Operation method of converter furnace

Abstract

To provide an operation method of a converter furnace capable of suppressing the wear of a refractory without lowering productivity.SOLUTION: An operation method of a converter furnace according to the present invention is a method for operating a converter furnace having a top-blowing lance configured to blow oxygen into molten iron from above the molten iron. The method comprises a step of controlling a height of slag foaming to be equal to or higher than a height of a lower end portion of the top-blowing lance and lower than a height of a throat during a blowing treatment. The height of the slag foaming is preferably set to be equal to or higher than the height of the lower end portion of the top-blowing lance when a basic unit of an oxygen supply amount after completion of a desiliconization treatment is 15 NM3 / t or less, and a slag basicity during the blowing treatment is preferably set to be 1.1 or more and 2.4 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for operating a converter equipped with a top blowing lance. [Background technology]

[0002] In a converter, when the blowing process is repeatedly performed, the refractory laid on the inner surface of the furnace body is worn out. For this reason, the slag remaining in the furnace body after tapping is made to adhere to the surface of the refractory to suppress the wear of the refractory. However, it is difficult to make the slag adhere to the surface of the refractory laid on the inner surface of the constricted part where the diameter of the furnace body gradually narrows toward the furnace mouth. For this reason, a method has been proposed in which gas is blown from above against the slag remaining in the furnace body to scatter the slag, thereby making the scattered slag adhere to the surface of the refractory laid on the inner surface of the constricted part (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5552846 [Non-patent literature]

[0004] [Non-Patent Document 1] Masaaki Tachikawa, Michihiko Shimada, Masae Ishibashi, and Tadamitsu Shiraishi: Iron and Steel, 55 (1969), S92. Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the method described in Patent Document 1 is used to deposit slag on the surface of the refractory laid on the inner surface of the cone section, the productivity is reduced because time must be secured for depositing the slag on the surface of the refractory after the end of the blowing treatment. For this reason, there has been a demand for a technology capable of suppressing the wear of the refractory without reducing the productivity.

[0006] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a method for operating a converter capable of suppressing wear of refractories without reducing productivity. [Means for solving the problem]

[0007] The inventors of the present invention have conducted extensive research to solve the above problems, and have found that by controlling the height of the slag foaming during the blowing process, slag can be attached to the surface of the refractory laid on the inner surface of the cone of the converter. Specifically, the inventors of the present invention have found that when the height of the slag foaming is higher than the height of the lower end of the top blowing lance, the amount of slag attached to the surface of the refractory laid on the inner surface of the cone increases, thereby suppressing wear of the refractory, and have arrived at the present invention. Slag foaming refers to a state in which the slag is foamed by bubbles of carbon monoxide gas, carbon dioxide gas, etc.

[0008] The method for operating a converter according to the present invention is a method for operating a converter equipped with a top-blowing lance that blows oxygen into the molten iron from above the molten iron, and includes a step of controlling the height of slag foaming during a blowing process to be equal to or greater than the height of the lower end of the top-blowing lance and less than the height of the furnace throat.

[0009] The above step is performed when the oxygen supply unit after the desiliconization process is 15NM 3 When the slag foaming temperature is 100° C. or less, the height of the slag foaming may be set to be equal to or higher than the height of the lower end of the top blowing lance.

[0010] In the above step, the slag basicity during the blowing process may be set to 1.1 or more and 2.4 or less. Effect of the Invention

[0011] According to the converter operating method of the present invention, wear of the refractory material can be suppressed without reducing productivity. [Brief description of the drawings]

[0012]

Figure 1

[0013] The method of operating a converter according to the present invention will now be described.

[0014] Fig. 1 is a schematic diagram showing the configuration of a converter to which the present invention is applied. As shown in Fig. 1, in the blowing process in a converter 1 to which the present invention is applied, molten iron M is charged into the inside of a furnace body 2 through a throat 2a, and then a flux such as lime is added to the molten iron M from the throat 2a. Then, nitrogen (N 2 While blowing oxygen (O) gas or argon (Ar) gas into the molten iron M from the lower end of the top blowing lance 3 installed above the molten iron M, oxygen (O 2 ) is injected into the molten iron M. This removes impurities such as carbon (C), silicon (Si), and phosphorus (P) from the molten iron M, producing slag S. The process of removing C from the molten iron M is called decarburization, the process of removing Si from it is called desiliconization, and the process of removing P from it is called dephosphorization.

[0015] Here, in order to perform dephosphorization efficiently, calcium oxide (CaO) and silica (SiO 2 It is important to control the composition of slag S such as SiO 2 The slag basicity is the ratio of the amount of CaO in the furnace to the amount of CaO in the furnace ((CaO concentration) / (SiO 2 The SiO concentration in slag S is used as an index of the composition of slag S. As the blowing process progresses, the SiO concentration in slag S increases due to the oxidation of Si and the addition of fluxes. 2 As the concentration increases, the slag basicity decreases, producing highly viscous slag S. At the same time, as the decarburization reaction progresses and the amount of carbon monoxide (CO) gas generated increases, the CO gas generates bubbles in the slag S, increasing the apparent volume of the slag S and causing the slag foaming height SH, which is the height of the surface of the slag S foamed by the bubbles (slag foaming), to rise.

[0016] The inventors of the present invention have investigated the relationship between the slag foaming height SH and the wear of the refractory laid on the inner surface of the constricted portion 2c of the converter 1, and have found that wear of the refractory of the constricted portion 2c can be suppressed when the slag foaming height SH is higher than the height of the lower end of the top blowing lance 3 (hereinafter referred to as the lance height) LH. Then, after a detailed study of the mechanism, it was found that the amount of slag scattering generated when the gas rises in the slag foam and passes through the slag foam becomes greater than the amount of slag scattering when the gas is blown from above to scatter the slag S, by reducing the distance between the refractory of the constricted portion 2c and the slag foam. The constricted portion 2c is a portion of the furnace body 2 that is constricted so that the diameter gradually narrows toward the throat 2a. The slag foaming height SH can be controlled by adjusting the oxygen supply rate and the lance height.

[0017] Furthermore, as a result of a detailed study of the conditions for the adhesion of slag S to the refractory in the cone section 2c, it was found that the amount of slag adhering to the refractory in the cone section 2c can be increased by increasing the slag foaming height SH in the early stage of the blowing process. This is thought to be because in the early stage of the blowing process, the surface temperature of the refractory is low and the temperature difference with the slag S is large, so that the slag S that comes into contact with the refractory is likely to solidify. On the other hand, when oxygen supply from the top blowing lance 3 begins, after the oxidation of Si and Mn, the decarburization reaction (C+1 / 2O 2 =CO) begins, and as the decarburization reaction increases, secondary combustion ((CO+1 / 2O 2 =CO 2 At this time, the exhaust gas temperature rises due to the heat generated by the secondary combustion, and the temperature of the refractory also rises due to thermal conduction. Therefore, in order to ensure the amount of slag attached to the refractory in the cone section 2c, the timing to set the slag foaming height SH to be equal to or higher than the lance height LH is set at the beginning of blowing, specifically, when the oxygen supply unit after the desiliconization process is 15NM 3 / t or less, preferably 10NM 3 Whether or not the desiliconization treatment is completed can be determined by a known analytical method or by estimation from the amount of oxygen supplied.

[0018] Moreover, in order to increase the slag foaming height SH, it is desirable that the slag basicity is low. Regarding the relationship between slag basicity and slag foaming SH, for example, Non-Patent Document 1 points out that when the slag basicity is within a certain range, the time constant of the collapse of slag foaming increases rapidly, i.e., slag foaming becomes stable. Therefore, when the slag foaming height SH is made higher than the lance height LH, it is desirable to set the slag basicity to 1.1 or less, or 2.4 or less. The slag basicity is determined by the amount of CaO, SiO 2 The amount of SiO generated by the combustion reaction in the furnace 2 It can be estimated from the quantity.

[0019] On the other hand, the amount of slag CS (see FIG. 1) adhering to the constricted portion 2c increases as the slag foaming height SH increases, but if the slag foaming height SH exceeds the height FH of the furnace opening 2a, the slag S overflows, and a large amount of high-temperature slag S goes outside the furnace, reducing productivity. For this reason, the slag foaming height SH must be less than the height FH of the furnace opening 2a. In addition, the means for measuring the slag foaming height SH is not limited, and for example, a microwave level meter, a lance vibration meter, or visual information can be used. EXAMPLES

[0020] In this example, molten iron and scrap were charged into a converter with a height of 8.5 m from the bottom of the furnace body to the throat, and quicklime and silica were added as fluxes, and oxygen was blown from a top lance to perform the blowing treatment. The operating conditions of the blowing treatment and the evaluation results of the change in refractory thickness are shown in Tables 1 and 2 below, respectively. The calculated minimum C / S in Table 2 is the amount of CaO in the furnace during the blowing treatment (kg) / SiO 2The minimum amount (kg) of slag (kg) was defined as the minimum value. The calculated minimum C / S was adjusted by the amount of quicklime and silica stone charged. The end point slag C / S was the slag basicity calculated from the analysis value obtained by sampling the slag discharged after the end of the blowing process. T.CaO (kg / t) was the value obtained by dividing the amount of CaO in the furnace by the total amount charged. During the blowing process, the slag foaming height was successively measured using a microwave level meter, and the slag foaming height was controlled by adjusting the oxygen supply rate and the lance height. In addition, in the blowing processes of Examples 1 to 3 and Comparative Examples 1 to 3, the presence or absence of slopping, in which slag overflowed from the furnace throat, was determined. In addition, the thickness of the refractory material in the furnace was measured using a laser profile meter before charging, after tapping steel, and after slag discharge, and the amount of change was obtained.

[0021] It was confirmed that in Examples 1 to 3, there was a timing when the slag foaming height became equal to or higher than the lance height during the blowing process, and the slag foaming height remained below the throat height. In contrast, in Comparative Example 1, there was a timing when the slag foaming height became equal to or higher than the lance height during the blowing process, but the slag foaming progressed rapidly, so the slag foaming height could not be controlled by the oxygen flow rate and the lance height, and slopping occurred in which the slag foaming height became equal to or higher than the throat height. In Comparative Examples 2 and 3, the calculated minimum C / S was large at 2.7 and 2.8, respectively, and the slag viscosity was low, so the slag foaming height did not reach the lance height. As a result, as shown in Table 2, in Examples 1 to 3 and Comparative Example 1, the refractory thickness change was low at -0.16 to -0.08 mm, but in Comparative Examples 2 and 3, the refractory thickness change was large at -0.29 and -0.40 mm. In Comparative Example 1, slopping occurred, and therefore it was determined to be outside the scope of the present invention based on the calculated minimum C / S. From the above, it was confirmed that the wear of the refractory material can be suppressed without reducing productivity by controlling the height of the slag foaming during the blowing process to be equal to or higher than the height of the lower end of the top blowing lance and lower than the height of the furnace throat.

[0022] [Table 1]

[0023] [Table 2]

[0024] Although the embodiments of the present invention have been described above, the present invention is not limited by the descriptions and drawings that form part of the disclosure of the present invention according to the present embodiments. In other words, other embodiments, examples, and operation techniques, etc., made by those skilled in the art based on the present embodiments are all included in the scope of the present invention. [Explanation of symbols]

[0025] 1 Converter 2 Furnace body 2a Hearth 2b Gas discharge tuyere 2c Squeezing section 3 Top blowing lance M Molten iron S slug

Claims

1. A method for operating a converter equipped with a top-blowing lance for blowing oxygen into molten iron from above the molten iron, comprising the steps of: A method for operating a converter, comprising: controlling a height of slag foaming during a blowing process to be equal to or higher than the height of a lower end of the top blowing lance and lower than the height of a furnace throat.

2. In the above step, the oxygen supply unit after the completion of the desiliconization treatment is 15 NM ３ 2. The method for operating a converter according to claim 1, wherein the height of the slag foaming is set to be equal to or higher than the height of a lower end of the top blowing lance when the melting temperature is equal to or lower than 1000° C. / t.

3. 3. The method for operating a converter according to claim 1 or 2, wherein the step of performing the blowing treatment sets the slag basicity at 1.1 or more and 2.4 or less.

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