Electric arc furnace for melting metallic materials and steelmaking plant equipped with said electric arc furnace

Abstract

An electric arc furnace (10) usable for melting a metal charge (M), the electric arc furnace (10) comprising a vessel (11) having at least one peripheral wall (20) with a top opening (21), a side slag discharge opening (22) and a side input opening (43). A selectively openable roof (15) can be placed over the top opening (21) of the vessel (11), the roof (15) having a central portion (30) with one or more through holes (31) through which electrodes (32) for melting the metal charge (M) can be inserted to provide clearance.

Description

[Technical field]

[0001] The present invention relates to an electric arc furnace that can be used in a process for melting metallic materials, preferably, but not exclusively, with a substantially continuous charge, and to a steelmaking plant equipped with said electric arc furnace. [Background technology]

[0002] Steel plants for melting metallic materials are known which comprise at least one electric arc melting furnace powered by alternating current (AC) or direct current (DC), such furnaces usually comprise a substantially cylindrical vessel having a lower part or hearth and an upper part which is open at the top, the upper part together defining a melting chamber, the furnace also comprising a cover or roof closing the vessel.

[0003] The hearth is usually made of a metal frame of refractory material inside which a metal charge, such as scrap iron, sponge iron or direct reduced iron (DRI), iron pellets or hot briquetted iron (HBI) or other ferrous material, is melted and has a volume appropriate to the volume of the hearth. A single metal charge may weigh several tons.

[0004] The open upper part of the vessel comprises or consists of a generally cylindrical peripheral wall capable of accommodating the large volume of scrap mass to be melted during the first steps of the process, and the purpose of the peripheral wall is to accommodate the layer of slag that covers the bath of steel, and is provided with suitable side panels, which are water-cooled, to protect the non-refractory upper part from thermal stresses.

[0005] The peripheral wall is provided with at least one outlet, also known by the term "slag outlet", through which the slag resulting from the melting process can be selectively removed. The slag includes the undesired elements removed from the bath and is generally referred to as "slag" in technical terms. The slag outlet can be selectively closed using a door, for example a gate valve, or it may not be provided with such a door, or if the slag outlet is not fully open during the melting process, it may be at least partially maintained to allow the introduction of an injection lance or a temperature measuring probe, the removal of samples, and the addition of additives or slag removers. In any case, in the prior art, the slag outlet door is located above the level of the steel bath and is therefore not watertight.

[0006] The known electric arc furnace also comprises an upper cover, called the "roof", of the type that can be selectively opened, which has a central part made of refractory material, also called the "arch", which has several openings or through-holes, usually three in number in the case of an alternating current power supply, also known by the term "cells", which allow the insertion of corresponding graphite electrodes, so as to provide clearance, into the melting chamber, which graphite electrodes are arranged to determine the generation of an electric arc when supplied with power, so as to allow the melting of the metal charge.

[0007] The roof further comprises at least one opening, also known by the term "fourth hole", into which a pipe or duct is inserted for sucking the treated fumes, which are then conveyed to a fume suction treatment plant, called "primary".

[0008] The metal charge may be charged or dumped by suitable charge buckets and dumping the metal charge through the top opening of the furnace, or it may be charged or dumped by a continuous charging system through a side opening formed in the peripheral wall.

[0009] When the metal charge is introduced by the charge bucket and reaches a suitable quantity for each melting process, the roof must be opened two or three times to unload the metal charge from the bucket, which releases a large amount of fumes that, if released into the atmosphere, can have a very high polluting power, especially if the scrap is contaminated, oily or moist. The airborne pollutants can be present in powder form, especially heavy metal oxides, but also in gaseous compounds, including CO, NOx, VOC, dioxins and furans. In fact, during the unloading of the bucket, the fumes are not sucked in by the suction duct of the primary fume treatment plant, which captures the emissions directly from the fourth hole in the roof of the furnace, but are actually released outside the melting chamber, and only after this release can they be captured by the hood placed above the electric arc furnace, which is generally placed on the roof of the hangar in which the furnace itself is located, and which sucks in the fumes and transports them to another treatment plant, called "secondary". Additionally, when the metal material is lowered from the bucket into the melting chamber, special radial gas burners are operated to help melt the charge, allowing the electrodes to enter the metal charge more quickly and shortening the melting time, but the use of gas burners creates more pollutants.

[0010] Burners in practice typically use methane, which when burned produces CO and CO2, as well as heat energy, of course.

[0011] When feeding is performed using a continuous feeding system, the metal charge is fed differently by means of a feeding conveyor, which is generally arranged to be selectively and removably inserted into an opening formed in the periphery of the furnace, and at least a part of the feeding conveyor is further associated with a preheating tunnel through which the process fumes generated in the furnace are sucked in, so that the heat of the process fumes can be utilized to preheat the feed material to be melted, thereby reducing and / or optimizing the time and consumption of the melting process.

[0012] During melting, oxygen is introduced using a suitable lance to oxidize the unwanted elements present in the bath, such as silicon, chromium, molybdenum, nickel, phosphorus, etc. The oxides and non-metallic compounds formed are less dense than the liquid bath and therefore migrate to the surface and are incorporated into the slag. In addition, oxygen injection is also necessary to carry out a decarburization treatment of the bath, which allows the carbon content to reach the target value of about 0.08%. The decarburization reaction occurs during the purification process of the liquid bath, and it is inevitable that the injected oxygen will combine with some of the carbon present in the bath to produce CO. However, the injection of oxygen also causes the oxidation of the iron present in the metal bath, which must then be deoxidized again by injecting carbon in powder form in order not to adversely affect the furnace yield. This powdered carbon injection is carried out by several injectors located in or above the melting chamber. The reaction of the iron oxide with carbon converts the molecule back to metallic iron, but also produces large amounts of CO, which, depending on the availability of oxygen, can be combusted to reduce it to CO2, releasing additional heat and producing process fumes.

[0013] An unstable balance between oxygen injection and carbon can result in very large amounts of CO being produced during each melting cycle, and therefore very large amounts of CO2 being produced.

[0014] The remaining CO not burned in the furnace is sucked in by the primary fume treatment plant through the fourth hole or the continuous charging and / or preheating system, the ducts of which work under reduced pressure as is known, and any remaining fumes are captured by the primary fume treatment plant, particularly as we have seen, using the bucket charging method.

[0015] When charging with buckets, a free space or gap is maintained between the inlet of the suction pipe inserted in the fourth hole of the furnace and the duct of the primary fume treatment plant, which allows a large amount of air to be sucked into the duct, which is necessary for the post-combustion step of the residual CO to reduce it to CO2 and to dilute and cool the fumes. This cooling prevents or at least reduces the formation of NOx by thermal means in the fume suction duct after the CO post-combustion.

[0016] In the case of continuous charging, the fumes are instead introduced into a preheating tunnel in which the post-combustion of CO takes place by injecting air or oxygen.

[0017] To prevent the escape of process fumes into the surrounding environment, fans of the primary fume extraction and treatment plant maintain a reduced pressure in the furnace, but due to all the openings in the furnace there is the drawback that a large amount of air (so-called "bad air") can enter the melting chamber even when the roof is closed. In fact, the air can enter through the passage gaps present in said openings, which are not hermetically sealed in the prior art.

[0018] Therefore, to maintain the furnace under vacuum, the suction plant fans are operated to remove a gas flow rate much higher than that required to remove only the process gas. This reduces the efficiency of carbon powder injection, since a significant proportion of the carbon is sucked into the suction flow without reaching the bath. To compensate for this loss and meet the above requirements, extra carbon must be introduced into the furnace, and the excess (free carbon) deposited in the slag reacts with the oxygen present there to produce more CO.

[0019] Furthermore, the inappropriate air entering through the openings contains nitrogen (N), which in the presence of oxygen and high temperatures of about 1500°C to about 850°C, forms polluting compounds such as NOx, corresponding to the electrodes, for example.

[0020] Among other prior art documents, GB 2076858 A1 describes a metallurgical process in a direct-fired steel converter or possibly an electric furnace. In this prior art document, the steel converter is equipped with oxy-fuel or air-fuel burners, but is configured without any electrodes for melting the metal charge contained in the furnace. Moreover, this prior art document does not address the problem of oxidation in the furnace.

[0021] US Pat. No. 4,027,095 describes a gas-tight electric arc furnace for the production of stainless steel, comprising vacuum sealing means between the roof and the body of the furnace, cooled telescopic sealing means between the roof and the electrodes, and an outlet associated with the furnace combustion chamber, to which a vacuum pump is connected for reducing the internal pressure of the electric arc furnace.

[0022] EP 0 515 249 A1 describes a closure device for forming a partial seal between an electrode of an electric arc furnace and a corresponding opening in the roof of the furnace, the closure device in particular comprising an annular closure element which is slidingly mounted in the opening and which is formed with an axial cavity into which the electrode is inserted.

[0023] The applicant's WO 2005 / 052196 describes a plant with an electric arc furnace for preheating, converting and melting a metal charge, the furnace being weighed at least periodically to detect the amount of metal charge present in the furnace in order to regulate the temperature of the liquid bath to a predetermined value.

[0024] Thus, there exists a need to develop an electric arc furnace that overcomes at least one of the disadvantages of the prior art.

[0025] To achieve this, it is necessary to solve the technical problem of preventing, or in any case significantly limiting, the undesired or uncontrolled ingress of air into the electric arc furnace during the entire process of melting the metal charge.

[0026] An object of the present invention is in particular to achieve a completely sealed electric arc furnace for melting metallic materials, which makes it possible to prevent or to greatly reduce the undesired or uncontrolled ingress of air into the electric arc furnace at least during the melting step.

[0027] Another object of the present invention is to complete or provide an electric arc furnace for melting metallic materials, which can reduce the generation of fumes containing large amounts of CO, CO2 and NOx.

[0028] Another object of the invention is to perfect known types of electric arc furnaces or to create new electric arc furnaces that are capable of reducing direct CO2 emissions by more than 50% compared to traditional plants.

[0029] Another object of the invention is to complete or create an electric arc furnace for melting metallic materials, which allows for a reduced use of chemical energy in the furnace and in particular a reduced input of carbon and oxygen.

[0030] Applicant has conceived, tested and embodied the present invention to overcome the shortcomings of the prior art and to achieve these and other objectives and advantages. Summary of the Invention

[0031] The invention is defined in the independent claims, which set out the particular characteristics thereof.The dependent claims set out further characteristics of the invention or variants of the main idea of ​​the invention.

[0032] In view of the above objectives, and in order to solve the technical problems disclosed above in a new and unique manner while providing a particular advantage over the prior art, the present invention provides an electric arc furnace that can be used to melt a metal charge, comprising both a vessel having a melting chamber and a plurality of main openings, the plurality of main openings including at least an upper opening, a side outlet for removing slag formed on the surface of the molten metal charge, and a side inlet for continuously feeding the metal charge into the melting chamber, and a cover that is placed over the upper opening and can selectively close the upper opening, the cover being provided with one or more first sub-openings, into each of the first sub-openings into which an electrode for melting the metal charge can be inserted to form a clearance.

[0033] In one aspect of the invention, the electric arc furnace further comprises sealing means, at least one of said sealing means being associated with at least one of said main openings so as to prevent or possibly suppress undesired or uncontrolled ingress of air from the external environment during the process of melting the metal charge.

[0034] In another aspect of the invention, the sealing means is preferably associated with at least two of the main openings, more preferably all of the main openings.

[0035] The sealing means includes at least a first sealing member, a second sealing member and a third sealing member for each of the main openings.

[0036] By sealing the electric arc furnace in this manner, at least a relatively low oxygen concentration atmosphere can be created within the electric arc furnace, which is independent of the air of the external environment, thereby preventing CO, CO2 and NO X The advantage is that the formation of

[0037] In one aspect of the present invention, the container has at least one peripheral wall with the upper opening formed at the top, and the first sealing member is sandwiched between the peripheral wall and the cover, and is configured to hermetically close the cover.

[0038] In one aspect of the invention, at least a portion of the first sealing member is disposed on an upper surface of the peripheral wall, the first sealing member including one or more sealing elements capable of ensuring an airtight seal at least under the action of the weight of the cover.

[0039] The electric arc furnace further comprises a closure member associated with the side discharge opening, the second sealing member being associated with the closure member for hermetically isolating the side discharge opening when a continuous charge is introduced.

[0040] In one aspect of the invention, the cover has a central portion, the central portion defining the one or more first sub-openings, the one or more first sub-openings being in fluid communication with the melting chamber. The central portion of the cover is provided with a top panel, the top panel defining one or more second sub-openings for passing the electrodes and for fluid communication with the external environment, vertically aligned with the one or more first sub-openings. Furthermore, the sealing means includes at least one cavity space defined between the top panel and the central portion, the cavity space being in fluid communication with both the one or more first sub-openings and the one or more second sub-openings.

[0041] In one aspect of the present invention, the hollow space is configured to form an intermediate space between the external environment and the melting chamber in which a mixed atmosphere is formed containing both internal processing fumes from the melting chamber and air from the external environment, and both the processing fumes from the melting chamber and the air from the external environment can flow into the hollow space through the one or more first sub-openings and the one or more second sub-openings formed in the cover.

[0042] In one aspect of the invention, suction means are associated with the cavity space and are configured to draw in the mixed atmosphere to create a reduced pressure in the cavity space such that a cavity space pressure (P.ELT) is created in the cavity space which is lower than the atmospheric pressure of the external environment (P.ATM) and the operating pressure in the melting chamber (P.EAF).

[0043] The introduction of the metal charge can be carried out continuously via an autonomous introduction device, which does not constitute an electric arc furnace in the strict sense, but which can be associated with an electric arc furnace, for example the introduction device is a continuous introduction and / or preheat introduction system.

[0044] In one aspect of the invention, the cover further comprises an additional through-hole to which an input means configured to input direct reduced iron (DRI) or hot briquetted iron (HBI) from above can be connected. The input means can comprise both an input duct, preferably sealingly insertable into the additional through-hole, and a hopper connected to the input duct and preferably pressurized.

[0045] In one aspect of the invention, the cover further comprises a suction opening connectable to a primary suction means configured to suction the process fumes from the melting chamber, the suction opening being disposed substantially opposite the additional through opening across the first sub-opening.

[0046] In one aspect of the invention, a steel making plant comprises an electric arc furnace as described above for melting a metal charge and a dosing device for dosing said metal charge into said electric arc furnace, to which a preheat tunnel is at least partially associated and which comprises a slide, the slide being provided with an end selectively insertable at least partially into said side dosing opening, in particular the third sealing member is a sealing device, the sealing device being connectable to the slide and configured to selectively seal a space that may exist between the slide and the electric arc furnace when said end is inserted into the side dosing opening, the sealing means and the sealing device being arranged to prevent or as far as possible limit undesired or uncontrolled ingress of air from the external environment into the electric arc furnace.

[0047] In another aspect of the invention, the sealing device comprises a sleeve surrounding the slide in use, the sleeve having a front face on the electric arc furnace side, the front face being associateable with the electric arc furnace, the front face being provided with an additional sealing member in contact with a peripheral wall of the electric arc furnace corresponding to the inlet.

[0048] These and other aspects, features and advantages of the invention are apparent from the following description of some embodiments, given as non-limiting examples, with reference to the attached drawings, in which: [Brief description of the drawings]

[0049] [Figure 1] FIG. 2 is a schematic cross-sectional elevation view of the intermediate zone of the electric arc furnace of the present invention; [Diagram 2] 2 is a cross-sectional view taken along line II-II in FIG. 1. [Diagram 3] FIG. 3 is an enlarged cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 2 is an enlarged detailed view of FIG. [Diagram 5]2A-2C are diagrams showing the sequence of operation of the closure member of the device for introducing a metal charge into the electric arc furnace of FIG. 1; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] It should be made clear here that the scope of protection is defined by the claims, and therefore the role of the wording and terminology in this specification and the description of each figure in the accompanying drawings is only to facilitate the illustration and explanation of the present invention, and its function is to provide a non-limiting example of the invention itself.

[0051] For ease of understanding, wherever possible, the same reference numbers have been used to identify identical common elements among the figures, and it is understood that elements and features of one embodiment can be combined or incorporated into other embodiments as appropriate without further discussion.

[0052] With reference to figure 1, an electric arc furnace 10 according to the invention can be used for melting a metal charge M as described above, said electric arc furnace 10 being installed, for example, in a steel making plant 100 and being of a basically known type and will not be described in detail apart from some innovative aspects which will be explained below.

[0053] The electric arc furnace 10 comprises a vessel 11 having an upper portion 13 having a substantially cylindrical planar shape and a lower portion or hearth 12 having a substantially elliptical planar shape. A selectively openable cover or roof 15 is provided for closing the upper portion 13.

[0054] Inside the vessel 11 there is generally formed a melting chamber 16 in which a metal charge M is placed for subsequent melting, and in which fumes resulting from the melting process, also called process fumes, are formed.

[0055] The hearth 12 has a concave bottom made of a refractory material capable of withstanding high temperatures of over 1600°C, inside which the melting process of the metal charge M takes place. As in the prior art, the hearth 12 is usually provided with an eccentric tap-hole 18 (FIG. 2) through which the molten steel can be removed. The eccentric tap-hole 18 is known to those skilled in the art by the term EBT (Eccentric Bottom Tap-hole). During the melting operation, the eccentric tap-hole 18 is kept gas-tight by a movable closure member 19 (slide gate) of the obvious kind.

[0056] The upper part 13, on the other hand, comprises or consists of a substantially cylindrical peripheral wall 20 (not shown) of known kind (FIGS. 1 and 2), having an upper opening 21 selectively closable by the roof 15 and provided with water-cooled panels, suitable for protecting the upper part of the melting chamber 16 from thermal stresses.

[0057] The peripheral wall 20 is also formed with a side drain or slag outlet 22 (FIGS. 1, 2 and 3) through which slag formed in the upper layer of the liquid bath B can be extracted or removed in a known manner.

[0058] The slag discharge port 22 is operatively associated with a shutter or slag discharge door 25, which may be cooled in a known manner. For example, and without any limitation of generality, the slag discharge gate 25 may be of the type described in the applicant's European Patent Application Publication No. 3715758.

[0059] In one aspect of the present invention, a mechanical sealing member 26 (Figures 1 and 3) is provided on the surface of the slag discharge door 25 facing the peripheral wall 20, and when the slag discharge door 25 is closed, the sealing member 26 forms an airtight seal of the slag discharge outlet 22.

[0060] In particular, the slag discharge door 25 is configured to be hermetically sealed to prevent undesired or uncontrolled ingress of outside air into the melting chamber 16 during the process of melting the metal charge M, and to be opened only during the slag discharge operation just enough to create a laminar discharge flow of slag toward the discharge channel 24 so as to prevent, or at least minimize as much, the ingress of air into the melting chamber 16. While the slag discharge door 25 in Figures 1 and 3 is shown in an open or raised position, in Figure 2, for clarity, the slag discharge door 25 is shown in a closed or lowered position.

[0061] Optionally, a robotic arm (not shown) of known type, such as a humanoid robot, may be operatively associated with the slag discharge door 25, the end of which is fitted with a device for cleaning and / or removing any slag remaining on the surface of the slag discharge opening 22 after slag removal has taken place, such as the device described in EP 3715758 A1.

[0062] In a preferred embodiment of the invention, the bath temperature can be sampled by means of a sampling probe installed through the peripheral wall 20 or through the roof 15, which can be moved into and out of the liquid bath B by an electromechanical, pneumatic or other actuation system. Said sampling probe is in any case installed so as to keep the atmosphere inside the electric arc furnace 10 isolated from the outside atmosphere and to prevent the undesired ingress of air.

[0063] In one aspect of the invention, a mechanical sealing member 29 (FIGS. 1 and 3) is arranged between the upper surface 27 of the peripheral wall 20 and the corresponding lower portion of the roof 15, preferably at the upper surface 27, and which includes or consists of, for example, a sealing ring or labyrinth system, configured to provide an airtight closure of the roof 15 to prevent undesired or uncontrolled ingress of outside air through the upper opening 21 of the peripheral wall 20 into the melting chamber 16 when the roof 15 is in the closed position during melting of the charge. Advantageously, the roof 15 can be kept closed for a period longer than one melting step, for example for hundreds of successive casting processes, since the introduction of the metal charge C, in particular scrap, is performed by a side charge introduction device 50 and / or by introduction of DRI / HBI from the roof 15 using a hopper system or hopper 71, preferably under pressure. Additionally, one event that may require opening of the roof 15 is the repair of worn refractory material in the hearth 12, which may occur approximately every 400-800 casts, which is related to the conditions under which the electric arc furnace 10 is operated. Thus, the electric arc furnace 10 is kept closed and sealed throughout this entire period, which dramatically reduces undesirable air ingress.

[0064] The covering roof 15 comprises a central portion 30 or arch, preferably made of a refractory material, in which one or more first sub-openings or circular through-holes 31, also called perforations, into each of which a substantially cylindrical electrode 32 can be inserted with clearance therebetween. In particular, between the inner surface of each circular through-hole 31 and the cylindrical surface of each corresponding electrode 32, a certain peripheral clearance or gap L is formed, which can be, for example, about 50 mm. The electrodes 32 are inserted axially into the melting chamber 16 so that melting of the metal charge M can be effected by igniting an electric arc.

[0065] In the example presented here, the electric arc furnace 10 is alternating current (AC) powered and has three electrodes 32 as shown in Figures 1, 2 and 4. However, the invention does not exclude the applicability of the above concepts to direct current (DC) powered furnaces which typically only use one or two electrodes.

[0066] In the embodiment of the invention arranged for the insertion of the metal charge M from above through the top opening 21, the roof 15 can be provided with a suction port 33 (shown in dashed lines in FIG. 1), also known as the "fourth hole", to which suction means can be connected, being a suction pipe 35 (shown in dashed lines in FIG. 1) of known type arranged for sucking the process fumes present in the melting chamber 16, which are then conveyed towards a primary fume treatment plant, which can be of known type and is not shown in the drawings. In particular, the suction pipe 35 allows the part of the melting chamber 16 above the liquid bath B to be brought to an operating pressure P.EAF, which is lower than the atmospheric pressure P.ATM of the external environment surrounding the electric arc furnace 10.

[0067] In another aspect of the present invention, an upper panel 36 is disposed above the central portion 30 of the roof 15 in correspondence with the zone in which the electrode 32 is provided, and the upper panel 36 is shaped to define a hollow space 37 on its inner side toward the outer surface of the central portion 30.

[0068] The upper panel 36 is formed with a through-hole 39 (FIGS. 1 and 4), which is formed here as a second sub-opening, through which the electrode 32 can pass to form a clearance. The through-hole 39 is vertically aligned with the circular through-hole 31 and has the same diameter as the circular through-hole 31, so that it also has the same gap "L" inside it. The upper panel 36 is also formed with an additional opening 40 into which is inserted a suction duct 41, which is connected to a fume treatment plant (primary or secondary), which is of known type and is not shown in the drawings.

[0069] The cavity space 37 fluidly isolates the melting chamber 16 of the vessel 11 in the upper part and the central zone, that is, at the location where the electrode 32 is inserted, thereby having the function of preventing the undesired or uncontrolled intrusion of external air into the melting chamber 16 through the circular through-hole 31. In fact, the cavity space 37 forms an intermediate space between the external environment and the melting chamber 16 in which a mixed atmosphere or intermediate atmosphere composed of both the internal process fumes that have intruded into the cavity space 37 through the gap "L" present in each circular through-hole 31 and the air of the external environment that has intruded into the cavity space 37 through the gap "L" present in each through-port 39 is formed.

[0070] The suction duct 41 associated with the cavity space 37 is configured to suck the above-mentioned mixed atmosphere and carry it towards the fume treatment plant. In particular, due to the action of the suction duct 41, a reduced pressure with respect to the atmospheric pressure P.ATM is formed within the cavity space 37.

[0071] Therefore, advantageously, a mixed atmosphere is formed and maintained within the cavity space 37, which isolates the melting chamber 16 from the external air and has a cavity space pressure P.ELT that is lower than the atmospheric pressure P.ATM and lower than the operating pressure P.EAF within the melting chamber 16, that is, P.ELT < P.EAF < P.ATM. In this way, the outflow of the gas within the cavity space 37 through the suction duct 41 is promoted. It should be noted that for proper operation, it is recommended that the difference between the cavity space pressure P.ELT and the operating pressure P.EAF be at least 15 mmH2O.

[0072] In one embodiment of the present invention, a side inlet or charging port 43 is also formed in the peripheral wall 20, and through this charging port 43, the metal charge M can be introduced so as to perform the substantially continuous charging of the metal charge M itself.

[0073] In one possible embodiment of the present invention, the steelmaking plant 100 (FIG. 1) also comprises an input device 50 cooperating with a side opening or charging port 43 of the electric arc furnace 10, the input device 50 being configured to input a metal charge M substantially continuously.

[0074] In one possible embodiment of the invention, at least a portion of the dosing device 50 is associated with a preheating tunnel (not shown) capable of sucking in the process fumes produced in the furnace, said preheating tunnel being of a known type.

[0075] The input device 50 (FIGS. 1, 2, 5A and 5B) includes a main input conveyor of known type, not shown in the drawings, the final section of which is formed by an auxiliary conveyor (hereinafter the "connecting conveyor") which is associated with an axially sliding tubular member or slide 51, known to those skilled in the art by the term "connecting car", which has an end 52 which is selectively inserted into the opening 43 to discharge the metal charge M within the melting chamber 16.

[0076] The slide 51 is movable along the sliding axis X between a retracted position (not shown) in which the end 52 is located completely outside the charging opening 43 and thus completely outside the electric arc furnace 10, and a charging position (Figures 5A and 5B) in which the end 52 is inserted into the charging opening 43 and the front surface 53 of the slide 51 is located at a distance D of several centimeters from the peripheral wall 20, so that the slide 51 can be moved away from the vessel 11 to allow tilting movements of the electric arc furnace 10 for deslagging and / or tapping.

[0077] In one aspect of the invention, a third sealing member, advantageously a sealing device 55 , is associated with the port 43 to form a seal at the port 43 .

[0078] The sealing device 55 can be connected to the slide 51, i.e. to the charging device 50. In particular, the sealing device 55 is configured to selectively seal the charging opening 43 in accordance with the operating requirements when the slide 51 is in its charging position, thereby preventing undesired or uncontrolled ingress of outside air into the melting chamber 16 and adaptively maintaining the seal both during the so-called deslagging and / or tapping phases, during which the electric arc furnace 10 is slightly inclined relative to the unloading plane of the charging device 50, and during the melting phase.

[0079] Furthermore, the sealing device 55 can be moved axially relative to the slide 51 along a sliding axis X, i.e. radially relative to the vessel 11 of the electric arc furnace 10 .

[0080] In the example presented here, the sealing device 55 comprises a sleeve 56 which surrounds the slide 51 in use, and a ring-shaped sealing member 57 is provided at the front part of the sleeve 56 so as to face the peripheral wall 20 of the electric arc furnace 10.

[0081] The sealing device 55 is attached to a plurality of movable sliders 59, which are arranged on opposite sides of a sliding axis X on a horizontal plane and slide parallel to the sliding axis X by being driven by an actuator of a known type not shown in the figure.

[0082] In the embodiment of the invention shown here, the movable slider 59 is coupled, as is known, to each corresponding guide 60 of the slide 51 by a respective corresponding support 61. In other embodiments, not shown, the movable slider 59 is separate from the slide 51.

[0083] One advantage of using the above-mentioned sealing device 55 is that the sealing isolation between the slide 51 and the melting chamber 16 of the vessel 11 also optimizes the suction treatment of process fumes via the preheat tunnel, for example by a primary fume extraction and treatment plant.

[0084] In fact, as is usual in known plants, said process fumes are sucked in a preheating tunnel of the dosing device 50 in a countercurrent flow to the flow of the metal charge M, in order to preheat said charge M before it is introduced into the vessel 11. This fume sucking is achieved by maintaining a pressure value in the preheating tunnel lower than the operating pressure P.EAF in the melting chamber 16. Preferably, this value decreases gradually in the direction along the fume sucking duct, starting from a position of maximum vacuum near the zone of the fan sucking the fumes.

[0085] On the one hand, the absence of oxygen-containing air in the melting chamber reduces oxidation of the bath, and on the other hand, the suction power of the primary fume plant can be reduced to prevent the escape of said fumes from the furnace, provided that the primary fume plant is essentially tasked with suctioning the treated fumes and does not have to suction large amounts of unsuitable air.

[0086] In fact, the suction of fumes from the electric arc furnace 10 of the present invention, which prevents or at least greatly limits the ingress of air, significantly reduces the internal fume flow rate, possibly by a factor of 5 to 7.

[0087] The reduced suction force reduces the amount of carbon powder sucked in with the fumes, which in turn reduces the need to inject excessive amounts of carbon into the melting chamber 16 to deoxidize the oxidized iron after the action of oxygen, which is used both to decarburize the bath and to remove undesirable elements such as silicon, chromium, molybdenum, nickel, phosphorus, etc. from the liquid bath.

[0088] Therefore, by reducing the amount of carbon injected into the furnace to deoxidize the iron oxide contained in the slag, the amount of CO produced by reaction of the free carbon with oxygen is reduced.

[0089] Additionally, the elimination of undue air ingress into the melting chamber results in a reduced amount of oxygen that can react with free carbon to form CO.

[0090] In particular, the use of continuous charging allows the use of burners to be greatly reduced: indeed, burners are mainly used in the initial melting step to aid the penetration of the electrodes into the charge, but this becomes unnecessary, provided that the melting step is able to gradually assimilate the scrap, which is continuously charged but enclosed in terms of volume.

[0091] This reduces the necessary combustion of hydrocarbons which produces CO and therefore CO2 as discussed above.

[0092] Additionally, because methane burners typically use excess oxygen, using the burner more sparingly reduces the supply of excess oxygen remaining unburned in the melting chamber.

[0093] The reduced carbon supply for the iron oxide deoxidation process, together with the reduced flow of oxygen from inadequate air and burners, reduces further CO formation during the melting process.

[0094] There are two ways in which the CO formed in the melting chamber as a result of the above reactions can be removed: 1) Preferably, the primary fume plant conveys the fumes through a preheat tunnel of the continuous charging system and releases heat energy by burning CO for the convenience of preheating the metal charge; 2) Using a dedicated system to extract and filter CO from the fumes for further use as fuel in the steelmaking process, e.g. in the burners of the electric furnaces mentioned above, or in the reheat furnaces of rolling mills, or in turbines for electricity generation. Indeed, by using the CO produced in the electric arc furnace 10 as fuel, the additional purchase of natural gas (methane) or other fuels is avoided, and the resulting formation of additional CO2 due to combustion is avoided.

[0095] In the first case, the CO mixed with the process fumes is carried in a countercurrent flow to the incoming metal charge. After a certain distance, air is injected into the preheat tunnel (preferably at a location that does not excessively cool the metal charge) to complete the above-mentioned CO post-combustion. Since there is no or a significant reduction in the ingress of air into the electric arc furnace 10, there is no or a significant reduction in the ingress of oxygen into the electric arc furnace 10, and there is also no or a significant reduction in the carbon used for the deoxidization of the iron, the total amount of CO produced is less than in the prior art, which reduces the amount of air required for the post-combustion of CO and the resulting CO2 and NO2. X The risk of formation is proportionally reduced. The flue flow rate is lower than with conventional technologies, making it easier to cool it down to below 850°C and to treat it.

[0096] In order to increase the cooling effect of the fumes, an injector (not shown) capable of supplying steam can be placed in the preheat tunnel, which combines the tasks of diluting and cooling the fumes, thereby making them less reactive.

[0097] It is particularly advantageous to place it downstream of the post-combustion zone and to use NO X Helps prevent the formation of

[0098] Another advantage of the present invention is that the electric arc furnace 10 divides the pressure into several different pressure ranges, which is different from prior art electric arc furnaces, in which the fume suction process requires a very high vacuum pressure because the pressure inside the furnace becomes equal to the pressure of the outside environment due to all the openings present in the furnace.

[0099] In particular, to maximize the effectiveness of the suction of molten fumes for proper use for preheating purposes without risk of the molten fumes mixing with the outside air, the following relationship must be satisfied: P.ELT <PECS<P.EAF<P.ATM In the formula, P.ELT is the pressure acting in the electrode zone of the cell cavity space / roof, P.ECS is the pressure acting in the zone of the slide 51 (connecting car) of the metal charge injection device 50, P.EAF is the pressure of the atmosphere above the molten metal and slag volume and P.ATM is the ambient pressure.

[0100] By way of example only, the optimal levels of the four pressures listed above are as follows: -P.ELT: Approximately -35~-25mmH2O, -P.ECS:Minimum -20mmH2O, -P.EAF: Approximately -10~-1mmH2O, -P.ATM: Approx. 1.033×10 4 mmH2O.

[0101] In other embodiments of the invention, the steel plant 100 may also comprise other dosing devices instead of or together with the dosing device 50 described above. For example, direct reduced iron (DRI) or hot briquetted iron (HBI) may be used, the dosing of HBI being carried out by means of an additional dosing device 70 through the roof of the furnace, as shown diagrammatically in dashed lines in FIG. 1. The additional dosing device 70 may comprise or consist of a hopper 71, preferably pressurized by inert gas, provided with a dosing duct or pipe 72 of known type, which may be sealingly inserted into an additional through-hole 73, also known as the "fifth hole", formed in the roof 15, which is formed substantially opposite the suction opening 33. In this way, dosing can be carried out from above, the dosing of DRI or HBI being carried out in the central zone of the melting chamber 16. Furthermore, the above-mentioned additional through hole 73 is preferably positioned at a certain distance from the suction pipe 35 to prevent the suction pipe 35 from sucking in parts and / or fragments of the DRI or HBI that are freely falling toward the melting chamber 16.

[0102] Advantageously, the pressure in the hopper 71 is higher than the atmospheric pressure P.ATM, and with such a configuration, when DRI or HBI is introduced into the melting chamber 16, the combustion fumes present in the melting chamber 16 will not escape to the outside.

[0103] Furthermore, when the electric arc furnace 10 is charged only by the additional charging device 70, the relational expression regarding the above pressure is simplified to P.ELT < P.EAF < P.ATM. This is because the cavity space pressure P.ELT is lower than both the operating pressure P.EAF of the melting chamber 16 and the atmospheric pressure P.ATM.

[0104] Regarding the electric arc furnace 10 described above, it is clear that improvements and / or additions can be made to each part without departing from the field and scope of the invention specified in the claims.

[0105] For example, in other embodiments of the present invention, the loading port 43 into which the end portion 53 of the carriage 51 can be inserted can be formed on the side surface of the roof 15.

[0106] Also, although the present invention has been described with reference to some specific examples, those skilled in the art will surely be able to achieve many other equivalent forms of the electric arc furnace and / or steelmaking plant having the features described in the claims. Therefore, it is also clear that all such equivalent forms belong to the protection scope described in the claims.

[0107] In the appended claims, the purpose of the reference signs in parentheses is only to make it easier to read and should not be regarded as limiting the protection scope determined by the claims.

Claims

1. 1. An electric arc furnace (10) usable for melting a metal charge (M), comprising: The apparatus includes both a vessel (11) having a melting chamber (16) and a plurality of main openings (21, 22, 43), The plurality of main openings (21, 22, 43) include at least an upper opening (21), a side discharge opening (22) for removing slag formed on the surface of the molten metal charge (M), and a side input opening (23) for inputting the metal charge (M) into the melting chamber (16), and also include a cover (15) that is placed over the upper opening (21) and can selectively close the upper opening (21); The cover (15) is provided with one or more first sub-openings (31); an electrode (32) for melting the metal charge (M) can be inserted into each of the first sub-openings (31) to form a clearance therebetween; The electric arc furnace (10) further comprises sealing means (26, 29, 37, 55), At least one of the main openings (21, 22, 43) is associated with at least one of the sealing means (26, 29, 37, 55) so as to prevent or as far as possible suppress the undesired or uncontrolled ingress of air from the external environment into the melting chamber (16), at least during the process of melting the metal charge (M). An electric arc furnace (10).

2. said sealing means (26, 29, 55) are preferably associated with at least two of said main openings (21, 22, 43), more preferably with all of said main openings (21, 22, 43); The sealing means includes at least a first sealing member (29), a second sealing member (26) and a third sealing member (55). The electric arc furnace (10) of claim 1.

3. The container (11) has at least one peripheral wall (20) having the upper opening (21) formed at its upper portion, The first sealing member (29) is sandwiched between the peripheral wall (20) and the cover (15) and configured to hermetically close the cover (15). The electric arc furnace (10) of claim 2.

4. At least a portion of the first sealing member (29) is disposed on an upper surface (27) of the peripheral wall (20); the first sealing member (29) comprises one or more sealing elements capable of ensuring a hermetic seal at least under the action of the weight of the cover (15); The electric arc furnace (10) of claim 3.

5. a closure member (25) associated with said side outlet (22), the second sealing member (26) is associated with the closure member (25) so as to hermetically isolate the side discharge opening (22) at least when the closure member (25) is in a lowered position; The electric arc furnace (10) of claim 2.

6. The cover (15) has a central portion (30) in which the one or more first sub-openings (31) are formed; the one or more first sub-openings (31) are in fluid communication with the melt chamber (16); a top panel (36) is provided in the central portion (30) and one or more second sub-openings (39) are provided in the top panel (36) for passing the electrodes (32) and for fluid communication with the external environment, the second sub-openings (39) being vertically aligned with the one or more first sub-openings (31); said sealing means including at least one hollow space (37) formed between said top panel (36) and said central portion (30); the cavity space (37) is in fluid communication with both the one or more first sub-openings (31) and the one or more second sub-openings (39); An electric arc furnace (10) according to any one of claims 1 to 5.

7. the hollow space (37) is arranged to form an intermediate space between the external environment and the melting chamber (16) in which a mixed atmosphere is formed containing both the processing fumes from the melting chamber (16) and air from the external environment, and both the processing fumes from the melting chamber (16) and the air from the external environment can flow into the hollow space (37) through the one or more first sub-openings (31) and the one or more second sub-openings (39). The electric arc furnace (10) of claim 6.

8. Said hollow space (37) is provided with associated suction means (41), said suction means (41) being adapted to suction said mixed atmosphere, thereby creating a reduced pressure in said cavity space (37) such that a cavity space pressure (P.ELT) exists in said cavity space (37) which is lower than the atmospheric pressure (P.ATM) of the external environment and the operating pressure (P.EAF) in said melting chamber (16); An electric arc furnace (10) according to claim 6 or 7.

9. the third sealing member (55) being associated with the inlet (43) to form a seal therewith; The electric arc furnace (10) of claim 2.

10. The cover (15) further comprises an additional through hole (73), A charging means (70) configured to charge directly reduced iron or hot briquetted iron from above can be connected to the additional through hole (73), said input means (70) comprises both an input duct (72) which can be inserted, preferably sealingly, into said additional through-hole (73) and a hopper (71) connected to said input duct and which is preferably pressurized; An electric arc furnace (10) according to any one of claims 1 to 9.

11. The cover (15) further includes a suction port (33). A suction means (35) configured to suck the process fumes from the melting chamber (16) is connectable to the suction port (33); The suction port (33) is disposed substantially opposite the additional through hole (73) across the first sub-opening (31). The electric arc furnace (10) of claim 10.

12. An electric arc furnace (10) for melting a metal charge (M) according to any one of claims 1 to 11, a dosing device (50) for continuously dosing said metal charge (M); A steelmaking plant (100) comprising: a pre-heat tunnel at least partially associated with said dosing device (50); The feeding device (50) is provided with a slide (51), The slide (51) is provided with an end (52) selectively insertable at least partially into the input port (43); the third sealing member is a seal device (55); The sealing device (55) is connectable to the slide (51); the sealing device (55) being configured to selectively seal a space that may exist between the slide (51) and the electric arc furnace (10) when the end (52) is inserted into the side inlet (43); The sealing means (26, 29, 37) and the sealing device (55) are arranged to prevent or as far as possible suppress the undesired or uncontrolled ingress of air from the external environment into the electric arc furnace (10). A steelmaking plant (100).

13. The sealing device (55) comprises a sleeve (56) which in use surrounds the slide (51); the sleeve (56) has a front surface (53) on the electric arc furnace (10) side, the front surface (53) being associable with the electric arc furnace (10); The front surface (53) is provided with an additional sealing member (57) which corresponds to the inlet (43) and comes into contact with the peripheral wall (20) of the electric arc furnace (10). The steelmaking plant (100) of claim 12.

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