Report: Combined-Cycle Plants Release Far Less CO2 Than Coal

by | Jan 10, 2014

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boulderPower plants that use natural gas and a new technology to squeeze more energy from the fuel release far less CO2 than coal-fired power plants do, according to research by NOAA and the University of Colorado, Boulder.

The so-called “combined cycle” natural gas power plants also release significantly less nitrogen oxides and sulfur dioxide, which can worsen air quality. Since more and more of our electricity is coming from these cleaner power plants, emissions from the power sector are lower by 20, 30 even 40 percent for some gases since 1997, according to Reduced Emissions of CO2, NOx and SO2 from US Power Plants Due to the Switch from Coal to Natural Gas with Combined Cycle Technology, which has been published in the journal Earth’s Future.

Researchers analyzed data from systems that continuously monitor emissions at power plant stacks around the country. Previous aircraft-based studies have shown these stack measurements are accurate for carbon dioxide and for nitrogen oxides and sulfur dioxide. Nitrogen oxides and sulfur dioxide can react in the atmosphere to form tiny particles and ozone, which can cause respiratory disease.

To compare pollutant emissions from different types of power plants, the scientists calculated emissions per unit of energy produced, for all data available between 1997 and 2012. During that period of time, on average:

  • Coal-based power plants emitted 915 grams (32 ounces) of CO2 per kWh of energy produced;
  • Natural gas power plants emitted 549 grams (19 ounces) COper kWh hour; and
  • Combined cycle natural gas plants emitted 436 grams (15 ounces) CO2 per kWh hour.

The researchers reported that between 1997 and 2012, the fraction of electric energy in the United States produced from coal gradually decreased from 83 percent to 59, and the fraction of energy from combined cycle natural gas plants rose from none to 34 percent.

That shift in the energy industry meant that power plants, overall, sent 23 percent less CO2 into the atmosphere last year than they would have, had coal been providing about the same fraction of electric power as in 1997. The switch led to even greater reductions in the power sector’s emissions of nitrogen oxides and sulfur dioxide, which dropped by 40 percent and 44 percent, respectively.

In September 2012, GE announced that it had secured $1.2 billion of orders for its FlexEfficiency 60 combined-cycle power plant, a plant that the company called the “most efficient power plant of its kind.”

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