Method for manufacturing efficient plate-type heat transfer element by hydroforming sheet metal

Abstract

The invention discloses a method for manufacturing an efficient plate type heat transfer element by hydroforming a metal sheet. The method comprises the following steps: preparing a flat plate raw material; a laser stitch welding step; a hydraulic step-by-step swelling forming step; a surface plating treatment step; a withstand voltage detection step; a quality detection step; and assembling to form the heat transfer element. According to the plate type heat transfer element produced through the manufacturing method, the sine corrugated plate surface is adopted, the smoke turbulence degree can be remarkably improved through the structural design, and therefore the heat transfer coefficient is greatly increased, and the heat exchange efficiency is high and stable. Compared with a traditional pipe type low-temperature economizer, smoke waste heat can be recycled more effectively, the energy utilization rate is increased, and power generation coal consumption is reduced. According to a series of manufacturing steps from preparation of flat plate raw materials to final assembly of the heat transfer elements, reliable quality and stable performance of each heat transfer element are ensured, efficient operation of the whole plate type low-temperature economizer is ensured, and the overall performance and reliability of equipment are improved.

Description

Technical Field

[0001] The invention relates to the field of plate type heat transfer element manufacturing, and in particular to a method for manufacturing a metal sheet hydraulically formed high-efficiency plate type heat transfer element. Background Art

[0002] In energy utilization systems such as thermal power units, the utilization of flue gas waste heat is an important link to improve energy efficiency and reduce energy consumption. As a key device for flue gas waste heat recovery, the performance of low-temperature economizers directly affects the operation effect and economy of the entire system. Traditional low-temperature economizers mainly include H-type finned tubes, spiral finned tubes, heat pipe economizers, etc. However, these traditional low-temperature economizers have exposed many problems in actual operation.

[0003] The H-type finned tube and spiral finned tube and other tubular low-temperature economizers have a low flue gas turbulence and heat transfer coefficient due to their smooth tube surface, resulting in low heat transfer efficiency. In addition, there are a large number of flow dead zones and leeward sides in the structure, which are prone to dust accumulation and scaling, seriously affecting the heat transfer effect and increasing the equipment operation resistance. At the same time, due to the frontal and large windward angle of dust particles scouring the heat exchange surface, the degree of wear is large, reducing the service life of the equipment. In addition, the center area of ​​the tube bundle becomes a blind area for soot blowing and cleaning. It is difficult to blow through due to its large depth, and it is extremely difficult to blow soot and remove scale, which further affects the stable operation of the equipment.

[0004] Although the heat pipe type low-temperature economizer has been improved in some aspects, it still has the problem of low heat transfer coefficient of the bare tube surface and irreversible loss of the intermediate heat medium temperature difference, which makes the heat transfer efficiency not only low but also decays year by year. Summary of the invention

[0005] The object of the present invention is to provide a method for manufacturing a high-efficiency plate-type heat transfer element by hydraulically forming a metal sheet, and more specifically, a method for manufacturing a high-efficiency plate-type heat transfer element by hydraulically forming a metal sheet.

[0006] To achieve the above object, the present invention provides the following technical solutions: a method for manufacturing a high-efficiency plate-type heat transfer element by hydraulic forming of a metal sheet, and a method for manufacturing a high-efficiency plate-type heat transfer element by hydraulic forming of a metal sheet, wherein the steps are as follows: Steps for preparing flat sheet materials: selecting two metal sheets suitable for manufacturing heat transfer elements as raw materials, and preparing for subsequent processing operations; Laser stitch welding steps: Use laser welding technology to stitch two plates along a predetermined welding track to tightly combine them into one to form a stitch-welded plate structure; Hydraulic step-by-step bulging forming steps: placing the lap-welded flat plate in a dedicated hydraulic forming device, applying hydraulic pressure step by step to gradually deform and bulge the flat plate, and finally forming a plate-tube structure with periodic peaks and troughs, and naturally forming flue gas flow channels for conveying boiler flue gas between adjacent plate-tubes, and the spacing between flue gas flow channels is controlled within the range of 1030mm, and at the same time, a closed channel for conveying boiler inlet water is formed inside the plate-tube; Surface coating treatment steps: Use supersonic plasma spraying alloy ceramic technology to coat a layer of wear-resistant and corrosion-resistant alloy ceramic on the surface of the plate tube. The alloy ceramic coating has the characteristics of adhesion of 40MPa, temperature resistance of 900℃, smooth and non-stick surface, and hydrophobic surface. The coating hardness is HRC60, and its corrosion rate is only about 1 / 3 of that of duplex stainless steel 2205; Pressure test steps: connect the plate tube plated with alloy ceramics to the pressure test equipment, conduct a water pressure test, gradually increase the water pressure to a maximum of 6.0-8.0 MPa, and maintain it for a certain period of time to test the sealing performance and pressure resistance of the plate tube under high pressure; Quality inspection steps: metallographic inspection is carried out on the plate and tube after the pressure test. Microscopic metallographic analysis is carried out on the weld area, heat-affected zone and parent material area of ​​the plate and tube to ensure that the welding quality of the corrugated plate is reliable and free of defects such as cracks and pores; Steps for assembling into heat transfer elements: assemble the qualified plate tubes according to the design requirements to form a heat exchange plate bundle, so that the boiler water can flow smoothly in the channel inside the plate tube, and at the same time ensure that the space formed between the two groups of plate tubes can effectively transport the boiler flue gas, and set an anti-wear plate on the windward side of the plate economizer, which plays the role of rectification and dust expansion energy reduction, so that the flow of flue gas and dust is parallel to the airway, thereby completing the manufacture of the metal sheet hydraulic forming high-efficiency plate heat transfer element, and the heat exchange units composed of multiple heat transfer elements can be arranged in parallel to form a plate-type low-temperature economizer. The flue gas flow rate of the plate-type low-temperature economizer is about 8m / s, and the windward angle of its heat exchange plate tube is basically close to 0 degrees.

[0007] Furthermore, the metal sheet is made of 09CrCuSb. Before surface coating, the ND steel sheet is pretreated, including surface cleaning and activation treatment, to enhance the bonding strength between the coating and the sheet substrate, ensuring that the coating adhesion reaches more than 40MPa, and heat treatment is performed after coating to further optimize the organizational structure and performance of the coating.

[0008] Furthermore, in the laser stitch welding step, the laser welding parameters are set as follows: laser power is between 1500-3000 W, welding speed is 8-15 mm / s, spot diameter is 0.8-1.5 mm, pulse laser welding mode is adopted, pulse frequency is 20-50 Hz, pulse width is 5-15 ms, so as to ensure welding quality and make the weld strength at the welding point not less than 85% of the strength of the thin plate matrix.

[0009] Furthermore, in the hydraulic step-by-step bulging forming step, the specific process of applying hydraulic pressure step by step is: first, the hydraulic pressure is increased to 10-15MPa at a rate of 1-3MPa / s, and maintained for 3-5s; then the pressure is continuously increased to 20-25MPa at a rate of 2-4MPa / s, and maintained for 5-8s; finally, the pressure is increased to the final forming pressure of 30-40MPa at a rate of 3-5MPa / s, and maintained for 8-12s. By precisely controlling the hydraulic pressure and time, the sheet tube forming accuracy is ensured to be within ±0.5mm, and the shapes of the peaks and troughs are uniform.

[0010] Furthermore, in the surface coating treatment step, the process parameters of the supersonic plasma spraying alloy ceramic technology are: the plasma gas adopts a mixture of argon and hydrogen, wherein the argon flow rate is 40-60L / min, and the hydrogen flow rate is 5-10L / min; the powder feeding rate is 30-50g / min; the spraying distance is 100-150mm; the spray gun current is 400-600A, and the voltage is 70-90V, so as to obtain an alloy ceramic coating with high bonding strength, good density, low porosity and excellent wear and corrosion resistance.

[0011] Furthermore, in the pressure resistance test step, the specific operations of the water pressure test include: first filling the plate tube with water and exhausting the air, then slowly increasing the pressure to 50% of the test pressure at a rate of 0.5-1MPa / min, and checking for leakage; if there is no abnormality, continue to increase the pressure to the test pressure at a rate of 0.5-1MPa / min, and maintain it for 30-60 minutes. During this period, the pressure drop must not exceed 5% of the test pressure, and then reduce the pressure to the working pressure for a comprehensive inspection to ensure that the plate tube has no deformation, no leakage, and the pressure resistance performance meets the requirements.

[0012] Furthermore, in the quality inspection step, the specific method of metallographic inspection is: cutting a sample from the plate tube, after inlaying, grinding and polishing, corroding with aqua regia, observing the organizational morphology of the weld area, heat-affected zone and parent material area under a metallographic microscope, requiring that the weld area is free of defects such as cracks, unfused, slag inclusions, the grains in the heat-affected zone are small and uniform, and the organization of the parent material area is normal, so as to ensure the reliable quality of the corrugated plate welding, thereby ensuring the performance and service life of the entire heat transfer element.

[0013] Furthermore, in the step of assembling the heat transfer element, the anti-wear plate is installed in the following manner: a detachable installation structure is adopted, and the anti-wear plate is fixedly connected to the plate tube by bolts or slots, so as to facilitate regular inspection and replacement of the anti-wear plate during operation; the anti-wear plate is made of high-strength wear-resistant alloy, with a hardness of not less than HRC50 and a thickness of 5-10mm, and the surface is specially treated with low roughness and good anti-adhesion performance, so as to effectively reduce the erosion and wear of the heat transfer element by smoke and dust.

[0014] Furthermore, the assembly method of the heat exchange unit in the plate-type low-temperature economizer is as follows: each heat exchange unit includes a plurality of modules arranged side by side, and the modules are connected by sealing connectors to ensure that the flue gas and boiler water flow in their respective channels without leaking each other; the sealing connectors use high-temperature and corrosion-resistant rubber sealing gaskets and metal fastening components, and the compression amount of the rubber sealing gaskets is controlled between 20%-30% to ensure a good sealing effect, while facilitating the installation, maintenance and overhaul of the heat exchange unit.

[0015] Furthermore, in the plate-type low-temperature economizer, in order to further improve the heat transfer efficiency and prevent ash accumulation and scaling, a spoiler is installed in the flue gas flow duct. The spoiler adopts a streamlined structure and is made of stainless steel or ceramic with a smooth surface. The installation position and angle of the spoiler are optimized according to the simulation results of the flue gas flow field, so that the flue gas forms uniform turbulence in the flow duct, thereby enhancing the heat transfer effect and avoiding local ash accumulation, thereby ensuring the long-term stable operation of the plate-type low-temperature economizer and improving energy utilization efficiency.

[0016] Compared with the prior art, the beneficial effects of the present invention are: the method for manufacturing a high-efficiency plate-type heat transfer element by hydraulically forming a metal sheet; The plate heat transfer element produced by the manufacturing method of the present invention adopts a sinusoidal corrugated plate surface. This structural design can significantly increase the turbulence of flue gas, thereby greatly improving the heat transfer coefficient and making the heat exchange efficiency high and stable. Compared with the traditional tubular low-temperature economizer, it can more effectively recover flue gas waste heat, improve energy utilization, and reduce coal consumption for power generation.

[0017] The windward angle of the heat exchange surface of the plate heat transfer element is close to 0°. Compared with the windward angle of 90° at the air inlet of the heat exchange surface of the tubular low-temperature economizer, there is airflow separation on the leeward side, and its resistance coefficient is greatly reduced to only 1 / 3-1 / 2 of that of the tubular type. This means that during operation, the pressure loss of flue gas passing through the plate low-temperature economizer is small, which reduces the energy consumption of the induced draft fan and the power consumption rate of the unit.

[0018] The unique flow channel design makes the flow channel of the plate heat transfer element straight and smooth, without leeward side, effectively avoiding the formation of dust and scaling. In sharp contrast to the traditional tubular economizer, which is prone to dust and scaling, it reduces the problem of heat transfer efficiency reduction caused by dust and scaling, ensures long-term stable and efficient operation of the equipment, and reduces maintenance costs and downtime risks.

[0019] On the one hand, the flue gas velocity of the plate economizer is about 8m / s, which is lower than that of the tube economizer. According to the relationship that the dust erosion and corrosion rate is proportional to the cube of the gas velocity, its wear rate is significantly reduced, about 30% of the tube type. On the other hand, the dust particles flow parallel to the heat exchange surface, which greatly reduces the degree of erosion and corrosion. In addition, the anti-wear plate arranged on the windward side plays a role in rectification and dust expansion energy reduction, which further protects the heat transfer components and extends the service life of the equipment.

[0020] The straight-through flow channel structure makes the plate-type low-temperature economizer have no blind area for soot blowing and cleaning, and the depth is small, making it easy for the soot blowing equipment to blow through and remove the soot. At the same time, it can realize online pressure leakage detection and perform isolation at the heat exchange plate and tube level, which is convenient for timely discovery and handling of possible leakage problems without affecting the normal operation of the entire equipment, improving the reliability and availability of the equipment, and reducing downtime and economic losses caused by equipment failure.

[0021] A series of manufacturing steps from the preparation of flat plate raw materials to the final assembly into heat transfer elements, such as laser lap welding, hydraulic step-by-step bulging forming, strict surface coating treatment, pressure resistance testing and metallographic testing, etc., have precise process parameters and quality control requirements. This ensures the reliable quality and stable performance of each heat transfer element, ensures the efficient operation of the entire plate-type low-temperature economizer, improves the overall performance and reliability of the equipment, enables it to play a greater role in energy utilization systems such as thermal power units, and helps promote technological progress and sustainable development in the energy field. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of a plate-type heat transfer element in the present invention; Figure 2 is a cross-sectional schematic diagram of the plate-type heat transfer element of the present invention; Figure 3 It is a schematic diagram of the plate-tube structure in the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Reference Figure 1 —3: The present invention provides a technical solution: a method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element, the specific manufacturing steps are as follows: 1. Prepare the raw materials for the plate 1. Raw material selection Metal sheets made of 09CrCuSb (ND steel) are selected as the basic raw materials. ND steel has good corrosion resistance and is particularly suitable for low-temperature corrosion environments that may exist in flue gas waste heat recovery systems. The thickness of the sheet is determined according to specific design requirements, generally between 1-3mm, for example, a 2mm thick ND steel sheet is selected. When selecting a sheet, strictly check the surface quality of the sheet to ensure that there are no obvious scratches, pits, oxide scale and other defects to ensure subsequent processing and product quality.

[0025] 2. Raw material pretreatment The selected ND steel sheets are cleaned on the surface. First, use an organic solvent (such as acetone) to wipe the sheet surface to remove impurities such as oil, grease, etc. Then use a mechanical grinding method, such as using sandpaper or a grinding wheel to lightly grind the sheet surface to remove surface oxide scale and other impurities that may affect the bonding strength of welding and coating. After grinding, wipe the surface again with a clean non-woven cloth dipped in acetone to ensure that the surface cleanliness meets the requirements of subsequent processing.

[0026] Surface activation treatment is carried out, and the surface of the thin plate is treated with a chemical activator (such as a phosphoric acid-chromic acid mixed solution) for 5-10 minutes, and the temperature is controlled at 20-30°C. After treatment, rinse with clean water and dry quickly to enhance the activity of the thin plate surface and improve the bonding strength between the subsequent coating and the thin plate substrate.

[0027] (II) Laser stitch welding 1. Welding equipment preparation A fiber laser with a power of 2000W is selected as the welding equipment, equipped with a high-precision welding table and an automated welding control system. The positioning accuracy of the welding table should reach ±0.1mm to ensure the precise alignment of the plate during the welding process.

[0028] 2. Welding parameter setting The laser power is set to 2000W, the welding speed is 10mm / s, and the spot diameter is 1.2mm. The pulse laser welding mode is adopted, the pulse frequency is 30Hz, and the pulse width is 10ms. Before welding, the laser focus position is precisely adjusted according to the plate thickness and welding process requirements to ensure that the laser energy can be concentrated on the welding part to achieve good penetration and weld formation.

[0029] 3. Welding operation process Place two pre-treated ND steel sheets on the welding table, use a clamp to accurately align and fix them, and ensure that the gap between the edges of the plates does not exceed 0.1mm. Start the laser welding equipment and perform welding according to the predetermined welding parameters and welding path. The welding path adopts linear welding, starting from one end of the sheet and welding to the other end at a constant speed. During the welding process, the changes in parameters during the welding process, such as laser power, welding speed, etc., are monitored in real time to ensure that the parameters are stable within the set range. After welding is completed, check the appearance of the weld. The weld should be continuous and uniform, without defects such as pores, cracks, and unfused welds.

[0030] (III) Hydraulic step-by-step bulging forming 1. Hydraulic equipment preparation A dedicated hydraulic forming equipment is used, which has a high-precision pressure control system and mold system. The pressure control accuracy of the pressure control system is ±0.5MPa, which can accurately control the rise and fall of hydraulic pressure and the holding time. The mold system is designed and manufactured according to the shape and size of the required plate and tube, and the mold surface roughness should not be higher than Ra0.8μm to ensure the surface quality of the plate and tube after forming.

[0031] 2. Hydraulic step-by-step swelling process Place the laser welded flat plate in the mold of the hydraulic forming equipment to ensure that the flat plate fits tightly with the mold. First, increase the hydraulic pressure to 12MPa at a rate of 2MPa / s and hold for 4s to allow the flat plate to begin to deform initially. Then continue to increase the pressure to 22MPa at a rate of 3MPa / s and hold for 6s. At this time, the flat plate swells further, and the crests and troughs begin to gradually form. Finally, increase the final molding pressure to 35MPa at a rate of 4MPa / s and hold for 10s to ensure that the plate and tube molding meets the design requirements. During the entire hydraulic step-by-step swelling process, closely observe the molding of the plate and tube, monitor the wall thickness changes and shape dimensions of the plate and tube through the sensors on the mold, and ensure that the molding accuracy is within ±0.5mm, and the crests and troughs are uniform. The flue gas flow channel spacing between adjacent plate tubes after molding is 20mm, which can provide sufficient heat exchange area while ensuring smooth flue gas circulation.

[0032] (IV) Surface coating treatment 1. Preparation of supersonic plasma spraying equipment The advanced supersonic plasma spraying system is used, which includes a plasma spray gun, a powder feeder, a gas supply system and a control system. The plasma spray gun uses a specially designed Laval nozzle, which can produce a high-energy-density, supersonic plasma jet. The powder feeder has a precise powder feeding amount control function, and the powder feeding accuracy can reach ±2g / min. The gas supply system can stably supply a mixed gas of argon and hydrogen, and the gas flow control accuracy is ±1L / min. The control system can realize precise control and real-time monitoring of the spraying parameters.

[0033] 2. Spraying material preparation Specially developed wear-resistant and corrosion-resistant alloy ceramic powder is selected as the spraying material. The particle size of the powder is between 15-45μm, and the main components include tungsten carbide, cobalt, chromium and other elements. Its ratio is optimized to obtain excellent wear resistance and corrosion resistance. Before spraying, the alloy ceramic powder is dried to remove moisture and impurities in the powder. The drying temperature is 100-120°C and the drying time is 2-3 hours to ensure the fluidity and stability of the powder.

[0034] 3. Setting of process parameters of supersonic plasma spraying The plasma gas is a mixture of argon and hydrogen, with an argon flow rate of 50L / min and a hydrogen flow rate of 8L / min. The powder feeding rate is 40g / min and the spraying distance is 120mm. The spray gun current is 500A and the voltage is 80V. By adjusting these parameters, the plasma jet can instantly melt the high melting point spraying material and accelerate the molten particles to a supersonic level of 450-900m / s, ensuring the violent collision of the powder or the secondary atomization of the particles after rapid melting, so as to obtain a fine coating structure.

[0035] 4. Spraying operation process Install the formed plate and tube on the spraying workbench to ensure that the surface of the plate and tube is clean and free of oil, dust and other impurities. Start the supersonic plasma spraying equipment and perform the spraying operation according to the set process parameters. During the spraying process, the plasma spray gun moves at a uniform speed to ensure that the coating thickness is uniform. The coating thickness is controlled between 0.3-0.5mm and is completed in multiple sprayings. The thickness of each spraying does not exceed 0.1mm to avoid defects such as cracks and peeling in the coating. After spraying, the coating is quality checked. A coating thickness detector is used to detect whether the coating thickness meets the requirements. A hardness tester is used to detect the coating hardness to ensure that the coating hardness reaches about HRC60. At the same time, check whether the coating surface is smooth and dense, without defects such as pores and cracks.

[0036] (V) Withstand voltage test 1.Preparation of pressure test equipment A water pressure tester is used for pressure resistance testing. The tester has precise pressure measurement and control functions, with a pressure measurement accuracy of ±0.1MPa and a pressure control accuracy of ±0.2MPa. The tester is equipped with components such as a high-pressure water pump, a pressure sensor, a safety valve, and a data acquisition system. The high-pressure water pump can provide sufficient water pressure to meet the test pressure requirements of 6.0-8.0MPa. The pressure sensor monitors the water pressure changes in real time, the safety valve ensures safety during the test, and the data acquisition system records the pressure change curve over time.

[0037] 2. Withstand voltage test operation process Connect the plate tube coated with alloy ceramics to the hydraulic testing machine to ensure that the connection parts are well sealed and there is no leakage. First, fill the plate tube with water, open the exhaust valve, exhaust the air in the channel until water flows out of the exhaust valve continuously, and close the exhaust valve. Then slowly increase the pressure to 50% of the test pressure, that is, 3.0-4.0MPa, at a rate of 0.8MPa / min, stop increasing the pressure, maintain the pressure for 10-15 minutes, and check for leakage. If there is no abnormality, continue to increase the pressure to 6.0-8.0MPa at a rate of 0.8MPa / min, and maintain it for 45 minutes. During this period, closely observe the pressure changes, and the pressure drop shall not exceed 5% of the test pressure, that is, 0.3-0.4MPa. If the pressure drop is within the allowable range, slowly reduce the pressure to the working pressure, which is determined according to the actual operating conditions, generally 2-4MPa, and conduct a comprehensive inspection of the plate tube, including the welds, the plate tube body and other parts, to check for abnormal conditions such as deformation and leakage. If the test result is qualified, proceed to the next step; if it is unqualified, analyze the cause and repair or scrap it.

[0038] (VI) Quality Inspection 1. Metallographic sample preparation Metallographic specimens are cut from the plate tubes that have passed the pressure test. The size of the specimen is determined according to the observation requirements of the metallographic microscope, generally 10mm×10mm×5mm. The wire cutting method is used to cut the specimen to reduce damage to the specimen structure. The cut specimens are inlaid, polished and polished in turn. The hot inlay method is used for inlay, and phenolic resin is used as the inlay material. The inlay temperature is 150-180°C and the time is 10-15 minutes. The polishing process uses 200, 400, 800, 1200 and 2000 sandpapers in turn, and the polishing direction is rotated 90° each time to ensure that the surface of the specimen is flat. The polishing method adopts a mechanical polishing method, using alumina polishing powder, and the polishing time is 10-15 minutes until the surface of the specimen is as bright as a mirror, without scratches, pits and other defects.

[0039] 2. Metallographic corrosion and observation The polished sample was corroded with aqua regia for 5-10 seconds. After corrosion, it was immediately rinsed with clean water and dried quickly. The corroded sample was placed under a metallographic microscope for observation at a magnification of 100-500 times. Focus on the organization morphology of the weld zone, heat-affected zone and parent metal zone. The weld zone should be free of defects such as cracks, unfused, slag inclusions, etc. The weld metal organization should be uniform and fine; the grains in the heat-affected zone should be small and uniform, without obvious overheating organization; the parent metal area organization should be normal, without obvious deformation and organizational changes. Judge whether the corrugated plate welding quality is reliable based on the observation results. If defects are found, analyze the causes and take corresponding measures to improve them, such as adjusting welding parameters and optimizing welding processes.

[0040] (VII) Assembling into heat transfer elements 1. Heat exchange plate bundle assembly The qualified plates and tubes that have passed the quality inspection are assembled into heat exchange plate bundles according to the design requirements. First, install the positioning fixture on the assembly workbench to ensure the accurate position of the plates and tubes during the assembly process. Determine the arrangement and quantity of the plates and tubes according to the heat exchange area and the parameters such as the flue gas and boiler water inlet flow. The plates and tubes are connected by sealed welding or sealed connectors to ensure that the flue gas channel and water inlet channel formed between the plates and tubes are well sealed and leak-free. For sealed welding, the argon arc welding process is adopted, the welding current is 100-150A, the voltage is 10-15V, and the welding speed is 5-8mm / s to ensure the quality of the weld. For sealed connectors, high temperature and corrosion resistant rubber gaskets and metal fastening components are selected. The compression of the rubber gasket is controlled at about 25%. By tightening the metal fastening components, the gasket is sufficiently compressed and deformed, thereby achieving a good sealing effect.

[0041] 2. Installation of wear plate The anti-wear plate is made of high-strength wear-resistant alloy, such as chromium-nickel alloy, with a hardness of not less than HRC50 and a thickness of 8mm. The surface of the anti-wear plate is specially treated, and a layer of ceramic coating is sprayed on the surface using supersonic flame spraying technology. The coating thickness is 0.1-0.2mm, so that the surface has a low roughness Ra0.4μm or less and good anti-adhesion performance. The anti-wear plate is fixedly connected to the plate tube by bolts, and threaded holes are pre-processed on the plate tube. The bolt specifications are M8-M10 and the bolt spacing is 50-100mm. During installation, apply high-temperature anti-loosening glue to the bolt connection to prevent the bolts from loosening during operation. The installation position of the anti-wear plate is on the windward side of the plate economizer, and the installation angle is adjusted according to the direction of flue gas flow to ensure that the anti-wear plate can effectively rectify and reduce the kinetic energy of dust, so that the flow of flue gas and dust is parallel to the airway, reducing the erosion and wear of the heat transfer elements.

[0042] 3. Heat exchange unit assembly Each heat exchange unit contains multiple modules arranged side by side. The number of modules is determined according to actual needs, generally 3-6. The modules are connected by sealing connectors, which are made of stainless steel flanges and rubber sealing rings. The sealing surface of the flange is in the form of tongue and groove or concave and convex surface. The rubber sealing ring is made of fluororubber with a Shore hardness of 70-80 degrees and a compression permanent deformation rate of less than 30%. During assembly, the rubber sealing ring is placed in the flange sealing groove, and then the flanges of the two modules are aligned and tightened with bolts. The bolt torque is determined according to the bolt specifications and sealing requirements, generally 20-50N·m. After assembly, the heat exchange unit is tested for sealing. The air pressure test method is used to pass 0.5-1.0MPa compressed air to check whether there is any leakage at the connection to ensure that the flue gas and boiler water flow in their respective channels without leakage, which is convenient for the installation, maintenance and overhaul of the heat exchange unit.

[0043] (VIII) Assembly and commissioning of plate-type low-temperature economizer 1. Overall assembly of plate-type low-temperature economizer Arrange multiple heat exchange units in parallel, and determine the arrangement of the heat exchange units according to the on-site installation space and the layout of the flue gas and water inlet systems. The heat exchange units are connected by pipe connectors, which are made of carbon steel or stainless steel elbows, tees and straight pipe sections. The inner diameter of the pipe is determined according to the flow requirements, generally 50-150mm. Welding or flange connection is used at the connection parts, and the quality of the weld is ensured during welding. When flange connection is used, the same sealing structure and sealing material as the heat exchange unit connection are used. At the same time, install the flue gas inlet and outlet pipes, boiler water inlet and outlet pipes, drainage pipes and other accessories to ensure that the entire plate-type low-temperature economizer system is firmly connected and reasonably laid out.

[0044] 2. Debugging and running After the assembly of the plate-type low-temperature economizer is completed, it is debugged and put into operation. First, conduct a comprehensive inspection of the entire system, including whether the equipment is firmly installed, whether the pipeline connection is sealed, and whether the instrumentation is normal. Then, slowly introduce the boiler flue gas and water, and gradually adjust the flue gas flow and water flow to the design conditions. During the debugging process, closely monitor the operating parameters of the plate-type low-temperature economizer, such as the inlet and outlet flue gas temperature, water temperature, pressure drop, etc., as well as the operating status of the equipment, such as abnormal vibration, noise, etc. Further optimize and adjust the equipment according to the monitoring results, such as adjusting the opening of the flue gas damper, optimizing the position of the anti-wear plate, etc., to ensure that the plate-type low-temperature economizer can operate stably and efficiently, and achieve the expected waste heat recovery effect and performance indicators.

[0045] Comparison and verification with existing technologies In order to verify the superiority of the plate type heat transfer element and the plate type low temperature economizer produced by the manufacturing method of the present invention, the following comparative test was carried out.

[0046] 1. Comparison of heat transfer performance 1. Experimental Setup Two identical test devices were built, and a traditional tubular low-temperature economizer and a plate-type low-temperature economizer manufactured by the present invention were installed respectively. The test device includes a flue gas generation system, a water circulation system, a temperature measurement system, a flow measurement system, and a data acquisition system. The flue gas generation system uses a fuel burner to generate high-temperature flue gas, and the flue gas flow rate can be adjusted in the range of 5000-15000m³ / h, and the flue gas temperature can be adjusted in the range of 150-300°C. The water circulation system uses a centrifugal pump to provide circulating water, and the water flow rate can be adjusted in the range of 10-50m³ / h, and the water temperature is 20-50°C. The temperature measurement system uses a thermocouple thermometer to measure the inlet and outlet flue gas temperature and water temperature, and the measurement accuracy is ±1°C. The flow measurement system uses an electromagnetic flowmeter to measure the flow of flue gas and water, and the measurement accuracy is ±0.5%. The data acquisition system collects temperature, flow and other data in real time.

[0047] 2. Experimental process and results Under the same flue gas flow rate, water inlet flow rate and initial temperature conditions, the tubular low-temperature economizer and the plate low-temperature economizer were tested respectively. The test results show that when the common flow rate of the tubular economizer, that is, the flue gas flow rate is 10m / s, the heat transfer coefficient of the tubular low-temperature economizer is 20-30W / (m²·K), while the heat transfer coefficient of the plate low-temperature economizer of the present invention can reach 40-60W / (m²·K), and the heat transfer efficiency is improved by 50%-100%. This is because the sinusoidal corrugated plate surface structure of the plate heat transfer element makes the flue gas turbulent and enhances the heat transfer effect. In addition, after long-term operation, the heat transfer efficiency of the tubular low-temperature economizer gradually decreases, while the heat transfer efficiency of the plate low-temperature economizer remains basically stable, which proves the advantages of the plate heat transfer element of the present invention in high heat exchange efficiency and stability.

[0048] 2. Resistance performance comparison 1. Experimental Setup Using the above test device, pressure sensors are installed on the inlet and outlet pipes to measure the pressure difference before and after the flue gas passes through the low-temperature economizer, and the resistance coefficient is calculated based on this. The measurement accuracy of the pressure sensor is ±0.1kPa.

[0049] 2. Experimental process and results When the flue gas flow rate is 10000m³ / h, the resistance coefficient of the tubular low-temperature economizer is 1.5-2.0, while the resistance coefficient of the plate-type low-temperature economizer of the present invention is 0.5-0.8, which is only 1 / 3-1 / 2 of that of the tubular type. This is because the windward angle of the heat exchange surface of the plate-type heat transfer element is close to 0°, which effectively reduces the airflow resistance. The lower resistance coefficient means that in actual operation, the plate-type low-temperature economizer can reduce the energy consumption of the induced draft fan and reduce the power consumption rate of the unit.

[0050] (III) Comparison of anti-dust and scaling performance 1. Experimental Setup After the above test device was operated for a period of time, 100 hours and 500 hours respectively, it was stopped and the low-temperature economizer was opened to observe the internal ash accumulation and scaling. At the same time, the composition analysis and thickness measurement of the ash accumulation and scaling were carried out. The composition of the ash accumulation and scaling was analyzed by X-ray fluorescence spectrometer, and the thickness of the ash accumulation and scaling layer was measured by micrometer.

[0051] 2. Experimental process and results After 100 hours of operation, obvious dust accumulation appeared inside the tube-type low-temperature economizer, with an average thickness of 3-5mm, and the dust accumulation was unevenly distributed on the surface of the tube bundle, and was more serious on the leeward side of the tube bundle and in the dead zone of the flow. The main components of the dust accumulation were fly ash particles, calcium sulfate, etc. However, only a small amount of dust was attached to the inside of the plate-type low-temperature economizer, with a thickness of no more than 1mm, and the dust was evenly distributed on the surface of the plate tube, without obvious dust accumulation areas.

[0052] After 500 hours of operation, the ash accumulation of the tubular low-temperature economizer further increased, reaching a thickness of 8-10mm, and scaling appeared in some areas. The scaling materials were mainly calcium sulfate, ammonium bisulfate, etc. The scaling layer was hard and difficult to remove, seriously affecting the heat transfer efficiency. Although the ash thickness of the plate-type low-temperature economizer increased, it remained within the range of 2-3mm, and no obvious scaling occurred. This is due to its straight and smooth flow channel and the absence of a leeward structural feature, which effectively avoids the generation of ash accumulation and scaling, ensures the long-term stable and efficient operation of the equipment, and reduces maintenance costs and downtime risks.

[0053] (IV) Comparison of wear and corrosion resistance 1. Experimental Setup A simulated wear and corrosion test device was used to place samples of tubular low-temperature economizers and plate-type low-temperature economizers in the device, and a flow containing a certain concentration of dust, simulating fly ash in flue gas, with a dust concentration of 10-15g / m³ and corrosive gas was introduced. The airflow velocity simulated the actual operating conditions, with a flue gas velocity of 10-12m / s for tubular economizers and 8m / s for plate-type economizers, and the test time was 500-1000 hours. During the test, the samples were taken out regularly, and the mass loss of the samples was measured using an electronic balance, and the wear and corrosion morphology of the sample surface was observed using a scanning electron microscope.

[0054] 2. Experimental process and results After 500 hours of testing, the mass loss rate of the tube-type low-temperature economizer sample reached 0.5%-1.0%, and obvious scouring marks and corrosion pits appeared on the sample surface, especially within the range of 30-50 degrees on both sides of the windward surface of the tube, where wear and corrosion were most serious. This was due to the dust particles scouring the heat exchange surface at the front and large windward angle. The mass loss rate of the plate-type low-temperature economizer sample was only 0.1%-0.3%, and the degree of surface wear and corrosion was relatively light, with only slight scratches in local areas. This was because the dust particles flowed parallel to the heat exchange surface, reducing the degree of scouring and corrosion, and the anti-wear plate set on the windward side played a good protective role.

[0055] After the test was continued for 1000 hours, the mass loss rate of the tube-type low-temperature economizer sample further increased to 1.5%-2.0%, perforation occurred in some areas, and the depth of the corrosion pit deepened, seriously affecting the structural strength and service life of the equipment. The mass loss rate of the plate-type low-temperature economizer sample was still controlled within 0.3%-0.5%, the surface condition was good, and there was no obvious structural damage, indicating that it has excellent wear and corrosion resistance and can operate stably for a long time in harsh flue gas environments.

[0056] (V) Comparison of soot blowing and descaling performance 1. Experimental Setup In the above-mentioned actual operation test device, the same type of soot blowing equipment, such as sonic soot blower or steam soot blower, is installed to perform soot blowing on the tubular low-temperature economizer and plate low-temperature economizer after a period of operation. Before and after soot blowing, the resistance coefficient, heat transfer coefficient and other performance parameters of the low-temperature economizer are measured, and the removal of ash accumulation is observed. The resistance coefficient is measured using a high-precision pressure sensor with an error of no more than ±0.05; the heat transfer coefficient is measured using a heat flow meter with an error of no more than ±5W / (m²·K).

[0057] 2. Experimental process and results For the tubular low-temperature economizer, soot blowing was performed after 200 hours of operation. Before soot blowing, the resistance coefficient increased by 30%-50% compared with the initial value, and the heat transfer coefficient decreased by 20%-30%, indicating that the soot accumulation had a great impact on its performance. After soot blowing, the resistance coefficient only decreased by 10%-15%, and the heat transfer coefficient did not recover significantly, only increasing by 5%-10%. It was observed that the soot accumulation in the center of the tube bundle was difficult to be removed by the soot blower, and a large amount of soot accumulation remained. This was due to the complex structure of the tube bundle, the existence of soot blowing cleaning blind spots, and the large depth that was difficult to blow through.

[0058] The plate-type low-temperature economizer was soot-blown after running for the same time. Before soot-blowing, the resistance coefficient increased slightly, at 10%-15%, and the heat transfer coefficient decreased slightly, at 10%-15%. After soot-blowing, the resistance coefficient basically returned to the initial value, and the heat transfer coefficient increased by 15%-20%. This is because the plate-type low-temperature economizer has a straight flow channel, no soot-blowing blind area, and a small depth, which makes it easy for the soot-blowing equipment to blow through and remove the ash and dirt, effectively restoring the performance of the equipment and ensuring the efficient operation of the equipment.

[0059] (VI) Online maintenance performance comparison 1. Experimental Setup During the operation of the test device, the leakage of the heat exchanger plate tube of the plate-type low-temperature economizer was simulated to observe the realization of its online leak detection and isolation functions. At the same time, the same simulation operation was performed on the tube-type low-temperature economizer.

[0060] 2. Experimental process and results When the plate-type low-temperature economizer simulates a heat exchanger tube leak, the built-in pressure sensor and leak detection system can quickly detect the leak location and isolate it at the heat exchanger tube level to prevent the leak from further expanding. The entire process does not require shutdown, and only the inlet and outlet valves of the module where the leaking plate tube is located need to be closed for maintenance or replacement, which does not affect the normal operation of other heat exchange units, ensuring the reliability and availability of the equipment.

[0061] For tubular low-temperature economizers, it is difficult to achieve online leak detection and isolation due to the large number of tube bundles and complex structure. Once a leak occurs, it is usually necessary to shut down for comprehensive inspection and maintenance, which will cause the entire system to stop operating, resulting in large economic losses. In addition, the maintenance process is complicated and requires the removal of a large number of tube bundles to find the leak point. The maintenance time is long, further reducing the operating efficiency of the equipment.

[0062] The above comparative tests have fully proved that the plate-type low-temperature economizer produced by the metal thin plate hydraulic forming high-efficiency plate heat transfer element manufacturing method of the present invention is significantly superior to the traditional tubular low-temperature economizer in terms of heat transfer performance, resistance performance, anti-ash accumulation and scaling performance, wear and corrosion resistance, soot blowing and descaling performance and online maintenance performance. It has broad application prospects and important practical significance, can effectively improve the flue gas waste heat recovery efficiency in energy utilization systems such as thermal power units, reduce operating costs, and promote technological progress and sustainable development in the energy field.

Claims

1. A method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element, characterized in that: The steps are as follows: Steps for preparing flat sheet materials: selecting two metal sheets suitable for manufacturing heat transfer elements as raw materials, and preparing for subsequent processing operations; Laser stitch welding steps: Use laser welding technology to stitch two plates along a predetermined welding track to tightly combine them into one to form a stitch-welded plate structure; Hydraulic step-by-step bulging forming steps: placing the lap-welded flat plate in a dedicated hydraulic forming device, applying hydraulic pressure step by step to gradually deform and bulge the flat plate, and finally forming a plate-tube structure with periodic peaks and troughs, and naturally forming flue gas flow channels for conveying boiler flue gas between adjacent plate-tubes, and the spacing between flue gas flow channels is controlled within the range of 1030mm, and at the same time, a closed channel for conveying boiler inlet water is formed inside the plate-tube; Surface coating treatment steps: Use supersonic plasma spraying alloy ceramic technology to coat a layer of wear-resistant and corrosion-resistant alloy ceramic on the surface of the plate tube. The alloy ceramic coating has the characteristics of adhesion of 40MPa, temperature resistance of 900℃, smooth and non-stick surface, and hydrophobic surface. The coating hardness is HRC60, and its corrosion rate is only about 1 / 3 of that of duplex stainless steel 2205; Pressure test steps: connect the plate tube plated with alloy ceramics to the pressure test equipment, conduct a water pressure test, gradually increase the water pressure to a maximum of 6.0-8.0 MPa, and maintain it for a certain period of time to test the sealing performance and pressure resistance of the plate tube under high pressure; Quality inspection steps: metallographic inspection is carried out on the plate and tube after the pressure test. Microscopic metallographic analysis is carried out on the weld area, heat-affected zone and parent material area of ​​the plate and tube to ensure that the welding quality of the corrugated plate is reliable and free of defects such as cracks and pores; Steps for assembling into heat transfer elements: assemble the qualified plate tubes according to the design requirements to form a heat exchange plate bundle, so that the boiler water can flow smoothly in the channel inside the plate tube, and at the same time ensure that the space formed between the two groups of plate tubes can effectively transport the boiler flue gas, and set an anti-wear plate on the windward side of the plate economizer, which plays the role of rectification and dust expansion energy reduction, so that the flow of flue gas and dust is parallel to the airway, thereby completing the manufacture of the metal sheet hydraulic forming high-efficiency plate heat transfer element, and the heat exchange units composed of multiple heat transfer elements can be arranged in parallel to form a plate-type low-temperature economizer. The flue gas flow rate of the plate-type low-temperature economizer is about 8m / s, and the windward angle of its heat exchange plate tube is basically close to 0 degrees.

2. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: The metal sheet is made of 09CrCuSb. Before surface coating, the ND steel sheet is pretreated, including surface cleaning and activation treatment, to enhance the bonding strength between the coating and the sheet substrate, to ensure that the coating adhesion reaches more than 40MPa, and to perform heat treatment after coating to further optimize the organizational structure and performance of the coating.

3. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: In the laser stitch welding step, the laser welding parameters are set as follows: laser power is between 1500-3000W, welding speed is 8-15mm / s, spot diameter is 0.8-1.5mm, pulse laser welding mode is adopted, pulse frequency is 20-50Hz, pulse width is 5-15ms, so as to ensure welding quality and make the weld strength at the welding point not less than 85% of the strength of the thin plate matrix.

4. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: In the hydraulic step-by-step bulging forming step, the specific process of applying hydraulic pressure step by step is: first, increase the hydraulic pressure to 10-15MPa at a rate of 1-3MPa / s, and maintain it for 3-5s; then continue to increase the pressure to 20-25MPa at a rate of 2-4MPa / s, and maintain it for 5-8s; finally, increase the pressure to the final forming pressure of 30-40MPa at a rate of 3-5MPa / s, and maintain it for 8-12s. By precisely controlling the hydraulic pressure and time, the forming accuracy of the plate and tube is ensured to be within ±0.5mm, and the shapes of the peaks and troughs are uniform.

5. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: In the surface coating treatment step, the process parameters of the supersonic plasma spraying alloy ceramic technology are: the plasma gas adopts a mixture of argon and hydrogen, wherein the argon flow rate is 40-60L / min, and the hydrogen flow rate is 5-10L / min; the powder feeding rate is 30-50g / min; the spraying distance is 100-150mm; the spray gun current is 400-600A, and the voltage is 70-90V, so as to obtain an alloy ceramic coating with high bonding strength, good density, low porosity and excellent wear and corrosion resistance.

6. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: In the pressure test step, the specific operations of the water pressure test include: first fill the plate tube with water and exhaust the air, then slowly increase the pressure to 50% of the test pressure at a rate of 0.5-1MPa / min, and check for leakage; if there is no abnormality, continue to increase the pressure to the test pressure at a rate of 0.5-1MPa / min, and maintain it for 30-60 minutes. During this period, the pressure drop must not exceed 5% of the test pressure, and then reduce the pressure to the working pressure for a comprehensive inspection to ensure that the plate tube has no deformation, no leakage, and the pressure resistance performance meets the requirements.

7. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: In the quality inspection steps, the specific method of metallographic inspection is: cut the sample from the plate tube, after inlaying, grinding and polishing, corrode with aqua regia, observe the organizational morphology of the weld area, heat-affected zone and parent material area under a metallographic microscope, and require that the weld area is free of defects such as cracks, lack of fusion, slag inclusions, the grains in the heat-affected zone are small and uniform, and the organization of the parent material area is normal, so as to ensure the reliable quality of the corrugated plate welding, thereby ensuring the performance and service life of the entire heat transfer element.

8. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: In the step of assembling the heat transfer element, the anti-wear plate is installed in the following way: a detachable installation structure is adopted, and the anti-wear plate is fixedly connected to the plate tube by bolts or slots, so as to facilitate regular inspection and replacement of the anti-wear plate during operation; the anti-wear plate is made of high-strength wear-resistant alloy, with a hardness of not less than HRC50 and a thickness of 5-10mm, and the surface is specially treated with low roughness and good anti-adhesion performance, so as to effectively reduce the erosion and wear of the heat transfer element by smoke and dust.

9. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: The heat exchange unit in the plate-type low-temperature economizer is assembled as follows: each heat exchange unit includes a plurality of modules arranged side by side, and the modules are connected by sealing connectors to ensure that the flue gas and boiler inlet water flow in their respective channels without leaking each other; the sealing connectors use high-temperature and corrosion-resistant rubber sealing pads and metal fastening components, and the compression amount of the rubber sealing pads is controlled between 20% and 30% to ensure a good sealing effect, while facilitating the installation, maintenance and overhaul of the heat exchange unit.

10. The method for manufacturing a metal sheet hydraulically formed high-efficiency plate-type heat transfer element according to claim 1, characterized in that: In the plate-type low-temperature economizer, in order to further improve the heat transfer efficiency and prevent ash accumulation and scaling, a spoiler is installed in the flue gas flow duct. The spoiler adopts a streamlined structure and is made of stainless steel or ceramic with a smooth surface. The installation position and angle of the spoiler are optimized according to the simulation results of the flue gas flow field, so that the flue gas forms uniform turbulence in the flow duct, enhances the heat transfer effect, and avoids local ash accumulation, thereby ensuring the long-term stable operation of the plate-type low-temperature economizer and improving the energy utilization efficiency.

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