Oxycombustion in pulverized coal-fired boiler: a promising technology for CO 2 capture

A promising technology that enables CO2 capture from pulverized coal-fired power plants is described. The technology involves the replacement of the combustion air by pure oxygen diluted with recirculated flue gases, and is referred to as oxycombustion process. The resulting CO2/O2 oxidizer provides a high flexibility for temperature and flowrate control inside the boiler. Therefore, both retrofit and new boiler applications are envisioned. The economics of the oxycombustion process have been assessed and compared to that of the same capacity air-blown coal-fired boiler equipped with amine (MEA) scrubber for carbon capture. Both capture technologies result in increased cost of electricity. However, this increase is expected to be at least 30% lower using O2/CO2 technology than using MEA system. The oxycombustion process leads to approximately $20/ton CO2 avoided, while MEA process requires more than $40/ton CO2. The main results of experimental tests performed on a pilot-scale boiler are also presented. Low-sulfur sub-bituminous coal was burned and the reported results highlight the characteristics of oxygen-fired mode versus air-fired mode. 70% NOx emission reduction has been observed, and emission level as low as 0.08 lb / 10 6 Btu has been measured. The flue gas flow rate has been reduced by 80%. Oxycombustion theoretically results in 95% of CO2 content in the flue gases. 80% CO2 content in the flue gas has been measured so far due to air-infiltration. Further investigations are in progress to reduce the air-infiltration and provide cost-effective flue gas purification technologies. It is concluded that the oxycombustion technology represents a costeffective and technically viable solution for CO2 capture from coal-fired power plants.