Application of spiral threaded tube heat exchanger in the production of API

China's APIs have developed rapidly and have become the world's largest pharmaceutical producers and exporters. At present, China is facing the golden development period of pharmaceutical raw materials and intermediates. “Breakthrough, development and innovation” is the development trend of the API industry. How to achieve energy conservation and consumption reduction is particularly important to improve the competitiveness of enterprises. The condensers that play a decisive role in the recovery of the solvent have an important influence on this. At present, there are many types of heat exchangers used in China, such as tube type, plate type, tube plate type, etc. Most of the heat exchangers are not working. Symmetrical flow heat transfer, that is, the flow of two fluids through the heat exchanger is different, which requires two different heat exchange areas. The design mechanism of the plate heat exchanger is symmetric flow heat transfer, which cannot provide a heat exchange area of ​​different sizes for the fluid. The world's *Spiral threaded tube JAD heat exchanger was developed in 1988 in Poland SECESPOL Group. The heat exchanger was designed to deal with this asymmetric flow heat transfer on the market, deliberately making the heat exchange areas on both sides different. To meet the requirements of complex working conditions, this paper introduces the characteristics and application of SECESPOL heat exchanger.

1. Structure and performance characteristics 1.1 Structural characteristics Compared with the traditional tube-and-tube heat exchange tube bundle, each heat exchange tube of the SECESPOL heat exchanger is uniformly wound in the shell according to a certain rule in a spiral structure. On the one hand, this structure lengthens the length of the heat exchange tube and the heat transfer is sufficient; on the other hand, the flow state of the fluid is greatly changed, the turbulence effect is enhanced, and heat transfer is enhanced. At the same time, the spirally wound elastic tube bundle design can effectively eliminate various stresses such as turbulent chattering and thermal stress of the heat exchanger, and achieve self-cancellation of stress. Figure 1 is a partial cross-sectional view of a SECESPOL heat exchanger.

1.2 Performance characteristics 1.2.1 High efficiency heat exchange, energy saving spiral tube heat exchanger layer and layer between the heat exchange tube reverse winding, this unique winding structure design, greatly change the flow state of the fluid, formed in the shell The strong turbulence effect, due to the strengthening effect of the spiral flow in the tube, the heat transfer film coefficient of the tube process is also increased, thereby increasing the overall heat transfer coefficient. Under the condition of steam-water exchange such as steam heating water, the heat transfer coefficient k of the conventional shell-and-tube heat exchanger is generally 6000w/(m2·°C). The SECESPOL heat exchanger has a heat transfer coefficient k of up to 14,000 w/(m·2 °C), which is more than three times that of a conventional shell-and-tube heat exchanger.

Because of its unique spiral winding structure, the heat exchange tube bundle is extended to a length of 4 to 6 times of the length of the casing. When heated, the heat medium can stay in the heat exchange tube for a long time, and the cooled medium can be cooled during condensation. It is more complete, without secondary heat exchange, ensuring full exchange of heat, improving energy utilization and saving energy.

The diameter of the threaded elastic tube is 8mm, 10mm, 12mm, and the wall thickness is only 0.6mm.

1.2.2 The unique 100° connection heat exchanger has the 100° connection between the two ends of the two flanges at the same end. It can make the heat exchanger participate in the heat exchange without leaving a dead angle. The fluid will automatically flush the pipeline and reduce the tendency of blockage. It cushions the fluid and reduces noise. Due to its unique 100° connection and spiral thread structure, unique surface treatment process and countercurrent heat transfer between the two sides of the medium, it has a high flow rate (the flow rate of the shell side water side can be as high as 5.5m/s during the steam-water heat exchange process). ), small temperature gradient and small fouling coefficient. The internal structure design takes into account the acoustic resonance permitting criteria (Eisinger criterion and Bevins criterion), which effectively suppresses the phenomenon of acoustic standing wave vibration. Zui greatly reduces the running noise, and the heat exchanger can operate under low noise conditions.

1.2.3 High temperature resistant, high pressure SECESPOL heat exchanger heat exchanger tube bundle and shell are all made of stainless steel, with a uniform expansion coefficient, will not cause deformation of the heat exchanger due to pressure and temperature instability. The heat exchanger is resistant to high temperature and high pressure, and there is no need to install a temperature reducing and pressure reducing device. The high temperature resistance is 400 ° C and the pressure is 2.0 MPa. Using the principle of Owen (OWEN) turbulent buffeting frequency criterion, the heat transfer tube bundle zui small gap design is adopted, and the spiral winding elastic tube bundle method effectively eliminates the turbulent chattering thermal stress phenomenon and prolongs the service life of the heat exchanger.

1.2.4 Compact structure, compact size The spiral winding method is compact, and it can meet the same heat load conditions. The SECESPOL heat exchanger is only about 1/10 of the volume of the traditional shell-and-tube heat exchanger, which has a small footprint and saves space. At the same time, because of its small size and light weight, it is easier to install and disassemble, reducing installation costs.

1.2.5 Low tendency to scale and easy maintenance Due to the tube winding design of the SECESPOL heat exchanger, the fluid in the tube passes through the spiral, which reduces the possibility of wall adhesion and the tendency of fouling. The shell side fluid crosses the tube transversely across the tube. Continuous separation and confluence between adjacent tubes and layers to strengthen the turbulence of the shell fluid, and reduce the probability of sedimentation at the same flow rate, ensuring long-term, high-load operation of the equipment.

The fouling tendency of SECESPOL heat exchanger is very low, but it does not mean no scaling. Once the fouling phenomenon occurs, the cleaning is also very simple due to the relatively small volume of the equipment. Usually, it is chemically cleaned and soaked with the prepared low-concentration dilute nitric acid. ~3h can be, the maintenance cost is very low.

2 Application Due to the advanced heat transfer technology advantages of SECESPOL heat exchanger, it is widely used in the field of recycling and condensation of domestic pharmaceutical raw material solvent.

Application of atmospheric distillation of methylene chloride in a large pharmaceutical factory in Northeast China: SECESPOL heat exchanger uses 25/30 °C ambient temperature circulating water to cool, while conventional heat exchanger requires secondary condensation, using SECESPOL heat exchange The motor power during operation is smaller than that of the conventional heat exchanger, because the use of secondary condensation requires the addition of a motor, and the cost of the freezer is a one-time investment, reducing the one-time investment.

The application of the process of distilling toluene in the raw material medicine process of a pharmaceutical group in Liaocheng, Shandong: the original process toluene vapor is condensed and cooled from 110 °C to 45 °C, using secondary condensation, the heat exchange area of ​​the first-stage condenser is 42 m2, and the heat exchange area of ​​the secondary cooler 28m2. After adopting the SECESPOL condenser, a JADX9.88 was selected, the heat exchange area was only 10.8 m2, and the condensation temperature was 3 °C lower than the original process, and the actual toluene recovery rate was increased by 2%. The volume of the heat exchanger is 1/20 of the original equipment, the equipment investment is reduced by 50%, and the installation cost is reduced by 80%.

3 Conclusion SECESPOL spiral-wound tubular heat exchanger is a high-efficiency heat exchanger with a small footprint. It can not only effectively reduce investment in new installations, especially in the reconstruction and expansion of old equipment, but the compact spiral winding structure is more conducive to equipment. Plane layout. The spiral wound tubular heat exchanger has the characteristics of sufficient heat exchange and small difference between cold and hot, which not only saves energy, but also optimizes the system and process, and has good energy saving effect.

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