Technical Overview of Carbon Dioxide Capture Technologies for Coal-Fired Power Plants

SUMMARY Concerns about global climate change have prompted interest in capturing and sequestering CO2 generated at coal-fired power plants. This document provides a technical introduction to methods of capturing CO2, which involves separating the CO2 from the other constituents in the flue gas. The methods discussed in this paper are post-combustion capture, oxygen-fired combustion, and pre-combustion capture: • Post-combustion capture of CO2 from flue gases uses proven chemical absorption methods that can be installed at existing power plants, but the impact on O&M and capital costs would be significant. For a coal-fired plant, the size and capital cost of the absorber would be comparable to an existing SO2 scrubber, but approximately 1/4 to 1/3 of the total steam produced by the plant would be consumed in the chemical absorbers, thus reducing the plant capacity by approximately 25% to 35%. This option allows continued use of existing coal-fired power plants and would likely be the first option implemented. Although significant technical challenges exist, developing this option is primarily an issue of technology transfer since the methods are currently in use on a smaller scale in other applications. • Oxygen-fired combustion, which produces a 90% CO2 exhaust stream, provides some multi-pollutant control, but the technology is less mature and the O&M and capital costs would be comparable to post-combustion capture. Specifically, the oxygen separation plant would consume about 23% to 37% of the total plant output and cost about the same as the absorber. This option is most appropriate for new plant projects and would become attractive only when new plant development becomes more desirable than retrofitting existing coal-fired plants. Significant technical challenges will need to be addressed before it can be implemented. • Pre-combustion capture, which involves capturing CO2 from syngas generated in a coal gasifier, is potentially less expensive than post-combustion capture. It is considered a promising long-term option but the required technology is still being developed. Power plants that use pre-combustion capture are also attractive because they are based on a combined cycle (Brayton and Rankine) design, which is inherently more efficient than the Rankine-only cycle that traditional coal plants use. In addition, since hydrogen production is a potential option, pre-combustion capture is also compatible with a hydrogen economy. This option is also only appropriate for new plant projects. Significant technical challenges will need to be addressed before it can be implemented. The main conclusion of the paper is that the technical challenges of CO2 capture appear to be similar in scope and complexity to the challenges the power industry has already overcome in successfully removing SO2 and NOX from the flue gas, but the economic impacts of CO2 capture