Method for obtaining sponge product having high metallization level

Abstract

The invention relates to a process for obtaining a sponge product with a high degree of metallization, comprising the steps: a) providing metallurgical residues, b) introducing the metallurgical residues into a rotary kiln, c) conveying the metallurgical residues through the rotary kiln in a reducing gas, in particular containing H2, d) removing them. The process takes place in a plant arrangement 100. A rotary kiln 1 is provided with an inlet section 2 and an outlet section 3. Metallurgical residues are conveyed through the rotary kiln along a conveying direction PR. Heating elements H1, H2, H3 arranged externally on the rotary kiln serve to heat the interior. Between a first coupling point 101 at the inlet section 2 and a second coupling point 102 at the outlet section 3, a gas discharge system 103 for discharging reaction gas and reaction products is provided. The gas discharge system leads to a gas processing system 104.A gas recirculation system 105 is connected downstream of the gas processing system 104 for the return of processed reaction gas.

Description

[0001] The invention relates to a process for obtaining a sponge product with a high degree of metallization.

[0002] In the context of efforts to reduce CO2 emissions in steel production, great attention is being paid to the increasing use of the long-established electric steel route as a replacement for the blast furnace-converter route.

[0003] One approach to this is to use a modified version of the electric steel converter route. First, a directly reduced iron carrier, also known as sponge iron, obtained by direct reduction is melted in a melting furnace. The melting furnace can, for example, be an electric arc melting furnace ( electric arc furnace,(EAF for short), as described, for example, in WO 2004 / 108971 A1. Direct reduction is particularly promising for low-CO2 or CO2-free steel production because direct reduction can be carried out using H2 as the reducing gas and H2 can be generated by electrolysis using renewable energy. The molten sponge iron can then be freed of oxygen-affine components in a converter by blowing oxygen into the melt. The result, depending on the C content, is pig iron or crude steel, which can be further processed into steel in subsequent steps. The advantage of this approach is that it is possible to continue using existing converters, which means that parts of existing know-how can still be used and, last but not least, the investment requirements can be kept within limits.

[0004] The use of existing converters to remove undesirable elements from the molten sponge iron means that even after the complete conversion from the blast furnace converter route to the electric steel converter route, the residues known from converter use can be expected to arise.

[0005] Furthermore, it is inevitable that the conversion from the blast furnace-converter route to the electric arc furnace-converter route will not take place simultaneously for all blast furnaces, but will instead be implemented gradually. This means that even after the conversion begins, the metallurgical residues from the blast furnace-converter route will continue to be generated for an extended period, albeit in decreasing quantities.

[0006] Against this background, there is an incentive to improve the utilization of the materials used.

[0007] The problem is solved by a process for obtaining a sponge product with a high degree of metallization.

[0008] A process for obtaining a sponge product with a high degree of metallization is provided. To obtain a corresponding sponge product, the following steps are performed: a) Providing metallurgical residues from the steel industry as a mixture of at least two reactants, at least one of which contains iron, selected in particular from converter dust, coke dust, blast furnace dust, top sludge, mill scale, and arc furnace dust; b) introducing the metallurgical residues into a rotary kiln; c) conveying the metallurgical residues along a conveying direction through the rotary kiln while rotating or by rotating the rotary kiln, i.e. by rotating the rotary tube of the rotary kiln, wherein, during the conveying of the metallurgical residues, the metallurgical residues are exposed to a reducing gas which is passed through the rotary kiln in a countercurrent flow direction, in order to bring about a reduction of the metallurgical residues; d) removing the metallurgical residues that have passed through the rotary kiln. As a result of the described procedure, these are present as a sponge product with a high degree of metallization.

[0009] The invention is based on the previously unknown finding that the treatment of typical metallurgical residues in a reducing atmosphere results in the formation of a sponge product which has a high degree of metallization and, in particular, has a high proportion of metallized iron, i.e. free iron.

[0010] Typical metallurgical residues, especially converter dust and top sludge, are primarily in the form of dust, sludge, or fine grains, for example, with a diameter of less than 5 mm. Such metallurgical residues can be very efficiently reduced in a rotary kiln by applying a reducing gas in a countercurrent flow, so that after passing through the rotary kiln, the materials are completely or almost completely reduced.

[0011] Optionally, the metallurgical residues provided in step a) may be partially or completely agglomerated or briquetted.

[0012] The previously required costly disposal, processing or landfilling of metallurgical residues is largely eliminated, since the resulting sponge product can be reintroduced into the electric steel route or the electric steel converter route in the same way as with sponge iron produced in the direct reduction reactor by direct reduction of iron ore, in the manner described above.

[0013] A converter dust to be used according to the invention is preferably a BOF converter dust or an LD converter dust. It is preferably a converter dust containing 60-75 wt.% Fe, 2-10 wt.% Zn, and 0.1-2.0 wt.% C.

[0014] A possible composition of a converter dust to be used according to the invention is (all values ​​in wt.%): Fe: 60-75, contained in Fe2O3 and FeO and as metallic Fe, for example with 10 to 20 wt.% of the converter dust being metallic iron and the rest in Fe2O3 and FeO, ZnO: 2.5-12.5; C: 0.1-2.0;

[0015] The remainder, in addition to impurities, comprises one or more of the oxides MnO, SiO2, TiO2, P2O5, Al2O3, CaO, MgO, PbO, K2O, V2O5, Cr2O3, BaO, NiO, ZrO2, SrO. Impurities may be metals, transition metals, semimetals, oxides, salts, and other substances, preferably with a total content of less than 10 wt.%, particularly preferably less than 2 wt.%.

[0016] For example, top sludge containing 5-20 wt% Fe, 2-12 wt% Zn, less than 2 wt% Pb and 25-50 wt% C can be used as top sludge.

[0017] A top sludge to be used according to the invention can, for example, consist of (all values ​​in wt.%): Fe: 5-20, contained in Fe2O3 and FeO and as metallic Fe, for example with 0.1 to 3.0 wt.% of the top sludge being metallic iron and the remainder in Fe2O3 and FeO; ZnO: 2-15 wt.%; PbO: < 2 wt.%; C unbound: 30-50 wt.%, preferably 35-45 wt.%; CO2: up to 10 wt.%;

[0018] The remainder, in addition to impurities, comprises one or more of the oxides MnO, SiO2, TiO2, P2O5, Al2O3, CaO, MgO, PbO, K2O, V2O5, Cr2O3, BaO, NiO, ZrO2, SrO. Impurities may be metals, transition metals, semimetals, oxides, salts, and other substances, preferably with a total content of less than 10 wt.%, particularly preferably less than 2 wt.%.

[0019] To ensure that the reduction processes taking place within the rotary kiln are carried out as efficiently as possible, a preferred development provides that during step c), the metallurgical residues transported in step c) are heated to a temperature between 800 degrees Celsius and 1050 degrees Celsius. Temperatures within this range have the advantage that, on the one hand, they are sufficiently high to significantly accelerate the reduction processes and ensure that resulting reaction products such as zinc oxides and lead chlorides are present in the gas phase, and, on the other hand, they are still sufficiently low to prevent an undesirable transition of the solid with a high Fe content into the liquid phase.

[0020] It is particularly preferred that the heating be carried out as indirect heating. This means that, in contrast to direct heating, in which combustion processes are induced within the rotary kiln, the heating is induced using heat generated outside the rotary kiln and introduced into the rotary kiln. Preferably, heating elements attached to the outer skin of the rotary kiln are used to generate heat. These heating elements preferably operate on the basis of electrical resistance heating, and the heat emitted by these elements is conducted through the metallic shell of the rotary kiln, which may be made of stainless steel, for example, into the interior of the rotary kiln. Indirect heating of the interior of the rotary kiln has the advantage of preventing reoxidation of the reduced constituents. It also eliminates the otherwise necessary introduction of combustible materials, such as coal or coke, into the kiln.

[0021] Optionally, it may be provided that a withdrawal preparation is carried out between step c) and step d).

[0022] The removal preparation may, for example, involve conveying the metallurgical residues that have passed through the rotary kiln to a cooling station arranged at the rotary kiln for cooling the metallurgical residues that have passed through the rotary kiln. This cooling station may, for example, be coupled to the outlet section of the rotary kiln.

[0023] Alternatively or additionally, the removal preparation may, for example, involve conveying the metallurgical residues that have passed through the rotary kiln through a briquetting station for briquetting the metallurgical residues that have passed through the rotary kiln. The briquetting station may, for example, be coupled to the outlet section of the rotary kiln.

[0024] If both cooling in a cooling station and briquetting in a briquetting station are provided, the cooling station can, for example, be coupled to the outlet section of the rotary kiln and the briquetting station to the cooling station, with cold briquetting being carried out in the briquetting station.

[0025] If both cooling in a cooling station and briquetting in a briquetting station are provided, the briquetting station can, for example, be coupled to the outlet section of the rotary kiln and the cooling station to the briquetting station, with hot briquetting being carried out in the briquetting station.

[0026] The provision of one or more steps of removal preparation has the advantage that the removed sponge product can be prepared in a form that is immediately ready for further use.

[0027] According to a preferred development of the method, gases produced during the reduction of the metallurgical residues are transported out of the rotary kiln using a transport gas and / or the reaction gas. For this purpose, a gas discharge system is preferably coupled to an inlet section of the rotary kiln, which, due to the countercurrent flow of the reducing gas, is located at the end of the flow path of the reducing gas. This process has the advantage that a largely consistently well-reducing atmosphere remains within the rotary kiln. The transport of the resulting gases, which can in particular be zinc oxides and / or lead compounds, in particular lead chlorides, takes place in particular using the reaction gas.To further support the transport of the resulting gases with the reaction gas, a transport gas can be additionally conducted in the same flow direction, i.e., based on the countercurrent principle, opposite to the movement of the metallurgical residues. The transport gas is preferably a protective gas, with N2 being preferred due to its lower cost compared to other protective gases. Alternatively or additionally, the use of one or more noble gases, such as argon, is also possible.

[0028] According to a preferred embodiment, it is provided that a gas discharge system is provided for discharging reaction gas passing through the rotary kiln as well as gaseous reaction products, through which gaseous reaction products are discharged from the rotary kiln.

[0029] Particularly preferably, a gas processing system is coupled to the rotary kiln for processing the reaction gas discharged in the gas discharge system, which has previously passed through the rotary kiln, together with the entrained gaseous reaction products. In particular, it can be provided that the gas processing system is coupled to the gas line system in such a way that the gas is guided into the gas processing system via the gas discharge system.

[0030] In the gas treatment system, preferably gaseous Zn or Zn-O compounds are separated; for this purpose, the gas treatment system may, for example, have a Zn trap, which is designed as cooled metal plates, for example made of copper, which provide condensation surfaces for Zn condensation.

[0031] Alternatively or additionally, gaseous Pb-O compounds are separated in the gas processing system; for this purpose, the gas processing system may, for example, have a metal vapor trap, which is designed as cooled metal plates, for example made of copper, which provide condensation surfaces for metal condensation, in particular for Pb condensation.

[0032] It is particularly preferred if the gas processing system comprises one or more of the following processing units: Zinc trap, dust separator, water separator, CO2 separator, reducing gas conditioner, backup reaction gas supply.

[0033] After successful gas processing in the gas processing system, the gas can be returned to the rotary kiln via a gas recirculation system located downstream of the gas processing system. To comply with the countercurrent principle mentioned above, the gas recirculation is preferably carried out via a coupling to an outlet section of the rotary kiln.

[0034] Particularly preferably, the mixture of reactants, i.e., the metallurgical residues fed into the rotary kiln, consists of at least 90 wt. %, preferably at least 98 wt. %, particularly preferably entirely, converter dust and top sludge. Experiments have shown that a mixture of converter dust and top sludge enables a very efficient production of a sponge product with a very high degree of metallization, in particular a very high proportion of metallic iron. Using a process carried out according to this development, it was possible to produce sponge iron which, depending on other process parameters, exhibited a degree of metallization of more than 80%, and in some cases almost 100%.

[0035] A sponge product with a high degree of metallization to be removed according to the invention in step d) preferably has a degree of metallization of more than 80 percent, preferably of more than 95%, particularly preferably of more than 98%.

[0036] A sponge product with a high degree of metallization to be removed in step d) according to the invention preferably has a degree of metallization of the iron contained in the sponge product of more than 80 percent, preferably more than 95%, particularly preferably more than 98%. For example, the Fe content of the sponge product is at least 75% by weight, preferably at least 80% by weight, particularly preferably at least 85% by weight.

[0037] According to a further development of the process, the ratio of converter dust to top sludge in the metallurgical residues, i.e. the mixture of reactants fed into the rotary kiln, is between 60 wt.%:40 wt.% and 90 wt.%:10 wt.%, preferably between 65 wt.%:35 wt.% and 80 wt.%:20 wt.%, particularly preferably between 65 wt.%:35 wt.% and 75 wt.%:25 wt.%. With the stated weight ratios, it has been shown that a degree of metallization of almost 100% could be achieved even with comparatively low H2 flows as the reaction gas flow in the rotary kiln.The developers have not yet been able to develop a complete theory for this; they presumably attribute the effect to the fact that a certain minimum proportion of top sludge, due to the carbon contained in the top sludge, contributes to a particularly efficient reduction of the substances present in the mixture of reactants under the thermodynamic conditions prevailing in the rotary kiln.

[0038] It is particularly preferred that the reaction gas comprises H2, preferably at least 90 vol.% H2, particularly preferably at least 98 vol.% H2. According to a particularly advantageous development, the hydrogen used as reaction gas is H2 obtained exclusively from water electrolysis, in particular exclusively from water electrolysis using renewable electricity, for example exclusively from electricity generated by wind turbines and / or photovoltaics.

[0039] Due to the dependence on the specific circumstances, for example, regarding the specific plant parameters, the person skilled in the art implementing the process is reliant on empirically adjusting the reaction gas flow, in particular the H2 gas flow, and / or the residence time of the metallurgical residues in the rotary kiln such that the resulting product exhibits the desired degree of metallization, in particular the desired degree of Fe metallization. This empirical determination of a sufficiently high gas flow or a sufficiently long residence time does not pose any particular difficulties for the person skilled in the art, since economic considerations are more important than technical ones.

[0040] A sponge product with a high degree of metallization obtained with one or more of the conditions described above may, for example, consist of: one or more of the oxides MnO, SiO2, TiO2, P2O5, Al2O3, CaO, MgO, PbO, K2O, V2O5, Cr2O3, BaO, NiO, ZrO2, SrO: 10-30 wt.%, C: less than 1 wt.%, Zn: less than 1 wt.%, Mn, Cu and Pb: total less than 2 wt.%, remainder, besides impurities: Fe.

[0041] Impurities may be metals, transition metals, semimetals, oxides, salts and other substances, preferably with a total content of less than 5 wt.%.

[0042] Tests have shown that the sponge products obtained consist of at least 68% by weight of metallic iron, and depending on the specific conditions, a significantly higher proportion.

[0043] The rotary kiln preferably has an inlet section and an outlet section as well as a rotary tube arranged between the inlet section and the outlet section, which is rotatably mounted relative to the inlet section and the outlet section, wherein the rotary kiln is designed as a gas-tight rotary kiln.

[0044] A rotary kiln has long been known in many applications. In many cases, the inlet section is designed as an inlet housing and / or the outlet section is designed as an outlet housing. In principle, however, the inlet section can also have a simpler design. The inlet section generally serves the purpose of feeding and introducing material to be treated in the rotary kiln into the rotary kiln; similarly, the outlet section generally serves the purpose of discharging material. In some designs, the inlet section and outlet section can also contribute to the bearing of the rotary kiln, which is mounted so that it can rotate relative to the inlet section and outlet section, or can utilize the bearing of the rotary kiln, which is mounted so that it can rotate relative to the inlet section and outlet section. The rotary kiln is cylindrical in some sections or along its entire longitudinal extent.The rotary tube is preferably circular-cylindrical or at least circular-cylindrical in every mounted section of the rotary tube, particularly preferably also between these and thus along its entire extent. At the beginning and end, the rotary tube is rotatably mounted, for example, on the inlet section and outlet section. Preferably, an inner bearing of a rolling bearing is arranged on the rotary tube on the inlet section and outlet section, the respective outer bearing of which is part of the inlet section and the outlet section, respectively. The rolling bearing is particularly preferably a ball bearing. In principle, another type of bearing is also possible, for example with a plain bearing.The rotary kiln also often has coupling means for coupling to a drive, whereby the drive itself is not considered to be a component of the rotary kiln in the definition in this description and the presence of coupling means for coupling the rotary kiln to the drive has no relevance for the considerations of the presented development, so that their potential presence is assumed but not considered to be a component of the invention or one of its developments.

[0045] Preferably, the rotary kiln is designed as a gas-tight rotary kiln. Thus, a rotary kiln is used which, in contrast to simpler rotary kilns, is equipped such that the interior of the rotary kiln is sealed off from the exterior in a gas-tight manner. The gas-tight seal of the rotary kiln from the exterior is to be understood as meaning that the rotary kiln is sealed at all points in such a way that no significant amounts of ambient air can enter the rotary kiln. For the process to be carried out, this results in the particular advantage that no significant amounts of ambient air can enter the rotary kiln, thereby enabling efficient deoxidation of the metallurgical residues reduced in the rotary kiln.

[0046] For the gas-tight closure of the rotary kiln in the manner described above, which is preferred in a further development, the rotary kiln has suitable provisions. This is unproblematic with regard to the inlet and outlet sections. For example, the inlet section can be coupled to an input lock for introducing metallurgical residues. In addition, the outlet section can be coupled to an extraction lock for extracting the sponge product with a high degree of metallization. The input lock can be coupled to the inlet section, for example, by means of a metallic sealing ring; the extraction lock can also be coupled to the outlet section, for example, by means of a metallic sealing ring. For example, a sealing ring in accordance with DIN 7603:2001-05 can be used as the metallic sealing ring.

[0047] For example, it may be provided that a first sealing arrangement is arranged in a transition region from the inlet section to the rotary kiln to seal the interior of the rotary kiln from the exterior. This means that the aim is that, at least in the region where the transition from an area stationary relative to the earth's surface, i.e. the inlet section, to the rotatable rotary kiln takes place, design measures are implemented which, as a whole, seal the interior of the rotary kiln from the exterior of the rotary kiln. The potential leakage from the interior of the rotary kiln to the exterior, which inevitably results from the required connection between the stationary and rotating areas, is thereby largely or completely eliminated.In an analogous manner, a second sealing arrangement is arranged in the transition area from the rotary tube to the outlet section, the purpose of which is to seal potential leaks at the interface between the rotating area and the stationary area.

[0048] According to an advantageous embodiment, at least one of the first sealing arrangement and the second sealing arrangement comprises a mechanical seal. This means that the functionality of the sealing arrangement is based on the principle of the mechanical seal.

[0049] It is preferred that both sealing arrangements have a mechanical seal.

[0050] Mechanical seals are known in several areas of technology. A mechanical seal is generally defined as a seal that seals a rotating shaft against a wall. To seal the wall against the rotating shaft, a mechanical seal has two components that slide over one another, one of which is called the sliding ring and one of which is called the counter ring. One of the two rings is rigidly arranged in the stationary part, for example, in the inlet section of the rotary kiln described above, while the other is non-rotatably coupled to the rotating part, for example, in the rotary kiln described above, to the rotary tube intended for rotation.A mechanical seal has the advantage that a very good seal can be achieved despite the movement of a rotating part against a stationary part, for example in this case a rotational movement of a rotary tube relative to the inlet section or the outlet section.

[0051] Although improved sealing of the exterior to the interior compared to previously known rotary kilns through the use of mechanical seals entails increased design effort, this can be worthwhile due to the resulting advantageous properties, which open up new, previously unknown applications. Because the rotary kiln is particularly well sealed from the exterior according to a further development, it is possible to create gas-containing atmospheres inside the rotary kiln, in which gas loss can be largely avoided and contamination with ambient air is largely prevented.This ensures that the gases present in the rotary kiln remain in the process, are used as efficiently as possible and, since they remain in the system, can potentially be continuously removed and - if necessary after a step or sequence of steps of processing the reaction gases and gaseous reaction products present in the system - - fed back into other processes or another process step of the same process.

[0052] The mechanical seal also has the advantage that the rotating drum, sometimes referred to as a annealing drum, is designed to be highly gas and dust-tight to the stationary inlet and outlet sections. The mechanical seal also has the advantage that, due to its design with sliding elements and their preload, it can also compensate for unavoidable wobbling movements of the drum, i.e., movements in the axial direction, to a certain extent.

[0053] In a particularly preferred embodiment, the sealing arrangement is realized in that the first mechanical seal has a sliding element that is coupled to the inlet section, wherein the sliding element is preferably designed as a sliding flange. This sliding element is preferably oriented such that the sliding surface of the sliding element points towards the interior of the rotary kiln, i.e. a normal on the flange points parallel to the axis of rotation of the rotary kiln in a direction in which the longer section of the rotary kiln, viewed from the flange, is mounted than the section of the rotary kiln mounted in the anti-normal direction. Analogously, the second mechanical seal preferably has a sliding element that is coupled to the outlet section, wherein the sliding element is preferably designed as a sliding flange.Preferably, this sliding element is oriented such that the sliding surface of the sliding element points toward the interior of the rotary kiln, i.e., a normal on the flange points parallel to the rotational axis of the rotary kiln in a direction in which the longer section of the rotary kiln, as viewed from the flange, is supported than the section of the rotary kiln pointing in the antinormal direction. In other words, the two normals are directed toward each other.

[0054] Preferably, the sealing arrangement, or each sealing arrangement, further comprises a compression spring designed to prestress the sliding element toward the interior of the rotary kiln. It is particularly preferred that the compression spring be adjustable. Prestressing the sliding element can be achieved by conventional means, for example, by screwing it against a suitably positioned counterflange that is fixed relative to the earth's surface. The counterflange can, in particular, be coupled to the rotary kiln, i.e., directly or indirectly connected.

[0055] The mechanical seal particularly preferably has two sealing elements provided for sealing against the sliding surface. One of these sealing elements is an inner sealing element and is coupled to the rotary tube in a fastening region of the sealing arrangement in a rotationally fixed manner. The inner sealing element is preferably designed as a sealing ring, in which case it can be referred to as an inner sealing ring. The second sealing element is designed as an outer sealing element, which is also coupled to the rotary tube in a rotationally fixed manner and is preferably designed as a sealing ring, in which case: an outer sealing ring. The inner sealing element and the outer sealing element are pressed together axially between the fastening region and the sliding surface, i.e. pointing in a direction parallel to the axis of rotation. The inner sealing element is spaced less far from the axis of rotation than the outer sealing element.The inner sealing element and / or outer sealing element are to be selected from suitable materials, preferably using graphitized sealing cord, particularly preferably graphitized glass fabric or graphitized ceramic fiber.

[0056] As is immediately apparent, it is also possible in a constructive reversal that the sealing elements are arranged at the inlet or outlet areas and the sliding surface is arranged in a rotationally fixed manner on the rotary tube.

[0057] The inner sealing element and the outer sealing element, on the one hand, as well as the fastening area and the sliding surface, on the other hand, are preferably dimensioned such that the inner sealing element, the outer sealing element, the fastening area, and the sliding surface define a continuous sealing space at every degree of rotation of the rotary kiln. By providing two sealing elements that are spaced at different distances from the rotation axis, a gap is formed between them, which, together with the fastening area on the one hand and the sliding surface on the other hand, forms a constantly closed sealing space, provided the four elements are also suitably dimensioned.This can be achieved in a particularly elegant design, for example, by having the inner sealing element and the outer sealing element each designed as a sealing ring, and by completely covering the hollow gap between the inner sealing ring and the outer sealing ring, both by the sliding surface of the sliding flange on the one hand and by the sealing area on the other. For geometric reasons, this cover would therefore necessarily remain completely closed even when the sealing tube rotates, and at every degree of rotation, i.e., along the entire 360° rotation. The double seal with two sealing elements has the advantage that even if one of the sealing elements deteriorates in its sealing performance, for example due to porosity or wear, the other of the sealing elements functions as a redundant sealing measure.

[0058] Particularly preferably, it is provided that, starting from the sliding surface, a passage leads from the sealing chamber to a sliding element outlet of the sliding element. The sliding element outlet is coupled to a gas supply device, for example via a docking nozzle surrounding the sliding element outlet. The gas supply device serves to introduce a gas into the sealing chamber. This means that the sealing chamber formed, which, as described, functions as such at every degree of rotation of the rotary kiln and is sealed against the interior, is filled with a gas from the outside. Filling it with a gas causes it to function, in a sense, as a sealing gas, thereby preventing, or at least partially preventing, gases present inside the rotary kiln from escaping to the outside. This can be achieved, in particular, by building up a sealing gas pressure in the sealing chamber that is higher than the pressure present in the rotary kiln.In particular, it can be provided that the pressure in the sealing chamber is up to 5 mbar higher than that in the interior of the rotary tube, preferably between 1 and 5 mbar higher, with which very good results have been shown in tests carried out on prototypes.

[0059] The sealing chamber is preferably filled with gas at an overpressure of up to 10 mbar, particularly preferably up to 5 mbar, compared to the process gas pressure inside the rotary kiln. In this pressure range, the penetration of ambient air into the process chamber and the escape of process gases and dust from the process chamber into the environment are effectively prevented, thus ensuring a gas-tight seal between the exterior and the interior of the rotary kiln. The gas pressure present in the pressure chamber can, for example, be set in a pressure-controlled manner, for example as a function of the pressure present in the process chamber, i.e. inside the rotary kiln. A mass flow controller, for example, can be used as the control element for this purpose. Furthermore, it can be provided that a pressure sensor is arranged in the sealing chamber for monitoring the sealing chamber pressure continuously or repeatedly at predetermined intervals.

[0060] In a particularly preferred embodiment, a number of sliding element outlets are arranged along the outer circumference of the sliding element, which are preferably positioned at equal angles to one another. Each of the existing sliding element outlets is coupled to a gas supply device, preferably coupled to the same gas supply device. Particularly preferably, a ring line is provided, which is coupled to the same gas supply device and has branches to the sliding element outlets. This implementation allows gas to be introduced into the sealing chamber at spaced-apart locations, particularly preferably at supply locations positioned at equal angles to one another, so that maintaining an overpressure relative to the process present inside can be implemented in a particularly efficient manner.

[0061] Nitrogen, N2, or a noble gas, in particular argon, Ar, can be used as a barrier gas.

[0062] Further details, features and advantages of the subject matter of the invention emerge from the following description in conjunction with the figures in which exemplary embodiments of the invention are shown.

[0063] It is understood that the features mentioned above and those explained below can be used not only in the combination specified, but also in other combinations or on their own.

[0064] They show: Fig. 1 : Plant layout for an exemplary explanation of the production of a sponge product with a high degree of metallization; Fig. 2 : Basic principle of a rotary kiln; Fig. 3 : Sectional view of a section of an embodiment of a rotary kiln.

[0065] Fig. 1shows, based on an exemplary embodiment, a plant arrangement 100 for producing a sponge product with a high degree of metallization. There is a rotary kiln 1 with an inlet section 2 and an outlet section 3. In the inlet section, metallurgical residues, at least one of which contains iron, are fed in, preferably via a lock. Converter dust and blast furnace sludge are particularly preferred. The metallurgical residues are conveyed through the rotary kiln as the rotary tube of the rotary kiln 1 rotates along a conveying direction PR. During conveying, the metallurgical residues are exposed to a reducing gas which is passed through the rotary kiln in the countercurrent principle, flowing against the conveying direction PR in the countercurrent direction PG. This achieves a reduction of the compounds contained in the metallurgical residues.During transport, the interior of the rotary kiln is heated by heating elements H1, H2, and H3 arranged externally on the rotary kiln. The temperature is selected so that the reduction processes occur sufficiently quickly, while not being so high that the reduction melts any metallized iron, but high enough to prevent condensation of initially gaseous metals or metal compounds of other metals, such as zinc oxides and / or lead chlorides. Tests have shown that temperatures in the range between 800 and 1050 degrees Celsius are suitable.After passing through the rotary kiln, the reduced product, which is a sponge product with a high iron content and a high degree of metallization, chemically and structurally very similar to sponge iron (HBI, hot briquetted iron), is removed from a discharge lock in outlet section 3 and then sent for further use, in particular as an intermediate product for the production of pig iron or crude steel. Due to the chemical and structural similarity to sponge iron (HBI, hot briquetted iron), it is preferred that briquetting be carried out after the treatment in the rotary kiln.

[0066] Between a first coupling point 101 at the inlet section 2 and a second coupling point 102 at the outlet section 3, a gas discharge system 103 is provided for discharging the reaction gas passing through the rotary kiln and the gaseous reaction products. The gas discharge system leads to a gas processing system 104, in which the gas mixture of the reaction gas passing through the rotary kiln and the gaseous reaction products is processed. Gaseous Zn-O compounds and / or gaseous Pb-O compounds are separated, and further processing takes place in one or more of the following processing units: Zinc trap, dust separator, water separator, CO2 separator, reducing gas conditioner, backup reaction gas supply.

[0067] A gas recirculation system 105 is coupled downstream of the gas processing system 104 for the purpose of recirculating processed reaction gas into the rotary kiln, whereby the recirculation is optional.

[0068] Fig. 2shows the basic principle of a rotary kiln 1. The functional heart of the rotary kiln 1 is a rotary tube 4, which in technical terminology is often referred to as an annealing drum. The rotary tube 4 is mounted to rotate. In the present example, the rotary tube 4 is circularly cylindrical and rotates about a rotation axis R. On one side of the rotary tube, an inlet section 2 is provided, which in the schematic diagram is designed in the form of a housing 2 and which serves in particular to allow the material to be treated in the annealing drum to be fed in and can be opened and resealed for this purpose. On the other side of the rotary tube, an outlet section 3 is provided, which receives the material that has passed through the rotary tube 4 in order to feed it to an openable and resealable removal opening or to another treatment station.The rotary tube 4 is arranged between the inlet section 2 and the outlet section 3, wherein the inlet section 2 and the outlet section 3 are stationary relative to the earth's surface, whereas the rotary tube 4 is rotatably mounted relative to the inlet section 2 and the outlet section 4.

[0069] To seal the interior 5 of the rotary kiln 1 from the exterior 6, a first sealing arrangement 8 is arranged in a transition region 7 from the inlet section 2 to the rotary tube 3. The transition region 7 is to be understood as an area that comprises at least a section of the inlet section 2, a section of the rotary tube 4, and structural measures for coupling the one to the other, whereby a demarcation to the outside is not important, since the transition region is the conceptual requirement to at least take the potential transition point into account. In a similar manner, a second sealing arrangement 10 is arranged in a transition region 9 from the outlet section 3 to the rotary tube 4. The first sealing arrangement 8 has a first mechanical seal 11. The second sealing arrangement 10 has a second mechanical seal 11'.

[0070] The material to be treated is transported in the direction of arrow P.

[0071] The Fig. 3 is a partial sectional view of a rotary kiln 1, in which the sealing arrangement 8 is shown to illustrate its function. In this exemplary embodiment, the sealing arrangement 8 is the entirety of the components used in the structural implementation, which either directly provide the seal or which are required for the positioning of the components providing the seal.

[0072] The mechanical seal has a sliding element 12 designed as a sliding flange 12. This sliding flange 12 is coupled to the inlet section 2 in a rotationally fixed manner via the fastening flange 17. The sliding flange 12 provides a sliding surface 13 in the direction of arrow I, which points toward the interior of the rotary tube. In other words, the sliding element 12 provides a sliding surface facing the interior of the rotary tube 4. Although the fastening flange 17 is, as already mentioned, coupled to the inlet area 2 in a rotationally fixed manner, it is axially movable, namely in the direction of arrow I. A compression spring 14, which, via a bolt 18 in cooperation with the counter flange 19, brings about a preload of the sliding element 12 towards the interior of the rotary kiln, i.e. in the direction of arrow I, ensures that the sliding element 12 compensates for a certain degree of wear of the sealing rings to be described below.In the event of further wear, the preload of the sliding element can be adjusted in the direction of arrow I by screwing the bolt 18 on this side of the expansion spring 14 and on the other side of the counter flange 19.

[0073] An inner sealing element 15, designed as an inner sealing ring 15, and an outer sealing element 16, designed as an outer sealing ring 16, are arranged on a fastening area 20, in this case designed as a fixed flange 20 connected to the rotary tube 4. The inner sealing element 15 and the outer sealing element 16 are axially pressed between the fastening area and the sliding surface to ensure a good seal. The maintenance of this axial force, which promotes the sealing effect, is ensured by the preload with the compression spring 14 explained above, as well as the possibility of its adjustment.

[0074] As can be seen from the figure, the inner sealing element 15, the outer sealing element 16, the fastening area 20 and the sliding surface 13 are dimensioned and positioned such that a continuous sealing space 21 is present between them.

[0075] With suitably dimensioned and positioned holes in the sliding element 12, a passage 22, starting from the sliding surface 13, leads from the sealing chamber 22 to a sliding element outlet 23 of the sliding element 12. The sliding element outlet, in turn, is provided with a Fig. 3 not shown, gas supply device to ensure introduction of a gas into the sealing chamber 22 and continuous maintenance of an overpressure in the sealing chamber 22.

[0076] A fixed bearing half 28 of a ball bearing 28, 29 is positioned with the counter flange 19 in order to effect the rotatable mounting of the rotary tube 4 with the rotating bearing half 29 coupled to the fastening area and thus to the rotary tube via the connecting flange 30.

[0077] In a rotary kiln in Fig. 1 Tests were carried out to demonstrate that a sponge product with a high degree of metallization can be produced from metallurgical residues.

[0078] A mixture of converter dust and blast furnace sludge was provided as metallurgical residues from the steel industry.

[0079] The composition of the converter dust and top sludge is given in the following lists: Converter dust (all values ​​in wt.%): 22,6 FeO, 49,0 Fe2O3, 15 Fe metallic, 4,6 ZnO; 0,5 C free (unbound carbon); 0,7 MnO; 1,1 SiO2; 0,03 TiO2; 0,14 P2O5; 0,27 Al2O3; 3,5 CaO; 0,7 MgO; 0,02 PbO. Top sludge (all values ​​in wt.%): 3,9 FeO, 19,4 Fe2O3, 1,1 Fe metallic, 4,6 ZnO; 32,6 C free (unbound carbon); 4, 1 CO2; 0,28 MnO; 11,0 SiO2; 0,13 TiO2; 0,20 P2O5; 3,42 Al2O3; 5,94 CaO; 1,1 MgO; 0,76 PbO; 2,80 K2O; 0,02 V2O5; 0,01 CrO3; 0,05 BaO; 0,01 NiO; 0,01 ZrO2; 0,04 SrO; Contaminants: 0.99N; 0.20F; 0.23 Cl; 1.84 p.

[0080] Three mixing ratios of the reactants converter dust and top sludge were provided: 1. 100 wt% converter dust, 0 wt% top sludge; 2. 85 wt% converter dust, 15 wt% top sludge; 3. 70 wt% converter dust, 30 wt% top sludge.

[0081] The mixture was fed into the rotary kiln and conveyed through it in one direction as the rotary kiln rotated. During the conveyance of the metallurgical residues, the mixture was exposed to a reducing gas, which flowed countercurrently through the rotary kiln. Pure H2 was used as the reducing gas, and as the mixture of converter dust and top sludge passed through the rotary kiln, the interior of the rotary kiln was heated to 950 degrees Celsius by indirect electrical heating. The passage time for the mixture through the rotary kiln was 45 minutes.

[0082] The experiment was conducted with two different reference flow rates of the reaction gas, namely 5 Nm 3 / h and 10 Nm 3 / h, where Nm 3 denotes one standard cubic meter and h denotes a period of one hour. The exact flow values ​​are not essential to the essence of the invention, as they depend in particular on the specific plant parameters, such as the volume of the rotary kiln and the upstream and downstream units. However, two different flow rates were used to experimentally demonstrate that the addition of the reducing gas, in addition to the selection of suitable reactants, is the decisive factor for the demonstrated production of the sponge product.Due to the dependence on the specific circumstances, for example, the specific plant parameters, the person skilled in the art carrying out the process is dependent on empirically adjusting the reaction gas flow, in particular the H2 gas flow, such that the resulting product exhibits the desired degree of metallization. This empirical determination of a sufficiently high gas flow does not pose any particular difficulties for the person skilled in the art.

[0083] The following results were obtained: At a flow rate of 10 Nm 3 / h and a mixing ratio according to point 3 above (70:30), a sponge product with a high degree of metallization was obtained, which had the following composition: 87, 46 Fe, of that: 86.1 Fe metallic and 0.3 Fe++; 0,56 Mn; 0,006 Cu; 0,02 Pb; 0,6 Zn; 0,69 C; 2,34 SiO2; 0,06 TiO2; 0,77 Al2O3; 4,73 CaO; 1, 1 MgO; 0,38 K2O; Contaminants: 0,09 P; 0,36 S; 0,03 Cr; 0,018 V; 0,021 Ni; 0,014 F; 0,011 Cl.

[0084] With a metallic iron content of 98.4% of the total iron, i.e., a degree of metallization of 98.4%, an Fe content of 87.46 wt.% Fe in the sponge product, and a solid, porous structure, the resulting product was very similar to a known iron sponge HBI. Large portions of the zinc (Zn) and lead (Pb) contained in the reactant mixture could be removed; both of these elements escape as gas or as part of a gas compound and could be separated in the gas processing system. Lower flow rates and different mixing ratios also produced sponge products, but with a somewhat lower degree of metallization.

[0085] Thus, demonstration experiments have demonstrated that a sponge product can be produced from metallurgical residues using relatively inexpensive aggregates that can be processed into pig iron or crude steel in a particularly usable manner. This makes large portions of metallurgical residues accessible for reuse, thereby achieving a positive sustainability effect and reducing disposal costs.

Claims

1. A process for obtaining a sponge product with a high degree of metallization, comprising the steps of: a) providing metallurgical residues from the steel industry as a mixture of reactants, at least one of which contains iron, selected in particular from converter dust, coke dust, blast furnace dust, top sludge, mill scale, arc furnace dust, b) introducing the metallurgical residues into a rotary kiln, c) conveying the metallurgical residues along a conveying direction through the rotary kiln while the rotary kiln rotates, wherein the metallurgical residues are exposed to a reducing gas during the conveying of the metallurgical residues, which is passed through the rotary kiln in a countercurrent flow direction against the conveying direction in order to bring about reduction reactions in the metallurgical residues, d) removing the metallurgical residues which have passed through the rotary kiln as a sponge product with a high degree of metallization.

2. Method according to claim 1, characterized by that between step c) and step d) a removal preparation is carried out, wherein the removal preparation comprises: c`) conveying the metallurgical residues which have passed through the rotary kiln to a cooling station arranged on the rotary kiln for cooling the metallurgical residues which have passed through the rotary kiln and / or c") conveying the metallurgical residues which have passed through the rotary kiln through a briquetting station for briquetting the metallurgical residues which have passed through the rotary kiln.

3. Method according to claim 1 or claim 2, characterized in that during step c), the metallurgical residues transported in step c) are heated to a temperature between 800 degrees Celsius and 1050 degrees Celsius, in particular by indirect heating.

4. Method according to one of the preceding claims, characterized in thatGases produced during the reduction of the metallurgical residues are transported out of the rotary kiln using a transport gas and / or the reaction gas.

5. Method according to one of the preceding claims, characterized in that a gas discharge system is provided for discharging reaction gas passing through the rotary kiln as well as gaseous reaction products, through which gaseous reaction products are discharged from the rotary kiln, wherein preferably a gas processing system is coupled to the rotary kiln for processing the reaction gas passing through the rotary kiln in the gas discharge system as well as the gaseous reaction products, wherein preferably gaseous Zn and / or gaseous Zn-O compounds and / or gaseous Pb and / or gaseous Pb-O compounds are separated in the gas processing system.

6. Method according to claim 5, characterized in thatthe gas treatment system comprises one or more of the following treatment units: - zinc trap, - dust separator, - water separator, - CO2 separator, - reducing gas conditioner, - replacement reaction gas supply.

7. Method according to claim 5 or claim 6, characterized in that A gas recirculation system is connected downstream of the gas processing system to return processed reaction gas into the rotary kiln.

8. Method according to one of the preceding claims, characterized in that the metallurgical residues consist of at least 90 wt.%, preferably at least 98 wt.%, particularly preferably entirely, converter dust and top sludge.

9. Method according to one of the preceding claims, characterized in thatin the metallurgical residues, the ratio of converter dust to top sludge is between 60 wt%:40 wt% and 90 wt%:10 wt%, preferably between 65 wt%:35 wt% and 80 wt%:20 wt%, particularly preferably between 65 wt%:35 wt% and 75 wt%:25 wt%.

10. Method according to one of the preceding claims, characterized in that the reaction gas comprises H2, preferably consists of at least 90 vol.% H2, particularly preferably consists of at least 98 vol.% H2, in particular green H2 obtained from water electrolysis.

11. Method according to one of the preceding claims, characterized in that the rotary kiln has an inlet section and an outlet section as well as a rotary tube arranged between the inlet section and the outlet section, which is rotatably mounted relative to the inlet section and the outlet section, in particular the rotary kiln is designed as a gas-tight rotary kiln.

12. Method according to one of the preceding claims, characterized in that for the gas-tight sealing of the interior of the rotary kiln from the exterior, a first sealing arrangement is arranged in a transition region from the inlet section to the rotary kiln and a second sealing arrangement is arranged in a transition region from the rotary kiln to the outlet section, wherein the first sealing arrangement has a first mechanical seal and / or the second sealing arrangement (10) has a second mechanical seal.

13. Method according to claim 12, characterized in thatthe mechanical seal has an inner sealing element which is coupled to the rotary tube in a fastening region of the rotary tube in a rotationally fixed manner, which is preferably designed as a sealing ring, and has an outer sealing element (16) which is coupled to the rotary tube in a rotationally fixed manner, which is preferably designed as a sealing ring, wherein the inner sealing element and the outer sealing element are arranged in an axially pressed manner between the fastening region and the sliding surface, wherein the outer sealing element is spaced further from a rotational axis of the rotary tube than the inner sealing element.

14. Method according to claim 13, characterized in that the inner sealing element and the outer sealing element on the one hand and the fastening area and the sliding surface on the other hand are dimensioned such that a continuous sealing space is delimited by the inner sealing element, the outer sealing element, the fastening area and the sliding surface at every degree of rotation of the rotary kiln.

15. Method according to claim 14, characterized in that a number of sliding element outlets are arranged along the outer circumference of the sliding element, which are preferably positioned at the same angle to one another, wherein each of the existing sliding element outlets is coupled to a gas supply device, preferably coupled to the same gas supply device, particularly preferably coupled to the same gas supply device via a ring line, wherein during the conveyance of the metallurgical residues by introducing a protective gas through the gas supply device into the sealing chamber, a protective gas overpressure is brought about in the sealing chamber in order to seal the interior of the rotary kiln from the exterior of the rotary kiln.

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