System and method for the direct reduction of powdered iron oxides using hydrogen

Abstract

The invention relates to a method for reducing iron oxides using a fluidized bed, the method being implemented in a set of several reduction reactors (3a), the method comprising, for each of the reduction reactors (3a), a processing method dedicated to the reactor comprising: - a sequence of loading the reactor (3a) with a predetermined quantity of iron oxides constituting a bed (1a); - a reduction sequence comprising: - heating the bed of iron oxides loaded into the reactor (3a), this heating being provided so as to reach a predetermined temperature in the reactor (3a), and injecting pressurized gas comprising hydrogen gas (H2) into the fluidized bed (1a); - a sequence of unloading the iron thus obtained from the reactor. The reactor (3a) is depressurized at the end of the reduction sequence and prior to the next iron oxide loading sequence.

Description

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 due to the energy dependencies of many countries worldwide are driving the search for green alternative energy sources for steam generation 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 in 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 latter 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 very energy-dense iron powder, which is easy to store and transport and whose energy production systems are less expensive.

[0004] The direct reduction systems for iron oxides, traditionally 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 to produce iron from green hydrogen (GravitHy, SSAB, etc.) or electrolysis (Electra, Boston Metals, etc.), aimed at decarbonizing this activity, are already emerging worldwide.

[0005] Processes for producing iron fuel from metal oxides via a reduction reaction are industrially proven and well-known 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. In this way, the unreacted hydrogen is recycled back to the reactor inlet.

[0006] US document 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 charge containing metal oxides, comprising the following steps: reducing the charge 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 document 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 includes 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 from the reactor 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 at the outlet 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 gas through several conical gas distributors, at least two, each fed by a separate cyclone gas-solids separator. The cyclones are located inside and feed the gas distributors directly.

[0012] However, these iron production processes, which involve reducing metal oxides, do not allow for the production of iron with a specific particle size suitable for use as fuel. The main drawback of these processes is the agglomeration of the iron particles produced, resulting in the loss of their physical properties that would allow combustion. Conversely, another drawback of some of these processes is the production of pyrophoric iron particles, which then reoxidize immediately. These two disadvantages create a barrier to the use of iron powders of a specific size as fuel. Pyrophoricity is explained by the auto-ignition of the particles within 5 minutes of contact with air or in air at a temperature below 54°C. This characteristic is specific to materials with a nanometric size and / or very high specific surface area.In the processes mentioned where fluidized beds are used, the problem of pyrophoricity of iron powders is common because of 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 considered 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 material's high surface specificity, 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 resulting materials.During reduction at high temperatures, metallic powders with a larger specific surface area are formed, thus promoting the pyrophoric appearance and the immediate reoxidation of these materials.

[0014] The term "agglomeration" also refers to 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, there will be a balance to be maintained between the temperature which limits the rate of reduction on one hand, and the agglomeration which leads to the production of particles not suitable for use as fuels.

[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 should be used as a starting material for iron combustion.

[0017] The conditions within the fluidized bed are such that the bed is typically a bubbling fluidized bed. In a bubbling fluidized bed, the gas flow rate exceeds the minimum fluidization rate. At a minimum fluidization rate, at a certain point, the upward force exerted on each particle equals 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 rapidly rise through 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 two distinct types of iron oxide: hematite (Fe2O3) and magnetite (Fe3O4). These materials can be reduced by electricity and / or reducing agents such as synthesis gas, carbon monoxide, methane, or hydrogen. The chemical

[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. A key 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. This energy can be added by preheating the incoming material or by incorporating 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, reducing iron oxide powders for subsequent use in a combustion process requires maintaining a consistent particle size at each cycle that meets the combustion criteria to ensure 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 | 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 wustite bridge formation occur at high temperatures, with agglomeration beginning at 575 °C and wustite formation starting around 700 °C (Sintering behavior of combusted iron powder in a packed bed reactor with nitrogen and hydrogen - ScienceDirect).

[0026] For the safe use of metallic iron powders as fuel, the particle size of the oxide powders before reduction, and consequently of the resulting iron powders, must be carefully controlled. Iron particles with a nanometric size and a large specific surface area are prone to immediate self-ignition 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 | 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 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 is required for the partially exhausted, fresh reducing gas before its introduction into the fluidized bed. The process also includes a pressure-drying system for 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 that operates continuously, requiring preheating and pressurization of the feed materials and hydrogen in an intermediate chamber before injection into the fluidized bed. The system thus necessitates 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 periphery and center of the bed. A temperature higher than the reduction temperature of iron oxides (close to 550°C) can cause agglomeration (and subsequent defluidization) and a reduction in kinetics due to the formation of wüstite bridges.The difficulty of being able to heat the fluidized bed from the inside, to homogenize the temperature, because of the risk of fouling by particles from the heating system, requires reworking the concept of the high inertia iron oxide reduction reactor.

[0028] Another drawback of these fluidized bed reactors is the inability to process material with a very wide particle size distribution, for example, from 10 to 2000 microns. This is because the minimum fluidization velocity is highly dependent on 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 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 aim of the present invention is to remedy the aforementioned drawbacks by proposing a new concept for reducing iron oxides which differs from the prior art by a modular and compact architecture and provides superior technical performance.

[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 loaded in the reactor, this heating being intended 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 loading sequence with iron oxides.

[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 to separate predetermined particle size slices in the iron oxides to be reduced, and a step to bring 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 with a predetermined average particle size.

[0040] At least one of the reactors in a reduction module can be configured to successively reduce iron oxides with 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, intended to reach a predetermined temperature in said reactor, means for injecting a pressurized gas comprising hydrogen gas (H2) into the fluidized bed, means for discharging the iron thus obtained out of each reduction reactor, means for controlling each reduction reactor, arranged so that a reactor is pre-depressurized before being discharged.

[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 from 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 of 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 temporally control all the treatment processes associated with each reactor or group of reactors within the reactor set, so as to produce a substantially continuous overall 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 strengthens the complete iron oxide reduction process and increases the drying efficiency of wet iron through 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 bed pressure. Heating is also more homogeneous (larger exchange surface area for the same total quantity of material to be reduced) to avoid strong thermal gradients in the bed that increase the risk of agglomeration and wüstite bridging.Furthermore, the process allows for the drying and depressurization of fuel powders produced in the fluidized bed directly using hydrogen or an inert gas, prior to unloading for cooling and storage. Finally, the process enables the dedication of one or more reactors to a portion of the material with a narrower size distribution than the overall size distribution of the initial material, 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 particle size of 10 to 2000 μm, and the iron fuel powders produced from the fluidized bed can have an average particle size of 10 μm 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.

[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 allows 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 (an average powder particle size 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 three reactors, each reactor can be assigned a different average particle size: 10 µm, 800 µm, and 3000 µm.Even though 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 to guarantee optimal fluidization in each one, the multi-reactor can adapt the material distribution within the reactors based on average particle size, depending on the nature of the iron oxide producers (ore) and the size distribution of their ore (or oxides). This allows for adjustments based on the average particle size distribution (dedicating one or more reactors to a new size distribution based 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, made with reference to the figures in which:

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

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

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

[0057] 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 Figure 1, an architecture S1 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 Figure 1, the common components and lines are indicated by common reference numerals.

[0059] The reduction process includes 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 methods). Preheating the iron oxide powders is not necessary (optional) in a case where there is a set of modular multi-reactors 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 the reactors), the heating of the oxide powders is sufficiently rapid 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 prevent the 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] Unconsumed hydrogen (duct 3b) is reinjected into reactor 2 via duct 3b and 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. Optional gas analysis 14 allows for the determination of the reduction rate evolution and thus more precisely controls the completion of the reduction of oxide-laden materials.

[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 integrate 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 where the new iron oxides are loaded into the fluidized bed of reactor 2 with the recovery of hydrogen under reduction conditions under atmospheric pressure or at higher pressure.

[0073] We will now describe, with reference to the, an alternative S2 to the architecture of the iron oxide reduction process S1.

[0074] Large particles carried by entrainment in the hydrogen and particle stream from 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 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 the.

[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, the condensation of steam 12, the heat exchanger that recovers heat from iron particles during their transfer (block 8), or 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 structure for honeycomb-shaped iron oxide multi-reactors, in reference to the.

[0085] The modules 4a can contain one or more reduction reactors 3a containing the fluidized bed of iron oxides 1a. These reactors 3a have a hydrogen injection 2a on their lower part to fluidize and supply a reducing agent. The entire bed 1a is heated peripherally by a heating system 6a, which can be implemented using an electric resistance heater, an induction heater, 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 reactor 3a, is extracted by trap equipment 5a located at the bottom of reactor 3a, after being 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

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 (1a), 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 an injection of pressurized gas including hydrogen gas (H2) into the fluidized bed (1a), 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. 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. 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. A method according to the preceding claim, characterized in that it further comprises 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. 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. 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). Reduction process according to any one of the preceding claims, characterized in that it further comprises a time programming of all said treatment 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. 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. 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). Reduction process according to the preceding claim, characterized in that one or more of said reduction modules (4a) is configured to process iron oxides having a predetermined average particle size. 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. System (S1-S4) for reducing iron oxides by fluidized bed, implementing the reduction process according to any one of the preceding claims, comprising: an assembly of several reduction reactors (2,3a), means for loading each reactor (2,3a) with a predetermined quantity of iron oxides constituting a bed (1a), 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 (1a), 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. 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. 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. 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. 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. 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. 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. 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). 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. Reduction system according to the preceding claim, characterized in that at least one of the reactors of a reduction module is configurable to successively reduce iron oxides having several predetermined average particle sizes.

Images