The vacuum extraction system is a core component of the direct air-cooling system; it primarily serves to establish and maintain low back-pressure for the steam turbine unit and a vacuum within the condenser. It rapidly evacuates accumulated gases from the piping during unit startup and continuously removes non-condensable gases-such as steam and air-during operation to ensure equipment efficiency and meet corrosion-prevention requirements. Additionally, it supports the proper functioning of the steam turbine's low-pressure section shaft seals and low-pressure heaters. The system comprises extraction piping, shut-off valves, and vacuum extraction equipment. Domestic units commonly employ water-ring vacuum pumps, with each unit equipped with three pump sets (each rated at 100% capacity); all operate at full load during startup, while one or two remain in service during normal operation. A vacuum-breaking valve is also installed to actively break the vacuum when necessary.
Regarding technical innovation, new systems enhance extraction efficiency through cryogenic cooling by installing a heat exchanger and a liquid nitrogen storage tank at the water-ring vacuum pump inlet.
