An electric arc furnace, a method of operating an electric arc furnace and a system for inducing vibrations

Abstract

This disclosure provides an electric arc furnace for melting metal containing material, in particular a pile of scrap, the electric arc furnace comprising a power supply (110); at least one electrode (121) being electrically connected to the power supply (110) for receiving an amount of electrical power from the power supply (110) to produce an arc; a furnace body (130) for accommodating the metal containing material; an electrode positioning system (120) to position the at least one electrode (121) with respect to the furnace body (130) and / or with respect to a melt level; and a control unit (140) to control operation of the electric arc furnace, the control unit (140) being connected to the power supply (110) and to the electrode positioning system (120) for controlling their operation; wherein the control unit (140) is configured for intermittently operating the electric arc furnace in a vibration-induction mode; wherein, in the vibration-induction mode, the control unit (140) operates the electric arc furnace to induce vibrations to the metal containing material. This disclosure further provides a method for operating an electric arc furnace and a system for inducing vibrations to metal containing material being melted in an electric arc furnace.

Description

DescriptionAn electric arc furnace, a method of operating an electric arc furnace and a system for inducing vibrationsTECHNICAL FIELD

[0001] This disclosure relates to an electric arc furnace for melting metal containing material, in particular a pile of scrap, to a method of operating an electric arc furnace for melting metal containing material, in particular a pile of scrap and to a system for inducing vibrations to metal containing material, in particular a pile of scrap, the metal containing material being melted in an electric arc furnace.BACKGROUND

[0002] An electric arc furnace may be used to melt solid matter as, e.g., ore, containing metals into desirable materials and undesirable materials using high heat. The heat is mainly generated using electric arcs which are produced between at least one electrode and, usually, the bath of material being melted within the furnace or a furnace body forming an anode. Electric arc furnaces may also be used for melting materials such as scrap steel, or for refining molten metals. To produce the arc, the at least one electrode of the electric arc furnace is usually powered by an electrical power supply.

[0003] Particularly when melting a pile of scrap within the electric arc furnace, a cave may form around the at least one electrode and the arc, that cave collapses from time to time. This may be referred to as a cave-in.

[0004] The collapsing cave may have various disadvantages affecting the productivity of the electric arc furnace. For example, it can cause an increase of the production time, an increase of losses, Health Safety Environment considerations as damaged electrodes need to be replaced under hazardous conditions, and an increased usage of consumables. The later in the melting process the cave-in happens the more impact on the process the cavein has.SUMMARY

[0005] Aspects and advantages of the disclosure will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the disclosure.

[0006] The present disclosure provides an electric arc furnace, a method of operating an electric arc furnace and a system for inducing vibrations to metal containing material being melted within an electric arc furnace so as the metal containing material is substantially continuously forced to move toward at least one electrode. Caves that are formed during the melting process may be forced to collapse at an earlier stage of forming compared to a standard operation of the electric arc furnace. When a cave collapses, gravity forces the metal containing material to fill up the cave, whereby the metal containing material is at least partially moving toward the at least one electrode.

[0007] In one example, the disclosure provides an electric arc furnace for melting metal containing material, in particular a pile of scrap. The electric arc furnace has a power supply and at least one electrode being electrically connected to the power supply for receiving an amount of electrical power from the power supply such that the at least one electrode produces an arc. The electric arc furnace further has a furnace body for accommodating the metal containing material and an electrode positioning system to position the at least one electrode with respect to the furnace body and / or with respect to a melt level. Further, the electric arc furnace includes a control unit to control operation of the electric arc furnace. The control unit is connected to the power supply and to the electrode positioning system for controlling their operation. The control unit is configured for intermittently operating the electric arc furnace in a vibration-induction mode. In the vibration-induction mode, the control unit operates the electric arc furnace to induce vibrations to the metal containing material.

[0008] In another example, the disclosure provides a method of operating an electric arc furnace for melting metal containing material, in particular a pile of scrap. The method includes accommodating metal containing material in a furnace body; supplying, via a power supply, an amount of electrical power to at least one electrode to produce an arc; positioning, via an electrode positioning system, the at least one electrode with respect to the furnace body; and controlling, via a control unit, operation of the electric arc furnace. The control unit is configured for intermittently operating the electric arc furnace in a vibration-induction mode. In the vibration-induction mode, vibrations are induced to the metal containing material.

[0009] In yet another example, the disclosure provides a system for inducing vibrations to metal containing material, in particular a pile of scrap. The metal containing material being melted in an electric arc furnace. The system includes a control unit to control operation of the electric arc furnace. The control unit is connected to a power supply for powering the electric arc furnace; and to an electrode positioning system to position at least one electrode with respect to a furnace body accommodating the metal containing material. The control unit is configured for intermittently operating the electric arc furnace in a vibration-induction mode. In the vibration-induction mode, vibrations are induced to the metal containing material.

[0010] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF DRAWINGS

[0011] A full and enabling disclosure of the present disclosure is set forth in the specification, which makes reference to the appended figures, in which:

[0012] Fig. 1 is a schematic view of an electric arc furnace according to embodiments of this disclosure.

[0013] Fig. 2 is a graph that shows schematically control of certain parameters during operation of an electric arc furnace according to embodiments of this disclosure.

[0014] Fig. 3 is a schematic view of a method of operating an electric arc furnace according to embodiments of this disclosure.DETAILED DESCRIPTION

[0015] This disclosure generally relates to an electric arc furnace which is controlled to avoid relatively large cave-ins through inducing vibrations to metal containing material. An electric arc furnace operating according to this disclosure is intermittently operated in avibration-induction mode for purposely inducing, e.g. significantly, stronger vibrations compared to a standard operating mode. Vibrations may also occur during operation of an electric arc furnace of the prior art, e.g. due to cave-ins or other reasons arising from the standard operation. As used herein, when it is referred to the induction of vibrations, typically it is referred to the vibration-induction mode that is used to purposely induce relatively strong vibrations. In the vibration-operation mode, the electric arc furnace is typically operated in a manner that differs from the standard operating mode. A cave collapses at least partially due to the induced vibrations. In some examples, the electric arc furnace is controlled to induce the vibrations to the metal containing material by an arc.

[0016] In general, this disclosure describes an electric arc furnace for melting metal containing material, in particular a pile of scrap. As used herein, the term "electric arc furnace" may refer to an AC-electric arc furnace being operated by an alternating current and / or a DC- electric arc furnace being operated by a direct current. The electric arc furnace may be used for melting the metal containing material, such as scrap steel.

[0017] The electric arc furnace includes a power supply. The power supply may include a power source such as an on-site generator, a utility grid and / or alike. The on-site generator may include a diesel power plant, a coal-fired power plant, a renewable energy power plant and / or similar. The power supply may include power electronics, one or more inverters, a transformer and / or a reactor. In some embodiments, the power source may be connected in series with the reactor and the transformer.

[0018] The electric arc furnace further includes at least one electrode. The electrode may be referred to as a smelting electrode. The electrode may be a graphite electrode. The at least one electrode is electrically connected to the power supply. The power supply provides an amount of electrical power to the at least one electrode such that the at least one electrode produces an arc. The electric arc furnace may include more than one electrode. In particular, an AC-electric arc furnace may include at least three electrodes, in some examples at least six electrodes. In embodiments, a DC-electric arc furnace may include more than one electrode, in particular more than two electrodes, in some examples more than three electrodes, such as four electrodes or five electrodes.

[0019] Further, the electric arc furnace includes a furnace body for accommodating the metal containing material. Typically, depending on the type of the electric arc furnace (e.g. AC- electric arc furnace or DC-electric arc furnace), the furnace body and / or the metalcontaining material act as an anode during operation of the electric arc furnace, while the at least one electrode typically acts as a cathode.

[0020] To position the at least one electrode with respect to the furnace body, the electric arc furnace includes an electrode positioning system. Typically, the electrode positioning system may include hydraulics, a motor, e.g. a linear motor and / or a servomotor, and / or similar for lifting or lowering the at least one electrode. Each electrode may be lifted or lowered independently from another. During operation of the electric arc furnace, the at least one electrode may be positioned with respect to a melt level. The melt level may substantially continuously be changed during operation of the electric arc furnace. In particular, when the metal containing material is melted, the melt level changes.

[0021] Operation of the electric arc furnace is controlled by a control unit. The control unit may be a single component or may include a plurality of units controlling mutually and / or individually operation of the electric arc furnace. The control unit is connected to the power supply and to the electrode positioning system to control their operation.

[0022] The control unit is configured for intermittently operating the electric arc furnace in a vibration-induction mode. According to an aspect, the vibration-induction mode is a dedicated mode of operation, and the controller is configured to enter and exit this dedicated mode of operation.

[0023] As used herein, the term "intermittently" may include entering and exiting the vibrationinduction mode multiple times during operation, so that the electric arc is operated repeatedly in vibration-induction mode, during short intervals interspersed within another (non-vibration-induction) operation mode. There may be a plurality of vibration-induction mode intervals, and the duration of a vibration-induction mode interval may be shorter than the surrounding intervals of another operation more. Thereby, the term "intermittently" may include, e.g., operating the electric arc furnace in the vibrationinduction mode for less than half of the operation time between a bore-in of the at least electrode and completion of the melting process, i.e. when the metal containing material is entirely in a melted condition, in particular at most a third of the operation time between a bore-in of the at least electrode and completion of the melting process. The term "intermittently" may also refer to a periodic operation of the electric arc furnace in the vibration-induction mode, e.g., within one or more steps of the melting process.

[0024] In the vibration-induction mode, the control unit operates the electric arc furnace to induce vibrations to the metal containing material. Operating an electric arc furnace according to this disclosure may include deliberately increasing vibration temporarily such that a cave or caves in the metal containing material, in particular in the scrap pile, are forced to substantially permanently collapse. By doing this, no large caves can be established. In other words, compared to a standard operating mode of the electric arc furnace, significantly stronger vibrations are purposely induced in the vibration-induction mode.

[0025] Embodiments of this disclosure may enable a reduced time of the melting process thereby reducing costs, safer operation of the electric arc furnace, reduced energy consumption both for electrical and chemical energy, reduced electrode wear as an oxidation time may be reduced and breakage of the electrode due to mechanical loads acting on the electrode particularly at large cave-ins may be avoided and / or a higher yield at the conversion of the metal containing material to, e.g., steel. Further, the scatter of the duration of the melting process may be reduced.

[0026] In some examples, the electric arc furnace may include a shaking arrangement for inducing vibrations to the metal containing material by inducing mechanically vibrations at least to the furnace body.

[0027] In embodiments, in the vibration-induction mode, the control unit may operate the electrode positioning system and the power supply such that the arc produced by the at least one electrode induces the vibrations to the metal containing material. Such embodiments may be advantageous as the vibration-induction mode may be implemented to the operation of the electric arc furnace without the need of costly adaptions of the electric arc furnace. Here, the vibration-induction mode is a dedicated mode that can be specifically enabled and disabled. In embodiments, the vibration-induction mode is enabled by modifying operation parameters in accordance with the vibration-induction mode, whereby the operation parameters are set differently (according to different prescriptions) than in another (normal) operation mode. The operation parameters may for example include setpoints for current, voltage, arc length, or parameters correlated with these. In embodiments, dedicated vibration-induction mode prescriptions for setting operation parameters may be activated, the vibration-induction mode prescriptions being different than those in another (normal) operation mode. In an embodiment, a vibration-induction mode may be set to TRUE, thereby activating the vibration-induction mode prescriptions. Inembodiments, when entering and exiting the vibration-induction mode, the operation parameters may be changed in a stepwise manner.

[0028] An instable arc typically induces significantly more vibrations than a stable arc, i.e., the more an arc "wriggles", the more vibrations are induced. For example, the arc may be destabilized by reducing an amount of current flowing through the at least one electrode. In other examples, the arc may be destabilized by increasing an arc length (e.g., compared to the modes of operation directly before and after the vibration-inducing mode of operation). Such embodiments may reduce the likelihood of a loss of arc event.

[0029] According to embodiments, the power supply may be configured to allow independent control of a first control variable correlated to a current, and of a second control variable correlated to a voltage. In particular, as the voltage is typically controlled by raising and lowering of the at least one electrode by the electrode positioning system, the power supply may allow control of the first control variable correlated to the current independent from the second control variable correlated to the voltage. In some examples, the power supply may include a power electronic converter. In embodiments, the first control variable and / or the second control variable may be correlated to an impedance.In the vibration-induction mode, the control unit may operate the power supply and / or the electrode positioning system to increase the voltage while not decreasing the current or vice versa. In the vibration-induction mode, the control unit may operate the electrode positioning system to increase the arc length of the at least one electrode. As used herein, "increasing an arc length" may refer to an increase compared to a standard operating mode. Typically, the arc length may be increased by increasing a vertical distance between the melt level and the at least one electrode. The arc length may be increased by lifting the at least one electrode by the electrode positioning system. Before and after (inbetween) the vibration-induction mode, the return to the standard operating mode, i.e., a mode different from the vibration-induction mode.

[0030] In embodiments, the arc length and / or the current may at least partially substantially continuously be adapted in the vibration-induction mode. As used herein, the term "at least partially adapted" may refer to at least one time interval in which the vibrationinduction mode is activated. For example, the control unit may be configured to operate the power supply and / or the electrode positioning system to alter the arc length of the at least one electrode. The current may remain constant. According to embodiments, in thevibration-induction mode, the electrode positioning system may be configured to lift and lower the at least one electrode substantially throughout the entire respective time interval in which the vibration-induction mode is activated. Such embodiments may induce vibrations with various frequencies, thereby increasing the likelihood of exciting the metal containing material such that the cave collapses. In particular, by sweeping or otherwise continuously modifying the operation parameters, such embodiments may induce vibrations with various frequencies, and possibly also achieve excitation of the metal containing material at a resonance frequency. By operating at resonance, eigenfrequencies of the metal containing material can be triggered to even more effectively force the cave to collapse.

[0031] The resonance frequency may be detected by adapting the arc length and / or the current in the vibration-induction mode and measuring vibrations, either directly or indirectly for example via an electrical signal indicative of vibrations, for detecting the resonance of the metal containing material. According to embodiments, the operation parameters may be tuned to values at which a resonance is detected, for operating at the resonance condition.

[0032] According to embodiments, a closed-loop control may be provided for tuning the operation parameters towards the resonance condition. The closed-loop control may include adapting the operation parameters - for example the arc length and / or the current in the vibration-induction mode, detecting a resonance condition indicative of a resonance of the metal containing material, and adjusting the operation parameters for operation at the resonance condition. The closed-loop control thereby aims to adjust the operation parameters towards the resonance condition. For example, if / as long as the resonance is detected, the closed-loop control may be configured to control the arc-length and / or the current to substantially remain constant.

[0033] In addition, the arc may be produced by supplying electrical power with an electrical frequency of the detected resonance to the at least one electrode. The electrical power with the electrical frequency of the detected resonance may be, for example, superimposed on a base power supplied to the electrode, e.g., from an AC or DC power source and powering the electrode.

[0034] In embodiments, the control unit may be configured to start the vibration-induction mode when the at least one electrode is at a predetermined height with respect to the furnace body and / or the melt level. According to embodiments, the control unit may be configuredto start the vibration-induction mode when the voltage is at a certain value. In embodiments, the control unit may be configured to start the vibration-induction mode when a certain amount of electrical energy has been applied to the electric arc furnace during a single melting process. A melting process may include steps like a bore-in of the at least one electrode, meltdown of the metal containing material and may end when substantially the entire metal containing material to be melted is in a melted condition. In embodiments, the control unit may be configured to start the vibration-induction mode when a current fluctuation and / or a voltage fluctuation drop below a certain value.

[0035] According to embodiments, the control unit may be configured to stop the vibrationinduction mode after a predetermined time of operation and / or when a predetermined amount of electrical energy (e.g. in MWh) from the power source is detected and / or when a predetermined arc power stability indicator is detected. "Stopping the vibration-induction mode" may refer to a stop in terms of for the entire melting process.

[0036] The arc power stability indicator may be correlated to the current fluctuation, to the voltage fluctuation, to acoustic signals, to vibrations of the furnace body and / or to a temperature within the furnace body. For example, harmonics, e.g. of voltage and / or current, may indicate, in particular a number of harmonics, more particularly a number of atypical harmonics, a stability of the arc. The acoustic signals may refer to a sound indicating that a cave is collapsing. The temperature typically increases towards end of the melting process. The arc power stability indicator may be correlated to an absolute value and / or to a relative value, e.g., for a certain time interval.

[0037] In embodiments, the control unit may operate the electric arc furnace in the vibrationinduction mode for at most 5 minutes within 10 minutes, in particular at most 4 minutes within 10 minutes, preferably at most 3 minutes within 10 minutes. According to embodiments, the control unit may operate the electric arc furnace in certain melting process steps in the vibration-induction mode for at least 1 second, in particular at least 3 seconds in the vibration induction mode. Such embodiments may avoid unfavorable feedback to the utility grid, in particular flicker.

[0038] According to embodiments, the control unit may be configured to operate only a single electrode of the at least one electrode, in particular for only two of the at least one electrode, at the same time in the vibration-induction mode.-io-

[0039] In some embodiments, the control unit may operate the electric arc furnace in the vibration-induction mode in a pattern. As used herein, "a pattern" may refer to a pattern of inducing the vibrations to the metal containing material. For example, the control unit may be configured to induce the vibrations by operating the power supply and / or the electrode positioning system to increase the voltage while not decreasing the current or vice versa for a first electrode; and the electrode positioning system to increase an arc length of the first electrode. Subsequently, the control unit may be configured to induce the vibrations by operating the power supply and / or the electrode positioning system to increase the voltage while not decreasing the current or vice versa for a second electrode; and the electrode positioning system to increase an arc length of the second electrode. In some embodiments, the control unit operates the electric arc furnace such that the first electrode and the second electrode both provide an increased arc length at the same time or alternating, e.g., depending on a process step of the melting process.

[0040] According to embodiments, the control unit may operate the electric arc furnace to induce the vibrations according to a scheme being based on artificial intelligence. For example, artificial intelligence may determine when to start the vibration-induction mode, when to stop vibration-induction mode and / or the pattern, e.g., based on a plurality of control parameters, such as parameters being correlated to voltage and / or current, acoustic signals and alike as also described within this disclosure. Such embodiments may include a learning process of the control unit.

[0041] In embodiments, the electric arc furnace may include at least three electrodes and the power supply may supply electrical power to the at least three electrodes such that each of the three electrodes receives a phase. Each of the phases may be controllable by current and voltage independently from one another.

[0042] According to embodiments, the control unit is configured to reduce the amount of electrical power received by at least one electrode that is not operated in the vibrationinduction mode, e.g. in an energy-saving mode.

[0043] In another aspect, a method of operating an electric arc furnace for melting metal containing material, in particular a pile of scrap, is provided. The method includes accommodating metal containing material in a furnace body; supplying, via a power supply, an amount of electrical power to at least one electrode to produce an arc; positioning, via an electrode positioning system, the at least one electrode with respect to the furnacebody and / or with respect to a melt level; and controlling, via a control unit, operation of the electric arc furnace; wherein the control unit is configured for intermittently operating the electric arc furnace in a vibration-induction mode; wherein, in the vibration-induction mode, vibrations are induced to the metal containing material.

[0044] In embodiments, in the vibration-induction mode the electrode positioning system and the power supply may be operated such, via the control unit, that the arc produced by the at least one electrode induces the vibrations to the metal containing material.

[0045] According to embodiments, supplying, via a power supply, an amount of electrical power to the at least one electrode to produce an arc may include: independent control of a first control variable correlated to a current, and of a second control variable correlated to a voltage. In the vibration-induction mode, the method may include operating, via the control unit, the power supply to increase the voltage while not decreasing the current or vice versa; and also, may include operating, via the control unit, the electrode positioning system to increase an arc length of the at least one electrode.

[0046] In embodiments, the arc length and / or the current may substantially continuously be adapted in the vibration-induction mode.

[0047] According to embodiments, the vibration-induction mode may be activated when the at least one electrode is at a predetermined height with respect to the furnace body and / or with respect to the melt level.

[0048] In embodiments, the vibration-induction mode may be deactivated after a predetermined time of operation and / or when a predetermined amount of electrical energy from the power source is detected and / or when a predetermined arc power stability indicator is detected.

[0049] According to embodiments, the electric arc furnace may be operated in the vibrationinduction mode for at most 5 minutes within 10 minutes, in particular at most 4 minutes within 10 minutes, preferably at most 3 minutes within 10 minutes. In embodiments, the vibration-induction mode may be activated for at least 1 second, in particular at least 3 seconds within 30 seconds of a process step of the melting process.

[0050] In embodiments, the vibration-induction mode may be activated for only a single electrode of the at least one electrode, in particular for only two of the at least one electrode, at the same time.

[0051] According to embodiments, the power supply may supply electrical power to at least three electrodes such that each of the three electrodes receives a phase.

[0052] In embodiments, the method may further include reducing the amount of electrical power received by an electrode that is not operating in the vibration-induction mode.

[0053] According to another aspect, a system for inducing vibrations to metal containing material, in particular a pile of scrap, is provided. The metal containing material being melted in an electric arc furnace. The system includes a control unit to control operation of the electric arc furnace. The control unit is connected to a power supply for powering the electric arc furnace. The control unit is further connected to an electrode positioning system to position at least one electrode with respect to a furnace body accommodating the metal containing material and / or with respect to a melt level. The control unit is configured for intermittently operating the electric arc furnace in a vibration-induction mode. In the vibration induction mode, vibrations are induced to the metal containing material.

[0054] Reference now will be made in detail to embodiments of the disclosure, some examples of which are illustrated in the drawings. Each example may be provided by way of explanation of the disclosure, not limitation of the disclosure. For instance, features illustrated or described as part of embodiments may be used with other embodiments to yield still further embodiments. The drawings may not be true-to-scale.

[0055] Fig. 1 schematically shows an electric arc furnace and a system for inducing vibrations to metal containing material according to embodiments of this disclosure.

[0056] The electric arc furnace may be used to melt metal containing material, such as a pile of scrap. The electric arc furnace includes a power supply 110, at least one electrode 121. The electrode is electrically connected to the power supply 110 and receives an amount of electrical power from the power supply 110. The power supply includes a power source 111, such as a utility grid or similar. The electric arc furnace further includes a furnace body 130 accommodating the metal containing material and an electrode positioning system 120 to position the electrode with respect to the furnace body 130.

[0057] A control unit 140 is provided for controlling operation of the electric arc furnace. The control unit 140 is connected to the power supply 110 and to the electrode positioning system 120 to control their operation.

[0058] For example, the control unit 140 may control the power supply 110 to provide an amount of electrical power to the electrode 121 and may control the electrode positioning system 120 such that the electrode 121 ignites an arc between the electrode 121 and the furnace body 130, the metal containing material and / or a fluid, such as a melt or a slag being accommodated by the furnace body 130.

[0059] A melting process may include filling of the furnace body 130 with the metal containing material, positioning the electrode 121 vertically over the furnace body 130, bore-in of the electrode 121 into the metal containing material and the furnace body 130, melting of the metal containing material. The arc melts the metal containing material. Typically, in particular after the bore-in, the metal containing material is melted from the bottom to the top, i.e. starting from a ground of the furnace body 130. This may lead to a cave.

[0060] The control unit 140 intermittently operates the electric arc furnace in a vibration-induction mode. In the vibration-induction mode, vibrations are induced to the metal containing material.

[0061] For example, the vibrations may force the metal containing material to move at least partially in a direction towards the electrode 121. In other words, instead of relying only on gravity, which gravity forces, e.g., the cave to collapse as metal containing material that initially supported other metal containing material above has been melted, the vibrations force the metal containing material to move up / fall down.

[0062] This may be achieved by inducing the vibrations mechanically to the metal containing material, for example by shaking the furnace body 130 with a shaking arrangement. Alternatively or additionally, the control unit 140 may operate the electrode positioning system 120 and the power supply 110 such that the arc produced by the electrode 121 induces the vibrations to the metal containing material.

[0063] In order to induce the vibrations by the arc, the power supply 110 allows for independent control of a first control variable correlated to a current (also referred to as arc current) and of a second control variable correlated to a voltage (also referred to as arc voltage), e.g., by including a power electronic converter 112. The power supply 110 may further include atransformer defining a low-voltage side towards the electrode 121 and a high-voltage side towards the power source 111. The power electronic converter 112 may be arranged on the high-voltage side and / or on the low-voltage side of the transformer. In the vibrationinduction mode, the control unit 140 operates the power supply 110 and / or the electrode positioning system to increase the voltage while not decreasing the current and the electrode positioning system 120 to increase an arc length of the electrode 120. Thereby, the vibrations are induced to the metal containing material without risking a loss of arc event which would lead to a reduced efficiency of the melting process.

[0064] Fig. 2 shows a graph that illustrates schematically control of certain parameters during operation of an electric arc furnace according to embodiments of this disclosure.

[0065] The electric arc furnace may be an electric arc furnace as described in conjunction with Fig. 1. The electric arc furnace may be embodied such that the control unit 140 operates the electrode positioning system 120 and the power supply 110 such that the arc produced by the at least one electrode 121 induces the vibrations to the metal containing material.

[0066] An x-axis 201 may refer, e.g., to a time, a first y-axis 202 may refer to a voltage and a second y-axis 203 may refer to a current.

[0067] The electric arc furnace includes three electrodes 121, namely a first electrode, a second electrode and a third electrode. The electric arc furnace may include any other number of electrodes 121.

[0068] The electric arc furnace may be, e.g. an AC-electric arc furnace. The first electrode may receive a first phase, the second electrode may receive a second phase and the third electrode may receive a third phase. Each phase includes an arc voltage 211, 212, 213 and an arc current 214, 215, 216. The arc voltage 211, 212, 213 is illustrated in Fig. 2 as a phase- to-phase voltage.

[0069] The control unit 140 controls the power supply 110 and the electrode positioning system 120 to set the arc voltage 211, 212, 213 and the arc current 214, 215, 216.

[0070] The electric arc furnace may be a DC-electric arc furnace. The arc voltages 211, 212, 213 and the arc currents 214, 215, 216 may in that case, similarly as with the AC-electric furnace, each refer to a single electrode.

[0071] In a first section 221, the control unit 140 may operate the electrode positioning system 120 and the power supply 110 to conduct the bore-in. In some examples, the vibrationinduction mode is not being used during the bore-in of the electrodes 121.

[0072] Subsequently, in a second section 222, the meltdown of the metal containing material begins or continues. The control unit 140 operates the electric arc furnace intermittently in the vibration-induction mode.

[0073] The control unit 140 starts the vibration-induction mode at start point 224. Start point 224 may refer to the time when the first electrode is at a predetermined height with respect to the furnace body and / or with respect to a melt level. Start point 224 may refer to the time when a certain amount of energy has been applied to the electric arc furnace. In some embodiments, start point 224 may be determined to be that moment when current fluctuations of arc current / -s 214, 215, 216 and / or voltage fluctuations of arc voltage / -s 211, 212, 213 drop below a certain value. The certain value may be an absolute value for a certain time interval, e.g. an average for the time interval. The certain value may be a relative value. The relative value may refer to the fluctuations of a certain time interval compared to the fluctuations of the previous time interval or similar.

[0074] In the vibration-induction mode, the control unit 140 controls the electrode positioning system 120 to raise the first electrode. A distance between the ground of the furnace body 130 and the bottom end of the first electrode increases. Consequently, the arc voltage 211 increases. As it can be seen from Fig. 2, the arc current 214 being also correlated to the first electrode does not decrease. This reduces the risk of a loss of arc event.

[0075] During a time interval 223 of, e.g., 15 to 25 seconds, the vibrations are induced to the metal containing material by the arc that is established by the first electrode. The second electrode and the third electrode may be controlled to continue operation regularly.

[0076] After the time interval 223, the control unit 140 returns to a standard-operating mode and the first electrode is lowered. The arc voltage 211 decreases. The arc current 214 substantially remains constant.

[0077] Subsequently, the control unit 140 returns to the vibration-induction mode by controlling the electrode positioning system 120 to raise the second electrode. A distance between the ground of the furnace body 130 and the bottom end of the second electrode increases. Consequently, the arc voltage 212 increases. As it can be seen from Fig. 2, the arc current215 being also correlated to the second electrode does not decrease. The arc length being correlated to the second electrode is substantially continuously adapted in the vibrationinduction mode. The control unit 140 then operates the electric arc furnace to return to the standard operating mode.

[0078] Subsequently, the control unit 140 returns to the vibration-induction mode by controlling the electrode positioning system 120 to raise the third electrode. A distance between the ground of the furnace body 130 and the bottom end of the third electrode increases. Consequently, the arc voltage 213 increases. As it can be seen from Fig. 2, the arc current216 being also correlated to the third electrode does not decrease.

[0079] In some embodiments, the control unit 140 operates the electric arc furnace intermittently in the vibration-induction mode in a pattern. The pattern may be used to determine when to start the vibration-induction mode, when to operate one or more electrodes in the vibration-induction mode, for which time interval to operate the one or more electrodes in the vibration-induction mode, when to end intermittently operating the electric arc furnace in the vibration-induction mode, a number of electrodes being used for inducing the vibrations at the same time and / or alike. The pattern may be a periodical pattern. The pattern may be based on artificial intelligence. For example, the control unit 140 may be configured to adapt the pattern based on artificial intelligence and process parameters, such as acoustic signals, temperature, arc current parameters and / or arc voltage parameters such as fluctuations or alike, and / or similar. The process parameters may be correlated to one or more previous melting processes.

[0080] As it is shown in Fig. 2, the control unit 140 operates the electric arc furnace intermittently in the vibration-induction mode according to a pattern. For example, a time interval between two phases of operating the electric arc furnace in the vibration-induction mode may increase and / or decrease towards the end of the graph.

[0081] In embodiments, the control unit 140 may reduce the amount of electrical power received by at least one electrode that is not operated in the vibration-induction mode. For example, the amount of power received by the second electrode and / or the amount of power received by the third electrode may be reduced when the control unit 140 controls the electrode positioning system 120 and the power supply 110 to increase the arc voltage 211 being correlated to the first electrode.

[0082] The control unit 140 ends the vibration-induction mode at end point 225. The end point 225 may refer to a time when a predetermined time of operation is elapsed. The end point 225 may refer to the time when a certain amount of energy has been applied to the electric arc furnace. In some examples, an arc power stability indicator may be detected in order to determine the end point 225. The arc power stability indicator may be correlated to a temperature within the furnace body 130 or, e.g., to a collapsing cave and / or to a number of collapsed caves.

[0083] Fig. 3 shows schematically a method of operating an electric arc furnace according to embodiments of this disclosure.

[0084] The method is used for meting metal containing material, in particular a pile of scrap. The method includes accommodating the metal containing material in a furnace body 310, supplying, via a power supply, an amount of electrical power to at least one electrode to produce an arc 320, positioning, via an electrode positioning system, the at least one electrode with respect to the furnace body 330 and / or with respect to a melt level; and controlling, via a control unit, operation of the electric arc furnace 340. The control unit intermittently operates the electric arc furnace in a vibration-induction mode 350 such that vibrations are induced to the metal containing material.

[0085] In some embodiments, the method may include to reduce the amount of electrical power received by an electrode that is not operating the vibration-induction mode 360.

[0086] Thus, an electric arc furnace for melting metal containing material, in particular a pile of scrap, a method of operating an electric arc furnace for melting metal containing material, in particular a pile of scrap and a system for inducing vibrations to metal containing material, in particular a pile of scrap, the metal containing material being melted in an electric arc furnace have been presented in the foregoing description with reference to specific examples. It is to be understood that various aspects disclosed herein may be combined in different combinations than the specific combinations presented in the accompanying drawings. It is appreciated that various modifications to the referenced examples may be made without departing from the scope of the disclosure and the following claims.

Claims

Claims1. An electric arc furnace for melting metal containing material, in particular a pile of scrap, the electric arc furnace comprising a power supply (110); at least one electrode (121) being electrically connected to the power supply (110) for receiving an amount of electrical power from the power supply (110) to produce an arc; a furnace body (130) for accommodating the metal containing material; an electrode positioning system (120) to position the at least one electrode (121) with respect to the furnace body (130) and / or with respect to a melt level; and a control unit (140) to control operation of the electric arc furnace, the control unit (140) being connected to the power supply (110) and to the electrode positioning system (120) for controlling their operation; wherein the control unit (140) is configured for intermittently operating the electric arc furnace in a vibration-induction mode; wherein, in the vibration-induction mode, the control unit (140) operates the electric arc furnace to induce vibrations to the metal containing material.

2. The electric arc furnace according to claim 1, wherein, in the vibration-induction mode, the control unit (140) operates the electrode positioning system (120) and the power supply (110) such that the arc produced by the at least one electrode (121) induces the vibrations to the metal containing material.

3. The electric arc furnace according to claim 2, wherein the power supply (110) is configured to allow independent control of a first control variable correlated to a current, and of a second control variable correlated to a voltage; in particular, wherein, in the vibration-induction mode, the control unit (140) operates the power supply (110) and / or the electrode positioning system (120) to increase the voltagewhile not decreasing the current or vice versa; and in particular, wherein, in the vibration-induction mode, the control unit (140) operates the electrode positioning system (120) to increase an arc length of the at least one electrode (121).

4. The electric arc furnace according to claim 3, wherein the arc length and / or the current are at least partially substantially continuously adapted in the vibrationinduction mode.

5. The electric arc furnace according to any of claims 2 - 4, wherein the control unit (140) is configured to start the vibration-induction mode when the at least one electrode (121) is at a predetermined height with respect to a melt level and / or the furnace body (130).

6. The electric arc furnace according to any of claims 2 - 5, wherein the control unit (140) is configured to end intermittently operating the electric arc furnace in the vibration-induction mode after a predetermined time of operation and / or when a predetermined amount of electrical energy provided by the power supply (110) is detected and / or when a predetermined arc power stability indicator is detected.

7. The electric arc furnace according to any of claims 2 - 6, wherein the control unit (140) operates the electric arc furnace in the vibration-induction mode for at most 5 minutes within 10 minutes, in particular at most 4 minutes within 10 minutes, preferably at most 3 minutes within 10 minutes.

8. The electric arc furnace according to any of claims 2 - 7, wherein the control unit (140) is configured to operate only a single electrode of the at least one electrode (121), in particular for only two of a plurality of electrodes (121), at the same time in the vibration-induction mode.

9. The electric arc furnace according to any of claims 2 - 8, wherein the electric arc furnace comprises at least three electrodes; and wherein the power supply (110)supplies electrical power to the at least three electrodes such that each of the three electrodes receives a phase.

10. The electric arc furnace according to any of claims 2 - 9, wherein the control unit (140) is configured to reduce the amount of electrical power received by at least one electrode that is not operated in the vibration-induction mode.

11. A method of operating an electric arc furnace for melting metal containing material, in particular a pile of scrap, comprising accommodating the metal containing material in a furnace body (310); supplying, via a power supply, an amount of electrical power to at least one electrode to produce an arc (320); positioning, via an electrode positioning system, the at least one electrode with respect to the furnace body (330); and controlling, via a control unit, operation of the electric arc furnace (340); wherein the control unit is configured for intermittently operating the electric arc furnace in a vibration-induction mode (350); wherein, in the vibration-induction mode, vibrations are induced to the metal containing material.

12. The method of operating an electric arc furnace according to claim 11, wherein, in the vibration-induction mode the electrode positioning system and the power supply are operated such, via the control unit, that the arc produced by the at least one electrode induces the vibrations to the metal containing material.

13. The method of operating an electric arc furnace according to claim 12, wherein supplying, via a power supply, an amount of electrical power to the at least one electrode to produce an arc includes:independent control of a first control variable correlated to a current, and of a second control variable correlated to a voltage; in particular, wherein the method further comprises, in the vibration-induction mode, operating, via the control unit, operating the power supply to increase the voltage while not decreasing the current or vice versa; and in particular, wherein the method further comprises, in the vibration-induction mode, operating, via the control unit, the electrode positioning system to increase an arc length of the at least one electrode; and in particular, wherein the arc length and / or the current are at least partially substantially continuously adapted in the vibration-induction mode.

14. The method of operating an electric arc furnace according to any of claims 12 - 13, wherein the vibration-induction mode is activated when the at least one electrode is at a predetermined height with respect to the furnace body.

15. The method of operating an electric arc furnace according to any of claims 12 - 14, wherein the control unit is configured to end intermittently operating the electric arc furnace in a vibration-induction mode after a predetermined time of operation and / or when a predetermined amount of electrical energy from the power source is detected and / or when a predetermined arc power stability indicator is detected.

16. The method of operating an electric arc furnace according to any of claims 12 - 15, wherein the electric arc furnace is operated in the vibration-induction mode for at most 5 minutes within 10 minutes, in particular at most 4 minutes within 10 minutes, preferably at most 3 minutes within 10 minutes.

17. The method of operating an electric arc furnace according to any of claims 12 - 16, wherein the vibration-induction mode is activated for only a single electrode of the at least one electrode, in particular for only two of a plurality of electrodes, at the same time.

18. The method of operating an electric arc furnace according to any of claims 12 - 17, wherein the power supply supplies electrical power to at least three electrodes such that each of the three electrodes receives a phase.

19. The method of operating an electric arc furnace according to any of claims 12 - 18, wherein the method further comprises: reducing the amount of electrical power received by at least one electrode that is not operated in the vibration-induction mode (360).

20. A system for inducing vibrations to metal containing material, in particular a pile of scrap, the metal containing material being melted in an electric arc furnace, the system comprising: a control unit (140) to control operation of the electric arc furnace; the control unit being connected to a power supply (110) for powering the electric arc furnace; and to an electrode positioning system (120) to position at least one electrode (121) with respect to a furnace body (130) accommodating the metal containing material and / or with respect to a melt level; wherein the control unit (140) is configured for intermittently operating the electric arc furnace in a vibration-induction mode; wherein, in the vibration-induction mode, vibrations are induced to the metal containing material.

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