SCR closed-loop crystallizers are used for constant crystallization of un-crystallized PET regrinds or pellets. Processed materials can then be dried and dehumidified directly. This system mainly consists of heating elements, insulated hopper and agitator screw mixing device. After un-crystallized PET materials fed into the hopper, the system starts crystallization and agitator starts blending to prevent formation in lumps. Crystallized materials can be conveyed to material storage bin or into drying hopper.