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•Article: Protective Materials For FGD Infrastructure

By Sauereisen

Flue gas desulfurization (FGD) is the technology used for removing sulfur dioxide (SO₂) from the exhaust flue gases in power plants and has a long tradition with more than 50 years of traceable references. Power plants that utilize FGD usually burn coal and/or oil to generate steam used for the steam turbines that drive electricity generators. Sulfur dioxide removal has become an increasingly important issue as the power and co-generation industries strive to increase efficiencies and meet more demanding environmental regulations. For a typical coalfired power plant, an FGD system can remove up to 90 percent or more of the SO₂ in the flue gases. Most FGD systems employ two stages – one for solids removal (precipitator or baghouse) and the other for SO₂ removal (absorber or scrubber). Attempts have been made to remove both the solids and SO₂ in one scrubbing vessel, however, most power plants still use two stages. Though there are others methods used, the most common FGD system utilized by USA power plants is called wet scrubbing.

Corrosion in FGD systems is an extremely important concern associated with wet scrubbers. After the hot SO₂-containing gasses from the boiler are quenched in a scrubber unit, the exiting flue gas is now saturated with water but still contains residual SO₂. The SO₂ reacts with pyritic iron and is converted to SO₃. The SO₃ and water combine to form highly corrosive sulfuric acid (H₂SO₄), and as the gas cools, the H₂SO₄ condenses on the downstream equipment such as fans, ducts, and the exhaust stack. The corrosive acid is more prevalent within the exhaust stack section due to increased condensation.

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•Article: Protective Materials For FGD Infrastructure