Environmental Engineering Reference
In-Depth Information
While DOE's fossil R and D program seeks to further reduce sulfur dioxide
and nitrogen oxide emissions, its overall objective is to drive all coal-fired power
plant emissions to “near-zero” levels by 2020. To enable industry to meet Clean
Air Act standards, as well as new goals set out by the administration's Clear Skies
Initiative and EPA regulations,[14] DOE has focused on reducing mercury and
carbon dioxide emissions—significant contributors to health hazards and global
warming, respectively. DOE's objective is to reduce mercury emissions by 95
percent and capture and store—or “sequester”—up to 90 percent of carbon
dioxide emissions by 2020. Carbon dioxide capture and storage technologies
would separate carbon dioxide from other gases produced during the combustion
process and would transport the captured carbon dioxide to a suitable long-term
storage site, such as geologic repositories or in the deep ocean.
DOE is also working to improve the efficiency of coal-fired plants by up to
50 percent by 2010 and 60 percent by 2020. According to DOE, pulverized coal-
fired plants using currently available technology are only about 35-percent
efficient—meaning about 65 percent of the energy generated by the plant is lost
during the conversion process, mostly as heat that is not converted to electricity.
Several of DOE's current fossil R and D projects aim to develop coal-based plants
that employ new, more efficient gasification technologies. Rather than burning
coal directly, gasification breaks coal down into a synthesis gas, comprised
primarily of carbon monoxide and hydrogen, which is combusted to turn a gas
turbine, generating electricity. Heat from the combustion process is captured and
directed toward a steam turbine, which also generates electricity. According to
DOE, industry, and association officials, power plants using an IGCC
configuration for gasification increase the efficiency of electricity generation and
substantially reduce harmful emissions in comparison with conventional
pulverized coal technology (see table 1).
Coal-based power plants that employ IGCC technologies break down coal
into its basic chemical elements, allowing for the capture of carbon dioxide as a
concentrated gas stream. In contrast, conventional pulverized coal plants burn coal
directly, creating a more diluted stream of carbon dioxide that is much more
costly to separate from the larger mass of gases flowing from the combustor. As
such, IGCC plants offer greater potential for carbon capture and sequestration to
reduce carbon dioxide emissions. Moreover, according to international climate
change experts at the United Nations Environment Programme and the World
Meteorological Organization, carbon dioxide capture and sequestration
technologies have the most potential for significantly mitigating climate change
when applied in IGCC plants. Currently, only two coal-based IGCC plants in the
