METHOD FOR PURIFYING CRYSTALLINE SUBSTANCE

PROBLEM TO BE SOLVED: To make a continuously crystallizing apparatus applicable to raw materials supplied from a relatively wide range and enable continuous operation by heating a supplied raw material crystal and loading the continuously crystallizing apparatus with the heated crystal. SOLUTION: A raw material crystal supplied at normal temperature is at first heated to a temperature not higher than melting point by a crystal heating apparatus 1 and then introduced into a crystallizing tower 2 from a crystal installation part 3. The introduced raw material crystal is dropped to the uppermost part of a mother liquid ascending in the tower and reaches the upper part of a slurry layer and a part of the crystal is dissolved in the mother liquid. Moreover, simultaneously with that, the raw material crystal lowers the ambient temperature to precipitate a crystal. The mother liquid layer formed by such a manner is called as a crystal descending region A. Dissolution and recrystallization of the crystal in the slurry layer in the lower part of the crystal descending region A is repeated while the crystal is descending and impurities in the crystal is transferred from the crystal to the mother liquid to purify the crystal. The region where crystal purification is carried out by such a manner is called a crystal purifying region B. The crystal purified in the crystal purifying region B and having high purity descends to a crystal melting region C and melted in the region and a part of the molten crystal becomes the mother liquid and the rest is taken out through a product extraction part 8.