Abstract: A flighted, horizontally inclined rotary retort, heated externally by flame, hot gases, steam or other sources of heat. The retort shall have sufficient flight area to transport the coal through the retort in the predetermined time. The coal being processed in this retort is prevented from becoming exothermic by provision for a countercurrent flow of blanket gas, heated to a predetermined temperature below exotherm, to prevent coal surface temperatures from rising above the ignition temperature. The retort accommodates oversize pieces of raw coal by having alternating long and short flights, thus allowing greater space between long flights and allowing the larger pieces to be carried over the center pipe by the wiping action of the long flights. The retort will also be provided with an internal pipe, mounted on the center line of the shell.