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Thermal efficiency?
A typical coal-fired power plant burns 310 metric tons of coal every hour to generate 780 MW of electricity. 1 metric ton= 1000 kg. The density of coal is 1500 kg/ m^3 and its heat of combustion is 28 MJ/kg. Assume that all heat is transferred from the fuel to the boiler and that all the work done in spinning the turbine is transformed into electrical energy.
What is the power plant's thermal efficiency?
1 Answer
- Anonymous1 decade agoFavorite Answer
Ignore the extraneous info -- coal density and comments about heat transfer. Efficiency is simply how much electrical energy comes out compared to how much thermal energy goes in. Add one piece of physical units information. By definition 1 joule = 1 watt*second, or 1MW = 1MJ/s. Then 780 MW output is divided by (310000 kg/hr times 28 MW*s/kg) times 3600 seconds per hour. Answer then is 32.3%. And this typical plant must be an obsolete design. New plants can reach up toward 40%. What happens to the rest of the heat? It warms up or evaporates the cooling water. Yes, coal plants, or any steam plant including nuclear, need lots of water!
Source(s): This is simply calculated from energy engineering fundamentals.