PLANT AND PROCEDURE FOR THE PRODUCTION OF SECONDARY ZINC

Description

Patent Description for Industrial Invention entitled: “PLANT AND PROCEDURE FOR THE PRODUCTION OF SECONDARY ZINC”. On behalf of: METALSIDER 2 SPA, a company incorporated and existing according to Italian law, with headquarters in 41122 MODENA (MO). Designated Inventor: DIGANI Fernando. DESCRIPTION The present invention relates to a plant and a process for the production of secondary zinc. In the metallurgical sector, the recovery of metals from waste is well known. previous processes and metal waste. In particular, zinc, thanks to its chemical-physical characteristics, It is widely used for the coating of structures and components metals in order to prevent corrosion. From this manufacturing process a waste product called “zinc skimming” is obtained which It appears as a powdery material and is composed of a finer part and a coarser part, called “zinc grain”. Zinc is also used in many European countries for the production of sheet metal for roofing buildings and for the production of gutters and other accessories. When such covers are dismantled, after several years due to wear and tear caused by bad weather, they are taken to special disposal plants that allow its recovery by producing zinc second smelting called “secondary zinc” with minimum zinc content equal to 98.5%. The known type of plants comprise a melting furnace which is maintained at a temperature sufficient to allow the zinc to melt, a feeding system designed to supply metal residues (grains and zinc scrap) to the melting furnace and a collection system through the where the molten zinc is taken from the vat and conveyed to a machine of forming called “ingot machine” with the aim of creating ingots of solid zinc. The metal residues are loaded into the melting furnace, immersed in a bath of molten zinc. In detail, the sheets are generally compacted, in order to reduce their volume, to form compacted packs. grain, on the other hand, is fed via hoppers. Inside the melting furnace the metal residues are melted and the resulting liquid zinc is conveyed to the forming machine. However, the known type of plants for the production of secondary zinc are susceptible to refinements to obtain better melting yields and purities higher. In fact, although zinc is a low melting metal, in the tank of even residues of other metals contained in the scrap can reach the melting point to partial melting or to erosion and / or corrosion, contaminating the zinc melted and compromising its chemical analysis. Furthermore, the known type of plants require very long processing times long due to the melting times of the sheet metal packs and consequently they lead to non-optimal production yields. The main task of the present invention is to devise a plant and a process for the production of secondary zinc which allow to obtain a finished product with a high degree of purity. Another object of the present invention is to devise a system and a process for the production of secondary zinc which allows for reduce processing times, improve the operating conditions of the operators and to optimize production yields, significantly reducing the production of waste, thus increasing the amount of zinc product. Another purpose of the present invention is to devise a system and a process for the production of secondary zinc which allows to overcome the aforementioned drawbacks of the prior art in the context of a solution simple, rational, easy and effective to use and low cost. The above mentioned purposes are achieved by this plant for the production of secondary zinc having the characteristics of claim 1. The above mentioned purposes are further achieved by the present process for the production of secondary zinc having the characteristics of claim 13. Other features and advantages of the present invention will be found more evident from the description of a form of execution preferred, but not exclusive, of a system and a procedure for the secondary zinc production, illustrated for illustrative purposes only, but not limiting, in the attached tables of drawings in which: Figure 1 is a side view of the system according to the invention; Figure 2 is a plan view of the system according to the invention; Figure 3 is a side sectional view of the system according to the invention. With particular reference to these figures, a globally indicated 1 has been indicated secondary zinc production plant. The plant 1 according to the invention comprises at least one melting group 2 suitable for containing a bath of molten zinc B and for heating and melting residues metals in the form of shredded scrap and / or granules, which are composed of metallic zinc. In the context of this discussion, the expression “metallic residues in the form of shredded scrap and / or granules” refers to metal waste composed mainly of metallic zinc and which are subjected to a recovery process in order to obtain purified metallic zinc, also called secondary zinc. In particular, the residues in the form of grains derive from zinc coating processes of metal structures and components. residues in the form of shredded scrap, on the other hand, derive from used sheet metal for the covering of buildings and / or for the production of gutters, subsequently shred into thin strips about 15 cm wide. Plant 1 also includes: - at least one power supply group 3 capable of supplying the metal waste to the fusion group 2; - at least one mixing and separation group 4 connected to the group power supply 3 and associated with the melting group 2 and capable of receiving the metal residues, mix them in the molten zinc bath and remove waste process from melting group 2; - at least one sampling group 5 capable of transferring molten zinc from the sampling group 2 melting to a solid secondary zinc forming machine. In practice, through the present plant 1, the metal residues, once introduced into the melting group 2 they are moved inside the bath of molten zinc B and the metallic zinc contained in them melts in turn. detail, the movement of metal residues in the molten zinc favors and speeds up the melting of the zinc contained in them. Furthermore, the mixing and separation group 4 determines the progress of process waste, that is, what remains of the metal residues following of the zinc smelting and removes them from the smelting group 2. In this way, the molten zinc bath B is free of components that can determine its pollution and is substantially composed of pure zinc. Specifically, the secondary zinc obtained by the 1 second plant the finding has a purity greater than 99%, preferably equal to 99.5%. Furthermore, this plant 1 allows to optimize the processing and relative extraction of zinc from metal residues and to reduce process waste as a consequence. In this case, process waste (ashes) resulting from the processing of metal waste using this plant 1 contain a percentage of zinc (metal) less than 50%. Plant 1 is described in more detail below. The melting group 2 comprises a melting tank 6 partially buried and deep, for example 2 metres, and suitable for containing the bathroom of molten zinc B. The melting unit also includes heating means, not shown. in detail in the figures, associated with the melting tank 6 and suitable for heating the latter and to maintain its contents at a temperature almost constant. In detail, in use, the melting tank 6 constantly contains a predefined quantity of molten zinc, maintained at the respective temperature of fusion, which allows the melting of metal residues. In practice, the heating means are designed to indirectly heat metal residues, which are instead heated by the same molten metal, in a sort of bain-marie. When a predefined quantity of liquid is reached in the tank, fusion 6, the extraction group 5 determines the release of the molten zinc from the same. The sampling group 5 includes an outlet duct 7 fluid-dynamically connected to the melting tank 6 and connectable to the forming machine. In particular, the forming machine, not shown in detail in the figures, It comprises a plurality of moulds into which the zinc is gradually poured molten metal which solidifies as it cools and leads to the formation of zinc ingots solid metal. The sampling group 5 also includes an associated valve device to the outlet duct 7 and is used to regulate the flow of molten zinc exiting the melting tank 6. In particular, the valve device is adjusted in so that the level of molten zinc inside the melting tank 6 is always above a certain limit, so as to ensure the heating of the new metal residues to be recovered. The feeding group 3 comprises at least one hopper 8a,8b suitable for contain the metal residues and at least one transfer device 9, of the such as a conveyor belt with paddles, used to transfer waste metals from hopper 8a,8b to melting tank 6. In accordance with a preferred embodiment shown in the figures, the power supply group 3 comprises a first hopper 8a suitable for contain the metal residues in the form of grit and a second hopper 8b suitable for containing metal residues in the form of lamellae. Hoppers 8a,8b are operated to release their respective contents onto the transfer device 9 according to a predefined ratio between them. However, it cannot be excluded that the power supply group 3 is of the different. Thanks to the presence of the mixing and separation group 4, which allows to speed up the melting of zinc and to remove waste process, power group 3 is configured to feed the tank of fusion 6 in a substantially continuous manner. Usefully, the mixing and separation group 4 comprises at least a handling unit 10 configured to handle the residues metals in melting group 2 along a feed direction A. Movement along the direction of advancement A allows the mixing of the metal residues with the molten zinc from the zinc bath B and the progressive increase in process waste. The handling unit 10 comprises at least one entry area 11 for metal waste and an exit area 12 for process waste, located downstream of the entrance area 11 with respect to the direction of advancement A. Power supply group 3 is located in the area of entrance 11. The mixing and separation group 4 also comprises at least one unit removal 18 suitable for receiving process waste from the unit movement 10 and to convey them towards the outside of the melting group 2. The removal unit 18 is arranged at the exit area 12. The removal unit 18 comprises a movable platen that extends towards the outside of the melting tank 6. In accordance with the embodiment shown in the figures, the moving plane It is of the type of a vibrating plane. However, it cannot be excluded that the moving plane be of a different type. Conveniently, the handling unit 10 is arranged in the melting tank 6. at a predefined height with respect to an upper edge of the melting tank itself and is configured, in use, to be partially immersed in zinc melted. In fact, given the specific weight of the molten zinc, the metal residues, once introduced into the melting tank 6 tend to float and remain on the free surface of the liquid. The handling unit 10 is configured to place the metal residues with molten zinc and to determine their movement in the same direction of travel A. During the journey, the zinc of the metal residues melts in turn and mixes with the zinc already melted in the melting tank 6, leaving the process waste. The latter, once reached the outlet area 12, are removed from the melting tank 6 by the unit of removal 18. In accordance with the embodiment shown in the figures, the unit of movement 10 comprises a screw body 13 which extends along the direction of advance A. The movement unit 10 also comprises an actuator 14 connected to the auger body 13 and suitable for rotating the latter. The rotation of the auger body 13 determines the movement of the molten zinc and residues metals along the direction of travel A. However, it cannot be excluded that the handling unit 10 is of the type different, for example of the type of a pallet conveyor. Specifically, the auger body 13 comprises a shaft R that can be rotated around to a respective axis of rotation R substantially parallel to the direction of advancement A and at least one spiral 16 associated with the shaft R. In accordance with the embodiment shown in the figures, the spiral 16 is of the type of a sector spiral. It cannot be ruled out, however, that spiral 16 is of the continuous spiral type. In detail, the removal unit 18 comprises a pair of blades associated opposite to the shaft 15 of the screw body 13 and rotatable in solidarity with it. Specifically, the blades are arranged on a plane passing through the axis of rotation R and are configured to determine the movement of process waste along a direction transverse to the direction of advance A, towards the outside of the melting tank 6. Advantageously, the auger body 13 comprises at least one fin mixing 17 associated with at least one turn of the spiral 16. Mixing fin 17 helps mix metal residues in molten zinc and, specifically, causes a temporary immersion which guarantees an optimal and substantially complete fusion of the zinc contained therein. In particular, the mixing fin 17 is associated with the outer edge of the spiral 16. In accordance with one possible embodiment, the mixing fin 17 is arranged transversely to the direction of travel A. In detail, the mixing vane 17 is folded towards the shaft R. Preferably, the auger body 13 comprises at least one pair of fins of mixing 17 associated with at least one turn of the spiral 16. Specifically, the auger body 13 comprises a plurality of vanes mixing 17 associated with respective turns of the spiral 16. It is easy to understand how the present system 1 can be used also for the processing of metals other than zinc. According to a further aspect, the present invention also refers to a process for the production of secondary zinc. The process according to the invention comprises at least the following phases: - supply of a molten zinc bath B; - supply of metal waste in the form of shredded scrap and / or granules, metal residues being composed of metallic zinc; - feeding of metal residues into the molten zinc bath B; - mixing of metal residues in the molten zinc bath B and removal of process waste from the molten zinc bath B, resulting from the melting of the zinc contained in metal residues; - removal of molten zinc from the molten zinc bath B to obtain zinc solid secondary. The process can be implemented using the system 1 according to the invention. The mixing phase allows you to speed up and optimize the melting of the metallic zinc contained in metal residues. Thanks to this, the phase of feeding can occur substantially continuously. The mixing and removal phase allows to obtain a zinc secondary of high purity, up to 99.5%, and to reduce waste process. In practice, it has been found that the described invention achieves the objectives proposed and in particular it is emphasized that the system and the process according to the invention for the production of secondary zinc allow to obtain a finished product with a high purity. Furthermore, the system and the process according to the invention allow for reduce processing times and achieve high production yields.

Claims

1) Plant (1) for the production of secondary zinc characterised by made of understanding: - at least one melting group (2) capable of containing a bath of molten zinc (B) and to heat and melt metal residues in the form of shredded scrap and / or grain, said metal residues being composed of metallic zinc; - at least one power supply unit (3) capable of supplying said waste metallic to said melting group (2); - at least one mixing and separation group (4) connected to said power supply group (3) and associated with said melting group (2) and suitable for receiving said metal residues, mixing them in said zinc bath melted and to remove process waste from said melting group (2); - at least one sampling group (5) capable of transferring molten zinc from said melting group (2) to a zinc forming machine solid secondary. 2) System (1) according to claim 1, characterised in that said mixing and separation group (4) comprises at least one unit of handling (10) configured to move said metal waste in said fusion group (2) along a direction of advancement (A). 3) System (1) according to one or more of the preceding claims, characterised by the fact that said movement unit (10) is equipped with at least one entry area (11) for said metal residues and at least one outlet zone (12) for said process waste, located downstream of said zone of input (11) with respect to said direction of advancement (A), said group of power supply (3) being arranged in correspondence with said area of entrance (11). 4) System (1) according to one or more of the claims previous, characterized by the fact that said mixing group and separation (4) comprises at least one removal unit (18) adapted to receive said process waste from said handling unit (10) and convey them towards the outside of said melting group (2), said unit of removal (18) being arranged in correspondence with said exit area (12). 5) System (1) according to one or more of the preceding claims, characterized in that said fusion group (2) comprises at least a melting tank (6) suitable for containing said molten zinc bath (B) and from fact that said movement unit (10) is arranged in said tank fusion (6) at a predefined height with respect to an upper edge of said melting tank (6) and is configured, in use, to be partially immersed in said molten zinc bath (B). 6) System (1) according to one or more of the preceding claims, characterised in that said movement unit (10) comprises at least one screw body (13) which develops along said direction of advancement (A). 7) System (1) according to one or more of the preceding claims, characterised in that said screw body (13) comprises a shaft (R) rotatable around a respective axis of rotation (R) substantially parallel to said direction of advancement (A) and at least one spiral (16) associated with said tree (R). 8) System (1) according to one or more of the preceding claims, characterized by the fact that said spiral (16) is of the type of a sector spiral. 9) System (1) according to one or more of the preceding claims, characterised in that said screw body (13) comprises at least a mixing vane (17) associated with at least one turn of said spiral (16). 10) System (1) according to one or more of the preceding claims, characterized by the fact that said mixing fin (17) is associated with the outer edge of said spiral (16). 11) System (1) according to one or more of the claims previous ones, characterized by the fact that the said fin of mixing (17) is arranged transversely to the said direction of advancement (A). 12) System (1) according to one or more of the preceding claims, characterised in that said screw body (13) comprises at least one pair of mixing vanes (17) associated with at least one turn of said spiral (16). 13) Process for the production of secondary zinc characterized by made to include at least the following phases: - supply of a molten zinc bath (B); - supply of metal waste in the form of shredded scrap and / or granules, said metallic residues being composed of metallic zinc; - feeding of said metal residues into said molten zinc bath (B); - mixing of said metal residues in said zinc bath molten (B) and removal of process waste from said zinc bath molten (B), resulting from the fusion of the zinc contained in said metal residues; - removal of molten zinc from said molten zinc bath (B) to obtain zinc solid secondary. Modena, July 23, 2024 For assignment Marco Brunacci