Industrial electric heating furnaces – Arc furnace device – For manipulation of the charge or melt
Patent
1998-01-06
1999-08-10
Hoang, Tu Ba
Industrial electric heating furnaces
Arc furnace device
For manipulation of the charge or melt
373 4, 373 64, F27D 2304
Patent
active
059369965
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a furnace plant for melting metal and/or holding molten metal which at least comprises: metal and/or solid metal, solid metal present in the furnace vessel, and vessel.
The invention preferably relates to a furnace plant for melting and/or holding aluminium which at least comprises: and/or solid aluminium, with walls and a bottom and at least one furnace roof arranged over the furnace vessel, which by convection and radiation heats aluminium present in the furnace vessel, and vessel.
BACKGROUND OF THE INVENTION
During melting and/or holding of aluminium, it is known to use electromagnetic stirrers placed below the furnace vessel to obtain a stirring of the molten metal in the furnace vessel and to reduce the temperature and the concentration gradients in the molten metal and to increase the productivity of the furnace plant. Especially, it is desired to reduce overtemperatures at the upper surface of the molten metal. Overtemperature in this patent application is meant the temperature difference which prevails between the maximum temperature to which any part of the molten metal is heated during the melting or holding and the melting temperature of the molten metal. A great overtemperature often leads to metal losses by oxidation and formation of dross and slag. At the same time, the energy utilization of the process is negatively influenced. Metal losses and a low energy efficiency are a problem in so-called reverberatory furnaces where oil and gas burners heat the metal by convection and radiation.
By stirring the molten metal, the temperature and concentration gradients in the molten metal are equalized so that overtemperatures may be reduced and the energy efficiency of the process be improved. This can be illustrated in that, during electromagnetic stirring, the effective coefficient of heat conduction in the molten metal is increased more than 10 times compared with the coefficient of heat conduction in a non-stirred melt. By effective coefficient of heat conduction in this patent application is meant the coefficient of heat conduction which describes the heat transport in the melt bath taking into consideration both the conductive heat flux in the molten metal and/or the solid metal and the extra contribution in the form of the convective heat flux which is obtained in the molten metal through the stirring.
It is known to arrange, in furnace plants for melting and holding of aluminium, electromagnetic stirrers below the furnace for achieving a bottom stirring, for example from U.S. Pat. No. 4,294,435. Typically, this gives an increase of the effective coefficient of heat conduction by a factor of 25-35. However, in certain cases, economic and constructive complications arise when it is desired to arrange bottom stirrers below furnaces or near the furnace bottom according to the prior art. This is particularly noticeable in those cases where it is intended to install stirrers in existing furnace plants to increase the energy efficiency and productivity of the furnace and to reduce the temperature and concentration gradients in the molten metal. In addition, such a supplementary installation of bottom stirrers in an existing furnace plant is, in many cases, rendered difficult by the fact that the furnace is standing on a floor and that its bottom is not, without extensive rebuilding of the furnace hall, available for such an installation. It is known to arrange electromagnetic means in or near the walls which separate different melt baths in a melting furnace in order to achieve a stirring of the molten metal by pumping molten metal between the different baths. In similar manner, a stirring can be obtained by allowing electromagnetic means to act on a channel which is arranged in or near the walls of the furnace vessel and which communicates, at both ends, with the molten metal present in the furnace vessel. Further, U.S. Pat. No. 4,294,435 discloses that it would be desirable, in a furnace plant for melting and holding aluminium, to arrange electro
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Eidem Magnus
Henriksson Per
Karlsson Lars
Nordekvist Lars
Oscarsson Petter
Asea Brown Boveri AB
Hoang Tu Ba
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