Particle design by optimized operation of the fluidized bed spray granulation process

Fluidized bed spray granulation is widely used in several industries as e.g. chemical, pharmaceutical and food industry. Spraying nozzles inject the solution, suspension or melt into the bed of fluidized particles. The liquid layer solidifies by the heated fluidization gas which results in an onion-like growth of the granules. In continuously operated spray granulation processes very often horizontally constructed fluidized beds with rectangular cross sections are used, which are divided by a variable number of plates (weirs) into several chambers of different functionalities (e.g. granulation, coating, drying). Commonly an external product processing, consisting of pneumatic conveying, screening, grinding of the oversize granules and recycling of grinded oversize and undersize granular material into the fluidized bed granulator is applied. The resulting internal and external networks of solids process unit operations as well as gas, liquid and solid flows lead to a complex and dynamic process behavior. By adjustment of the process parameters the granule properties can be adjusted and optimized for example regarding the flowability or the morphology of the product. The spray rate and the drying temperature were found to have a major effect on the surface structure of sodium benzoate granules (Figure 1).

The understanding of the flow behavior in continuously operated fluidized beds is of great importance for the adjustment of the process parameters. To obtain a homogeneous product quality the residence time behavior of the particles in the whole process and in the single chambers needs to be known. Therefore, a novel tracer method was developed in which magnetizable tracer particles are used. The particles are produced by coating the bed material particles with a magnetizable paint. When adding the tracer as an impulse into the continuously operated fluidized bed, the time-dependent concentration of the tracer can be determined by weighing, which allows the calculation of the residence time distribution. It was shown that the installation of the weirs at different heights above the distributor plate has a big influence on the residence time and the back-mixing between the chambers. Besides the experimental investigations, rCFD (recurrence CFD) simulations were performed to quantify the residence time of particles in the process. This novel simulation approach is based on data obtained from CFD-DEM simulations and makes use of recurrence patterns of the gas-solid process allowing particle flow calculations in real time.

Fig. 1: Simplified process flow diagram of continuous fluidized bed process with schematic representation of the internal zone formation and external process chain (left); Influence of the process conditions on the morphological structure (SEM pictures) of the product granules (right).


Prof. Dr.-Ing. habil. Dr. h.c. Stefan Heinrich studied Process Engineering at the University of Magdeburg and received his Diploma in 1996 and his Ph.D. at the same university in 2000 in the field of fluidized bed spray granulation. From 2000 to 2002, he was Assistant Professor and from 2002 to 2008 Junior Professor at the University of Magdeburg, where he also received the Habilitation and the “venia legendi” in particle technology in 2006. In 2008 he became full professor and director of the Institute of Solids Process Engineering and Particle Technology of the Hamburg University of Technology, Germany. Also in 2008 he denied a call for a full professorship for Particle and Materials Treatment Technology at the TU Bergakademie Freiberg, Germany. From 2011-2012 he was also the Dean of the Department of Process and Chemical Engineering of the Hamburg University of Technology. In 2015 Stefan became a Honorary Doctor of the DonNTU (National University of the Ukraine).

He is an executive board member of the German Working Party on Drying and chairman of the executive board of the German Working Party on Agglomeration and Bulk Solid Materials of VDI-ProcessNet. He is also chairman of the Working Party on Agglomeration and member of the Working Party on Mechanics of Particulate Solids of the EFCE. Stefan is also the Coordinator of the German Research Foundation (DFG) Priority programme 1679 „Dynamic simulation of interconnected solids processes, Vice-Spokesperson of the DFG Research Training Group 2462 „Processes in natural and technical particle-fluid-systems” and a member of the DFG Collaborative Research Centre 986 „Tailor-made multiscale materials systems“, member of the „Center of Advanced Materials (ZHM)“, Hamburg, member of the Scientific Advisory Board of the Helmholtz Institute Freiberg for Resources Technology, Freiberg, Germany and a member of the Scientific Advisory Board of the Research Center Pharmaceutical Engineering (RCPE) of the TU Graz, Austria. He works also as Executive Editor of the journal „Advanced Powder Technology“ and as Thematic Editor of the journal „Particuology“. Stefan was also the chairman of the 2nd Nordic Baltic Drying Conference (NBDC 2017), Hamburg, Germany, June 2017 and he is the chairman of the Partec 2019 - International Congress on Particle Technology, Nürnberg, Germany, April 2019.

His main research interests are fluidized bed technology, particle formulation with granulation, coating and agglomeration, drying of solids, development of particular composite materials, particle based simulation methods (discrete element modelling, population balance modelling) and coupling with continuum approaches (CFD), contact and breakage mechanics of particles as well as steady-state and dynamic flowsheet simulation of solids processes. For his research activities in fluidized bed spray granulation Stefan received the DECHEMA-Prize 2015 of the Max Buchner Research Foundation and numerous other research awards.