WO2014062063A1

WO2014062063A1 - Method and reactor for melting of solid metal

Info

Publication number: WO2014062063A1
Application number: PCT/NO2013/050164
Authority: WO
Inventors: Karl VENÅS
Original assignee: ALU INNOVATION AS
Current assignee: ALU INNOVATION AS
Priority date: 2012-10-18
Filing date: 2013-09-30
Publication date: 2014-04-24
Anticipated expiration: 2015-04-18
Also published as: NO334541B1; NO20121216A1

Abstract

The publication relates to a method for melting solid metal, such as scrap aluminum, where the solid material is placed in a closed, insulated container (12) of a material having refractory qualities, the container (12) being provided with a bottom contact or electrode (26) and where the scrap metal preferably is compacted at least on the bottom of the container (12), and where an electrode (25) is lowered down into contact with the preferably compacted metal (11). Electric current is connected to the bottom contact (26) and the electrode (25) so that an electric current passes between the electrode (25) and the bottom contact (26) through the solid material (11). As an electrode a rotatable hollow cylinder (16) with a downwards open end (18) is used, the electrode (25) being arranged inside the rotatable hollow cylinder (16) and that the container (12) moreover is provided with a cylinder (19), for example made of graphite, surrounding the rotatable electrode (25); that solid metal at least is arranged inside the cylinder (19); that a light arc (29\8) is established between the electrode (25) and the metal (11) in contact with the bottom contact (26); and that the electrode is maintained in a non-rotating, stationary mode until the solid metal at least inside the cylinder (19) more or less has melted, whereupon the electrode (25) is brought to rotate. The publication also relates to a reactor (19) that uses an electrode forming a part of a hollow and rotatable rotor (15), the electrode (25) being arranged med a lower end inside the hollow rotatable rotor (15), and that the rotor (15) is arranged inside a stationary cylinder (19) surrounding the rotor(15), the cylinder (19) being provided with apertures (20,20') communicating with a space (13) in the container (12) that surrounds the cylinder (19).

Description

METHOD AND REACTOR FOR MELTING OF SOLID METAL

The Technical Field of the Invention

The present invention relates to a method and a reactor for melting solid metal, such as scrap aluminum, where the solid metal is introduced into a closed, insulated container, made of a refractory material, and arranged at the bottom region of the container, and where a rotor with an electrode is lowered down in direction towards the preferably compacted metal, whereupon electrical current is supplied to the bottom contact and rotor together with the electrode, for adding melting energy to the solid material to be melted.

Background for the Invention

As known recirculation of scrap aluminum requires only 5% of the energy required for producing the primary metal. Both from an environmental and

economical aspect it is therefor desirable to recover and recycle as much metal from the scrap metal as possible in an effective and energy saving manner. As the total volume of aluminum scrap increases, the need for effective and energy saving melting processes are also needed.

The metal to be melted may have a thickness down to 0.0006 mm, meaning that aluminum easily will oxidize if air is present in the melting process. Possible presence of oxygen will in addition have a negative effect on the melting of aluminum, since the degree of recovery of aluminum may be heavily reduced.

Another problem related to melting of scrap aluminum, and in particular aluminum used as packages or containers for beverages, is that such scrap metal may contain not negligible volumes of liquid which may be included in the scrap aluminum. During the heating process of such cold, solid metal in a melting reactor, steam may easily be formed, sometimes causing an explosion in the melting container and thus easily may make the process unstable and dangerous. In this respect it should be appreciated that 1 mole of water (18 g) has a volume of 0.018 dm³ and will when evaporated at 25 °C increase its volume to 24.5 dm³ at a pressure of 1 atmosphere. As the scrap metal is heated up to around 700 °C, the volume will increase to 80 dm³. Water trapped inside the pores of the scrap metal may thus create a very high pressure, causing the metal to burst. The water vapor may then cause an explosion.

It is previously known to use fuel burned furnaces for melting cold solid metal.

Such furnaces have a relatively low effect concentration, kW/ton melted metal, requiring a disproportionally high energy consumption with a correspondingly poor recovery economy. Moreover, it is established practice to compress or compact scrap metal in packages that is loaded into the furnace. This means that heat from the burners is transferred to the package via the surface of the package and the heat is transported further into the package by means of thermal conductance in the compressed or compacted metal. At the start, before a melt is established in the furnace, the thermal efficiency is low.

US 4,322,245 describes a method for melting and circulating scrap aluminum in a container. The container consists of two chambers with openings there between, so that the molten metal may flow between the chambers. One of the chambers is closed and uses burners for heating, and the other chamber is open with supply inlet for introducing scrap aluminum, and a rotor that contributes to the circulation of the molten metal. It is established a half dividing wall at the rotor in order to obtain an optimal circulation of the molten metal.

EP 2266371 discloses a method for heating a fluid, in particular a fluid lacking electrical conductivity. According to this solution the rotor body is an electrode arranged in a rotor chamber and a light arc is established between the electrode and the bottom of the rotor body, so that the fluid may be heated.

Hence there is a need for providing an improved method and an improved melting reactor giving a higher metal pay off and where a higher thermal efficiency is achieved, and where the drawbacks of burner heated furnaces also are eliminated or at least reduced.

Summary of the invention

These needs may be achieved by a method and a melting reactor according to the invention.

An object of the present invention is to provide a solution where the drawbacks and deficiencies related to burner heated furnaces are overcome or at least reduced.

Another object of the invention is to provide a method and a reactor for melting scrap metal with a high thermal efficiency and preferably an efficiency in excess of 80 %.

Yet another object of the present invention is to provide a method and a reactor where the degree of recovery of aluminum is increased.

Yet another object of the invention is to provide a method and a reactor enabling use of and providing a more efficient and energy saving melting process.

A further object of the invention is to provide a method and a reactor that reduces the possibilities for formation of oxides in the melting process and/or that is suited for melting aluminum tins or cans and/or aluminum foils or sheets with a thickness down to 0.0006 mm.

Yet another object of the invention is to provide a method and a reactor that secures improved efficiencies in a safe manner for removal of versatile environ- menttally detrimental gases and/or particles from the melting process.

A still further object of the invention is to provide a method and a reactor for melting where exposure of the electrode against solid metal is eliminated or at least substantially reduced.

A still further object of the invention is to provide a solution that reduces wear and tear on the rotor and the electrode and that protects the rotor and the electrode against detrimental contact with solid state metal.

The above identified objects are met by a method and a melting reactor as defined by the independent claims, while variants or different embodiments of the invention or equivalent solutions may be derived from the dependent claims.

According to the invention it is provided a method for melting solid metal, such as scrap aluminum. The solid metal is introduced into a closed refractory insulated container provided with a bottom contact or electrode and where the metal preferably is compressed and/or compacted, at least at the bottom of the container, and where an electrode is lowered down into more or less contact with the preferably

compacted or compressed metal. Electrical voltage is then applied to the system of contact/electrode and electrical current passes through the system, so that an electric current flows between the electrode and the bottom contact through the solid metal. In this manner an electric light arc is established between the end of the rotor/electrode and solid metal. According to the invention an electrode in the form of a rotatable, hollow cylinder with a downwards open end is used. Moreover, the container is provided with a cylinder, for example of graphite, surrounding the rotatable electrode. According to one embodiment of the invention, the solid metal to be melted is at least placed within said cylinder and the lower end of the rotor is preferably brought into physical contact with the solid material placed inside the cylinder. An electric light arc is then established between the electrode and the bottom contact. At least during substantial portions of the heating period where the metal is in a solid condition, the electrode is kept in a stationary condition, and rotation of the rotor is initiated only when the solid metal at least inside the cylinder more or less has melted. Thereupon, the rotor with the electrode is brought to rotate continuously. According to the present invention heat is directly transferred to the scrap aluminum which quickly is changed to melted metal. Hot exhaust gasses from the light arc are circulated around the surrounding scrap metal and contribute to effective preheating of the scrap metal.

According to an embodiment of the method the melting may be performed as a continuous melting process, where additional solid metal may be supplied to the container through an inlet supply device as the originally supplied solid metal in the container is melted. Incidentally, it should be appreciated that the additional solid metal is supplied to the space around the cylinder. Surrounding the rotor and the electrode. Alternatively, the melting process may be more or less dis-continuous and performed as a batch process.

The rotational speed of the rotating cylinder and/or the electrode and/or the vertical position of the cylinder and/or the electrode may be regulated. Moreover, the molten metal in the container may circulated inside the container and possibly through openings in the vertical side walls for increasing the supply of and spreading of heat energy to the metal outside the cylinder, whether this is in solid or floating state. Hence a circulation system that contributes to a more effective distribution of heat and energy inside the entire container is established.

According to a preferable variant the height of the cold, solid metal placed inside the cylinder prior to initiating the melting process may be lower that the corresponding height of the scrap metal arranged outside of the cylinder. The purpose of such difference in height may inter alia be to ensure that cold metal introduced into the container does not get in contact with the up and down moveable rotor ore electrode.

According to the invention also a device for melting of cold, solid metal, such as scrap aluminum, is provided. The device comprises an insulated and gastight container of a refractory material, the container being provided with an electric bottom contact and one down into the container projecting electrode. Electric current is connected to the bottom contact for supply of melting energy to the metal.

Moreover, the container is provided with devices for removal of possible exhaust gases produced during the melting process. According to the invention the electrode is surrounded by the rotor and is terminated in a hollow cavity positioned at the lower end of the rotor. The rotor with its electrode is arranged inside a stationary cylinder that surrounds the rotor, the cylinder at its lower end being provided with openings communicating with a space surrounding the cylinder in the container. According to an embodiment the electrode and the bottom contact are configured in such way that an electric light arc is formed between an end of the electrode and the metal, the metal being in electrical contact with the bottom contact.

Moreover, the cylinder may preferably be made of graphite and may be provided with apertures extending through the cylinder wall, so that the molten metal is allowed to circulate from a space inside the cylinder and to the surrounding space and back again. The rotor may preferably be provided with a smooth external, vertical surface, such that possible solid particles of solid metal in the molten metal is prevented from getting stuck on the rotor and from causing damage to the rotor or to the surrounding cylinder.

Moreover, according to an embodiment the container may be provided with a closable device for supply of cold metal in a solid state into the container and a drain plug for tapping of metal in a floating state and/or that the container is provided with an exit duct for waste gasses from the melting process, such exit duct preferably being connected to a plant for cleaning and recovery.

According to the present invention a solution is provided where the effect concentration, kW/ton of molten metal is increased substantially compared with burner heated furnaces. Moreover, removal of versatile gases that are detrimental to the environment and particles from the melting of the scrap metal are made more efficient in that the concentration in the exhaust gases due to the size of the furnace is high and much higher than for burner heated furnaces. Per mass unit of scrap metal, the volume of versatile gases and particles are the same. As the melting level of the gas room is low, the concentration (detrimental compounds from an

environmental point of view + particles)/(volume of gas) will be high and much higher than for burner fired furnaces.

The solution according to the present invention gives also the possibility of increasing the total amount of recovered aluminum, while at the same time very thin aluminum sheets or foils, such as sheets or foils having a thickness down to 0.0006 mm may be recovered.

Moreover, according to the present invention it is possible to achieve a thermal efficiency degree of more than 80 %, making the solution particularly suitable for melting tins or boxes of aluminum and very thin foils or sheet without causing oxidation during the melting process.

Since the heating process extends over a certain period, also the presence of water is given the possibility for gradually evaporate into steam, such that the melting process becomes more equalized and the risk for sudden explosion in the furnace is reduce, thus providing a more predictable process. With the solution according to the present invention the effect concentration, kW per ton molten metal, will be substantially higher than for burner heated furnaces. Correspondingly, removal of versatile detrimental environmental gases and particles from the scrap metal will be more efficient in that it is possible to establish a high concentration of exhaust gases inside the furnace, - much higher that the

corresponding concentrations in respect of burner heated furnaces. Other

advantages are:

• high and enhanced metal recovery;

• high thermal efficiency; and

· good control of exhaust gases produced by the scrap metal during the melting process. Some of these gases can be dangerous from an environmental point of view and may be treated in a closed system.

According to the invention it is provided a cylinder that surrounds the rotor and the electrode. Since the cylinder is arranged around the rotor and the electrode, the cylinder will function as a protective shield for the rotor and the electrode against wear and tear caused by particles in the molten metal or larger or smaller solid particles or scrap portions of solid material.

Short Description of the Drawings

In order to better understand the invention, reference is made to the accompanying drawings showing a possible embodiment of the present invention , wherein:

Figure 1 shows schematically a side view in section through a melting reactor according to the present invention, where solid metal is loaded into the reactor, at an early stage of the melting process;

Figure 2 shows schematically a side view, partly in section of a rotor with incorporated electrode according to the present invention; and

Figure 3 shows schematically a side view corresponding to the side view shown in Figure 1 , but where the melting process has reach a stage where the metal is in molten state.

Detailed Description of the Invention

Figure 1 shows schematically a side view in section through a melting reactor 10 according to the present invention. The reactor 10 is in the form of an insulated refractory container 12 and an insulated refractory top or cap 14, removably arranged on the container 12. A light arc rotor 15 extends downwards into the melting space or room 13 through the top or cap 14. In the melting room or space 13 a stationary cylinder 19 is arranged, preferably fixed to the bottom of the container, surrounding the rotor. The cylinder 19 may be made of graphite or possibly of a refractory material and is resting on the bottom plate of the container 12. At least along the lover region of the cylinder 19, the cylinder 19 is provided with apertures 20,20' extending through the side wall of the cylinder 19. Preferably the cylinder 19 may also be provided with corresponding apertures higher up on the cylinder 19 wall. In this way fluid communication between the inner space or room of the cylinder 19 and the room or space of the container 12 surrounding the cylinder 19 is provided. The rotor 19, mounted on the top or cap 14 is preferably centrally and coaxially placed inside the cylinder 19. The cylinder 19 shown has a circular cross-sectional shape. It should be appreciated, however, that the cylinder 15 may have any other suitable cross-sectional shape such as rectangular, square, pentagonal, hexagonal shape, etc.

The Figure shows a stage at the start of the melting process where the metal 1 1 in solid, compressed or compacted state has been placed into the melting room or space 13 of the reactor through the upper end of container 12, with the top or cap with the light arc rotor removed. The solid metal, which may contain boxes or tins, caps, chips of aluminum, or similar scrap metal, is arranged around the cylinder 19. Also a part of the metal is placed and compacted inside the cylinder 19 such that such metal establishes electrical contact with the bottom electrode 26.

The cap or top 14 and the adjacent parts of the container 12 are provided with sealing and locking devices (not shown) in order to provide sealing and locking effect between the top 14 and the container 12. The sealing and locking devices (not shown) may be of any suited type providing the required sealing and locking effect. Said devices together with the other parts and the ducts into the melting space 13 of the reactor 10 are of a type and are configured in such way that it is possible to form a sub-pressure or a vacuum inside the melting space 13. Moreover, at the bottom of container 12 a bottom contact 26 is arranged, the bottom contact 26 being

connected to an electricity source (not shown).

The sub-pressure or the vacuum is formed by means of a vacuum pump or a suction fan (not shown), connected to a hose connector on an exit duct 22 leading to a cleaning plant (not shown). In the container 12 a light arc rotor 15 is arranged, driven by a motor 29 via a belt transmission 30 or the like and a pulley mounted on a shaft on the rotor 15. The rotor 15 is hollow and at its lower end provided with an aperture 18 that freely communicates with the metal 1 1 below and/or the surrounding molten metal 1 1 '. The shaft is connected to the motor 29 which is mounted on a bracket. The bracket may be mounted on the top 14 of the container 1 1 or on a separate supporting structure (not shown). Sealing devices between the rotating shaft and the container may be in the form of a suitable seal. On the bracket a bearing guiding the rotating shaft may be arranged. An electrode 25 may be arranged centrally and axially inside the shaft. The upper end of the electrode 25 may be connected to power cable, connected by means of a cable contact. If desirable a centrally arranged hole may be drilled through the electrode 25, extending in axial direction, for supply of gas. The hole may in such case be connected to a connector attached to the end of the electrode.

The rotor 15 projects downwards through the container top 14 and down into the melting space 13. Reference is made to Figure 2 showing schematically a side view, partly in section of the rotor 15 with incorporated electrode 25 according to the present invention. The rotor 15 is suspended and supported in such way that movement up and down in axial direction with respect to the cap or top 14 and bottom of the container is facilitated. Moreover, the rotor is also supported in such way that it is allowed to rotate with respect to the top 14 about a vertical axis of rotation. In order to facilitate this, a sealing and rotation device (not shown) is arranged between the top 14 and the rotor 15. As indicated by the arrows in Figure 2, the rotor comprises a hollow, cylindrical jacket or mantel 16, the lower end of which being provided with a chamber 17 having a larger cross-sectional area than the remaining part of the mantel or the jacket 17. Moreover, at its lower end the chamber 17 is provided with an aperture 18 communicating with the space outside the jacket 16. The rotor 15 is of a type disclosed and described in the applicant's own publication No. WO 2012/093943, the entire content of which hereby is included by the reference with respect to mode of function and configuration of the rotor with incorporated electrode, but also other features of significance for the mode of operation, configuration and function. Moreover, centrally and concentrically in the rotor 15, an electrode 25 is arranged, the electrode 25 being configured to be moved up and down with respect to jacket 16, such that the lower end of the electrode may be moved up and down into the chamber 17.

The melting reactor 10 is further provided with a pipe 21 , extending from outside the reactor 10, through the top 14 and into the melting space 13. The pipe 21 is configured for introduction of additional solid scrap metal if and when the melting process requires supply of new, additional solid metal for melting. The supply duct 21 is for this purpose provided with seals (not shown) that can be opened and kept sealed without to any degree affecting the vacuum or sub-pressure inside the chamber 13.

Moreover, the reactor is provided with an exit duct 22 that is connected to a cleaning plant and suction plant (not shown in the Figure) for cleaning the gases from the process and possibly to recover other metals or compounds that have evaporated during the process. Moreover, the exit duct 22 is also provided with seals that enable periodical or continuous removal of exhaust gases and at the same time maintaining the vacuum or sub-pressure inside the container.

At it lower end the container 12 is provided with discharge duct and a discharge plug 23 of a known type 23 that may opened or plugged and that is in communication with a receiving container 25 for receipt of molten metal.

Figure 3 shows schematically a view corresponding to the one shown in Figure 1 , but where the melting process has come to a stage where all the metal 1 1 ' is molten and is in a floating state. As indicated above, the rotor 15 and the electrode 25 is rotated during this stage, thus contributing to circulation of the melted metal 1 1 ', firstly inside the cylinder 19 and thereupon out through the apertures 20 in the cylinder wall 19 and then back again through lower apertures 20' in the cylinder wall 19. A possible circulation pattern is indicated with arrows in Figure 3. In this manner the temperature is leveled out in the molten metal 1 1 '.

In the following the operation of the reactor shall be described in more detail, referring to the Figures. The removable top or cap 14, including rotor 15 with electrode 25 and supply duct 21 and exhaust pipe 22, are removed from the top of the container 12. Metal in solid form, for example in the form of compacted boxes, chips, thin foils or sheets and/or other types of scrap metal 1 1 , is placed on the bottom of the container and is compacted. Such scrap metal is placed and

compressed or compacted preferably up one height outside the cylinder 19 and to another height inside the cylinder 19, where the height inside the cylinder 19 preferably is lower than the height of scrap metal outside the cylinder 19. The solid scrap metal inside the cylinder 19 is compressed so much that an electric contact with the bottom contact 26 in the container 12 is established. The top or cap 14 with rotor 15 and electrode 25 is mounted in position on the top of the container 12 and is locked in a sealing manner to the container 12. Vacuum or sub-pressure is

established inside the closed, sealed container 12. The rotor 15 with the electrode 25 is then lowered down to desired level above the scrap metal 1 1 inside the cylinder 19.

Electrical current is then supplied to the bottom contact 26 and the electrode via the connector 27 or by means of collector ring 16 (not shown), while the rotor and electrode are maintained in a stationary position. The electrode 25 inside the jacket 16 of the rotor 15 and the bottom contact 26 have the same potential or exposure to the same voltage. The melting process is started by means of a light arc 29 formed by the electrode 25 inside the enlarged space 17 inside the rotor 15, the light arc 28 extending between the end of the electrode and the scrap metal 1 1 on the bottom of the cylinder 19 or against the lower part of the jacket 16 of the rotor 15, since this metal 1 1 is in electrical contact with the bottom contact 26. After a certain time the metal 1 1 below the rotor inside the cylinder and a part of the metal outside the cylinder 19 will melt. The rotor is kept in a non-rotating condition in order to ensure that the rotor does not contact solid metal fractions 1 1 and is damaged. The rotor 15 and the electrode will not start rotating until sufficient volume of melted metal 1 1 ' is formed. After a certain period of time, when the solid metal is melted, as shown in Figure 3, the molten metal 1 1 ' will be circulated through the side holes 20 and eventually as more energy also is supplied, the temperature of the molten metal 1 1 ' will be equalized. At such stage more solid scrap metal may possibly be added through the supply duct 21 , and the molten metal 1 1 ' may be transferred to the receipt container 24 by removing the drain plug 23. The process may either be a batch or a continuous process. During start-up the rotor is not rotated and is lowered down onto the solid scrap metal until a electrical contact is established. When the metal surrounding the electrode is melted, the rotor may start to rotate. The height of the rotor may be kept constant while the height of the electrode 25 inside the rotor may be adjusted such that a maximum or optimal light arc is obtained. Rotation of the rotor 15 and the electrode are achieved in a known manner, for example as described and disclosed in the applicant's own publication WO 2012/093943.

Rotation of the rotor 15 causes the free surface of the molten metal 1 1 ' inside the cylinder 19 to take a shape of a hyperbola, causing increased and improved circulation of the melted metal out through the openings 20 in the side wall of the cylinder 19 and back into the cylinder 19 through apertures 20' at the bottom, for supply of more heat energy from the light arc 28. The cylinder 19 functions as an effective pump in that gas and molten metal flows upwards inside the cylinder 19 and out through the side apertures 20. When sufficient volume of molten metal is formed, the rotational speed of the rotor may be increased, such that the molten metal inside the cylinder forms a rotational parabola. This will increase the pumping velocity through the side apertures 20 and will also increase the turbulence in the molten metal 1 1 ', increasing the rate of melting of the supplied scrap metal.

Claims

1 . Method for melting solid metal, such as scrap aluminum, where the solid metal is introduced into a closed insulated refractory container (12) provided with a bottom contact or electrode (26), the solid metal preferably being compacted or compressed at least on the bottom of the container(12) and where an electrode (25) is lowered down into contact with the preferably compacted or compressed metal (1 1 ) whereupon electrical current is supplied to the bottom contact (26) and the electrode (25), such that the electrical current flows between the electrode (25) and the bottom contact (26) through the solid metal (1 1 ),

c h a r a c t e r i z e d i n that the electrode (25) is arranged inside a rotatable hollow cylinder (16) and that the container (12) is provided with a cylinder (19) for example made of graphite, surrounding the rotatable electrode (25); that a light arc (28) is established between the electrode (25) and the metal (1 1 ) in contact with the bottom contact (26) and that the electrode (25) is maintained in a non-rotating modus until the solid metal at least around the electrode (25) is more or less melted, whereupon the electrode (25) is brought to rotate.

2. Method according claim 1 , wherein the melting may be a continuous process where additional solid metal (1 1 ) is supplied to the container through a supply device (21 ) as the solid metal (1 1 ) inside the container (12) is melting.

3. Method according to claim 1 or 2, wherein the rotational speed of the rotating cylinder (16) and/or the electrode (25) and/or vertical position may be adjusted.

4. Method according to one of the claims 1 to 3, wherein the melted metal is made to circulate inside the cylinder (19) and through apertures (20,20') in the side wall of the cylinder (19) for increasing and distributing heat energy to the metal (1 1 ) outside the cylinder (19).

5. Method according to one of the claims 1 to 4, wherein the level of cold solid metal (1 1 ) that is placed inside the container (12) is such that the cold solid metal (1 1 ) does not come in contact with the electrode (25) lowered down into the container.

6. Reactor (10) for melting cold solid metal (1 1 ), such as scrap aluminum, comprising an insulated and gas tight refractory container (12) where the container (12) is provided with an electrical bottom contact (26) and one down into the container (12) projecting electrode (25), where electrical current may be supplied to the bottom contact (26) and the electrode (25) and where the container (12) is provided with devices (22) for removal of gases that may be formed as a part of the melting process,

c h a r a c t e r i z e d i n that the electrode (25) is arranged with a lower end into a hollow, rotatable rotor (15) and that the rotor (15) is arranged inside a stationary cylinder (19) surrounding the rotor (15), the cylinder (19) being provided with apertures (20,20') at its lower part, communicating with a space (13) in the container (12) surrounding the cylinder (19).

7. Reactor (10) according to claim 6, wherein the electrode (25) and the bottom contact (26) are configured in such way that a light arc (28) is formed between one end of the electrode (25) and the metal (1 1 ), the metal (1 1 ) being in electrical contact with the bottom contact (26).

8. Reactor (10) according to claim 6 or 7, wherein the cylinder (19) is made of graphite and is provided with apertures (20,20') extending through the cylinder (19) wall, such that molten metal (1 1 ') is allowed to circulate from a space inside the cylinder (19) to the space surrounding the cylinder (19).

9. Reactor (10) according to one of the claims 6 to 8, wherein the rotor (15) has an external smooth vertical surface, such that possible solid particles or cold metal in the molten metal (1 1 ') are prevented from sticking to the rotor (15) and cause damage to the rotor and/or to the surrounding cylinder (19).

10. Reactor according to one of the claims 6 to 9, wherein the container (12) is provided with a closable device (21 ) for supply of solid metal (1 1 ) to the container

(12) and a tapping plug (23) for discharging metal in floating state and/or that the container (12) is provided with an exit duct (22) for exhaust gases from the melting process, such exit preferably being connected to a cleaning and recovery plant.