A power plant that produces 1.5 GW of electricity, the steam turbines take in steam at a temperature of 510°C, and the waste heat is expelled into the environment at 25°C. (a) What is the maximum possible efficiency of the plant? (b) Suppose you develop a new material for making pipes and turbines, which allows the maximum steam temperature to be raised to 610°C. Roughly how much money can you make in a year by installing your improved hardware if you sell the additional electricity for 6 cents per kilowatt-hour? (Assume that the amount of fuel consumed at the plant is unchanged). (c) The efficiency of a typical coal-fired power plant is around 40% (much lower than the ideal). For each GW of useful power, how much waste heat is expelled into the environment? (d) Assume first that the cold reservoir for this plant is a river whose flow rate is 120m3s. By how much will the temperature of the river water increase on passing through the power plant? (e) To avoid this ‘thermal pollution’ of the river (the increased temperature can kill fish and cause algal blooms), the plant could instead be cooled by evaporation of river water. At what rate must the water evaporate? What fraction of the river must be evaporated?

Answer

Power Plant Efficiency and Energy Analysis – Thermodynamic Explanation