Materials enter the inner side of the drum through the feeding device to realize current flow drying process,then the materials enter the middle layer of the inner wall through the other end to realize counter current drying process.They are lifted in over and over in the middle layer which advance in two-steps forward and one-step back way.The three-drum dryers absorb heat from both inner drum and middle drum,which extend the drying time and realize the best drying condition.Finally,materials fall into the external layer of the drum from the other end of the middle layer, processing in a rectangle multi-loop way.The dried materials move quickly out of the drum under the hot air,while the wet ones remain because of their own weight.Materials are dried completely inside the rectangle shoveling plate and then cooled by the single drum cooler, thus finishing the whole drying process.