Figure 1. A chemical scrubber.[1]

A scrubber or scrubber system is a system that is used to remove harmful materials from industrial exhaust gases before they are released into the environment. There are two main ways to scrub pollutants out of exhaust, and they are:[2]

  • Wet Scrubbing: The removal of harmful components of exhausted flue gases by spraying a liquid substance through the gas.
  • Dry Scrubbing: The removal of harmful components of exhausted flue gases by introducing a solid substance to the gas - generally in powdered form.

Both of these methods work similarly and perform the same process of removing pollutants. The main difference is the materials they use to filter the gases. By removing acidic gases from the exhaust before it is released into the sky, scrubbers help prevent the formation of acid rain.[2]


Scrubbing, sometimes referred to as flue gas desulfurization is the most effective sulfur-removal technique that is in widespread use. Removing the sulfur oxides is fairly simple, the flue gases pass through a spray of water in a wet scrubber that contains a variety of chemicals. Generally speaking, the main chemical is calcium carbonate. If a dry scrubber is used, the flue gas comes into contact with pulverized limestone - which is mainly calcium carbonate. The chemical reaction between the calcium carbonate and the sulfur dioxide yield calcium sulfite.[3] This calcium sulfite either falls out of the gas stream or is removed with other particulates.

Scrubbers are very effective, removing about 98% of sulfur from flue gases, but they are very expensive to maintain and install. Additionally, it is energy intensive as the flue gas must be reheated after coming into contact with water vapour in the wet scrubber for the gas to be buoyant enough to exit through the smokestacks.[3]

Environmental Impacts

The use of scrubbers to clean flue gases before they leave the smokestacks has a drastic, beneficial impact on the environment. By collecting particulate matter and acidic gases, the amount of different pollutants that can exit the plant and be introduced into the environment is dramatically reduced. This increases air quality and lowers the health risks for people who could come into contact with the different pollutants.

Although there are many positive side-effects of using scrubbers, there are still waste products from the scrubbing process whether wet or dry scrubbing is used. These by-products must be disposed of safely since they can rarely be reused because of their chemical content. This is one reason that dry scrubbing has become more common, as the sheer volume of the waste products is less significant than the waste from a wet scrubbing operation.

For Further Reading


  1. Wikimedia Commons. (July 14, 2015). Chemical Scrubber [Online]. Available:
  2. 2.0 2.1 WiseGeek. (July 14, 2015). What is a Scrubber System? [Online]. Available:
  3. 3.0 3.1 R. Wolfson. Energy, Environment and Climate, 2nd ed. New York, U.S.A.: Norton, 2012