Heat exchanger can be broadly divided into
Shell And Tube Heat Exchanger and plate heat exchanger and so on according to the structure. Among them, the shell and tube type has a long history, is the most widely used type of heat exchanger, has the advantages of easy manufacturing, low production cost, wide range of materials, easy to clean, adaptable, large capacity, reliable, adaptable to high temperature and high pressure.
I. Fixed tube and plate heat exchanger
Fixed tube and plate heat exchanger tube plate at both ends, the use of welding methods and shell connection fixed
Advantages:
1. simple and compact structure, in the same shell diameter, the largest number of rows of tubes, the minimum bypass.
2. each heat exchanger tube can be replaced, and easy to clean the tube.
3. Compared with other shell and tube
Heat Exchangers, the tube plate is the thinnest, low cost.
Disadvantages.
1. Shell process cannot be mechanically cleaned;
2. when the temperature difference between the heat exchanger tube and the shell is large (greater than 50 ℃) when the temperature stress, the need to set up expansion joints in the shell, and thus the shell pressure by the expansion joints can not be too high strength limitations.
Fixed tube and plate heat exchanger for the shell side of the fluid is clean and not easy to scale, the temperature difference between the two fluids is not large or large temperature difference but the shell pressure is not high occasions. Because of such heat exchangers have concentrated the advantages of shell and tube heat exchanger, so it is widely used.
II. Floating head type heat exchanger
Floating head type heat exchanger for fixed tube and plate heat exchanger defects in the structure of the improvement, the two ends of the tube plate only one end of the tube plate and shell fixed, while the other end of the tube plate can move freely in the shell, the end is called floating head.
Advantages:
1. the shell and tube bundle is free of thermal expansion, so when the temperature difference between the two media is large, the temperature difference between the tube bundle and the shell does not produce stress.
2. Floating head end is designed as a detachable structure, so that the tube bundle can be easily inserted or withdrawn (also designed as non-detachable), so as to provide a convenient maintenance, cleaning.
Disadvantages:
1. the small cap on the floating head end can not know the leakage situation during operation, so special attention should be paid to its sealing during installation.
2. Complex structure, bulky, the cost is about 20% higher than the fixed tube plate type, material consumption.
3. the gap between the tube bundle and the shell is large, so the harmful E flow path is more serious, in the design should try to avoid this short circuit.
4. The pressure in the shell stroke is limited by the sealing of the sliding contact surfaces.
Floating head type heat exchanger is suitable for the temperature difference between the shell and tube wall is large, or easy to corrode and easy to scale the occasion.
III.
U-Tube Heat Exchanger U-tube Heat Exchanger has only one tube plate, the tube is bent into a U-shape, and the two ends of the tube are fixed on the same tube plate.
Advantages:
1. Because the shell and tube are separated, the tube bundle can be freely expanded and contracted, and will not produce thermal stress due to the temperature difference between the tube wall and shell wall, and has good thermal compensation performance;
2. the tube course is a double-tube course, the process is longer, the flow rate is higher, the heat transfer performance is good, and the pressure capacity is strong;
3. U-tube heat exchanger has only one tube plate, and no floating head, so the structure is simple, the cost is cheaper than other heat exchangers;
4. The tube bundle can be withdrawn from the shell, and the outside of the tube is easy to clean.
Disadvantages:
1. it is difficult to clean inside the tube, so the fluid inside the tube must be clean and not easy to scale the material;
2. due to the structure of the heat transfer tube type relationship, the replacement of the tube in addition to the outer tube, most of the internal tube can not be replaced;
3. there is a gap in the center part of the tube bundle, so the fluid is easy to go short-circuit, affecting the heat transfer effect, so there is usually a dummy tube or intermediate baffle to reduce the flow of this dead zone;
4. The tube plate arranged on the tube is less, the structure is not compact;
5. the curvature of the U-tube part of the curvature is different, the length of the tube is not the same, so the distribution of materials is not as uniform as the fixed tube-plate heat exchanger;
6. After the tube is blocked due to leakage, it will cause the loss of heat transfer area;
U-tube heat exchanger, generally used in the case of high temperature and high pressure. Especially when used in the case of high pressure, the wall thickness in the bend section should be thicker to make up for the thinning of the tube wall after the bend.
Ⅳ. Stuffing box heat exchanger
Stuffing box type heat exchanger tube plate also has only one end fixed with the shell, the other end of the packing box seal.
Advantages:
1. has the advantages of floating head type heat exchanger, but also to overcome the shortcomings of the fixed heat exchanger, the structure is simpler than the floating head, easy to manufacture, easy to repair and clean. 2;
2. tube bundle can also be free to expand, so do not need to consider due to the tube wall, shell wall temperature difference caused by thermal stress, and the tube and shell process can be cleaned, processing and manufacturing than the floating head is convenient, and less expensive.
Disadvantages:
1. packing seal is easy to leak, so the shell process pressure can not be too high, generally less than 4.0MPa;
2. not easy to use in the shell process for volatile, flammable, explosive and toxic media occasions.
Packing box type heat exchanger for the tube, shell wall temperature difference or medium easy to scale, need to be cleaned often and the pressure is not high occasions. For some serious corrosion, temperature difference and often have to replace the tube cooler, the use of packing box type heat exchanger than floating head or fixed heat exchanger is much superior. Currently used packing box type heat exchanger are smaller, used in the diameter of 700mm or less, large diameter packing box type heat exchanger used very little, especially in the operation of the pressure and temperature under the conditions of the higher less.
Source: Reprint
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