Question

Which one of the following is most commonly used raw material in flue gas desulfurization units?

• A. Limestone
• B. Titanium Oxide
• C. Fenton reagent
• D. Beryllium Oxide

Hint:

Wet limestone scrubbing accounts for more than 90% of world FGD installations due to high efficiency and low cost.

Answer 1

The Correct Option is A

Flue Gas Desulfurization (FGD) units remove SO$_2$ from exhaust gases of coal-based and industrial boilers.
The most widely used method globally is the wet limestone–gypsum process.
Limestone (CaCO$_3$) is preferred because it is low-cost, widely available, and reacts efficiently with SO$_2$.
The key chemical reactions occurring inside an FGD absorber are:
\[ \text{SO}_2 + \text{CaCO}_3 \rightarrow \text{CaSO}_3 + \text{CO}_2 \]
\[ \text{CaSO}_3 + \tfrac{1}{2}\text{O}_2 + 2\text{H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \]
The final product gypsum can be sold to the cement and construction industry.
Titanium oxide is used as a catalyst/pigment, not for SO$_2$ removal.
Fenton reagent is used in wastewater oxidation, not air pollution control.
Beryllium oxide is toxic and not used industrially for flue gas treatment.
Hence, limestone is the correct and universally used raw material in FGD systems.
Final Answer: Limestone