Pulp drying with superheated steam under pressure – Part 3: Operating measurements on several evaporation driers and basic research

Evaporation drying in a fluidized bed is a novel system of pulp drying in sugar industry, contrary to the hot gas drying in drum driers. This new system has been installed in several sugar factories in eastern parts of Germany. The Braunschweig Sugar Institute has conducted performance tests and basic research on this new drier type. The performance tests covered both the operations with full load and with partial load. The operation with partial load could only insufficiently reduce the steam superheating due to the low level of pulp. An extended retention time of the pulp might improve the utilization of heating energy of the turbine bled steam. However, the quality of the product “pulp”, which is sensitive to heat, has to be considered. Topics of the basic research are drying rates, drying periods and sorption isobars for the evaporation drying of beet pulp. Pulp samples taken from several cells of the drier were analized concerning their dry substance content. These values were compared with the course of the dry substance content supplied by an enthalpy balance for the circulating steam inside the separate cells. Further studies will concentrate on the determination of the equilibrium moisture of pulp depending on parameters of the superheated drying steam.