JP2009191347A - Method for operating electric arc furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating an electric arc furnace by which the injection ratio of gas from a furnace bottom can be improved. <P>SOLUTION: The electric arc furnace, for use in melting of steelmaking raw materials, is provided with a replacement furnace bottom 31 constituted so as to be replaceable while including the center portion of the furnace bottom, and an outside furnace bottom 32 as the furnace bottom at the outside of the replacement furnace bottom 31. Before the replacement furnace bottom reaches its usable life, the replacement furnace bottom 31 is replaced once or more than once. Until replacing the replacement furnace bottom 31 at the last time, the gas is injected only from a tuyere 43 at the outside furnace bottom 32, and after replacing the furnace bottom 31 at the last time, the gas is injected from a tuyere 44 in the replacement furnace bottom 31b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention comprises an exchange furnace bottom that is used for melting a steelmaking raw material and is configured to be exchangeable including a central part of the furnace bottom, and an outer furnace bottom that is a furnace bottom part outside the exchange furnace bottom. The present invention relates to a method of operating an arc furnace in which the exchange furnace bottom is exchanged once or a plurality of times until the useful life is reached.

  Hot metal used as a material for steelmaking is produced in a blast furnace or an electric furnace. The electric furnace has the advantages that the installation area is smaller than that of the blast furnace and the equipment cost is low. Among electric furnaces, arc furnaces are widely used for melting steelmaking raw materials because of their high productivity in addition to the above-mentioned advantages. FIG. 6 schematically shows a configuration of a conventional general arc furnace 1. The arc furnace 1 includes a furnace body 2 and an electrode 3. An arc furnace 1 shown in FIG. 6 is a three-phase AC type furnace having three electrodes 3. The furnace body 2 includes an iron shell 4 and a refractory 5 lined on the shell 4. In the arc furnace 1, electric power is supplied to the electrode 3 from a power source (not shown) to generate an arc between the electrodes, and a steelmaking raw material such as scrap is melted with the heat of the arc to produce hot metal.

  In recent years, a tuyere 7 is provided in the furnace bottom 6 of the arc furnace 1, and a non-oxidizing gas or an inert gas is blown into the hot metal in the arc furnace 1 from the furnace bottom 6 to stir the unheated steel. Efficient transmission to the raw material is performed. By efficiently utilizing the heat of the hot metal, it is possible to reduce power consumption by reducing the power required to produce a unit weight of hot metal, and to shorten the time required for melting.

  In the arc furnace 1, the lining refractory 5 is worn by erosion or melting as the number of charge charges increases. When the wear of the refractory 5 proceeds to some extent, the operation is stopped during the charge, and the refractory 5 is repaired. In particular, the tuyere bricks 8 constituting the tuyere 7 are subject to impacts caused by gas blowing in addition to thermal wear, and therefore wear out more easily than the surrounding refractory bricks 9, and need to be repaired or replaced at a relatively high frequency. Occurs. Although the refractory 5 is repaired on both the furnace wall 10 and the furnace bottom 6, the refractory 5 is removed from the worn part and the removed refractory 5 is discharged. Work becomes complicated and takes a long time. Since the furnace bottom 6, particularly the central part thereof, is located under the electrodes, it is easily affected by the heat of the arc, and when the furnace body 2 is returned after the furnace body 2 is tilted and the molten metal is discharged, the center of the furnace bottom 6 is restored. It is affected by heat from the remaining hot water remaining in the area. Therefore, compared with the furnace wall 10, the wear of the refractory 5 at the center portion is more likely to progress in the furnace bottom 6 and in the furnace bottom 6. Although the refractory repair of the furnace bottom 6 is more difficult than the furnace wall 10, the furnace bottom 6 tends to wear out the refractory 5 more easily than the furnace wall 10. The bottom repair causes a reduction in efficiency in the operation of the arc furnace 1.

As prior art to solve such problems, tuyere bricks located at the center of the furnace bottom and surrounding refractory bricks are arranged to be attached to the center of the furnace bottom, and the outer periphery is wound with a steel strip. A method has been proposed in which a cassette brick that has been fastened is prepared in advance and the central portion of the furnace bottom is replaced at once by replacing the cassette brick (see Patent Document 1). According to the method of Patent Document 1, since the center portion of the bottom of the furnace is replaced as a cassette brick at the same time, it can be replaced instead of repairing the furnace bottom refractory, and the operation efficiency of the arc furnace can be improved.
Japanese Patent Laid-Open No. 05-87458

  However, the method of Patent Document 1 has the following problems. In Patent Document 1, a tuyere is provided on cassette bricks that can be exchanged all at once, and gas is blown from the center of the furnace bottom. The center part of the furnace bottom is affected by the heat of the arc and the remaining hot water. Further, since the impact due to gas blowing is applied to the tuyere, the tuyere brick provided in the center portion of the furnace bottom is particularly prone to wear. When the wear of the tuyere bricks progresses more than the refractory bricks provided in the vicinity, and the tuyere bricks become thinner, the operation is temporarily interrupted during the melting charge and the tuyere part is closed by casting or the like. After closing the tuyere, melting is performed without blowing gas until the thickness of the refractory brick reaches the service life.

  Therefore, if a tuyere is provided only at the center portion of the furnace bottom and the gas is blown, the tuyere tends to wear out, and after closing the tuyere, a large number of charges can be dissolved without blowing the gas. Therefore, there is a problem that the furnace bottom gas blowing rate becomes low. Here, the furnace bottom gas blowing rate is a percentage of the number of charges that can be dissolved while blowing gas from the furnace bottom and the total number of charges that are dissolved during the useful life of the arc furnace. Say. The service life of an arc furnace means that all refractories on the furnace bottom and the furnace wall are newly lined and started operation. Until you have to renew and line up again. When the furnace bottom gas blowing rate decreases, the charge that cannot effectively use the heat of the hot metal for melting increases, so that the power required for melting and the time required increase.

  An object of the present invention includes an exchange furnace bottom configured to be exchangeable including a central part of the furnace bottom, and an outer furnace bottom that is a furnace bottom part outside the exchange furnace bottom, until the useful life of the furnace bottom is reached. An arc furnace in which the bottom gas is blown from a tuyere provided on the bottom of the exchange furnace or the outer furnace so that the bottom of the exchange furnace is exchanged one or more times. It is to provide a method of operation.

The present invention includes an exchange furnace bottom configured to be exchangeable including a central part of the furnace bottom, and an outer furnace bottom that is an outer furnace bottom part outside the exchange furnace bottom, and is exchanged until the useful life of the furnace bottom is reached. In an arc furnace operating method in which the furnace bottom is changed once or several times,
Until the bottom of the exchange furnace is changed to the final round, gas is blown only from the tuyere provided at the outer furnace bottom,
After exchanging the bottom of the exchange furnace in the final round, the arc furnace operating method is characterized in that gas is blown only from the tuyere provided at the bottom of the exchange furnace.

  In the present invention, the useful life of the furnace bottom is determined by the thickness of the refractory according to the degree of wear of the refractory used for the furnace bottom.

  According to the method for operating an arc furnace of the present invention, when a new furnace body is manufactured or a refractory of a furnace body is completely renewed, an exchange furnace bottom without tuyere is used, and a new furnace body is manufactured or In the operation after the refractory is completely renewed, the replacement furnace bottom is replaced once or a plurality of times until the life of the furnace bottom is reached. Until the last of the exchange furnace bottom is replaced, gas is blown from only tuyere provided on the outer furnace bottom. The tuyere provided at the outer furnace bottom is hardly affected by the heat of the arc and the remaining hot water, and thus has a longer life than the tuyere provided at the bottom of the exchange furnace. By blowing gas from the long-life tuyeres provided at the outer furnace bottom, the number of charges dissolved while blowing gas is lower than when gas is blown from the short-lived tuyere provided at the bottom of the exchange furnace. Can be increased. Until the replacement furnace bottom is replaced in the final round in this way, the number of charges that can be dissolved while blowing gas by blowing gas only from the tuyeres provided on the outer furnace bottom, and the durability of the furnace It is possible to increase the ratio of the total number of charges that can be melted throughout the lifetime and improve the furnace bottom gas blowing rate.

  In addition, by determining the useful life of the furnace bottom by the thickness of the refractory according to the degree of wear of the refractory used at the furnace bottom, the useful life of the tuyere bricks can be determined accurately, and gas can be blown. Since it is possible to reliably grasp the limit that can be dissolved while being poured, it is possible to contribute to the improvement of the furnace bottom gas blowing rate.

  FIG. 1 shows an outline of an arc furnace operating method according to the present invention. FIG. 2 shows a simplified configuration of an arc furnace 21 suitable for the operation method of the present invention. Prior to the description of the operation method of the arc furnace, the configuration of the arc furnace 21 will be described. The arc furnace 21 includes a furnace body 22 and an electrode (not shown). The furnace body 22 includes an iron shell 23 and a refractory 26 lined on the furnace wall 24 and the furnace bottom 25 of the shell 23. The shell 23 may be called an iron skin.

  The furnace bottom 25 of the arc furnace 21 includes an exchange furnace bottom 31 including a central portion of the furnace bottom 25 and a furnace bottom 32 outside the exchange furnace bottom 31. A furnace bottom 32 outside the exchange furnace bottom 31 is referred to as an outer furnace bottom 32. The exchange furnace bottom 31 is an iron skin that constitutes a part of the shell 23 of the furnace bottom 25, and a refractory 26 is lined on the iron skin 23 a that can be separated from the furnace body 22. And a refractory as a unit member, which is the same as the cassette brick of Patent Document 1. As the exchange furnace bottom 31, either an exchange furnace bottom 31a having no tuyere or an exchange furnace bottom 31b having a tuyere is used.

  The replacement furnace bottom 31 is assembled into the furnace body 22 as follows. The replacement furnace bottom 31 is placed on the lifting / lowering tool 33 and inserted into the central portion 34 that is a space in the furnace bottom 25 by the lifting / lowering tool 33. After the insertion, the replacement furnace bottom 31 is connected to the outer furnace bottom 32, that is, the furnace body 22 by connecting the extension 35 of the core 23 a of the replacement furnace bottom 31 with the extension 36 of the core 23 of the outer furnace bottom 32. To do. A connecting portion 37 of the refractory 26 on the inner surface side of the furnace bottom is filled with an irregular refractory. Thereafter, an operation for melting the steelmaking raw material is performed, and when the refractory 26 of the exchange furnace bottom 31 is worn out, the exchange furnace bottom 31 is removed from the furnace body 22 in the reverse order as described above, and is replaced by a unit member in advance. A new replacement furnace bottom 31 is incorporated into the furnace body. Thus, the exchange furnace bottom 31 is configured to be exchangeable with respect to the furnace body 22. It should be noted that the removed exchange furnace bottom 31 is regenerated as a new exchange furnace bottom 31 used for replacement by removing the worn refractory 26 and using the new refractory 26.

  When the furnace body 22 is newly produced or when all the refractories 26 of the furnace body 22 are updated, the exchange furnace bottom 31 a having no tuyere is incorporated into the furnace body 22. When the operation is started after the furnace body 22 is newly created or the refractory 26 is completely renewed, the replacement furnace bottom 31 is replaced once or a plurality of times according to the service life of the refractory 26 on the furnace bottom 25. At this time, either the exchange furnace bottom 31a having no tuyere or the exchange furnace bottom 31b having a tuyere is selected and used. How to select one of the exchange furnace bottom 31a having no tuyere or the exchange furnace bottom 31b having a tuyere will be described later.

  FIG. 3 shows the relative arrangement of the electrodes with respect to the furnace bottom 25 and the positions where the tuyere can be arranged. The electrode projection position 41 with respect to the furnace bottom 25 is indicated by a broken-line circle. The exchange furnace bottom 31 includes a central portion 34 of the furnace bottom 25 that is susceptible to the thermal effects of the arc under the electrodes. By using the replacement furnace bottom 31 as a part that is easily affected by heat under the electrodes and is severely worn, the central part of the furnace bottom 25 can be easily replaced, and repair work for the refractory 26 can be made unnecessary.

  The A system, the B system, and the C system in FIG. 3 indicate that three gas piping systems for supplying bottom gas are provided. A flange 42 to which a flange of a gas pipe (not shown) can be connected is provided on the iron shells 23 and 23a of the furnace bottom 25 portion. A position indicated by a solid line square in FIG. 3 is a position where the flanges 42 are provided on the iron shells 23 and 23a. A1 and A2 are provided as flanges 42 that can be connected to the A system piping, B1 to B5 are provided as flanges 42 that can be connected to the B system piping, and C1 to C4 as flanges 42 that can be connected to the C system piping. Is provided. By providing the tuyere brick 27 so as to correspond to the position of the flange 42, a non-oxidizing gas supplied from a gas pipe (not shown) connected to the flange 42 through the tuyere 43 of the tuyere brick 27 or An inert gas can be injected as the bottom gas. The tuyere can be provided at any position selected from the positions where the flange 42 is provided. In addition, the tuyere may not be provided even at the position where the flange 42 is provided. When the tuyere is not provided, the flange 42 is closed by the lid member 45.

  Returning to FIG. 1, the method of operating the arc furnace will be described. In FIG. 1, only the portion of the bottom 25 of the arc furnace 21 is shown. The operation method of the arc furnace is an operation method in which the exchange furnace bottom 31 is exchanged one or more times until the useful life of the furnace bottom 25 is reached, and the outer furnace bottom 31 is exchanged until the exchange furnace bottom 31 is exchanged in the final round. The gas is blown only from the tuyere 43 provided at 32 and the gas is blown from only the tuyere 44 provided at the exchange furnace bottom 31b after the exchange furnace bottom 31 is exchanged in the final round.

  Here, the number of exchanges is counted as follows. The replacement furnace bottom 31a that does not have a tuyere that is used when the furnace body 22 is newly created or when all the refractories are renewed is not counted in the number of replacements. After the furnace body 22 is newly manufactured or the refractory is completely renewed, the operation for melting the steelmaking raw material is started, and the first time when the furnace body 22 is replaced for the first time because the refractory on the replacement furnace bottom 31 is worn out is the first time. Thereafter, the exchange furnace bottom 31 exchanged for the first time is worn out, and the case where the exchange is further performed is referred to as the second, and the case where the exchange is performed twice or more is referred to as a plurality of exchanges. The last exchange means the first exchange when the exchange bottom 31 is exchanged only once before reaching the useful life of the furnace, and the last exchange when the exchange number is two or more. For example, when the number of exchanges is 2, it means the second exchange, and when the number of exchanges is 3, it means the third exchange.

  This will be described in detail below. FIG. 1A shows a state where the furnace wall 24 of the arc furnace 21 and the refractory 26 on the furnace bottom 25 are all newly lined. At this time, the exchange furnace bottom 31 used is the exchange furnace bottom 31 a having no tuyere, and the tuyere 43 is provided only on the outer furnace bottom 32. The tuyere 43 is provided in the position of the flange B4 shown in FIG. 3, and can blow in the gas supplied from piping of B system | strain. In addition, the tuyere 43 provided in the outer furnace bottom 32 is not limited to one, Two or more may be sufficient.

  After the refractory 26 is newly lined and started to operate, the hot metal is stirred by blowing gas only from the tuyere 43 of the outer furnace bottom 32 until the life of the refractory 26 of the exchange furnace bottom 31a having no tuyere is reached. To do. The lifetimes of the refractory bricks 28 and tuyere bricks 27, which are the refractory 26, are determined by the thickness of the refractory 26 according to the degree of wear of the refractory 26 used in the furnace bottom 25. The thickness of the refractory 26 related to the life, that is, the remaining size may be determined based on the wear rate of the specification of the refractory, or may be determined based on an empirical rule based on the accumulation of operation results. However, it is preferable to obtain the thickness of the refractory 26 as follows. A thermocouple is embedded in a predetermined position of the refractory brick 28 and the tuyere brick 27 on the furnace bottom 25, and the temperature of the brick is measured. When the measurement temperature is low, the refractory 26 is thick, and when the measurement temperature is high, the refractory 26 is thin. Depending on the type of brick, the relationship between the measurement temperature and the thickness is obtained in advance, and the temperature corresponding to the thickness of the brick considered to be the useful life is set as the reference temperature for determining the useful life of the brick. With this reference temperature, the lifetime can be determined by the thickness of the refractory.

  Since the central portion 34 of the furnace bottom 25 included in the exchange furnace bottom 31 is affected by the heat of the arc and the remaining hot water, the refractory 26 is more easily worn out than the outer furnace bottom 32. Therefore, when the melting operation is performed while controlling the life with the thickness of the refractory 26 by measuring the temperature, even if the refractory 26 on the outer furnace bottom 32 has a sufficient thickness, that is, a remaining life, it does not have tuyere. The thickness of the refractory 26 on the exchange furnace bottom 31a becomes thin, and it is necessary to replace it after reaching the service life. In this case, whether or not the replacement of the replacement furnace bottom 31 is the final replacement is determined as follows. When the life of the refractory 26 on the new replacement furnace bottom 31 used for replacement and the remaining life of the refractory 26 on the outer furnace bottom 32 are substantially the same, it is determined that the replacement is the last time. When the remaining life of the refractory 26 on the outer furnace bottom 32 is substantially the same as the refractory life of the new replacement furnace bottom 31b to be replaced, even if gas is continuously blown from the tuyere 43 of the outer furnace bottom 32, , Does not contribute to increasing the number of charges dissolved while blowing gas. Therefore, the charge can be exchanged for a new exchange furnace bottom 31b having tuyere 44, gas can be blown from tuyere 44 that is unused and wear-free on new exchange furnace bottom 31b, and melted while blowing gas. Expect to increase the number. The tuyere 44 of the new exchange furnace bottom 31b is provided at the position of the flange B2 shown in FIG. 3, and can blow in the gas supplied from the piping of the B system. In addition, the tuyere 44 provided in the new exchange furnace bottom 31b is not limited to one, and may be two or more. In addition, when gas is blown from the tuyere 44 of the new exchange furnace bottom 31b, if gas is blown from the tuyere 43 of the outer furnace bottom 32, too much gas is consumed. When replacing with a new replacement furnace bottom 31b having 44, the tuyere 43 of the outer furnace bottom 32 is repaired and closed by casting or the like.

  Conversely, if the remaining life of the refractory on the outer furnace bottom 32 is sufficiently longer than the refractory life of the new replacement furnace bottom 31b to be replaced, it is determined that the replacement of the replacement furnace bottom 31 is not yet the final round. Then, exchange is made with an exchange furnace bottom 31a having no tuyere. Further, it is not necessary to consider the remaining life due to the remaining size of the refractory 26 on the outer furnace bottom 32. For example, from the empirical rule based on the operation results, the replacement furnace is reached until the useful life of the refractory 26 on the outer furnace bottom 32 is reached. Even when it is known that the bottom 31 can be replaced a plurality of times, it can be determined that the replacement of the replacement furnace bottom 31 is not yet the final time. When the remaining life of the refractory 26 on the outer furnace bottom 32 is sufficiently longer than the refractory life of the new replacement furnace bottom 31b to be replaced, the outer furnace bottom can be replaced with the replacement furnace bottom 31b having tuyere. Prior to 32 reaching the useful life, the replacement furnace bottom 31b reaches the useful life. In particular, the tuyere bricks at the bottom of the exchange furnace 31b are even shorter than the service life of the whole of the exchange furnace bottom 31b. Therefore, the number of dissolved charges that can be injected from the tuyere 44 at the bottom of the exchange furnace 31b has a sufficient service life. This is less than the number of melting charges that can be injected from the tuyere 43 of the outer furnace bottom 32. Therefore, when the remaining life of the refractory 26 on the outer furnace bottom 32 is sufficiently longer than the life of the refractory 26 on the new replacement furnace bottom 31b to be replaced, it is replaced with a new replacement furnace bottom 31a having no tuyere. Even after the replacement to the replacement furnace bottom 31a, the gas is blown only from the tuyere 43 provided in the outer furnace bottom 32.

  Here, when the remaining life of the refractory 26 on the outer furnace bottom 32 is sufficiently longer than the life of the refractory 26 on the new replacement furnace bottom 31b to be replaced, the replacement furnace bottom 31 needs to be replaced. When the remaining life of the outer furnace bottom 32 is ts and the life of the new replacement furnace bottom 31 used for replacement is tk, for example, the case where the life ratio: ts / tk is 1.4 or more is mentioned. Can do. However, the life ratio is not limited to 1.4 or more, and is desirably set appropriately in consideration of the type and price of the refractory used, the influence on the operation efficiency of the refractory renewal operation, and the like.

(Example)
Examples of the present invention will be described below. In this example, an operation test was conducted in which scrap and alloy iron were used as raw materials for steelmaking, and an arc furnace was used to continuously produce hot metal having a temperature of about 150 tons per charge and a temperature of about 1400 ° C. Arc furnace, the furnace volume in a three-phase alternating current type 105m ^3, a furnace inner diameter 6700Mm, gas piping and the arrangement of the flange of the furnace bottom was used for structure shown in FIG. Nitrogen gas was used as the blowing gas, and the flow rate was 80 NL / min to 200 NL / min. During the operation test, the hot metal was poured out of the furnace every time one charge was completed.

  FIG. 4 shows the outline of the operation method of an Example. FIG. 4A shows the state of the furnace bottom 25 after all the refractories 26 of the arc furnace 21 have been updated, that is, newly lined. The tuyeres 43a and 43b are provided only on the outer furnace bottom 32a, and the exchange furnace bottom 31a has no tuyere. The tuyere 43a is provided at the position of the flange B4 that receives gas supply from the piping of the B system, and the tuyere 43b is provided at the position of the flange C3 that receives gas supply from the gas piping of the C system. The operation was started after the refractory 26 was completely renewed, and before the refractory 26 on the replacement furnace bottom 31a reached the useful life, gas was injected from only the two tuyere 43a and 43b provided on the outer furnace bottom 32a. .

  The service life of the refractory brick 28 and tuyere brick 27 on the outer furnace bottom 32a and the service life of the refractory brick 28 on the replacement furnace bottom 31a were determined by measuring the temperature of the brick. That is, a thermocouple was embedded in each of the refractory brick 28 and the tuyere brick 27, and the temperature was measured with the thermocouple. The relationship between the temperature measured by transferring heat through the brick and the brick thickness was obtained in advance, and the temperature corresponding to the brick thickness considered to be the useful life was used as the reference temperature for the useful life judgment.

  The exchange furnace bottom 31a located under the electrode reached the useful life earlier than the outer furnace bottom 32a. At this time, since the remaining refractory life of the outer furnace bottom 32a was almost equal to the refractory life of the new replacement furnace bottom 31 to be replaced, it was determined that the replacement was the last time and a new replacement having tuyere 44 was made. It replaced with the furnace bottom 31b. Although the exchange of the exchange furnace bottom 31 was limited to this one time, the first exchange was made the last time.

  FIG. 4 (b) shows the state of the furnace bottom 25 after replacement with a new replacement furnace bottom 31 b having tuyere 44. The tuyere 44 is provided at the position of the flange B2 that receives gas supply from the piping of the B system on the new exchange furnace bottom 31b to be used after replacement. When replacing with a new replacement furnace bottom 31b having tuyere 44, tuyeres 43a and 43b of outer furnace bottom 32 used for gas blowing before replacement were repaired and closed by casting or the like. Therefore, after replacing with the new replacement furnace bottom 31b having the tuyere 44, gas was blown only from the tuyere 44 of the exchange furnace bottom 31b. The service life of the refractory brick 28 and tuyered brick 27 on the replacement furnace bottom 31b and the refractory brick 28 on the outer furnace bottom 32a after the replacement was determined by the temperature measured by the thermocouple embedded in the refractory 26 as before the replacement. . Even after the replacement, the replacement furnace bottom 31b has reached the service life before the outer furnace bottom 32. Therefore, when the replacement furnace bottom 31b has reached the service life, the service life of the arc furnace 21 was determined.

  FIG. 5 shows an outline of the operation method of the comparative example. FIG. 5A shows the state of the furnace bottom 25 after all the refractories 26 of the arc furnace 21 have been updated, that is, newly lined. The tuyeres 44a and 44b are provided only on the exchange furnace bottom 31c, and no tuyere is provided on the outer furnace bottom 32b. The tuyere 44a of the exchange furnace bottom 31c is provided at the position of the flange B2 that receives gas supply from the B system pipe, and the tuyere 44b is provided at the position of the flange C1 that receives gas supply from the C system gas pipe. Therefore, the operation is started after the refractory 26 is completely renewed, and before the refractory 26 on the replacement furnace bottom 31c reaches the service life, gas is injected from only the two tuyere 44a and 44b provided on the replacement furnace bottom 31c. went. The service life of the refractory brick 28 and tuyere brick 27 on the exchange furnace bottom 31c and the service life of the refractory brick 28 on the outer furnace bottom 32b were determined by temperature measurement in the same manner as in the example. The exchange furnace bottom 31c located under the electrode reached the useful life earlier than the outer furnace bottom 32b. In the comparative example, it was replaced with a new replacement furnace bottom 31c having tuyere 44a and 44b regardless of whether or not the replacement was final. However, in the comparative example, the exchange furnace bottom 31c was exchanged only once.

  FIG. 5 (b) shows the state of the furnace bottom 25 after replacement with a new replacement furnace bottom 31c having tuyere 44a and 44b. The tuyeres 44a and 44b are provided at the same position as before the replacement in the new replacement furnace bottom 31c used for replacement. Therefore, even after replacing the replacement furnace bottom 31, gas was injected from only the two tuyere 44a and 44b provided on the new replacement furnace bottom 31c.

  The tuyere brick 27 is subjected to an impact caused by gas blowing, and thus has reached its useful life earlier than the refractory brick 28. When the tuyere brick 27 reaches the end of its useful life, the hot metal of the charge that the tuyere brick 27 has reached the end of its useful life is poured out, and then the tuyere is repaired and closed by casting or the like. Dissolution was continued without mixing. Therefore, a dissolved charge was generated without blowing a gas in the dissolved charge until the useful life of the arc furnace 21 was reached. For each of the operation methods of the example and the comparative example, the ratio of the dissolved charge number, that is, the furnace bottom gas blowing rate is obtained while performing the gas blowing with respect to the total charge number dissolved until reaching the service life of the arc furnace 21. And compared.

  The test results are shown in Table 1. In Table 1, the charge is abbreviated as “ch” and indicated as follows to identify the tuyere 43 and 44 provided in the outer furnace bottom 32 and the exchange furnace bottom 31. In the embodiment, the tuyere 43a of the outer furnace bottom 32b is designated as the outer furnace bottom first tuyere, the tuyere 43b is designated as the outer furnace bottom second tuyere, and the tuyere 44 of the exchange furnace bottom 31b is designated as the replacement furnace bottom tuyere. The tuyere 44a of the initial exchange furnace bottom 31c is the first tuyere of the exchange furnace bottom, the tuyere 44b is the second tuyere of the exchange furnace bottom, and the tuyere 44a of the exchange furnace bottom 31c after the last exchange is the exchange furnace bottom. The 3rd tuyere and tuyere 44b were made into the 4th tuyere of the exchange furnace bottom. Hereinafter, the test results will be described according to the names of tuyere 43 and 44 in accordance with the notations in Table 1.

  In the operation method of the embodiment, the service life of the outer bottom 1st tuyere 43a of the outer bottom 32a used for gas blowing is 906 charged until the replacement to the new replacement bottom 31b, and the outer bottom 2nd tuyere. The useful life of 43b was 880 charges. At this time, the service life of the exchange furnace bottom 31a was 906 charges, which is the same as that of the outer furnace bottom first tuyere 43a of the outer furnace bottom 32a. Therefore, all the melting charges from the start of operation until the service life of the replacement furnace bottom 31a is reached, that is, 906 charges until the service life of the outer bottom 1st tuyere 43a is reached, can be dissolved while blowing gas. It was.

After the melting of the 906th charge was completed, it was replaced with a new replacement furnace bottom 31b having a replacement furnace bottom tuyere 44. Simultaneously with the replacement, the outer furnace bottom first and second tuyere 43a, 43b of the outer furnace bottom 32a were repaired and closed. After replacement with a new replacement furnace bottom 31b having a replacement furnace bottom tuyere 44, before the refractory brick on the replacement furnace bottom 31b reaches the useful life, the replacement furnace bottom tuyere 44 reaches the useful life when 285 charges are melted. did. Therefore, after the molten metal at the 285th charge was discharged, the bottom tuyere 44 of the exchange furnace was repaired and closed, and the 286th and subsequent charges were melted without blowing gas. When 434 charges were melted after replacement in the replacement furnace bottom 31b, the refractory brick 28 of the replacement furnace bottom 31b, that is, the replacement furnace bottom 31b reached the useful life. Therefore, the 149 charge, which is the difference between the 434 charge and the 285 charge, was dissolved without blowing gas. The service life of the arc furnace was 1340 charge, which was 906 charge dissolved before replacement plus 434 charge dissolved after replacement. The furnace bottom gas blowing rate in the examples was given by the formula (1) and was 88.9%.
88.9% = (906 + 285) / 1340 × 100 (1)

  On the other hand, in the operation method of the comparative example, the service life of the replacement furnace bottom first tuyere 44a of the replacement furnace bottom 31c used for gas blowing is 385 charges, and the service life of the replacement furnace bottom second tuyere 44b is used until the replacement. It was also 385 charges. Although the exchange furnace bottom first and second tuyere 44a and 44b reached the service life due to melting of 385 charges, the refractory brick 28 was in a state with a sufficient service life. Therefore, after the hot metal at the 385th charge was discharged, the first and second tuyere 44a, 44b of the exchange furnace were repaired and closed, and the 386th and subsequent charges were melted without blowing gas. . When the number of melts from the start of operation reached 488 charges, the refractory bricks 28 on the exchange furnace bottom 31c, that is, the exchange furnace bottom 31c reached the useful life. Therefore, 103 charge, which is the difference between 488 charge and 385 charge, was dissolved without performing gas blowing.

After the dissolution of the 488th charge, the exchange was performed with a new exchange furnace bottom 31c having exchange furnace bottom third and fourth tuyere 44a and 44b at the same position as before the exchange. After replacement with the new replacement furnace bottom 31c, the service life of the replacement furnace bottom third tuyere 44a used for gas blowing was 226 charges, and the service life of the replacement furnace bottom fourth tuyere 44b was 126 charges. Further, the useful life of the new exchange furnace bottom 31c after the exchange was 226 charges, which is the same as that of the exchange furnace bottom third tuyere 44a. Therefore, all the melting charges until the service life of the new replacement furnace bottom 31c after the replacement is reached, that is, the 226 charges until the service life of the third tuyere 44a of the replacement furnace is reached, are dissolved while blowing gas. I was able to. The service life of the arc furnace was 714 charges, which was 488 charges dissolved before replacement plus 226 charges dissolved after replacement. The furnace bottom gas blowing rate in the comparative example was given by the formula (2) and was 85.6%.
85.6% = (385 + 226) / 714 × 100 (2)

  Thus, until the replacement furnace bottom 31a is replaced, gas is blown from the outer furnace bottom first and second tuyere 43a, 43b provided on the outer furnace bottom 32 and replaced with a new replacement furnace bottom 31b. Was able to improve the furnace bottom gas blowing rate by adopting an operation method in which gas was blown from the replacement furnace bottom tuyere 44 provided in the new exchange furnace bottom 31b. Further, until the replacement furnace bottom is replaced in the final round, gas is blown from only the outer furnace bottom first and second tuyere 43a and 43b provided on the outer furnace bottom 32, and gas is blown from the replacement furnace bottom 31a. By avoiding this, the service life of the exchange furnace bottom 31a having no tuyere could be extended. As a result, the bottleneck of the arc furnace life has become the furnace bottom due to the tuyere at the bottom of the furnace, but by applying the arc furnace operation method, the effect of extending the useful life of the entire arc furnace is also exhibited. I was able to.

  In the embodiment, the service life of the new replacement furnace bottom 31b after replacement is longer than the service life of the new replacement furnace bottom 31c after replacement in the comparative example. This is considered to be a difference between one and two tuyere provided on the new exchange furnace bottom after exchange. If two exchange furnace bottom third and fourth tuyere 44a, 44b are provided as in the comparative example, the tuyere is caused by the interference of gas blown from the two exchange furnace bottom third and fourth tuyere 44a, 44b. It is considered that the wear of the refractory bricks 28 provided in the periphery is promoted, and the life is shortened as compared with the case where there is one replacement furnace bottom tuyere 44 as in the embodiment. Therefore, if two tuyere are provided in the new replacement furnace bottom in the embodiment, the service life of the new replacement furnace bottom after replacement is estimated to be equivalent to that in the comparative example. However, even in this case, although the useful life of the entire arc furnace of the embodiment is slightly shortened, the number of dissolved charges that cannot be injected after the replacement of the exchange furnace bottom decreases, so the bottom gas blowing rate On the other hand, it will increase, and the target effect will not change.

  As described above, in this embodiment, the arc furnace operating method is used when the replacement furnace bottom is replaced once throughout the useful life of the arc furnace bottom. However, the present invention is not limited to this, and even when the replacement furnace bottom is replaced a plurality of times throughout the useful life of the furnace bottom, it can be effectively used to improve the furnace bottom gas blowing rate.

It is a top view which shows the outline | summary of the operating method of the arc furnace of this invention. It is sectional drawing which simplifies and shows the structure of the arc furnace 21 suitable for the operating method of this invention. It is a top view which shows relative arrangement | positioning of the electrode with respect to the furnace bottom 25, and the arrangement | positioning position of a tuyere. It is a top view which shows the outline of the operating method of an Example. It is a top view which shows the outline of the operation method of a comparative example. It is sectional drawing which shows the structure of the conventional common arc furnace 1 roughly.

Explanation of symbols

1,21 Arc furnace 2,22 Furnace 3 Electrode 4,23 Shell 5,26 Refractory 6,25 Furnace bottom 7,43,44 tuyere 31 Exchange furnace bottom

Claims (2)

An exchange furnace bottom including a central part of the furnace bottom and configured to be exchangeable and an outer furnace bottom that is a furnace bottom part outside the exchange furnace bottom are provided. In the operation method of the arc furnace to be replaced once or several times,
Until the bottom of the exchange furnace is changed to the final round, gas is blown only from the tuyere provided at the outer furnace bottom,
A method of operating an arc furnace, characterized in that after the exchange furnace bottom is replaced in the final round, gas is blown only from tuyere provided at the exchange furnace bottom.   The arc furnace operating method according to claim 1, wherein the service life of the furnace bottom is determined by the thickness of the refractory according to the degree of wear of the refractory used for the furnace bottom.

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