Which statement describes flue gas desulfurization systems used in power plants?

• A. Systems that preheat combustion air to improve efficiency.
• B. Wet or dry scrubbers that remove sulfur oxides from flue gas to meet emission limits.
• C. Systems that remove carbon dioxide from flue gas for sequestration.
• D. Devices that increase sulfur content in coal.

Answer: (B)

Flue gas desulfurization is a pollutant control method that targets sulfur oxides in the exhaust, removing them before the gases go to the atmosphere. In power plants, this is done with wet or dry scrubbers that scrub the flue gas to reduce sulfur oxides and meet emission limits. In a wet scrubber, the flue gas contacts a slurry of lime or limestone; the SO2 in the gas reacts with the slurry to form calcium sulfite or calcium sulfate, with gypsum often produced as a solid byproduct. Dry scrubbers work similarly, but use dry sorbents injected into the gas stream to capture SO2. This approach directly reduces sulfur emissions, unlike preheating combustion air (which aims to improve boiler efficiency), removing CO2 (carbon capture), or increasing sulfur content in coal (which would raise emissions).