Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B7/00—Heating by electric discharge
  • H05B7/02—Details
  • H05B7/10—Mountings, supports, terminals or arrangements for feeding or guiding electrodes
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/52—Manufacture of steel in electric furnaces
  • C21C5/5205—Manufacture of steel in electric furnaces in a plasma heated furnace
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/52—Manufacture of steel in electric furnaces
  • C21C5/5229—Manufacture of steel in electric furnaces in a direct current [DC] electric arc furnace
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• FIELD OF APPLICATION This invention concerns an electric arc furnace system as set forth in the main claim.
• the invention is applied in the field of steel production and particularly, but not only, to electric arc furnaces which are loaded with scrap which has been pre-heated by the fumes from the furnace itself during the melting cycles.
• the electric furnace system according to the invention makes it possible to accelerate the loading operations, drastically reduce the times of the cycle and to limit to a minimum any heat losses and leakages of gases and powders from the furnace towards the outside environment.
• the invention makes it possible to leave the area above the furnace free, so that it can thus be used to pre-heat the scrap which is to be loaded into the furnace.
• the loading operations of the furnace can be completely automated, the spaces occupied can be kept to a minimum both above and at the side of the furnace, and also it is possible to drastically reduce the times, the equipment and the movements involved in the loading process.
• the invention can work either in direct current only, or in a mixed system with both direct and alternating current.
• the scrap is loaded into the furnace in a single lot, or semi-continuously , by means of baskets or containers, or continuously by means of carrier devices, for example belts.
• the furnace When the furnace is loaded by means of baskets or containers, they are first filled with scrap, then transported by means of lifting and/or moving means to the mouth of the furnace which is kept momentarily open, and then their content is unloaded into the furnace.
• Such a loading system has very long operating times because of the combination of movements of opening the roof and positioning the baskets; this not only reduces the productivity of the furnace, it also causes a huge loss of heat to the outside environment, and also the leakage of fumes and gases containing noxious and polluting substances.
• opening the roof necessarily involves removing the electrodes; this causes a further increase in the loading times, oxidation of the electrode and thus a greater consumption thereof, risks of damage for the electrodes, space occupied at the sides of the furnace " , difficult and complex movements and yet other problems.
• the state of the art provides to make the fumes leaving the furnace circulate inside the baskets containing the scrap which is still to be loaded, by means of conduits connected on one side to the fourth hole of the roof and on the other side to the structure of the basket .
• This pre-heating system has various disadvantages; for example, it requires complex and costly constructions, considerable installation spaces, complex moving systems and also problems in the automation of the loading steps of the furnace .
• the present applicant has designed, tested and embodied this invention to overcome the shortcomings of the state of the art and to achieve further advantages.
• the purpose of the invention is to provide an electric arc furnace system able to drastically reduce the times and movements required by the scrap-loading cycles.
• Another purpose is to limit the space occupied at the side of the furnace and free the part above the furnace in such a way as to make it usable for the direct pre-heating of the scrap which is to be unloaded into the furnace.
• a further purpose is to minimise the actions and movements needed, and also the spaces occupied, to momentarily free the mouth of the furnace during the loading step.
• the electric furnace according to the invention comprises at least one electrode functioning as a cathode and one or more electrodes functioning as anodes.
• the cathode is positioned, together with the anodes, in correspondence with the bottom or floor of the furnace.
• the cathode is positioned at the centre and the anodes are arranged around the cathode.
• the anodes are distributed symmetrically with respect to the central cathode.
• the cathode extends upwards to a height greater than that of the meniscus of the steel; this encourages the electric arc to spread and propagate, and thus to act on a considerable part of the mass of scrap inside the furnace.
• Both the cathode and the anodes are of a type whose upper part melts during the melting cycle of the furnace, and solidifies during the inactive cycles of the furnace, which guarantees a substantially unlimited duration both of the cathode and of the anodes .
• the cathode and/or the anodes are associated at their lower part with a cooling system which extends upwards as far as at least inside the floor of the furnace.
• the lower part of the cathode and/or the anodes, associated with the cooling system is made of material with high heat conductivity, for example, copper, while the upper part, that is to say, the part which melts and then re-solidifies, is made of steel or similar material.
• the electric furnace has a lower portion where the scrap is melted and an upper portion where the scrap is temporally contained and pre-heated.
• the upper, pre-heating portion can be obtained as a continuous structural part of the lower portion.
• the upper and lower portions are made in a single body; according to a variant, the portions are independent and can be associated/ disassociated at least temporally.
• the upper portion functioning as a temporary container and pre-heating chamber, is equipped at the lower part with movable means to retain the scrap.
• the upper portion has at the top at least an aperture to discharge the fumes leaving the furnace after they have lapped the scrap, and an aperture to load the scrap to be pre-heated.
• the loading aperture cooperates with air-tight movable closing means which cover the furnace during the melting cycles.
• the movable means to retain the scrap are structured in such a way as to allow the passage of the fumes produced during the melting cycles in the lower portion of the furnace.
• the fumes Before being discharged through the discharge aperture, the fumes lap the scrap which is temporally retained by the movable means in the upper portion of the furnace, and give up at least part of their heat to the scrap.
• the melted metal produced is unloaded from the furnace; subsequently, when the movable retaining means are opened, the furnace is immediately reloaded with the pre-heated scrap temporally retained in the upper portion of the furnace itself. Then, the movable retaining means are closed, so that new scrap loaded from above can be retained and pre-heated.
• the scrap which is to be preheated is unloaded into the upper portion of the furnace by means of feeder means cooperating with the afore-said air- tight movable closing means.
• the feeder means are of the conveyor belt type .
• the upper portion of the furnace can be loaded by means of baskets, containers, with arm-type carrier means movable on a bridge crane or in other ways .
• the walls of the upper containing and pre-heating portion and the walls of the lower melting portion at least partially consist of cooled panels.
• the furnace system according to the invention makes it possible to load the pre-heated scrap, where the lower part of the scrap has the highest temperature, in extremely limited times and with drastically limited movements. This guarantees a reduction in the flicker which is generated when the electric arc is struck between the cathode and the anodes, which are all arranged on the floor of the furnace.
• Fig. 1 shows a first embodiment of the electric arc furnace system according to the invention
• Fig. 2 shows a variant of Fig. 1
• Figs. 3 and 4 show in diagram form some further applications of the invention.
• the electric arc furnace 10 shown in the embodiment of Fig. 1 comprises a lower portion 10b, which functions as a chamber to melt the scrap 11, and an upper portion 10a, which functions as a chamber to contain and pre-heat the scrap which is to be unloaded into the lower portion 10b.
• the variant shown in Fig. 3 shows a conventional furnace 10 with a fourth hole 33 connected to a conduit to discharge the fumes 23, while the variant shown in Fig. 4 shows a furnace 10 whose fourth hole 33 is connected by means of the conduit 23 to a basket 34 to pre-heat the scrap 11 arranged in a position at the side of and in proximity to the furnace 10.
• the mouth of the furnace 10 is associated directly with loading means 18 including a conveyor belt 19 for a possible continuous loading of the scrap 11.
• the furnace 10 comprises a floor 14 made of refractory material and sidewalls 30 equipped with cooling panels 29.
• the cathode 12 and the anodes 13 are arranged on the floor 14; the cathode 12 is arranged in a substantially central position with respect to the floor 14 and the anodes 13 are arranged symmetrically around the central cathode 12.
• the anodes 13 are arranged asymmetrically with respect to the central cathode 12.
• the respective upper segments 12a and 13a of both the cathode 12 and the anodes 13 are made of a first material, for example steel, which melts during the melting cycles and solidifies when the furnace 10 is inactive.
• the respective lower segments 12b and 13b are made of a second material with a high heat conductivity, for example copper, and are associated with a cooling system 31, for example of the type with circulating water, which extends as far as a defined height inside the refractory floor 14.
• the top of the central cathode 12 is placed at a greater height than the anodes 13 and above the level of the meniscus of the molten metal; this encourages the generation of electric arcs 17 which develop from the top downwards and therefore act on a considerable part of the scrap 11 which has accumulated in the lower portion 10b of the furnace 10.
• a covering 28 made of high resistance material which protects it from falling scrap 11 during the loading cycle and facilitates extraction for operations of replacement and/or maintenance.
• the lower portion 10b and the upper portion 10a of the furnace 10 are separated by movable means 15 suitable to momentarily retain the scrap 11 which is contained in the upper portion 10a and which is to be pre-heated; this allows the fumes 22 produced during the melting cycles to pass upwards .
• the movable means 15 consist of sliding, counter-opposed grids 16; as the grids 16 slide towards the outside of the furnace 10, and take the position of non- contact as shown by the line of dashes in Fig. 1, it is possible to unload the pre-heated scrap 11 into the lower portion 10b of the furnace 10.
• the grids 16 cooperate with retaining means 116 which prevent the heat and fumes inside the furnace 10 from escaping towards the outside environment .
• the scrap 11 is loaded into the upper portion 10a of the furnace 10 by means of loading means 18 consisting of a conveyor belt 19 which cooperates with air-tight closing means 20 associated with the top of the upper portion 10a.
• the function of the air-tight closing means 20 is to cover the furnace 10 at the top during the melting cycles.
• the ring-type fume-intake chamber encourages the fumes to rise uniformly over the whole volume of the upper portion 10a and therefore the scrap 11 placed in the pre-heating position in the upper portion 10a is heated homogeneously.
• the air-tight closing means 20 are able to slide and are taken to the open position, indicated by a line of dashes, when the loading means 18 unload the scrap 11 into the upper portion 10a of the furnace 10.
• the loading means 18 also comprise covering and containing means 21 which facilitate the delivery of the scrap 11 into the upper portion 10a of the furnace 10 and limit heat losses into the outer environment.
• the furnace 10 has a circular section and a height/diameter ratio which is suitable to exploit as much as possible the heat generated by the fumes 22 so as to preheat the scrap 11 retained by the retaining means 15.
• the fumes 22 produced during the melting cycles in the lower portion 10b pass through the retaining means 15 and ascend into the upper portion 10a, lap the scrap 11 and give up at least part of their heat; they are subsequently discharged through the fume-intake chamber 32 and the duct 23 towards the purifying plants and discharged into the atmosphere.
• burners 24 arranged on one or more levels.
• burners 24 on the upper part of the upper portion 10a, in order to achieve a process of post-combustion of the fumes 22 so as to abate the noxious and polluting substances present therein before the fumes 22 are discharged through the duct 23.
• the lower portion 10b is also equipped with supersonic lances 25 to inject oxygen and with tuyeres 26 to blow oxygen and/or carbon into the liquid metal from below.
• stirring means 27 of the electromagnetic type in the lower portion 10b in order to mix the molten metal efficiently so as to achieve a homogeneous bath, a uniform temperature, and also to accelerate the chemical reactions, there are also stirring means 27 of the electromagnetic type in the lower portion 10b.
• the loading means 18 not only feed but also momentarily retain and possibly pre-heat the scrap 11, at least part of the fumes 22 deriving from the melting process lapping the scrap 11 on the conveyor belts 19.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Vertical, Hearth, Or Arc Furnaces (AREA)
• Furnace Details (AREA)
• Discharge Heating (AREA)
• Arc-Extinguishing Devices That Are Switches (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=11422377

Family Applications (1)

Country Status (3)

Cited By (2)

Citations (5)

• 1997
  • 1997-04-21 IT IT97UD000076 patent/IT1295102B1/it active IP Right Grant
• 1998
  • 1998-04-01 WO PCT/IB1998/000474 patent/WO1998048060A1/en active Application Filing
  • 1998-04-01 AU AU66328/98A patent/AU6632898A/en not_active Abandoned

Patent Citations (5)

Non-Patent Citations (2)

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