Question

Which of the following is a method used to control sulfur dioxide (SO$_2$) emissions?

• A. Wet scrubbing
• B. Catalytic converters
• C. Baghouse filters
• D. Electrostatic precipitators

Hint:

• Wet scrubbing (a type of Flue Gas Desulfurization, FGD) is a widely used technology to remove sulfur dioxide (SO$_2$) from flue gases.
• It involves contacting the flue gas with an alkaline scrubbing liquid (e.g., lime or limestone slurry) that reacts with and removes SO$_2$.
• Catalytic converters target CO, HC, and NOx from vehicles.
• Baghouse filters and ESPs are for particulate matter control.

Answer 1

The Correct Option is A

Sulfur dioxide (SO$_2$) is a major air pollutant primarily from the combustion of fossil fuels containing sulfur (e.g., coal in power plants) and industrial processes. Various methods are used to control its emissions:

• Wet Scrubbing (Flue Gas Desulfurization - FGD) (option a): This is a common and effective method. In a wet scrubber, the flue gas containing SO$_2$ is brought into contact with a liquid scrubbing solution (slurry).
  • Lime/Limestone Scrubbing: A common type uses a slurry of limestone (CaCO$_3$) or lime (CaO). SO$_2$ reacts with these alkaline materials to form calcium sulfite (CaSO$_3$) or calcium sulfate (CaSO$_4$, gypsum if oxidized), which can be removed as a solid byproduct. $\text{SO}_2 + \text{CaCO}_3 \rightarrow \text{CaSO}_3 + \text{CO}_2$ $\text{SO}_2 + \text{Ca(OH)}_2 \rightarrow \text{CaSO}_3 + \text{H}_2\text{O}$ (lime is CaO, which forms Ca(OH)$_2$ with water)
• Dry Sorbent Injection (DSI): A dry alkaline sorbent (e.g., powdered lime, sodium bicarbonate) is injected into the flue gas. SO$_2$ reacts with the sorbent to form solid particles that are then removed by particulate control devices (like baghouses or ESPs).
• Switching to low-sulfur fuels.

Other options:

• Catalytic Converters (option b): Primarily used in vehicles to reduce emissions of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). They are not designed for SO$_2$ control from large industrial sources.
• Baghouse Filters (option c): Used to remove particulate matter, not gaseous SO$_2$ (unless used in conjunction with DSI where SO$_2$ has reacted to form particles).
• Electrostatic Precipitators (ESPs) (option d): Used to remove particulate matter by using electrostatic forces, not gaseous SO$_2$.

Therefore, wet scrubbing is a primary method for SO$_2$ emission control. \[ \boxed{\text{Wet scrubbing}} \]