Investigation of the complex process dynamics of the continuous spray granulation in multi-staged horizontal fluidized beds

Eugen Diez, M.Sc.

Poster

Introduction

Fig. 1. Principle of spray granulation (top) and simplified process flow diagram of the multi-staged fluidized bed with schematic representation of the internal zone formation and external process chain (bottom).

The fluidized bed spray granulation is a special application of the fluidization technology. This process is an important method for producing granular products with defined particle properties in industry.

This research project aims at a detailed investigation of the complex process dynamics arising in continuously operated multi-stage fluidized bed granulation. This process has prototypic character for the dynamic simulation of coupled particle processes, due to the presence of different process chambers, the presence of zones with different functionality in each process chamber, the high flexibility in designing the internal coupling between different chambers and zones with different classification characteristics, the coupling between particle and fluid phase due to drying, varying positions and classification characteristics of external recycles, and multiple internal coordinates to characterize product properties. Consequently, the project follows a multi scale approach, which combines experimental work with different modeling methods and a nonlinear analysis of process dynamics.

Experimental setup

For the experimental studies sodium benzoate is mainly used since granules of this model substance show stable structures over a wide parameter range.

The experimental research is done in a horizontal fluidized bed (Procell 25) of the company Glatt. The process chamber has a length of 1 m and a width of 0.25 m. The process chamber can be divided into four chambers with an equal length and width of 0.25 m by using weirs, selectively with different configurations (overflow, underflow or lateral flow). The periphery of the whole plant consists of a two-deck tumbler screen, a pin mill as well as a separate dosing unit which can be used to feed new nuclei to the process. The mill is used to grind the oversize fraction and feeding them back to the process chamber. The undersize fraction is automatically recycled while the particles with product grain size are discharged by the screen.

One main field of research within this project is the investigation regarding the resulting product properties in dependence of the process conditions. This part in the project 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 is investigated experimentally for different weir configurations. For this purpose Tracer particles are used to analyze the transport behavior across the stages under different weir configurations, process conditions and particle size ranges.

Figure 3. Morphological design of the product granules due to different spraying and drying conditions.

Discrete-Particle Modelling

In addition to the experimental studies, the investigation according to the particle transport behavior and the fluid mechanics in the horizontal fluidized bed is 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 compartments of the horizontal fluidized bed while utilizing different weir configurations and process conditions.

Figure 4. Instantaneous particle transport in the two-staged geometry of the fluidized bed (left) and particle transport between the two chambers for different weir configurations

Project funding and Start Date

November 2014

Within the DFG priority program 1679 - Dynamic Simulation of Solids Processes -

Cooperation partners

Prof. Dr.-Ing. habil. Dr. h.c. A. Kienle

Chair of Automation and Modelling

Otto-von-Guericke-University Magdeburg

Prof. Dr.-Ing. habil. E. Tsotsas

Chair of Thermal Process Engineering

Otto-von-Guericke-University Magdeburg

Selected Publications

• Bück, A., Neugebauer, C., Meyer, K., Palis, S., Diez, E., Kienle, A., Heinrich, S., Tsotsas, E., 2016. Influence of operation parameters on process stability in continuous fluidized bed layering with external product classification, Powder Technology 300, 37-45.

• Neugebauer, C, Palis, S., Bück, A., Diez, E., Heinrich, S., Tsotsas, E., Kienle, A., 2016. Influence of mill characteristics on stability of continuous layering granulation with external product classification, Computer Aided Chemical Engineering 38, 1275-1280.

• Palis, S., Neugebauer, C., Bück, A., Heinrich, S., Tsotsas, E., Kienle, A., 2016. Control of multi-chamber continuous fluidized bed spray granulation, Proceedings of the International Congress on Particle Technology (PARTEC), April 19-21, Nürnberg.

• Neugebauer, C., Palis, S., Bück, A., Tsotsas, E., Heinrich, S., Kienle, A., 2017. A dynamic two-zone model of continuous fluidized bed layering granulation with internal product classification, Particuology 31, 8-14.

• Diez, E., Meyer, K., Bück, A., Tsotsas, E., Heinrich, S., 2019. Influence of process conditions on the product properties in a continuous fluidized bed spray granulation process, Chemical Engineering Research and Design 139, 104-115.