is shown in fig1 it receives in known manner a stream of hot gas g which travels upwardly in it lengthwise of the axis a of the tube the gas stream g is to entrain dry and preheat or dry or preheat depending upon whether the operation is be carried out in one or more stages one or more flight stream tubes particulate material such as finely comminuted particles of moist coal the particulate material s is admitted into the tube 1 via two oppositely located feed chutes or pipes 2 through which the material s slides under the influence of gravity the longitudinal axes of the pipes 2 are transversely inclined with reference to the axis a of tube 1 and the material s is discharged into the tube 1 in direction generally opposite to the flow of gas g into a constricted area 8 of rectangular cross section opposite the outlet ends of the pipes 2 the inner cross section of tube 1 is reduced by walls forming a passage of rectangular cross section fig2 and upwardly of this passage the tube 1 has a conically divergent diffuser section 5 which finally merges with a tube section 6 of circular cross section and of a diameter corresponding to the illustrated fig1 circular cross section 1a of tube 1 installed in the section of tube 1 which extends from.