First, the causes of condenser vacuum
The cause of the formation of vacuum in the condenser is, due to the turbine exhaust steam is cooled into condensate, its specific volume is sharply reduced. Such as steam at an absolute pressure of 4KPa, the volume of steam is more than 30,000 times larger than the volume of water. When the exhaust steam condenses into water, the volume is greatly reduced, so that the condenser vapor side of the formation of a high degree of vacuum, which is the necessary conditions for the completion of the cycle of vapor system. It is because of the high vacuum inside the condenser, so all the equipments connected with it may leak air into the condenser because of the laxity, plus the non-condensable gases in the exhaust steam of the steam turbine, if it is not pumped out in time, it will gradually raise the pressure value inside the condenser and the vacuum will fall, resulting in the enthalpy of the steam exhaust rising, the effective enthalpy drop decreasing, and the efficiency of the steam cycle of the turbine decreasing. According to some data, if the vacuum drops by 1KPa, the heat consumption of the unit will increase by 70kj/kw and the thermal efficiency will decrease by 1.1%. The function of water injection extractor or water ring vacuum pump is to extract the non-condensable gas of condenser to maintain the vacuum of condenser. : ] N4d& f4 K9 h( j6 @% S
Second, the hazards of poor vacuum tightness# E S( }+ Z" p7 l/ s
The hazards of poor turbine vacuum tightness are mainly manifested in the following three aspects, firstly, when the vacuum tightness is poor, the air leaking into the vacuum system is more, and the water jet extractor or the water ring vacuum pump is not able to pump out the leaking air in time. The exhaust steam pressure and temperature of the unit will rise, which will undoubtedly reduce the efficiency of the turbine unit, increase the coal consumption of power supply, and may threaten the safe operation of the turbine. On the other hand, due to the presence of air, the heat exchange coefficient between steam and cooling water will be reduced, resulting in the increase in the temperature difference between the exhaust steam and the cooling water. Secondly, although the air leaked into the vacuum system can be pumped out in time, it needs to increase the load of the water jet extractor or vacuum pump, which wastes the electricity and industrial water of the plant. Third, due to the leakage of air, resulting in condenser subcooling is too large, the system thermal economy is reduced, the condensate dissolved oxygen increases, can cause oxygen corrosion of low-pressure equipment.