MXPA99010718A - Loading system for electric arc furnaces - Google Patents

Abstract

Loading system for electric arc furnaces (11) including at least a roof (11a) including at least a"fourth hole"which can be connected to a conduit to discharge the fumes (22) associated at the end with an air-tight cover (23) to temporally close at least one loading element (16) containing scrap, the bottom part of the loading element (16) able to be at least partly opened, the system comprising a pick up and moving device (15) equipped with at least a rotary manipulator arm (17), the loading element (16), arranged in the pre-heating station (20b), directly cooperating with means to convey the fumes from the furnace (11) and with air-tight temporary closing means (23), the loading element (16) being configured as a container or basket (12, 112, 212) arranged in a removable manner suspended on gripper elements (17a, 17b) of the manipulator arm (17), the container or basket (12, 112, 212) in the pre-heating station (20b) being arranged above and in direct cooperation with a combustion chamber (21) wherein the pre-heating fumes pass and are partly burnt after having passed through the container or basket (12) through the scrap from the top downwards, the air-tight cover (23) of the container or basket (12) being able to be removed vertically and rotatably and being temporally directly connected with the fume-discharge conduit (22) from the fourth hole of the furnace (11) by conduit means at least partly coaxial with the axis of rotation.

Description

LOADING SYSTEM FOR ELECTRIC ARC OVENS FIELD OF APPLICATION This invention relates to a charging system for electric arc furnaces as presented in the main claim. The invention is applied to the field of steel production for charging electric furnaces with scrap, or base material similar to scrap, which is preheated by means of fumes coming from the same electric furnaces and flowing from the from top to bottom. The electric arc furnaces to which the invention is applied can be of the type fed either by direct or alternating current. The invention can be used both in new suitably prepared installations, and also for renovating existing installations using ovens of a conventional type. The invention makes it possible to reduce the times required to open the roof of the furnace in order to load it, limiting the heat losses from inside the furnace to the external environment. Moreover, the invention makes it possible to automate the movements necessary to load the furnace, to drastically reduce the cycle times by reducing the stops of the furnace, to limit the movements and the equipment necessary for the load, to reduce the spaces occupied at the sides of the furnace , and also use cargo baskets of either small or large capacity according to availability. Another advantage of the invention is that, in order to preheat the scrap and discharge it into the furnace, it is possible to directly use the baskets arriving from the scrap storage bin or baskets that are loaded when they are ready in the preheating station; the baskets may be of variable shape, size and type, and do not require stationary support structures when in the preheat position near the furnace.

STATE OF THE ART The state of the art includes electric arc furnaces used to produce steel from scrap and regenerated material of various types. In the state of the art, the ovens can be loaded continuously, for example by means of transport such as a band, connected to the internal part of the furnace and fed continuously with new scrap that gradually replaces the one already loaded in the furnace. In another solution, the ovens are loaded discontinuously by means of baskets or containers. The baskets, in one or more successive steps, are loaded in a scrap loading zone and then transported, by means of lifting and moving elements, for example bridge cranes in correspondence with the mouth of the furnace which is kept temporarily open. The bottom of the basket is then opened and the material is discharged into the furnace. For this purpose the baskets are equipped in the background with movable doors, valves, teeth, sliding grilles or other suitable opening system. The systems that use baskets to load the oven that are known in the state of the art have a plurality of disadvantages. First, it takes a long time to load the oven due to the combination of movements required to open the oven and place the basket; this causes a considerable loss of heat from the inside of the oven outside, and also the escape into the surrounding environment of fumes containing dust, particles and other contaminants. Another disadvantage is that if the scrap is loaded cold in the furnace, it takes longer to melt and causes problems for the penetration of the electrodes. At present, in some steel mills the furnaces are loaded with scrap that is preheated by the heat of the fumes discharged from the same furnace through the fourth roof hole. The charging systems known in the state of the art where the scrap is preheated use load baskets located in suitable spaces in which the fumes are transported before they are purified and discharged by suitable plants. There are also known solutions for the state of the art that include a single room containing several cargo baskets, or several rooms connected to each other, each of which contains a single cargo basket. These systems cause problems in the structuring of the rooms, the movements of the baskets and also in the wear of the baskets. Moreover, in the case of baskets heated inside the room, the scrap loses some of the heat it has accumulated, both when it is removed from the room and when it is transported near the mouth of the oven and also when it is discharged in the oven, from which there is always considerable loss of heat in any case. Moreover, the scrap does not heat evenly from one basket to the next. These systems are also not very functional, are very expensive, and take up a lot of space inside the plant. Another disadvantage is that the preheating rooms are usually located in positions that are not very close to the oven, and therefore the times needed to transport the baskets from this position to the oven are very long and the heat losses are very large. WO 96/32616 shows heating the scrap in a container which is solid with a movement structure, the scrap heating from the bottom up. This teaching does not give the advantage of heating the scrap from the top down, does not allow the use of autonomous baskets, rio allows easy maintenance operations. WO 92/10594 uses a handling tower comprising at least one rotating arm that is used to place a container filled with scrap from a preheating position to a position where the scrap is loaded in the oven and vice versa. W? '594 includes a preheating environment which opens at the top and bottom, inside which a cargo container is placed, with a bottom that can be opened. The preheating environment is located on a stationary base that constitutes a pedestal accommodated in proximity to the oven; it is associated, in the preheating position, with an air-tight lock element for sealing its ends, and an element for introducing and discharging the preheating fumes taken from the furnace. The preheating environment includes a jacket that widens to the bottom and which connects to the bottom pedestal to form an air tight seal. The pedestal communicates with a lower chamber where fumes pass and burn. The hot fumes coming out of the furnace are first directed to the combustion chamber under the preheating container where they are burned, and then transported through suitable conduits, either inside the container from top to bottom, during the preheating step , or they go towards the unloading plant, during the movement of filling of the same container. This solution involves expensive and complex equipment of the pipes, installation difficulties, temperature losses from the fumes which, due to the long and tortuous path that they have to follow are colder when they reach the scrap. Moreover, this solution involves problems of contamination and wear of the filtration system because after the fumes have passed through the scrap, they are sent directly to the treatment and discharge plant and therefore they are carried with them all the dust, the slag and the particles that they have absorbed during their passage through the container. In general, the solution given by WO'594 does not make it possible, or even easy, to use cargo baskets of any shape and size, since the baskets need to be inserted inside the preheating environment arranged in the stationary base. EP-A-629830 provides a variant to WO'594 where the fumes are introduced into the container filled with scrap from the top down, and where there is a pre-combustion of the fumes entering the container and also a post-combustion of the fumes as they come out of it. WO 95/12690 describes a system of movement with a rotating tower for containers in which the scrap is preheated; the system does not use removable type baskets but a substantially stationary single block structure, which implies obvious limitations to the versatility, flexibility and operability of the plant. Moreover, the means by which the preheating fumes are treated and discharged after they have passed through the scrap container are not explained. FR-A-2, 435, 684 includes a motion system with articulated arms associated with a movable structure which can be moved above a melting furnace. This document does not include the preheating of the scrap or any process to transport and discharge the fumes. EP-A-287,550 provides a method for preheating several baskets or containers accommodated in proximity to the furnace which are then placed and moved by means of a bridge crane in order to carry out loading operations. All these documents do not provide a completely versatile and flexible solution, that is practical, that has a high performance, and that can be adapted to various types of facilities and plants, which is limited in overall volume and requires only limited civil engineering works. in its preparation. The present applicant has designed, tested and incorporated this invention to overcome the disadvantages of the state of the art to obtain other advantages.

DESCRIPTION OF THE INVENTION The invention is presented and characterized in the main claim, while the dependent claims describe variants of the idea of the main mode. The purpose of the invention is to provide a charging system for electric arc furnaces which will give an automated and functional operation cycle, which will allow the use of scrap preheated by the fumes coming out of the furnace, and which will involve opening times shorter of the oven. Another purpose of the invention is to achieve a loading system for ovens which will limit the space occupied above and to the sides of the oven and which will easily be adaptable to existing structures, without requiring substantial modifications to the basic plant of the oven. Another purpose is to provide a system that will allow the furnace to be loaded both by means of baskets of a substantially conventional type and also by means of convenient containers that cooperate with the related systems to feed the scrap. Still another purpose of the invention is to have a flue pipe that can deflect the heating basket to send fumes directly to the chimney without passing through the baskets. Another purpose of the invention is to use baskets of substantially any type or shape in general. Still another purpose is to obviate the need for stationary structures or a pedestal on which the baskets are supported and to which they adapt. Another purpose is to include a direct connection, which can also be excluded and diverted, between the fourth hole in the oven and the top of the basket, so that the fumes can be introduced into the basket at the highest possible temperature and can in this way provide the maximum available energy supply. Another purpose is to minimize the polluting content of the fumes that come out of the basket containing the scrap metal in a way that preserves the plant which treats and discharges the fumes, and minimizes the deterioration thereof. Another purpose is to avoid environmental contamination during transport of the basket from the preheating position to the position where the scrap is discharged into the furnace. The invention uses a device for collecting and moving the loading elements of the oven, whether baskets or containers. The pick-up / move device comprises at least one manipulator arm rotatable with respect to a central or pivot position. According to a variant, the device that collects / moves is of the type with two arms and such that it allows the simultaneous movement of two baskets, thus reducing to a minimum the time when the preheating is not being carried out, which always affects at least one of the two baskets. The pick-up / move device accommodates one side of and in proximity to the furnace and co-operates with a plurality of accommodation stations for the load elements that are arranged on the circumference having as their center the axis around which the arm rotates manipulator; the electric furnace itself also fits over this circumference.

The load basket is placed directly suspended on the gripping elements of the arms; the gripping elements are configured as forks and cooperate with hook elements present advantageously opposite each other on the external wall of the basket. According to a variant, the gripping elements of the arms are at least partially adjustable and allow baskets of different size and shape to be placed and held. According to the invention, there are two stations for housing a single loading element or basket, for loading the furnace: a first loading station in which the loading element is filled with scrap and a second different station for preheating the scrap in which the load element is connected to the duct to discharge the fumes from the furnace. In a second mode, there are at least two accommodation stations for the relative load elements; the charging step and the preheating step are carried out alternately in these two stations. In this mode, the duct for discharging fumes from the furnace is articulated and / or telescopic, and is arranged in cooperation with one or the other of the two stations according to the stage of the work being carried out. In another mode, there are at least three stations for at least two load elements.

In this mode, apart from the loading and preheating stations, there is at least one supplementary station, where the loading element is accommodated, as soon as the scrap has been discharged in the furnace, while it is waiting to be accommodated in the filling station. load. The supplementary standby station allows the other load element to be moved by the manipulator arm from the loading station to the preheating station. According to a variant, a conveyor system for transporting the scrap cooperates with the supplementary holding station, and fills with scrap the load element located there. ~ Another embodiment includes a plurality of charging and preheating stations cooperating with one or more manipulator arms; this mode allows smaller baskets, which are easier to maneuver, to load the oven. The systems used to load the scrap can be of various types according to the characteristics of the plant, the load element used and other contingent requirements. Systems can for example include bridge cranes, crane carriers with buckets or conveyor belts.

The configuration of the charging system according to the invention, and therefore the number and arrangement of the accommodation and equipment stations and number of the loading elements, can be modified according to the requirements of use and / or existing structures to which the system has to apply. However, the invention ensures a coordinated, fast and functional charging cycle for the furnace, it also reduces the opening times of the furnace and takes advantage of the furnace fumes to preheat the scrap. According to another variant, the smoke conveyor conduit includes fans and / or burners that intervene in the combustion of the CO contained in the fumes and increases its heat output. According to a variant, the smoke conveyor conduit is connected at the end to a mobile structure that functions as a cover for the basket at least during the preheating step.

ILLUSTRATION OF THE DRAWINGS The attached figures are given as a non-restrictive example and show some preferred embodiments of the invention as follows: Figure 1 shows a top view of an electric arc furnace using the charging system according to the invention; Figure 2 shows a section A-A of Figure 1; Figures 3 and 4a show a section of A-A of Figure 1 in two successive steps of the furnace charging cycle; Figure 4b shows a variant of Figure 4a; Figure 5 shows in diagram form a variant of the charging system for electric arc furnaces according to the invention; Figures 6a and 6b show another embodiment of the charging system for electric arc furnaces according to the invention. Figures 7a and 7b show a variant of the invention from the side and from the top.

DESCRIPTION OF THE DRAWINGS The system 10 according to the invention is associated, in this case, with an electric furnace 11 powered by alternating current, although the invention can also be applied to electric furnaces operating with direct current. The system 10 provides the loading of the furnace 11 with scrap metal, or other raw material similar to scrap, which has been preheated by the fumes derived from the melting process inside the same furnace 11. The preheated scrap is contained inside of loading elements 16 which can be associated with a device that collects and moves 15. In Figures 1-4 the loading element 16 of the oven 11 consists, in a removable basket 12, having a capacity correlated with the scrap volume that is available to be introduced into the furnace 11 for each melt cycle, inside which the scrap is discharged by means of the containers 13, which can also be baskets similar to the basket 12 and which move on a bridge crane 14. agreement with a variant, the loading element 16 consists of specialized removable containers 12. The upper end of the baskets or containers 12 is open, and the lower end is partially closed by movable elements such as knives, grids, valves, or the like that retain the scrap contained inside while allowing fumes to pass. According to the variant shown in Figure 5, the loading element 16 is filled by means of a conveyor belt 19. According to another variant that is not shown here, the loading element 16 is filled by means of a crane with buckets The collecting and moving device 15 comprises, in the embodiment shown in Figures 1-6, a manipulator arm 17 mounted rotatably and vertically movable about a central pivot 18. The manipulator arm 17 has two extensions 17a, 17b, substantially in the form of a fork, which can be restricted at the ends with the respective hook-type connection elements 12a, 12b made to the side of the external wall of the container 12, advantageously opposite each other. According to a variant the fork-type extensions 17a, 17b can be adjusted at least partially to allow the use of removable baskets or containers 12 of different size and / or shape. The central pivot 18 fits next to the electric furnace 11 and cooperates with the stations 20 to house the containers 12; the different operations to prepare the scrap are carried out in these stations 20, which are arranged in a circle having the central pivot 18 as the center, the same furnace 11 being on the same circumference. In the solutions shown in Figures 1-4 the loading system 10 has two stations 20, respectively the charging station 20a and the preheating station 20b, and a single container 12. At the loading station 20a, the container or basket 12 is filled by the baskets 13 that can be moved on a bridge crane 14 with the scrap arriving from the storage area (Figure 2).

As soon as the container 12 has been filled, the manipulator arm 17 moves the container 12 to the adjacent preheating station 20b (Figure 3), where the container 12 is associated with an air-tight cover 23 connected with the conduit for discharging the fumes 22 of furnace 11 and vertically movable and rotatable about a vertical axis. The smoke discharge conduit 22 comprises a first segment 22a connected to the tubular element 24 associated with the fourth hole in the roof of the furnace 11, a second, substantially vertical segment, 22b and two branches, the upper branch 22c and the lower branch 22d, which are derived from the second segment 22b. The upper branch 22c, which has at least one segment coaxial with the vertical axis of rotation of the airtight cover 23, is associated at the end of the air-tight cover 23 and has a lock valve at an intermediate point. The lower branch 22d is associated at the end with a combustion chamber 21 for the fumes associated with the systems for discharging the fumes and has a lock valve 26 at an intermediate point. The smoke combustion chamber 21 is located directly below the container 12 located in the preheating position; the fumes passing through the basket during the preheating step then pass through the combustion chamber 21. The smoke combustion chamber 21 may be equipped with burners, which are not shown here, which serve to burn all the residual organic and inorganic compounds contained in the fumes, and to help the powders to be deposited so that the fumes can reach the processing plant and discharge at least partially free of these polluting substances that are harmful for the useful life of the system of filter. The smoke combustion chamber 21 also makes it possible to collect any residual scrap falling from the container or from the previous basket 12. The smoke combustion chamber 21 advantageously is connected downstream with an inlet and with a fume cleaning plant. In the preheating station 20b (Figure 3), the lower part of the container 12 is connected to an upper opening 21a of the combustion chamber 21 by means of its own opening 27 for the exit of the fumes. When the scrap is being preheated, the valve 26 in the lower branch 22d is closed, while the valve 25 in the upper branch 22c is open; in this way, the fumes coming from the furnace 11 pass through the smoke discharge conduit 22 and are transported towards the cover 23. The fumes therefore pass through the container 12 from the top, wrapping and heating the scrap, contained therein from the upper part to the lower part, until they exit through the opening 27, towards the combustion chamber 21. The fumes leave the combustion chamber 21 at a lower temperature, having lost at least part of the its heat in heat exchange with scrap, and therefore are easier to process and discharge. Moreover, as they advance from the top down into the container or basket 12, they do not damage the opening systems of the bottom of the container or basket 12, preserving the integrity and lifespan of these systems. When the furnace 11 has finished its current melting cycle the roof is moved sideways (dotted lines in Figure 1) and the manipulator arm 17, rising and rotating around the central pivot 18, places the container 12 on top of the furnace 11 , thereby allowing the preheated scrap to discharge into the furnace 11 (Figure 4). According to the variant shown in Figure 4b, the container or basket 12 is associated with a cover 123, solid with the manipulator arm 17, which moves with the basket 12 and closes it as it passes from its preheating position to its position of cargo. The presence of the second cover 123 prevents any spillage of the fumes in the surrounding environment, thus limiting contamination, and also prevents heat from being dispersed from the scrap which reaches the oven warmer. When this operation is concluded, the manipulator arm 17 takes the container 12 back to the loading station 20a to begin a new filling cycle. While the container 12 is maintained in the charging station 20a, the fumes coming from the furnace 11 are transported directly to the combustion chamber 21, closing the valve 25 of the upper branch 22c and opening the valve 26 of the lower branch 22d; in this condition the upper opening 21a of the combustion chamber 21 is closed. In the embodiment shown in Figure 5, the electric furnace 11 is alternatively charged by two containers 12, respectively the first container 112 and the second 212. In this embodiment, there are three stations 20 for housing the containers 12, each of the which has a structure (not shown here) to support the containers 12: a filling station 20a, a preheating station 20b and a supplementary holding station, 20c.

When the first loading cycle has been completed, the first container 112 is accommodated by the manipulator arm 17 in the supplementary stand-by position 20c. Then, the manipulator arm 17 picks up the second container 212 from the loading station 20a, where it has been loaded meanwhile, in this case by means of a conveyor belt 19, and places it in the preheating station 20b. In the preheating position 20b, the second container 212 is connected in the upper part with the air-tight cover 23 and in the lower part with the combustion chamber 21, in order to heat the scrap contained therein. While the scrap is heating up in the container 212, the manipulator arm 17 picks up the first container 112 of the supplementary holding station 20c and places it in the loading station 20a where it is filled. At the end of the melting cycle, the furnace 11 is charged by means of the second container 212 which is subsequently placed in the supplementary holding station 20c; the first container 112 that has been filled in the meantime is then moved to the preheating station 20b to begin a new charging cycle. According to a variant, in the supplementary waiting station 20c, one - for example the first 112 - of the two containers 12 is loaded, while the other container 12 - for example the second 212, - is loaded in the load 20a (Figure 5). The containers 112, 212 are then placed in sequence and the preheating station 20b before being used to load the furnace 11. The elements for transporting the scrap, in this case consist of a conveyor belt 19, which cooperates with the supplementary station of Wait 20c (shown by a dotted line) may consist of the same elements that cooperate with the filling station 20a or may be autonomous elements. In the embodiment shown in Figures 6a and 6b, two containers 12 are used, the first container 112 and the second container 212, accommodated in the respective housing stations 120, 220, in which the loading step is carried out and the preheating step alternately. In this case, the housing station 220 is obtained in the upper part of the combustion chamber 21, so that the lower part of the second container 212 is connected to the upper opening 21a of the combustion chamber. 21. The receiving station 120 is obtained in a supporting structure 28 associated with a connection pipe 29, which is connected to the combustion chamber 21 and is equipped with its own lock valve 29a. In the embodiment shown, the upper branch 22c of the smoke discharge conduit 22 can extend telescopically and rotate with respect to the second section 22b; the smoke discharge conduit 22 can therefore be alternatively associated together with the cover 23, with both containers 112, 212. In the loading cycle, the first container 112 is filled, with elements not shown here, while the upper branch 22c of the smoke discharge conduit 22 is arranged in cooperation with the second container 212, in order to heat the scrap contained therein, closing the second container 212 on the upper part by means of the air-tight cover 23 (Figure 6a). In this condition, the valve 29a of the connection pipe 29 is kept closed, while the upper mouth 21a opens, thereby allowing the fumes to enter the combustion chamber 21. At the end of the melting cycle, the manipulator arm 17 brings the second container 212 above the electric oven 11 in order to load it. Subsequently, the second container 212 is brought back to its position 220 to be filled, while the upper branch 22c rotates and extends until it takes the air-tight cover 23 to cover the first container 112 so that the scrap contained therein. it can be heated (Figure 6b). During this warm-up step, the valve 29a opens and allows the fumes to pass through to the combustion chamber 21, while at the same time the upper mouth 21a of the latter is closed. The electric furnace 11 is subsequently loaded by means of the first container 112, while the upper branch 22c is accommodated in cooperation with the second container 212. In the other embodiment shown in Figures 7a and 7b, a manipulator arm 117 of the type is used. double, convenient to support and move two baskets or containers 112, 212 simultaneously. In this embodiment, at least one of the containers is always in the preheating step, in this case 112, while the other 212 is ready to be filled, in this case by a basket 13 moved on a bridge crane. When the preheating is completed, the air-tight cover 23 connected to the smoke discharge conduit 22 can be moved from the container 112 to the container 212 in order to begin the pre-heating of the scrap contained therein, while the scrap the container 112 is discharged into the furnace 11. In another embodiment, with each cycle the containers 112 and 212 invert their position, respectively for 2 ^ 5 preheating and loading the scrap, the air-tight cover 23 being simply lifted and lowered to associate alternatively with one or another of the containers 112, 212. With this embodiment, the times when the scrap is not being preheated are substantially reduced to nothing and the spaces and movements are rationalized and optimized. There may also be burners 31 and / or fans along the conduit 22 in order to regulate the flow rate and / or the combustion of fumes before they are sent into the basket or container 12. Apart from the described modalities above there are other possible embodiments that are not shown here, which use a greater number of loading elements 16 cooperating with respective and autonomous charging stations 20a and preheating stations 20b; these embodiments allow smaller loading elements 16, which are easier to manipulate, to be used.

Claims (13)

1. Loading system for electric arc furnaces (11), whether they are of the direct or alternating current type, including electric arc furnaces (11), a roof (lia) which can be moved from a closed position to a non-interference position, including the roof to a "fourth hole" for the discharge of smoke which can be connected to a conduit (22) associated at the end with an air-tight cover (23), the cover being hermetic air (23) suitable for temporarily closing at least one loading element (16) containing scrap or other raw material similar to scrap, the loading element (16) has the lower part closed by openable elements, the system a collecting and moving device (15) equipped with at least one autonomous manipulator arm (17) the manipulator arm (17) is rotatable and vertically movable around a central pivot (18), the manipulator arm (17) cooperates at least with a preheating station (20b) for the at least one load element (16) accommodated on the circumference having the central pivot (18) as the center, the electric oven (11) also being accommodated on this circumference, the system is characterized in that it comprises at least one loading station (20a), different from the preheating station (20b), accommodated on the circumference having the central pivot (18) as center and passing through the electric oven (11) and through the preheating station (20b), the charging station (20a) can be associated with elements (14, 19) for loading -the scrap inside an empty loading element (16), the manipulating arm (17) is convenient first to transfer the loading element (16) from the charging station (20a) to the preheating station (20b), then from the preheating station (20b) to a position above the furnace (11) and over the same axis as that, to discharge the scrap and then back to the loading station (20a) to perform another scrap loading cycle, the air-tight cover (23) being convenient for cooperating in the pre-heating station (20b) , with means for transporting the fumes from the furnace (11), the loading element (16) being adapted in the preheating station (20b) above a combustion chamber (21) where the preheating fumes passing from the room pass. roof hole (lia) after passing from the upper part downwards of the loading element (16). System as in claim 1, characterized in that the air-tight cover (23) is able to move vertically and rotatably with respect to the loading element (16) and temporarily connects directly with the smoke discharge conduit (22) to starting from the fourth hole (lia) by means of conduction elements at least partially coaxial to the axis of rotation of the air-tight cover (23). System as in claim 1 or 2, characterized in that it comprises a supplementary waiting station (20c), different from the preheating station (20b) and the charging station (20a), accommodated on the circumference having the central pivot (18) As its center, the waiting station (20c) is pre-accommodated for temporary placement, by means of the manipulator arm (17), of a first loading element (16) after the scrap contained therein has been discharged into the electric furnace (11), while a second load element (16) is accommodated in the charging station (20c). System as in claim 3, characterized in that the supplementary waiting station (20c) is convenient for cooperating with the elements (14, 19) for loading the scrap. System as in claim 1 and 4, characterized in that the scrap loading element (13, 19), by itself, is convenient to cooperate alternatively with the charging station (20a) and with the supplementary holding station (20c) ) different from the charging station (20a). 6. System as in claim 1, characterized in that the smoke discharge duct (22) and the air-tight cover (23) are movable from the preheating station (20b) to the charging station (20a), different from the preheating station (20b). ), and vice versa to preheat the scrap contained in the first of the load elements (16), temporarily arranged in its preheating station, at the same time as the scrap is loaded by the elements (14, 19) in a second element of load (16) temporarily arranged on this loading station. System as in claim 1, characterized in that it comprises a double-type manipulator arm (17) for simultaneously supporting and moving two containers or baskets (12) in the different respective positions of preheating (20b) or loading (20a). System as in any of the preceding claims herein, characterized in that the manipulator arm (17) has two fork-type extensions (17a, 17b) suitable for cooperating with hook-type connection elements (12a, 12b) made in one position opposite on the external wall of the loading element (16). System as in any of the preceding claims herein, characterized in that the smoke discharge conduit (22) at least partially coaxial with the vertical axis of rotation has a first branch (22c) connected to the air-tight cover ( 23) and a second branch (22d) directly connected to the combustion chamber (21), the branches (22c, 22d) are governed by respective closure elements with the valves (25, 26) to send the fumes alternately inside the element of charge (16) or inside the combustion chamber (21). System as in any of the preceding claims herein, characterized in that it comprises a movable cover element (123) suitable for covering the loading element (16) during the transfer of said element (16) from the preheating station ( 20b) to the position above the oven (11). System as in any of the preceding claims herein, characterized in that the combustion chamber (21) is equipped with burners. System as in any of the previous claims hereinabove, characterized in that the combustion chamber (21) is connected downstream with inlet and cleaning elements for the fumes. System as in any of the preceding claims herein, characterized in that the smoke discharge conduit (22) includes burners and / or fans (31). SUMMARY Loading system for electric arc furnaces (11) including at least one roof (lia) including at least one "fourth hole" which can be connected to a conduit to discharge the fumes (22) associated at the end with a air-tight cover (23) for temporarily closing at least one loading element (16) containing scrap, the lower part of the loading element (16) can at least be partially open, the system comprises a device that collects and moves ( 15) equipped with at least one rotating manipulator arm (17), the loading element (16), accommodated in the preheating station (20b), cooperates directly with elements for transporting the fumes from the furnace (11) and with elements of air-tight temporary closure (23), the loading element (16) is configured as a container or basket (12, 112, 212) accommodated in a suspended manner on fasteners (17a, 17b) of the manipulator arm (17), the container or basket (12, 112, 212) in the preheating station (20b) is accommodated above and in a direct cooperation with a combustion chamber (21) where the Preheating fumes pass and are partially burned after passing through the container or basket (12) through the scrap from top to bottom, the air-tight cover (23) of the container or basket (12) can be removed vertically and rotatably and temporarily connected directly with the smoke discharge conduit (22) from the fourth hole of the furnace (11) by conduit elements at least partially coaxial with the axis of rotation.