How can a power plant capture sulfur dioxide with a limestone slurry?

Some fuels release sulfur dioxide when they burn. A wet flue-gas scrubber brings exhaust into contact with many droplets of liquid containing finely divided limestone. The droplets provide a large area across which sulfur dioxide can move into the liquid.

Dissolved sulfur dioxide produces acidic conditions that promote reaction with the limestone. This chemical reaction helps keep removing dissolved sulfur species, allowing further gas absorption rather than simply filling a fixed volume of water with pollutant.

In a process using added air, sulfur-containing products can be oxidized toward calcium sulfate, which forms gypsum with water. Solids can then be separated from the circulating slurry, while some liquid is reused and some requires treatment.

Pollution has been captured and transformed rather than made to disappear. The installation must manage water, energy, equipment corrosion and the quality of its solid products. Whether gypsum can be sold or must be disposed of depends on its composition and local requirements.