Method for heating sponge iron (DRI) between a direct reduction plant and a further-processing plant

Abstract

The invention relates to a method for heating DRI (abbreviation for "direct reduced iron", also referred to as sponge iron) between a direct reduction plant and a further-processing plant, wherein the DRI (2) is conducted in the form of a DRI stream (3) from the direct reduction plant to the further-processing plant by means of a line arrangement (1) and the line arrangement (1) has one or more induction coils (4) in the form of a heating element for contactless heating of the DRI stream (3) conducted through the line arrangement (1), wherein the induction coil (4) or the induction coils (4) is / are operated with alternating current. The invention is characterized in that a frequency of at least 10 kHz is specified and / or set as the frequency of the alternating current.

Description

[0001] Description

[0002] Method for heating sponge iron (DRI) between a direct reduction plant and a further processing plant

[0003] The invention relates to a method for heating DRI (abbreviation for “Direct Reduced Iron”, also known as sponge iron) between a direct reduction plant and a further processing plant.

[0004] Direct reduction of iron ores produces sponge iron, also known as DRI (Direct Reduced Iron). In this process, iron-containing feedstocks, such as lump ore, pellets, and fine iron ore (typically sinter feed to pellet feed), are reduced by contact with reducing gases, such as carbon monoxide (CO) and / or hydrogen (H2), typically at temperatures of approximately 550°C to 1100°C. The reducing gases remove oxygen from the solid, unmolten iron ore, resulting in the aforementioned DRI. This DRI is a semi-finished product that is fed into further processing plants. Examples include further processing for transport and crude steel production in an electric arc furnace (EAF) or a basic oxygen furnace (BOF).

[0005] For example, DRI is briquetted for transport, especially by sea, using hot briquetting machines. If the briquetting temperature is at least 650°C, the briquetted product is called HBI, short for "Hot Briquetted Iron". The quality of the HBI produced is determined by its apparent density, which must be at least 5.0 g / cm³. 3The temperature of the DRI during briquetting is crucial, as it is characterized by its strength and abrasion / fines generation behavior (tumbler index). When processing in an electric arc furnace, energy and thus electricity costs can be saved if the DRI is introduced into the furnace in its hot state. Furthermore, this reduces the cycle time between two taps, the so-called tap-to-tap time (TTT), and thus increases the productivity of the electric arc furnace. For example, charging hot DRI into the electric arc furnace can save up to 140 kWh of electrical energy per ton of steel, thereby reducing the associated electricity costs.

[0006] These examples show that it is essential that the DRI is supplied to the respective processing plant in the hottest possible form, i.e., supplied to the hot briquetting machine or the electric arc furnace as hot as possible.

[0007] However, it is often not possible to feed the DRI directly into the hot briquetting machine with the required minimum briquetting temperature of 650°C, or into the electric arc furnace with the desired high temperature, which would lead to significant savings in electrical energy. This is because the reduction of iron oxides in direct reduction takes place in a temperature range of 550–1100°C. Due to the endothermic carburization of the DRI, in-situ reforming, and heat losses (for example, through cooled shaft internals in shaft-based processes) in the reduction unit, the temperature of the DRI discharged from the reduction unit of the direct reduction plant decreases.

[0008] Especially in fluidized bed processes for direct reduction, the reduction temperature is limited to prevent sticking of the DRI (due to the risk of defluidization). Therefore, the DRI temperature is even lower than in shaft-based direct reduction processes. To bring the DRI temperature to the desired temperature before further processing or to maintain the desired temperature, US 2021 / 0301360 A1 discloses the method of heating the DRI between the direct reduction plant and the further processing plant. For this purpose, a DRI line equipped with an induction heating device is provided between the direct reduction plant and the further processing plant. The DRI line receives the DRI from the direct reduction plant and conveys it to the further processing plant. Induction coils are used as heating elements, providing a magnetic flux through which the DRI moves.This induces an electric current in the DRI, which in turn generates heat due to the electrical resistance of the DRI, so that the DRI is heated without contact by the induction coils.

[0009] Inductive heating is a contactless heating method based on the transformer principle: A conductor or inductor carrying alternating current generates a magnetic field oscillating at the same frequency, which, according to Faraday's law of induction, induces a voltage in a workpiece with weak to high conductivity (e.g., made of metal). This voltage generates an electrical conduction current, also known as an eddy current or induced current, which, due to the electrical resistance of the material, creates Joule heating elements directly within the workpiece.

[0010] Induction is accompanied by two essential electrical effects that are characteristic of the heating principle: firstly, the skin effect (current displacement effect), and secondly, the proximity effect. Together, these two effects cause the induced current, and thus the heat sources, to closely follow the contours of the inductor. This allows the heating profile to be directly influenced via the inductor geometry. In addition to the geometric parameters, the electrical parameters of the inductor current and its frequency play a crucial role in process design. An important design parameter is the electromagnetic penetration depth.

[0011] 5=1 / (n • po • Pr • K-f)

[0012] Here, f is the current frequency with which the inductor is supplied, po is the magnetic constant, p rThe relative magnetic permeability and K the specific electrical conductivity of the workpiece to be heated. The ratio of penetration depth 5 to workpiece diameter d (here the mean diameter of the DRI) provides information about the efficiency and type of heating process. For the homogeneous heating of rotationally symmetrical workpieces, the requirement is that d / 5 = 3.5. Then both the volume power density and the electrical efficiency are high, enabling rapid and efficient heating of the workpiece. With increasing frequency, the skin effect becomes more pronounced, resulting in increasing absorption of the field and thus near-surface heating of the workpiece. Heating then occurs predominantly through heat conduction.

[0013] US Regulation 2021 / 0301360 A1 stipulates that the induction coils are powered by special inverters set to a frequency optimal for heating. Further details regarding this optimal frequency are not provided.

[0014] The invention is based on the objective of providing an improved method for heating the DRI between the direct reduction plant and the downstream processing plant by means of one or more induction coils, in particular a method in which a frequency setting for the alternating current for operating the induction coils is specified, with which a desired heating of the DRI is achieved. This objective is achieved by the features of the method according to claim 1. Embodiments and further developments are specified in the dependent claims.

[0015] The method according to the invention is a method for heating DRI between a direct reduction plant and a further processing plant.

[0016] The DRI produced from the direct reduction plant is available, for example, in the form of individual DRI components such as DRI pellets, DRI fines, reduced sinter, and / or reduced lump ore. The iron ore from which the DRI is produced is available, for example, in the form of pellets, lump ore, sinter, and / or fine ore (e.g., sinter feed and / or pellet feed). DRI is produced from this without remelting. Therefore, the DRI can also exist in these forms and / or configurations.

[0017] The processing plant could be, for example, a hot briquetting machine or an electric arc furnace, as explained earlier. It could also be other compaction or melting plants.

[0018] The invention provides that the DRI is conveyed as a DRI current from the direct reduction plant to the downstream processing plant via a conductor arrangement. The conductor arrangement includes one or more induction coils as heating elements for the contactless heating of the DRI current conveyed through the conductor arrangement. The induction coil(s) are operated with alternating current. The heating of the DRI thus occurs through electric current and induction, and therefore through contactless energy transfer.

[0019] The conduit system includes one or more conduits for the DRI flow. These conduits can be pipes and / or ducts, which can have any cross-section, such as a round or rectangular cross-section (e.g., square). The DRI is transported through the conduits by gravity, with the conduits being arranged at a suitable incline for this purpose.

[0020] The cable arrangement can be configured as follows, for example: One or more induction coils are attached to each cable, i.e., to the pipe or duct, particularly to its outer circumference. The cable itself is made of a non-conductive material. The cable is, in turn, surrounded by an outer sheath, such as an outer pipe. The induction coil(s) can be embedded in the space between the cable and the outer sheath. Additionally, thermal and / or magnetic insulation can be arranged in this space, with the insulation also potentially provided by an air gap.The outer casing serves for mechanical stability and / or for shielding from magnetic fields and / or for targeted guidance of the external magnetic field in order to improve the electrical efficiency of the induction coil and increase the energy input into the DRI, and / or for thermal insulation.

[0021] If the outer casing is electrically conductive, then magnetic flux conductors, for example made of highly permeable material such as laminated ferrite sheet, can be installed inside it. This prevents the magnetic field lines from passing through the outer casing, which would otherwise cause undesirable heating of the casing. Additionally, this extra flux conductor increases the efficiency of the induction coil(s).

[0022] Examples of conductor arrangements in which the method according to the invention can be applied are described in US 2021 / 0301360 A1. The method according to the invention is characterized in that the frequency of the alternating current with which the induction coil or coils are operated is specified and / or set to a frequency of at least 10 kHz.

[0023] The background of the invention is that the frequency of the alternating current of the induction coil(s) is adjustable. According to the invention, this frequency is thus set to at least 10 kHz. For example, the selection and setting of the frequency is carried out taking into account the (in particular average) diameter of the DRI, which is passed through the conductor arrangement as DRI current. Furthermore, the power with which the induction coil(s) are operated can also be taken into account when selecting and setting the frequency, whereby the frequency is selected in particular such that the desired heating is achieved with the lowest possible power.

[0024] The preset frequency can remain constant for each heating cycle. However, it is also possible for the frequency to be changed during heating, for example by a control and / or regulation system, as explained below.

[0025] The invention is based on the understanding that the penetration depth of the magnetic field and its coupling to the DRI can be varied by adjusting the frequency. For example, a higher frequency leads to a shallower penetration depth. Higher frequencies couple better to finer-grained DRI. Low frequencies significantly below 10 kHz, such as typical mains and medium frequencies, exhibit weak coupling and prevent the eddy currents induced in the DRI from closing within the individual DRI components. This results in uneven heating and lower energy efficiency compared to higher frequencies. The advantages of the invention lie particularly in the fact that the process requirement of setting at least a comparatively high frequency of 10 kHz leads to accelerated heating of the individual DRI components.This allows the magnetic field to couple very effectively to the DRI, resulting in relatively high heating efficiency. A further advantage is higher electrical efficiency compared to lower frequencies, such as mains and medium frequencies.

[0026] Increasing the heating of individual DRI components is associated with a reduction in the induction of global eddy currents within the DRI flow. Due to the high contact resistances between the individual DRI components within the DRI flow compared to the specific electrical resistance of the DRI itself, induced eddy currents that close across the entire diameter of the DRI flow (global eddy currents) are only very unevenly distributed (corresponding to the position of the individual components) around the circumference. This is due to the continuous flow of the DRI flow, which constantly redistributes the individual DRI components within the flow. Furthermore, in the case of global eddy currents, sparks and / or arcs can occur, which can erode the surface of the individual DRI components and damage the conductor assembly, leading to a reduced service life and increased wear, for example, of a refractory material.Therefore, the avoidance or at least reduction of global eddy currents in favor of DRI component heating through the intended high frequencies of at least 10 kHz is a further advantage of the invention.

[0027] A further development of the invention addresses the problem that, at least for some downstream processing of DRI, the temperature of the DRI must not become too high due to heating, as this can lead to undesirable effects such as sticking (the DRI components sticking together) and the appearance of liquid phases, i.e., the at least partial melting of the DRI components. For example, the optimal briquetting temperature of a hot briquetting machine is in the range of 650°C to 750°C. Higher temperatures result in significantly higher maintenance costs for the hot briquetting machine. Furthermore, cementite (iron carbide), the desired form of carbon content in HBI for steel production, is a metastable compound that is quite stable up to about 750°C and thus remains well preserved, but decomposes rapidly into iron and carbon at higher temperatures.

[0028] This problem is addressed in a further development of the method by adjusting the frequency of the alternating current used to operate the induction coils such that the temperature of the DRI reaches the Curie temperature of iron after heating, and any further temperature increase beyond the Curie temperature is largely prevented. This means that, with an unchanged frequency, the temperature of the DRI no longer increases after reaching the Curie temperature, or at most increases significantly more slowly. Thus, upon reaching the Curie temperature, there is a point of abrupt change in the inductive energy transfer from the induction coils to the DRI.

[0029] The Curie temperature is the temperature at which a material's ferromagnetic properties completely disappear, leaving it only as paramagnetic above this temperature. The Curie temperature thus marks the reversible phase transition of ferromagnetic materials into their paramagnetic high-temperature form.

[0030] This phase transition causes the heating process to self-regulate and largely stagnate upon reaching the Curie temperature. This is because, upon reaching the Curie temperature, the penetration depth of the magnetic fields increases abruptly due to the aforementioned phase transition and the associated demagnetization of the material. Consequently, the ratio between the diameter of the individual DRI components and the penetration depth becomes very small. This ratio is an indicator of the expected efficiency between the induction coil(s) and the DRI being heated, and ultimately means that upon reaching the Curie temperature, hardly any energy is converted into heat within the DRI.

[0031] The Curie temperature of iron is 768°C. The aforementioned further development is based on the understanding that limiting the heating of the DRI to the Curie temperature of iron, i.e., 768°C, results in a maximum DRI temperature that is desirable for the respective subsequent processing. It should be taken into account, however, that the DRI temperature may drop again after heating before being used in the further processing plant.

[0032] Furthermore, the advanced training is based on the understanding that the following physical effect can be used to prevent the temperature of the DRI from rising beyond the Curie temperature: The induced current in the DRI decreases when the DRI reaches the Curie temperature. This is because the magnetic permeability of the material decreases upon reaching the Curie temperature, and consequently, the electromagnetic penetration depth increases. Additionally, the magnetic field weakens progressively, which also reduces the induced current in the DRI. A lower induced current in the DRI leads to less heat generation, which is either insufficient to further increase the temperature of the DRI or, at most, results in a significantly slower further temperature increase.Taking into account the throughput time of the DRI through the pipe arrangement, it is ensured that the temperature of the DRI does not increase further after reaching the Curie temperature, or at most only increases slightly, and thus the temperature of the DRI is within the desired temperature range of the respective further processing.

[0033] If the goal is to overheat the DRI above the Curie temperature, the frequency must be increased while maintaining the same power output. As the frequency increases, the electromagnetic penetration depth decreases, thereby increasing the energy input into the DRI. The frequency must be selected such that, after reaching the Curie temperature, the electromagnetic penetration depth is sufficiently small to induce enough energy into the DRI for the heating process. The higher frequency results in pronounced surface layer heating below the Curie temperature, which becomes more uniform with increasing temperature.

[0034] Besides the frequency, the available power is a crucial component of this approach. If more power is available than is necessary for the desired temperature rise, the DRI can overheat. Therefore, the described method requires only the minimum necessary power. This minimum power is calculated as the quotient of the mass-flow-dependent enthalpy requirement of the DRI and the product of its electrical and thermal efficiencies.

[0035] The aforementioned dip in inductive energy transfer upon reaching the Curie temperature is thus used to avoid undesirably high temperatures of the DRI. The frequency and power are selected so that the heating of the DRI beyond the Curie temperature occurs only slowly, if at all.

[0036] One embodiment of the invention provides that the frequency of the alternating current is set to less than 40 kHz. This embodiment builds in particular on the further development described above. It has been shown that typical DRI components, which, for example, have a diameter on the order of 12 mm, heat up to the Curie temperature when passing through the conductor arrangement with the induction coil(s) at frequencies between 10 and 40 kHz. However, the described kink in the inductive energy transfer then ensures that no or at most a minimal further temperature increase occurs, and thus the DRI components have a temperature within the desired temperature range when they enter the downstream processing plant.

[0037] An alternative embodiment of the invention involves further processing of the DRI in which a higher temperature of the DRI, exceeding the Curie temperature, is desired while minimizing the power consumption of the induction coil(s). The previously described limitation of the temperature to the order of the Curie temperature is therefore not desirable here. Against this background, this alternative embodiment provides that the frequency of the alternating current with which the induction coil(s) are operated is set to at least 40 kHz, and in particular to at least 60 kHz.At higher frequencies, the kink in inductive energy transfer is less pronounced, so that at sufficiently high frequencies, the heating of the DRI continues rapidly even after reaching the Curie temperature. Consequently, significantly higher temperatures of the DRI can be reached as it passes through the conductor assembly with the induction coil(s), while maintaining the lowest possible power output from the induction coil(s). It has been shown that with typical DRI components, which, for example, have a diameter on the order of 12 mm, significantly higher temperatures can be achieved at frequencies above 40 kHz, even with low power output from the induction coil(s), than at lower frequencies. The effect of frequency on inductive energy transfer has already been explained above.As a further objective of the method, both in the aforementioned further development and generally in all methods according to the invention, it can be sought to achieve the smallest possible, in particular the smallest possible, necessary power of the induction coil or induction coils and thus of the converter(s) connected thereto by suitable selection and setting of the frequency, and thus to minimize the power accordingly.

[0038] Generally speaking, with increasing frequency and the same diameter of the DRI (Direct Resonance Inductor), the inductor efficiency—that is, the coupling between the generated magnetic field and the induced energy in the DRI—increases. A measure of this is the ratio of DRI diameter to electromagnetic penetration depth. A common guideline for frequency selection is a ratio of three or greater.

[0039] In general, the invention and the described further developments are based on the understanding that the choice of frequency plays a crucial role in the heating of the DRI, both with regard to the temperature of the DRI itself and with regard to the temperature distribution across the numerous individual DRI components, which should be as uniform as possible even for DRI components with different diameters. For example, high frequencies above 60 kHz couple well to very well into a wide range of diameters of the DRI components. However, after passing through the conductor arrangement at very high frequencies, larger DRI components may already be partially melted due to high temperatures, while smaller DRI components remain at their Curie temperature.

[0040] Against this background, it can be provided that the frequency of the alternating current is set to a maximum of 100 kHz.

[0041] One embodiment of the method according to the invention provides that a target temperature of the DRI, which the DRI is to reach after heating, is defined, the temperature of the DRI after heating is measured and thus an actual temperature is determined, and the power of the induction coil(s) and / or the frequency of the alternating current are regulated and / or controlled as a function of the difference between the actual temperature and the target temperature with the aim of reaching the target temperature. For example, it can be provided that – in each case compared to the target temperature – the frequency of the alternating current is set higher at a lower actual temperature and lower at a higher actual temperature.

[0042] A further embodiment of the method according to the invention provides that a target differential temperature of the DRI is defined before and after heating, the temperature of the DRI before and after heating is measured, and an actual differential temperature is determined from this measurement. The power of the induction coil(s) and / or the frequency of the alternating current are then regulated and / or controlled as a function of the difference between the actual differential temperature and the target differential temperature, with the aim of achieving the target differential temperature. For example, it can be provided that—in each case, compared to the target differential temperature—the frequency of the alternating current is set higher at a lower actual differential temperature and lower at a higher actual differential temperature. The same control and / or regulation can be achieved by adjusting the power while maintaining a constant frequency.

[0043] A further embodiment of the method according to the invention provides that a target temperature of the DRI, which the DRI is to reach after heating, and / or a target differential temperature of the DRI before and after heating, is defined; the mass flow rate of the DRI through the conductor arrangement is determined; and the power of the induction coil(s) and / or the frequency of the alternating current are regulated and / or controlled as a function of the determined mass flow rate, with the aim of providing the heating power required to reach the target temperature and / or the target differential temperature, calculated from the determined mass flow rate. The mass flow rate can be determined, for example, from the rotational speed of a briquetting machine or a rotary feeder of an electric arc furnace.The required heating power (without losses) is calculated from this mass flow rate multiplied by the required temperature increase to reach the target temperature or the target differential temperature and further multiplied by the specific heat capacity cp of the DRI :.

[0044] Heating power without losses = mass flow rate x temperature increase x cp

[0045] A further embodiment of the method according to the invention provides that the conductor arrangement comprises several induction coils as heating elements for contactless heating of the DRI current conducted through the conductor arrangement, wherein the induction coils are arranged successively in the direction of the DRI current, each induction coil being independently supplied with alternating current, and wherein the frequency of the alternating current of each induction coil is individually predetermined and / or set for each induction coil. This makes it possible for the induction coils to be operated at the same frequency or at different frequencies, each frequency being at least 10 kHz.

[0046] One embodiment of the invention provides that the conductor arrangement comprises two or more individual conductors and that the DRI current is divided into a corresponding number of DRI partial currents, each individual conductor having one or more induction coils for heating the respective partial current. Optionally, the partial currents can be combined again to form a single DRI current after heating. A further development of the invention provides that, to assist in heating the DRI, at least one susceptor is integrated into the conductor arrangement such that the DRI current flows past the susceptor, the susceptor being inductively heated by means of the one or more induction coils and transferring its heat to the passing DRI current by means of thermal conduction and / or thermal radiation.The susceptor can be made of iron, steel, or other ferro- or ferrimagnetic materials, or it can comprise iron, steel, or other ferro- or ferrimagnetic materials, and / or it can be rod-shaped or tubular, for example, an iron rod or tube. In particular, the diameter of the susceptor is selected such that, at the set frequency of the alternating current, the susceptor reaches the Curie temperature of iron, and either a further temperature increase beyond the Curie temperature is largely prevented, or at least a further temperature increase does not lead to the susceptor melting. The susceptor serves to aid in the heating and homogenization of the DRI pellets.

[0047] One embodiment of the method according to the invention provides that the one or more induction coils have a cooling system, in particular a fluid cooling system, for example, a water cooling system. The cooling temperature is set depending on the cooling medium. In the case of water cooling, the induction coil or coils can, for example, be operated such that the outlet temperature is a maximum of 90°C, for example, 80°C. Typical inlet temperatures for water cooling of inductors are around 40°C. At higher outlet temperatures, there is a risk of film evaporation on the copper profile, and at the same time, the electrical resistance of the copper increases almost abruptly, thereby increasing copper losses and reducing the energy input into the DRI. The aforementioned limitation of the outlet temperature thus reduces wear and maintenance requirements and increases the stability of the cable assembly with the induction coil(s).

[0048] To increase the thermal efficiency of the heating process according to the invention, it can be provided that the conductor arrangement, in particular an optionally internal conductor of the conductor arrangement, is thermally insulated.

[0049] The proposed method can be used, for example, to heat DRI from a direct reduction plant, both from direct reduction plants with shaft furnaces and from direct reduction plants operated with fluidized bed, fluidized bed processes, rotary kilns, rotary hearth furnaces or similar units and / or processes.

[0050] The proposed method can be used to heat DRI, which is then used in a hot briquetting machine, an electric arc furnace, or another melting unit. The conduit arrangement for carrying out the method can consist of one or more feedlegs through which the DRI is fed to a hot briquetting machine. The one or more induction coils can then be integrated into these feedlegs.

[0051] The conduit arrangement for carrying out the process may also include one or more discharge lines for discharging DRI from one or more DRI storage units located upstream of an electric arc furnace or other melting unit. In the case of multiple DRI storage units, the conduit arrangement may, for example, include the lines downstream of the DRI storage units and upstream of a control device such as a rotary feeder. Furthermore, the conduit arrangement may include one or more feed lines through which the DRI is supplied to an electric arc furnace or other melting unit. The one or more induction coils may then be integrated into these one or more discharge lines and / or into these lines upstream of the control device and / or into these one or more feed lines.

[0052] Overall, a method is proposed which, by appropriately adjusting the frequency of the alternating voltage with which the induction coil or coils are operated, whereby comparatively high frequencies of at least 10 kHz are set, forces the DRI single-part heating, for example the single-pellet heating, and according to the described further developments, the Curie temperature of iron and the associated kink in the inductive energy transfer are used to limit the temperature of the DRI reached by the heating.

[0053] The line arrangement provided for carrying out the method according to the invention is explained in more detail below with regard to further features and advantages by means of a description of exemplary embodiments and with reference to the accompanying schematic drawings. These show

[0054] FIG 1 shows a cross-sectional view of a first embodiment of a conduit arrangement provided for carrying out the method according to the invention.

[0055] FIG 2 shows a cross-sectional view of a section of a second embodiment of a conduit arrangement provided for carrying out the method according to the invention.

[0056] FIG 3 shows a cross-sectional view of a third embodiment of a conduit arrangement provided for carrying out the method according to the invention.

[0057] FIG 4 shows a cross-sectional view of a section of a fourth embodiment of a conduit arrangement provided for carrying out the method according to the invention.

[0058] FIG 5 shows a cross-sectional view of a section of a fifth embodiment of a conduit arrangement provided for carrying out the method according to the invention, and

[0059] FIG 6 shows a cross-sectional view of a sixth embodiment of a conduit arrangement provided for carrying out the method according to the invention.

[0060] Corresponding parts and components are each marked with the same reference symbols.

[0061] FIGS 1 to 4 each show in a schematic cross-sectional view a section of a conduit arrangement 1 provided for carrying out the method according to the invention.

[0062] By means of the conduit arrangement 1, DRI 2, in the form of individual DRI components, for example, two DRI pellets which may differ in size, is conveyed as DRI stream 3 from a direct reduction plant to a further processing plant. The DRI stream 3 is indicated by arrows; it originates from the direct reduction plant on the left side of the figures and is conveyed to the further processing plant on the right side of the figures. The transport of the DRI 2 through the conduit arrangement 1 occurs by means of gravity; that is, in practice, the conduit arrangement 1 is arranged with a corresponding incline from left to right or vertically.

[0063] For guiding the DRI current 3, the conductor arrangement 1 includes a conductor 5. This conductor 5 can be a pipe or a channel, which, for example, can have a round, oval, or rectangular (e.g., square) cross-section in a plane perpendicular to the plane of the drawing. The conductor 5 is made of a non-electrically conductive material.

[0064] The conductor arrangement 1 includes an induction coil 4 as a heating element for contactless heating of the DRI current 3 conducted through the conductor arrangement 1. The induction coil 4 is operated with alternating current, the frequency of which is set between 10 kHz and 100 kHz. The heating of the DRI 2 thus occurs by electric current and via induction, and therefore by contactless energy transfer.

[0065] In FIG. 1, the conductor 5 is surrounded by an outer sheath 6, for example, an outer tube, with the induction coil 4 arranged in a space 8 between the conductor 5 and the outer sheath 6. The induction coil 4 can, for example, be cast into the space 8. Additionally, thermal and / or magnetic insulation can be arranged in this space 8, whereby the insulation can also be provided by an air gap, i.e., an air-filled space 8. The outer sheath 6 serves for mechanical stability, for shielding against magnetic fields, for the targeted guidance of the external magnetic field to improve the electrical efficiency of the induction coil 4 and to increase the energy input into the DRI, and for thermal insulation.

[0066] In FIG. 2, unlike in FIG. 1, the induction coil 4 is not located in the space 8, but rather outside the outer sheath 6, around its outer circumference. In FIG. 3, unlike in FIG. 1 and FIG. 2, there is no outer sheath 6; instead, the induction coil 4 is located on the conductor 5, around its outer circumference.

[0067] FIG. 4 shows an embodiment of the conductor arrangement corresponding to FIG. 2, in which a susceptor 7 is additionally arranged inside the conductor 5. The susceptor 7 is, for example, an iron rod or an iron tube. The induction coil 4 inductively heats the susceptor 7. The DRI current 3 flows past the susceptor 7. The susceptor 7 transfers its heat to the passing DRI current 3 by means of thermal conduction and / or thermal radiation. The susceptor serves to support the heating and homogenization of the temperature of the DRI 2.

[0068] FIGS. 5 and 6 show two further embodiments of the design of the conduit arrangement 1. In the illustrated examples, only a conduit 5 and no outer sheath 6 are provided, although this outer sheath could easily be provided, for example in arrangements according to FIGS. 1, 2 and 4. The DRI current 3 flows through the conduit 5, the direction of flow being indicated by the arrow.

[0069] FIG. 5 shows only one induction coil 4, which is arranged around the conductor 5. The supply of alternating current to the induction coil 4 from an AC power source is shown schematically. The frequency of the alternating current is adjustable; the adjustment is made according to the method of the invention. In the illustrated example, the induction coil 4 is operated with a power of 2 MW and a frequency of 40 kHz.

[0070] Figure 6 shows several induction coils 4, specifically four in this example, arranged around the conductor 5. The induction coils 4 are arranged sequentially along the conductor 5. Each induction coil 4 is supplied with alternating current from an AC power source, as shown schematically. The frequency of the alternating current is adjustable individually for each induction coil 4. The adjustment is made according to the method of the invention. In the illustrated example, all four induction coils 4 are operated with a power of 500 kW and a frequency of 40 kHz; that is, the sum of the powers of the four induction coils 4 corresponds to the power of the single induction coil 4 in the example according to Figure 5.

[0071] Reference character list

[0072] 1. Cable arrangement

[0073] 2 DRI 3 DRI current

[0074] 4 induction coils

[0075] 5 lines

[0076] 6 Outer shell

[0077] 7 Susceptor 8 Space between conductor 5 and outer shell 6

Claims

Patent claims 1. Method for heating DRI between a direct reduction plant and a processing plant, wherein the DRI (2) is conveyed as DRI current (3) from the direct reduction plant to the processing plant by means of a line arrangement (1) and the line arrangement (1) includes one or more induction coils (4) as a heating element for contactless heating of the DRI current conveyed through the line arrangement (1). (3) comprising the induction coil (4) or the induction coils (4) being operated with alternating current, characterized in that the frequency of the alternating current is specified and / or set to a frequency of at least 10 kHz.

2. The method of claim 1, wherein the frequency of the alternating current is adjusted such that the temperature of the DRI (2) after heating the Curie temperature of iron is reached and a further temperature increase beyond the Curie temperature is at least largely avoided.

3. Method according to claim 1 or 2, wherein the frequency of the alternating current is set to less than 40 kHz.

4. The method of claim 1, wherein the frequency of the alternating current is set to at least 40 kHz.

5. Method according to one of the preceding claims, wherein the frequency of the alternating current is set to a maximum of 100 kHz.

6. A method according to any of the preceding claims, wherein a target temperature of the DRI (2) which the DRI (2) is to reach after heating is determined, the temperature of the DRI after heating is measured and thus an actual temperature is determined, and the power of the induction coil or coils and / or the frequency of the alternating current in The system is regulated and / or controlled based on the difference between the actual temperature and the target temperature, with the aim of reaching the target temperature.

7. Method according to one of the preceding claims, wherein a target differential temperature of the DRI (2) is set before and after heating, the temperature of the DRI is measured before and after heating and an actual differential temperature is determined from this, and the power of the induction coil or induction coils and / or the frequency of the alternating current is regulated and / or controlled as a function of the difference between actual differential temperature and target differential temperature with the aim of achieving the target differential temperature.

8. Method according to one of the preceding claims, wherein a target temperature of the DRI (2) which the DRI (2) is to reach after heating, and / or a target differential temperature of the DRI (2) before and after heating is determined, the mass flow rate of the DRI through the conductor arrangement (1) is determined, and the power of the induction coil or induction coils and / or the frequency of the alternating current is regulated and / or controlled as a function of the determined mass flow rate with the aim of providing the heating power required to reach the target temperature and / or the target differential temperature, calculated from the determined mass flow rate.

9. A method according to any of the preceding claims, wherein the conductor arrangement (1) comprises several induction coils (4) as heating elements for contactless heating of the DRI current (3) conducted through the conductor arrangement (1), wherein the induction coils (4) are arranged successively in the direction of the DRI current (3), wherein each induction coil (4) is independently supplied with alternating current, and wherein the frequency of the alternating current of each induction coil is individually controlled. The duel is specified and / or set for each induction coil.

10. Method according to one of the preceding claims, wherein the conductor arrangement (1) comprises two or more individual conductors and the DRI current (3) is divided into a corresponding number of DRI partial currents, each individual conductor comprising one or more of the induction coils (4) for heating the respective partial current.

11. Method according to claim 10, wherein the partial streams are recombined to form a DRI stream (3) after heating.

12. Method according to one of the preceding claims, wherein, to assist the heating of the DRI (2), at least one susceptor (7) is integrated into the conductor arrangement (1) such that the DRI current (3) flows past the susceptor (7), wherein the susceptor (7) is inductively heated by means of one or more induction coils (4) and transfers its heat to the DRI current (3) flowing past it by means of thermal conduction and / or thermal radiation.

13. The method of claim 12, wherein the susceptor (7) is made of or comprises iron or steel or other ferro- or ferrimagnetic materials.

14. Method according to claim 12 or 13, wherein the susceptor (7) is rod-shaped or tubular.

15. Method according to any one of claims 12 to 14, wherein the diameter of the susceptor (7) is selected such that the susceptor (7) reaches the Curie temperature of iron at the set frequency of the alternating current and either a further temperature increase above the Curie temperature is at least largely prevented or at least a further The temperature increase does not lead to the melting of the susceptor (7).

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