Accelerating the Drying Process by Spherical Agglomeration: The Case of Benzoic Acid

Spherical agglomeration is a well-known process intensification method that offers several advantages, including material and energy savings associated with the reduction of processing steps and improvement in compressibility, packability, and flowability of the solid products. However, the energy-saving potential of spherical agglomeration is still underexplored in the context of energy conservation and carbon reduction in filtration and drying processes. By using benzoic acid, a common food preservative and precursor for industrial synthesis, as a model system, its fine crystals and spherical agglomerates were prepared separately, and the resulting drying behavior was evaluated. It was found that the round granules produced by spherical agglomeration could not only reduce the initial moisture content of the filter cake and shorten the drying time but also enhance the overall drying rate, having distinct drying curves and internal mechanisms compared to the ones of fine crystals by recrystallization. Notably, by comparison against the fine crystals of benzoic acid, spherical agglomerates had 3.4 times less specific cake resistance, 24% faster drying rate, and 71% reduction in the energy consumption for drying. In addition, the effect of different operating parameters (filter cake washing, amount and type of bridging liquid used, and mass of benzoic acid being handled per batch) on the drying behavior was investigated as well. It was revealed that filter cake washing and changes in the bridging liquid volume had a minimal impact on the drying behavior of benzoic acid round granules, while the choice of bridging liquid type and the mass of material being handled per batch showed significant differences in the drying behavior. Upon drying, the drying temperatures could influence both the drying behavior and the total energy consumption. These findings may serve as a platform for optimization in a bulk solid filtration and drying processes.