In the nearly decade-long saga to regulate greenhouse gas (GHG) emissions from fossil fuel-fired power plants, the U.S. EPA recently began the rulemaking process for a new set of regulations that would impose restrictions on emission units at new and existing power plants. On May 23, the U.S. EPA published a proposed rule titled "New Source Performance Standards for Greenhouse Gas Emissions From New, Modified, and Reconstructed Fossil Fuel-Fired Electric Generating Units; Emission Guidelines for Greenhouse Gas Emissions From Existing Fossil Fuel-Fired Electric Generating Units; and Repeal of the Affordable Clean Energy Rule" (proposed rule), starting a comment period that ends on July 24, 88 Fed. Reg. 33,240 (May 23, 2023). The EPA's proposed rule relies heavily on hydrogen co-firing and carbon capture and sequestration (CCS) deployment as part of the decarbonization of the power-producing sector.

In the proposed rule, the EPA proposes five distinct actions under Section 111 of the Clean Air Act (CAA). First, the EPA is proposing to amend existing new source performance standards (NSPS) for GHG emissions from new and reconstructed fossil fuel-fired stationary combustion turbine EGUs. Second, the EPA is proposing to amend existing NSPS for GHG emissions from fossil fuel-fired steam generating units that undergo a large modification. Third, the EPA is proposing emissions guidelines for GHG emissions from existing fossil fuel-fired steam generating EGUs (including coal, oil, and gas-fired steam generating EGUs). Fourth, the EPA is proposing emissions guidelines for GHG emissions from the "largest, most frequently operated" existing stationary combustion turbines. Lastly, the EPA is proposing to repeal the Affordable Clean Energy (ACE) Rule promulgated by the Trump administration in 2019 because "the emissions guidelines established in ACE do not reflect the best system of emissions reduction (BSER) for steam generating EGUs and are inconsistent with Section 111 of the CAA in other respects."