SYSTEM AND METHOD FOR THE DIRECT REDUCTION OF IRON OXIDE POWDER BY HYDROGEN

Abstract

A process for reducing iron oxides by fluidized bed, implemented in a set of several reduction reactors (3a), this process comprising, for each of said reduction reactors (3a), a treatment process dedicated to said reactor comprising: a loading sequence of said reactor (3a) with a predetermined quantity of iron oxides constituting a bed (1a), a reduction sequence comprising: heating of the bed of iron oxides loaded in the reactor (3a), this heating being intended to reach a predetermined temperature in said reactor (3a), and injection of pressurized gas including hydrogen gas (H2) into the fluidized bed (1a), a discharge sequence of the iron thus obtained, from said reactor. The reactor (3a) is depressurized at the end of the reduction sequence and prior to the next loading sequence with iron oxides. See Figure 4

Description

Title of the invention: SYSTEM AND METHOD FOR THE DIRECT REDUCTION OF IRON OXIDE POWDER BY HYDROGEN FIELD OF INVENTION

[0001] The present invention relates to an innovative process for the direct reduction by hydrogen of iron oxide powder (comprising a mixture of Fe2O3 / Fe3O4 / FeO). STATE OF THE ART

[0002] Most current energy production systems use fuels that emit CO2 (natural gas, coal, fuel oil, etc.). Furthermore, the rising cost of energy and the risk of shortages linked to the energy dependencies of many countries worldwide are a reason for seeking a green alternative energy source for generating steam for industrial applications.

[0003] In this context, metallic fuels, as detailed in the 2015 Applied Energy article "Direct combustion of recyclable metal fuels for zero-carbon heat and power," are a proposed solution for producing CO2-free combustion for all types of energy production applications. Metallic fuels (magnesium, aluminum, iron) have the advantage of generating only solid metal oxides during combustion, which are easily recovered in a combustion system. These oxides can then be recycled using renewable energy via an inert anode electrolysis process or a zero-CO2 thermal reduction process using solar energy.Using hydrogen in this reduction process as a reducing agent allows the role of energy carrier to be transferred from this gas, which is very complex to store and transport, to highly energy-dense iron powder, which is easy to store and transport and for which energy production systems are less expensive.

[0004] Direct reduction systems for iron oxides, conventionally used in metallurgy to produce "iron sponges," employ coal or gas (from methane cracking), composed primarily of hydrogen and carbon monoxide, as reducing agents. These processes are highly emissive in terms of greenhouse gas emissions, and projects for iron production using green hydrogen (GravitHy, SSAB, etc.) or electrolysis (Electra, Boston Metals, etc.), aimed at decarbonizing this activity, are already emerging worldwide.

[0005] The processes for producing iron fuels from metal oxides via a reduction reaction are industrially proven and well known as These processes are used for reducing iron ore with hydrogen mixtures as a reducing agent. These steelmaking processes are not intended for the use of iron particles as fuel. The input material for these processes is primarily iron ore, which exhibits varying properties in terms of particle size, morphology, and composition. Furthermore, these processes are designed for steelmaking, with less stringent requirements regarding the morphology of the iron particles after reduction, and include a carburizing step (addition of carbon) to harden the steel. In such steelmaking processes, iron oxide reacts with hydrogen in the reactor to reduce it to iron. The gas exiting the reactor is filtered to remove any solids, which are then returned to the reactor and cooled to condense the water vapor produced during the reaction.Thus, the unreacted hydrogen is recycled back to the reactor inlet.

[0006] US patent 4,082,545 describes a process for the direct reduction of iron ore, progressively in a series of fluidized beds, by passing the reducing gas through beds, then recovering, cooling and partially recycling the reducing gas to feed it back through beds.

[0007] US patent 2016 / 348199 discloses a method for reducing the feed containing metal oxides, comprising the following steps: reducing the feed containing metal oxides by counter-currently passing a reducing gas through at least two fluidized bed units. The reducing gas exiting the first fluidized bed unit is recycled via the following steps: recovery, compression in a gas compressor, cooling of the hot recycled gas in a secondary cooler, and at least partial removal of CO2. The recycled gas is mixed with the reducing gas to feed the second fluidized bed unit, optionally after preheating in a heating device.

[0008] US patent 3,288,590 discloses a process for the continuous reduction of iron oxides with a reducing gas, predominantly hydrogen, in dilute phase suspension.The process steps include: 1) grinding the iron oxide particles to a size below 100 mesh with an average size of about 200 mesh, 2) heating the reducing gas to a temperature in the range of 480 °C under a pressure of 11 to 35 atm, 3) continuously feeding the preheated reducing gas (upward direction) into the vertical reactor at a velocity between 1.5 and 7.6 m / s, 4) preheating the iron oxide to at least 480 °C, 5) continuously feeding the preheated fine iron oxide particles to the reducing gas riser at a rate that maintains an average solids density in the range of 80 to 240 kg of metal oxide per cubic meter of gas under column conditions, 6) separating the effluent from the reaction zone for the recovery of the gas (without solids) and the reduced iron fines. The reaction zone consists of a series of . vertical chambers forming interconnected stages to achieve a downward flow of gas from the top of one stage to the upward flow of the next stage.

[0009] US patent 4,420,332 discloses a process for simultaneously producing iron (via oxide reduction) and thermally cracking heavy oil, which comprises the following steps: 1) introducing iron ore fines and heavy oil into a fluidized bed thermal cracking reactor to crack the heavy oil at a temperature between 500 °C and 600 °C into carbonaceous products and co-products; 2) the iron ore, consisting of particles with a diameter of approximately 10–30 micrometers and deposits of carbonaceous material, is introduced into a first fluidized bed reduction furnace and comes into contact with a high-temperature reducing gas blown into it to fluidize and reduce the iron oxides to metallic iron at a temperature in the range of 800 °C to 1000 °C; 3) the cracked gas, light oil, and residual oil are separated by distillation of the thermal products in a fractionation system,and part of the reduced iron is transferred to a gas reformer, 4) in the reformer, a fluidized bed of iron is created and the cracking gas or oil residue reacts by contact with the fluidized reduced iron in the reformer to produce a gas mainly composed of H2 and CO.

[0010] Document WO 00 / 01856 discloses a process for reducing iron oxide particles to metallic iron in a moving bed reduction reactor using a reducing gas mainly composed of hydrogen and / or carbon monoxide.The process consists of: 1) introducing iron oxide-containing particles into the reducing zone at the first level to form a moving bed of particles in the lower part of the reducing zone and extending to a discharge zone of the reactor, 2) injecting the reducing gas below the first level into the moving bed to define a reducing sub-zone of the moving bed above it, 3) recovering the reactor from the overflow of fine metallic iron particles at the top of the fluidized bed, 4) recovering the reduced metallic iron particles from the non-fluidized part of the moving bed in the discharge zone, and 5) recovering the reduction / fluidizing gas from the top of the fluidized bed of the reduction zone.

[0011] US patent 3,303,017 discloses a process for the direct reduction of iron ore in a fluidized bed by injecting the gas through several conical gas distributors, at least two, each of which is fed by a separate cyclone gas-solids separator. The cyclones are located inside and directly feed the gas distributors.

[0012] However, these iron production processes, via the reduction of metal oxides, do not allow the production of iron with a specific size for use as fuel. The main drawback of these processes is the agglomeration of the iron particles produced, and thus the loss of their physical appearance. enabling combustion. Conversely, another drawback of some of these processes is the production of pyrophoric iron particles, and their immediate reoxidation. These two drawbacks create a barrier to the use of iron powders of a specific size as fuels. Pyrophoricity is explained by the auto-ignition of particles within 5 minutes of contact with air or in air at a temperature below 54°C. This parameter is specific to materials with a nanometric size and / or very high specific surface area. In the aforementioned processes where fluidized beds are used, the problem of pyrophoricity of iron powders is common due to the formation of particles with a high specific surface area.

[0013] The term "pyrophoricity" should be understood as a property of a material. A material is described as pyrophoric if it spontaneously ignites in air at a temperature of 54 °C or lower, or within 5 minutes of contact with air. This is caused by the high surface specificity of the material, which allows for an extremely low ignition temperature for oxidation. When the ignition temperature is sufficiently low, auto-ignition under atmospheric conditions can occur. The pyrophoricity of iron particles after reduction has been reported as a problem in fluidized bed reduction, where a large surface area of ​​the material is obtained. The reoxidation of the particles is dependent on the reduction temperature, which controls the physical properties of the materials produced.During reduction at high temperatures, metallic powders with a larger specific surface area are formed, thus promoting the pyrophoric aspect and the immediate reoxidation of these materials.

[0014] The term "agglomeration" is also a property of the materials produced. It is explained by the adhesion of particles to one another and represents a major problem during fluidized bed reduction because it leads to defluidization of the particle bed, thus limiting the reduction of oxides. Parameters affecting the agglomeration phenomenon include, for example, the reduction temperature, the metallization ratio, the fluidizing gas flow rate, the reducing atmosphere, and the particle properties. Generally, agglomeration begins above a certain critical temperature and occurs after the formation of metallic iron, which creates iron whiskers at a higher metallization ratio, increasing the adhesion between particles. To limit this phenomenon, it is necessary, for example, to limit the reduction temperature.Thus, a balance must be maintained between the temperature, which limits the reduction rate on the one hand, and the agglomeration, which leads to the production of particles unsuitable for use as fuel.

[0015] One of the objects of the present invention is the production of iron particles, via the direct reduction of iron oxides, having a particle size and specific surface area allowing the use of these particles as combustion materials.

[0016] The agglomeration and pyrophoricity of the particles can be limited. The iron powder thus produced must be used as a starting material for iron combustion.

[0017] The conditions in the fluidized bed are such that the bed is generally a bubbling fluidized bed. In a bubbling fluidized bed, the gas flow rate is greater than the minimum fluidization rate. In a minimum fluidization rate situation, at a certain point, the upward force exerted on each particle is equal to the particle's weight, and the particle is in suspension. This gas flow rate is called the minimum fluidization rate. Any further increase in the rate creates gas bubbles that flow rapidly upward in the system, a phenomenon known as bubbling fluidized bed flow. Increasing the surface velocities of the gases will lead to a transition from the bubbling to the turbulent fluidized bed regime.

[0018] The combustion of iron produces different distinct types of iron oxide: hematite (Fe2O3) and magnetite (Fe3O4). These materials can be reduced by electricity and / or reducing agents, including synthesis gas, carbon monoxide, methane, or hydrogen. The chemical product

[0019] The processes that take place during the reduction of iron oxides by hydrogen are described by the equilibrium reaction:

[0020] FeO(s) + H2 (g) ~ Fe(s) + H2O(g)

[0021] Since the iron (oxide) does not reach a molten state in the process, it is a direct reduction. The chemical reactions show that the process involves reactions between solid and gaseous reactants. An important difference between reduction with hydrogen and with carbon monoxide, which is traditionally used for steel production in blast furnaces, is that reduction with hydrogen is endothermic. This means that energy must be added to the system to ensure a constant temperature reduction. The addition of energy to the system can be achieved by preheating the incoming material or by integrating some form of heating into the system design.

[0022] The main drawback of industrially used reduction processes in metallurgy is that they do not address the agglomeration that occurs in pre-reduced iron. However, in the context of reducing iron oxide powders for subsequent use in a combustion process, it is necessary to maintain a fixed particle size at each cycle that meets the criteria set by the combustion process in order to maintain stable and high boiler performance.

[0023] The agglomeration of iron particles and the formation of wustite bridges was explained thermodynamically by the eutectoid point separating the stable phases of metallic iron, magnetite and wustite in the phase diagram of the Fe-OH system. This point corresponds to a temperature of 567 °C and a partial pressure of hydrogen (H2 / H2+H2O) of 75.8% (Thermochemical reduction of iron oxide powders with hydrogen: Review of selected thermal analysis studies - ScienceDirect).

[0024] This phenomenon limits the rate of reduction and the formation of pure metallic iron, thus producing mixtures containing up to 31% FeO with the development of an iron-wustite intergrowth layer limiting the reduction of wustite grains (Studies on the Reduction Behavior of Iron Oxide Pellet Fines with Hydrogen Gas: Mechanism and Kinetic Analysis I Journal of Sustainable Metallurgy (springer.com)).

[0025] The agglomeration phenomenon directly affects fluidization in the fluidized bed, as shown previously (Minimum fluidization velocity and reduction behavior of combusted iron powder in a fluidized bed - ScienceDirect). Both agglomeration phenomena involved in the formation of wustite bridges occur at high temperatures, with agglomeration starting at 575 °C and wustite formation beginning around 700 °C (Sintering behavior of combusted iron powder in a packed bed reactor with nitrogen and hydrogen - ScienceDirect).

[0026] For the use of metallic iron powders as fuels without any risk of pyrophoricity, the particle size of the oxide powders before reduction, and thus of the iron powders produced, must be carefully controlled. Iron particles with a nanometric size and a large specific surface area are likely to self-ignite immediately due to their pyrophoric nature (Pyrophoricity of Fine Metal Powders: Powder Metallurgy: Vol 19, No 1 (tandfonline.com))(On the Nature of the Pyrophoricity of Metal Nanopowders I International Journal of Self-Propagating High-Temperature Synthesis (springer.com)).

[0027] Document WO 2023 / 121465 discloses a system for reducing iron oxides in a fluidized bed using hydrogen as the reducing agent, taking into account agglomeration and pyrophoricity. The process includes systems for preheating and pressurizing the iron oxide-laden materials to a temperature of 40–1000 °C in an intermediate chamber before their introduction into the fluidized bed. Furthermore, a preheating step of the partially exhausted and fresh reducing gas is required before its introduction into the fluidized bed. The process also includes a system for pressure-drying iron powders produced during transport and cooling using an inert gas. The iron powder stream is then returned to atmospheric pressure for storage. This process is implemented in a high-inertia fluidized bed reactor operating continuously, requiring the preheating and pressurization of the materials. Charged with hydrogen in an intermediate chamber before injection into the fluidized bed, the aforementioned system requires additional equipment and higher energy consumption. Furthermore, temperature homogenization in a reactor with high thermal inertia and wall heating is very difficult. This can cause a significant temperature gradient between the bed's periphery and its center. A temperature higher than the iron oxide reduction temperature (close to 550°C) can lead to agglomeration (and subsequent defluidization) and a reduction in kinetics due to the formation of wüstite bridges. The difficulty of internally heating the fluidized bed to homogenize the temperature, due to the risk of fouling by particles from the heating system, necessitates a redesign of the high-inertia iron oxide reduction reactor concept.

[0028] Another drawback of these fluidized bed reactors is the inability to process material with a particle size distribution that is too wide, for example, from 10 to 2000 microns. This is because the minimum fluidization velocity depends heavily on the particle size. If the gas flow is too fast, the material is carried out of the reactor; if it is too slow, the flow is insufficient to fluidize the bed, and the reaction between the reducing agent and the oxides cannot occur efficiently. However, in all iron oxide ores, the particle size distribution is often very wide. A process dedicated to reducing fine iron oxides from the ore (for the production of iron fuel) must also be able to utilize the larger particles for other applications (for the production of green steel, etc.), or vice versa.The initial material with a large size distribution can be divided into several groups of the same material with narrow size distributions by a separation process (dry or wet, such as sieving or other).

[0029] The object of the present invention is to remedy the aforementioned drawbacks by proposing a new concept for the reduction of iron oxides which differs from the prior art by a modular and compact architecture and provides superior technical performance. Description of the invention

[0030] This objective is achieved with a process for reducing iron oxides by fluidized bed, implemented in a set of several reduction reactors, this process comprising, for each of said reduction reactors, a treatment process dedicated to said reactor comprising: - a loading sequence of said reactor with a predetermined quantity of iron oxides constituting a bed, - a reduction sequence comprising: - heating of the bed of iron oxides charged in the reactor, this heating being designed to reach a predetermined temperature in said reactor, and - an injection of pressurized gas including hydrogen gas into the fluidized bed, - a discharge sequence of the iron thus obtained out of said reactor, this reactor being depressurized at the end of the reduction sequence and prior to the next iron oxide loading sequence.

[0031] The discharge sequence may advantageously include a step to cool the iron obtained by reduction and a step to recover the heat thus removed.

[0032] When the reduction process according to the invention is implemented for iron oxides having a wide particle size distribution, at least one of the reactors is configured to reduce iron oxides having a predetermined average particle size within said wide particle size distribution.

[0033] The process according to the invention may further include an initial step for separating predetermined particle size slices in the iron oxides to be reduced, and a step for bringing each particle size slice thus separated corresponding to a predetermined average particle size into the inlet of a reactor configured for this predetermined average particle size.

[0034] The reactor loading sequence with oxides can be carried out at ambient pressure and / or ambient temperature.

[0035] The reduction process according to the invention may further include, at the end of the reduction sequence, a step of drying the iron in the reduction reactor.

[0036] The reduction process according to the invention may further include a time programming of all said treatment processes associated with each reactor or group of reactors within the reactor set, so as to produce an overall substantially continuous or semi-continuous flow of iron powders from respective time-shifted loading and unloading sequences.

[0037] The iron oxide loading sequences and the iron powder discharge sequences can then be carried out while the heating in the reactor is maintained.

[0038] The set of reduction reactors can be organized into a plurality of reduction modules, each comprising one or more reduction reactors.

[0039] One or more of these reduction modules is configured to process iron oxides having a predetermined average particle size.

[0040] At least one of the reactors of a reduction module is configurable to successively reduce iron oxides having several predetermined average particle sizes.

[0041] According to another aspect of the invention, a system is proposed for reducing iron oxides by fluidized bed, implementing the reduction process according to the invention, comprising: - a set of several reduction reactors, - means for loading each reactor with a predetermined quantity of iron oxide constituting a bed, - means for heating the iron oxide loaded into the reactor, designed to reach a predetermined temperature in said reactor, - means for injecting a pressurized gas including hydrogen gas (H2) into the fluidized bed, - means of unloading the iron thus obtained from each reduction reactor, - means to control each reduction reactor, arranged so that a reactor is pre-depressurized before being unloaded.

[0042] The reduction system according to the invention may further include means for cooling the iron obtained by reduction and means for recovering the heat thus extracted.

[0043] When the reduction system according to the invention is intended to reduce iron oxides having a wide particle size distribution, at least one of the reactors is configured to reduce iron oxides having a predetermined average particle size within said wide particle size distribution.

[0044] The reduction system according to the invention may further include means for separating predetermined particle size slices in the iron oxides to be reduced, and means for bringing each particle size slice thus separated corresponding to a predetermined average particle size into the inlet of a reactor configured for this predetermined average particle size.

[0045] The means for charging the reactor with oxides can be operated at ambient pressure and / or ambient temperature.

[0046] The reduction system according to the invention may further include means for drying the iron in the reduction reactor.

[0047] The control means can be programmed to control in time all the processing operations associated with each reactor or group of reactors within the reactor set, so as to produce an overall substantially continuous flow of iron powders from respective time-shifted loading and unloading sequences.

[0048] The set of reduction reactors can be organized into a plurality of reduction modules, each comprising one or more reduction reactors.

[0049] The present invention preferably relates to low-inertia oxide reduction reactors operating individually or in multi-reactor combinations in alternating batches. The invention simplifies and makes more robust the complete iron oxide reduction process and increases the drying efficiency of wet iron by means of a fluidization reactor integrating the two aforementioned functions. The proposed process optionally allows operation without additional preheating or pressurization units. The design of low-inertia fluidized bed multi-reactors eliminates the need for preheating the materials loaded into the fluidized bed and for maintaining the bed under pressure. Heating is also more homogeneous (larger exchange surface for the same total quantity of material to be reduced) in order to avoid strong thermal gradients in the bed that increase the risk of agglomeration and wüstite bridging.Furthermore, the process allows the fuel powders produced in the fluidized bed to be dried and depressurized directly using hydrogen or an inert gas, before being unloaded for cooling and storage. Finally, the process allows one or more reactors to be dedicated to a portion of the material whose size distribution is narrower than the overall size distribution of the initial material, thus ensuring efficient fluidization in each reactor.

[0050] The invention relates to the production of iron fuels via the reduction of iron oxides in a fluidized bed reactor using a reducing agent, preferably green hydrogen. The process according to the invention allows for semi-continuous operation where the loaded and produced materials are fed into and recovered from a fluidized bed reactor in several cycles. The loaded materials contain metallic iron oxides, preferably pure, or with common impurities, such as nickel, manganese, copper, lead and cobalt, carbon and sulfur, or mixtures thereof. The iron oxide-loaded materials can have an average size of 10 to 2000 µm, and the iron fuel powders produced from the fluidized bed can have an average size of 10 to 2000 µm. The overall particle size distribution of the oxides can be wide, for example, from 0.01 microns to 3000 microns.The process works for a fluidized bed unit or preferably for a multi-reactor system combined in alternating batch operation.

[0051] Alternating batch fluidized bed reactors can receive iron oxide materials of different sizes, allowing the different fractions to be fractionated and reduced under suitable conditions.

[0052] This will allow one unit to be stopped and drained while reduction continues in the others; then the next unit is stopped and drained while the first is in reduction mode. Each alternating batch fluidized bed reactor can receive iron oxide powder (or grains) of different sizes (a (average particle size of the powder per reactor), allowing the hydrogen injection rate to be adjusted in each reactor to achieve optimal fluidization for each particle size fraction. For example, if the multi-reactor consists of 3 reactors, each reactor can be assigned a different average particle size: 10 µm, 800 µm, and 3000 µm. While in reality more reactors would be needed to achieve a finer particle size distribution (ideally with 90% of the mass within a range where the difference between the minimum and maximum particles is approximately 50 to 1000 microns, depending on the average size of the iron oxides) in each reactor and guarantee optimal fluidization in each one.Depending on the nature of the iron oxide producers (ore), and the size distribution of their ore (or oxides), the multi-reactor can adapt the distribution of the material within the reactors by average particle size (dedicating one or more reactors to a new size distribution depending on the overall distribution of the material to be reduced). DESCRIPTION OF THE FIGURES

[0053] Other features and advantages will become apparent from the following description of two particular embodiments and two non-limiting modes of operation of the invention, given with reference to the figures in which:

[0054] [Fig. 1] is a schematic representation of a first embodiment of the invention.

[0055] [Fig.2] is a schematic representation of a second embodiment of the invention.

[0056] [Fig.3] is a schematic representation of a third embodiment of the invention.

[0057] [Fig.4] is a schematic representation of an embodiment of the invention with multi-reactors in a honeycomb configuration. DETAILED DESCRIPTION

[0058] We will now describe, with reference to [Fig. 1], an SI architecture of an iron oxide reduction system according to the invention, along with the reduction process implemented in this system. It should be noted that in Figures 2 and 3, which illustrate alternatives to the architecture described in [Fig. 1], the common components and lines are indicated by common reference numerals.

[0059] The reduction process comprises all or part of the following elements:

[0060] At the beginning of each cycle, the iron oxide powders 0 are loaded into the fluidized bed by direct transport at ambient pressure via a screw conveyor 1 (or other powder transport means). Preheating the iron oxide powders is not necessary (optional) in the case of a multi-reactor assembly. modular with a common heating system and alternating batch operation. Indeed, since each reactor 2 contains a relatively small quantity of powder (compared to the total quantity in all reactors), the heating of the oxide powders is rapid enough to justify not preheating them before their injection into reactor 2.

[0061] Hydrogen 3c is injected under pressure from 1 bar to 15 bar (preferably under pressure to reduce the minimum fluidization velocity and accelerate the reduction which is controlled by chemical kinetics) into the fluidized bed reactor 2 which is heated by a heating unit 4 thermally coupled 5 to the reactor 2. By way of non-limiting example, this heating unit 4 can be made in the form of electrical resistances surrounding the body of the reactor 2.

[0062] The temperature of reactor 2 is maintained between 400 and 600 °C to avoid agglomeration of the iron particles produced.

[0063] The partially spent reducing gas exiting the fluidized bed is recovered and recycled by injection with fresh hydrogen 3. This step is preceded by a filtration stage to remove entrained coarse particles or fine solids. The spent reducing gas 3b passes through a heat exchanger 12 connected by conduit 11 to the outlet of reactor 2, to recover heat and condense water for removal before mixing it with fresh hydrogen. The heat exchanger 12 can be used to preheat the mixture of fresh and partially spent gas before its injection into the fluidized bed reactor.

[0064] The unconsumed hydrogen (duct 3b) is reinjected into reactor 2 through duct 3b and the condensed steam (duct 13) is used to produce hydrogen later (or recycled for another purpose).

[0065] The partially spent reducing gas is continuously analyzed after prior removal of particles and water. The optional gas analysis 14 allows the evolution of the reduction rate to be determined and thus the completion of the reduction of oxide-laden materials to be more precisely controlled.

[0066] The fluidized bed reactor preferably operates under pressure conditions of 1 to 15 bar, a temperature in a range of 300 to 600 °C and a reducing gas fluidization velocity of 1 to 500 cm / s.

[0067] At the end of each reduction cycle, the iron produced is dried directly in the fluidized bed using an inert gas and / or the reducing gas, in this case hydrogen, under pressure or at atmospheric pressure, in order to accelerate drying by utilizing the existing heat. This step is preferably used in a set of reactors operating in alternating batches.

[0068] The iron produced is transferred by opening the controlled hatch 7 and transported by the block 8 which can incorporate a screw conveyor, a suction or overpressure system, and cooled under inert gas during transport to a storage area 9. The iron can come into contact with the ambient air once sufficiently cooled.

[0069] During the discharge of reactor 2, it is possible to recover on a line 6 the hydrogen present in reactor 2 and downstream of the controlled hatch 7.

[0070] In the case of pneumatic transport (under pressure or by suction) a cyclofilter receives the flow of iron and lets the inert transport gas escape.

[0071] In all cases, the iron is transported dry to a temporary or final storage system for transport to the consumption area (big bag, container, silo or other).

[0072] The hatch 7 is then closed and a new cycle begins in which the new iron oxides are loaded into the fluidized bed of reactor 2 with recovery of hydrogen under reduction conditions under atmospheric pressure or at higher pressure.

[0073] We will now describe, with reference to [Fig. 2], an alternative S2 to the architecture of the iron oxide reduction process SL

[0074] The large particles transported by entrainment in the hydrogen and particle stream from the outlet duct 11 of reactor 2 are captured in a cyclone separator 15 to be reinjected into a line 17 towards the fluidized bed with the oxide powder 0 of the next batch, or directly into the bed.

[0075] The fine particles of the gas from the fluidized bed are separated with a separator 16.

[0076] A compressor 19 compresses recycled hydrogen 3b and fresh hydrogen 3. The compressed hydrogen is then preheated by an electric furnace 22 before being injected into the fluidized bed inside the reactor 2.

[0077] The hydrogen captured at the time of the iron draining is recovered to be reinjected into reactor 2 after being filtered.

[0078] The iron oxide powder 0 is preheated with an electric furnace 21 before being injected into reactor 2.

[0079] This preheating can also be achieved by recovering heat from either the condensation of water vapor 12, or from an exchanger which recovers heat from iron particles during their transfer (8), or by a combination of this heat recovery and the electric furnace 21.

[0080] The iron powder can be dried after the opening of the hatch 7. It can be provided that the iron falls by gravity into a chamber where nitrogen is injected to dry the powder and then transport it while cooling it.

[0081] S3 is an alternative to the iron oxide reduction process architecture of S2, with reference to [Fig.3].

[0082] The spent hydrogen 3b from reactor 2, after passing through separator 16 and condenser 12, is injected with fresh hydrogen 3 into compressor 19 and then preheated by recovering heat from either the heat exchanger 23 or from The condensation of water vapor 12 occurs either from the heat exchanger that recovers heat from the iron particles during their transfer (block 8), or via an electric furnace. The preheated hydrogen 3c is then injected into the fluidized bed inside reactor 2.

[0083] In all the reduction system architectures according to the invention, a control unit (not shown) is provided, for example in the form of locally or remotely controlled industrial computing equipment, which is programmed to control and command each reduction module and / or each reduction reactor, in particular to manage their batch loading or batches of iron oxides and their unloading, so as to ensure semi-continuous production.

[0084] S4 is a possible honeycomb iron oxide multi-reactor structure, with reference to [Fig.4].

[0085] The modules 4a may contain one or more reduction reactors 3a containing the fluidized bed of iron oxides la. These reactors 3a have, on their lower part, a hydrogen injection 2a, to fluidize and supply a reducing agent. The entire bed la is heated peripherally by a heating system 6a, which may be implemented by an electric resistance, an induction system, a heat transfer fluid, or any other heating method, in order to bring the mixture close to the reduction temperature of the iron oxides.

[0086] The iron, once reduced in a reactor 3a, is extracted by a trap equipment 5a located at the bottom of the reactor 3a, after having been dried in that reactor.

[0087] Of course, the invention is not limited to the examples described above, and many other embodiments can be considered without departing from the scope of the present invention.

Claims

Demands

1. A process for reducing iron oxides by fluidized bed, implemented in a set of several reduction reactors (2,3a), this process comprising, for each of said reduction reactors (2,3a), a treatment process dedicated to said reactor (2,3a), comprising: - a loading sequence of said reactor (2,3a) with a predetermined quantity of iron oxides constituting a bed (la), - a reduction sequence comprising: - heating of the bed of iron oxides loaded in the reactor (2,3a), this heating being intended to reach a predetermined temperature in said reactor (2,3a), and - injection of pressurized gas comprising hydrogen gas (H2) into the fluidized bed (la), - a discharge sequence of the iron thus obtained, out of said reactor (2,3a), said reactor (2,3a) being depressurized at the end of the reduction sequence and prior to the next loading sequence with iron oxides.

2. Reduction process according to the preceding claim, characterized in that the discharge sequence includes a step to cool the iron obtained by reduction and a step to recover the heat thus removed.

3. A reduction process according to any one of the preceding claims, implemented for iron oxides having a wide particle size distribution, characterized in that at least one of the reactors (2,3a) is configured to reduce iron oxides having a predetermined average particle size within said wide particle size distribution.

4. A method according to the preceding claim, characterized in that it further comprises an initial step for separating predetermined particle size fractions in the iron oxides to be reduced, and a step for bringing each particle size fraction thus separated, corresponding to a predetermined average particle size, into input of a reactor configured for this predetermined average particle size.

5. Reduction process according to any one of the preceding claims, characterized in that the reactor loading sequence with oxides is carried out at ambient pressure and / or ambient temperature.

6. Reduction process according to any one of the preceding claims, characterized in that it further comprises, at the end of the reduction sequence, a step of drying the iron in the reduction reactor (2,3a).

7. A reduction process according to any one of the preceding claims, characterized in that it further comprises a time programming of all said processing processes associated with each reactor (2,3a) or group (4a) of reactors within the reactor set, so as to produce an overall substantially continuous or semi-continuous flow of iron powders from respective time-shifted loading and unloading sequences.

8. Reduction process according to the preceding claim, characterized in that the iron oxide loading sequences and the iron powder discharge sequences are carried out while heating in the reactor (2,3a) is maintained.

9. Reduction method according to the preceding claim, characterized in that the set of reduction reactors (3a) is organized into a plurality of reduction modules (4a) each comprising one or more reduction reactors (3a).

10. Reduction process according to the preceding claim, characterized in that one or more of said reduction module (4a) is configured to process iron oxides having a predetermined average particle size.

11. Reduction process according to the preceding claim, characterized in that at least one of the reactors (3a) of a reduction module (4a) is parameterizable to successively reduce iron oxides having several predetermined average particle sizes.

12. A system (S1-S4) for reducing iron oxides by fluidized bed, implementing the reduction process according to any one of the preceding claims, comprising: - a set of several reduction reactors (2,3a), - means for loading each reactor (2,3a) with a predetermined quantity of iron oxides constituting a bed (la), - means (6a) for heating the bed of iron oxides loaded in the reactor (3a), intended to reach a predetermined temperature in said reactor (2,3a), - means for injecting a pressurized gas comprising hydrogen gas (H2) into the fluidized bed (la), - means for discharging the iron thus obtained out of each reduction reactor (2,3a), - means for controlling each reduction reactor (2,3a), arranged so that a reactor is pre-depressurized before being reloaded.

13. Reduction system (S1-S4) according to the preceding claim, characterized in that it further comprises means for cooling the iron obtained by reduction and means for recovering the heat thus extracted.

14. Reduction system (S1-S4) according to one of the two preceding claims, intended to reduce iron oxides having a wide particle size distribution, characterized in that at least one of the reactors (2,3a) is configured to reduce iron oxides having a predetermined average particle size within said wide particle size distribution.

15. Reduction system (S1-S4) according to the preceding claim, characterized in that it further comprises means for separating in the iron oxides to be reduced slices of predetermined particle size, and means for bringing each slice of particle size thus separated corresponding to a predetermined average particle size into the inlet of a reactor (2,3a)) configured for this predetermined average particle size.

16. Reduction system (S1-S4) according to any one of claims 12 to 15, characterized in that the means for charging the reactor (2,3a) with oxides are operated at ambient pressure and / or ambient temperature.

17. Reduction system (S1-S4) according to any one of claims 12 to 16, characterized in that it further comprises means for drying the iron in the reduction reactor.

18. Reduction system (S1-S4) according to any one of claims 12 to 17, characterized in that the control means are programmed to time-control all the processing processes associated with each reactor (2,3a) or group of reactors (4a) within the reactor set, so as to produce a substantially continuous overall flow of iron powders from respective time-shifted loading and unloading sequences.

19. Reduction system according to any one of the preceding claims, characterized in that the set of reduction reactors is organized into a plurality of reduction modules (4a) each comprising one or more reduction reactors (3a).

20. Reduction system according to the preceding claim, characterized in that one or more of said reduction modules is configured to process iron oxides having a predetermined average particle size.

21. Reduction system according to the preceding claim, characterized in that at least one of the reactors of a reduction module is parameterizable to successively reduce iron oxides having several predetermined average particle sizes.