Transfer arc plasma apparatus and method for gas-based reduction of metal oxides

Abstract

This invention provides a transferred arc plasma device and method for gas-based reduction of metal oxides. The device comprises a high-temperature anode container at the bottom of a reactor body, a plasma cathode positioned vertically above the anode container, and a gas outlet on the furnace wall. A circumferential inlet nozzle is located at the root of the plasma cathode nozzle, and an intermittent baffle surrounds the outlet of the circumferential inlet nozzle. A gas channel inside the nozzle of the plasma cathode is connected to a gas supply device. The reactor body is connected to a cooling unit via a gas collection port on the furnace wall. The bottom of the cooling unit is connected to the collection unit via a pipe. This invention features a simple structure, convenient operation, high heat and mass transfer efficiency, no reaction byproducts (tailings), in-situ detection capability, improved product production efficiency and purity, and reduced raw material and tail gas treatment costs, aligning with the development direction of green metallurgy and a circular economy.

Description

Technical Field

[0001] This invention belongs to the field of metal smelting, and particularly relates to a transfer arc plasma device and method for gas-based reduction of metal oxides. Background Technology

[0002] Vacuum carbothermic / silicothermic reduction is an important technique for extracting corresponding elemental metals from metal oxides. Its core lies in using a reducing agent to carry out a carbothermic or silicothermic reduction reaction under high-temperature vacuum conditions, thereby achieving the separation and enrichment of metal elements. The Pidgeon process, a widely used silicothermic reduction process, typically uses calcined ferrosilicon and other raw materials to produce metallic magnesium through a silicothermic reduction reaction under high-temperature vacuum conditions. This process generates approximately 6.5 to 8 tons of magnesium slag for every ton of magnesium produced, resulting in significant solid waste and environmental pressure. Existing improvements still have significant shortcomings: while treating magnesium smelting waste slag, they cannot achieve source reduction; the externally heated vertical tank process is limited by the "external heat transfer, solid-solid mass transfer" model, resulting in a single-tank reduction cycle of 8 to 12 hours, and the limited temperature resistance of the reduction tank material makes it difficult to improve the reaction kinetic rate, affecting product production efficiency.

[0003] In recent years, plasma arcs have begun to be used as a heat source in the production of elemental metals, utilizing their ultra-high temperature characteristics of 2000~30000℃ to achieve rapid melting, and are used in metal reduction smelting equipment. However, while existing plasma / arc magnesium smelting technologies have made some progress in reducing waste, they still have the following shortcomings: Firstly, plasma arcs generally suffer from poor arc flame stability during actual operation. Their arc morphology is easily affected by factors such as current fluctuations, atmosphere changes, and electrode wear, leading to uneven distribution of the reaction heat field and making it difficult for the reduction reaction to proceed stably and continuously, directly affecting the metal yield and product quality. Secondly, existing technologies still rely on ground-state material reactions, without effectively activating the reducing agent and controlling the reverse reaction between carbon oxides and magnesium, resulting in a low reduction rate. Furthermore, there is a lack of in-situ real-time monitoring methods for arc flame morphology and the evolution of reduced species, making signal acquisition difficult under high-temperature and strong interference environments. The production process remains in a "black box" state, making it difficult to achieve closed-loop precise control of process parameters. In addition, some schemes still use external heating methods, failing to utilize plasma to excite the reducing gas, resulting in slow heating rates, long reaction times, low production efficiency, and no consideration for the recycling of the reaction gas, leading to high production costs, which does not meet the requirements of green and low-carbon development.

[0004] In response to the problems of large slag production, low heat and mass transfer efficiency, unstable plasma arc in the traditional process, and the fact that existing plasma technology still requires solid reducing agents and lacks in-situ monitoring, this invention provides a transfer arc plasma device and method for gas-based reduction of metal oxides. Summary of the Invention

[0005] The main objective of this invention is to provide a transfer arc plasma device and method for gas-based reduction of metal oxides, aiming to solve the problem of difficulty in simultaneously achieving plasma arc stability and reaction mass transfer efficiency without generating reduction byproduct tailings.

[0006] To achieve the above objectives, the present invention provides a transfer arc plasma device for gas-based reduction of metal oxides, comprising a plasma arc furnace, a cooling unit, and a collection unit. The plasma arc furnace includes a reactor body and a power supply. The reactor body contains a plasma cathode and an anode high-temperature container. The top of the plasma cathode is connected to the negative terminal of the power supply, and the anode high-temperature container is connected to the positive terminal of the power supply. The anode high-temperature container is disposed at the bottom of the reactor body, and the plasma cathode is disposed vertically above the anode high-temperature container. A gas outlet is disposed on the furnace wall of the reactor body. The plasma cathode has a circumferential air inlet nozzle head at the nozzle root, and an intermittent enclosure is provided around the outlet of the circumferential air inlet nozzle head. The reactor body is connected to the cooling unit through a gas collection port on the furnace wall; The bottom of the cooling unit is connected to the collection unit via a pipe.

[0007] Furthermore, the vertical distance between the circumferential air intake nozzle and the anode high-temperature container is 1~10cm.

[0008] Furthermore, the same size enclosures are evenly distributed around the outlet circumference of the circumferential air inlet nozzle. The longitudinal length L of the enclosure and the current I satisfy: 1000≤I×L≤2000, and the current I≥5A, the longitudinal length L≥3mm, and the longitudinal length L≤2 / 3 of the vertical distance between the circumferential air inlet nozzle and the anode high-temperature container. The ratio of the arc of the fence to the interval between two adjacent fences is 1 to 2:1.

[0009] Preferably, the current I is 5~500A, more preferably 300~500A.

[0010] Furthermore, an optical measurement window is provided on the side wall of the reactor body, and an optical emission spectrometer and a high-speed camera are equipped outside the optical measurement window.

[0011] Furthermore, the cooling unit includes a cooling collection tank, a sintered filter element, and a cooling sleeve. The cooling collection tank is connected to the collection port. The sintered filter element is disposed inside the cooling collection tank. The cooling sleeve is connected to an extension glove window on the tank wall of the cooling collection tank. The cooling sleeve is provided with an inner extension glove. The cavity outlet of the sintered filter element is connected to the gas channel of the plasma cathode through a circulation pipe, and a gas circulation pump is installed on the circulation pipe.

[0012] Furthermore, the collection unit includes an isolation box, a hopper, a material valve, and a material dispensing valve. The hopper is connected to the bottom of the cooling collection tank via a pipe. The hopper, material valve, and material dispensing valve are located inside the isolation box. The material valve and material dispensing valve are located on the pipe, and the material dispensing valve is located near the hopper.

[0013] Furthermore, the gas channel inside the nozzle of the plasma cathode is connected to the gas supply device; The gas outlet of the reactor body is connected to a vacuum pump, which extracts the gas after the reaction is completed.

[0014] The present invention also provides a method for gas-based reduction of metal oxides based on a transferred arc plasma device, comprising the following steps: S1, after the magnesium oxide material is pressed into shape, it is placed in a vacuum atmosphere anode high temperature container, and then the mixed gas is introduced into the interior of the reactor body through the circumferential gas inlet nozzle. S2, start the power supply to discharge, so that an electric arc plasma is formed inside the reactor body, and the circumferential gas inlet nozzle head continues to supply gas to ensure that the working pressure inside the reactor body is constant. At the same time, the electric arc plasma is used to ionize the reducing agent gas to excite the active groups formed to reduce the metal oxide material, generating metal vapor and by-product synthesis gas. S3, the metal vapor is extracted into the cooling collection tank, the metal powder is scraped out in the cooling unit, and the non-condensable gas is extracted into the gas channel of the plasma cathode by the gas circulation pump for recycling. S4, after the gas-based reduction reaction is completed, the scraped metal powder is collected in an isolation box, sealed, and transferred.

[0015] Furthermore, in step S1, the vacuum atmosphere is achieved by using a vacuum pump to evacuate the reactor body, so that the vacuum degree of the reactor body is ≤10Pa. The mixed gas is composed of a reducing agent gas and an inert gas in a volume ratio of 0.1 to 8:1; After the mixed gas is introduced into the reactor body, the working pressure inside the reactor body is maintained at 0.1~1.5 atm; The reducing agent gas is one or more of hydrogen, CO, and C1-C4 light hydrocarbon gases.

[0016] Furthermore, in step S2, the working pressure inside the reactor is kept constant at 0.1~1.5 atm.

[0017] Furthermore, the extraction rate of the metal vapor is 0.5~50L / s, and the temperature of the cooling unit is below 150℃.

[0018] Furthermore, the method for scraping metal powder is as follows: the inner extension glove inside the cooling jacket is inserted into the cooling collection tank through the extension glove window to scrape off the metal powder deposited on the sintered filter element.

[0019] The beneficial effects of this invention are as follows: 1. This invention uses transferred arc plasma as the core heat source, which can efficiently transfer heat, reduce energy consumption, and improve the reduction rate of metal products.

[0020] 2. This invention adopts a circumferential air intake structure, using reducing agent gas as the reducing agent to replace traditional solid ferrosilicon. The special intermittent enclosure structure improves the efficiency of reducing agent gas supply, realizes efficient "gas-based reduction", eliminates the source of solid waste, eliminates the need to discharge traditional reducing slag, and solves the problem of metallurgical solid waste discharge.

[0021] 3. This invention enables “visualized” and “quantifiable” monitoring of the high-temperature core reaction zone, breaking through the measurement blind zone and providing a physical basis for the digital regulation and closed-loop control of the reduction process.

[0022] 4. This invention constructs a circuit for directional gas flow and recycling, realizing the directional transport and precise capture of metal vapor, improving the reduction efficiency and collection rate of metal products, reducing raw material costs and exhaust gas treatment costs, and conforming to the development direction of green metallurgy and circular economy.

[0023] 5. The present invention has a simple structure and is easy to operate. By combining the scraping glove and the isolation box, it realizes the integrated non-destructive transfer of metal products, thereby improving the production efficiency and quality of the products. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of the transfer arc plasma device applied to the gas-based reduction of metal oxides in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the circumferential air intake nozzle head in an embodiment of the present invention.

[0026] Figure labels: 100, Reactor body; 110, Plasma cathode; 111, Circumferential inlet nozzle; 112, Enclosure; 120, Anode high-temperature container; 130, Optical measurement window; 131, Optical emission spectrometer; 132, High-speed camera; 140, Gas circulation pump; 150, Sintered filter element; 160, Vacuum pump; 170, Outlet flow meter; 180, Inlet flow meter; 200, Cooling collection tank; 210, Inner glove; 220, Cooling jacket; 230, Isolation box; 240, Material valve; 250, Feed valve; 260, Hopper; 300, Power supply. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0029] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0030] like Figure 1 As shown, this invention provides a transfer arc plasma device for gas-based reduction of metal oxides, comprising a plasma arc furnace, a cooling unit, and a collection unit. The plasma arc furnace includes a reactor body 100 and a power supply 300. The reactor body 100 contains a plasma cathode 110 and an anode high-temperature container 120. The top of the plasma cathode 110 is connected to the negative terminal of the power supply 300, and the anode high-temperature container 120 is connected to the positive terminal of the power supply 300. The anode high-temperature container 120 is located at the bottom of the reactor body 100, and the plasma cathode 110 is located vertically above the anode high-temperature container 120. A gas outlet (not shown in the figure) is provided on the furnace wall of the reactor body 100. In this invention, the furnace wall refers to the entire shell constituting the reactor chamber, including the side walls, furnace top, and furnace bottom.

[0031] The transferred arc plasma reaction system of this invention is centered on a reactor body 100, which integrates a plasma cathode 110 vertically arranged above an anode high-temperature container 120 and an anode high-temperature container 120 at the bottom. The current is provided by a power supply 300. The power supply 300 discharges to generate transferred arc plasma in the plasma cathode 110. Utilizing the plasma's center temperature of 2000~30000℃ and its circuit conductivity, the plasma directly acts on the metal oxide material in the anode high-temperature container 120 within the reactor body 100 through heat conduction, heat convection, and Joule heating, thus providing efficient heat transfer for the strongly endothermic metal reduction reaction.

[0032] In this invention, metal oxides refer to materials that generate metals upon reaction with a reducing agent. They may contain impurities, including but not limited to one or additional metals, as well as the same metal having more than one oxidation state. Metal oxides include, but are not limited to, iron oxide, copper oxide, nickel oxide, tin oxide, cobalt oxide, manganese oxide, zinc oxide, magnesium oxide, aluminum oxide, calcium oxide, silver oxide, and platinum oxide.

[0033] In some embodiments of the present invention, the power supply 300 is an IGBT constant current power supply or a thyristor power supply. Preferably, the power supply 300 used in the embodiments of the present invention is an IGBT constant current power supply, which has a high frequency and strong adaptability to parameter fluctuations, making it more suitable for plasma metallurgical processes with complex phase changes, and providing a stable current for the reactor body 100 of the present invention.

[0034] In some embodiments of the present invention, the anode high-temperature container 120 is an anode crucible, which is conductive and heat-resistant. As a container for metal oxide materials, it enables the reactor body 100 and the power supply 300 to form a complete electrical circuit, ensuring the formation of the transfer arc plasma. The anode crucible can be made of any of the following materials that are both heat-resistant and conductive: graphite, water-cooled copper, water-cooled stainless steel, etc. The preferred anode crucible in this invention is a graphite crucible, which has a higher temperature resistance and stable chemical properties under a plasma atmosphere.

[0035] like Figure 2 As shown, in this invention, a circumferential inlet nozzle head 111 is provided at the root of the nozzle of the plasma cathode 110. This circumferential inlet nozzle head 111 directly cuts into the strongest electric field and high-temperature core region of the plasma arc at a vertically downward angle, providing the plasma with raw material gas. Unlike conventional furnace atmosphere reduction, the structure of the circumferential inlet nozzle head 111 forces the reducing agent gas through the arc column, utilizing the extremely high density of electrons in the core region to induce deep ionization and dissociation of the reducing agent molecules, generating high concentrations of excited-state hydrogen, carbon species, and free radicals.

[0036] In this invention, an intermittently spaced enclosure 112 is provided around the outlet of the circumferential air inlet nozzle 111. The longitudinal length L of the enclosure and the current I satisfy the following conditions: 1000≤I×L≤2000, and the current I≥5A (i.e., the working current of the plasma arc), the longitudinal length L≥3mm, and the longitudinal length L≤2 / 3 of the vertical distance between the circumferential air inlet nozzle and the anode high-temperature container. The invention sets enclosures of the same size to be evenly distributed around the outlet circumference of the circumferential air inlet nozzle, with the arc ratio of the enclosure to the interval between two adjacent enclosures (hereinafter referred to as the interval) being 1~2:1. By setting the intermittently spaced enclosure, this invention can maximize the utilization of the plasma jet effect and the resulting Venturi effect, drawing reducing agent gas molecules into the plasma in a circumferential direction, thereby improving the utilization efficiency of the reducing agent gas and achieving stable confinement of the plasma arc.

[0037] In some embodiments of the present invention, the current I is 5~500A, preferably 300~500A.

[0038] In some embodiments of the present invention, 10 barriers of the same size are evenly distributed around the outlet of the circumferential air inlet nozzle. One barrier and one spacer form a group, and the total arc of each group of barriers and spaces is 36°. This not only achieves the stability of the plasma arc, but also optimizes the utilization efficiency of the reducing agent gas and the yield of metal products in the present invention.

[0039] The cathode jet effect refers to the spontaneous formation of a high-speed, high-temperature plasma jet near the cathode surface during high-pressure or high-current DC-transferred arc plasma discharge. This jet travels along the arc axis from the cathode to the anode, carrying enormous energy and high-speed particles. The effect is most pronounced at the cathode tip, and the plasma typically introduces gas from outside the electrode into the ionization region through the Venturi effect induced by this effect. Therefore, in the gas-based reduction of metal oxides in this invention, the reducing agent gas source in the core reaction region is divided into three parts: reducing agent gas supplied by the gas supply device, circulating mixed gas, and gas drawn in by the Venturi effect. The reducing agent gas supplied by the gas supply device and the circulating mixed gas are directly supplied to the plasma arc through the circumferential inlet nozzle 111, while the gas drawn in by the Venturi effect is radially supplied to the plasma arc through the intervals of the circumferential inlet nozzle 111, making full use of the reducing agent gas outside the plasma region.

[0040] It should be noted that, in actual production operations, the internal pressure of the reactor body 100 needs to be kept stable. Therefore, an outlet flow meter 170 is installed on the pipeline between the vacuum pump 160 and the reactor body 100 to regulate the gas flow rate discharged from the reactor body outlet; an inlet flow meter 180 is installed at the outlet of the gas supply device to regulate the gas flow rate from the gas supply device. The flow rate of the outlet flow meter 170 of the present invention is determined in the following way: based on the set flow rate of the inlet flow meter 180, combined with the stoichiometric relationship in the metal oxide reduction process, the flow rate of the gas generated after the reducing gas has completely reacted is calculated, and the flow rate of the outlet flow meter 170 is controlled to be consistent with the flow rate of the generated gas, so as to achieve a dynamic balance between the inlet and outlet gas volumes.

[0041] Preferably, the vertical distance between the circumferential inlet nozzle 111 and the anode high-temperature container 120 is 1~10cm, which is used for plasma-excited gas to form excited-state hydrogen, carbon species and free radicals, resulting in stronger reactivity. If the vertical distance is too large, it will cause the plasma arc column to lengthen, increase the radiative heat release into space, and decrease the Joule heat transfer ratio to the crucible, thus reducing the thermal efficiency of the core reaction zone; if the vertical distance is too small, the reducing agent gas molecules will not have sufficient flight time to ionize, resulting in decreased reactivity.

[0042] In this invention, the gas channel inside the nozzle of the plasma cathode 110 is connected to a gas supply device (not shown in the figure), wherein the gas supply device is used to supply a reducing agent gas and an inert gas with a volume ratio of 0.1 to 8:1.

[0043] The plasma cathode 110 of the present invention also includes a cathode electrode (the position of the cathode electrode and the nozzle is a conventional design, and the cathode electrode is perpendicular to the nozzle outlet). The cathode electrode is made of tungsten-based electrode, such as thorium tungsten electrode, cerium tungsten electrode, lanthanum tungsten electrode, etc., or other cathode materials suitable for non-oxidizing atmospheres.

[0044] In this invention, the reactor body 100 is connected to the cooling unit via a gas collection port (not shown in the figure) on the furnace wall, and the bottom of the cooling unit is connected to the collection unit via a pipe. The arrangement of the cooling unit and the collection unit allows the generated metal vapor to be quickly withdrawn from the reactor body 100 (high-temperature zone) for condensation and metal product collection.

[0045] Preferably, the cooling unit includes a cooling collection tank 200, a sintered filter element 150, and a cooling sleeve 220. The cooling collection tank 200 is connected to the gas collection port. The sintered filter element 150 is disposed inside the cooling collection tank 200. The cooling sleeve 220 is connected to the glove window (not shown in the figure) on the tank wall of the cooling collection tank 200. The cooling sleeve 220 is provided with an inner glove 210. The cavity outlet of the sintered filter element 150 is connected to the gas channel of the plasma cathode 110 through a circulation pipe. A gas circulation pump 140 is provided on the circulation pipe.

[0046] The gas collection port of the reactor body of this invention is connected to a cooling collection tank 200. By controlling the gas circulation pump 140 to drive the directional flow of gas within the reactor body 100, the product vapor (metal vapor) is rapidly withdrawn from the high-temperature zone with the gas flow and enters the cooling collection tank 200, where it is captured by the sintering filter element. Simultaneously, uncondensed gases (supplying inert gas, by-product synthesis gas, and unused reducing agent gas) are transported from the cavity of the sintering filter element 150 through a circulation pipe to the gas channel of the plasma cathode 110 for recycling. The directional flow of uncondensed gas improves the overall utilization rate of the reducing agent gas and reduces raw material costs. The by-product synthesis gas refers to all gases other than metal vapor generated by the reaction of metal oxide materials and reducing agent gas in the reactor body.

[0047] This invention features an inner glove 210 and a matching cooling sleeve 220 mounted on the wall of a cooling collection tank 200. During the high-temperature phase of the reaction, the inner glove 210 retracts into the cooling sleeve 220 to prevent damage from high temperatures. However, after the reaction is complete and the cooling collection tank 200 has cooled down, the inner glove 210 can be inserted into the cooling collection tank 200 through the glove window to scrape and collect the product (metallic element) on the sintered filter element 150. During the scraping process, the cooling collection tank 200 (which undergoes vacuuming and protective gas replacement before the entire device is put into operation) does not come into contact with the external environment, ensuring that the product remains in an oxygen-free and water-free environment. This means that the product is not easily oxidized during the cooling and scraping collection process, thus ensuring the purity of the product.

[0048] In some embodiments of the present invention, the cooling collection tank 200 is a stainless steel or carbon steel water-cooled collection tank, which allows the metal vapor rapidly withdrawn from the high-temperature zone (reactor body) to condense quickly and be efficiently collected within a specific temperature range (<150°C), reducing the probability of the metal vapor being easily oxidized again. If the temperature inside the cooling collection tank 200 is greater than 150°C, the gas-based reduction products (H2O, CO, CO2, and other oxygen-containing gases) will undergo a reverse reaction with the active metal products.

[0049] In this invention, the sintered filter element 150 has a cylindrical structure, is made of stainless steel or titanium, has a filtration accuracy of 10~40μm, a diameter of 80mm, and a length of 240mm. When the metal vapor, inert gas, by-product synthesis gas, and unused reducing agent gas of this invention enter the cooling collection tank 200 from the high-temperature zone, the metal vapor cools and deposits on the outer surface of the sintered filter element 150. The gas circulation pump 140 collects the uncondensed gas into the cavity of the sintered filter element and draws it from the circulation pipe through the cavity outlet into the gas channel of the plasma cathode 110.

[0050] In some embodiments of the present invention, the cooling sleeve 220 is a water-cooled protective tube, which forms a linkage protection mechanism with the inner glove 210. During the high-temperature stage, it provides a low-temperature safe environment for the inner glove 210 that retracts into the cooling sleeve 220, preventing damage to the inner glove 210.

[0051] Preferably, an optical measurement window 130 is provided on the side wall of the reactor body 100, and an optical emission spectrometer (OES) 131 and a high-speed camera 132 are equipped on the outside of the optical measurement window 130. This invention integrates an in-situ optical monitoring system (i.e., optical emission spectrometer 131 and high-speed camera 132) under extreme conditions through the optical measurement window 130, enabling in-situ intelligent diagnosis and control. Specifically, by capturing the spectral intensity and dynamic evolution characteristics of excited-state particles in the arc flame in situ, it achieves real-time online monitoring and digital evaluation of the reduction efficiency, species distribution, and arc stability of the metallurgical process under extreme conditions. This solves the problem of the high-temperature core reaction zone being "invisible and unmeasurable," providing a physical basis for the digital control of the reduction process.

[0052] When the reducing agent gas is a C1-C4 light hydrocarbon gas, such as methane, ethane, propane, acetylene, or propyne, the excited state particles are CH3, CH, C2, H, etc.; when the reducing agent gas is hydrogen, the excited state particles are H atoms; when the reducing agent gas is carbon monoxide (CO), the excited state particles are CO, as shown in equations (I) and (II) below: (I); (II).

[0053] Preferably, the collection unit includes an isolation box 230, a hopper 260, a material valve 240, and a dispensing valve 250. The hopper 260 is connected to the bottom of the cooling collection tank 200 via a pipe. The hopper 260, material valve 240, and dispensing valve 250 are located inside the isolation box 230, and the material valve 240 and dispensing valve 250 are located on the pipe, with the dispensing valve 250 close to the hopper 260. Opening the material valve 240 and dispensing valve 250 allows the scraped metal product to fall directly into the hopper 260. Closing the material valve 240 and dispensing valve 250 simultaneously removes the dispensing valve 250 along with the hopper 260, completing the sealing process in the isolation box 230. Alternatively, the metal product can be directly removed from the hopper 260, sealed in the isolation box 230, and then transferred. The isolation box 230 of this invention provides an oxygen-free and water-free closed environment (vacuuming and protective gas replacement are performed before the entire device is operated), ensuring that the magnesium metal is not oxidized during sealing and transfer.

[0054] In this invention, the isolation box 230 is a sealed glove box, which can realize the non-destructive transfer and packaging of metal products, ensure that the products do not come into contact with external oxygen, guarantee product purity, and facilitate subsequent testing and application.

[0055] Preferably, the gas outlet of the reactor body 100 is connected to the vacuum pump 160. Before the reduction reaction of the present invention begins, the vacuum pump 160 is controlled to evacuate the reactor body 100. During the reaction, in order to maintain stable pressure in the reactor body, the pumping rate of the vacuum pump 160 is controlled to match the linkage between the inlet flow meter and the outlet flow meter of the reactor body 100, ensuring a balance between the inlet and outlet gas volumes. After the reaction is completed, the gas in the reactor body 100 is extracted by the vacuum pump 160.

[0056] The present invention relates to a gas-based reduction method for metal oxides based on a transferred arc plasma device, comprising the following steps: S1. After the metal oxide material is pressed into shape, it is placed in the high-temperature anode container 120. The vacuum pump 160 is used to evacuate the reaction furnace body 100 until the vacuum degree is ≤10Pa.

[0057] S2, a gas supply device is used to fill the nozzle gas channel of the plasma cathode 110 with a volume ratio of reducing agent gas and inert gas of 1:1, and introduces it into the reactor body 100 through the circumferential gas inlet nozzle head 111, so that the working pressure inside the reactor body 100 is maintained at 0.1~1.5 atm. If the working pressure is lower than 0.1 atm, the number of reducing agent gas molecules is low and the metal reduction rate is too slow; if the working pressure is higher than 1.5 atm, the metal vapor volatilization rate is low and the production efficiency is reduced.

[0058] Preferably, the reducing agent gas is one or more of hydrogen, CO, and C1-C4 light hydrocarbon gases.

[0059] S3, start the IGBT power supply 300 to discharge, adjust the working voltage to 40~80V and the working current to not less than 5A, so that an electric arc plasma is formed inside the reactor body 100, and the circumferential air inlet nozzle 111 is kept continuously supplying air. At the same time, the vacuum pump 160 is turned on to evacuate air, ensuring that the pressure inside the reactor body is 0.1~1.5atm. The electric arc plasma is used to ionize the reducing agent gas to excite the active groups formed to reduce the metal oxide material, generating metal vapor and by-products.

[0060] S4. As metal vapor is generated, in order to avoid reverse reaction, gas circulation pump 140 is started to drive the metal vapor (which also contains inert gas, by-product synthesis gas and unreacted reducing agent gas) away from the high temperature zone (i.e., the reaction furnace body 100) at a pumping rate of 0.5~50L / s. The metal vapor is then quickly cooled in a cooling collection tank 200 at a temperature below 150°C and deposited on the sintered filter element 150. Non-condensable gas is drawn into the gas channel of the plasma cathode 110 by gas circulation pump 140 and recycled.

[0061] In some embodiments of the present invention, the synthesis gas, a byproduct of the hydrocarbon gas reducing agent, is H2 or CO.

[0062] It is worth noting that after the gas circulation pump 140 of the present invention is turned on, the pressure inside the reaction furnace 100 must still be kept constant (pressure of 0.1~1.5 atm) to ensure that the metal oxide reduction reaction of the present invention continues.

[0063] In some embodiments of the present invention, the gas circulation pump 140 is a vortex pump with a pumping speed of 0.5~50 L / s. In the present invention, if the pumping speed of the vortex pump is too low, the metal vapor and reaction tail gas cannot diffuse into the collection chamber in time, resulting in a decrease in yield and reaction efficiency; if the pumping speed of the vortex pump is too high, the flow field behavior inside the reactor becomes more complex, increasing the instability of the plasma arc, suppressing the stabilizing effect of the interval enclosure on the arc of the present invention, and consequently reducing the compatibility between the arc and the insulating material.

[0064] S5. After the gas-based reduction reaction is completed, the inner extension glove 210 inside the cooling sleeve 220 enters the cooling collection tank 200 through the extension glove window to scrape off the metal powder deposited on the sintered filter element 150. The material valve 240 and the material receiving valve 250 are opened, and the scraped metal powder falls into the silo 260.

[0065] S6, close the material valve 240, remove the material valve 250 together with the hopper 260, and complete the sealing and transfer in the isolation box 230 under inert atmosphere to ensure that the product does not come into contact with external oxygen.

[0066] The gas-based reduction method for metal oxides based on a transfer arc plasma device according to the present invention will be described below with reference to specific embodiments.

[0067] Example 1 A gas-based reduction method for magnesium oxide based on a transferred arc plasma device includes: S1. Magnesium oxide powder is pressed into shape and placed in an anode crucible. The reactor body is evacuated to 1 Pa using a vacuum pump. Then, ethane and argon gas with a volume ratio of 1:1 are introduced into the reactor body through circumferential inlet nozzles at an inlet rate of 500 ml / min until the working pressure reaches 0.8 atm. The longitudinal length of the circumferential inlet nozzle enclosure is 3.5 mm, the total arc of each enclosure and the interval is 36°, and the arc ratio of the enclosure to the interval is 1:1.

[0068] S2. Start the IGBT power supply to discharge at 40V and 300A to form an electric arc plasma inside the reactor. Maintain continuous gas intake through the circumferential gas inlet nozzle. Based on the reaction equation of ethane and magnesium oxide, turn on the vacuum pump to pump gas at a rate of 3000ml / min to ensure that the pressure inside the reactor is constant at 0.8atm, generating metallic magnesium vapor and byproducts (H2 and CO).

[0069] S3. Start the vortex pump to pump gas at a rate of 9L / s, and extract the magnesium vapor, unreacted C2H6, byproducts H2 and CO from the reactor body to a water-cooled collection tank at a temperature of 25°C for cooling. The magnesium vapor is deposited on the sintered filter element. The non-condensable gases (unreacted C2H6, H2 and CO) are pumped by the vortex pump into the gas channel of the plasma cathode for recycling.

[0070] S4. After the reaction is complete, use an inner glove to scrape the magnesium metal from the sintered filter element, open the material valve and the feed valve, and the magnesium metal product falls into the hopper. Close the material valve, remove the feed valve and the hopper together, and complete the sealing and transfer in a sealed glove box.

[0071] The magnesium oxide reduction reaction rate was 5.3 g / min, the magnesium metal yield was 96%, the purity of the obtained magnesium metal was 95%, and no reduction by-product waste residue was generated. The volume concentration of unreacted ethane in the tail gas was 0.1%.

[0072] Example 2 Compared with Example 1, the reducing gas in Example 2 is acetylene, the acetylene inlet rate is 3000 ml / min, the vacuum pump is turned on to pump gas at a rate of 9500 ml / min, the working pressure in the reactor body is 0.8 atm; the IGBT power supply discharge voltage is 45V, and the current is 300A; metallic magnesium vapor and byproducts H2 and CO are generated; the pumping rate of the vortex pump is 9 L / s, and the temperature of the water-cooled collection tank is 25°C.

[0073] The magnesium oxide reduction reaction rate was 5.6 g / min, the magnesium metal yield was 94%, the purity of the obtained magnesium metal was 97%, and after the reaction was completed, the volume concentration of unreacted acetylene in the tail gas was 1.1%, and no reduction by-product waste residue was generated.

[0074] Example 3 Compared to Example 1, the current in Example 3 is 500A, while other conditions remain the same.

[0075] The magnesium oxide reduction reaction rate was 6.4 g / min, the magnesium metal yield was 92%, the purity of the obtained magnesium metal was 96%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 2.3%, and no reduction by-product waste residue was generated.

[0076] Example 4 Compared with Example 1, the vortex pump pumping speed in Example 4 is 5 L / s, while other conditions remain the same.

[0077] The magnesium oxide reduction reaction rate was 4.7 g / min, the magnesium metal yield was 94%, the purity of the obtained magnesium metal was 94%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 2.6%, and no reduction by-product waste residue was generated.

[0078] Example 5 Compared with Example 1, the working pressure of Example 5 is 0.5 atm, while other conditions remain the same.

[0079] The magnesium oxide reduction reaction rate was 4.5 g / min, the magnesium metal yield was 95%, the purity of the obtained magnesium metal was 92%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 0.9%, and no reduction by-product waste residue was generated.

[0080] Example 6 Compared with Example 1, the ratio of the arc of the enclosure to the interval in Example 6 is 2:1, while other conditions remain the same.

[0081] The magnesium oxide reduction reaction rate was 5.0 g / min, the magnesium metal yield was 97%, the purity of the obtained magnesium metal was 90%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 0.2%, and no reduction by-product waste residue was generated.

[0082] Example 7 Compared with Example 1, in Example 7, the ratio of the curvature of the enclosure to the interval is 1.5:1, while other conditions remain the same.

[0083] The magnesium oxide reduction reaction rate was 4.6 g / min, the magnesium metal yield was 96%, the purity of the obtained magnesium metal was 92%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 0.4%, and no reduction by-product waste residue was generated.

[0084] Example 8 Compared with Example 1, the longitudinal length of the fence in Example 8 is 5mm, while other conditions remain the same.

[0085] The magnesium oxide reduction reaction rate was 5.1 g / min, the magnesium metal yield was 89%, the purity of the obtained magnesium metal was 94%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 1.5%, and no reduction by-product waste residue was generated.

[0086] Example 9 Compared with Example 1, the longitudinal length of the enclosure in Example 9 is 6.5mm, while other conditions remain the same.

[0087] The magnesium oxide reduction reaction rate was 5.4 g / min, the magnesium metal yield was 88%, the purity of the obtained magnesium metal was 92%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 1.3%, and no reduction by-product waste residue was generated.

[0088] Example 10 Compared with Example 1, the reaction raw material in Example 10 is iron oxide, the reducing agent gas is carbon monoxide, and other conditions remain the same.

[0089] The test results showed that the iron oxide reduction reaction rate was 5.1 g / min, the yield of metallic iron was 93%, the purity of the obtained metallic iron was 96%, and after the reaction was completed, the volume concentration of unreacted carbon monoxide in the tail gas was 1.6%, and no reduction by-product residue was generated.

[0090] Example 11 Compared with Example 1, the reaction raw material in Example 11 is iron oxide, the reducing agent gas is hydrogen, and other conditions remain the same.

[0091] The test results showed that the iron oxide reduction reaction rate was 4.9 g / min, the yield of metallic iron was 91%, the purity of the obtained metallic iron was 94%, and after the reaction was completed, the volume concentration of unreacted hydrogen in the tail gas was 0.9%, and no reduction by-product residue was generated.

[0092] Example 12 Compared with Example 1, the total arc of each group of fences and intervals in Example 12 is 60° (i.e., there are 6 interval fences), the arc ratio of fences to intervals is 2:1, and other conditions remain the same.

[0093] The magnesium oxide reduction reaction rate was 3.8 g / min, the magnesium metal yield was 94%, the purity of the obtained magnesium metal was 90%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 0.9%, and no reduction by-product waste residue was generated.

[0094] Example 13 Compared with Example 1, the total arc of each group of fences and intervals in Example 13 is 40° (i.e., there are 9 interval fences), the longitudinal length of the fence is 4mm, and other conditions remain the same.

[0095] The magnesium oxide reduction reaction rate was 3.6 g / min, the magnesium metal yield was 89%, the purity of the obtained magnesium metal was 92%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 1.7%, and no reduction by-product waste residue was generated.

[0096] Example 14 Compared with Example 1, the total arc of each group of fences and intervals in Example 14 is 40° (i.e., there are 9 interval fences), the longitudinal length of the fence is 6mm, and other conditions remain the same.

[0097] The magnesium oxide reduction reaction rate was 4.1 g / min, the magnesium metal yield was 90%, the purity of the obtained magnesium metal was 92%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 3.5%, and no reduction by-product waste residue was generated.

[0098] Example 15 Compared with Example 1, the total arc of each group of fences and intervals in Example 15 is 30° (i.e., there are 12 interval fences), the longitudinal length of the fence is 5.5mm, and other conditions remain the same.

[0099] The magnesium oxide reduction reaction rate was 4.6 g / min, the magnesium metal yield was 89%, the purity of the obtained magnesium metal was 95%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 2.8%, and no reduction by-product waste residue was generated.

[0100] Comparative Example 1 Compared to Example 1, the pumping speed of the comparative vortex pump in this example is 60 L / s.

[0101] Tests showed that when the magnesium oxide reduction reaction rate was 4.3 g / min, the yield of metallic magnesium was 91%, the purity of the obtained metallic magnesium was 51%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 16.7%, and no reduction by-product waste residue was generated.

[0102] Comparative Example 2 Compared with Example 1, this Comparative Example 2 did not include a vortex pump, meaning that the reducing agent gas was not recycled.

[0103] Tests showed that when the magnesium oxide reduction reaction rate was 5.5 g / min, the yield of metallic magnesium was 90%, the purity of the obtained metallic magnesium was 93%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 20.4%, and no reduction by-product waste residue was generated.

[0104] Comparative Example 3 Compared to Example 1, the temperature of the water-cooled collection tank in Comparative Example 3 is 200°C.

[0105] Tests showed that when the magnesium oxide reduction reaction rate was 5.1 g / min, the yield of metallic magnesium was 62%, the purity of the obtained metallic magnesium was 55%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 0.4%, and no reduction by-product waste residue was generated.

[0106] Comparative Example 4 Compared with Example 1, Comparative Example 4 did not use a circumferential air intake nozzle with an intermittent enclosure around the outlet; instead, it used only a regular air intake nozzle.

[0107] Tests showed that when the magnesium oxide reduction reaction rate was 1.6 g / min, the yield of metallic magnesium was 54%, the purity of the obtained metallic magnesium was 93%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 5.1%, and no reduction by-product waste residue was generated.

[0108] Comparative Example 5 Compared with Example 1, in Comparative Example 5, the ratio of the interval of the spaced enclosure to the curvature of the enclosure is 5:1.

[0109] Tests showed that when the magnesium oxide reduction reaction rate was 2.7 g / min, the yield of metallic magnesium was 61%, the purity of the obtained metallic magnesium was 90%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 4.6%, and no reduction by-product waste residue was generated.

[0110] Comparative Example 6 Compared with Example 1, the longitudinal length of the spaced enclosure around the exit in Comparative Example 6 is 2 mm.

[0111] Testing revealed that the arc stability deteriorated during the reduction process, and the reaction rate decreased significantly. When the magnesium oxide reduction reaction rate was 1.4 g / min, the yield of metallic magnesium was 75%, and the purity of the obtained metallic magnesium was 88%. After the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 4.7%, and no reduction by-product residue was generated.

[0112] Comparative Example 7 Compared with Example 1, in Comparative Example 7, the longitudinal length of the spaced enclosure around the outlet is 10mm.

[0113] Tests showed that when the magnesium oxide reduction reaction rate was 2.5 g / min, the yield of metallic magnesium was 78%, the purity of the obtained metallic magnesium was 91%, and after the reaction was completed, the volume concentration of unreacted ethane in the tail gas was 8.6%, and no reduction by-product waste residue was generated.

[0114] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A transfer arc plasma device for gas-based reduction of metal oxides, comprising a plasma arc furnace, a cooling unit, and a collection unit, characterized in that, The bottom of the plasma arc furnace is provided with an anode high-temperature container, and a plasma cathode is provided vertically above the anode high-temperature container. The furnace wall of the furnace body is provided with a gas outlet. The plasma cathode has a circumferential air inlet nozzle head at the nozzle root, and an intermittent enclosure is provided around the outlet of the circumferential air inlet nozzle head. The reactor body is connected to the cooling unit through a gas collection port on the furnace wall; The bottom of the cooling unit is connected to the collection unit via a pipe.

2. The transferred arc plasma device for gas-based reduction of metal oxides according to claim 1, characterized in that, The vertical distance between the circumferential air intake nozzle and the anode high-temperature container is 1~10cm.

3. The transferred arc plasma device for gas-based reduction of metal oxides according to claim 1, characterized in that, The same size enclosures are evenly distributed around the outlet circumference of the circumferential air inlet nozzle. The longitudinal length L of the enclosure and the current I satisfy: 1000≤I×L≤2000, and the current I≥5A, the longitudinal length L≥3mm, and the longitudinal length L≤2 / 3 of the vertical distance between the circumferential air inlet nozzle and the anode high-temperature container. The ratio of the arc of the fence to the interval between two adjacent fences is 1 to 2:

1.

4. The transferred arc plasma device for gas-based reduction of metal oxides according to claim 1, characterized in that, An optical measurement window is provided on the side wall of the reactor body, and an optical emission spectrometer and a high-speed camera are equipped outside the optical measurement window.

5. The transferred arc plasma device for gas-based reduction of metal oxides according to claim 1, characterized in that, The cooling unit includes a cooling collection tank, a sintered filter element, and a cooling sleeve. The cooling collection tank is connected to the collection port. The sintered filter element is disposed inside the cooling collection tank. The cooling sleeve is connected to the glove window on the tank wall of the cooling collection tank. The cooling sleeve is provided with an inner glove. The cavity outlet of the sintered filter element is connected to the gas channel of the plasma cathode through a circulation pipe, and a gas circulation pump is installed on the circulation pipe.

6. The transferred arc plasma device for gas-based reduction of metal oxides according to claim 5, characterized in that, The collection unit includes an isolation box, a hopper, a material valve, and a material dispensing valve. The hopper is connected to the bottom of the cooling collection tank via a pipe. The hopper, material valve, and material dispensing valve are located inside the isolation box. The material valve and material dispensing valve are located on the pipe, and the material dispensing valve is located near the hopper.

7. The transferred arc plasma device for gas-based reduction of metal oxides according to claim 1, characterized in that, The gas channel inside the nozzle of the plasma cathode is connected to the gas supply device. The gas outlet of the reactor body is connected to a vacuum pump.

8. The method for gas-based reduction of metal oxides using a transferred arc plasma apparatus according to any one of claims 1-7, characterized in that, Includes the following steps: S1, after the metal oxide material is pressed into shape, it is placed in a vacuum atmosphere anode high temperature container, and then the mixed gas is introduced into the interior of the reactor body through the circumferential gas inlet nozzle. S2, start the power supply to discharge, so that an electric arc plasma is formed inside the reactor body, and the circumferential gas inlet nozzle head continues to supply gas to ensure that the working pressure inside the reactor body is constant. At the same time, the electric arc plasma is used to ionize the reducing agent gas to excite the active groups formed to reduce the metal oxide material, generating metal vapor and by-product synthesis gas. S3, the metal vapor is extracted to the cooling unit, the metal powder is scraped out in the cooling unit, and the non-condensable gas is extracted to the gas channel of the plasma cathode by the gas circulation pump for recycling; S4, after the gas-based reduction reaction is completed, the scraped metal powder is collected in an isolation box, sealed, and transferred.

9. The method for reducing metal oxides using gas-based methods according to claim 8, characterized in that, In step S1, the vacuum degree of the reactor body is ≤10Pa; The mixed gas is composed of a reducing agent gas and an inert gas in a volume ratio of 0.1 to 8:1; After the mixed gas is introduced into the reactor body, the working pressure inside the reactor body is maintained at 0.1~1.5 atm; The reducing agent gas is one or more of hydrogen, CO, and C1-C4 light hydrocarbon gases.

10. The method for reducing metal oxides using gas-based methods according to claim 8, characterized in that, In step S3, the extraction rate of the metal vapor is 0.5~50L / s, and the temperature of the cooling unit is below 150℃.

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