Method for producing iron fuel

Abstract

The present invention relates to a method for producing iron fuel from a raw material containing metal oxides by reducing the raw material containing metal oxides. The object of the present invention is to produce iron in a specific powder form with a particle size distribution and specific surface area, which is used as a starting material for iron fuel combustion.

Description

[Technical field]

[0001] The present invention relates to a method for producing iron fuel from a feedstock containing metal oxides. [Background technology]

[0002] Iron ore reduction using hydrogen mixtures as reducing agent has been industrially proven and is well known as such. Examples of industrial implementation concern direct reduction processes. The input material in these processes is mainly iron ore with a wide range of different properties in terms of particle size, morphology and composition. Furthermore, these processes are designed for (usually liquid) steelmaking, which has relatively less stringent requirements for the particle morphology after reduction and includes a carburization step to add carbon to the iron. In such steelmaking processes, iron oxide and hydrogen are transported to a reactor, where the iron oxide is reduced to iron. The iron produced leaves the reactor and is then transported and stored. The solids present in the exhaust gas are separated in a gas-solid separation operation and returned to the reactor. The exhaust gas is subjected to a gas separation operation to remove the water vapor produced during the reaction. Unused hydrogen in the reactor exhaust gas is recycled to the inlet of the reactor. These steelmaking processes are not based on the use of iron as a fuel source.

[0003] U.S. Pat. No. 4,082,545 relates to a process for the direct reduction of iron ore which includes establishing a plurality of fluidized beds, heating and progressively reducing the iron ore by passing it through the plurality of fluidized beds in succession, fluidizing the fluidized beds by passing a reducing gas through them from below, removing partially spent reducing gas from each bed, cooling and scrubbing the partially spent reducing gas to remove substantially all solids therefrom, heating the scrubbed gas, and feeding the heated fluidizing gas back into the beds.

[0004] US Patent Application Publication No. 2016 / 348199 relates to a method for reducing a feedstock comprising metal oxides, the method comprising: reducing the feedstock comprising metal oxides with a reducing gas in at least first and second fluidized bed units; flowing the reducing gas through the fluidized bed units against the flow direction to the feedstock comprising metal oxides; removing the reducing gas used during the reduction of the feedstock comprising metal oxides in the at least two fluidized bed units as exhaust gas from the first fluidized bed unit; compressing at least a portion of the exhaust gas in at least one recycle gas compressor to generate a hot recycle gas; then cooling the hot recycle gas in at least one aftercooler to generate a cold recycle gas; at least partially removing CO2 from the cold recycle gas to generate a product gas; mixing the product gas with the reducing gas; and optionally transporting the feedstock comprising metal oxides, after preheating in a heating device, into the first fluidized bed unit via a pipeline by a propelling gas from at least one delivery tank.

[0005] U.S. Pat. No. 3,288,590 discloses a method for continuously reducing iron oxide in granular solid form with a reducing gas containing primarily hydrogen under dilute suspension conditions, comprising crushing the iron oxide to an average particle size of about 200 mesh so that all of the iron oxide passes 100 mesh, heating the reducing gas to a temperature in the range of 480° C. under a pressure of 11 atm to 35 atm, passing the gas upward through a substantially vertical reaction zone at a velocity in the range of 1.5 m / s to 7.6 m / s, preheating the iron oxide to at least about 480° C., and grinding the fine iron oxide to a temperature of about 480° C. under a pressure of 11 atm to 35 atm. continuously feeding preheated iron oxide divided into 100% and 150% by weight into a rising column of reducing gas at a rate that maintains an average solids density in the range of 80 kg to 240 kg of metal oxide per cubic meter of gas under conditions within the rising column; and separately removing substantially solids-free gas and reduced iron fines from the effluent of a reaction zone, the reaction zone consisting of a series of vertical chambers forming stages interconnected to achieve a downward flow of gas from the top of one stage interconnected to the upward flow of the next stage.

[0006] US Patent No. 4,420,332 relates to a process for simultaneously producing reduced iron and pyrolysis of heavy oil, comprising the steps of introducing fine iron ore and heavy oil into a fluidized bed pyrolysis reactor and pyrolyzing the heavy oil into pyrolysis products and carbonaceous by-products at a temperature in the range of 500° C. to 600° C. The fine iron ore is in the form of particles having an average diameter of about 10 micrometers to 30 micrometers, and the fine iron ore having a deposit of carbonaceous material is introduced into a first fluidized bed reduction furnace and contacted with a hot reducing gas blown therein in a fluidized state to reduce the fine iron ore into reduced iron at a temperature in the range of 800° C. to 1000° C. and form an exhaust gas. The cracked gas, diesel and residual oil are separated from the heat product by distillation in the fractionation system, and a portion of the reduced iron is transferred to a gas reformer, where a fluidized bed of the transferred reduced iron is formed in the gas reformer, and the cracked gas or residual oil is reformed into a reducing gas mainly composed of hydrogen and carbon monoxide by contact with the reduced iron fluidized in the gas reformer.

[0007] WO 00 / 01856 relates to a process for reducing iron oxide-containing particles to metallic iron-containing particles in a reduction zone of a moving bed reduction reactor using a reducing gas composed primarily of hydrogen and / or carbon monoxide, the process comprising introducing the iron oxide-containing particles into a first level of the reduction zone to form a moving bed of particles in the lower part of the reduction zone and spreading downwardly to a discharge zone of the reactor, injecting a reducing gas below the first level of the moving bed to define a moving bed reduction subzone there above, recovering metallic iron-containing particle fines that overflow from the reactor from an upper part of the fluidized bed, recovering reduced metallic iron-containing particles from the non-fluidized moving bed in the discharge zone, and recovering spent reducing / fluidizing gas from above the fluidized bed in the reduction zone.

[0008] US Patent No. 3,303,017 relates to a process for reducing iron ore by direct reduction in a fluidized bed, which comprises introducing a fluidizing gas into the fluidized bed through a plurality of conical gas distributors, each of which is fed by a separate cyclone gas-solid separator, the fluidized bed comprising at least two conical gas distributors, each of which is fed by a separate cyclone gas-solid separator, the cyclones being arranged internally and feeding and introducing gas directly into the conical gas distributors.

[0009] The drawback of the present processes for producing iron fuel from raw materials containing metal oxides by reducing the raw materials containing metal oxides is that these processes are unable to produce the specific powder form of iron used for the purpose of iron fuel combustion. One negative problem here is that particle agglomeration occurs during the process. Another negative problem is that the material produced is pyrophoric. Both particle agglomeration and the formation of pyrophoric material are barriers to the use of the specific powder form of iron as a starting material in iron fuel combustion.

[0010] The term "pyrophoric" should be understood as a property of a material. More specifically, a material qualifies as pyrophoric if it spontaneously ignites in air below 54°C or within 5 minutes of contact with air. This is due to the extremely low ignition temperature of oxidation due to the high specific surface area of ​​the material. When the ignition temperature is low enough, self-ignition under atmospheric conditions can occur. Pyrophoricity of iron particles after reduction has been reported to be a serious problem in fluidized bed reduction, where a high surface area of ​​the material is obtained. The tendency to reoxidize depends on the reduction temperature. Studies have shown that the surface area of ​​fine metal powders generally decreases with reduction temperature.

[0011] The term "agglomeration or sticking" should also be understood as a property of a material. Particle sticking is considered the most serious problem encountered in the reduction of iron oxide. In fluidized bed reduction, this is particularly problematic, since it leads to defluidization of the particle bed. And once the particle bed defluidizes, the iron oxide reduction process cannot continue. Factors influencing the sticking problem are, for example, temperature, metallization ratio, gas flow rate, reduction atmosphere and particle characteristics. In general, sticking is observed above a critical temperature and occurs only after the appearance of metallic iron. The latter is often believed to be due to the formation of iron whiskers at higher metallization ratios, which increase the tendency of particles to stick. An example of a method to prevent sticking is the application of a lower reduction temperature. Agglomeration leads to a decrease in the quality of the product, since it no longer meets the desired requirements regarding particle size. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Pat. No. 4,082,545 [Patent Document 2] US Patent Application Publication No. 2016 / 348199 [Patent Document 3] U.S. Pat. No. 3,288,590 [Patent Document 4] U.S. Pat. No. 4,420,332 [Patent Document 5] International Publication No. 00 / 01856 [Patent Document 6] U.S. Pat. No. 3,303,017 Summary of the Invention

[0013] The object of the present invention is to produce iron in a specific powder form with a particle size distribution and specific surface area, which iron powder is used as a starting material for iron fuel combustion.

[0014] The invention therefore relates to a method for producing iron fuel from a raw material comprising metal oxides by reducing the raw material comprising metal oxides according to the subject matter of claim 1.

[0015] The inventors have found that by applying certain process design features, it is possible to limit particle agglomeration and pyrophoricity. The iron powder thus produced is then used as the starting material for iron fuel combustion.

[0016] The conditions within the fluidized bed are such that the bed is typically a bubbling fluidized bed. In a bubbling fluidized bed, the gas rate is above the minimum fluidization rate. In the minimum fluidization rate situation, at some point, the force exerted upwards on all particles is equal to the particle weight, the particles are suspended, and the gas rate is called the minimum fluidization rate. Any extra increase in rate creates bubbles of gas that flow rapidly upwards in the system, i.e., known as a bubbling fluidized bed. Increasing the superficial gas velocity creates a transition from a bubbling fluidized bed to a turbulent fluidized bed regime.

[0017] Combustion of iron produces a variety of different types of iron oxide, hematite (Fe2O3) and magnetite (Fe3O4). These substances can be reduced by electricity and / or gaseous reducing agents including syngas, carbon monoxide, methane or hydrogen. The chemical processes occurring during the reduction of iron oxide by hydrogen are described by equilibrium reactions:

[0018] TIFF2025500259000001.tif20170

[0019] TIFF2025500259000002.tif20170

[0020] TIFF2025500259000003.tif20170

[0021] The iron (oxide) does not reach a molten state during the process, and is therefore also called direct reduction. The chemical reactions show that the process involves a reaction between solid and gaseous reactants. An important difference between reduction with hydrogen, traditionally used in steel production in blast furnaces, and reduction with carbon monoxide is that reduction with hydrogen is endothermic. This means that energy must be added to the system to ensure a constant reduction temperature. According to the present invention, the addition of energy to the system can be done by preheating the input materials or by incorporating a form of heating into the system design. According to the present invention, a fluidized bed reactor is used to contact the gas with the solids. The system operates at specific process conditions, which are described later in this specification.

[0022] According to the method, the stream containing the iron fuel is transported to a vessel. It is clear that such a vessel is to be understood as a structure in which there are two or more vessels, for example a system of vessels arranged in parallel. The situation is the same for fluidized bed units. It is clear that several fluidized bed units may be arranged in parallel or in series and the method is in no way limited to a specific number of fluidized bed units.

[0023] In one example, removing the partially spent reducing gas from the fluidized bed unit further comprises separating crude solids from the partially spent reducing gas and returning these crude solids to the fluidized bed unit.

[0024] In one example, the method for producing iron fuel further includes separating fine solids from the partially spent reducing gas after the step of separating the coarse solids.

[0025] In one example, the method for producing iron fuel further includes removing water from the partially spent reducing gas before returning the partially spent reducing gas to the fluidized bed unit.

[0026] In one example, the method for producing iron fuel further includes removing water from the mixture of partially spent reducing gas and fresh reducing gas before returning the mixture to the fluidized bed unit.

[0027] In one example, both of the above steps of removing water may be applied in a method for producing iron fuel.

[0028] In one example, water is removed from the partially consumed reducing gas via one or more processes selected from the group of condensation, adsorption, absorption and membrane filtration, or combinations thereof.

[0029] In one example, the method for producing iron fuel further includes preheating and / or drying the feedstock comprising metal oxides before supplying the feedstock to the fluidized bed unit, the preheating temperature being preferably in the range of 40 to 1000°C.

[0030] In one example, the step of feeding the metal oxide-containing feedstock to the fluidized bed unit further comprises pressurizing the metal oxide-containing feedstock to a pressure prevailing in the fluidized bed unit.

[0031] In one example, the method for producing iron fuel further includes a step of heat exchange between the partially consumed reducing gas from the fluidized bed unit and the mixture of the partially consumed reducing gas and fresh reducing gas, the heat exchange being performed before returning the mixture of the partially consumed reducing gas and fresh reducing gas to the fluidized bed unit.

[0032] In one example, the method for producing iron fuel further includes preheating the mixture of partially spent reducing gas and fresh reducing gas before returning the mixture of partially spent reducing gas and fresh reducing gas to the fluidized bed unit.

[0033] The fluidized bed unit is preferably operated under conditions of a pressure of at least 3 atm and at most 13 atm, more preferably at least 4 atm and at most 12 atm, a temperature of at least 400° C. and at most 800° C., more preferably at least 400° C. and at most 700° C., and a reducing gas velocity within the fluidized bed unit of at least 5 cm / s and at most 200 cm / s, more preferably at least 10 cm / s and at most 150 cm / s. The reactor temperature may be controlled by an external heating source.

[0034] In another example, the method comprises: providing a feedstock comprising metal oxides to a fluidized bed unit; reducing a feedstock comprising metal oxides by flowing a reducing gas through a fluidized bed unit, the fluidized bed unit being operated under conditions of pressure in the range of 1 atm and 15 atm, temperature in the range of 300°C and 1000°C, and reducing gas velocity within the fluidized bed unit in the range of 0.9 cm / s and 270 cm / s; removing the partially spent reducing gas from the fluidized bed unit; mixing the partially spent reducing gas with fresh reducing gas and returning the mixture of the partially spent reducing gas and the fresh reducing gas to the fluidized bed unit; removing a stream comprising iron fuel from the fluidized bed unit; Removing a stream comprising iron fuel from the fluidized bed unit, transporting the iron fuel containing stream to a vessel; reducing the pressure in the vessel to ambient pressure; and the substep of cooling the iron fuel containing stream.

[0035] In one example, the stream containing the iron fuel while under pressure is cooled to a temperature below the point at which agglomeration of the iron fuel occurs.

[0036] In one example, the steps of transporting the iron fuel containing stream and cooling the iron fuel containing stream while under pressure are performed simultaneously.

[0037] The metal oxide containing raw material consists of oxides of iron and inevitable impurities such as metals, e.g. nickel, manganese, copper, lead and cobalt, carbon and sulfates, or mixtures thereof.

[0038] In one example, the fluidized bed unit includes multiple fluidized bed units arranged in series.

[0039] In one example, the fresh reducing gas comprises hydrogen in an amount of at least 50% by volume.

[0040] The iron fuel removed from the fluidized bed has a Sauter mean particle size of at least 10 μm, preferably at least 20 μm and up to 200 μm, preferably up to 150 μm.

[0041] The metal oxide containing raw material has a Sauter mean particle size of at least 10 μm, preferably at least 20 μm and up to 300 μm, preferably up to 200 μm.

[0042] The drawings show, in a schematic manner, an example of the method according to the invention, which is not limited to the particular examples disclosed herein. [Brief description of the drawings]

[0043] [Figure 1] 1 is an example of a method for producing iron fuel. [Diagram 2] 1 is another example of a method for producing iron fuel. [Diagram 3] 1 is another example of a method for producing iron fuel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The metal oxide-containing feedstock 10, preferably oxides of iron, nickel, manganese, copper, lead or cobalt or mixtures thereof, is at least partially reduced or more specifically reduced by the reducing gas 28 flowing through the fluidized bed unit 11 of the metal oxide-containing feedstock 10. The metal oxide-containing feedstock 10 can undergo a pretreatment consisting of a storage 1 and a transport of the metal oxide-containing feedstock, i.e. iron oxide, a preheating unit 3, a lock hopper 5, a solids preheating 7 and a solids feed 9. The metal oxide-containing feedstock originating from the storage 1 is transported to the optional preheating unit 3. If the feedstock is heated, the heated stream 4 is sent to the lock hopper 5. The function of the lock hopper 5 is to introduce the metal oxide particles into a pressurized environment to allow the solids to be introduced at high pressure into the fluidized bed unit 11. An additional function of the lock hopper 5 is to prevent agglomeration of the starting material due to its fluidization. In addition, the function of the lock hopper 5 is to purge the gaseous oxygen present in and between the metal oxide particles to ensure that the oxygen does not substantially enter the fluidized bed unit 11. In one embodiment, the feed 6 originating from the lock hopper 5 is sent to an optional preheating unit 7. After such treatment, the feed 8 is sent to a solids feed unit 9. The function of unit 9 is to dose metal oxide particles 10 to a fluidized bed unit 11. The preheating unit 7 may be integrated into unit 9. In the fluidized bed unit 11, the metal oxide particles are contacted with a reducing agent, i.e., a hydrogen-containing gas, thereby converting the metal oxide particles into metal particles. The fluidized bed unit 11 may also include a heating unit 30 for controlling the reaction temperature. Coarse particles from the gas stream exiting the particle bed present in the fluidized bed unit 11 are separated from the gas stream, and the coarse particles thus separated are returned to the particle bed present in the fluidized bed unit 11. The gas stream 12 exiting the fluidized bed unit 11 is sent to a heat exchanger 14. In the heat exchanger 14, the energy of the gas stream 12 is exchanged for the energy of a hydrogen gas stream 27. Thus, the functional heat exchanger 14 cools the gas stream 12 exiting the coarse particle separation while preheating the hydrogen gas stream 27 that ultimately enters the fluidized bed unit 11, thereby increasing the energy efficiency of the overall system.The gas stream 15 originating from the heat exchanger 15 is sent to a separator unit 16. The function of the separator unit 16 is to separate and discharge fine particles from the gas stream 15 leaving the heat exchanger 14. The fine particles 17 are discharged and stored. A make-up hydrogen gas stream 20 is combined with the gas stream 21. The hydrogen gas stream 19 may be compressed in a compressor 18 to become a hydrogen gas stream 20. The combined hydrogen gas stream, i.e., the hydrogen gas stream 20 and the hydrogen gas stream 21, may contain water and other impurities, which are removed in a water removal unit 22 and the resulting stream 24 is discharged. The function of the water removal unit 22 is not only to cool the gas stream 21 and condense water vapor from the gas stream 21, but also to separate and discharge the condensed water from the gas stream to be recycled. A gas stream 26 originating from the water removal unit 22 is sent to a compressor 25 and the gas stream 27 thus compressed is sent to the heat exchanger 14. The function of the compressor 25 is to pressurize the recycle gas to overcome the pressure drop across the system and generate gas velocity in the fluidized bed unit 11. The heated gas stream 28 is sent to the fluidized bed unit 11. The product stream 29 originating from the fluidized bed unit 11 is sent to the lock hopper unit 31. The lock hopper unit 31 has multiple functions, namely, to cool the particles comprising the product stream 29 with an inert gas, thereby preventing adhesion and agglomeration of the particles, and to prevent oxidation when the particles are exposed to the outside air. Agglomeration leads to a decrease in the quality of the product, since the product no longer meets the desired requirements regarding particle size. Contact with the ambient air also leads to a decrease in the product quality. In addition, the lock hopper unit 31 may be provided with an inert gas stream to fluidize the iron particles during cooling, to prevent them from sticking in the lock hopper system itself. Furthermore, in the lock hopper unit 31, the pressure of the iron particle stream 29 is returned from the system pressure to atmospheric pressure. The product stream 29 may also contain hydrogen gas, and the remaining parts of the hydrogen and water are flashed out. Removal of hydrogen from product stream 29 ensures that no reactions occur outside of fluidized bed unit 11 and allows for the safe operation of downstream operations. Iron particle containing stream 32 is stored in iron fuel reservoir 33.It should be noted that the dry particles 32 ensure safe storage without the risk of the iron particles being oxidized by water in the storage container 33 or becoming clogged as a result of condensation.

[0045] The process scheme according to FIG. 2 is similar to that shown in FIG. 1, except for the surroundings of the fluidized bed unit 11. Metal oxide particles 10 are fed to the fluidized bed unit 11, and a mixed stream 35 of coarse particles and hydrogen is sent to the separator 13. In the separator 12, a stream 38 of coarse particles is recycled to the fluidized bed unit 11. A gas stream 12 containing hydrogen and fine particles originating from the fluidized bed unit 11 is sent to the heat exchanger 14. In the heat exchanger 14, the energy of the gas stream 12 is exchanged with the energy of the hydrogen gas stream 27. The function of the heat exchanger 14 is thus to cool the gas stream 12 discharged from the coarse particle separation while preheating the hydrogen gas stream 27 that finally enters the fluidized bed unit 11, thereby increasing the energy efficiency of the entire system. The heated gas stream 28 can be further heated by the heater 30 to be sent to the fluidized bed unit 11 and become the hydrogen gas stream 34. All remaining process units and streams are similar to those described above in connection with FIG. 1.

[0046] The process scheme according to FIG. 3 is similar to that shown in FIG. 2, except for the situation at the discharge site of the fluidized bed unit 11. The product stream 29 coming from the fluidized bed unit 11 is sent to a unit 39 for cooling the particle-containing product stream 29, preferably with an inert gas, in order to prevent the particles from sticking / agglomerating when exposed to ambient air and to prevent oxidation of the particles. Agglomeration leads to a decrease in the quality of the product, since the product no longer meets the desired requirements regarding particle size. Contact with ambient air also leads to a decrease in the product quality. The thus cooled stream 40 is sent to a lock hopper unit 31, which may also be provided with an inert gas stream for fluidizing the iron particles during cooling, in order to prevent sticking in the lock hopper system itself. Furthermore, in the lock hopper unit 31, the pressure of the iron particle stream 40 is returned from the system pressure to atmospheric pressure. The iron particle-containing stream 32 is stored in an iron fuel storage 33. It should be noted that the dry particles 32 ensure safe storage without the risk of the iron particles being oxidized by water in the storage container 33 or becoming clogged as a result of condensation.

Claims

1. 1. A method for producing iron fuel from a metal oxide-containing feedstock by reducing the metal oxide-containing feedstock, comprising: feeding a metal oxide-containing feedstock to a fluidized bed unit, said metal oxide-containing feedstock having a Sauter mean particle size of at least 10 μm, preferably at least 20 μm, and up to 300 μm, preferably up to 200 μm; reducing the metal oxide comprising feedstock by flowing a reducing gas through the fluidized bed unit, the fluidized bed unit being operated under conditions of a pressure in the range of 3 atm to 13 atm, preferably 4 atm to 12 atm, a temperature in the range of 400° C. to 800° C., preferably 400° C. to 700° C., and a reducing gas velocity in the fluidized bed unit in the range of 5 cm / s to 200 cm / s, preferably 10 cm / s to 150 cm / s; removing partially spent reducing gas from the fluidized bed unit; mixing the partially spent reducing gas with fresh reducing gas and returning the mixture of partially spent reducing gas and fresh reducing gas to the fluidized bed unit; removing a stream comprising ferrous fuel from the fluidized bed unit, wherein the ferrous fuel removed from the fluidized bed has a Sauter mean particle size of at least 10 μm, preferably at least 20 μm, and up to 200 μm, preferably up to 150 μm; removing the stream comprising iron fuel from the fluidized bed unit; transporting the stream containing the iron fuel to a vessel and cooling the stream containing the iron fuel while under pressure, wherein a flow of inert gas is applied to remove moisture from the iron fuel during cooling; reducing the pressure in the vessel to ambient pressure; and storing the iron fuel thus obtained.

2. 2. The method of claim 1, wherein the step of removing the partially spent reducing gas from the fluidized bed unit further comprises the steps of separating crude solids from the partially spent reducing gas and returning these crude solids to the fluidized bed unit.

3. 3. The method of claim 2, further comprising separating fine solids from the partially consumed reducing gas and / or the mixture of partially consumed reducing gas and fresh reducing gas after the step of separating the coarse solids.

4. 4. The method according to claim 1, further comprising removing water from a stream selected from the group of the partially spent reducing gas, and the mixture of partially spent reducing gas and fresh reducing gas, or combinations thereof, before returning the stream to the fluidized bed unit.

5. 5. The method of claim 4, wherein the water is removed from the partially consumed reducing gas via one or more processes selected from the group of condensation, adsorption, absorption and membrane filtration, or combinations thereof.

6. 6. The method of any one or more of the preceding claims, further comprising preheating and / or drying the metal oxide-containing feedstock prior to feeding the material to the fluidized bed unit.

7. The method of claim 6, wherein the preheat temperature ranges from 40°C to 1000°C.

8. 8. The method according to claim 1 , wherein the step of feeding the metal oxide-containing feedstock to the fluidized bed unit further comprises the step of pressurizing the metal oxide-containing feedstock to a pressure prevailing in the fluidized bed unit.

9. 9. The method according to claim 1, further comprising a step of heat exchange between the partially consumed reducing gas from the fluidized bed unit and the mixture of partially consumed reducing gas and fresh reducing gas, the heat exchange being carried out before returning the mixture of partially consumed reducing gas and fresh reducing gas to the fluidized bed unit.

10. 10. The method according to claim 1, further comprising preheating the mixture of partially spent reducing gas and fresh reducing gas before returning the mixture of partially spent reducing gas and fresh reducing gas to the fluidized bed unit.

11. 11. The method according to any one or more of claims 1 to 10, wherein the metal oxide-containing raw material consists of oxides of iron and inevitable impurities such as metals, e.g. nickel, manganese, copper, lead and cobalt, carbon and sulfates, or mixtures thereof.

12. 12. The method according to any one or more of the preceding claims, wherein the fluidized bed unit comprises a plurality of fluidized bed units arranged in series.

13. 13. The method according to any one or more of the preceding claims, wherein the fresh reducing gas comprises hydrogen in an amount of at least 50% by volume.

14. 14. The method of any one or more of claims 1 to 13, wherein the stream containing the iron fuel while under pressure is cooled to a temperature below the point at which agglomeration of the iron fuel occurs.

15. 15. The method of any one or more of claims 1 to 14, wherein the steps of transporting the stream containing iron fuel and cooling the stream containing iron fuel while under pressure are performed simultaneously.

Images