Atmospheric Vortex Engine

Frequently Asked Questions



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3. Thermal Power Plants

3.1 Why do thermal power plants need to reject heat? How much heat is rejected in a typical thermal power plant?

Over 80% of the worlds electricity is produced in thermal power plants; the major exception is hydraulic power plants. Thermal power plants include: coal, gas-fired, and nuclear. Thermal power plants convert a portion of the heat received from their fuel into work. In accordance with the Carnot principle, the portion not converted into work ends up as waste heat. A thermal power plant with an electrical output of 1000 MW(e) and an efficiency of 35% requires a heat input of 2860 MW(t). The part of the heat input that is not converted to work 1860 MW(t) is rejected as low temperature waste heat to the environment.

3.2 How do thermal power plants reject heat?

The heat sink for thermal power plants can be:

  • Once through cooling water from a river or a large body or water,
  • Recirculated cooling water cooled in a wet cooling tower,
  • Atmospheric air blown through a dry cooling tower.

Heat can only flow from hot to cold. In order for heat to flow from the cold sink to the atmosphere the temperature of the cold sink must be higher than the temperature of the cooling medium. Therefore the condensation temperature of steam turbines is typically 10 to 20°C higher than the temperature of the cooling medium. The actual efficiency of thermal power plants is always lower than the Carnot efficiency based on hot and cold source temperatures. The majority of thermal power plants are steam plants wherein the waste heat is rejected at the steam turbine condenser. Lowering the condenser pressure increases power output. Decreasing condenser temperature decreases turbine exhaust pressure. In order to keep turbine exhaust pressure as low as possible, the cooling water temperature must be as low as practical.


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