LAYER DRYING - A MANAGEMENT MODEL FOR LOW-TEMPERATURE CORN DRYING SYSTEMS

A comprehensive layer drying model was developed to provide the operators of natural air or low-temperature corn drying systems with the technical information needed to make sound management decisions. The model as designed for use on AGNET, an interactive computer system developed in Nebraska, so that recommendations can be calculated for individual drying system setups. Development of the layer drying model emphasized the formulation of a procedure for determining maximum allowable layer filling rates. It is necessary to define the drying system setup and to project harvest conditions and bin drying rates in order to calculate allowable layer filling rates. Several individual simulation models are used to make these performance projections. The layer drying model is structured around a low-temperature drying model which is also used to predict drying performance once bin filling has been completed. Support subroutines include airflow and field dry down models. The maximum fill rate procedure uses minimum airflow rate requirements and equivalency ratios (which relate the corn in the bin to an equivalent amount of corn at the field moisture content) to determine allowable load sizes. Simulation results indicate that layer filling can be completed in a 2-3 week period for typical Lincoln, Nebraska conditions. Harvest can normally be started when field moisture contents reach 26% w.b. with the last corn loaded into the bin at 20-22%. Fan energy utilization values of 700 kJ/kg of water evaporated are not uncommon. For single fill applications, the bin can be filled in a one or two day period once field moisture contents reach 20-21%. Drying times are generally longer with single filled systems and thus energy requirements are also slightly higher. Field experiments which were performed to evaluate the loading procedure indicated disparities between projected and measured field and bin drying rates. Some of the difference was due to the fact that drying rate projections were based upon average year weather conditions. Nonuniformity of airflow within the bin was also identified as a potential problem. Sensitivity analyses were performed with the layer drying model to determine the relative importance of airflow rate, field dry down rate, minimum allowable daily loading amount, and year-to-year weather conditions upon bin filling recommendations. Field dry down rates were shown to have a considerable effect upon allowable layer filling rates