Wet cooling is a cooling process used in power stations. This process comprises a condenser which converts vapour into water by means of a heat exchanger.
Cooling can be achieved with fresh water, a cooling tower or a combination of fresh water and cooling tower.
An alternative form of cooling is dry cooling. A distinction is made between three wet cooling processes:
Cooling using fresh water
The fresh water used for this cooling type is drawn from a river, lake or the sea. It is pumped through heat exchangers by cooling water pumps and then discharged to the same water bodies.
Cooling via cooling tower
For cooling using a cooling tower, the water is drawn once from a river, lake or the sea depending on the power station's location, and fed into a collecting tank underneath the cooling tower. The water is drawn from there with pumps and transported through heat exchangers, then returned to the collecting tank via the cooling tower. The water lost as a result of evaporation or leakage must be replaced.
Cooling using fresh water and cooling tower
Depending on the heat load capacity of a river or lake, cooling is switched from fresh water to combined fresh water/cooling tower operation.
In this case, the cooling water pump must be able to develop the head for both fresh water and cooling tower operation. If this is not feasible for hydraulic reasons, cost-effective operation cannot be achieved. Under these circumstances, other solutions must be considered.
Alternatives providing the required heads for fresh water and cooling tower operation
- The cooling circuit is split into a fresh water cooling and cooling tower circuit. This ensures that the water downstream of the heat exchanger is not directly discharged into the river but routed to the cooling tower pumps. They first pump the water through the cooling towers before the cooled water is discharged into the river or directly returned to the cooling water pump.
- An electric motor with fixed rotational speed is usually employed as a drive. Depending on the required power input, it is possible to use a speed-controlled motor with a frequency inverter (see Closed loop control) or a motor with pole changing option (see Number of poles).
- In exceptional cases, speed modulation gear units which allow speed control during operation are employed on small-sized pumps.