Flue Gas Desulfurisation

Summary: The removal of SO₂ from power station flue gases, typically by reaction with CaO or CaCO₃ (wet scrubbing). Tags: igcse chemistry definition environmental-chem Created: 2026-07-14 Last Updated: 2026-07-14

Flue gas desulfurisation (FGD) is a chemical process used to remove sulfur dioxide (SO₂) from the exhaust gases of coal- and oil-fired power stations before they are released into the atmosphere, thereby preventing the formation of acid rain. The most common method, known as wet scrubbing, involves passing the flue gas through a slurry of calcium oxide (quicklime, CaO) or calcium carbonate (limestone, CaCO₃), which reacts with the acidic SO₂ to form calcium sulfite (CaSO₃) or, with further oxidation, calcium sulfate (CaSO₄), better known as gypsum. The key reaction using limestone is: CaCO₃ + SO₂ → CaSO₃ + CO₂, or with forced oxidation: 2CaCO₃ + 2SO₂ + O₂ → 2CaSO₄ + 2CO₂; the gypsum produced is a saleable by-product used in the manufacture of plasterboard and cement. FGD systems can remove over 90 percent of the sulfur dioxide from flue gases, making them one of the most effective technologies for reducing industrial air pollution. IGCSE exams typically ask students to state the environmental problem caused by SO₂ (acid rain), write a balanced equation for one of the scrubbing reactions, and explain why removing SO₂ from power station emissions is an essential pollution-control measure.

Key term — IGCSE Chemistry (0620/0971) glossary.