10 Air extraction equipment
The objectives of the air extraction plant are:
- To remove air which has leaked into the condenser via flanges and glands effectively.
- To remove other incondensable gases that are present in the steam exhausting from the LP turbines.
It is important that both are removed from the condenser, as their presence in any quantity impairs the heat transfer performance of the condenser. Conversely, excessive air extraction capacity should be avoided, and reasons for this are discussed later.
The air extraction plant must be capable of functioning under two regimes: one during normal operation, the other when raising vacuum on the turbine-generator unit.
When raising vacuum, the air extraction equipment is faced with a large quantity of air which must be removed, and must therefore have the capacity for reducing the pressure in the condenser quickly to a level which allows the turbine to be started.