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Scrubbing Away Pollution

2010 April 19

In general, the action of scrubbing can be quite effective at cleaning things. For example, scrubbing helps remove dried leftovers from dirty dishes or soap scum from shower walls. But can scrubbing actually clean up pollution? Well, not exactly the same type of scrubbing described above, but “scrubbers” are one of several pollution control technologies used by power plants to reduce harmful emissions and comply with the Acid Rain Program.

As we’ve discussed, the point of the Acid Rain Program is to have power plants reduce emissions of SO2 and NOX (contributors to acid rain). One way they can do that is to install advanced pollution control technologies, like scrubbers (technically called flue gas desulfurization). Scrubbers are devices that are used to remove pollutants from power plant emissions. They are one of the most common pollution control devices found in the power sector today.

There are many types of scrubbers that use different methods and technologies, and they can generally be grouped into two categories: wet and dry. Both achieve the same goal of cleaning up emissions before they enter the air.

Fast Facts

  • The wet scrubber is the most common type found in the United States. It cleans the emissions from power plants by rinsing them down with a liquid pollution removal agent.
  • Dry scrubbers remove SO2 emissions without using liquid. A limestone slurry is added to the emissions and as this slurry dries out, the limestone particles are suspended in the mixture. The SO2 then reacts with the limestone particles instead of the air.

Other types of advanced control technologies power plants use to reduce SO2 emissions include fluidized bed combustion and reagent injection.

To find out where scrubbers are installed and how effective they have been in reducing SO2 pollution, you can go to the following table and sort by the column titled, “SO2 Controls.”  Take a look at the data and tell us what you discover about SO2 controls in your state.

This blog was a joint effort between Colleen Mason and Elyse Procopio. Colleen Mason is a Physical Scientist and Elyse Procopio was an intern in EPA’s Clean Air Markets Division.

Flue gas desulfurization (“scrubber”) at Dickerson Generating Facility in Dickerson, Maryland. Photo courtesy of Maryland Department of the Environment.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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2 Responses leave one →
  1. April 23, 2010

    The dry scrubbing SO2 removal technology is based on using LIME not limestone. Limestone is not sufficiently reactive to remove SO2. It can be either lime slurry or dry, hydrated lime with separate water injection.

  2. cmason permalink*
    April 26, 2010

    Good technical point. Usually, the limestone is heated to produce calcium oxide (lime) and then made into a slurry. This can be done either on-site or purchased.

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