Study of Hg and SO3 behavior in flue gas of oxy-fuel combustion system

Oxy-fuel combustion systems have been under development to reduce CO2 emissions from coal-fired power plants. In oxy-fuel combustion system, Hg in the flue gas causes corrosion in CO2 purification and compression units. Also, SO3 in the flue gas corrodes the equipment and ducts of oxy-fuel combustion system. Therefore, Hg and SO3 need to be removed.Babcock-Hitachi conducted tests using a 1.5 MWth Combustion & Air Quality Control System (AQCS) test facility which consists of oxygen supply unit, furnace, Selective Catalytic Reduction (SCR) catalyst, Clean Energy Recuperator (CER), Dry Electrostatic Precipitator (DESP), flue gas recirculation system, Wet Flue Gas Desulfurization (WFGD), and CO2 Compression and Purification Unit (CPU). In both cases of air and oxy-fuel combustion, the Hg removal across the DESP could be improved, and SO3 concentration at the DESP outlet could be reduced to less than 1 ppm by installing a CER upstream of the DESP and reducing the gas temperature at the DESP inlet. Hg was not dissolved in the drain recovered from CO2 compressor, and may be adsorbed at an inner part of CO2 compressor. This indicated that Hg needs to be removed at a location upstream of the CO2 compressor to prevent corrosion of the compressor.