Abstract: An apparatus for drying/calcining comprises a horizontally extending rotatable drum and a center tube, concentrically positioned within the rotatable drum to provide an annular combustion chamber between the outer wall of the center tube and the inner wall of the rotatable drum. One or more gas jet burners are positioned to inject gas fuel and combustion air into the annular combustion chamber in a tangential direction to create a vortex flow of combustion gases through the annular combustion chamber. The flue gas is discharged through the center tube. In operation, a material to be dried and/or calcined is applied to the external wall of the rotatable drum as it rotates toward a scraper or doctor blade where the dried or calcined product is removed by scraping.