Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Scrubber Basics

In a wet scrubber process air is drawn through a mist of water made by spray nozzles, then through separators where water droplets with dust and particles are removed.

Air scrubbers are commonly used in process-air applications to eliminate potentially harmful dust and pollutants. A liquid, in general water added with active chemicals adapted to the process, is sprayed in to the air flow. Aerosol and gaseous pollutants in the air stream are removed by either absorption or chemical reactions with the water solution.

A schematic drawing of a typical spray nozzle scrubber configuration is shown below.


Water with chemicals are sprayed with high pressure through nozzles into the air flow. Some of the water evaporates, especially if the process-air is hot, and disappear with the exhaust. Water droplets are separated from the exhaust and re-circulated back to the water reservoir. Evaporated water is replaced by fresh water and chemicals. Dust and pollution products from the process are removed periodically through the drain. 

Wet Scrubber Basic Configurations

The basic scrubber configurations are:

  • Orifice scrubbers - air or gas velocity is increased through an orifice - increased turbulence atomize the water droplets
  • Venturi scrubbers - air or gas velocity is increased through a venturi shape - increased turbulence atomize the water droplets
  • Fiber-bed scrubbers - air passes through wet-laden fiber mats where mists are collected. Not suited if solid particles are present in the air since the fiber mats may plug
  • Mechanical scrubbers - a mechanical driven rotor produces the fine water droplets in the air
  • Impingement-plate scrubber - vertical scrubber with horizontal plates, air flows from bottom to top, water flows from top to bottom 
  • Spray nozzle scrubbers - water are sprayed with high pressure through nozzles to produce the droplets in the air

Typical Scrubber Data

  • Cleaning efficiency: 70% of fine dust and 80% of coarse dirt
  • Air velocity through the washer: 2 - 3 m/s
  • Air flow pressure drop resistance: 50 - 140 N/m2
  • Water pressure before nozzles: 100 - 170 kN/m2
  • Water consumption: 0.45 - 0.55 l/m3 air (depends on the temperature of the process air)

Scrubber humidifying efficiency

Some industrial processes need more cleaning than a single scrubber can provide. In smell polluted processes, like exhaust air from fish meal or fish feed dryers, bio beds are commonly used. A bio bed, which is an organic organism, require process air with as little dust as possible and temperature and humidity within certain limits.

scrubber and bio bed

The humidifying efficiency of the scrubber may be expressed as:

μh = (t1 - t2) / (t1 - tw) 100%                                   (1)


μh = scrubber humidifying efficiency (%)

t1 = initial dry bulb temperature (oC)

t2 = final dry bulb temperature (oC)

tw = initial wet bulb temperature (oC)

Scrubber Efficiencies

Typical nozzle scrubber efficiencies

  • 60-70 % with one bank of nozzles downstream
  • 65-75 % with one bank of nozzles upstream
  • 85-100 % with two banks of nozzles

Note! Be aware that low temperature scrubbers can be a potential source for the Legionella disease. Special cleaning and disinfection precautions should always be taken when the temperature in the scrubber is in the "Legionella range".

Related Topics

  • Ventilation Systems

    Design of systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

Related Documents

  • Legionella

    The Legionella Pneumophila bacterium thrives in water supply systems and air conditioning systems - and may cause the Legionnairs disease.


Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .


This page can be cited as

  • The Engineering ToolBox (2003). Scrubber Basics. [online] Available at: [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter