(130b) Spray Granulation in Continuously Operated Horizontal Fluidized Beds: Investigation of the Particle Transport Behaviour and the Product Properties in a Multi-Staged System

Authors: 
Diez, E., Hamburg University of Technology
Heinrich, S., Hamburg University of Technology
Fluidized bed spray granulation is an important process to produce granules with a desired particle size and structure. The particle properties can be influenced by several process parameters like gas inlet temperature, liquid feed rate as well as droplet size of the atomized liquid feed.

For continuous treatment of powders progressively horizontal fluidized beds are used. These horizontally structured apparatuses are characterized by a rectangular cross section. An advantage of a horizontal fluidized bed is the flexible partitioning of the process chamber into several stages due to weirs to apply different processes simultaneously, like granulation, drying or cooling in one single apparatus. The separation into several compartments provides a targeted impact on the transport behavior and the residence time of the particles, which are feed into the process chamber.

In this contribution, we present an overview on the process, investigating the dependency of the resulting product properties on the process conditions and highlighting possibilities of influencing the transport behavior in a horizontal fluidized bed.

This work focuses on the particle properties of sodium benzoate granules, which are produced by fluidized bed spray granulation during different process conditions. The drying process has a decisive influence on the kinetics of the growth rate and thus also on the properties of the particles, like the morphological structure, particle moisture and porosity.

Based on the granulation process, particles, which reach a certain product grain size, should be discharged as fast as possible in order to prevent further growth. To achieve this objective the residence time of the particles in the multi-staged process chamber has been investigated experimentally for different weir configurations (over, under and lateral flow). For this purpose Tracer particles with a magnetic coating have been used to analyze the transport behavior across the stages under different weir configurations, process conditions and particle size ranges.

Additionally, the investigation according to the particle transport and the fluid mechanics in the horizontal fluidized bed was performed by simulations based on Discrete Particle Modelling (DPM) and verified by experiments in a pilot plant. Using DPM, it is possible to examine the particle dynamics on a microscopic level in order to analyze particle exchange rates between the individual stages of the fluidized bed while utilizing different weir configurations and process conditions.

The financial support of DFG (Deutsche Forschungsgemeinschaft) within the priority program SPP 1679 "Dynamic simulation of interconnected solids processes DYNSIM-FP" is gratefully acknowledged.