CO2 Capture from PC Boilers with O2-Firing

The U.S. Department of Energy (DOE) is investigating CO2 recovery from fossil-fuelbased power cycles as a greenhouse gas mitigation strategy. Given that the most common such cycle is the conventional pulverized coal-fired plant, a system that could be retrofit to such boilers for CO2 recovery would have broad applicability. Argonne National Laboratory (ANL) was an early investigator of such systems, proposing them as a source of CO2 for enhanced oil recovery. Removal of CO2 from conventional pulverized coal plant flue gas requires treatment of a large volume of gas dilute in CO2. By substituting nearly pure O2 for air as oxidant, the volume of the gas is greatly reduced and the CO2 concentration increased, permitting more economical CO2 recovery. Such a system was originally proposed by researchers at ANL as a source of CO2 for enhanced oil recovery (EOR), but it has recently been studied as a means of reducing CO2 emissions from coal-fired power plants. There is particular interest in this CO2 recycle boiler as a means of retrofitting CO2 control to existing plants. ABB Power Plant Laboratories (Windsor, Connecticut, now Alstom Power) has performed a CO2/O2 retrofit design study of the Trans Alta Corporation’s Sundance Unit 1 boiler. Significantly, that study found that no major modification of the boiler was required for the retrofit. These results confirm technical viability. The high cost of air separation will determine economic viability. Our interest has been in extending this analysis to U.S. plants that might be retrofit candidates. A key difference is that the Sundance plant uses extremely low sulfur coal and requires no post-combustion sulfur removal. A major retrofit at a U.S. plant will result in post-combustion sulfur cleanup requirements. We have therefore focused on the fate of sulfur in the gas path and the performance of sulfur removal equipment. We have also extended previous analyses by considering upstream and downstream processes with the ultimate goal of completing a life cycle assessment. Product transport, in particular, introduces important technical and economic challenges.