Abstract: Based on the analysis of cavitation of centrifugal pump and the comparison of several schemes to improve the cavitation resistance of centrifugal pump, the problem of pump cavitation should be solved on the premise of not affecting the normal production. Induction wheel. After the actual transformation, achieved good results. Keywords: centrifugal pump; cavitation; the inductive wheel is analyzed and the kinds of the schemes are compared. Introduction 1. The m-cresol unit of Yanhua Chemicals Group is one of the largest cresol production plants in the world and due to its inherent deficiencies, Carried out several transformations. During the process of transformation, the process parameters of the pump changed greatly, resulting in severe cavitation of several pump units in the unit, among which 143-J / JA and 217-J / JA were the most serious ones. The disintegration inspection showed that the impeller and the suction inlet of the pump had been severely pitting. Meanwhile, these pumps not only vibrated heavily and noisy while operating, but their efficiency remarkably dropped. Table 1 is the operation of these two groups of equipment questionnaire. Table 1 Survey of 143-J / JA, 217-J / JA Operation Type Amplitude (mm) Noise (dB) Efficiency (%) Maintenance Period Pits Maximum Pit Depth (mm) 143-J / JA0.464943.08 .52.3217-J / JA 0.475246.57.32.7 It can be clearly seen from the above table that the two sets of equipment have experienced serious cavitation phenomenon, which caused frequent maintenance of equipment inspection, increased consumption of spare parts, increased cost, Great threat to the device's security, stability, length, full, excellent production. Therefore, it is inevitable to solve this actual problem that affects production. 2. Cavitation phenomena and solutions 2.1 Cavitation The liquid evaporates when the liquid pressure near the inlet of the impeller is less than or equal to the saturated steam pressure at the liquid transport temperature and gas dissolved in the liquid may also escape to form A large number of bubbles, bubbles with the flow of liquid to the higher pressure at the leaf when the instantaneous coagulation collapse. At the moment when the bubbles condense and collapse, the liquid around the bubbles rapidly flushes into the cavities formed by the bubbles to form a strong local high-frequency and high-pressure water hammer, and the metal surface is denuded due to fatigue. At the same time, the electrochemical corrosion of the metal surface occurs due to the presence of an active gas (such as oxygen) and the local high temperature generated when the bubbles condense. This process is called cavitation. 2.2 Factors Affecting Cavitation Influencing liquid pressure and saturated steam pressure will affect the occurrence of cavitation. 2.2.1 The impact of factors ①pump inlet structural parameters: including the shape of the impeller suction inlet, the width of the inlet edge of the blade and the edge of the blade inlet edge and the shape of the front cover. ② pump operating conditions: It includes the pump flow, head and speed and so on. ③ pump installation location: It includes the pump suction pipe hydraulic loss and installation height. ④ environmental factors: it includes the installation of atmospheric pressure at the pump site. 2.2.2 Influencing Factors It includes the nature of the media itself and the media operating temperature. 2.3 to solve several problems of centrifugal pump cavitation According to the above analysis of the impact of cavitation factor, we can get the following several solutions to solve the problem of centrifugal pump centrifugal pump: ①improve the structural parameters of the pump inlet This program is suitable for centrifugation Pump design and manufacturing phase, the method is rarely used in the production site. ② In the suction inlet of the pump, the induction wheel is added with the induction wheel to improve the anti-cavitation performance of the centrifugal pump and solve the cavitation problem. The effect is remarkable. And its simple structure easy to manufacture and install, easy operation and maintenance, low cost, without prejudice to the premise of production can be installed and debugged, especially suitable for promotion and application in the production site. ③ Reasonable design suction pipe and adjust the installation height Although this method can completely eliminate cavitation problems, but rarely used in the production site. This is because the pump suction pipe and installation height adjustment, large quantities, high construction costs, and by the construction environment constraints, only when the device parking or overhaul can be carried out at the same time, due to process conditions, adjust the pump Inhalation pipe and installation height will affect the follow-up process, with a chain reaction. ④ optimize the operating conditions of the process conditions permitting, change the pump flow, lift, speed and medium operating temperature and other operating parameters, to avoid the occurrence of cavitation. However, due to the limitation of the process conditions, the optimization of the process operation conditions has great limitations, and the effect is not significant in most cases. Therefore, this method can be used as a secondary solution to cavitation problems. 2.4 program to determine Through the analysis and comparison of the above programs, without affecting the normal production under the premise of the pump to solve the problem of cavitation should be preferred at its entrance to install induction wheel. Induction wheel design When the liquid flows through the induction wheel, the induction wheel does work on the liquid, which is equivalent to pressurizing the liquid entering the impeller behind to increase the pressure. Although this method increases the load on the motor, the power of the motor is usually relatively large (usually 20-30% larger than the shaft power of the centrifugal pump), and the size of the inducer is affected by the diameter of the suction port. The supercharging range limited. The motor can still meet the general requirements, do not need to replace the motor. Due to the current understanding of induction wheel is still in the exploratory stage, there is no unified view on some theoretical issues. Therefore, the induction wheel design is largely based on experience, combined with the actual structure of the pump carried out. The 217-J / JA (model D1011 3 × 11/2 × 8) pump (Figure 1) will be taken as an example to introduce the design method of the inducer and provide some references for solving the pump cavitation problems in the field. 3.1 Characteristic Parameters and Operating Parameters Table 2 Characteristic Parameters and Operating Parameters Impeller Diameter Flow Rate Head Speed ​​Ratio Number of Revolutions Characteristic Parameter 1734181.5355051.0 Operating Parameters 3051.4296051.43.2 Design and Calculation of Induction Wheel [1] Assuming that the outer diameter of the induction wheel is, When the diameter of the hub is taken, the outer diameter of the induction wheel is taken as; the diameter of the hub is taken as; the number of blades taken as is, the distance between the outer circumferences of the blades is taken as; the length of the blades at the outer circle is taken as; The round angle of the blade is; the radius of the blade entrance edge is; the axial length of the blade at the outer circumference of the induction wheel is; the angle of the blade at the hub is; the maximum thickness of the blade at the hub is taken as; 4. Calculation of anti-cavitation performance after induction wheel 4.1 Induced NPSH [2] Induction turbine flow is the leakage of the induced rim clearance, which is the amount of pump leakage that affects the induced rotation. Induction wheel cavitation than the speed of which is the inlet flow coefficient, induced wheel inlet axial velocity, rim import circumferential velocity. Therefore, the induced wheel NPSH 4.2 After the introduction of induction wheel main vane cavitation performance analysis of the general induction wheel lift coefficient, the induction wheel actually produced lift 217-J / JA pump without induction wheel, when the flow rate is Q = 30m3 / h, NPSH is. After the induction wheel is added, the NPSH of the main impeller is reduced after the induction wheel is added. According to the above calculation results of the transformation of the equipment, as shown in Figure 1, the transformation of its operation after the investigation and analysis, the results in Table 3. Table 3 Before and after the transformation Table 6 Comparison of the changes before and after the transformation Items Reformed After the transformation Amplitude (mm) 0.47 0.02 Impeller pitting At the entrance of the impeller spongy impeller No significant pit on the surface of the impeller Maintenance cycle (days) 7.3> 90 Motor current (A ) 6.9 ~ 7.0 7.0 ~ 7.2 It can be seen from the above calculation that the induction wheel is installed at the suction inlet of the pump, the anti-cavitation performance of the pump is significantly increased, the cavitation phenomenon is prevented, the operation period of the equipment is greatly increased, Thus stabilizing the device production, reducing the cost of inspection and maintenance of the equipment and improving the economic benefits of the enterprise. 5. Conclusions Addition of inducer has become one of the important measures to improve the anti-cavitation performance of centrifugal pumps, especially in the production site, not only because of its remarkable effect, simple structure, easy manufacture and installation, but more importantly, its cost Low, versatility, easy maintenance.
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