METHOD OF OPERATION OF AN ELECTRIC ARC FURNACE
Patent Information
- Authority / Receiving Office
- MX · MX
- Patent Type
- Patents
- Current Assignee / Owner
- PRIMETALS TECH GERMANY GMBH
- Filing Date
- 2023-12-11
- Publication Date
- 2026-06-12
AI Technical Summary
Existing arc furnace operations face challenges with electrode current fluctuations, leading to mechanical stress and reduced energy efficiency due to the limitations of voltage step control and low dynamic positioning, especially in the flat bath phase where arcs are not fully enveloped by foamy slag, resulting in suboptimal energy input into molten steel.
An operating method where the control device independently determines positioning control values during the flat bath phase, regardless of electrical parameters, to manage electrode voltages and currents, allowing for flexible frequency adjustment and maintaining a minimum arc length to prevent short circuits, thereby optimizing arc control and reducing mechanical load.
This approach enables quick and high-quality arc control, reducing mechanical stress on components and improving energy efficiency by maintaining optimal arc length and energy input into molten steel, while minimizing the risk of short circuits and electrode wear.
Smart Images
Figure MX435189B0
Abstract
Description
[0001] Description
[0002] Title of the invention
[0003] Operating procedure for an arc furnace
[0004] field of technology
[0005] The present invention is based on an operating method for an arc furnace,
[0006] - wherein a control device of the arc furnace initially controls a power supply device of the arc furnace with first control values in a melting phase and then in a flat bath phase following the melting phase, so that the power supply device draws electrical energy from a supply network and supplies it to electrodes of the arc furnace via a furnace transformer, and further controls a positioning device of the arc furnace with second control values, so that the positioning device positions the electrodes in the melting phase relative to steel-containing material in a furnace vessel of the arc furnace in a solid aggregate state, so that arcs form between the electrodes and the steel-containing material in the melting phase, by means of which arcs the steel-containing material is melted into a steel melt, and in the flat bath phase positions the electrodes relative to the steel melt,so that in the shallow bath phase, arcs form between the electrodes and the molten steel, through which the molten steel is further heated,
[0007] - wherein the control device determines both the first control values and the second control values during the melting phase in such a way that electrical parameters are approximated as closely as possible to the desired values corresponding to the electrical energy supplied to the electrodes,
[0008] - wherein the control device determines the first control values during the flat bath phase in such a way that the electrical parameters are brought as close as possible to the corresponding target values.
[0009] The present invention further relates to a control program for a control device of an arc furnace, wherein the control program comprises machine code that can be processed by the control device, wherein the processing of the machine code by the control device causes the control device to operate an arc furnace according to such an operating method.
[0010] The present invention further relates to a control device of an arc furnace, wherein the control device is programmed with such a control program, so that the control device operates the arc furnace according to such an operating method.
[0011] The present invention further relates to an arc furnace,
[0012] - the arc furnace having a furnace vessel to which steel-containing material in solid aggregate state can be fed,
[0013] - wherein the arc furnace comprises a power supply device and electrodes as well as a furnace transformer,
[0014] - the energy supply device is connected on the input side to a supply network and on the output side to the electrodes via the furnace transformer,
[0015] - wherein the arc furnace has a positioning device by means of which the electrodes can be positioned in a melting phase relative to the steel-containing material and in a flat bath phase following the melting phase relative to a steel melt produced by melting the steel-containing material,
[0016] - wherein the arc furnace has a control device by which the energy supply device can be controlled with first control values and the positioning device can be controlled with second control values both in the melting phase and in the shallow bath phase, - wherein the control device is designed as explained above.
[0017] State of the art
[0018] The aforementioned subject matters are generally known. For example, reference can be made to WO 2015 / 176899 A1. EP 1026921 A1 and EP 3124903 A1 can also be mentioned in this context.
[0019] An operating method for an arc furnace is also known from WO 2019 / 207 611 A1. In this operating method, the power supply device for the arc furnace electrodes is designed as an intermediate circuit converter. The intermediate circuit converter appears to be arranged downstream of the furnace transformer. WO 2019 / 207 611 A1 does not elaborate on the position control of the electrodes.
[0020] EP 3124 903 A1 discloses an operating method for an arc furnace in which a power supply device for the electrodes and a positioning device for the electrodes are jointly controlled as a function of electrical operating variables of the arc furnace.
[0021] US 5115 447 A discloses an operating method for an arc furnace during the so-called drilling phase, in which the electrodes are individually checked for short circuits and arc interruption and, if such a condition occurs, the electrode position is adjusted.
[0022] Summary of the invention
[0023] When melting steel in an arc furnace, the electrical energy is supplied to the arc furnace electrodes via a furnace transformer. The furnace transformer is often connected to the power grid via a medium-voltage transformer. The furnace transformer provides several voltage levels. For constant power and other high-current applications, the respective voltage level can be selected on the furnace transformer. Fine control within a specific voltage level can be achieved, for example, using impedance control.
[0024] With this approach, only a few voltage levels are possible, and the electrode currents are subject to strong fluctuations. To reduce these fluctuations, the electrode positions are mechanically controlled, usually via hydraulic adjustment devices. The mechanical adjustment of the electrodes exhibits significantly less dynamic response than the actual behavior of the arcs. The fluctuations can therefore only be adequately compensated for. Furthermore, the fluctuations lead to considerable stress on the components, for example, the high-current cables, the current-carrying support arms, the hydraulic cylinders, etc. The fluctuations occur both in the melting phase and in the flat bath phase.
[0025] During the shallow bath phase, relatively low voltages are generally applied to the electrodes, and the electrodes are positioned relatively close to the surface of the molten steel. This results in high currents. At the same time, heat losses are reliably shielded by the foamed slag. However, depending on the arc furnace's power level or in the production of certain steels (particularly stainless and high-grade steels), the arcs are only partially or not at all enveloped by the foamed slag. This reduces the arc furnace's energy efficiency.
[0026] When adjusting the electrode voltage via the voltage levels of the furnace transformer, the positioning of the electrodes must be continuously adjusted. Adjustment can be achieved, for example, by controlling for a specific impedance or power. However, since the dynamics of the positioning device are relatively low compared to the changes in the electrical system of the arc, certain fluctuations remain that cannot be compensated for. These fluctuations are further magnified by wave movements and currents in the molten steel. As a result, the energy input into the molten steel is not optimal.
[0027] Prior art documents, in particular WO 2015 / 176899 A1 and EP 3124 903 A1, and to a limited extent also EP 1026 921 A1, disclose procedures in which the electrode voltages can be continuously adjusted. These embodiments offer significant advantages over adjusting the electrode voltage via voltage steps of the furnace transformer. Firstly, the electrode voltages can be varied continuously, rather than just in steps. Secondly, the furnace transformer can be designed more simply because it does not have to provide multiple voltage steps. Furthermore, these embodiments enable additional types of control.
[0028] The object of the present invention is to create possibilities by means of which a fast and high-quality control of the arcs is possible in a simple and reliable manner during the flat bath phase.
[0029] The problem is solved by an operating method having the features of claim 1. Advantageous embodiments of the operating method are the subject of dependent claims 2 to 8.
[0030] According to the invention, an operating method of the type mentioned at the outset is designed in that the control device determines the second control values during the shallow bath phase either completely independently of the electrical parameters or only as a function of the electrical parameters when the control device detects the risk of an arc break and / or a short circuit based on the electrical parameters. The first control values are therefore determined by the control device during the shallow bath phase - as in the prior art - in such a way that the electrical parameters are brought as close as possible to the corresponding target values. The second control values, on the other hand, are determined independently of the electrical parameters - except in the case of a risk of special operating conditions that must be avoided at all costs.As a result, the electrode voltages and electrode currents are adjusted exclusively by adjusting the control of the energy supply device.
[0031] The electrical parameters of the electrical energy supplied to the electrodes can be determined as required. For example, the electrical parameters can be the electrode currents. Active currents are particularly suitable as electrode currents. In individual cases, however, the electrical parameters can also be the reactive currents and / or the apparent currents. Alternatively, the electrical parameters can be the electrical power. Active power is particularly suitable as power. In individual cases, however, the electrical parameters can also be the reactive powers and / or the apparent powers.
[0032] The voltages applied to the electrodes, and thus also the currents supplied to the electrodes, are generally alternating quantities, i.e., alternating voltages and alternating currents. Alternating quantities can be characterized by their amplitude, frequency, and their waveform during a period (e.g., sinusoidal, triangular, sawtooth, rectangular, etc.). The temporal waveform is preferably sinusoidal.
[0033] The amplitude must always be adjusted appropriately. The frequency can be kept constant in some cases. In other cases, however, it is preferable for the control system to determine the initial control values during the flat bath phase in such a way that, in order to approximate the electrical parameters to the corresponding target values, the frequency of the electrode currents supplied to the electrodes and / or the electrode voltages applied to the electrodes is also varied. This approach offers greater flexibility in optimizing arc furnace operation.
[0034] Preferably, the frequency of the electrode currents supplied to the electrodes and / or the electrode voltages applied to the electrodes during the shallow bath phase is lower than a base frequency of the supply network. This approach has proven particularly advantageous in experiments.
[0035] At the beginning of the shallow bath phase, the electrodes are spaced from the surface of the molten steel. Consequently, the arcs have a base length at the beginning of the shallow bath phase.
[0036] In some situations, it is advantageous for the control system to move the electrodes toward the molten steel during the shallow bath phase, so that after moving toward the molten steel, the arcs only have a residual length that is less than the base length. To avoid the risk of a short circuit, however, a certain minimum length should not be exceeded. For this reason, the residual length is preferably at least 20% of the base length.
[0037] The base length can be determined or at least estimated based on the electrical parameters present at the beginning of the shallow bath phase. This determination / estimation can be performed intellectually by a person, but it is preferably performed by the control device.
[0038] The object is further achieved by a control program having the features of claim 9. According to the invention, the processing of the machine code by the control device causes the control device to operate an arc furnace according to an operating method according to the invention. The object is further achieved by a control device having the features of claim 10. According to the invention, the control device is programmed with a control program according to the invention, so that the control device operates the arc furnace according to an operating method according to the invention.
[0039] The object is further achieved by an arc furnace having the features of claim 11. According to the invention, the control device is designed as a control device according to the invention.
[0040] Short description of the drawings
[0041] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of the embodiments, which are explained in more detail in conjunction with the drawings. In this case, a schematic representation shows:
[0042] FIG 1 is a block diagram of an arc furnace,
[0043] FIG 2 a furnace vessel during a melting phase,
[0044] FIG 3 a flow chart,
[0045] FIG 4 shows the operation of a control device in the
[0046] melting phase,
[0047] FIG 5 the furnace vessel during a flat bath phase,
[0048] FIG 6 the operation of the control device in the
[0049] shallow bath phase,
[0050] FIG 7 a modification of FIG 6,
[0051] FIG 8 a flow chart,
[0052] FIG 9 an investigation block,
[0053] FIG 10 an investigation block and a supplementary block,
[0054] FIG 11 a timing diagram,
[0055] FIG 12 a modification of FIG 5,
[0056] FIG 13 a timing diagram and
[0057] FIG 14 shows a flowchart. Description of the embodiments
[0058] According to FIG. 1, an arc furnace has a furnace vessel 1. Steel-containing material 2 can be fed into the furnace vessel 1 (see FIG. 2). The steel-containing material 2 is fed into the furnace vessel 1 in a solid state. The steel-containing material 2 can be scrap, for example.
[0059] The arc furnace further comprises a power supply unit 3. The power supply unit 3 is connected on the input side to a supply network 4. The supply network 4 is generally a medium-voltage network with a nominal voltage in the two-digit kV range and operates at a base frequency fO (see FIG. 11). The base frequency fO is generally 50 Hz or 60 Hz. The supply network 4 is generally a three-phase network, as shown in FIG. 1.
[0060] The arc furnace further comprises a furnace transformer 5 and electrodes 6. The power supply device 3 is connected on the output side to the electrodes 6 via the furnace transformer 5. As a rule, as shown in FIG. 1, several electrodes 6 are present, and the furnace transformer 5 is designed as a three-phase transformer. However, other designs are also possible, in particular a single-phase design. Regardless of the specific design, the electrode voltages U applied to the electrodes 6 are significantly below the nominal voltage of the supply network 4. The electrode voltage U is shown in FIG. 1 for only one of the electrodes 6. The electrode voltages U are usually in the range of several hundred V. In individual cases, voltages above 1 kV are also possible. However, 2 kV is generally not exceeded.
[0061] As a rule, switching devices are also provided by means of which the power supply device 3 can be separated from the supply network 4. Furthermore, switching devices can be provided by means of which the power supply device 3 can be separated from the furnace transformer 5 and / or the furnace transformer 5 can be separated from the electrodes 6.
[0062] The switching devices perform purely binary switching operations, but do not adjust voltages or currents. Furthermore, active or passive filter devices can be arranged on the primary or secondary side of the furnace transformer 5. The switching devices and the filter devices are of secondary importance for the inventive operation and are therefore not shown in FIG. 1 (or the other FIGS) for the sake of clarity.
[0063] The energy supply device 3 can draw electrical energy from the supply network 4 and supply the drawn electrical energy to the electrodes 6 via the furnace transformer 5. For this purpose, the energy supply device 3 typically has many semiconductor switches. Possible embodiments of the energy supply device 3 are described in WO 2015 / 176899 A1 ("gold standard"). Alternatively, the embodiments according to EP 3124 903 A1 or EP 1026 921 A1 can also be used. Regardless of the specific embodiment of the energy supply device 3, however, the energy supply device 3 is capable of performing a quasi-continuous gradation of the electrode voltages U applied to the electrodes 6 and / or the electrode currents I supplied to the electrodes 6 on the output side—that is, toward the furnace transformer 5.Analogous to the representation for the electrode voltages U, the electrode current I in FIG 1 is also shown only for one of the electrodes 6.
[0064] Furthermore, the arc furnace has a positioning device 7. By means of the positioning device 7, the electrodes 6 can be positioned, as indicated in FIG. 1 by a double arrow 8 next to one of the electrodes 6.
[0065] In the simplest case, the electrodes 6 are positioned together. However, they can also be positioned individually. The direction of movement in which the electrodes 6 are positioned can be vertical. Alternatively, the direction of movement can also be slightly inclined relative to the vertical. In this case, too, the vertical component is the dominant component of the movement. The positioning device 7 can, for example, comprise one or more hydraulic cylinder units.
[0066] Finally, the arc furnace has a control device 9. The control device 9 controls (at least) the energy supply device 3 and the positioning device 7. The control device 9 thus generates first control values A1, with which it controls the energy supply device 3, and second control values A2, with which it controls the positioning device 7. The energy supply device 3 and the positioning device 7 are operated according to the respective control values A1, A2.
[0067] The control device 9 is designed as a software-programmable control device. This is indicated in FIG. 1 by the designation "mR" (for microprocessor-controlled). The effect and mode of operation of the control device 9 is thus determined by a control program 10 with which the control device 9 is programmed. The control program 10 includes machine code 11 that can be processed by the control device 9. The processing of the machine code 11 by the control device 9 causes the control device 9 to operate the arc furnace according to an operating method, as explained in more detail below in conjunction with the other FIGS.
[0068] First, the furnace vessel 1 is charged with the steel-containing material 2 in a step S1 according to FIG. 3. This process can, but does not have to, be controlled by the control device 9. Step S1 is therefore only shown in dashed lines in FIG. 3. Charging with the steel-containing material 2 is followed by a melting phase of the arc furnace. The melting phase comprises steps S2 to S4. The melting phase is followed by a shallow bath phase. The shallow bath phase comprises steps S5 to S7.
[0069] In the melting phase, the control device 9 determines in step S2 the first control values A1 for the energy supply device 3 and the second control values A2 for the positioning device 7. The determination takes place according to FIG 4 in corresponding determination blocks 12 and 13. In step S3, the control device 9 controls the energy supply device 3 and the positioning device 7 according to the determined control values A1, A2.
[0070] The first control values A1 are determined in such a way that the energy supply device 3 draws electrical energy from the supply network 4 based on the corresponding control and supplies it to the electrodes 6 via the furnace transformer 5. The second control values A2 are determined in such a way that the positioning device 7 positions the electrodes 6 relative to the steel-containing material 2. The determination of the first control values A1 and the second control values A2 by the control device 9 is coordinated with one another in such a way that arcs 14 (see FIG. 2) form between the electrodes 6 and the steel-containing material 2. The arcs 14 melt the steel-containing material 2, thus gradually generating a steel melt 15 (FIG. 5).
[0071] To determine the first control values A1 and the second control values A2, characteristic variables U, I, P of the electrical energy supplied to the electrodes 6 are supplied to the control device 9 according to FIG 4. The characteristic variables U, I, P can be, for example, the electrode voltages U and / or the electrode currents I and / or values derived therefrom. A derived value is, for example, the instantaneous power P (= the product of electrode voltage U and electrode current I). Another derived value can result from the temporal progression of electrode voltages U and electrode currents I. Such values are, for example, the active current, the active power, the apparent power, reactive current and the reactive power. The characteristic variables can alternatively be given or derived for all of the electrodes 6 or individually for the respective electrode 6.To determine the first control values A1 and the second control values A2, the control device 9 is further supplied with setpoint values U*, I*, P* for the characteristic variables U, I, P, for example, setpoint values U*, I* for the electrode voltages U and / or the electrode currents I or other suitable setpoint values (for example, a setpoint value P* for the power P). Both the characteristic variables U, I, P and the setpoint values U*, I*, P* are supplied to both determination blocks 12, 13 during the melting phase.
[0072] Based on the characteristic variables U, I, P and the associated target variables U*, I*, P*, the control device 9 determines the first control values A1 and the second control values A2. The determination is performed in both determination blocks 12, 13 such that the electrical characteristic variables U, I, P are as close as possible to the corresponding target variables U*, I*, P*. This procedure, and thus the implementation of step S2, is generally known to those skilled in the art. It therefore requires no further explanation.
[0073] In step S4, the control device 9 checks whether the melting phase is complete. The melting phase is complete when the molten steel 15 has completely or at least essentially formed a continuous horizontal surface, as shown in FIG. 5. Thus, either the steel-containing material 2 has completely melted, or the not-yet-melted elements of the steel-containing material 2 are located completely below the surface of the molten steel 15, or the not-yet-melted elements of the steel-containing material 2 only protrude insignificantly above the surface of the molten steel 15. Furthermore, a slag layer 16 may have formed on the surface of the molten steel 15.
[0074] It is possible for the control device 9 to evaluate actual measured variables of the arc furnace as part of the check to determine whether the melting phase has ended. For example, it is possible for the control device 9 to evaluate the electrode currents I and / or the electrode voltages U, in particular their fluctuations. The control device 9 can also evaluate acoustic variables of the arc furnace, for example the noise level or the acoustic spectrum of the generated noise. Alternatively, it is possible for an operator (not shown) to indicate to the control device 9 that the melting phase has ended.
[0075] If the melting phase is not yet complete, the control device 9 returns to step S2. However, if the melting phase is complete, the control device 9 proceeds to the shallow bath phase and thus to step S5.
[0076] In the flat bath phase, the control device 9 determines in step S5 the first control values A1 for the energy supply device 3 and the second control values A2 for the positioning device 7. In step S6, the control device 9 controls the energy supply device 3 and the positioning device 7 according to the determined control values A1, A2.
[0077] The first control values A1 are determined in such a way that the energy supply device 3 draws electrical energy from the supply network 4 due to the corresponding control and supplies it to the electrodes 6 via the furnace transformer 5. The second control values A2 are determined in such a way that the positioning device 7 positions the electrodes 6 relative to the molten steel 15. In this respect, the procedure in steps S5 and S6 corresponds to the procedure in steps S2 and S3. The procedure in steps S5 and S6 also corresponds to the procedure in steps S2 and S3 in that the first control values A1 and the second control values A2 are coordinated with one another in such a way that arcs 14 form. However, the arcs 14 form in the shallow bath phase between the electrodes 6 and the molten steel 15 as shown in FIG. 5.The steel melt 15 is further heated by the arcs 14.
[0078] According to FIG. 6, the control device 6 continues to receive the characteristic variables U, I, P of the electrical energy supplied to the electrodes 6 and the associated target variables U*, I*, P*. However, the characteristic variables U, I, P and the associated target variables U*, I*, P* are only supplied to the determination block 12 within the control device 9. Thus, the control device 9 continues to determine the first control values A1 such that the electrical characteristic variables U, I, P are brought as close as possible to the corresponding target variables U*, I*, P*.
[0079] The determination block 13, however, is deactivated in the shallow bath phase. Instead, a determination block 17 is activated as shown in FIG. 6. Using the determination block 17, the control device 9 determines the second control values A2 in the shallow bath phase. In particular, it is possible for the control device 9 to determine the second control values A2 as shown in FIG. 3 completely independently of the electrical parameters U, I, P. In this case, it is possible for the electrical parameters U, I, P not to be fed to the determination block 17 at all, as shown in FIG. 6. Instead, the control device 9 can determine the second control values A2 based on another internal determination or based on external specifications V (for example, specifications originating from an operator). In step S7, the control device 9 checks whether the shallow bath phase has ended.It is possible for the control device 9 to evaluate actual measured values of the arc furnace as part of the check to determine whether the flat bath phase has ended. Alternatively, it is possible for the operator to indicate to the control device 9 that the flat bath phase has ended.
[0080] If the shallow bath phase is not yet complete, the control device 9 returns to step S5. If, however, the shallow bath phase is complete, the control device 9 proceeds to step S8. In step S8, the produced steel melt 15 is removed from the furnace vessel 1, for example, poured into a ladle (not shown). This process can, but does not have to, be controlled by the control device 9. Therefore, step S8 is only shown in dashed lines in FIG. 3—analogous to step S1.
[0081] With the execution of step S8, a complete cycle in the operation of the arc furnace is completed. A new cycle can therefore be started, beginning with step S1.
[0082] In the simplest embodiment, the determination of the second control values, as already mentioned, is carried out independently of the electrical parameters U, I, P. Alternatively, it is possible for the second control values A2 to be determined by the determination block 17, although generally independent of the electrical parameters U, I, P, under special circumstances they may still be taken into account. In this case, the corresponding electrical parameters U, I, P are fed to the determination block 17 as shown in FIG. 7. The corresponding setpoint values U*, I*,
[0083] P*, however, is not required.
[0084] In this case, the determination block 17 (and, because the determination block 17 is a component of the control device 9, thus the control device 9) checks whether the electrical parameters U, I, P satisfy predetermined conditions or not. In particular, the determination block 17 checks in this case whether, based on the electrical parameters U,
[0085] I, P detects the risk of an arc interruption and / or a short circuit. Only then does the determination block 17 take the electrical parameters U, I, P into account when determining the second control values A2. However, even in this case, these are only taken into account as long as the risk of an arc interruption and / or a short circuit exists. If the risk no longer exists, the second control values A2 are again determined independently of the electrical parameters U, I, P. This is explained in more detail below in conjunction with FIG. 8.
[0086] FIG 8 shows the procedure in the shallow bath phase. The procedure in the melt phase can remain unchanged.
[0087] According to FIG 8, the control device 9 initially proceeds from step S4 to a step S11. In step S11, the control device 9 checks whether it detects the risk of an arc breaking off. As part of the check in step S11, the control device 9 evaluates the electrical parameters U, I, P. If the control device 9 detects the risk of an arc breaking off, it proceeds to a step S12. In step S12, the control device 9 determines the first control values A1 and the second control values A2 such that the risk of an arc breaking off is counteracted. For example, the control device 9 can vary the first control values A1 such that the electrode voltages U are increased and the second control values A2 such that the electrodes 6 are lowered towards the molten steel 15.
[0088] If the control device 9 does not detect the risk of an arc breaking off in step S11, the control device 9 proceeds to step S13. In step S13, the control device 9 checks whether it detects the risk of a short circuit. As part of the check in step S13, the control device 9 also evaluates the electrical parameters U, I, P. If the control device 9 detects the risk of a short circuit, it proceeds to step S14. In step S14, the control device 9 determines the first control values A1 and the second control values A2 such that the risk of a short circuit is counteracted. For example, the control device 9 can vary the first control values A1 such that the electrode voltages U are reduced, and in particular vary the second control values A2 such that the electrodes 6 are raised in the direction away from the molten steel 15.
[0089] If the control device 9 does not detect the risk of a short circuit in step S13, the control device 9 proceeds to step S5. In step S5, the first control values A1 and the second control values A2 are determined as already explained in connection with FIG. 6.
[0090] Regardless of whether the control device 9 has executed step S12, step S14, or step S5, the control device 9 next proceeds to step S6, in which it controls the energy supply device 3 and the positioning device 4 according to the determined first and second control values A1, A2. The control device then proceeds to step S7. From there, it either proceeds to step S8 or the control device 9 returns to step S11.
[0091] The parameters U, I, P can be selected in various ways. For example, according to the illustration in FIG 9, it is possible that - at least during the shallow bath phase - the electrical parameters U, I, P are the electrode currents I. Alternatively, according to the illustration in FIG 10, it is possible that - at least during the shallow bath phase - the electrical parameters U, I, P are the electrical powers P. In this case, for example, a supplementary block 18 can be arranged upstream of the determination block 12. In this case, for example, the electrode voltages U and the electrode currents I can be supplied to the supplementary block 18. In this case, the supplementary block 18 determines, for example, the instantaneous power instantly or the average electrical power over a period of the electrode voltages U and outputs the determined value as the electrical parameter P to the determination block 12.
[0092] It is possible for the control device 9 to determine the first control values Al during the shallow bath phase in such a way that a frequency f of the electrode voltages U (or, correspondingly, a frequency f of the electrode currents I) is varied. This is indicated in FIG. 11 by varying a corresponding period T. The variation of the period T and, correspondingly, the frequency f is indicated in FIG. 11 by a double arrow 19. It is done for the purpose of approximating the electrical parameters U, I, P to the corresponding target values U*, I*, P*.
[0093] The variation of the frequency f preferably takes place in a range lying between 70% and 90% of the base frequency fO, in particular between 75% and 85% of the base frequency fO.
[0094] At the beginning of the shallow bath phase, i.e. when the control device 9 moves from step S4 to step S5 (or in the case of the embodiment according to FIG 8 moves to step S11), the arcs 14 have a base length L0 as shown in FIG 5. In some cases it is advantageous if the control device 9 moves the electrodes 6 towards the molten steel 15 during the shallow bath phase. After moving towards the molten steel 15, the arcs 14 only have a residual length LR as shown in FIG 12. The residual length LR is shorter than the base length L0. However, as shown in FIG 13, it should be at least 20% of the base length L0.
[0095] The base length L0 can be made known to the control device 9 in various ways. For example, the base length L0 can be specified to the control device 9 by the operator. Alternatively, it is possible for the control device 9 to first execute a step S21 immediately after step S4, as shown in FIG 14. In this case, the control device 9 determines the base length L0 in step S21 based on the electrical parameters U, I, P, as they are present at the beginning of the shallow bath phase. Corresponding procedures are known to those skilled in the art. Step S21, if present, is only executed once. It is therefore not included in the loop of steps S5 to S7. This also applies analogously if steps S11 to S14 are present.
[0096] It is possible for the control device 9 to determine the remaining length LR based on the base length L0. Alternatively, it is possible for the control device 9 to determine only a minimum permissible value for the remaining length LR, or for a corresponding minimum permissible value for the remaining length LR to be specified for the control device 9. In this case, it is possible for the control device 9 to continue moving the electrodes 6 until the control device 9, based on an evaluation of the parameters U, I, P, detects optimized operation of the arc furnace or the remaining length RL reaches the minimum permissible value. Regardless of the specific procedure adopted, step S5 in this case is implemented such that the first control values A1 are determined as already explained, but the second control values A2 are determined such that the length of the arcs 14 is reduced, starting from the base length L0.
[0097] By reducing the length of the arcs 14 to the residual length LR, the energy efficiency of the arc furnace can be improved in some operating states of the arc furnace.
[0098] The present invention has many advantages. In particular, the mechanical load on the positioning device 7 can be reduced, and energy efficiency during operation of the arc furnace can be improved. Although the invention has been illustrated and described in detail using the preferred embodiment, the invention is not limited to the disclosed examples, and other variants can be derived therefrom by those skilled in the art without departing from the scope of the invention.
[0099] List of reference symbols
[0100] 1 oven vessel
[0101] 2 steel-containing material
[0102] 3 Energy supply facility
[0103] 4 Supply network
[0104] 5 Furnace transformer
[0105] 6 Electrodes 7 Positioning device
[0106] 8, 19 double arrows
[0107] 9 Control device
[0108] 10 Control program 11 Machine code
[0109] 12, 13, 17 investigation blocks
[0110] 14 arcs
[0111] 15 steel melt
[0112] 16 Slag layer 18 Supplementary block
[0113] Al, A2 Control values f Frequency fO Base frequency
[0114] I Electrode currents
[0115] L0 base length
[0116] LR remaining length
[0117] P electrical power
[0118] S1 to S21 steps
[0119] T period duration
[0120] U Electrode voltages
[0121] U, I, P Parameters U*, I*, P* Target values V Specifications
Claims
Claims 1. Operating procedure for an electric arc furnace, - wherein a control device (9) of the electric arc furnace first controls an energy supply device (3) of the electric arc furnace with first control values (Al) in a melting phase and then in a flat bath phase following the melting phase, so that the energy supply device (3) draws electrical energy from a supply network (4) and supplies electrodes (6) of the electric arc furnace via a furnace transformer (5), and furthermore controls a positioning device (7) of the electric arc furnace with second control values (A2), so that the positioning device (7) positions the electrodes (6) in the melting phase relative to steel-containing material (2) in a solid state in a furnace vessel (1) of the electric arc furnace, so that electric arcs (14) form in the melting phase between the electrodes (6) and the steel-containing material (2), by means of which the steel-containing material (2) becomes a steel molten (15) is melted,and positioned in the flat bath phase relative to the molten steel (15), so that arcs (14) form in the flat bath phase between the electrodes (6) and the molten steel (15), through which the molten steel (15) is further heated, - wherein the control device (9) determines both the first control values (Al) and the second control values (A2) during the melting phase such that electrical parameters (U, I, P) corresponding to the setpoint values (U*, I*, P*) should be approximated as closely as possible, - wherein the control device (9) continues to determine the first control values (Al) during the flat bath phase in such a way that the electrical parameters (U, I, P) are approximated to the corresponding setpoint values (U*, I*, P*) as closely as possible, but the second control values (A2) are either completely independent of the electrical parameters (U, I, P) determined or only then depending on the electrical parameters (U, I, P) are determined when the control device (9) is based on the electrical parameters (U, I, P) recognizes the danger of arc interruption and / or a short circuit.
2. Operating method according to claim 1, characterized in that at least during the flat bath phase the electrical parameters (U, I, P) are the electrode currents (I).
3. Operating method according to claim 1, characterized in that, at least during the flat bath phase, the electrical parameters (U, I, P) are the electrical powers (P).
4. Operating method according to claim 1, 2 or 3, characterized in that the control device (9) determines the first control values (Al) during the flat bath phase such that a frequency (f) of the electrode currents (I) supplied to the electrodes (6) and / or of the electrode voltages (U) applied to the electrodes (6) is varied to approximate the electrical parameters (U, I, P) to the corresponding setpoints (U*, I*, P*).
5. Operating method according to claim 4, characterized in that the frequency (f) of the signal supplied to the electrodes (6) Electrode currents (I) and / or the electrode voltages (6) applied to the electrodes (6) during the flat bath phase are smaller than a basic frequency (fO) of the supply network (4).
6. Operating method according to one of the above claims, characterized in that the arcs (14) have a base length (L0) at the beginning of the flat bath phase and that the control device (9) moves the electrodes (6) towards the molten steel (15) during the flat bath phase, so that the arcs (14) after the process on the molten steel (15) to have only a residual length (LR) which is smaller than the base length (L0).
7. Operating method according to claim 6, characterized in that the residual length (LR) is at least 20% of the base length (L0).
8. Operating method according to claim 6 or 7, characterized in that the control device (9) determines the base length (L0) based on the electrical parameters (U, I, P) as they are present at the beginning of the flat bath phase.
9. Control program for a control device (9) of an electric arc furnace, wherein the control program comprises machine code (11) that can be executed by the control device (9), wherein the execution of the machine code (11) by the control device (9) causes the control device (9) to operate an electric arc furnace according to an operating method according to one of the above claims.
10. Control device of an electric arc furnace, wherein the control device is programmed with a control program (10) according to claim 9, such that the control device operates the electric arc furnace according to an operating method according to one of claims 1 to 8.
11. Electric arc furnace, - wherein the electric arc furnace has a furnace vessel (1) to which steel-containing material (2) can be supplied in a solid state, - wherein the electric arc furnace comprises a power supply unit (3) and electrodes (6) as well as a furnace transformer (5), - wherein the energy supply device (3) is connected on the input side to a supply network (4) and on the output- is connected to the electrodes (6) via the furnace transformer (5) on one side, - wherein the electric arc furnace has a positioning device (7) by means of which the electrodes (6) can be positioned in a melt phase relative to the steel-containing material (2) and in a flat bath phase following the melt phase relative to a steel melt (15) produced by melting the steel-containing material (2), - wherein the electric arc furnace has a control device (9) which is active both during the melting phase and in the The flat bath phase can be controlled by the energy supply device (3) with first control values (Al) and the positioning device (7) can be controlled with second control values (A2), - wherein the control device (9) is designed according to claim 10.