1971

Power Plant Scrubber

Modern society needs electricity. As with any product, the less expensive the electricity becomes, the better. One inexpensive way to produce electricity has been to burn coal.

In the ideal case, coal would contain nothing but carbon and hydrogen. Unfortunately, coal often contains mercury and sulfur as well. The mercury goes straight into the air and then falls as rain into lakes and rivers. Sulfur combines with oxygen to form sulfur dioxide, which, when mixed with moisture in the air, becomes sulfuric acid. This is where the term “acid rain” comes from. Sulfur from coal-fired power plants is the main source of acid rain.

So engineers were asked to clean the sulfur and mercury from the flue gases of power plants. They solved the problem with scrubbers—but only because the Environmental Protection Agency forced them to with sulfur dioxide laws in 1971.

To eliminate mercury, engineers spray powdered activated carbon into the exhaust stream. The mercury atoms bind to the carbon, which then allows them to be filtered out.

The sulfur removal process is more interesting. By spraying lime—Ca(OH)₂—mixed with water into the exhaust stream, the sulfur combines with the lime to create CaSO3. By adding oxygen and water, gypsum gets formed. So engineers have taken sulfur pollution out of the air and used it to create gypsum as a product. The power plant can sell the gypsum and it is used to create things like wallboard.

What engineers have not figured out yet is the inexpensive, easy way to extract all of the carbon dioxide from the exhaust stream and store it somewhere safe. Once they do that, we will have truly clean power plants.

SEE ALSO Power Grid (1878), Light Water Reactor (1946), Carbon Sequestration (2008).

The power plant scrubber is an innovation that emerged due to concerns about phenomena such as acid rain.