(194b) Environmental Challenges in Meeting Ambient Air Quality Standards

In the last five years, the United States Environmental Protection Agency (USEPA) has revised three national ambient air quality standards (NAAQS) became more stringent. USEPA is currently reviewing several other NAAQS and the outcomes are expected in next couple of years.

Meeting NAAQS is a key requirement for permitting any major facility, including ethylene plants, in an attainment area. The permitting process requires estimating the air quality impact of the project’s emissions using specialized air dispersion modeling techniques. The modeling requires numerous input data, site-specific assumptions and model defaults to ensure compliance with USEPA approved modeling methodologies, which are continuously evolving based on the latest scientific data. Special modeling demonstrations are required for Class I areas.

Ethylene crackers are typically subjected to nitrogen oxides (NOx) and particulate (PM₁₀/PM_2.5) NAAQS. Compliance is required with both short-term and annual NAAQS for these pollutants. Higher Hydrogen content in fuel gas more commonly used in the current and future USGC ethane crackers typically increases NOx formation and poses challenges in meeting the NOx NAAQS. Particulate emissions during decoking pose challenges in meeting the short term and annual PM₁₀/PM_2.5 NAAQS.

This presentation will provide an overview of the various NAAQS applicable to ethylene plants, discuss the air dispersion modeling techniques available and bring awareness to the challenges of meeting the NAAQS. The challenges will be explained through a few case studies. The case studies will be based on published permitted data on emissions from typical sized ethylene plants and publicly available land-use and meteorological data. The presentation will conclude providing recommendations for meeting the challenges of demonstrating compliance with the NAAQS.