Coal combustion with flue gas recirculation for CO2 recovery

Among gases responsible for greenhouse effect, carbon dioxide is one of the most important, in part due to the very large quantity emitted. Worldwide, coal consumption for electric power generation accounts for 11% of CO2 emissions. The identification of environmentally sound methods of CO2 storage or sequestration coupled with the development of more energy and cost efficient schemes for CO2 recovery from existing and emerging coal-fired power generation plants may be necessary as part of mitigation strategies to reduce global CO2 emissions. The present work aims at investigating coal combustion behaviour when part of the flue gases are recirculated in order to maximize CO2 concentration in the flue gas prior to its recovery. Combustion then takes place in a medium that contains, at least 85-98 vol.% of CO2. Coal combustion in a high CO2 concentration environment was first simulated by conducting experiments in O-2/CO2 mixtures, for oxygen concentrations ranging from 28 to 42%, in order to identify the influence of CO2 on key combustion parameters such as flame temperature, heat flux and pollutant formation. The next stage was to run coal combustion experiments with flue gas recirculation. This paper describes the pilot-plant facility and presents and compares results obtained for coal combustion in air, in O-2/CO2 mixtures, and with flue gas recirculation.