Closed seed crystal adding system for crystallization kettle

The closed seed crystal adding system comprises the crystallization kettle, a crystal adding tank and a centrifugal pump, a circulation inlet is formed in the top end of the crystallization kettle, a circulation outlet is formed in the bottom end of the crystallization kettle, and the circulation outlet is connected with a liquid inlet of the centrifugal pump. A liquid outlet of the centrifugal pump is connected with the bottom end of the crystal adding tank through a first guide pipe, and the top end of the crystal adding tank is connected with the circulating inlet through a second guide pipe. According to the invention, under the condition that an external circulation is added outside the crystallization kettle and valves on a circulation inlet and a circulation outlet are closed, seed crystals are added into the crystal adding tank, and then the centrifugal pump is started under the condition that the crystal adding tank is isolated from the outside, so that the seed crystals can be added into the crystal