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Biden EPA proposes stronger standards to regulate NOx from combustion turbines

The future of the proposal, which would establish size- and capacity factor-based categories for turbines, is unclear under the incoming Trump administration.
Biden EPA proposes stronger standards to regulate NOx from combustion turbines
(TVA's Colbert Combustion Turbine Plant. Source: TVA.)

The U.S. Environmental Protection Agency (EPA) last week proposed to strengthen limits on nitrogen oxide (NOx) emissions from most new and existing combustion turbines.

The proposed New Source Performance Standards (NSPS) are based on the application of combustion controls and selective catalytic reduction (SCR).

EPA said the proposed standards would ensure that new turbines built at natural gas-fired plants or industrial facilities — especially large ones that could operate for decades — would be among the lowest-emitting turbines ever built.

To strengthen the NOx performance standards for new stationary combustion turbines, EPA is specifically proposing:

  • To determine that combustion controls with the addition of post-combustion SCR is the best system of emission reduction (BSER) for most combustion turbines. Post-combustion SCR is already widely used in the power sector.
  • To lower the NOx standards of performance for affected sources based on the application of the BSER.
  • To establish more protective NOx standards for affected new sources that plan to fire or co-fire hydrogen, ensuring that these units have the same level of control for NOx emissions as sources firing natural gas or non-natural gas fuels. 

The proposed standards would establish size-based categories based on base load heat input. The proposed size-based categories include:

  • Large combustion turbines — facilities with a base load heat input rating of > 850 MMBtu/h (> ~ 85 MW).
  • Medium combustion turbines — facilities with a base load heat input rating of > 250 and ≤ 850 MMBtu/h (> ~ 25 MW and ≤ ~ 85 MW). 
  • Small combustion turbines — facilities with a base load heat input rating of ≤ 250 MMBtu/h (≤ ~ 25 MW).

EPA is proposing to further subcategorize sources based on whether they operate at high, intermediate or low loads, as well as whether they burn natural gas or non-natural gas fuels. When classifying low, intermediate or base load units, EPA will consider the 12-calendar-month capacity factor of these combustion turbines.

  • High load — capacity factor greater than 40% (i.e., base load).
  • Intermediate load — capacity factor greater than 20% and less than or equal to 40%.
  • Low load — capacity factor of less than or equal to 20%.

For non-EGU stationary combustion turbines, the capacity factor would be determined based on the prior 12 calendar months of data on a rolling basis updated each month.

EPA acknowledged that SCR technology becomes less cost-effective and efficient at smaller scales or variable operating levels. Therefore, the agency is proposing standards for certain combustion turbines relying on combustion controls instead of SCR. This applies to small turbines at low or intermediate loads, and medium and large turbines at low loads.

The agency estimated the proposal would reduce NOx emissions by 198 tons in 2027 and 2,659 tons in 2032. The present value of net benefits to society is estimated at up to $340 million, with an equivalent value of up to $46.4 million per year. 

NOx contributes to harmful health effects, such as asthma and respiratory infections. Children, the elderly, and people with chronic heart, lung or other cardiopulmonary diseases are most at risk. 

EPA is also proposing to maintain the current limits for sulfur dioxide, which is well-controlled in the sector based on the long-term required use of low-sulfur natural gas and distillate fuels.

The agency last established New Source Performance Standards (NSPS) for stationary combustion turbines in 2006. The future of the proposal, as with other EPA power plant rules finalized in the last year, is unclear under the incoming Trump presidency.

EPA will accept comments for 90 days after the proposal is published in the Federal Register.

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