Rotary drying is one of the many drying methods existing in unit operations of chemical engineering. The drying takes place in rotary dryers, which consist of a cylindrical shell rotated upon bearings and usually slightly inclined to the horizontal. Wet feed is introduced into the upper end of the dryer and the Feed progresses through it by virtue of rotation, head effect, and slope of the shell and dried product with-Drawn at the lower end. The direction of gas flow through the cylinder relative to the solids is dictated mainly by the properties of the processed material. Co current flow is used for heat-sensitive materials even for high inlet gas temperature due to the rapid cooling of the gas during initial evaporation of surface moisture, whereas for other Materials countercurrent flow is desirable in order to take advantage of the higher thermal efficiency that Can be achieved in this way. In the first case, gas flow increases the rate of solids flow, whereas it retards it In the second case.