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Flue Gas Desulphurization is a technology used to remove sulfur dioxide (SO₂) from industrial exhaust gases produced during fuel combustion in power, cement, chemical, and waste-to-energy plants. FGD systems prevent acid gas emissions from entering the atmosphere and mitigate environmental and health risks.

There are three main FGD methods: wet scrubbing, spray-dry (semi‑dry) scrubbing, and dry sorbent injection. In wet systems, sulfur dioxide is absorbed using a limestone or lime slurry and the reaction produces gypsum, which can often be reused. Spray-dry or semi-dry systems use lime-based sorbents with no wastewater but generate dry by-products, while dry injection systems introduce powdered sorbents directly into flue gas for removal of SO₂ without liquid handling.

Wet FGD achieves the highest SO₂ removal rates (typically over 90 %) and can produce reusable gypsum. However, it has higher installation and operational costs, requires wastewater treatment, and can lead to corrosion if not managed correctly. Semi-dry systems offer lower water use, smaller footprint, and reduced waste handling, but are somewhat less efficient. Dry injection methods are simple and flexible, but efficiency can vary based on process conditions.