Flue Gas Desulphurization (FGD)
Historically Gaseus Sulphur Dioxide (SO2) emissions have been controlled by either dispersion or reduction. However worldwide environmental legislation now requires everyone to address SO2 emission, consequently regulations are in place in Indonesia to impose such controls on the operators of Coal Fired Power Plant. There are various methods to implement such reduction, and in coal fired power plant, the most common initial approach being to select, purchase and burn lower Sulphur fuel and frequently by the installation and operation of FGD systems. At Tanjung Jati B we burn low shulphur coals and apply a sea water, wet limestone FGD Process.
The FGD system at Tanjung Jati B principally comprices; limestone (reagent) offloading and handling system, limestone (reagent) preparations system, a dedicated Absorber area system, primary dewatering and chloride purge system, secondary dewatering system comprising two drum vacuum filter trains, and dedicated water systems.
Each unit combustion gas is directed to dedicated absorbers, where the gas passes through a slurry spray comprising the ground limestone and sea water. The absorber sump from where the slurry is recirculated is subject to forced aeration.
The simple FGD chemistry can be expressed :
SO2 + CaCO3 + 1/2H2O - CO2 + CaSO3.1/2H2O (Calcium Sulfite)
The oxidation process converts all of the liquid sulfite (and bisulfite) ions to sulfate ions, sulfate precipitates with calcium as gypsum CaSO3.1/2H2O + O2 + H2O - CaSO4.2H2O (Calcium sulfate/Gypsum). Water evaporates from the flue gas scrubbing liquid (sprays), as the flue gas cools to the adiabatic saturation temperature, consequently under equilibrium conditions, water must be added to the system to make up for water loss. If the scrubbing water was not bled from the system, the salts (chlorides) in the incoming make up water would gradually concentrate. Concequently chemistry and density (15% Suspended solids) is maintained by limestone slurry addition and slurry extraction in order to adjust pH.