Simultaneous Removal of SO_2 and Trace As_2O_3 from Flue Gas: Mechanism, Kinetics Study, and Effect of Main Gases on Arsenic Capture

摘要

Sulfur dioxide (SO_2) and trace elements are pollutants derived from coal combustion. This study focuses on the simultaneous removal of SO_2 and trace arsenic oxide (As_2O_3) from flue gas by calcium oxide (CaO) adsorption in the moderate temperature range. Experiments have been performed on a thermogravimetric analyzer (TGA). The interaction mechanism between As_2O_3 and CaO is studied via XRD detection. Calcium arsenate [Ca_3(AsO_4)_2] is found to be the reaction product in the range of 600-1000℃. The ability of CaO to absorb As_2O_3 increases with the increasing temperature over the range of 400-1000℃. Through kinetics analysis, it has been found that the rate constant of arsenate reaction is much higher than that of sulfate reaction. SO_2 presence does not affect the trace arsenic capture either in the initial reaction stage when CaO conversion is relatively low or in the later stage when CaO conversion is very high. The product of sulfate reaction, CaSO_4, is proven to be able to absorb As_2O_3. The coexisting CO_2 does not weaken the trace arsenic capture either.