This diffuser tube is provided with diffusion holes arranged on the upper side, and solids discharge openings arranged on the lower side. The plurality of diffusion holes may be arranged discretely along the axial direction. The centers of the diffusion holes may be arranged so as to substantially coincide with a vertical plane passing through the central axis. The centers of the solids discharge openings may also be arranged so as to substantially coincide with a vertical plane passing through the central axis. The solids discharge openings may be formed in slit shapes parallel to the central axis. The diffusion holes and the solids discharge openings may be arranged so as to face each other about a horizontal plane passing through the central axis. The diffusion holes and the solids discharge openings may be alternatingly arranged along the axial direction.
