The ball-milled slurry is further stirred evenly in the stirring tank and heated to above 35°C, and then pressure is applied to the stirring tank. Under the effect of the pressure, the slurry is sent to the atomizer and atomized by the atomizer After chemical conversion, it is sprayed into the tower body from the bottom of the tower body. The N2 heated by the oil-gas heat exchanger is sent by a blower to the gas distributor at the top of the tower. After passing through the gas distributor, N2 enters the tower evenly and in a cyclone shape, and the granulated slurry is dried and granulated. The liquid on the surface quickly evaporates after the pellets are in contact with the hot gas, and the internal gas migrates to the surface and is taken away by the hot gas in the subsequent drying process. The dried pellets fall to the bottom of the tower, and are recovered gapwise through a pair of disc valves.