EP4110015A1 - Operating method for a an arc furnace - Google Patents

Abstract

A control device (9) of an arc furnace controls an energy supply device (3) with first control values (A1) in a melting phase and then in a flat bath phase, so that this electrical energy is supplied to electrodes (6) of the arc furnace via a furnace transformer (5). In both phases, it also controls a positioning device (7) with second control values (A2), so that it positions the electrodes (6) in the melting phase relative to as yet unmelted steel-containing material (2) and in the flat bath phase relative to the molten steel (15). positioned. As a result, arcs (14) form in both phases, through which the steel-containing material (2) is melted or the molten steel (15) is further heated. During the melting phase, both the first control values (A1) and the second control values (A2) are determined in such a way that electrical parameters (U, I, P) of the electrical energy supplied to the electrodes (6) correspond to setpoint values (U*, I*, P*) should be approximated as closely as possible. In the flat bath phase, this only applies to the first control values (A1). The second control values (A2), on the other hand, are either determined completely independently of the electrical parameters (U, I, P) or are only determined as a function of the electrical parameters (U, I, P) if, based on the electrical parameters (U, I , P) the risk of arcing and/or a short circuit being detected.

Description

field of technology

• wobei eine Steuereinrichtung des Lichtbogenofens zunächst in einer Schmelzphase und sodann in einer sich an die Schmelzphase anschließenden Flachbadphase eine Energieversorgungseinrichtung des Lichtbogenofens mit ersten Ansteuerwerten ansteuert, so dass die Energieversorgungseinrichtung elektrische Energie aus einem Versorgungsnetz bezieht und über einen Ofentransformator Elektroden des Lichtbogenofens zuführt, und weiterhin eine Positioniereinrichtung des Lichtbogenofens mit zweiten Ansteuerwerten ansteuert, so dass die Positioniereinrichtung die Elektroden in der Schmelzphase relativ zu in einem Ofengefäß des Lichtbogenofens befindlichem stahlhaltigem Material in festem Aggregatszustand positioniert, so dass sich in der Schmelzphase zwischen den Elektroden und dem stahlhaltigen Material Lichtbögen ausbilden, durch welche das stahlhaltige Material zu einer Stahlschmelze geschmolzen wird, und in der Flachbadphase relativ zu der Stahlschmelze positioniert, so dass sich in der Flachbadphase zwischen den Elektroden und der Stahlschmelze Lichtbögen ausbilden, durch welche die Stahlschmelze weiter aufgeheizt wird,
• wobei die Steuereinrichtung während der Schmelzphase sowohl die ersten Ansteuerwerte als auch die zweiten Ansteuerwerte derart ermittelt, dass elektrische Kenngrößen der den Elektroden zugeführten elektrischen Energie korrespondierenden Sollgrößen so weit wie möglich angenähert werden,
• wobei die Steuereinrichtung während der Flachbadphase die ersten Ansteuerwerte derart ermittelt, dass die elektrischen Kenngrößen den korrespondierenden Sollgrößen so weit wie möglich angenähert werden.

The present invention is based on an operating method for an electric arc furnace,

• wherein a control device of the arc furnace controls an energy supply device of the arc furnace with first control values, first in a melting phase and then in a flat bath phase that follows the melting phase, so that the energy supply device obtains electrical energy from a supply network and supplies electrodes of the arc furnace via a furnace transformer, and furthermore 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-bearing material in a solid state of aggregation in a furnace vessel of the arc furnace, so that arcs are formed in the melting phase between the electrodes and the steel-bearing material, through which the steel-bearing material is melted into a molten steel, and positioned relative to the molten steel in the flat bath phase, so that in the flat bath ph arcs form between the electrodes and the molten steel, which further heat the molten steel,
• 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 of the electrical energy supplied to the electrodes are approximated as closely as possible to the corresponding target values,
• wherein the control device determines the first control values during the flat bath phase in such a way that the electrical Parameters are approximated as closely as possible to the corresponding target values.

The present invention is also based on a control program for a control device of an arc furnace, the control program comprising machine code which can be processed by the control device, the processing of the machine code by the control device causing the control device to operate an arc furnace in accordance with such an operating method.

The present invention is also based on a control device for an arc furnace, the control device being programmed with such a control program so that the control device operates the arc furnace according to such an operating method.

• wobei der Lichtbogenofen ein Ofengefäß aufweist, dem stahlhaltiges Material in festem Aggregatszustand zuführbar ist,
• wobei der Lichtbogenofen eine Energieversorgungseinrichtung und Elektroden sowie einen Ofentransformator aufweist,
• wobei die Energieversorgungseinrichtung eingangsseitig mit einem Versorgungsnetz verbunden ist und ausgangsseitig über den Ofentransformator mit den Elektroden verbunden ist,
• wobei der Lichtbogenofen eine Positioniereinrichtung aufweist, mittels derer die Elektroden in einer Schmelzphase relativ zum stahlhaltigen Material und in einer sich an die Schmelzphase anschließenden Flachbadphase relativ zu einer durch Schmelzen des stahlhaltigen Materials erzeugten Stahlschmelze positionierbar sind,
• wobei der Lichtbogenofen eine Steuereinrichtung aufweist, von der sowohl in der Schmelzphase als auch in der Flachbadphase die Energieversorgungseinrichtung mit ersten Ansteuerwerten ansteuerbar ist und die Positioniereinrichtung mit zweiten Ansteuerwerten ansteuerbar ist,
• wobei die Steuereinrichtung so wie obenstehend erläutert ausgebildet ist.

The present invention is also based on an electric arc furnace

• wherein the arc furnace has a furnace vessel to which steel-containing material can be fed in the solid state of aggregation,
• wherein the arc furnace has an energy supply device and electrodes as well as a furnace transformer,
• wherein the energy supply device is connected to a supply network on the input side and is connected to the electrodes via the furnace transformer on the output side,
• 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 that follows the melting phase relative to a molten steel produced by melting the steel-containing material,
• 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 flat bath phase,
• wherein the control device is designed as explained above.

State of the art

The items mentioned are generally known. For example, on the WO 2015/176 899 A1 to get expelled. Also the EP 1 026 921 A1 and the EP 3 124 903 A1 can be mentioned in this context.

Summary of the Invention

When melting steel in an electric arc furnace, the electrical energy is supplied to the electrodes of the electric arc furnace via a furnace transformer. The furnace transformer is often connected to the supply network via a medium-voltage transformer. The furnace transformer provides several voltage levels. For the range of constant power and other high-current ranges, the respective voltage level can be selected on the furnace transformer. Fine control within a specific voltage level can be done, for example, by means of impedance control.

With this procedure, only a few voltage levels are possible and the electrode currents are subject to strong fluctuations. To reduce the fluctuations, the positioning of the electrodes is controlled mechanically, mostly via hydraulic adjustment devices. The mechanical adjustment of the electrodes shows a significantly lower dynamic than the real behavior of the arcs. The fluctuations can therefore only be adequately compensated. Furthermore, the fluctuations lead to considerable loads 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.

In the flat bath phase, relatively low voltages are generally applied to the electrodes and continue to be applied to the electrodes 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 performance level of the electric arc furnace or when producing certain steels (especially stainless steels and high-grade steels), the arcs are only partially or not at all enveloped by the foamy slag. This reduces the energy efficiency of the arc furnace.

When setting the electrode voltage via the voltage levels of the furnace transformer, the positioning of the electrodes must be continuously readjusted. The readjustment can, for example, take place in such a way that a specific impedance or a specific power is controlled. 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 corrected. The fluctuations are increased by wave movements and currents of the molten steel. As a result, the energy input into the molten steel is not optimal.

From the documents of the prior art, in particular from WO 2015/176 899 A1 and the EP 3 124 903 A1 and to a limited extent also from the EP 1 026 921 A1 , Procedures are known in which the electrode voltages can be adjusted continuously. These configurations offer significant advantages over setting the electrode voltage via voltage steps of the furnace transformer. On the one hand, the electrode voltages can be varied not only gradually, but continuously. On the other hand, the furnace transformer can be designed more simply because it does not have to provide several voltage levels. Furthermore, further types of regulation are made possible by these configurations.

The object of the present invention is to create possibilities by means of which a quick and high-quality regulation of the arcs is possible in a simple and reliable manner in the flat bath phase.

The object is achieved by an operating method with the features of claim 1. Advantageous configurations of the operating method are the subject matter of dependent claims 2 to 8.

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 flat bath phase either completely independently of the electrical parameters or only as a function of the electrical parameters if the control device detects the risk of arcing due to the electrical parameters and/or a short circuit.

The first control values are thus determined by the control device during the flat bath phase—as in the prior art—in such a way that the electrical parameters are approximated as closely as possible to the corresponding setpoint values. The second control values, on the other hand, are determined independently of the electrical parameters, except when there is a risk of special operating states, which must be avoided at all costs. As a result, the electrode voltages and the electrode currents are tracked exclusively by adapting the activation of the energy supply device.

The electrical characteristics of the electrical energy supplied to the electrodes can be determined as required. For example, the electrical parameters can be the electrode currents. The active currents in particular come into consideration 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 be the electrical power. The active powers in particular come into consideration as powers. In individual cases, however, the electrical parameters can also be the reactive power and/or the apparent power.

The voltages applied to the electrodes and thus also the currents supplied to the electrodes are generally alternating quantities, ie alternating voltages and alternating currents. Alternating variables can be characterized by their amplitude, their frequency and their shape during a period (e.g. sinusoidal, triangular, sawtooth, rectangular, etc.). The course over time is preferably sinusoidal.

The amplitude must always be set appropriately. The frequency can be kept constant in some cases. In other cases, however, it is preferable for the control device to determine the first control values during the flat bath phase in such a way that, in order to approximate the electrical parameters to the corresponding setpoint values, a frequency of the electrode currents supplied to the electrodes and/or of the electrode voltages applied to the electrodes is also varied. This approach offers greater flexibility in optimizing the operation of the arc furnace.

The frequency of the electrode currents supplied to the electrodes and/or of the electrode voltages applied to the electrodes in the flat bath phase is preferably lower than a base frequency of the supply network. This procedure has proven to be particularly advantageous in tests.

At the beginning of the flat bath phase, the electrodes are spaced apart from the surface of the molten steel. Consequently, the arcs have a base length at the beginning of the flat bath phase. In some situations it is advantageous for the control device to move the electrodes towards the molten steel during the flat bath phase, so that the arcs only have a residual length after moving towards the molten steel have that is less than the base length. In order to avoid the risk of a short circuit, a certain minimum length should not be undershot. For this reason, the residual length is preferably at least 20% of the base length.

The base length can be determined or at least estimated using the electrical parameters as they exist at the beginning of the flat bath phase. It is possible that this determination/assessment is done intellectually by a person. However, it is preferably carried out by the control device.

The object is also achieved by a control program with 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 electric arc furnace in accordance with an operating method according to the invention.

The object is also 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 electric arc furnace according to an operating method according to the invention.

The object is also achieved by an electric 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.

Brief description of the drawings

FIG 1

ein Blockschaltbild eines Lichtbogenofens,

FIG 2

ein Ofengefäß während einer Schmelzphase,

FIG 3

ein Ablaufdiagramm,

FIG 4

die Wirkungsweise einer Steuereinrichtung in der Schmelzphase,

FIG 5

das Ofengefäß während einer Flachbadphase,

FIG 6

die Wirkungsweise der Steuereinrichtung in der Flachbadphase,

FIG 7

eine Modifikation von FIG 6,

FIG 8

ein Ablaufdiagramm,

FIG 9

einen Ermittlungsblock,

FIG 10

einen Ermittlungsblock und einen Ergänzungsblock,

FIG 11

ein Zeitdiagramm,

FIG 12

eine Modifikation von FIG 5,

FIG 13

ein Zeitdiagramm und

FIG 14

ein Ablaufdiagramm.

The characteristics, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawings. This shows in a schematic representation:

FIG 1

a block diagram of an electric arc furnace,

FIG 2

a furnace vessel during a melting phase,

3

a flowchart,

FIG 4

the mode of operation of a control device in the melting phase,

5

the furnace vessel during a flat bath phase,

6

the mode of operation of the control device in the flat bath phase,

FIG 7

a modification of 6 ,

8

a flowchart,

9

an investigation block,

10

a determination block and a supplementary block,

11

a time chart,

12

a modification of 5 ,

13

a timing chart and

14

a flowchart.

Description of the embodiments

According to FIG 1 an arc furnace has a furnace vessel 1 . The furnace vessel 1 can - see FIG 2 - Steel-containing material 2 are supplied. The steel-containing material 2 is fed to the furnace vessel 1 in a solid state. The steel-containing material 2 can be scrap, for example.

The arc furnace also has an energy supply device 3 . The energy supply device 3 is connected to a supply network 4 on the input side. The supply network 4 is usually a medium-voltage network that has a nominal voltage in the 2-digit kV range and with a base frequency f0 (see 11 ) is operated. The base frequency f0 is usually 50 Hz or 60 Hz. The supply network 4 is as shown in FIG 1 usually a three-phase network.

The arc furnace also has a furnace transformer 5 and electrodes 6 . The power supply device 3 is connected to the electrodes 6 via the furnace transformer 5 on the output side. As a rule, according to the representation in FIG 1 several electrodes 6 are present and the furnace transformer 5 is also designed as a three-phase transformer. However, other configurations are also possible, in particular a single-phase configuration. Irrespective of the specific configuration, however, 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 in FIG 1 only shown for one of the electrodes 6. The electrode voltages U are usually in the range of several 100 V. In individual cases, voltages above 1 kV are also possible. However, 2 kV are generally not exceeded.

As a rule, switching devices are also present, by means of which the energy supply device 3 can be separated from the supply network 4 . Furthermore, switching devices can be present, by means of which the energy supply device 3 can be separated from the furnace transformer 5 and/or the furnace transformer 5 from the electrodes 6. The switching devices perform purely binary switching operations, but no adjustment of voltages and 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 also the filter devices are of secondary importance for the functioning according to the invention and are therefore FIG 1 (and also the other FIGs) are not shown for the sake of clarity.

The energy supply device 3 can draw electrical energy from the supply network 4 and feed the drawn electrical energy to the electrodes 6 via the furnace transformer 5 . For this purpose, the energy supply device 3 generally has a large number of semiconductor switches. Possible Configurations of the energy supply device 3 are in WO 2015/176 899 A1 ("gold standard") described. Alternatively, for example, the configurations according to EP 3 124 903 A1 or the EP 1 026 921 A1 be used. Irrespective of the specific configuration of the energy supply device 3, however, the energy supply device 3 is able on the output side - i.e. towards the furnace transformer 5 - to carry out 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. The electrode current I in is analogous to the representation for the electrode voltages U FIG 1 also only shown for one of the electrodes 6 .

Furthermore, the arc furnace has a positioning device 7 . By means of the positioning device 7, the electrodes 6, as in FIG 1 is indicated by a double arrow 8 next to one of the electrodes 6 are positioned. In the simplest case, the electrodes 6 are positioned together. However, the electrodes 6 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 with respect to the vertical. Also in this case, however, the component in the vertical direction is the dominating component of the movement. The positioning device 7 can have, for example, one or more hydraulic cylinder units.

Finally, the arc furnace has a control device 9 . (At least) the energy supply device 3 and the positioning device 7 are controlled by the control device 9 . 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 in accordance with the respective control values A1, A2.

The control device 9 is designed as a software-programmable control device. this is in FIG 1 indicated by the specification "µP" (for microprocessor-controlled). The mode of action and 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 which 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 is explained in more detail below in connection with the other FIGS.

First, the furnace body 1 according to 3 charged with the steel-containing material 2 in a step S1. This process can, but does not have to, take place under the control of the control device 9 . Step S1 is therefore in 3 shown only as dashed lines.

The charging of the steel-containing material 2 is followed by a melting phase of the electric arc furnace. The melting phase includes steps S2 to S4. A flat bath phase follows the melting phase. The shallow bath phase includes steps S5 through S7.

In the melting phase, the control device 9 determines the first control values A1 for the energy supply device 3 and the second control values A2 for the positioning device 7 in step S2. The determination takes place according to FIG 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.

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 on the basis of the corresponding control and via the furnace transformer 5 the Electrodes 6 supplies. 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 FIG 2 ) train. The steel-containing material 2 is melted by the arcs 14 and gradually a molten steel 15 ( 5 ) generated.

To determine the first control values A1 and the second control values A2, the control device 9 according to FIG 4 Parameters U, I, P of the electrical energy supplied to the electrodes 6 are supplied. The parameters 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 time profile of electrode voltages U and electrode currents I. Such values are, for example, the active current, the active power, the apparent power, the reactive current and the reactive power. Alternatively, the parameters can be given or derived for the entirety 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 also supplied with target values U*, I*, P* for the parameters U, I, P, for example target values U*, I* for the electrode voltages U and/or the Electrode currents I or other suitable target values (for example a target value P* for the power P). Both the parameters U, I, P and the target values U*, I*, P* are supplied to both determination blocks 12, 13 in the melting phase.

The control device 9 uses the parameters U, I, P and the associated setpoint values U*, I*, P* to determine the first control values A1 and the second control values A2. The determination takes place in both determination blocks 12, 13 in such a way that the electrical parameters U, I, P are approximated as closely as possible to the corresponding setpoint values U*, I*, P*. This procedure and thus the implementation of step S2 is generally known to those skilled in the art. It therefore does not need to be explained in more detail.

In step S4, the control device 9 checks whether the melting phase has ended. The melting phase is complete when the molten steel 15, as shown in FIG 5 has completely or at least essentially formed a continuous horizontal surface. Either the steel-containing material 2 is completely melted or the elements of the steel-containing material 2 that have not yet melted are located completely under the surface of the steel melt 15 or the not yet melted elements of the steel-containing material 2 only protrude slightly above the surface of the steel melt 15 . Furthermore, a slag layer 16 may have formed on the surface of the molten steel 15 .

It is possible for the control device 9 to evaluate measured actual variables of the electric arc furnace as part of the check as to 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 parameters of the arc furnace, for example the noise level or the acoustic spectrum of the noise generated. Alternatively, it is possible for an operator (not shown) to specify to the control device 9 that the melting phase has ended.

If the melting phase has not yet ended, the control device 9 goes back to step S2. On the other hand, when the melting phase has ended, the control device 9 goes to the flat bath phase and thus to step S5.

In the flat bath phase, the control device 9 determines the first control values A1 for the energy supply device 3 and the second control values A2 for the positioning device 7 in step S5. 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 .

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 on the basis of the corresponding control and feeds 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 . To this extent, the procedure for steps S5 and S6 corresponds to the procedure for steps S2 and S3.

The procedure of steps S5 and S6 also corresponds to the procedure of steps S2 and S3 in that the first control values A1 and the second control values A2 are matched to one another in such a way that arcs 14 form. However, the arcs 14 form in the flat bath phase as shown in FIG 5 between the electrodes 6 and the molten steel 15. The molten steel 15 is further heated by the arcs 14 .

The controller 6 are according 6 the parameters U, I, P of the electrical energy supplied to the electrodes 6 and the associated setpoint variables U*, I*, P* are also supplied. However, the parameters U, I, P and the associated setpoint values U*, I*, P* are only supplied to the determination block 12 within the control device 9 . The control device 9 thus continues to determine the first control values A1 in such a way that the electrical parameters U, I, P correspond to the Target variables U*, I*, P* are approximated as closely as possible.

In contrast, the determination block 13 is deactivated in the flat bath phase. Instead, according to 6 a determination block 17 activated. The control device 9 uses the determination block 17 to determine the second control values A2 in the flat bath phase. In particular, it is possible for the control device 9 to set the second control values A2 in accordance with the representation in 3 determined completely independently of the electrical parameters U, I, P. In this case it is possible that the determination block 17 as shown in 6 the electrical parameters U, I, P are not supplied at all. Instead, the control device 9 can determine the second control values A2 on the basis of another internal determination or on the basis of external specifications V (for example specifications originating from an operator).

In step S7, the control device 9 checks whether the flat bath phase has ended. It is possible for the control device 9 to evaluate measured actual variables of the electric arc furnace as part of the check as to whether the flat bath phase has ended. Alternatively, it is possible for the operator to specify to the control device 9 that the flat bath phase has ended.

If the shallow bath phase has not yet ended, the controller 9 goes back to step S5. On the other hand, if the flat bath phase has ended, the control device 9 proceeds to a step S8. In step S8, the molten steel 15 produced is removed from the furnace body 1, for example poured into a ladle (not shown). This process can, but does not have to, take place under the control of the control device 9 . Step S8 is therefore in 3 - analogous to step S1 - shown only in dashed lines.

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.

In the simplest embodiment, the second control values are determined, as already mentioned, independently of the electrical parameters U, I, P. Alternatively, it is possible that the second control values A2 from the determination block 17 are generally independent of the electrical parameters U, I, P can be determined, but can still be taken into account under special circumstances. In this case, the determination block 17 as shown in FIG 7 the corresponding electrical parameters U, I, P are supplied. However, it is not necessary to also supply the corresponding setpoint values U*, I*, P*.

In this case, the determination block 17 (and, because the determination block 17 is part of the control device 9, therefore the control device 9 as a result) checks whether the electrical parameters U, I, P meet predetermined conditions or not. In particular, the determination block 17 checks in this case whether it recognizes the risk of an arc breaking and/or a short circuit based on the electrical parameters U, I, P. Only then does the determination block 17 take into account the electrical parameters U, I, P when determining the second control values A2. In this case, too, the consideration only takes place as long as there is a risk of arcing and/or a short circuit. If the danger no longer exists, the second control values A2 are determined again independently of the electrical parameters U, I, P. This is explained below in connection with 8 explained in more detail.

8 shows the procedure in the flat bath phase. The procedure in the melt phase can be unchanged.

According to 8 the control device 9 proceeds from step S4 to a step S11. In step S11, the control device 9 checks whether it recognizes the risk of an arc breaking. As part of the check in step S11, the control device 9 evaluates the electrical parameters U, I, P. If the control device 9 recognizes the risk of an arc breaking off, it goes 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 the arc breaking is counteracted. For example, the control device 9 can vary the first control values A1 in such a way that the electrode voltages U are increased and the second control values A2 can be varied in such a way that the electrodes 6 are lowered in the direction of the molten steel 15 .

If, in step S11, the control device 9 does not recognize the risk of an arc breaking, the control device 9 goes to a step S13. In step S13, the control device 9 checks whether it recognizes 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 recognizes the risk of a short circuit, it goes to a 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 actuation values A1 such that the electrode voltages U are reduced, and in particular the second actuation values A2 can vary such that the electrodes 6 are raised in the direction away from the molten steel 15 .

If the control device 9 does not recognize the risk of a short circuit in step S13, the control device 9 goes to step S5. In step S5, the first control values A1 and the second control values A2 are determined in the same way as was already done in connection with 6 was explained.

Irrespective of whether the control device 9 has carried out step S12, step S14 or step S5, the control device 9 next moves 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 , drives A2. Then the controller proceeds to step S7. From there, either go to step S8 or the control device 9 goes back to step S11.

The parameters U, I, P can be selected in different ways. For example, as shown in 9 It is possible that - at least during the flat bath phase - the electrical parameters U, I, P are the electrode currents I. Alternatively, as shown in 10 It is possible that - at least during the flat bath phase - the electrical parameters U, I, P are the electrical power P. In this case, for example, the determination block 12 can be preceded by a supplementary block 18 . 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 instantaneously or the average electrical power over a period of the electrode voltages U and outputs the determined value as an electrical parameter P to the determination block 12 .

It is possible for the control device 9 to determine the first control values A1 during the flat 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 in 11 indicated by the fact that a corresponding period T is varied. Varying the period T and the corresponding frequency f is in 11 indicated by a double arrow 19. It is done for the purpose of approximating the electrical parameters U, I, P to the corresponding setpoint values U*, I*, P*.

The frequency f is preferably varied in a range that lies between 70% and 90% of the base frequency f0, in particular between 75% and 85% of the base frequency f0.

At the beginning of the flat bath phase, i.e. when the control device 9 switches from step S4 to step S5 (or in the case of the embodiment according to 8 goes to step S11), the arcs 14, as shown in FIG 5 has a base length L0. In some cases it is advantageous if the control device 9 moves the electrodes 6 towards the molten steel 15 during the flat bath phase. According to the method of molten steel 15, the arcs 14 according to 12 only a remaining length LR. The remaining length LR is smaller than the base length L0. However, it should be as shown in 13 be at least 20% of the base length L0.

The base length L0 can become known to the control device 9 in various ways. For example, the base length L0 of the control device 9 can be specified by the operator. Alternatively, it is possible that the control device 9 as shown in 14 first executes a step S21 immediately after the step S4. In this case, the control device 9 determines the base length L0 in step S21 using the electrical parameters U, I, P as they exist at the beginning of the flat bath phase. Appropriate procedures are known to those skilled in the art. Step S21, if present, is executed only once. It is therefore not included in the loop of steps S5 to S7. This also applies in an analogous manner if steps S11 to S14 are present.

It is possible for the control device 9 to determine the remaining length LR using 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 the control device 9 to provide a corresponding minimum permissible value for the Residual length LR is specified. In this case it is possible for the control device 9 to continue moving the electrodes 6 until the control device 9 recognizes optimized operation of the arc furnace based on an evaluation of the parameters U, I, P or the remaining length RL reaches the minimum permissible value. Regardless of the specific procedure taken, step S5 is implemented in this case in such a way that the first control values A1 are determined as already explained, but the second control values A2 are determined in such a way that the length of the arcs 14, starting from the base length L0, is reduced. By reducing the length of the arcs 14 to the remaining length LR, the energy efficiency of the arc furnace can be improved in some operating states of the arc furnace.

The present invention has many advantages. In particular, however, the mechanical load on the positioning device 7 can be reduced and the energy efficiency during operation of the electric arc furnace can also be improved.

Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variants can be derived therefrom by a person skilled in the art without departing from the protective scope of the invention.

Reference List

1

furnace vessel

2

steely material

3

power supply device

4

supply network

5

furnace transformer

6

electrodes

7

positioning device

8, 19

double arrows

9

control device

10

control program

11

machine code

12, 13, 17

investigation blocks

14

electric arc

15

molten steel

16

slag layer

18

supplementary block

A1, A2

control values

f

frequency

f0

base frequency

I

electrode currents

L0

base length

LR

remaining length

P

electrical services

S1 to S21

steps

T

period duration

u

electrode voltages

U, I, P

parameters

U*, I*, P*

target sizes

V

Requirements

Claims (11)

operating method for an electric arc furnace, - wherein a control device (9) of the arc furnace controls an energy supply device (3) of the arc furnace with first control values (A1), first in a melting phase and then in a flat bath phase that follows the melting phase, so that the energy supply device (3) receives electrical energy from a supply network (4) and supplies electrodes (6) of the arc furnace via a furnace transformer (5), and also controls a positioning device (7) of the arc furnace with second control values (A2), so that the positioning device (7) places the electrodes (6) in the The melting phase is positioned in the solid aggregate state relative to the steel-containing material (2) in a furnace vessel (1) of the electric arc furnace, so that arcs (14) are formed in the melting phase between the electrodes (6) and the steel-containing material (2), through which the Steel-bearing material (2) is melted into a molten steel (15), and in the Flachbadp Hase positioned relative to the molten steel (15), so that in the flat bath phase between the electrodes (6) and the molten steel (15) arcs (14) form, through which the molten steel (15) is further heated, - wherein the control device (9) determines both the first control values (A1) and the second control values (A2) during the melting phase in such a way that electrical parameters (U, I, P) of the electrical energy supplied to the electrodes (6) correspond to setpoint values ( U*, I*, P*) are approximated as closely as possible, - wherein the control device (9) continues to determine the first control values (A1) during the flat bath phase in such a way that the electrical parameters (U, I, P) are approximated as closely as possible to the corresponding setpoint values (U*, I*, P*). , but the second control values (A2) are determined either completely independently of the electrical parameters (U, I, P) or only as a function of the electrical parameters (U, I, P) determined when the control device (9) detects the risk of arcing and/or a short circuit based on the electrical parameters (U, I, P). Operating method according to claim 1,
characterized ,
that at least during the flat bath phase the electrical parameters (U, I, P) are the electrode currents (I). Operating method according to claim 1,
characterized,
that at least during the flat bath phase the electrical parameters (U, I, P) are the electrical powers (P). Operating method according to claim 1, 2 or 3,
characterized,
that the control device (9) determines the first control values (A1) during the flat bath phase in such a way that, in order to approximate the electrical parameters (U, I, P) to the corresponding setpoint values (U*, I*, P*), a frequency (f) is varied by the electrode currents (I) supplied to the electrodes (6) and/or by the electrode voltages (U) applied to the electrodes (6). Operating method according to claim 4,
characterized,
that the frequency (f) of the electrode currents (I) supplied to the electrodes (6) and/or of the electrode voltages (6) applied to the electrodes (6) in the flat bath phase is lower than a base frequency (f0) of the supply network (4). Operating method according to one of the above claims,
characterized,
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) the process towards the molten steel (15) only have a remaining length (LR) which is smaller than the base length (L0). Operating method according to claim 6,
characterized,
that the remaining length (LR) is at least 20% of the base length (L0). Operating method according to claim 6 or 7,
characterized,
that the control device (9) determines the base length (L0) using the electrical parameters (U, I, P) as they exist at the beginning of the flat bath phase. Control program for a control device (9) of an arc furnace, the control program comprising machine code (11) which can be processed by the control device (9), the processing of the machine code (11) by the control device (9) causing the control device (9 ) operates an arc furnace according to an operating method according to any one of the above claims. Control device of an arc furnace, wherein the control device is programmed with a control program (10) according to claim 9, so that the control device operates the arc furnace according to an operating method according to one of claims 1 to 8. arc furnace, - wherein the arc furnace has a furnace vessel (1) to which steel-containing material (2) can be fed in the solid state of aggregation, - wherein the arc furnace has an energy supply device (3) and electrodes (6) and a furnace transformer (5), - The energy supply device (3) being connected to a supply network (4) on the input side and on the output side is connected to the electrodes (6) via the furnace transformer (5), - wherein the arc furnace has a positioning device (7) by means of which the electrodes (6) are positioned relative to the steel-containing material (2) in a melting phase and in a flat bath phase which follows the melting phase relative to a steel melt produced by melting the steel-containing material (2). (15) are positionable, - wherein the arc furnace has a control device (9) by which the energy supply device (3) can be controlled with first control values (A1) and the positioning device (7) can be controlled with second control values (A2) both in the melting phase and in the flat bath phase, - wherein the control device (9) is designed according to claim 10.

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