JP3982389B2 - Operation method of horizontal blowing refining furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating a horizontal blowing refining furnace, and more specifically, decarburization, reduction, and component adjustment by blowing a refining gas into molten steel from a horizontal blowing tuyere provided substantially horizontally on the furnace wall. It is related with the operating method of the horizontal blowing smelting furnace which performs etc.
[0002]
[Prior art]
In recent years, the so-called high-grade steel produced by converters and electric furnaces has become strict due to the stricter quality requirements of users seeking products with a high degree of cleanliness, with significantly reduced non-metallic inclusions and gas components in steel. Low alloy steels and special steels are processed in some form by vacuum refining, or an alternative furnace refining process. For example, there is an AOD refining method as a refining method of stainless steel that combines vacuum refining and out-of-furnace refining processes. In this AOD refining method, molten steel melted in a converter, electric furnace, etc. is transferred to an AOD furnace (argon oxygen decarburization furnace), which is a type of horizontal blown refining furnace, using a transfer pan, and the inside of the vessel is depressurized by a vacuum exhaust device. However, decarburization, reduction, component adjustment, and the like are performed while suppressing oxidation loss of Cr by blowing a refining gas such as an inert gas (Ar, N ₂ ) together with oxygen gas into the molten steel.
[0003]
In the AOD furnace, as shown in FIG. 4 or FIG. 5, a vessel 12 that is a main body of the furnace 10 is supported so as to be tiltable through support bodies 11 and 11, and its vertical axis P is set up vertically, Blowing is performed in a vertical posture in which a steel outlet 12a for charging an additive and taking out molten steel to a ladle or the like faces directly above. In addition, when the molten steel that has been refined is discharged, the molten steel is removed from the outlet hole 12a by tilting the vessel 12 with the support bodies 11 and 11 as fulcrums using a tilting device (not shown) such as a motor. Steel is put out to pans. The vessel 12 includes an outer shell 14 made of a steel plate and refractories 16 and 18 stretched doubly inside the outer shell 14. Further, as shown in FIG. 5, the vessel wall of the vessel 12 has a plurality of portions near the bottom of a portion (lower side in the drawing) that is biased to the opposite side of the steel output side that is the lower side when steel is output. Horizontal blowing tuyere 20 are provided spaced apart in the circumferential direction. The horizontal blowing tuyere 20 is opened in the molten steel through the outer shell 14 and the refractories 16 and 18 in a substantially horizontal posture orthogonal to the longitudinal axis P of the vessel 12. Then, a refining gas such as oxygen gas, argon gas, nitrogen gas or the like is blown into the molten steel in the vessel 12 from each side blowing tuyere 20, and the molten steel is vigorously stirred.
[0004]
The refractory is made up of permanent bricks 16 facing the outer shell 14 and lining bricks 18 in contact with the molten steel, and is constructed by building bricks 16 and 18 formed in a block shape of a required size. Furnace). As the permanent tension brick 16, fired magnesia brick or the like is used, and as the lining brick 18, magchromatic direct bond brick or dolomite brick or the like is used. The lining brick 18 is used under fairly severe conditions such as vigorous stirring of molten steel and slag during blowing, large generation of dust and gas, and rapid temperature change.
[0005]
The lining brick 18 melts down due to various factors when the operation is repeated. As the cause of the erosion of the lining brick 18, the temperature of the molten steel is increased by the reaction heat of the refining gas and the molten steel component injected in large quantities from the side blowing tuyere 20 provided near the bottom of the furnace wall, and the gas flow In addition, there is mechanical friction caused by a friction phenomenon or the like with respect to the surface of the lining brick 18 due to the molten steel flow. In addition, thermal spalling that causes cracking or peeling due to thermal stress caused by a decrease in the surface temperature of the lining brick 18 between the end of blowing and the next blowing, and further slag enters the lining brick 18 By doing so, structural spalling that peels due to the difference in thermal expansion between the altered layer and the unaltered layer formed on the surface of the lining brick 18 due to the chemical erosion action can be cited.
[0006]
When melting of the lining brick 18 progresses and the remaining size of the brick 18 becomes shorter, the brick 18 falls off from the vessel 12. Therefore, repair by spraying, partial replacement, and total replacement (disassembly-furnace) are required. Further, in the vessel 12, the erosion speed of the lining brick 18 varies depending on the part, and particularly, the lining brick 18 located above and around the side blowing tuyere 20 is agitated by the blown gas. Because of mechanical friction due to heat and thermal spalling due to temperature changes, local erosion is remarkable. That is, the melting rate of the lining brick 18 near the upper side of the horizontal blowing tuyere 20 affects the useful life of the entire lining brick 18 in the vessel 12. Therefore, in order to extend the useful life of the lining brick 18, the thickness of the lining brick 18 (the length in the inner and outer directions) is set as shown in FIG. The lining bricks 18 above and around the horizontal blowing tuyere 20 are set thick.
[0007]
Moreover, there exists a thing which improves durability by changing the shape of the refractory in the vicinity of the horizontal blowing tuyere 20 (for example, refer patent document 1). Further, a refractory material having improved wear resistance has been adopted for the refractory near the side blow tuyere 20 (see, for example, Patent Document 2).
[0008]
[Patent Document 1]
JP-A-7-253278 [Patent Document 2]
Japanese Patent Laid-Open No. 11-1000025
[Problems to be solved by the invention]
However, when the lining brick 18 is thickened, the weight increases and the volume in the vessel 12 is reduced. Moreover, the thing which changes the shape and material of a refractory raises the problem that equipment cost increases.
[0010]
OBJECT OF THE INVENTION
SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-described problems related to the prior art, and it is proposed to suitably solve this problem. In a horizontal blowing refining furnace provided with horizontal blowing tuyere substantially horizontally, no cost is applied. An object of the present invention is to provide a method for operating a horizontal blowing smelting furnace that can extend the useful life of a refractory lined on a vessel.
[0011]
[Means for Solving the Problems]
In order to overcome the above-mentioned problems and achieve the intended purpose, the operation method of the horizontal blowing smelting furnace according to the present invention is:
The horizontal blown tuyeres are provided with a horizontal blown refining furnace provided with a vessel provided with a horizontal blower tuyere at a lower part of a furnace wall made of a refractory lined on the outer shell and being unevenly distributed in the circumferential direction. From the operation of blowing the gas for refining into the molten steel in the vessel from
The horizontal blowing tuyere is operated while maintaining the inclined posture of the vessel so that the required angle is upward.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, the operation method of the horizontal blowing smelting furnace according to the present invention will be described below with reference to preferred embodiments. Although the AOD furnace will be described as an example of the horizontal blowing refining furnace, the structure of the AOD furnace itself is basically the same as the conventional technique described with reference to FIG. 4 or FIG. About the member, the same referential mark is used and the detailed description is abbreviate | omitted.
[0013]
As described above, the vessel 12 shown in FIG. 1 includes a portion biased toward the furnace wall in the direction opposite to the steel output side (biased toward a portion in the circumferential direction), and a plurality (for example, 5 in the embodiment) at a predetermined interval in the circumferential direction. Although it is a book, it is not limited to the number, and may be one.) The horizontal blowing tuyere 20 is provided. The horizontal blowing tuyere 20 has a double structure, and its axis is set substantially orthogonal to the vertical axis P of the vessel 12, that is, substantially horizontal. In operation, the vessel 12 charged with molten steel is passed through the tilting center O along the vertical axis P of the vessel 12 passing through the tilting center O, with the support bodies 11 and 11 as the tilting center O by the tilting device. Blowing is performed in a state where the horizontal blowing tuyere 20 is tilted with respect to the vertical line S and is held in an inclined posture in which the side blowing tuyere 20 faces upward (the gas blowing port faces upward). Even when the vessel 12 is operated in a vertical posture as in the prior art, the molten steel is scattered from the steel outlet 12a by blowing a refining gas into the molten steel, and the molten steel is inclined by inclining the vessel 12. When the distance between the interface and the steel outlet 12a becomes shorter, the amount of molten steel scattered increases. That is, the inclination angle θ of the vertical axis P with respect to the vertical line S in the inclined posture of the vessel 12 is preferably in the range of 0 ° <θ ≦ 10 °, particularly optimally 3 ° ≦ θ ≦ 5, considering the scattering of molten steel. It is in the range of °.
[0014]
Operation of Embodiment Example
Next, the effect | action of the operating method of the horizontal blowing smelting furnace which concerns on the example of an embodiment is demonstrated. As shown in FIG. 1, by tilting the vessel 12 so that the steel outlet 12a of the vessel 12 faces away from the steel output side, the horizontal blowing tuyere 20 is directed upward. The lining brick 18 positioned above the mouth 20 is retreated in a direction to escape with respect to the blowing direction of the gas blown out from the side blowing tuyere 20. When operating in this state, gas is blown into the molten steel from the horizontal blowing tuyere 20 in a direction away from the lining brick 18 above the horizontal blowing tuyere 20. That is, molten steel agitation in the vicinity of the lining brick 18 above the side blow tuyere 20 is reduced, thereby suppressing the erosion of the lining brick 18 and improving the service life of the refractory. Moreover, since it is not necessary to change the thickness, shape, and material of the refractory, the equipment cost does not increase.
[0015]
The vessel 12 can be tilted using an existing tilting device, and there is no need to change equipment such as gas blowing equipment or waste gas treatment equipment. That is, the operation method of the horizontal blowing smelting furnace according to this embodiment can be easily implemented without changing existing facilities.
[0016]
Here, during the blowing by the AOD furnace 10, the stirring energy of the molten steel by the gas blown from the horizontal blowing tuyere 20 has a certain relationship between the blowing outlet of the horizontal blowing tuyere 20 and the molten steel interface. That is, by inclining the vessel 12 as in the embodiment, the distance L between the blowout port of the horizontal blowing tuyere 20 and the molten steel interface is increased, and the stirring energy by the gas is increased accordingly, and the refining ability is increased. improves. Further, the refining cost can be reduced by reducing the blowing gas.
[0017]
【Example】
A 70 t stainless steel molten steel is charged into the vessel 12 provided with five horizontal blow tuyere 20 at a position corresponding to the third-stage lining brick 18 from the bottom of the furnace. Introduce argon gas. This argon gas is not blown until the C (carbon) concentration in the molten steel is 0.6% from the start of refining, and then 1000 Nm ³ / hr when C is in the range of 0.6 to 0.3% and C is 0.00. In the range of ^{3 to} 0.1%, argon gas of 2100 Nm ³ / hr is blown. In the above conditions, the conventional example operates in a vertical posture in which the vertical axis P of the vessel 12 coincides with the vertical line S, and the vertical axis P of the vessel 12 is inclined by 5 ° with respect to the vertical line S. The number of service life (ch) of the lining brick 18 was compared with that of the example operating in an upward inclined posture. In addition, the service life (ch) of the lining brick 18 is represented by a charge, and this one charge is one cycle from charging, blowing, and taking out of molten steel. Here, the expected useful life (ch) of the lining brick 18 is derived from the Al reduction ch ratio, active time, intermittent degree, vacuum processing time, magnesia usage, basicity, and reprocessing ratio by multiple regression analysis. In the operation of the conventional example, the actual service life of the lining brick 18 converges to the expected service life (theoretical value) shown in FIG. On the other hand, in the operation of the example, it was confirmed that the actual service life improved from the expected service life.
[0018]
Next, when operating under the above-mentioned conditions [0017], the erosion speeds due to the number of lining bricks 18 above the horizontal blowing tuyere 20 were compared, and the results are shown in FIG. As apparent from FIG. 3, the fourth to eighth lining bricks 18 above the third lining brick 18 provided with the horizontal blow tuyere 20 are of the embodiment compared to the conventional example. It was confirmed that the melting rate decreased, that is, the service life was extended.
[0019]
【The invention's effect】
As described above, according to the operation method of the horizontal blowing refining furnace according to the present invention, the refractory above the horizontal blowing tuyere is blown by tilting the vessel so that the horizontal blowing tuyere is facing upward. Melting loss can be suppressed, and the useful life of the refractory in the vessel can be extended. As a result, the refractory replacement period becomes longer, and the cost required for furnace repair and replacement can be reduced. In addition, by tilting the vessel, the distance from the outlet of the horizontal blowing tuyere to the molten steel interface is increased, and accordingly, the stirring efficiency is improved and the refining ability is improved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a state of a vessel during blowing according to a preferred embodiment of the present invention.
FIG. 2 is a graph in which data relating to the endurance life of the lining bricks of an example and a conventional example is plotted with the expected service life on the horizontal axis and the actual service life on the vertical axis.
FIG. 3 is a graph showing the erosion rate of the lining bricks above the horizontal blowing tuyere of the example and the conventional example.
FIG. 4 is a longitudinal sectional view showing a state of a vessel during blowing according to a conventional technique.
FIG. 5 is a cross-sectional view of a vessel.
[Explanation of symbols]
10 AOD furnace (horizontal blown refining furnace), 12 vessel, 14 outer shell 16 permanent tension brick (refractory), 18 lining brick (refractory), 20 horizontal blow tuyere P vertical axis, S vertical line, θ inclination angle

Claims (2)

A horizontal blowing tuyere (20) is provided in the lower part of the furnace wall made of refractory (16, 18) lined on the outer shell (14), and is provided with a vessel (12) provided in a substantially horizontal and circumferentially distributed manner. When performing the operation by blowing a refining gas from the horizontal blowing tuyere (20) into the molten steel in the vessel (12) using the horizontal blowing refining furnace (10),
A method for operating a horizontal blown refining furnace, characterized in that the horizontal blown tuyere (20) is operated while maintaining the inclined posture of the vessel (12) so that the required angle is upward. The inclined posture of the vessel (12) is such that the angle (θ) of the vertical axis (P) of the vessel (12) with respect to the vertical line (S) is set in a range of 0 ° <θ ≦ 10 °. The operation method of the horizontal blowing smelting furnace described.

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