The main feature of the OSLO crystallizer is that the region where supersaturation occurs and the crystal growth zone are located at two different points in the crystallizer. The crystals are fluidized and suspended in the circulating mother liquor, providing a good condition for crystal growth and enabling the growth of larger and more uniform crystals. This crystallizer belongs to the typical mother liquor circulation type, with the advantage that the circulating mother liquor contains almost no crystals, which can effectively avoid crystal collision and breakage generated by the circulation pump. It can be combined with the FC forced circulation type crystallizer. Suitable for evaporation, cooling, and vacuum cooling methods.