The ISU process was originally invented and tested for the desulfurization of natural anhydrite rock (calcium sulfate) into calcium oxide and sulfur dioxide in a fluidized bed reactor. The innovative concept involved the presence of two zones within the fluidized bed; a reducing zone in the bottom portion of the bed and an oxidizing zone in the upper portion. The overall process concept at the beginning of the project consisted of the following steps: (a) Clean-up of the phosphogypsum to reduce impurities. (b) Particle size enlargement of the feed to the thermal decomposition step as part of the pretreatment process to minimize unreacted particle entrainment in the off-gas as a result of the high gas velocities in the reactor. (c) Decomposition was carried out in a two-zone fluidized bed reactor using high-sulfur coal as the fuel. (d) The reactor off-gas would be converted to sulfuric acid in a plant similar to those being used in sulfur-burning processes. This report describes and discusses in detail the test work and results of this project.
A. P. Kouloheris, Zellars-Williams, Inc. August 1982.