Title of Invention	METHOD FOR DETERMINING AT LEAST ONE STATE VARIABLE OF AN ELECTRIC ARC FURNACE, AND ELECTRIC ARC FURNACE
Abstract	The invention relates to a method for determining a state variable of an electric arc furnace, especially for determining the level of the foamed slag (15) in an electric arc furnace. According to said method, the energy supplied to the electric arc furnace is determined with the aid of at least one electric sensor (13a, 13b, 13c) while solid-borne noise is measured in the form of oscillations on the electric arc furnace. The at least one state variable, particularly the level of the foamed slag (15), is determined by means of a transfer function which is determined by evaluating the measured oscillations, i.e. the solid-borne noise, and evaluating measured data of the at least one electric sensor (13a, 13b, 13c). The state of the level of the foamed slag (15) can thus be reliably recognized and be monitored over time. The level of the foamed slag (15) is decisive for the effectiveness with which energy is fed into the electric arc furnace. Furthermore, losses caused by radiation are reduced by covering the arc (18) with the foamed slag (15). The improved measuring method allows the level of the foamed slag to be automatically controlled or regulated in a reliable manner.

Title of Invention

METHOD FOR DETERMINING AT LEAST ONE STATE VARIABLE OF AN ELECTRIC ARC FURNACE, AND ELECTRIC ARC FURNACE

Abstract

The invention relates to a method for determining a state variable of an electric arc furnace, especially for determining the level of the foamed slag (15) in an electric arc furnace. According to said method, the energy supplied to the electric arc furnace is determined with the aid of at least one electric sensor (13a, 13b, 13c) while solid-borne noise is measured in the form of oscillations on the electric arc furnace. The at least one state variable, particularly the level of the foamed slag (15), is determined by means of a transfer function which is determined by evaluating the measured oscillations, i.e. the solid-borne noise, and evaluating measured data of the at least one electric sensor (13a, 13b, 13c). The state of the level of the foamed slag (15) can thus be reliably recognized and be monitored over time. The level of the foamed slag (15) is decisive for the effectiveness with which energy is fed into the electric arc furnace. Furthermore, losses caused by radiation are reduced by covering the arc (18) with the foamed slag (15). The improved measuring method allows the level of the foamed slag to be automatically controlled or regulated in a reliable manner.

Full Text	2005P11628 WO - 1 - PCT/EP2006/064156 Dcscription Method for determining at least one state variable of an electric arc furnace, and electric arc furnace The invention relates to a method for determining at least one state variable of an electric arc furnace with at least one electrode, wherein the energy supplied to the electric arc furnace is determined with the aid of at least one electric sensor. The invention also relates to an electric arc furnace with a furnace casing and with at least one electrode, wherein a current lead is provided for each electrode. If is known from DE 197 48 310 C1 to predict foamed slag in an electric arc furnace on the basis of feed materials of the electric arc furnace, such as scrap, steel, alloying agents or admixed materials, in combination with the energy supplied to the electric arc furnace. However, it has been found that state variables of the electric arc furnace cannot be determined sufficiently reliably and accurately enough in this way. European patent application EP 0 637 638 A1 discloses a method for producing a molten metal in an electric arc furnace. Here, the layer height of a foamed slag is measured as the state variable of the electric arc furnace and possibly used for regulating the layer height of a foamed slag. Disclosed for measuring the level of the foamed slag are noise emissions originating from the electric arc furnace, which are used in the form of a measured noise level for controlling the layer height of the foamed slag. It is also disclosed that the electric operating parameters voltage and current intensity of the electric arc furnace may be used for measuring the level. 2005P11628 WO - 1a - PCT/EP2006/064156 A method for regulating the electrode of a DC arc furnace and an electrode regulating device are known from the laid-open application EP 0 661 910 A1. Here, the supply of energy to the electric arc furnace is determined with the aid of at least one electric sensor. D2 also discloses that the slag level in the arc: furnace is a state variable. The object of the invention is to make an improved determination of state variables of the electric arc furnace possible. This object is achieved by a method of the type mentioned at the beginning, wherein oscillations on the electric arc furnace are measured and wherein the state variable of the electric arc furnace is determined with the aid of a transfer function which is determined by evaluating the measured oscillations and by evaluating measured data of the at least one electric sensor. 2005P11628 WO - 2 - PCT/EP2006/064156 State variables of the electric arc furnace, in particular state variables concerning the content of the electric arc furnace, can be determined according to the invention very accurately and reliably while the electric arc furnace is in operation, that is to say can be determined online. This satisfies an important prerequisite for improved automatic process control and regulation of the electric arc furnace. The level of the foamed slag can be advantageously determined as the state variable. Oscillations, i.e. structure-borne noise, on the electric arc furnace can expediently be measured with the aid of at least one acceleration sensor. Oscillations, i.e. structure-borne noise, which emanate from an arc of the at least one electrode of the electric arc furnace arc advantageously measured. If may be of advantage to determine the transfer function from an excitation signal and from an output signal, the excitation signal being determined by evaluating measured data of the at least one electric sensor and the output signal being determined by evaluating the oscillations measured on the electric arc furnace. It may be expedient to measure a current signal with the aid of the at least one electric sensor and use it to form the excitation signal. in an advantageous development of the method, the excitation signal may be formed by multiplication of the current signal by itself, i.e. by squaring. PCT/EP2006/064156 - 3 - 2005P11628WOUS A voltage signal may advantageously be measured with the aid of the at least one electric sensor and used to form the excitation signal. if appropriate, the measurement and/or use of the voltage signal is performed as an alternative or in addition to the measurement and use of the current signal. The excitation signal may advantageously be formed by multiplication of the current signal by the voltage signal. The transfer function may advantageously be determined by way of a cross-power spectrum. The transfer function may preferably be evaluated at at least one discrete frequency. The at least one discrete frequency may advantageously be a multiple of the frequency of the power feed into the arc or into the electric arc furnace. If may bo expedient to determine the level of the foamed slag in dependence on the change in the transfer function at the one or more discrete frequencies. further advantageous forms of the method described above are specified in patent claims 14 to 20. The object is also achieved by an electric arc furnace with a furnace casing and with at least one electrode, wherein a current lead is provided for each electrode and, to carry out a method as given above in the various forms it takes, at least one electric sensor is provided on a current lead and at least one structure-borne noise sensor for sensing oscillations is provided on the wall of the furnace casing. PCT/EP2006/064156 - 4 - 2005P11628WOUS The advantages of the electric arc furnace according to the invention are to the greatest extent analogous to the advantages of the method according to the invention. An electric sensor may preferably be provided for each electrode. The at least one structure-borne noise sensor may advantageously be formed as an acceleration sensor. A structure-borne noise sensor may preferably be provided for each electrode. The one or more structure-borne noise sensors may advantageously be arranged on a wall of the furnace casing that is opposite the respective electrode. The at least one electric sensor and the at least one structure-borne noise sensor may advantageously be coupled with a signal processing device. For coupling the at least one structure-borne noise sensor with the signal, processing device, at least one optical waveguide may preferably be provided. In an advantageous development of the electric arc furnace, the at least one structure-borne noise sensor may be connected to the optical waveguide by way of at least one signal line and by way of an optical device arranged ahead of the optical waveguide. The at least one signal line may advantageously be routed in a protected manner. The signal processing device may advantageously be coupled with a regulating device for the electric arc furnace. PCT/EP2006/064156 - 5 - 2005P11628WOUS Further advantages and details of the invention are described below on the basis of examples in conjunction with the drawings, in which: FIGURE 1 schematically shows an electric arc furnace according to the invention, FIGURE 2 schematically shows a section through the electric arc furnace. Figure 1 shows an electric arc furnace with a number of electrodes 3a, 3b, 3c, which are coupled with a current supply device 12 by way of current leads. The current supply device 12 preferably has a furnace transformer. With the aid of at least one electrode, in the example shown three electrodes 3a, 3b, 3c, feed materials, such as for example scrap and/or steel, possibly with alloying agents and/or admixed materials, are melted in the electric arc furnace. When producing steel in the electric arc furnace, slag or foamed slag 15 (see Figure 2) is formed and is made to foam by blowing in a media mixture, as a means of improving the energy introduced by way of an arc 18 (see Figure 2), which forms at the at least one electrode 3, 3a, 3b, 3c. In the example shown, electric sensors 13a, 13b, 13c are provided on the current leads of the electrodes 3a, 3b, 3c and can be used to measure the current and/or voltage or the energy supplied to the electrodes 3a, 3b, 3c. The electric sensors 13a, 13b, 13c are coupled with a signal processing device 8, for examp e by way of signal lines 14a, 14b, 14c for electric measuring signals, formed as cables. PCT/EP2006/064156 - 6 - 2005P11628WOUS Arranged on the wall 2 or on the panels of the furnace casing 1, i.e. on the outer delimitation of the furnace casing 1, are structure-borne noise sensors 4a, 4b, 4c for measuring oscillations on the furnace casing 1. The structure-borne noise sensors 4, 4a, 4b, 4c may be arranged such that they are connected indirectly and/or directly to the furnace casing 1 or to the wall 2 of the furnace casing 1. As indicated in the example shown, the sensors for measuring structure-borne noise, i.e. the structure-borne noise sensors 4, 4a, 4b, 4c, may be arranged on the outer wall of the furnace casing 1. Structure-borne noise sensors 4, 4a, 4b, 4c may, for example, be arranged at equal intervals around the furnace casing 1. In order to increase the accuracy of the structure- borne noise measurements, it may be expedient to provide a structure-borne noise sensor 4a, 4b, 4c respectively for each electrode 3a, 3b, 3c. In this case, the structure-borne noise sensors 4a, 4b, 4c do not necessarily have to be arranged on the outer wall of the furnace casing 1. At least one sensor 4a, 4b, 4c that is assigned to an electrode 3a, 3b, 3c may preferably be arranged at a location at the smallest possible distance from this electrode 3a, 3b, 3c, preferably at a location on the outer wall of the furnace casing 1. The structure-borne noise is passed through the steel bath 16 and/or through the foamed slag 15 to the furnace casing 1 and can be measured indirectly and or directly on the furnace casing 1 in the form of oscillations. The structure-borne noise sensors 4, 4a, 4b, 4c are connected to the signal processing device 8. The signals that are emitted by the structure-borne noise sensors 4, 4a, 4b, and 4c to the signal processing device 8 are at least partially passed by way of an optical waveguide 7. Arranged between the optical waveguide 7 and the structure-borne noise sensors 4, 4a, 4b, 4c is at least one optical device 6, which serves for amplifying PCT/EP2006/064156 - 6a - 2005P1162 8WOUS and /or converting signals of the one or more st.ructurc-borne noise sensors PCT/EP2006/064156 - 7 - 2005P11628WOUS 4, 4a, 4b, 4c. Signal lines 5, 5a, 5b, 5c, which carry the signals of the structure-borne noise sensors 4a, 4b, 4c, may be provided in close proximity to the furnace casing 1, or under some circumstances even directly on the furnace casing 1. The signal lines 5, 5a, 5b, 5c are preferably routed such that they arc protected from heat, electromagnetic fields, mechanical loading and/or other loads. The electric sensors 13a, 13b, 13c may preferably be connected by way of signal lines 14a, 14b, 14c, which are formed as cables, to the signal processing device 8. In the signal processing device 8, evaluation data are determined from the measuring signals of the structure-borne noise sensors 4, 4a, 4b, 4c and from the measuring signals of the electric sensors 13a, 13b, 13c. The evaluation data relate to at least one state variable of the electric arc furnace, the evaluation data preferably relating to the foamed slag 15 (see Figure 2) or its level. The signal processing device 8 emits a state signal 10, preferably the currently calculated and/or pre-calculated level of the foamed slag 15, to a regulating device 9 for the electric arc furnace. The state signal 10 at least partially represents the evaluation data. Taking the state signals 10 into account, the regulating device 9 determines regulating signals 11 for the electric arc furnace, for example for controlling the blowing-in of media mixture, the introduction of coal, the introduction of oxygen and/or other substances into the electric arc furnace. In an advantageous refinement of the invention, regulating signals 11 for controlling or regulating the position or the level of the at least one electrode 3, 3a, 3b, 3c may also be determined. In order to influence the position, in particular the level, of the electrodes 3, 3a, 3b, 3c, one or more control means for controlling the PCT/EP2006/064156 - 8 - 2005P11628WOUS raising or lowering of the electrodes 3, 3a, 3b, 3c are provided and coupled with the regulating device 9. A control computer, which is not represented any more specifically and with the aid of which the buildup and level of the foamed slag 15 can be controlled or regulated, may be coupled with the electric arc furnace. The control computer emits actuating signals 11, in particular to a feeding device of the electric arc furnace. The control computer may include the signal, processing device 8 and/or the regulating device 9. A feeding device of the electric arc furnace may, for example, have a so-called injection lance, with the aid of which carbon, oxygen and/or lime are blown into the electric arc furnace, i.e. into the furnace casing 1 of the electric arc furnace. The substances mentioned above are blown in particular into the foamed slag 15 above the steel bath 16. With the aid of the feeding device, preferably carbon mixed with air is fed into the foamed slag 15. In the foamed slag, the carbon is transformed into carbon dioxide and/or carbon monoxide, so that foamed slag 15 is produced. By blowing in a media mixture with the aid of the feeding device, the introduction of energy by means of the arc 18 (see FIGURE 2) is improved. Furthermore, losses through radiation in the electric arc furnace are reduced. If is possible to measure the concentration of substances, in particular of gases, in the electric arc furnace directly or indirectly or determine such concentrations with the aid of models. The data on the concentration of substances, such as for example carbon, oxygen, carbon dioxide and/or carbon monoxide, are preferably fed to the control computer or the signal processing device and/or the regulating device 9. The fed data can be processed and used for determining regulating signals 11. PCT/EP2006/064156 - 9 - 2005P11628WOUS In a refinement given by way of example, the electric arc furnace shown in FIGURE 1 is formed as a three-phase AC arc furnace. In principle, the invention can be applied to arc furnaces of a wide variety of types, for example also to DC furnces. Figure 2 shows in a simplified representation an electrode 3, 3a, 3b, 3c with an arc 18 in an electric arc furnace. Arranged on the wall 2 of the furnace casing 1 of the electric arc furnace is a structure-borne noise sensor 4, 4a, 4b, 4c, which is connected to a signal line 5, 5a, 5b, 5c, with the aid of which measuring signals can be passed to a signal processing device 8 (see Figure 1). The steel bath 16 and the foamed slag 15 in the furnace casing 1 are schematically represented. The level of the foamed slag 15 can be determined in the signal processing device 8 with the aid of a transfer function of the structure-borne noise in the electric arc furnace. The transfer function characterizes the transfer path 17, schematically indicated in Figure 2, of the structure-borne noise from excitation to detection. The excitation of the structure-borne noise takes place by the power feed at the electrodes 3, 3a, 3b, 3c in the arc 18. The structure-borne noise, i.e. the oscillations caused by the excitation, are transferred through the liquid steel bath 16 and/or through the foamed slag 15 that at least partially covers the steel bath 16 to the wall 2 of the electric arc furnace. A transfer of structure-borne noise may additionally also take place, at least partially, through not yet melted food material in the electric arc furnace. The detection of the structure-borne noise takes place by structure-borne noise sensors 4, 4a, 4b, 4c, which are arranged on the wall 2 of the furnace casing 1 of the electric arc furnace. The structure- borne noise sensors 4, 4a, 4b, 4c pick up oscillations on the walls 2 of the furnace PCT/EP2006/064156 - 10 - 2005P11628WOUS casing 1. The structure-borne noise sensors 4, 4a, 4b, 4c are preferably formed as acceleration sensors. The structure-borne noise sensors 4, 4a, 4b, 4c are preferably provided above the foamed slag zone. Structure-borne noise sensors 4, 4a, 4b, 4c are preferably arranged on the opposite sides of the electrodes 3, 3a, 3b, 3c on the wall 2 of the electric arc furnace. The electric sensors 13a, 13b, 13c sense current and/or voltage signals of the electrodes 3, 3a, 3b, 3c. Current and/or voltage signals are preferably sensed in a time-resolved manner. The signals of the structure-borne noise sensors are led by way of protected lines 5, 5a, 5b, 5c into an optical device 6 (see Figure 1). The optical device 6 is preferably arranged relatively close to the actual electric arc furnace. The optical device 6 serves for amplifying and converting the signals of the structure-borne noise sensors 4, 4a, 4b, 4c. In the optical device 6, the signals are converted into optical signals and are passed by way of an optical waveguide 7 free from interference over comparatively longer distances, for example 50 to 200 m, into a signal processing device 8. In the signal processing device 8, signals are sensed and evaluated. In the signal processing device 8, the signals are preferably digitized at an adequately high sampling rate, for example 6000 samples/second. The excitation signals of the electrodes 3, 3a, 3b, 3c are preferably formed by multiplication of the associated current signals and/or associated voltage signals. The output signals form the structure-borne noise signals. The following applies here to the signals in the time domain: (1) Y(t)-h(t) ° X(t) , PCT/EP2006/064156 - 11 - 2005P11628WOUS where Y(t,) denotes a structure-borne noise signal, X(t) denotes the power feed in the arc 18 and h(t) denotes the step response. The variables h(t) and X(t) are linked to one another by a convolution operator. The transfer function H(ω) is determined in the frequency domain: (II) y(ω)=H(ω).x(ω) , where x (Ω) and y(ω) are the Fourier transforms of the excitation and output signals. The variables x (Ω) , y(ω) and H(Ω) are complex. To avoid complex division, H(Ω) is calculated by way of the cross-power spectrum: (III) \|H(ω) \| = \|Wxy(ω) \|/Wxx(ω) , where WXY(Ω) denotes the cross-power spectrum and Wxx denotes the power spectrum at the input, i.e. on the side of the excitation. The transfer function H(Ω) is only determined at discrete frequencies, the discrete frequencies being multiples (harmonics) of the fundamental frequency of the power supply to the electrodes 3, 3a, 3b, 3c, since the excitation only takes place by way of the fundamental wave and the harmonic waves of the coupled power. In the case of a power supply device 12 for the electric arc furnace that operates for example at 50 Hz, the discrete frequencies are multiples of 100 Hz. The transfer function H(ω) characterizes the medium in the electric arc furnace. Therefore, the variation of the medium over time, for example the level of the foamed slag 15, can be determined by the change in the transfer function. PCT/EP2006/064156 - 12 - 2005P11628WOUS The attenuation or amplification of the transfer function values can be used to calculate a resultant value that correlates with the level of the foamed slag 15. This has been confirmed in measuring experiments with a time resolution of about 1 to 2 seconds. The evaluation in the signal processing device 8 may be adapted with the aid of empirical values from the operation of the electric arc furnace. The signal sensing and evaluation and the slag determination are performed online during operation, so that the state signal that characterizes the slag level in the electric arc. furnace can be used for automatically regulating the process. The improved knowledge of the foamed slag process, improved by the measuring techniques according to the invention, makes improved process control and regulation possible, leading to the following advantages: - Increase in productivity through higher specific smelting capacity by reducing the downtimes caused in particular by furnace repairs. - Reduction in the specific smelting energy while maintaining a constant, tapping temperature. - Reduction in the wearing of the wall by reducing the radiant energy to the inner wall of the furnace casing 1. - Reduction in electrode consumption. A concept that is important for the invention can be summarized as follows: The invention relates to a method for determining a state variable of an electric arc furnace, in particular for determining the level of the foamed slag 15 in an electric arc furnace, wherein the energy supplied to the electric arc furnace is determined with the aid of at least one electric sensor 13a, 13b, 13c and wherein structure-borne noise in the form of oscillations on the electric arc furnace is measured, the at least one PCT/EP2006/064156 - 13 - 2005Pl1628WOUS state variable, in particular the level of the foamed slag 1b, being determined with the aid of a transfer function which is determined by evaluating the measured oscillations, i.e. the structure-borne noise, and by evaluating measured data of the at Least one electric sensor 13a, 13b, 13c. The state of the level of the foamed slag 15 is in this way reliably defected and monitored over time. The level of the foamed slag 15 is decisive for the effectiveness with which energy is introduced into the electric arc furnace. Moreover, losses through radiation are reduced by covering the arc 18 with the foamed slag lb. The improved measuring method makes it possible for the level of the foamed slag to be automatically controlled or regulated in a reliable manner. 2005l1628 Foreign - 14 - Patent claims 1. A method for determining at least one state variable of an electric arc furnace with at least one electrode (3, 3a, 3b, 3c), wherein the energy supplied to the electric arc Curnace is determined with the aid of at least one electric sensor (13a, 13b, 13c), characterized in that structure- borne noise oscillations on the electric arc furnace are measured, and in that the at least one state variable is determined with the aid of a transfer function which is determined by evaluation of the measured structure-borne noise oscillations and by evaluation of measured data of the at least one electric sensor (13a, 13b, 13c) . 2. The method as claimed in patent claim 1, wherein the level of the foamed slag (15) is determined as the state variable. 3. The method as claimed in one of the preceding patent: claims, wherein structure-borne noise oscillations on the electric arc furnace are measured with the aid of at least one acceleration sensor. 4 . The method as claimed in one of the preceding patent claims, wherein structure-borne noise oscillations which emanate from at least one arc (18) of the at least one electrode (3, 3a, 3b, 3c) of the electric arc furnace arc measured. b. The method as claimed in one of the preceding patent claims, wherein the transfer function is determined from an excitation signal and from an output signal, the excitation signal being determined by evaluating measured data of the at least one electric sensor (13a, 13b, 13c), and the output signal being determined by evaluating the structure- 200511628 Foreign - 14a - borne noise oscillations measured on the electric arc furnace. 200511628 Foreign - 15 - 6. The method as claimed in patent claim 5, wherein a current signal is measured with the aid of the at least one electric sensor (13a, 13b, 13c) and is used to form the excitation signal. 7. The method as claimed in patent claim 6, wherein the excitation signal is formed by squaring the current signal. 8. The method as claimed in one of the preceding patent claims, wherein a voltage signal is measured with the aid of the at least one electric sensor (13a, 13b, 13c) and is used to form the excitation signal. 9. The method as claimed in patent claim 8, wherein the excitation signal is formed by multiplication of the current signal by the voltage signal. 10. The method as claimed in one of the preceding patent claims, wherein the transfer function is determined by way of a cross-power spectrum. 11. The method as claimed in one of the preceding patent claims, wherein the transfer function is evaluated at at least one discrete frequency. 12. The method as claimed in patent claim 11, wherein the at least one discrete frequency is a multiple of the frequency of the power feed into the arc (18). 13. The method as claimed in patent claim 11 or 12, wherein the level of the foamed slag (15) is determined in dependence on the change in the transfer function at the one or more discrete frequencies. 14. A method for controlling an electric arc furnace, wherein at 1 east one state variable of the electric arc furnace is 200511628 foreign - 15a - determined according to a method as claimed in one of the preceding 200511628 Foreign - 16 - patent, claims, and wherein actuating and/or regulating signals (11) for the electric arc furnace are determined with the aid of the at least one specific state variable. 15. The method as claimed in patent claim 14, wherein actuating and/or regulating signals (11) are emitted to a feeding device of the electric arc furnace. 16. The method as claimed in patent claim 14 or 15, wherein actuating and/or regulating signals (11) that influence the blowing-in of oxygen are emitted. 17. The method as claimed in one of patent claims 14 to 16, wherein actuating and/or regulating signals (11) that influence the blowing-in of carbon are emitted. 18. The method as claimed in one of patent claims 14 to 17, wherein actuating and/or regulating signals (11) that influence the blowing-in of lime are emitted. 19. The method as claimed in one of patent claims 14 to 18, wherein actuating and/or regulating signals (11) for influencing the position of the at least one electrode (3, 3a, 3b, 3c) are emitted. 20. The method as claimed in one of patent claims 14 to 19, wherein a neural network is used for determining the actuating and/or regulating signals (11). 21. An electric arc furnace with a furnace casing (1) and with at least one electrode (3, 3a, 3b, 3c), a current lead being provided for each electrode (3, 3a, 3b, 3c), characterized in that, to carry out a method as claimed in one of the preceding claims, at least one electric sensor (13a, 13b, 13c) is provided on a current lead and at least one structure-borne noise sensor (4, 200511628 Foreign - 17 - 4a, 4b, 4c) for sensing structure-borne noise oscillations is provided on the wall (2) of the furnace casing (1). 22. The electric arc furnace as claimed in patent claim 21, wherein an electric sensor (13a, 13b, 13c) is provided for each electrode (3, 3a, 3b, 3c). 23. The electric arc furnace as claimed in patent claim 21 or 22, wherein the at least one structure-borne noise sensor (4, 4a, 4b, 4c) is formed as an acceleration sensor. 24. The electric arc furnace as claimed in one of patent claims 21 to 23, wherein a structure-borne noise sensor (4, 4a, 4b, 4c) is provided for each electrode (3, 3a, 3b, 3c). 25. The electric arc furnace as claimed in patent claim 24, wherein the one or more structure-borne noise sensors (4, 4a, 4b, 4c) are arranged on a wall (2) of the furnace casing (1) that, is opposite the respective electrode (3, 3a, 3b, 3c). 26. The electric arc furnace as claimed in one of patent claims 21 to 25, wherein the at least one electric sensor (13a, 13b, 13c) and the at least one structure-borne noise sensor (4, 4a, 4b, 4c) are coupled with a signal processing device (8) . 27. The electric arc furnace as claimed in one of patent claims 21 to 26, wherein, for coupling the at least one structure- borne noise sensor (4, 4a, 4b, 4c) with the signal processing device (8), at least one optical waveguide (7) is provided. 28. The electric arc furnace as claimed in patent claim 27, wherein the at least one structure-borne noise sensor (4, 4a, 4b, Ac) is connected to the optical waveguide (7) by 200b11628 Foreign - 17a - way of at least one signal line (5, 5a, 5b, 5c) and by way of an 200511628 Foreign - 18 - optical device (6) arranged ahead of the optical waveguide (7). 29. The electric arc furnace as claimed in patent claim 28, wherein the at least one signal line (5, 5a, 5b, 5c) is formed such that it is routed in a protected manner. 30. The electric arc furnace as claimed in one of patent claims 26 to 29, wherein the signal processing device (8) is coup.l ed with a regulating device (9) for the electric arc furnace. The invention relates to a method for determining a state variable of an electric arc furnace, especially for determining the level of the foamed slag (15) in an electric arc furnace. According to said method, the energy supplied to the electric arc furnace is determined with the aid of at least one electric sensor (13a, 13b, 13c) while solid-borne noise is measured in the form of oscillations on the electric arc furnace. The at least one state variable, particularly the level of the foamed slag (15), is determined by means of a transfer function which is determined by evaluating the measured oscillations, i.e. the solid-borne noise, and evaluating measured data of the at least one electric sensor (13a, 13b, 13c). The state of the level of the foamed slag (15) can thus be reliably recognized and be monitored over time. The level of the foamed slag (15) is decisive for the effectiveness with which energy is fed into the electric arc furnace. Furthermore, losses caused by radiation are reduced by covering the arc (18) with the foamed slag (15). The improved measuring method allows the level of the foamed slag to be automatically controlled or regulated in a reliable manner.

Full Text

2005P11628 WO - 1 -
PCT/EP2006/064156
Dcscription
Method for determining at least one state variable of an
electric arc furnace, and electric arc furnace
The invention relates to a method for determining at least one
state variable of an electric arc furnace with at least one
electrode, wherein the energy supplied to the electric arc
furnace is determined with the aid of at least one electric
sensor. The invention also relates to an electric arc furnace
with a furnace casing and with at least one electrode, wherein
a current lead is provided for each electrode.
If is known from DE 197 48 310 C1 to predict foamed slag in an
electric arc furnace on the basis of feed materials of the
electric arc furnace, such as scrap, steel, alloying agents or
admixed materials, in combination with the energy supplied to
the electric arc furnace. However, it has been found that
state variables of the electric arc furnace cannot be
determined sufficiently reliably and accurately enough in this
way.
European patent application EP 0 637 638 A1 discloses a method
for producing a molten metal in an electric arc furnace. Here,
the layer height of a foamed slag is measured as the state
variable of the electric arc furnace and possibly used for
regulating the layer height of a foamed slag. Disclosed for
measuring the level of the foamed slag are noise emissions
originating from the electric arc furnace, which are used in
the form of a measured noise level for controlling the layer
height of the foamed slag. It is also disclosed that the
electric operating parameters voltage and current intensity of
the electric arc furnace may be used for measuring the level.

2005P11628 WO - 1a -
PCT/EP2006/064156
A method for regulating the electrode of a DC arc furnace and
an electrode regulating device are known from the laid-open
application EP 0 661 910 A1. Here, the supply of energy to the
electric arc furnace is determined with the aid of at least one
electric sensor. D2 also discloses that the slag level in the
arc: furnace is a state variable.
The object of the invention is to make an improved
determination of state variables of the electric arc furnace
possible.
This object is achieved by a method of the type mentioned at
the beginning, wherein oscillations on the electric arc furnace
are measured and wherein the state variable of the electric arc
furnace is determined with the aid of a transfer function which
is determined by evaluating the measured oscillations and by
evaluating measured data of the at least one electric sensor.

2005P11628 WO - 2 -
PCT/EP2006/064156
State variables of the electric arc furnace, in particular
state variables concerning the content of the electric arc
furnace, can be determined according to the invention very
accurately and reliably while the electric arc furnace is in
operation, that is to say can be determined online. This
satisfies an important prerequisite for improved automatic
process control and regulation of the electric arc furnace.
The level of the foamed slag can be advantageously determined
as the state variable.
Oscillations, i.e. structure-borne noise, on the electric arc
furnace can expediently be measured with the aid of at least
one acceleration sensor.
Oscillations, i.e. structure-borne noise, which emanate from an
arc of the at least one electrode of the electric arc furnace
arc advantageously measured.
If may be of advantage to determine the transfer function from
an excitation signal and from an output signal, the excitation
signal being determined by evaluating measured data of the at
least one electric sensor and the output signal being
determined by evaluating the oscillations measured on the
electric arc furnace.
It may be expedient to measure a current signal with the aid of
the at least one electric sensor and use it to form the
excitation signal.
in an advantageous development of the method, the excitation
signal may be formed by multiplication of the current signal by
itself, i.e. by squaring.

PCT/EP2006/064156 - 3 -
2005P11628WOUS
A voltage signal may advantageously be measured with the aid of
the at least one electric sensor and used to form the
excitation signal. if appropriate, the measurement and/or use
of the voltage signal is performed as an alternative or in
addition to the measurement and use of the current signal.
The excitation signal may advantageously be formed by
multiplication of the current signal by the voltage signal.
The transfer function may advantageously be determined by way
of a cross-power spectrum.
The transfer function may preferably be evaluated at at least
one discrete frequency.
The at least one discrete frequency may advantageously be a
multiple of the frequency of the power feed into the arc or
into the electric arc furnace.
If may bo expedient to determine the level of the foamed slag
in dependence on the change in the transfer function at the one
or more discrete frequencies.
further advantageous forms of the method described above are
specified in patent claims 14 to 20.
The object is also achieved by an electric arc furnace with a
furnace casing and with at least one electrode, wherein a
current lead is provided for each electrode and, to carry out a
method as given above in the various forms it takes, at least
one electric sensor is provided on a current lead and at least
one structure-borne noise sensor for sensing oscillations is
provided on the wall of the furnace casing.

PCT/EP2006/064156 - 4 -
2005P11628WOUS
The advantages of the electric arc furnace according to the
invention are to the greatest extent analogous to the
advantages of the method according to the invention.
An electric sensor may preferably be provided for each
electrode.
The at least one structure-borne noise sensor may
advantageously be formed as an acceleration sensor.
A structure-borne noise sensor may preferably be provided for
each electrode.
The one or more structure-borne noise sensors may
advantageously be arranged on a wall of the furnace casing that
is opposite the respective electrode.
The at least one electric sensor and the at least one
structure-borne noise sensor may advantageously be coupled with
a signal processing device.
For coupling the at least one structure-borne noise sensor with
the signal, processing device, at least one optical waveguide
may preferably be provided.
In an advantageous development of the electric arc furnace, the
at least one structure-borne noise sensor may be connected to
the optical waveguide by way of at least one signal line and by
way of an optical device arranged ahead of the optical
waveguide.
The at least one signal line may advantageously be routed in a
protected manner.
The signal processing device may advantageously be coupled with
a regulating device for the electric arc furnace.

PCT/EP2006/064156 - 5 -
2005P11628WOUS
Further advantages and details of the invention are described
below on the basis of examples in conjunction with the
drawings, in which:
FIGURE 1 schematically shows an electric arc furnace according
to the invention,
FIGURE 2 schematically shows a section through the electric
arc furnace.
Figure 1 shows an electric arc furnace with a number of
electrodes 3a, 3b, 3c, which are coupled with a current supply
device 12 by way of current leads. The current supply device
12 preferably has a furnace transformer.
With the aid of at least one electrode, in the example shown
three electrodes 3a, 3b, 3c, feed materials, such as for
example scrap and/or steel, possibly with alloying agents
and/or admixed materials, are melted in the electric arc
furnace. When producing steel in the electric arc furnace,
slag or foamed slag 15 (see Figure 2) is formed and is made to
foam by blowing in a media mixture, as a means of improving the
energy introduced by way of an arc 18 (see Figure 2), which
forms at the at least one electrode 3, 3a, 3b, 3c.
In the example shown, electric sensors 13a, 13b, 13c are
provided on the current leads of the electrodes 3a, 3b, 3c and
can be used to measure the current and/or voltage or the energy
supplied to the electrodes 3a, 3b, 3c. The electric sensors
13a, 13b, 13c are coupled with a signal processing device 8,
for examp e by way of signal lines 14a, 14b, 14c for electric
measuring signals, formed as cables.

PCT/EP2006/064156 - 6 -
2005P11628WOUS
Arranged on the wall 2 or on the panels of the furnace casing
1, i.e. on the outer delimitation of the furnace casing 1, are
structure-borne noise sensors 4a, 4b, 4c for measuring
oscillations on the furnace casing 1. The structure-borne
noise sensors 4, 4a, 4b, 4c may be arranged such that they are
connected indirectly and/or directly to the furnace casing 1 or
to the wall 2 of the furnace casing 1.
As indicated in the example shown, the sensors for measuring
structure-borne noise, i.e. the structure-borne noise sensors
4, 4a, 4b, 4c, may be arranged on the outer wall of the furnace
casing 1. Structure-borne noise sensors 4, 4a, 4b, 4c may, for
example, be arranged at equal intervals around the furnace
casing 1. In order to increase the accuracy of the structure-
borne noise measurements, it may be expedient to provide a
structure-borne noise sensor 4a, 4b, 4c respectively for each
electrode 3a, 3b, 3c. In this case, the structure-borne noise
sensors 4a, 4b, 4c do not necessarily have to be arranged on
the outer wall of the furnace casing 1. At least one sensor
4a, 4b, 4c that is assigned to an electrode 3a, 3b, 3c may
preferably be arranged at a location at the smallest possible
distance from this electrode 3a, 3b, 3c, preferably at a
location on the outer wall of the furnace casing 1. The
structure-borne noise is passed through the steel bath 16
and/or through the foamed slag 15 to the furnace casing 1 and
can be measured indirectly and or directly on the furnace
casing 1 in the form of oscillations.
The structure-borne noise sensors 4, 4a, 4b, 4c are connected
to the signal processing device 8. The signals that are
emitted by the structure-borne noise sensors 4, 4a, 4b, and 4c
to the signal processing device 8 are at least partially passed
by way of an optical waveguide 7. Arranged between the optical
waveguide 7 and the structure-borne noise sensors 4, 4a, 4b, 4c
is at least one optical device 6, which serves for amplifying

PCT/EP2006/064156 - 6a -
2005P1162 8WOUS
and /or converting signals of the one or more st.ructurc-borne
noise sensors

PCT/EP2006/064156 - 7 -
2005P11628WOUS
4, 4a, 4b, 4c. Signal lines 5, 5a, 5b, 5c, which carry the
signals of the structure-borne noise sensors 4a, 4b, 4c, may be
provided in close proximity to the furnace casing 1, or under
some circumstances even directly on the furnace casing 1. The
signal lines 5, 5a, 5b, 5c are preferably routed such that they
arc protected from heat, electromagnetic fields, mechanical
loading and/or other loads.
The electric sensors 13a, 13b, 13c may preferably be connected
by way of signal lines 14a, 14b, 14c, which are formed as
cables, to the signal processing device 8. In the signal
processing device 8, evaluation data are determined from the
measuring signals of the structure-borne noise sensors 4, 4a,
4b, 4c and from the measuring signals of the electric sensors
13a, 13b, 13c. The evaluation data relate to at least one
state variable of the electric arc furnace, the evaluation data
preferably relating to the foamed slag 15 (see Figure 2) or its
level. The signal processing device 8 emits a state signal 10,
preferably the currently calculated and/or pre-calculated level
of the foamed slag 15, to a regulating device 9 for the
electric arc furnace. The state signal 10 at least partially
represents the evaluation data. Taking the state signals 10
into account, the regulating device 9 determines regulating
signals 11 for the electric arc furnace, for example for
controlling the blowing-in of media mixture, the introduction
of coal, the introduction of oxygen and/or other substances
into the electric arc furnace.
In an advantageous refinement of the invention, regulating
signals 11 for controlling or regulating the position or the
level of the at least one electrode 3, 3a, 3b, 3c may also be
determined. In order to influence the position, in particular
the level, of the electrodes 3, 3a, 3b, 3c, one or more control
means for controlling the

PCT/EP2006/064156 - 8 -
2005P11628WOUS
raising or lowering of the electrodes 3, 3a, 3b, 3c are
provided and coupled with the regulating device 9.
A control computer, which is not represented any more
specifically and with the aid of which the buildup and level of
the foamed slag 15 can be controlled or regulated, may be
coupled with the electric arc furnace. The control computer
emits actuating signals 11, in particular to a feeding device
of the electric arc furnace. The control computer may include
the signal, processing device 8 and/or the regulating device 9.
A feeding device of the electric arc furnace may, for example,
have a so-called injection lance, with the aid of which carbon,
oxygen and/or lime are blown into the electric arc furnace,
i.e. into the furnace casing 1 of the electric arc furnace.
The substances mentioned above are blown in particular into the
foamed slag 15 above the steel bath 16. With the aid of the
feeding device, preferably carbon mixed with air is fed into
the foamed slag 15. In the foamed slag, the carbon is
transformed into carbon dioxide and/or carbon monoxide, so that
foamed slag 15 is produced. By blowing in a media mixture with
the aid of the feeding device, the introduction of energy by
means of the arc 18 (see FIGURE 2) is improved. Furthermore,
losses through radiation in the electric arc furnace are
reduced.
If is possible to measure the concentration of substances, in
particular of gases, in the electric arc furnace directly or
indirectly or determine such concentrations with the aid of
models. The data on the concentration of substances, such as
for example carbon, oxygen, carbon dioxide and/or carbon
monoxide, are preferably fed to the control computer or the
signal processing device and/or the regulating device 9. The
fed data can be processed and used for determining regulating
signals 11.

PCT/EP2006/064156 - 9 -
2005P11628WOUS
In a refinement given by way of example, the electric arc
furnace shown in FIGURE 1 is formed as a three-phase AC arc
furnace. In principle, the invention can be applied to arc
furnaces of a wide variety of types, for example also to DC
furnces.
Figure 2 shows in a simplified representation an electrode 3,
3a, 3b, 3c with an arc 18 in an electric arc furnace. Arranged
on the wall 2 of the furnace casing 1 of the electric arc
furnace is a structure-borne noise sensor 4, 4a, 4b, 4c, which
is connected to a signal line 5, 5a, 5b, 5c, with the aid of
which measuring signals can be passed to a signal processing
device 8 (see Figure 1). The steel bath 16 and the foamed slag
15 in the furnace casing 1 are schematically represented.
The level of the foamed slag 15 can be determined in the signal
processing device 8 with the aid of a transfer function of the
structure-borne noise in the electric arc furnace. The
transfer function characterizes the transfer path 17,
schematically indicated in Figure 2, of the structure-borne
noise from excitation to detection.
The excitation of the structure-borne noise takes place by the
power feed at the electrodes 3, 3a, 3b, 3c in the arc 18. The
structure-borne noise, i.e. the oscillations caused by the
excitation, are transferred through the liquid steel bath 16
and/or through the foamed slag 15 that at least partially
covers the steel bath 16 to the wall 2 of the electric arc
furnace. A transfer of structure-borne noise may additionally
also take place, at least partially, through not yet melted
food material in the electric arc furnace. The detection of
the structure-borne noise takes place by structure-borne noise
sensors 4, 4a, 4b, 4c, which are arranged on the wall 2 of the
furnace casing 1 of the electric arc furnace. The structure-
borne noise sensors 4, 4a, 4b, 4c pick up oscillations on the
walls 2 of the furnace

PCT/EP2006/064156 - 10 -
2005P11628WOUS
casing 1. The structure-borne noise sensors 4, 4a, 4b, 4c are
preferably formed as acceleration sensors. The structure-borne
noise sensors 4, 4a, 4b, 4c are preferably provided above the
foamed slag zone. Structure-borne noise sensors 4, 4a, 4b, 4c
are preferably arranged on the opposite sides of the electrodes
3, 3a, 3b, 3c on the wall 2 of the electric arc furnace.
The electric sensors 13a, 13b, 13c sense current and/or voltage
signals of the electrodes 3, 3a, 3b, 3c. Current and/or
voltage signals are preferably sensed in a time-resolved
manner. The signals of the structure-borne noise sensors are
led by way of protected lines 5, 5a, 5b, 5c into an optical
device 6 (see Figure 1). The optical device 6 is preferably
arranged relatively close to the actual electric arc furnace.
The optical device 6 serves for amplifying and converting the
signals of the structure-borne noise sensors 4, 4a, 4b, 4c. In
the optical device 6, the signals are converted into optical
signals and are passed by way of an optical waveguide 7 free
from interference over comparatively longer distances, for
example 50 to 200 m, into a signal processing device 8.
In the signal processing device 8, signals are sensed and
evaluated. In the signal processing device 8, the signals are
preferably digitized at an adequately high sampling rate, for
example 6000 samples/second. The excitation signals of the
electrodes 3, 3a, 3b, 3c are preferably formed by
multiplication of the associated current signals and/or
associated voltage signals. The output signals form the
structure-borne noise signals. The following applies here to
the signals in the time domain:
(1) Y(t)-h(t) ° X(t) ,

PCT/EP2006/064156 - 11 -
2005P11628WOUS
where Y(t,) denotes a structure-borne noise signal, X(t) denotes
the power feed in the arc 18 and h(t) denotes the step
response. The variables h(t) and X(t) are linked to one
another by a convolution operator.
The transfer function H(ω) is determined in the frequency
domain:
(II) y(ω)=H(ω).x(ω) ,
where x (Ω) and y(ω) are the Fourier transforms of the
excitation and output signals.
The variables x (Ω) , y(ω) and H(Ω) are complex. To avoid
complex division, H(Ω) is calculated by way of the cross-power
spectrum:
(III) |H(ω) | = |Wxy(ω) |/Wxx(ω) ,
where WXY(Ω) denotes the cross-power spectrum and Wxx denotes
the power spectrum at the input, i.e. on the side of the
excitation.
The transfer function H(Ω) is only determined at discrete
frequencies, the discrete frequencies being multiples
(harmonics) of the fundamental frequency of the power supply to
the electrodes 3, 3a, 3b, 3c, since the excitation only takes
place by way of the fundamental wave and the harmonic waves of
the coupled power. In the case of a power supply device 12 for
the electric arc furnace that operates for example at 50 Hz,
the discrete frequencies are multiples of 100 Hz.
The transfer function H(ω) characterizes the medium in the
electric arc furnace. Therefore, the variation of the medium
over time, for example the level of the foamed slag 15, can be
determined by the change in the transfer function.

PCT/EP2006/064156 - 12 -
2005P11628WOUS
The attenuation or amplification of the transfer function
values can be used to calculate a resultant value that
correlates with the level of the foamed slag 15. This has been
confirmed in measuring experiments with a time resolution of
about 1 to 2 seconds.
The evaluation in the signal processing device 8 may be adapted
with the aid of empirical values from the operation of the
electric arc furnace. The signal sensing and evaluation and
the slag determination are performed online during operation,
so that the state signal that characterizes the slag level in
the electric arc. furnace can be used for automatically
regulating the process. The improved knowledge of the foamed
slag process, improved by the measuring techniques according to
the invention, makes improved process control and regulation
possible, leading to the following advantages:
- Increase in productivity through higher specific smelting
capacity by reducing the downtimes caused in particular by
furnace repairs.
- Reduction in the specific smelting energy while maintaining a
constant, tapping temperature.
- Reduction in the wearing of the wall by reducing the radiant
energy to the inner wall of the furnace casing 1.
- Reduction in electrode consumption.
A concept that is important for the invention can be summarized
as follows:
The invention relates to a method for determining a state
variable of an electric arc furnace, in particular for
determining the level of the foamed slag 15 in an electric arc
furnace, wherein the energy supplied to the electric arc
furnace is determined with the aid of at least one electric
sensor 13a, 13b, 13c and wherein structure-borne noise in the
form of oscillations on the electric arc furnace is measured,
the at least one

PCT/EP2006/064156 - 13 -
2005Pl1628WOUS
state variable, in particular the level of the foamed slag 1b,
being determined with the aid of a transfer function which is
determined by evaluating the measured oscillations, i.e. the
structure-borne noise, and by evaluating measured data of the
at Least one electric sensor 13a, 13b, 13c. The state of the
level of the foamed slag 15 is in this way reliably defected
and monitored over time. The level of the foamed slag 15 is
decisive for the effectiveness with which energy is introduced
into the electric arc furnace. Moreover, losses through
radiation are reduced by covering the arc 18 with the foamed
slag lb. The improved measuring method makes it possible for
the level of the foamed slag to be automatically controlled or
regulated in a reliable manner.

2005l1628 Foreign - 14 -
Patent claims
1. A method for determining at least one state variable of an
electric arc furnace with at least one electrode (3, 3a,
3b, 3c), wherein the energy supplied to the electric arc
Curnace is determined with the aid of at least one electric
sensor (13a, 13b, 13c), characterized in that structure-
borne noise oscillations on the electric arc furnace are
measured, and in that the at least one state variable is
determined with the aid of a transfer function which is
determined by evaluation of the measured structure-borne
noise oscillations and by evaluation of measured data of
the at least one electric sensor (13a, 13b, 13c) .
2. The method as claimed in patent claim 1, wherein the level
of the foamed slag (15) is determined as the state
variable.
3. The method as claimed in one of the preceding patent:
claims, wherein structure-borne noise oscillations on the
electric arc furnace are measured with the aid of at least
one acceleration sensor.
4 . The method as claimed in one of the preceding patent
claims, wherein structure-borne noise oscillations which
emanate from at least one arc (18) of the at least one
electrode (3, 3a, 3b, 3c) of the electric arc furnace arc
measured.
b. The method as claimed in one of the preceding patent
claims, wherein the transfer function is determined from an
excitation signal and from an output signal, the excitation
signal being determined by evaluating measured data of the
at least one electric sensor (13a, 13b, 13c), and the
output signal being determined by evaluating the structure-

200511628 Foreign - 14a -
borne noise oscillations measured on the electric arc
furnace.

200511628 Foreign - 15 -
6. The method as claimed in patent claim 5, wherein a current
signal is measured with the aid of the at least one
electric sensor (13a, 13b, 13c) and is used to form the
excitation signal.
7. The method as claimed in patent claim 6, wherein the
excitation signal is formed by squaring the current signal.
8. The method as claimed in one of the preceding patent
claims, wherein a voltage signal is measured with the aid
of the at least one electric sensor (13a, 13b, 13c) and is
used to form the excitation signal.
9. The method as claimed in patent claim 8, wherein the
excitation signal is formed by multiplication of the
current signal by the voltage signal.
10. The method as claimed in one of the preceding patent
claims, wherein the transfer function is determined by way
of a cross-power spectrum.
11. The method as claimed in one of the preceding patent
claims, wherein the transfer function is evaluated at at
least one discrete frequency.
12. The method as claimed in patent claim 11, wherein the at
least one discrete frequency is a multiple of the frequency
of the power feed into the arc (18).
13. The method as claimed in patent claim 11 or 12, wherein the
level of the foamed slag (15) is determined in dependence
on the change in the transfer function at the one or more
discrete frequencies.
14. A method for controlling an electric arc furnace, wherein
at 1 east one state variable of the electric arc furnace is

200511628 foreign - 15a -
determined according to a method as claimed in one of the
preceding

200511628 Foreign - 16 -
patent, claims, and wherein actuating and/or regulating
signals (11) for the electric arc furnace are determined
with the aid of the at least one specific state variable.
15. The method as claimed in patent claim 14, wherein actuating
and/or regulating signals (11) are emitted to a feeding
device of the electric arc furnace.
16. The method as claimed in patent claim 14 or 15, wherein
actuating and/or regulating signals (11) that influence the
blowing-in of oxygen are emitted.
17. The method as claimed in one of patent claims 14 to 16,
wherein actuating and/or regulating signals (11) that
influence the blowing-in of carbon are emitted.
18. The method as claimed in one of patent claims 14 to 17,
wherein actuating and/or regulating signals (11) that
influence the blowing-in of lime are emitted.
19. The method as claimed in one of patent claims 14 to 18,
wherein actuating and/or regulating signals (11) for
influencing the position of the at least one electrode (3,
3a, 3b, 3c) are emitted.
20. The method as claimed in one of patent claims 14 to 19,
wherein a neural network is used for determining the
actuating and/or regulating signals (11).
21. An electric arc furnace with a furnace casing (1) and with
at least one electrode (3, 3a, 3b, 3c), a current lead
being provided for each electrode (3, 3a, 3b, 3c),
characterized in that, to carry out a method as claimed in
one of the preceding claims, at least one electric sensor
(13a, 13b, 13c) is provided on a current lead and at least
one structure-borne noise sensor (4,

200511628 Foreign - 17 -
4a, 4b, 4c) for sensing structure-borne noise oscillations
is provided on the wall (2) of the furnace casing (1).
22. The electric arc furnace as claimed in patent claim 21,
wherein an electric sensor (13a, 13b, 13c) is provided for
each electrode (3, 3a, 3b, 3c).
23. The electric arc furnace as claimed in patent claim 21 or
22, wherein the at least one structure-borne noise sensor
(4, 4a, 4b, 4c) is formed as an acceleration sensor.
24. The electric arc furnace as claimed in one of patent claims
21 to 23, wherein a structure-borne noise sensor (4, 4a,
4b, 4c) is provided for each electrode (3, 3a, 3b, 3c).
25. The electric arc furnace as claimed in patent claim 24,
wherein the one or more structure-borne noise sensors (4,
4a, 4b, 4c) are arranged on a wall (2) of the furnace
casing (1) that, is opposite the respective electrode (3,
3a, 3b, 3c).
26. The electric arc furnace as claimed in one of patent claims
21 to 25, wherein the at least one electric sensor (13a,
13b, 13c) and the at least one structure-borne noise sensor
(4, 4a, 4b, 4c) are coupled with a signal processing device
(8) .
27. The electric arc furnace as claimed in one of patent claims
21 to 26, wherein, for coupling the at least one structure-
borne noise sensor (4, 4a, 4b, 4c) with the signal
processing device (8), at least one optical waveguide (7)
is provided.
28. The electric arc furnace as claimed in patent claim 27,
wherein the at least one structure-borne noise sensor (4,
4a, 4b, Ac) is connected to the optical waveguide (7) by

200b11628 Foreign - 17a -
way of at least one signal line (5, 5a, 5b, 5c) and by way
of an

200511628 Foreign - 18 -
optical device (6) arranged ahead of the optical waveguide
(7).
29. The electric arc furnace as claimed in patent claim 28,
wherein the at least one signal line (5, 5a, 5b, 5c) is
formed such that it is routed in a protected manner.
30. The electric arc furnace as claimed in one of patent claims
26 to 29, wherein the signal processing device (8) is
coup.l ed with a regulating device (9) for the electric arc
furnace.

The invention relates to a method for determining a state variable of an electric arc furnace, especially for determining
the level of the foamed slag (15) in an electric arc furnace. According to said method, the energy supplied to the electric arc
furnace is determined with the aid of at least one electric sensor (13a, 13b, 13c) while solid-borne noise is measured in the form of
oscillations on the electric arc furnace. The at least one state variable, particularly the level of the foamed slag (15), is determined by
means of a transfer function which is determined by evaluating the measured oscillations, i.e. the solid-borne noise, and evaluating
measured data of the at least one electric sensor (13a, 13b, 13c). The state of the level of the foamed slag (15) can thus be reliably
recognized and be monitored over time. The level of the foamed slag (15) is decisive for the effectiveness with which energy is fed
into the electric arc furnace. Furthermore, losses caused by radiation are reduced by covering the arc (18) with the foamed slag (15).
The improved measuring method allows the level of the foamed slag to be automatically controlled or regulated in a reliable manner.

Documents:

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Patent Number

270595

Indian Patent Application Number

256/KOLNP/2008

PG Journal Number

02/2016

Publication Date

08-Jan-2016

Grant Date

31-Dec-2015

Date of Filing

17-Jan-2008

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, 80333 MUNCHEN

Inventors:

#	Inventor's Name	Inventor's Address
1	DIETER FINK	BUSSARDSTR. 50 91088 BUDENREUTH
2	THOMAS MATSCHULLAT	PETER-HENLEIN-STR. 15 90542 ECKENTAL
3	DETLEF RIEGER	ALPENROSENSTR. 26 85598 BALDHAM
4	REINHARD SESSELMANN	DORFSTR. 29 95488 ECKERSDORF
5	DETLEF GERHARD	HANIKLSTR. 40 81829 MÜNCHEN

PCT International Classification Number

F27B 3/28,F27D 19/00

PCT International Application Number

PCT/EP2006/064156

PCT International Filing date

2006-07-12

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102005034379.1	2005-07-22	Germany
2	102005034409.7	2005-07-22	Germany