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The University of Southampton

Research project: Enhancing Mercury Capture by wet FGD Systems

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The project was funded by a grant from the British Coal Utilisation Research Association (BCURA).

Wet Flue Gas Desulphurisation (FGD) systems are widely employed at power stations to remove gaseous sulphur dioxide from coal combustion flue gases. They also offer the additional benefit of being able to remove significant amounts of mercury (Hg) from the flue gas. However, mercury removal efficiencies vary widely and are strongly dependent on the form of Hg in the flue gas: Whereas oxidised mercury species can be efficiently captured by the scrubbing solution, elemental mercury vapour is not retained. A major problem that still needs to be resolved is that the absorbed ionic mercury is not stable in the scrubber liquor, but can be reduced to volatile elemental mercury and re-emitted to the gas phase. Mercury transformation and re-emission is highly dependent on the scrubber chemistry and operating conditions and is regarded as the main limitation on the Hg capture efficiency of wet FGD systems.

The aim of the current project was to gain a better understanding of the absorber chemistry and mercury re-emission, with a view to maximising Hg removal by wet scrubbers. This was studied through a combination of bench-scale tests and field sampling of FGD scrubber liquors.

The main objectives of the project were:

  • To set up a bench-scale FGD system that will allow us to explore the chemistry of wet scrubbers and the factors influencing mercury absorption and retention
  • To investigate the extent of Hg retention and emission under various experimental conditions
  • To evaluate the effect of different types of scrubber additives on Hg absorption and elemental Hg re-emission
    with the overall aim of maximising Hg removal by wet scrubbers.

Related research groups

Water and Environmental Engineering Group
Ratcliffe FGD at night (photograph courtesy of E.ON)
Ratcliffe FGD at night
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