FGD refers to flue gas desulfurization, which removes sulfur oxides from flue gas or other industrial waste gas. In flue gas desulfurization technology, according to the types of desulfurizers, it can be divided into the following five methods: calcium method based on CaCO3 (limestone), magnesium method based on MgO, sodium method based on Na2SO3, ammonia method based on NH3 and organic alkali method based on organic alkali.

SO2 in flue gas? It is acidic in nature and can remove SO2 from flue gas by reacting with appropriate alkaline substances. The most commonly used alkaline substance for flue gas desulfurization is limestone (calcium carbonate,? CaCO3), quicklime (calcium oxide, CaO) and hydrated lime (calcium hydroxide, Ca(OH)2).

Limestone is abundant, so it is relatively cheap. Both quicklime and hydrated lime are made by heating limestone. Other alkaline substances such as sodium carbonate (soda ash), magnesium carbonate and ammonia are sometimes used.

Extended data:

In wet flue gas desulfurization system, alkaline substances (usually alkaline solution, more commonly alkaline slurry) meet with flue gas in spray tower. SO2 in flue gas is dissolved in water to form dilute acid solution, and then neutralized with alkaline substances dissolved in water.

Sulfite and sulfate produced by the reaction are precipitated from the aqueous solution, which depends on the relative solubility of different salts in the solution. For example, the solubility of calcium sulfate is poor, so it is easy to precipitate;

In dry and semi-dry flue gas desulfurization systems, flue gas is injected into flue gas stream through alkaline absorbent bed, or solid alkaline absorbent contacts with flue gas.