EP2299222B1

EP2299222B1 - Counterbalanced metallurgical furnace

Info

Publication number: EP2299222B1
Application number: EP20090170919
Authority: EP
Inventors: Shaolong Chen; Hannu Mansikkaviita
Original assignee: Kumera Oy
Current assignee: Kumera Oy
Priority date: 2009-09-22
Filing date: 2009-09-22
Publication date: 2014-03-19
Anticipated expiration: 2029-09-22
Also published as: EP2299222A1

Description

FIELD OF THE INVENTION

The invention relates to a metallurgical furnace for melting and refining nonferrous metals. More particularly the invention is relating to a metallurgical furnace for melting and refining nonferrous metals having the following features:

a) at least partly cylindrical outer shell of steel material surrounding the interior of the furnace and being at its both ends in the longitudinal direction closed by end walls,
b) a refractory lining provided in the furnace to cover the inside surfaces of the outer shell and the end walls of the furnace,
c) means for providing process media such as gas, liquid or solid powder into the interior of the furnace,
d) at least one burner opening into the interior of the furnace, for combustion of fuels with air or oxygen enriched air in the interior of the furnace,
e) openings for mass transfer of materials in solid and/or liquid and/or gaseous form into and/or out of the interior of the furnace,
f) the furnace is mounted for rotation about a longitudinal, horizontal axis of rotation.

BACKGROUND OF THE INVENTION

A number of different types of furnaces for processing nonferrous metals are known from the state of the art. Among these types can be mentioned eg. drum type furnaces and tilting furnaces. Common features for these furnaces are an outer jacket made of steel for example and a refractory lining provided on the inside of the outer steel jacket surrounding a processing chamber for metals to be melted, refined or processed in a corresponding way. Normally these furnaces are further provided with means for supplying gas to the processing chamber and a burner for firing said processing chamber. These types of furnaces are usually further mounted to rotate about a horizontal axis of rotation. Depending on the type and purpose of the furnace they can be rotated a full circle, i.e. 360°, or only a part of a full circle.
Drum type furnaces are disclosed eg. in US Patent No. 4,245,821 and International Published Patent Application No. WO 91/15607 . A tilting furnace is disclosed in US Patent No. 1,856,716 .
It is quite common to construct these types of furnaces so that they have an interior or a processing chamber with a circular cross section area. An advantage of a circular furnace, due to geometrical symmetry, is that the metal and the slag to be processed inside the processing chamber create only a very low unbalance to the horizontal axis of the furnace at any angle of rotation when it processes molten metal and slag. However, the furnace of this shape has also a considerable disadvantage when it is used for melting a large quantity of solid metals because the surface area of the solid metals exposed to the burner flame is relatively small. The circular shape of the processing chamber is not very effective for such application. Therefore, this type of furnaces are mainly used to process molten metals with limited addition of scraps.
To improve the effectiveness of furnaces processing chambers of other shapes have also been disclosed. As an example one furnace of this kind is disclosed in EP Patent No. 1634027 . This publication shows a furnace provided with a processing chamber with an oval or elliptical cross-sectional area. The furnaces having an interior of this shape are mainly employed for melting and refining metals. An advantage of the furnaces of this particular shape is that the surface area of solid metals exposed to the burner flame can be considerably larger than in the furnaces with a circular cylindrical processing chamber. However, they also have a disadvantage, namely the centre of gravitation of the metal deviates from the furnace axis when the furnace is rotated to an angle at which the cross-sectional area of the molten metal is not symmetrical in respect of the vertical centreline of the cross-section of the furnace, thus the furnace is under an unbalanced condition in most of its operation angles.
It is previously known to provide rotary furnaces with a fixed counter weight in order to try to get the furnace balanced. However, the counter weight is only used against the unbalance due to the eccentric construction of the furnace. The counter weight is fixed and it forms a part of the furnace and it is determined by other parts of the furnace.
Regarding further prior art reference is made to document GB 400956 . This document discloses a furnace for melting metals, so that any gas refining function is not described in this document. The melting chamber of the furnace of this document is cylindrical having a circular cross section and so the molten metal in the melting chamber is self balanced. Therefore GB 400956 does not recognize any unbalance created by the liquid metal in the melting chamber. The furnace of GB 400956 is provided with a flue having an overhanging portion which is a stationary and constant overweight forming an unbalancing effect to the furnace. In order to balance this unbalancing effect a counterweight is placed in a fixed position in the furnace said counterweight being a fixed and solid piece.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a metallurgical furnace for melting and refining metals, skimming slag and casting molten metal, in which furnace the melting effectiveness is improved by a large surface area of solid metals exposed to the burner flame in the processing chamber and which furnace is balanced over the unbalance created by the solid and/or liquid metal inside the furnace when it is rotated to different angles.
In view of achieving this and other objectives of the invention, the present invention is mainly characterized in that

g) the interior of the furnace is divided into at least two separate chambers, namely a primary chamber and a secondary chamber, by a partition wall parallel to the longitudinal axis of rotation of the furnace,
h) whereby the primary chamber is a processing chamber the bottom of which is formed of said partition wall, in which processing chamber the processing of metals takes place and the inner surface of which processing chamber is covered by said refractory lining, and
i) whereby the secondary chamber consists of at least one counter weight chamber in which a counter weight for the furnace is arranged.

According to one embodiment of the invention the counter weight arranged inside the counter weight chamber or counter weight chambers is formed of a loose material filling said counter weight chamber(s) only partly and being movable so that it is able to move in said counter weight chamber(s) during rotation of the furnace.
According to another embodiment of the invention the counter weight arranged inside the counter weight chamber or counter weight chambers is comprised of one or several solid pieces of material adjustably fixed in said counter weight chamber(s) so that said counter weight moves along with the counter weight chainber(s) during rotation of the furnace.
In both embodiments of the invention the material of the counter weight may consist of dense solids, preferably of steel and/or iron. If the counter weight is formed of a loose material it may be in the form of grains, balls or rods or a combination of at least two of them. If the counter weight is comprised of solid pieces of material fixed in said counter weight chamber(s) it may comprise rods, plates or blocks or a combination of at least two of them.
The partition wall forming a bottom for the processing chamber and joined with the shell and the end walls of the furnace may be a straight and planar plate or a curved plate being concave with respect to the longitudinal axis of the furnace as seen from the processing chamber.
At least one of the openings arranged in the furnace is a charging opening to receive the charge of metal, flux or equivalent in a solid or liquid form into the processing chamber. Said charging opening(s) can also be used to skim slag and to discharge molten metal from the processing chamber when required. Alternatively the furnace may have at least one additional opening for skimming slag.
Further, at least one of the openings arranged in the furnace is a tapping hole to cast the molten metal and at least one of the openings is an exhaust gas opening for discharging exhaust gases from the processing chamber.
The furnace is used for processing nonferrous metals with a complete operation cycle, including stages such as, if needed, metal melting, slag skimming, metal refining, and molten metal casting. The rotary furnace is flexible to complete the functions by rotating the furnace to different angles needed at different stages. Normally uneven distribution of the solid or molten metal in the processing chamber creates unbalance of the furnace. The counter torque against the unbalance is usually considerable high, requiring high mechanical drive power for rotation. The solid or molten metal that are not symmetrically distributed cause unbalance and the direction of unbalance torque changes when the furnace is rotated from one side to other side respect to its neutral position. According to the preferred embodiment the present invention uses a movable counter weight, which automatically finds suitable location to balance the furnace. So the counter weight automatically balances the torque created by the metals inside processing chamber, thus the drive power for rotating the furnace is minimised.
As an alternative the present invention provides further an embodiment in which a fixed but adjustable counter weight is used to balance the furnace when it is rotated from its neutral position.

BRIEF DESCRIPTION OF THE DRAWINGS

The further advantages, characteristic features and embodiments of the invention will come out in more detail in the following detailed description of the invention, in which the invention is described with reference to the figures in the accompanying drawing.

Fig. 1 is a schematic cross-sectional view of the furnace in accordance with the invention taken along line I - I of Fig 2. The furnace is at melting position.
Fig. 2 is a schematic longitudinal side view of the furnace.
Fig. 3 is a cross-sectional view of the furnace corresponding to Fig. 1. The furnace is at gas blowing position.
Fig. 4 corresponds to Figs. 1 and 3 while the furnace is at molten metal casting position.
Fig. 5 is a schematic cross-sectional view of an alternative embodiment of the furnace corresponding to Fig. 1. The alternative embodiment is provided with a fixed but adjustable counter weight.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings the furnace according to the present invention is generally denoted with the reference numeral 10. The furnace 10 comprises an outer shell 11 made of steel material, which shell 11 is at least partly cylindrical. As especially Fig. 2 is showing the outer shell 11 is at its both ends in the longitudinal direction closed by end walls 23a, 23b. A partition wall 13 substantially parallel to the longitudinal axis A of the furnace 10, i.e. the axis of rotation of the furnace 10 is provided inside the outer shell 11 of the furnace 10 dividing the interior of the furnace 10 into at least two separate chambers 14, 15.
The primary chamber 14 is a processing chamber in which metal and slag 21 are processed, and the secondary chamber 15 is a counter weight chamber in which the counter weight 22, 32 is arranged. As seen in the attached drawings the cross-sectional area of the processing chamber is preferably larger than that of the counter weight chamber. According to the first embodiment of the invention as shown in Figs. 1, 3 and 4 the counter weight 22 inside the counter weight chamber 15 is movable and it fills the counter weight chamber 15 only partly so that it is able to move in the counter weight chamber 15 when the furnace 10 is turned or rotated. The material of the counter weight 22 may be e.g. steel and/or iron in the form of grains, balls or rods or it may consist of a combination of grains, balls and rods.
In the processing chamber 14 of the furnace 10 a refractory lining 12 is arranged on the inside surfaces of the outer shell 11 and the end walls 23a, 23b of the furnace 10. The refractory lining 12 may be made of refractory bricks or castable refractory.
The partition wall 13 forms a bottom for the processing chamber 14 of the furnace 10 and it may be a straight and planar plate or a curved plate joined with the shell 11 and the walls 23a, 23b of the furnace 10. If the partition wall 13 is a curved wall it is preferably concave with respect to the longitudinal axis A of the furnace 10 as seen from the processing chamber 14.
The furnace 10 is provided with at least one burner 16 opening into the processing chamber 14. In the embodiments shown in the drawings said burner 16 is arranged on the first end wall 23a of the furnace 10. Only one burner 16 for combustion of fuels with air or oxygen enriched air is shown in Fig. 2 but there may be two or more burners if necessary. The burner 16 does not necessarily be located on the first end wall 23a of the furnace 10 but it can also be arranged on the shell 11. The furnace 10 is further provided with means 17 for providing process media, such as gas, liquid or solid powder into the processing chamber 14. Nozzles are preferably used as said means 17 and there may be several nozzles arranged along the length of the processing chamber 14. However, at least one nozzle is necessary. An exhaust gas opening 19 is arranged on the second end wall 23b of the processing chamber 14, through which opening 19 combustion exhaust gases and process exhaust gases can be removed from the processing chamber 14. Also the exhaust gas opening 19 can be located on the shell 11 instead of the second end wall 23b of the processing chamber 14.
For charging the furnace 10 it is provided with at least one charging opening 18, through which the processing chamber 14 receives the charge that is in a state of solid and/or liquid. The furnace 10 is rotated to a suitable angle at which the charge has access to the furnace 10 through the charging opening 18. The charging opening 18 can also be used for skimming slag or for discharging molten metal if required. Alternatively the furnace, 10 can have one or several additional openings (not shown) for skimming slag. At least one tapping hole 20 is provided to cast the molten metal. Finally, the furnace 10 is constructed to be rotatable. It is therefore provided with means for rotation 24, 25 and a drive system (not shown) for rotating the furnace about its substantially horizontal axis of rotation A to a position necessary for its operations. The angle of rotation depends on the stage of operation. The means for rotation 24, 25 shown in the drawings comprise riding rings 25 or bands on the shell 11 of the furnace and rollers 24 on which the furnace 10 is resting. It is, however to be understood that the arrangement of the means for rotation as shown is exemplary only.
In Fig. 1 the furnace 10 is shown at a melting position. In this position the charges in the processing chamber 14, i.e. metal and flux 21 to be melted are located evenly and symmetrically distributed with respect to the vertical centreline B of the furnace 10 in the processing chamber 14 on the bottom of it, i.e. on the refractory lining of the partition wall 13 between the two chambers 14, 15. The counter weight 22 inside the counter weight chamber 15 is movable and it may be eg. granular or in the form of balls or rods or it may consist of a combination of grains, balls and rods. At the melting position of the furnace 10 the movable counter weight 15 is located substantially symmetrically with respect to the vertical centreline B on the bottom of the furnace.
In Fig. 3 the furnace 10 is shown at a so called gas blowing position in which position gas, liquid or powder for refining is supplied through the nozzles 17 into the processing chamber 14 to chemically react with the impurities in the molten metal. To reach this position the furnace 10 has been rotated clockwise, so that the nozzles 17 are immersed under the surface of molten metal and so that the process media are supplied straight into the molten metal. When the furnace 10 is rotated to the gas blowing position more molten metal is located on that side of the furnace to which it is rotated (to the right in Fig. 3) than on the other side of the furnace (on the left side) with respect to the vertical centreline B of the furnace. In this position the depth of molten metal over the nozzles 17 is higher than the depth when the furnace 10 is located at the neutral position with respect to the vertical centreline B. When the furnace 10 is rotated clockwise to the position shown in Fig. 3 the counter weight in the counter weight chamber 15 moves towards the corner S which results in an anticlockwise torque balancing the clockwise torque caused by the molten metal in the processing chamber 14.
In Fig. 4 the furnace 10 is shown at a molten metal casting position in which position molten metal is poured out of the processing chamber 14 through the tapping hole 20. The furnace 10 has been rotated anticlockwise to reach this position so that more molten metal is located on that side of the furnace to which it is rotated (to the left in Fig. 4) than on the other side of the furnace (on the right side) with respect to the vertical centreline B of the furnace 10. When the furnace 10 is rotated anticlockwise to the position shown in Fig. 4 the counter weight 22 in the counter weight chamber 15 moves towards the corner T which results in an clockwise torque balancing the anticlockwise torque caused by the molten metal in the processing chamber 14. So the furnace 10 with a moveable counter weight 22 according to the first embodiment of the present invention is self-adjustable to overcome the unbalance. During the tapping stage, the furnace 10 is rotated either continuously or step-by-step to adjust molten metal flow from the processing chamber 14 of the furnace 10.
Fig. 5 is a schematic cross-sectional view of the furnace 10 showing an alternative embodiment of the invention. Except the counter weight and the arrangement of the counter weight in the counter weight chamber 15 this alternative embodiment is substantially identical with the first embodiment already explained above. Same reference numerals for the same parts of the furnace 10 have been used in connection with both embodiments and only those parts of the embodiment according to Fig. 5, which differ from the first embodiment of the furnace will be explained.
In the embodiment shown in Fig. 5 the counter weight 32 arranged in the counter weight chamber 15 is not movable but instead it is fixed in the counter weight chamber. Fixing means of the counter weight 32 are provided with reference numerals 33. The counter weight 32 is comprised of one or several solid pieces of material fixed immovable in the counter weight chamber 15. The counter weight 32 is adjustable so that the number of said pieces can be varied and adjusted when necessary. Because the counter weight 32 is immovably fixed in the counter weight chamber 15 it moves along with the counter weight chamber 15 during rotation of the furnace 10. The material of the counter weight 32 consists of dense solids, preferably of steel and/or iron and preferably it comprises rods, plates or blocks or a combination of at least two of them.
Instead of one counter weight chamber only the secondary chamber of the furnace may in both of the above-described embodiments be divided into two or more counter weight chambers when necessary.
Above, the invention has been described by way of examples with reference to the exemplifying embodiments illustrated in the figures in the accompanying drawing. The invention is, however, not confined to the exemplifying embodiments shown in the figures alone, but different embodiments of the invention may show variations within the scope of the inventive idea defined in the accompanying claims.

Claims

A metallurgical furnace for melting and refining nonferrous metals having the following features:
a) at least partly cylindrical outer shell (11) of steel material surrounding the interior of the furnace (10) and being at its both ends in the longitudinal direction closed by end walls (23a, 23b),

b) a refractory lining (12) provided in the furnace (10) to cover the inside surfaces of the outer shell (11) and the end walls (23a,23b) of the furnace (10),

c) means (17) for providing process media such as gas, liquid or solid powder into the interior of the furnace (10),

d) at least one burner (16) opening into the interior of the furnace (10), for combustion of fuels with air or oxygen enriched air in the interior of the furnace (10),

e) openings (18, 19, 20) for mass transfer of materials in solid and/or liquid and/or gaseous form into and/or out of the interior of the furnace (10),

f) the furnace (10) is mounted for rotation about a longitudinal, horizontal axis of rotation (A),
characterized in that

g) the interior of the furnace is divided into at least two separate chambers (14, 15), namely a primary chamber (14) and a secondary chamber (15), by a partition wall (13) parallel to the longitudinal axis of rotation (A) of the furnace (10),

h) whereby the primary chamber (14) is a processing chamber the bottom of which is formed of said partition wall (13), in which processing chamber the processing of metals takes place and the inner surface of which processing chamber (14) is covered by said refractory lining (12), and

i) whereby the secondary chamber (15) consists of at least one counter weight chamber in which a counter weight (22, 32) for the furnace (10) is arranged.
A metallurgical furnace as claimed in claim 1, characterized in that the counter weight (22) arranged inside the counter weight chamber (15) or counter weight chambers is formed of a loose material filling said counter weight chamber(s) only partly and being movable so that it is able to move in said counter weight chamber(s) (15) during rotation of the furnace (10).
A metallurgical furnace as claimed in claim 1, characterized in that the counter weight (32) arranged inside the counter weight chamber (15) or counter weight chambers is comprised of one or several solid pieces of material adjustably fixed (33) in said counter weight chamber(s) (15) so that said counter weight (32) moves along with the counter weight chamber(s) (15) during rotation of the furnace (10).
A metallurgical furnace as claimed in claim 2 or 3, characterized in that the material of the counter weight (22, 32) consists of dense solids.
A metallurgical furnace as claimed in claim 4, characterized in that the material of the counter weight (22, 32) consists of steel and/or iron.
A metallurgical furnace as claimed in claim 2, characterized in that the counter weight (22) is in the form of grains, balls or rods or a combination of at least two of them.
A metallurgical furnace as claimed in claim 3, characterized in that the counter weight (32) comprises rods, plates or blocks or a combination of at least two of them.
A metallurgical furnace as claimed in any one of the preceding claims, characterized in that the partition wall (13) is joined with the shell (11) and the end walls (23a, 23b) of the furnace (10).
A metallurgical furnace as claimed in any one of the preceding claims, characterized in that the partition wall (13) is a straight and planar plate.
A metallurgical furnace as claimed in any one of claims 1 - 8, characterized in that the partition wall (13) is a curved plate being concave with respect to the longitudinal axis (A) of the furnace as seen from the processing chamber (14).
A metallurgical furnace as claimed in any one of the preceding claims, characterized in that at least one of the openings arranged in the furnace (10) is a charging opening (18) to receive the charge of metal, flux or equivalent in a solid or liquid form into the processing chamber (14).
A metallurgical furnace as claimed in claim 11, characterized in that said at least one charging opening (18) is a skimming hole for skimming slag therethrough and a discharge hole to discharge molten metal from the processing chamber (14) when required.
A metallurgical furnace as claimed in any one of claims 1 - 10, characterized in that at least one of the openings in the furnace (10) is a skimming hole for skimming slag therethrough from the furnace.
A metallurgical furnace as claimed in any one of the preceding claims, characterized in that at least one of the openings arranged in the furnace (10) is a tapping hole (20) to cast the molten metal.
A metallurgical furnace as claimed in any one of the preceding claims, characterized in that at least one of the openings arranged in the furnace (10) is an exhaust gas opening (19) for discharging exhaust gases from the processing chamber (14).