||NATO Committee on the Challenges of Modern Society, Brussels (Belgium). ;Environmental Protection Agency, Washington, DC. Office of Research and Development. ;PEDCo-Environmental, Inc., Cincinnati, OH.
The double alkali/gypsum of flue gas desulfurization (FGD) was developed to reduce scaling and plugging problems associated with direct lime (CaO) or limestone (CaCO3) systems. One of the first large-scale installations of this process to control SO2 emissions and produce gypsum (CaSO4) was put in operation in 1973 at the Showa Denko plant in Chiba, Japan. By December 1977, 25 systems were operating, all in Japan. The double alkali system is especially applicable in situations requiring high (98 percent) SO2 removal, high availability, and low maintenance. The process is particularly applicable to areas where lime/limestone resources are abundant and where gypsum is a marketable by-product. If it is not marketable, gypsum and fly ash can be used as landfill to form a base with load-bearing capacities sufficient for some construction.