Vibration damping measures for high temperature and high pressure chemical pump units under flood conditions

Vibration damping measures for high temperature and high pressure chemical pump units under flood conditions

　　 In the flood, it is more common to be forced to shut down due to severe vibration of the high temperature and high pressure chemical pump unit, resulting in "closed door flooding". The severe vibration of some pumping stations during abnormal operation broke the glass of the pump room.

High temperature and high pressure chemical pump

According to the different interference forces, the vibration of the high temperature and high pressure chemical pump unit can be divided into three categories: hydraulic vibration, mechanical vibration and electromagnetic vibration. Vibration is inevitable in production. The vibration of different types of pump units always occurs at the same time. May separate them completely. The direct factors that induce these vibrations are also different. The main disturbing source of the abnormal and severe vibration of the pump unit during the flood is the hydraulic imbalance. The cause should be correctly analyzed according to the actual situation at the time, and the main contradictions should be grasped and effective vibration reduction measures should be taken.

　　 1. The flood level in the outer river is extremely high, and the pumping station needs to increase the lift. The pump works in the saddle-shaped unstable area near the inflection point. The main characteristics of this vibration are instability and periodic repetition within an instant. If the frequency of this cycle coincides with the oscillation frequency of the system, it may induce resonance and cause more serious damage. The main vibration reduction measures are:

　　(1) Remove local blockages, dredge the flow channels such as water diversion, inlet and outlet, on the one hand, improve the flow pattern, on the other hand, reduce the required head of the pumping station as much as possible.

　　(2) For a fully-regulated water pump, it is possible to avoid the inflection point by changing the blade angle, reducing or increasing the blade angle. Adjusting the blade angle can also improve the Q～H performance curve of the pump and reduce the unstable working area.

　　(3) When possible, use variable speed adjustment to change the working point of the pump to a stable working area.

　　(4) Small and medium-sized water pumps can be equipped with bypass pipes or bypass valves to control the outlet flow of the pump not to be less than the unstable working flow.

　　 2. The flood level outside the river is extremely high, and some are even 2 to 3 meters high. In this case, starting the water pump, the air in the water outlet channel is difficult to discharge, and the air carrying capacity of the water flow is greatly reduced. The repeated compression and expansion of air causes pressure pulsation and induces unit vibration. In severe cases, the unit cannot be started. According to the actual engineering situation, the exhaust facilities of the water outlet can be dredged, improved or added to increase the exhaust speed and air-carrying capacity, and shorten the starting process as much as possible.

3. The water level in the front pool is too low, changing the flow state of the inlet water, forming surface vortices entrained by the inlet water and coanda vortices. After entering the impeller working room, they are cut by the blades and cause vibration. The frequency is proportional to the number of blades, and often accompanied There is a lot of noise. Emergency measures such as diversion and baffles can usually be used to effectively reduce vibration.

　　4. The flood in the outer river has large fluctuations, the effluent flow is turbulent, and the wave pressure wave is reflected into the water flow channel to cause the unit to vibrate. Effective and practical outlet wave prevention and wave stabilization measures should be actively taken.

5. The waterlogged water (which may overflow the trash rack) rushes foreign matter into the flow channel and even the impeller working room, causing partial blockage and forming an asymmetric flow field, which may aggravate the arcuate mechanical vibration while causing hydraulic vibration. . Vibration can be effectively reduced if the dirt is thoroughly cleaned in time.

　　6. ​​Because the pump working point is far away from the normal working range, the necessary cavitation margin Δhr of the pump itself increases abnormally, or cavitation occurs due to the deterioration of the inlet flow state, causing the vibration of the pump unit. The frequency of cavitation vibration is high, up to tens of thousands of times per second, and accompanied by strong noise, the relevant vibration reduction measures are as follows:

　　(1) Use angle change, speed change or bypass method to adjust the working condition of the water pump, reduce the necessary NPSH Δhr of the water pump, and avoid the cavitation working point.

　　(2) Adopt feasible diversion, water isolation and other measures to improve the flow pattern of influent.

(3) Consider introducing the pressurized water in the pump outlet pipe (or flow channel) into the inlet pipe (or flow channel), or additionally install a pressurizing pump device, and use the nozzle as a ring mixer to increase the pump inlet Pressure to eliminate or reduce cavitation and its vibration, one nozzle can be used for small pumps, and multiple nozzles can be considered for large pumps. The length of the mixing section, the position of the nozzle and the flow rate of injection should be reasonably determined according to factors such as water intake pressure, booster water head, nozzle flow rate, mainstream velocity and number of nozzles.

　　(4) Adding (0.4～1%) gas (calculated by volume flow rate) at the inlet of the water pump can greatly reduce the cavitation intensity of the water pump and significantly reduce the erosion, noise and vibration. The specific air supplement method and location should be determined according to the difference of cavitation phenomena and relevant engineering experience. 5. If possible, consider installing a guide wheel in front of the main impeller of the axial flow pump. On the one hand, it can rectify, and on the other hand, it can provide energy for the main impeller inlet, improve its cavitation performance, and eliminate or reduce cavitation vibration.

7. The foreign matter carried by the waterlogged water is blocked and adsorbed on the rotating impeller. In addition to causing the aforementioned asymmetric hydraulic vibration of the flow field, it will also destroy the static and dynamic balance of the rotor, and the mechanical imbalance will cause mechanical disturbance. The phenomenon of vibration. The vibration will be greatly reduced when the pump is stopped and part of the water body is backflowed back and then turned on again.

8. Under the effect of long-term external floods and internal waterlogging, if the pump house has uneven settlement, its inclination may cause asymmetric hydraulic vibration of the flow field due to the uneven clearance of the impeller; it is caused by the uneven clearance of the guide bearing. Mechanical vibrations such as dry friction and vibrating, and unbalanced electromagnetic tension caused by uneven air gaps. The corresponding vibration reduction measures are:

　　 (1) Deviation correction of the main building of the pump station.

(2) For large vertical axial flow pump units, within the allowable adjustment range, the vertical concentricity and horizontality of the fixed parts of the unit can be re-measured and adjusted based on the inlet flow channel, the verticality, swing, center of the rotor, and the motor The magnetic field center and bearing gap, blade gap and air gap.

　　9. At present, most pumping station projects have serious aging problems. In this case, long-term flooding may cause failures such as short-circuit of the rotor winding due to insulation damage and other reasons, resulting in electromagnetic tension imbalance vibration. After confirmation, corresponding repair measures can be taken.