CO₂ quality control in oxy-fuel combustion: a dynamic study on the absorption of SO₂ into sodium based aqueous solutions relevant to scrubbing prior to CO₂ compression

Oxy-fuel combustion is an emerging technology to mitigate CO₂ emissions from power plants. Compared with other CO₂ capture technologies, gas impurities in oxy-fuel flue gas are highly concentrated, among which SO₂ is of concern. Dynamic transient experiments have been conducted in a semi-batch well stirred reactor (WSR) relevant to the conditions of the flue gas scrubbers operating at atmospheric pressure prior to CO₂ compression in oxyfuel technology for CCS. SO₂ in N₂ as well as in CO₂ were considered. The initial pH of the solutions considered was those of NaOH (with concentrations of 0.01 M and 1 M), Na₂CO₃ (0.005 M) and NaHCO3 (0.01 M). Analysis of the liquid solutions showed that the concentration of bicarbonate increases with pH at a pH larger than 5.5 indicating a loss of effectiveness of the sodium reagent. A practical discharge pH of the liquid discharge from the scrubber is also greater than 4 as at a lower pH the absorption rate of SO₂ reduced. This operating range is consistent with the reported operating range of the scrubber used in the Vattenfall oxyfuel pilot plant