Cooling Water

In 2008, the U.S. Department of Energy National Energy Technology Laboratory reported the following breakdown of thermoelectric generating capacity cooling systems:
  • 42.7% – once-through cooling
  • 41.9% – cooling towers
  • 0.9% – dry cooling
  • 14.5% – cooling ponds

The following are four types of cooling systems employed by U.S. power plants (U.S. Government Accountability Office Energy Energy–Water Nexus, 2009):

Once-Through Cooling
Once-Through Cooling – Water is withdrawn directly from the source waterbody, diverted through a condenser where it absorbs heat from the boiler stream, and then discharged back into the source waterbody at elevated temperatures. Because once-through cooling systems do not recirculate the cooling water, water withdrawal rates can be as high as a billion gallons of water a day. However, consumption is very low and limited to evaporative losses.

Recirculating Cooling System
Recirculating Cooling – Cooling water is sent from the condenser to cooling towers or ponds, where the heat from the boiler steam dissipates through evaporation and convection. The cooling water is then recirculated through the condensers. Compared with once-through cooling systems, recirculating cooling systems reduce water withdrawal by approximately 95%, yet consume a greater amount of water.

Dry Cooling System
Dry Cooling Systems – Boiler steam is run through radiator-like coils, where heat is transferred directly to the air by convection. Dry cooling systems use water and energy to run cooling fans.

Hybrid Cooling System
Hybrid Cooling Systems – represent middle ground between wet and dry cooling systems. Wet and dry components can be used in any combination to fit water and energy demands. System configurations may help reduce a plant’s overall water consumption. As shown in the figure, both wet and dry components operate in unison, increasing overall cooling efficiency.