Arc furnace operation method

Abstract

The furnace vessel (1) of the arc furnace is charged with the metal (2) in the form of solid agglomerates. The energy supply (3) of the arc furnace then draws electrical energy from the supply network (4) and supplies it to the electrodes (6) of the arc furnace via the furnace transformer (5), so that an arc (12) is formed between the electrodes (6) and the metal (2) or molten metal (13), which melts the metal (2) to form the molten metal (13). Finally, the molten metal (13) is removed from the furnace vessel (1). The number of electrodes (6) is at least three. The energy supply (3) adjusts the operating frequency (fa, fb) of each electrode (6A, 6B) separately for at least two electrodes (6). The current (Ic) through the third electrode (6C) is determined by the current (Ia) through the first electrode (6A) and the current (Ib) through the second electrode (6B). Of all the electrodes (6) in the arc furnace, which electrodes are the first electrodes (6A), which electrodes are the second electrodes (6B), and which electrodes are the third electrodes (6C) are dynamically assigned to the electrodes (6).

Description

Technical Field

[0001] The present invention is based on an operating method of an arc furnace. The energy supply device of the arc furnace draws electrical energy from a supply network between charging of the metal in a solid agglomerated state into the furnace vessel of the arc furnace and extraction of the molten metal from the furnace vessel, and supplies the drawn electrical energy to at least one first electrode, at least one second electrode, and at least one third electrode of the arc furnace via a furnace transformer. Thereby, an arc is formed between the electrodes and the metal or molten metal, and the metal is melted by the arc to form molten metal. The energy supply device individually adjusts the operating frequency of the first electrode and the operating frequency of the second electrode, whereby the current passing through the third electrode is determined by the currents passing through the first and second electrodes.

[0002] The present invention is further based on a control program related to a control device of an arc furnace. The control program includes machine code that can be processed by the control device, and by processing the machine code by the control device, the control device operates the arc furnace according to such an operating method.

[0003] The present invention is further based on a control device of an arc furnace. The control device is programmed with a control program such that the control device operates the arc furnace according to such an operating method by processing machine code by the control device.

[0004] The present invention is further based on an arc furnace, - The arc furnace has a furnace vessel, and it is possible to charge the furnace vessel with metal and extract molten metal from the furnace vessel. - The arc furnace has an energy supply device, electrodes, and a furnace transformer. - The energy supply device is connected to the supply network on the input side and to the electrodes via the furnace transformer on the output side. - The arc furnace has a control device capable of operating at least one energy supply device. - The control device is configured as described above. [Background technology]

[0005] The subject described above is known, for example, from Patent Document 1.

[0006] When melting metals, especially steel, in an arc furnace, the electrical energy supplied to the arc furnace electrodes is provided via a furnace transformer. Furnace transformers are often connected to the power grid via medium-voltage transformers. Furnace transformers supply multiple voltage steps. Each voltage step can be selected in the furnace transformer for a certain output range and other high-current ranges. Fine-tuning within a specific voltage step can be achieved, for example, by impedance control.

[0007] In this approach, only small voltage steps are possible, and the electrode current is subject to strong fluctuations. To mitigate these fluctuations, electrode positioning is mechanically controlled, usually through a hydraulic adjustment device. Mechanical adjustment of the electrodes has significantly lower dynamics than the actual behavior of the arc. Therefore, fluctuations can only be adequately compensated. Furthermore, fluctuations place significant loads on components such as high-current cables, energizing brackets, and hydraulic cylinders. Fluctuations occur in both the melting phase and the subsequent flat bath phase.

[0008] When adjusting the electrode voltage through the voltage steps of the furnace transformer, the electrode positioning must be continuously readjusted. This readjustment can be performed, for example, to control a specific impedance or output. However, since the dynamics of the positioning device are relatively small compared to the changes in the arc's electrical system, some uncompensable fluctuations remain. This results in suboptimal energy input to the molten steel.

[0009] Approaches for continuously adjusting electrode voltage are known from prior art documents, particularly from Patent Documents 2 and 3, and to a limited extent from Patent Document 4. These embodiments offer significant advantages over adjusting the electrode voltage through voltage steps of a furnace transformer. For example, it is possible to change the electrode voltage continuously as well as in steps. Furthermore, the furnace transformer does not need to provide multiple voltage steps, resulting in a simpler configuration. Moreover, electrode voltage adjustment is possible with significantly greater dynamics than electrode positioning. Finally, these embodiments enable further types of control.

[0010] Despite the flexibility offered by the possibility of continuously adjusting the electrode voltage during arc furnace operation, conventional techniques often still result in suboptimal operation. For example, suboptimal energy input to the metal or molten metal, as well as arc extinction, can still occur. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] International Publication No. 2021 / 115573 brochure [Patent Document 2] International Publication No. 2015 / 176899 brochure [Patent Document 3] European Patent Application Publication No. 3124903 [Patent Document 4] European Patent Application Publication No. 1026921 [Overview of the project] [Problems that the invention aims to solve]

[0012] The object of this invention is to provide a possibility to avoid the drawbacks of the prior art. [Means for solving the problem]

[0013] This problem is solved by an operating method having the features of claim 1. Advantageous embodiments of this operating method are covered by dependent claims 2 to 11.

[0014] According to the present invention, the type of operation method described at the beginning is configured by dynamically assigning to the electrodes which of the entire electrodes of the arc furnace are the first electrode, which are the second electrode, and which are the third electrode.

[0015] This allows the operating frequencies of at least the first and second electrodes to be optimally adjusted for the specific operation of each electrode.

[0016] It is possible for the operating frequencies of the first electrode and the second electrode to be the same. However, this is only the case if the operating frequencies happen to be the same as a result of individually adjusting them. Generally, however, the operating frequencies of the first electrode and the second electrode are different.

[0017] It is possible for the operating frequency of the first electrode to be constant over time. However, generally, better operation of the arc furnace is achieved when the operating frequency of the first electrode changes over time. Preferably, the operating frequency of the first electrode changes depending on the process state of the arc furnace. The process state can be determined in particular by evaluating the electrical or acoustic operating variables of the arc furnace. Obviously, the same approach can be used for the second electrode.

[0018] It is also possible to adjust the operating frequency of the second electrode independently of the operating frequency of the first electrode. However, it is often advantageous to adjust the operating frequency of the second electrode in consideration of the operating frequency of the first electrode. For example, the operating frequency of the second electrode can be adjusted to have a specific interval with respect to the operating frequency of the first electrode. Furthermore, while the operating frequency of the second electrode can initially be determined independently of the operating frequency of the first electrode, such a determined operating frequency can only be adopted if it has at least a specific interval with respect to the operating frequency of the first electrode. In other cases, the operating frequency of the second electrode can be adjusted to have a specific interval with respect to the operating frequency of the first electrode.

[0019] In other words, in this invention, the states of the first, second, and third electrodes are not fixed and determined only once, but change from time to time, considering each state in relation to the period between the charging of metal into the furnace vessel and the removal of molten metal from the furnace vessel. That is, the same electrode in an arc furnace may be the first electrode at one point in time, the second electrode at another point in time, and neither the first nor the second electrode at yet another point in time. If there are three electrodes in total in an arc furnace, and at a certain time x electrode a operates at frequency fa and electrode b operates at frequency fb, and the current flowing through electrode c is determined by the currents flowing through electrodes a and b, then for example, at a later time y, it is possible to operate electrode b at frequency fa and electrode c at frequency fb, and therefore the current flowing through electrode a may be determined by the currents flowing through electrodes b and c. The transition can be abrupt or continuous, and in the latter case it is particularly sinusoidal.

[0020] The electrodes of an arc furnace are generally adjustable in height. In this case, the heights of the electrodes may be adjustable together or independently of each other. When adjustable independently, the dynamic assignment of each "role" to the electrodes can be combined with an approach in which the position of each electrode of the arc furnace is determined depending on whether each electrode is the first, second or third electrode. The concept of "depending on" should not mean that the "role" of each electrode completely determines the positioning of each electrode. Rather, it is sufficient if the "role" of each electrode is also taken into account.

[0021] To achieve individual height adjustment, in addition to adjusting the electrodes together, it may already be sufficient if it is possible to slightly superimpose additional movement of the individual electrodes. In this case, if there are n electrodes, only n - 1 devices are required to provide the additional movement.

[0022] Between the charging of metal into the furnace vessel and the withdrawal of molten metal from the furnace vessel, the arc furnace is first operated in a melting stage and then in a flat bath stage. In the melting stage, the metal melts to form molten metal. The melting stage can be divided into an initial stage and a final stage. The initial stage is often called the piercing stage. Most of the melting of the metal takes place in the final stage. In the flat bath stage, the molten metal is further heated.

[0023] Furthermore, in some cases, the charging of metal into the furnace vessel is also very uneven, with large metal fragments in the area below one electrode and small metal fragments in the area below another electrode. In this case, it may be advantageous to determine the operating frequency of the first electrode in the melting stage depending on the size of the metal fragments to be melted using the first electrode. The operating frequency of the first electrode can be determined such that during the melting stage, especially, the larger the metal fragments to be melted using the first electrode, the lower the operating frequency of the first electrode. Furthermore, preferably, the operating frequency of the first electrode in the melting stage or the final stage of the melting stage is greater than the power supply frequency at which the supply network operates, especially at least 10 Hz greater. Needless to say, the same approach can also be used for the second electrode.

[0024] Preferably, the electrical energy supplied to the electrodes is determined so that each electrode introduces the same amount of energy into the metal or molten metal on a time-averaged basis. In this case, the time average is formed not over individual periods of each operating frequency of each electrode, but over the entire operation of the electrodes between the charging of metal into the furnace vessel and the removal of molten metal from the furnace vessel, or over at least one operating stage of the arc furnace (the initial stage of the melting stage, the final stage of the melting stage and the flat bath stage, or the melting stage and the flat bath stage). This, in particular, ensures temperature equalization of the molten metal.

[0025] This problem is further solved by a control program having the features of claim 12. According to the present invention, the control device operates the arc furnace according to the operating method according to the present invention by processing machine code by the control device.

[0026] This problem is further solved by a control device having the features of claim 13. According to the present invention, since the control device is programmed with the control program according to the present invention, the control device operates the arc furnace in accordance with the operating method according to the present invention.

[0027] This problem is further solved by an arc furnace having the features of claim 14. According to the present invention, the control device is configured as the control device according to the present invention.

[0028] The features, characteristics, and advantages of the present invention described above, as well as the methods for obtaining them, will become clearer and easier to understand in connection with the following description of embodiments, which will be described in more detail with reference to the drawings. In this regard, the following is schematically shown. [Brief explanation of the drawing]

[0029] [Figure 1] This is a block diagram of an arc furnace. [Figure 2] This is a diagram showing the furnace vessel during the melting stage. [Figure 3]This is a flowchart diagram. [Figure 4] This is a diagram showing the furnace vessel during the flat bath stage. [Figure 5] This is a flowchart diagram. [Figure 6] This is a timing diagram. [Figure 7] Here is another timing diagram. [Figure 8] This is a diagram illustrating functional dependencies. [Modes for carrying out the invention]

[0030] As shown in Figure 1, the arc furnace has a furnace vessel 1. Metal 2 can be charged into the furnace vessel 1 (see Figure 2). When charged, metal 2 is supplied to the furnace vessel 1 in a solid aggregated state. Metal 2 is, for example, steel, and in the case of steel, it may be scrap in particular.

[0031] The arc furnace also has an energy supply device 3. The energy supply device 3 is connected to a power grid 4 on the input side. The power grid 4 is generally a medium-voltage network with a nominal voltage in the two-digit kV range and operates at a power frequency f0. The power frequency f0 is generally 50Hz or 60Hz. As shown in Figure 1, the power grid 4 is generally a three-phase power grid.

[0032] The arc furnace further includes a furnace transformer 5 and electrodes 6. The energy supply device 3 is connected to the electrodes 6 via the furnace transformer 5 on the output side. Within the scope of the present invention, there are at least three electrodes 6. In many cases, there are exactly three electrodes 6. Furthermore, the furnace transformer 5 is generally configured as a three-phase transformer. However, regardless of the specific embodiment, the electrode voltage U applied to the electrodes 6 is clearly lower than the nominal voltage of the power supply network 4. The electrode voltage U is shown for only one of the electrodes 6 in Figure 1. In most cases, the electrode voltage U is in the range of several hundred volts. In individual cases, voltages exceeding 1 kV are also possible. However, generally it does not exceed 2 kV.

[0033] In general, there is a switching device that can disconnect the energy supply device 3 from the supply network 4. Furthermore, there may be a switching device that can disconnect the energy supply device 3 from the furnace transformer 5 and / or the furnace transformer 5 from the electrodes 6. The switching device performs a purely binary switching process but does not adjust voltage and current. Furthermore, an active or passive filter device may be located on the primary or secondary side of the furnace transformer 5. The switching device and filter device are of secondary significance to the function of the present invention and are therefore not shown in Figure 1 (and other figures) for clarity.

[0034] The energy supply device 3 can draw electrical energy from the power grid 4 and supply the drawn electrical energy to the electrodes 6 via the furnace transformer 5. The energy supply device 3 generally has a number of semiconductor switches for this purpose. Possible embodiments of the energy supply device 3 are described in Patent Document 2 ("Gold Standard"). Alternatively, embodiments relating to Patent Document 3 or Patent Document 4 can be used, for example. However, regardless of the specific embodiment of the energy supply device 3, the energy supply device 3 can provide quasi-continuous stepping of the electrode voltage U applied to the electrodes 6 and / or the electrode current I supplied to the electrodes 6 at the output side, i.e., toward the furnace transformer 5. As with the electrode voltage U, the electrode current I is also shown in Figure 1 with respect to only one of the electrodes 6. Each operating frequency f when the electrode voltage U applied to the electrodes 6 or the electrode current I supplied to the electrodes 6 changes can also be adjusted using the energy supply device 3. Each operating frequency f can be above or below the power supply frequency f0 as needed.

[0035] Furthermore, the arc furnace has a positioning device 7. Using the positioning device 7, the electrodes 6 can be positioned as shown by the bidirectional arrows 8 next to the electrodes 6 in Figure 1. In the simplest case, joint positioning of the electrodes 6 is performed. However, preferably, individual positioning of the electrodes 6 is performed. This is indicated in Figure 1 by the different lengths of the bidirectional arrows 8. The direction of movement in which the electrodes 6 are positioned may be vertical. Alternatively, the direction of movement may be slightly inclined with respect to the vertical line. However, even in this case, the vertical component is the dominant component of the movement. The positioning device 7 may have, for example, one or more hydraulic cylinder units.

[0036] Finally, the arc furnace has a control device 9. The control device 9 controls at least the energy supply device 3. The control device 9 generates an activation value A1 that activates the energy supply device 3. The energy supply device 3 operates according to the activation value A1.

[0037] The positioning device 7 is often controlled by the control device 9, in which case the control device 9 further generates operating values ​​A2 that operate the positioning device 7. In this case, the positioning device 7 operates according to these operating values ​​A2.

[0038] The control device 9 is configured as a software-programmable control device. This is indicated in Figure 1 by the notation "μP" (meaning microprocessor control). The operation and method of operation of the control device 9 are determined by the control program 10, and the control device 9 is programmed by the control program 10. The control program 10 includes machine code 11 that can be processed by the control device 9. Through the processing of machine code 11 by the control device 9, the control device 9 operates the arc furnace according to an operating method that will be described in detail below in relation to other figures.

[0039] According to Figure 3, in step S1, metal 2 is first charged into the furnace vessel 1. Figure 2 shows the state of the furnace vessel 1 after charging, immediately after the ignition of the arc 12 by the corresponding operation of the energy supply device 3 by the control device 9 (see Figures 2 and 4).

[0040] Subsequently, in step S2, the actual operation of the arc furnace is carried out. In step S2, an electrode voltage U is applied and an electrode current I is supplied to electrode 6. As a result, an arc 12 is first formed between electrode 6 and metal 2, and the metal 2 is melted by the arc 12 to form molten metal 13. This operating stage of the arc furnace is generally called the melting stage. The melting stage may be divided into an initial stage and a final stage, the initial stage generally called the drilling stage and the final stage called the main melting stage. Subsequently, an arc 12 is formed between electrode 6 and molten metal 13 and is further heated. This operating stage of the arc furnace is generally called the flat bath stage. This state is shown in Figure 4. In the flat bath stage, the top surface of the molten metal 13 may be covered with a slag layer 14. The slag layer 14 may be foamed slag.

[0041] Finally, in step S3, the formed molten metal 13 is removed from the furnace vessel 1 and poured into, for example, a ladle (not shown).

[0042] Step S2, i.e., the actual operation of the arc furnace, is carried out by the corresponding operation of the energy supply device 3. Steps S1 and S3 can similarly be carried out under the control of the control device 9. However, it is not necessary to carry out steps S1 and S3 under the control of the control device 9. Therefore, steps S1 and S3 are shown only by dashed lines in Figure 3.

[0043] In the following, with reference to Figure 5, the actual operation of the arc furnace between step S2, i.e., the charging of metal 2 into the furnace vessel 1 and the removal of molten metal 13 from the furnace vessel 1, will be described in detail. For this purpose, step S2 is divided into steps S11 to S20. Furthermore, within the scope of the following description, individual electrodes 6 will be distinguished. To this end, when individual electrodes 6 are distinguished, a small letter is additionally assigned to each electrode 6 in order. In this case, electrodes 6 will be denoted as the first electrode 6a, the second electrode 6b, the third electrode 6c, and so on. In contrast, when referring to electrodes 6 in general, only the general reference symbol 6 is used. The same applies to electrode-specific variables such as electrode voltage U, electrode current I, and operating frequency f.

[0044] As shown in Figure 5, in step S11, the control device 9 determines the state Z of the arc furnace. State Z indicates how far the operation of the arc furnace has progressed between the charging of metal 2 and the removal of molten metal 13. In the simplest case, the state Z of the control device 9 is set by the operator 15 (see Figure 1). Alternatively, the control device 9 may directly determine the state Z based on the time t that has elapsed since the first ignition of the arc 12 after charging the furnace vessel 1. However, preferably, in step S12, the control device 9 evaluates the current values ​​of the arc furnace as detected by measurement techniques. For example, the control device 9 can evaluate the electrode current I and / or electrode voltage U, in particular its fluctuations. The control device 9 can also evaluate the acoustic variables of the arc furnace, such as the noise level or the acoustic spectrum of the noise generated.

[0045] In step S12, the control device 9 determines which of the electrodes 6 is the first electrode 6a, the second electrode 6b, and the third electrode 6c. This determination may depend directly on the time t that has elapsed since the arc 12 was first ignited after charging the furnace vessel 1. Alternatively, the determination may depend directly on the time that has elapsed since the start of each state Z. In the latter two cases, the electrodes 6 are dynamically assigned which of the electrodes 6 is the first electrode 6a, which is the second electrode 6b, and which is the third electrode 6c. In other words, the electrodes 6 can occasionally swap their roles.

[0046] In step S13, the control device 9 determines the desired frequency range F for the electrode current I and / or electrode voltage U. The frequency range F may, in particular, depend on the state Z. For example, as shown in Figure 6, the frequency range F in the final stage of the melting phase (state Z=2) may exclusively include frequencies f greater than the power supply frequency f0. Similarly, the frequency range F in the flat bath phase (state Z=3) may exclusively include frequencies f lower than the power supply frequency f0. Finally, the frequency range F in the initial stage of the melting phase (state Z=1) may alternatively exclusively include frequencies f greater than the power supply frequency f0, or exclusively include frequencies f less than the power supply frequency f0.

[0047] Preferably, the frequency range F always has a certain minimum interval with respect to the power supply frequency. This minimum interval is, for example, between 7 Hz and 13 Hz, and may particularly be about 10 Hz. If the frequency range F is higher than the power supply frequency f0, the lower limit frequency of the frequency range F at a power supply frequency f0 of 50 Hz is preferably "somewhere" between 57 Hz and 63 Hz, for example 60 Hz. Similarly, if the frequency range F is lower than the power supply frequency f0, the upper limit frequency of the frequency range F when the power supply frequency f0 is 50 Hz is preferably "somewhere" between 37 Hz and 43 Hz, for example 40 Hz. When the power supply frequency f0 is 60 Hz, 10 Hz must be added to each of the above limit frequencies.

[0048] Preferably, the output P to be introduced into metal 2 or molten metal 13.* As shown in Figure 7, it is adjusted as a function of time t, specifically depending on the state Z. Figure 7 shows a preferred embodiment, according to which the output P to be introduced is * The value is relatively low in the initial stage of the melting phase (state Z=1), relatively high in the final stage of the melting phase (state Z=2), and between the initial and final stages of the melting phase in the flat bath stage (Z=3).

[0049] In step S14, the control device 9 determines the operating frequency fa of the first electrode 6a. This determination is made such that the operating frequency fa is within the currently valid frequency range F. The operating frequency fa may be fixed. Alternatively, the operating frequency fa may be fixed within each state Z but dependent on state Z. Further alternatively, the operating frequency fa may depend on time, for example, the progress of the process, within each state Z (see Figure 6). Figure 6 shows the possible temporal changes of the operating frequency fa for state Z=1, both for the frequency range F above and below the power supply frequency f0. Obviously, in practice, only one of the two operating frequencies fa is valid.

[0050] In step S15, the control device 9 determines the operating frequency fb of the second electrode 6b. This determination is made separately if the operating frequency fb does not necessarily have to match the operating frequency fa. In other words, the operating frequency fb may be different from the operating frequency fa.

[0051] The determination in step S15 can also be made independently of the determination in step S14. However, there may also be certain dependencies. For example, it may be required that the operating frequency fb of the second electrode 6b maintains a minimum distance from the operating frequency fa of the first electrode 6a. Alternatively, it may be required that the operating frequency fb of the second electrode 6b is within the currently valid frequency range F. In other cases, embodiments for determining the operating frequency fa of the first electrode 6a may be similarly applied.

[0052] It is no longer possible to determine the operating frequency of the third electrode 6c. This is because the operating mode of the third electrode 6c is determined by the fact that the current I passing through electrodes 6a, 6b, and 6c must be zero at all times (considering the sign of the current I).

[0053] In step S16, the control device 9 determines the operating value A1 of the energy supply device 3. When determining the operating value A1, the control device 9 takes into account the operating frequencies fa and fb of the first and second electrodes 6a and 6b.

[0054] If the control device 9 also controls the positioning device 7, the control device 9 performs positioning pa, pb, and pc of the first, second, and third electrodes 6a, 6b, and 6c in step S17. In this case, the control device 9 determines the additional operating value A2 in step S18. It is also possible to determine this uniformly for all electrodes 6. However, it is also possible to perform positioning pa, pb, and pc individually depending on whether each electrode 6 is the first, second, or third electrode 6a, 6b, or 6c.

[0055] In step S19, the control device 9 activates the energy supply device 3 according to the determined operating value A1. If the control device 9 also controls the positioning device 7, in step S19, the control device 9 also activates the positioning device 7 with an additional operating value A2.

[0056] In step S20, the control device 9 checks whether each cycle of operation of the arc furnace has been completed, that is, whether the metal 2 has been completely melted to form molten metal 13, and whether the molten metal 13 has been further heated if necessary. If it has been completed, the control device 9 proceeds to step S3. Otherwise, the control device 9 returns to step S11.

[0057] Figure 8 shows one possibility for determining the operating frequency fa of the first electrode 6a during the melting stage. The dependency shown in Figure 8 may alternatively exist throughout the entire melting stage, or only during the initial or final stages of the melting stage. According to Figure 8, the control device 9 determines the operating frequency fa of the first electrode 6a depending on the dimensions G of the metal 2 fragment to be melted using the first electrode 6. In particular, the operating frequency fa of the first electrode 6a may decrease monotonically or very monotonically as the dimensions G of the metal 2 fragment increase. That is, it is preferable that the operating frequency fa of the first electrode 6a is determined during the melting stage such that it decreases as the size of the metal 2 fragment to be melted using the first electrode 6a increases. Obviously, a similar approach can be adopted for the second electrode 6b and its operating frequency fb. In the approach shown in Figure 8, different or identical operating frequencies fa and fb may occur depending on the dimensions G of the metal 2 fragment. As dimensions G, for example, the statistical average of the dimensions of individual pieces of metal 2 can be used. Alternatively, extreme values ​​(minimum or maximum values) can be used.

[0058] The integral of the electrical energy supplied to electrode 6, i.e., the power supplied to electrode 6, is determined by the control device 9, preferably such that electrode 6 introduces the same amount of energy into metal 2 or molten metal 13 over time. In this case, the time average is formed over a number of periods, rather than over individual periods of each operating frequency fa, fb. Particularly preferred is averaging over each operating stage of the arc furnace, i.e., the initial stage of the melting stage, the final stage of the melting stage, and the flat bath stage, or over the melting stage and the flat bath stage.

[0059] The present invention has many advantages. In particular, the operation of the arc furnace can be flexibly adapted to the requirements of individual cases. Furthermore, it is often possible to reduce the specific energy (e.g., kilowatt-hours per ton) required to produce a certain amount of molten metal 13, and the cycle time can also often be reduced.

[0060] Although the present invention has been illustrated and described in more detail through preferred embodiments, the present invention is not limited to the disclosed embodiments, and those skilled in the art can derive other variations without departing the scope of protection of the present invention. [Explanation of Symbols]

[0061] 1 Furnace vessel 2 metal 3. Energy supply device 4 Supply network 5. Furnace transformer 6 electrodes 7 Positioning device 8. Two-way arrow 9 Control device 10 Control Program 11 Machine Code 12 Arc 13 Molten metal 14 Slag Layer 15. Driver A1, A2 Operating Values f, fa, fb Operating frequency f0 Power supply frequency F frequency range G Dimension I, Ia, Ib, Ic Power supply current PA, PB, PC positioning P * Output to be introduced S1~S20 Steps t time U electrode voltage Z state

Claims

1. A method for operating an arc furnace, wherein the energy supply device (3) of the arc furnace draws electrical energy from a supply network (4) between the charging of solid aggregated metal (2) into the furnace vessel (1) of the arc furnace and the removal of molten metal (13) from the furnace vessel (1), and supplies the drawn electrical energy to at least one first electrode (6a), at least one second electrode (6b), and at least one third electrode (6c) of the arc furnace via a furnace transformer (5), thereby forming an arc between the electrode (6) and the metal (2) or the molten metal (13), and the metal ( 2) is melted to form the molten metal (13), and the energy supply device (3) individually adjusts the operating frequency (fa) of the first electrode (6a) and the operating frequency (fb) of the second electrode (6b), thereby so that the currents (Ia, Ib, Ic) passing through the first to third electrodes (6a, 6b, 6c) sum to zero at any given time, taking into account the signs of the currents (Ia, Ib, Ic), in an arc furnace operation method in which the current (Ic) passing through the third electrode (6c) is determined by the current (Ia) passing through the first electrode (6a) and the current (Ib) passing through the second electrode (6b), A method for operating an arc furnace, characterized in that, of the electrodes (6) of the arc furnace, which electrode is the first electrode (6a), which electrode is the second electrode (6b), and which electrode is the third electrode (6c) are dynamically assigned to the electrodes (6).

2. The operating method according to claim 1, characterized in that the operating frequency (fa) of the first electrode (6a) and the operating frequency (fb) of the second electrode (6b) are different from each other.

3. The operating method according to claim 1 or 2, characterized in that the operating frequency (fa) of the first electrode (6a) changes over time.

4. The operating method according to claim 3, characterized in that the operating frequency (fa) of the first electrode (6a) changes depending on the process state of the arc furnace.

5. The operating method according to claim 4, characterized in that the process state is determined through evaluation of the electrical or acoustic operating variables of the arc furnace.

6. The operating method according to claim 1, characterized in that the operating frequency (fb) of the second electrode (6b) is adjusted taking into consideration the operating frequency (fa) of the first electrode (6a).

7. The operating method according to claim 1, characterized in that the electrodes (6) of the arc furnace can be adjusted in height independently of each other, and the positioning (pa, pb, pc) of each electrode (6) of the arc furnace depends on whether the electrode (6) is a first electrode (6a), a second electrode (6b), or a third electrode (6c).

8. The operating method according to claim 1, characterized in that the arc furnace is operated first in the melting stage and then in the flat bath stage between the charging of metal (2) into the furnace vessel (1) and the removal of molten metal (13) from the furnace vessel (1), the metal (2) is melted in the melting stage to form molten metal (13), the molten metal (13) is further heated in the flat bath stage, and the operating frequency (fa) of the first electrode (6a) is determined in the melting stage depending on the dimensions (G) of the metal (2) fragments to be melted using the first electrode (6a).

9. The operating method according to claim 8, characterized in that the operating frequency (fa) of the first electrode (6a) is determined such that, in the melting stage, the operating frequency decreases as the size of the metal (2) fragment to be melted using the first electrode (6a) increases.

10. The operating method according to claim 8 or 9, characterized in that the supply network (4) operates at the power supply frequency (f0), and the operating frequency (fa) of the first electrode (6a) during the melting stage or the final stage of the melting stage is greater than the power supply frequency (f0).

11. The operating method according to claim 1, characterized in that the electrical energy supplied to the electrode (6) is determined such that the electrode (6) introduces the same amount of energy into the metal (2) or molten metal (13) on a time average.

12. A control program for an arc furnace control device (9), wherein the control program includes machine code (11) that can be processed by the control device (9), and the control device (9) operates the arc furnace in accordance with the operating method described in claim 1 by processing the machine code (11) by the control device (9).

13. A control device for an arc furnace, wherein the control device is programmed with the control program (10) described in claim 12, and the control device (9) processes the machine code (11), causing the control device (9) to operate the arc furnace in accordance with the operating method described in claim 1.

14. It is an arc furnace, - The arc furnace has a furnace vessel (1) that can be charged with metal (2) and from which molten metal (13) can be removed. - The arc furnace has an energy supply device (3), electrodes (6), and a furnace transformer (5), - The energy supply device (3) is connected to the supply network (4) on the input side and to the electrode (6) via the furnace transformer (5) on the output side. - The arc furnace has a control device (9), and the control device is capable of operating at least the energy supply device (3), - An arc furnace wherein the control device (9) is configured according to claim 13.

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