Application of bellows technology in heat exchanger
化工企业普遍使用列管式换热器。该换热器价格低, 制造简单。缺点是换热效果欠佳, 管程易堵, 冷媒消耗大。1999 年, 我厂冰机系统技术改造中, 采用了北京某公司的波纹管技术, 将其合作单位制造的波纹管换热器(F = 500m 2) 用于生产。经过一年多的生产试运行, 该技术在节约水源, 提高换热效果, 降低系统压力降等方面明显优于传统技术, 且波纹管换热器具有操作简单,占地小, 管程不易堵等优点。贵州波纹管厂家以该台换热器为例, 介绍波纹管技术, 以供参考。
Chemical companies generally use tubular heat exchanger. The heat exchanger is low in price and simple in manufacture. The disadvantage is that the heat transfer effect is not good, the tube process is easy to plug, and the consumption of the cold medium is great. In 1999, during the technical transion of our plant's ice machine system, we adopted the bellows technology of a company in Beijing, and used the bellows heat exchanger made by our cooperation unit (F = 500m 2) to produce. After more than a year of production trial run, the technology in water conservation, improve the heat transfer effect, reduce the system pressure drop is obviously superior to the traditional technology, and the corrugated tube heat exchanger has the advantages of simple operation, small occupied area, the tube is not easy to block etc.. The Guizhou bellows manufacturers take the heat exchanger as an example to introduce the bellows technology for reference.
1 theoretical analysis
1.1 structure characteristics
波纹管换热器与普通换热器的区别在于以波纹管代替直管。波纹管是由<25mm ×0.8mm 的薄壁不锈钢(0Cr18N i10T i) 管通过专用设备加工而成。波纹管与直管采用搭焊接。
The difference between the bellows heat exchanger and the ordinary heat exchanger lies in the replacement of the straight pipe with the bellows. The bellows are made from a <25mm * 0.8mm thin-walled stainless steel (0Cr18N i10T I) tube through a special equipment. The bellows are welded with the straight pipe.
1.2 possible problems
波纹管壁厚只有0.8 mm , 最薄处为0.75mm。我们自然会对其稳定性, 抗腐蚀性及耐介质的冲刷能力等产生疑问。事实上, 这也是技术人员必须考虑到的问题。
The wall thickness of the bellows is only 0.8 mm, and the thinnest is 0.75mm. We will naturally question its stability, corrosion resistance and the ability to resist the erosion of the medium. In fact, this is a problem that the technicians must take into consideration.
1.3 technical analysis
(1) working conditions
该台波纹换热管的作用是用冷却水将气氨冷却成液氨。管程通水, 壳程通气氨(液氨) , 水压p 水= 0.3M Pa, 气(液) 氨p 氨= 1.3M Pa, 进口水温t水进= 9.5 ℃, 出口水温t水出= 16 ℃, 气(液) 氨平均温度tW = 37 ℃。
The function of the corrugated heat exchanger is to cool the ammonia into liquid ammonia with cooling water. The pipe passes through the water, the shell side aeration ammonia (liquid ammonia), the water pressure P water = 0.3M Pa, the gas (liquid) ammonia, P ammonia = 1.3M Pa, the inlet water temperature T water intake = 9.5 degrees, the outlet water temperature T water out = 16 degrees, the average temperature of gas (liquid) ammonia is tW = 37 degrees.
(2) stability analysis
由工况及结构特点可知, 波纹管主要失效破坏应力来自气氨的压力和由于管子两端固定温差引起管子热胀并转换为轴向压应力。所以波纹管的侧向和轴向同时受均布外压p 的作用。轴向外压对管子失稳影响不大。可以直接将波纹管仅受侧向外压圆筒的失稳作为主要失效问题进行讨论和设计。管子的失效可能是当外压达到一定值时,管壁的径向挠度随压缩应力的增加而急剧增大,直到管子被压瘪。
According to the working condition and structural characteristics, the main failure of bellows is the pressure of gas ammonia and the thermal expansion and transion to axial compressive stress due to the fixed temperature difference between two ends of the tube. So the lateral and axial direction of the bellows are simultaneously subjected to the effect of the uniform external pressure of P. The axial outward pressure has little effect on the instability of the tube. It is possible to discuss and design the failure of the bellows directly under the lateral pressure cylinder as the main failure problem. The failure of the tube may be that when the external pressure reaches a certain value, the radial deflection of the tube wall increases sharply with the increase of the compressive stress, until the tube is compressed.
The bellows of Guizhou bellows are made from light tube billets. It is introduced that the failure parts of the bellows are located in the straight pipe section at both ends of the bellows.
该波纹管长度L = 4950 mm , 直径(以光管计) D 0= 25 mm , 壁厚n= 0.8 mm , L C 为临界长度。
The length of the bellows is L = 4950 mm, the diameter is D 0= 25 mm, the thickness of the wall is n= 0.8 mm, and L C is the critical length.
由于L C= 1.17D 0 (D 0/n) 1/2 = 1.17×25 (25/0.8) 1/2 = 163.5 mm ,L > L C, 故为长圆筒。已知壁厚、管长及管径, 根据图算法原理, 可以算出波纹管在37 ℃下的许用外压〔p 〕为21784 M Pa(计算过程略) , 〔p 〕> p 氨, 故波纹管不会发生稳定失效。
Because L C= 1.17D 0 (D 0/n) 1/2 = 1.17 * 25 (25/0.8) 1/2 = 163.5 mm, L > L C, so it is a long cylinder. The known wall thickness, tube length and diameter, according to the principle of the algorithm can calculate the corrugated pipe at 37 DEG C under the allowable external pressure of P for 21784 M Pa (computational process slightly), P > P ammonia, the bellows stability failure does not occur.
(3) corrosion failure
对于奥氏体不锈钢波纹管换热管来说, Cl-应力腐蚀是失效的主要破坏形式, 腐蚀一般先以裂纹出现, 后快速向前发展, 直至失效。Cl- 应力腐蚀的温度范围一般为70～ 250 ℃, 这里的温度为37 ℃, 故发生Cl- 应力腐蚀的可能性极小。另外, Cl- 也是产生腐蚀的一个重要因素, 对于不锈钢材料, 其工作环境中Cl- 浓度应小于或等于25×10- 6, 经检测, 巨化工业用水中的Cl- 浓度为4×10- 6, 气氨和液氨中的Cl- 浓度可以忽略不计。所以, 波纹管在这种工况下是比较安全的。
For austenitic stainless steel bellows heat exchanger tubes, Cl- stress corrosion is the main form of failure. Corrosion usually starts with cracks and then develops rapidly until failure occurs. The temperature range of Cl- stress corrosion is generally 70~250 C, and the temperature is 37 C, so the possibility of Cl- stress corrosion is very small. In addition, Cl- is also an important factor for the corrosion of stainless steel materials, the concentration of Cl-, the working environment should be less than or equal to 25 x 10-6, after testing, the concentration of Cl- in industrial water Juhua is 4 * 10-6, Cl- concentration in liquid ammonia and ammonia gas can be ignored. Therefore, the bellows are safer in this condition.
(4) scour wear
至于水中泥沙的冲刷, 造成不锈钢管管壁减薄, 从而缩短波纹管的寿命。目前, 在技术分析上还存在很大的困难, 但据我们对廊房管道输送局供暖设备进行考察, 结果比较理想。该局水质含沙量较大, 一个9m 直径的沉淀槽, 运行5 个月, 积沙深达1.5m。但自1995 年11 月至1999 年1 月, 该局投用的波纹管换热器运行正常, 从未检修。
As for the erosion of sediment in the water, the wall of the stainless steel tube is thinned and the life of the bellows is shortened. At present, there are still great difficulties in the technical analysis, but according to the investigation of the heating equipment in the Pipeline Transportation Bureau of the corridor room, the result is ideal. The water quality of the bureau is large, a sedimentation tank with 9m diameter, running for 5 months, and the sediment is up to 1.5m. But from November 1995 to January 1999, the bellow heat exchanger operated by the bureau had run normally and had never been overhauled.
As the application of bellows technology in the chemical industry is not much, there may be other forms of failure. Guizhou corrugated pipe manufacturers also only with tubular heat exchanger were compared.
2 practical application effect
波纹管换热器由于波纹节的存在, 增大了换热面积, 由于壁厚只有018 mm , 换热效果较好。最为重要的是由于波纹节的存在, 液体流经管内时不断湍动, 换热效果很好。另一方面, 由于液体湍流, 不断冲刷内壁, 使污垢很难形成, 波纹管几乎不会出现管堵现象。
The heat exchange area of the bellows heat exchanger is increased because of the presence of the bellows. The heat transfer effect is better because the thickness of the wall is only 018 mm. The most important thing is that because of the presence of the bellows, the liquid flow is constantly turbulent in the tube, and the heat transfer effect is very good. On the other hand, as a result of liquid turbulence, continuous erosion of the inner wall makes the dirt difficult to form, and the bellows will hardly appear in pipe plugging.
为充分考查波纹管换热器的使用情况, 我们在1999 年11 月至2000 年4 月, 停掉4 台立式列管换热器, 且波纹管的冷媒(冷却水) 减至夏季用水量的1/3, 结果生产基本稳定。通过一年的性能考核, 基本完成了当初预计目标: 年节约水量600万t, 节约水费66 万元, 由于气氨总管压力下降,节电600 kW ·h, 年节约电费约31.3 万元, 排污达标, 设备运行情况良好。
In order to fully examine the usage of bellows heat exchangers, we stopped 4 vertical tube heat exchangers from November 1999 to April 2000, and the cooling medium (cooling water) of bellows was reduced to 1/3 of summer water consumption, and the production was basically stable. Through a year's performance assessment, we basically completed the original target: annual water saving 6 million T, and water saving 660 thousand yuan. Because of the pressure drop of gas ammonia pipe, the electricity saving is 600 kW H. Annual electricity saving is about 313 thousand yuan, sewage discharge is up to standard, and the equipment runs well.
2000 年年初, 巨化集团公司压力容器检测站对波纹管进行了检测: 打开封头时, 未发现列管中有污物堵塞情况。对任意抽取的6 根管进行内窥镜检查(深入长度为1.6～ 1.8 m ) , 结果表明内壁腐蚀情况不明显, 未见腐蚀坑或其他严重腐蚀现象, 管波峰内也未发现污物积存。
In early 2000, Juhua Group Corporation, pressure vessel inspection station of the bellows were detected: open the head, did not find the tube in case of clogging dirt. An endoscopy (6 to 1.8 m) was carried out for any of the extracted tubes. The results showed that the corrosion of the inner wall was not obvious, no corrosive pits or other serious corrosion occurred, and no accumulation of dirt was found in the peak of the pipe wave. It was also found that there was no corrosion in the top of the tubes. The results showed that there was no corrosion in the top of the tubes. The results showed that there was no corrosion in the top of the tubes. There was no accumulation of pollutants in the pipes. It was also found that there was no corrosion in the top of the tubes. The results showed that there was no corrosion in the top of the tubes. There was no accumulation of pollutants in the pipes. The
3 problems to be paid attention to by using bellows heat exchanger
When using a bellows heat exchanger, be sure to pay attention to the following points:
(1) 针对具体情况选取。不锈钢波纹管换热器对工况要求较严(特别是对Cl- 的浓度) , 冷媒介质的压力也不能太高。
(1) the selection of specific circumstances. The stainless steel bellows heat exchanger is strict with the working conditions (especially the concentration of Cl-), and the pressure of the medium is not too high.
(2) 波纹管换热器管束的抗震性较差, 运输及吊装时, 不得出现过度碰撞。
(2) the aseismic property of the bellows heat exchanger tube bundle is poor, and no excessive collision may occur when transportation and hoisting are transported and hoisting.
(3) 波纹管换热器运行10 个月左右应停车一次, 便于波纹管收缩复原。波纹管的收缩也有利于污垢的剥落。
(3) the bellows heat exchanger should be stopped for about 10 months to facilitate the contraction of the bellows. The contraction of the bellows is also beneficial to the exfoliation of the dirt.
(4) 每个厂冷媒清洁程度不同, 新上的波纹管换热器最好能在进口加装一台过滤设备, 同时应定期打开封头检查
(4) the cleanliness of the refrigerants in each plant is different. The new bellows heat exchanger should be able to install a filter in the inlet and open the head check at regular intervals.