Modeling the Fractional Drying and Aerodynamic Separation of Alfalfa into Leaves and Stems in a Rotary Dryer

A computerized mathematical model was developed to predict fractional drying and aerodynamic separation of alfalfa into leaves and stems in one process in a rotary dryer. Aerodynamic separation was characterized by separation efficiency or the total amount of the desired component (leaf or stem) recovered, relative to the amount entering the process, and by purity of leaf or stem component collected at exit ports of the dryer. The model development assumed 100% separation efficiency and purity. The model was validated by comparing model predicted results with measured experimental and field test data obtained from a small industrial rotary dryer and a full-scale industrial dryer. Changes in leaf, stem, and drying gas moisture contents and temperatures were measured and predicted by the model under various drying conditions. The model-predicted results agreed well with measured data. The model was also used to simulate the performance of industrial rotary dryers under various operating conditions. The model can be used to determine the optimum drying and aerodynamic separation parameters. It can also be used to design and redesign new and existing industrial rotary dryers in order to combine drying and aerodynamic separation into one process.