Venturi Scrubber and Filters - TNPSC - Environmental Scientist

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Notes on Venturi Scrubber and Filters (Air Pollution Control)

🌬️ 1. Venturi Scrubber

Definition:

A Venturi scrubber is a type of wet scrubber that uses a narrow constriction (venturi throat) to create high-velocity airflow and intense mixing between polluted gases and a scrubbing liquid (typically water). This interaction helps remove particulate matter and gaseous pollutants from the air stream.



Working Principle:

  • The polluted gas is forced through a converging–diverging nozzle called a Venturi.

  • As the gas enters the narrow throat section, it accelerates dramatically.

  • Scrubbing liquid is injected into this throat, forming fine droplets.

  • High-speed gas shears the liquid into tiny droplets, increasing surface area for pollutant contact and absorption.

  • Particles and soluble gases are captured by the droplets through impaction, interception, and diffusion.

  • The mixture then enters a separator (cyclone or mist eliminator) where clean air is released and dirty water is collected for treatment.

Key Features:

  • Very efficient for capturing fine particulates (< 2.5 microns).

  • Can also absorb certain gaseous pollutants, especially when combined with reactive scrubbing solutions (e.g., lime for SO₂).

  • Often used in high-temperature or corrosive environments.

Advantages:

  • High collection efficiency for submicron particles.

  • Cools and cleans hot gases.

  • Compact and simple design.

Disadvantages:

  • Generates a high pressure drop, requiring powerful fans.

  • Produces liquid waste that needs treatment.

  • Higher operating and maintenance costs than dry systems.

Applications:

  • Metal smelting

  • Chemical manufacturing

  • Boiler exhaust treatment

  • Fertilizer plants

2. Filters (Baghouse Filters or Fabric Filters)

Definition:

A filter or fabric filter system (commonly called a baghouse) is a dry air pollution control device used to remove particulate matter from industrial exhaust gases by passing them through filter media (fabric bags).

Working Principle:

  • Dirty air enters the filter chamber.

  • It passes through fabric filter bags that capture dust and particles.

  • Clean air exits through the other side.

  • Accumulated dust on the bag surface is periodically removed using mechanical shaking, reverse air, or pulse-jet cleaning.

  • Collected dust falls into a hopper for disposal or recycling.

Key Features:

  • Works best for dry, non-sticky particles.

  • Highly efficient—can remove over 99% of particulate matter.

  • Does not treat gases—only particulates.

Advantages:

  • High collection efficiency across a wide range of particle sizes.

  • No water use—suitable for dry systems.

  • Filters can be customized for temperature and chemical resistance.

Disadvantages:

  • Not suitable for wet or sticky particles.

  • Filter replacement is needed periodically.

  • Limited to gases below certain temperatures (unless special high-temp fabrics are used).

Applications:

  • Cement plants

  • Pharmaceutical industries

  • Food processing

  • Power plants (coal or biomass)

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