The process proceeds in two main stages:
To remove sulphur oxides (SOx) and other acidic components (HCl, HF), the flue gas is brought into intensive contact with seawater in the absorption zone to ensure mass transfer from the gaseous into the liquid phase. The seawater from the absorption zone is gassed with air before being returned to the sea in order to ensure oxidation of the separated SO2 to sulphate.
The core of seawater FGD engineering is the absorber that separates SO2 from flue gas. A spraying tower is used for this purpose, with the flue gas flowing from bottom to top. The absorbent seawater is evenly sprayed via several spraying levels to ensure ideal conditions for mass transfer with the gas flow. The seawater required for absorption is pumped to the spraying levels. The seawater can be co-currently and counter-currently distributed, with a combination of co-current and counter-current normally being used. The arrangement of the nozzles in the spraying tower is essential to the separation 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 seawater from the absorption zone is mixed with fresh seawater from the power plant condenser to increase the pH value and is then conveyed to the further treatment system. To treat the seawater, blowers and suitable aeration devices blow a finely distributed air flow into the water to ensure oxidation of the separated SO2 to sulphate. Depending on the required water quality, it may be necessary to blow in more air (in addition to the air required for oxidation) and thus to increase the pH value by stripping CO2 from the water.
Depending on the conditions, oxidation can take place in the sump of the absorber or in a downstream basin. Once treated, the seawater is returned to the sea