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How does graphite heat exchanger exchange heat?
Release time:
2022-10-27
With the research of opaque graphite materials, countries have developed a variety of structures of heat exchangers, of which the tube heat exchanger is the first standardization, serialization and large-scale development of the damage in the tube graphite heat exchanger has a large proportion.
From the use of the situation, the domestic graphite heat exchanger used in the pressure pipe is mainly broken pipe; imports of heat exchangers used in the impregnated graphite pipe is mainly pipe rupture (longitudinal rupture). How to repair the heat exchanger damage is a difficult problem faced by phosphate production enterprises.
Graphite heat exchanger is divided into block hole type heat exchanger and column tube type heat exchanger. The main advantages of the block heat exchanger are: high strength, high intensity, high vapor pressure, high phosphate flow, high heat transfer rate, high heat transfer coefficient; the device has a large temperature difference, small size, not easy to damage. Disadvantages: once the leakage, it is difficult to find and repair. Advantages of tube heat exchanger: leakage, easy to find, easy to repair after damage to the pipe. Disadvantages: low pipe strength, steam pressure less than 0.15MPa; low flow rate of phosphoric acid, can only be controlled at 2m/s ~ 3m/s, the outlet temperature can only be controlled at 2 ~ 4. Large size. In phosphoric acid production, most manufacturers use tube heat exchangers.
The tubes are impregnated with graphitized tubes with a diameter of 50 7. After a second high temperature graphitization of graphite carbonized tubes, the tubes have many small gaps. After vacuum impregnation, the gaps are filled with impregnating resin, which has good impermeability. The tensile strength is higher than the pressure tube. High heat transfer efficiency due to high degree of graphitization. However, the bending strength (longitudinal) is slightly lower than that of the pressure tube. At present, most of the graphite heat exchangers manufactured abroad use this type of pipe.
Graphite heat exchanger structure for the floating head type, the upper (fixed tube plate) tube plate and lower (sliding tube plate) tube plate for 400mm thick impregnated graphite block. In order to prevent phosphoric acid flushing tube plate, in the acid end of the tube plate (sliding tube plate) on the paste a layer of 50 mm thick high-strength carbon fiber.
Domestic graphite heat exchanger using shaped graphite tube. Thermosetting resin (such as phenolic resin, furan resin) and artificial graphite powder as raw materials, mixed according to a certain ratio, into the extruder, compression molding, and then processed by 300 high temperature. The internal density of the pipe is high strength, but the heat transfer efficiency is low. The linear expansion coefficient is twice as much as that of impregnated graphite pipe. Impregnated graphite tube and resin extruded tube. The form of heat exchanger is floating head type. The thickness of the upper and lower tube plate is 400mm, made of thick impregnated graphite plate, and the anti-corrosion layer of the acid end (sliding tube plate) is 6mm thick 316L stainless steel plate. However, due to the 316L graphite plate is not tightly combined, there are gaps, where eddy currents are generated, resulting in serious damage to the lower tube plate. Later this plate was canceled. For nearly a year, the end of the repaired tube plate has not been washed away.
When repairing a graphite heat exchanger, how to quickly repair the heat exchanger on the spot presupposes how to quickly check the heat exchanger for leaks. After several years of operation, I have summarized the following three methods, as long as the cross use, can quickly improve the speed of leak detection.
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