In several countries, perhaps especially in the United States, it has become profitable to replace coal with it in the last 10 years natural gas as a fuel for electricity production. It contributes to reduced carbon dioxide emissions because natural gas emits less carbon dioxide per unit of energy than coal during combustion. The change from coal to gas takes place at ffa two different ways:

• Switching from coal-fired to natural gas-fired in existing steam power plants.

• Older coal-fired power plants are being closed down and new gas turbine plants are being built.

In this task, you will investigate how much carbon dioxide emissions are reduced by an older coal-fired power plant replaced with a gas turbine. An older coal-fired steam power plant produces 2400,000 MWh of electricity in one year. It has an efficiency of 33%. Now it is planned to replace it with some gas turbines that burn natural gas instead. The gas turbines can be assumed to work as an ideal Brayton cycle with a pressure ratio of 10. The air and exhaust gases in the gas turbine can be assumed to be ideal gases with a constant Cp = 1.1 kJ / kg and k = 1.4. Calculate how much carbon dioxide emissions are reduced in a year if the same amount of electricity is produced instead of the gas turbines. Emissions of carbon dioxide during combustion of natural gas = 205 kg / MWh fuel Emissions of carbon dioxide when burning coal = 335 kg / MWh fuel.

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