f GHG emission standards for existing natural gas and oil-fired steam EGU ’s are based on load subcategories. Generally, the intent is to hold these units to existing levels of CO2 efficiency or have them switch to lower-emitting fuels such as natural gas (NG) and distillate oil (fuel oil or diesel fuel oil numbers 1 and 2, kerosene, biodiesel or biodiesel blends), as shown in Table 1. f The new Subpart TTTTa regulation specifies GHG emission standards for new and reconstructed stationary combustion turbines (after May 23, 2023) with a base load rating¹ >250 MMBtu/hr and that serves a generator(s) capable of selling >25 MW of electricity, the established subcategories and requirements are shown in Table 2.
The new finalized rules under 40 CFR Part 60, Subpart TTTT and Subpart TTTTa incorporate new standards for the following new, modified, reconstructed and existing sources in both the continental and non-continental areas of the US: f GHG emissions standards for existing coal-fired steam electric generating units (EGU) would require the utilization of CCS by January 1, 2032, with at least 90% capture rate. EPA establishes a subcategory of coal-fired EGUs with planned retirement dates before January 1, 2039, with the requirement to co-fire with natural gas at a level of 40% of the unit’s annual heat input by January 1, 2030. There is an exemption for these EGUs who plan to cease operation prior to January 1, 2032.
Table 1: GHG Emission Standards for Existing Oil or NG-Fired Steam EGUs
Subcategory
Annual Capacity Factor
Utilization of:
Required Technolog y GHG Emission Standards
Base load existing oil or NG-fired
1,400 lb CO2/MWh- gross 1,600 lb CO2/MWh- gross
≥45%
Routine methods of operation and maintenance
Intermediate load existing oil or NG-fired
≥8% but <45%
--
170 lb CO2/MWh-gross
Low load, existing oil-fired
<8%
Lower-emitting fuels
Low load, existing NG-fired
130 lb CO2/MWh-gross
Table 2: GHG Emission Standards for New and Reconstructed Stationary Combustion Turbines
Subcategory
Annual Capacity Factor
Utilization of:
Required Technolog y
GHG Emission Standards
- 800 to 1,250 lb CO2/MWh- gross before Jan. 2032 - 100 to 150 lb CO2/MWh- gross after Dec. 2031
Highly efficient combined cycle generation
CCS @ 90% capture rate by January 1, 2032
Base load
≥40%
Highly efficient simple cycle generation
1,170 to 1,560 lb CO2/MWh- gross
Intermediate load
>20% but <40%
--
Low load
≤20%
Lower-emitting fuels
120 to 160 lb CO2/MMBtu
1 EPA defines base load rating as the maximum amount of heat input (fuel) that an EGU can combust on a steady state basis plus the maximum amount of heat input derived from non- combustion source (i.e. solar thermal), as determined by the physical design and characteristics of the EGU at ISO conditions. For a stationary combustion turbine, base load rating includes the heat input from duct burners.
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