Method for supplying power to a furnace for melting and / or heating metallic materials and corresponding device - Patents.com

Abstract

The present invention relates to a method for supplying power to a furnace (100) for melting and / or heating a metallic material (M), the method comprising: supplying a utility voltage (Ur) and a utility current (Ir) having a predetermined utility frequency (fr), converting the utility voltage (Ur) and the utility current (Ir) into selectively settable alternating secondary voltage (Us) and secondary current (Is), rectifying the secondary voltage (Us) and secondary current (Is), converting a direct intermediate voltage (Ui) and an intermediate current (Ii) into selectively settable alternating supply voltage (Ua) and supply current (Ia), and supplying the supply voltage (Ua) and supply current (Ia) to a number of electrodes (102) of the furnace (100). The present invention further relates to an apparatus (10) for supplying power to a furnace (100) for melting and / or heating a metallic material (M).

Description

[Technical field]

[0001] The present invention relates to a method for supplying power to a furnace for melting and / or heating metallic materials, and to a corresponding device for supplying power.

[0002] The invention is applicable in the field of steel making and other metal processing fields, for example electric furnaces such as electric arc furnaces, ladles, submerged arc furnaces, melting or refining furnaces. [Background technology]

[0003] Plants for heating and / or melting metallic materials are known, which comprise an electric furnace and one or more feed devices connected to an electrical grid.

[0004] The electric furnaces of the above mentioned types may be selected from the group comprising electric arc furnaces, submerged arc furnaces, ladle furnaces or generally melting furnaces, smelting furnaces, heating furnaces etc.

[0005] For example, the melting cycle of an arc melting furnace includes the following steps: - charging the furnace with metal material (usually scrap) by removing it from the top using baskets or by using a continuous charging conveyor system to which scrap and / or reduced iron (DRI) are fed; - lowering the electrode towards the metal material until a melting electric arc is generated between the end of the electrode and the material to be melted; - boring the layer of metallic material through the electric arc generated, during which melting of the scrap begins; - forming a bath of molten metal; - refining the molten material in order to adjust the temperature of the bath and the carbon content of the steel and / or to define the desired composition of the steel by adding chemical compounds; - Removing the molten material from the electric furnace after slag has formed, if any.

[0006] The refining steps of the material may substantially correspond to those occurring in the ladle furnace, for the final adjustment of the chemical composition of the steel used in the process downstream of removal.

[0007] During the boring process, the electric arc between the electrode and the charge of metallic material exhibits a very unstable behavior that gradually improves as the melting progresses, which can cause rapid and sudden fluctuations in the absorbed power, which can also have negative effects on the power grid, for example causing the so-called flicker phenomenon and damaging user equipment powered by the grid.

[0008] In fact, during boring and melting, the unmelted accumulated scrap breaks up in the vicinity of the electrodes, creating a short circuit condition which corresponds to a significant reduction in the available power required for the melting operation and a rapid increase in the current absorbed by the power grid.

[0009] As melting progresses, i.e. when the arc is adequately shielded by a solid material or foamy liquid (slag), the behavior of the electric arc becomes more and more stable, which allows the arc length to be increased and therefore the thermal power transferred to the material being melted to increase. The voltage and length of the arc are adjusted according to the melting process in order to prevent excessive wear of the refractory material.

[0010] In order to reduce undesirable effects on the power grid, it is known to perform rapid adjustments of the power supplied to the furnace by continuous adjustment of at least the position of the electrodes and the parameters of the voltage and current applied to the electrodes.

[0011] In particular, the voltage and current parameters, and the position of the electrodes are appropriately adjusted at each step of the process.

[0012] In plants for heating and / or melting such metallic materials, electric furnaces are usually supplied with three-phase AC power provided by the public power grid.

[0013] 1 shows a schematic of the baseline or setpoint electrical parameters supplied to the electrodes as a three-basket melting cycle proceeds in which a first basket of metallic material is charged to the furnace and melted, a second basket of metallic material is charged and melted, a third basket of metallic material is charged and the resulting liquid material is melted in its entirety, and then refined.

[0014] It is noted that, in general, the electrical parameters of current I, voltage U and power P are varied, but the supply frequency f of the electrodes during the dissolution cycle remains constant and is generally equal to the line frequency.

[0015] Generally, melting and / or heating plants require high furnace power supplies, for example the required power supplies can be several tens of megawatts (MW), between 5 MW and 300 MW depending on the size of the plant and / or furnace in particular.

[0016] As mentioned above, known power supplies have drawbacks related to wide variations in the instantaneous power absorption drawn from the grid, especially those caused by scrap movements during boring, which can lead to short circuits of phases.

[0017] If the power absorption by the furnace during boring is variable, fluctuations in the utility voltage occur, causing the so-called flicker phenomenon. For the same frequency, the current fluctuations and therefore the voltage drop fluctuations of the melting process can vary greatly, so it is important to try to keep the electric arc as stable as possible, thus reducing the flicker phenomenon.

[0018] Known devices and methods for supplying power to a furnace are described in WO 2019 / 207611, WO 2021 / 111484 and WO 2021 / 084566.

[0019] There is therefore a need for a method for supplying electrical power, in particular alternating current, to a furnace for melting and / or heating metallic materials, which method overcomes at least one of the disadvantages of the prior art.

[0020] Among other things, it is an object of the present invention to complete a method for supplying power to a furnace for melting and / or heating metallic materials, which method increases the efficiency and reduces the power requirements of the melting and / or heating process, and to provide a corresponding apparatus.

[0021] It is also an object of the present invention to complete a method for supplying power to a furnace for melting and / or heating metallic materials, which method allows for a reduction in melting time.

[0022] Another object is to provide an apparatus for supplying power to a furnace for melting and / or heating metallic materials, which is simple, economical and reliable and allows reducing interference phenomena on the power grid, such as the generation of harmonics and flicker.

[0023] Applicant has conceived, tested and embodied the present invention to overcome the shortcomings of the prior art and to achieve these and other objectives and advantages. Summary of the Invention

[0024] The invention is defined in the independent claims, which set out the particular features thereof.The dependent claims set out further features of the invention or variants of the main idea of ​​the invention.

[0025] In view of the above objectives, and in order to solve the above-mentioned technical problem in a novel and original manner and to provide significant advantages over the prior art, the present invention provides a method for supplying power to a furnace for melting and / or refining and / or heating metallic materials, comprising: -using a power supply means to supply an AC commercial voltage and current at a predetermined commercial frequency; - converting the commercial voltage, commercial current and commercial frequency using a transformer into an alternating secondary voltage and secondary current and a secondary frequency having a selectably settable value substantially equal to the commercial frequency; - rectifying the secondary voltages and the secondary currents using a plurality of rectifiers to obtain DC voltages and DC currents; - converting said DC voltages and currents using a plurality of converters into AC supply voltages and supply currents that are selectively settable by a control and instruction unit connected to said converters; - supplying said supply voltage and said supply current to a plurality of electrodes of said furnace.

[0026] In one aspect of the present invention, the power supply method includes an adjustment device of the control command unit that adjusts the supply frequency of the supply voltage and the supply current so that the supply frequency is equal to or lower than the commercial frequency for at least 80% of the duration of the operating cycle of the furnace, and so that the supply frequency is 40% to 80% of the commercial frequency in at least one step of the operating cycle.

[0027] In one aspect of the invention, the power supply method includes a control command unit that adjusts the supply frequency of the supply voltage and the supply current so that the supply frequency is lower than the mains frequency for at least 80% of the duration of the operating cycle of the furnace.

[0028] In a preferred embodiment, the supply frequency of the supply voltage and supply current is less than or equal to the mains frequency for at least 90% of the total duration of one operating cycle.

[0029] In another embodiment, the supply frequency of the supply voltage and supply current is less than or equal to the mains frequency for at least 95% of the entire duration of an operating cycle.

[0030] In another embodiment, the supply frequency is lower than the power frequency for 100% of the duration of an operating cycle.

[0031] By being able to adjust the frequency lower than the commercial frequency in this manner, it is possible to reduce losses in the conductor due to, for example, the skin effect, improve the flow of current within the copper conductor, and increase the proportion of the cross section of the conductor through which current flows.

[0032] Additionally, powering the electrodes with low frequency current can improve the mixing effect in the molten bath, increase heat exchange, and improve temperature uniformity within the bath, thereby improving the efficiency of the system.

[0033] In some embodiments, the supply frequency is higher than the power frequency, for example 101% to 200% of the power frequency, during at least one step of the operating cycle.

[0034] By being able to adjust the supply frequency to be higher than the commercial frequency in this way, the stability of the electric arc can be improved and the time required to melt the metal material can be shortened.

[0035] In some embodiments, under conditions of unstable absorbed power, i.e. fast oscillations in the power supply of the electric furnace, the supply frequency is maintained higher than the utility frequency to counteract said oscillations and improve the melting process.

[0036] This has the advantage at least of improving the transfer of energy in the molten material, which reduces the power consumption required by the electric furnace for the same temperature gradient in the bath of metallic material.

[0037] This allows a lower current to be used to perform the casting, or if the same current is maintained, the melting run time can be reduced to reduce the power on time.

[0038] In a preferred embodiment, the supply frequency is 1% to 80% of the commercial frequency in at least one step of the operating cycle.

[0039] In some embodiments, the method further comprises the step of: during at least one step of the operating cycle, the supply frequency is between 10% and 80% of the power frequency.

[0040] In some embodiments the method comprises adjusting the supply frequency to a value in the range of 1 to 45 Hz during at least one step of the operating cycle.

[0041] In another embodiment the method further comprises adjusting the supply frequency to about half the line frequency during at least one step of the operating cycle.

[0042] In some embodiments, the method further comprises the step of: during at least one step of the operating cycle, the supply frequency is between 101% and 200% of the power frequency.

[0043] In some embodiments the method further comprises adjusting the supply frequency to a value in the range of 51 to 120 Hz during at least one step of the operating cycle.

[0044] The supply frequency can be adjusted dynamically during the operating cycle, either manually by an operator or automatically in conjunction with the processes and instructions executed by a control unit.

[0045] In some embodiments, the electric smelting furnace is an electric arc furnace, the operating cycle includes, in sequence, a boring step, a melting step, and a smelting step, and the method comprises maintaining the supply frequency substantially equal to the utility frequency during the boring step and the melting step, and reducing the supply frequency by approximately half at least during the smelting step.

[0046] In another embodiment, the furnace is a ladle furnace, the operating cycle includes at least one step of refining the molten metallic material, and the method comprises maintaining the supply frequency in the range of 0.45 to 0.55 times the utility frequency throughout the duration of the operating cycle.

[0047] Some embodiments of the invention relate to an apparatus for powering a furnace for melting and / or heating a metallic material, the apparatus comprising: a transformer connected to a power supply means for supplying an AC commercial voltage and a commercial current having a predetermined commercial frequency, the transformer converting the AC commercial voltage and the AC commercial current into an AC secondary voltage and a secondary current, respectively; a plurality of rectifiers connected to the transformer, the rectifiers converting the AC secondary voltages and currents into DC voltages and currents; a number of converters connected to the rectifier and to the electrodes of the furnace and to a control and command unit, for converting the DC voltages and currents into AC supply voltages and currents; Equipped with The control and command unit is configured to control and command operation of the converter to regulate the supply voltage and the supply current of an AC current over time.

[0048] In another aspect of the invention, the control command unit is provided with an adjusting device which adjusts the power supply frequency so that in each step of the melting cycle of the furnace, the supply frequency of the AC supply voltage and the supply current is equal to or lower than the commercial frequency for at least 80% of the duration of the operating cycle, and the supply frequency is between 40% and 80% of the commercial frequency in at least one step of the operating cycle of the furnace.

[0049] Such a device configuration makes it possible to protect the power supply means from disturbances caused by the melting process (reduction of flicker, harmonics, etc.) and at the same time ensure arc stability during all steps.

[0050] In some embodiments, the rectifiers and converters are arranged in a modular configuration, where the power supply comprises a plurality of conversion modules, each including at least one rectifier and at least one converter, each conversion module capable of providing a minimum of 1 MW and a maximum of 30 MW of power.

[0051] These and other aspects, features and advantages of the invention are apparent from the following description of some embodiments, given as non-limiting examples, with reference to the attached drawings, in which: [Brief description of the drawings]

[0052] [Figure 1] 1 is a graph showing the temporal variation of electrical parameters applied to the electrodes of an arc furnace during a melting cycle of the prior art; [Diagram 2] FIG. 1 is a schematic diagram of an apparatus for supplying power to a furnace for melting and / or heating metallic materials of the present invention. [Diagram 3] 4 is a graph illustrating the temporal variation of electrical parameters applied to electrodes of an arc furnace during an operating cycle of a melting furnace according to some embodiments of the present invention. [Figure 4] 4 is a graph illustrating the temporal variation of electrical parameters applied to electrodes of an arc furnace during an operating cycle of a melting furnace according to some embodiments of the present invention. [Diagram 5] 1 is a graph of the power trend during the operating cycle of an electric arc furnace. [Figure 6] 4 is a graph illustrating the temporal variation of electrical parameters applied to an electrode of an arc ladle furnace during an operating cycle of some embodiments of the present invention. [Figure 7] 1 is a graph showing frequency fluctuations of power consumption in a ladle furnace. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] The words and terminology used in this specification and the figures in the accompanying drawings, even though disclosed, only have the function of illustrating and explaining the present invention, and their functions are to provide non-limiting examples of the present invention, since the protection scope of the present invention is defined by the claims.

[0054] For ease of understanding, the same reference numbers have been used, where possible, in the drawings to refer to identical common elements, and it should be understood that elements or features of one embodiment may be readily combined or incorporated into other embodiments without the need for detailed description.

[0055] Referring to FIG. 2, some embodiments of the present invention relate to an apparatus 10 for powering a furnace 100 for melting and / or heating metallic materials.

[0056] In some embodiments, the device 10 may be powered by a power supply means 200. A three-phase power grid 201 is described herein by way of example and not by way of limitation.

[0057] The utility voltage Ur and utility current Ir supplied from the power grid 201 may have a predetermined utility frequency fr.

[0058] In a possible solution, the power frequency fr is a value selected from 50 Hz to 60 Hz, i.e. according to the frequency of the power grid of the country in which the furnace 100 is installed.

[0059] In some embodiments, the system 10 may be configured to power a three-phase type load, particularly a three-phase furnace.

[0060] Such a furnace 100 may be an electric arc furnace, a submerged arc furnace, a ladle furnace, or generally any melting, smelting or heating furnace of the type suitable for use in a steel mill or metal processing plant, etc. Advantageously, the present invention is applicable to electric arc furnaces (EAF), ladle furnaces (LF), and smelters that use electrodes 102 to transfer heat energy to the material being processed.

[0061] 2 shows an apparatus 10 connected, by way of example, to an electric arc furnace EAF and a ladle furnace LF. If both an electric arc furnace EAF and a ladle furnace LF are installed in one steel plant, two apparatuses 10 can be provided, each connected to one of the furnaces, or one apparatus 10 can be provided, suitable for supplying power to each of the two furnaces EAF, LF.

[0062] When the furnace 100 is an electric arc furnace EAF type, it comprises a vessel 101 or shell into which the metallic material M to be melted is introduced.

[0063] The EAF furnace is also provided with a number of electrodes 102, in the illustrated example three electrodes 102, through which an electric arc is struck to melt the metallic material M.

[0064] In the case of a ladle furnace LF, it generally comprises a ladle 104 suitable for containing the liquid metal removed from the EAF furnace, a vault 105 closing the top of the ladle 104, and a number of electrodes 106 arranged through the vault 105.

[0065] In the following description, the EAF furnace will be mainly taken as an example.

[0066] In some embodiments of the present invention, the electrodes 102, 106 are mounted on a moving device 103 configured to selectively move the electrode 102 towards and away from the metal material M, or generally the metal bath.

[0067] The movement device 103 may be selected from the group including at least one of a mechanical actuator, an electrical actuator, a pneumatic actuator, a hydraulic actuator, an articulated mechanism, a mechanical movement motion, other similar or similar members, or possible combinations of the above devices.

[0068] In one possible solution of the invention, if the number of electrodes 102, 106 is three, each electrode is connected to one of the power supply phases of the device 10 respectively.

[0069] If there are more than three electrodes 102, 106, each power supply phase may be connected to two or more electrodes.

[0070] In some embodiments, the device 10 is capable of receiving energy supplied from the power grid 201 and converting it into a supply voltage and a supply current having specific electrical parameters Ua, Ia, fa suitable for powering the furnace 100.

[0071] In some embodiments, the device 10 comprises at least one transformer 11, which is connected to the power grid 201 and configured to convert a primary AC voltage Up and a primary AC current Ip into a secondary AC voltage Us and a secondary AC current Is.

[0072] In a possible solution, the transformer 11 may comprise a transformer primary 12 magnetically coupled to at least one transformer secondary 13 .

[0073] Such a solution makes it possible to reduce the effects of grid-side disturbances, ie to reduce the harmonic content and reactive power exchanged with the power grid 201.

[0074] The secondary electrical energy provided by transformer 11 includes a secondary voltage Us, a secondary current Is, and a secondary frequency fs, all of which are predetermined and set by the design characteristics of transformer 11 itself.

[0075] In some embodiments, the secondary frequency fs may be substantially lower than the power frequency fr mentioned above, or generally lower than the primary frequency fp of the current circulating in the primary side 12.

[0076] The secondary voltage Us and secondary current Is can be correlated to the utility voltage Ur and utility current Ir, respectively, by the transformation ratio of the transformer 11, or generally, can be correlated to the primary voltage Up and primary current Ip, respectively, of the primary side 12.

[0077] The transformer 11 may be provided with an adjusting device, not shown, arranged to selectively adjust the electrical transformation ratio of the transformer 11 in relation to specific requirements.

[0078] The device 10 of the present invention also comprises a number of rectifiers 14 connected to the transformer 11, which are configured to convert the AC secondary voltage Us and secondary current Is into DC intermediate voltages Ui and intermediate currents Ii.

[0079] The rectifier 14 may be selected from a group including a diode bridge or a thyristor bridge, or the like.

[0080] In one possible solution, the rectifier 14 may be, for example, a device selected from the group including a diode, a silicon controlled rectifier (SCR), a gate turn-off thyristor (GTO), an integrated gate-commutated thyristor (IGCT), a metal-oxide semiconductor controlled thyristor (MCT), a bipolar junction transistor (BJT), a metal-oxide semiconductor field-effect transistor (MOSFET), and an insulated-gate bipolar transistor (IGBT).

[0081] In some embodiments, the device 10 comprises a number of converters 15 connected to the rectifier 14, which are configured to convert the above-mentioned DC voltages and currents into AC supply voltages Ua and supply currents Ia for the electrodes 102.

[0082] In one possible solution, the converter 15 may be, for example, a device selected from the group including: SCR (Silicon Controlled Rectifier), GTO (Gate Turn-Off thyristor), IGCT (Integrated Gate-Commutated Thyristor), MCT (Metal-Oxide Semiconductor Controlled Thyristor), BJT (Bipolar Junction Transistor), MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor), and IGBT (Insulated-Gate Bipolar Transistor).

[0083] In a possible solution, the rectifier 14 can be connected to the converter 15 by means of at least one intermediate circuit 16 operating on direct current.

[0084] The intermediate circuit 16 provides a decoupling between the rectifier 14 and the converter 15, and thus between the power supply means 200 connected upstream of the intermediate circuit 16 with respect to the furnace 100. In particular, fast power fluctuations caused by the process are partly filtered by the intermediate circuit 16, so that the impact of such fast power fluctuations on the power supply means 200 side is reduced.

[0085] The intermediate circuit 16 may also be configured to continuously store electrical energy. In some embodiments, the intermediate circuit 16 is a "DC link" and comprises at least one capacitor.

[0086] In some embodiments, the device 10 comprises a control command unit 17 configured to control the converter 15 to selectively set at least the parameters of the supply voltage Ua and the supply current Ia generated by the converter 15 and supplied to the electrode 102.

[0087] In particular, the supply voltage Ua and the supply current Ia can be selectively adjusted in relation to the required operating power and, in the case of an EAF furnace, for example in relation to the melting power used.

[0088] Furthermore, in some embodiments of the present invention, the control and command unit 17 is also connected to a movement device 103 so as to be able to adjust the position of the electrode 102 in relation to the various steps of the melting process. In particular, the electrode 102 is moved by the movement device 103 to follow the position of the material, thereby changing the length of the arc.

[0089] Indeed, if it is assumed that the arc is shrouded and away from the furnace vault, thereby avoiding the risk of damage to the vault, the power supplied to the electrode 102 during the melting step can be increased compared to the boring step.

[0090] By using the control and command unit 17, the supply voltage Ua and supply current Ia criteria can be modified to increase the active power. In the process, the arc is protected by scrap or slag, thus improving the stability of the arc.

[0091] Furthermore, the process becomes much more stable during the refining process and power requirements are reduced.

[0092] In this way, the control and command unit 17 can manage and command at least the following parameters in relation to a specific step of the process: supply voltage Ua, supply current Ia, power supply frequency fa, and the position of the electrodes 102, 106. The increased possibility to control these parameters allows to maximize the transfer of energy to the process, while at the same time reducing the impact on the power grid 201 caused by fast fluctuations in the power on the furnace side.

[0093] The electrical topology adopted for the converter 15 also makes it possible to protect the power grid 201 from disturbances caused by the melting process (flicker, harmonics, poor power factor, etc.) and at the same time ensures arc stability during all operating phases of the furnace 100, both in the case of the EAF furnace and in the case of the ladle furnace LF.

[0094] The control command unit 17 may be equipped with a regulating device 18 .

[0095] In a possible solution of the invention, the regulator 18 may comprise, by way of example only, a hysteresis modulator or a PWM (Pulse Width Modulation) modulator or the like.

[0096] Such a modulator can be used to command the semiconductor devices of the rectifier 14 and converter 15 which, when appropriately controlled, generate voltages or currents supplied to the furnace 100, and in this embodiment, to the electrodes 102, 106. In particular, the modulator processes these voltages and currents and generates commands to drive at least the rectifier 14 and converter 15 so that the voltages and currents required for control are supplied to the connection terminals of the electrodes 102, 106.

[0097] The voltages and currents to be operated are the result of actions taken by a control command unit based on values ​​read from the process and a process model.

[0098] According to the invention, the regulating device 18 is arranged to regulate the power supply frequency fa of the supply voltage Ua and the supply current Ia during each step of the melting cycle of the furnace 100 .

[0099] The coordinator 18 receives commands from a control command unit 17 .

[0100] In particular, the regulator 18 receives commands from the control command unit 17 such that the supply frequency fa is less than or equal to the power frequency fr for at least 80% of the total duration of one working cycle.

[0101] In some embodiments, the supply frequency fa is 0.5% to 200% of the commercial frequency fr in at least one step of the above operating cycle.

[0102] In some embodiments, the supply frequency fa is always equal to or lower than the commercial frequency fr immediately after the start of the above-mentioned operating cycle, and further, in at least one step of the operating cycle of the furnace 100, the supply frequency fa is lower than the commercial frequency fr of the power supply means 200, in particular 40% to 80% of the commercial frequency fr.

[0103] In some embodiments, the supply frequency fa is generally lower than the primary frequency fp of the current circulating in the primary side 12 of the transformer 11 during at least one step of the operating cycle of the furnace 100.

[0104] In a possible solution, the rectifier 14 and the converter 15 are connected in a modular configuration and together form a power supply module 19 .

[0105] In some embodiments, the apparatus 10 includes a plurality of power supply modules 19, each including at least one rectifier 14 and at least one converter 15, each capable of supplying a minimum of 1 MW to a maximum of 30 MW of power.

[0106] In some embodiments, each power supply module 19 also comprises at least one intermediate circuit 16 or DC link connected between said at least one rectifier 14 and said at least one converter 15 .

[0107] In a possible embodiment, for each phase of the three-phase power grid 201 , each power supply module 19 comprises at least one rectifier 14 , a DC link 16 and a converter 15 .

[0108] Preferably, all power supply modules 19 may be the same size, i.e. all power supply modules 19 may be capable of supplying the same range of power.

[0109] Typically, the preferred size range for each power supply module 19 varies between 5-20 MW respectively.

[0110] In one preferred embodiment, all power supply modules 19 are the same size, eg, all 10 MW, all 20 MW, etc.

[0111] In some embodiments, each power supply module 19 also includes a respective transformer 11 .

[0112] When the or each module 19 comprises a rectifier 14, an intermediate circuit 16 and a converter 15 for each phase of the power grid 201, the transformer 11 may comprise one transformer primary 12 and multiple transformer secondaries 13, each of which is connected to a rectifier 14.

[0113] In some embodiments, the apparatus 10 may be provided with multiple power supply modules 19 connected in parallel to the power grid 201 and to the furnace 100 .

[0114] By combining multiple power supply modules 19, an apparatus 10 can be provided that is scalable in size relative to the particular size of the furnace 100 being powered.

[0115] In one possible solution, the control and command unit 17 is connected to all power supply modules 19 in order to control at least each converter 15 so that each module 19 supplies the electrodes 102 with the same values ​​of supply voltage Ua, supply current Ia and supply frequency fa. Such an arrangement makes it possible to prevent malfunctions of the entire system.

[0116] In another variant, the power supply modules 19 can be configured to be controllable so that each power supply module 19 supplies different values ​​of the supply voltage Ua, supply current Ia and supply frequency fa to each electrode 102, for example to vary the distribution of power within the melting bath.

[0117] In one possible solution, the device 10 may include an inductor 20 configured to achieve a desired reactance of the overall device.

[0118] The inductor 20 can be connected downstream of the converter 15 and sized to achieve a desired overall equivalent reactance. Such a configuration results in an overall reactance given by the contribution of the inductor 20 and the reactance presented by the conductors connecting the apparatus 10 to the furnace 100, in this example the conductors connecting to the electrodes 102.

[0119] In general, inductance is a (design) parameter that cannot be changed once the part is assembled.

[0120] By changing the frequency (e.g. relative to the 50Hz or 60Hz of a power grid), the reactance values ​​taken on by components in the circuit can be changed for the same inductance, thereby achieving a desired overall equivalent reactance value.

[0121] The operation of the device 10 for supplying power to a furnace for melting and / or heating a metallic material M described above in accordance with the method of the present invention is as follows: - using the power supply means 200, supplying an AC commercial voltage Ur and a commercial current Ir at a predetermined commercial frequency fr; - converting the AC utility voltage Ur and the utility current Ir by means of a transformer 11 into a selectively settable AC secondary voltage Us and secondary current Is having a secondary frequency fs substantially equal to the utility frequency fr; - rectifying the secondary voltages Us and secondary currents Is using a number of rectifiers 14 to obtain direct intermediate voltages Ui and intermediate currents Ii; - converting, by means of a number of converters 15, intermediate voltages Ui and intermediate currents Ii into alternating supply voltages Ua and supply currents Ia which can be selectively set by a control and instruction unit 17 connected to the converters 15; The electrodes 102 of the furnace 100 are supplied with a supply voltage Ua and a supply current Ia.

[0122] In this method, in each step of the operating cycle of the furnace 100, the adjusting device 18 of the control command unit 17 adjusts the supply frequency fa of the supply voltage Ua and the supply current Ia to be equal to or lower than the commercial frequency fr for at least 80% of the duration of the operating cycle, and in at least one step of the operating cycle of the furnace 100, the supply frequency is lower than the commercial frequency fr, preferably 40% to 80% of the commercial frequency fr.

[0123] In a preferred embodiment, the supply frequency fa is less than or equal to the power frequency fr for at least 90% of the entire duration of one operating cycle.

[0124] In another embodiment, the supply frequency fa is less than or equal to the power frequency fr for at least 95% of the entire duration of one operating cycle.

[0125] In a preferred embodiment, the supply frequency fa is lower than the power frequency fr for at least 90% of the total duration of one working cycle, preferably for at least 95% of the total duration.

[0126] In some embodiments, the method comprises a supply frequency that is between 10% and 80% of the line frequency during at least one step of the operating cycle.

[0127] In some embodiments, the method comprises the step of: during at least one step of the operating cycle, the supply frequency fa is between 45% and 75% of the power frequency fr.

[0128] In some embodiments, the method comprises the step of: during at least one step of the operating cycle, the supply frequency fa is between 101% and 200% of the power frequency fr.

[0129] In some embodiments the method comprises adjusting the supply frequency fa to a value in the range of 55 to 120 Hz during at least one step of the operating cycle.

[0130] The supply frequency fa can be adjusted dynamically during the operating cycle, either manually by an operator or automatically in conjunction with the processes and instructions executed by the control command unit 17.

[0131] As used herein, the term "operating cycle" refers to a set of operating steps for a particular furnace 100.

[0132] For example, as shown in Figures 3, 4, 4(A) and 4(B), in the case of an electric arc furnace EAF, an operating cycle may include at least a step of boring a metallic material M, a step of melting, and optionally a step of refining the melted material.

[0133] Specifically, in the boring process, the electrode 102 is brought close to the discharged solid metal material M to ignite an electric arc and start melting the metal material M. As the metal material M gradually melts, the electrode 102 penetrates a part of the metal material M that is still in a solid state and gradually melts the metal material M. When the electrode 102 reaches a position within the container 101, the main melting of the remaining metal material M around the electrode 102 starts.

[0134] In one possible solution (FIG. 3), the boring and melting steps are repeated several times before the refining step, with additional metallic material M being charged into the electric furnace 100 between these steps.

[0135] For example, referring to Figure 3, a charge of metallic material M is introduced and the metallic charge is drilled and melted by electrode 102. This sequence of operations is repeated three times, each time introducing a different charge of metallic material M.

[0136] In the solution shown in Figures 4, 4(A) and 4(B), a substantially continuous charge is provided which starts before the boring process and continues until the furnace is full in the process of melting the metallic material.

[0137] In the above embodiment, the supply frequency fa is equal to or lower than the power frequency fr over the entire period, ie, 100%, of one operating cycle.

[0138] In some embodiments, the method may decrease the supply frequency fa over time as the operating cycle of the furnace 100 progresses.

[0139] The supply frequency fa can be decreased starting from a preset value, for example the value of the primary frequency fp of the primary side 12 of the transformer 11 or the value of the commercial frequency fr, and preferably the supply frequency fa starts from the value of the commercial frequency fr.

[0140] The supply frequency fa can be decreased continuously over time, for example linearly or exponentially, as shown by the dashed-dotted line in FIG. 4(B).

[0141] The supply frequency fa can be decreased discontinuously over time, for example, in a step-like manner, as shown by the two-dot chain line in Fig. 4(B). Therefore, the supply frequency fa can take multiple values ​​f1 lower than the commercial frequency fr.

[0142] The method allows the supply frequency fa to be substantially constant at least for the time corresponding to each operating step of the furnace 100 .

[0143] The method can ensure that the supply frequency fa reaches a value at least 20% lower than the power frequency fr at the end of the operating cycle in the furnace 100, preferably at least 40% lower, and more preferably approximately half the power frequency fr.

[0144] In this method, the supply frequency fa can have a value of substantially 30-40 Hz in at least one step or steps of the operating cycle of the furnace 100 .

[0145] For example, for an EAF furnace, the supply frequency fa may be substantially equal to the commercial frequency fr during the boring process, and the supply frequency fa may be 0.45 to 0.55 times the commercial frequency fr during the refining process.

[0146] The method allows the EAF furnace to have a feed frequency fa substantially equal to the commercial frequency fr during the boring step and to reduce the feed frequency fa in the subsequent operating step until it assumes a value f1, e.g. a value substantially equivalent to half the value of the commercial frequency fr (FIG. 3).

[0147] In another example, the method may be as shown in FIG. 4(A) in which the EAF furnace has a feed frequency fa substantially equal to the utility frequency fr during the boring and charge melting steps, and the feed frequency fa is reduced in a stepwise manner during subsequent operating steps.

[0148] In some embodiments, not shown, the supply frequency fa can be lower than the power frequency fr during all operating steps.

[0149] In some variations, the method provides that in at least one step of the operating cycle, the supply frequency fa is higher than the power frequency fr, for example between 101% and 200% of the power frequency fr.

[0150] In some embodiments the method comprises adjusting the supply frequency to a value in the range of 51-100 Hz or in the range of 61-120 Hz, depending on the value of the power frequency, during at least one step of the operating cycle.

[0151] In some embodiments, the supply frequency fa is adjusted higher than the power frequency fr at least in situations where there are fast oscillations in the power absorbed by the EAF furnace, for example in response to charging of metallic material.

[0152] For example, in the graph shown in FIG. 5, the upper part shows the trend of the power absorbed by the charge during the operating cycle, and the lower part shows how the supply frequency fa is adjusted relative to the utility frequency fr.

[0153] The highlighted area indicates a situation where fast oscillations or fluctuations in power occur, and as can be seen, the supply frequency fa is correspondingly higher than the utility frequency fr, and at the same time, for the remainder of the operating cycle, the supply frequency fa is equal to or lower than the utility frequency fr.

[0154] Thus, in the present invention, once an operating point has been established for at least the power, voltage, current and frequency of the furnace 100, the method can attempt to have the control command unit 17 follow this operating point, and even to follow it by continuous adjustment of the supply frequency fa.

[0155] The operating point may be determined by an operator or may be determined automatically by the control command unit 17, for example based on a mathematical model of the furnace 100 and / or a mathematical model of a given melting and / or heating process, or may be calculated based on input data received relating to the type of material to be melted, the end product to be obtained, the characteristics of the furnace 100, or the required output per hour or other factors.

[0156] Thus, the present invention allows the electrical parameters during each of several steps of the process to be optimized by adjusting the frequency during each step.

[0157] As another example, such as that described with reference to FIG. 6, in a ladle furnace LF the operating cycle includes at least one step of refining a molten metallic material M.

[0158] In a possible embodiment, the method can maintain the supply frequency fa constant for the entire duration of the operating cycle of the ladle furnace LF, or can reduce the supply frequency fa over time according to a linear, stepwise, exponential or other mathematical curve, possibly a combination of these.

[0159] In any case, in a ladle furnace LF, the supply frequency fa is preferably maintained lower than the power frequency fr throughout the entire operating cycle.

[0160] For example, in the embodiment described with reference to FIG. 6, in the present method, in a ladle furnace LF, the supply frequency fa is constant throughout the entire operating cycle and can have a value lower than the commercial frequency fr, preferably 0.4 to 0.6 times the commercial frequency fr.

[0161] Preferably, the supply frequency fa in the ladle furnace LF is substantially equal to half the value of the commercial frequency fr until the end of the refining process.

[0162] Advantageously, when the temperature gradients are equalized, for example in the case of an LF furnace as shown in FIG. 7, the present invention allows a reduction in the power consumption required for the furnace 100, for example, a reduction of approximately 12% in the power consumption achieved at an operating frequency of 40 Hz in an LF furnace compared to the power required at a frequency of 50 Hz, other operating conditions being equal.

[0163] Another advantage is that, for example, at an operating frequency of 40 Hz, all other things being equal, the power factor in one operating cycle can be increased from 0.90 to 0.96.

[0164] Another advantage is that melt time can be reduced by increasing the arc power through lowering the operating frequency.

[0165] For example, in an electric arc furnace EAF the reduction in melting time can be about 20% at a frequency of 25 Hz and 35% at a frequency of 10 Hz. As another example, in an LF furnace with an operating frequency of 40 Hz the power-on time can be reduced by an average of about 20-22 minutes.

[0166] Advantageously, the consumption of the electrodes 102, 106 can also be reduced, for example at an operating frequency of 40 Hz, the consumption of the electrodes 102, 106 can be reduced by approximately 10%.

[0167] It will be apparent that modifications and / or additions of various parts may be made to the apparatus 10 and method described above without departing from the field and scope of the invention as defined in the appended claims.

[0168] It is also clear that although the invention has been described with reference to some specific examples, a person skilled in the art can certainly achieve many other equivalent embodiments of the method and device 10 for supplying power to a furnace for melting and / or heating metallic materials having the characteristics set out in the claims, all such equivalent embodiments falling within the scope of protection set out in the claims.

[0169] The purpose of the parenthetical signs in the accompanying claims is only to facilitate reading; such parentheses shall not be considered as a limiting factor on the scope of protection defined by the claims.

Claims

1. 1. A method for supplying power to a furnace (100) for melting and / or heating a metallic material (M), comprising the steps of: Supplying an AC commercial voltage (Ur) and a commercial current (Ir) having a predetermined commercial frequency (fr) using a power supply means (200); converting the commercial voltage (Ur) and the commercial current (Ir) into a selectively settable AC secondary voltage (Us) and secondary current (Is) having a secondary frequency (fs) substantially equal to the commercial frequency (fr) using a transformer (11); rectifying the secondary voltage (Us) and the secondary current (Is) using a plurality of rectifiers (14) to obtain a direct intermediate voltage (Ui) and an intermediate current (Ii); - converting said DC intermediate voltages (Ui) and intermediate currents (Ii) by means of a plurality of converters (15) into AC supply voltages (Ua) and supply currents (Ia) which can be selectively set by a control and instruction unit (17) connected to said converters (15); supplying said supply voltage (Ua) and said supply current (Ia) to a number of electrodes (102, 106) of said furnace (100); Including, The adjustment device (18) of the control command unit (17) adjusts the supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) so that in each step of the operating cycle of the furnace (100), the supply frequency (fa) is equal to or lower than the commercial frequency (fr) for at least 80% of the duration of the operating cycle, and the power supply frequency (fa) is 40% to 80% of the commercial frequency (fr) in at least one step of the operating cycle of the furnace (100). A method comprising:

2. 1. A method for supplying power to a furnace (100) for melting and / or heating a metallic material (M), comprising the steps of: Supplying an AC commercial voltage (Ur) and a commercial current (Ir) having a predetermined commercial frequency (fr) using a power supply means (200); converting the commercial voltage (Ur) and the commercial current (Ir) into a selectively settable AC secondary voltage (Us) and secondary current (Is) having a secondary frequency (fs) substantially equal to the commercial frequency (fr) using a transformer (11); rectifying the secondary voltage (Us) and the secondary current (Is) using a plurality of rectifiers (14) to obtain a direct intermediate voltage (Ui) and an intermediate current (Ii); - converting said DC intermediate voltages (Ui) and intermediate currents (Ii) by means of a plurality of converters (15) into AC supply voltages (Ua) and supply currents (Ia) which can be selectively set by a control and instruction unit (17) connected to said converters (15); supplying said supply voltage (Ua) and said supply current (Ia) to a number of electrodes (102, 106) of said furnace (100); Including, A regulating device (18) of the control and command unit (17) regulates the supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) so that the supply frequency (fa) is lower than the mains frequency (fr) for at least 80% of the duration of the operating cycle of the furnace (100). A method comprising:

3. The supply frequency (fa) is lower than the power frequency (fr) for at least 90% of the entire duration of one operating cycle; 3. The method according to claim 1 or 2.

4. The supply frequency (fa) is lower than the power frequency (fr) for at least 95% of the entire duration of one operating cycle; 3. The method according to claim 1 or 2.

5. The supply frequency (fa) is lower than the power frequency (fr) for 100% of the entire period of one operating cycle; 3. The method according to claim 1 or 2.

6. In at least one step of the operating cycle, the supply frequency (fa) is higher than the power frequency (fr) and is 101% to 200% of the power frequency (fr); 5. The method according to any one of claims 1 to 4.

7. the supply frequency (fa) decreases continuously or stepwise during the operating cycle of the furnace (100) starting from the value of the power frequency (fr) and reaching a value at least 20% lower than the power frequency (fr), more preferably approximately half the power frequency (fr), at the end of the operating cycle of the furnace (100); 6. The method according to any one of claims 1 to 5.

8. The furnace (100) is an electric arc furnace (EAF); The operating cycle includes at least one step of boring the metal material (M), a melting step, and a step of refining the melted material, the supply frequency (fa) is substantially equal to the power frequency (fr) at least during the step of melting the charge and is reduced during the subsequent steps of operation of the electric arc furnace (EAF); 8. The method according to any one of claims 1 to 7.

9. The supply frequency (fa) is higher than the utility frequency (fr) during the boring process and / or under conditions of fast oscillations of the electric arc furnace (EAF) power supply; The method according to claims 6 and 8.

10. the supply frequency (fa) is substantially constant during each operation step of the furnace (100) and is at least 20% lower than the power frequency (fr); 10. The method according to any one of claims 1 to 9.

11. The furnace (100) is a ladle furnace (LF), said operating cycle including at least one step of refining said molten material; During the entire refining process in the ladle furnace (LF), the supply frequency (fa) is constant and is lower than the commercial frequency (fr), and is preferably 0.45 to 0.55 times the commercial frequency (fr); The method of claim 10.

12. The furnace (100) is a ladle furnace (LF), The supply frequency (fa) is constant throughout the duration of the operating cycle and has a value between 0.4 and 0.6 times the commercial frequency (fr); The method of claim 10.

13. said supply frequency (fa) having a value between 30 and 40 Hz during at least one step of said operating cycle of said furnace (100); 13. The method according to any one of claims 1 to 12.

14. establishing an operating point for the furnace (100) for power, voltage, current and frequency supplied to at least the electrodes (102, 106); said control command unit (17) commands at least said regulating device (18) to try to follow said operating point also through a continuous adjustment of said supply frequency (fa); 14. The method according to any one of claims 1 to 13.

15. An apparatus (10) for supplying power to a furnace (100) for melting and / or heating a metallic material (M), comprising: a transformer (11) connected to a power supply means (200) for supplying an AC commercial voltage (Ur) and a commercial current (Ir) having a predetermined commercial frequency (fr), the transformer (11) converting the AC commercial voltage (Ur) and the AC commercial current (Ir) into an AC secondary voltage (Us) and a secondary current (Is), respectively; a plurality of rectifiers (14) connected to the transformer (11), the rectifiers (14) converting the AC secondary voltage (Us) and the AC secondary current (Is) into a DC voltage and a DC current; a plurality of converters (15) connected to the rectifier (14) and to the electrodes (102, 106) of the furnace (100), for converting the DC voltage and current into an AC supply voltage (Ua) and a supply current (Ia); a control and command unit (17) for controlling and commanding the operation of said converter (15) to regulate said supply voltage (Ua) and said supply current (Ia) over time; Equipped with The control and command unit (17) is provided with an adjusting device (18) for adjusting the power supply frequency (fa) so that in each step of the melting cycle of the furnace (100), the supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) is equal to or lower than the commercial frequency (fr) for at least 80% of the duration of the operating cycle, and the supply frequency (fa) is 40% to 80% of the commercial frequency (fr) in at least one step of the operating cycle of the furnace (100). An apparatus (10).

16. An apparatus (10) for supplying power to a furnace (100) for melting and / or heating a metallic material (M), comprising: a transformer (11) connected to a power supply means (200) for supplying an AC commercial voltage (Ur) and a commercial current (Ir) having a predetermined commercial frequency (fr), the transformer (11) converting the AC commercial voltage (Ur) and the AC commercial current (Ir) into an AC secondary voltage (Us) and a secondary current (Is), respectively; a plurality of rectifiers (14) connected to the transformer (11), the rectifiers (14) converting the AC secondary voltage (Us) and the AC secondary current (Is) into a DC voltage and a DC current; a plurality of converters (15) connected to the rectifier (14) and to the electrodes (102, 106) of the furnace (100), for converting the DC voltage and current into an AC supply voltage (Ua) and a supply current (Ia); a control and command unit (17) for controlling and commanding the operation of said converter (15) to regulate said supply voltage (Ua) and said supply current (Ia) over time; Equipped with The control and instruction unit (17) is provided with a regulating device (18) for adjusting the power supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) so that the supply frequency (fa) is lower than the utility frequency (fr) for at least 80% of the duration of the operating cycle during each step of the melting cycle of the furnace (100). An apparatus (10).

17. the adjustment device (18) is selected from a hysteresis modulator or a PWM (Pulse Width Modulation) modulator; 17. Apparatus (10) according to claim 15 or 16.

18. a plurality of power supply modules (19) each including at least one rectifier (14) and converter (15); The plurality of power supply modules (19) are connected in parallel to the power supply means (200) and to the furnace (100); said control and instruction unit (17) is connected to all said power supply modules (19) in order to control at least each of said converters (15) so that each supply (19) supplies the electrodes (102, 106) with the same values ​​of supply voltage (Ua), supply current (Ia) and supply frequency (fa); The device (10) according to any one of claims 15 to 17.

19. said rectifier (14) is connected to said converter (15) and comprises at least one intermediate circuit (16) operating on direct current, the intermediate circuit (16) continuously stores electrical energy and provides a decoupling between the converter (15) and the rectifier (14) and thus between the power supply means (200); The device (10) according to any one of claims 15 to 18.

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