In wet flue gas desulphurisation, open spray tower absorbers have prevailed which are divided into two principal zones. These are the absorption zone exposed to the flue gas and the absorber sump, in which the limestone slurry is trapped and collected. To prevent deposits in the absorber sump, the slurry is suspended by means of mixing mechanisms.
The flue gas flows into the absorber above the fluid level and then through the absorption zone, which comprises overlapping spraying levels and a mist eliminator.
The limestone slurry sucked from the absorber sump is finely sprayed co-currently and counter-currently to the flue gas through the spraying levels. The arrangement of the nozzles in the spraying tower is essential importance to the removal efficiency of the absorber. Flow optimisation is therefore extremely necessary. In the mist eliminator, the drops carried from the absorption zone by the flue gas are returned to the process. At the outlet of the absorber, the clean gas is saturated and can be directly removed via a cooling tower or wet stack. Optionally the clean gas can be heated and routed to a dry stack.
The slurry removed from the absorber sump undergoes preliminary dewatering by way of hydrocyclones. Generally this pre-concentrated slurry is further dewatered through filtration. The water, obtained from this process, can be largely returned to the absorber. A small portion is removed in the circulatory process in the form of waste water flow.