A method for supplying power to a furnace for melting and / or heating metallic materials, and a corresponding apparatus.

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 a metallic material, and to a corresponding device for supplying power.

[0002] The present invention is applicable in the field of steel manufacturing and other fields where metals are processed, such as electric furnaces like electric arc furnaces, ladle furnaces, submerged arc furnaces, melting or refining furnaces, etc.

Background Art

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

[0004] The above types of electric furnaces can be selected from the group including electric arc furnaces, submerged arc furnaces, ladle furnaces, or generally melting furnaces, refining furnaces, heating furnaces, etc.

[0005] As an example, the melting cycle of an arc melting furnace includes the following working steps: - Charging the furnace with a metallic material (usually scrap) from above using a basket or using a continuous charging conveyor device to which scrap and / or direct reduced iron (DRI) is supplied; - Lowering the electrodes towards the metallic material until the melting electric arc generated between the ends of the electrodes and the material to be melted is activated; - Drilling through the layer of metallic material through the generated electric arc, during which the melting of the scrap starts; - Forming a bath of molten metal; - Refining the above-mentioned molten material to adjust the temperature of the above-mentioned bath and the carbon content of the steel, and / or to determine the desired composition of the steel by adding chemical compounds; - Removing the molten material in the electric furnace if slag is formed.

[0006] The material refining step can substantially correspond to what is produced in the ladle furnace, used in processes downstream from extraction, and is intended to ultimately adjust the chemical composition of the steel.

[0007] During the boring process, the electric arc between the electrode and the charge of the metal material exhibits highly unstable behavior, which gradually improves as melting progresses. This can cause abrupt and sudden fluctuations in the absorbed power, which can negatively impact the power grid, for example, causing so-called flicker and potentially damaging user equipment that receives power from the grid.

[0008] In reality, during boring and melting, unmelted, accumulated scrap disintegrates near the electrodes, creating short-circuit conditions that result in a significant decrease in the active power required for the melting operation and a rapid increase in the current absorbed by the power grid.

[0009] As melting progresses, that is, as the arc is properly shielded by the solid material or foamy liquid (slag), the behavior of the electric arc gradually stabilizes, which allows for an increase in arc length and thus increases the thermal power transferred to the material being melted. The voltage and length of the arc are adjusted according to the melting process to prevent excessive wear of the refractory material.

[0010] To minimize undesirable impacts on the power distribution network, it is known that rapid adjustment of the power supplied to the furnace is possible by continuously adjusting at least the electrode positions and the voltage and current parameters applied to the electrodes.

[0011] In particular, the voltage and current parameters, as well as the electrode positions, are appropriately adjusted at each step of the process.

[0012] In plants that heat and / or melt such metallic materials, electric furnaces are typically supplied with three-phase alternating current power from the public power grid.

[0013] Figure 1 schematically shows the reference or set values ​​of the electrical parameters supplied to the electrodes as the three-basket melting cycle progresses. In this three-basket melting cycle, the metal material in the first basket is charged into the furnace and melted, the metal material in the second basket is charged and melted, the metal material in the third basket is charged and all of the resulting liquid material is melted, and then refining is performed.

[0014] Generally, while the electrical parameters of current I, voltage U, and power P are varied, it should be noted that the electrode supply frequency f during the dissolution cycle is kept constant and is generally equal to the commercial frequency.

[0015] Generally, melting and / or heating plants require high power supply to the furnace; for example, the required power supply can be tens of megawatts (MW), and especially 5 MW to 300 MW depending on the size of the plant and / or furnace.

[0016] As described above, known power supply devices have a drawback related to the wide range of fluctuations in the instantaneous power absorption amount taken in from the distribution network, and such wide fluctuations are particularly caused by the movement of scrap during boring, which can lead to phase short circuits.

[0017] During drilling, if the power absorption by the furnace is variable, fluctuations in the commercial voltage occur, causing the so-called flicker phenomenon. When the frequency is the same, the current fluctuations in the melting process and, consequently, the voltage drop fluctuations can vary greatly. Therefore, it is important to try to reduce the flicker phenomenon by maintaining the electric arc as stably as possible.

[0018] Known apparatuses and methods for supplying power to a furnace are described in International Publication Nos. 2019 / 207611, 2021 / 111484, and 2021 / 084566.

[0019] Therefore, there is a request for the completion of a method for supplying electricity, particularly alternating current, to a furnace for melting and / or heating metallic materials, which can overcome at least one of the shortcomings of the prior art.

[0020] In particular, one objective of the present invention is to provide a method for supplying power to a furnace for melting and / or heating a metallic material, which improves the efficiency of the melting and / or heating process and reduces the power required, and to provide a corresponding apparatus.

[0021] Another objective of the present invention is to complete a method for supplying power to a furnace for melting and / or heating a metal material, which can shorten the melting time.

[0022] Another objective is to provide a device for supplying power to a furnace for melting and / or heating metallic materials that is simple, economical, highly reliable, and capable of reducing interference phenomena to the power grid, such as the generation of harmonics and flicker.

[0023] The applicant has conceived, tested, and embodied the present invention in order to overcome the shortcomings of the prior art and achieve the above and other objectives and advantages. [Overview of the project]

[0024] The present invention is described in the independent claims, which describe its features. Other features of the present invention or variations of the main concept of the present invention are described in the dependent claims.

[0025] In view of the above objectives, the present invention provides a method for supplying power to a furnace for melting and / or refining and / or heating a metallic material, which solves the technical problems described above by novel and unique means and also offers significant advantages compared to conventional technologies. - Using a power supply means, supply AC commercial voltage and commercial current at a predetermined commercial frequency, - Using a transformer to convert the commercial voltage, commercial current, and commercial frequency into an alternating current secondary voltage and secondary current, and a secondary frequency having a value that can be selectively set to be substantially equal to the commercial frequency; - Obtaining a DC voltage and a DC current by rectifying the secondary voltage and the secondary current using a plurality of rectifiers; - Using a plurality of converters to convert the DC voltage and DC current into an alternating current supply voltage and supply current that can be selectively set by a control command unit connected to the converter; - Supplying the supply voltage and the supply current to a plurality of electrodes of the furnace.

[0026] In one aspect of the present invention, in each step of the operating cycle of the furnace, the adjustment device of the control command unit adjusts the supply frequency so that the supply frequency of the supply voltage and the supply current is below the commercial frequency over at least 80% of the period of the operating cycle, and in at least one step of the operating cycle, the supply frequency is 40% - 80% of the commercial frequency.

[0027] In one aspect of the present invention, in each step of the operating cycle of the furnace, the adjustment device of the control command unit adjusts the supply frequency so that the supply frequency of the supply voltage and the supply current is lower than the commercial frequency over at least 80% of the period of the operating cycle.

[0028] In a preferred embodiment, the supply frequency of the supply voltage and supply current is below the commercial frequency over at least 90% of the entire period of one operating cycle.

[0029] In another embodiment, the supply frequency of the supply voltage and supply current is below the commercial frequency over at least 95% of the entire period of one operating cycle.

[0030] In another embodiment, the supply frequency is lower than the commercial frequency over 100% of the entire period of one operating cycle.

[0031] By adjusting the frequency to be lower than the commercial frequency in this way, it is possible to reduce losses in the conductor due to the skin effect, for example, and improve the flow of current within the copper conductor, thereby increasing the proportion of the conductor's cross-section that is used for current flow.

[0032] Furthermore, by supplying power to the electrodes using low-frequency current, the stirring effect in the dissolution bath can be improved, heat exchange can be increased, and the uniformity of temperature within the bath can be enhanced, thereby improving the efficiency of the system.

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

[0034] By adjusting the supply frequency to be higher than the commercial frequency in this way, the stability of the electric arc can be improved, and the melting time of metal materials can be shortened.

[0035] In some embodiments, under conditions where the absorbed power is unstable, i.e., under conditions where rapid oscillations occur in the power supply of the electric furnace, the oscillations are canceled out and the melting process is improved by maintaining the supply frequency higher than the commercial frequency.

[0036] This approach offers the advantage of improving energy transfer in the molten material, thereby reducing the power consumption required for the electric furnace when the temperature gradient of the metal material bath is the same.

[0037] This allows for a lower current to be used to perform the casting, or, if the same current is maintained, the dissolution execution time can be shortened, thereby reducing 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 is such that the supply frequency is 10% to 80% of the commercial frequency in at least one step of the operating cycle.

[0040] In some embodiments, the method is adjusted so that the supply frequency is set to a value in the range of 1 to 45 Hz in at least one step of the operating cycle.

[0041] In another embodiment, the method is such that the supply frequency is adjusted to approximately half the commercial frequency in at least one step of the operating cycle.

[0042] In some embodiments, the method is such that the supply frequency is 101% to 200% of the commercial frequency in at least one step of the operating cycle.

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

[0044] The supply frequency can be dynamically adjusted during the operating cycle, manually by the operator, or automatically in relation to the processes and commands executed by the control unit.

[0045] In some embodiments, the electric melting furnace is an electric arc furnace, and the operating cycle includes, in order, a boring step, a melting step, and a refining step, wherein the method maintains the supply frequency substantially equal to the commercial frequency during the boring step and the melting step, and reduces it to approximately half during at least the refining step.

[0046] In other embodiments, the furnace is a ladle furnace, the operating cycle includes at least one step of refining the molten metal material, and the method maintains the supply frequency in the range of 0.45 to 0.55 times the commercial frequency for the entire duration of the operating cycle.

[0047] Some embodiments of the present invention also relate to an apparatus for supplying power to a furnace for melting and / or heating a metallic material, the apparatus is - A transformer connected to a power supply means that supplies AC commercial voltage and commercial current having a predetermined commercial frequency, the transformer converts the AC commercial voltage and commercial current into AC secondary voltage and secondary current, respectively. - A plurality of rectifiers connected to the transformer, which convert the AC secondary voltage and secondary current into DC voltage and DC current, - A plurality of converters connected to the rectifier and also connected to the electrodes and control command unit of the furnace, the converters that convert the DC voltage and DC current into AC supply voltage and supply current, It is equipped with, The control command unit is configured to control and command the operation of the converter, thereby adjusting the AC supply voltage and supply current over time.

[0048] In another aspect of the present invention, the control command unit is provided with an adjustment device that 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 less than or equal to the commercial frequency for at least 80% of the duration of the operating cycle, and the supply frequency is 40% to 80% of the commercial frequency in at least one step of the operating cycle of the furnace.

[0049] This device configuration protects the power supply from interference caused by the melting process (reducing flicker, harmonics, etc.) while simultaneously ensuring arc stability throughout the entire process.

[0050] In some embodiments, the rectifier and the converter are arranged in a modular configuration. In this case, the power supply device comprises a plurality of conversion modules, each containing at least one rectifier and at least one converter, and each conversion module is capable of supplying power from a minimum of 1 MW to a maximum of 30 MW.

[0051] The above and other aspects, features and advantages of the present invention will become apparent from the following description of some non-limiting embodiments with reference to the accompanying drawings. [Brief explanation of the drawing]

[0052] [Figure 1] This graph shows the temporal variation of electrical parameters applied to the electrodes of an arc furnace during a conventional melting cycle. [Figure 2] This is a schematic diagram of an apparatus for supplying power to a furnace for melting and / or heating a metal material of the present invention. [Figure 3] This graph shows the temporal variation of electrical parameters applied to the electrodes of an arc furnace during the operating cycle of a melting furnace according to some embodiments of the present invention. [Figure 4] This graph shows the temporal variation of electrical parameters applied to the electrodes of an arc furnace during the operating cycle of a melting furnace according to some embodiments of the present invention. [Figure 5] This graph shows the power consumption trend during the operating cycle of an arc furnace. [Figure 6] This graph shows the temporal variation of electrical parameters applied to the electrodes of an arc ladle furnace during the operating cycle of some embodiments of the present invention. [Figure 7] This graph shows the frequency fluctuations in the power consumption of a ladle stove. [Modes for carrying out the invention]

[0053] The language and terminology used in this specification, as well as the figures in the accompanying drawings, even if disclosed, serve only to illustrate and explain the present invention, and their function is to provide non-limiting examples of the present invention, for the scope of protection of the present invention is determined by the claims.

[0054] For ease of understanding, the same reference numerals are used for identical common elements in the drawings where possible. It should be understood that elements and features of one embodiment can be easily combined or incorporated into other embodiments without requiring detailed explanation.

[0055] Referring to Figure 2, some embodiments of the present invention relate to a device 10 for supplying power to a furnace 100 for melting and / or heating a metallic material.

[0056] In some embodiments, power to the device 10 can be supplied by a power supply means 200. In this specification, a three-phase power grid 201 is described as an example, but this does not exclude other configurations.

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

[0058] In a possible solution, the commercial frequency fr is a value selected from 50Hz to 60Hz, that is, it follows the frequency of the power grid of the country where the furnace 100 is installed.

[0059] In some embodiments, the device 10 can be configured to supply power to a three-phase load, particularly a three-phase furnace.

[0060] This type of furnace 100 can be an electric arc furnace, a submerged arc electric furnace, a ladle furnace, or any type of melting, refining, or heating furnace suitable for use in a steel mill or metalworking plant. Preferably, the present invention is applicable to electric arc furnaces (EAF), ladle furnaces (LF), and refining machines that use electrodes 102 to transfer thermal energy to a material to be processed.

[0061] Figure 2 shows an example of a device 10 connected to an electric arc furnace EAF and a ladle furnace LF. When both an arc furnace EAF and a ladle furnace LF are installed in a single steelmaking plant, two devices 10 can be provided, each connected to one of the furnaces, or a single device 10 suitable for supplying power appropriately to both furnaces EAF and LF can be provided.

[0062] If the furnace 100 is an electric arc furnace of type EAF, the furnace 100 includes a container 101 or shell into which the metal material M to be melted is introduced.

[0063] The EAF furnace is also equipped with multiple electrodes 102 that ignite an electric arc through a metal material M to melt the metal material M, and in the illustrated example, three electrodes 102 are provided.

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

[0065] The following explanation will primarily use the EAF reactor as an example.

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

[0067] The moving device 103 can be selected from the group including at least one of the following: a mechanical actuator, an electrical actuator, a pneumatic actuator, a hydraulic actuator, a multi-joint mechanism, a mechanical motion mechanism, other similar or equivalent components, or a possible combination of the above devices.

[0068] In one possible solution of the present invention, when the number of electrodes 102,106 is 3, each electrode is connected to one of the power supply phases of the device 10.

[0069] If there are more than 3 electrodes 102 and 106, each power supply phase can be connected to 2 or more electrodes.

[0070] In some embodiments, the device 10 can receive energy supplied from the power grid 201 and convert it into a supply voltage and supply current having specific electrical parameters Ua, Ia, fa suitable for supplying power to the furnace 100.

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

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

[0073] This solution makes it possible to reduce the impact of interference from the power grid, that is, to reduce harmonic components and reactive power exchanged with the power grid 201.

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

[0075] In some embodiments, the secondary frequency fs can be substantially less than or equal to the above-mentioned commercial frequency fr, or generally less than or equal to 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 commercial voltage Ur and commercial current Ir, respectively, depending on the conversion ratio of the transformer 11, or, more generally, to the primary voltage Up and primary current Ip of the primary side 12, respectively.

[0077] The transformer 11 may be provided with an adjustment device (not shown) that is designed to selectively adjust the electrical conversion ratio of the transformer 11 in relation to specific requirements.

[0078] The apparatus 10 of the present invention also includes a plurality of rectifiers 14 connected to the transformer 11, and these rectifiers 14 are configured to convert the AC secondary voltage Us and secondary current Is into DC intermediate voltage Ui and intermediate current Ii.

[0079] The rectifier 14 can be selected from a group that includes diode bridges or thyristor bridges, etc.

[0080] In one possible solution, the rectifier 14 can be a device selected from the group including, for example, a diode, an SCR (Silicon Controlled Rectifier), a GTO (Gate Turn-Off Thyristor), an IGCT (Integrated Gate-Commutated Thyristor), an MCT (Metal-Oxide Semiconductor Controlled Thyristor), a BJT (Bipolar Junction Transistor), a MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor), and an IGBT (Insulated-Gate Bipolar Transistor).

[0081] In some embodiments, the device 10 includes a plurality of converters 15 connected to a rectifier 14, which are configured to convert the DC voltage and DC current into AC supply voltage Ua and supply current Ia for the electrode 102.

[0082] In one possible solution, the converter 15 can be a device selected from the group including, for example, 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 using at least one intermediate circuit 16 that operates on DC.

[0084] The intermediate circuit 16 creates separation between the rectifier 14 and the converter 15, and consequently, between the furnace 100 and the power supply means 200 connected upstream of the intermediate circuit 16. In particular, since some of the rapid power fluctuations generated by the process are filtered by the intermediate circuit 16, the impact of such rapid power fluctuations on the power supply means 200 is reduced.

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

[0086] In some embodiments, the device 10 includes a control command unit 17, which controls the converter 15 to selectively set the parameters of the supply voltage Ua and supply current Ia that are generated by the converter 15 and supplied to the electrode 102.

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

[0088] Furthermore, in some embodiments of the present invention, the control command unit 17 is also connected to the moving device 103 so that the position of the electrode 102 can be adjusted in relation to various steps of the melting process. In particular, the length of the arc is changed by moving the electrode 102 in accordance with the position of the material via the moving device 103.

[0089] In fact, if the arc is expected to be covered and separated from the furnace vault, thereby avoiding the risk of vault damage, the power supplied to electrode 102 during the melting process can be increased compared to the boring process.

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

[0091] Furthermore, the process becomes significantly more stable during the refining stage, and the amount of electricity required is reduced.

[0092] In this way, the control command unit 17 can manage and command at least the supply voltage Ua, supply current Ia, power supply frequency fa, and the positions of electrodes 102 and 106 in relation to specific steps of the process. The increased possibility of controlling the above-mentioned parameters maximizes the transfer of energy to the process and, at the same time, reduces the impact on the power grid 201 caused by rapid power fluctuations on the furnace side.

[0093] The electrical topology employed in the converter 15 protects the power grid 201 from interference caused by the melting process (flicker, harmonics, power factor reduction, etc.), and at the same time, ensures arc stability throughout all operating processes of the furnace 100, in both the case of an EAF furnace and a ladle furnace LF.

[0094] The control command unit 17 may be equipped with an adjustment device 18.

[0095] In possible solutions of the present invention, the adjustment device 18 may, as an example, include a hysteresis modulator or a PWM (pulse width modulation) modulator.

[0096] The modulator described above can be used to instruct the semiconductor devices of the rectifier 14 and converter 15. If properly controlled, these semiconductor devices generate voltage or current values ​​supplied to the furnace 100, and in this specific example, they generate voltage or current values ​​supplied to electrodes 102 and 106. In particular, the modulator processes the above voltage and current values ​​to generate commands to drive at least the rectifier 14 and converter 15 so that the voltage and current values ​​required for control are supplied to the connection terminals of electrodes 102 and 106.

[0097] The voltages and currents that should operate as described above are the result of the actions taken by the control instruction unit based on the values ​​read from the process and the process model.

[0098] In the present invention, the adjustment device 18 is configured to adjust the power supply frequency fa of the supply voltage Ua and supply current Ia in each step of the melting cycle of the furnace 100.

[0099] The adjustment device 18 receives commands from the control command unit 17.

[0100] In particular, the adjustment device 18 receives commands from the control command unit 17 to ensure that the supply frequency fa is less than or equal to the commercial frequency fr for at least 80% of the entire duration of one operating 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 below the commercial frequency fr from immediately after the start of the operating cycle described above, and furthermore, in at least one step of the operating cycle in the furnace 100, the supply frequency fa becomes lower than the commercial frequency fr of the power supply means 200, and is particularly 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 within the primary side 12 of the transformer 11 during at least one step of the operating cycle in the furnace 100.

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

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

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

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

[0108] Preferably, all power supply modules 19 can be the same size, that is, all power supply modules 19 can supply power within the same range.

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

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

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

[0112] If, as described above, each module 19 is equipped with a rectifier 14, an intermediate circuit 16, and a converter 15 for each phase of the power grid 201, the transformer 11 can be equipped with one transformer primary side 12 and multiple transformer secondary sides 13, in which case each transformer secondary side 13 is connected to the rectifier 14.

[0113] In some embodiments, the device 10 can be provided with a plurality of power supply modules 19 connected in parallel to each other to the power grid 201 and the furnace 100.

[0114] By combining multiple power supply modules 19, a device 10 can be realized whose size can be scaled in relation to the specific size of the reactor 100 that receives the power supply.

[0115] In one possible solution, the control command unit 17 is connected to all power supply modules 19 to control at least each converter 15 so that each module 19 supplies the same supply voltage Ua, supply current Ia, and supply frequency fa to the electrode 102. This configuration prevents malfunctions of the entire system.

[0116] In other variations, each power supply module 19 can be controlled to supply different values ​​of supply voltage Ua, supply current Ia, and supply frequency fa to each electrode 102, for example, to change the power distribution in the dissolution bath.

[0117] In one possible solution, the device 10 may include an inductor 20, which is configured to achieve a desired reactance for the entire device.

[0118] The inductor 20 can be connected downstream of the converter 15 and is sized to achieve the desired overall equivalent reactance. With this configuration, the overall reactance can be obtained from the contribution of the inductor 20 and the reactance generated by the conductor connecting the device 10 to the furnace 100, which in this specific example is the conductor connected to the electrode 102.

[0119] In general, inductance is a (design) parameter that cannot be changed after the component has been assembled.

[0120] By changing the frequency (for example, using the 50Hz or 60Hz of the power grid as a reference), the reactance value of components in a circuit can be changed while the inductance remains the same, thereby achieving the desired overall equivalent reactance value.

[0121] The operation of the apparatus 10 for supplying power to a furnace for melting and / or heating the above-mentioned metal material M corresponding to the method of the present invention is as follows: - Using the power supply means 200, AC commercial voltage Ur and commercial current Ir are supplied at a predetermined commercial frequency fr. - Using transformer 11, the AC commercial voltage Ur and commercial current Ir are converted into a selectively configurable AC secondary voltage Us and secondary current Is having a secondary frequency fs substantially equal to the commercial frequency fr. -By rectifying the secondary voltage Us and secondary current Is using multiple rectifiers 14, a DC intermediate voltage Ui and intermediate current Ii are obtained. - Multiple converters 15 are used to convert the DC intermediate voltage Ui and intermediate current Ii into AC supply voltage Ua and supply current Ia, which can be selectively set by the control command unit 17 connected to the converters 15. - A supply voltage Ua and a supply current Ia are supplied to multiple electrodes 102 of the furnace 100.

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

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

[0124] In other embodiments, the supply frequency fa is less than or equal to the commercial 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 commercial frequency fr for at least 90% of the entire operating cycle, preferably for at least 95% of that entire cycle.

[0126] In some embodiments, the method is such that the supply frequency is 10% to 80% of the commercial frequency for at least one step of the operating cycle.

[0127] In some embodiments, the method is such that the supply frequency fa is 45% to 75% of the commercial frequency fr during at least one step of the operating cycle.

[0128] In some embodiments, the method is such that the supply frequency fa is 101% to 200% of the commercial frequency fr during at least one step of the operating cycle.

[0129] In some embodiments, the method adjusts 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 dynamically adjusted during the operating cycle, manually by the operator, or automatically in relation to the processes and commands executed by the control command unit 17.

[0131] In this specification, "operating cycle" means a set of multiple operating processes relating to a specific furnace 100.

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

[0133] Specifically, during the boring process, the electrode 102 is brought close to the ejected solid metal material M to ignite an electric arc and begin melting the metal material M. As the metal material M gradually melts, the electrode 102 penetrates a portion of the still-solid metal material M, gradually dissolving it. When the electrode 102 reaches a position inside the container 101, the main melting of the remaining metal material M around the electrode 102 begins.

[0134] In one possible solution (Figure 3), the boring and melting processes are repeated multiple times before the refining process, and a process of charging additional metal material M into the electric furnace 100 is provided between these processes.

[0135] For example, referring to Figure 3, a charge of metal material M is introduced, and the electrode 102 is used to drill into this metal charge and melt it. This operation sequence is repeated three times, with metal material M introduced each time.

[0136] The solution shown in Figures 4, 4(A), and 4(B) includes a substantially continuous charge that starts before the boring process and continues until the furnace is full during the process of melting the metal material.

[0137] In the above embodiment, the supply frequency fa is less than or equal to the commercial frequency fr for the entire duration of one operating cycle, i.e., 100%.

[0138] In some embodiments, this method allows the supply frequency fa to be gradually reduced over time as the operating cycle of the furnace 100 progresses.

[0139] The supply frequency fa can start from a predetermined value and decrease, and this predetermined value is, for example, the primary frequency fp of the primary side 12 of the transformer 11 or the commercial frequency fr, and preferably the supply frequency fa starts from the commercial frequency fr.

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

[0141] The supply frequency fa can decrease discontinuously over time, as shown by the dashed line in Figure 4(B), for example, in a stepwise manner. Therefore, the supply frequency fa can take on multiple values ​​f1 that are lower than the commercial frequency fr.

[0142] This method makes it possible to keep the supply frequency fa substantially constant for a duration corresponding to at least each operating process of the furnace 100.

[0143] This method allows the supply frequency fa to reach a value at least 20% lower than the commercial frequency fr at the end of the operating cycle in the furnace 100, preferably at least 40% lower, and more preferably approximately half of the commercial frequency fr.

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

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

[0146] In this method, in an EAF reactor, the supply frequency fa can be made substantially equal to the commercial frequency fr during the boring process, and the supply frequency fa can be reduced in the subsequent operating process until it reaches a value f1, which is substantially equivalent to, for example, half the value of the commercial frequency fr (Figure 3).

[0147] In another example, as shown in Figure 4(A), this method allows the supply frequency fa to be substantially equal to the commercial frequency fr during the boring and charge melting processes in an EAF furnace, and then the supply frequency fa to be gradually reduced in a stepwise manner during the subsequent operating processes.

[0148] In some embodiments not shown, the supply frequency fa can be lower than the commercial frequency fr in all operating processes.

[0149] In some modified forms, this method allows the supply frequency fa to be higher than the commercial frequency fr in at least one step of the operating cycle, for example, to 101% to 200% of the commercial frequency fr.

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

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

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

[0153] The areas highlighted by the enclosed lines indicate situations where rapid oscillations or fluctuations in power are occurring. As can be seen from these areas, the supply frequency fa is higher than the commercial frequency fr in response to these conditions, and for the remainder of the operating cycle, the supply frequency fa is lower than or equal to the commercial frequency fr.

[0154] Therefore, in this invention, once the operating point for at least the power, voltage, current, and frequency of the furnace 100 is established, the method can attempt to have the control command unit 17 follow this operating point, and moreover, to follow the operating point by continuously adjusting the supply frequency fa.

[0155] The operating point can be determined by the operator, or it can be automatically determined 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 it can be calculated based on input data received in relation to the type of material to be melted, the final product to be obtained, the characteristics of the furnace 100, or the required output per hour or other factors.

[0156] Therefore, the present invention makes it possible to optimize the electrical parameters in each of the multiple steps of the process by adjusting the frequency during each step.

[0157] For example, in another example, as illustrated with reference to Figure 6, the operating cycle of a ladle furnace LF includes at least one step of refining the molten metal material M.

[0158] In possible embodiments, the method can maintain a constant supply frequency fa in the ladle furnace LF throughout the entire operating cycle, or it can decrease the supply frequency fa over time according to a linear, stepwise, exponential, or other mathematical curve, or possibly a combination thereof.

[0159] In any case, in the ladle furnace LF, the supply frequency fa is preferably kept lower than the commercial frequency fr for the entire duration of the operating cycle.

[0160] For example, in the embodiment described with reference to Figure 6, in this method, the supply frequency fa in the ladle furnace LF is constant throughout the entire operating cycle and is 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, as shown in Figure 7, if the temperature gradient is made equal in the case of an LF furnace, for example, the present invention can reduce the power consumption required for the furnace 100. For example, if other operating conditions are the same, the power consumption achieved at an operating frequency of 40 Hz in an LF furnace can be reduced by approximately 12% compared to the power required at a frequency of 50 Hz.

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

[0164] Another advantage is that by lowering the operating frequency, the arc power increases, which can shorten the melting time.

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

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

[0167] It is clear that improvements and / or additions can be made to the apparatus 10 and method described above without departing from the field and scope of the present invention as defined in the claims.

[0168] Furthermore, although the present invention has been described with reference to some specific examples, it is clear to those skilled in the art that many other equivalent forms of the method and apparatus 10 for supplying power to a furnace for melting and / or heating a metallic material having the features described in the claims can be achieved, and all such equivalent forms fall within the scope of protection described in the claims.

[0169] The parenthetical symbols in the attached claims are for readability purposes only and should not be considered limiting factors to the scope of protection defined by the claims.

Claims

1. A method for supplying power to a furnace (100) for melting and / or heating a metal material (M), The furnace (100) is an electric arc furnace (EAF) or a ladle furnace (LF), The aforementioned method, Using a power supply means (200), a commercial voltage (Ur) and commercial current (Ir) of alternating current having a predetermined commercial frequency (fr) are supplied. Using a transformer (11), the commercial voltage (Ur) and commercial current (Ir) are converted into selectively configurable AC secondary voltage (Us) and secondary current (Is) having a secondary frequency (fs) substantially equal to the commercial frequency (fr). By using multiple rectifiers (14), the secondary voltage (Us) and the secondary current (Is) are rectified to obtain a DC intermediate voltage (Ui) and an intermediate current (Ii), Using multiple converters (15), the DC intermediate voltage (Ui) and intermediate current (Ii) are converted into AC supply voltage (Ua) and supply current (Ia) that can be selectively set by a control command unit (17) connected to the converters (15). The supply voltage (Ua) and the supply current (Ia) are supplied to the multiple electrodes (102, 106) of the furnace (100), Includes, The above method further, To establish the operating point of the furnace (100) with respect to the power, voltage, current, and frequency supplied to the electrodes (102, 106). Includes, The operating point is automatically determined by the control command unit (17) based on a mathematical model of the furnace (100) and a given melting and / or heating process, or calculated based on input data received in relation to at least one of the following: the type of material to be melted, the final product to be obtained, the characteristics of the furnace (100), and the required output per unit time. In each step of the operating cycle of the furnace (100), the supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) is set to be less than or equal to the commercial frequency (fr) for at least 80% of the operating cycle period, and the power supply frequency (fa) is set to 40% to 80% of the commercial frequency (fr) in at least one step of the operating cycle of the furnace (100). The adjustment device (18) of the control command unit (17) dynamically adjusts the supply frequency (fa) to follow the established operating point by continuously adjusting the supply frequency (fa), and over time the supply frequency (fa) decreases as the operating cycle of the furnace (100) progresses. A method characterized by the following:

2. A method for supplying power to a furnace (100) for melting and / or heating a metal material (M), The furnace (100) is an electric arc furnace (EAF) or a ladle furnace (LF), The aforementioned method, Using a power supply means (200), a commercial voltage (Ur) and commercial current (Ir) of alternating current having a predetermined commercial frequency (fr) are supplied. Using a transformer (11), the commercial voltage (Ur) and commercial current (Ir) are converted into selectively configurable AC secondary voltage (Us) and secondary current (Is) having a secondary frequency (fs) substantially equal to the commercial frequency (fr). By using multiple rectifiers (14), the secondary voltage (Us) and the secondary current (Is) are rectified to obtain a DC intermediate voltage (Ui) and an intermediate current (Ii), Using multiple converters (15), the DC intermediate voltage (Ui) and intermediate current (Ii) are converted into AC supply voltage (Ua) and supply current (Ia) that can be selectively set by a control command unit (17) connected to the converters (15). The supply voltage (Ua) and the supply current (Ia) are supplied to the multiple electrodes (102, 106) of the furnace (100), Includes, The above method further, To establish the operating point of the furnace (100) with respect to the power, voltage, current, and frequency supplied to the electrodes (102, 106). Includes, The operating point is automatically determined by the control command unit (17) based on a mathematical model of the furnace (100) and a given melting and / or heating process, or calculated based on input data received in relation to at least one of the following: the type of material to be melted, the final product to be obtained, the characteristics of the furnace (100), and the required output per unit time. In each step of the operating cycle of the furnace (100), the supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) is set lower than the commercial frequency (fr) for at least 80% of the operating cycle period, and the supply frequency (fa) is lowered over time as the operating cycle of the furnace (100) progresses, so that the adjustment device (18) of the control command unit (17) dynamically adjusts the supply frequency (fa) to follow the established operating point by continuously adjusting the supply frequency (fa). A method characterized by the following:

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

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

5. The supply frequency (fa) is lower than the commercial frequency (fr) for 100% of the entire duration of one operating cycle. 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 commercial frequency (fr), and is between 101% and 200% of the commercial frequency (fr). The method according to claim 1 or 2.

7. The supply frequency (fa) decreases continuously or in a stepwise manner during the operating cycle in the furnace (100), starting from the value of the commercial frequency (fr), and reaching a value at least 20% lower than the commercial frequency (fr) at the end of the operating cycle in the furnace (100), and more preferably becoming approximately half of the commercial frequency (fr). The method according to claim 1 or 2.

8. The furnace (100) is an electric arc furnace (EAF), The aforementioned operating cycle includes at least one step of boring the metal material (M), a melting step, and a step of refining the molten material, The supply frequency (fa) is substantially equal to the commercial frequency (fr) at least during the process of melting the metal material, and decreases in the subsequent operating process of the electric arc furnace (EAF). The method according to claim 1 or 2.

9. The supply frequency (fa) is higher than the commercial frequency (fr) when there is a rapid oscillation in the power supply of the electric arc furnace (EAF) and / or during the boring process. The method according to claim 8.

10. The supply frequency (fa) is substantially constant during each operating process of the furnace (100) and is at least 20% lower than the commercial frequency (fr). The method according to claim 1 or 2.

11. The furnace (100) is a ladle furnace (LF), The aforementioned operating cycle includes at least one step of purifying the molten material, Throughout the entire duration of the refining process in the ladle furnace (LF), the supply frequency (fa) remains constant and is lower than the commercial frequency (fr), preferably 0.45 to 0.55 times the commercial frequency (fr). The method according to claim 10.

12. The furnace (100) is a ladle furnace (LF), The supply frequency (fa) is constant throughout the entire operating cycle and takes a value of 0.4 to 0.6 times the commercial frequency (fr). The method according to claim 10.

13. The supply frequency (fa) takes a value of 30 to 40 Hz in at least one step of the operating cycle in the furnace (100). The method according to claim 1 or 2.

14. A device (10) for supplying power to a furnace (100) for melting and / or heating a metal material (M), The furnace (100) is an electric arc furnace (EAF) or a ladle furnace (LF), The aforementioned device (10) A transformer (11) connected to a power supply means (200) that supplies AC commercial voltage (Ur) and commercial current (Ir) having a predetermined commercial frequency (fr), the transformer (11) converts the AC commercial voltage (Ur) and commercial current (Ir) into AC secondary voltage (Us) and secondary current (Is), respectively. A plurality of rectifiers (14) connected to the transformer (11), the rectifiers (14) convert the AC secondary voltage (Us) and secondary current (Is) into DC voltage and DC current, A plurality of converters (15) connected to the rectifier (14) and connected to the electrodes (102, 106) of the furnace (100), the converters (15) that convert the DC voltage and DC current into AC supply voltage (Ua) and supply current (Ia), A control command unit (17) controls and commands the operation of the converter (15) to adjust the supply voltage (Ua) and the supply current (Ia) over time, It is equipped with, The control command unit (17) is configured to establish the operating point of the furnace (100) with respect to the power, voltage, current, and frequency supplied to the electrodes (102, 106). The operating point is automatically determined by the control command unit (17) based on a mathematical model of the furnace (100) and a given melting and / or heating process, or calculated based on input data received in relation to at least one of the following: the type of material to be melted, the final product to be obtained, the characteristics of the furnace (100), and the required output per unit time. In each step of the operating cycle of the furnace (100), the supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) is set to be less than or equal to 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 (fa) is set to 40% to 80% of the commercial frequency (fr), and the supply frequency (fa) is lowered over time as the operating cycle of the furnace (100) progresses, thereby dynamically adjusting the power supply frequency (fa) to follow the established operating point, through continuous adjustment of the supply frequency (fa). A device (10) characterized by the following.

15. A device (10) for supplying power to a furnace (100) for melting and / or heating a metal material (M), The furnace (100) is an electric arc furnace (EAF) or a ladle furnace (LF), The aforementioned device (10) A transformer (11) connected to a power supply means (200) that supplies AC commercial voltage (Ur) and commercial current (Ir) having a predetermined commercial frequency (fr), the transformer (11) converts the AC commercial voltage (Ur) and commercial current (Ir) into AC secondary voltage (Us) and secondary current (Is), respectively. A plurality of rectifiers (14) connected to the transformer (11), the rectifiers (14) convert the AC secondary voltage (Us) and secondary current (Is) into DC voltage and DC current, A plurality of converters (15) connected to the rectifier (14) and connected to the electrodes (102, 106) of the furnace (100), the converters (15) that convert the DC voltage and DC current into AC supply voltage (Ua) and supply current (Ia), A control command unit (17) controls and commands the operation of the converter (15) to adjust the supply voltage (Ua) and the supply current (Ia) over time, It is equipped with, The control command unit (17) is configured to establish the operating point of the furnace (100) with respect to the power, voltage, current, and frequency supplied to the electrodes (102, 106). The operating point is automatically determined by the control command unit (17) based on a mathematical model of the furnace (100) and a given melting and / or heating process, or calculated based on input data received in relation to at least one of the following: the type of material to be melted, the final product to be obtained, the characteristics of the furnace (100), and the required output per unit time. The control command unit (17) is provided with an adjustment device (18) that, in each step of the operating cycle of the furnace (100), lowers the supply frequency (fa) of the supply voltage (Ua) and the supply current (Ia) to the commercial frequency (fr) for at least 80% of the duration of the operating cycle, and dynamically adjusts the power supply frequency (fa) so as time progresses, the supply frequency (fa) decreases as the operating cycle of the furnace (100) progresses. A device (10) characterized by the following.

16. The adjustment device (18) is selected from a hysteresis modulator or a PWM (pulse width modulation) modulator. The apparatus (10) according to claim 14 or 15.

17. It comprises multiple power supply modules (19), each equipped with at least one rectifier (14) and a converter (15), The plurality of power supply modules (19) are connected in parallel to the power supply means (200) and the furnace (100), The control command unit (17) is connected to all of the power supply modules (19) in order to control each of the converters (15) so that each supply unit (19) supplies the same value of supply voltage (Ua), supply current (Ia), and power supply frequency (fa) to the electrodes (102, 106). The apparatus (10) according to claim 14 or 15.

18. The rectifier (14) is connected to the converter (15), and the system includes at least one intermediate circuit (16) that operates on DC. The intermediate circuit (16) continuously stores electrical energy, causing separation between the converter (15) and the rectifier (14), and consequently causing separation between it and the power supply means (200). The apparatus (10) according to claim 14 or 15.

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