Before carbon dioxide (CO2) gas can be sequestered from power plants and other point sources, it must be captured as a relatively pure gas. On a mass basis, CO2 is the 19th largest commodity chemical in the United States, and CO2 is routinely separated and captured as a by-product from industrial processes such as synthetic ammonia production, H2 production, and limestone calcination.

Existing capture technologies, however, are not cost-effective when considered in the context of sequestering CO2 from power plants. Most power plants and other large point sources use air-fired combustors, a process that exhausts CO2 diluted with nitrogen. Flue gas from coal-fired power plants contains 10-12 percent CO2 by volume, while flue gas from natural gas combined cycle plants contains only 3-6 percent CO2. For effective carbon sequestration, the CO2 in these exhaust gases must be separated and concentrated.

CO2 is currently recovered from combustion exhaust by using amine absorbers and cryogenic coolers. The cost of CO2 capture using current technology, however, is on the order of $150 per ton of carbon - much too high for carbon emissions reduction applications. Analysis performed by SFA Pacific, Inc. indicates that adding existing technologies for CO2 capture to an electricity generation process could increase the cost of electricity by 2.5 cents to 4 cents/kWh depending on the type of process.

Furthermore, carbon dioxide capture is generally estimated to represent three-fourths of the total cost of a carbon capture, storage, transport, and sequestration system.

The program is pursuing evolutionary improvements in existing CO2 capture systems and also exploring revolutionary new capture and sequestration concepts. The most likely options currently identifiable for CO2 separation and capture include:

• Absorption (chemical and physical)
• Adsorption (physical and chemical)
• Low-temperature distillation
• Gas separation membranes
• Mineralization and biomineralization

Opportunities for significant cost reductions exist since very little R&D has been devoted to CO2 capture and separation technologies. Several innovative schemes have been proposed that could significantly reduce CO2 capture costs, compared to conventional processes. "One box" concepts that combine CO2 capture with reduction of criteria pollutant emissions are being explored as well.

Examples of activities for this program element include:

• Research on revolutionary improvements in CO2 separation and capture technologies
  • new materials (e.g., physical and chemical absorbents, carbon fiber molecular sieves, polymeric membranes);
  • micro-channel processing units with rapid kinetics;
  • CO2 hydrate formation and separation processes;
  • oxygen-enhanced combustion approaches;
• Development of retrofittable CO2 reduction and capture options for existing large point sources of CO2 emissions such as electricity generation units, petroleum refineries, and cement and lime production facilities;
• Integration of CO2 capture with advanced power cycles and technologies and with environmental control technologies for criteria pollutants.