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Original author of improvement of tube bundle structure of wet air cooler: Origin of Liu Chuanbao: [Keywords] Air cooler, tube bundle, structure, design, improvement [Abstract] In view of the existing problems in the operation and manufacturing of wet air coolers, the tube bundle structure has been improved with reference to the new schemes, new structures and manufacturing characteristics adopted in the design of domestic and foreign air coolers, with good results. Classification number TQ 051.503 Air-cooled heat exchanger (hereinafter referred to as air cooler) is an important heat exchange equipment in petrochemical plants. It has the characteristics of low operating cost, long service life, energy saving and environmental pollution reduction. In order to meet the needs of technological transformation for energy saving and environmental pollution reduction in petrochemical plants, and to reflect the contemporary advanced technology level, in view of the severe corrosion and scaling, reduced thermal efficiency, high energy consumption and manufacturing problems that occurred in the operation of our company's in-service wet air coolers, the author improved the tube bundle structure of the wet air cooler based on the latest design standards and with reference to new plans, new structures and new processes for air cooler design at home and abroad. 1 Fin tube 1.1 Form The fin tube is a key component for heat transfer in the air cooler, and its quality directly affects the heat transfer efficiency. According to the article [1], some foreign manufacturers, such as the American Hudson Company and the French Crusoe-Royal Company, do not advocate the use of single L-shaped fin tubes on wet air coolers. think directly * * It will aggravate the electrochemical corrosion of the fins and base tubes, leading to an increase in thermal resistance, a decrease in heat transfer efficiency, and a shortening of the life of the air cooler. Therefore, the author changed the single L-shaped fin tube (Figure 1a) used in the wet air cooler to a bimetallic fin tube (Figure 1b). Compared with the former, the latter has the following characteristics: ①The flexibility of the fins creates a self-cleaning effect as the temperature changes. ②Dirt and layer of dust are generated along the outside of the fins, and the root of the L-shaped wound fin tube will not be blocked. ③The fins are strong and not easily deformed, and can be cleaned with high-pressure water or high-pressure steam. ④The price is expensive and the one-time investment is high, but the overall benefits are good. file:///G:/new folder/learn * /Professional knowledge PDF file/Professional library/Wet air cooler tube bundle structure improvement .files/35.gif Figure 1 Forms and parameters of finned tubes before and after improvement Since the rolled tubes of bimetallic finned tubes closely match the base tube, it completely overcomes the shortcomings of scaling and electrochemical corrosion caused by single L-shaped finned tubes due to lax coverage of the base tube, significantly improves heat exchange efficiency and extends service life. 1.2 Parameter (1) Increase the pitch of the fin tube from the original 2.3 mm to 3.4 mm. This will reduce the heat exchange area of the air cooler and have some impact on the thermal coefficient of the outer film of the tube. However, when the heat exchange area margin is large, appropriately increasing the pitch of the fin tube can reduce air resistance, reduce the energy consumption of the fan, and make it easier to clean dirt. (2) Increase the thickness of the fins. The thickness of the fins is increased from the original 0.3 mm to 0.38/0.5 mm (trapezoidal), which increases the rigidity of the fins. The fins are not easily deformed when cleaned with steam blowing or high-pressure water. (3) Increase the center distance of the fin tube and reduce the height of the fin. The center distance s of the fin tube increases from the original 62 mm to 64 mm, and the fin height h decreases from 16 mm to 12.5 mm. The arrangement is shown in Figure 2. In this way, the gap between the fins increases from 5 mm to 14 mm, and water can be sprayed to the second and third rows of fin tubes, improving the heat exchange effect. At the same time, it can reduce the resistance drop and facilitate the purging and cleaning of the tube bundle. According to [1], when the fin height remains unchanged, the center distance s of the fin tubes increases from 62 mm to 64 mm, and the external resistance of the tubes decreases. Taking a wet air cooler tube bundle with four rows of fin tubes as an example, the external resistance of the tubes decreases from 88.26 Pa/row to 82.37 Pa/row. file:///G:/new folder/learn * /Professional knowledge PDF file/Professional library/Wet air cooler tube bundle structure improvement .files/36-1.gif Figure 2 Arrangement form of finned tubes 2 Pipe box groove pipe box is the main pressure component of the air cooler tube bundle. Foreign countries mainly refer to the ASME code for its design and manufacture, and the requirements are very strict. my country's GB/T 15386-94 "Air-cooled Heat Exchanger" requires that the welds of rectangular pipe boxes should be fully penetrated and fully fused, and should be double-sided or single-sided with a backing plate close to the base metal along the entire length of the weld root. Due to the special structure of the rectangular pipe box, it is difficult to perform double-sided welding. Therefore, single-sided welding is generally allowed, but full penetration must be ensured. Article [2] recommends the use of the groove form in Figure 3a. It is believed that this groove leaves sufficient gaps, and the backing plate is only spot welded on it. The deformation is small, the process is simple, the fusion after welding is good, and the quality is stable. However, in the process of manufacturing pipe boxes using this groove form, the author found that there is often slag inclusion between the backing plate and the base metal, and it is difficult to determine the specific location of the slag inclusion, which affects the quality of the weld. Therefore, the groove is changed to the form shown in Figure 3b, and the base is first made with argon arc welding, and then welded with automatic welding. The weld is beautiful and the non-destructive inspection pass rate is higher than that in Figure 3a. After a period of manufacturing practice, it was found that most cracks occurred in the argon arc welding base layer, which was caused by the too large thickness difference between the tube sheet or plugging plate and the cover plate. After many discussions, research and screening, and welding process evaluation, the groove form shown in Figure 3c was finally obtained. This kind of groove is not only simple to process, but also reduces the thickness difference between the tube plate or plug plate and the cover plate, thus avoiding weld cracks caused by the thickness difference. This groove can be directly welded by automatic welding. * * Improved work efficiency and weld appearance quality, pipe box welds are fully penetrated and well fused. Since its use, the quality has been stable, and after non-destructive inspection, more than 99% of its Grade I welds have been found. file:///G:/new folder/learn * /Professional knowledge PDF file/Professional library/Wet air cooler tube bundle structure improvement .files/36-2.gif Figure 3 Improvement of pipe box groove form 3 Fin tube support document [4] introduces a spacer box as shown in Figure 4a as a support member for the fin tubes of the wet air cooler tube bundle. It is believed that using the spacer box as a support member for the fin tubes can force the fin tubes all around and prevent the fin tubes from sagging. In fact, due to the accumulated error and corrosion of the distance box, the finned tube has a large deflection (up to 30 mm), which will exert an additional force on the expansion port of the tube and tube plate, causing damage to the expansion port of the tube and tube plate, causing device leakage, reduced efficiency, and even affecting the operation of the device. After research and discussion, the author designed the fin tube support as shown in Figure 4b, which absorbs the advantage of the distance box to force all sides of the fin tube, and the maximum sagging amount is only 3 mm. The support member is welded by a support plate and a sleeve, and the support plate is fixed to the beam with bolts. During processing, file:///G:/New Folder/Study on the support board * /Professional knowledge PDF file/Professional library/Wet air cooler tube bundle structure improvement .files/s-37.gif The hole is drilled together with the tube plate, and then expanded to file:///G:/New Folder/Study * /Professional knowledge PDF file/Professional library/Wet air cooler tube bundle structure improvement .files/s-37.gif , this can ensure the coaxial axis of the support plate hole and the tube plate hole to reduce the difficulty of pipe penetration. The sleeve is created by file:///G:/new folder/learn * /Professional knowledge PDF file/Professional library/Wet air cooler tube bundle structure improvement.files/o.gif It is processed from 60 mm×3.5 mm steel pipe. The length of the sleeve is suitable to support 10 pitch fins. Too much will increase the difficulty of pipe penetration, and too little will not provide good support. Generally, it is 30 mm. The fin tube support is a structure that cannot be replaced. In order to prevent corrosion from affecting the operation of the air cooler, the material of the support was changed from Q235-AF to 18-8 stainless steel. file:///G:/new folder/learn * /Professional knowledge PDF file/Professional library/Wet air cooler tube bundle structure improvement .files/37.gif Figure 4 Improved front and rear fin tube supports 4 Conclusion The wet air cooler tube bundle used in our company's lightweight workshop was put into use in February 1996 after the above improvements. After 5 months of operation, even in high-temperature weather above 30 °C, no safety valve tripping due to poor cooling effect was found, and no leakage accident occurred. Because the cooling effect of the air cooler is good, the outlet temperature of the ammonia compressor is low, and the outlet pressure is also low accordingly, which reduces the energy consumption of the ammonia compressor by 12% and the number of maintenance times of the ammonia compressor is also reduced by 1/3. It shows that the improvement of the air cooler tube bundle is successful, improving the manufacturing quality, heat transfer efficiency and service life, and achieving good economic benefits. Author's affiliation: Liu Chuanbao (Assistant Engineer at Maoming Petrochemical Company Machinery Factory (Maoming 525024)) References Editor-in-Chief of Lanzhou Petroleum Machinery Research Institute. Heat Exchanger, Volume 2. Beijing: Hydrocarbon Processing Press, 1990.297～326 Xie Weisheng. Progress in structural design of air cooler. Petrochemical Equipment, 1990, 19(5): 31～33 Xiao Qian, Shen Yujian. Integral rolling of bimetallic finned tubes. Chemical Refining Machinery, 1982, 11(5): 38～40 Cui Mingyuan, Xu Xinrong. Introduction to new structure air cooler. Chemical Refining Machinery, 1982, 11(5): 42～43 Compiled by Ma Yiwei, Liu Jifu, Qian Huiguang. Air Cooler. Beijing: Chemical Industry Press, 1982.8～50