Flue gas desulfurisation (FGD) is a technique used for the removal of sulfur dioxide from the exhaust gases in power stations.
As sulfur dioxide is responsible for acid rain formation, tall chimneys were once built to get rid of the nuisance. However, this act only leads to the transfer of the problem to another region.
In 1988 Prince Charles said, "I would have thought that the Central Electricity Generating Board was doing too little and too late. Our responsibilities do lie in not exporting our problems abroad." His words highlighted the fact that sulfur dioxide exhaust should be removed, rather than blown high into the atmosphere where it affects many more people.
As a result, SO2 (a 0.3% component of flue gas) is now being removed by a variety of methods.
- A slurry of limestone or lime is used to scrub the gases. Carbon dioxide gases or calcium sludge, such as gypsum, is produced as a result.
- A slurry of magnesium oxide is used as a scrubber. The product, magnesium sulfite can be decomposed by heat to form SO2 and MgO for recycling.
- Sodium sulfite may be used for scrubbing. Similarly, the product sodium hydrogensulfite may be decomposed for the recycling of the process.
For a typical coal-fired power station, 90% of the SO2 may be removed.