What Is BACT for CO2?

Assume, for the moment, that the U.S. Congress is unable to agree on legislation aimed at reducing carbon emissions from industry, vehicles, and power plants (the carrot approach). Further, assume that the Environmental Protection Agency (EPA) eventually promulgates rules that require power plants to reduce carbon emissions (the stick approach). Have you given any thought to the range of possible best available control technologies (BACT) that the EPA might require under the Clean Air Act (CAA)?

The first domino fell when the Supreme Court found in its April 2007 decision in Massachusetts v. EPA that the EPA has the authority to regulate six key greenhouse gases as pollutants under the CAA. Relying on this decision, the EPA, as required by the CAA, rapidly prepared an "endangerment finding" to establish the cause-and-effect relationship "that greenhouse gases in the atmosphere endanger the public health and welfare of current and future generations." Sources within the agency say that the final decision is expected by the end of this year.

Despite the predictable judicial review, it’s inevitable that an endangerment finding is coming. I have no doubt that the EPA will then immediately begin preparing draft rules to control those six gases, the principal one being CO2.

Let’s take this thought experiment one step further. Should the endangerment finding pass judicial scrutiny (and that’s a big "if"), then expect a flood of new regulations related to CO2 (of most interest to power generators using fossil fuels) to blanket our economy within a year or two. For power plants, those emissions would fall under the EPA’s New Source Review permit program.

My guess is that the rules would necessarily cover all fossil plants, as little CO2 reduction would be achieved if they only applied to new permits. If this were true, then the next question becomes: What is BACT for CO2?

Changing the Rules of the Road

The rules for identifying a BACT have a long history. When a plant developer selects the generation technology for a project, an environmental, technical, and economic assessment of emissions control technology options is performed. This is a very important point: For the past 20 years, the practice has been for the developer to select the plant’s generation technology, and then the emissions control options for each pollutant are evaluated, guided by precedent set by prior projects. This practice is precisely why the EPA in the past did not deem integrated gasification combined cycle (IGCC) a BACT technology for the combustion of coal when the plant developer had selected a conventional combustion technology. However, this practice has recently been dealt a severe blow.

On September 25, the EPA Appeals Board granted a request by the EPA to voluntarily remand a permit that the agency had issued to the Desert Rock Energy Facility, located in northwest New Mexico. Desert Rock, a 1,500-MW coal-fired plant, is to be located on Navajo Nation property. The EPA already had taken almost six years to approve the final permit after deeming the application complete in 2002. Nine months after issuing the permit, EPA Administrator Lisa Jackson requested that the Appeals Board grant a voluntary remand. The Appeals Board subsequently ordered the developer to prepare another BACT report, but this time the developer was directed to consider IGCC as a potential alternative combustion technology.

The Appeals Board decision contravenes two other state court decisions in Texas and Georgia that found that an IGCC analysis was not required because it requires a complete redesign of the plant. The EPA seems to have shifted its rudder and is now sailing against 20 years of its own BACT guidance and several court precedents.

Much Uncertainty Remains

If the EPA prevails in the legal fight over the Appeals Board decision on Desert Rock, and thereby effectively defines plant generation technology as part of its BACT analysis, then we will reach a completely different answer to the question of BACT selection for CO2 than we would have in prior years.

For a conventional steam generator, reductions in CO2 emissions are achieved by increasing thermal efficiency. If BACT emission levels continue to be set on a per-unit-fuel basis, then I would expect emission levels for future plants to be set by the EPA such that only those technologies with the highest efficiency, such as the ultrasupercritical boiler under construction at SWEPCO’s John W. Turk Jr. plant in Arkansas, could be selected. That means, in effect, that the EPA would be determining generation technology: ultrasupercritical technology for coal combustion and the most efficient gas turbine in a size-class for gas combustion (plus carbon capture and sequestration for both). As a result, siting approval will become contingent upon available sequestration fields rather than on fuel sources or transmission lines.

If retrofits are required for existing units (which would be necessary to have any appreciable effect on CO2 emissions), then these are some likely BACT options:

  • Cofire with biomass at existing coal plants (perhaps up to 25%).

  • Dry coal using plant waste heat.

  • Use renewables at existing plants to form hybrid cycles to reduce fuel consumption. An example is using concentrating solar power systems to produce thermal energy for feedwater heating or photovoltaic systems to produce electricity for plant auxiliary systems.

My hope, should this scenario prove true, is that the EPA’s stick be used to redirect rather than bludgeon the power industry into submission.

Dr. Robert Peltier, PE, is POWER’s editor-in-chief.