Air cooled Roots Vacuum Pump Unit in Thermal Power Plant
The main function of the vacuum pump unit is to extract the non-condensable gas-air mixture from the condenser to maintain the high vacuum of the condenser. However, the large selection of the original vacuum pump unit results in a higher energy consumption for maintaining the vacuum of the condenser, which is not conducive to the improvement of the unit economy and can not meet the requirements of energy saving and consumption reduction advocated by the state. In addition, the rotating parts of the water-ring vacuum pump unit are eroded by cavitation. Easy to occur damage overhaul costs. Therefore, it is necessary to study and propose improved measures to reduce the energy consumption of vacuum pump units and further improve the condenser vacuum as far as possible.
When the original impeller and the pump body of the vacuum pump unit are installed, there is no overlap between the two centers. Eccentricity injects a certain amount of secondary desalted water into the pump body before starting. When the impeller rotates clockwise, the centrifugal force acts on the impeller to drive the working fluid to form an equal thickness water ring on the surface of the pump body, which is similar to the shape of the pump body. The upper part of the inner surface of the water ring and the lower part of the blade root of the impeller are slightly higher than the top part of the impeller. A number of cavities of different sizes are formed between the hub and the water ring of the impeller.
From the top, the volume of the cavity is observed clockwise from small to large and then to the maximum at the bottom. Therefore, when the impeller rotates, the volume of the chamber expands and the pressure decreases, the volume of the chamber is reduced and the pressure is increased gradually. The process of suction of non-condensable gas and air is realized through the exhaust hole removal. The design purpose of steam turbine condenser is to satisfy all kinds of operation conditions of steam turbine based on pure condensation condition and to operate continuously and safely for a long time. In actual condition, the steam discharged into the condenser under pure condensation condition is far less than that under pure condensation condition. In addition, the selection requirement of water ring vacuum pump unit is that it can meet the extraction condensation of steam turbine under various load conditions. When the air and non-condensable gas in the steam turbine need to start, two vacuum pump units run side by side and meet the start-up time requirements.
Therefore, under the condition that the condenser tightness can be better, the original vacuum pump unit obviously wastes energy because of the excessive selection and high power consumption. When the bubbles run over the saturated pressure region, the vapor in the bubbles will condensate and the bubbles will burst, causing the surrounding water to fill the region rapidly. If it occurs near the impeller surface, the impeller will be impacted. The impact frequency is very high and the instantaneous pressure reaches 30 MPa. The impeller will be damaged by pits or pits in the weak part and the frequent part of high frequency impact.