METHOD AND DEVICE FOR THE REDUCTION OF METAL OXIDE BY MEANS OF A REDUCING GAS OR GAS MIXTURE USING SOLAR THERMAL ENERGY

Description

[0001] The present invention relates to a method for reducing metal oxides using a reducing gas or gas mixture and thermal energy obtained from concentrated solar radiation. The present invention further relates to a device for reducing metal oxides using a reducing gas or gas mixture and thermal energy obtained from concentrated solar radiation.

[0002] The reduction of metal oxides sometimes requires considerable amounts of heat to heat the metal oxide and / or the gas or gas mixture being reduced to the temperatures necessary for the reduction reaction. Iron oxide, for example, can be reduced to pig iron in the blast furnace process, where carbon monoxide, produced by burning coke in the blast furnace itself, serves primarily as the reducing agent. This process generates significant amounts of carbon dioxide. Furthermore, burners are known that are suitable for burning natural gas or hydrogen. The production of hydrogen also generates considerable amounts of carbon dioxide if renewable energy sources are not used. Finally, there are a number of electric heating options.The generation of this electricity also produces large amounts of carbon dioxide if renewable energy sources are not used for its production.

[0003] Electricity is generated in a variety of ways today, using both renewable and non-renewable energy sources. Renewable energy sources include, in particular, solar, hydropower, and wind power. Solar energy is converted into electricity using solar cells, which can then be used as needed. Non-renewable energy sources include nuclear power, oil, gas, and coal-fired power plants.

[0004] Various methods and devices for the reduction of metal oxides are known from the prior art. US patent 2011 / 0135566 A1 discloses a method and a reactor for the quasi-continuous execution of a chemical reaction on the surface of a solid reactant in a gas-solid phase reaction, wherein the surface is the surface of a metal oxide in a gas-solid phase reaction.

[0005] From DE 10 2013 211 249 A1 it is known to effectively store solar thermal energy from concentrating solar power plants that use air as the working medium in order to convert it into electricity later when the sun has set or is covered by clouds.

[0006] From US patent 2016 / 0208362 A1, processes, systems, and components suitable for carbothermal reduction processes are known. Exemplary systems include a reactor, such as a hybrid solar thermal electric reactor, a solar thermal reactor, an electric reactor, or a gas combustion-heated reactor, a pellet source, a gas reactant source, and a vacuum source.

[0007] From US patent 2006 / 0188433 A1, a method for reducing metal oxide particles using a high-temperature solar aerosol reactor is known.

[0008] US Patent 2019 / 0346177 A1 describes a device that can be operated with concentrated solar radiation, wherein the device comprises a body with a cavity designed to receive concentrated solar radiation, a heat energy absorber connected to the cavity to absorb heat from the concentrated solar radiation within the cavity, and a chamber containing a material body, wherein the chamber is in a heat exchange relationship with the heat energy absorber to receive heat from it.

[0009] The 2011 overview report of the hydrogen research program of the Swiss Federal Office of Energy (SFOE) describes a solar thermal reactor for the production of hydrogen and synthesis gas using cerium oxide (CeO2) as a redox ceramic.

[0010] The publication "Solar carbothermal reduction of aerosolized ZnO particles under vacuum", DOI: 10.1016 / J.CEJ.2016.12.057 describes a carbon-based reduction of zinc oxide (ZnO) using concentrated solar radiation.

[0011] The publication "Combined ZnO reduction and methane reforming for co-production of pure Zn and syngas in a prototype solar thermochemical reactor", 30 DOI: 10.1016 / J.FUPROC.2020.106572 describes a combined zinc oxide reduction (ZnO) and synthesis gas production using concentrated solar radiation.

[0012] The present invention is based on the objective of providing a process for the reduction of metal oxides by means of which, compared to processes known from the prior art, a significant reduction in the emission of greenhouse gases and in particular a reduction in the emission of carbon dioxide is achieved.

[0013] The problem underlying the present invention is solved by a method having the features specified in claim 1. Embodiments of the method are described in the dependent claims.

[0014] More precisely, the problem underlying the present invention is solved by a method for reducing metal oxide using a reducing gas or gas mixture, wherein the method comprises a process step for combining the metal oxide to be reduced and the gas or gas mixture used for the reduction of the metal oxide to be reduced. The method further comprises a process step for heating the metal oxide and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced, wherein the thermal energy used for heating the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced is obtained at least partially by means of concentrated solar radiation, wherein the gas or gas mixture used for the reduction of the metal oxide contains more than 10% hydrogen gas.

[0015] The process according to the invention has the advantage that significantly less energy, and possibly no energy at all, is required to heat the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide. This energy is obtained from fossil fuels or nuclear power. Consequently, significantly less carbon dioxide, and possibly no carbon dioxide at all, is produced when heating the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide.

[0016] Due to the use of concentrated solar radiation, and thus solar thermal energy, the process according to the invention exhibits a high efficiency with regard to the energy fraction of solar radiation used for heating. Because of the use of concentrated solar radiation, 30% or more of the radiant energy of the concentrated solar radiation can be used to heat the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide. This efficiency is considerably higher than that achieved with photovoltaics. Photovoltaics uses sunlight to generate electrical energy, with industrially usable photovoltaic modules having an efficiency of approximately 25%. Consequently, only 25% of the energy of the solar radiation is converted into electrical energy.This electrical energy still needs to be converted into heat energy, which further reduces the overall efficiency until the metal oxide to be reduced and / or the gas or gas mixture used to reduce the metal oxide is heated.

[0017] According to the invention, a reduction of metal oxide is understood to mean a chemical reduction of metal oxide.

[0018] Preferably, the process is designed such that the metal oxide used is a metal oxide selected from the group consisting of iron oxide, aluminum oxide, copper oxide, magnesium oxide, tin oxide, zinc oxide, and mixtures thereof. There are therefore no restrictions regarding the composition of the metal oxide.

[0019] If the metal oxide contains iron oxide, then the iron oxide may be present, for example, in the form of iron ore. In this case, it is also possible to describe the present invention as a method for reducing iron ore using a reducing gas or gas mixture.

[0020] Preferably, the process is designed such that the reducing gas or gas mixture used is a gas or gas mixture selected from the group consisting of hydrogen, carbon monoxide, methane, alkanes, alkenes, water vapor, hydrogen carriers in the form of hydrogen compounds, and mixtures thereof. For example, alkanes, alkenes, and methane are hydrogen carriers in the form of hydrogen compounds.

[0021] Preferably, the gas or gas mixture used for the reduction of the metal oxide contains more than 30% and further preferably more than 50% hydrogen gas. The percentage can be expressed as volume percent or weight percent.

[0022] In a preferred embodiment of the process, the thermal energy used to heat the metal oxide to be reduced and / or the gas or gas mixture is obtained entirely by means of concentrated solar radiation.

[0023] Preferably, the process is designed such that heat energy from the reaction product generated by the redox reaction is used to preheat the metal oxide to be reduced and / or the gas or gas mixture used to reduce the metal oxide to be reduced and / or a reactor in which the redox reaction of the metal oxide with the gas or gas mixture is carried out.

[0024] The appropriately designed process exhibits improved energy efficiency. This is because, by utilizing the thermal energy of the reaction product generated by the redox reaction to preheat the metal oxide to be reduced and the gas or gas mixture used for its reduction, less thermal energy is required to heat the metal oxide and / or the gas or gas mixture, which is obtained from concentrated solar radiation.

[0025] The heat energy for preheating the metal oxide and / or the gas or gas mixture can, for example, be supplied to a reactor or a furnace in which the metal oxide and the gas or gas mixture react with each other.

[0026] The thermal energy of the reaction product resulting from the reaction of the metal oxide and the gas or gas mixture is transferred, for example, by means of a heat exchanger to a heat transfer fluid, which is then used to heat the metal oxide and / or the gas or gas mixture. However, it is also possible for the reaction product resulting from the reaction of the metal oxide and the gas or gas mixture to be passed directly through the furnace or reactor in which the metal oxide reacts with the gas or gas mixture.

[0027] If water in the form of water vapor is produced as a reaction product from the reaction of the metal oxide and the gas or gas mixture, the condensation heat of the water vapor is preferably also used to preheat the metal oxide and / or the gas or gas mixture.

[0028] Preferably, the process is designed such that the water produced by the redox reaction of the metal oxide to be reduced with the gas or gas mixture is used to obtain hydrogen.

[0029] The appropriately designed process has the advantage that, due to the stoichiometry of the redox reaction, the water or water vapor produced during the redox reaction is in exactly the right ratio to the metal oxide used, so that the production of hydrogen from the water / water vapor produced as a product of the redox reaction generates precisely the amount of hydrogen required to continue the process – i.e., the reduction of further metal oxide.

[0030] The production of hydrogen from water, which is generated from the redox reaction of the metal oxide to be reduced with the hydrogen, is carried out, for example, by high-temperature electrolysis and / or by steam reforming and / or by thermolysis. Preferably, at least partially or entirely, thermal energy obtained from concentrated solar radiation is used in each of these processes.

[0031] Preferably, the process is designed such that the metal oxide to be reduced is supplied to the redox reaction in the form of lumpy metal oxide, in particular in the form of lumpy iron oxide with an average particle size in the range between 5 mm and 50 mm.

[0032] Preferably, the process is designed such that the metal oxide to be reduced is supplied to the redox reaction in the form of powdered metal oxide, in particular in the form of powdered iron oxide with an average particle size of less than 10 mm.

[0033] Preferably, the process is designed such that the metal oxide to be reduced is supplied to the redox reaction in the form of crushed metal oxide or crushed iron ore with an average particle size in the range between 1 mm and 50 mm.

[0034] Preferably, the process is designed such that the metal oxide to be reduced is supplied to the redox reaction in the form of ground metal oxide with an average particle size in the range between 10 µm and 1 mm.

[0035] The corresponding process has the advantage that the metal oxide present in this particle size is rapidly reduced by means of the gas or gas mixture. Thus, the corresponding process enables efficient reduction of metal oxides.

[0036] Preferably, the process is designed such that the metal oxide to be reduced is supplied to the redox reaction in the form of metal oxide pellets and / or iron ore pellets with a mean diameter in the range between 10 mm and 20 mm.

[0037] The appropriately developed process facilitates the handling (transport, conveying) of the metal oxide to be reduced.

[0038] Preferably, the process is designed such that the metal oxide to be reduced and / or the gas or gas mixture used to reduce the metal oxide to be reduced are heated to a temperature in the range between 200°C and 1500°C.

[0039] Preferably, the process is further configured such that the metal oxide to be reduced is heated to a temperature in the range between 200°C and 1200°C and the gas or gas mixture used to reduce the metal oxide to be reduced is heated to a temperature in the range between 500°C and 1200°C.

[0040] The heating of the metal oxide to be reduced and / or the gas or gas mixture to temperatures in these temperature ranges is preferably carried out essentially or exclusively by means of the thermal energy obtained from concentrated solar radiation.

[0041] Preferably, the metal oxide to be reduced and / or the gas or gas mixture is heated to a temperature between 700°C and 1100°C. The higher the temperature to which at least one of the reactants (metal oxide and / or gas or gas mixture) is heated, the greater the conversion rate of the metal oxide to metal.

[0042] Preferably, the metal oxide to be reduced and / or the gas or gas mixture and / or at least one other component supplied to the redox reaction (e.g. hydrogen or carbon monoxide and / or carbon dioxide and / or methane and / or an alkane and / or water) is heated for a duration between 20 minutes and 140 minutes using heat energy obtained from concentrated solar radiation.

[0043] Preferably, the process is designed such that, in addition to the heat energy obtained by means of concentrated solar radiation, further heat energy is obtained by means of at least one burner and / or by means of at least one heat exchanger and / or by means of at least one electric heater and is used to heat the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0044] Additional thermal energy can be obtained, for example, by inductively heating metallic elements, such as metallic pipes in which the gas or gas mixture is transported, or from a specially installed absorber. Furthermore, additional thermal energy can be obtained by means of an electric resistance heater over which the gas or gas mixture flows or is in contact. Finally, additional thermal energy can be obtained by means of a plasma generator.

[0045] The additional heat energy can be used in phases or continuously to heat the metal oxide and / or the gas or gas mixture to be reduced.

[0046] The appropriately designed process has the advantage that the reduction of the metal oxide is ensured even during periods when, for example, insufficient thermal energy from solar thermal sources is available to carry out the redox reaction of the metal oxide with the gas or gas mixture. Thus, the appropriately designed process exhibits improved reliability.

[0047] Preferably, the process is designed such that it includes a process step for heating a primary heat transfer fluid (HTF1) by means of concentrated solar radiation and a process step for transferring heat energy from the primary heat transfer fluid to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0048] The appropriately designed process offers the advantage that heating the metal oxide to be reduced and / or the gas or gas mixture used for its reduction can be made even more efficient, since the primary heat transfer fluid can be designed or selected to be heated particularly efficiently using concentrated solar radiation. Consequently, even less, and possibly no, carbon dioxide is produced when heating the metal oxide to be reduced and / or the gas or gas mixture used for its reduction.

[0049] The primary heat transfer fluid is heated by concentrated solar radiation, preferably to a temperature in the range of 500°C to 1700°C, more preferably in the range of 700°C to 1700°C, more preferably in the range of 800°C to 1650°C, more preferably in the range of 900°C to 1650°C, more preferably in the range of 900°C to 1600°C, more preferably in the range of 1100°C to 1650°C, more preferably in the range of 1200°C to 1600°C, more preferably in the range of 1300°C to 1600°C, more preferably in the range of 1400°C to 1550°C, more preferably in the range of 1400°C to 1500°C.

[0050] For example, the process is designed such that in the process step of transferring the heat energy of the primary heat transfer fluid to the metal oxide to be reduced and / or to the gas or gas mixtures used for the reduction of the metal oxide to be reduced, the heat energy of the primary heat transfer fluid is not converted into electrical energy before being transferred to the metal oxide to be reduced and / or to the gas or gas mixtures used for the reduction of the metal oxide to be reduced.

[0051] Consequently, the (concentrated) solar radiation is not converted into electrical energy (e.g., by means of solar cells) before heating the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced. Furthermore, the thermal energy of the primary heat transfer fluid is also not converted into electrical energy (e.g., by means of a generator) in order to subsequently supply a heating device with this electrical energy.

[0052] The appropriately designed process has the advantage that the primary heat transfer fluid is heated more efficiently by the concentrated solar radiation. Consequently, the metal oxide to be heated and reduced, and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced, is also heated more efficiently, so that a larger quantity of metal oxide and / or gas or gas mixture can be heated using the available concentrated solar radiation.

[0053] Furthermore, the process is designed such that a partial flow of the primary heat transfer fluid is diverted to generate electrical energy, for example by means of a generator. This electrical energy can then be used, for example, to supply individual plant components with electrical power.

[0054] Preferably, the process is designed such that at least one gas is used as the primary heat transfer fluid, selected from the group consisting of carbon dioxide, water vapor, methane, ammonia, carbon monoxide, sulfur dioxide, sulfur trioxide, hydrochloric acid, nitrogen monoxide, nitrogen dioxide, nitrogen, air and mixtures thereof.

[0055] It is also possible that the primary heat transfer fluid contains or is a molten salt, wherein the molten salt contains, for example, NaNO₃ and / or KNO₃. More preferably, the primary heat transfer fluid contains or is a molten metal. For example, the molten metal contains tin and / or zinc and / or aluminum and / or lead.

[0056] Preferably, the method is designed such that the primary heat transport fluid is heated directly in a fluid heating device of a solar thermal system illuminated by concentrated solar radiation.

[0057] For example, the primary heat transfer fluid flows through the fluid heating unit, into which the solar radiation reflected by reflectors is concentrated. The primary heat transfer fluid interacts directly with the concentrated solar radiation and is heated by it.

[0058] Preferably, the method is designed such that a primary heat transfer fluid is used which has no solid components, in particular no ceramic components.

[0059] A gas, for example, can be used as the primary heat transfer fluid. A primary heat transfer fluid without solid components has the advantage that the transport device (e.g., pipes or a pipe system) used to transport the heat transfer fluid is subject to less wear. Furthermore, solid components cannot accumulate in areas of the transport device where the heat transfer fluid flows at lower velocities.

[0060] It is particularly advantageous if the primary heat transfer fluid does not transport any ceramic components, especially no ceramic powder. This is because ceramic components lead to particularly high wear of the transport device.

[0061] Preferably, the process comprises a process step of transferring heat energy from the primary heat transfer fluid to a heat storage device and a process step of transferring heat energy from the heat storage device to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0062] The appropriately designed process has the advantage that the thermal energy obtained from concentrated solar radiation can also be used during periods when no or comparatively less solar radiation is available. This allows for more uniform heating of the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide.

[0063] For example, the process is designed such that the primary heat transfer fluid is used to transfer heat energy from the heat storage device to the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0064] A reservoir of the primary heat transfer fluid can serve as a heat storage device. Alternatively, a heat transfer fluid different from the primary heat transfer fluid (e.g., a molten salt, for example, containing NaNO₃ and / or KNO₃) can be used as a heat storage device. A solid can also be used as a heat storage device. There are no restrictions regarding the design of the solid. The solid can, for example, consist of stones and / or concrete and / or metal bodies, or the like.

[0065] Furthermore, it is also in line with the inventive method that thermal energy from the primary heat transfer fluid is transferred to a secondary heat transfer fluid and / or to a tertiary heat transfer fluid, and subsequently, thermal energy from the secondary heat transfer fluid and / or the tertiary heat transfer fluid is transferred to a heat storage device. Thus, the thermal energy of the primary heat transfer fluid is indirectly transferred to the heat storage device.

[0066] Preferably, the process is configured such that the transfer of thermal energy from the primary heat transfer fluid to the heat storage device occurs in a different time window than the transfer of thermal energy from the heat storage device to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced. For example, the process is configured such that the transfer of thermal energy from the primary heat transfer fluid to the heat storage device occurs before the transfer of thermal energy from the heat storage device to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0067] Preferably, the process comprises a process step of transferring heat energy from the primary heat transfer fluid to a secondary heat transfer fluid in a heat exchanger device and a process step of transferring heat energy from the secondary heat transfer fluid to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced in a heating device.

[0068] The appropriately designed process has the advantage that the thermal energy of the primary heat transfer fluid can be used more effectively for heating the metal oxide and / or the gas or gas mixture, which is to be heated to a significantly lower temperature than that of the primary heat transfer fluid. This is because the temperature of the secondary heat transfer fluid is lower than the temperature of the primary heat transfer fluid.

[0069] As described above, the heat storage device can be heated using the secondary heat transfer fluid. Furthermore, it is also possible for a first heat storage device to be heated using the primary heat transfer fluid and a second heat storage device to be heated using the secondary heat transfer fluid. Consequently, the first heat storage device would be arranged in a primary fluid circuit and the second heat storage device in a secondary fluid circuit.

[0070] For example, the secondary heat transfer fluid comprises or is a molten salt, wherein the molten salt comprises, for example, NaNO₃ and / or KNO₃. More preferably, the secondary heat transfer fluid comprises or is a molten metal. For example, the molten metal comprises tin and / or zinc and / or aluminum and / or lead.

[0071] The heating device can, for example, be designed as a reactor in which the metal oxide to be reduced and the gas or gas mixture react with each other.

[0072] Preferably, the method is designed such that a heat transport fluid is used as the secondary heat transport fluid whose heat capacity is greater than the heat capacity of the primary heat transport fluid.

[0073] The appropriately designed process has the advantage that the heat energy obtained by means of concentrated solar radiation can be transported over greater distances with lower heat losses to a heating device (for example, a reactor or a furnace) by means of which the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced is to be heated.

[0074] Preferably, the method is designed such that a heat transport fluid is used as the secondary heat transport fluid whose specific heat capacity is greater than the specific heat capacity of the primary heat transport fluid.

[0075] Preferably, the method is designed such that a heat transport fluid is used as the secondary heat transport fluid whose density is greater than the density of the primary heat transport fluid.

[0076] Preferably, the method is designed such that a heat transport fluid is used as the secondary heat transport fluid whose product of specific heat capacity and density is greater than the product of the specific heat capacity and density of the primary heat transport fluid.

[0077] The density of the respective heat transport fluids refers to their mass per unit volume.

[0078] Preferably, the process comprises a step of transporting the primary heat transfer fluid to the heat exchanger via a first path, wherein thermal energy is transferred from the primary heat transfer fluid to the secondary heat transfer fluid in the heat exchanger. Furthermore, the process comprises a step of transporting the secondary heat transfer fluid to the heating device via a second path, which is longer than the first path, wherein thermal energy is transferred from the secondary heat transfer fluid to the metal oxide and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced in the heating device.

[0079] The appropriately designed method enables the efficient transport of heat energy generated by concentrated solar radiation over a long distance with minimal heat energy losses. Consequently, the appropriately designed method allows a fluid heating device, configured to heat a primary heat transfer fluid using concentrated solar radiation, to be located at a greater distance from the heating device in which the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced is heated by the energy obtained from concentrated solar radiation.

[0080] This is particularly advantageous when the concentrated solar radiation from a solar thermal plant is used to heat the primary heat transfer fluid. A solar tower power plant has a fluid heating unit mounted on a tower structure. The fluid heating unit is also referred to as a receiver and / or absorber station and / or combustion chamber. A plurality of reflector devices, also called heliostats, are arranged below the fluid heating unit to reflect solar radiation onto the fluid heating unit. The reflector devices cover a large area around the tower structure, so that a heating unit for heating the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced can typically be located outside the area where the reflector devices are arranged.Consequently, the described method allows for an increase in the distance between the fluid heating device and the heating device for heating the metal oxide and / or the gas or gas mixture.

[0081] Preferably, the first path is shorter than 1000 meters. Further preferably, the first path is shorter than 800 meters. Further preferably, the first path is shorter than 600 meters. Further preferably, the first path is shorter than 400 meters. Further preferably, the first path is shorter than 200 meters.

[0082] Preferably, the first path is between 100 meters and 1000 meters. More preferably, the first path is between 110 meters and 900 meters. More preferably, the first path is between 120 meters and 800 meters. More preferably, the first path is between 130 meters and 700 meters. More preferably, the first path is between 140 meters and 600 meters. More preferably, the first path is between 150 meters and 500 meters. More preferably, the first path is between 160 meters and 400 meters. More preferably, the first path is between 170 meters and 300 meters. More preferably, the first path is between 180 meters and 200 meters.

[0083] Preferably, the process comprises a process step of transferring heat energy from the secondary heat transfer fluid to a tertiary heat transfer fluid in a third heat exchanger device and a process step of transferring heat energy from the tertiary heat transfer fluid to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced in the heating device.

[0084] For example, a gas selected from the group consisting of carbon dioxide, water vapor, methane, ammonia, carbon monoxide, sulfur dioxide, sulfur trioxide, hydrochloric acid, nitrogen monoxide, nitrogen dioxide, nitrogen, air and mixtures thereof is used as the tertiary heat transport fluid.

[0085] For example, the tertiary heat transport fluid contains or is a molten salt, for example containing NaNO 3 and / or KNO 3.

[0086] Preferably, the tertiary heat transfer fluid contains or is a molten metal. For example, the molten metal contains tin and / or zinc and / or aluminum and / or lead.

[0087] Preferably, the method is designed such that a heat transport fluid is used as the tertiary heat transport fluid whose heat capacity differs from the heat capacity of the secondary heat transport fluid.

[0088] Preferably, the method is further designed such that a heat transport fluid is used as the tertiary heat transport fluid whose specific heat capacity differs from the specific heat capacity of the secondary heat transport fluid.

[0089] Preferably, the method is designed such that a heat transport fluid is used as the tertiary heat transport fluid whose density differs from the heat capacity of the secondary heat transport fluid.

[0090] Preferably, the method is further designed such that a heat transport fluid is used as the tertiary heat transport fluid whose heat capacity and / or density is smaller than the heat capacity and / or density of the secondary heat transport fluid.

[0091] Preferably, the method is further designed such that a heat transport fluid is used as the tertiary heat transport fluid whose heat capacity and / or density is greater than the heat capacity of the secondary heat transport fluid.

[0092] Preferably, the process is designed such that the heat energy obtained by means of concentrated solar radiation is supplied to a reactor in which the metal oxide to be reduced and the gas or gas mixture used for the reduction of the metal oxide to be reduced are combined.

[0093] The transfer of thermal energy from the primary heat transfer fluid to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide takes place in the reactor. A reactor is defined as a device into which the metal oxide to be reduced and the gas or gas mixture used for reduction can be introduced and which can heat a predetermined area to a higher temperature than an adjacent area. For example, the reactor is designed as a furnace. The furnace can be, for example, a rotary kiln or a fluidized bed reactor. A heat transfer fluid flows through the reactor. According to the invention, there are no restrictions regarding the design of the reactor.

[0094] The reactor can also be referred to as a heating device.

[0095] Preferably, the process is designed such that the gas or gas mixture used for the reduction of the metal oxide to be reduced is supplied to the reactor in a first region of the reduction reactor, wherein the metal oxide to be reduced is supplied to the reactor in a second region of the reactor, which is arranged below the first region in the operating state of the reactor, and wherein the reaction product generated by the redox reaction of the metal oxide and the gas or gas mixture is at least partially removed from the reactor in a third region, wherein the third region is arranged below the second region in the operating state of the reactor.

[0096] The reaction product generated in the redox reaction has a higher density than the gas or gas mixture. Furthermore, the reaction product has a lower temperature than the gas or gas mixture. By removing the reaction product in the third section of the reduction reactor, cooling of the gas or gas mixture is prevented or counteracted, thus enabling a more efficient and faster reduction of the metal oxide with this appropriately designed process.

[0097] The reaction product can be water or water vapor. For example, water is produced as a reaction product when iron oxide is reduced using hydrogen.

[0098] Preferably, the process is designed such that carbon monoxide and / or carbon dioxide and / or methane and / or an alkane and / or water are added to the metal oxide to be reduced, in addition to the gas or gas mixture.

[0099] If the metal oxide contains, for example, iron oxide, then the process is designed such that, after the reduction of the iron oxide, the iron produced is brought into contact with carbon monoxide and / or hydrogen, so that the iron is carburized to cementite (Fe 3 C).

[0100] For example, the process is further designed such that after the reduction of the iron oxide, the iron produced is brought into contact with methane, so that the iron is carburized to cementite (Fe 3 C).

[0101] The corresponding reactions are as follows: 3Fe + CH4 -> Fe3C + 2H2 3Fe + 2CO -> Fe3C + CO2 3Fe + CO + H2 -> Fe3C + H2 0

[0102] The appropriately developed process has the advantage that cementite is significantly more inert to oxygen than iron. Transporting cementite is therefore easier than transporting iron, which would oxidize, at least superficially, during transport.

[0103] This offers the advantage that, for direct reduction of the metal oxide to be reduced, the metal oxide can be transported to the location where the reduction takes place. Due to the use of solar thermal energy, this location is preferably in an area of ​​the world with high solar irradiance. If hydrogen is used as the reducing gas, it does not need to be transported to the metal oxide to be reduced. Transporting hydrogen over long distances is complex, as it is typically transported in pressure vessels under high pressures of around 700 bar.

[0104] Another advantage of carburizing iron is that the resulting cementite has a lower tendency to clump. This is beneficial, for example, when using the cementite in a melting furnace for steel production.

[0105] Another advantage is that when cementite is melted, the carbon in the cementite reacts with the available oxygen to form carbon monoxide and / or carbon dioxide, with this reaction being exothermic, so that the melting unit requires little external energy input to melt the iron.

[0106] Furthermore, the carbon monoxide formed during the melting of cementite creates gas bubbles that can absorb undesirable substances such as nitrogen within the melt, resulting in improved purity of the steel produced.

[0107] The present invention further aims to provide a device for the reduction of metal oxides, by means of which, compared to devices known from the prior art, a significant reduction in the emission of greenhouse gases and in particular a reduction in the emission of carbon dioxide is achieved.

[0108] The problem underlying the present invention is solved by a device having the features specified in claim 12. Embodiments of the devices are described in the dependent claims.

[0109] In more detail, the problem underlying the present invention is solved by a device for the reduction of metal oxide by means of a reducing gas or gas mixture, wherein the device is configured to heat the metal oxide and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced by means of thermal energy obtained at least partially from concentrated solar radiation, and wherein the device has a reactor for receiving the metal oxide to be reduced and for introducing the gas or gas mixture.

[0110] The device according to the invention has the advantage that significantly less energy, and possibly no energy at all, is required to heat the metal oxide to be reduced and / or the gas or gas mixture used for its reduction. This energy is obtained from fossil fuels or nuclear power. Consequently, significantly less carbon dioxide, and possibly no carbon dioxide at all, is produced when heating the metal oxide to be reduced and / or the gas or gas mixture used for its reduction.

[0111] Due to the use of concentrated solar radiation, and thus solar thermal energy, the device according to the invention exhibits a high efficiency with regard to the energy fraction of solar radiation used for heating. Because of the use of concentrated solar radiation, 30% or more of the radiant energy of the concentrated solar radiation can be used to heat the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced. This efficiency is considerably higher than that achieved with photovoltaics. Photovoltaics uses sunlight to generate electrical energy, with industrially usable photovoltaic modules having an efficiency of approximately 25%. Consequently, only 25% of the energy of the solar radiation is converted into electrical energy.This electrical energy still needs to be converted into heat energy, which further reduces the overall efficiency until the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced is heated.

[0112] Preferably, the device is designed such that the metal oxide used is a metal oxide selected from the group consisting of iron oxide, aluminum oxide, copper oxide, magnesium oxide, tin oxide, zinc oxide, and mixtures thereof. There are therefore no restrictions regarding the composition of the metal oxide. The metal oxide can, for example, be in the form of iron ore.

[0113] If the metal oxide contains iron oxide, then the iron oxide can be present, for example, in the form of iron ore. In this case, it is also possible to describe the present invention as a device for reducing iron ore using a reducing gas or gas mixture.

[0114] Preferably, the device is designed such that the reducing gas or gas mixture used is a gas or gas mixture selected from the group consisting of hydrogen, carbon monoxide, methane, alkanes, alkenes, water vapor, hydrogen carriers in the form of hydrogen compounds, and mixtures thereof. For example, alkanes, alkenes, and methane are hydrogen carriers in the form of hydrogen compounds.

[0115] In a preferred embodiment of the device, the thermal energy used to heat the metal oxide to be reduced and / or the gas or gas mixture is obtained entirely by means of concentrated solar radiation.

[0116] Preferably, the device is designed such that the reactor is configured to be heated by means of thermal energy obtained from concentrated solar radiation.

[0117] The device includes a fluid heating device configured to heat a primary heat transfer fluid by means of concentrated solar radiation, wherein the reactor is configured to transfer heat from the primary heat transfer fluid at least indirectly to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0118] The appropriately designed device exhibits a further improved efficiency with regard to the transfer of heat energy to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0119] The fluid heating device is, for example, part of a solar thermal system and is arranged on a tower that is positioned within a field of heliostats, which reflect solar radiation into / onto the fluid heating device. It is also possible for the fluid heating device to be located at the focal point of a reflecting parabolic trough, a Fresnel mirror array, or a Fresnel lens array, so that solar radiation reflected by the parabolic trough or Fresnel mirror array, or solar radiation collected by the Fresnel lens array, can be absorbed by the primary heat transfer fluid.

[0120] A reactor is understood to be a device into which the metal oxide to be reduced and the gas or gas mixture used for reduction can be introduced. The reactor can, for example, be designed such that a predetermined area can be heated to a higher temperature than an adjacent area. For example, the reactor is designed as a furnace. The furnace can be, for example, a rotary kiln or a fluidized bed reactor. A heat transfer fluid flows through the reactor. According to the invention, there are no restrictions regarding the design of the reactor.

[0121] The reactor can also be referred to as a heating device.

[0122] The device is preferably designed to heat the primary heat transfer fluid to a temperature in the range of 500°C to 1700°C, preferably in the range of 700°C to 1700°C, more preferably in the range of 800°C to 1650°C, more preferably in the range of 900°C to 1650°C, more preferably in the range of 900°C to 1600°C, more preferably in the range of 1100°C to 1650°C, more preferably in the range of 1200°C to 1600°C, more preferably in the range of 1300°C to 1600°C, more preferably in the range of 1400°C to 1550°C, more preferably in the range of 1400°C to 1500°C.

[0123] Preferably, the device is designed such that at least one gas is used as the primary heat transfer fluid, selected from the group consisting of hydrogen, carbon dioxide, water vapor, methane, ammonia, carbon monoxide, sulfur dioxide, sulfur trioxide, hydrochloric acid, nitrogen monoxide, nitrogen dioxide, nitrogen, air and mixtures thereof.

[0124] It is also possible that the primary heat transfer fluid contains or is a molten salt, wherein the molten salt contains, for example, NaNO₃ and / or KNO₃. More preferably, the primary heat transfer fluid contains or is a molten metal. For example, the molten metal contains tin and / or zinc and / or aluminum and / or lead.

[0125] Preferably, the device is designed such that the primary heat transfer fluid is heated directly in a fluid heating device of a solar thermal system illuminated by concentrated solar radiation.

[0126] For example, the primary heat transfer fluid flows through the fluid heating unit, into which the solar radiation reflected by reflectors is concentrated. The primary heat transfer fluid interacts directly with the concentrated solar radiation and is heated by it.

[0127] Preferably, the device is designed such that a primary heat transfer fluid is used which has no solid components, in particular no ceramic components.

[0128] A gas, for example, can be used as the primary heat transfer fluid. A primary heat transfer fluid without solid components has the advantage that the transport device (e.g., pipes or a pipe system) used to transport the heat transfer fluid is subject to less wear. Furthermore, solid components cannot accumulate in areas of the transport device where the heat transfer fluid flows at lower velocities.

[0129] It is particularly advantageous if the primary heat transfer fluid does not transport any ceramic components, especially no ceramic powder. This is because ceramic components lead to particularly high wear of the transport device.

[0130] The reactor can be designed such that the primary heat transfer fluid is transported through the reactor, whereby the reactor transfers the heat energy thus obtained to the metal oxide and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced (for example by means of thermal radiation).

[0131] Furthermore, the reactor can be designed in such a way that the primary heat transfer fluid can be brought into direct interaction and / or contact with the metal oxide and / or the gas or gas mixture in order to transfer the heat energy to the metal oxide and / or to the gas or gas mixture.

[0132] Preferably, the device has a heat storage device, wherein the device is designed to transfer heat energy of the primary heat transport fluid at least indirectly to the heat storage device.

[0133] The suitably designed device has the advantage that the thermal energy obtained by means of concentrated solar radiation can also be used during periods when no or comparatively less solar radiation is available. This allows for more uniform heating of the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide.

[0134] For example, the device is designed such that the primary heat transfer fluid is used to transfer heat energy from the heat storage device to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0135] A reservoir of the primary heat transfer fluid can serve as a heat storage device. Alternatively, a heat transfer fluid different from the primary heat transfer fluid (e.g., a molten salt, for example, containing NaNO₃ and / or KNO₃) can be used as a heat storage device. A solid can also be used as a heat storage device. There are no restrictions regarding the design of the solid. The solid can, for example, consist of stones and / or concrete and / or metal bodies, or the like.

[0136] Furthermore, it is also in line with the invention that heat energy of the primary heat transport fluid is transferred to a secondary heat transport fluid and / or to a tertiary heat transport fluid, wherein heat energy of the secondary heat transport fluid and / or the tertiary heat transport fluid is subsequently transferred to a heat storage device.

[0137] Thus, the thermal energy of the primary heat transport fluid is indirectly transferred to the heat storage device.

[0138] The device includes a heat exchanger assembly by means of which the thermal energy of the primary heat transfer fluid can be transferred to a secondary heat transfer fluid, wherein the reactor is designed to transfer heat from the secondary heat transfer fluid at least indirectly to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0139] The suitably designed device has the advantage that the thermal energy of the primary heat transfer fluid can be used more effectively for heating the metal oxide to be reduced and / or for heating the gas or gas mixture used for its reduction, which are to be heated to a significantly lower temperature than the temperature of the primary heat transfer fluid. This is because the temperature of the secondary heat transfer fluid is lower than the temperature of the primary heat transfer fluid.

[0140] As described above, the heat storage device can be heated using the secondary heat transfer fluid. Furthermore, it is also possible for a first heat storage device to be heated using the primary heat transfer fluid and a second heat storage device to be heated using the secondary heat transfer fluid. Consequently, the first heat storage device would be arranged in a primary fluid circuit and the second heat storage device in a secondary fluid circuit.

[0141] For example, the secondary heat transfer fluid comprises or is a molten salt, wherein the molten salt comprises, for example, NaNO₃ and / or KNO₃. More preferably, the secondary heat transfer fluid comprises or is a molten metal. For example, the molten metal comprises tin and / or zinc and / or aluminum and / or lead.

[0142] The reactor can be designed such that the secondary heat transfer fluid is transported through the reactor, whereby the reactor transfers the heat energy thus obtained to the metal oxide and / or the gas or gas mixture used for the reduction of the metal oxide (for example by means of thermal radiation).

[0143] Furthermore, the reactor can be designed in such a way that the secondary heat transfer fluid can be brought into direct interaction and / or contact with the metal oxide to be reduced and / or the gas or gas mixture intended for its reduction, in order to transfer the heat energy to the metal oxide to be reduced and / or the gas or gas mixture.

[0144] Preferably, the device is designed such that the fluid heating device is thermally coupled to the heat exchanger device by means of the primary heat transfer fluid circulating in a primary fluid circuit, wherein the heat exchanger device is thermally coupled to the reactor by means of the secondary heat transfer fluid circulating in a secondary fluid circuit, wherein a primary fluid inlet line of the primary fluid circuit, through which the primary heat transfer fluid is transported from the fluid heating device towards the heat exchanger device, has a first length, and wherein a secondary fluid inlet line of the secondary fluid circuit, through which the secondary heat transfer fluid is transported from the heat exchanger device towards the reactor, has a second length that is greater than the first length.

[0145] The appropriately designed device enables the efficient transport of heat energy generated by concentrated solar radiation over a long distance with minimal heat energy losses. Consequently, the appropriately designed device allows a fluid heating unit, configured to heat a primary heat transfer fluid using concentrated solar radiation, to be located at a greater distance from the reactor in which the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced is heated by the energy obtained from concentrated solar radiation.

[0146] This is particularly advantageous when the concentrated solar radiation from a solar tower power plant is used to heat the primary heat transfer fluid. A solar tower power plant has a fluid heating unit mounted on a tower structure. The fluid heating unit is also referred to as a receiver, absorber station, and / or combustion chamber. A number of reflector devices, also called heliostats, are arranged below the fluid heating unit to reflect solar radiation onto the fluid heating unit. The reflector devices cover a large area around the tower structure, so that a reactor for heating the metal oxide to be reduced and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced can typically be located outside the area where the reflector devices are located.Consequently, the described device enables an increase in the distance between the fluid heating device and the reactor.

[0147] Preferably, the first length is shorter than 1000 meters. More preferably, the first length is shorter than 800 meters. More preferably, the first length is shorter than 600 meters. More preferably, the first length is shorter than 400 meters. More preferably, the first length is shorter than 200 meters.

[0148] Preferably, the first length is between 100 meters and 1000 meters. More preferably, the first length is between 110 meters and 900 meters. More preferably, the first length is between 120 meters and 800 meters. More preferably, the first length is between 130 meters and 700 meters. More preferably, the first length is between 140 meters and 600 meters. More preferably, the first length is between 150 meters and 500 meters. More preferably, the first length is between 160 meters and 400 meters. More preferably, the first length is between 170 meters and 300 meters. More preferably, the first length is between 180 meters and 200 meters.

[0149] Preferably, the device has a third heat exchanger device by means of which the heat energy of the secondary heat transfer fluid can be transferred to a tertiary heat transfer fluid, wherein the reactor is designed to transfer heat from the tertiary heat transfer fluid at least indirectly to the metal oxide to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

[0150] For example, a gas selected from the group consisting of hydrogen, carbon dioxide, water vapor, methane, ammonia, carbon monoxide, sulfur dioxide, sulfur trioxide, hydrochloric acid, nitrogen monoxide, nitrogen dioxide, nitrogen, air and mixtures thereof is used as the tertiary heat transport fluid.

[0151] For example, the tertiary heat transport fluid contains or is a molten salt, for example containing NaNO 3 and / or KNO 3.

[0152] Preferably, the tertiary heat transfer fluid contains or is a molten metal. For example, the molten metal contains tin and / or zinc and / or aluminum and / or lead.

[0153] Preferably, the device is designed such that a heat transport fluid is used as the tertiary heat transport fluid whose heat capacity differs from the heat capacity of the secondary heat transport fluid.

[0154] Preferably, the device is designed such that a heat transport fluid is used as the tertiary heat transport fluid whose density differs from the heat capacity of the secondary heat transport fluid.

[0155] Preferably, the device is designed such that a heat transport fluid is used as the tertiary heat transport fluid whose heat capacity and / or density is smaller than the heat capacity of the secondary heat transport fluid.

[0156] Preferably, the device is designed such that a heat transport fluid is used as the tertiary heat transport fluid whose heat capacity and / or density is greater than the heat capacity of the secondary heat transport fluid.

[0157] Preferably, the device is designed such that the reactor has a first region for supplying the gas or gas mixture used for the reduction of the metal oxide to be reduced into the reactor, a second region for supplying the metal oxide to be reduced into the reactor, and a third region for at least partially removing the reaction product generated by the redox reaction of the metal oxide and the gas or gas mixture from the reactor, wherein the second region is arranged below the first region in the operating state of the reactor, and wherein the third region is arranged below the second region in the operating state of the reactor.

[0158] The reaction product generated in the redox reaction has a higher density than the gas or gas mixture. Furthermore, the reaction product has a lower temperature than the gas or gas mixture. By removing the reaction product in the third section of the reduction reactor, cooling of the gas or gas mixture is prevented or counteracted, so that the appropriately designed device enables a more efficient and faster reduction of the metal oxide.

[0159] The reaction product can be water or water vapor. For example, water is produced as a reaction product when iron oxide is reduced using hydrogen.

[0160] Further advantages, details, and features of the invention will become apparent from the exemplary embodiments described below. These will show in detail: Figure 1: shows a process flow diagram of a process according to the invention for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation; Figure 2: shows a process flow diagram of a further embodiment of the process according to the invention for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation; Figure 3: shows a process flow diagram of yet another embodiment of the process according to the invention for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation; Figure 4: shows a process flow diagram of yet another embodiment of the process according to the invention for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation;Figure 5: shows a process flow diagram of a further embodiment of the process according to the invention for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation; Figure 6: shows a schematic setup of a device for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation; Figure 7: shows a schematic setup of a device for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation according to a further embodiment of the present invention; Figure 8: shows a schematic setup of a device for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation according to a further embodiment of the present invention;Figure 9 shows a schematic setup of a device for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation according to a further embodiment of the present invention; Figure 10 shows a schematic setup of a device for the reduction of metal oxide using a reducing gas or gas mixture and concentrated solar radiation according to a further embodiment of the present invention; and Figure 11 shows the schematic setup of a reactor of a device for the reduction of metal oxide using a reducing gas or gas mixture.

[0161] In the following description, identical reference numerals denote identical components or identical features, so that a description of a component in relation to one figure also applies to the other figures, thus avoiding repetitive descriptions. Furthermore, individual features described in connection with one embodiment can also be used separately in other embodiments.

[0162] Figure 1 Figure 1 shows a process flow diagram of a process according to the invention for the reduction of metal oxide M1 using a reducing gas or gas mixture using concentrated solar radiation.

[0163] In process step V1, the metal oxide M1 to be reduced and the gas or gas mixture used for its reduction are combined. In a subsequent process step V2, the metal oxide M1 and / or the gas or gas mixture used for its reduction are heated, with the thermal energy used for heating the metal oxide M1 and / or the gas or gas mixture being obtained at least partially from concentrated solar radiation.

[0164] Figure 2 Figure 1 shows a process flow diagram of a further embodiment of the process according to the invention for the reduction of metal oxide M1 using a reducing gas or gas mixture and concentrated solar radiation. The process can be carried out on any of the surfaces shown in the figure 1. Figures 6 to 10The devices shown 1 are designed for the reduction of metal oxide M1 using a reducing gas or gas mixture and concentrated solar radiation.

[0165] As described above, in process step V1 the metal oxide M1 to be reduced and the gas or gas mixture used for the reduction of the metal oxide M1 are combined. In process step S1, a primary heat transfer fluid HTF1 is heated by means of concentrated solar radiation. For this purpose, the device 1 has a fluid heating unit 3, which is configured to heat a primary heat transfer fluid HTF1 by means of concentrated solar radiation.

[0166] In the in the Figures 6 to 10In the illustrated embodiments of the device 1, the fluid heating unit 3 is designed as an absorber station 3 in which solar radiation SR emitted by the sun S is concentrated. For this purpose, the solar radiation SR is reflected onto / into the fluid heating unit 3 by reflection devices 2 designed as heliostats 2. The primary heat transfer fluid HTF1 passes through the fluid heating unit 3 and is thus heated by the concentrated solar radiation SR.

[0167] The device 1 further comprises a heating unit 40 configured as a reactor 40, which is designed to transfer heat from the primary heat transfer fluid HTF1, at least indirectly, to the metal oxide M1 and / or to the gas or gas mixture used for the reduction of the metal oxide M1, in accordance with process step S11. For this purpose, the primary heat transfer fluid HTF1 circulates between the fluid heating unit 3 and the reactor 40. Consequently, the metal oxide M1 and / or the gas or gas mixture used for the reduction of the metal oxide M1 is heated, which corresponds to process step V2 above.

[0168] The in Figure 7 The device 1 shown is designed to perform the method whose process flow diagram is shown in Figure 3 The process steps V1 and S1 are the same as in the process whose process flow diagram is shown in Figure 2is shown, so reference is made to the description above. The in Figure 7 The device shown in 1 differs from the one in Figure 6The device 1 shown is characterized by the fact that it has a heat storage device 30, wherein, in a process step S1S, thermal energy from the primary heat transfer fluid HTF1 is transferred at least indirectly to the heat storage device 30. A heat storage medium 31, which preferably has a large heat capacity, is arranged in the heat storage device 30. However, the primary heat transfer fluid HTF1 can also function as the heat storage medium 31. The heat storage device 30 is thermally coupled to the reactor 40 by means of a heat transfer fluid circulating between the heat storage device 30 and the reactor 40.In the illustrated embodiment, the primary heat transfer fluid HTF1 circulates between the heat storage device 30 and the reactor 40, so that, according to process step SS1, thermal energy from the heat storage device 30 is transferred to the metal oxide M1 and / or to the gas or gas mixture used for the reduction of the metal oxide M1. Consequently, the metal oxide M1 and / or the gas or gas mixture used for the reduction of the metal oxide M1 is heated, which corresponds to process step V2 above.

[0169] The in Figure 8 The device 1 shown is designed to perform the method whose process flow diagram is shown in Figure 4 The process steps V1 and S1 are the same as in the process whose process flow diagram is shown in Figure 2 is shown, so reference is made to the description above. The in Figure 8The device shown in 1 differs from the one in Figure 7The device 1 shown is characterized by the fact that the device 1 has a heat exchanger 60 by means of which, in a process step S12, thermal energy from the primary heat transfer fluid HTF1 can be transferred to a secondary heat transfer fluid HTF2. For this purpose, the fluid heating device 3 is thermally coupled to the heat exchanger 60 by means of the primary heat transfer fluid HTF1 circulating in a primary fluid circuit 10. The reactor 40 is configured to transfer heat from the secondary heat transfer fluid HTF2, at least indirectly, to the metal oxide M1 and / or to the gas or gas mixture used for the reduction of the metal oxide M1 in a process step S21. For this purpose, the heat exchanger 60 is thermally coupled to the reactor 40 by means of the secondary heat transfer fluid HTF2 circulating in a secondary fluid circuit 20.Consequently, the metal oxide M1 and / or the gas or gas mixture used for the reduction of the metal oxide M1 to be reduced is heated, which corresponds to the above process step V2.

[0170] The in Figure 9 The device shown in 1 differs from the one in Figure 8 The device 1 shown differs in that it does not have a heat storage device 30 arranged between the fluid heating device 3 and the heat exchanger device 60. However, the device shown in Figure 9 The device 1 shown also includes the heat storage device 30, which is arranged between the fluid heating device 3 and the heat exchanger device 60.

[0171] Out of Figure 9It is evident that a primary fluid supply line 11 of the primary fluid circuit 10, through which the primary heat transfer fluid HTF1 is transported from the fluid heating device 3 towards the heat exchanger device 60, has a first length L1. Furthermore, it is evident from Figure 9 It is evident that a secondary fluid inlet line 21 of the secondary fluid circuit 20, through which the secondary heat transfer fluid HTF2 is transported from the heat exchanger device 60 towards the reactor 40, has a second length L2 that is greater than the first length L1.

[0172] Consequently, the primary heat transfer fluid HTF1 is transported to the heat exchanger 60 via a first path L1, whereby thermal energy is transferred from the primary heat transfer fluid HTF1 to the secondary heat transfer fluid HTF2 in the heat exchanger 60. Furthermore, the secondary heat transfer fluid HTF2 is transported to the reactor 40 via a second path L2, which is larger than the first path L1, whereby thermal energy is transferred from the secondary heat transfer fluid HTF2 to the metal oxide M1 and / or to the gas or gas mixture used for the reduction of the metal oxide M1 in the reactor 40.

[0173] Preferably, the secondary heat transfer fluid HTF2 is a heat transfer fluid whose heat capacity is greater than that of the primary heat transfer fluid HTF1. More preferably, the secondary heat transfer fluid HTF2 is a heat transfer fluid whose specific heat capacity is greater than that of the primary heat transfer fluid HTF1. More preferably, the secondary heat transfer fluid HTF2 is a heat transfer fluid whose density is greater than that of the primary heat transfer fluid HTF1. More preferably, the secondary heat transfer fluid HTF2 is a heat transfer fluid whose density-heat capacity product is greater than the density-heat capacity product of the primary heat transfer fluid HTF1.

[0174] The device 1, which is in Figure 10 The depiction can be designed accordingly, so that the features relating to Figure 9The described length ratios of the first lengths L1 of the primary fluid supply lines 11 and the second lengths L2 of the secondary fluid supply lines 21 also apply in the case described in Figure 10 The illustrated embodiment of the device 1 can be realized.

[0175] The in Figure 10 The device 1 shown is designed to perform the method whose process flow diagram is shown in Figure 5 The process steps V1, S1 and S12 are the same as in the process whose process flow diagram is shown in Figure 4 is shown, so reference is made to the description above. The in Figure 10 The device shown in 1 differs from the one in Figure 8The device 1 shown is modified by the fact that the device 1 additionally comprises a second heat exchanger 70. In process step S23, thermal energy from the secondary heat transfer fluid HTF2 is transferred to a tertiary heat transfer fluid HTF3 in the second heat exchanger 70. The heating device 40 is configured, according to process step S31, to transfer heat from the tertiary heat transfer fluid HTF3, at least indirectly, to the metal oxide M1 and / or to the gas or gas mixture used for the reduction of the metal oxide M1 to be reduced. Consequently, the metal oxide M1 and / or the gas or gas mixture used for the reduction of the metal oxide M1 to be reduced is heated, which corresponds to process step V2 above.

[0176] Figure 11 shows a reactor 40, which is located in each of the in the Figures 6 to 10The devices 1 shown are usable. The reactor 40 has a first section 41 for supplying the gas or gas mixture used to reduce the metal oxide M1 to be reduced into the reactor 40. For this purpose, the reactor 40 has a supply port 41_1 opening into the first section 41. Furthermore, the reactor 40 has a second section 42 for supplying the metal oxide M1 to be reduced into the reactor (40), wherein the second section 42 is arranged below the first section 41 in the operating state of the reactor 40. For this purpose, the reactor 40 has a supply port 42_1 opening into the second section 42. Furthermore, reactor 4) has a third area 43 for at least partially removing the reaction product generated by the redox reaction of the metal oxide M1 and the gas or gas mixture from reactor 40, wherein the third area is located below the second area 42 in the operating state of reactor 40.For this purpose, reactor 40 has a discharge connection 43_1 leading into the third area 43.

[0177] The above-described methods for the reduction of metal oxide M1 using a reducing gas or gas mixture are applicable when using a device 1 in which the Figure 11 The reactor 40 shown is configured such that the gas or gas mixture used to reduce the metal oxide M1 is fed into the reactor 40 in the first section 41 via the feed port 41_1. Furthermore, the metal oxide M1 to be reduced is fed into the reactor 40 in the second section 42 via the feed port 42_1. The reaction product generated by the redox reaction of the metal oxide M1 and the gas or gas mixture is at least partially discharged from the reactor 40 in the third section 43 via the discharge port 43_1.

[0178] The reaction product generated in the redox reaction has a higher density than the gas or gas mixture. Furthermore, the reaction product has a lower temperature than the gas or gas mixture. By removing the reaction product in the third section 43 of reactor 40, cooling of the gas or gas mixture is prevented or counteracted, so that the appropriately designed process enables a more efficient and faster reduction of the metal oxide M1.

[0179] The reaction product can be water or water vapor. For example, water is produced as a reaction product when iron oxide M1 is reduced using hydrogen. Reference symbol list

[0180] 1 Device 2 Reflection device / Heliostat 3 Fluid heating device 10 Primary fluid circuit 11 Primary fluid inlet line 12 Primary fluid outlet line 20 Secondary fluid circuit 21 Secondary fluid inlet line 22 Secondary fluid outlet line 30 Heat storage device 31 Heat storage medium 40 Heating device / Reactor 41 First section (of the heating device / reactor) 41.1 Inlet connection (of the first section) 42 Second section (of the heating device / reactor) 42.1 Inlet connection (of the second section) 43 Third section (of the heating device / reactor) 43.1 Outlet connection (of the third section) 60 First heat exchanger device 70 Second heat exchanger device HTF1 Primary heat transport fluid HTF2 Secondary heat transport fluid HTF3 Tertiary heat transport fluid M1 Metal oxide L1 first path segment / first length L2 second path segment / second length Sun SRSun radiation S1Procedure step S11Procedure step S1SProcedure step S21Procedure step S23Procedure step S31Procedure step SS1Procedure step V1Procedure step V2Procedure step

Claims

1. Process for reducing metal oxide (M1) by means of a reducing gas or gas mixture, having the following process steps: - combining (V1) the metal oxide (M1) to be reduced and the gas or gas mixture used to reduce the metal oxide (M1) to be reduced; - heating (V2) the metal oxide (M1) and / or the gas or gas mixture used for the reduction of the metal oxide to be reduced, wherein - the heat energy used to heat (V2) the metal oxide (M1) to be reduced and / or to heat the gas or gas mixture used for the reduction of the metal oxide to be reduced is produced at least partially by means of concentrated solar radiation, wherein the process is characterized in that the gas or gas mixture used for the reduction of the metal oxide contains more than 10% hydrogen gas.

2. Process according to claim 1, characterized by the following features: - heating (S1) a primary heat transfer fluid (HTF1) by means of concentrated solar radiation; - transferring (S11, SS1, S21, S31) heat energy from the primary heat transfer fluid (HTF1) to the metal oxide (M1) to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide to be reduced.

3. Process according to claim 2, characterized by the following features: - transferring (S1S) heat energy from the primary heat transfer fluid (HTF1) to a heat storage device (30); and - transferring (SS1) heat energy from the heat storage device (30) to the metal oxide (M1) to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide (M1) to be reduced.

4. Process according to either of claims 2 and 3, characterized by the following features: - transferring (S12) heat energy from the primary heat transfer fluid (HTF1) to a secondary heat transfer fluid (HTF2) in a heat exchanger device (60); and - transferring (S21) heat energy from the secondary heat transfer fluid (HTF2) to the metal oxide (M1) to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide (M1) to be reduced, in a heating device (40).

5. Process according to claim 4, characterized in that a heat transfer fluid with a greater heat capacity than the heat capacity of the primary heat transfer fluid (HTF1) is used as the secondary heat transfer fluid (HTF2).

6. Process according to either of claims 4 and 5, characterized by the following steps: - transporting the primary heat transfer fluid (HTF1) to the heat exchanger device (60) via a first path (L1), wherein in the heat exchanger device (60) heat energy is transferred from the primary heat transfer fluid (HTF1) to the secondary heat transfer fluid (HTF2); and - transporting the secondary heat transfer fluid (HTF2) to the heating device (40) via a second path (L2) which is larger than the first path (L1), wherein in the heating device (40) heat energy is transferred from the secondary heat transfer fluid (HTF2) to the metal oxide (M1) and / or to the gas or gas mixture used for the reduction of the metal oxide (M1) to be reduced.

7. Process according to any of claims 4 to 6, characterized by the following features: - transferring (S23) heat energy from the secondary heat transfer fluid (HTF2) to a tertiary heat transfer fluid (HTF3) in a second heat exchanger device (70); and - transferring (S31) heat energy from the tertiary heat transfer fluid (HTF3) to the metal oxide (M1) to be reduced and / or to the gas or gas mixture used for the reduction of the metal oxide (M1) to be reduced, in the heating device (40).

8. Process according to claim 7, characterized in that a heat transfer fluid with a heat capacity that differs from the heat capacity of the secondary heat transfer fluid (HTF2) is used as the tertiary heat transfer fluid (HTF3).

9. Process according to any of the preceding claims, characterized in that the heat energy produced by means of concentrated solar radiation is supplied to a reactor (40) in which the metal oxide (M1) to be reduced and the gas or gas mixture used for the reduction of the metal oxide (M1) to be reduced are combined.

10. Process according to claim 9, characterized by the following features: - the gas or gas mixture used to reduce the metal oxide (M1) to be reduced is fed to the reactor (40) in a first region (41) of the reactor (40); - the metal oxide (M1) to be reduced is fed to the reactor (40) in a second region (42) of the reactor (40), which is located below the first region (41) in the operating state of the reactor (40); and - the reaction product generated by the redox reaction of the metal oxide (M1) with the gas or gas mixture is at least partially discharged from the reactor (40) in a third region (43), wherein the third region is located below the second region (42) in the operating state of the reactor (40).

11. Process according to any of the preceding claims, characterized in that in addition to the gas or gas mixture, carbon monoxide and / or carbon dioxide and / or methane and / or an alkane and / or water are fed to the metal oxide (M1) to be reduced.

12. Apparatus (1) for reducing metal oxide (M1) by means of a reducing gas or gas mixture, wherein the apparatus (1) has the following features: - the apparatus (1) is designed to heat the metal oxide (M1) and / or the gas or gas mixture used to reduce the metal oxide (M1) to be reduced, by means of heat energy produced at least partially from concentrated solar radiation; - the apparatus (1) has a reactor (40) for receiving the metal oxide (M1) to be reduced and for introducing the gas or gas mixture; - the apparatus (1) has a fluid heating device (3) designed to heat a primary heat transfer fluid (HTF1) by means of concentrated solar radiation; - the reactor (40) is designed to transfer heat from the primary heat transfer fluid (HTF1) at least indirectly to the metal oxide (M1) to be reduced and / or to the gas or gas mixture used to reduce the metal oxide (M1) to be reduced; - the apparatus (1) has a heat exchanger device (60) by means of which heat energy from the primary heat transfer fluid (HTF1) can be transferred to a secondary heat transfer fluid (HTF2); and - the reactor (40) is designed to transfer heat from the secondary heat transfer fluid (HTF2) at least indirectly to the metal oxide (M1) to be reduced and / or to the gas or gas mixture used to reduce the metal oxide (M1) to be reduced.

13. Apparatus (1) according to claim 12, characterized in that the reactor (40) is designed to be heated by means of heat energy produced from concentrated solar radiation.

14. Apparatus (1) according to claim 12 or 13, characterized in that the apparatus (1) has a heat storage device (30), wherein the apparatus (1) is designed to transfer heat energy from the primary heat transfer fluid (HTF1) at least indirectly to the heat storage device (30).

15. Apparatus (1) according to any of claims 12 to 14, characterized by the following features: - the fluid heating device (3) is thermally coupled to the heat exchanger device (60) by means of the primary heat transfer fluid (HTF1) circulating in a primary fluid circuit (10); - the heat exchanger device (60) is thermally coupled to the reactor (40) by means of the secondary heat transfer fluid (HTF2) circulating in a secondary fluid circuit (20); - a primary fluid inlet line (11) of the primary fluid circuit (10), via which line the primary heat transfer fluid (HTF1) is transported from the fluid heating device (3) toward the heat exchanger device (60), has a first length (L1); - a secondary fluid inlet line (21) of the secondary fluid circuit (20), via which line the secondary heat transfer fluid (HTF2) is transported from the heat exchanger device (60) toward the reactor (40), has a second length (L2) that is greater than the first length (L1).

16. Apparatus (1) according to any of claims 12 to 15, characterized by the following features: - the apparatus (1) has a second heat exchanger device (70) by means of which the heat energy from the secondary heat transfer fluid (HTF2) can be transferred to a tertiary heat transfer fluid (HTF3); and - the reactor (40) is designed to transfer heat from the tertiary heat transfer fluid (HTF3) at least indirectly to the metal oxide (M1) to be reduced and / or to the gas or gas mixture used to reduce the metal oxide (M1) to be reduced.

17. Apparatus (1) according to any of claims 12 to 16, characterized by the following features: - the reactor (40) has a first region (41) for feeding the gas or gas mixture used to reduce the metal oxide (M1) to be reduced into the reactor (40); - the reactor (40) has a second region (42) for feeding the metal oxide (M1) to be reduced into the reactor (40), wherein the second region (42) is located below the first region (41) in the operating state of the reactor (40); and - the reactor (40) has a third region (43) for at least partially discharging the reaction product generated by the redox reaction of the metal oxide (M1) with the gas or gas mixture from the reactor (40), wherein the third region is located below the second region (42) in the operating state of the reactor (40).