Generating Electricity with Heat
A thermal power plant is a power station in which heat energy is converted to electric power. The vast majority of electricity worldwide is generated this way, using a variety of heat sources. The fundamental thermodynamic cycle that describes this process is the Rankine cycle.
The Rankine Cycle
The Rankine cycle is a model used to predict the performance of steam turbine systems. It is a closed loop where a working fluid (usually water) is constantly circulated and changes phase between liquid and vapor.
The four stages are:
1.Pumping (Pump): The cycle begins with low-pressure liquid water. A pump pressurizes the water and sends it to the boiler. This step requires a small energy input.
2.Boiling (Boiler): In the boiler, the high-pressure liquid water is heated at constant pressure by an external heat source, causing it to boil and turn into high-pressure, high-temperature steam.
3.Expansion (Turbine): The high-pressure steam is directed at the blades of a turbine. As the steam expands and cools, it pushes on the blades, causing the turbine to spin at high speed. This is the stage where useful work is produced. The spinning turbine is connected to a generator.
4.Condensation (Condenser): The now low-pressure steam passes into a condenser, where it is cooled by a separate loop of cold water (often from a river or cooling tower). This causes the steam to condense back into a low-pressure liquid, ready to be sent back to the pump to start the cycle over.
Fuel Sources
The only difference between most thermal power plants is the fuel used to heat the water in the boiler.
Fossil Fuels: Coal, natural gas, and oil are burned (combustion) to heat the boiler. This is the most common source.
Nuclear Power: The heat from a controlled nuclear fission reaction is used.
Geothermal Power: Natural steam from the Earth is used directly, or geothermal hot water is used to heat a secondary fluid.
Concentrated Solar Power: Mirrors focus sunlight to heat a fluid that runs the boiler.