Simulation of plug flow fluidized bed dryers

A mathematical model of plug flow fluidized bed dryers has been formulated. The model was based on analytical equations previously derived to simulate well-mixed fluidized bed dryers, combined with axial dispersion theory. It was implemented on Microsoft Excel 2000; the calculations were fully automated with the aid of a macro programmed in Visual Basic. The model outputs include moisture, temperature and specific energy consumption profiles along the length of the dryer, the condition of the outlet streams, and the overall specific energy consumption. The effects of dryer geometry and the principal operating parameters were investigated and followed logical trends. Dispersion had a negligible effect on the results under the industrially realistic conditions employed in the simulations. The outlet moisture content of the solids was found to depend on the difference between the temperature and dewpoint of the exhaust air and the drying kinetics. Specific energy consumption increased with decreasing outlet moisture content and was in good agreement with values calculated assuming an ideal adiabatic dryer.