the period between now and 2020 could be sufficient for assessing the viability of CCS if demonstration projects proceed as rapidly as possible. If these investments are made now, 10 GW of CCS projects could be in place by 2020. If not, the ability to introduce CCS will be further delayed. Public acceptance of CCS as a viable strategy can be secured only as a result of demonstration projects that perform reliably.
In 2006, power plants generated about 52 percent of U.S. electricity from coal and 16 percent from natural gas. Many of these plants could operate for 60 years or more, a period that plant operators do not want to shorten, given that constructing new plants requires obtaining large amounts of capital and numerous permits. Yet, significantly limiting U.S. greenhouse gas emissions will require dramatically reducing emissions from these plants. Alternatives include (1) retiring the plants; (2) raising the generating efficiency, thereby reducing greenhouse gas emissions per unit of electricity produced; (3) retrofitting with CO2 post-combustion capture capability; or (4) repowering/rebuilding at the site, resulting in a unit that is entirely or mostly new.
The two principal technologies for future coal-burning power plants are (1) those using an integrated gasification and combined cycle, which converts coal into a synthesis gas, then removes impurities from the coal gas before it is combusted, and finally utilizes excess heat from the primary combustion and generation in a steam cycle similar to that of a combined-cycle gas turbine and (2) enhancements to traditional pulverized-coal technologies. These technologies have varying potential for reducing coal plants’ greenhouse gas emissions. Pulverized-coal units now produce nearly all of the coal-based electric power in the United States. Compared with older steam plants, which have an efficiency of about 34–38 percent, these “ultrasupercritical” plants could reach 40–44 percent efficiency between 2020 and 2035. Replacing a plant of 37 percent efficiency with one of 42 percent efficiency would result in a 12 percent reduction in CO2-equivalent emissions and fuel consumption per kilowatt-hour of output.
Reducing emissions more dramatically in pulverized-coal plants will require CCS. With today’s technology, the cost for retrofitting to 90 percent CO2 capture at an existing pulverized-coal plant would be nearly as high as the cost of the original plant. In addition, 20–40 percent of the plant’s energy would be diverted for the separation, compression, and transmission of the CO2, thus reducing its effi-