SOLID COMPOUND RAPID REDUCTION SYSTEMS AND METHODS

Abstract

Fully electrified microwave (MW) hydrogen (H2) plasma reduction systems and methods. With some embodiments, a plasma-flash ironmaking process is provided in which iron ore fines or particles are reduced.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims the benefit of the filing dates of U.S. Provisional Patent Application No. 63/339,715, filed May 9, 2022, and U.S. Provisional Patent Application No. 63/408,218, filed Sep. 20, 2022, the entire teachings of each of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to reduction of solid compounds. More particularly, it relates to systems and methods for rapid direct reduction of a compound, for example rapid direct reduction of iron ore.

Steel, one of the most important fabrication and construction materials, is one of the cornerstones of today's society. The iron and steel making industry is the largest industrial emitter of CO₂ directly responsible for 2.6 Gt CO₂ emissions per year. When including indirect emissions such as from the power sector, the total amount of CO₂ emissions attributable to the iron and steel sector rises to −10% of the total world-wide anthropogenic CO₂ emissions. Apart from scrap, steel is produced from iron ore (containing Fe₃O₄ or Fe₂O₃, or iron in oxide form, mixed with silicates and other minerals as mined). Iron ore reduction is the conversion of iron oxide minerals to metallic iron. In the US, 90% of the iron ore is processed by the integrated blast furnace reduction (BFR) and basic oxygen furnace (BOF) steel making route. The associated CO₂ emission of this process amounts to 1% CO₂ emission (55 Mt CO₂) in the US and 5% globally. Coke acts as energy source and reduction agent in BFR, producing large amounts of CO₂. As global steel production is forecast to rise at 0.3% per annum, disruptive technology changes in iron ore reduction are required to achieve the industry's CO₂ emission reduction targets.

Direct reduction of iron ore (DRI) is a promising alternative to BFR. Only 7% of the iron produced from iron ore stems from DRI. Direct reduction of iron is the removal of oxygen from iron ore in the solid state (e.g., without melting, as with the BFR approach). The state of the art industrially proven DRI process uses natural gas or a derivative as reductant and requires further processing in an electric arc furnace (EAF) to convert DRI into crude steel. While the current DRI-EAF route has 62% of the carbon footprint of traditional integrated BFR, it has a higher decarbonization potential. The HIsarna process (smelting reduction process with two directly coupled process stages in which the production of liquid pig iron takes place) represents another innovative approach utilizing DRI in molten state and reducing CO₂ emission up to 50% compared to BFR. Other suggested techniques entail molten oxide electrolysis and directly uses renewable electricity to reduce iron ores; while promising, several challenges remain such as dealing with the consequences of the copious amounts of oxygen released in the iron melt at the anode of the electrolysis process.

Over the past decades, large efforts have been devoted in developing innovative steel making processes. Significant efforts have been focused on plasma enabled iron making. The Bethlehem falling-film reactor (patented in 1979) uses an Argon-H₂ plasma arc to reduce melted iron ore flowing along a cylindrical reactor wall. Despite its high efficiency, it was not implemented by industry due to the difficulties in developing high-power plasma arc torches with sufficient lifetime. Hydrogen plasma smelting reduction (HPSR), using similar arc technology, was introduced in 1992 and a first pilot plant was recently built. It has the potential to reduce cost by 20% compared to BRF and enables a one step process from iron ore to crude steel but the reduction rate is significantly impacted by transport limitations and iron oxide conversion progress leading to a larger energy consumption when highly pure iron is the intended product.

The in-flight reduction of iron ore fines by H₂ developed by the University of Utah has emerged as a highly promising technology currently demonstrated in a large-scale bench reactor with a capacity of 10 kg/h. The process reduces iron ore particles less than 100 μm by H₂—CO mixtures at temperatures in excess of 1450 K in a few seconds. Reduction during these very short reactor residence times is enabled by very fast reduction reactions and is more efficient than the BFR. Nonetheless, particle sticking to the reactor walls likely due to the overheating and convection induced by the burner remains a hurdle for this technology.

To date, none of these potentially carbon-free approaches have been shown to be economically viable or established at scale.

SUMMARY

The inventors of the present disclosure recognizes that a need exists for reduction systems and methods, such as iron ore reduction systems and methods, which overcome one or more of the above-mentioned problems. Systems and methods for reduction of other solids compounds (e.g., metal oxides, metal sulfides, silicates, etc.) raise similar concerns. To date, none of the potentially carbon-free approaches have been shown to be economically viable or established at scale.

Some aspects of the present disclosure provide systems and methods for solid compound reduction, such as carbon-free iron ore reduction. Some systems and methods of the present disclosure include or incorporate a fully electrified microwave (MW) hydrogen (H₂)-containing plasma-flash ironmaking process in which fines or particles of the solid compound to be reduced (e.g., iron ore fines or particles) are processed. With the non-limiting examples of iron ore reduction, the direct use of iron ore fines bypasses pelletization/sintering and coke making steps in the conventional blast furnace process, and maximizes the iron oxide reduction rate by minimizing transport limitations of reactants and products to the iron oxide gas interface. The MW plasma serves three major purposes: 1) fully-electric bulk gas heating, 2) particle charging to overcome the sticking issues (e.g., a concern associated with flash ironmaking process, and 3) fast solid compound reduction (e.g., fast iron oxide reduction) enabled by highly dispersed solid compound particles at elevated temperatures in the presence of energetic species such as H radicals, vibrationally excited hydrogen, ions and electrons utilizing the entire plasma volume. Microwave plasma can operate at gas temperatures required for reduction of the solid compound fines with renewable H₂, eliminates the needs of carbon-based energy carriers, and negatively charges particles and reactor walls causing Coulombic confinement of particles to eliminate their sticking to the reactor walls.

In some non-limiting embodiments, the systems and methods of the present disclosure can be combined with subsequent smelting to become a cost-effective carbon free integrated process producing crude steel that will decarbonize the steel making industry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a reduction system in accordance with principles of the present disclosure;

FIG. 2 schematically illustrates another reduction system in accordance with principles of the present disclosure;

FIG. 3 schematically illustrates another reduction system in accordance with principles of the present disclosure;

FIG. 4 schematically illustrates a microwave plasma reduction system described in the Examples section;

FIG. 5 schematically illustrates a thermal reduction system using hot gas heated insides an electric furnace as described in the Examples section;

FIGS. 6-8B report results of testing to assess iron ore reduction using microwave plasma described in the Examples section;

FIG. 9A are SEM micrographs of an untreated and almost fully reduced iron ore samples described in the Examples section;

FIG. 9B is an energy dispersive X-ray spectrometry (EDS) elemental mapping of the sample of FIG. 9A;

FIG. 10 reports the results of testing to compare microwave plasma and thermal reduction described in the Examples section;

FIG. 11 reports the results of testing to assess mass scaling and energy efficiency on the reduction of magnetite particles described in the Examples section;

FIG. 12 schematically illustrates an in-flight microwave plasma iron ore reduction system described in the Examples section;

FIGS. 13A-13E report the in-flight reduction results for natural unrefined magnetite iron ore particles described in the Examples section;

FIG. 14 is a photograph of a hydrogen plasma running with iron ore particles described in the Examples section;

FIGS. 15A and 15B report the results of reduction testing of iron ore samples treated with different total flow rates described in the Examples section;

FIGS. 16A-16D report the results of reduction testing of differently-sized iron ore particles at a total flow rate of 6 standard liter per minute described in the Examples section;

FIG. 17 reports the results of reduction testing of natural magnetite particles described in the Examples section; and

FIGS. 18A and 18B report the results of testing for the reduction of cobalt sulfide using a hydrogen plasma effluent described in the Examples section.

DETAILED DESCRIPTION

Aspects of the present disclosure provide systems and methods for reducing solid compound materials using a hydrogen plasma effluent. The systems and methods of the present disclosure can be employed to reduce a wide range of solid compounds, including metal ores, metal oxides, metal sulfides, silicates, other natural unrefined solid particles, etc. While some explanations below discuss the direct, rapid reduction of iron ore, the present disclosure is in no way limited to iron ore reduction. Numerous other metal ores, metal oxides (e.g., cupric oxides, cobalt oxides, nickel oxides, etc.), sulfides (e.g., cobalt sulfides, nickel sulfides, etc.), silicates, etc., can be reduced using the systems and methods of the present disclosure. In other embodiments, the systems and methods of the present disclosure can be employed to transform micron-sized solid compound particles to nanometer-sized metal particles.

One embodiment of a reduction system 20 in accordance with principles of the present disclosure is shown in FIG. 1. The system 20 includes a supply unit 30 (referenced generally), a reactor chamber 32, a collection chamber 34, and a microwave energy unit 36 (referenced generally). Details on the various components are provided below. In general terms, the supply unit 30 generates and continuously delivers a supply stream 40 of particles of the solid compound to be reduces (e.g., iron ore particles) entrained in a gas containing hydrogen (H₂) and an optional background gas such as argon (Ar). The reactor chamber 32 is configured and arranged to facilitate interaction of energy generated by the microwave energy unit 36 with gas of the so-provided supply stream 40. This interaction generates hydrogen plasma in the reactor chamber 32 through which the entrained particles pass as they continuously flow through the reactor chamber 32. The hydrogen plasma effects reduction of the entrained particles (i.e., H₂ acts as the reducing agent), resulting in reduced particles (e.g., metallic iron particles where the system 20 is employed to reduce iron ore) and water (H₂O) that are received in the collection chamber 34. The collection chamber 34 is generally formatted to remove at least a majority of the water and retain or collect the reduced particles. Optionally, the collection chamber 34 can include or be connected to a condenser to remove a majority of the water to facilitate recirculation/re-use of unused H₂ at the collection chamber 34. The systems and methods of the present disclosure, and in particular the use of hydrogen plasma for solid compound reduction, can achieve, in some non-limiting examples, iron ore reduction in less than 0.1 second and do not directly generate CO₂ emissions. Along these same lines, the systems and methods of the present disclosure can be considered carbon-free when performed, for example, with renewable electricity and hydrogen produced by electrolysis with renewable electricity.

The supply unit 30 can assume various forms appropriate for entraining particles in a stream of hydrogen-containing gas. In some embodiments, the supply unit 30 includes a particle supply (or “Particle feeder”) 50, an H₂ (molecular hydrogen gas) source 52, and one or more optional background gas sources 54 (e.g., argon). Various lines 60, that include various flow control devices 62 such as valves, mass flow controllers, etc. (several of which are labeled in FIG. 1) as shown, fluidly connect the H₂ source 52 and the background gas source 54 to an inlet of the particles supply 50 and at which particles of the solid compound to be reduced are entrained into the gas flow. The particle-entrained gas flow exits from an outlet of the particle supply 50. A supply line 64 (labeled “Coaxial gas” in FIG. 1) is fluidly connected to the reactor chamber 32. The valves 62 are operable such the gas flow along the supply line 64 (and thus to the reactor chamber 32) may or may not include the supplied particles (e.g., the valves 62 can be operated such that a particle-entrained gas flow is delivered to the reactor chamber 32 via the supply line 64, to bypass the particle supply 50 and deliver gas flow consisting of only the gas of the background gas source 54 to the reactor chamber 32 via the supply line 64, etc.). In some embodiments, the entrainment unit 30 further includes an auxiliary line 66 (labeled “Swirl gas”) that fluidly connects one or both of the H₂ source 52 and the background gas source 54, via operation of the valves 62, to the reactor chamber 32 as described in greater detail below.

The particle supply 50 is generally configured to feed or provide a continuous supply of particles (of the solid compound to be reduced) into a container for entrainment into gas flow. With non-limiting examples directed to iron ore reduction, the systems and methods of the present disclosure can be useful for reducing iron ore in various forms as described below, such that the iron ore particles of the particle supply 50 can, in some embodiments, be mined iron ore particles or fines, mined iron ore that has been rendered into particle form, etc. For example, the iron ore particles can be or include Fe₃O₄ (magnetite), Fe₂O₃ (hematite), goethite, etc. An average particle size of the iron ore particles can be not greater than 100 microns in some embodiments, optionally not greater than 50 microns, optionally not greater than 10 microns. In other embodiments, the systems and methods of the present disclosure are highly beneficial and useful with iron ore particles having an average particle size in the range of 38-75 microns. Other iron ore particle, powder, or fine formats/sizes are also acceptable. With other solid compound reduction systems and methods of the present disclosure (e.g., systems and methods for reducing a metal oxide other than iron, metal sulfides, silicates, etc.), various particle sizes of the solid compound to be reduced can be employed. In some examples, the particles of the solid compound to be reduced can be nano-sized.

As mentioned above, the supply unit 30 is operable, via the valves 62, such that gas flow as delivered to/by the supply line 64 (either including particles from the supply 50 or bypassing the supply 50) and to/by the auxiliary line 76 can be the gas of the H₂ source 52 alone, the gas of the background gas source 54 alone, or a mixture of the gases of the H₂ source 52 and the background gas source 54 at a desired ratio (a desired argon:H₂ ratio). Examples of some operational parameters/ratios are described alone.

A gas of the H₂ source 52 can be less than 100 percent H₂ in some embodiments. For examples, the gas of the H₂ source 52 can be a mixture of a background gas (e.g., an inert background gas such as argon) and H₂, for example 50-98 percent argon and 2-50 percent H₂. In other embodiments, the gas of the H₂ source 52 can be a mixture of H₂ with gas(es) other than or in addition to argon.

A gas of the background gas source 54 can be 100 percent argon in some examples. Other gas compositions selected to ignite plasma formation in the presence of microwave energy, can also be employed.

The reactor chamber 32 can assume various forms appropriate for guiding the continuous supply stream 40 to interface with the microwave energy unit 36, contain plasma induced by the microwave energy, and direct reduced particles to the collection chamber 34. In some embodiments, the reactor chamber 32 can be or include a quartz tube, although other dielectric materials appropriate for passage of microwave energy and maintaining a structural integrity at expected operational plasm temperatures (e.g., on the order of 500-3000 Kelvin) are also acceptable. In some embodiments, the reactor chamber 32 can have an elongated shape, and defines an inlet side 80 opposite an outlet side 82. With these and related configurations, the reactor chamber 32 is arranged relative to the microwave energy unit 36 such that the inlet side 80 is above the outlet side 82. The supply stream 40 enters the reactor chamber 32 at the inlet side 80 and flows toward the outlet side 82, for example due to gas flow, gravity, etc. As shown, the supply line 64 is arranged relative to a shape of the reactor chamber 32 such that that a flow pattern of the supply stream 40 at the inlet side 80 is generally co-axial with a central axis of the reactor chamber 32. Where provided, the auxiliary line 66 is also connected to the inlet side 80. An arrangement of the auxiliary line 66 and/or a format of the reactor chamber 32 can be configured such that gas from the auxiliary line 66 has a swirl or helical flow pattern along the reactor chamber 32. For example, the reactor chamber 32 can have a tubular shape, with a port from the auxiliary line 66 arranged to be generally tangent to the circular cross-sectional shape of the reactor chamber 32, thus inducing a swirling flow pattern. Other constructions appropriate for generating a swirl flow are also acceptable. In yet other embodiments, the auxiliary line 66 can be omitted (e.g., gas flow to the inlet side 80 of the reactor chamber 32 is provided solely by the supply line 64). Regardless, and as described below, in some embodiments the reduction systems and methods of the present disclosure can be operated at normal or room atmospheric pressure (e.g., approximately 760 Torr), such that a pumping or vacuum system is not required with the reactor chamber 32.

The outlet side 82 of the reactor chamber 32 is open to the collection chamber 34. The collection chamber 34 can assume various forms conducive to collecting reduced particles and separating/exhausting byproduct water and gas. By way of non-limiting example, the collection chamber 34 can include a housing 90 maintaining a catch plate 92 formatted to capture/retain iron particles while permitting passage of water (or other reduction byproduct), such as a mesh with a pore size less than an expected particle size of the reduced iron particles. Water (or other byproduct) can be removed or exhausted from the housing 90 in various manners. In some examples, H₂, Ar (or other background gas) existing in the housing 90 can be extracted and recirculated to the supply unit 30 as appropriate.

The microwave energy unit 36 can assume various forms appropriate for generating and applying microwave energy sufficient to create microwave plasma at gas temperatures appropriate for reduction of iron ore particles with H₂ (e.g., on the order of 100 W-500 kW). Thus, for example, the microwave energy unit 36 can include one or more of a magnetron and circulator device 100, a directional coupler 102, and a waveguide 106, each of which can have format known to one of ordinary skill in the art. In some non-limiting examples, the waveguide 106 can have a surfaguide-type construction (e.g., a waveguide-based electromagnetic-surface-wave launcher that allows sustaining long plasma columns using microwaves). Other waveguide configurations for the waveguide 106 as understood by one of ordinary skill are also acceptable, and may or may not be directly implicated by the illustration of FIG. 1.

The system 20 can be operated in accordance with methods of the present disclosure to achieve rapid, carbon-free reduction of iron ore or other solid compounds in a hydrogen gas plasma. The supply unit 30 is operated to provide a continuous flow of the supply stream 40 of particles entrained in a gas containing hydrogen (H₂) and optionally the background gas (e.g., Ar) to the reactor chamber 32. Several of the particles (.e.g., iron ore particles) are shown in enlarged form in FIG. 1, and labeled at 110. In some embodiments, the gas of the supply stream 40 is a mixture of Ar and H₂, for example 50-98 percent argon and 2-50 percent H₂; in some embodiments, the gas of the particle-laden supply stream 40 (e.g., iron ore particle-laden supply stream) is 95 percent Ar and 5 percent H₂. Regardless, the microwave energy unit 36 is operated to generate hydrogen plasma (labeled at 112 in FIG. 1) in the reactor chamber 32. In some embodiments, plasma in the reactor chamber 32 can be initiated or ignited in various manners as would be apparent to one of ordinary skill. For example, pure background gas (e.g., pure argon) could be delivered to the reactor chamber 32 and ignited by microwave energy. Other modes of ignition are also acceptable, for example (but not limited to) igniting a mixture of background gas (e.g., argon) and H₂, igniting the background gas/H₂ carrying particles, rod ignition, etc. Once ignited, a continuous flow of the supply stream 40 of particles entrained in a gas containing hydrogen (H₂) as described above is delivered to the reactor chamber 32; the so-provided H₂ interacts with the previously-ignited plasma to generate the hydrogen plasma 112. The hydrogen plasma 112 produces excited hydrogen species (H atoms, H ions, vibrationally excited H₂). The hydrogen plasma 112 can operate at gas temperatures in excess of 1623 K, the temperature above which magnetite concentrate particles melt for example. As they travel from the inlet side 80 to the outlet side 82, the particles 110 are effectively injected into and carried through the hydrogen plasma 112. The hydrogen plasma 112 serves as a reducing agent, treating all surfaces of the particles 110 while they are in flight through the plasma 112. The particles 110 thus experience reduction, and are converted to reduced particles (e.g., iron ore particles are reduced to metallic iron particles) several of which are shown in enlarged form in FIG. 1 and labeled at 114. The reduced particles 114 travel to and are collected in the collection chamber 34. Water (and perhaps other byproducts) are removed or exhausted from the collection chamber 34. In some embodiments, the supply stream 40 has a flow pattern at the inlet side 80 that is coaxial with the central axis of the reactor chamber 32. With these and other embodiments, a secondary flow of gas is provided to the inlet side 80 via the auxiliary line 66 simultaneously with the coaxial supply stream 40. The secondary gas flow can be 100 percent argon (or other inert background gas) or a mixture of the inert background gas and H₂ (e.g., 95 percent argon, 5 percent H₂). Regardless, the secondary flow (or “swirl gas”) establishes a swirling flow pattern along the reactor chamber 32 that can stabilize the hydrogen plasma 112. The swirl gas can serve to reduce the heat load to the reactor chamber 32, and may assist in preventing particles from sticking to walls of the reactor chamber 32.

The particles 110 are continuously delivered to the reactor chamber 32 and continuously pass through the hydrogen plasma 112. Thus, the solid compound particle reduction process can operate on an effectively continuous basis. Moreover, the particles 110 pass through an entirety of the hydrogen plasma 112 (thus avoiding potentially excessive energy losses). In some non-limiting embodiments, an extent of the hydrogen plasma 112 is formatted such that the systems and methods of the present disclosure can achieve iron ore particle (e.g., micron or submicron) reduction (e.g., at least 70 percent reduction, alternatively at least 90 percent reduction, alternatively on the order of 95 percent reduction) in less than 1.0 second, alternatively less than 0.5 seconds, and in some embodiments less than 0.1 seconds. The fast iron oxide reduction of the present disclosure can be enabled by highly dispersed iron oxide particles at elevated temperatures utilizing the entire plasma volume. The hydrogen plasma 112 can maximize the iron oxide reduction rate by minimizing transport limitations of reactants and products to the iron oxide gas interface. Similar results can be provided for the reduction of other solid compounds, including metal oxides, metal sulfides, silicates, etc.

With some systems and methods of the present disclosure, for example the system 20 and the methods as described above, the hydrogen plasma 112 is generated and maintained at normal atmospheric pressure (e.g., approximately 760 Torr), and thus do not need or incorporate (and avoid the costs of) a vacuum or pumping systems that are otherwise required by low pressure (less than 10 Torr) microwave plasma designs. In other embodiments of the present disclosure, a reduced pressure (e.g., 1-100 Torr) can be employed (with the corresponding systems incorporating or including appropriate components or devices for establishing a lower pressure within the reactor chamber 32).

In addition to effecting solid compound (e.g., iron oxide) reduction with H₂ as the reducing agent, the plasma process charges particles negatively while in flight. Thus, the plasma 112 negatively charges the wall(s) of the reactor chamber 32 causing Coulombic confinement of particles to eliminate their sticking to the reactor walls. As a result, particles are repelled from the reactor chamber walls and do not stick to the walls, which is a common problem in thermal approaches.

Another reduction system 220 in accordance with principles of the present disclosure is shown in FIG. 2. The system 220 can be similar to the system 20 described above, and includes a supply unit 230 (referenced generally), a reactor chamber 232, a collection chamber 234, and a microwave energy unit 236 (referenced generally). The system 220 can be operated, for example, to perform the iron oxide particle reduction methods of the present disclosure as described above, as well as the reduction of other solid compounds such as other metal oxides, metal sulfides, silicates, etc. As compared to the system 20, the system 220 can heat the H₂ (and/or other inert background gases such as Ar, if utilized) prior to delivery to the collection chamber 234, and the secondary, swirl flow need not be generated. As implicated by FIG. 2, in some embodiments, the system 220 can recycle/recirculate H₂ and argon (or other inert background gas), and can utilize heat recovered from the microwave energy unit 236 to heat the H₂.

Another reduction system 320 in accordance with principles of the present disclosure is shown in FIG. 3. The system 320 can be similar to the systems 20, 220 described above and includes a supply unit 330, a reactor chamber 332, a collection chamber 334, and a microwave energy unit 336 (referenced generally). In general terms, and as with other embodiments, the supply unit 330 delivers a gas containing hydrogen (H₂) and optionally the background gas (e.g., Ar) to the reactor chamber 332. The microwave energy unit 336 operates to generate hydrogen plasma (labeled at 340) in the reactor chamber 332. In some non-limiting examples, the microwave energy unit can include a magnetron, a cyclotron, and a power supply that operates to generate microwaves when are then directed using a waveguide. The reaction chamber 332 (e.g., a quartz tube) runs transversely to the waveguide and allows microwave energy to interact with the flow. In some embodiments, owing to the high microwave energy density in the overlapping section of the waveguide and quartz tube, plasma can be ignited using, for example, a sharp tungsten tip. The plasma heats the gas and creates reactive species such as dissociated hydrogen atoms.

As compared to the systems 20, 220, operation of the system 320 does not entail passing particles 350 through the plasma 340 (e.g., the supply unit 330 does not include a supply of particles). Instead, the to-be-reduced particles 350 are positioned on a catch plate 360 (e.g., a mesh-type body such as a 400 mesh body) downstream of the plasma 340 where they are treated by the plasma species. The catch plate 360 (e.g., mesh) allows the flow to pass through the particles 350 effectively. The plasma effluent carrying hot, excited hydrogen atoms and molecules react with the particles to produce reduced particles (e.g., the plasma effluent reacts with iron ore particles to produce iron).

The particles 350 can be provided to the catch plate 360, and reduced particles removed from the catch plate 360, in various fashions. For example, a mechanism that facilitates continuous supply and removal can be provided, such as, for example, a rotating cylinder, a rotating disk, a conveyor belt, etc. Alternatively or in addition, the particles 350 can be delivered suspended in a gas flow (similar to other embodiments in which the particles are passed through the plasma) or delivered in a batch approach, such as, for example, a fluidized bed approach.

Other reduction systems of the present disclosure can be akin a combination of the systems 20, 220, 320, configured to deliver particles entrained in the gas stream as delivered to the reactor chamber (e.g., the systems of FIGS. 1 and 2) and to place particles either in the plasma or somewhere further downstream (e.g., the system of FIG. 3).

EXAMPLES

Embodiments and advantages of features of the present disclosure are further illustrated by the following non-limiting examples. The particular materials and amounts thereof recited in these examples, as well as operating conditions and details, should not be construed to unduly limit the scope of the present disclosure.

Example 1

To assess the systems and methods of the present disclosure in effecting iron ore reduction using the microwave (MW) plasma, testing was preformed to compare two different methods: i) an atmospheric pressure MW plasma and ii) a thermal reduction process using the same argon-hydrogen gas mixture, heated inside an electric furnace. With Example 1, iron ore particles were placed steadily on a mesh for a specific distance away from plasma center. FIG. 4 shows a detailed schematic of the reactor used for the MW plasma-based reduction. A magnetron was used to generate microwaves at 2.45 GHz, which were then directed through a circulator into a waveguide. The MW power was measured using a directional coupler and power meter (Anritsu ML2438a). The forward power was set to 1.8 kW, while the reflected power varied only slightly between 120 W and 160 W depending on the discharge conditions. Thus, the net discharge power was about 1.7 kW in all experiments reported under Example 1.

The plasma source used was a surfaguide with a tapered waveguide designed to intensify the electric field and enable an easier ignition at atmospheric pressure. A quartz tube with a 22 millimeter (mm) inner diameter crossed through a hole in the tapered waveguide allowed the microwaves to interact with the gas flow. An argon-hydrogen gas mixture (90:10 volume %) entered the quartz tube from the top at flow rates between 20 standard liter per minute (slm) and 45 slm. A small part of the gas flow entered the quartz tube in the axial direction (5 slm) while the rest was injected tangentially through two side ports at the inlet to create a swirl flow that stabilized the plasma and reduced the heat flux to the walls. The plasma was ignited using a sharp tungsten tip that was inserted into the reactor from the bottom and removed after ignition.

The plasma heats the gas and plasma electrons create reactive hydrogen atoms, ions, and vibrationally excited molecules which are carried along the gas flow. This plasma effluent was then directed onto iron ore particles resting on a stainless steel mesh (400 mesh, hole size of 37 μm), placed below the plasma at a distance of 185 mm from the top of the waveguide. The mesh allowed the flow to pass through the iron ore powder, enabling efficient interaction between particles and gas. The distance between the visible plasma edge and the particles was estimated to be about 140 mm. The iron ore particles used in this study were magnetite with an average size <5 microns (μm), purchased from Millipore Sigma with product number: 310069.

The sample treatment was performed by first igniting the plasma at 5 slm pure argon gas flow and 1.4 kW MW power. Low flow rates, low input MW power, and less efficient coupling of MW power to argon flow reduced early particle heating before the hydrogen plasma treatment starts. Consequently, the temperature during this first step was only about 440 K. Next, gas flow and MW power were increased to the desired values, while still flowing pure argon, increasing the temperature to about 600 K. The gas flow was then quickly switched to the argon-hydrogen mixture, starting the reduction process. After the desired treatment time, the gas flow was switched back to pure argon and the plasma terminated. A cooling argon gas flow was maintained for a few seconds, to cool the particles below the temperature at which a possible re-oxidation might occur when exposed to air.

To facilitate a comparison between the MW plasma reduction and a purely thermal hydrogen reduction, the setup shown in FIG. 5 was used. It consisted of an electric furnace (Thermo Scientific Lindberg/Blue M STF55346C) with a steel tube of 35 mm inner diameter passing through the heating zone. The same argon-hydrogen (90:10 volume %) gas mixture was used as in the MW plasma reduction, flowing at a rate of 35 slm. Crumpled-up stainless steel mesh was placed in the path of the gas before it interacted with the iron ore particles to enhance the heat transfer. A mass of 10 mg of iron ore particles were placed inside a cup formed from the stainless steel mesh and attached to a push rod. The push rod allowed the introduction of particles into the furnace once the desired temperature was achieved.

To perform the reduction, initially, pure argon was flowed through the tube while introducing particles into the furnace. Once the particles reached the desired position in the middle of the furnace, the flow was switched to the argon-hydrogen mixture. After the desired treatment time was achieved, the flow was switched back to pure argon, thus terminating the reduction process. The particles were then pulled out of the furnace heating zone. The main flow was turned off and a cooling flow of pure argon, not passing the heating zone of the furnace, was used to lower the particle temperature to prevent a possible re-oxidation upon air exposure. Gas temperatures during the reduction process were varied between 1200 K and 1350 K to explore the temperature dependence of the reduction.

Treated samples were characterized through X-ray diffraction (XRD). Each sample was crushed and mixed thoroughly to form a homogeneous mixture prior to the analysis. The sample was characterized at multiple locations and an average pattern was analyzed using the Reference Intensity Ratio (RIR) method to calculate the reduction percentage and weight percentage of different phases present in the sample. RIR is an instrument independent constant, specific to the material and the reference material, used in XRD for quantitative phase analysis. The weight percentages of different phases are calculated using the following Equation 1:

$\begin{array}{cc}{X}_{\alpha }=\frac{I_{\alpha }}{{\mathrm{RIR}}_{\alpha }}{\left(\sum _{j=1}\frac{I_j}{{\mathrm{RIR}}_j}\right)}^{-1}& \mathrm{Eq}.\left(1\right)\end{array}$

where X_α is the weight percent of the phase α and I_α stands for the integrated intensity of the strongest line of phase α. The index j denotes all other phases of the mixture. RIR_α is defined as RIR_α=I_α/I_c, i. e. the ratio of the intensity of the strongest peak of the phase α to the strongest peak of the reference material corundum for a 1:1 mixture by weight. The RIR values of magnetite, wüstite, and metallic iron are 5.22, 5.29, and 11.91, respectively. After calculating the weight percentage X_α for each phase, the reduction percentage is calculated as

$\begin{array}{cc}\mathrm{Reduction}\%=100\frac{\mathrm{mass}\mathrm{of}\mathrm{oxygen}\mathrm{removed}}{\mathrm{mass}\mathrm{of}\mathrm{oxygen}\mathrm{in}\mathrm{the}\mathrm{sample}\mathrm{initially}}& \mathrm{Eq}.\left(2\right)\end{array}$

The Powder Diffraction Files (PDF) used were #98-000-0294 (magnetite), #98-001-3836 (wüstite), and #98-000-0259 (metallic iron)

Initially, 10 milligram (mg) of magnetite particles were treated with the MW plasma, using different treatment times to study the reduction kinetics. The total gas flow was 45 slm while the treatment time was varied between 2 seconds (s) and 8 s. FIG. 6 shows the XRD pattern of the samples, highlighting the different peaks belonging to Fe₃O₄ (magnetite), FeO (wüstite) and Fe (iron). As a point of reference, in the plot of FIG. 6, the vertical lines indicate peaks belonging to the different iron oxide phases and pure iron. For the untreated control sample, Fe₃O₄ peaks were exclusively observed, confirming the composition of our iron ore samples. For a treatment time of 2 s, strong FeO and Fe peaks become apparent, demonstrating partial reduction. As the treatment time increases, the FeO peak decreases in its intensity whereas the Fe peak grows, indicating increasing reduction.

This trend is shown more clearly by FIG. 7A which shows the weight percentage of the different phases of the 10 mg magnetite particles treated with the plasma for different times at a gas flow rate of 45 slm, calculated from the analysis of FIG. 6. Already after 2 s, the iron ore is mostly reduced to FeO, with further treatment time being necessary to facilitate the reduction from FeO to pure Fe. This result confirms the reduction pathway of Fe₃O₄→FeO→Fe, in agreement with the reduction of Fe₃O₄ at temperatures above 840K. After 8 s treatment the sample is 97% Fe by weight.

FIG. 7B shows the overall reduction percentage (weight or atomic percentage of oxygen removed) for the different treatment times together with the particle temperatures measured during the trials. As a point of reference, the information of FIG. 7B reports the percentage reduction of the 10 mg magnetite particles treated with the plasma for different times at a gas flow rate of 45 slm. The particle temperature was almost constant at around 1300 K for all treatment times. Thus, the temperature of the particles likely reached a steady state during the experiment, which is the same for all treatment times. For the 6 s treatment times, the trials were performed three times to allow for an error estimation. The data point shown in FIG. 7B is the mean of these trials, while the error bars indicate ±2 standard error of the mean.

The reduction already reached about 30% after only 2 s treatment time, while nearly complete reduction is reached after 8 s. This reduction speed is comparable to the thermal reduction reported by Choi et al., “Development of green suspension ironmaking technology based on hydrogen reduction of iron oxide concentrate: rate measurements.” Ironmaking & Steelmaking 37, 81-88, who reduced 30 μm magnetite particles suspended in hot hydrogen at 1370 K.

A more detailed comparison with prior research is presented below. FIGS. 8A and 8B demonstrate the effect of the gas flow rate on the reduction process and particle temperature at a constant treatment time of 6 s. In the data of FIG. 8B, selected data points were replicated three times to allow for an error estimation; the error bars indicate ±2 standard error of mean. FIG. 8B shows only partial reduction to FeO for low flow rates of 20 slm, while higher flow rates show much stronger reduction peaking around 85% for 35 slm and then slightly reducing again for larger flows. This trend can be understood to reflect the transport of both heat as well as reactive species from the plasma toward the mesh. Increasing the gas flow will speed up the gas velocity, allowing reactive species like atomic hydrogen to reach the particles before recombining to molecules. An increased gas flow will also result in a higher gas temperature at the particle position, since faster heat transport minimizes the losses to the cool reactor walls. Correspondingly, the particle temperature, shown in FIG. 8B increases with the gas flow to about 1350K at 30 slm. Even larger gas flows then lower the temperature, presumably because these high gas flows now begin to lower the temperature inside the plasma, as the energy input per gas molecule is lowered. These two competing processes cause the peak in particle temperature and reduction between 30 slm to 35 slm.

FIG. 9A shows a representative SEM (scanning electron microscopy) image of an untreated (before) and an almost fully reduced sample (after), obtained after a treatment time of 8 s at a gas flow rate of 45 slm. The untreated iron ore samples are composed of aggregates, formed from small grains, ranging from hundreds of nm to several μm. Upon reduction, they undergo a large morphological change. The reduced sample shown in FIG. 9A is highly porous with whisker-like structures. The formation of whiskers is a common phenomenon observed when reducing iron ore with hydrogen. Thus, the hydrogen plasma effluent treatment is observed to cause the same morphological changes as observed with hot hydrogen gas.

FIG. 9B shows the EDS (energy dispersive X-ray spectrometry) elemental mapping of the sample performed with SEM (an EDS elemental mapping of the 97% reduced sample, obtained after a treatment time of 8 s at a gas flow rate of 45 slm). The elemental mapping shows the particle surface to consist almost entirely of Fe. Notably, only very little remaining oxygen can be observed in the image, corresponding to an atomic percentage of 1.9%. This confirms the XRD results which indicate a weight percentage of 97% iron for the above-mentioned sample.

To investigate the influence of reactive plasma species, the MW plasma reduction was compared to a fully thermal reduction. Samples of 10 mg of particles were treated at different temperature with hot argon-hydrogen (90:10) flowing at 35 slm for varying times from 8 s to 60 s and their reduction measured with XRD. The results of this study are shown in FIG. 10, together with the MW plasma reduction, performed at a gas flow rate of 35 slm. More particularly, the plot of FIG. 10 reflects iron ore reduction using a hot argon-hydrogen (90:10 volume %) gas mixture inside the electric furnace at gas temperatures of 1200K, 1275K and 1350K; for comparison, FIG. 10 also shows the plasma-based reduction at 35 slm gas flow, with particles reaching a temperature of 1350K.

For all treatment conditions shown in FIG. 10, the measured reduction increases with treatment time, as expected. For the three thermal reductions performed in the furnace, the speed of reduction increases with temperature. Interpolating between the data points, it was observed that it takes about 50 s to reach 95% reduction for 1200 K. For 1275 K and 1350 K, this level of reduction is already reached after about 35 s and 30 s, respectively.

For the initial 70% reduction, the reduction rate (weight % of oxygen removed per second) is almost constant, as can be deduced from the linear trend visible in FIG. 10. For the furnace trials at 1200 K, 1275 K, and 1350 K, values of around 2.2, 3 and 5%/s, respectively, were found. The increase in reduction rate is expected due to the higher reaction and diffusion rates at higher temperatures. The apparent activation energy for the furnace trials is estimated to be around 70 kJ/mol. In comparison, the plasma-based process has a relative reduction rate of 15%/s, about three times higher than the purely thermal reduction performed at the same temperature. This speed advantage becomes even more pronounced if the time needed to reach 95% reduction is instead considered. Since the thermal reduction performed in the electric furnace slows down at higher reduction percentages, the plasma is about four times faster in reaching 95% reduction, needing only 8 s instead of 30 s needed for the thermal reduction. Assuming a 3 times faster reduction with plasma and the same reaction kinetics law for furnace and plasma reduction, the apparent activation energy for plasma trial can be estimated as 60 kJ/mol, indicating a 15% decrease in activation energy due to plasma species such as atomic hydrogen.

Having demonstrated that hydrogen plasma can rapidly reduce small amounts of iron ore, the impact of increasing mass load on the reduction of magnetite particles was assessed. To this end, the MW plasma reduction was conducted with 10 mg, 100 mg, and 500 mg of magnetite particles placed on the mesh. FIG. 11 shows the reduction of particles as a function of the treatment time at three different mass loads and a constant gas flow rate of 35 slm. The particle temperature reduced slightly with increasing treatment time, but did otherwise not vary significantly for the different mass loads and was always between 1350K and 1270K.

The time needed to reduce the magnetite particles increases with the mass load. The 10 mg sample needed only 6 s to reach a reduction above 90%, while 20 s and 40 s were needed for the 100 mg and 500 mg samples, respectively. The increased reduction time at higher mass load seems to be caused by hydrogen transport limitations to the particles positioned at the bottom of the particle pile. At a mass load of 10 mg, particles form only a few layers on top of the mesh, whereas at 100 mg and 500 mg, the particle pile reaches a depth of up to 1 mm and 4 mm, respectively. Consequently, at higher mass loads the top of the particle pile was observed to be reduced first, with particles located at the bottom only showing evidence of reduction after much longer treatment times. This is indicated by the color change of the material from initially black towards metallic silver after reduction. For the 500 mg sample and a treatment time of 20 s, samples from the top and the bottom of the pile we collected to confirm this finding with XRD analysis, which revealed that the particles collected from the top of the pile were 65% reduced whereas the bottom particle showed only 6% reduction. It should be noted that the results shown in FIG. 11 were obtained after thoroughly mixing the samples after the treatment, thus showing average reduction values.

As FIG. 11 demonstrates, increasing the mass load 10 and 50 times, increases the required time for reduction only by about a factor of 4 and 7, respectively. This indicates an improvement in energy efficiency for 500 mg trials versus 10 mg trials by about an order of magnitude. The reduction of 500 mg of magnetite to 92% Fe within 40 s corresponds to an electrical energy consumption of about 170 GJ/t of Fe produced. In comparison, the energy consumption of conventional ironmaking, including blast furnace, coking, and pelletization, is around 16 GJ/t of Fe. Thus, the lab-scale MW plasma of the Examples section consumes about 10 times more energy than the conventional process, when only considering the electrical power needed for the reduction. However, achieving the gas temperature just above the mesh of 1350K requires only a heating power of about 600 W, of the totally supplied 1700 W. Thus, about 65% of the energy is lost to the reactor walls. If this energy loss is avoided, the setup has the potential to achieve an energy consumption of about 60 GJ/t of Fe produced, only 4 times more than the conventional route. A system recovering the heat lost as the hot gas exits the reactor can further improve the energy efficiency of the process. Given the favorable increase in treatment time with mass load, demonstrated in FIG. 11, even higher mass loads might lead to better energy efficiencies.

Example 2

FIG. 12 shows a detailed schematic of the reactor used for the in-flight MW plasma-based reduction of Example 2, and which shares many similarities with the previous section. However, instead of placing iron ore particles on a mesh several inches after the plasma, the particles are now introduced into the reactor via gas flow. To enable in-flight injection, the Ar:H₂ mixture flows through a particle feeder that contains iron ore (Fe₃O₄) particles, which the gas flow carries into the system. The solid/gas mixture is then injected into the center of the plasma reactor as the coaxial gas. To achieve stable particle feeding, a vibration motor (DIANN 12000 rpm) is attached to the bottom of the particle feeder. The swirl gas remains the same as the Ar:H₂ mixture. The hydrogen plasma then in-flight reduces the particles, which are collected by a cotton filter far from the plasma to avoid steady reduction. The plasma was ignited with the forward power set to 1.5 kW, while the reflected power varied only slightly around 100 W. Thus, the net discharge power was about 1.4 kW in all experiments reported in this section.

With the experiments of Example 2, natural unrefined magnetite iron ore particles with an average size of 400-500 mesh (25-37 μm) were used. The particles were purchased from Alpha Chemical under the product name “Black Iron Oxide—Natural,” with a Fe₃O₄ content of 94% and impurities such as SiO₂, MgO, Ca, etc. The particles were sieved using a 200-mesh sieve and a 400-mesh sieve to obtain particles <38 μm and 38-75 μm in size for further analysis.

After the reduction process, the cotton filter containing the collected reduced particles was submerged in a vial filled with methanol. To extract the particles, the solution was sonicated for 3 minutes to dislodge the reduced particles from the filter into the solution. The solution was then transferred to a different vial without the filter. A Schlenk line system was used to condense the solution, which was subsequently drop-cast onto a substrate, with further evaporation of methanol, leaving the particles behind for XRD analysis, or onto a Cu grid for TEM analysis.

The initial study utilized <38 μm magnetite particles with a total flow rate of 6 slm, and various aspects of which are provided in FIGS. 13A-13E. FIG. 13A displays the XRD pattern for magnetite particles treated in-flight with and without plasma. The vertical lines indicate peaks belonging to the different iron oxide phases and pure iron. In the absence of plasma, the particles were first injected into the reactor and collected by the filter without plasma activation for 1 minute. Then, the hydrogen plasma was activated for 1 minute to steadily reduce the particles. Since the filter was located far away from the plasma, the temperature on the filter was only slightly elevated to 28° C., a few degrees higher than the ambient temperature of 24° C. As a result, the particles were not reduced and exhibited only magnetite peaks in the XRD pattern. When the hydrogen plasma was activated to reduce the particles in-flight, however, the reduced particles exhibited only metallic iron peak in the XRD pattern. This indicates that the hydrogen plasma successfully reduced the magnetite particles in-flight, resulting in 100% metallic iron particle collection by the filter, as shown in FIG. 13B (that otherwise summarizes the composition of the samples treated with and without plasma), under a total flow rate of 6 slm.

A representative TEM image of reduced particles is provided in FIG. 13C and shows that the reduced particles have a spherical shape and a clear lattice pattern. The measured d-spacing of around 2.02 Å aligns with the d-spacing value of (110) plane on PDF #98-000-0259, indicating the formation of metallic iron particles. By counting 300 nanoparticles, the size distribution of the reduced particles was obtained and is shown in FIG. 13D. The histogram was fitted with a log-normal distribution, and the mean size of the reduced particles was found to be around 15 nm, with a geometric standard deviation of 1.39. In contrast, Error! Reference source not found. FIG. 13E shows an SEM image of <38 μm magnetite particles without plasma treatment, which have a random shape and size ranging from several μm to several tens of μm.

The inventors of the present disclosure have surmised that two explanations are plausible explanations for the observed changes in particle size and shape during in-flight reducing by the hydrogen plasma. The first is that the magnetite particles were fragmented into smaller pieces during the reduction process, which were then reduced to metallic iron particles. The second is that the magnetite particles were fully vaporized and then reacted with the reactive hydrogen species to form iron atoms, which then grew into nanoparticles. Both mechanisms are possible and may have contributed to the observed changes in particle size and shape.

FIG. 14 provides a picture the hydrogen plasma running with particles taken with the aid of a high-speed camera. The camera operated at 1000 fps with an exposure time of 0.993 ms. The velocity of a single particle was computed by dividing the length of its trace by the exposure time. The particles that traveled through the center of the reactor, approximately 4 cm downstream of the waveguide center, directly after the shielding cylinder, exhibited a velocity of roughly 3.5 m/s. The plasma length was approximately 15 cm, implying that a magnetite particle passing through the hydrogen plasma had a residence time of only around 40 ms. This is over 100 times faster than the previously reported flash in-flight iron ore reduction by thermal hydrogen.

FIGS. 15A and 15B show the flow study for <38 μm magnetite particles with different total flow rates, 6 slm, 9 slm and 12 slm. The XRD pattern (FIG. 15A) of the samples, highlighting the different peaks belonging to Fe₃O₄ (magnetite), FeO (wüstite) and Fe (iron). For a total flow rate of 6 slm, exclusive metallic iron peak was observed. As the total flow rate increases, both the FeO peaks and Fe₃O₄ and appear and increase with higher total flow rate, indicating decreasing reduction. FIG. 15B (that otherwise reports the composition and percentage reduction, respectively, of the samples treated with different total flow rates, 6 slm, 9 slm, and 12 slm) shows the weight percentage of the different phases and the overall reduction percentage, calculated from the analysis of FIG. 15A via RIR analysis. It is shown that the weight percentage of metallic iron drops from 100% with total flow rate of 6 slm to 67% and 54% with total flow rate of 9 slm and 12 slm, respectively. The overall reduction percentage also decreased to 72% and 60% with total flow rates of 9 slm and 12 slm, respectively. This is due to the shorter residence time of particles traveling through the plasma and lower temperature at higher total flow rates.

Various size study experiments were performed, the results of which are generally reported in FIGS. 16A-16D. For example, a size study was performed with a total flow rate of 6 slm for feeding <38 μm and 38-75 μm. Comparing with the 100% metallic iron peak for feeding <38 μm particles, the XRD patterns show that feeding larger particles 38-75 μm shows a dominant metallic iron peak associated with tiny wüstite and magnetite peaks, shown in FIG. 16A. FIG. 16B shows the composition and percentage reduction, respectively, of the samples started with different feeding particle size of magnetite particles. Feeding larger particles results in 85% of the metallic iron while 11% wüstite and around 4% magnetite, which exhibits 87% of the percentage reduction. FIG. 16C compares the size distribution for feeding different sizes of particles. Feeding 38-75 μm particles results in the size distribution of reduced particles being around 19 nm, with a geometric standard deviation of 1.47, which shows a larger mean size comparing with feeding smaller <38 μm particles. Moreover, reduced particles with their size ranging from 50 nm to 100 nm were found for feeding 38-75 μm particles, as shown in FIG. 16D, while the larger reduced particles were not found for feeding <38 μm particle.

A size study was conducted with a total flow rate of 6 slm using magnetite particles of two different sizes, <38 μm and 38-75 μm. The XRD patterns in FIG. 16A show that feeding larger particles (38-75 μm) resulted in a dominant metallic iron peak, accompanied by small wüstite and magnetite peaks, whereas feeding smaller particles (<38 μm) showed a 100% metallic iron peak. The composition and percentage reduction of the samples are shown in FIG. 16B, which reveals that feeding larger particles resulted in 85% metallic iron, 11% wüstite, and 4% magnetite, with an overall reduction percentage of 87%.

The size distribution of the reduced particles was around 19 nm, with a geometric standard deviation of 1.47, as shown in FIG. 16C. The TEM image of FIG. 16D shows reduced particles for feeding 38-75 μm particles also included particles ranging from 50 nm to 100 nm, which were hardly observed for feeding <38 μm particles.

Experiments were conducted using natural magnetite particles without sieving, which contains a wide range of particles size, to simulate a more practical scenario. A filter was placed right after the reactor vertically to collect all the particles. FIG. 17 is an obtained XRD pattern for reduction of natural magnetite particles with a total flow rate of 6 slm (with the inside bars showing the composition of the sample). The XRD pattern in FIG. 17 shows the strongest peak for metallic iron, with weaker peaks for wüstite and magnetite. The weight percentage for metallic iron, wüstite, and magnetite are 68%, 17%, and 16%, respectively, with an overall reduction percentage of 71%.

Example 3

Testing was performed to confirm reduction of cobalt sulfide via the systems and methods of the present disclosure (e.g., using a hydrogen plasma effluent). A bench-type system akin to the arrangement of FIG. 3. A magnetron was used to generate microwaves at 2.45 GHz, which were then directed through a circulator into a waveguide. The microwave power in this study was fixed at 1.5 kW forward power, with 100 W reflected power being observed on the power meter, yielding a net power of 1.4 kW. A quartz tube, through which hydrogen-argon mixture flows, runs transversely to the waveguide to allow the microwaves to interact with the gas flow. Owing to the high microwave energy density in the overlapping section of the waveguide and quartz tube, plasma can be ignited using a sharp tungsten tip. The plasma heats the gas and creates reactive species like dissociated hydrogen atoms. This plasma effluent is then directed to the cobalt sulfide particles resting on a 400 mesh. The mesh allows the flow to pass through the particles effectively. The plasma effluent carrying hot, excited hydrogen atoms and molecules reacted with the cobalt sulfide particles to produce metallic cobalt.

A 10% H₂-90% Ar gas mixture was used as the reducing gas. The distance of the mesh from the waveguide top was fixed at d=330 mm (13 inch). High-purity cobalt sulfide powder was sieved to a particle size between 38 μm and 75 μm. 10 mg of the particles were then placed on the mesh and treated with the plasma. The treatment time was varied between 1 minute and 10 minutes.

The reduced particles were analyzed using X-ray diffraction (XRD) to calculate the reduction percentage and weight % of different phases present in the samples. FIGS. 18A and 18B show the XRD results for the original, untreated sample as well as for the treated samples after different treatment times. In particular, FIG. 18A shows the XRD pattern while FIG. 18B shows the weight percentage of the different identified phases of cobalt sulfide. The untreated sample was identified to be pure CoS₂. Already after a 1 minute of plasma treatment, the sample was fully converted to Co₉S₈, with minor traces of metallic cobalt visible in the sample. This corresponds to a reduction percentage of almost 60%. The subsequent reduction from Co₉S₈ to metallic Co was found to require considerably longer treatment times. Nevertheless, 90% metallic cobalt was obtained after 10 minutes, corresponding to a reduction percentage of 95%. The fully electrified microwave plasma was used to heat the gas and produce reactive species, and was demonstrated to be able to reduce a 10 mg sample of cobalt sulfide to cobalt within 10 minutes.

The reduction systems and methods of the present disclosure provide a marked improvement over previous designs. In some non-limiting examples, microwave plasma-flash iron reduction up to 95% is possible with the systems and methods of the present disclosure solely based on gas heating and enhancement of the reduction rate by plasma specific reactions is available. Rapid reduction of other metal ores is equally available with the systems and methods of the present disclosure. In other non-limiting examples, the systems and methods of the present disclosure can reduce metal sulfides using a hydrogen plasma. Microwave plasma operates at moderate electron energies <2.5 eV for which more than 90% of the plasma energy is channeled into gas heating. The energy efficiency is thus, as in a thermal chemical reactor, critically dependent on reducing heat loss or reusing sensible heat for pre-heating of inlet gases or possibly additional heating for smelting vessel that collects reduced iron particles. The latter will provide energy savings compared to the traditional EAF and might further relax the energy requirements for systems and methods of the present disclosure. With non-limiting examples in which the systems and methods of the present disclosure are employed to reduce iron ore, the direct use of iron ore particles, powder or fines not only bypasses pelletization/sintering and coke making steps in the conventional blast furnace process, but also maximizes the iron oxide reduction rate by minimizing transport limitations of reactants and products to the iron oxide gas interface. Microwave plasma can operate at gas temperatures required for reduction of iron ore fines with renewable H₂, eliminates the needs of carbon-based energy carriers, and negatively charges particles and reactor walls causing Coulombic confinement of particles to eliminate their sticking to the reactor walls.

As indicated above, the systems and methods of the present disclosure can be combined with known (or modified) smelting process to provide a cost-effective, integrated process from iron or to crude steel. Other applications are also envisioned by the present disclosure. For example, the systems and methods of the present disclosure can be used to recharge iron-air batteries, serving to effect direct reduction of the iron oxide that develops over time as the battery discharges, akin, in certain respects, to the iron-air batteries available from Form Energy of Somerville, MA. Applications of the systems and methods of the present disclosure to transform or reduce micron-sized compound particles to nanometer-sized metal particles can be useful for many production processes, for example the in-line production of catalyst particles. Non-limiting examples in which the systems and methods of the present disclosure are employed to reduce silicates can have various end-use applications, for example as a method for oxygen or water production (e.g., on the moon, Mars, etc.). With these and related end-use applications, there may be little or no interest in recovering reduced particles; rather, it is the gaseous or liquid (H₂O) product that is of interest and the silicates are simply used as a resource to make them (e.g., an end-use application on the moon could use regolith to produce water/oxygen.

Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.

Claims

1. A method for reducing a solid compound, comprising:

creating a hydrogen plasma in a reactor chamber; and

exposing solid compound particles to the plasma;

wherein the solid compound particles are reduced by the hydrogen plasma.

2. The method of claim 1, wherein the step of exposing includes flowing the solid compound particles through the plasma.

3. The method of claim 2, wherein the step of flowing includes entraining the solid compound particles in a gas stream that continuously flows to the reactor chamber.

4. The method of claim 3, wherein a gas of the gas stream is a mixture of H2 and argon.

5. The method of claim 2, further comprising:

generating a secondary swirl gas flow in the reactor chamber.

6. The method of claim 2, wherein the step of flowing the solid compound particles through the plasma includes at least some of the solid compound particles being negatively charged.

7. The method of claim 1, wherein the step of exposing includes bringing the solid compound particles into contact with an effluent of the plasma.

8. The method of claim 1, wherein the step of exposing includes suspending the solid compound particles in or downstream of the plasma while exposing the solid compound particles to hot hydrogen gas and plasma species.

9. The method of claim 8, wherein the step of creating a hydrogen plasma includes delivering a gas stream to the reactor chamber, and further wherein a gas of the gas stream is a mixture of H2 and argon.

10. The method of claim 8, wherein the solid compound particles are moved through the plasma in a continuous fashion.

11. The method of claim 1, wherein the step of exposing includes:

passing the solid compound particles through the plasma;

after passing through the plasma, continuing to treat the solid compound particles with an effluent of the plasma.

12. The method of claim 1, wherein the solid compound is iron ore.

13. The method of claim 12, wherein the solid compound particles comprise iron ore particles with an average particle size in the range of 38-75 microns.

14. The method of claim 12, wherein the iron ore particles experience at least a 90% reduction to elemental iron.

15. The method of claim 14, wherein the iron ore particles are treated by the plasma for a treatment time of not greater than 10 seconds.

16. The method of claim 14, wherein the iron ore particles experience at least a 95% reduction over a plasma treatment time of not greater than 9 seconds.

17. The method of claim 1, wherein the solid compound is a metal oxide.

18. The method of claim 1, wherein the solid compound is a metal sulfide.

19. The method of claim 1, wherein the solid compound is a silicate

20. The method of claim 1, wherein prior to the step of exposing, the solid compound particles are micron-sized, and further wherein following the step of exposing, the solid compound particles are reduced to nanometer-sized metal particles.