Mode Selection of Flue Gas Recirculation and Balance Calculation of Water Vapor Content for Oxy-Coal Combustion Boilers

Taking the 300 MW oxy-coal combustion boiler as an object of study,the water vapor content in flue gas and the auxiliary power consumption were calculated and compared,at different modes of secondary flue gas recirculation,with the flue gas dehydrated by DCC method or dehydrated and desulphurized by FGD+DCC process.Results show that when the flue gas is merely dehydrated by DCC,if dehydration is not applied in the secondary flue gas recirculation,the volumetric fraction of water vapor in flue gas from oxy-coal combustion system will be 10%-15% higher than that from air combustion;if dehydration is applied in the secondary flue gas recirculation,the former one will be 3% higher than the latter one.Whereas in a FGD+DCC arrangement,when both desulphurization and dehydration are applied in the secondary flue gas recirculation,the water vapor content in flue gas will be slightly higher than that only DCC is used and no dehydration is adopted in the secondary flue gas recirculation.At a recirculating water temperature of 30 ℃,the volumetric fraction of water vapor at DCC outlet is about 4.28%.The total power consumption of fan reaches the minimum under single DCC condition at the mode of dry flue gas recirculation.