Gypsum wallboard, sulfur

An important technology for removal of S02 is Flue Gas Desulfurization (FGD), carried out in units known as scrubbers. Most scrubbers contact the flue gas with a slurry of lime or limestone to capture the sulfur oxides and produce a sludge containing calcium sulfite and calcium sulfate. However, disposal of sludge is another environmental problem, and some scrubbers include oxidation to convert all the calcium sulfite to sulfate (gypsum), which can be used for wallboard manufacture. Fluidized-bed combustion units add a sulfur... 

Flue gas desulfurization systems are classifled in two general categories. One group involves throwaway product systems where sulfur product (untreated or treated) is disposed of as a landfill. The other group produces saleable products such as sulfuric acid, elemental sulfur or, as in Japan, gypsum for wallboard and sodium sulfite for paper mills. 

---