After the lignite is crushed, it is transported to the feeding box by belt conveyor, and then slides into the rotary dryer. It is guided to the inclined lifting area by the guiding plate. With the rotation and the inclination of the cylinder, the lignite is lifted from the bottom to the top of the cylinder, then falls to form a “material curtain”. At the same time, the high-temperature flue gas passes through the lignite and forms convective heat exchange with the wet material, preheating and evaporating part of the water. The above process is repeated between the material and the flue gas until the thermal balance of the target moisture is reached, and the material is discharged from the drum. The tail gas containing a large amount of water vapor and dust can be directly discharged after being double-purified by cyclone dust collector and bag filter.