Application of corrugated pipe technology in heat exchanger
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 pipe is easy to block, the cooling medium consumption. In 1999, we used the corrugated pipe technology of a company in Beijing, which was used in the production of the corrugated pipe heat exchanger (F = 500m 2). After more than a year of production trial run, the technology in water conservation, improve the effect of heat transfer, reduce the system pressure drop is obviously superior to the traditional technology and corrugated tube heat exchanger has the advantages of simple operation, small occupation of land, tube side is not easy to be blocked and other advantages. The author takes the heat exchanger as an example, introduces the corrugated pipe technology for reference. 1.1 theoretical analysis 1 Structure Characteristics
The difference between the corrugated tube heat exchanger and the common heat exchanger is that the corrugated pipe is replaced by a straight pipe. Corrugated pipe is made of <25mm * 0.8mm I 0Cr18N (i10T) tube through special equipment. Corrugated pipe and pipe welding. 1.2 possible problems
The wall thickness of the corrugated pipe is only 0.8 mm, and the 0.75mm is the most thin. We will naturally be on the stability, anti - corrosive and medium - resistant ability, etc.. In fact, this is also the problem of technical personnel must take into account. 1.3 technical analysis (1) working condition
The heat exchanger is the role of the ammonia gas into liquid ammonia with cooling water cooling. Process through the water pipe, shell side ventilation ammonia (ammonia), pressure P water = 0.3 m PA, gas (liquid) ammonia P ammonia = 1.3 m PA, inlet water temperature T water = 9.5 degrees, outlet water temperature T = 16 degrees, gas (liquid) average ammonia temperature TW = 37 degrees Celsius. (2) stability analysis
Known by the working conditions and structural characteristics, the corrugated pipe main failure stress from ammonia gas pressure and the pipe at both ends of the fixed temperature difference caused by thermal expansion of the pipe and conversion for axial compressive stress. So the lateral and axial direction of the corrugated pipe is influenced by both the external pressure P. The external pressure has little effect on the instability of the pipe. It can be directly used to discuss and design the instability of the corrugated tube only by the side of the lateral pressure cylinder. The failure of the tube may be when the external pressure reaches a certain value, the radial deflection of the tube wall increases sharply with the increase of the compressive stress, which is the pressure of the tube.
The corrugated pipe is processed by the light pipe blank. With information, the failure of the bellows is located at the end of the pipe body.
The corrugated tube length L = 4950 D, diameter (in light tube) 0= mm 25 mm, wall thickness n= 0.8 L, C mm as the critical length.
As C= 1.17D 1/2 0 (0/n D) mm = 1.17 x 25 (25/0.8) 1/2 = 163.5 L, L > C L, so it is a long cylinder. Known wall thickness, length and diameter, according to the principle of graph algorithm can calculate the corrugated tube in 37 DEG Xu with external pressure [P] for 21784 m PA (computational process slightly), [P] P > ammonia. Therefore, the corrugated pipe does not occur stability failure. (3) corrosion failure
For austenitic stainless steel corrugated pipe for heat pipe, Cl- stress corrosion is the main failure mode, the corrosion is generally first crack appears, after the rapid development, until failure. The temperature range of Cl- stress corrosion is generally 70 ~ 250, and the temperature is 37, so the possibility of Cl- stress corrosion is very small. Also CL is corrosion is one of the important factors, for the stainless steel material, its working environment in Cl - concentration should is less than or equal to 25 x 10 - 6, after testing, the Cl concentration in Juhua industrial water for 4 x 10 - 6, Cl - concentration ammonia gas and liquid ammonia can be neglected. Therefore, bellows in this condition is relatively safe. (4) erosion wear
As for the water sediment erosion, caused by the stainless steel pipe wall thinning, thus shortening the life of bellows. At present, there is still a great difficulty in the technical analysis, but it is the ideal of the research on the heating equipment of the Pipeline Transportation Bureau. The Bureau of water more sediment, a 9m diameter sedimentation tank, 5 months of operation, sand depth of 1.5m. But from November 1995 to January 1999, the board voted with the corrugated tube heat exchanger is running normal, never repair.
As a result of the corrugated pipe technology used in the field of chemical industry is not much, may also have other forms of failure. The author also is with the tubular heat exchanger were compared. 2 practical application effect
Corrugated tube heat exchanger due to the existence of the corrugated section, increased the heat exchange area, because the wall thickness is only 18 mm, the effect of heat transfer is better. The most important is because of the existence of the bellows, the flow of liquid flow in the time of constant turbulence, heat transfer effect is very good. On the other hand, due to the liquid turbulence, and constantly scouring the inner wall, so that the dirt is difficult to form, the corrugated pipe is almost no pipe blockage phenomenon.
In order to fully examine the use of corrugated tube heat exchanger, we stopped 4 vertical column tube heat exchangers in April 2000 and November 1999, and the cooling medium (cooling water) of the corrugated tube was reduced to 1/3 of the summer water consumption. Through a year of performance assessment, the basic completion of the original target: the annual savings of 600 t, save water 66 yuan, due to the pressure drop of gas ammonia, 600 kW - H, annual savings of about 31.3 yuan, sewage discharge standards, equipment running well.
At the beginning of the year 2000, the Juhua Group Corporation, the pressure vessel inspection station of bellows were detected: open the head, did not find column pipe is provided with a dirt clogging situation. On a random selection of six tube endoscopy (in depth, length of 1.6 ~ 1.8 m). The results show that the internal corrosion is not obvious, no corrosion pits or other serious corrosion, tube wave peak also found no accumulation of dirt. 3 the use of corrugated tube heat exchanger should pay attention to the problem
When using the corrugated tube heat exchanger, we must pay attention to the following points: (1) for the specific circumstances of the selection. Stainless steel corrugated tube heat exchanger on the condition of the more stringent requirements (especially for the concentration of Cl-), the pressure can not be too high, cold media media. (2) the seismic performance of the tube bundle of the corrugated tube bundle is poor, and the transportation and hoisting of the tube bundle shall not appear excessive collision. (3) the bellows heat exchanger is operated for 10 months or so should be stopped at a time, so that the corrugated pipe can be recovered. The shrinkage of the bellows is also conducive to the dirt off. (4) each plant cooling medium is different, the new corrugated tube heat exchanger is best able to install a filter in the inlet, and should be regularly opened head inspection.