Scrubbers remove particles and waste gases from exhaust (Figure22.14). Wet scrubbers
use a liquid solution to scrub pollutants. Dry scrubbers use alkali or other materials to
neutralize acid gas pollutants. Other techniques are used to eliminate other toxic gases.
Nitrogen oxides, for example, can be broken down at very high temperatures.
Figure 22.14: Diagram of one type of scrubber. ( 14 )Gasificationis a developing technology. This method removes some of the toxins present in
coal before they are released into the atmosphere. In gasification, coal is heated to extremely
high temperatures. The gas that is produced is filtered and the energy goes on to drive a
generator. About 80% less pollution is released over regular coal plants, and greenhouse
gases are also lower. Clean coal plants do not need scrubbers or other pollution control
devices. Although the technology is ready, clean coal plants are more expensive to construct
andoperateandsotheyareseldombuilt. Also, heatingthecoaltohighenoughtemperatures
uses a great deal of energy, so the technology not very energy efficient. In addition, large
amounts of the greenhouse gas CO 2 are still released even with clean coal technology.