Thermal Power Plant

By | April 4, 2019

A thermal power plant is a power station which converts thermal energy to electrical energy.

A thermal power plant is different from hydro power plant, where energy (kinetic and potential) of water is converted into electrical energy.

For operating a thermal power plant, thermal energy can be obtained by burning fossil fuel, nuclear fuel, solar heat etc. However, the use of fossil fuel dominates here.

A thermal power station can use either gas turbine or steam turbine. However, use of steam turbine dominates here.

Thermal Power Plant

Thermal Power Plant

Following are the sources of thermal energy used in thermal power stations

  • Coal
  • Petroleum
  • Nuclear energy
  • Geothermal energy
  • Solar energy
  • Energy obtained from waste incineration
  • Natural gas
  • Biomass

Natural gas can be used as a fuel to both gas and steam turbine.

Power plants operating on coal, fuel oil or natural gas as often known as fossil fuel power stations.

Non-nuclear thermal power plants which do not use co-generation are generally known as conventional power plants.

Now let us discuss both gas turbine and steam turbine

  1. Steam turbine

A steam turbine works on high pressure super-heated steam. This steam is generated by a boiler. Steam exchanges its pressure energy with turbine blades and thermal energy of steam gets converted into mechanical energy of turbine.

This mechanical energy is then converted into electrical energy with the help of an electrical alternator.

Used steam is then sent to a condenser where it becomes water. This water is then pumped to the boiler and the cycle repeats. Steam power plants run on Rankine cycle.

Steam turbines are external combustion engines.

Steam turbine diagram

Advantages of steam turbine

  • Low mass flow rate compared to gas turbine of same power rating
  • They are suitable for large thermal power plants
  • Almost all types of fuels can be used with steam turbines
  • It remains unaffected from the atmospheric conditions because it operates on closed cycle
  • High operating efficiency compared to gas turbines
  • Thermal efficiency of steam turbine is more than reciprocating engine
  • It has very high power to weigh ratio compared to reciprocating engine of same power rating
  • It has greater reliability where sustained power output is required
  • Less vibrations compared to reciprocating engines
  • Fewer moving parts compared to reciprocating engine, which results into less maintenance and greater reliability.
  • It has lower peak combustion pressure compared to reciprocating internal combustion engines
  • Waste exhaust heat can be used in co-generation

Disadvantages of steam turbine

  • It has more startup time compared to both gas turbines and reciprocating engines
  • It is less responsive to change in power demand compared to both gas turbines and reciprocating engines
  • It requires more components compared to both gas turbines and reciprocating engines. For example, boiler, cooling tower, feed-water system etc.
  • It is required to be installed near large water bodies
  • It requires more space compared to both gas turbines and reciprocating internal combustion engine of same power rating
  • At part load it has less efficiency than reciprocating engines
  1. Gas turbine

In gas turbine, compressed hot gas is directly sent to the turbine. This compressed hot air can either be obtained by burning fuel or it can be obtained by taking heat from a heat exchanger.

Hence a gas turbine can either be internal combustion engine or external combustion engine.

Compressed hot gas gets expended in turbine and pressure energy of the gas gets converted into mechanical energy of turbine. This mechanical energy is then converted into electrical energy with the help of an electrical alternator.

Advantages of gas turbine

  • It has very low toxic emissions
  • It can run on wide variety of fuel when compared to reciprocating Internal combustion engines
  • It has low consumption of lubricating oil
  • It has lower peak combustion pressure compared to reciprocating internal combustion engines
  • Waste exhaust heat can be used in co-generation
  • Greater reliability, particularly in applications where sustained high-power output is required.
  • Fewer moving parts result into low maintenance and high reliability
  • It produces less vibration compared to reciprocating engines
  • It occupies less space compared to both steam turbine and reciprocating internal combustion engine of same power rating
  • Very high power to weight rating compared to reciprocating Internal combustion engines
  • It has less startup time compared to steam turbines
  • It is more responsive to change in power demand compared to steam turbine

Disadvantages of gas turbine

  • Core engine cost is high due to the use of exotic material
  • Less variety of fuel can be used compared to steam turbine
  • It is less responsive to change in power demand compared to reciprocating internal combustion engines
  • It has more startup time compared to reciprocating internal combustion engines
  • It is less efficient than reciprocating internal combustion engine at part load

Featured image source:

By Kristoferb – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=51403058

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