December 1, 2009

What Is BACT for CO2?

Dr. Robert Peltier, PE

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.