PURPOSE: To obtain a uniform granulated product, by a method wherein rotary plates are arranged in a treatment chamber at definite intervals in a multistage fashion through ring shaped venting members and the gas is further injected in the treatment chamber while being introduced from the inside of each ring shaped venting member to treat a particulate material by the rotation of the rotary plates and the action of a gas stream.
CONSTITUTION: A rotary shaft 5 is provided to the bottom part of a treatment chamber and rotary plates 8 are arranged to the upper part of said rotary shaft 5 in a multistage structure so as to be spaced apart by the height of each venting ring 10 and to successively reduce the diameters of each rotary plates to the upward direction. The rotary plates 8 are provided with venting openings 12 inside the venting rings in the radius direction except the uppermost one and an annular space 16 is formed between the lowermost rotary plate 18 and a container 1. When a particulate stock material is changed in the treatment chamber, the stock material is fluidized from the gas stream from the annular space 16 and tumbled while receiving centrifugal tumbling action by the rotation of the rotary plates 8. Further, said stock material receives the force to the outside in the radius direction from the venting rings 10 and is pressed to the inner wall surface of the treatment container 1 to be formed into a heavy particulate material having a uniform particle size.