Operation method of batch-type heating furnace
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- NIPPON STEEL CORPORATION
- Filing Date
- 2022-09-27
- Publication Date
- 2026-08-05
AI Technical Summary
【0013】 本開示に係るバッチ式加熱炉の操業方法によれば、生産性を確保することができる。
Smart Images
Figure 0007900661000001 
Figure 0007900661000002 
Figure 0007900661000003
Abstract
Description
Technical Field
[0001] The present disclosure relates to an operation method of a batch heating furnace.
Background Art
[0002] In the blooming rolling process in steelmaking, blooms, slabs, billets, etc. (hereinafter collectively referred to as steel pieces) are manufactured by performing hot rolling on a slab obtained by casting. During hot rolling, the slab is heated to a temperature at which it can be rolled. As a furnace for heating the slab to a predetermined temperature, a batch heating furnace (sometimes also called a soaking pit) and various types of continuous heating furnaces are known. For example, a batch heating furnace is described in Patent Document 1.
[0003] A batch heating furnace (hereinafter sometimes abbreviated as a heating furnace) includes a furnace body capable of accommodating steel pieces and a burner for heating the atmosphere inside the furnace body. Generally, the upper part of the furnace body is open and is closed by a movable cover. By moving the cover, the furnace body is opened and closed. The procedure for heating a steel piece using the heating furnace is as follows. First, a plurality of steel pieces are charged into the furnace body with the cover open. Then, the cover is closed and the atmosphere inside the furnace body is heated by the burner. As a result, the steel pieces inside the furnace body are heated to a temperature at which they can be rolled (for example, 1300°C).
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] Once the heating furnace has finished raising the temperature of the cast slab, the burner output is reduced and the cast slab is continuously extracted from the furnace. The continuous extraction of cast slabs is carried out in the following procedure. First, the cover of the heating furnace is opened and one cast slab is removed using a crane or similar device. Once a cast slab has been removed, the cover is closed and the furnace is left in this state until the next slab is removed. The cast slab removed from the heating furnace is transported to a rolling mill where hot rolling is performed. This process is repeated until all the cast slabs in the furnace are removed. Each cast slab removed from the heating furnace and transported to the rolling mill is rolled in the rolling mill.
[0006] During continuous extraction, the cover is repeatedly opened and closed, causing the ambient temperature inside the furnace to gradually decrease. This is because heat is released from the furnace when the cover is open. As continuous extraction of slabs progresses and the ambient temperature inside the furnace decreases, the temperature of the slabs inside the furnace also decreases accordingly, and the cooled slabs are removed from the heating furnace. The removed slabs cool slightly during the process of being transported to the rolling mill, and further heat is lost during the rolling process to become steel billets. Therefore, as continuous extraction of slabs progresses, the temperature of the slabs inside the furnace decreases, and the temperature of the slabs during rolling may fall below the rolling temperature. If low-temperature slabs are rolled, there is a risk of operational problems such as excessive loads exceeding the rolling mill's tolerance being applied. Alternatively, surface cracks may occur, potentially degrading the quality of the steel billet.
[0007] Conventionally, to prevent such operational problems and deterioration of steel billet quality, when continuous extraction has progressed to a certain extent and the temperature of the slab during rolling is about to fall below the rolling temperature, continuous extraction of the slab is stopped and the atmosphere inside the furnace is reheated with a burner. This reheating raises the temperature of the slab inside the furnace in order to raise the temperature of the slab during rolling. Then, after the slab inside the furnace has risen sufficiently in temperature, continuous extraction is resumed.
[0008] Figure 1 is a schematic diagram showing the temperature changes of steel billets immediately after hot rolling when they are continuously extracted. In Figure 1, the vertical axis represents the surface temperature of the steel billet, and the horizontal axis represents the number of continuously extracted billets (number of continuously extracted billets). In Figure 1, the temperature changes of the steel billet without reheating are shown by a dotted line, and the temperature changes of the steel billet with reheating are shown by a solid line. Note that the surface temperature of the steel billet immediately after hot rolling corresponds to the temperature of the billet during rolling. The trends in these surface temperature changes substantially coincide with the trends in the temperature changes of the billet being removed from the heating furnace. Therefore, the temperature of the billet inside the heating furnace and the temperature of the billet being removed from the heating furnace can be inferred from the surface temperature of the steel billet immediately after hot rolling. The temperature of the billet will be explained below using the surface temperature of the steel billet immediately after hot rolling.
[0009] Referring to Figure 1, the surface temperature of the steel billet (casting temperature) decreases as the number of continuously extracted billets increases. For example, if reheating is not performed, when the number of continuously extracted billets reaches 12, the temperature of the 12th billet will drop to near the temperature at which operational troubles may occur or the quality of the steel billet may deteriorate (hereinafter also referred to as the unrollable temperature range). If continuous extraction continues in this state, it is expected that the temperature of the steel billet immediately after hot rolling will reach the unrollable temperature range. On the other hand, if the above reheating is performed in the middle of continuous extraction, it can be seen that even when the number of continuously extracted billets reaches 16, the temperature of the steel billet does not reach the unrollable temperature range.
[0010] However, if reheating is performed during continuous extraction, the total time required for continuous extraction increases by the amount of time the extraction was stopped. Therefore, in the operation of the heating furnace, it is necessary to suppress the extension of the total time required for continuous extraction and ensure productivity.
[0011] The purpose of this disclosure is to provide a method for operating a batch-type heating furnace with high productivity. [Means for solving the problem]
[0012] The operating method described herein is an operating method for a batch-type heating furnace for heating cast slabs. The heating furnace comprises a furnace body and a burner. The furnace body is opened and closed by a cover. The burner heats the atmosphere inside the furnace body. The operating method for the heating furnace comprises a charging step, a main heating step, and a continuous extraction step. In the charging step, the cover is opened and multiple cast slabs are charged into the furnace body. In the main heating step, the cover is closed and the atmosphere inside the furnace body is heated by the burner. In the continuous extraction step, the unloading step and the auxiliary heating step are repeated alternately. In the unloading step, the output of the burner is set to a reference value, and the cover is opened to unload one of the multiple cast slabs inside the furnace body. In the auxiliary heating step, the cover is closed and the output of the burner is set to a value greater than the reference value to heat the atmosphere inside the furnace body. [Effects of the Invention]
[0013] The operating method of the batch-type heating furnace described herein can ensure productivity. [Brief explanation of the drawing]
[0014] [Figure 1] Figure 1 is a schematic diagram showing the temperature changes of steel billets immediately after hot rolling when cast slabs are continuously extracted. [Figure 2] Figure 2 is a schematic diagram showing the changes in ambient temperature inside the furnace and burner output during conventional continuous extraction. [Figure 3] Figure 3 is a cross-sectional view of a heating furnace used in the operating method according to the embodiment. [Figure 4] Figure 4 is a flowchart showing the operation method of the heating furnace according to the embodiment. [Figure 5] Figure 5 is a cross-sectional view of a heating furnace used in the operating method according to the embodiment. [Figure 6] Figure 6 is a cross-sectional view of a heating furnace used in the operating method according to the embodiment. [Figure 7] Figure 7 is a schematic diagram showing the changes in the ambient temperature inside the furnace and the burner output during continuous extraction in the operating method according to the embodiment. [Figure 8]FIG. 8 is a diagram showing the results of the examples.
BEST MODE FOR CARRYING OUT THE INVENTION
[0015] To solve the above problems, the inventors intensively studied and as a result obtained the following findings.
[0016] As described above, in the conventional continuous extraction of a slab, after heating the atmosphere in the furnace body with a burner, the cover of the furnace body is opened and one slab is carried out from the furnace body (hereinafter also referred to as step A), and the cover is closed and waiting until the next slab is carried out (hereinafter also referred to as step B) are alternately repeated. During continuous extraction, the output of the burner is set and maintained at a predetermined reference value. That is, the output of the burner is substantially reduced when the atmosphere in the furnace body is heated by the burner. This is because if the output of the burner is large, the flame of the burner will interfere with the slab carrying operation. Here, the output of the burner corresponds to the flow rate of the fuel gas blown out from the burner. By adjusting the flow rate of the fuel gas, the output of the burner is adjusted.
[0017] FIG. 2 is a schematic diagram showing the transition of the atmosphere temperature in the furnace body and the output of the burner during conventional continuous extraction. In FIG. 2, the vertical axis represents the atmosphere temperature in the furnace body and the output of the burner, respectively, and the horizontal axis represents the elapsed time.
[0018] [[ID=!9]] Referring to FIG. 2, during the period of step A, since the cover of the heating furnace is open, the atmosphere temperature in the furnace body gradually decreases. On the other hand, during the period of step B, the atmosphere temperature in the furnace body is gradually rising. This is presumably because during the period when the cover is closed, the atmosphere in the furnace body is reheated by the heat held by the furnace wall and the slab in the furnace body. However, in the conventional continuous extraction, since the next slab is carried out before the atmosphere temperature in the furnace body rises sufficiently, the temperature in the furnace body decreases every time the cover is repeatedly opened and closed. Then, in continuous extraction, if the atmosphere temperature in the furnace body can be sufficiently increased during the period when the cover of the heating furnace is closed, it is considered that the decrease in the atmosphere temperature in the furnace body can be suppressed even if the cover is repeatedly opened and closed.
[0019] The operation method of the heating furnace according to the embodiment of the present disclosure is completed based on the above findings.
[0020] The operation method according to this embodiment is an operation method of a batch-type heating furnace for heating a slab. The heating furnace includes a furnace body and a burner. The furnace body is opened and closed by a cover. The burner heats the atmosphere inside the furnace body. The operation method of the heating furnace includes a charging step, a main heating step, and a continuous extraction step. In the charging step, the cover is opened and a plurality of slabs are charged into the furnace body. In the main heating step, the cover is closed and the atmosphere inside the furnace body is heated by the burner. In the continuous extraction step, a carrying-out step and an auxiliary heating step are alternately repeated. In the carrying-out step, the output of the burner is set to a reference value, and the cover is opened to carry out one of the plurality of slabs inside the furnace body. In the auxiliary heating step, the cover is closed, and the output of the burner is set to a value larger than the reference value to heat the atmosphere inside the furnace body (the first configuration).
[0021] In the operation method of the first configuration, in the continuous extraction step, the carrying-out step and the auxiliary heating step are alternately repeated. In the carrying-out step, the slab is carried out with the cover open. Therefore, in the carrying-out step, the heat inside the furnace body is released to the outside of the furnace body, and the atmospheric temperature inside the furnace body decreases. Also, during the carrying-out step, the output of the burner is set to the reference value. As a result, during the carrying-out step, compared with the main heating step, the output of the burner is substantially reduced, and heating by the burner is not performed. On the other hand, in the auxiliary heating step, with the cover closed, the output of the burner is set to a value larger than the reference value. As a result, during the auxiliary heating step, compared with the carrying-out step, the output of the burner is increased, and heating by the burner is performed. In short, in the auxiliary heating step, during the period when waiting for the next slab to be carried out in the conventional continuous extraction, the output of the burner is increased compared with the carrying-out step, and the atmosphere inside the furnace body is heated.
[0022] In this continuous extraction process, the atmosphere inside the furnace is sufficiently reheated in the auxiliary heating process each time a slab is extracted. This is because the atmosphere inside the furnace is supplied with heat from the slabs inside the furnace and is further heated by the burner. Therefore, even if the cover is repeatedly opened and closed during the continuous extraction process, the decrease in the atmosphere temperature inside the furnace can be suppressed, and the atmosphere temperature inside the furnace is maintained at a high level. As a result, the temperature of the slabs inside the furnace is also maintained at a high level, and high-temperature slabs are discharged from the heating furnace. If high-temperature slabs are rolled, the situation in which the temperature of the steel billet immediately after rolling reaches the unrollable temperature range will not occur. In this case, the conventional reheating process, which involves stopping the continuous extraction, becomes unnecessary. Therefore, according to the operation method of the first configuration, the extension of the total time required for continuous extraction can be suppressed, and as a result, productivity can be ensured.
[0023] In the operation method of the first configuration, preferably, when the temperature of the atmosphere inside the furnace during the main heating process is T1 (°C) and the temperature of the atmosphere inside the furnace during the auxiliary heating process is T2 (°C), T2 satisfies the condition of the following formula (1) (second configuration). In this specification, temperature T1 may be referred to as the first temperature and temperature T2 as the second temperature. T1-50≦T2≦T1+30 (1)
[0024] In the second configuration of the operating method, the temperature of the atmosphere inside the furnace heated in the auxiliary heating process (second temperature T2) satisfies the condition of equation (1) in relation to the temperature of the atmosphere inside the furnace heated in the main heating process (first temperature T1). That is, the second temperature T2 is (T1-50) or higher and (T1+30) or lower. In short, the temperature of the atmosphere inside the furnace that has decreased during the discharge process rises to about the same level as the temperature of the atmosphere when heated in the main heating process. Therefore, according to the second configuration, even if the cover is opened and closed repeatedly in the continuous extraction process, the decrease in the temperature of the atmosphere inside the furnace can be suppressed more reliably.
[0025] Embodiments of this disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.
[0026] [Heating furnace] Referring to Figure 3, the configuration of the heating furnace 10 used in the operating method according to this embodiment will be described. Figure 3 is a cross-sectional view of the heating furnace 10 used in the operating method according to this embodiment. The heating furnace 10 comprises a furnace body 20, a cover 30, a burner 40, and a thermometer 50. The furnace body 20 has, for example, a box shape and can accommodate a plurality of cast slabs. Figure 3 shows the state before the cast slabs are placed inside the furnace body 20.
[0027] The furnace body 20 has a furnace bottom 21 and furnace walls 22. In this embodiment, the top of the furnace body 20 is open for loading and unloading of cast slabs. In other words, the furnace body 20 does not have an upper wall. However, the location of the opening in the furnace body 20 is not limited to this. For example, a part of the furnace wall 22 may be open.
[0028] The top (opening) of the furnace body 20 is closed by a cover 30. The cover 30 is slidable horizontally perpendicular to the vertical direction of the heating furnace 10. The top of the furnace body 20 is opened and closed by the sliding movement of the cover 30. In other words, the furnace body 20 is opened and closed by the movement of the cover 30. In short, by sliding the cover 30, the top of the furnace body 20 can be switched between an open state and a closed state. Figure 3 shows the state in which the cover 30 is closed, that is, the state in which the top of the furnace body 20 is closed.
[0029] The burner 40 is installed in the furnace wall 22. The burner 40 penetrates the furnace wall 22, with its tip exposed inside the furnace body 20. The burner 40 emits a flame by blowing combustion gas from its tip. In the heating furnace 10, the atmosphere inside the furnace body 20 is heated by the burner 40 with multiple cast slabs contained inside the furnace body 20. As a result, the cast slabs are heated to a temperature suitable for rolling.
[0030] The burner 40 is preferably positioned at the top of the furnace wall 22. This is to prevent the flame from the burner 40 from directly hitting the slab when the inside of the furnace body 20 is heated by the burner 40 while the slab is contained inside the furnace body 20. The output of the burner 40 can be set as appropriate, corresponding to the flow rate of fuel gas blown out from the burner 40. The output of the burner 40 is adjusted by adjusting the flow rate of fuel gas.
[0031] A flue 23 is provided at the bottom of the furnace wall 22. When the atmosphere inside the furnace body 20 is heated by the burner 40, combustion exhaust gas is generated. This combustion exhaust gas is discharged outside the furnace body 20 through the flue 23.
[0032] A thermometer 50 is installed inside the furnace body 20. The thermometer 50 is attached, for example, to the furnace wall 22. The thermometer 50 can measure the ambient temperature inside the furnace body 20. The ambient temperature inside the furnace body 20 is monitored by the thermometer 50. The thermometer 50 is, for example, a thermocouple.
[0033] [Operating methods] Figure 4 is a flowchart showing the operation method of the heating furnace 10 according to this embodiment. As shown in Figure 4, the operation method of this embodiment includes a charging process (#5), a main heating process (#10), and a continuous extraction process (#15). The continuous extraction process (#15) includes an unloading process (#15A) and an auxiliary heating process (#15B). In the operation method of this embodiment, multiple cast slabs are heated to a rollable temperature so that the temperature of the steel slabs does not reach the unrollable temperature range in the subsequent rolling process. The heated cast slabs are unloaded one by one from the furnace body 20 and subjected to hot rolling. In the continuous extraction process (#15), the unloading process (#15A) and the auxiliary heating process (#15B) are repeated alternately. In the unloading process (#15A), the output of the burner 40 is kept as low as possible. The output of burner 40 in the auxiliary heating process (#15B) is set to be greater than the output of burner 40 in the discharge process (#15A). Each process shown in Figure 4 will be explained in detail below.
[0034] [Charging process (#5)] Figure 5 is a cross-sectional view of the heating furnace 10 used in the operating method according to this embodiment. Figure 5 shows the state at the completion of the charging process (#5), that is, the state in which multiple cast slabs 60 have been charged into the furnace body 20. In the charging process (#5), as shown in Figure 3, the cover 30 is slid horizontally from a closed state to a state in which the opening of the furnace body 20 is opened. As shown in Figure 5, after opening the cover 30, multiple cast slabs 60 are charged into the furnace body 20. The material of the multiple cast slabs 60 is not particularly limited.
[0035] Each slab 60 is loaded through an opening in the furnace body 20. In this embodiment, since the top of the furnace body 20 is open, each slab 60 is loaded from above the furnace body 20. For example, a crane (not shown) can be used to load each slab 60. The number of slabs 60 loaded into the furnace body 20 in the loading process (#5) is not particularly limited and depends on the specifications of the heating furnace 10 and other operating conditions. However, if the number of slabs 60 loaded is small, the number of times the cover 30 is opened and closed in the continuous extraction process (#15) will decrease, and the temperature drop of the atmosphere inside the furnace body 20 will be smaller. In this case, there is no need to deliberately increase the output of the burner 40 in the auxiliary heating process (#15B) of the continuous extraction process (#15), and it may be more economical to perform continuous extraction with the output of the burner 40 reduced as in the conventional method. In the operating method of this embodiment, a certain number of slabs or more can be expected to have a productivity effect. Furthermore, in the operating method of this embodiment, the conventional reheating process can be omitted, thereby reducing fuel consumption for reheating. However, it is necessary to increase the output of the burner 40 in the auxiliary heating process (#15B). Therefore, the fuel required for continuous extraction in this embodiment is about the same as that for conventional continuous extraction.
[0036] [Main heating process (#10)] Figure 6 is a cross-sectional view of the heating furnace 10 used in the operating method according to this embodiment. Figure 6 shows the process during the main heating process (#10). In the main heating process (#10), as shown in Figure 5, the cover 30 is slid horizontally from an open state to a state in which the opening of the furnace body 20 is closed. As shown in Figure 6, after closing the cover 30, the atmosphere inside the furnace body 20 is heated by the burner 40. As a result, the atmosphere inside the furnace body 20 is heated to a set first temperature T1 (°C).
[0037] Upon completion of the main heating process (#10), the temperature of each cast slab 60 in the furnace body 20 becomes the same as the ambient temperature (first temperature T1) inside the furnace body 20. In other words, the main heating process (#10) raises the temperature of each cast slab 60 in the furnace body 20 to a temperature at which it can be rolled. The first temperature T1 may be set appropriately depending on the material of the cast slab 60, for example, 1200°C to 1300°C.
[0038] In the main heating process (#10), the output of the burner 40 is not particularly limited and may be set appropriately within a range that can heat the atmosphere inside the furnace body 20 to a first temperature T1. The output of the burner 40 may gradually increase or remain constant during the period until the atmosphere inside the furnace body 20 reaches the first temperature T1. In addition, the output of the burner 40 may gradually decrease after the atmosphere inside the furnace body 20 reaches the first temperature T1 until the start of the continuous extraction process (#15) described later, within a range that can maintain the atmosphere inside the furnace body 20 at the first temperature T1.
[0039] [Continuous extraction process (#15)] As described above, in the continuous extraction process (#15), the unloading process (#15A) and the auxiliary heating process (#15B) are repeated alternately. In the unloading process (#15A), the output of the burner 40 is set to the smallest possible value so that the flame of the burner 40 does not go out. The output of the burner 40 at this time is called the reference value N0. During the unloading process (#15A), by setting the output of the burner 40 to the reference value N0, the output of the burner 40 is effectively reduced compared to the main heating process (#10), and heating by the burner 40 is not performed. This is because if the output of the burner 40 is high, the flame of the burner 40 will interfere with the unloading of the cast slab 60.
[0040] In the removal process (#15A), the output of the burner 40 is set to the reference value N0, and the cover 30 is opened to remove one of the multiple cast slabs 60 inside the furnace body 20. A crane, for example (not shown), is used to remove the cast slab 60. The crane may be the same as the one used in the charging process (#5), or it may be different.
[0041] The cast slabs 60 removed in the removal process (#15A) are transported to a rolling mill (not shown) and hot-rolled to become steel billets. Steel billets are, for example, blooms, slabs, and billets. During the rolling of a cast slab 60, the next cast slab 60 is not usually removed from the furnace body 20. If the next cast slab 60 were removed during the rolling of a cast slab 60, the removed cast slab 60 would wait outside the furnace body 20, and its temperature would drop significantly during that waiting time. In conventional continuous extraction, to prevent the removed cast slabs 60 from waiting outside the furnace body 20, the cover 30 was simply closed and the output of the burner 40 was kept at a standard value in the heating furnace 10 during the rolling of the cast slabs 60 to keep the cast slabs 60 warm. This warming process is the above-mentioned process B (see Figure 2).
[0042] In the operating method according to this embodiment, an auxiliary heating step (#15B) is performed instead of the conventional continuous extraction step B. In the auxiliary heating step (#15B), the cover 30 is closed and the output of the burner 40 is set to a value greater than the reference value N0 (set value N). As a result, during the auxiliary heating step (#15B), the output of the burner 40 is increased compared to the discharge step (#15A), and heating is performed by the burner 40.
[0043] In the auxiliary heating step (#15B), the atmosphere inside the furnace body 20 is heated to a second temperature T2 (°C). Figure 7 is a schematic diagram showing the changes in the ambient temperature inside the furnace body 20 and the output of the burner 40 during continuous extraction in the operating method according to this embodiment. Figure 7 shows the changes in the ambient temperature inside the furnace body 20 and the output of the burner 40 during the main heating step (#10) and the continuous extraction step (#15) (discharge step (#15A) and auxiliary heating step (#15B)), respectively.
[0044] Referring to Figure 7, during the unloading process (#15A), the cover 30 is open, so the ambient temperature inside the furnace body 20 gradually decreases. At this time, as described above, the output of the burner 40 is set to the reference value N0. On the other hand, during the auxiliary heating process (#15B), the cover 30 is closed and the output of the burner 40 is set to the set value N. Since the set value N is greater than the reference value N0, the inside of the furnace body 20 is heated by the burner 40 during the auxiliary heating process (#15B). Therefore, when the auxiliary heating process (#15B) is performed, the atmosphere inside the furnace body 20 is reheated more significantly compared to when process B in the conventional continuous extraction is performed. This is because, during the auxiliary heating process (#15B), the atmosphere inside the furnace body 20 is given heat from the heat contained in the cast slabs 60 inside the furnace body 20 and is further heated by the burner 40.
[0045] As the unloading process (#15A) and the auxiliary heating process (#15B) are repeated alternately, the atmosphere inside the furnace body 20 may be heated to the same temperature each time, or it may be heated to a different temperature each time. In short, the second temperature T2 may be the same value throughout the auxiliary heating process (#15B) which is performed many times in the continuous extraction process (#15), or it may be a different value each time.
[0046] In the example shown in Figure 7, the second temperature T2 is set such that T1-50 ≤ T2 ≤ T1+30 in relation to the ambient temperature (first temperature T1) during the main heating process (#10). In other words, the ambient temperature inside the furnace body 20 is heated to approximately the same temperature as the first temperature T1 each time the auxiliary heating process (#15B) is performed. If the second temperature T2 is T1-50 (°C) or higher, the ambient temperature inside the furnace body 20 can be reliably maintained at a high level even if the unloading process (#15A) and the auxiliary heating process (#15B) are repeated alternately during the continuous extraction process (#15). Furthermore, if the second temperature T2 is T1+30 (°C) or lower, it is possible to prevent the slab 60 from being overheated and its quality from deteriorating.
[0047] 〔effect〕 In the operating method according to this embodiment, the continuous extraction process (#15) alternately repeats the unloading process (#15A) and the auxiliary heating process (#15B). In the continuous extraction process (#15), each time a slab 60 is extracted in the unloading process (#15A), the atmosphere inside the furnace body 20 is sufficiently reheated in the auxiliary heating process (#15B). Therefore, even if the cover 30 is repeatedly opened and closed in the continuous extraction process (#15), the decrease in the ambient temperature inside the furnace body 20 can be suppressed, and the ambient temperature inside the furnace body 20 is maintained at a high level. As a result, the temperature of the slabs 60 inside the furnace body 20 is also maintained at a high level, and high-temperature slabs 60 are unloaded from the heating furnace 10. If high-temperature slabs 60 are rolled, the situation in which the temperature of the steel billet immediately after rolling reaches the unrollable temperature range will not occur. In this case, conventional reheating, which is performed by stopping continuous extraction, is unnecessary. Therefore, according to the operating method according to this embodiment, the extension of the total time required for continuous extraction can be suppressed, and as a result, productivity can be ensured.
[0048] In the auxiliary heating process (#15B), the second temperature T2 is set such that, in relation to the first temperature T1, T1-50 ≤ T2 ≤ T1+30. In other words, the ambient temperature inside the furnace body 20, which has decreased during the discharge process (#15A), rises to approximately the same level as the ambient temperature when heated in the main heating process (#10). Therefore, according to the operating method of this embodiment, even if the cover 30 is opened and closed repeatedly in the continuous extraction process (#15), the decrease in the ambient temperature inside the furnace body 20 can be suppressed more reliably.
[0049] As described above, the operating method according to this embodiment does not require the conventional reheating process that is performed by stopping continuous extraction. Therefore, the operating method according to this embodiment can reduce the fuel gas consumption of the burner 40 by eliminating the need for reheating. On the other hand, in the auxiliary heating step (#15B), fuel gas consumption increases compared to step B in conventional continuous extraction in order to increase the output of the burner 40. Consequently, the total fuel gas consumption for the continuous extraction step (#15) is about the same as that for conventional continuous extraction. Thus, according to the operating method according to this embodiment, fuel gas consumption remains at the same level as in conventional continuous extraction, while suppressing the extension of the total time required for continuous extraction, and as a result, productivity can be ensured. [Examples]
[0050] To confirm the effectiveness of the operation method of the heating furnace 10 according to this embodiment, continuous extraction of cast slabs 60 was actually performed. In this embodiment, two continuous extractions were performed: one for the present invention example and one for the comparative example. In the present invention example, first, 12 cast slabs 60 were charged into the furnace body 20 (charging process (#5)). Then, the inside of the furnace body 20 was heated with a burner 40 for 550 minutes (main heating process (#10)). After that, the unloading process (#15A), in which one cast slab 60 was unloaded, and the auxiliary heating process (#15B), in which the cover 30 of the heating furnace 10 was closed and the inside of the furnace body 20 was heated with a burner 40 for 3 minutes were repeated alternately (continuous extraction process (#15)). Each cast slab 60 unloaded in the unloading process (#15A) was quickly hot-rolled to become a steel billet of a predetermined shape. The surface temperature of each steel billet immediately after rolling was measured and its changes were investigated.
[0051] In the comparative example, the change in surface temperature of steel billets after hot rolling in a conventional continuous extraction process was investigated. In the comparative example, after heating the slabs 60 in the furnace body 20, process A, in which one slab 60 is removed, and process B, in which the body waits until the next slab 60 is removed, were repeated alternately (see Figure 2). In the comparative example, all other conditions were the same as in the present invention example.
[0052] Figure 8 shows the results of the embodiment. In Figure 8, the vertical axis represents the surface temperature of the steel billet, and the horizontal axis represents the number of cast slabs 60 continuously extracted. Referring to Figure 8, in the present invention example, even when the extraction of cast slabs 60 was repeated, the temperature of the steel billet never fell below 900°C and a high temperature was maintained. On the other hand, in the comparative example, the temperature gradually decreased as continuous extraction progressed, and when the number of cast slabs 60 continuously extracted reached 7, the temperature of the steel billet had dropped to near the rolling-impossible temperature range. From this, it can be seen that the continuous extraction process (#15) of the present invention example employing the operating method according to this embodiment can suppress the decrease in the temperature of the cast slab 60.
[0053] The embodiments of this disclosure have been described above. However, the embodiments described above are merely examples for implementing this disclosure. Therefore, this disclosure is not limited to the embodiments described above, and the embodiments described above can be modified as appropriate without departing from the spirit of this disclosure. [Explanation of Symbols]
[0054] 10:Heating furnace 20:Furnace body 30: Cover 40: Burner 60: Cast slab N0: Reference value T1: First temperature T2: Second temperature
Claims
1. A method for operating a batch-type heating furnace for heating cast slabs, The heating furnace comprises a furnace body that is opened and closed by a cover, and a burner that heats the atmosphere inside the furnace body. The operating method of the aforementioned heating furnace is: A charging step involves opening the cover and loading a plurality of castings into the furnace body, The main heating step involves closing the cover and heating the atmosphere inside the furnace body with the burner, A method for operating a batch-type heating furnace, comprising: a continuous extraction process that alternately repeats an unloading process and an auxiliary heating process, wherein in the unloading process, the output of the burner is set to a reference value smaller than the output of the burner in the main heating process, and the cover is opened to unload one of the plurality of cast slabs inside the furnace body; and in the auxiliary heating process, the cover is closed and the output of the burner is set to a value larger than the reference value to heat the atmosphere inside the furnace body.
2. A method for operating a batch-type heating furnace according to claim 1, The temperature of the atmosphere inside the furnace at the completion of the main heating process is T １ Let (°C) be the temperature of the atmosphere inside the furnace body at the completion of the auxiliary heating step, and T ２ When (°C), T ２ The following describes an operating method for a batch-type heating furnace that satisfies the conditions of equation (1) below. T １ -50≦T ２ ≦T １ +30 (1)