FgD

FGD (Flue‑Gas Desulfurization) refers to a set of technologies used to remove sulfur dioxide (SO₂) from the exhaust flue gases of fossil‑fuel power plants and other industrial processes. The primary purpose of FGD is to reduce air‑pollution emissions, thereby helping facilities comply with environmental regulations such as the United States Clean Air Act and the European Union Sulphur Directive. The most common approach is wet scrubbing, in which flue gas is contacted with an aqueous slurry of limestone or lime; SO₂ reacts chemically to form gypsum (calcium sulfate dihydrate), which can be removed and, in many cases, sold for use in construction materials. Alternative methods include dry and semi‑dry processes that inject sorbents like hydrated lime into the gas stream, allowing the reaction products to be captured on filters or electrostatic precipitators.

Typical FGD installations consist of gas‑flow ducts, spray nozzles or injectors, reaction chambers, and downstream particulate control devices. Performance is measured by the percentage of SO₂ removal, which modern wet scrubbers can achieve at 90–95 % efficiency. Operational considerations involve water consumption, slurry handling, and disposal or utilization of the by‑product gypsum. Environmental benefits include reduced acid rain formation and lower concentrations of fine particulate matter, though the processes generate secondary waste streams that must be managed.

Research continues on improving reagent utilization, reducing energy penalties, and integrating FGD with carbon‑capture and nitrogen‑oxide reduction technologies. In addition to power generation, FGD systems are employed in cement kilns, steel mills, and waste‑incineration plants where sulfur‑containing fuels are burnt.