WO2025160681A1 - Plasma heating and melting of metals - Google Patents

Abstract

A process for heating and melting metals wherein the heat is supplied by one or several electric plasma torches and is the result of using one or different several plasma forming gases at different stages of the heating and melting process, as well as in previous or subsequent stages. An associated system using plasma as the heat source includes the one or more electric plasma torches, a refractory lined furnace, and a plasma gas recovery sub-system that comprises a cleaning module, a heat recovery module, and a recompressing module. The plasma forming gas contributes to the inerting of the atmosphere inside a furnace. In a method of installing one or several plasma torches on a new or existing furnace, the plasma torches are mounted specifically to allow for thermal and/or electrical insulation, and the positioning of the plasma torch can be adjusted to reduce metal oxidation and/or improve heat transfer.

Description

TITLE

PLASMA HEATING AND MELTING OF METALS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority on U.S. Provisional Application No. 63/548,846, now pending, filed on February 1 , 2024, which is herein incorporated by reference.

FIELD

[0002] The present subject matter relates to the heating and melting of metals, and, more particularly to the use of a one or several plasma torches in a furnace to achieve this heating and melting operation.

BACKGROUND

[0003] Industrial users have a need to melt metals such as aluminium for alloying purposes or for further processing such as casting operations. Industrially useful metals include (but not limited to), in addition to aluminium, zinc, copper, nickel, iron, and steel.

[0004] Currently, the predominant method to melt these metals relies on the use of burners using fossil fuels like pulverized coal, natural gas or other hydrocarbons (bunker oil, heavy fuel oil, light fuel oil, etc.). The combustion of these types of fuels generates carbon dioxide emission as combustion byproduct.

[0005] The use of fossil fuels generates large amounts of greenhouse cases, in the form of carbon dioxide. According to the Paris agreement signed in 2015, 194 parties have agreed to substantially reduce global greenhouse gas emissions to limit the global temperature increase in this century to 2 degrees Celsius while pursuing efforts to limit the increase even further to 1.5 degrees Celsius. [0006] Newer approaches have been proposed, such as the use of hydrogen as fuel since the combustion of hydrogen releases only water vapor as a combustion byproduct. However, water vapor is also considered a greenhouse gas and large amounts of water vapor in the atmosphere can amplify the greenhouse gas effect. In addition, hydrogen is mostly derived from hydrocarbons through the steam methane reforming process, using natural gas as a feed stream and generating carbon dioxide emissions through its production process.

[0007] 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.

[0008] Industries are under intense pressure to reduce greenhouse emissions from their processes, notably for the heating and melting of metals.

[0009] In the case of lower melting temperature metals, whose melting point tends to be below 1100 °C, 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.

[0010] 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.

[0011] Alongside dross formation, conventional furnaces face the problem of product ignition from the presence of highly reactive elements in the metal charge, as in the case of aluminum magnesium alloys, very commonly found in common melting applications such as recycling of beverage cans. When treating these materials, fires in the chamber of these type of furnaces are thus inherent to their design, which allows oxygen presence in the furnaces’ atmosphere, and ultimately result in added metal loss, further lowering productivity and increasing the environmental impact of the furnace’s operation because of increased emissions from metal product fires and the need for processing of an increased amount of oxides from the lost metal.

[0012] To alleviate the shortcomings of the conventional furnaces (technical and/or environmental), alternative methods to heat and melt a metal charge using electricity have been proposed in the past, mainly induction and resistive heating.

[0013] In the case of 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). Chiefly, 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. In addition, furnaces with resistive elements tend to generate more dross, specially when used as holders, compared to the conventional combustion furnaces. This is because, due to the high reflectivity of the molten metal, they usually require a large bath area for heating to be effective, and this high surface area of metal exposed to an air atmosphere containing oxygen increases the potential for dross formation and hydrogen pick-up during holding. Moreover, resistive heating elements tend to get prematurely damaged at the operating conditions present in these furnaces, mainly due to high temperature oxidation of the manufacturing material of the elements but also because of dust and metal splashes present in the environment. This results in a less reliable equipment and an increase in maintenance and operation costs (higher OPEX).

[0014] To try to limit these negative impacts on the resistive elements, manufacturers tend to try to get the elements as far as possible from the melt, increasing the distance from the molten metal line to the roof of the furnace, which translates in a bigger chamber for the same capacity of furnace, when compared to conventional furnaces with burners. It also translates in bigger size of air handling and dust collection equipment. All these result in an increase in construction materials costs, initial investment costs, refractory repair and reconstruction costs, namely higher capital expenditures (CAPEX) and operating expenditures (OPEX).

[0015] In the case of induction 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. In the coil 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. For the coil to surround the metal, it is embedded inside the refractory lining of the crucible. It means that special care must be taken to prevent the refractory lining from becoming thin or from cracking, which could result in the metal charge, now molten, coming in contact with the coil and its cooling water resulting in an explosion. Furthermore, to decrease this safety risk, the coil should ideally be manufactured in a single piece, to avoid or decrease the need of welding seams that represent potential failure spots.

[0016] Because of the above limitations, 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.

[0017] Given the shortcomings mentioned above of large-scale industrial implementation of the usual electric furnace options in the market today, it would therefore be desirable to have other methods to electrify the operation of reverberatory furnaces. 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.

[0018] Several methods and apparatus have been proposed for the melting of metals using plasma.

[0019] For example, 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.

[0020] US5122181A describes a process and apparatus for melting contaminated metalliferous scrap material. This description comprises a rotary furnace heated by means of a contained arc plasma torch and an incinerator for oxidizing the volatile contaminants withdrawn from the furnace. [0021] JP2015068576A describes a plasma melting device comprising a pair of crucibles, a rotary mechanism acting as a moving mechanism for moving the crucibles to a melting position and a non-melting position and a plasma torch for irradiating an object to be melted housed in a crucible.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] However, the proposed methods suffer from several limitations, leading to difficulty in scale-up, excessive costs or low energy efficiency.

[0026] For example, 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.

[0027] 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.

[0028] JP2015068576A suffers from several limitations, notably a complex system due to the rotating crucibles, leading to high maintenance. In addition, 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.

[0029] 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.

[0030] The process described in US20231 10818A1 will be difficult to industrialize as continuous operation would require several manual steps to reload the material and collect the resulting product in a crucible. An additional limitation is that the initial material needs to be in block form, which is not always the case. Sometimes, the feed material will be in the form of pellets or shavings. The fact that the feed material is in block form also limits the possibility of making alloys.

[0031] 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.

SUMMARY

[0032] It would thus be desirable to provide a novel method and/or system for heating and melting metals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, which show at least one exemplary embodiment, and in which: [0034] 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;

[0035] Figures 2 to 7 show detailed views of different alternatives for installation of the plasma torch on the wall of the furnace;

[0036] Figure 8 is a graph showing the effect of plasma gas nature on the time to melt the aluminum charge; and

[0037] Figure 9 is a graph showing a Carbon footprint comparison (kg CO2_eq/tAi) of different heating methods.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] A method and system for heating and melting metals having melting temperatures up to 2000 °C is disclosed and 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.

[0039] Accordingly, 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.

[0040] In the present system, as shown in Figure 1 , a substantial metal charge [00], that occupies the entirety of a furnace [01 ] bottom surface area and the majority of its available internal volume, is heated and melted by a plasma torch [02], The remaining volume constitutes the furnace’s atmosphere [03],

[0041] The metal charge can be various metals, of relatively low or high melting temperatures, such as aluminium, zinc, copper, nickel, iron, and steel. [0042] The furnace [01 ] can be of the reverberatory or hearth type. The furnace can be box-shaped or cylindrically shaped. The furnace [01 ] is composed of a steel shell lined with a refractory.

[0043] The plasma torch [02] is preferably of the non transferred arc type, meaning that it will heat a plasma forming gas inside the torch, resulting in the production of a plasma plume, similar to a flame. The plasma torch is preferably of the direct current (DC) type but can also be of the alternating current (AC) type, microwave or radiofrequency (RF) type. DC arc plasma torches are the most commonly type of torches available industrially at high power, meaning at 500 kW and more.

[0044] One or more non-transferred arc DC plasma torches [02] 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. In the case of 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.

[0045] Since the plasma torch [02] converts electricity to heat by the means of an electric arc, no combustion is involved in the generation of the plasma plume. Since the heat produced by the plasma torch is electric in origin, no direct carbon dioxide emissions are produced. Specifically, in this system usable heat is produced when a compressed gas is forced to pass through an electric arc inside the torch which causes the gas to ionize and exit the torch in form of a plasma jet or plume, at bulk temperatures up to 5000 °C.

[0046] 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.

[0047] 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. With this adjustable positioning, a better heat transfer and temperature distribution can be achieved, as well as metal oxidation can be reduced.

[0048] In this system, 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.

[0049] In this system, as shown in Figure 2, 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. In the alternative shown in Detail A of Figure 2, the stud and nut fixation system that holds the installation block against the furnace’s outer steel shell can be used to fixate a plasma torch directly to the installation block by adding insulation cylinders and insulation washers to prevent the metal studs (welded to a plate and in contact with the steel shell) and corresponding nut to come in contact with the metal of the torch’s flange, as depicted in Detail A1 of Figure 3. A U-support or pipe saddle, welded or bolted to the mounting bracket, can be used for extra structural support, provided electrical insulation (for example, with insulating fiber) is properly installed between the torch and the saddle.

[0050] In the alternative shown in Detail B of Figure 4, a 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. For that purpose, 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. In addition, 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.

[0051] In another alternative for installation of the torch, use of the electrical insulation elements can be omitted, provided that the furnace body (and therefore the ensemble torch and furnace) has been properly grounded.

[0052] Alternatives described above (in the three preceding paragraphs [0049], [0050], and [0051 ]) allow for safe operation of the torch in the furnace system. They also offer safe ways to mount and unmount it, increasing thus maintainability and practical solutions for different torch setups, ranging from the small-sized torches (in the kW level), as in the case of [0049], to the higher power bigger torches (in the multiple MW level), as in the case of [0050], In all cases, flexible insulation pieces may serve a double purpose as insulators and dust seals, also contributing to the cleanliness of the exterior of the furnace and a better environment for maintenance interventions.

[0053] In the present system, 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.

[0054] With the gas recovery subsystem, savings in operation cost (OPEX) associated to the reuse of inert gas can be equivalent to those obtained in commercially available systems, that is up to 45% of the cost of supply of the inert gas being recirculated.

[0055] Further to the operation cost savings described in [0054], additional savings are possible with the present system, by means of eliminating dross generation.

[0056] In an alternative embodiment, 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. In addition, 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.

[0057] In an alternative embodiment, 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. In addition, it increases the pressure in the furnace decreasing the possibility of cold air ingress in the chamber, which positively affects performance of the furnace. [0058] Accordingly, 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.

[0059] In addition, 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).

[0060] Furthermore, 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).

[0061] In the present system, 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).

[0062] In the present system, the inner atmosphere may be flooded and kept permanently under 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.

[0063] In an alternative, a nitrogen atmosphere is combined with the use of a nitrogen plasma torch and generation of near zero nitrogen oxides can be achieved. [0064] For specialty metal alloys, the above alternative can be implemented with the same results of near zero nitrogen oxides but using an argon atmosphere and an argon torch.

[0065] In the above alternative [0064], a lower flow rate plasma torch can be used, which usually implies smaller equipment, with the objective to optimize operation (OPEX) and investment cost (CAPEX).

[0066] Furthermore, 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. In this alternative, 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.

[0067] In an alternative, 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.

[0068] 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.

[0069] In an alternative, liquid nitrogen can be used in the cooling stage of the gas recovery subsystem. In this cooling process, 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.

Example [0070] As shown in Table 1 , several trials were done using different plasma gases (argon, air and nitrogen) and different plasma gas flow rates in a bench scale (60 kg) furnace.

[0071] 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).

[0072] 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.

[0073] 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:

[0074] 1 - Energy consumption of an oxy-gas industrial reverberatory furnace for both operation with natural gas and hydrogen: 510 kWh/t Al

[0075] 2- Energy consumption of industrial reverberatory furnace equipped with a nitrogen plasma torch: 453 kWh_e/t Al

[0076] 3- Natural gas carbon footprint: 0.21 kgCO2/kWhi_cv

[0077] 4- Oxygen carbon footprint: 0.143 kgCO2/Nm3

[0078] 5- Hydrogen carbon footprint: 0.12 kgCO2/kWhi_cv

[0079] 6- Electricity carbon footprint: 0.0845 kgCO2/kWh_e. France electricity grid

[0080] 7- Electricity carbon footprint: 0.0013 kgCO2/kWh_e. Quebec electricity grid, 2022, 99 % renewable. [0081] In the case of the grid in Quebec, Canada, which consists of 99% renewables, the carbon footprint is reduced by 99% when comparing plasma to the natural gas oxyfuel case.

Table 1 . Summary of main test operating conditions.

Table 2. Summary of main test results. [0082] While the above description provides examples of the embodiments, it will be appreciated that some features and/or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. Accordingly, what has been described above has been intended to be illustrative of the embodiments and non-limiting, and it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto.

Claims

1. A process for heating and melting metals wherein the heat is supplied by one or several electric plasma torches.

2. A process according to claim 1 for heating and melting metals wherein the heat supplied is the result of using one or several plasma forming gases at different stages of the heating and melting process, as well as in previous or subsequent stages.

3. A system for heating and melting metals using plasma as the heat source comprising one or several 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.

4. A system according to claim 3 for heating and melting metals using plasma as the heat source wherein the use of a plasma forming gas contributes to the inerting of the atmosphere inside a furnace.

5. A method of installing one or several plasma torches on a new or existing furnace wherein the plasma torches are mounted specifically to allow for thermal and/or electrical insulation.

6. A method according to claim 5 wherein the positioning of the plasma torch can be adjusted to reduce metal oxidation and/or improve heat transfer.