May 18: The U.S. Government Accountability Office (GAO) released a report requested by Senator Sheldon Whitehouse (D-RI), Chairman OF THE Subcommittee on Oversight Committee of the Committee on Environment and Public Works regarding, Air Emissions and Electricity Generation at U.S. Power Plants (GAO-12-545R, Apr 18, 2012). The report responds in part to Senator Whitehouse's request for information on electricity generation and emissions at U.S. electricity generating units and the implementation of NSR. Our objective is to provide information on how older fossil fuel electricity generating units compare with newer units in terms of their air emissions and electricity generation.
To respond to the objective, GAO reviewed selected data elements in the Ventyx Velocity Suite EV Market-Ops database. The proprietary database contains consolidated energy and emissions data from EPA, the Energy Information Administration (EIA), and other sources. Specifically, GAO analyzed how older plants compare with newer plants in their emissions, energy production, location, and fuel type. GAO reviewed energy and emissions data from calendar year 2010. It reviewed data from units that: (1) listed a fossil fuel (coal, natural gas, or oil) as a primary fuel; (2) generated electricity in 2010; and (3) had a net summer capacity greater than 25 megawatts, making them subject to EPA emissions monitoring and reporting requirements.
In all, GAO examined the characteristics of 3,443 electricity generating units -- 1,485 older units and 1,958 newer units. GAO focused the analysis on power plant emissions of three regulated pollutants: sulfur dioxide (as a proxy for sulfur oxides), nitrogen oxides, and carbon dioxide (a greenhouse gas). To assess the reliability of the Ventyx data, GAO reviewed existing documentation about the data and the system that produced them, interviewed Ventyx staff who were knowledgeable about the data, and consulted with EPA and EIA agency officials knowledgeable in energy issues. We determined the Ventyx data to be sufficiently reliable for the purpose of this report.
GAO indicates that older electricity generating units -- those that began operating in or before 1978 -- provided 45 percent of electricity from fossil fuel units in 2010 but produced a disproportionate share of emissions, both in aggregate and per unit of electricity generated. Overall, in 2010 older units contributed 75 percent of sulfur dioxide emissions, 64 percent of nitrogen oxides emissions, and 54 percent of carbon dioxide emissions from fossil fuel units. For each unit of electricity generated, older units collectively emitted about 3.6 times as much sulfur dioxide, 2.1 times as much nitrogen oxides, and 1.3 times as much carbon dioxide as newer units. The difference in emissions between older units and their newer counterparts may be attributed to a number of factors.
- First, 93 percent of the electricity produced by older fossil fuel units in 2010 was generated by coal-fired units. Compared with natural gas units, coal-fired units produced over 90 times as much sulfur dioxide, twice as much carbon dioxide and over five times as much nitrogen oxides per unit of electricity, largely because coal contains more sulfur and carbon than natural gas.
- Second, fewer older units have installed emissions controls, which reduce emissions by limiting their formation or capturing them after they are formed. Among coal-fired units -- which produce nearly all sulfur dioxide emissions from electric power generation -- approximately 26 percent of older units used controls for sulfur dioxide, compared with 63 percent of newer units. Controls for nitrogen oxide emissions were more common among all types of fossil fuel units, but these controls vary widely in their effectiveness. Among older units, 14 percent had installed selective catalytic reduction (SCR) equipment, the type of control capable of reducing the greatest amount of nitrogen oxides emissions, compared with 33 percent of newer units. In addition, approximately 38 percent of older units did not have any controls for nitrogen oxides, compared with 6 percent of newer units.
- Third, lower emissions among newer units may be attributable in part to improvements in the efficiency with which newer units convert fuel into electricity. Nonetheless, older units remain an important part of the electricity generating sector, particularly in certain regions of the United States.
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