Alert

The Push to Strengthen NOx Emission Limits Before President Biden’s Term End: Will It Survive the 90-Day Comment Period?

December 17, 2024

The U.S. Environmental Protection Agency (EPA) proposed new standards on November 22, 2024, to significantly tighten nitrogen oxides’ (NOx) emission limits from fossil fuel-fired stationary combustion turbines. These proposed regulations, targeting new, modified, and reconstructed units, aim to address persistent ozone pollution and mitigate public health risks. The EPA’s rationale, technical considerations, and projected impacts are not likely to withstand the challenges from industry. By reviewing current emission trends, technological capabilities, and regulatory precedents, a comprehensive evaluation of the proposed rule’s implications needs to be further analyzed before becoming law.

Introduction

NOx are critical precursors to ground-level ozone and fine particulate matter, both of which have been shown to pose potential environmental and health risks. The EPA’s November 2024 proposal seeks to implement stricter NOx emission limits on stationary combustion turbines. This move aligns with the Biden administration’s broader climate and air quality goals, leveraging advanced technology to reduce emissions from the fossil fuel sector.

Stationary combustion turbines are widely used in power generation and industrial applications. While these systems provide operational flexibility and high efficiency, they contribute to localized NOx emissions, exacerbating non-attainment areas for ozone under the National Ambient Air Quality Standards (NAAQS). The proposed rule addresses these concerns by setting revised limits, informed by recent technological advancements in emissions control. The proposed New Source Performance Standards (NSPS) are predicated on the implementation of combustion controls and selective catalytic reduction (SCR) technology.

Regulatory Background

The Clean Air Act (CAA) mandates the EPA to periodically review and update emission standards for major sources of air pollutants. In particular, Section 111 of the CAA empowers the EPA to set performance standards for new, modified, and reconstructed stationary sources. The current NOx standards for turbines, last updated in the early 2000s, do not reflect recent improvements in emissions control technology, such as selective catalytic reduction (SCR) systems.

Ozone pollution remains a persistent issue, with several regions in the United States failing to meet ozone NAAQS. By proposing updated NOx limits, the EPA aims to reduce the formation of ozone and its associated health impacts, which may include respiratory disorders, cardiovascular disease, and premature mortality.

The agency last established 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.

Overview of the Proposed Rule

The 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, the 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).

The 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, the 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.

The 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. 

Studies have shown that NOx may contribute to harmful health effects, such as asthma and respiratory infections. The 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.

Industry Challenges

Compliance costs for operators will increase significantly. However, the EPA’s preliminary analysis indicates that public health savings and environmental benefits outweigh these expenses.

Retrofitting older turbines with advanced NOx controls may pose logistical and financial challenges for certain facilities, leading to retiring the older facilities.

The EPA maintains the rule could accelerate the transition to renewable energy as operators evaluate the cost-effectiveness of continued fossil fuel use. However, the Trump administration is likely to pause the accelerated push to renewable energy.

The proposed rule is likely to face intense legal scrutiny from industry stakeholders. The EPA would be wise to ensure robust stakeholder engagement and transparent cost analyses to mitigate opposition.

Stakeholder Perspectives

Environmental Advocates: Generally support the proposal as a necessary step toward cleaner air and reduced climate impacts.

Industry Groups: Will raise concerns about compliance costs and operational disruptions, particularly for smaller operators or legacy units.

Next Steps

The EPA’s proposed tightening of NOx limits for stationary combustion turbines represents a significant step toward addressing ozone pollution and its associated risks. The 90 Day Public Comment period ends January 25, 2025. Industry stakeholders are sure to submit extensive comments to the proposed rule along with lawsuits. Open, transparent, and continued dialogue among stakeholders are crucial to ensure some form of new NOx standards.

References

1. Environmental Protection Agency. (2024). Proposed Rule: Strengthening Limits on NOx from Stationary Combustion Turbines. Retrieved from EPA.gov.

2. U.S. Clean Air Act, 42 U.S.C. § 7401 et seq. (1970).

3. National Research Council. (2010). Advancing the Science of Climate Change. Washington, DC: The National Academies Press.

4. Bell, M. L., & Dominici, F. (2008). “Effect of ozone on mortality: Results from the National Morbidity, Mortality, and Air Pollution Study.” Environmental Health Perspectives, 116(12), 1591–1595.

5. Rubin, E. S., Yeh, S., Hounshell, D. A., & Taylor, M. R. (2004). “Experience curves for power plant emission control technologies.” International Journal of Energy Technology and Policy, 2(1-2), 52–69.