Environmental Chemistry

Scrubber – Definition, Working, Types

Traditionally, the term “scrubber” is being referred to pollution control devices which are using liquid to wash unwanted pollutants from a gas stream. Scrubber systems such as chemical scrubbers, gas scrubbers are a diverse group of air pollution control devices. In this article, we will study the scrubber system. Scrubbers remove the unwanted gases and particulate matter from industrial smokestacks before they enter the atmosphere. Here we will have some answers to questions like definition and types of scrubber system. Also, its working will be explained in a simple way.

scrubber

Definition of Scrubber

Scrubbers are devices to control air pollution and used to remove some particulates and gases from industrial exhaust streams.

Actually, in the scrubber system, the exhaust gas is passed in the column from downside and scrubbing solution/material is sprayed at top. Here Liquid-Gas i.e. wet scrubber or Gas-Solid powder i.e. dry scrubber operation takes place.

Working of Scrubber

A scrubber is a cleaning installation whose main purpose is to neutralize harmful components in industrial air or waste gas streams. The removal of gas particles causing many problems from the gas stream during the process is necessary before disposing of the gases in the open air.

In some cases, the use of a gas scrubber may allow recovering certain raw materials after the treatment. A big advantage is the versatility of a gas scrubber in different areas. It includes the chemical industry, the pharmaceutical industry, and surface treatment.

The installation functions by bringing a gas stream in contact with a washing liquid. Due to this contact, certain gaseous components dissolve and remain in the water.

There is a transfer of the components from the gas phase to the liquid phase. This is the absorption process. The solubility of the elements in the liquid will determine to what extent the gaseous components dissolve into the liquid phase.

Thus it is of great importance to work with the correct fluid being as the absorption agent. Also besides the water, several organic or inorganic washing liquids can also be used for this purpose.

In these cases, certain chemicals or micro-organisms are added to the washing liquid in order to convert or neutralize the dissolved gases.

More strict measures are taken in terms of allowed air pollution.  Companies are being encouraged to take the necessary measures about it. Gas scrubbers are essential in industries where employees face exposed to potentially contaminated gases.

When we use a scrubber in an optimal manner, we can achieve a very high removal efficiency of the harmful gas particles. Therefore the fumes released in the outside air are no longer damaging to the environment.

Types of Scrubber

The two main types of scrubbers are wet scrubbers and dry scrubbers.

  1. Wet Scrubbers

Wet scrubbers force the polluted fumes to pass through a wet limestone slurry which traps sulfur particles. These can be used to control particulate matter less than 10 micrometers as well as inorganic gases such as SO2, H2S, NH3, and various chlorides and fluorides. Wet scrubbers may also be useful to control volatile organic compounds i.e. VOCs.

Condensation scrubbing causes the pollutants to condense so that they can be easily removed. Impingement-plate scrubbers force the emissions up a vertical chamber with water flowing down the sides of the chamber to trap sulfur particles. Coal-fired power plants with scrubbers mostly use a wet scrubber system.

  1. Dry Scrubbers

Dry scrubbers have an efficiency of more than 90 percent for removing SO2 under the right conditions, but they are limited to small- to medium-sized power plants of about 200 MW. Of the 120 thousand megawatts of power generated from coal-fired power plants with scrubbers.

Also, only 16,200 megawatts come from facilities using a dry scrubber system. There are some advantages of using this technology, including low waste disposal costs and low water consumption. Other contaminants treated by dry scrubbers are polycyclic aromatic hydrocarbons i.e. PAHs, HF, HCL, and heavy metals.

Question on Scrubber

Q: How effective are scrubbers?

Ans: Scrubbers are very efficient air pollution control devices, and can remove greater than 95 percent of the SO2 from power plant stack emissions.  In fact, SO2 removal efficiencies sometimes are as high as 98 percent to 99 percent. Scrubbers with advanced designs routinely meet targeted efficiencies of more than 95 percent.

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