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WO2025160681A1 - Chauffage et fusion de métaux par plasma - Google Patents

Chauffage et fusion de métaux par plasma

Info

Publication number
WO2025160681A1
WO2025160681A1 PCT/CA2025/050138 CA2025050138W WO2025160681A1 WO 2025160681 A1 WO2025160681 A1 WO 2025160681A1 CA 2025050138 W CA2025050138 W CA 2025050138W WO 2025160681 A1 WO2025160681 A1 WO 2025160681A1
Authority
WO
WIPO (PCT)
Prior art keywords
plasma
furnace
heating
melting
heat
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/CA2025/050138
Other languages
English (en)
Inventor
Juan Ernesto SALAZAR PENA
Pierre Carabin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Pyrogenesis Inc
Original Assignee
Pyrogenesis Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pyrogenesis Inc filed Critical Pyrogenesis Inc
Publication of WO2025160681A1 publication Critical patent/WO2025160681A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/16—Remelting metals
    • C22B9/22—Remelting metals with heating by wave energy or particle radiation
    • C22B9/226—Remelting metals with heating by wave energy or particle radiation by electric discharge, e.g. plasma
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Electric arc furnaces ; Tank furnaces
    • F27B3/10—Details, accessories or equipment, e.g. dust-collectors, specially adapted for hearth-type furnaces
    • F27B3/20—Arrangements of heating devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D11/00—Arrangement of elements for electric heating in or on furnaces
    • F27D11/08—Heating by electric discharge, e.g. arc discharge
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D99/00—Subject matter not provided for in other groups of this subclass
    • F27D99/0001—Heating elements or systems
    • F27D99/0033—Heating elements or systems using burners
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H2245/00—Applications of plasma devices
    • H05H2245/80—Burners or furnaces for heat generation, for fuel combustion or for incineration of wastes

Definitions

  • Hydrogen can also be produced via electrolysis of water. When a clean electricity grid is used, the process of production of hydrogen can be considered carbon neutral. However, the process of producing hydrogen through electrolysis, compressing and transporting it to its final use destination and combusting it for industrial heating is generally inefficient, with overall efficiency of electricity to heat of 50% or less.
  • the conventional system used is the reverberatory or hearth-type furnace.
  • These conventional furnaces are usually box-shaped (and less frequently cylinder-shaped), with a refractory lined chamber that holds a metal charge that occupies the entirety of the furnace bottom area while the remaining space, above the metal charge, constitutes a chamber to which the burners inject combustion products and heat.
  • the chamber in conventional furnaces is not usually sealed and allows for large quantities of air ingression. Therefore, combustion products like carbon dioxide, water vapor and nitrogen interact with air, which in turn interact with the metal charge, with undesirable effects like formation of oxides on the metal surface, also known as dross, and production of nitrogen oxides in the chamber’s atmosphere.
  • the former represents a metal loss and thus lower productivity, while the latter are harmful acid gases that find their way to the outside of the furnace in the form of fume emissions.
  • furnaces that are supplied with resistive heating elements
  • these are usually installed in the roof of the chamber (also called the vault) and generate heat via Joule effect, which then radiates to the metal charge below.
  • the use of this method also comes with substantial disadvantages that have hindered its widespread adoption in mid to large-scale industrial settings, where furnace capacities can be in the range of 50 to 120 t (metric tons).
  • heating elements have a low energy density, which means that they pose a limitation on the size of the furnaces they can heat. In other words, they are not powerful enough for a majority of reverberatory furnaces at industrial scale.
  • furnaces with resistive elements tend to generate more dross, specially when used as holders, compared to the conventional combustion furnaces.
  • a conductive metal charge or load is heated by electromagnetic induction.
  • the prevalent type in industrial applications is the coreless induction furnace, where the metal is placed inside a refractory lined crucible and heated via Joule effect by eddy currents induced in it by the magnetic field generated in a coil that surrounds the metal charge.
  • the magnetic field is generated with current from an AC power supply.
  • the coil is usually made of copper and is hollow to allow cooling water (or another fluid) to circulate through it.
  • it is embedded inside the refractory lining of the crucible.
  • induction furnaces tend to be of low capacity and are considered more difficult to operate and maintain, specially for the embedded induction coil in the refractory wall of the furnace. It means that these furnaces are inherently complex and more prone to accidents without special controls and supervision, that large-scale capacities (as defined in hereinabove [0013]) are not attainable in practice with these furnaces, and that refractory changes need to be made more frequently to decrease safety risks, resulting in increasing operating and maintenance costs, namely higher CAPEX and OPEX.
  • One such method is using a plasma torch, which directly converts electricity to a high temperature plume or flame with near-zero emissions, in the case of access to a clean grid (electricity produced from renewable resources).
  • a plasma torch directly heats a reactive gas such as air or a neutral gas such a argon with electricity, without any combustion process.
  • US4583229A describes a method and apparatus for heating and melting electrically conductive material.
  • the method includes the steps of heating a jet of gas or gaseous mixture, directing a heated jet of gas or gaseous mixture to the material, and drawing a diffuse current through said gas jet to said material by seeding it with an additive having a low ionization potential so as to increase the rate at which the material is heated.
  • the apparatus includes means for heating gas(es), means for directing a jet of said gas(es) to the material, means for introducing an additive having a low ionization potential into the gas(es) for purposes of ionizing said gas(es), and means for drawing a diffuse current through the jet of ionized gas to the material.
  • W02004050939 describes a device whereby a solid is added to a melting region, a plasma is formed in a cavity by subjecting a gas to electromagnetic radiation of less than about 333 GHz, and a plasma is sustained in the cavity such that the plasma melts the metal into a liquid.
  • US2023110818A1 describes an apparatus for melting metals using a plasma aligned in the direction of a material to be melted, and a melting tank or crucible is arranged in the melting furnace to receive the molten metal.
  • CN112762463A discloses a plasma melting furnace device based on flue circular heating.
  • the plasma melting furnace device comprises a furnace body connected with a furnace cover in a sealed mode and plurality of plasma torch channels.
  • US4583229A suffers from several limitations, such as the need to use a complex bottom anode at high cost and the requirement to use an additive with low ionization potential, also at high cost.
  • US5122181A suffers from several limitations, notably that the furnace is large and complex.
  • the furnace has low filling volume, meaning that it is unnecessarily large and has therefore a low energy efficiency.
  • JP2015068576A suffers from several limitations, notably a complex system due to the rotating crucibles, leading to high maintenance.
  • the fact that the torch is inside the furnace means that it is exposed to highly exposed to process heat leading to excessive heat losses from the torch exposed surfaces which need to be cooled.
  • W02004050939 suffers from limited industrial applicability and scalability since high power magnetrons are not widely available and need to be custom designed and produced, resulting in high costs.
  • CN1 12762463A will require complex and costly refractory installation for the amount of heat that may be recovered. Potential heat recovery is limited due to the low expected temperature differential between the exhaust and the refractory layer below the molten pool. Having a cavity below the molten pool also creates risk of potential metal leaks. To decrease the risk of molten metal leaks, stronger refractory materials and more complicated construction is required, thereby increasing construction costs.
  • Figure 1 is a general overview of the process for melting metal using a plasma torch in a closed furnace with recirculation of the plasma forming gas;
  • FIGS 2 to 7 show detailed views of different alternatives for installation of the plasma torch on the wall of the furnace
  • Figure 8 is a graph showing the effect of plasma gas nature on the time to melt the aluminum charge.
  • Figure 9 is a graph showing a Carbon footprint comparison (kg CO2 eq /tAi) of different heating methods.
  • a method and system for heating and melting metals having melting temperatures up to 2000 °C includes one or several DC nontransferred electric plasma torches, a refractory lined furnace, and a plasma gas recovery sub-system comprised of a cleaning module, a heat recovery module, and a recompressing module.
  • the system is intended to melt the metal inside the furnace by indirect heating provided by the torch using an inert gas as plasma forming gas while maintaining the furnace’s inner atmosphere under the same inert gas.
  • a present object is to provide a method and system to minimize or eliminate the detrimental effects to production described above, while at the same time decreasing environmental impact at an industrially implementable scale.
  • One or more non-transferred arc DC plasma torches can be used to provide heat to the inner furnace atmosphere of a reverberatory or hearth-type furnace.
  • the plasma plume of the torches is created using a compressed gas, such as (but not limited to) air, nitrogen, or argon.
  • a compressed gas such as (but not limited to) air, nitrogen, or argon.
  • an inert gas such as argon, oxidation of the metal is minimized since there is no residual oxygen available to oxidize the metal in the furnace atmosphere.
  • the plasma plume generated by the plasma torch [02] increases the temperature of a full metal charge in the furnace by convection and radiation, without being oriented directly to the charge or having to touch it. This mode of operation reduces metal oxidation effect and thus metal loss.
  • the metal is melted in place without having to be transferred from one part of the furnace to another, creating a pool of molten material suitable for alloying and blending with new or reused material to be melted or recycled, at an industrial scale.
  • Positioning of the plasma torch [02] can be adjusted using a swivel mount (not shown) or fixed at different preset angles in order to modify the angle of attack of the plume relative to the metal charge, either using a mounting block method (as in Figure 4) or a mounting plate method (as in Figure 3), in both cases incorporating oversized openings (flange holes, steel shell and refractory wall holes, mounting block or mounting plate holes) and the use of flexible and/or rigid insulators sized accordingly, as shown in Figure 6.
  • a swivel mount (not shown) or fixed at different preset angles in order to modify the angle of attack of the plume relative to the metal charge
  • a mounting block method as in Figure 4
  • a mounting plate method as in Figure 3
  • the heating up of the furnace is done to temperatures above the melting point of the metal to melt while at the same time not exceeding the working operation temperature of the refractory employed in normal foundry operations for the metals such as aluminium, zinc, copper, nickel, iron, and steel.
  • the furnace [01 ] can be an existing furnace which can be retrofitted with one or more plasma torches, by means of changing the installation port (or installation block), which is usually a precast refractory shape. In that way, no changes to the refractory wall are needed for installation or operation, as mentioned above (in preceding [0048], and only care needs to be taken to keep the plasma torch electrically insulated from the furnace wall and from the bracket structure or any other structural support attached to the steel shell or connected to the furnace (via direct or indirect conduction) that will be used for installing the plasma torch in operating position. This can be achieved in different ways.
  • thermoelectric insulator piece shall be installed on all surfaces that may come in contact with the torch’s body, both on the furnace wall and on the supporting structure.
  • a mounting block (different than the installation port) placed on the supporting bracket may have a hole pattern that will receive the flange of the torch.
  • Tubular insulators (insulation cylinders) shall be installed in those holes to allow passing bolts.
  • the bolts themselves will be insulated from the torch's flange with washers made with an electrical or thermoelectrical insulating material such as mica.
  • a layer of insulating fiber or flexible insulation may fill up the space between the torch's body and the hole through which the torch is introduced in the installation block. All these elements can be seen in greater detail in Figure 5.
  • the heated gases in the furnace’s atmosphere [03], or exhaust are directed to a gas recovery subsystem that includes a stage of gas cleaning or filtering [04], a stage of cooling down [05] (with or without heat recovery), and a stage of recompression [06], as shown in Figure 1.
  • the stage of cooling down may involve transferring heat from the exhaust gas to another process application.
  • a nitrogen plasma torch with a high enough flow rate is used to improve furnace performance, that is to decrease the time it takes to heat the furnace (from ambient to melting temperature) and to decrease the time it takes to melt the metal charge (from solid state to liquid state of all the metal), both of which result in increasing productivity.
  • This higher flow rate tends to improve the heat transfer by convection in the furnace and thus improves thermal efficiency.
  • it increases the pressure in the furnace decreasing the possibility of cold air ingress in the chamber, which positively affects performance of the furnace and limits oxidation.
  • an argon plasma torch with a higher flow rate (as compared with air or nitrogen) is used to improve furnace performance, that is to decrease melting time and holding time, thus increasing productivity.
  • This higher flow rate tends to improve the heat transfer by convection in the furnace and thus improves thermal efficiency.
  • it increases the pressure in the furnace decreasing the possibility of cold air ingress in the chamber, which positively affects performance of the furnace.
  • performance of the system can be improved by up to 30% when comparing net energy consumption to melt the charge with the present system (kWh/kg of melted metal) versus that of a natural gas fired furnace in equivalent conditions.
  • the plasma plume allows increased heating because it combines convective, due to the high-speed plasma jet, and radiative heating, compared to conventional heating which relies mainly on radiative heating.
  • time to reach melting temperature of the charge can be decreased by up to 35% when comparing a furnace operating with the present system versus equivalent natural gas fired furnaces or hydrogen fired furnaces (both of which tend to have the same melting time).
  • the carbon footprint of the present system can be practically eliminated, representing less than 1 % of the emissions of melting with natural gas (in terms of kg CO2eq/ kg of melted metal) when compared with a plasma torch running with nitrogen and clean electricity (grid with 99% renewable sources). Even in a mixed grid (55% renewables and non-GHG sources), there could still be a reduction in carbon footprint, of up to 5% (compared to 99% in the case of clean electricity).
  • the inner atmosphere of a new furnace ([03] in Figure 1 ) may be designed to be a lot smaller compared to a conventional furnace, thanks to the lower amount of input gas compared to a natural gas or oxy gas operation of existing furnaces, thus decreasing construction and equipment cost (CAPEX).
  • the inner atmosphere may be flooded and kept permanently under inert gas, such as nitrogen, argon, or a mix.
  • inert gas such as nitrogen, argon, or a mix.
  • the inert gas in the system protects the molten metal from oxidation and thus prevents metal loss.
  • a nitrogen atmosphere is combined with the use of a nitrogen plasma torch and generation of near zero nitrogen oxides can be achieved.
  • the above alternative can be implemented with the same results of near zero nitrogen oxides but using an argon atmosphere and an argon torch.
  • a set of multiple torches can be used where, one or more are run using air as plasma forming gas, and one or more are run using an inert gas as plasma forming gas.
  • the air torch is run during most of the melting cycle, the period where the metal charge is still in solid form. Once the metal starts to melt, to decrease metal oxidation, the air torch is turned off and the argon torch is turned on. This combination results in a more cost-effective operation (much lower OPEX) and in less metal loss, making it more economically feasible for the specialty alloy market.
  • a sealing mechanism by means of mechanical action (for example, hydraulic) and common ceramic rope or mineral wool seals in the furnace door is installed to prevent air ingress in operating conditions of low flow rate of plasma injected to the furnace.
  • Near zero nitrogen oxides can also be achieved in the present system by combination of a high flow argon plasma torch with or without a mechanically assisted sealing system.
  • liquid nitrogen can be used in the cooling stage of the gas recovery subsystem.
  • liquid nitrogen will change into nitrogen gas, that can in turn be fed to the furnace atmosphere or compressed as plasma forming gas or as sheath gas to shield electrodes inside the plasma torch.
  • Liquid nitrogen cooling systems are commercially available from companies in the USA and elsewhere.
  • Table 2 shows that the net specific energy requirement is consistently less than the reference oxyfuel natural gas case.
  • the reduction in net energy requirements ranges from 15% (Test #8) to 29% (Test #6).
  • Figure 8 compares the melting time for the oxyfuel natural gas case with three examples from the trials. The heating time is reduced from 29% (test #8) to 35% (test #6) when using plasma.
  • Figure 9 compares the carbon footprint of plasma heating to that of natural gas heating with oxyfuel. The following data, obtained from the aforementioned trials as well as equivalent trials with competing heating technologies, was used in the comparison:
  • Table 1 Summary of main test operating conditions.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Furnace Details (AREA)
  • Vertical, Hearth, Or Arc Furnaces (AREA)

Abstract

L'invention concerne un procédé de chauffage et de fusion de métaux, la chaleur étant fournie par une ou plusieurs torches à plasma électriques et étant le résultat de l'utilisation d'un ou de plusieurs gaz de formation de plasma à différentes étapes du processus de chauffage et de fusion, ainsi que dans des étapes précédentes ou ultérieures. Un système associé utilisant du plasma en tant que source de chaleur comprend la ou les torches à plasma électrique, un four à revêtement réfractaire, et un sous-système de récupération de gaz plasma qui comprend un module de nettoyage, un module de récupération de chaleur et un module de recompression. Le gaz plasmagène contribue au retardement de l'atmosphère à l'intérieur d'un four. Dans un procédé d'installation d'une ou de plusieurs torches à plasma sur un nouveau four ou un four existant, les torches à plasma sont montées spécifiquement pour permettre une isolation thermique et/ou électrique, et le positionnement de la torche à plasma peut être ajusté pour réduire l'oxydation métallique et/ou améliorer le transfert de chaleur.
PCT/CA2025/050138 2024-02-01 2025-02-03 Chauffage et fusion de métaux par plasma Pending WO2025160681A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US202463548846P 2024-02-01 2024-02-01
US63/548,846 2024-02-01

Publications (1)

Publication Number Publication Date
WO2025160681A1 true WO2025160681A1 (fr) 2025-08-07

Family

ID=96589267

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CA2025/050138 Pending WO2025160681A1 (fr) 2024-02-01 2025-02-03 Chauffage et fusion de métaux par plasma

Country Status (1)

Country Link
WO (1) WO2025160681A1 (fr)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3429564A (en) * 1965-08-02 1969-02-25 Titanium Metals Corp Melting furnace
WO2001053434A1 (fr) * 2000-01-21 2001-07-26 Integrated Environmental Technologies, Llc. Procedes et appareil de traitement de dechets

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3429564A (en) * 1965-08-02 1969-02-25 Titanium Metals Corp Melting furnace
WO2001053434A1 (fr) * 2000-01-21 2001-07-26 Integrated Environmental Technologies, Llc. Procedes et appareil de traitement de dechets

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