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.
The basic scrubber configurations are:
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.
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)
Typical nozzle scrubber efficiencies
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".