| Automatic control of continuous-flow grain dryers has been commercially available for a decade. These feedback control systems are temperature-activated and relatively inexpensive, but are not able to control the outlet moisture content of the grain in dryers adequately when the inlet moisture varies by more than two percentage points. The goal of this study was to develop a feedforward grain-moisture activated controller, and test the system commercially on crossflow grain dryers. The design objective was to control the exit moisture content to within ;Subsequently, the control system consisting of an empirical drying model, an on-line moisture meter, a tachometer, a data acquisition software, a microcomputer, and the feedforward/feedback control software was implemented, and tested during two drying seasons, on two commercial crossflow maize(corn) dryers. The inlet grain moisture content varied between 16.1% to 34.3% (w.b.). The new control system controlled the outlet grain moisture content to ;The automatic control system can be adopted to different dryer types and different cereal types. Advantages of the feedforward control system include: (1) improved dryer control, (2) improved grain quality, (3) improved energy efficiency, (4) improved drying records, and (5) improved dryer economics.;First, an unsteady state model of crossflow grain drying was developed consisting of four differential equations. Solution of the model requires excessive computer power and time, and thus several empirical models were tested at the process model in the feedforward dryer control system. The simplified empirical drying models predict the exit grain moisture from a crossflow dryer well compared to that predicted by the unsteady-state dryer simulation model and to that measured experimentally. |
