(1) slow pump caustic soda evaporator can be classified as evaporative crystallizer recycling type crystallizer. Flow through the circulating pump, pipeline pump contains 6% ~ l0% (mass fraction), and even higher salt crystals. The rotating impeller has a crushing effect on the crystal and induces the formation of secondary nuclei. According to the theory of non-elastic crystal collision, the energy of crystal breaking is directly proportional to the m-th power of the crystal relative to the impeller speed. The index m is related to the characteristics of the crystal, the crystal size distribution and the concentration of the crystal slurry. In addition, the flow from the axial pump Q and impeller diameter and speed of the relationship, that is, Q = KDs know, under the premise of constant flow, such as the impeller diameter increased twice, then the pump speed can be reduced to 1 / 8, tip circumference speed reduced to 1/4. Therefore, according to the crystallization process requirements, should be used slow circulation pump. In addition, the slow pump can also reduce the impeller wear and prolong the service life. Slow pump necessary NPSH is small, good anti-cavitation performance. Today's latest valid order information free to send! Morning latest buyers information free to send! Punch grab Rob here! (2) Head-down characteristic curve requiring steep descent When the circulation resistance increases due to salt formation in the late stage of the evaporator operation, the decreasing characteristic of the head characteristic curve of the steep drop makes the decrease of the flow rate small, that is, the decrease of the heat transfer coefficient is slow, Beneficial to the evaporation process. (3) Reasonable match between evaporator and circulating pump The evaporator designer should correctly calculate the circulating resistance of evaporator alkali liquor, and put forward the exact lift to ensure the circulating pump operate at high efficiency area for a long time. The circulating pump should also have the flow regulating means Variable speed, variable axial flow pump blade installation angle) to meet different user requirements, ease of production to adjust operating parameters. Requirements in the design of the evaporator, should avoid harmful vortex into the pump; Tangential circulation of the evaporation chamber should be changed to the axial center of the feed; pure tangential should be transformed into a partial tangential; Vortex or deflector; positive cycle evaporator to reverse cycle. In order to reduce the thermal expansion force acting on the inlet and outlet tubes of the circulating pump, the thermal compensation of the evaporator should be considered. The traditional method of thermal compensation is to set up a circulating expansion pump import and export of wave expansion joint. Advanced thermal compensation structure is the choice of suspended circulating pump or spring-based circulating pump, the two circulating pumps in large-scale forced circulation evaporator have been used. (4) high reliability diaphragm pump, pump evaporation pump can not set the standby circulation pump, circulation pump requires continuous operation of a single machine, such as failure will lead to the entire evaporator shutdown. Therefore, it is required that the whole machine has good reliability. 2. Structural characteristics (1) Cantilever type and general water axial flow pump is different, the slurry can not be transported in the bearing. China's salt evaporation industry early circulation pump for the vast majority of double-support axial-flow pump, u-shaped pump for the curved tube; and cantilever axial-flow pump body is 90. Elbow type, the former is the amount of corrosion-resistant material 1.5 to 1.7 times the latter, and the number of the latter two seals. At present, the domestic evaporative circulation pump has been widely used cantilever structure. (2) Shaft Seal In view of the harsh operating conditions of the shaft seal of caustic soda evaporation circulating pump, the idea of ​​designing a shaft seal is to change the condition of the sealing medium from a highly corrosive suspension with high temperature and solid particles into a clear liquid with a low temperature. For this purpose, an annular inner isolation chamber is arranged at the bottom of the shaft sealing cavity, an inner flushing is carried out by using an electrolyte containing no salt crystals (dilute lye of an effective feed), and a labyrinth throttling sleeve is provided to increase the flushing effect and reduce Flushing fluid flow. In the middle of a double-ended mechanical seal, use temperature electrolyte pressure> seal lye pressure. Evaporation unit for each circulation pump dedicated a small condensate pump water supply pump motor connected to the accident power supply, water supply pipeline pressure accumulator can be completely avoided seal liquid pressure and pressure drop, mechanical seal life of more than one year. Pneumatic diaphragm pump advanced shaft seal structure can also achieve the evaporator can be safely discharged without changing the filler to reduce the time-consuming device asked. (3) The thermal compensation method The circulating pump hanging on the evaporator, with the evaporator expansion and contraction, eliminating the expensive waveform expansion joint, eliminating the import and export of circulation pump on the thermal expansion force. Figure 3-25 is a suspended type slow circulation pump on the caustic soda evaporator of Yuanxi Electrochemical Plant, which has been used for more than 20 years. (4) center line of the pump body support (non-hanging type) due to the evaporation circulating pump diameter, the medium temperature of l00 ~ 165 ℃, (5) adjustable axial flow pump performance parameters of the narrower area, if required the same Specifications of the pump to meet the requirements of different users, so that the pump in the high-efficiency zone, the pump parameters required to be able to adjust. In addition, the operating conditions of the evaporator often change, or pump impeller wear also requires regulation of its performance. Commonly used self-tuning method is to change the pump speed and blade mounting angle. Electric diaphragm pump pump body in the exclusive 樘 and foot support, can Turtle turtle body axis of the pump and the rotor axis of the thermal offset, reducing the radial clearance between the impeller and the pump body to improve the pump volume effectiveness.
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