Flue Gas De-Suphurisation (FGD) simply requires that SO2-laden exhaust gases to come into intimate contact with water (H2O) and typically Limestone (CaCO3). The reactions that take place are:
CaCO3 + 2SO2 + H2O = Ca(HSO3)2 + CO2
Secondary oxidation with Limestone converts the resultant Calcium Sulphite to the more useable Gypsum:
Ca(HSO3)2 + CaCO3 + O2 + H2O = 2CaSO4•2H2O + CO2
There are many FGD processes used – some with separate reaction chambers – others with combined reaction chambers. They are predominantly fitted after waste heat has been recovered and the solids have been removed. They typically use spray chambers to maximise contact between the flue gas and the reactant.
Where the exhaust gas is reheated before release to atmosphere, CODEL GCEM-40 direct in-situ analysers provide the most convenient solution for both pre- and post-FGD gas analysis. Without re-heat, it may be necessary to use a CODEL GCEM-40E hot-extractive system post-FGD to eliminate liquid droplets prior to analysis.