Control of the Number of Fine Crystals by Using Dissolution Water in Salt Crystallization

Abstract

Industrial crystallization should be carried out under high suspension conditions in order to obtain NaCl products efficiently. However, the nucleation rate rises under such conditions. Excess nuclei cause wide crystal size distribution (CSD) with a small mean size. Therefore, it is necessary to control the number of fine crystals in a crystallizer. This study focused on and discussed undersaturation operation with the NaCl-water system. Based on the experimental results, the destruction mechanisms of fine crystals were discussed and a novel operation technology for controlling the number of fine crystals was proposed. Undersaturation operation in this study was carried out by injection of dissolution water into the supersaturated solution. The following mechanisms contributed to the decrease in the number of fine crystals in the product by injection of dissolution water.(1) Preferential dissolution of fine crystals.(2) Inhibition of generation of fine crystals generated by crystal surfaces. It became clear that CSD was improved by the injection of dissolution water, and the injection operation strategy of dissolution water was proposed.