STEAM DRYING AND FLUIDIZED-BED CALCINATION OF LIME MUD

A novel lime-mud-reburning system is described wherein lime mud is dri ed in a steam dryer and then calcined in a fluidized bed. Energy in th e flue gases leaving the calcination unit is recovered in a flue-gas b oiler. Calculations show that a system with a steam dryer utilizes the energy input better than conventional systems, where flue gases dry t he lime mud. Experiments in a pilot-scale steam dryer show that lime m ud (initial dry solids of 69-71%) was dried to >99% dry solids. The dr ied lime mud was then heated and calcined in a pilot fluidized-bed rea ctor at about 900-degrees-C. The resulting ''soft burned'' lime was hi ghly reactive during slaking and causticizing. However, it produced a lime mud with a higher specific filtration resistance than reburned li me from industrial rotary kilns.