Fluorine plastic low temperature heat exchanger is a small diameter fluorine plastic hose as a heat exchanger tube bundle. Commonly used fluoroplastics are polytetrafluoroethylene (PTFE,F4), polytetrafluoroethylene (PEP,F46) and meltable polytetrafluoroethylene (PFA). It is a heat exchanger that can be highly resistant to corrosion at higher operating temperatures and pressures. Due to the difference in physical and chemical properties between fluoroplastics and metal materials, it is gradually being valued and applied in the field of energy saving. Through continuous improvement, fluorine plastic heat exchanger will be more and more widely used.

Physical and Chemical Properties of Fluoroplastics

The molecular structure of fluoroplastics determines its good heat resistance and cold resistance. Its long-term use temperature range is wide, up to -192 ℃ ~ 260 ℃, and it can be used at 300 ℃ in the short term. It is still soft below -100 ℃. After 240h aging at 250 ℃, its mechanical properties are basically unchanged. Fluoroplastics are chemically inert materials that can work in almost all media except elemental fluorine, molten alkali metals, chlorine trifluoride, uranium hexafluoride, and perfluorinated kerosene at high temperatures. In addition, fluoroplastics are one of the materials with the lowest surface free energy among known solid materials, and almost all materials cannot adhere to their surfaces, soRecycling fluoroplasticsWhen used as a heat exchanger, the surface of the tube wall is basically free of fouling. At the same time, because its surface molecules have little attraction to other molecules, the friction coefficient is very small (the ratio of static and dynamic friction coefficient to steel is 0.04), and the flow friction resistance of the fluid is also small.

From the calculation formula of the heat transfer coefficient, it can be seen that when the influence of pipe wall fouling is not considered, the thermal resistance of the pipe wall determines the limit of the heat transfer coefficient, that is, no matter what method is taken to strengthen the convective heat transfer of the fluid on both sides of the pipe wall, the heat transfer coefficient is finally determined by the thickness of the pipe wall. The thermal conductivity of fluoroplastics is dozens of times smaller than that of metals, and the large thermal resistance is the main defect of fluoroplastics. Therefore, the fluorine plastic low-temperature heat exchanger is designed with thin-walled small-diameter tubes, and a large number of small-diameter tubes are used in the recovery of fluorine plastic process, which overcomes the shortcomings of low thermal conductivity of fluorine plastic, and makes it a reality for fluorine plastic heat exchanger to replace metal heat exchanger in high corrosion environment. Although the initial heat transfer coefficient of the metal heat exchanger is larger than that of the fluoroplastic heat exchanger, the thickness of the masonry layer of the heat exchange tube bundle gradually increases with the use of the metal heat exchanger over time, resulting in a decrease in the heat transfer coefficient. The fluoroplastic heat exchange tube wall is smooth and not easy to scale, and the heat exchange tube bundle expands and contracts along the axial and radial directions under the action of fluid temperature changes during operation. It is beneficial to remove dirt and improve heat exchange. After running for a period of time, the difference between the two heat transfer coefficients is reduced. In the long run, the fluorine plastic heat exchanger has strong competitiveness.

Structure type

The main part of the fluoroplastic cryogenic heat exchanger is a tube bundle composed of many small-diameter thin-walled fluoroplastic heat transfer hoses. There are a variety of commonly used pipe specifications, with a wall thickness of about 1mm. Each tube bundle contains thousands of tubes, which are suspended and separated by multiple partitions. Depending on the heat exchange area, one or more tube bundles may be provided. The tube bundle support components are coated with stainless steel and PTFE for corrosion protection, the fasteners are stainless steel anti-corrosion bolts, and the inner wall of the heat exchanger shell is lined with fluorine plastic plate for corrosion protection.

Practical Application of Fluoroplastic Heat Exchanger

Small-diameter fluoroplastic hoses with a wall thickness of less than 1mm can work safely for a long time under a pressure of ≤ 1.0MPa. Fluoroplastic low-temperature heat exchanger is used to heat condensate and heat network return water. Since the condensate pressure is greater than the safe working pressure of fluoroplastic hose, indirect heat exchange is adopted in the system, I .e. the flue gas exchanges heat with the closed circulating water in the low-temperature heat exchanger. The closed circulating water absorbing the waste heat of the flue gas performs secondary heat exchange on the condensate (or heat network return water) through the plate heat exchanger, and then transfers the heat to the condensate (or heat.

Operation adjustment

The stability of the operating parameters of the fluoroplastic heat exchanger is closely related to the change of the external load and the change of the internal factors of the heat exchanger. As long as any one of the above factors changes, will affect the stability and safety of its operation, therefore, the heat exchanger must be a series of control and adjustment, so that the parameters of the heat exchanger and the external changes or internal changes to adapt, so that can achieve safe and economic operation. When the heat exchanger is running, the pressure, water temperature and water volume must be controlled to fluctuate within the allowable range to ensure safe and economical water supply and meet the needs. At the same time, the heat exchanger must be flushed every day to improve the heat exchange efficiency.

Water quantity control of flue gas heat exchanger

The flue gas heat exchanger adopts continuous water intake and variable frequency water pump, and the amount of water intake is adjusted by variable frequency water pump to maintain the normal water supply to adapt to the water output required by the heat exchanger load.

Pressure Control of Heat Exchanger

When the fluoroplastic heat exchanger is running, the water pressure should be kept stable, and the water pressure adjustment is automatically adjusted by the system water supply valve. When the water pressure of the heat exchanger is lower than the specified working pressure, it cannot meet the requirements of the production process and cannot achieve the best effect; when the pressure of the heat exchanger exceeds the specified maximum allowable working pressure, it will cause an overpressure accident. The reasons for the change of water pressure are as follows:

a. Changes in external load. It mainly reflects the contradiction between the thermal power of the flue gas heat exchanger and the external heat load. When the flue gas heat exchanger is in operation, the hot water generated in the heating surface continuously enters the outlet water chamber and leaves continuously. When the hot water flowing out of the outlet water chamber of the heating surface is more than the external demand, the water pressure of the heat exchanger will rise; on the contrary, the water pressure of the heat exchanger will drop.

B. The change of the inlet flue gas volume and flue gas temperature of the heat exchanger will directly lead to the change of the thermal power of the heat exchanger. The output of the heat exchanger is hot water, and the temperature change is changed with the change of the pressure value of the heat exchanger, and the temperature control is the pressure control. Therefore, the heat exchanger takes the heat exchange at the heat exchange end as the main adjustment, and adapts to the parameter change of the flue gas heat exchanger side by changing the flow rate on the user side.

The new type of fluorine plastic low temperature heat exchanger, the heat exchange tube adopts fluorine plastic small diameter thin wall hose, the surface is smooth and not easy to scale, has strong corrosion resistance, can effectively prevent low temperature acid corrosion, can maximize the use of flue gas waste heat, improve the economy of the unit. Although the cost is higher than the metal low temperature heat exchanger, but the use of flue gas waste heat more, long life, its potential capacity is gradually being recycled fluorine plastic manufacturers attention, with the design and manufacture of fluorine plastic heat exchanger more reasonable, and the correct use and careful maintenance and management, fluorine plastic heat exchanger will be more and more widely used.

This article comes from:www.tflpfa.com

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