Hydroelectric power stations handle large amounts of water, consequently there is a high risk of damage to machinery and control systems due to moisture through condensation.
Places in a power station where drying is recommended during shut down include:
Generator – it is important to keep the windings dry to prevent corrosion and ensure a shorter starting time. Dry air can also supplement generator heaters.
Condenser – must be kept dry after flushing to allow recoating of water boxes and tube plates.
Reheater – tubes are thinner than super heater tubes and more susceptible to corrosion. Intergranular attacks on austenic stainless steel can be minimised using dry air.
Feed and condensate pipes – important to eliminate internal corrosion on pipes as oxides can contaminate feed water.
Boiler – surface temperatures of fireside boiler tubing drop below the dew point and form condensate. The condensate reacts with sulphurous parts of the ash and acid deposits and hydrolyses, forming a highly acidic solution. The end result is rapid, localized attack of the metal surface.
Reactor vessel – Where access is required, dry air is required to purge out CO2, eliminate corrosion and to dry the graphite prior to refilling with CO2.