The paddle dryer is a horizontal agitated dryer with conduction as the main component. The main structure is a W-shaped shell with a jacket. A pair of hollow low-speed rotary hollow shafts are installed in the shell. A number of mixing blades are welded on the shaft. The jacket and the hollow mixing blade are both filled with heat carrier. The materials are heated by two kinds of heating surfaces at the same time. The heat carrier is usually fed from the middle of the dryer and discharged from the other side through the agitated surface of the material layer. The hollow shaft is densely arranged with wedge-shaped hollow blades, and the hot medium flows through the hollow shaft. The heat transfer area per unit effective volume is very large, and the temperature of hot medium ranges from - 40 ° C to 320 ° C. It can be steam or liquid type, such as hot water, heat transfer oil, etc. Indirect conduction heating does not carry air to take away heat, heat is used to heat materials, and the heat loss is only heat dissipation to the environment through the insulation layer. The heat transfer surface of wedge-shaped blade has the function of self-cleaning. The relative movement of material particles and wedge-shaped surface produces washing effect, which can wash off the attached materials on the wedge-shaped surface and keep the clean heat-transfer surface in motion.