Mercury re-emission from adipic acid enhanced FGD absorber - Full scale investigations on ∼400 MWe boiler (lignite) with oxidant injection to flue gas

The paper presents the results of an industrial scale study of mercury re-emission phenomenon from the flue gas desulphurization (FGD) absorber that purifies the lignite combustion gases. The available research results on re-emission phenomena at a laboratory and pilot scale were reviewed and verified in full scale conditions. It was confirmed that the phenomenon of re-emission is dependent on the FGD absorber operating conditions (pH, ORP) and the concentration of adipic acid in the sorption solution. Based on the conducted tests it was found that proper regulation of the FGD absorber's operating parameters can significantly reduce Hg-0 re-emission to the atmosphere. The interesting phenomenon was observed during the test, when the oxidant was fed to flue gas (X > 0.75) and average values of ORP < 140 mV and pH < 6.0 a large amount of Hg-T was released from tested FGD absorber to atmosphere (up to 200 mu g/m(3) ).