An unsteady-state simulation to study the control of concurrent and counter-flow grain driers

Abstract

A steady-state simulation of a drier is adapted to predict the unsteady states caused by varying inputs. Any drier consisting of grain beds ventilated in concurrent or counter-flow can be modelled by the unsteady-state simulation. A simple concurrent-flow drier, with counter-flow cooling was used to provide data to test the simulation. The moisture content of the output grain was predicted well, particularly the changes due to changing grain throughput. The changes due to changing input moisture content reflected the effect of mixing in the drier. Mixing is not modelled by the simulation and so greater changes were predicted than were found experimentally. The simulation was used to choose parameters for a proportional and integral feedback controller, which altered the throughput of the drier, dependent on the output moisture content of the grain. The drier was simulated, with and without the controller. With given input moisture content data the controller reduced the variations in output moisture content in most cases, but in some situations the variation was greater than for the uncontrolled drier. Non-linearities in the drier dynamics are not taken into account in the design of this controller, which may explain why the controller is unstable under certain conditions.