Particle formulation using the fluidized bed technology is wide spread in chemical and pharmaceutical industry. By spraying a solution or suspension into a fluidized bed and evaporation of the solvent by hot air, free flowing and abrasion-resistant granules can be formulated due to layering of the solid material in the liquid onto nuclei particles. The fluidized bed drying using superheated steam as drying agent and fluidization medium is wide spread. The recirculation and reheating of superheated steam are only two of the advantages of superheated steam processing. These advantages imply that emissions coming from the drying product are not emitted to the environment, but will appear in the condensate. Only the amount of steam that corresponds to the amount of evaporated water will be removed from the closed loop. Therefore atmosphere in the process is inert, in the sense that no oxidation of the products and no fire or explosion risks exist [1].

The presentation incorporates the coupling of the advantages of superheated steam drying and the particle formulation by layering in a fluidized bed. Therefore experimental studies at a pilot plant of the university will be presented, that is able to operate gas or superheated steam mode. In order to predict the efficiency of the liquid deposition onto the solid particles, two-dimensional steam temperature distributions have been measured in superheated steam atmosphere by using an encapsulated thermocouples (Figure). The experiments where carried out with non-porous glass beads and porous aluminium oxide particles and can be compared with experiments by using air as fluidization and drying medium [2]. In addition, the transient temperature at the outlet of the fluidized bed was measured to determine the amount of liquid hold up in the bed. To simulate the transient behavior of the system a model was derived, which contains beside kinetic expressions for mass transfer between particle and solid phase a population balance model to describe the particle growth.

Figure: Measured temperature distribution of a superheated steam fluidized bed with 14 kg glass beads (steam inlet temperature: 245 °C), atomized liquid: water (30 °C).

[1] Heinrich, S., Ihlow, M., Henneberg, M., Mörl, L., Machnow, E.: Studies of steam drying in fluidized beds, Drying Techn. 20 (2002) 1, 174-194

[2] Heinrich, S., Blumschein, J., Henneberg, M., Ihlow, M., Peglow, M., Mörl, L.: Study of dynamic multi-dimensional temperature and concentration distributions in liquid sprayed fluidized beds, Chem. Eng. Sci. 55 (2003) 23-24, 5135-5160