The Environmental Protection Agency (EPA) has significantly relaxed requirements needed to build new coal-fired power units in the U.S.
The revisions proposed on December 6 for performance standards governing carbon dioxide emissions from new, reconstructed, and modified coal power units respond to the Trump Administration’s Executive Order on Promoting Energy Independence and Economic Growth, which directed the EPA and other agencies to review existing regulations and revise or rescind “those that unduly burden the development of domestic energy resources beyond the degree necessary to protect the public interest or otherwise comply with the law.”
Among the proposal’s key changes to the Obama administration’s 2015-finalized New Source Performance Standards (NSPS) are that they drop partial carbon capture and storage (CCS) as the best system of emission reduction (BSER) for new coal units, citing “high costs and limited geographic availability of CCS.”
Instead, for new units, the EPA proposed limits for CO2 emissions based on “the most efficient demonstrated steam cycle in combination with the best operating practices.” For large units, it proposes the BSER should be supercritical steam conditions and meet an emission rate of 1,900 pounds of CO2 per megawatt-hour on a gross output basis (lb CO2/MWh-gross). For small units, the BSER is subcritical steam conditions to meet emission rate will be 2,000 lb. CO2/MWh-gross.
The rule says subcritical coal-fired boilers are designed and operated with a steam cycle below the critical point of water (22 MPa or 3,205 psi). Units using supercritical steam conditions operate at pressures greater than 22 MPa and temperatures greater than 550C (1,022F). “Increasing the steam pressure and temperature increases the amount of energy within the steam, so that more energy can be extracted by the steam turbine, which in turn leads to increased efficiency and lower emissions,” it notes.
The EPA also proposed separate standards of performance for newly constructed and reconstructed coal refuse-fired units. For those units, the BSER is “best available subcritical steam conditions, and if finalized, the emission rate for these sources will be 2,200 lb. CO2/MWh-gross, regardless of the size of the unit,” it said.
In addition, EPA proposed to revise the standards of performance for reconstructed fossil fuel-fired steam units based on the “most efficient demonstrated steam cycle” to make them consistent with the emission rates for large and small newly constructed units.
Significantly, the EPA also called for public comment on the regulatory threshold under section 111(b) of the Clean Air Act that a source category “causes, or contributes significantly to,” air pollution. The clause provides the EPA the authority to address emissions from new, modified, and reconstructed power plants. “EPA asks for the public’s views on the proper interpretation of this phrase, the agency’s historic approach to this requirement, and whether this requirement should apply differently in the context of greenhouse gases than for traditional pollutants,” it said.
The EPA’s proposal comes four months after it issued the Affordable Clean Energy (ACE) rule, which is proposed to replace the 2015 Clean Power Plan. Like the Clean Power Plan, the ACE rule could have several important implications for power generators—specifically at 600 coal-fired units at about 300 facilities.
However, the ACE rule diverges largely from the 2015 Clean Power Plan in that it defines BSER for carbon dioxide emissions from existing power plants as on-site, heat-rate efficiency improvements. Comparatively, in the Clean Power Plan, the EPA determined that BSER should be comprised of three building blocks: increasing operational efficiency of coal plants; shifting power generation from coal to natural gas; and increasing power generation from renewables. The ACE Rule also provides states with “candidate technologies” that could be used to establish standards of performance (see a detailed list below). States will determine which of these technologies are appropriate for each plant and establish a standard of performance that reflects the degree of emission reduction from their application, it noted.
—Sonal Patel is a POWER associate editor (@sonalcpatel, @POWERmagazine).
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