Zinc steam condensation recovery system

Abstract

The invention belongs to the field of metallurgical solid waste dezincification, and relates to a zinc steam condensation recovery system which mainly comprises a condensation tank, the side wall of the condensation tank is connected with a zinc steam inlet pipe, and the top surface of the condensation tank is connected with an exhaust pipe; the crucible is arranged at the bottom of the condensation tank and is configured to contain solid zinc in a normal temperature state and / or liquid zinc in a heating state; the bottom of the crucible is connected with a zinc liquid conveying pipe, and the zinc liquid conveying pipe penetrates out of the condensation tank and is branched into a zinc liquid recycling branch pipe and at least one zinc liquid circulating branch pipe; the zinc liquid circulating branch pipe is led into the condensation tank from the side wall of the condensation tank and is fixedly arranged on the tank wall, and a plurality of nozzles facing the bottom of the condensation tank are formed in the pipe section, located in the tank, of the zinc liquid circulating branch pipe; and the arrangement position of the zinc steam inlet pipe is lower than that of the zinc liquid circulating branch pipe. According to the zinc vapor condensation device, zinc liquid with the low temperature is sprayed downwards, zinc vapor with the high temperature is extracted upwards, the zinc vapor makes full contact with sprayed zinc mist in the rising process for heat exchange, and the condensation efficiency of the zinc vapor is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of metallurgical solid waste dezincification and relates to a zinc vapor condensation recovery system. Background Art

[0002] In the extraction process of metallic zinc, pyrometallurgical extraction occupies a pivotal position with its high efficiency and directness. This process is complex and delicate, in which zinc metal undergoes a series of key steps to achieve its effective separation and recovery. First, zinc ore or zinc-containing waste is sent to the high-temperature reduction stage after pre-treatment steps such as crushing, grinding, and mixing. In this stage, zinc metal is reduced from the ore through heating and the action of reducing agents to form zinc vapor. Subsequently, the zinc vapor enters the gas evaporation stage. In this process, the zinc vapor is further purified at a specific temperature and pressure to remove impurities and residues. The evaporated zinc vapor has a high purity, which provides favorable conditions for subsequent condensation recovery.

[0003] Condensation is one of the key steps in the zinc extraction process. Under certain conditions, zinc vapor is condensed into liquid zinc. In this process, the performance and efficiency of the condenser are crucial. An efficient condenser can ensure that the zinc vapor is fully condensed, improving the liquefaction rate and recovery rate. An inefficient condenser may result in incomplete condensation of zinc vapor, or even the formation of powdered zinc, which affects subsequent processing and product quality.

[0004] At present, the condensation recovery of zinc vapor mainly relies on traditional splash condensers and water-cooled tank condensers. However, both condensers have certain limitations in practical applications. Although the design principle of the traditional splash condenser is simple, it occupies a large area and has low condensation efficiency. This not only increases the production cost, but also limits its scope of application. Especially in some occasions where space is limited or efficient condensation is required, the traditional splash condenser often cannot meet the requirements.

[0005] In contrast, water-cooled tank condensers use water as the condensing medium, which has a certain cooling effect. However, when the condensation temperature is not accurately controlled, zinc vapor is easy to solidify into powder. This not only affects the liquefaction effect of zinc, but also makes the zinc unable to meet the standards of ingot casting. Powdered zinc is not only difficult to handle, but also reduces the market value of the product. Therefore, water-cooled tank condensers also have certain limitations in practical applications.

[0006] With the continuous growth of zinc metal market demand and the continuous progress of production technology, the requirements for zinc vapor condensation recovery devices are also increasing. Traditional condensation methods can no longer meet the urgent needs of modern zinc smelting industry for high efficiency, energy saving and environmental protection. In order to improve the condensation efficiency and liquefaction rate of zinc vapor, reduce production costs and environmental pollution, it is imperative to research and develop a new type of zinc vapor condensation recovery device. Summary of the invention

[0007] In view of this, an object of the present invention is to provide a zinc vapor condensation recovery system to improve the condensation efficiency of zinc vapor.

[0008] To achieve the above-mentioned purpose, the present invention provides a zinc vapor condensation recovery system, comprising a condensing tank, a zinc vapor inlet pipe is connected to the side wall of the condensing tank, and an exhaust pipe is connected to the top surface of the condensing tank; a crucible is arranged at the bottom of the condensing tank, and is configured to contain solid zinc at room temperature and / or liquid zinc in a heated state; a zinc liquid delivery pipe is connected to the bottom of the crucible, the zinc liquid delivery pipe passes through the condensing tank and branches into a zinc liquid recovery branch pipe and at least one zinc liquid circulation branch pipe; the zinc liquid circulation branch pipe passes into the condensing tank from the side wall and is fixed on the tank wall, and the pipe section located in the tank is provided with a plurality of nozzles facing the bottom of the condensing tank; wherein the setting position of the zinc vapor inlet pipe is lower than the setting position of the zinc liquid circulation branch pipe.

[0009] Zinc vapor enters the tank from the zinc vapor inlet pipe and moves toward the top of the condensation tank under the action of the exhaust pipe. During this process, the zinc vapor exchanges heat with the zinc mist sprayed from the zinc liquid circulation branch pipe, thereby condensing to form zinc liquid and falling into the crucible.

[0010] Optionally, at least one penetration plate for slowing down the flow rate of zinc vapor is provided in the condensation tank, and a plurality of through holes are provided on the penetration plate for the flow of zinc mist.

[0011] Optionally, when there are multiple penetration plates in the condensation tank, the overlap degree of projections of the through holes of two adjacent penetration plates on the horizontal plane is less than 100%.

[0012] Optionally, the number of penetration plates is the same as the number of zinc liquid circulation branch pipes, the penetration plates and zinc liquid circulation branch pipes are alternately arranged in the condensing tank, and a penetration plate is arranged under each zinc liquid circulation branch pipe.

[0013] Optionally, the penetration plate is horizontally placed in the condensation tank, or the penetration plate is inclinedly placed in the condensation tank.

[0014] Optionally, each nozzle is provided with a nozzle protection cover with an opening toward the bottom of the condensation tank, and the nozzle protection cover is made of a high-temperature resistant and corrosion-resistant alloy plate.

[0015] Optionally, a heating device is provided on the outer wall of the crucible to melt the solid zinc into liquid zinc.

[0016] Optionally, when there are multiple zinc liquid circulation branch pipes in the condensing tank, the nozzles on two adjacent zinc liquid circulation branch pipes are arranged in a staggered manner.

[0017] Optionally, the system further comprises a high-pressure nitrogen pipe, which is respectively connected to the zinc liquid conveying pipe and each zinc liquid circulation branch pipe.

[0018] Optionally, a graphite pump is provided on the zinc liquid delivery pipe.

[0019] The beneficial effects of the present invention are:

[0020] The zinc vapor condensation recovery system provided by the present invention sprays the zinc liquid with a lower temperature downward through the zinc liquid circulation branch pipe, and extracts the zinc vapor with a higher temperature upward through the exhaust pipe, so that the zinc vapor is fully in contact with the ejected zinc mist for heat exchange during the rising process, which significantly improves the condensation efficiency of the zinc vapor. Furthermore, the present invention is provided with a plurality of penetration plates in the condensation tank to reduce the flow rate of the zinc vapor while allowing the zinc liquid to pass through, further increasing the heat exchange time of the zinc vapor and the zinc mist. The present invention uses the zinc liquid with a lower temperature than the zinc vapor as the condensation medium, and can also avoid the introduction of additional impurities in the condensation process, so that the condensed product does not need to be subjected to stratification or filtering procedures.

[0021] Furthermore, the condenser tank of the present invention has a compact structure, concentrated functions, and can be arranged vertically. Compared with the traditional splash condenser, the condenser system of the present invention has greatly reduced the floor space by optimizing the structural design. This not only reduces the cost of building a factory, but also provides more space utilization possibilities for the production site, and is particularly suitable for production environments with limited space.

[0022] In addition, the zinc vapor condensation recovery system provided by the present invention adopts a fully enclosed design, which effectively prevents the leakage of zinc vapor during the condensation process, thereby meeting certain specific process requirements that have extremely high requirements on the production environment. This design not only ensures production safety, but also reduces environmental pollution, and meets the strict requirements of the modern metallurgical industry for environmental protection. The fully enclosed design also effectively reduces heat loss, improves energy utilization efficiency, and reduces production costs.

[0023] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0025] Figure 1 A schematic diagram of the structure of the zinc vapor recovery condensation system provided by the present invention;

[0026] Figure 2 A schematic diagram of the structure of a penetration plate of the zinc vapor recovery condensation system provided by the present invention.

[0027] Figure markings: 1-condenser; 2-zinc vapor inlet pipe; 3-exhaust pipe; 4-crucible; 5-zinc liquid delivery pipe; 6-zinc liquid recovery branch pipe; 7-zinc liquid circulation branch pipe; 7.1-first zinc liquid circulation branch pipe; 7.2-second zinc liquid circulation branch pipe; 8-nozzle; 9-nozzle protection cover; 10-penetration plate; 10.1-first penetration plate; 10.2-second penetration plate; 11-through hole; 12-heating device; 13-high-pressure nitrogen pipe; 14-graphite pump; 15-inspection door; 16-cleaning liquid recovery pipe. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0029] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0030] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0031] The present invention provides a zinc vapor condensation recovery system, which is intended to improve the condensation efficiency of zinc vapor. Figure 1As shown, the system mainly includes a condensing tank 1, the lower part of which is connected to a zinc vapor inlet pipe 2 for introducing zinc vapor into the tank; the top surface of the condensing tank 1 is provided with an exhaust pipe 3 for extracting gas in the tank. A crucible 4 is provided at the bottom of the condensing tank 1 for containing solid zinc, and a heating device 12 is provided outside the crucible 4 to heat the solid zinc in the crucible 4 into zinc liquid. Furthermore, a zinc liquid delivery pipe 5 is connected to the bottom of the crucible 4. After passing through the condensing tank 1, the zinc liquid delivery pipe 5 branches into a zinc liquid recovery branch pipe 6 and at least one zinc liquid circulation branch pipe 7 to extract the zinc liquid in the crucible 4 for recovery or to introduce it into the zinc vapor condensation cycle.

[0032] The zinc liquid recovery branch pipe 6 is connected to the ingot casting equipment to guide the condensed zinc liquid out of the ingot. The zinc liquid circulation branch pipe 7 passes into the condensation tank 1 from the side wall and is firmly fixed on the tank wall. The pipe section located in the tank is provided with multiple nozzles 8 facing the bottom of the condensation tank 1 to spray the zinc liquid with a lower temperature downward. The number and spacing of the nozzles 8 on the zinc liquid circulation branch pipe 7 must ensure that the sprayed zinc mist can completely cover the internal space of the condensation tank 1.

[0033] In particular, the zinc vapor inlet pipe 2 is set at a position lower than the zinc liquid circulation branch pipe 7 to ensure that the zinc vapor is fully in contact with the ejected zinc mist for heat exchange during the rising process. Preferably, the zinc vapor inlet pipe 2 is set close to the top of the crucible 4, and the zinc liquid circulation branch pipe 7 is set close to the top of the condenser 1. When there are multiple zinc liquid circulation pipes 7 in the condenser 1, the nozzles 8 on two adjacent zinc liquid circulation pipes 7 are staggered to ensure uniform condensation of the zinc vapor.

[0034] During operation, zinc vapor enters the condensation tank 1 from the zinc vapor inlet pipe 2, and moves to the top of the condensation tank 1 under the suction of the exhaust pipe 3. In this process, the relatively high temperature zinc vapor (about 900°C) fully contacts and exchanges heat with the relatively low temperature zinc mist (about 400-500°C) ejected from the zinc liquid circulation branch pipe 7, thereby condensing to form zinc liquid, which falls into the crucible 4. This design significantly improves the condensation efficiency of zinc vapor, and uses zinc liquid with a lower temperature than zinc vapor as the condensation medium, avoiding the introduction of additional impurities in the condensation process, so that the condensed product does not need to be layered or filtered.

[0035] In order to further optimize the condensation effect, at least one penetration plate 10 may be optionally provided in the condensation tank 1 to slow down the flow rate of the zinc vapor. Figure 2As shown, a plurality of circular through holes 11 are provided on the penetration plate 10 for the circulation of zinc mist. When a plurality of penetration plates 10 are provided in the condensing tank 1, the projection overlap of the through holes 11 of two adjacent penetration plates 10 on the horizontal plane is less than 100%, that is, the through holes 11 of two adjacent penetration plates 10 do not completely overlap, and preferably, the through holes 11 of two adjacent penetration plates 10 half overlap each other. In addition, the number of penetration plates 10 is the same as the number of zinc liquid circulation branch pipes 7, and the two are alternately arranged in the condensing tank 1, and a penetration plate 10 is arranged under each zinc liquid circulation branch pipe 7 to further increase the heat exchange time of zinc vapor and zinc mist.

[0036] In some possible implementations, the specific shape of the penetration plate 10 matches the inner wall of the condenser tube 1, and the shape is circular or elliptical. The penetration plate 10 can be horizontally placed in the condenser tank 1, or can be placed obliquely in the condenser tank 1, preferably installed obliquely in the condenser tank 1, so that the zinc liquid can flow from the high point of the penetration plate 10 to the low point under the action of gravity, so as to reduce the residence time of the zinc liquid on the penetration plate 10.

[0037] In some possible embodiments, the penetration plate 10 and the inner wall of the condensation tank 1 are detachably connected, and the relevant mechanisms for connecting the two are made of high-temperature resistant alloy materials, and are sprayed after the penetration plate 10 is installed. For example, several connecting blocks are set on the inner wall of the condensation tank 1, and the edge of the penetration plate 10 is placed on the connecting block on the inner wall of the condensation tank 1, and the penetration plate 10 and the connecting block are connected by bolts.

[0038] In some possible implementations, there are two zinc liquid circulation branch pipes 7, both of which are arranged near the top of the condensing tank 1. The first zinc liquid circulation branch pipe 7.1 is located above the second zinc liquid circulation branch pipe 7.2. There are two penetration plates 10, the first penetration plate 10.1 is arranged below the first zinc liquid circulation branch pipe 7.1, and the second penetration plate 10.2 is arranged below the second zinc liquid circulation branch pipe 7.2.

[0039] In some possible implementations, each nozzle 8 is provided with a nozzle protection cover 9 with an opening toward the bottom of the condensation tank 1, and the protection cover is made of a high temperature resistant and corrosion resistant alloy plate. The nozzle protection cover 9 is a trumpet-shaped structure with an opening toward the bottom of the condensation tank 1, so that the zinc liquid flows along the surface of the nozzle protection cover 9 to the crucible 4 at the bottom of the condensation tank 1.

[0040] In some possible embodiments, the recovery system further includes a high-pressure nitrogen pipe 13, which is respectively connected to the zinc liquid delivery pipe 5 and each zinc liquid circulation branch pipe 7, wherein the pressure of the nitrogen introduced must meet the purging requirements so as to purge each pipe section after the material is stopped.

[0041] In some possible implementations, a graphite pump 14 is further provided on the zinc liquid delivery pipe 5 to pump the zinc liquid to the zinc liquid recovery branch pipe 6 and / or the zinc liquid circulation branch pipe 7. The type of the graphite pump 14 needs to meet the following requirements: the flow rate provided in the fully open state needs to match the flow rate requirement of the ingot casting process. Furthermore, a cleaning liquid recovery pipe 16 is provided near the inlet and outlet of the graphite pump 14 to guide the cleaning waste liquid in each pipe section into the cleaning pool.

[0042] In some possible implementations, each pipeline is provided with a valve for controlling the opening and closing of the pipe section, and each valve is made of a high temperature resistant and corrosion resistant alloy material, or each valve is sprayed with a graphite protective layer. When there is a vertical bend in the pipeline, an arc-shaped connecting pipe section is used for transition to reduce the flow pressure of the zinc liquid or other liquids. All pipelines and the condensation tank 1 are covered with insulation materials and wrapped with aluminum foil to isolate the influence of the external environment on the steam condensation process.

[0043] In some possible implementations, the crucible 4 is a graphite crucible, which is hemispherical in shape to reduce the flow resistance of the zinc liquid. The inner wall of the graphite crucible is sprayed with a graphite layer, and its end face is welded to the inner wall of the condenser tube. A certain gap needs to be maintained between its outer wall and the inner wall of the condenser tube to ensure that maintenance personnel can pass smoothly. The heating device 12 at the outer wall of the crucible 4 is a resistance heater, which is connected to the PLC control cabinet to adjust the heating temperature.

[0044] In some possible implementations, the exhaust pipe 3 is made of a high-temperature resistant alloy or stainless steel, and is installed at the center of the top of the condenser pipe. A graphite layer is sprayed at the welding point between the exhaust pipe 3 and the condenser tank 1. When the condenser tank 1 starts working, the exhaust pipe 3 extracts zinc vapor and moves upward. During this process, the zinc vapor exchanges heat with the zinc liquid and condenses. The formed zinc liquid falls into the crucible 4 at the bottom of the condenser tank 1, and other impurities in the zinc vapor are extracted through the exhaust pipe 3.

[0045] In some possible embodiments, a plurality of inspection doors 15 are provided on the side wall of the condensation tank 1, preferably at the top, middle and bottom of the condensation tank 1, and the opening position of the inspection door 15 is opposite to the opening position of the zinc steam inlet pipe 2 to avoid mutual influence between the two.

[0046] The operation steps of the zinc vapor condensation recovery system provided by the present invention include:

[0047] S1, turn on the heating device 12 to melt the solid zinc in the crucible 4 into zinc liquid, and close the zinc liquid recovery branch pipe 6 and the high-pressure nitrogen pipe 13;

[0048] S2, opening the zinc liquid delivery pipe 5, the graphite pump 14 and the zinc liquid circulation branch pipe 7, pumping the zinc liquid into the condensation tank 1 and spraying it out in the form of zinc mist;

[0049] S3, opening the zinc vapor inlet pipe 2 and the exhaust pipe 3, the zinc vapor exchanges heat with the zinc mist in the condensation tank 1 to condense and fall into the crucible 4;

[0050] S4, opening the zinc liquid recovery branch pipe 6 to transport the zinc liquid to the ingot casting process;

[0051] S5. After the zinc liquid is transported, the high-pressure nitrogen pipe 13 and the cleaning liquid recovery pipe 16 are opened to purge the pipelines.

[0052] The zinc vapor condensation recovery system of the present invention realizes the compact layout and functional concentration of the condensation tank by optimizing the structural design. Compared with the traditional splash condenser, the condensation system of the present invention greatly reduces the floor space, which not only reduces the cost of plant construction, but also provides more space utilization possibilities for the production site. In particular, the fully enclosed design effectively prevents the leakage of zinc vapor during the condensation process, and meets certain specific process requirements that have extremely high requirements on the production environment. At the same time, the fully enclosed design also reduces heat loss, improves energy utilization efficiency, and reduces production costs. In summary, the zinc vapor condensation recovery system of the present invention, with its high efficiency, compactness, and environmental protection, provides a new solution for the field of metallurgical solid waste dezincification, with significant technical effects and economic benefits.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A zinc vapor condensation recovery system, characterized in that: It comprises a condensation tank (1), the side wall of the condensation tank (1) is connected to a zinc vapor inlet pipe (2), and the top surface of the condensation tank (1) is connected to an exhaust pipe (3); The crucible (4) is arranged at the bottom of the condensation tank (1), and is configured to contain solid zinc at room temperature and / or liquid zinc in a heated state; The bottom of the crucible (4) is connected to a zinc liquid delivery pipe (5), the zinc liquid delivery pipe (5) passes through the condensation tank (1) and branches into a zinc liquid recovery branch pipe (6) and at least one zinc liquid circulation branch pipe (7); The zinc liquid circulation branch pipe (7) passes into the condensation tank (1) from the side wall and is fixed on the tank wall, and the pipe section located in the tank is provided with a plurality of nozzles (8) facing the bottom of the condensation tank (1); wherein the setting position of the zinc vapor inlet pipe (2) is lower than the setting position of the zinc liquid circulation branch pipe (7); Zinc vapor enters the tank from the zinc vapor inlet pipe (2) and moves toward the top of the condensation tank (1) under the action of the exhaust pipe (3). During this process, the zinc vapor exchanges heat with the zinc mist sprayed from the zinc liquid circulation branch pipe (7), thereby condensing to form zinc liquid, which falls into the crucible (4).

2. The zinc vapor condensation recovery system according to claim 1, characterized in that: At least one penetration plate (10) for slowing down the flow rate of zinc vapor is arranged in the condensation tank (1), and a plurality of through holes (11) are opened on the penetration plate (10) for the circulation of zinc mist.

3. The zinc vapor condensation recovery system according to claim 1, characterized in that: When the condensation tank (1) has a plurality of penetration plates (10), the overlap of projections of the through holes (11) of two adjacent penetration plates (10) on a horizontal plane is less than 100%.

4. The zinc vapor condensation recovery system according to claim 2, characterized in that: The number of the penetration plates (10) is the same as the number of the zinc liquid circulation branch pipes (7); the penetration plates (10) and the zinc liquid circulation branch pipes (7) are alternately arranged in the condensation tank (1); and a penetration plate (10) is arranged below each of the zinc liquid circulation branch pipes (7).

5. The zinc vapor condensation recovery system according to claim 2, characterized in that: The penetration plate (10) is horizontally placed in the condensation tank (1), or the penetration plate (10) is tiltedly placed in the condensation tank (1).

6. The zinc vapor condensation recovery system according to claim 1, characterized in that: Each of the nozzles (8) is provided with a nozzle protection cover (9) with its opening facing the bottom of the condensation tank (1), and the nozzle protection cover (9) is made of a high temperature resistant and corrosion resistant alloy plate.

7. The zinc vapor condensation recovery system according to any one of claims 1 to 6, characterized in that: The outer wall of the crucible (4) is provided with a heating device (12) to melt solid zinc into liquid zinc.

8. The zinc vapor condensation recovery system according to any one of claims 1 to 6, characterized in that: When the condensing tank (1) has a plurality of the zinc liquid circulation branch pipes (7), the nozzles (8) on two adjacent zinc liquid circulation branch pipes (7) are arranged in a staggered manner.

9. The zinc vapor condensation recovery system according to any one of claims 1 to 6, characterized in that: The system further comprises a high-pressure nitrogen pipe (13), wherein the high-pressure nitrogen pipe (13) is respectively connected to the zinc liquid conveying pipe (5) and each of the zinc liquid circulation branches (7).

10. The zinc vapor condensation recovery system according to any one of claims 1 to 6, characterized in that: The zinc liquid delivery pipe (5) is provided with a graphite pump (14).

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