Fossil fuel fired electric generating plants are the cornerstone of America's central power system. Currently, the existing fossil fuel fleet accounts for about two-thirds of all electricity generated domestically, over 40% from coal alone. Electricity demand is expected to increase dramatically over the next 30 years, and adding new generating capacity typically requires long lead time. In the meantime, the United States will continue to rely on existing plants to provide a substantial amount of affordable electric power for years to come.
Retrofitting the Existing Fleet of Power Plants
There is vast potential for retrofitting carbon capture technologies to the existing fossil fuel fleet. In 2011, coal-fired power plants produced nearly 35 percent of the total U.S. carbon dioxide (CO2) emissions. In addition, over 40 percent of the existing U.S. coal generating capacity is located directly above potential geologic sequestration sites according to the Carbon Sequestration Atlas of the United States and Canada. This includes almost 150 electric generating sites, or nearly one-sixth of the total U.S. CO2 emissions. By retrofitting CO2 capture technologies to just the coal-fired plants near geologic sinks, billions of tons of CO2 can be permanently sequestered over the remaining life of the existing fleet.
However, today’s capture technologies are not cost-effective when considered in the context of storing CO2 from existing power plants. DOE/NETL analyses suggest that today’s commercially available post-combustion capture technologies may increase the cost of electricity for a new pulverized coal plant by up to 80 percent and result in a 20 to 30 percent decrease in efficiency due to parasitic energy requirements. Additionally, many of today’s commercially available post-combustion capture technologies have not been demonstrated at scales large enough for power plant applications.
Since very little R&D has historically been devoted to carbon capture systems for existing power plants, there is significant potential to reduce the cost and energy demand of CO2 capture and compression processes through technological advancements. The Post-Combustion Capture Research area is pursuing innovative improvements in existing post-combustion CO2 capture systems and also exploring transformational new capture concepts. Additionally, this research area will focus on advanced CO2 compression technologies in order to reduce the cost of increasing the pressure to the 1,200-2,000 pounds per square inch (psi) required for pipeline transportation and geologic storage.
Several advanced technologies and processes have been proposed that could significantly reduce CO2 capture and compression 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 research area include:
- Research on revolutionary improvements in CO2 separation and capture technologies — new materials (e.g., physical and chemical solvents and sorbents, ionic liquids, carbon fiber molecular sieves, polymeric membranes);
- Development of retrofittable CO2 reduction and capture options for existing large point sources of CO2 emissions such as electricity generation units;
- Integration of CO2 capture with advanced power cycles and technologies and with environmental control technologies for criteria pollutants; and
- Development of advanced technologies for CO2 compression such as "shockwave compression."
DOE's R&D in Carbon Control Technologies
The Office of Fossil Energy is engaged in several innovative schemes that could significantly reduce CO2 capture costs, compared to conventional processes. These include:
- Oxyfuel Combustion processes use oxygen rather than air for combustion of fuel. This produces exhaust gas that is mainly water vapor and CO2. The exhaust gas has a relatively high CO2 concentration (greater than 80 percent by volume). Oxyfuel combustion represents an opportunity to improve the economics of CO2 capture.
- Solvents and Sorbents for CO2 separation from flue gas (both physical and chemical) can be further enhanced to reduce cost, improve reaction rates and regeneration loads, and eliminate contamination from other pollutants. This includes technologies such as aqueous ammonia, advanced amines, ionic liquids, metal organic frameworks, and amine-enriched sorbents.
- Advanced Membranes for both oxygen-separation and CO2 capture are key enabling technologies. This effort will evaluate needs for advanced membranes applicable to pulverized coal systems and other conventional combustion systems that will minimize the cost and efficiency losses for CO2 separation.
- Chemical Looping processes that prevent direct contact of air and fuel offer the ability to produce a relatively pure stream of CO2 that does not need to be separated from flue gas. Technical challenges remain in key areas such as solids handling and oxygen carrier capacity, reactivity, and attrition.