DESIGN AND CONTROL OF DRUM DRYERS FOR THE FOOD-INDUSTRY .2. AUTOMATIC-CONTROL

Changes in operating conditions and process disturbances produce uneve nness in the final moisture content of a product dried on a drum dryer . Moisture unevenness exists as a function of both time and drum width . The aim of this work is to control the final moisture content of the product and to reduce its unevenness, in order to obtain a high quali ty product and to increase dryer productivity. Among all input process variables, two control variables were chosen: the drum speed (Vrc), a nd the heating steam pressure (pv). These variables were used to keep constant the average final moisture content Xf. In this paper we pres ent a case where classic control is not enough to correct some process perturbations. Therefore, the facility has been modified by adding an actuator, in this case an inductive electric heater. Local complement ary heating power (Pind) is used to correct local heterogeneity of Xf to obtain Xf = Xf at every point across the drum. Copyright (C) 1996 Elsevier Science Limited