A method for operating a plant network comprising an electrolytic melting furnace and a direct reduction plant.

Abstract

A method for operating a plant network comprising an electric melting furnace and a direct reduction plant is described. The molten bath volume is measured while the plant network is operating. When a predetermined molten bath volume limit is reached or exceeded, tapping takes place. Before tapping, the presence of a collection container for the molten metal is checked. If a portable collection container is not available, the plant network is switched from normal operation mode to buffer operation mode.

Description

Technical Field

[0001] The present invention relates to a method for operating a plant network comprising an electric melting furnace and a direct reduction plant.

Background Art

[0002] In efforts to reduce CO2 emissions associated with ironmaking, so-called electric furnace routes for steel production have received significant attention. In the electric furnace route, directly reduced iron (sponge iron) in a partially reduced form, and / or scrap is used as starting materials. This starting material is melted in an electric arc furnace (abbreviation: EAF), and if necessary, in a further step, oxygen-affinity components are removed by blowing in oxygen.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Since an increase in the use of ironmaking by the electric furnace route is expected, efforts towards improving the efficiency of such ironmaking are becoming increasingly important. Against this background, an object of the present invention is to provide improved coordination of the process steps of the electric furnace route.

Means for Solving the Problems

[0004] This object is achieved by a method having the features of claim 1.

[0005] A method for operating a plant network is provided. This plant network comprises at least one electric melting furnace and a direct reduction plant arranged upstream of the melting furnace. This method is particularly intended to be designed as a method for producing a molten metal, preferably a molten metal containing iron (Fe), particularly preferably pig iron.

[0006] In other words, the essential idea of ​​the presented invention is that the operation of the plant network is considered as a whole, and the plant network comprises both a melting furnace and a direct reduction plant. For the coordinated operation of the plant network, its components, particularly the melting furnace and the direct reduction plant, are coupled to one another via a common control device, such as a control room. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram illustrating an exemplary embodiment of the method according to the present invention, particularly in the production of molten metal consisting of direct reduction products generated as sponge iron obtained from iron ore. [Modes for carrying out the invention]

[0008] The concept of a direct reduction plant positioned upstream of the dissolution furnace means that in the method sequence, the dissolution furnace is immediately following the direct reduction plant. That is, the product produced in the direct reduction plant is transported to the dissolution furnace and / or temporarily stored there.

[0009] A direct reduction plant is a plant in which the intentional reduction of one or more reactants takes place. When iron ore is provided as a reactant, a solid reaction occurs in the direct reduction plant to remove oxygen from the iron ore. Reducing agents used in this process include, for example, coal or natural gas, especially carbon-containing gases and / or hydrogen-containing gases and / or hydrocarbon-containing gases, or atomic hydrogen or molecular hydrogen, which have been increasingly used in recent years and are expected to see increased use in the future. The reaction takes place at a temperature below the melting point of the iron ore, and therefore its external form is hardly altered.

[0010] A direct reduction plant can be designed, for example, as a shaft furnace with a reduction zone through which reactants such as iron ore are passed in the opposite direction to the reducing gas flow. In an alternative embodiment, the direct reduction plant can also be designed, for example, as a rotary cylindrical furnace through which reactants such as iron ore are transported in the opposite direction to the reducing gas flow. Direct reduction plants themselves are well known in practice.

[0011] An electric melting furnace, also referred to as an electric heating device for melting metals or heating liquid metals, may be, for example, an electric arc furnace (EAF) having direct arc action, where an arc is generated between an electrode and the metal. Possible forms include alternating current arc melting furnaces (EAFac), direct current arc melting furnaces (EAFdc), and ladle furnaces (LF).

[0012] However, preferably, the melting furnace used according to the present invention is designed as an arc-resistance heated melting furnace. Such a melting furnace operates on the principle of generating an arc between the electrode and the charge, heating the charge or slag, particularly by the Joule effect. An arc-resistance heated melting furnace can be designed, for example, as a submerged electric arc furnace (SAF), an AC arc reducer (SAFac), or a DC arc reducer (SAFdc), where the electrode is immersed in the charge or slag. Another form is a furnace in which the electrode terminates just above the slag. In this type of furnace, the slag is not shielded by the charge, at least in the area of ​​the electrode. Thus, the slag is open to the top, and the brush arc generated in the slag can be seen from above. This type of furnace is called an open slag bath furnace (OSBF).

[0013] Particularly preferably, in the method according to the present invention, the melting furnace is designed as a submerged electric arc furnace (SAF).

[0014] Alternatively, and more preferably, in the method according to the present invention, the melting furnace is designed as an open slag bath furnace (OSSF).

[0015] Basically, pig iron production is carried out by directly melting reduced iron and / or scrap in an arc-resistance heating furnace, for example, to produce molten metal, during which slag is generated. The slag is adjusted by adding slag-forming agents, and in particular, the composition of the slag is controlled. The addition of carbon carriers, such as coal or coke, may also be considered.

[0016] According to the present invention, as described above, the plant network comprising at least an electrolytic melting furnace and a direct reduction plant located upstream of the melting furnace is intended to have at least two operating modes, namely a normal operating mode and a buffer operating mode for the plant network.

[0017] In the normal operating mode of the plant network, the reduction products, particularly sponge iron, are directly melted in the melting furnace to form molten metal, especially pig iron, and the extraction of the molten metal from the melting furnace is carried out in discrete steps by tapping the molten metal.

[0018] In normal operation mode, the following steps are performed, and these steps are preferably all performed in parallel.

[0019] A) In the continuous operation of the direct reduction plant, one or more iron-containing reactants are reduced by a reducing gas, particularly hydrogen, especially preferably molecular hydrogen H2, and / or natural gas, and / or a further gas such as coke oven gas, to obtain a direct reduction product. Particularly preferred is reduction by as high a proportion of molecular hydrogen as possible in the reducing gas used, for example, more than 90% by volume of molecular hydrogen.

[0020] Preferably, iron ore is used as the reactant. Optionally, further substances such as scrap, carbon carriers, and / or slag-forming agents may be added. In this case, so-called sponge iron is obtained as the direct reduction product.

[0021] However, it is also possible to use other iron-containing reactants. For example, a mixture of converter dust and top sludge produced in the LD converter process can be considered as reactants. Optionally, further substances such as scrap, carbon carriers, and / or slag-forming agents can also be added. In such cases, a direct reduction product containing a high proportion of metallized iron is obtained, which exists as a sponge product. The sponge product is a solid that is morphologically similar to sponge iron.

[0022] B) The manufactured direct reduction product is continuously transported to an electric melting furnace and fed into the melting furnace. Continuous transport can be carried out continuously, for example using a conveyor belt, or semi-continuously, for example by filling transport containers and transporting each transport container after a certain amount has been reached. Transport containers may be, for example, railcars. A further possible embodiment of semi-continuous transport is transport via pipes and / or bunkers. In addition to the direct reduction product, further substances are preferably also fed into the melting furnace, particularly preferably additives, optionally further carbon carriers such as coke and / or coal, and optionally iron-containing substances such as scrap as a substitute or addition, which are transported to the melting furnace and fed into the melting furnace.

[0023] C) In the melting furnace, the introduced direct reduction product is preferably dissolved together with similarly introduced additives, thereby creating a molten metal bath, on which similarly formed slag floats. The properties of the slag are preferably intentionally influenced by additives such as lime, sand, and / or bauxite.

[0024] D) The tapping is carried out in discrete steps. That is, the molten metal is discharged from the melting furnace and placed into a portable collection container that is pre-positioned at a predetermined collection location. For example, the discharge opening located at the lower side or side wall of the melting furnace can be appropriately opened for a long period of time, and thus the molten metal flows out therefrom. A collection container designed, for example, as a so-called collection ladle can be placed below the discharge opening. For example, the collection ladle can be provided as a component of a ladle transport cart known to those skilled in the art.

[0025] During operation of the plant network, the monitoring of the molten bath volume of the molten metal present in the melting furnace is carried out.

[0026] During operation of the plant network, continuously, i.e., without interruption, or quasi-continuously, i.e., at regular or irregular time intervals repeated in short sequences, for example, at intervals of several minutes or up to several hours, for example, at time intervals from 1 minute to 480 minutes, or from 1 minute to 240 minutes, or from 1 minute to 60 minutes, or from 1 minute to 30 minutes, the molten bath volume is determined. The specific value regarding the time interval between two confirmations can be determined by those skilled in the art based on empirical findings, for example, in a specific process flow, and under the requirements regarding the desired process safety, for example, specific to the company.

[0027] For example, the determination of the periodically repeated melt bath volume can be carried out by making the time interval between two directly consecutive determinations of the melt bath volume constant, and this time interval can be, for example, a value from 1 minute to 480 minutes, or for example a value from 1 minute to 240 minutes, or for example a value from 1 minute to 60 minutes, or for example a value from 1 minute to 30 minutes. Alternatively, for example, the determination of the non-periodically repeated melt bath volume may be carried out without making the time interval between two directly consecutive determinations of the melt bath volume constant, but this time interval can be, for example, always a value from 1 minute to 480 minutes, or for example always a value from 1 minute to 240 minutes, or for example always a value from 1 minute to 60 minutes, or for example always a value from 1 minute to 30 minutes. As a measure related to the melt bath volume, for example, the height level of the slag in the melting furnace can be measured, which can be measured optically, for example. The optical measurement can be carried out using, for example, a thermal imaging camera. Sensor measurements using, for example, radar sensors or ultrasonic sensors can also be provided. The measurement of the melt bath volume can basically be carried out directly, for example, by optical inspection. Alternatively, for example, it can also be determined indirectly by continuously creating a mass balance from the input material and the output material. A further possible method of indirect determination is measurement based on the electromagnetic properties of the molten metal, which can be measured, for example, by the current characteristics, such as the electrical resistance, at the electrodes of the melting furnace.

[0028] According to the present invention, it is contemplated that tapping will be carried out when a predetermined melt bath volume limit is reached or exceeded. In a particularly preferred embodiment, this can mean that the predetermined melt bath volume limit is less than the maximum capacity of the melting furnace, for example within the range of 40 percent to 90 percent, preferably 60 percent to 90 percent of the capacity in terms of volume. Alternatively, it can also be contemplated that the predetermined melt bath volume corresponds to the maximum capacity, or that the predetermined melt bath volume is at most 10 percent, preferably at most 5 percent lower than the maximum capacity.

[0029] According to the present invention, before actual iron tapping takes place, the presence of a portable collection container at the collection location is confirmed as part of the iron tapping process. This can be done, for example, by checking with an electronic switch located at the container's installation location. However, manual detection by visual inspection by factory workers may also be attempted to confirm the presence of the portable collection container.

[0030] According to the present invention, when the confirmation of the presence of a portable collection container at the collection location is positive, tapping is performed. On the other hand, when the confirmation of the presence of a portable collection container is negative, the plant network is intended to be switched from normal operation mode to buffer operation mode.

[0031] Buffer operation mode is a plant network operating mode in which the throughput of material input to the melting furnace, particularly direct reduction products to the melting furnace, is reduced or completely stopped compared to normal operation mode.

[0032] Therefore, the plant network as a whole, comprising at least one electrolytic melting furnace and a direct reduction plant located upstream of the melting furnace, is intended to be able to operate in both normal and buffered operating states. The transition to the buffered operating state is made in response to the reception of two monitored parameters.

[0033] 1. The first parameter is the amount of molten bath, measured by monitoring and detected, for example, continuously or semi-continuously, and when it reaches or exceeds a predetermined molten bath limit, the conditions for transitioning to buffer operation mode are provided.

[0034] 2. The second parameter is the result of the inquiry regarding the presence of collection containers at the collection location. The absence of collection containers at the collection location is a sufficient condition for the transition of the plant network to buffer operation mode, and this must be given together with the necessary condition for the transition to buffer operation mode described in 1.

[0035] The described method is a control that can be part of an adjustment loop and is based on the detection of two parameters, for example, regularly performed in a predetermined manner, i.e., the detection of the two parameters described above. The described method is advantageous in that, as long as a sufficient supply of collection containers is guaranteed, normal operating conditions are maintained within the framework of the parameters considered. A further advantage is that a controlled method is provided when a sufficient supply of collection containers is temporarily not guaranteed.

[0036] In an advantageous development of the method according to the present invention, instead of the continuous transport of the produced direct reduction product to the electromelting furnace and the direct reduction product upon arrival at the electromelting furnace being fed into the furnace, as in the normal operating state, a buffer operating mode may be used, in which the direct reduction product is still produced, but a portion of the direct reduction product supplied to the electromelting furnace is temporarily stored in a temporary storage location. Preferably, the first modification step is the switch from the transport of the direct reduction product to the melting furnace and its feeding into the melting furnace to a method procedure in which the direct reduction product is first temporarily stored, and particularly preferably, the buffer operating mode is also the only modification step in which the buffer operating mode differs from the normal operating mode of the plant network for the maximum possible first period. Thus, this described development is intended to be carried out in the buffer operating mode in which steps A), C), and D) carried out according to the present invention are initially carried out unchanged, and only step B) is carried out in the modified manner described. This approach can be advantageous in that, during the first period, the plant network's operating mode can be switched to buffer operation, ensuring continued operation of the plant network without requiring greater intervention on individual components of the plant network, particularly the melting furnace and the direct reduction plant.

[0037] In a further advantageous development of this method, or, or even further, the operating power of the electric melting furnace may be reduced in buffer operation mode, which may result in the advantageous consequence of saving electrical energy. Particularly preferably, the operating power is reduced to minimum operating power. Thus, this advantageous development is intended to modify step C) compared to normal operation mode. The minimum operating power may be, for example, the operating power that ensures the molten metal still in the melting furnace remains liquid and / or avoids irreversible damage due to the cooling of the melting furnace. Operating the melting furnace at lower energy acceptance results in significant power savings and is particularly advantageous when it is anticipated that it will still take a considerable amount of time to prepare a new portable collection container at the collection location of the electric melting furnace.

[0038] A preferred development of the method in buffer operation mode is to provide at least two temporary storage locations for the temporary storage of direct reduction products, with the intention that the first temporary storage location is preferentially filled with the still-warm direct reduction product from step A), particularly still-warm hot direct reduced iron (HDRI). Particularly preferably, only after the capacity limit of the first temporary storage location is reached, is the second temporary storage location filled for longer-term storage, preferably cold direct reduced iron (CDRI). The two temporary storage locations also differ in that, after returning to normal operation mode, the direct reduction product from the temporary storage section can be preferentially introduced from the first temporary storage location. The advantage of this is that, if the storage is not too long, the direct reduction product from the first temporary storage location, e.g., HDRI, still retains thermal energy, making it more energetically advantageous to introduce it into the electric melting furnace than to introduce a colder direct reduction product, e.g., CDRI, instead. It is also conceivable that there be multiple bunkers of each of the above types.

[0039] The first and second temporary storage locations can be designed, for example, as two bunker housings that can be filled independently of each other and are each connected to a melting furnace, each having an openable and closable supply port to the melting furnace, preferably positioned above the melting bath, so that the reduction product is directly fed into the melting furnace by gravity after the supply port is opened.

[0040] In an advantageous development of the method procedure in buffer operation mode, the continuous operation of the direct reduction plant is switched to throttled operation. This means that, in an advantageous development, as a further measure, the buffer operation mode provides a method that modifies step A) of the normal operation mode compared to the normal operation mode.

[0041] In a particularly preferred development of the method procedure in buffer operation mode, the continuous operation of the direct reduction plant is switched to throttled operation only after the capacity limit of the second temporary storage location has been reached. This means that, as a further measure, the buffer operation mode also provides a modification of the method in step A) of the present invention in normal operation mode. Throttled operation can be characterized, for example, by reducing or completely stopping the throughput of direct reduction product production. This measure has the advantage of avoiding the production of direct reduction product that is not needed for a certain period of time when the temporary storage unit is already full, and also has the further advantage of providing time flexibility to restart production, and consequently has economic advantages that may arise.

[0042] Particularly preferred modified forms of throttle operation are described below.

[0043] In a particularly preferred method variant of throttled operation, the plant network is intended to include n melting furnaces, at least two of which are melting furnaces, where n is an integer greater than or equal to 2. In this method variant, the switching of the direct reduction plant from continuous operation to throttled operation is intended to involve reducing the amount of direct reduction product produced by the direct reduction plant per unit time in the buffer operation mode of the plant network and in the throttled operation of the direct reduction plant within that mode. This specifically means that the throttled operation is not intended to completely shut down the direct reduction plant, but simply to switch from producing a smaller amount of direct reduction product per unit time in the normal operation mode to producing a smaller amount of direct reduction product per unit time, which can be achieved, for example, by reducing the supply of reactants and reaction gases.

[0044] Therefore, particularly preferably, the plant network comprises n melting furnaces, at least two of which are melting furnaces. This means that the plant network comprises the electromelting furnaces described above and n-1 further melting furnaces, preferably electromelting furnaces. In this preferred evolution, it is intended that in buffer operation mode, the n-1 further melting furnaces remain unchanged, i.e., continue to operate as in normal operation mode. This yields a preferred evolution of the method in which, in buffer operation mode, the amount of direct reduction product produced per unit time in the direct reduction plant is reduced, but not to zero, as long as other triggering events occur (specifically, confirmation of the presence of portable collection containers is negative, and both the first and second temporary storage locations have reached their capacity limits). This means that the direct reduction plant is throttled, but its operation is not stopped. This consequently means that continuous operation of the direct reduction plant is guaranteed with a high probability, thereby advantageously providing corresponding operational safety.

[0045] Particularly preferably, the reduction in the production of direct reduction products in throttling operation is adjusted to match a specific amount of direct reduction products that are no longer produced in throttling operation compared to normal operation mode, i.e., preferably adjusted to correspond to the reduced requirement in a melting furnace operating in a buffer operation mode different from normal operation mode compared to normal operation mode. That is, it is reduced by the direct reduction product throughput that is no longer required, i.e., the amount of direct reduction products per unit time. In an exemplary case where the continuous transport of the produced direct reduction products to the electromelting furnace is adjusted by temporarily storing the produced direct reduction products in a temporary storage location, and the feeding of the direct reduction products that have reached the electromelting furnace into the melting furnace is adjusted, the amount of direct reduction products produced in the direct reduction plant during throttling operation corresponds to the amount of direct reduction products processed in n-1 additional melting furnaces rather than in the melting furnace that is no longer receiving transport.

[0046] In other words, preferably, in the throttled operation of the direct reduction plant, the decrease in the amount of direct reduction product per unit time is adjusted so that the decrease in the amount of direct reduction product corresponds to an amount no longer needed by an electromelting furnace operating at a lower operating power in buffer operation mode, or preferably an electromelting furnace operating at the minimum operating power, or an electromelting furnace that is not filled with direct reduction product, or in buffer operation mode, an amount no longer needed by an electromelting furnace that is no longer supplied by the feeding of direct reduction product that has reached the electromelting furnace into the melting furnace.

[0047] Alternatively, throttling operation can also be used in a standby mode in which no direct reduction products are produced. Such a form of throttling operation is preferred, for example, when the plant network has only one melting furnace, or when the plant network has multiple melting furnaces, but all melting furnaces in the plant network have a melting bath volume exceeding a predetermined melting bath volume limit, and the presence of a portable collection container cannot be confirmed in any of the melting furnaces.

[0048] For example, if the plant network comprises two electromelting furnaces, i.e., the aforementioned electromelting furnace and one further electromelting furnace, the direct reduction plant is switched to throttled operation after the capacity limit of the first temporary storage location is reached and after the capacity limit of the second temporary storage location is reached. During throttled operation, the direct reduction plant produces an amount of direct reduction product per unit time that is essentially reduced by the amount of direct reduction product demanded by the electromelting furnace during normal operation. Therefore, the amount of direct reduction product still being produced during throttled operation corresponds to the amount of direct reduction product per unit time that can be processed for dissolution by the further melting furnace, i.e., the second melting furnace, alone.

[0049] In a favorable development, in buffer operation mode, confirmation of the presence of collection containers at collection locations is repeated at predetermined time intervals (for example, periodically at intervals of up to 5 minutes), and when a positive result for confirmation of the presence of portable collection containers at collection locations is obtained for the first time, tapping is performed, and if necessary, the operating mode of the plant network is switched from buffer operation mode to normal operation mode after a predetermined waiting time.

[0050] In an advantageous development, in buffer operation mode, the confirmation of the presence of the collection container at the collection location is repeated quasi-continuously, that is, the amount of molten bath is determined in short sequences of regularly or irregularly repeated time intervals, such as several minutes or up to several hours, for example, at intervals of 8 hours or 4 hours, or for example, several minutes or up to 1 hour, and is intended to be repeated regularly, for example, at intervals of up to 5 minutes. For example, in buffer operation mode, periodically repeated confirmations of the presence of the collection container at the collection location can be made at predetermined intervals, and the time interval between two consecutive confirmations of the presence of the collection container at the collection location is constant, and this time interval is, for example, from 1 minute to several minutes, for example, 8 hours or 4 hours, or for example, from 1 minute to 1 hour. Alternatively, for example, in buffer operation mode, aperiodic repeated confirmations of the presence of the collection container at the collection location can also be made, and the time interval between two consecutive confirmations of the presence of the collection container at the collection location is not constant, but this time interval is, for example, always from 1 minute to 30 minutes. Here, during the verification process, once a positive result is obtained for the first time regarding the presence of a portable collection container at the collection location, tapping will be performed, and if necessary, the plant network's operating mode will be switched from buffer operation mode to normal operation mode after a predetermined waiting time.

[0051] The volume of the molten bath can be measured, for example, by optical inspection, or by creating a mass balance, i.e., by balancing the mass of the reactants introduced into the melting furnace with the mass of the products or by-products discharged from the melting furnace.

[0052] In an optional development of the method or an advanced version of the present invention, the plant network may be configured to include at least one additional direct reduction plant in addition to the direct reduction plant, and the operation of all direct reduction plants in the plant network may be controlled via a common control device. In this case, in buffer operation mode, after reaching the capacity limit of the temporary storage location, the continuous operation of exactly one of the direct reduction plants in the plant network may be switched to a first throttling operation to reduce the amount of direct reduction product produced. Preferably, this reduction is made to the extent that it is no longer required in the buffer operation mode of the melting furnace. If the demand for direct reduction product from the melting furnace or group of melting furnaces decreases further, the amount of direct reduction product produced in the first throttling operation can be reduced, and finally, the first direct reduction plant is switched to standby mode. After this switchover, if the demand for direct reduction product decreases further, any further direct reduction plants in the plant network may also be switched to throttling operation.

[0053] In alternative operation management of a group of multiple direct reduction plants, in contrast to the method described above, the continuous operation of at least two, preferably all, direct reduction plants in the plant network is switched to throttled operation. Preferably, all direct reduction plants in the plant network are controlled so that the reduction in the production of direct reduction products is distributed in an essentially uniform manner. This means that, as in the first alternative form, the amount of direct reduction products produced is reduced, but this reduction is borne equally by all direct reduction plants, either at the same total processing capacity or at the same proportion to their respective maximum processing capacity. In particular, if the need for throttled operation is expected to be short-lived, this method has the advantage that all direct reduction plants can continue to operate in a manner that is only slightly different from normal operation without interruption.

[0054] Figure 1, shown as an example, illustrates a principle diagram illustrating an exemplary embodiment of the method according to the present invention, particularly in the production of molten metal consisting of direct reduction products generated as sponge iron, obtained from iron ore.

[0055] In exemplary embodiments, the plant network comprises a direct reduction plant and two electromelting furnaces, for example, of the SAF type. The adjustments described with reference to one of the two melting furnaces are made, while the other melting furnace is referred to as the “further melting furnace” or second melting furnace.

[0056] The plant network is preferably operated in a normal operating mode as shown in part A of the flowchart, as far as possible. In either melting furnace, sponge iron is melted to molten metal, particularly pig iron, with the optional addition of further iron-containing material, such as scrap. In the continuous operation of the direct reduction plant, the iron ore is reduced to sponge iron by a reducing gas, preferably hydrogen and / or natural gas. The produced sponge iron is continuously transported to an electric melting furnace, and upon reaching the electric melting furnace, the sponge iron is fed into the melting furnace. In the melting furnace, the sponge iron is melted to produce a molten bath consisting of molten metal and slag floating on top of the molten metal. This operation of the plant network in normal operating mode is represented by rectangle 1 in the flowchart.

[0057] While the plant network is operating, the molten bath volume is monitored, for example, by continuous or semi-continuous measurement (represented by branch 2). For example, an inquiry can be made after a predetermined molten bath volume limit is reached or exceeded. Unless the conditions are met, the above process continues in normal operation mode (see branch "No"). If the conditions are met, tapping is attempted in normal operation mode (branch "Yes"), but prior to that, branch 3 checks for the presence of a portable collection container, such as a molten ladle, at the collection location (see branch "Yes"). After the check for the presence of a portable collection container at the collection location is positive, i.e., if a ladle is placed at the collection location, tapping 4 is performed. Otherwise, i.e., if the check for the presence of a portable collection container is negative, the plant network switches from normal operation mode to buffer operation mode along branch "No" from branch 3. Buffer operation mode is shown in part B of the flowchart.

[0058] Rectangle 5 represents the following: In buffer operation mode, according to the embodiment, the operating power of the electric melting furnace is reduced to, for example, the minimum allowable operating power for the current type of melting furnace in order to conserve electrical energy. Furthermore, the amount of sponge iron that was intended to be added to the melting furnace is not reduced in the amount produced per unit time, but is not introduced into the melting furnace and is instead temporarily stored in a temporary storage location.

[0059] In the illustrated exemplary variant, temporary storage is carried out by preferentially filling a first temporary storage location with still-warm sponge iron (HDRI) from step A) (represented by branch 6, branch "no", and rectangle 7). After the first temporary storage location is filled, specifically after the capacity limit of the first temporary storage location is reached, a second temporary storage location (CDRI) for longer-term storage is filled (represented by branch 8, branch "no", and rectangle 9).

[0060] In buffer operation mode, a quasi-continuous check is performed to confirm the presence of collection containers at the collection locations (represented by circle 10). When a positive result is obtained for the first time in the check regarding the presence of portable collection containers at the collection locations, tapping is performed and the plant network operation mode is returned from buffer operation mode to normal operation mode.

[0061] When the capacity limit of the second temporary storage location is reached, the direct reduction plant is switched to throttled operation (see Branch 8, Branch "Yes"). Subsequently, the direct reduction plant operates at reduced output, and the output is adjusted so that the remaining output matches the supply to the second electric melting furnace, which is operating at no change (see Square 11). Thus, the throttled operation of the direct reduction plant matches the capacity of the second melting furnace for sponge iron.

[0062] Alternative embodiments of this method are also possible. In an alternative configuration where the plant network has only one melting furnace instead of two, the throttling operation is intended to transition the direct reduction plant to standby mode, in which sponge iron production no longer takes place.

[0063] In other words, the plant network is adjusted, and the amount of molten bath and the presence of collection containers are used as control variables. The above procedure of checking the operating conditions and taking measures ensures high stability and operational safety. A particular advantage of the described series of steps is that the continuous operation of the direct reduction plant is guaranteed at a relatively high rate of operation, which can be achieved, in particular, by the prior temporary storage of the produced sponge iron. Furthermore, the use of multiple melting furnaces, which are planned according to several developmental forms, offers the possibility of avoiding a complete shutdown of the plant network with a high probability.

Claims

1. A method for operating a plant network to produce molten metal, particularly pig iron, wherein the plant network comprises an electric melting furnace and a direct reduction plant located upstream of the melting furnace. In the normal operating mode of the plant network, in the melting furnace, the direct reduction product, particularly sponge iron, is melted with the optional addition of further substances such as scrap, carbon carriers, and / or slag-forming agents to form molten metal, particularly pig iron, in discrete steps. A) In the continuous operation of a direct reduction plant, the step of reducing one or more iron-containing reactants with a reducing gas, particularly hydrogen and / or natural gas, to obtain a direct reduction product, B) The steps of continuously transporting the manufactured direct reduction product to the electromelting furnace and introducing the direct reduction product that has reached the electromelting furnace into the melting furnace, C) A step of dissolving the direct reduction product introduced into the melting furnace to form a molten metal bath containing molten metal and slag floating on the molten metal, D) A discrete process of extracting molten metal, that is, discharging molten metal from the melting furnace into a portable collection container placed at a predetermined collection location. By performing this, the molten metal and / or slag are removed from the melting furnace by tapping. During the operation of the aforementioned plant network, the amount of molten metal in the melting bath within the melting furnace is monitored. When the predetermined molten bath volume limit is reached or exceeds it, the aforementioned tapping is performed. Prior to the tapping of molten metal, a check is performed regarding the presence of the portable collection container at the collection location. If the check is positive, tapping is performed. If the check is negative, the plant network is switched from the normal operation mode to the buffer operation mode. method.

2. In the buffer operation mode, In order to conserve electrical energy, the operating power of the electric melting furnace is reduced. Preferably, the power is reduced to the minimum operating power. The method according to feature 1.

3. In the buffer operation mode, By temporarily storing the manufactured direct reduction product in a temporary storage location, the continuous transport of the manufactured direct reduction product to the electromelting furnace is adjusted, and the feeding of the direct reduction product into the electromelting furnace after it has reached it is adjusted. The method according to 1 or 2, characterized by the features described above.

4. In the buffer operation mode, After the capacity limit of the temporary storage location is reached, the continuous operation of the direct reduction plant is switched to reduced operation. The method according to feature 3.

5. In the buffer operation mode, The first temporary storage location is filled with the still-warm direct reduction product from step A), preferably still-warm iron sponge (HDRI). The method according to feature 3 or 4.

6. In the buffer operation mode, the first temporary storage position and the second temporary storage position are filled with the direct reduction product produced in step A), Preferably, first, the still-warm direct reduction product from step A) is filled into the first temporary storage location, and after the capacity limit of the first temporary storage location is reached, the direct reduction product (CDRI) preferably produced as sponge iron is filled into a second temporary storage location for longer-term storage. The method according to specification 5.

7. The method according to 6, wherein the first temporary storage position and the second temporary storage position are two bunker housings that can be filled independently of each other and are each coupled to the melting furnace, at least the first temporary storage position is connected to the melting furnace and has an openable and closable supply port to the melting furnace, preferably positioned above the melting bath for gravity-fed direct reduction product into the melting furnace, preferably both temporary storage positions are connected to the melting furnace, each bunker housing has an openable and closable supply port to the melting furnace, preferably the bunker housing is positioned above the melting bath for gravity-fed direct reduction product into the melting furnace.

8. In the buffer operation mode, After the capacity limit of the second temporary storage location is reached, the continuous operation of the direct reduction plant is switched to throttled operation. The method according to 6 or 7, characterized by the features described above.

9. The method according to 4 or 8, wherein the plant network comprises n melting furnaces, at least two of which are integers of 2 or more, and in the buffer operation mode, the direct reduction plant is switched to throttle operation to reduce the amount of direct reduction product produced.

10. The method according to 4, 8, or 9, wherein the direct reduction plant is switched to throttled operation to reduce the production of the direct reduction product, preferably operated in a buffer operation mode different from the normal operation mode, particularly operated according to claim 2 or 3, characterized in that the melting furnace is reduced by the amount of direct reduction product throughput that is no longer required in the buffer operation mode.

11. The plant network comprises n melting furnaces, at least two melting furnaces, i.e., the electric melting furnace and n-1 further melting furnaces, wherein in the buffer operation mode, the n-1 further melting furnaces are operated continuously as in the case of normal operation, and n is an integer of 2 or more, as described in any one of claims 1 to 10.

12. The method according to 11, characterized in that if all dissolution furnaces have a dissolution bath volume exceeding the predetermined dissolution bath volume limit, and the presence of a portable collection container cannot be confirmed in any of the dissolution furnaces, the direct reduction plant is switched to a throttle operation designed as a standby mode, thereby stopping the production of the direct reduction product.

13. The method according to any one of claims 1 to 12, characterized in that, in the buffer operation mode, the confirmation regarding the presence of the collection container at the collection location is repeated at predetermined time intervals, and when a positive result for the confirmation regarding the presence of the portable collection container at the collection location is obtained for the first time again, tapping is performed and the operation mode of the plant network is switched from the buffer operation mode to the normal operation mode.

14. The amount of the molten bath is measured by optical inspection, or The amount of the molten bath is measured by creating a mass balance, or The measurement of the amount of molten bath is performed by touch, or The amount of molten bath is measured using a radar sensor or an ultrasonic sensor. The method according to any one of claims 1 to 13, characterized by the features described herein.

15. The plant network comprises at least one additional direct reduction plant in addition to the direct reduction plant, and the operation management of all direct reduction plants in the plant network is controlled via a common control device, and in the buffer operation mode, after the capacity limit of the temporary storage location is reached, The continuous operation of exactly one of the direct reduction plants in the plant network is switched to a first throttled operation to reduce the production of direct reduction products, preferably by the amount of direct reduction product throughput that the melting furnace operating in a buffer operation mode different from the normal operation mode, particularly according to claim 2 or 3, no longer requires in the buffer operation mode, and only after the direct reduction plant that has been switched to the first throttled operation is switched to a throttled operation designed as a standby mode in which the production of direct reduction products is stopped, further direct reduction plants in the plant network of the direct reduction plant are also switched to throttled operation, or The continuous operation of at least two, preferably all, direct reduction plants in the plant network is switched to throttled operation to reduce the production of direct reduction products in the throttled operation, preferably the melting furnace operating in a buffer operation mode different from the normal operation mode, particularly operating according to claim 2 or 3, is reduced by the amount of direct reduction product throughput that is no longer required in the buffer operation mode, and preferably all direct reduction plants in the plant network are controlled so that the reduction in the production of direct reduction products is distributed essentially uniformly. The method according to any one of claims 1 to 14, characterized by the features described herein.

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