What is flue gas desulfurization, and why is it used?

• A. A system (wet or dry scrubber) that removes sulfur oxides from flue gas to meet emission limits and environmental regulations.
• B. A device that increases sulfur content for corrosion protection.
• C. A method to condense sulfur into liquid form.
• D. A system to preheat combustion air.

Answer: (A)

Flue gas desulfurization is a system that removes sulfur oxides from the exhaust of a boiler or power plant, usually using a wet scrubber or a dry scrubber. As the hot flue gas passes through the scrubber, a reagent—like lime or limestone slurry in a wet system or a dry sorbent in a dry system—reacts with sulfur oxides (mainly SO2) to form a solid or slurry byproduct such as gypsum. The cleaned gas then goes to the stack, while the byproduct is collected and disposed of or sold.

It is used to meet emission limits and environmental regulations because sulfur oxides contribute to acid rain, air quality problems, and corrosion of downstream equipment. By removing SO2 before release, plants reduce their environmental impact and comply with standards. The other options describe actions that do not remove sulfur oxides from flue gas: increasing sulfur content, condensing sulfur into liquid, or preheating combustion air.