See the latest EHS federal and state regulatory updates due to COVID-19

On August 3, 2015, EPA issued a final rule (40 CFR 60 Subpart TTTT) regulating carbon dioxide (CO2) from new, modified, and reconstructed electric generating units (EGUs). Affected units include steam generating units (i.e., boilers), integrated gasification combined cycle (IGCC) plants, and stationary combustion turbines. The final rule applies to the following affected EGUs:

  •  Sources that commence construction after January 8, 2014
  • Sources reconstructed after June 18, 2014
  • Steam generating units and IGCC plants modified after June 18, 2014

EPA deferred adoption of standards for modified combustion turbines during this final rulemaking.

What Sources Are Not Regulated by Subpart TTTT?

The final rule includes exemptions for several EGUs based on electric output, capability of combusting non-fossil fuel, etc. Examples include:

  • Steam generating/IGCC units subject to a federally enforceable restriction limiting electrical sale to 1/3 potential electric output limit or 219,000 MWh, whichever is greater
    • Non-fossil units (capable of >50% non-fossil combustion) with fossil fuel use limited by permit to 10% or less capacity factor
    • Combined heat and power units with annual net electric sales limited by permit to less than design efficiency times potential electric output, or 219,000 MWh, whichever is greater  
  • EGUs that serve a generator with effective generation capacity, pro-rated on a heat input basis, of 25 MW or less
  • Combustion turbines not capable of being fueled with natural gas.

 Please refer to the final rule for a complete list of exempted units and exemption details.

Emission Standards for Steam Generating and IGCC Units
  • New units   
    • 1,400 lb CO2/MWh-gross
  • Reconstructed units
    • Base load heat input rating <= 2,000 MMBtu/hr (HHV): 2,000 lb CO2/MWh-gross
    • Base load heat input rating > 2,000 MMBtu/hr (HHV): 1,800 lb CO2/MWh-gross
  • Modified units
  • Determined based on the unit’s best historical annual CO2 emission rate (from 2002 to the date of modification)

Although the final rule does not include a categorical exemption for simple cycle combustion turbines, the majority of these would be operated as non-base load units, and compliance can be demonstrated by using natural gas or other uniform fuels.
When interpreting the rule, beware of distinctions in gross vs. net electrical output, LHV vs. HHV ratings for efficiency and heat input, and design characteristics vs. actual operating performance.
 EQ_Carbon Chart

What’s Next?

The final rule is yet to be published in the Federal Register and EPA may issue a red-line version to address several inadvertent errors in the final rule issued on August 3, 2015.  Similar to the Clean Power Plan, this rule is expected to go through a lengthy legal appeal process.  In the meantime, it is important to understand the implications of this final rule on EGUs – definitions, applicability criteria, best system of emission reduction for each source category, and calculation techniques – so that you can ensure the units can comply with the applicable emission limits and reporting requirements by the compliance deadline. 
Note that this is a simple summary of a complex rule.  The final rule and preamble are available on EPA’s website at: