Indirect heat-drying apparatus, indirect heat-drying method of drying substance to be dried, and method and apparatus for producing solid fuel

An indirect heat-drying apparatus comprising a first and second indirect-heating rotary dryer, each comprising:

• a revolving cylinder configured to freely revolve about its axial direction;
• a plurality of heating pipes arranged in the revolving cylinder in parallel with the revolving cylinder axis;
• a carrier gas treatment system configured to supply a carrier gas into the revolving cylinder from one side of the revolving cylinder and to discharge the gas with evaporant out of the system from another side of the revolving cylinder,
• wherein a substance to be dried is supplied from a first side of the revolving cylinder and a dried substance is discharged out of a second side opposite thereto,
• wherein the first and second rotary dryers are arranged in series so that a dried substance from the first indirect-heating rotary dryer is supplied to and dried in the second indirect-heating rotary dryer as a substance to be dried, and
• wherein the apparatus comprises a carrier gas supplier configured to supply the carrier gas co-currently in the first indirect-heating rotary dryer and counter-currently in the second indirect-heating rotary dryer with respect to the flow direction from substance to be dried to dried substance.