1. Brief analysis of the reasons for cavitation of the water ring vacuum pump. The size of the water ring vacuum pump of the steam turbine condenser in Wusashan Power Plant is determined according to the design and operation conditions of the generator set in the factory. When running within the design range, the vacuum pump can operate normally, such as related reasons, such as: the unit runs at full load for a long time; the cooling water temperature is high or the cooling water flow is too small in summer, resulting in poor cooling effect of the vacuum pump heat exchanger, and the vacuum pump will operate under high vacuum, which is equivalent to running close to or in a suffocated state. Due to inherent physical phenomena, under certain conditions of water temperature, the higher the vacuum, the higher the water temperature, and the water in the pump is close to boiling And a large number of bubbles will be generated. The generation and rupture of the bubbles will cause cavitation damage to the impeller, destroy the dynamic balance of the impeller, cause strong vibration of the pump body, and damage the auxiliary equipment of the vacuum pump (pressure vacuum gauge, pressure switch, inlet pneumatic door). feedback device, etc.), and will emit very large cavitation noise, which seriously affects the safe operation of the vacuum pump unit and the safe operation of the turbo-generator set.

2. The basis and detailed description of the technical transformation plan If you want to solve the problem of cavitation of the vacuum pump, the cost of reducing the water temperature is relatively large, and it is even more impossible to reduce the vacuum degree, that is, to increase the back pressure of the condenser, which will seriously affect the load capacity of the unit. The ideal way is to solve the generation of cavitation under the condition that the original water temperature and system vacuum remain unchanged. At present, the best choice is to install an atmospheric ejector for the vacuum pump, and the extraction performance of the entire vacuum pump group will be better. Therefore, the vacuum of the condenser can still be guaranteed to be at the current level or higher, but the internal vacuum of the vacuum pump body is only 12Kpa (at this time, the system vacuum is within the range of 3-8Kpa), which can effectively avoid cavitation Produce.

The atmospheric jet pump is composed of: nozzle, suction chamber, and diffuser, and its exhaust port is connected with the air inlet of the water ring pump.

Introduction to the principle of the atmospheric ejector: Start the water ring vacuum pump first, so that a pressure difference is formed between the nozzle inlet and the exhaust port, and the atmosphere can enter the pump from the nozzle. When the pressure difference is 1/2 of the atmospheric pressure, the air medium passes through the nozzle. The contraction section is accelerated, and the speed of sound can be reached when it reaches the throat, and it can be further accelerated to the speed of sound when it reaches the expansion section, and a high-speed jet is fired to the diffuser, which causes the pressure in the suction chamber to be lower than the pressure in the pumped container. Inhaled into the chamber, due to the mixing of the two airflows in the suction chamber, the loss of momentum exchange gradually slows down the airflow rate. When entering the throat of the diffuser Drop below the speed of sound, further reduced by the expansion section of the diffuser, the pressure continues to rise, and finally reaches the exhaust pressure of the atmospheric ejector, that is, the suction pressure of the water ring pump, the water ring pump sucks the gas and then discharges it out of the pump, that is, Complete the suction and exhaust process.

3. Specific steps and detailed instructions for technical transformation

3.1. Mechanical transformation part

It can be known that the modified intake pipeline is about 700mm longer than the original pump group pipeline, and the added parts have been marked on the drawing. If the position is not enough, the gate valve on the pipeline can be changed to be installed vertically on the pipeline. There is room to cut off the 700mm pipeline.

3.2. Change the control part of the pump group (refer to FIG. 3) to increase the pressure switch 47a (double touchpoint 47a1, 47a2). Its function is to control the pneumatic butterfly valve (16b) between the intake tee and the injector tee and the injector. The opening and closing of the pneumatic butterfly valve (19a) on the injector, thereby controlling the input and exit of the injector.

3.2.1. When a main pump is running, when the pressure measured by the pressure switch is less than 10kpa (specifically can be set), the atmospheric injector switching valve [16b] is closed, and the atmospheric injector driving gas valve [19a] is opened. After the above two valve actions are completed, the atmospheric injector is in the input state.

3.2.2. When a main pump is running, when the pressure measured by the pressure switch [47a2] is greater than 14Kpa (this value can be set by yourself), the atmospheric ejector drives the gas valve [19a] to close, and the atmospheric ejector switch valve [16b] is closed. Open, when the above two valve actions are completed, the atmospheric ejector is in the exit state.

3.2.3. The set values of the pressure switch and differential pressure switch of the original unit do not need to be changed.

4. Comparison of the advantages after the transformation with the performance and economy before and after the transformation 4.1. The advantages after the transformation: ① The most important thing is to ensure that the vacuum pump will not cavitate, the noise and vibration will be greatly reduced, and the service life of the vacuum pump will be improved., the noise and vibration of the modified No. 3 A vacuum pump will be greatly reduced since the installation of the atmospheric ejector in August 2008, and there has never been a phenomenon that the impeller is broken and the vibration is too large to damage the thermal control equipment. ② Due to the good tightness of the condenser of this unit, the pumping performance of the pump group equipped with an atmospheric ejector in the high vacuum stage is better than that of a single pump. The load rate creates good conditions.

4.2. Comparison of performance and economy before and after transformation ① Before the installation of the atmospheric injector, the vacuum in the vacuum pump is maintained at about 6Kpa. After the installation of the atmospheric injector, the vacuum in the vacuum pump is maintained at about 12Kpa. Refer to the power curve of the vacuum pump. At 12Kpa, its shaft power is 113KW. Since the vacuum of the condenser is constantly changing, the pumping vacuum of the vacuum pump currently used is also changing, so it is not very specific how much the shaft power is increased. Generally, we press 6Kpa (power is 99KW) compared with 12Kpa (power is 113KW).

That is to say, the power will increase by about 14KW after the installation of the atmospheric injector. ② After the installation of the atmospheric injector, the pumping performance of the vacuum pump has been improved. According to our observation and the historical curve of the DCS host computer, the vacuum of the condenser of the unit is more stable, and the vacuum can be increased by about 1Kpa compared with the original year-on-year conditions, and there is a trend towards higher vacuum.