Water Eductors for Condensor Evacuation

Thermal Powerplant condensors often operate at very low pressures as it enables the last turbine stage to maximize steam expansion and in turn maximize energy extraction from steam.
Because of the complexity of the power plant piping and the vast number of joints it is impossible to avoid air leakage into the system. This leaked air tends to collect in the condenser and raises its pressure thus affecting operation. Hence external vacuum has to be maintained in the condenser to remove the leakage air and maintain vacuum.

The condensors used in Thermal Powerplants are considerable in size and have large internal volumes. During start-up, the condenser pressure has to be first lowered before starting the turbines. Due to the large internal volume the primary vacuum system takes a lot of time for attaining the required vacuum. Hence a secondary Vacuum source is also used for quickly lowering the pressure.

Water Eductors are essentially Liquid jet Vacuum Ejectors that operate on the basis of the jet Venturi principle.
Water Eductors utilize the energy in pumped water for their operation and can be put to use to create vacuum conditions at its suction inlet.

A Water Eductor or Liquid jet Vacuum ejector can develop ultimate vacuum upto 30 Torr i.e 40mbar.
The water Eductor commonly operates with wide range of motive liquid pressure from 2.5 bar(a) to 7 bar(a).
Water Eductors tend to have large suction flows at ambient & low vacuum pressures, this helps the Water Eductor in performing rapid evacuation initially. Combining that with its ability to develop high ultimate vacuum, the Water Eductors are a perfect fit for evacuating Condensors during start up.

Water Eductors are suited for Condensor Evacuation because of their inherent characteristics
• Water Eductors are secondary vacuum source and are used only during start-up. Service Water at 2.5~7 bar(a) is a commonly available utility and hence no additional infrastructure is required for operating the Water Eductor. It helps to keep the capital costs low for the start-up vacuum source
• Ability to evacuate the condensor to high vacuum conditions – decreases the load on the primary vacuum system.
• Low Evacuation time.
• Water Eductors do not contain any moving parts and have large internal passage areas, hence are not vulnerable to liquid entry or clogging by solid particles.
• As they have no moving parts, maintenance requirements are very less. Also it reduces largely the risk of abrupt breakdowns, helps in maintaining the regular production schedule
• Service Water at 2.5~7 bar(a) is a commonly available utility and hence no additional infrastructure is typically required.