2. Experimental method
The experiments are conducted with a test-rig consisting of a
continuously operated lab-scale wet FGD and a batch-wise operated
waste water treatment unit. The functional principle of the
test-rig is shown in Fig. 1. The composition of the synthetic flue
gas is 15 vol.% CO2, 3.5 vol.% O2 and balance N2, which is typical
for hard coal firing power plants. At a temperature of 150 C, the
synthetic flue gas is spiked with 2000 mg/m3
STP SO2 and introduced
into the wet FGD. In the absorber, it is brought into contact with the
circulating slurry in a continuous countercurrent process at a temperature
of 60 C. In the sump section of the FGD, the slurry is continuously
stirred and electrically heated. The pH-value in the sump is
controlled to a constant value of 5.1 by dosing CaCO3 slurry. In addition,
the oxidation–reduction–potential (ORP) is measured. The
forced oxidation of dissolved SO2 and its aqueous dissociation products
(S(IV) species) is enhanced by aeration of the sump. The volume
of the slurry is held constant by integration of a fixed overflow channel.
The 3.5 wt.% solid content of the slurry consists of 99 wt.% gypsum.
Aqueous concentrations are adjusted to 1.25 106 mol/l
(=250 lg/l) Hg2+ and 0.014 0.423 mol/l (=0.5 15 g/l) Chloride
Fig