Abstract

An overview of coal cleaning and desulfurization schemes designed to minimize contaminants from coal combustion systems is presented. Coal cleaning can be divided into two basic categories: physical and chemical processes. Physical cleaning involves specific gravity-controlled processes. Surface-force-controlled processes, such as flotation and selective agglomeration, dominate newer developments. Whereas chemical and biological coal cleaning processes have shown potential to produce deep-cleaned coal, most of these processes have yet to be tested at commercial scale.

As coal is burned, and also following combustion, sulfur dioxide can be removed at a number of locations as the combustion gas gives up its heat and entrained particulate matter before being exhausted to the atmosphere. Atmospheric and circulating fluidized-bed combustors are commercially available, and pressurized fluidized-bed combustors are being developed to collect sulfur dioxide in limestone injected into the combustion zone. Limestone injection just after combustion in a pulverized coal furnace, and processes whereby lime or limestone can be injected into the ductwork following the boiler and in dry scrubbers for desulfurization, have been installed at coal-fired power plants and these and both wet and dry regenerable scrubbers are described.