As discussed elsewhere in this edition of The Climate Report, U.S. EPA's April 1 adoption of greenhouse gas emissions standards for vehicles will trigger regulation of stationary sources, such as manufacturing plants, under the Clean Air Act, beginning in 2011. New or modified stationary sources thus subject to the Act's preconstruction permitting requirements for greenhouse gas emissions would be required to include the Best Available Control Technology ("BACT") for those emissions in their designs. By law, BACT is set on a case-by-case basis.

However, there is currently no commonly available "add-on" technology (like a smokestack scrubber) to capture greenhouse or destroy gases from stationary sources, so both regulators and business managers are uncertain how this new obligation will be implemented. Initially, BACT might range from energy efficiency requirements that reduce the amount of fossil fuel consumed to incorporation of technologies that reduce the amount of greenhouse gas produced.

Carbon Capture and Storage

The feasibility of the elements of carbon capture and storage ("CCS") have been demonstrated. Several coal and natural gas power plants in the United States use either pre- or post-combustion technologies to capture carbon emissions on a small scale for commercial purposes. A few states have pipeline networks capable of transporting liquefied carbon dioxide. Companies currently capture and store carbon in various geological formations in places such as North Dakota, Wyoming, Canada, Norway, and Algeria.

However, commercially viable implementation of CCS on the scale necessary to address fossil fuel emissions is likely at least a decade away. Additional investment in research and development, and progress on permitting and liability issues, must occur. Estimates of the cost of implementing large-scale CCS vary drastically, from $29 to $180 per ton of carbon dioxide avoided. Even estimates at the lower end of this scale would translate into millions of dollars in implementation costs for stationary sources at the currently proposed emissions thresholds.

Biomass Cofiring

In biomass cofiring, coal-burning sources (such as boilers) replace a percentage of the coal with carbon-neutral biomass, such as wood by-products. According to the National Renewable Energy Laboratory, cofiring 15 percent biomass with coal reduces greenhouse gas emissions by 18 percent and may also reduce emissions of other air pollutants, such as sulfur dioxide and nitrous oxides. Accordingly, various commentators, as well as at least four Attorneys General, have proposed biomass cofiring as potential BACT for greenhouse gas emissions from certain coal-fired emissions sources.

However, biomass may decrease efficiency, because it produces only two-thirds as much energy as coal. Facilities must typically make an initial capital investment of several million dollars to modify a combustion system's burner and feed-intake systems to accommodate biomass. They also incur annual costs such as the cost of the biomass (which may fluctuate with demand) and the cost of storing and drying the biomass to prepare it for burning. Finally, coal presents facilities with a far more established and reliable supply chain than biomass.

Integrated Gasification Combined Cycle Technology

The integrated gasification combined cycle ("IGCC") technology gasifies coal with oxygen or air, and the resulting "syngas" fuels a gas turbine to generate electricity. The exhaust from the gas turbine passes through a heat recovery system, producing steam that drives a steam turbine, which also generates electricity. IGCC is extremely efficient, because the combined cycle technology captures the otherwise wasted exhaust from the gas turbine and uses it to produce additional electricity without additional carbon dioxide emissions.

IGCC systems are also attractive as BACT because they would be amenable to greater emissions reductions in the future, if carbon capture and storage technology becomes viable. Carbon dioxide could be captured before combustion, during the IGCC gasification process. Retrofitting an IGCC power plant for carbon capture is expected to be easier and less expensive than retrofitting a conventional coal-fired power plant.

IGCC power plants cost 20 to 25 percent more to build than conventional coal power plants. Only a few exist in the United States, and the Department of Energy provided substantial funding for those projects. In addition, IGCC technology is a controversial proposed BACT, because some courts, commentators, and even a past EPA Director of the Office of Air Quality, Planning, and Standards believe that requiring the use of IGCC would involve a redesign of the facility, rather than addition of a control technology.

Other Proposed BACT

Coal drying is a likely BACT for coal-powered combustion sources, while use of high-efficiency boilers and cogeneration technology are potential BACT for any fossil fuel combustion source. Additionally, a number of natural-gas power stations are in the process of implementing solar-thermal technology, which might be deemed BACT for coal-fired power plants as well. Finally, though some argue that fuel-switching to alternative energy sources, such as nuclear, geothermal, wind, solar, and natural gas, ought to constitute BACT, others argue that such a radical change would redefine the emissions unit and exceed the limits of the BACT requirement.

The Climate Change Work Group

EPA created the Climate Change Work Group ("CCWG") to "discuss and identify the major issues and potential barriers" to implementing greenhouse gas regulation for stationary sources under the Clean Air Act. The primary task is to provide guidance on establishing BACT for greenhouse gas emissions, including when a proposed BACT crosses the line from limiting emissions to unacceptably redefining the source. The work group is specifically considering the feasibility of CCS technology. Thus far, the CCWG has issued only a scoping-level Interim Report, which notes that for CCS to be a feasible BACT option, both capture and sequestration technologies must be available for the particular facility.