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

Abstract

The present invention relates to an innovative process for the direct hydrogen reduction of iron oxide powder (comprising a mixture of Fe2O3 / Fe3O4 / FeO).

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 direct hydrogen reduction 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 present invention relates to a process for producing iron fuels from metal oxides via a reduction reaction. This process is This process is 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. Thus, the unreacted hydrogen is recycled back to the reactor inlet.

[0006] US patent 4,082,545 consists of 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 recycling the reducing gas partially to feed it back through beds.

[0007] US patent 2016 / 348199 describes 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 patent 3,288,590 consists of a process for the continuous reduction of iron oxides with a reducing gas, predominantly hydrogen, in suspension in dilute phase.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 iron oxide fines to the reducing gas riser at a rate sufficient to maintain 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 gas recovery (without . solids) and 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 relates to a process for simultaneously producing iron (via oxide reduction) and thermally cracking heavy oil, comprising 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 system of fractionation,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] Patent WO 00 / 01856 relates to 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 relates to 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 feed the gas distributors directly.

[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 leads to the loss of their physical properties, hindering combustion. Conversely, another drawback of some of these processes is the production of pyrophoric iron particles, which then immediately reoxidize. These two disadvantages create a barrier to the use of iron powders of a specific size as fuels. Pyrophicity 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 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. More specifically, 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 pyrophyric 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 each other 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 properties of the particles. 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 current inventors have found that by applying specific process design features, the

[0017] 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.

[0018] 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; this is known as a bubbling fluidized bed. Increasing the surface velocities of the gases will lead to a transition from the bubbling to the turbulent fluidized bed regime.

[0019] 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

[0020] The processes that take place during the reduction of iron oxides by hydrogen are described by the equilibrium reactions:

[0021] FeO(s) + H2 (g) ~ Fe(s) + H2 0(g)

[0022] Since the iron (oxide) does not reach a molten state in the process, it is also subjected to 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.

[0023] 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, the reduction of iron oxide powders for subsequent use in a combustion process requires maintaining a fixed particle size at each cycle which respects the criteria set by the combustion so that the performance of the boiler is kept stable and high.

[0024] The agglomeration of iron particles and the formation of wustite bridges was thermodynamically explained 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). This phenomenon limits the reduction rate and the formation of pure metallic iron, thus producing mixtures containing up to 31% FeO with the development of an iron-wustite intergrowth layer that limits 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).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).

[0025] 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)).

[0026] Patent WO 2023 / 121465 relates to a system for reducing iron oxides in a fluidized bed using hydrogen as a 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 necessary before its introduction into the fluidized bed. The process consists of a large fluidized bed reactor that operates continuously, requiring the preheating and pressurization of the laden materials and hydrogen in an intermediate chamber before injection into the fluidized bed. The aforementioned system This requires additional equipment and higher energy consumption. The process also includes a pressure drying system for iron powders produced during transport and cooling using an inert gas. The stream of iron powders is then returned to atmospheric pressure for storage. Description of the invention

[0027] Our 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 the low-inertia fluidized bed reactors eliminates the need for preheating the materials loaded into the fluidized bed and for maintaining the bed under pressure. 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 discharged for cooling and storage. DESCRIPTION OF THE FIGURES

[0028] 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:

[0029] - Fig. 1 is a schematic representation of a first embodiment of the invention.

[0030] - [Fig.2] is a schematic representation of a second embodiment of the invention.

[0031] - [Fig. 3] is a schematic representation of a third embodiment of the invention. DETAILED DESCRIPTION

[0032] 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 consists of a semi-continuous operation where the loaded and produced materials are fed into and recovered from the fluidized bed reactor in several cycles. The loaded materials contain metallic iron oxides, preferably pure, or with unavoidable impurities, such as nickel, manganese, copper, lead and cobalt, carbon and sulfates, or mixtures thereof. The iron oxide-loaded materials have an average size of 10 to 300 µm, and the iron fuel powders produced from the fluidized bed have an average size of 20 µm to 200 µm. The process works for a single fluidized bed unit or, preferably, for a multi-reactor system combined in alternating batch operation. This allows one unit to be shut down and drained while reduction continues in the others; then the next unit is shut down and drained while the first is in reduction mode. The process includes the following elements:

[0033] 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 a case where there is a set of modular multi-reactors with a common heating system and alternating batch operation. Indeed, since each reactor 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 the reactor.

[0034] Injection of 3c hydrogen under pressure of 1 bar to 15 bar into the fluidized bed reactor, the temperature of the reactor is maintained between 400 and 600 °C to avoid agglomeration of the iron particles produced.

[0035] Recovery of the partially spent reducing gas exiting the fluidized bed and recycling by injection with fresh hydrogen. This step is preceded by a filtration stage to remove entrained coarse particles or fine solids. The spent reducing gas is passed through a heat exchanger 12 connected by a link 11 to the reactor outlet, to recover heat and condense water for removal before mixing it with fresh hydrogen. The heat exchanger can be used to preheat the mixture of fresh and partially spent gas before its injection into the fluidized bed reactor.

[0036] The unconsumed hydrogen (line 3b) is reinjected into reactor 2 via line 3b and the condensed steam (line 13) is used to produce hydrogen later (or recycled for another purpose).

[0037] The partially spent reducing gas is continuously analyzed after prior removal of particles and water. Gas analysis 14 (optional) makes it possible to determine the evolution of the reduction rate and thus more precisely control the completion of the reduction of oxide-laden materials.

[0038] 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 fluidization velocity of the reducing gas of 5 to 200 cm / s.

[0039] At the end of each reduction cycle, the iron produced is dried directly in the fluidized bed using an inert gas or, preferably, the reducing gas hydrogen, under pressure or at atmospheric pressure, in order to accelerate drying by taking advantage of the heat already present (this step is preferably used in a set of reactors operating in alternating batches).

[0040] Transfer the iron produced by opening the hatch 7 (screw block 8 or suction or overpressure) and cool under inert gas during transport to a storage area 9. The iron can come into contact with the ambient air once sufficiently cooled.

[0041] In the case of pneumatic transport (under pressure or by suction) a cyclofilter 10 receives the flow of iron and lets the inert transport gas escape.

[0042] 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).

[0043] Closure of the hatch 7 and start of a new cycle where the new iron oxides are loaded into the fluidized bed 2 with recovery of hydrogen under reduction conditions under atmospheric pressure or at higher pressure.

[0044] Ancillary structures and variants (figures 2 and 3):

[0045] -The large particles transported by entrainment in the hydrogen and particle stream 11 is captured in a separator (of cyclonic type 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.

[0046] -Separating the fine particles from the gas coming from the fluidized bed with a separator 16

[0047] -hydrogen is compressed by 19 to reach 3, just like fresh hydrogen 3

[0048] -The hydrogen accidentally captured during the iron draining process is recovered and reinjected into 2 after being filtered

[0049] - The iron oxide powder 0 is preheated with 21 before its injection by heat recovery from either the condensation of water vapor 12, or from the exchanger which recovers heat from iron particles during its transfer (8), or by an electric furnace 21, or a combination.

[0050] -The hydrogen is preheated by recovering heat from either the exchanger 23 or the condensation of water vapor 12, or the exchanger which recovers heat from iron particles during its transfer (block 8), or by an electric furnace (block 22).

[0051] -The iron powder can be dried after the hatch is opened, or the iron falls by gravity into an enclosure where nitrogen is injected to dry the powder and then transport it while cooling it.

Claims

10 Demands

0.

Images