District Energy 2012 Q2

Feature
Story
What to Know When
Leaving Coal:
Maximizing your new air permit
Robynn Andracsek, PE, Associate Environmental Engineer, Burns & McDonnell

Many district-size facilities are considering repowering or eplacing existing coal combustion assets with newer, cleaner technology. Whether the motivation is regulatory, political or economic, the essential strategic step is obtaining a new air emissions permit. Recognizing the permitting requirements and planning in advance are crucial to avoiding schedule delays and maximizing operational flexibility in the permit.

A soon-to-be-retired resource often has significant past actual emissions that can be used to offset the emissions from new equipment. Essentially, you are trading an old emissions source for a newer emissions source, with no net increase in pollution. If an old coal-fired boiler has a higher emissions level than a new gas-fired turbine, there are air permitting techniques that can be used to benefit the project. This does not mean that the new equipment cuts corners; it just means that the permitting process will be faster. Likewise, the final permit will have more operational flexibility.

Without proper planning and knowledge, however, your project will miss out on these opportunities. Before you can get the most out of your new permit, you must understand the basic Clean Air Act requirements.

Basics of “Netting”

Although the Clean Air Act is the governing regulation, the U.S. Environmental Protection Agency delegates authority to each state or local agency to implement the regulation in its own slightly different way. However, the basics of the air permitting process stay the same.

New major permitting projects are subject to New Source Review, a permitting process divided into Prevention of Significant Deterioration (PSD) for attainment pollutants and Nonattainment New Source Review (NNSR) for nonattainment pollutants. An area is designated as “attainment” for a pollutant if the measured air quality is in compliance with the National Ambient Air Quality Standards for that pollutant (fig. 1).

In determining whether a modification triggers PSD or NNSR, you must determine if the project will result in a significant emissions increase. This is called “netting” and is accomplished using past actual (or baseline) emissions compared to future potential emissions. Since the objective of this type of project is to replace coal with natural gas (or another lower-emitting technology), it is expected that the new plant will result in an emissions decrease when compared to the actual emissions of the existing coal plant. The catch is that the coal plant emissions used in the netting analysis must be based on past actuals, not potentials.

Table 1 shows the pollutants and their permitting thresholds for attainment areas. Once a facility has emissions over the major source thresholds it is classified as a major source, and future modifications that exceed the major project thresholds are subject to PSD permitting.