With the increase of power consumption, the technical requirements of the power plant are getting higher and higher, and the vacuum pump is widely used in the power plant. Its advantages are that the main working medium is composed of water, the maintenance cost is low, and it can work in the harsh environment. However, the operation efficiency of the pressure pump is low, generally around 30%, and the maximum is only 50%. This paper analyzes the working principle of the liquid ring vacuum pump, from the working environment of the vacuum pump in the power plant The main factors affecting the efficiency of vacuum pump are analyzed, and the corresponding measures are put forward
1. Liquid ring vacuum pump of working principle
The water rotates around the pump body, forming a closed-loop water flow, because the impeller installation position deviates from the center of the pump body. When the impeller rotates, the water entering the liquid ring vacuum pump is thrown around the pump body under the centrifugal force, and the rotating water is impacted by the impeller one time and divided several times. When the impeller rotates from 0 ℃ to 80 ℃, the volume of the small cavity gradually increases to small volume, which makes the pressure in the pump body strong The volume of the gas in the pump body is larger and smaller. According to the principle of air pressure balance, the air pressure in the pump body is larger and larger. When the compressed gas reaches the exhaust pressure, exhaust from the exhaust port, so as to realize the working principle of continuous suction and exhaust.
Therefore, the liquid ring pump relies on the rotation of blades and the separation of water flow to change the volume of the pump body so as to achieve the functions of suction, compression and displacement, so it belongs to the variable volume vacuum pump.
2. Liquid ring vacuum pump of analysis of factors influencing the operation efficiency
Although the liquid ring vacuum pump is widely used due to its simple structure and low maintenance cost, its operation efficiency is low, generally around 30%, and the maximum is only 50%. We will analyze the following according to its problems.
2.1 low operation efficiency caused by external reasons
(1) The effect of crystal precipitated by carbonate in water on operation efficiency. As the water contains carbonate materials such as calcium and magnesium, and as the working medium of liquid ring vacuum pump, water is used. As the solubility of carbonate materials decreases with the rise of temperature, during the normal operation of liquid ring vacuum pump, friction generates heat, and the temperature of water in the pump body increases gradually. During the high-speed operation of water, calcium and magnesium are obtained, which form crystals. After daily accumulation, the pump body The internal, disc and impeller are covered with scale, which causes the gap between the pump body and impeller to become smaller, noise occurs during operation, too large instantaneous current during startup, reduced absorption and vacuum degree, resulting in low working efficiency of liquid ring vacuum pump
(2) The influence of working fluid temperature in vacuum pump on operation efficiency. The vacuum system of power plant unit and steam turbine adopts two liquid ring
vacuum pumps, one for operation and one for standby. The liquid ring vacuum pump has high requirements on working fluid temperature. China has issued the international GB / t13929-92 code, which stipulates that the working fluid of vacuum pump is water with a temperature of 15 ° C, and the corresponding suction medium temperature is 20 ° C, The temperature of working medium directly affects the treatment of vacuum pump, and then affects the vacuum and economy of the unit. The temperature of the working medium depends on the heat exchange effect of the cooler. If the cooler is dirty and the heat exchange effect is poor, the temperature of the working medium will be seriously affected.
As the vacuum pump cooler of our plant is plate cooler, the advantages of this cooling are large contact area of heat exchanger, high efficiency, and small flow area of plate cooler, and the circulating water quality of our plant is relatively poor, which is easy to cause scaling. At the same time, the cooling water inlet of the vacuum pump cooler of our plant is equipped with filter screen, and there are many impurities in the circulating water, mainly due to the old packing of cooling tower Dunning device If the cooler is not cleaned for a long time and the filter screen is not cleaned, the heat exchange effect of the cooler will be poor and the cooling water will be insufficient, resulting in the low output of the vacuum pump, the low vacuum, the increase of coal consumption and the decrease of unit economy.
2.2 low operation efficiency caused by internal structural component problems
The liquid ring vacuum pump plays the role of sealing the slide, both sides of the pump need to be sealed, in order to ensure its sealing, each liquid ring pump has four slide, two on each side. The working principle of the liquid ring pump is to make use of the back and forth moving slide, and with the steady rotation of the impeller, to ensure its continuous suction and exhaust. Polytetrafluoroethylene (PTFE) material is used for sliding piece, which is easy to appear after long-term use. The sliding piece is seriously deformed and damaged, and the sliding piece of liquid ring pump is not suitable.
3. Vacuum pump of measures to improve the operation efficiency
3.1 regularly deal with dirt to improve the operation efficiency of vacuum pump
The scale produced by carbonate can be completely removed by using 10% oxalic acid. If it is found that the dirt is used strictly, the pump body needs to be disassembled for partial cleaning, which is troublesome. This requires us to check the dirt of the pump body frequently, eliminate it in time, increase the internal volume of the vacuum pump, and improve its operation efficiency.
3.2 enhance the function of cooler and reduce the working fluid temperature in vacuum pump
Select the best time to clean the cooler and check whether the filter screen is blocked in time. In view of the fouling problem of the cooler, due to the heavy workload of disassembly and cleaning of the plate cooler, and the frequent disassembly, cleaning and reinstallation of the plate cooler are prone to leakage, so our factory mainly adopts the strong alkali online cleaning method.
3.3 strengthen the inspection of the tie bar of the vacuum pump impeller
Strengthen the inspection of the tie bar of the impeller of the vacuum pump. If the rotor is unstable during operation, which causes vibration and noise, repair welding shall be carried out according to the actual situation, and detailed correction shall be made to find the balance point that meets the requirements of the impeller.
4. Summary
There are many factors that affect the actual operation efficiency of the liquid ring pump. We need to strengthen daily maintenance to ensure that the vacuum system works in the best condition, save maintenance expenses, and effectively improve the mechanical efficiency of the actual operation of the vacuum system.
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