CYCLIC OPERATION OF A FLUIDIZED BED REACTOR FOR DECOMPOSING CALCIUM SULFATE

Calcium sulfate can be decomposed at a high temperature (e.g., 1100°C) in the presence of reducing agents such as carbon monoxide and hydrogen. However, conditions must be carefully controlled to avoid over-reduction and the formation of calcium sulfide. The problem of over-reduction can be avoided by using a fluidized bed reactor in which the gas phase is alternated in a periodic manner between reducing conditions and oxidizing conditions. This method was demonstrated with a bench-scale fluidized bed reactor which was fed continuously with granulated waste gypsum and a mixture of air and natural gas. The ratio of air to natural gas was varied in a periodic manner to provide alternating reducing and oxidizing conditions. Calcium sulfate was largely converted into the desired products while producing very little calcium sulfide. Operating performance was found to depend on cycle time, air to fuel ratio, temperature, and feed rate.