Optimum reactor configuration for prevention of gypsum scaling during continuous sulphuric acid neutralization

Gypsum scale forms in industrial reactors during neutralization of acidic sulphate streams with calcium-containing compounds, such as limestone. A Population Balance Model was built to describe gypsum precipitation and scale formation kinetics in a CSTR with multiple stages and feed stream. The model was used to simulate several neutralization circuit configurations to optimize gypsum precipitation and thus, minimize scaling. The optimum configuration determined by this study is two-stage neutralization with all neutralizing base added in the first stage. Gypsum seeding is most effective up to a 100% seed recycle. A final polishing stage (reactor) where no base is added should be included at the end of any neutralization configuration to ensure that the outlet stream has a minimum supersaturation and thus minimize downstream gypsum fouling.