Sugar drying and cooling in a fluidized-bed drier

The so-called stationary fluidized-bed principle has for about 10 years now been employed in the drying and cooling of white sugar, refined sugar and raw sugar. Using white sugar as an example, the pneumatic conditions of fluidization in a fluidized-bed system are explained. Fluidization makes almost the entire surface of the sugar crystals available for contact with the circulating drying and cooling air. The resulting conditions of intensive heat and mass transfer render surface moisture removal highly effective. To avoid the inhibiting skin-effect on drying the crystal surfaces, the moist sugar is, in a later version of the BMA fluidized-bed drier/ cooler, subjected at the beginning of the drying process to the combined action of mechanical and sectional fluidized transport. For the technological conditions of a white-sugar drier/cooler with a downstream outlet-air filter, the safety measure designed to “prevent ignition sources” proved to be adequate, provided certain requirements are met. Following conversion in 1996, the fluidized-bed drying and cooling plant for crystal sugar (throughput 100 t/h) installed at the Offstein sugar factory of Südzucker AG meets the guaranteed technological parameters at a currently available average sugar throughput of approx. 75 t/h. The investment costs remained below the comparable costs for a drying and cooling system using a drying drum. The comparatively higher electrical power requirements were more than compensated by the low investment costs.