What are flue gas desulfurization scrubbers and how do they remove sulfur dioxide from exhaust streams?

• A. Water scrubs dissolve SO2 into moisture.
• B. Filters capture SO2 without chemical change.
• C. Catalytic converters oxidize SO2 to sulfur trioxide.
• D. A sorbent such as lime or limestone reacts with SO2 to form gypsum.

Answer: (D)

Flue gas desulfurization scrubbers remove sulfur dioxide by chemically reacting it with a reactive sorbent. In a wet scrubber, a slurry of lime or limestone is sprayed into the exhaust. The sulfur dioxide reacts with the calcium-based sorbent in the presence of water to form calcium sulfite, which is then oxidized to calcium sulfate dihydrate (gypsum). The solid gypsum is trapped and removed from the gas stream, greatly reducing SO2 levels. This approach relies on a chemical reaction that converts a gaseous pollutant into a solid byproduct, not just dissolving it in water or trapping it with a filter.