Electric arc furnace for melting metal 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 such an electric arc furnace. [Background technology]

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

[0003] The hearth is typically made of a metal frame of refractory material within 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. The metal charge 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 usually comprises or consists of a cylindrical peripheral wall capable of accommodating the large volume of scrap mass melted during the first stages of processing, and the purpose of the peripheral wall is to accommodate the layer of slag that covers the bath of steel, with side panels suitable for protecting the non-refractory upper part from thermal stresses, the side panels being water-cooled.

[0005] The peripheral wall is provided with at least one outlet, also known as a "slag outlet," through which slag generated during the melting process can be selectively removed. The slag contains unwanted elements removed from the bath and is collectively referred to as "slag" in technical terms. The slag outlet can be selectively closed using a door, such as a gate valve, or it can be omitted. Alternatively, if the slag outlet does not fully open during the melting process, the slag outlet can remain at least partially open to allow for the introduction of an injection lance or temperature measurement probe, sample removal, or the addition of additives or slag removers. In either case, in the prior art, slag outlet doors are located above the level of the steel bath and are therefore not watertight.

[0006] Known electric arc furnaces also have an upper cover, called a "roof," which can be selectively opened, and a central section, also called an "arch," made of refractory material, with several openings or through-holes, usually three in number in the case of an AC power supply, also known as "cells." These through-holes allow the insertion of corresponding graphite electrodes, which, in order to provide clearance, into the melting chamber and which, when supplied with power, determine the generation of an electric arc, thereby enabling the melting of the metal charge.

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

[0008] The metal charge can be loaded or dropped by suitable charge buckets and released through the top opening of the furnace, or it can be loaded or dropped by a continuous charging system through a side opening formed in the peripheral wall.

[0009] Once the metal charge is loaded by the charge bucket and reaches a suitable volume for each melting process, the roof must be opened two or three times to unload the bucket, releasing a large amount of fumes that, if released into the atmosphere, can be highly polluting, especially if the scrap is contaminated, oily, or moist. Airborne pollutants exist in powder form, particularly heavy metal oxides, but also in gaseous compounds, including CO, NOx, VOCs, dioxins, and furans. During bucket unloading, the fumes are not directly drawn into the primary fume treatment plant's suction duct, which captures the emissions through a fourth opening in the furnace roof, but are instead released outside the melting chamber. Only after this release can they be captured by the hood above the electric arc furnace, which is generally located on the roof of the furnace's hangar and transports them to another, so-called "secondary," treatment plant. Additionally, when the metal material is lowered from the bucket into the melting chamber, special radial gas burners are activated to help melt the charge, allowing the electrodes to be inserted into the metal charge more quickly and reducing melting time, but the use of gas burners also generates more pollutants.

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

[0011] When using a continuous charging system, the metal charge is introduced by means of an introduction conveyor, which is generally configured to be selectively inserted into an opening formed in the peripheral wall of the furnace, and at least a part of the introduction conveyor is associated with a preheating tunnel through which the process fumes generated in the furnace are sucked, thereby utilizing the heat of the process fumes to preheat the introduced material to be melted, thereby reducing and / or optimizing the time and consumption of the melting process.

[0012] During melting, oxygen is introduced using an appropriate lance to oxidize undesirable elements in the bath, such as silicon, chromium, molybdenum, nickel, and phosphorus. 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. Oxygen injection is also necessary to decarburize the bath, achieving a target carbon content of approximately 0.08%. While decarburization occurs during the liquid bath refining process, the injected oxygen inevitably combines with some of the carbon in the bath to produce CO. However, oxygen injection also oxidizes the iron in the metal bath, and to prevent this from adversely affecting furnace yield, the iron must be deoxidized again by injecting powdered carbon. This powdered carbon injection is carried out by multiple injectors located within or above the melting chamber. The reaction of the iron oxide with carbon returns the molecule to metallic iron, but also produces large amounts of CO, which, depending on the availability of oxygen, can be burned and reduced to CO2, releasing additional heat and producing process fumes.

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

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

[0015] When charging using buckets, a free space or gap is maintained between the entrance of the suction pipe inserted into 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. This 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 CO post-combustion.

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

[0017] To prevent the escape of process fumes into the environment, fans in the primary fume extraction and treatment plant maintain a reduced pressure inside 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, air can enter through the passage gaps that exist in the 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 drawn 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 that enters 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 in contact with the electrodes.

[0020] Among other prior art documents, GB 2076858 A1 describes a metallurgical process in a direct-fired steel converter or, in some cases, 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 within the furnace. Furthermore, this prior art document does not address the problem of oxidation within the furnace.

[0021] US Patent No. 4,027,095 describes a gas-tight electric arc furnace for the production of stainless steel, which comprises 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, which closure device in particular comprises an annular closure element that is slidably mounted in the opening and that has 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 determine the amount of metal charge present in the furnace in order to regulate the temperature of the liquid bath to a predetermined value.

[0024] Therefore, there is a need to develop an electric arc furnace that overcomes at least one of the drawbacks of the prior art.

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

[0026] In particular, one object of the present invention is to achieve a completely sealed electric arc furnace for melting metallic materials, which makes it possible to prevent or significantly reduce the unwanted 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 that can reduce the generation of fumes containing large amounts of CO, CO2, and NOx.

[0028] Another object of the present 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 present invention is to complete or create an electric arc furnace for melting metallic materials, which allows for reduced use of chemical energy in the furnace, and in particular reduced carbon and oxygen injection.

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

[0031] The invention is defined in the independent claims, which describe its features, while the dependent claims describe further features 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 significant advantages 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 discharge port for removing slag formed on the surface of the molten metal charge, and a side input port for continuously introducing 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 having one or more first sub-openings, into each of which an electrode for melting the metal charge can be inserted so as to form a clearance.

[0033] In one aspect of the invention, the electric arc furnace further comprises sealing means, at least one of the sealing means being associated with at least one of the main openings so as to prevent or minimize as much as possible the unwanted 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, it is possible to create an atmosphere in the electric arc furnace with a relatively low oxygen concentration that is independent of the air in the external environment, thereby reducing CO, CO2 and NO X The advantage is that the formation of hydroxybenzoates can be significantly prevented and / or suppressed.

[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, so as to hermetically close the cover.

[0038] In one aspect of the present invention, at least a portion of the first sealing member is disposed on an upper surface of the peripheral wall, and the first sealing member includes one or more sealing elements that can ensure 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 to hermetically isolate the side discharge opening when continuous charging is introduced.

[0040] In one aspect of the present invention, the cover has a central portion, and the one or more first sub-openings are formed in the central portion, and the one or more first sub-openings are in fluid communication with the melting chamber. The cover has a top panel in the central portion, and one or more second sub-openings are formed in the top panel in vertical alignment with the one or more first sub-openings for passing the electrodes and for fluid communication with the external environment. Furthermore, the sealing means includes at least one cavity space formed between the top panel and the central portion, and the cavity space is 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 containing both internal processing fumes from the melting chamber and air from the external environment is formed, 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 that 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 opening to which a charging means configured to charge direct reduced iron (DRI) or hot briquetted iron (HBI) from above can be connected. The charging means can comprise both a charging duct preferably sealably insertable into the additional opening and a hopper connected to the charging duct and preferably pressurized.

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

[0046] In one aspect of the present invention, a steelmaking plant comprises an electric arc furnace as described above for melting a metal charge, and a dosing device for dosing the metal charge into the electric arc furnace, a preheat tunnel at least partially associated with the dosing device, the dosing device comprising a slide having an end selectively insertable at least partially into the side dosing opening, and the third sealing member is a sealing device connectable to the slide and configured to selectively seal a space that may exist between the slide and the electric arc furnace when the end is inserted into the side dosing opening, the sealing means and the sealing device being configured to prevent or minimize as far as possible the 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 facing the electric arc furnace, the front face being associateable with the electric arc furnace, the front face being provided with an additional sealing member that contacts a peripheral wall of the electric arc furnace corresponding to the inlet.

[0048] These and other aspects, features and advantages of the present invention will become apparent from the following description of some embodiments, given as non-limiting examples, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0049] [Figure 1] 1 is a schematic cross-sectional elevation view of the intermediate zone of an electric arc furnace of the present invention; FIG. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is an enlarged cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 2 is an enlarged detail view of FIG. [Figure 5]2A to 2C show 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 INVENTION

[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 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 numerals have been used to identify the same common elements in the figures, and it is understood that elements and features of one embodiment may 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 to melt a metal charge M as described above, said electric arc furnace 10 being installed, for example, in a steelmaking plant 100 and being of a basically known type, which will not be described in detail except for some innovative features 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 to close the upper portion 13.

[0054] The interior of the vessel 11 generally defines a melting chamber 16 in which the metal charge M is placed for subsequent melting, and in which fumes, also referred to as process fumes, resulting from the melting process are formed.

[0055] The hearth 12 has a concave bottom made of a refractory material capable of withstanding temperatures exceeding 1,600°C, inside which the metal charge M is melted. 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 airtight by a movable closure member 19 (slide gate) of a self-evident kind.

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

[0057] The peripheral wall 20 also has 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 around the slag discharge outlet 22.

[0060] In particular, the slag discharge door 25 is hermetically sealed to prevent unwanted or uncontrolled intrusion of outside air into the melting chamber 16 during the process of melting the metal charge M, and is configured to open 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 intrusion 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, for clarity in Figure 2, the slag discharge door 25 is shown in a closed or lowered position.

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

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

[0063] In one aspect of the invention, a mechanical sealing member 29 (FIGS. 1 and 3) is disposed between the upper surface 27 of the peripheral wall 20 and the corresponding lower portion of the roof 15, preferably on the upper surface 27, and the sealing member 29 may include or consist of, for example, a sealing ring or labyrinth system, configured to provide an airtight closure of the roof 15 to prevent unwanted or uncontrolled ingress of outside air into the melting chamber 16 through the upper opening 21 of the peripheral wall 20 when the roof 15 is in the closed position during melting of the charge. Advantageously, the roof 15 can be maintained in a closed state for a period longer than a single melting process, for example, for hundreds of consecutive casting processes, since the metal charge C, particularly scrap, is introduced by a side charge introduction device 50 and / or by introduction of DRI / HBI through the roof 15 using a hopper system or hoppers 71, preferably under pressure. Furthermore, one event that may require opening 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 the ingress of unwanted air.

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

[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 present invention does not exclude the applicability of the above concepts to direct current (DC) powered furnaces, which typically use only one or two electrodes.

[0066] In an embodiment of the invention configured for insertion of the metal charge M from above through the upper opening 21, the roof 15 may be provided with a suction port 33 (shown in dashed lines in FIG. 1 ), also known as a "fourth hole," to which suction means may be connected, in the form of a suction pipe 35 (shown in dashed lines in FIG. 1 ) of known type, configured to suck in process fumes present in the melting chamber 16, which are then conveyed towards a primary fume treatment plant, which may be of known type and is not shown in the drawings. In particular, the suction pipe 35 enables the part of the melting chamber 16 above the liquid bath B to be at 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 positioned above the central portion 30 of the roof 15 in correspondence with the zone in which the electrode 32 is provided, and this 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 (Figures 1 and 4), here formed 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, and therefore also has the same gap "L" inside it. The upper panel 36 is also formed with an additional opening 40 through which a suction duct 41 is inserted, which suction duct 41 is connected to the fume treatment plant (primary or secondary) and is of a known type and is not shown in the drawings.

[0069] The cavity space 37 fluidly isolates the melting chamber 16 of the container 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 where a mixed atmosphere or an intermediate atmosphere composed of both the internal processing fumes that have intruded into the cavity space 37 through the gap "L" existing 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" existing 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 function of the suction duct 41, a reduced pressure with respect to the atmospheric pressure P.ATM is formed in the cavity space 37.

[0071] Therefore, advantageously, a mixed atmosphere is formed and maintained in 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 in the melting chamber 16, that is, P.ELT < P.EAF < P.ATM. In this way, the outflow of the gas in 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 the side opening or charging port 43 of the electric arc furnace 10, the input device 50 being configured to input the metal charge M substantially continuously.

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

[0075] The charging device 50 (FIGS. 1, 2, 5A, and 5B) includes a main charging conveyor of a known type, not shown in the drawings, the final section of which is formed by an auxiliary conveyor (hereinafter referred to as the "connecting conveyor") associated with an axially sliding tubular member or slide 51, known to those skilled in the art as a "connecting car," having an end 52 selectively insertable into the charging opening 43 to discharge the metal charge M into 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 (FIGS. 5A and 5B) in which the end 52 is inserted into the charging opening 43 and the front face 53 of the slide 51 is located at a distance D of several centimeters from the peripheral wall 20, thereby enabling the electric arc furnace 10 to be moved away from the vessel 11 to tilt for deslag and / or tapping.

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

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

[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 are driven by a known type of actuator (not shown) to slide parallel to the sliding axis X.

[0082] In the embodiment of the invention shown here, the movable sliders 59 are coupled, as is known, to their respective guides 60 of the slide 51 by respective supports 61. In other embodiments not shown, the movable sliders 59 are separate from the slide 51.

[0083] One advantage of using the sealing device 55 described above is that the sealing separation between the slide 51 and the melting chamber 16 of the vessel 11 also optimizes the suction treatment of process fumes via the preheating tunnel, e.g. by a primary fume extraction and treatment plant.

[0084] In fact, as is usual in known plants, the process fumes are sucked into the preheating tunnel of the dosing device 50 in a countercurrent flow to the flow of the metal charge M, in order to preheat the metal charge M before it is introduced into the vessel 11. This fumes suction 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 is gradually reduced along the fume suction duct, with the maximum pressure reduction occurring near the zone of the fan that sucks 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 fumes from escaping from the furnace, provided that the primary fume plant is essentially tasked with sucking in the process fumes and no longer has to suck in large amounts of undesirable air.

[0086] In fact, the suction of fumes from the electric arc furnace 10 of the present invention, which prevents or at least greatly reduces 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, and phosphorus 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 free carbon with oxygen is reduced.

[0089] Additionally, the elimination of inadvertent air infiltration 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 a significant reduction in the use of burners: indeed, burners are mainly used in the initial melting step to aid the penetration of the electrodes into the charge, but this can be obviated provided that the melting step is able to gradually assimilate the continuously charged but volumetrically enclosed scrap.

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

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

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

[0094] There are two ways in which the CO formed as a result of the above reaction in the melting chamber can be removed: 1) Preferably, the primary fume plant conveys the fumes through a preheating 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 power 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 CO post-combustion. Since the intrusion of air into the electric arc furnace 10 is eliminated or significantly reduced, the intrusion of oxygen into the electric arc furnace 10 is eliminated or significantly reduced, and the carbon used for the iron deoxidation treatment is also eliminated or significantly reduced, the total amount of CO produced is less than in the prior art, which reduces the amount of air required for the CO post-combustion and the resulting CO2 and NO2. X The risk of formation is also reduced proportionately. The flue flow rate is lower than with conventional technology, making it easier to cool it below 850°C and process it.

[0096] To increase the cooling effect of the fumes, an injector (not shown) capable of supplying steam can be placed in the preheating tunnel, which combines the tasks of diluting and cooling the fumes, thereby reducing their reactivity.

[0097] Its location is particularly advantageous downstream of the post-combustion zone, and 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 differs from prior art electric arc furnaces in that, due to all the openings in the furnace, the pressure inside the furnace becomes equal to the pressure of the external environment when fume extraction is performed, and therefore, fume extraction must be performed at a very low pressure.

[0099] In particular, to maximize the effectiveness of suction of molten fumes for proper use in preheating without risk of mixing of the molten fumes with external 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 present invention, the steelmaking plant 100 may include other dosing devices instead of or in addition to the dosing device 50. For example, direct reduced iron (DRI) or hot briquetted iron (HBI) may be used, and the dosing of HBI may be performed by means of an additional dosing device 70 through the furnace roof, as shown diagrammatically in dashed lines in FIG. 1 . The additional dosing device 70 may comprise or consist of a hopper 71, preferably pressurized with inert gas, and provided with a known dosing duct or pipe 72, which may be sealingly inserted into an additional through-hole 73, also known as a "fifth hole," formed in the roof 15, substantially opposite the suction port 33. In this way, dosing may be performed from above, and the dosing of DRI or HBI may be performed 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 do not escape to the outside.

[0103] Furthermore, when the electric arc furnace 10 is charged only by the additional charging device 70, the above relational expression regarding the pressure is simplified to P.ELT < P.EAF < P.ATM. This is because the cavity space pressure P.ELT becomes 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 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 scope of protection described in the claims. [[ID=IS]]

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

Claims

1. An electric arc furnace (10) for melting a metal charge (M), comprising: The apparatus comprises 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 first side discharge opening (22) for removing slag formed on the surface of the molten metal charge (M), and a second side input opening (43) for inputting the metal charge (M) into the melting chamber (16), and also includes a cover (15) that is placed over the upper opening (21) to 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) is inserted into each of the first sub-openings (31) to form a clearance; The electric arc furnace (10) further comprises sealing means (26, 29, 55); at least one sealing means (26, 29, 55) is associated with at least one of the main openings (21, 22, 43) so as to prevent or possibly suppress 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), The sealing means comprises at least a hollow space (37) which serves to fluidly isolate the container (11) from the electrode (32). An electric arc furnace (10) characterized in that

2. 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); the central portion (30) is provided with an upper panel (36), and the upper panel (36) is provided with one or more second sub-openings (39) 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); The hollow space (37) is formed between the top panel (36) and the central portion (30), the hollow 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); The electric arc furnace (10) of claim 1.

3. The hollow space (37) is provided to form an intermediate space between the external environment and the melting chamber (16) in which a mixed atmosphere containing both the processing fumes from the melting chamber (16) and air from the external environment is formed, and is configured so that both the processing fumes from the melting chamber (16) and the air from the external environment 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 2.

4. A suction means (41) is associated with said hollow space (37), the suction means (41) is configured to suction the mixed atmosphere, thereby creating a reduced pressure in the cavity space (37) so that a cavity space pressure (P.ELT) is created in the cavity space (37) which is lower than the atmospheric pressure of the external environment and the operating pressure in the melting chamber (16); The electric arc furnace (10) of claim 3.

5. The container (11) has at least one peripheral wall (20) having the upper opening (21) formed at the top thereof; A first sealing member (29) is sandwiched between the peripheral wall (20) and the cover (15) and configured to hermetically close the cover (15). An electric arc furnace (10) according to any one of claims 1 to 4.

6. 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 configured to ensure an airtight seal at least under the action of the weight of the cover (15); The electric arc furnace (10) of claim 5.

7. a closure member (25) associated with said first side outlet (22); 2. The electric arc furnace (10) of claim 1, wherein a second sealing member (26) is associated with the closure member (25) to hermetically isolate the first side discharge opening (22) at least when the closure member (25) is in a lowered position.

8. a third sealing member (55) associated with said second side inlet (43) for forming a seal of said second side inlet (43); The electric arc furnace (10) of claim 1.

9. The cover (15) also has an additional through hole (73), The additional through-hole (73) is connected to a charging means (70) configured to charge directly reduced iron or hot briquette iron from above, The feeding means (70) includes both the feeding duct (72) inserted into the additional through-hole (73) so as to seal the gap between the additional through-hole (73) and the feeding duct (72), and a hopper (71) connected to the feeding duct and pressurized. An electric arc furnace (10) according to any one of claims 1 to 4 or claims 7 and 8.

10. The cover (15) further includes a suction port (33), The suction port (33) is connected to a suction means (35) configured to suck process fumes from the melting chamber (16); 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 9.

11. an electric arc furnace (10) for melting a metal charge (M) according to claim 8; a feeding device (50) for continuously feeding the metal charge (M); A steelmaking plant (100) comprising: a preheating tunnel at least partially associated with said dosing device (50); The feeding device (50) is provided with a slide (51), The slide (51) has an end (52) selectively inserted at least partially into the second side inlet (43); the third sealing member (55) is a sealing device; The sealing device (55) is connected to the slide (51), the sealing device (55) is configured to selectively seal a space that exists between the slide (51) and the electric arc furnace (10) when the end (52) is inserted into the second side inlet (43); The sealing means (26, 29, 37) and the sealing device are arranged to prevent or as far as possible suppress the unwanted or uncontrolled ingress of air from the external environment into the electric arc furnace (10). A steelmaking plant (100) characterized in that

12. the sealing device 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 associated with the electric arc furnace (10); The front surface (53) is provided with an additional sealing member (57) that contacts the peripheral wall (20) of the electric arc furnace (10) in correspondence with the second side inlet (43). The steelmaking plant (100) of claim 11.

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