The U.S. Environmental Protection Agency claims that its proposal to ease carbon dioxide limits on new and modified coal-fired power plants will spark increased investment in efficient coal generation and allow the country to export that technology.
But environmental groups argued March 18 that the technology the EPA selected in its proposed rewrite of an Obama-era climate rule has existed for decades, and hundreds of modern coal plants abroad are already operating with more efficient technology than the rule would require.
The EPA unveiled a proposal in December 2018 that would allow large coal-fired electric generating units to emit up to 1,900 pounds of CO2 per MWh and smaller units to emit up to 2,000 pounds. That would be a significant increase over the current standard of 1,400 pounds of CO2 per MWh set under a 2015 companion rule to the Obama administration's climate regulations for existing fossil fuel-fired generators.
The 1,400-pound limit effectively required new and modified coal plants to capture at least some of their CO2 emissions using a technology known as carbon capture and storage, or CCS. However, the Trump administration's proposal would establish that the best system of emission reduction for large coal plants is "supercritical" generation technology in combination with best operating practices.
"Although supercritical technology is already developed, establishing it as the basis for control requirements in the U.S. for new and reconstructed sources would help establish it in other nations, resulting in a reduction in global CO2 emissions," the EPA said in its proposal.
As for the U.S., the EPA said it does not expect any new coal-fired generation to be built here even if the proposal is adopted, absent drastic changes in energy prices or policy.
Supercritical vs. ultra-supercritical
Even if the EPA decides the best system of emission reduction is supercritical technology and not CCS, the agency's proposed standard of 1,900 pounds of CO2 per MWh is "dramatically higher" than what the most efficient generating units can actually achieve, the Sierra Club said in comments on the proposal.
Compared to subcritical power plants, supercritical and ultra-supercritical plants operate at higher temperatures and pressures that allow them to burn less coal and emit less CO2.
The Sierra Club noted that supercritical generating technology was originally developed in the U.S. in the 1950s, while 250 GW of even more efficient ultra-critical technology has been deployed abroad in recent decades, with about 90% of that capacity located in Asia. In addition, the group noted that nearly half of the U.S. units the EPA analyzed for its proposal — 316 of 678 — satisfied the agency's proposed emissions limit for large coal plants for at least one full year in the past 10 years.
"Not only does EPA's revised standard not nearly reflect the performance achievable by the most advanced new coal plant designs, it greatly exceeds the performance of the best existing coal plants in the United States, which are not even subject to the standard," the group said.
The Sierra Club also noted that the Organization for Economic Development and Cooperation will not fund large coal-fired plants if they cannot effectively meet a limit of 1,500 pounds of CO2 per MWh. "EPA's emission limit for new coal plants operating in the world's largest economy should not exceed the OECD ... limit for plants even in the poorest nations," the group said.
'Adequately demonstrated' and 'achievable'
However, the Utility Air Regulatory Group, or UARG, said supercritical power plants' long operating history makes the technology an ideal alternative to CCS.
"Owners of these sources ... have extensive experience with the design, cost, and operating characteristics of this technology for a wide range of coal types, load duties, emission control configurations, and ambient conditions," said the trade group, which represents utilities with significant coal-fired generation. "The costs of the proposed system are well-characterized and reasonable."
Therefore, the UARG said, supercritical technology satisfies the Clean Air Act's requirement that the best system of emission reduction be "adequately demonstrated" and "achievable."
And in contrast to the Sierra Club, the group said its own analysis of actual performance data from coal plants showed that the proposed standards "are far from achievable," noting that eight out of the 16 most recently constructed large coal plants with supercritical technology exceeded 1,900 pounds of CO2 per MWh.
"EPA should adjust its standards of performance so that they are actually achievable for new units," the group said. The UARG also noted that only one ultra-supercritical generator has been built in the U.S. so far: American Electric Power Co. Inc.'s 609-MW John W. Turk Jr. UPC facility in Hempstead, Ark., which came online in 2012. Materials and equipment necessary to build additional ultra-supercritical capacity "do not appear to be available for units at the low end of what qualifies as a 'large'" coal plant, the group said.