[Shell and Tube Heat Exchanger]Shell and Tube Heat Exchanger Type Shell and Tube Heat Exchanger Structure
Shell and Tube Heat Exchanger Structure
Shell and tube heat exchangers consist of shells, heat transfer tube bundles, tube sheets, baffles (baffles) and tube boxes. The shell is mostly cylindrical, with tube bundles installed inside, and both ends of the tube bundles are fixed on the tube sheet. Two fluids, hot and cold, for heat exchange, one flows inside the tube, called the tube side fluid; the other flows outside the tube, called the shell side fluid. In order to improve the heat transfer coefficient of the fluid outside the tube, several baffles are usually installed in the shell. The baffle can increase the velocity of the fluid on the shell side, forcing the fluid to pass through the tube bundle several times laterally according to the prescribed path, and enhance the degree of fluid turbulence. The heat exchange tubes can be arranged in equilateral triangles or squares on the tube sheet. The equilateral triangle arrangement is compact, the fluid outside the tube has a high degree of turbulence, and the heat transfer coefficient is large; the square arrangement is convenient for cleaning outside the tube, and is suitable for fluids that are prone to scaling.
Each time the fluid passes through the tube bundle is called a tube pass; each time it passes through the shell is called a shell pass. In order to improve the fluid velocity in the pipe, partitions can be set in the pipe boxes at both ends to divide all the pipes into several groups. In this way, the fluid only passes through part of the tubes at a time, so it goes back and forth in the tube bundle many times, which is called multi-tube pass. Similarly, in order to increase the flow velocity outside the pipe, longitudinal baffles can also be installed in the shell to force the fluid to pass through the shell space multiple times, which is called multi-shell pass. Multi-tube pass and multi-shell pass can be used together.
Shell and tube heat exchangers (also known as tube condensers) are divided into carbon steel shell and tube heat exchangers, stainless steel shell and tube heat exchangers and carbon steel and stainless steel mixed columns according to their materials. There are three types of tubular heat exchangers, which are divided into fixed tube sheet type, floating head type and U-shaped tubular heat exchanger according to the form. Can be customized according to user needs.
Classification of shell and tube heat exchangers
Due to the different temperatures of the fluid inside and outside the tube, the shell of the heat exchanger is The temperature of the tube bundle is also different. If the two temperatures are very different, there will be a lot of thermal stress in the heat exchanger, causing the tubes to bend, break, or pull off the tube sheet. Therefore, when the temperature difference between the tube bundle and the shell exceeds 50°C, appropriate compensation measures should be taken to eliminate or reduce thermal stress. According to the compensation measures adopted, shell and tube heat exchangers can be divided into the following main types:
①The tube sheets at both ends of the tube bundle of the fixed tube sheet heat exchanger are integrated with the shell, and the structure is simple , but it is only suitable for heat exchange operations when the temperature difference between the hot and cold fluids is not large, and the shell side does not need mechanical cleaning. When the temperature difference is slightly larger and the shell side pressure is not too high, an elastic compensation ring can be installed on the shell to reduce thermal stress.
②The tube sheet at one end of the tube bundle of the floating head heat exchanger can float freely, completely eliminating thermal stress; and the entire tube bundle can be pulled out from the shell, which is convenient for mechanical cleaning and maintenance. The floating head heat exchanger is widely used, but the structure is more complicated and the cost is higher.
③Each heat exchange tube of the U-shaped tube heat exchanger is bent into a U shape, and the two ends are fixed on the same tube plate and the upper and lower areas respectively. . This kind of heat exchanger completely eliminates thermal stress, the structure is simpler than the floating head type, but the tube side is not easy to clean.
④ Eddy current film heat exchanger The eddy current film heat exchanger adopts the latest eddy current film heat transfer technology, which increases the heat transfer effect by changing the fluid motion state. When the medium passes through the surface of the vortex tube, the strong Flush the surface of the tube, thereby improving the heat exchange efficiency. Up to 10000W/m2℃. At the same time, this structure realizes the functions of corrosion resistance, high temperature resistance, high pressure resistance and anti-scaling. The fluid passages of other types of heat exchangers are in the form of flow in a fixed direction, and a circumflow is formed on the surface of the heat exchange tube, and the convective heat transfer coefficient is reduced.
The data shows that the biggest feature of eddy current thermal film heat exchanger is the unity of economy and safety. Due to the consideration of the flow relationship between the heat exchange tubes and between the heat exchange tubes and the shell, the turbulent flow is no longer forced by the baffle plate, but the alternating vortex flow is naturally induced between the heat exchange tubes, and the On the premise of ensuring that the heat exchange tubes do not rub against each other, the vibration should be maintained. The rigidity and flexibility of the heat exchange tubes are good, and they will not collide with each other, which not only overcomes the problem of damage caused by the collision between the floating coil heat exchangers, but also avoids the problem of easy scaling of ordinary shell-and-tube heat exchangers.
Shell and tube heat exchangers are general-purpose process equipment for heat exchange operations. Widely used in chemical, petroleum, petrochemical, electric power, light industry, metallurgy, atomic energy, shipbuilding, aviation, heating and other industrial sectors. Especially in petroleum refining and chemical processing equipment, it occupies an extremely important position. Type of heat exchanger.
Key points for shell and tube heat exchanger selection
1) According to the known flow of cold and hot fluid, initial and final temperature and specific heat capacity of fluid Determine the required heat transfer area. To preliminarily estimate the heat exchange area, generally assume the heat transfer coefficient first, determine the structure of the heat exchanger, and then check the K value of the heat transfer coefficient.
2) When choosing a heat exchanger, pay attention to the pressure level, operating temperature, and connection conditions of the interface. Under the premise that the pressure drop and the installation conditions allow, the shell and tube heat exchanger should be selected with a small diameter and an elongated type, which is conducive to improving the heat exchange.
3), the pressure drop of the heat exchanger should not be too large, generally controlled between 0.01 ~ 0.05MPa;
4), the flow rate should consider the fluid viscosity, the viscosity of the large The flow rate should be less than 0.5~1.0m/s; the flow rate in the general fluid pipe should be 0.4~1.0m/s; the fluid that is easy to scale should be 0.8~1.2m/s.
5) A filter should be installed before the high temperature water enters the heat exchanger.
6) The combined results of the single processing and configuration of the heat exchangers in the heat exchange station should meet the total heating load and regulation requirements of the heat exchange station. On the premise of meeting the user’s heat load regulation requirements, the number of heat exchangers in the same heating coefficient should not be less than 2, and should not be more than 5.
Key points of shell and tube heat exchanger installation
1) The heat exchanger should be hydraulically tested at 1.5 times the maximum working pressure. It should not be lower than the steam supply pressure plus 0.3MPa; the hot water part should not be lower than 0.4MPa. Under the test pressure, keep the pressure without drop for 10min.
2) The front end of the shell-and-tube heat exchanger should have space for extracting and unloading the tube bundle, that is, the distance between its head and the wall or roof should not be less than the length of the heat exchanger, and the clear width of the equipment operation channel It should not be less than 0.8m.
3) The installation height of various valves and instruments should be easy to operate and observe.
4) The vertical clear distance from the highest point of the upper part of the heater (generally refers to the safety valve) to the lowest point of the building structure shall meet the requirements of installation and testing, and shall not be less than 0.2m.
