Method and apparatus for producing directly reduced metal

Abstract

Method of producing a directly reduced metallic material, comprising the steps of: a) loading a metallic material to be reduced (142) into a furnace space (120); b) providing heat and a reducing gas to the furnace space (120) such that the heated reducing gas heats the loaded metallic material (142) to a temperature high enough for metal oxides present in the loaded metallic material (142) to be reduced, in turn causing water vapour to form; and c) condensing and collecting the water vapour formed in step c in a condenser (280); the method being characterised in that in step a) the metallic material (142) is loaded onto a gas permeable floor (151), the reducing gas passes up through said floor (151), through the loaded metallic material (142), and is further circulated in a closed loop via said condenser (280) and a gas forced circulation device (250), and the method further comprises the step of d) supplying additional reducing gas to achieve and / or maintain a predetermined pressure in said furnace space (120). The invention also relates to a system.

Description

Technical Field

[0001] This invention relates to methods and apparatus for producing directly reduced metals, particularly directly reduced iron (also known as sponge iron) with a very low carbon content. Specifically, this invention relates to the direct reduction of metal ores under a controlled hydrogen atmosphere to produce such directly reduced metals. By providing a carbon-containing gas as part of the same process used for carburizing reduced metal materials, the invention can be further used to produce carburized versions of such directly reduced metals. Background Technology

[0002] The use of hydrogen as a reducing agent to produce directly reduced metals is well known. For example, these methods are described in SE7406174-8 and SE7406175-5, in which a charge of metal ore is subjected to an atmosphere of hydrogen flowing through the charge, resulting in reduction to form directly reduced pure metals.

[0003] Furthermore, Swedish applications SE1950403-4 and SE1951070-0, which were not published at the priority date of this application, disclose a process for directly reducing metallic materials in a closed hydrogen atmosphere and further carburizing such directly reduced metallic materials.

[0004] This invention is particularly suitable for situations involving the batch loading and processing of raw materials awaiting return.

[0005] Several issues exist with the existing technology, including concerns about heat loss and the efficiency of hydrogen utilization. There are also control problems, as it is necessary to measure when the reduction process is complete.

[0006] Furthermore, known methods for carburizing metallic materials include using carbon monoxide as the source of carburizing carbon. This results in the generation and release of carbon dioxide, and often also the generation of carbon monoxide.

[0007] In the technical solution described in the aforementioned Swedish patent application, it may be appropriate to increase the downward flow of water to the condenser described in the patent application, depending on the size of the furnace space and the amount of metal material to be reduced.

[0008] Furthermore, the described technical solution uses a mass of metal material to be reduced, such as a sphere of metal material. In some cases, forming such a sphere requires the use of excessive binder. When using granular materials, the reduction process may result in the breakage of individual particles and contamination of the condenser with the metal material.

[0009] Therefore, there is a need for a method that utilizes efficient heat and energy for the direct reduction and carburizing of metallic materials, without releasing carbon monoxide or carbon dioxide into the atmosphere. This technical solution should be scalable to large production volumes and capable of handling metallic materials with diverse structures. Summary of the Invention

[0010] The present invention solves the above-mentioned problems.

[0011] Therefore, the present invention relates to a method for producing directly reduced metallic materials, comprising the following steps: a) loading the metallic material to be reduced into a furnace space; b) providing heat and reducing gas to the furnace space such that the heated reducing gas heats the loaded metallic material to a sufficiently high temperature, causing the metal oxides present in the loaded metallic material to be reduced, thereby resulting in the formation of water vapor; and c) condensing and collecting the water vapor formed in step c in a condenser; the method is characterized in that, in step a), the metallic material is loaded onto a permeable base plate, the reducing gas passes upward through the base plate, through the loaded metallic material, and further circulates in a closed loop via the condenser and a forced gas circulation device, and the method further comprises step d) supplying additional reducing gas to achieve and / or maintain a predetermined pressure in the furnace space.

[0012] The present invention also relates to a system for producing directly reduced metallic materials, comprising: a furnace space arranged to receive and contain the metallic material to be reduced; a heating and reducing gas supply device arranged to supply heat and reducing gas to the furnace space; a control device arranged to control the heating and reducing gas supply device such that the heated reducing gas heats the loaded metallic material to a sufficiently high temperature, causing the metal oxides present in the loaded metallic material to be reduced, thereby resulting in the formation of water vapor; and a condenser arranged to condense and collect the water vapor. The system is characterized in that the furnace space includes a permeable base plate arranged to support the loaded metallic material and a forced gas circulation device, wherein the heating and reducing gas supply device is arranged to allow the reducing gas to circulate upward through the base plate, through the loaded metallic material, and further via the condenser and the forced gas circulation device in a closed loop, and the control device is arranged to control the heating and reducing gas supply device to supply additional reducing gas, thereby achieving and / or maintaining a predetermined pressure in the furnace space. Attached Figure Description

[0013] In the following, the invention will be described in detail with reference to exemplary embodiments and accompanying drawings, wherein:

[0014] Figure 1a It is a cross-section of a simplified furnace used in the system according to the invention and in the continuous process of the method according to the invention, according to the first embodiment;

[0015] Figure 1b This is a cross-sectional view of a simplified furnace used in the system according to the invention according to the second embodiment, and for a batching process according to the method according to the invention;

[0016] Figure 2 This is a schematic diagram of the system according to the present invention;

[0017] Figure 3 This is a flowchart of the method according to the present invention;

[0018] Figure 4a This is a schematic diagram illustrating the possible relationship between the partial pressure of H2, the partial pressure of carburizing gas, and temperature in the heating furnace space according to a first embodiment of the present invention;

[0019] Figure 4b This is a schematic diagram illustrating the possible relationship between the partial pressure of H2, the partial pressure of carburizing gas, and temperature in the heating furnace space according to a second embodiment of the present invention;

[0020] Figure 4c This is a schematic diagram illustrating the possible relationship between the partial pressure of H2, the partial pressure of carburizing gas, and temperature in the heating furnace space according to a third embodiment of the present invention;

[0021] Figure 5 It is a graph showing the functional relationship between temperature and the reducing power of H2 relative to the metal material to be reduced; and

[0022] Figure 6 This is a schematic diagram of a loading and unloading mechanism for continuous material processing according to the present invention. Detailed Implementation

[0023] Figure 1a , 1b The corresponding component reference numerals are shared with 6.

[0024] therefore, Figure 1a and 1b Each depicts its own furnace 100 for producing metallic materials for direct reduction and possible carburization. Figure 2 The image shows two such furnaces, 210 and 220. Furnaces 210 and 220 can be connected with... Figure 1a or Figure 1b The furnace 100 shown may be the same as, or different in detail from, furnace 210. However, it should be understood that everything described herein regarding furnace 100 applies equally to furnaces 210 and / or 220, and vice versa.

[0025] Furthermore, it should be understood that everything described herein regarding this method also applies to system 200 and / or furnaces 100, 210, 220, and vice versa.

[0026] As used herein, the term "metallic material" is intended, depending on the context, to include materials containing metals. Thus, "metallic material" to be reduced typically refers to metal oxide materials; "metallic material" to be directly reduced typically refers to pure or substantially pure metals; and "metallic material" to be carburized typically refers to carbon-containing metallic materials.

[0027] Furnace 100 is part of a closed furnace system that includes a heated furnace space 120, preferably arranged to be pressurized, for example, to a pressure greater than 1 bar, such as at least 1.5 bar, or at least 2 bar, or at least 3 bar, or at least 4 bar, or at least 5 bar, or even at least 6 bar. In any case, the furnace space 120 is constructed to withstand the operating pressures described herein. The upper portion 110 of furnace 100 may be bell-shaped.

[0028] Furnace 100 may be provided with one or more conventional doors (not shown) for loading and unloading the metal material 142 to be processed, and these doors are provided with airtight seals for airtight sealing when closed. Optionally, the upper part 110 itself may be openable for loading the material to be processed, and can then be closed airtightly using a fastening device (not shown).

[0029] The furnace space 120 can be enclosed internally with refractory materials such as brick.

[0030] Unless otherwise stated, the term "pressure" in this document refers to the total gas pressure, and in particular to the total gas pressure within the furnace space 120, as opposed to "partial pressure," which refers to the partial pressure of a specific gas.

[0031] Furthermore, since atmospheric pressure is approximately 1 bar, the expressions "pressure greater than 1 bar" and "pressure above atmospheric pressure" are intended to have the same meaning. Similarly, the expressions "pressure less than 1 bar" and "pressure below atmospheric pressure" are intended to have the same meaning.

[0032] The furnace space 120 is arranged to be heated using one or more heating elements 175, preferably located in a gas heating device 174, which will be described below. Preferably, the heating element 175 is an electric heating element. However, a radiator combustion tube or similar fuel heating element may also be used. However, the heating element 175 preferably does not produce any combustion gases that directly interact chemically with the furnace space 120 or the rest of the enclosed furnace system in which the gas circulates (see below), and for the purposes of the invention, the enclosed furnace system preferably maintains controlled chemistry.

[0033] Typically, furnace 100 may include a volume located upstream (e.g., below) of a permeable base plate 151 (in Figure 1a and 1bIn the case shown, inside the heating device 174, the reducing gas reaches the fluidized bed 141 through the permeable bottom plate 151, and is heated in the volume. Heating the gas to be supplied to the furnace space 120 individually in a closed loop in this way makes it possible to achieve faster heating of the metallic material 142.

[0034] Preferably, in the main heating process described below, the only gaseous substance supplied to the furnace space 120 is an inert gas and / or hydrogen, as well as any carbon-containing gas used as a carbon source for carburizing the reduced metal material 142.

[0035] The heating element 175 may preferably be made of a heat-resistant metal material, such as a molybdenum alloy.

[0036] Additional heating elements, similar to heating element 175, can also be arranged in the furnace space 120. Such heating elements not only help heat the gas but also help heat the loaded material via thermal radiation.

[0037] The furnace 100 may also include a lower portion 150, which together with the upper portion 110 forms a sealed container or when the furnace is sealed shut using the fastening device described above.

[0038] Therefore, the furnace space 120 is arranged to receive and contain the metal material 142 to be reduced. The furnace 100 also includes heating and reducing gas supply devices 174, 175, 250, which are arranged to supply heating and reducing gases to the furnace space 120 as described above.

[0039] The “heat and reducing gas supply device” can be any device arranged to supply heat and reducing gas to the furnace space 120. Contrary to the technical solution described in SE1950403-4, according to the invention, the reducing gas circulates through the furnace space 120 in a closed loop (the aforementioned closed furnace system). For this purpose, the heating and reducing gas supply device may include a forced gas circulation device (also referred to herein as a “gas propulsion device”), such as a fan or compressor 250, to propel the reducing gas in the closed loop by creating a pressure differential in the circulation device 250. Heat energy can be indirectly supplied to the furnace space 120 by heating the reducing gas in a gas heating device 174, which can then be a space that is part of the closed loop and contains the gas heating device 174 through which the reducing gas is propelled. The heating and reducing gas supply device may also include a separate pressurized reducing gas supply device, such as a regulated supply source from a high-pressure reducing gas source and / or a separate compressor. This is true for any carburizing gas used (see below).

[0040] In addition, system 200 includes a control device 201 arranged to control the heating and reducing gas supply devices 174, 175, 250, such that the heated reducing gas heats the loaded metal material 142 to a sufficiently high temperature, causing the metal oxides present in the loaded metal material 142 to be reduced, thereby resulting in the formation of water vapor.

[0041] System 200 also includes a condenser 280, which is arranged to condense and collect water vapor formed due to the evaporation of any water contained in the loaded metallic material 142 and due to the reduction reaction described herein. The condenser 280 may include a gas-to-gas heat exchanger, which may advantageously be a tubular heat exchanger as known per se, and may transfer heat energy from the reducing gas flow downstream of the closed loop through the furnace space 120 to the reducing gas flow upstream of the closed loop through the furnace space 120 via heat exchange. Such a heat exchanger may also be a counter-current heat exchanger. For the condenser 280, for example, for the heat exchanger of the condenser 280, for example below the heat exchanger, a closed tank may be connected for collecting and containing condensate from the hot condenser 280. This tank may also be configured to withstand the operating pressure of the furnace space 120 in an airtight manner.

[0042] Preferably, the condenser 280 is connected to the furnace space 120 such that the cold / cooled gas passes through the condenser 280, particularly the heat exchanger of the condenser 280, along externally / peripherally provided heat exchanger pipes, and further through a channel via valve V17 to the heating device 174. Then, the heated gas flowing out of the furnace space 120, after passing through and heating the loaded material 142 (see below), again passes through the condenser 280, for example, through an internally / centrally arranged heat exchange tube, thereby heating the cold / cooled gas. Thus, the exhaust gas from the furnace space 120 heats the incoming cold / cooled gas through heat transfer caused by the temperature difference between them, and through the condensation heat of the water vapor contained in the condensed exhaust gas.

[0043] The condenser 280 may also include an optional liquid-gas heat exchanger 281 for further cooling of the reducing gas using a circulating coolant (such as water). Thus, the liquid-gas heat exchanger 281 may be in the form of a water pipe arranged to have thermal contact with the reducing gas to be cooled.

[0044] The condensate formed from the exhaust gas is collected in the tank.

[0045] Furnace 100 may include a set of temperature and / or pressure sensors in the tank, at the bottom of furnace space 120 (e.g., below bottom plate 151 (see below)) and / or at the top of furnace space 120. These sensors may be used by control unit 201 to control the reduction and / or carburizing process, as described below.

[0046] Condensate can be introduced downwards from the condenser 280 into the tank via nozzles or the like, flowing out at the bottom of the tank, preferably, for example, at a local low point of the tank, such that the orifices of the nozzles are arranged completely below the main bottom of the tank, as shown below. Figure 2 This is illustrated in a simplified manner. This will reduce liquid water turbulence in the tank, providing more controllable operating conditions.

[0047] The tank can be designed to receive and contain all the water formed during the reduction process of the loaded material. Therefore, the tank size can accommodate the type and volume of a batch of reducing material. For example, the complete reduction of 1000 kg Fe3O4 results in the formation of 310 liters of water, and the complete reduction of 1000 kg Fe2O3 results in 338 liters of water. However, the tank can also be equipped with a venting mechanism, including a valve, that allows water to be completely or partially emptied from the tank during the reduction process while maintaining a desired overpressure in the closed loop, as described below.

[0048] According to the present invention, the furnace space 120 includes: a breathable bottom plate 151 arranged to support the loaded metal material 142; and the gas forced circulation device 250.

[0049] Furthermore, according to the invention, the heating and reducing gas supply devices 174, 250 are arranged such that the reducing gas passes upward through the base plate 151, through the loaded metal material 142, and further circulates in the closed loop via the condenser 280 and the forced gas circulation device 250. It is understood that the condenser 280 and the forced gas circulation device 250 can be arranged in any order, but it is preferred that the condenser 280 is arranged upstream of the forced gas circulation device 250 relative to the furnace space 120 in the closed loop.

[0050] Furthermore, according to the invention, the control device 201 is arranged to control the heating and reducing gas supply devices 174, 250 to supply additional reducing gas, thereby achieving and / or maintaining a predetermined pressure in the furnace space 120.

[0051] As mentioned above, in Figure 2 The diagram shows system 200, in which system 200 can be used Figure 1a and 1b Furnaces of the type shown. Specifically, one or both furnaces of 210 and 220 may be... Figure 1a and1b The type shown, or at least the type according to claim 1.

[0052] 230 represents a gas-to-gas heat exchanger. 240 represents a gas-to-liquid heat exchanger, such as a gas-to-water heat exchanger. 261 represents a storage container for or supplying N2 or another inert gas (such as Ar or He). 262 represents a storage container for or supplying H2 or another reducing gas. 263 represents a storage container for or supplying CH4 or other carburizing gases. 270 represents a cyclone separator, or any other device suitable for separating residual solid metallic material entrained in the gas flowing out of furnace space 120. 282 represents a gas dryer, such as any conventional adsorption, cooling, or film-type gas dryer, for further reducing water content. 290 represents a pump, such as a vacuum pump. Pump 290 is operated to vent the system by opening valves V4 and V42 while simultaneously closing valve V41.

[0053] The aforementioned control device 201 is connected to any sensors used, and is also connected to valves V1-V17 to control valves V1-V17, thereby controlling... Figure 2 The airflow in the various ducts shown. Control device 201 is typically arranged to control the process described herein. Control device 201 may also be connected to a user control device, such as a graphical user interface presented to the user of system 200 by a computer (not shown), for monitoring and further control.

[0054] Figure 3 A method according to the present invention is shown, which uses Figure 2 System 100 of the type shown, in particular Figure 1a and 1b Furnace 100 of the type shown in the figure. In particular, the method uses gaseous reducing agent gas and possibly carbon-containing gas as carburizing carbon source to produce directly reduced and possibly carburized metallic materials.

[0055] The reducing gas can be hydrogen or any other reducing gas, such as gaseous hydrocarbons. In the following text, hydrogen will be used as an example of a reducing gas.

[0056] Following this direct reduction and possible carburizing, the metallic material 142 can form a pure or substantially pure metal, or, after carburizing, a "sponge" metal. In particular, the metallic material can be an iron oxide material, and the product obtained after direct reduction can be pure iron, which can be carburized to become "sponge iron." The resulting reduced, potentially carburized metallic material can then be used in subsequent process steps to produce cast iron, steel, etc.

[0057] Note that the carburizing described in this article usually results in an increase in the carbon content on and around the surface of the carburized material; otherwise, the carbon content of the carburized material may be very low.

[0058] The loaded metallic material may include or consist entirely of scale, grinding residue and / or iron or other metallic ores.

[0059] In the first step, the method begins.

[0060] In possible subsequent material supply steps, the metal material 142 to be reduced is ground, crushed, and / or sieved to form granular material with a desired particle size. Preferably, the material 142 is processed into powder form having an average particle size of at least 1 μm, for example at least 5 μm, for example at least 10 μm, for example at least 50 μm, for example at least 150 μm, and at most 20,000 μm, for example at most 10,000 μm, for example at most 5,000 μm. Optionally or additionally, particularly, if the metal material 142 is already in a granular structure, larger spheres or microspheres are formed from the metal material 142, for example by pressing the metal material 142 into objects of desired shape and size, for example using an appropriate amount of water or other binder as a binder. The average particle size of such larger spheres or microspheres can be at least 1 mm, for example at least 3 mm, and at most 100 mm, for example at most 50 mm, for example at most 20 mm, for example at most 10 mm.

[0061] Alternatively, the metallic material 142 may be provided in the form of larger objects or as granular material having a particle size larger than that of powder. Such larger objects may have an average particle size of at least 0.5 mm, preferably at least 2 mm, and at most 100 mm, preferably at most 50 mm, and most preferably at most 10 mm.

[0062] When the metal material 142 is provided in powder form Figure 1a Fluidized bed 141 of the type shown (which is a “bubbling fluidized bed reactor”, BFBR) has proven useful. In the fluidized bed, the reaction surface between the metallic material 142 and the reducing / carburizing gas used becomes very large, resulting in a rapid and efficient reaction. Alternatively, a “circulating fluidized bed reactor” (CFBR) can be used. This situation is as follows... Figure 1b As shown. It should be recognized that, Figure 1a and Figure 1b The diagram of the fluidized bed is simplified.

[0063] In cases where the metal material 142 is provided not as powder but as larger particles (e.g., the spheres, pellets, or objects), it is preferable not to use a fluidized bed at all, but to treat the metal material 142 with heated reducing gas that penetrates the bed of metal material 142 from below.

[0064] In the CFBR / BFBR type fluidized bed, particle movement is as follows: heavier particles tend to move to the bottom of the bed, while lighter particles tend to move to the top. During the reduction process, the particles become lighter over time and eventually move to the top of the bed.

[0065] This material preparation step can be advantageously carried out in direct relation to the reduction of metallic materials, so that the entire process, including material preparation and reduction, is carried out in a continuous process under the same physical premise.

[0066] In the subsequent steps, the metal material 142 to be reduced is loaded into the furnace space 120. For example... Figure 1a As shown, this loading can be carried out continuously, or as... Figure 1b As shown, the process can be carried out in batches. This will be described in detail below. As a result of loading, the loaded metal material 142 will be arranged within the furnace space 120, thereby forming part of the closed gas loop as described above, which is hermetically closed and sealed to allow overpressure to be achieved and maintained therein.

[0067] In a subsequent step, the existing air can be vented from the furnace space 120, preferably from the entire closed loop, thereby achieving a gas pressure of less than 1 bar. It should be noted that this lower gas pressure is below atmospheric pressure. This can be achieved by closing valves V1-V3 and V41 and opening valves V4-V9, V12, V15-V17, and V42. Pump 290 then draws the atmosphere contained within the furnace space 120 and the entire closed loop through a conduit via valve V42 and thus vents it into the surrounding atmosphere. If the furnace space 120 and the closed loop are not filled with air, but rather with the hydrogen and / or carbon-containing gas in use, this gas can alternatively be vented to container 262 or 263, depending on the circumstances, by appropriately setting valves V1-V5 and V41-V42.

[0068] During this evacuation step, and in other steps described below, the control device 201 may be used to control the pressure in the furnace space 120 and / or the pressure at other locations in the closed loop including the furnace 220, separator 270, condenser 280 and forced circulation device 250, for example based on readings from available pressure sensors.

[0069] The evacuation can continue until a pressure of up to 0.5 bar, preferably up to 0.3 bar, is reached in the furnace space 120 or in the entire closed loop that forms part of the furnace space 120.

[0070] As an alternative to this venting step, furnace space 120 and the entire closed loop can be ventilated using an inert gas, such as N2 from container 261. Atmospheric pressure can then be maintained throughout the venting step.

[0071] In a subsequent initial heating step, heat and hydrogen are supplied to furnace space 120. During this initial heating step, a reducing gas or inert gas may be circulated through the loaded metal material 142 to heat the loaded metal material 142. The method may then include a second reduction and possibly carburizing step, wherein the reducing gas is circulated through the loaded metal material to achieve reduction of the loaded metal material 142.

[0072] In both steps, hydrogen can be supplied by container 262. As described above, since the closed loop is hermetically sealed, virtually no supplied hydrogen escapes during the process. In other words, hydrogen loss (aside from the hydrogen consumed in the reduction reaction) will be very low or even non-existent. Instead, only the hydrogen chemically consumed in the reduction reaction will be used. Furthermore, the only hydrogen required in the reduction process is the amount necessary to maintain the required pressure and the chemical equilibrium between hydrogen and water vapor.

[0073] Hydrogen container 262 can be arranged to contain and supply both fresh and used / reusable hydrogen. This can be achieved, for example, by providing two separate hydrogen containers and suitable valves. This "used" hydrogen is hydrogen that has already been used in one or more reduction steps and has been collected in system 200. During the first reduction process, only fresh hydrogen supplied by said container is used. In subsequent reduction processes, reused hydrogen from said container is used, supplemented with fresh hydrogen as needed. This correspondence with inert gas container 261 and / or carbonaceous gas container 263 may or may not be true.

[0074] As a substitute for hydrogen, an inert gas can be supplied to the closed loop during the initial heating step. This can be achieved by opening valve V1 instead of valve V2 and closing valves V4, V16, and V42.

[0075] Subsequently, for example, when a predetermined pressure is reached, such as between 1 bar and 2 bar, the heating element 175 is switched on and the forced circulation device 250 is activated; valves V7 and V15 are closed, and the liquid-gas heat exchanger 281 in the condenser 280 provides a flow of cooling liquid, such as cooling water. Then, the gas circulates in a closed loop via the forced circulation device 250 and valves V5 and V6, further through the gas-gas heat exchanger in the condenser 280 (where it is preheated by gas from the furnace space 120), and further through valve V17 into the gas heating device 174 (where it is heated by the heating element 175). Afterward, the gas enters the bottom 150 of the furnace 100, where it is evenly distributed on the bottom plate 151 in the gas distribution chamber, and flows upward through the metal material 142 to be reduced. Subsequently, the gas continues to flow in a closed loop through valve v12 and separator 270, where any entrained metal material 142 will be separated from the gas through condenser 280, the gas-to-gas heat exchanger and liquid-to-gas heat exchanger (if used), thereby releasing the entrained water vapor due to cooling by the heat exchangers, and finally returning to the forced circulation device 250 through valves V7 and / or V8. This closed loop cycle is controlled using valves V1-V42 controlled by control unit 201.

[0076] The heat from the heating gas from furnace 220 will cause any moisture contained in the metal material 142 to evaporate. Later, as the temperature rises (see below), the reduction of the metal material 142 caused by the reducing properties of the reducing gas flowing upwards through it will also produce water in the form of water vapor. The formed water vapor is carried away by the flowing reducing gas and condensed in the condenser 280 by the heat exchange cooling, and collected in the tank. Optionally, by opening valves V10 and V11, allowing the gas to pass through an open dryer 282, additional drying of the gas circulating in the closed loop can be performed in the dryer 282.

[0077] Typically, the reducing gas can be preheated in a heat exchanger arranged to transfer heat energy from the water evaporated from the loaded metal material 142 to the reducing gas that will be supplied to the furnace space 120 via the bottom plate 151.

[0078] Therefore, during this initial heating step, control device 201 is arranged to control heating and reducing gas supply devices 274, 275, 250 to provide heat and reducing gas (or, optionally, heat and inert gas) to furnace space 120, such that the heated gas heats the loaded metal material 142 to a temperature above the boiling point of water contained in the metal material 142. As a result, the water contained in the metal material 142 evaporates.

[0079] Throughout the initial heating and main reduction steps (see below), under the control of control device 201, additional gas is slowly supplied into the closed loop to achieve and maintain the desired pressure within the closed loop (particularly in furnace space 120). Typically, control device 201 is arranged to continuously add gas, thereby maintaining a desired increase (e.g., monotonically increasing) gas pressure profile within the closed loop, particularly within furnace space 120, such as a desired increase in hydrogen partial pressure (and total pressure). The additional gas is also supplied to counteract the pressure drop caused by water vapor condensation in absorber 280.

[0080] Preferably, the cold hydrogen and / or inert gas supplied to the heat exchanger of the condenser 280, as well as any carbon-containing gas supplied thereto, are at room temperature or have a temperature slightly below room temperature.

[0081] It should be recognized that this initial heating step (in which the loaded material 142 is thus dried to remove any liquid water contained therein) is a preferred step in this method. In particular, this makes it easy to produce and supply the loaded material 142 as a granular material as described above, for example in the form of material balls, without having to introduce an expensive and complex drying step before loading the material into the furnace space 120.

[0082] However, it should be recognized that it is possible to load already dried or dehydrated material into furnace space 120. In this case, the initial heating steps described herein will not be performed, but the method will immediately jump to the main reduction and carburizing steps (hereinafter).

[0083] Furthermore, the mechanism of adding hydrogen and / or inert gases in the initial heating step described above can also be applied to the subsequent main reduction and possible carburizing steps. However, it is preferable not to add carbon-containing gases in the initial heating step. In particular, it is preferable that the only gas added in the initial heating step is a reducing gas and / or an inert gas.

[0084] In one embodiment of the invention, the gas supply to the furnace space 120 is controlled slowly, such that a substantially constant pressure is maintained throughout the execution of the initial heating step, preferably such that a substantially equal pressure is always present throughout the furnace space 120, and possibly throughout the entire closed loop. Specifically, the gas supply can be controlled such that the equilibrium gas pressure does not increase, or only increases insignificantly, during the initial heating step. In this case, the gas supply is controlled to increase the pressure of the furnace space 120 over time only after all or substantially all of the liquid water has evaporated from the loaded material 142. The point at which this occurs can be determined, for example, by an upward change in the slope of the temperature-time curve measured by the temperature sensor, where the change in slope marks the point where substantially all of the liquid water has evaporated but reduction has not yet begun. Alternatively, the gas supply can be controlled such that the pressure is increased once the measured temperature in the furnace space 120 exceeds a predetermined limit, which may be between 100°C and 150°C, for example, between 120°C and 130°C.

[0085] In the subsequent main reduction and possible carburizing steps, heat and hydrogen are further supplied to the furnace space 120 in a manner corresponding to the supply during the initial heating step described above, such that the heated hydrogen heats the loaded metal material 142 to a sufficiently high temperature to reduce the metal oxides present in the metal material 142, thereby causing water vapor to form.

[0086] As described above, the water vapor is condensed and collected in the condenser 280.

[0087] As described above, according to the present invention, the metal material 142 is loaded onto the breathable base plate 151, and the reducing gas flows upward through the base plate 151, through the loaded metal material 142, and further through the condenser 280 and the forced gas circulation device 250 in a closed loop.

[0088] The method also includes the step of supplying additional reducing gas to achieve and / or maintain a predetermined pressure in the closed loop, such as the step performed in the main reduction and possible carburizing steps.

[0089] During the main reduction and possible carburizing steps, additional hydrogen is supplied and heated as the pressure within the furnace space 120 gradually increases, thereby heating the loaded metal material 142 to the temperature at which the reduction chemical reaction begins and is sustained.

[0090] In the exemplary case where Fe2O3 is the metal material to be reduced 142, the theoretical energy required for heating the oxide, the thermally compensated endothermic reaction, and reducing the oxide is approximately 250 kWh / 1000 kg Fe2O3. For Fe3O4, the corresponding value is approximately 260 kWh / 1000 kg Fe3O4.

[0091] In the case of iron oxide materials and hydrogen as the reducing gas, hydrogen will begin to reduce the loaded material at approximately 350-400°C to form metallic iron, which will then generate self-igniting iron and water vapor according to the following formula:

[0092] Fe₂O₃ + 3H₂ = 2Fe + 3H₂O

[0093] Fe3O4 + 4H2 = 3Fe + 4H2O

[0094] The reaction is endothermic and is driven by thermal energy supplied via hot hydrogen, which flows from below over the metal material 142, over the permeable bottom plate 151, and over / through the loaded material 142 in the furnace space 120.

[0095] Therefore, water vapor is generated in the loaded material 142 during the initial heating step, the main reduction, and possibly the carburizing step. This formed water vapor is continuously condensed and collected in the condenser 280.

[0096] The material to be processed includes metal oxides, preferably iron oxides, such as Fe2O3 and / or Fe3O4. In this method, if the iron ore additionally contains oxides that evaporate at a temperature lower than the final temperature of the loaded material, these oxides can be condensed in condenser 280 and easily collected in powder form. These oxides may include metal oxides, such as oxides of Zn and Pb.

[0097] In one embodiment of the invention, the reducing gas is arranged such that the flow of the loading metal material 142 upward through the base plate 151 and further through the loading metal material 142 forms a fluidized bed 141 together with the reducing gas. Figure 1a and 1b As shown in the diagram, the reducing gas enters the gas heating device through conduit 171, is heated by heating element 175, and is then supplied to the lower part 150 of the furnace space 120 through conduit 172. In the lower part 150, the reducing gas is evenly distributed on a permeable bottom plate 151, through which the reducing gas is compressed in an upward direction to mix with the loaded material 142.

[0098] The base plate 151 may advantageously include a perforated plate (shrink plate), such as a ceramic plate, or be made of a woven heat-resistant material, such as woven metal wire.

[0099] Depending on the target and the type of metal material 142, the fluidized bed 141 can be a so-called “bubbling bed” (BFBR, as described above), in which the loaded metal material 142 remains on the permeable bottom plate 151, supported by the gas flowing upwards through 143. This means that the fluidized bed 141 (a mixture of metal material 142 and upwardly flowing reducing gas) at least partially behaves like a liquid contained in the furnace space 120 and on the bottom plate 151.

[0100] Alternatively, the fluidized bed 141 may be a so-called “circulating bed” (CFBR, as described above), in which the loaded metal material 142 is not, substantially not, or at least not fully supported on the base plate 151 at all, but is at least partially (e.g., completely or at least substantially completely) suspended above the base plate 151 within the furnace space 120 by means of flowing gas 143. This means that the fluidized bed 141 at least partially behaves like a gas, filling at least the lower volume of the furnace space 120 located above the base plate 151.

[0101] In both cases, the metal material 142 can advantageously be loaded into the furnace space 120 (placed on the bottom plate 151) via an inlet 144 and discharged via different outlets 145. The outlet 145 can be located at the height from which the metal material 142 can be discharged during operation of the fluidized bed 141 (in other words, the height at which the metal material 142 is at least partially raised by suspension or expansion provided by the gas flowing through it). If the upper surface of the fluidized bed 141 has an average height during operation, the outlet 145 is therefore preferably arranged below that average height.

[0102] It should be understood that the characteristics of the fluidized bed in terms of gas throughput and fluidization type are determined particularly based on the size and shape of the furnace space 120, the characteristics of the bottom plate 151, and the capacity and operation of the propulsion device 250, all of which are related to the characteristics and quantity of the loaded metal material 142. Therefore, the propulsion device 250 pushes the gas through the fluidized bed 141. Of course, additional fans, etc., can be provided to assist in this propulsion.

[0103] The fact that the gas flows upward over the material causes any loose metallic material 142 to be carried upward. In the case of metal powder, this includes particles leaking from the furnace space 120. In the case of larger metallic objects, this includes small particles that have detached from such larger metallic objects, for example, due to pressure from the metallic object arranged on top of such an object and / or from the pressure of the reduction and / or carburizing reactions described herein. In the latter case, these particles risk falling and clogging the gas passage unless carried away by the upward-flowing gas. In all cases, the separator 270 can effectively capture such stray particles.

[0104] Even for larger metallic objects, the upward flow of gas reduces the pressure exerted by the higher object on the lower object, increasing the reaction surface available for reduction / carburization reactions.

[0105] Then, the metallic material 142 can be continuously loaded into the furnace space 120 through inlet 144. Furthermore, the reduced (and possibly carburized) material can be continuously discharged from the furnace space 120 for transport and / or additional processing. In this way, a fully continuous process can be achieved, wherein the metallic material 142 to be reduced and possibly carburized is continuously loaded, the reduced / carburized material is continuously discharged, and the reducing (and possibly carburizing) gas is continuously added according to its consumption in the chemical process. It should be recognized that the process can be cyclical, for example, switching between loading-reduction-carburizing-discharge-loading, etc., while still being “continuous”; in this sense, the process does not stop, and the furnace space 120 is opened between cycles. Alternatively, by maintaining a predetermined constant temperature and reducing / carburizing gas pressure within the furnace space 120, the process can be completely continuous, with the metal material 120 continuously loaded at inlet 144 and discharged at outlet 145, conveyed between ports 144 and 145 due to the movement of the fluidized bed 141. In this case, the bottom plate 151 can be inclined from inlet 144 to outlet 145, or the movement of the metal material 142 can be entirely driven by gas 143 and then propelled by the propulsion device 250.

[0106] It should be noted that, for a completely continuous process, the initial and main steps described herein will be a single step, which involves heating the loaded material 142 by providing the heat and gas and reducing it (and possibly carburizing it).

[0107] In a continuous process, condensate needs to be discharged from condenser 280 continuously or intermittently. This can be achieved, for example, by using a check valve that is itself similar to a conventional device, to release water without causing the pressure in the closed loop to drop beyond the amount of water released.

[0108] Figure 6 An apparatus for loading and unloading metallic material 142 relative to the furnace space 120 is shown. The inlet 144 may include at least one, preferably at least two, inlet collectors 181, 182 for the material to be reduced, arranged to convey such material into the furnace space 120. In the case of more than one such collector 181, 182, they are preferably arranged in parallel for alternating use, such that one collector 181, 182 loads new material while the other collector conveys its material into the furnace space 120.

[0109] The outlet 145 may further include a first outlet collector 191, which is arranged to receive reduced metal material from the furnace space 120. The outlet 145 may also include a second outlet collector 192, which is connected in series with the first outlet collector 191 and located downstream of the first outlet collector 191.

[0110] Each of collectors 181, 182, 191, and 192 can be equipped with a valve (in... Figure 6 (Displayed as a circle with an "X") is airtight. Collectors 191 and 192 are interconnected by a screw feeder 191a, which is arranged to convey the reduced metal material from the bottom of collector 191 to the top of collector 192, and which also provides an airtight seal between collectors 191 and 192. Figure 6 As shown, a valve may also be present between collectors 191 and 192. In other embodiments, collectors 191 and 192 may be interconnected, and gas venting and filling may be achieved through only one of these collectors 191 and 192.

[0111] Each of the inlet collectors 181 and 182 may include a corresponding input for the metal material to be reduced; and may further include bottom screw feeders 181a and 182a, which are arranged to convey the metal material along the respective bottom of the collectors 181 and 182 to the respective outlet ends of the collectors 181 and 182 leading to the furnace space 120.

[0112] The most upstream of the outlet collectors 191 and 192, outlet collector 191, may include an inlet arranged to receive reduced metallic material from the furnace space 120.

[0113] The most downstream outlet collector 192 of the outlet collectors 191 and 192 may include a screw feeder 192a, which is configured to convey the reduced metal material along the bottom of the collector 192 to the outlet of the reduced material.

[0114] A vacuum pump V may be connected to each of the collectors 181, 182, 191, 192. Additionally, a pressurized inert and / or reducing gas (e.g., nitrogen and / or hydrogen) source H may be connected to each of the collectors 181, 182, 191, 192.

[0115] Then, each inlet collector 181, 182 of inlet 144 can be operated using a vacuum pump V to purge the existing atmosphere from the inlet collectors 181, 182. Then, source H can flush each inlet collector 181, 182 with an inert gas. Then, source H can fill each inlet collector 181, 182 with a reducing gas to achieve a desired pressure, such as the overpressure currently present in furnace space 120. Thereafter, the corresponding valves can be opened to release the metal material to be reduced from the inlet collectors 181, 182 into furnace space 120. When inlet collectors 181, 182 are empty, the corresponding valves leading to the furnace space can be closed, and the inlet collectors 181, 182 can be replenished with new metal material to be reduced via corresponding valves in the top of the inlet collectors 181, 182, and the inlet collectors 181, 182 will be placed under vacuum again; possibly flushed with an inert gas and / or filled with a reducing gas. Then, inlet collectors 181 and 182 can again convey the metal material to be reduced into furnace space 120. Preferably, inlet collectors 181 and 182 operate alternately, such that one is replenished with fresh material and ready to be conveyed into furnace space 120. In this way, a continuous flow of metal material to be reduced and possibly carburized can be conveyed into furnace space 120 under desired overpressure without any atmospheric leakage into the closed loop described herein.

[0116] At the start of the process, outlet collectors 191 and 192 are sealed using appropriate valves. The existing atmosphere in at least one downstream collector 192 (preferably all outlet collectors) can be purged using a vacuum pump V. Then, one or more of the outlet collectors 191 and 192 can be flushed with inert gas, and reducing gas can be replenished using source H in a manner corresponding to the process described with respect to inlet collectors 181 and 182.

[0117] Then, the reduced and potentially carburized metal material is received from the furnace space 120 into collector 191 via the corresponding open valves, with the metal material falling to the bottom of collector 191. From there, it can be conveyed into collector 192 via a valve opened between the screw feeder 191a and collectors 191 and 192. During this transfer between collectors 191 and 192, the outlet valve of the downstream collector 192 can be closed. When the downstream collector 192 is emptied, the valve between the upstream collector 191 and the downstream collector 192 can be closed, effectively creating an airlock.

[0118] Typically, the inlet metal material conveying mechanism according to the invention may include at least one, preferably several, inlet metal material collectors 181, 182, which may be independently hermetically sealed and arranged to be emptied, flushed with an inert gas and / or filled with a reducing gas, and arranged to selectively convey the metal material to be reduced and possibly carburized from such hermetically sealed and reducing gas-filled space to the furnace space 120 via a closable valve.

[0119] Accordingly, the discharge mechanism for the reduced and possibly carburized metal material at the outlet may include at least one, preferably several, outlet metal material collectors 191, 192 connected in series, which may be hermetically sealed and arranged to be emptied, flushed with an inert gas and / or filled with a reducing gas, and arranged to selectively receive the reduced and possibly carburized metal material from the furnace space 120 into this hermetically sealed space filled with reducing gas via a closable valve.

[0120] Figure 1a and 1b The fluidized bed 141 shown is primarily applicable when the metal material 142 is in powder form. As an alternative to the fluidized bed 141, the metal material 142 can be completely rested on the base plate 151, while gas passes upward through the base plate 151 and through the material 142 at a velocity insufficient to lift the material 142, thus forming a fluidized bed. This alternative is useful when the metal material 142 is loaded as a granular material with a relatively large particle size.

[0121] Then, during operation, the metal material 142 is placed on a permeable bottom plate 151, and gas flows upward over the bottom plate 151 and over the metal material 142 without causing the metal material 142 to expand or become suspended, thus forming a fluidized bed. In this case, the metal material 142 can be loaded and unloaded in batches, for example by opening the furnace space 120 to remove the reduced / carburized material and refill with new metal material to be reduced / carburized. It should be recognized that, regarding Figure 1a and 1bThe contents described therein and those shown therein are similarly applicable to non-fluidized bed alternatives.

[0122] The advantage is that, Figure 1a and 1b In the fluidized bed alternative or non-fluidized bed alternative shown, furnace space 120 is not loaded with a very large amount of material 142 to be reduced / carburized. Each furnace 100 is preferably loaded with a maximum of 50 tons, for example, a maximum of 25 tons, or for example, 5 to 10 tons, in each batch of a continuous process or at any given point. Depending on production requirements, several furnaces 100 can be used in parallel, and the waste heat from one furnace 220 can then be used to preheat another furnace 210 (see [link]). Figure 2 (and below).

[0123] The system 200 is provided, which is suitable for direct installation and use at the mining site, eliminating the need for expensive ore transportation prior to reduction. Instead, directly reduced and potentially carburized metal materials can be produced on-site, packaged under a protective atmosphere, and transported to different locations for further processing.

[0124] In the case where water-rolled iron ore balls and other granular materials are processed in batches in furnace 100, it is foreseeable that furnace 100 can be installed to connect to a material production system (e.g., an iron ore ball production system) so that loading metal material 142 into furnace 100 can be carried out in a fully automated manner.

[0125] For example, material 142 can be loaded into and unloaded from a container with a breathable bottom, wherein such container can be placed on a breathable bottom plate 151, or the breathable bottom plate can be formed after the container is loaded into the furnace space 120.

[0126] Then, this container can be automatically circulated from the material production system to furnace 100 and returned, filled with material to be reduced and possibly carburized; inserted into furnace space 120; subjected to hydrogen / heat / carbon-containing gas treatment for reduction and possibly carburization as described herein; removed from and emptied from furnace space 120; brought back to the material production system; refilled; and so on. Several furnaces 100 can be used in parallel; and a greater number of containers than furnace 100 can be used, so that in each batch changeover, the reduced and possibly carburized load in a particular container in furnace 100 is immediately replaced by a different container containing unreduced or uncarburized material. Using several smaller furnaces 100 instead of a very large furnace, such a larger system, for example in a mining site, can be fully automated and is very flexible in terms of output.

[0127] The main reduction and possible carburizing steps, including the condensation, can be performed to establish a pressure greater than 1 bar relative to atmospheric pressure in the furnace space 120. Specifically, hydrogen can be provided to achieve and maintain this pressure greater than 1 bar. Note that this pressure greater than 1 bar is above atmospheric pressure.

[0128] The method may further include a carbon-supplying step, namely, supplying a carbon-containing gas to the furnace space 120 such that the metal material 142, which has been heated by the supplied heat and reduced by reacting with the reducing gas, is carburized by the carbon-containing gas. The supply of the carbon-containing gas can then be performed as part of the main reduction and possibly carburizing steps, and then performed before venting the gas from the furnace space 120 back to atmospheric pressure. This venting can be performed as a step of the method, as will be explained below, for example, as part of a material cooling sub-step.

[0129] The carbon-containing gas can be any carbon-containing gas capable of chemically reacting with a reduced metallic material to carburize it. Examples of suitable carbon-containing gases include various gaseous hydrocarbons (present at the temperature and pressure during the implementation of this method) such as methane, ethane, propane, propylene, etc. Preferably, the carbon-containing gas does not contain more than trace amounts of carbon monoxide, as this effectively prevents the formation of residual products from carbon monoxide and carbon dioxide after the current carburizing process has concluded. In particular, it is preferred that no carbon monoxide is supplied to the furnace space 120 during the carbon supply step.

[0130] As will be described and illustrated below, the carbon supply step can be performed at least partially concurrently with the supply of hydrogen and heat described above. In particular, the carbon supply step can be performed as part of the main reduction and possibly carburizing steps.

[0131] As described above, during the reduction of iron, free iron (Fe) is formed, which then opens to accept carbon (C) to form Fe3C.

[0132] Figure 5 This illustrates the functional relationship between the ability of H2 to reduce Fe2O3 and the increase in temperature. For example... Figure 5 As shown, reduction using hydrogen is particularly active in the temperature range of approximately 400°–700°.

[0133] Correspondingly, carburizing with the same Fe2O3 using a gaseous carbon source is most active in the range of approximately 650°–900°.

[0134] For example, Fe3O4 exhibits similar properties in terms of reduction / carburization and temperature.

[0135] This means that the process of first reducing most of the metallic material at a relatively low temperature and then carburizing most of the metallic material 142 after additional heating would be highly efficient.

[0136] There are also cases where the carburizing process is aided by the presence of water vapor, which turns out to be due to the reduction process of the same metallic material 142.

[0137] Under specific conditions where methane is used as a carbon-containing gas and hematite / magnetite is used as a metallic material, the following carburizing chemical reaction occurs in the furnace space:

[0138] Fe3O4 + 4H2 = 3Fe + 4H2O

[0139] 3Fe + CH4 = Fe3C + 2H2

[0140] The reaction between CH4 and Fe includes a sub-reaction in which methane reacts with water vapor formed from reduced hydrogen gas:

[0141] CH4 + H2O = 2CO + 3H2

[0142] Then, carburizing itself occurs primarily through the well-known hydrogen-water reaction, in which carbon monoxide and hydrogen react with the formed iron surface to form water vapor, and the released carbon atoms can be absorbed at the sites of previously released oxygen atoms.

[0143] Because the surface of reduced iron particles is porous due to reduction, the total iron surface area is usually still very large even when the loaded metal material 142 is in the form of larger particles (such as small balls or spheres). This results in a highly efficient carburizing process, especially when the metal material is provided as particulate material.

[0144] As can be seen from the above formula, a certain amount of hydrogen is generated during the carburizing process, which is why less hydrogen is needed compared to other cases.

[0145] Preferably, after the carbon supply step is completed, the final carburized metal material has a carbon content of 1% to 4% by weight.

[0146] The hydrogen supply in the main reduction and possible carburizing steps can preferably be controlled to achieve and maintain a predetermined hydrogen partial pressure or predetermined total pressure above 1 bar within the furnace space 120. Correspondingly, the supply of carbon-containing gas in the carbon feeding step can be controlled to achieve and maintain a predetermined partial pressure or predetermined total pressure above 1 bar within the furnace space 120.

[0147] Preferably, no hydrogen gas is released from the closed loop before the metal material 142 has completed the desired reduction (e.g., complete reduction). Similarly, preferably, no carbon-containing gas is released from the closed loop before the metal material 142 has completed the desired carburizing (e.g., complete reduction).

[0148] Specifically, the hydrogen supply in the main reduction and possible carburizing steps can be controlled to achieve and maintain a predetermined pressure above 1 bar in the furnace space 120, which can be at least 2.3 bar, more preferably at least 2.5 bar, or even about 3 bar or higher. The same applies to the possible pressure regulation supply of carbon-containing gases in the reduction and possible carburizing steps.

[0149] Also independent of gas pressure, the gas must pass through the base plate 151 at a speed high enough to “lift” the powder or particle layer (as the case may be) to separate them from each other and open the particle surface to allow gas to permeate.

[0150] In some implementations, additional reducing gas is provided to maintain the predetermined pressure until no further reducing gas is actually needed to maintain the predetermined pressure.

[0151] Optionally or additionally, additional reduction may be provided to maintain the predetermined pressure until a predetermined amount of water has been collected in the condenser 280.

[0152] Both scenarios indicate that a full restore has been achieved. Upon receiving such an instruction, a new batch can be loaded, or the next cycle in the continuous process can begin.

[0153] Further optionally, during the main reduction and possible carburizing steps, the supply of reducing gas and heat can continue until the loaded metal material 142 to be reduced reaches a predetermined temperature, which can be at least 600°C, for example between 640-680°C, preferably about 660°C, or until the loaded metal material reaches a temperature between 700-1100°C, for example between 800-1100°C (see below). The temperature of the loaded material 142 can be measured directly, for example by measuring the thermal radiation from the loaded material using a suitable sensor, or indirectly by measuring the temperature of the gas that has passed through the metal material 142.

[0154] In some implementations, for each specific loaded material 142 (regardless of whether a batch or continuous process is used), any major reduction and possible carburizing steps may be carried out over a continuous time period of at least 0.25 hours, such as at least 0.5 hours, or even at least 1 hour. Throughout this time period, the pressure and temperature of the furnace space 120 may be monotonically increased to a predetermined value and then maintained constant.

[0155] In some implementations, the main reduction and possible carburizing steps can be performed iteratively, in which, in each iteration, control device 201 allows the interior of furnace space 120 to reach steady-state pressure before supplying an additional amount of hydrogen to the furnace space. The heat supply can also be iterative (pulsed) or kept on throughout the main reduction and possible carburizing steps.

[0156] During the initial steps and the main reduction and possible carburizing steps, except for the possible time period associated with the start of the carburizing step, where the total pressure in the furnace space 120 may be temporarily reduced, the control device 201 can control the system 200 to continuously maintain or increase the pressure by supplying additional hydrogen and / or carbon-containing gas. The supplied hydrogen is used to compensate for the hydrogen consumed during the reduction process and also to gradually increase the pressure to the desired final pressure. The carbon-containing gas can be supplied using any of a number of different strategies (described below) and can, for example, be controlled such that a set target total pressure is achieved in the furnace space 120 during such supply.

[0157] It should be understood that pressure can be increased using a suitable compressor or available overpressure from sources 261, 262, 263, which is standard practice.

[0158] As described above, the method may also include a carburizing step performed before the metal material 142 is discharged from the furnace space 120, as part of the main heating and possible carburizing steps. In this carburizing step, a carbon-containing gas (e.g., gaseous hydrocarbons) is provided to the furnace space so that the heated and reduced metal material is carburized by the carbon-containing gas.

[0159] The carbon-containing gas can be supplied using one of several different strategies, as described below.

[0160] First Embodiment

[0161] like Figure 4a As shown, in this first strategy, reduction using a reducing gas is followed directly by carburizing of the metallic material. First, as described above, hydrogen and heat can be supplied to a closed loop to increase and maintain the pressure in furnace space 120, while simultaneously increasing the temperature in furnace space 120, ultimately reducing the metallic material 142. The ultimately maintained pressure can be, as described above, for example, at least 1.1 bar, preferably at least between 2.3 and 2.5 bar.

[0162] In this and other embodiments, when the reduction of all metal materials loaded 142 is completed, the furnace space 120 has reached a temperature of approximately 700°C, and the temperature of the hydrogen entering the furnace space 120 is the same as the temperature of the gas entering the heat exchanger of the condenser 280.

[0163] Typically in this first strategy, heat may be provided in the main reduction and possible carburizing steps before the supply of carbon-containing gas is started in the carbon supply step, until the metal material 142 reaches a temperature of at least 500°C, for example, at least 600°C.

[0164] In this scenario, no carbon-containing gas is supplied when reduction is complete. Before doing so, or before performing steps related to doing so, some hydrogen can be vented, causing a decrease in hydrogen partial pressure. That is, valve V2 can be closed to terminate the hydrogen supply. Then, by opening / closing appropriate valves, compressor 250 can be used to vent some hydrogen into a storage container for hydrogen. When the pressure has decreased to a lower pressure between 1.1 bar and 1.8 bar, such as between 1.3 bar and 1.6 bar, for example, approximately 1.5 bar, valve V2 is closed, valve V3 is opened, and the carbon supply step begins.

[0165] like Figure 4a As shown, in this embodiment, after some of the hydrogen is vented, the total pressure in the furnace space 120 is approximately 1.5.

[0166] Typically, the carbon feeding step can be carried out at least partially, preferably entirely, under a furnace space 120 pressure that is lower than the furnace space 120 pressure at which the reduction process is completed.

[0167] Using a suitable airflow controlled by control device 201, and by controlling valves and compressors as needed, fresh carbohydrate gases, such as methane, can be stored in one container, while previously used carbohydrate gases (such as a mixture of methane and hydrogen) can be stored in different containers.

[0168] At this point, the newly reduced metal material 142 can accept the supplied carbon. Carburizing occurs in the furnace space 120, where the temperature is increased, by heating with heating element 175. Depending on the composition of the metal material, carburizing is completed when the temperature reaches approximately 700°C-1100°C. As mentioned above, a certain amount of hydrogen gas is eventually formed during carburizing.

[0169] After this, the following cooling and evacuation steps can be started.

[0170] Figure 4a The diagram illustrates the method according to the first strategy, in which a carbon-containing gas is added after reduction. The diagram shows that, in this process, the partial pressure of hydrogen (solid line) is a function of the furnace space temperature 120°C, and the partial pressure of the carbon-containing gas (dashed line) is a function of the furnace space temperature 120°C.

[0171] It should be noted that, Figure 4a ,as Figure 4b and 4cThe situation is similar, but simplified in a sense, ignoring any residual gas present in the furnace space 120 or the remainder of the closed loop after the initial venting.

[0172] Second Embodiment

[0173] In the second strategy, carbon-containing gas is supplied before the reduction is complete.

[0174] During heating and the initiation of reduction, hydrogen is supplied to achieve and maintain an increase in total furnace space 120 pressure of at least 1.1 bar, preferably at least 2.3 bar. In this case, shortly after the start of reduction, in other words, after the temperature in furnace space 120 has reached at least 350°C, for example, between 350-450°C, such as at approximately 400°C, carbon-containing gas is supplied. Typically, in this second strategy, the carbon supply step begins only after the metallic material has reached a temperature between 350-450°C.

[0175] In this strategy, reduction and carburizing occur in parallel during the main reduction and carburizing steps, and pressure is maintained by the supply of carbon-containing gas. The supply is executed in a suitable manner by a control device 201, such as a control valve or any compressor.

[0176] Throughout the reduction process, until near completion, heating and the introduction of more carbon-containing gas occur at approximately 700°C. At this point, the temperature is raised to a final temperature exceeding 700°C, preferably up to 1100°C, while pressure is maintained by continuously supplying a mixed gas containing a mixture of hydrogen and carbon-containing gas.

[0177] After this, the following cooling and evacuation steps can be started.

[0178] Figure 4b It corresponds to Figure 4a The chart shown illustrates a second strategy.

[0179] Third Embodiment

[0180] In the third strategy, the supply of carbon-containing gas begins when reduction reaches its maximum. For hematite and magnetite, this occurs at approximately 550–570°C.

[0181] In this strategy, as described above, the pressure is increased to at least 1.1 bar, preferably at least 2.3-2.5 bar, by supplying hydrogen to the furnace space 120 and heating it.

[0182] When the temperature of the gas leaving the carrier approaches 550°C, the hydrogen supply is cut off. At this point, the main part of the carrier has been completely reduced and now consists of self-igniting iron, ready to receive carbon supplied via carbon-containing gas. This is achieved by opening, for example, valve V3.

[0183] Then, carburizing is performed after reduction or in parallel with the reduction section, and the pressure is maintained by supplying carbon-containing gas. As described above, a certain amount of hydrogen is formed as a result of carburizing, and the undesirable pressure increase can be handled, for example, by venting part of the atmosphere in the furnace space 120 into a container for the mixture of hydrogen and carburizing gas.

[0184] The temperature rises throughout the process. After a predetermined temperature, such as 650-750°C, preferably 690-700°C, at a constant pressure, more precisely at least 1.1 bar, preferably at least 2.3-2.5 bar, the temperature then rises to a higher temperature, at least 800°C, for example 800-1100°C. This constant pressure is maintained by supplying carbon-containing gas (preferably fresh carbon-containing gas) using appropriate valve settings and a suitable compressor (if necessary).

[0185] After this, the following cooling and evacuation steps can be started.

[0186] Typically, in this third strategy, the carbon supply step begins only after the metal material reaches a temperature between 450-550°C, and the hydrogen supply can be terminated thereafter. Alternatively, the carbon supply step may also include continuing to supply heat to the furnace space 120.

[0187] In addition, in this third strategy, heat is typically provided during the main reduction and carburizing steps, especially during the carburizing step, until the metal material reaches a temperature between 700-1100°C, for example, between 800-1100°C.

[0188] As described above, the carbon supply step in this third strategy may include supplying heat to the furnace space 120 at a constant pressure controlled by a controlled supply of carbon-containing gas, which may or may not be mixed with hydrogen.

[0189] Figure 4c It corresponds to Figure 4a The chart shown illustrates a third strategy. Of particular note is the decrease in hydrogen partial pressure above 600°C, due to the formation of hydrogen during the carburizing reaction.

[0190] After complete reduction and possible carburization, the method according to the invention includes cooling and venting steps, which will be described below.

[0191] Therefore, in the subsequent cooling step, the hydrogen / carbon-containing gas atmosphere in the furnace space 120 is then cooled to a temperature of up to 100°C, preferably about 50°C, and then discharged from the furnace space 120, preferably from the entire closed loop, and collected.

[0192] In the absence of a single furnace 100 / 220 connected to one or more furnaces, the gas can be forced into a closed loop (propulsion device 250; valves V5, V6; heat exchanger in condenser 280; furnace 220; valve V16; heat exchanger 240; valve V9) via a gas-water type cooler 240 to cool the loaded material, which is further arranged to cool hydrogen / carbon-containing gas.

[0193] Therefore, heat exchanger 240 transfers heat energy from circulating hydrogen / carbon-containing gas to water (or different liquids), where the heat energy can be utilized in a suitable manner, such as in a district heating system.

[0194] Because in this case, hydrogen / carbon-containing gas circulates through the loaded material 241 in furnace 220, which absorbs heat energy from the loaded material 212, providing effective cooling of the loaded material 241 while the hydrogen / carbon-containing gas circulates in a closed loop.

[0195] In different embodiments, the thermal energy available from the cooling of furnaces 100 / 220 is used to preheat different furnaces 210. This is achieved by control device 201 (compared to the cooling closed loop described above), closing valve V15 and opening valves V13 and V14. Thus, hot hydrogen / carbon-containing gas from furnace 220 is carried to a gas-to-gas heat exchanger 230, preferably a counter-current heat exchanger, in which hydrogen supplied for the initial or main reduction and possibly carburizing steps associated with another furnace 210 is preheated. Thereafter, slightly cooled hydrogen / carbon-containing gas from furnace 220 can be circulated through heat exchanger 240 for further cooling before being reintroduced into furnace 220. Similarly, hydrogen / carbon-containing gas from furnace 220 is circulated in a closed loop using propulsion device 250.

[0196] Therefore, the cooling of hydrogen / carbon-containing gas in the cooling step can be achieved by heat exchange with hydrogen supplied to different furnace 210 spaces 120, as described above, for the initial and main heating / carburizing steps and condensation associated with the different furnace 210 spaces 120.

[0197] If the hydrogen / carbon-containing gas is not hot enough to heat the hydrogen supplied to furnace 210, control device 201 closes valves V13 and V14 again and reopens valve V15 so that the hydrogen / carbon-containing gas from furnace 220 is directly carried to heat exchanger 240.

[0198] Regardless of how its heat energy is handled, the hydrogen / carbon-containing gas from furnace 220 is cooled until it (or more importantly, the loaded material) reaches a temperature below 100°C to prevent the loaded material from being re-oxidized upon subsequent contact with air.

[0199] Cooling of hydrogen / carbon-containing gas can be carried out while maintaining the pressure of hydrogen / carbon-containing gas, or the pressure of hydrogen / carbon-containing gas can be reduced by allowing hot hydrogen / carbon-containing gas to occupy a larger volume (closed-loop conduit and heat exchanger).

[0200] In a subsequent step, hydrogen / carbon-containing gas is vented from furnace space 120, preferably from the entire closed loop, and collected in a suitable container for the gas. Typically, furnace space 120 will at this point contain reducing gas or a mixture of reducing gas and carbon-containing gas, possibly along with other gases such as residual water vapor, and then this gas or gas mixture is vented into the container for the carbon-containing gas. Venting of furnace space 120 is preferably performed until a pressure of at most 0.5 bar, or even at most 0.3 bar, is detected within furnace space 120.

[0201] Because a closed-loop system is used, in which all gases are circulated through the propulsion device 250, only the hydrogen / carbon-containing gases consumed in the chemical reduction reaction are removed from the system. The remaining hydrogen is the gas necessary to maintain the hydrogen / water vapor balance in the furnace space 120 during the main reduction and possible carburizing steps. This discharged hydrogen is very useful for subsequent batch operations of newly loaded metal materials to be reduced.

[0202] Afterward, the closed loop can be refilled with air, inert gas, or hydrogen for new batch operations. Condensate can also be drained.

[0203] In subsequent steps, the furnace space 120 can thus be opened, for example by releasing the fastening devices and opening the upper part 110. If a container is used, it is removed and replaced with a container containing a new batch of loaded metal material to be reduced.

[0204] In subsequent steps, to avoid re-oxidation during transportation and storage, the removed reduced material can be placed in an inert atmosphere, such as a nitrogen atmosphere.

[0205] For example, the reduced metallic material can be arranged in a flexible or rigid transport container filled with an inert gas. Several such flexible or rigid containers can be arranged in the transport container, and then the space around the flexible or rigid containers can be filled with inert gas. Thereafter, the reduced metallic material can be safely transported without the risk of re-oxidation.

[0206] In alternative cases of continuous processing, it may still be possible and sometimes necessary to use heat exchangers 230, 240 in a corresponding manner and to arrange them downstream of furnace 120 in the closed loop to cool the water-containing hot gas leaving furnace space 120, thereby achieving more complete condensation of entrained water.

[0207] The table below shows the approximate equilibrium between hydrogen (H2) and water vapor (H2O) at different temperatures within furnace space 120:

[0208]

[0209] Reducing 1000 kg of Fe2O3 requires approximately 417 Nm 3 Hydrogen (H2) requires approximately 383 mg / L of hydrogen gas (H2) to reduce 1000 kg of Fe3O4. 3 Hydrogen gas (H2).

[0210] The table below shows the amount of hydrogen required to reduce 1000 kg of Fe₂O₃ and Fe₃O₄ in an open system (according to the prior art) but at different temperatures:

[0211]

[0212] The table below shows the amount of hydrogen required to reduce 1000 kg of Fe2O3 and Fe3O4 at different pressures and temperatures:

[0213]

[0214]

[0215] As described above, the main reduction and possible carburizing steps according to the invention are preferably carried out at a pressure and temperature of at most 1 bar. During most of the main reduction and possible carburizing steps, partial reduction is carried out, and it has been found advantageous to use a combination of a heated hydrogen temperature of at least 500°C and a furnace space pressure of at least 2.3 bar.

[0216] It should be noted that the final product obtained by the method and system according to the present invention can be (possibly carburized) metal powder.

[0217] Fourth embodiment

[0218] The following are embodiments of the method of the present invention, used for batch processing of metal materials to be reduced.

[0219] A container containing a certain amount of metal oxide, either in powder or sphere / particle form, is placed into furnace space 120. Furnace space 120 is sealed and airtight.

[0220] Then, using pump 290, for example to 0.5 bar, the air contained in furnace space 120 and the closed loop is purged by closing valves V1, V2, V3, and V41 and opening valves V4, V5, V6, V7, V8, V9, V12, V15, V16, V17, and V42. If additional drying of the gas is subsequently required, valves V10 and V11 will also be opened.

[0221] When purging is complete, the closed loop is filled with nitrogen or hydrogen by opening valve V1 or V2 while simultaneously closing valves V4, V16, and V42.

[0222] When the pressure in the closed loop reaches 1 bar, heating element 175 is activated, and propulsion device (fan) 250 is started. Valves V7 and V15 are closed, and the water supply to water cooler 281 and heat exchanger 240 is turned on. Gas flows from fan 250 through valves V5 and V6 to the outer tube of the gas-to-gas heat exchanger in condenser 280, and further through valve V17 into heating device 174 located at the bottom of furnace 220, where the gas is heated by heating element 175. The heated gas then flows upward through the gas distribution space and upward through the permeable bottom plate 151, entering the material 142 to be reduced for mixing. Thus, the gas reduces material 142, and the resulting water vapor is carried to cyclone separator 270, where any particulate matter is separated. The gas then flows to condenser 280, where the water vapor is condensed and water is collected. The gas flows through gas-to-water heat exchanger 281, where any remaining water vapor is finally condensed. The condensate is collected in a condensate tank below, and the cooled gas continues to enter the gas-water heat exchanger 240 via V8, where it is further cooled. Then, the gas flows back to the fan 250 through valve V9.

[0223] If additional drying of the gas is required, valve V9 can be closed and valves V10 and V11 opened, allowing the gas to pass through gas dryer 282 before reaching fan 250 again. The drier the hydrogen, the faster the reduction process, and hydrogen is consumed as long as material 142 is being reduced, which needs to be compensated by adding hydrogen. If an inert gas (such as nitrogen) is used in the initial heating step, the inert gas can be vented and collected before the main heating step and replaced with hydrogen in the main heating step.

[0224] For example, when hydrogen is used in the initial heating step and a suitable temperature, such as 350-400°C, has been reached, reduction begins, and the pressure in the furnace space 120 can be increased to 2-3 bar or higher, allowing a larger mass of hydrogen to be used for reduction, thereby accelerating the process.

[0225] When using hydrogen, the temperature provided at heating element 175 should be higher than the required temperature to compensate for the endothermic oxide reduction reaction. The more severe the oxidation of material 142, the higher the heating temperature should be.

[0226] If the loaded material 142 is acidic, the heat provided by the heating element 175 can be advantageously higher to compensate for the endothermic reaction when using hydrogen to reduce the oxide. The more severely the material 142 is oxidized, the higher the temperature should be.

[0227] Using fan 250, the gas can circulate in two different paths: If the gas needs to be "dried," it travels from condenser 280 to heat exchanger 240 via valves V8 and V9, where it is further cooled and thus dried. In this case, valve V7 is closed. If the gas is still not dry enough, a gas dryer 282 is arranged between the gas-water heat exchanger 240 and fan 250, then valve V9 is closed while valves V10 and V11 are open. If the gas does not require additional drying, which may be the case for carburizing, for example, with methane, valves V8, V9, V10, and V11 are closed while valve V7 is open, and fan 250 is used to bring the gas back to condenser 280 via valves V5 and V6. If valves V7-V11 are open or partially open, the reduced hydrogen can have the desired moisture content for the process to be performed (e.g., when carburizing occurs on material 142 associated with reduction).

[0228] Throughout the process, additional hydrogen is supplied to maintain the desired hydrogen pressure in the closed loop, particularly in the furnace space 120.

[0229] Once reduction is complete, for example, by measuring the predetermined amount of condensate, or once it is clear that no additional hydrogen supply is needed to maintain pressure, and hydrogen consumption has ceased, the cooling process can begin.

[0230] In this cooling step, valve V17 is closed and valve V16 is opened. Heating element 175 is turned off.

[0231] For a single-furnace setup, valves V7, V8, and V12 are closed, while valve V15 is opened. Fan 250 is set to high or maximum fan speed. Gas then passes through valves V5 and V6, through external pipes in condenser 280, through V16, through the distribution space in furnace 220, upwards through bottom plate 151, through reduced metal material 142 (either in powdered form of metal oxide or in the form of large particles), and enters the upper part of furnace space 120, circulating through reduced metal material 142. The gas then flows through valve V15 to heat exchanger 240, where heat is transferred from the gas to the water, thus facilitating its use in systems such as district heating or similar systems. The cooled gas returns to fan 250 through valve V9.

[0232] For a multi-furnace setup, valves V7, V8, and V15 are closed, while valves V9, V13, and V14 are opened. Gas flows through valves V5 and V6, through the external pipes of condenser 280, into the gas distribution space, upwards through the base plate 151, through the reduced metal material 142, out through valve V13 to heat exchanger 230, further through valve V14 to heat exchanger 240, and back to fan 250 via valve V9. When heat is transferred from furnace 220 to furnace 210 in this manner, only about half of the usable heat energy in furnace 220 can be utilized in furnace 210 before temperature equilibrium is reached between the two furnaces 220 and 210. When this has occurred, valves V13 and V14 can be closed, valve V15 can be opened, and additional cooling of the metal material 142 can be achieved using heat transferred to water via heat exchanger 240. Similarly, when needed, dryer 282 can be used to dry cooled hydrogen by closing valve V9 and closing valves V10 and V11.

[0233] Once the reduced metal material 142 has been cooled to below 100°C, the hydrogen is discharged into a storage tank using a compressor. In the case of a multi-furnace setup, valves V13 and V14 need to be opened to purge the hydrogen contained in the sub-loops.

[0234] Finally, the container holding the reduced metal material 142 is removed from the furnace space 120, and the reduced metal powder or granules are packaged on pallets or in containers for further transport. Preferably, this transport occurs directly at the user of the reduced metal powder, such as a steel mill or smelter, to be used as a substitute for scrap steel to be smelted. The metal powder can be blown directly into the molten steel.

[0235] When transporting reduced metallic materials (e.g., scale, grinding residue to be returned to the original steel mill) from a steel mill, no additional protection is required to prevent re-oxidation. However, in cases where the original material is highly oxidized, such as hematite, magnetite, or pyrite, the reduced material should be packaged under an inert gas atmosphere to prevent re-oxidation, unless it has already undergone some carburizing in the process according to the invention. The transport itself can be carried out in small container modules.

[0236] When the material to be reduced is reduced iron or an iron alloy, such as scale or grinding residue, the product can be directly loaded into the electric steel furnace without any additional treatment before being loaded into the smelting furnace.

[0237] Fifth Embodiment

[0238] Embodiments will now be described in the form of a continuous process according to the invention.

[0239] Typically, the system for continuous processes corresponds to the system for batch processing described in the fourth embodiment, but with additional arrangements at the inlet 144 and outlet 145 of the furnace space 120. In particular, the inlet 144 and outlet 145 are preferably arranged to allow the furnace space 120 to operate under slight negative and overpressure conditions without allowing any atmospheric air to enter the closed loop during the loading or unloading of the metal material 142.

[0240] To address this problem, an additional supply of reducing gas (to maintain a predetermined pressure while the reducing gas is consumed during the reduction process) can be combined with the supply of additional material via inlet 144, such that the small, transient overpressure generated by the supply of reducing gas offsets the air leaking into the furnace space 120 via inlet 144.

[0241] The material discharged via outlet 145 will be hot and will therefore preferably be conveyed to a connected, completely independent cooling system for cooling the reduced and possibly carburized discharged material.

[0242] In a continuous process, metal material 142 can be loaded into loading containers, as described above for a batch process. Several such bottom-ventilated loading containers can then be connected and continuously transported through the furnace space, passing through the ventilated bottom plate 151. In the first stage of this transport from inlet 144 to outlet 145, the metal material in these loading containers is heated / dried, and in the second stage of this transport, the metal material in these loading containers is reduced. Thereafter, the metal material can be discharged through outlet 145 into its container and undergo a cooling step.

[0243] In bubbling or circulating fluidized bed reactors, no loading container is required—the metal material 142 is conveyed by a combination of gravity and a supply via inlet 144 and a supply of fluidizing gas via bottom plate 151. The same type of first and second stages described for the loading container case can also be applied to this containerless implementation.

[0244] Preferred embodiments have been described above. However, it will be apparent to those skilled in the art that many modifications can be made to the disclosed embodiments without departing from the basic spirit of the invention.

[0245] For example, the geometry of furnace 100 can vary depending on the specific prerequisites.

[0246] The heat exchanger in condenser 280 is described as a tubular heat exchanger. While this has been found particularly advantageous, it should be recognized that other types of gas-to-gas heat exchangers / condensers are also possible. Heat exchanger 240 can be of any suitable construction.

[0247] The residual heat from the cooled hydrogen / carbon-containing gas can also be used for other processes that require thermal energy.

[0248] The metallic material to be reduced and potentially carburized is described as iron oxide. However, the method and system of the present invention can also be used to reduce and carburize metallic materials, such as the aforementioned metal oxides containing Zn and Pb, which evaporate at temperatures below about 600-700°C.

[0249] The direct reduction and carburizing principles combined in this invention can also be used to reduce metallic materials with a higher reduction temperature than iron ore, for example, by appropriately adjusting the structure of furnace 100 relative to the building materials used.

[0250] In several respects, the present invention utilizes a “closed loop” through which gas is circulated using the propulsion device 250. It should be understood that the exact flow path of the closed loop can be altered by controlling the corresponding valves, but the closed loop is always closed in an airtight manner to prevent gas from escaping from the closed loop unless actively vented.

[0251] All implementation schemes and embodiments described herein can be freely combined, provided they are compatible. For example, all descriptions of this system also apply to this method, and vice versa. Another embodiment is, Figure 1a A continuously charged "bubbling bed" is shown, while Figure 1b The diagram shows a segmented loading "circulating bed". However, the present invention can be used for continuous or batch loading / unloading in a bubbling bed or circulating bed.

[0252] Therefore, the present invention is not limited to the described embodiments, but may vary within the scope of the appended claims.

Claims

1. A method for producing a directly reduced metallic material, comprising the steps of: a) continuously charging a metallic material (142) to be reduced into a furnace space (120) via an inlet (144) onto a gas permeable floor (151); b) providing heat and hydrogen gas into the furnace space (120) such that the heated hydrogen gas heats the charged metallic material (142) to a temperature high enough for metallic oxides present in the charged metallic material (142) to be reduced, in turn causing water vapour to form; and c) condensing and collecting the water vapour formed in step b in a condenser (280); characterized in that the gaseous substance provided into the furnace space (120) during the main reduction step is hydrogen gas, or hydrogen gas and an inert gas; the hydrogen gas is circulated in a closed loop upward through the floor (151), through the charged metallic material (142), and further through the condenser (280) and a gas forced circulation device (250), no hydrogen gas is discharged from the closed loop during the main reduction step until the metallic material (142) has completed the desired reduction, and the method further comprises the steps of: d) supplying additional hydrogen gas to achieve and / or maintain a predetermined pressure in the furnace space (120); and e) continuously discharging the reduced metallic material (142) from the furnace space (120) via an outlet (145), wherein the hydrogen gas stream upward through the floor (151) and further through the charged metallic material (142) is arranged such that the charged metallic material (142) forms a fluidized bed (141) with the hydrogen gas, and wherein the metallic material (142) is transported from the inlet (144) to the outlet (145) due to the movement of the fluidized bed (141).

2. The method of claim 1, wherein, The fluidized bed (141) is a bubbling bed, wherein the charged metallic material (142) is placed on the gas permeable floor (151).

3. The method of claim 1, wherein, The fluidized bed (141) is a circulating bed, wherein the charged metallic material (142) is suspended above the gas permeable floor (151) within the furnace space (120).

4. The method of claim 1, wherein, The method further comprises an initial metallic material supply step, in which a metallic material (142) in powder form is provided by grinding and / or sieving.

5. The method of claim 1, wherein, In step d) the additional hydrogen gas is provided such that a pressure greater than 1 bar is established within the furnace space (120).

6. The method of claim 1, wherein, The method further comprises a carburization step performed before the evacuation of the gas from the furnace space (120) back to atmospheric pressure, in which a carbon-containing gas is provided to the furnace space (120) such that the heated and reduced metallic material (142) is carburized by the carbon-containing gas; wherein the carbon-containing gas comprises a gaseous hydrocarbon.

7. The method of claim 1, wherein, The hydrogen gas is preheated in a heat exchanger arranged to transfer heat energy from the water evaporated from the charged metallic material (142) to the hydrogen gas to be provided in step b.

8. The method of claim 1, wherein, In step d additional hydrogen is provided until no additional hydrogen is required to maintain the predetermined pressure and / or until a predetermined amount of water has been collected in the condenser (280).

9. The method of claim 1, wherein, The predetermined pressure is at least 2.3 bar.

10. The method of claim 9, wherein, The predetermined pressure is at least 2.5 bar.

11. The method of claim 9, wherein, The predetermined pressure is at least 3 bar.

12. The method of claim 1, wherein, Steps b and c are performed for at least 0.25 hours.

13. The method of claim 1, wherein, In step c the heat is provided until the loaded metal material (142) reaches a temperature between 700-1100 °C.

14. The method of claim 13, wherein, In step c the heat is provided until the loaded metal material (142) reaches a temperature between 800-1100 °C.

15. A system for producing directly reduced metal material (142), comprising: a furnace space (120) arranged to continuously receive and contain metal material (142) to be reduced via an inlet (144), the furnace space (120) comprising a gas permeable floor (151) arranged to support the loaded metal material (142); a heating and reducing gas supply (174; 175; 250) arranged to provide heat and hydrogen to the furnace space (120), the heating and reducing gas supply (174; 175; 250) comprising a gas heating device (174), a heating element (175) and a gas forced circulation device (250); a control device (201) arranged to control the heating and reducing gas supply (174; 175; 250) such that the heated hydrogen heats the loaded metal material (142) to a temperature high enough for metal oxides present in the loaded metal material (142) to be reduced, in turn causing water vapour to form; and a condenser (280) arranged to condense and collect water vapour, characterized in that the control device (201) is further arranged such that the gaseous substance provided into the furnace space (120) during the main reduction step is hydrogen, or hydrogen and an inert gas; no hydrogen is vented from the closed loop during the main reduction step before the metal material (142) has completed the desired reduction; and a predetermined pressure is achieved and / or maintained in the furnace space (120) with the supply of additional hydrogen; the heating and reducing gas supply (174; 175; 250) is arranged to cause the hydrogen to pass upwards through the floor (151), through the loaded metal material (142), and further to be circulated in a closed loop via the condenser (280) and the gas forced circulation device (250); wherein the flow of hydrogen passing upwards through the floor (151) and further through the loaded metal material (142) is arranged such that the loaded metal material (142) forms a fluidized bed (141) with the hydrogen; wherein the furnace space (120) further comprises an outlet (145) configured to continuously discharge reduced metal material (142) from the furnace space (120); and wherein the control device (201) is further arranged to control the gas forced circulation device (250) to provide a predetermined amount of water vapour to the furnace space (120) during the main reduction step. wherein the fluidized bed (141) is configured to cause the metal material (142) to be transported from the inlet (144) to the outlet (145) due to movement of the fluidized bed (141).

Images