What Does Flue-Gas Desulfurization (FGD) Mean?

Flue-gas desulfurization (FGD) is the removal process of sulphur dioxide (SO2) from flue gas emissions. Sulphur dioxide in gases is produced by many industrial processes such as gasoline refining as well as cement, paper, glass, steel, iron and copper production. Sulphur dioxide emissions are a primary contributor to acid rain and have been regulated by every industrialized nation in the world. SO2 is removed from flue gases by a variety of methods, common ones being:
  • Wet scrubbing using a slurry of alkaline sorbent, usually limestone, lime or seawater to scrub gases
  • Spray-dry scrubbing using similar sorbent slurries
  • Wet sulphuric acid process recovering sulphur in the form of commercial-quality sulphuric acid
  • SNOX flue gas desulphurization removing sulphur dioxide, nitrogen oxides and particulates from flue gases
  • Dry sorbent injection systems
In wet scrubbing systems(the most common form), the flue gas normally passes first through a fly ash removal device, either an electrostatic precipitator or a wet scrubber, and then into the SO2 absorber. The flue gas exiting the absorber is saturated with water and still contains some SO2. These gases are highly corrosive to any downstream equipment such as fans, ducts and stacks.The widely accepted method that may minimize corrosion are: Using materials of construction and designs that allow equipment to withstand the corrosive conditions Corrosion Conditions for equipment used in wet FGD process.
Equipments Corrosion Conditions
Inlet piping, cooling tower SO₂,vapor,etc.
Circulation Tank H₂SO₃, H₂SO₄, fog, etc., Aspirating agent, soot, reaction products
Feed pipe, discharge pipe SO₂, H₂SO₃, H₂SO₄, fog
Absorber SO₂, H₂SO₃, fog of H₂SO₄, pH=3~12
Circulating Tower, Oxidation Tower pH=3~14
Acid Mist Separator Vapor of SO₂, H₂SO₃, fog of H₂SO₄
Concentrator pH=3~12
Duct ≤100°C
Tank Room temperature
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