addition to oxygen gas.

[0031] By selecting the total supply amount of oxygen gas from the above calculation items, preferable results can be obtained. In addition to the total supply amount of oxygen gas, calculation items can also be selected from the flow rate of oxygen gas, the total supply amount or flow rate of inert gas such as Ar gas or nitrogen gas, and the ratio of oxygen gas to inert gas. [Example]

[0032] The present invention was applied to the refining of Cr-containing molten steel using an AOD furnace with a molten metal charge of 60 tons.

[0033] Total oxygen supply (Nm 3 / t) in the comparative example, the conventional method was used up to 50 furnace cycles, and the 3 / t, 51 to 100 times is 20.5Nm 3 / t, 101 to 300 times is 20.1Nm 3 / t, 301 to 350 times is 19.7Nm 3 / t, 19.3Nm after 351 times 3 / t was set.

[0034] In the present invention, the relationship between the molten metal surface area based on the results measured by the profile meter 6 and the appropriate total oxygen supply amount required for refining was clarified. 2 ) and the appropriate required total oxygen supply (Nm 3 / t) was determined as shown in Figure 4. The amount of reducing material to be added was determined based on the relationship shown by the straight line in Figure 5.

[0035] Next, as shown in Table 1, measurements were taken with a profile meter 6 at predetermined intervals as the furnace cycle progressed, and the molten metal surface area was calculated. 2 ) based on the relationship shown in Figure 4, the total oxygen supply (Nm 3 The amount of reducing material input (kg / t) was determined based on the relationship shown by the straight line in Figure 5, and refining was performed.

[0036] [Table 1]

[0037] FIG. 6 shows the actual results of the total oxygen supply amount for each furnace run for the present invention and the comparative example.

[0038] Figure 7 shows the actual amount of reducing material input for each furnace run for the present invention example and the comparative example. As shown in Figure 7, when the total cost of one furnace run from the initial stage to the final stage of refractory construction is taken into account, it is clear that the reducing material consumption rate for the present invention example is lower than that for the comparative example. [Explanation of symbols]

[0039] 1. Refining vessel 2 Ironhide 3 Refractories 4 Bottom-blown tuyere 5 Top blowing lance 6 Profile Total 7 Hearth 11 Computing machine 12 Flow control device 13 Reducing material supply device 21 Internal shape 22 Molten Metal 23 Slag 24 Water surface 25 Refining gas 26 Profile meter field of view 31 Initial interior shape 33 Slag position at the beginning of construction 34 Water level at the beginning of construction

Claims

1. The present invention comprises a molten metal refining vessel having a refractory-lined inner surface of a steel shell, a device for supplying a refining gas into the refining vessel, and a profile meter for measuring the internal shape of the refining vessel by irradiating a laser into the refining vessel, a calculator that determines one or more of the type, flow rate, and total supply amount of refining gas (hereinafter referred to as "calculation items") using the internal shape measured by the profile meter; a flow rate control device that adjusts the calculation items according to the calculation results obtained by the calculator; A molten metal refining apparatus comprising:

2. 2. The apparatus for refining molten metal according to claim 1, wherein the molten metal is chromium-containing molten steel, the refining gas is oxygen gas, and the calculation item is a total supply amount of oxygen gas.

3. The apparatus for refining molten metal further comprises a reducing material supply device for supplying a reducing material into the refining vessel; 3. The molten metal refining apparatus according to claim 2, wherein the computing device calculates a surface area of ​​the molten metal in the refining vessel using the internal shape measured by the profile meter, determines a total supply amount of the oxygen gas in accordance with the calculated surface area of ​​the molten metal, and determines a supply amount of the reducing material to be supplied from the reducing material supply device in accordance with the calculated total supply amount of the oxygen gas.

4. an appropriate total supply amount of the oxygen gas corresponding to the calculated molten metal surface area is determined in advance based on the refining result of the molten metal and stored in the computing device; 4. The apparatus for refining molten metal according to claim 3, wherein an appropriate supply amount of the reducing agent corresponding to the total supply amount of the oxygen gas is determined in advance based on the refining result of the molten metal and then stored in the computer.

5. A molten metal refining vessel having a refractory-lined inner surface of a steel shell is used, a refining gas is supplied into the refining vessel to perform refining, and the internal shape of the refining vessel is measured using a profile meter that irradiates a laser into the refining vessel; Using the internal shape measured by the profile meter, one or more of the type, flow rate, and total supply amount of refining gas (hereinafter referred to as "calculation items") is determined; A method for refining molten metal, characterized in that the calculation items are adjusted in accordance with the result of the determination and refining is carried out.

6. 6. The method for refining molten metal according to claim 5, wherein the molten metal is Cr-containing molten steel, the refining gas is oxygen gas, and the calculation item is a total supply amount of oxygen gas.

7. The method for refining molten metal further comprises supplying a reducing agent into the refining vessel; 7. The method for refining molten metal according to claim 6, further comprising the steps of: calculating a surface area of ​​the molten metal in the refining vessel using the internal shape measured by the profile meter; determining a total supply amount of the oxygen gas in accordance with the calculated surface area of ​​the molten metal; and determining an amount of the reducing agent to be supplied in accordance with the calculated total supply amount of the oxygen gas.

8. determining in advance an appropriate total supply amount of the oxygen gas corresponding to the calculated molten metal surface area based on a refining result of the molten metal; 8. The method for refining molten metal according to claim 7, wherein an appropriate supply amount of the reducing agent corresponding to the total supply amount of the oxygen gas is determined in advance based on the result of refining the molten metal.

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