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Cause Analysis and Improvement Measures of Demagnetization of Nikkiso Magnetic Pump

Due to the new equipment and new technology, the Nikkiso Magnetic Pump is very demanding in terms of process and operation during operation. After the accident, the manufacturer questioned our process and operation. In order to thoroughly analyze the cause of demagnetization of the Nikkiso magnetic pump, we did the following work.   The external process system and the pump operating procedures were first examined.
(1) Careful and detailed inspection of the inlet pipe and pump outlet from the storage tank to the pump to the loading train pipeline, through process inspection and confirmation, to confirm that our process flow is not wrong, and the reasons for the process system are eliminated.
(2) The filter in front of the pump inlet was inspected and no impurities were found, thus eliminating the possibility of inlet blockage.
(3) The Nikkiso magnetic pump was fully pumped and completely emptied, negating the judgment of the air in the pump.
(4) At the time, the liquid level of the storage tank was 8.6 meters, and there was no low liquid level.
(5) The craftsman in the tank area paying operation and loading the train loading operation shall strictly follow the operation rules, and there is no illegal operation.
(6) The operation of the pumping department of the tanker department is strictly carried out, and the technicians of the manufacturer are also on site, and there is no misoperation.
After excluding the reasons for the process system and operating factors, we have carefully and carefully analyzed the structure design of the Nikkiso magnetic pump.
Since the sliding bearing of the Nikkiso magnetic pump is lubricated and cooled by the medium being transported, the lubrication flow path must provide sufficient flow of the medium to the annulus region between the inner magnetic rotor and the spacer sleeve and the sliding bearing and the thrust plate during operation. The friction pair between the rotating shafts is lubricated and cooled. The manufacturer only opens a return hole between the pair of sliding bearings, that is, the middle part of the pump shaft, and the shaft and the return hole are not through holes, so that the flow of the cooling lubricating medium passing through the friction pair is insufficient, and the generated heat cannot be timely. Take away, can not establish and maintain a good liquid friction state. The self-lubricating and cooling is not good, causing the dry friction of the sliding bearing to cause the axle to be hung, and the outer magnetic rotor continues to rotate to generate heat. Below the operating limit temperature of the inner magnetic rotor (NdFeB is 120 ° C), the drop in transmission capacity is reversible, and above the limit temperature is irreversible. That is, after the inner magnetic rotor is cooled, the lost transmission capacity can no longer be recovered, so that the inner magnetic rotor gradually loses magnetism, and finally the high-temperature demagnetization of the inner magnetic rotor occurs. Therefore, the design flaw of the self-lubricating system of the Nikkiso magnetic pump is the main cause of demagnetization.
In addition to the design flaws of the Nikkiso magnetic pump itself, we also made the following analysis based on the nature of the media.
(1) The medium to be transported (pure benzene) is volatile, and the temperature rises easily to vaporize. Moreover, the inner magnetic rotor and the isolating sleeve in the isolating sleeve generate heat during operation (the annulus region between the inner magnetic rotor and the isolating sleeve generates high heat due to the eddy current), which will increase the operating temperature. Due to the design defects of the Nikkiso magnetic pump, the lubrication is not good. If the temperature of the medium into the pump is higher than the vaporization temperature corresponding to the inlet pressure, the medium will vaporize and form bubbles, which is the Nikkiso magnetic force for transporting the easily vaporized liquid. Pumps create a significant safety hazard.
(2) The static pressure energy obtained by the medium is too low, causing the vaporization temperature to decrease and severe cavitation to cause the medium to be interrupted. Dry friction causes the bearing to burn and hang the shaft. The pressure inside the impeller is different when the pump is running. The Nikkiso magnetic pump has the lowest pressure at the inlet due to the centrifugal force, but the medium will cavitation when it is lower than the saturated vapor pressure under working conditions. When the pump first started cavitation, the cavitation area was small, which had no obvious effect on the normal operation of the pump, and was not clearly reflected in the pump performance curve. However, when the cavitation develops to a certain extent, a large amount of bubbles are generated, the flow channel is blocked, and the continuity of the liquid flow in the pump is destroyed, and finally the pump is evacuated and dry friction occurs, and the eddy current loss heat is generated due to the cooling failure. Severe, will cause the temperature of the medium and the temperature of the inner magnetic rotor to rise sharply.
Based on the above analysis, we will take corresponding measures to prevent it.
How to improve the self-lubricating cooling condition of the Nikkiso magnetic pump to prevent the frictional sub-liquid film from vaporizing and causing dry friction is the key to solving the demagnetization of the magnetic rotor in the Nikkiso magnetic pump. At the same time, considering that the medium to be transported has the characteristics of volatilization and vaporization, according to the principle of energy conservation, the vaporization temperature of the medium can be increased by lowering the velocity energy of the medium and increasing the static pressure energy, so that the medium can be vaporized due to the temperature increase. Effective prevention. According to the above ideas, it is proposed that the Nikkiso magnetic pump shaft and impeller can be modified at the same time, and it is expected to completely solve the problem of magnetic rotor demagnetization in the Nikkiso magnetic pump. The specific transformation measures are as follows:
(1) Change the Nikkiso magnetic pump shaft from a semi-hollow to a full hollow and change the return hole to a through hole to increase the cooling and lubrication flow of the medium.
(2) When installing, make the spiral groove of a pair of sliding bearings (the spiral groove helps the medium to flush and lubricate the shaft, and the direction of the spiral groove should be paid special attention), so that the cooling medium flows more smoothly, and the outer magnetic rotor rotates at a high speed. The heat generated by the induced eddy current can be taken away in time to improve the cooling lubrication effect of the sliding bearing and the pump shaft and the thrust ring, so that a liquid film is maintained between the friction pairs to achieve liquid friction.
(3) Cutting the impeller. Cutting the impeller while ensuring that the efficiency is basically unchanged, on the one hand, by increasing the speed of the liquid, increasing the static pressure energy to increase the vaporization temperature of the medium; on the other hand, reducing the introduction of external energy to avoid an increase in the temperature of the medium. And vaporization. It also expands the operating range of the Nikkiso magnetic pump and reduces the impact of process fluctuations on the pump.
(4) Install the Nikkiso magnetic pump protection system. When the driven parts of the magnetic actuator are operated under overload or the inner magnetic rotor is stuck due to the holding shaft, the main and driven parts of the magnetic actuator will automatically slip off the protection pump.