Deposit Formation in the Evaporator of a Sulfuric Acid Recovery Plant for TiO2 Pigment Production

To produce high-quality white pigment, concentrated sulfuric acid is used to separate TiO2 from the raw material, which is usually an ore or a slag produced from titanium-rich iron ore. After dilution of the sulfuric acid in the crystallizer, it is reconcentrated in a multiple-effect evaporator set to a concentration of about 95%. The large variety of dissolved components in the process acid leads to the formation of very hard and resistant deposits on the surfaces of the high-temperature heat exchangers. The typical cleaning intervals of these heat exchangers, which are made from tantalum to resist corrosion, are 5-7 days. The present paper reports the results of an extensive investigation into the mechanisms and mitigation of scale formation in an industrial TiO2 plant. Numerous side-stream measurements have been performed to study the effects of the operating conditions on the deposition rates and the potential of various mitigation techniques such as turbulence promoters, fluidized beds, and magnetic fields.