The sludge is sent to the dryer from the feed port, and the working medium flows between the body casing and the hollow shaft. The heat is transferred through the C-shaped jacket, the hollow shaft and the hollow disk welded on the shaft, and the sludge is indirectly heated and dried. The generated water vapor collects on the dome of the dryer and is carried out of the dryer by the carrier gas. The hollow disc is substantially perpendicular to the shaft, and the sludge is stirred and advanced by the action of the propeller/mixer on the disc, and the dry surface is continuously updated to achieve the purpose of drying. Indirect heating with steam, by stirring the material to make the water evaporate faster, drying, not only suitable for semi-drying of materials, but also suitable for the material dry process.