Which of the following does not discharge the dust collected as a dry solid ?

ANS:B - Wet scrubber

A wet scrubber is an air pollution control device used to remove particulate matter and gases from industrial exhaust streams. It works by passing the polluted gas stream through a liquid (usually water) where pollutants are absorbed, dissolved, or chemically reacted with the liquid. Wet scrubbers are commonly used in industries such as power generation, chemical processing, metallurgy, and manufacturing to reduce emissions of harmful pollutants before they are released into the atmosphere. Here's how a wet scrubber typically operates:

1. Gas-liquid Contact: The polluted gas stream enters the wet scrubber and is directed through a chamber or tower filled with a liquid scrubbing solution. This liquid can be water or a chemical solution depending on the specific pollutants being targeted for removal.
2. Absorption and Scrubbing: As the gas stream passes through the liquid, pollutants such as dust, smoke, sulfur dioxide (SO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs) come into contact with the liquid. Depending on the properties of the pollutants and the scrubbing solution, various mechanisms may occur:
   • Particulate matter may be trapped or captured in the liquid through impaction, interception, or diffusion.
   • Gaseous pollutants may dissolve into the liquid through absorption or chemical reaction.
3. Particle Removal: The liquid scrubbing solution absorbs or captures the pollutants, effectively removing them from the gas stream. The now-cleaned gas exits the wet scrubber and is released into the atmosphere.
4. Liquid Treatment: The liquid containing the absorbed pollutants, often referred to as scrubber liquor or effluent, is collected at the bottom of the scrubber. Depending on the specific application and pollutants, the scrubber liquor may undergo further treatment, such as pH adjustment, filtration, or chemical precipitation, to neutralize or remove the pollutants.
5. Disposal or Recycling: Once treated, the scrubber liquor may be discharged into a wastewater treatment system, recycled back into the scrubber system, or disposed of in an environmentally responsible manner.

Wet scrubbers offer several advantages, including high efficiency in removing both particulate matter and gases, versatility in treating a wide range of pollutants, and relatively low operating costs compared to some other air pollution control technologies. However, they require careful design, operation, and maintenance to ensure optimal performance and compliance with environmental regulations. Additionally, the management of the scrubber liquor and disposal of captured pollutants are important considerations in the overall effectiveness and sustainability of wet scrubber systems.