A new environment-friendly galvanized steel pipe production process

Abstract

This invention discloses a novel environmentally friendly galvanized steel pipe production process, belonging to the field of metal corrosion protection technology. The technical solution adopted by this invention includes the following steps: S1: After uncoiling, welding the ends of the coil, and temporary storage, the surface of the steel strip is cleaned and then formed into pipes; S2: The pipes are fed into a zinc pot for online hot-dip galvanizing. After galvanizing, the pipes are cooled, sized, passivated, cut, chamfered, and packaged to obtain the finished product. In step S2, the high-temperature flue gas generated by the zinc pot combustion is led out through a flue and flows sequentially through a primary heat exchanger and a secondary heat exchanger. The 400-550℃ flue gas exchanges heat with the combustion air in the primary heat exchanger. Through the cascade utilization of waste heat from the flue gas and closed-loop temperature control, efficient heat recovery and precise stability of the zinc liquid temperature are achieved, resulting in significant advantages such as reduced energy consumption, reduced flue gas emissions, improved production stability, and improved product quality.

Description

Technical Field

[0001] This invention belongs to the field of metal corrosion protection technology, specifically relating to a novel environmentally friendly galvanized steel pipe production process. Background Technology

[0002] Hot-dip galvanizing, which involves immersing steel in molten zinc to form a zinc-iron alloy protective layer, is an economical and efficient method of metal corrosion protection. It is widely used in building structures, power transmission towers, highway guardrails, automobile manufacturing, and pipeline transportation, playing an irreplaceable role in reducing corrosion, extending the service life of steel materials, and conserving resources. However, with the deepening of global green manufacturing and sustainable development goals, the hot-dip galvanizing industry urgently needs to address its high energy consumption and high emission issues.

[0003] Currently, the steel pipe galvanizing industry generally adopts the "form first, then galvanize" model, which means that the steel pipes are manufactured first and then sent to the galvanizing plant for processing in batches. This process has multiple technical bottlenecks. The galvanizing heating furnace uses natural gas or coal gas as fuel to maintain the zinc liquid temperature at 440-470℃, but the waste heat utilization of the high-temperature flue gas generated by combustion is seriously insufficient. The exhaust gas temperature is often higher than 400℃, and a large amount of heat energy is directly lost to the environment. Existing waste heat recovery technologies are mostly limited to single-stage heat exchange structures, which cannot achieve tiered utilization of heat based on the flue gas temperature gradient, resulting in low thermal efficiency and insufficient exploitation of recovery potential.

[0004] Controlling the temperature stability of molten zinc faces severe challenges. When room temperature zinc ingots (approximately 25°C) are directly added to a high-temperature zinc pot, the sudden temperature drop causes a large amount of zinc dross to precipitate and deteriorates the wettability of the coating. Subsequently, the compensatory heating of the combustion system is prone to temperature overshoot, resulting in periodic fluctuations, leading to uneven coating thickness, surface runs, or increased brittleness. At the same time, temperature monitoring generally relies on a single measuring point, making it difficult to accurately capture the overall temperature distribution of the molten zinc. The physical separation of pipe manufacturing and galvanizing processes not only increases the logistics costs and carbon emissions in the steel pipe transportation process and extends the overall production cycle, but also forces the heating of the fluxing solution to rely on steam or electricity, consuming unnecessary energy.

[0005] Furthermore, the waste heat recovery system and the temperature control of the galvanizing process are disconnected. Changes in flue gas heat directly affect the thermal balance of the zinc pot, but there is a lack of an automated mechanism to coordinate waste heat utilization, zinc bath temperature regulation, and flux heating. This leads to the mutual transmission and amplification of temperature disturbances in each stage, further exacerbating production instability issues. These shortcomings collectively restrict the environmental performance and product quality of galvanized steel pipe production. Summary of the Invention

[0006] This invention provides a novel environmentally friendly galvanized steel pipe production process to solve at least one of the above-mentioned technical problems.

[0007] The technical solution adopted in this invention is as follows: A new environmentally friendly galvanized steel pipe production process includes the following steps: S1: After uncoiling, welding the ends of the coil, and temporarily storing the material, the surface of the steel strip is cleaned and then made into a pipe. S2: The pipe is sent into a zinc pot for online hot-dip galvanizing. After galvanizing, it is cooled, sized, passivated, cut, chamfered and packaged to obtain the finished product. In step S2, the high-temperature flue gas generated by the zinc pot combustion is led out through the flue and flows sequentially through the primary heat exchanger and the secondary heat exchanger. The flue gas at 400-550°C exchanges heat with the combustion air in the primary heat exchanger, preheating the combustion air to 180-250°C before sending it into the zinc pot burner. After heat exchange, the flue gas temperature drops to 250-300°C. The flue gas at 250-300°C exchanges heat with the flux in the secondary heat exchanger, heating the flux to 60-80°C. After heat exchange, the flue gas temperature drops to 120-150°C before being discharged. A pre-melting pot is located next to the zinc pot. Bypass flue gas is separated from the first-stage heat exchanger and introduced into the pre-melting pot to melt the zinc ingots into liquid zinc at 440-460℃ and then send it into the zinc pot. Temperature detection devices are installed at the zinc pot, the inlet and outlet of the primary heat exchanger, the inlet and outlet of the secondary heat exchanger, the pre-melting pot, and the flue gas outlet. Each device is electrically connected to the central controller. The central controller adjusts the opening of the flue gas damper, the opening of the bypass flue gas valve, and the feeding speed of the pre-melting pot according to the detection signals to ensure that the temperature fluctuation of the zinc liquid is ≤±3℃.

[0008] Furthermore, this application also proposes that, in step S1, the uncoiling is to unfold the steel coil into a continuous strip; the end welding of the coil is to weld the ends of the front and rear steel coils together to form a continuous strip; and the temporary storage is to store the strip through a looper storage device to ensure that the main production line is not interrupted when switching coils.

[0009] Furthermore, this application also proposes that, in step S1, the cleaning is a two-stage cleaning process: the first cleaning removes oxide scale and oil stains from the surface of the strip steel, and the second cleaning removes oxide scale and oil stains from the surface of the pipe before galvanizing.

[0010] Furthermore, this application also proposes that, in step S2, the primary heat exchanger is a shell-and-tube heat exchanger, with flue gas flowing through the shell side and combustion air flowing through the tube side, and the heat exchange tubes are made of high-temperature resistant stainless steel.

[0011] Furthermore, this application also proposes that, in step S2, the secondary heat exchanger adopts an immersion heat exchange tube arranged in the plating bath, and the material is perfluoroalkoxy resin.

[0012] Furthermore, this application also proposes that, in step S2, the bypass flue gas is introduced into the flue gas jacket or immersion flue gas pipe provided at the bottom of the pre-melting pot; the liquid zinc overflows into the zinc pot through the heat-insulating chute.

[0013] Furthermore, this application also proposes that, in step S2, the cooling is direct cooling with cooling water; the sizing is shaping by a sizing unit to calibrate the outer diameter of the steel pipe; the passivation is covering the galvanized layer with a transparent passivation film; the cutting is cutting at right angles to a specified length; the chamfering is chamfering and flattening the ends; and the packaging is bundling with steel straps.

[0014] Furthermore, this application also proposes that in step S2, the temperature detection device is a thermocouple or a resistance temperature detector, and the temperature detection device inside the zinc pot is 3 to 5 thermocouples distributed at different depths of the zinc pot.

[0015] Furthermore, this application also proposes that in step S2, the central controller is a PLC or an industrial computer with a built-in PID control algorithm or fuzzy control algorithm; the central controller adjusts the opening of the flue gas damper according to the outlet temperature signal of the first-stage heat exchanger to stabilize the outlet flue gas temperature of the first-stage heat exchanger at 250-300℃.

[0016] Furthermore, this application also proposes that, in step S2, the central controller adjusts the opening degree of the bypass flue gas valve and the feeding speed according to the pre-melting pot temperature signal, so that the zinc liquid temperature in the pre-melting pot is stabilized at 440-460℃; the zinc pot is a mobile main pot, and the pre-melting pot and the mobile main pot are connected by a heat-insulating chute.

[0017] Due to the adoption of the above technical solution, the beneficial effects achieved by this invention are as follows: 1. Flue gas is recycled and reused in stages through primary and secondary heat exchangers. High-temperature flue gas is used to preheat combustion air, improving combustion efficiency; medium-temperature flue gas is used to heat the plating flux, replacing traditional heating methods. Bypass flue gas is used for zinc melting in the pre-melting pot. This staged utilization significantly reduces exhaust gas temperature, decreasing fuel consumption and external energy input.

[0018] 2. Zinc ingots are pre-melted in a pre-melting pot and overflow into the main zinc pot through an insulated chute. With the help of multi-point thermocouple three-dimensional temperature measurement and central controller, the temperature fluctuation of the zinc liquid is controlled within a very small range, thereby improving the uniformity of the coating and the surface quality.

[0019] 3. The central controller receives temperature signals from multiple points and coordinates the adjustment of multiple actuators to ensure the stability of the flue gas temperature at the outlet of the first-stage heat exchanger and the temperature of the pre-melting pot, avoiding the coupling amplification of temperature fluctuations in each link and achieving global stability of the thermal state throughout the entire process.

[0020] 4. Uninterrupted steel strip supply is achieved through uncoiling, welding, and looper storage, integrating pipe making with online hot-dip galvanizing, eliminating intermediate transfer links. The mobile main boiler, combined with an insulated chute, allows for rapid switching between galvanizing types, reducing downtime and achieving continuous, efficient production.

[0021] 5. The secondary heat exchanger is made of corrosion-resistant material, which effectively resists the corrosion of the plating solution, avoids pollution and maintains heat exchange efficiency; the primary heat exchanger is made of high-temperature resistant material, which ensures long-term operation, extends the service life of core equipment and reduces maintenance costs. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the overall production process of a specific embodiment of the present invention. Figure 2 The flow chart of the flue gas cascade waste heat recovery and pre-melting system is shown in the specific embodiment of the present invention. Figure 3 This is a logic block diagram of the temperature control system according to a specific embodiment of the present invention.

[0023] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Detailed Implementation

[0024] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0026] In this invention, unless otherwise expressly specified and limited, the first feature "on" or "below" the second feature may be in direct contact with the first and second features, or indirect contact through an intermediate medium. In the description of this specification, references to terms such as "implementation," "example," "aspect," "specific example," or "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0027] Reference Figures 1 to 3This embodiment provides a novel environmentally friendly galvanized steel pipe production process, including uncoiling steel strips, welding the ends of the coils, temporarily storing the material, cleaning, and forming pipes. The pipes are then fed into a zinc pot for online hot-dip galvanizing. The high-temperature flue gas generated by the zinc pot combustion is recycled in stages: the flue gas flows sequentially through a primary heat exchanger and a secondary heat exchanger. The primary heat exchanger preheats the combustion air, and the secondary heat exchanger heats the fluxing solution. Simultaneously, a pre-melting pot is located beside the zinc pot, using bypass flue gas from before the primary heat exchanger to pre-melt zinc ingots into liquid zinc before feeding it into the zinc pot. Furthermore, this process incorporates temperature detection devices at the zinc pot, the inlet and outlet of the primary heat exchanger, the inlet and outlet of the secondary heat exchanger, the pre-melting pot, and the exhaust port. These devices are electrically connected to a central controller, which adjusts the opening of the flue gas damper, the opening of the bypass flue gas valve, and the feeding speed of the pre-melting pot based on the detection signals, thereby achieving precise control of the zinc liquid temperature, ensuring that the zinc liquid temperature fluctuation is ≤±3℃.

[0028] For ease of understanding, the following explains some key terms in this embodiment: Online hot-dip galvanizing refers to the continuous galvanizing process carried out directly on the steel pipe production line, rather than sending pre-formed steel pipes to the galvanizing plant in batches for processing, thereby integrating the pipe manufacturing and galvanizing processes.

[0029] A zinc pot is a container used to hold molten zinc, in which steel pipes are immersed to complete the galvanizing reaction. In this application, the preferred operating temperature of the zinc pot is 445–465°C.

[0030] The primary heat exchanger is a device used to recover the waste heat of high-temperature flue gas generated by the combustion of zinc pots. Its main function is to transfer the heat of the flue gas to the combustion air.

[0031] The secondary heat exchanger is a device used to further recover the waste heat of the flue gas after the primary heat exchanger has processed it. Its main function is to transfer the heat of the flue gas to the plating solution.

[0032] Combustion air refers to the air mixed with fuel to support combustion during the zinc pot combustion process. Preheating can improve combustion efficiency.

[0033] Fluxing solution is a solution used to clean or pretreat the surface of pipes before galvanizing, and its temperature affects the galvanizing effect.

[0034] A pre-melting pot is an auxiliary device located next to a zinc pot, used to pre-melt zinc ingots into liquid zinc before they are added to the zinc pot.

[0035] Bypass flue gas refers to the flue gas diverted from the main flue gas duct of the zinc pot combustion and used to heat the pre-melting pot.

[0036] Temperature detection devices are sensors used to monitor the temperature at key points in a process in real time, such as thermocouples or resistance temperature detectors (RTDs).

[0037] The central controller is an automated control unit that receives signals from temperature detection devices and adjusts process parameters according to preset logic or algorithms.

[0038] A flue gas damper is a mechanical device installed in a flue to regulate the flow of flue gas.

[0039] A bypass flue gas valve is a valve installed in the bypass flue gas passage to regulate the flow rate of bypass flue gas.

[0040] The feeding rate of the pre-melting pot refers to the rate at which zinc ingots are added to the pre-melting pot, and its adjustment affects the temperature and level of the zinc liquid in the pre-melting pot.

[0041] The process flow of this embodiment includes the following main steps: First, in step S1, the steel strip is fed into the production line for pretreatment. The steel strip is uncoiled by an uncoiler, unfolding it into a continuous strip; the ends of the coil are connected by welding to form a continuous strip; temporary storage is achieved through a looper storage device. Subsequently, the surface of the steel strip is cleaned, for example, using a two-stage cleaning process: the first cleaning removes oxide scale and oil from the strip surface, and the second cleaning removes oxide scale and oil from the pipe surface before galvanizing. After cleaning, the steel strip is fed into a forming unit, where it is rolled into pipes.

[0042] Secondly, in step S2, the manufactured pipes are fed into a zinc bath for online hot-dip galvanizing. Online hot-dip galvanizing uses a continuous immersion method to form a zinc layer on the pipe surface. After galvanizing, the pipes undergo a series of post-processing steps. Cooling is achieved through direct cooling with cooling water to solidify the zinc layer. Sizing is performed using a sizing unit to shape and calibrate the outer diameter of the steel pipe. Passivation involves covering the zinc layer with a transparent passivation film to form a protective film. Cutting is done by cutting the pipe at right angles to a specified length. Chamfering is performed by beveling and flattening the ends to remove sharp edges from the pipe ends. Finally, the finished pipes are packaged using steel strapping.

[0043] Further, in step S2, the high-temperature flue gas generated by the zinc pot combustion is drawn out through a flue and flows sequentially through a primary heat exchanger and a secondary heat exchanger to achieve cascaded waste heat recovery. The flue gas at 400–550°C exchanges heat with the combustion air in the primary heat exchanger, preheating the combustion air to 180–250°C before it is sent to the zinc pot burner, thereby improving combustion efficiency. The primary heat exchanger uses a shell-and-tube heat exchanger, with the flue gas flowing through the shell side and the combustion air flowing through the tube side, forming counter-current heat exchange and improving heat exchange efficiency. After heat exchange, the flue gas temperature drops to 250–300°C. Subsequently, the 250–300°C flue gas exchanges heat with the flux in the secondary heat exchanger, heating the flux to 60–80°C to meet the temperature requirements of the galvanizing process. The secondary heat exchanger uses immersion heat exchange tubes arranged in the flux tank, with the flux circulating within the tank and fully contacting the tube walls for heat exchange. After heat exchange, the flue gas temperature is further reduced to 120-150℃ before being discharged. Through the above-mentioned two-stage heat exchange, the high-grade heat of the high-temperature flue gas is used to preheat the combustion air, and the low-grade heat of the medium-temperature flue gas is used to heat the plating solution, realizing the graded extraction and step-by-step utilization of heat.

[0044] In addition, a pre-melting pot is located beside the main zinc pot for pre-melting zinc ingots. Bypass flue gas is diverted from the primary heat exchanger and introduced into a flue gas jacket or immersion flue gas pipe at the bottom of the pre-melting pot. The bypass flue gas heats the walls of the pre-melting pot through the flue gas jacket, or directly contacts the liquid zinc through the immersion flue gas pipe for heat exchange, melting the zinc ingots into liquid zinc at 440–460°C. The pre-melting pot separates the melting process of "solid zinc ingot → liquid zinc" from the main zinc pot, ensuring that the liquid zinc entering the main zinc pot is already at the correct temperature. The main zinc pot only needs to maintain a constant temperature, thus fundamentally eliminating the temperature shock caused by directly introducing cold ingots into the pot. The molten liquid zinc overflows into the main zinc pot through an insulated chute, ensuring minimal heat loss during transport.

[0045] Furthermore, to achieve precise control of the process, temperature detection devices are installed at the zinc pot, the inlet and outlet of the primary heat exchanger, the inlet and outlet of the secondary heat exchanger, the pre-melting pot, and the exhaust port. Each device is electrically connected to the central controller. The central controller adjusts the opening of the flue gas damper, the opening of the bypass flue gas valve, and the feeding speed of the pre-melting pot based on the detection signals to achieve stable control of the zinc liquid temperature. The central controller is a PLC or industrial computer with built-in PID control or fuzzy control algorithms. The central controller adjusts the opening of the flue gas damper based on the primary heat exchanger outlet temperature signal to stabilize the flue gas temperature at 250–300℃; and adjusts the opening of the bypass flue gas valve and the feeding speed based on the pre-melting pot temperature signal to stabilize the zinc liquid temperature in the pre-melting pot at 440–460℃. Through this coordinated control, the temperature fluctuation of the zinc liquid in the zinc pot is controlled within ±3℃.

[0046] This application achieves integrated continuous production of pipe making and galvanizing, effectively recovers waste heat from zinc pot combustion flue gas, and utilizes a stepped heat exchanger to preheat combustion air and heat the plating solution. Simultaneously, a pre-melting pot is set up to pre-melt zinc ingots using bypass flue gas. Combined with multi-point temperature detection and coordinated regulation by a central controller, this significantly reduces production energy consumption, stabilizes zinc liquid temperature, improves coating quality, simplifies the production process, and achieves global synergistic optimization of waste heat recovery and the galvanizing process. This effectively solves problems such as high energy consumption, unstable coating quality, low production efficiency, and lack of coordinated control in traditional processes.

[0047] Reference Figures 1 to 3 This application further proposes that in step S1, uncoiling is to unfold the steel coil into a continuous strip; end welding of the coil is to weld the ends of the front and rear steel coils together to form a continuous strip; and temporary storage is to store the strip through a looper storage device to ensure that the main production line is not interrupted when switching coils.

[0048] Specifically, the uncoiling operation aims to smoothly and continuously unfold the coiled steel into a strip, providing a stable starting material for subsequent processes. This process is achieved through an uncoiler, which precisely controls the rotational speed of the coil and the tension of the strip, ensuring that the strip does not deform or get damaged during unfolding. End welding of the coil involves precisely aligning and securely connecting the tail end of a coil with the head end of the next new coil when it is almost exhausted, thus seamlessly connecting multiple independent coils into a single, ultra-long continuous strip. This welding process uses automated welding equipment, such as flash butt welders or laser welders, to ensure the strength and surface smoothness of the weld, allowing it to pass smoothly through subsequent processing equipment. Temporary storage is achieved through a looper storage device, which forms a variable-length strip buffer area on the strip production line. When upstream uncoiling or welding operations are temporarily stopped or slowed down due to coil switching, the looper storage device releases its stored strip steel to maintain continuous supply to downstream main production line; conversely, when upstream operations resume or accelerate, the looper storage device re-accumulates strip steel to prepare for the next switchover.

[0049] The aforementioned technical solution uncoils the steel coil into continuous strip, providing a stable material input for the entire production line. The coil end welding technology ensures seamless connections between different coils, eliminating production gaps caused by coil changes. Crucially, the temporary material storage via the looper storage device ensures a continuous supply of strip steel to the main production stages such as galvanizing, cooling, and sizing during intermittent operations like coil switching and welding, effectively isolating upstream process fluctuations from downstream continuous production. This significantly improves the overall operating efficiency and automation level of the galvanized steel pipe production line, reduces downtime, lowers production costs, and ensures product quality uniformity and stability, avoiding coating defects or dimensional deviations that may occur due to production interruptions.

[0050] Reference Figures 1 to 3 This application further proposes that in the above step S1, the cleaning is a two-stage cleaning process. The first cleaning removes the oxide scale and oil stains from the surface of the strip steel, and the second cleaning removes the oxide scale and oil stains from the surface of the pipe before galvanizing.

[0051] Specifically, double cleaning refers to performing two independent cleaning operations on the surface of the steel strip or pipe during the steel pipe production process. This staged cleaning aims to improve the cleaning effect, ensure surface cleanliness, and provide an ideal base for the subsequent galvanizing process.

[0052] The initial cleaning is typically performed before the steel strip is formed into tubing. Its main purpose is to remove the oxide scale and attached oil that forms on the steel strip during rolling, storage, and transportation. Oxide scale is a layer of iron oxides formed on the steel surface by the reaction of oxygen, while oil may originate from lubricants or rust inhibitors. To effectively remove these contaminants, pickling (e.g., soaking or spraying with dilute hydrochloric acid or dilute sulfuric acid solutions) combined with mechanical brushing or high-pressure water rinsing is used. Pickling dissolves the oxide scale, while mechanical brushing and high-pressure water rinsing help remove loose oxides and most of the oil, providing a relatively clean surface for subsequent processing steps.

[0053] The second cleaning is performed after the pipe is formed but before it enters the galvanizing bath. Its main purpose is to further remove newly formed oxides, residual oil, and trace impurities that may have been generated during the pipe forming process, as well as those not completely removed in the first cleaning. This cleaning is crucial for ensuring a good bond between the galvanized layer and the steel substrate. Methods such as weak acid washing, electrolytic degreasing, or alkaline cleaning are used, supplemented by multi-stage rinsing with clean water, to ensure that the pipe surface reaches an optimal activation state—that is, a surface free of any contaminants and with a certain degree of roughness—thus providing a clean and easily wettable substrate for subsequent hot-dip galvanizing.

[0054] The above technical solution refines the cleaning process into two independent cleaning operations: the first cleaning removes oxide scale and oil stains from the steel strip surface, and the second cleaning removes oxide scale and oil stains from the pipe surface before galvanizing. This application can more thoroughly remove various contaminants from the steel strip and pipe surface. The first cleaning lays a good foundation for subsequent pipe forming and the second cleaning, effectively reducing the difficulty and workload of subsequent cleaning. The second cleaning ensures that the pipe surface is highly clean and activated before entering the zinc bath, avoiding quality problems such as poor adhesion of the galvanized layer, incomplete galvanizing, or uneven zinc layer caused by incomplete cleaning. This step-by-step, targeted cleaning strategy significantly improves the surface quality and corrosion resistance of galvanized steel pipes, extends the product's service life, and also helps reduce the scrap rate in the production process.

[0055] Reference Figures 1 to 3 This application further proposes that, in step S2, the primary heat exchanger is a shell-and-tube heat exchanger, with flue gas flowing through the shell side and combustion air flowing through the tube side, and the heat exchange tubes are made of high-temperature resistant stainless steel.

[0056] Specifically, the primary heat exchanger adopts a shell-and-tube structure, consisting of a shell, tube bundle, tube sheet, end caps, and baffles. This structure offers advantages such as large heat transfer area, compact design, high operational flexibility, and strong adaptability, making it particularly suitable for high-temperature and high-pressure conditions. Shell-and-tube heat exchangers can be designed as single-pass or multi-pass systems to optimize fluid flow paths in the tube and shell sides, thereby improving heat exchange efficiency.

[0057] Meanwhile, the fluid arrangement, with flue gas flowing through the shell side and combustion air flowing through the tube side, allows the high-temperature zinc pot flue gas to flow within the shell side and exchange heat with the combustion air in the tube side. This arrangement is advantageous for treating flue gas containing small amounts of particulate matter or possessing a certain degree of corrosiveness, as the shell side is relatively easy to clean and maintain. Furthermore, placing the relatively cooler and cleaner combustion air in the tube side effectively protects the heat exchange tubes and extends their service life.

[0058] To ensure the long-term stable operation of the primary heat exchanger in a high-temperature flue gas environment, the heat exchange tubes are made of high-temperature resistant stainless steel. High-temperature resistant stainless steel has excellent oxidation resistance, high-temperature strength, and corrosion resistance. It can maintain good mechanical properties and chemical stability in a high-temperature flue gas environment of 400-550℃, effectively resisting the erosion of corrosive substances that may be present in the flue gas, thereby avoiding heat exchanger damage or efficiency reduction due to material failure.

[0059] By employing a shell-and-tube heat exchanger and optimizing fluid flow, combined with high-temperature resistant stainless steel heat exchange tubes, the above technical solutions effectively address the issues of heat exchange efficiency and equipment reliability in high-temperature flue gas waste heat recovery. This design ensures that the primary heat exchanger can operate stably and efficiently in high-temperature flue gas environments containing potentially corrosive substances, stably preheating the combustion air to 180–250°C, thereby significantly improving the combustion efficiency of the zinc pot and reducing fuel consumption. Simultaneously, the use of high-temperature resistant stainless steel greatly extends the service life of the heat exchanger, reduces maintenance frequency and costs, and enhances the economic and environmental benefits of the entire galvanized steel pipe production process.

[0060] This application further proposes that, in step S2, the secondary heat exchanger adopts an immersion heat exchange tube arranged in the plating bath, and its material is perfluoroalkoxy resin.

[0061] Specifically, in the secondary heat exchanger, the immersed heat exchange tubes are placed directly inside the fluxing bath, directly contacting the fluxing solution for heat exchange. This arrangement maximizes the heat exchange area, reduces heat loss, and thus significantly improves heat exchange efficiency. The immersed heat exchange tubes can be designed in various forms, such as coils, serpentine tubes, or U-shaped tubes, depending on the shape of the fluxing bath and available space, to ensure that the fluxing solution circulates fully outside the tubes while the flue gas flows inside, avoiding localized overheating or uneven heat exchange. Simultaneously, the fixing method of the heat exchange tubes must be carefully designed to prevent displacement or damage within the fluxing solution. The immersed heat exchange tubes are made of perfluoroalkoxy resin. Perfluoroalkoxy resin (PFA) is a high-performance fluoroplastic, characterized by excellent corrosion resistance, high-temperature resistance, and non-stick properties. Using PFA as the material for the heat exchange tubes is primarily to effectively resist the strong corrosiveness of the fluxing solution, thereby significantly extending the service life of the heat exchange tubes and preventing fluxing solution contamination due to corrosion, ensuring the quality of zinc plating. Furthermore, the non-stick properties of PFA material help reduce the adhesion of dirt to the surface of the heat exchange tubes, thus maintaining high heat exchange performance over a long period. Since the PFA heat exchange tubes are immersed in a fluxing solution at 60–80°C, the tube wall temperature is mainly determined by the fluxing solution temperature, which is far below the upper limit of the long-term operating temperature of PFA material. Therefore, the service life of the PFA heat exchange tubes will not be affected by high flue gas temperatures. PFA material is manufactured into the required tubes through processes such as extrusion molding or injection molding.

[0062] Through the above technical solution, this application effectively solves the problems of corrosion, efficiency, and space utilization encountered in the heating process of fluxing solution. The immersion heat exchange tubes are in direct contact with the fluxing solution, significantly improving heat exchange efficiency and allowing the waste heat from the zinc pot flue gas to be more fully absorbed by the fluxing solution, thereby reducing energy consumption. Simultaneously, the excellent corrosion resistance of the perfluoroalkoxy resin ensures the long-term stable operation of the heat exchange tubes in a highly corrosive fluxing solution environment, avoiding the problems of corrosion and fluxing solution contamination found in traditional metal heat exchangers, extending equipment lifespan, and reducing maintenance costs. This design also makes the heat exchanger structure compact, fully utilizing the internal space of the fluxing tank, avoiding additional floor space, achieving stable and efficient heating of the fluxing solution, and ensuring the continuity of the zinc plating process and product quality.

[0063] Furthermore, the bypass flue gas is introduced into the flue gas jacket or immersion flue gas pipe set at the bottom of the pre-melting pot; liquid zinc overflows into the zinc pot through the insulated chute.

[0064] Specifically, bypass flue gas is introduced into a flue gas jacket or an immersed flue gas pipe located at the bottom of the premelting pot. The flue gas jacket is a closed channel structure forming around the outer wall or bottom of the premelting pot. The bypass flue gas flows within it, transferring its heat to the pot wall through convection and radiation, thereby heating the zinc ingots and liquid zinc inside the pot. This structure provides a large heat exchange area and ensures uniform heat transfer to the bottom of the premelting pot, helping to improve the melting efficiency of the zinc ingots and the uniformity of the zinc liquid temperature. The flue gas jacket is made of high-temperature resistant and corrosion-resistant alloy steel to ensure long-term stable operation in high-temperature flue gas environments. Alternatively, bypass flue gas is introduced into an immersed flue gas pipe located at the bottom of the premelting pot. An immersed flue gas pipe is a tubular heat exchange element that extends directly into the liquid zinc inside the premelting pot. The bypass flue gas flows through the interior of these immersed flue gas pipes, achieving efficient convective heat transfer through direct contact with the liquid zinc via the pipe wall. This direct immersion heat exchange method significantly improves heat transfer efficiency, allowing heat to act more quickly and directly on the molten zinc, accelerating the melting process of the zinc ingots. The material of the immersion flue gas pipe must possess excellent high-temperature resistance and corrosion resistance to molten zinc, such as using special ceramics or corrosion-resistant alloys. Whether it's a flue gas jacket or an immersion flue gas pipe, placing it at the bottom of the pre-melting pot maximizes the use of the buoyancy effect of the hot flue gas and the principle of upward heat convection, ensuring that heat first acts on the newly added solid zinc ingots, accelerating their melting and maintaining the temperature of the liquid zinc at the bottom, thereby improving overall melting efficiency and temperature uniformity.

[0065] In addition, liquid zinc overflows into the zinc pot through an insulated chute. The insulated chute is a channel with excellent thermal insulation properties, used to connect the pre-melting pot and the main zinc pot. Its interior is lined with refractory insulation material, and its exterior is wrapped with an insulation layer to minimize heat loss of liquid zinc during transport. The insulated chute ensures that the liquid zinc transported from the pre-melting pot to the main zinc pot remains within a set temperature range, preventing temperature drops from affecting the temperature stability of the zinc liquid in the main zinc pot. Overflow is a simple and reliable method for level control and transport. When the liquid zinc in the pre-melting pot reaches a certain level, it automatically flows into the main zinc pot under gravity through the overflow port of the insulated chute. This method enables continuous and stable replenishment of liquid zinc, avoiding complex pump or valve control systems, simplifying operation, and helping to maintain a constant zinc liquid level in the main zinc pot, thereby ensuring the continuity and stability of the galvanizing process. By placing the pre-melting pot in the waste heat recovery chain, the combustion efficiency improved by the preheating of the combustion air and the heat load stability achieved by the pre-melting pot in eliminating the impact of cold ingots form a synergistic effect, which together contributes to the precise control of the zinc liquid temperature.

[0066] Through the above technical solutions, a flue gas jacket or an immersed flue gas pipe is installed at the bottom of the pre-melting pot. The bypass flue gas can transfer heat to the zinc ingots and liquid zinc inside the pre-melting pot more efficiently. The flue gas jacket increases the heat exchange area and ensures uniform heat transfer, while the immersed flue gas pipe significantly improves the melting rate of the zinc ingots and the heat utilization efficiency through direct contact heat exchange, ensuring that the molten zinc in the pre-melting pot can quickly reach and be stably maintained at the set temperature of 440–460°C. Simultaneously, the liquid zinc overflows into the main zinc pot through an insulated chute. The insulated chute effectively reduces heat loss during the transport of liquid zinc, ensuring a stable temperature of the molten zinc entering the main zinc pot. The overflow method enables continuous and automatic replenishment of liquid zinc, avoiding drastic fluctuations in the liquid zinc level and temperature in the main zinc pot. These measures work together to not only improve the melting efficiency of zinc ingots and the temperature control accuracy of the pre-melting pot, but also ensure the long-term stability of the zinc liquid temperature in the main zinc pot, thus providing a solid guarantee for the production of high-quality galvanized steel pipes and further improving the energy utilization efficiency and automation level of the entire production process.

[0067] Reference Figures 1 to 3 This application further proposes that in step S2, cooling is direct cooling with cooling water; sizing is shaping by a sizing unit to calibrate the outer diameter of the steel pipe; passivation is covering the galvanized layer with a transparent passivation film; cutting is cutting at right angles to a specified length; chamfering is chamfering and flattening the ends; and packaging is bundling with steel straps.

[0068] Specifically, direct cooling with cooling water involves immersing the galvanized pipe directly into a cooling water tank or spraying it with cooling water. Utilizing water's high specific heat capacity and good thermal conductivity, the heat from the pipe surface is quickly removed. This cooling method achieves rapid and uniform cooling, effectively avoiding problems such as coarse coating grains and surface defects caused by uneven cooling rates, ensuring a good bond between the galvanized layer and the substrate. Sizing refers to the mechanical shaping of the cooled pipe using a specialized sizing unit. The sizing unit consists of multiple sets of rollers. By precisely controlling the gap and shape of the rollers, the pipe is extruded and corrected, thereby calibrating the outer diameter of the steel pipe to a preset tolerance range. This aims to eliminate dimensional deviations and ovality that may occur during the forming and galvanizing processes, ensuring the accuracy and consistency of product dimensions. Passivation treatment forms a dense, corrosion-resistant protective film on the surface of the galvanized layer. A transparent passivation film is applied by immersion or spraying a solution containing a passivating agent, causing a chemical reaction on the surface of the galvanized layer to form a colorless or slightly colored transparent conversion film. This transparent passivation film not only effectively prevents the zinc layer from direct contact with the external environment, improving the corrosion resistance of the galvanized steel pipe, but also maintains the original metallic luster and aesthetics of the galvanized layer, without affecting subsequent painting or welding. Cutting involves precisely segmenting the continuous pipe that has undergone sizing and passivation treatment according to a preset finished length. Right-angle cutting means that the cutting surface is perpendicular to the pipe axis, ensuring a smooth, burr-free cut and that the length meets standard requirements. This is achieved using high-speed flying saws or plasma cutting equipment to ensure cutting efficiency and precision, reducing the need for subsequent processing. Chamfering involves trimming the edges of both ends of the cut pipe, removing sharp corners to form a smooth bevel or arc. End beveling refers to beveling the edge of the pipe end into a gentle slope, making it less sharp, thereby improving safety during handling and installation, facilitating subsequent connections or welding, and improving the product's appearance. Packaging involves neatly bundling finished steel pipes after all processing steps for easy storage, transportation, and delivery. Steel strapping is used, employing high-strength steel straps to tightly bind multiple steel pipes together, forming a stable bundle. Steel strapping is characterized by high strength and reliability, effectively preventing the steel pipes from scattering or colliding during transportation, ensuring the product arrives at the customer intact.

[0069] The above technical solutions refine and standardize the post-processing of galvanized steel pipes. Specifically, direct cooling with cooling water enables rapid and uniform cooling of the galvanized pipe, effectively inhibiting coating grain growth, reducing surface defects, and thus ensuring coating quality and adhesion. Sizing by a sizing unit precisely calibrates the outer diameter of the steel pipe, eliminating dimensional deviations during production, ensuring the product meets strict dimensional standards, and improving product consistency and interchangeability. Covering the galvanized layer with a transparent passivation film significantly enhances the corrosion resistance of the galvanized steel pipe, extends its service life, maintains its aesthetic appeal, and broadens its application range. Right-angle cutting to specified lengths and chamfering / flattening the ends ensure dimensional accuracy and the safety and aesthetics of the ends, reducing subsequent processing costs. Finally, packaging with steel strapping ensures the integrity and safety of the product during storage and transportation. Overall, these specific post-processing measures work synergistically to significantly improve the overall quality, production efficiency, and market competitiveness of galvanized steel pipes, effectively solving problems such as unstable quality and low efficiency that may exist in the post-processing stage of traditional processes.

[0070] Reference Figures 1 to 3 This application further proposes specific optimizations to the temperature detection device. Specifically, the temperature detection device can be a thermocouple or a resistance temperature detector (RTD). A thermocouple is a commonly used temperature sensor. Its working principle is based on the Seebeck effect, which states that when two different conductors or semiconductors form a closed circuit, an electromotive force will be generated in the circuit when the temperatures of the two junctions are different. Thermocouples have advantages such as a wide measurement range, fast response speed, simple structure, and robustness, making them suitable for temperature measurement in high-temperature environments. An RTD is another commonly used temperature sensor. Its working principle utilizes the characteristic that the resistance of a conductor or semiconductor changes with temperature to measure temperature. RTDs typically have high measurement accuracy and stability, especially performing excellently in the lower temperature range.

[0071] Furthermore, the temperature detection device inside the zinc pot consists of 3 to 5 thermocouples distributed at different depths within the pot. Distributing multiple thermocouples at different depths aims to obtain information about the temperature gradient of the molten zinc in the vertical direction. Because the temperature of the molten zinc may differ at different depths due to factors such as convection, radiation, and conduction during heating, melting, and contact with the steel pipe, placing thermocouples at 3 to 5 different depths allows for more comprehensive and accurate monitoring of the temperature distribution of the molten zinc within the pot. This avoids localized errors caused by single measuring points, thus providing the central controller with more representative molten zinc temperature data.

[0072] By employing thermocouples or resistance temperature detectors (RTDs) as temperature sensing devices, stable and reliable temperature measurement signals can be provided. Furthermore, by distributing 3-5 thermocouples at different depths within the zinc pot, potential temperature stratification or localized unevenness in the molten zinc can be effectively overcome, allowing for accurate acquisition of the true temperature distribution of the molten zinc in the vertical direction. The central controller can then perform comprehensive analysis and judgment based on this multi-point, multi-depth temperature data, thereby more accurately grasping the overall thermal state of the molten zinc and achieving refined control of the zinc pot heating system. This enables the central controller to more precisely adjust the opening of the flue gas damper, the opening of the bypass flue gas valve, and the feeding speed of the pre-melting pot, ensuring that the temperature fluctuations of the molten zinc are stably controlled within a strict range of ≤±3℃, significantly improving the stability of the galvanizing process and the consistency of product quality.

[0073] Reference Figures 1 to 3 This application further proposes that the central controller is a PLC or an industrial computer with a built-in PID control algorithm or fuzzy control algorithm; the central controller adjusts the opening of the flue gas damper according to the outlet temperature signal of the first-stage heat exchanger to stabilize the outlet flue gas temperature of the first-stage heat exchanger at 250-300℃.

[0074] Specifically, the central controller is the intelligent control core of the entire production process. It is responsible for receiving signals from various temperature detection devices and outputting corresponding control commands according to the preset control strategy. Specifically, it is defined as a PLC (Programmable Logic Controller) or an industrial computer, aiming to provide a stable, reliable, and powerful control platform. A PLC is a digital electronic system designed specifically for industrial environments, possessing advantages such as high reliability, strong anti-interference capabilities, simple programming, and ease of maintenance. It is suitable for process control with high real-time requirements. An industrial computer, on the other hand, has stronger computing and data processing capabilities, capable of handling more complex control algorithms and data analysis tasks, providing the system with more flexible control strategies.

[0075] The PID control algorithm or fuzzy control algorithm built into the central controller is key to achieving precise temperature control. The PID control algorithm is a classic closed-loop control algorithm that, through a combination of proportional (P), integral (I), and derivative (D) parameters, adjusts the control output based on the current error, accumulated error, and rate of change of error, thereby enabling the controlled variable (such as temperature) to quickly and accurately reach and stabilize at the setpoint. The fuzzy control algorithm, on the other hand, is an intelligent control method based on fuzzy logic, suitable for complex systems where it is difficult to establish precise mathematical models. It achieves intelligent control of the system by transforming human experience and knowledge into fuzzy rules for reasoning. Both algorithms can perform fine-tuning of the controlled object according to actual operating conditions.

[0076] The central controller adjusts the opening of the flue gas damper based on the outlet temperature signal of the first-stage heat exchanger, which is the specific control method to stabilize the outlet flue gas temperature of the first-stage heat exchanger. The outlet temperature signal of the first-stage heat exchanger is collected in real time by a temperature detection device (such as a thermocouple or resistance temperature detector) located at that location and transmitted to the central controller. Upon receiving the temperature signal, the central controller compares it with a preset target range of 250–300°C. If the detected temperature deviates from the target range, the central controller calculates the required adjustment amount of the flue gas damper opening based on a built-in PID or fuzzy control algorithm and sends a command to the damper's actuator. The flue gas damper is installed in the flue duct; by changing its opening, the flow rate of the flue gas passing through the first-stage heat exchanger can be precisely controlled, thereby adjusting the heat exchange and ultimately stabilizing the outlet flue gas temperature of the first-stage heat exchanger within the set range of 250–300°C.

[0077] By employing the aforementioned technical solution, specifically limiting the central controller to a PLC or industrial computer and incorporating a built-in PID control algorithm or fuzzy control algorithm, this application enables more precise and intelligent control of the heat recovery system. Specifically, the central controller can adjust the flue gas damper opening in real-time and accurately based on the outlet temperature signal of the primary heat exchanger. For example, when the flue gas temperature at the primary heat exchanger outlet deviates from the set range of 250–300°C, the PID or fuzzy control algorithm can quickly calculate the required damper opening adjustment and instruct the actuator to make precise adjustments. This refined control ensures the stability of the flue gas temperature at the primary heat exchanger outlet, thereby providing a stable heat source for the secondary heat exchanger and ensuring that the fluxing solution can be continuously and stably heated to 60–80°C. This avoids instability in the fluxing solution temperature caused by flue gas temperature fluctuations, thus improving the efficiency of the entire heat recovery system and the stability of the galvanizing production line. Simultaneously, a stable flue gas temperature also helps protect downstream equipment and extend its service life.

[0078] Reference Figures 1 to 3 This application further proposes that the central controller adjusts the opening of the bypass flue gas valve and the feeding speed according to the pre-melting pot temperature signal, so that the temperature of the zinc liquid in the pre-melting pot is stabilized at 440-460℃; the zinc pot is a mobile main pot, and the pre-melting pot and the mobile main pot are connected by an insulated chute.

[0079] Specifically, the central controller (e.g., a PLC or industrial computer with built-in PID or fuzzy control algorithms) receives real-time temperature signals from temperature detection devices (e.g., thermocouples or resistance temperature detectors) in the pre-melting pot. Based on these signals, the central controller can precisely adjust the opening of the bypass flue gas valve, thereby controlling the amount of flue gas entering the pre-melting pot to adjust the heating power for the zinc ingots. Simultaneously, the central controller can intelligently adjust the feeding rate of the zinc ingots based on the deviation between the set and actual values ​​of the zinc liquid temperature in the pre-melting pot. For example, when the pre-melting pot temperature is too low, the feeding rate of the zinc ingots can be reduced or the opening of the bypass flue gas valve can be increased to introduce more heat; when the temperature is too high, the feeding rate can be increased or the opening of the bypass flue gas valve can be decreased to reduce the heating power. Through this dual coordinated adjustment of the bypass flue gas valve opening and the feeding rate, the temperature of the zinc liquid in the pre-melting pot is ensured to be accurately and stably maintained within the ideal range of 440–460°C, providing a stable heat source and quality assurance for the liquid zinc subsequently fed into the main zinc pot. The above-mentioned control and the first-stage heat exchanger outlet temperature control of Quan Jiu are carried out simultaneously. The two share the same central controller and achieve global temperature stability throughout the entire process through multi-variable collaborative optimization.

[0080] Furthermore, in this application, the zinc pot is designed as a mobile main pot. A mobile main pot refers to a structure in which the main zinc pot body can be moved or replaced along a preset track. When it is necessary to switch the production of different coating products (such as pure zinc coating and zinc-aluminum coating), the main pot can be moved out along the track, and another main pot can be moved into the workstation, realizing flexible switching between different coating types, while significantly shortening downtime and ensuring production continuity. The pre-melting pot and the mobile main pot are connected by an insulated chute. The insulated chute is a channel with excellent heat insulation performance, which integrates an electric heating device or uses multi-layer heat insulation materials to minimize heat loss of liquid zinc during the process of transporting liquid zinc from the pre-melting pot to the main zinc pot, effectively preventing the zinc liquid from solidifying or the temperature from dropping sharply. The insulated chute has a certain degree of flexibility and adjustable length to adapt to changes in position after the main pot is moved. Through the connection of the insulated chute, continuous, stable and efficient transportation of liquid zinc can be achieved, ensuring sufficient zinc liquid supply and small temperature fluctuations in the main zinc pot, further ensuring the stability of the galvanizing process.

[0081] Through the above technical solution, the central controller can precisely adjust the opening of the bypass flue gas valve and the feeding speed of zinc ingots based on the real-time temperature signal of the pre-melting pot, thereby stabilizing the temperature of the zinc liquid in the pre-melting pot within the ideal range of 440-460℃. This ensures that the liquid zinc entering the main zinc pot has a stable temperature and quality, avoiding thermal shock or temperature instability in the main zinc pot caused by temperature fluctuations in the pre-melting pot. Simultaneously, the adoption of a mobile main pot design, combined with the connection between the pre-melting pot and the main pot via an insulated chute, not only improves the flexibility and maintenance convenience of the production line, but more importantly, the insulated chute effectively reduces heat loss of liquid zinc during transportation, ensuring a continuous supply of zinc liquid to the main zinc pot at a stable temperature and flow rate. This collaborative control and efficient transportation mechanism significantly improves the temperature stability of the entire galvanizing process, reduces energy consumption, and ultimately guarantees the product quality and production efficiency of galvanized steel pipes.

[0082] The following example will provide a more detailed explanation of the above technical solution: In a new environmentally friendly galvanized steel pipe production base, the production line adopts an integrated continuous production process. This process first processes the steel strip, then performs online hot-dip galvanizing, supplemented by efficient waste heat recovery and a precise temperature control system.

[0083] At the start of production, step S1 is initiated. First, a steel coil is uncoiled into a continuous strip using an uncoiler. When a coil is nearly used up, its tail is welded to the head of the next coil using a coil end welding device, ensuring the continuity of the production line and preventing interruptions to main line production due to coil switching. After welding, the strip enters a looper storage device for temporary storage. This device can store a certain length of strip, further ensuring the smooth operation of the main line. Subsequently, the strip surface undergoes two cleanings. The first cleaning aims to remove oxide scale and oil stains from the strip surface. After being formed into pipes, a second cleaning is performed to ensure that the pipe surface is free of oxide scale and oil stains before galvanizing, providing a clean substrate for subsequent galvanizing. The cleaned strip is then formed into pipes by a forming unit.

[0084] Next, in step S2, the pipes are continuously fed into a zinc pot for online hot-dip galvanizing. The temperature of the molten zinc in the pot is maintained at 445–465°C. After galvanizing, the pipes undergo a series of processes including cooling, sizing, passivation, cutting, chamfering, and packaging to obtain the final product. Cooling is achieved using direct water cooling; sizing is performed by calibrating the outer diameter of the steel pipe using a sizing unit; passivation involves covering the galvanized layer with a transparent passivation film; cutting is done at right angles to a specified length; chamfering is performed to flatten the pipe ends; and finally, the pipes are bundled with steel straps for packaging.

[0085] One of the core innovations of this process lies in its highly efficient flue gas waste heat recovery system and zinc liquid pre-melting device. The high-temperature flue gas generated by the zinc pot combustion, typically ranging from 400 to 550°C, is drawn out through a flue. This flue gas first flows through a primary heat exchanger. This primary heat exchanger is a shell-and-tube type, with the flue gas flowing through the shell side and the combustion air flowing through the tube side; the heat exchange tubes are made of high-temperature resistant stainless steel. In this process, the high-temperature flue gas exchanges heat with the combustion air, preheating the combustion air to 180–250°C before it is sent to the zinc pot burner, significantly reducing fuel consumption. Compared to the traditional process where combustion air is directly fed into the burner, this effectively recovers the heat from the flue gas, solving the problem of severe waste heat from the flue gas. After passing through the primary heat exchanger, the flue gas temperature drops to 250–300°C.

[0086] Subsequently, the cooled flue gas continues to flow through a secondary heat exchanger. This secondary heat exchanger uses immersion heat exchange tubes arranged within the fluxing bath, made of perfluoroalkoxy resin. In the secondary heat exchanger, the flue gas exchanges heat with the fluxing solution, heating the solution to 60–80°C. This replaces the traditional method of relying on steam or electric heating for the fluxing solution, further reducing energy consumption and production costs. After passing through the secondary heat exchanger, the flue gas temperature drops to 120–150°C, and then it is discharged through the exhaust port, achieving cascade utilization of flue gas heat and significantly improving waste heat recovery efficiency.

[0087] To address the issue of large temperature fluctuations in the molten zinc caused by directly adding room-temperature zinc ingots to the zinc pot in traditional processes, this production line incorporates a pre-melting pot alongside the zinc pot. Bypass flue gas is diverted from the primary heat exchanger and introduced into a flue gas jacket at the bottom of the pre-melting pot via a bypass flue gas valve. This bypass flue gas melts the zinc ingots into liquid zinc at 440–460°C. The liquid zinc in the pre-melting pot overflows into the zinc pot through an insulated chute, ensuring that the molten zinc entering the zinc pot remains close to the operating temperature of the zinc pot, preventing a sharp drop in temperature and thus stabilizing the zinc liquid temperature and improving coating quality. By placing the pre-melting pot within the waste heat recovery chain, the increased combustion efficiency from preheating the combustion air and the heat load stability achieved by the pre-melting pot in eliminating the impact of cold ingots create a synergistic effect, jointly contributing to precise temperature control of the molten zinc. The zinc pot is a mobile main pot, and the pre-melting pot is connected to the mobile main pot via an insulated chute.

[0088] Temperature control throughout the entire production process is managed by a central controller. Temperature detection devices are installed at the zinc pot, the inlet and outlet of the primary heat exchanger, the inlet and outlet of the secondary heat exchanger, the pre-melting pot, and the flue gas outlet. These devices use thermocouples or resistance temperature detectors (RTDs). The temperature detection devices inside the zinc pot consist of 3-5 thermocouples distributed at different depths, providing a more accurate reflection of the overall temperature distribution of the molten zinc. All temperature detection devices are electrically connected to the central controller. The central controller uses a PLC or industrial computer with built-in PID control or fuzzy control algorithms.

[0089] The central controller makes precise adjustments based on various detection signals. For example, based on the outlet temperature signal of the first-stage heat exchanger, the central controller adjusts the opening of the flue gas damper to stabilize the outlet flue gas temperature at 250–300℃. Simultaneously, based on the pre-melting pot temperature signal, the central controller adjusts the opening of the bypass flue gas valve and the feeding speed of the pre-melting pot to stabilize the zinc liquid temperature in the pre-melting pot at 440–460℃. These two controls operate simultaneously, sharing the same central controller, achieving global temperature stability throughout the entire process through multi-variable collaborative optimization. Through this collaborative control, the temperature fluctuation of the zinc liquid in the zinc pot is precisely controlled within ≤±3℃, significantly better than the temperature control accuracy of traditional processes. This ensures the uniformity of the coating thickness and surface quality, solving the problem of large zinc liquid temperature fluctuations and difficulty in guaranteeing coating quality. This automated method, which unifies and collaboratively controls waste heat recovery, zinc liquid temperature control, and flux heating, solves the problem of lack of collaborative control between waste heat recovery and galvanizing processes in existing technologies, avoiding the mutual transmission and coupling amplification of temperature fluctuations in each stage.

[0090] Through the aforementioned integrated and continuous production process, the production base has achieved seamless integration of pipe manufacturing and galvanizing, eliminating the problems of fragmented production processes, low efficiency, and high costs in the traditional "forming first and then galvanizing" model. This reduces logistics costs and transportation carbon emissions, and shortens the production cycle.

[0091] For any parts not mentioned in this invention, existing technologies can be used or referenced.

[0092] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0093] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A novel environmentally friendly galvanized steel pipe production process, characterized in that, Includes the following steps: S1: After uncoiling, welding the ends of the coil, and temporarily storing the material, the surface of the steel strip is cleaned and then made into a pipe. S2: The pipe is sent into a zinc pot for online hot-dip galvanizing. After galvanizing, it is cooled, sized, passivated, cut, chamfered and packaged to obtain the finished product. In step S2, the high-temperature flue gas generated by the zinc pot combustion is led out through the flue and flows sequentially through the primary heat exchanger and the secondary heat exchanger. The flue gas at 400-550°C exchanges heat with the combustion air in the primary heat exchanger, preheating the combustion air to 180-250°C before sending it into the zinc pot burner. After heat exchange, the flue gas temperature drops to 250-300°C. The flue gas at 250-300°C exchanges heat with the flux in the secondary heat exchanger, heating the flux to 60-80°C. After heat exchange, the flue gas temperature drops to 120-150°C before being discharged. A pre-melting pot is located next to the zinc pot. Bypass flue gas is separated from the first-stage heat exchanger and introduced into the pre-melting pot to melt the zinc ingots into liquid zinc at 440-460℃ and then send it into the zinc pot. Temperature detection devices are installed at the zinc pot, the inlet and outlet of the primary heat exchanger, the inlet and outlet of the secondary heat exchanger, the pre-melting pot, and the flue gas outlet. Each device is electrically connected to the central controller. The central controller adjusts the opening of the flue gas damper, the opening of the bypass flue gas valve, and the feeding speed of the pre-melting pot according to the detection signals to ensure that the temperature fluctuation of the zinc liquid is ≤±3℃.

2. The novel environmentally friendly galvanized steel pipe production process according to claim 1, characterized in that, In step S1, uncoiling means unfolding the steel coil into a continuous strip; the end welding of the coil means welding the ends of the front and rear steel coils together to form a continuous strip; and the temporary storage means storing the strip through a looper storage device to ensure that the main production line is not interrupted when switching coils.

3. The novel environmentally friendly galvanized steel pipe production process according to claim 1, characterized in that, In step S1, the cleaning is performed in two stages. The first cleaning removes oxide scale and oil stains from the surface of the strip steel, and the second cleaning removes oxide scale and oil stains from the surface of the pipe before galvanizing.

4. The novel environmentally friendly galvanized steel pipe production process according to claim 1, characterized in that, In step S2, the primary heat exchanger is a shell-and-tube heat exchanger, with flue gas flowing through the shell side and combustion air flowing through the tube side, and the heat exchange tubes are made of high-temperature resistant stainless steel.

5. The novel environmentally friendly galvanized steel pipe production process according to claim 3, characterized in that, In step S2, the secondary heat exchanger uses an immersion heat exchange tube arranged in the plating bath, and the material is perfluoroalkoxy resin.

6. The novel environmentally friendly galvanized steel pipe production process according to claim 1, characterized in that, In step S2, the bypass flue gas is introduced into the flue gas jacket or immersion flue gas pipe provided at the bottom of the pre-melting pot; the liquid zinc overflows into the zinc pot through the heat-insulating chute.

7. The novel environmentally friendly galvanized steel pipe production process according to claim 2, characterized in that, In step S2, the cooling is direct cooling with cooling water; the sizing is shaping by a sizing unit to calibrate the outer diameter of the steel pipe; the passivation is covering the galvanized layer with a transparent passivation film; the cutting is cutting at right angles to a specified length; the chamfering is chamfering and flattening the ends; and the packaging is bundling with steel straps.

8. The novel environmentally friendly galvanized steel pipe production process according to claim 1, characterized in that, In step S2, the temperature detection device is a thermocouple or a resistance temperature detector (RTD), and the temperature detection device inside the zinc pot consists of 3 to 5 thermocouples distributed at different depths within the zinc pot.

9. The novel environmentally friendly galvanized steel pipe production process according to claim 1, characterized in that, In step S2, the central controller is a PLC or an industrial computer with a built-in PID control algorithm or fuzzy control algorithm; the central controller adjusts the opening of the flue gas damper according to the outlet temperature signal of the first-stage heat exchanger to stabilize the outlet flue gas temperature of the first-stage heat exchanger at 250-300℃.

10. The novel environmentally friendly galvanized steel pipe production process according to claim 1, characterized in that, In step S2, the central controller adjusts the opening of the bypass flue gas valve and the feeding speed according to the pre-melting pot temperature signal to stabilize the zinc liquid temperature in the pre-melting pot at 440-460℃; the zinc pot is a mobile main pot, and the pre-melting pot and the mobile main pot are connected by an insulated chute.

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