In-line measurement of particle properties

Inline-detection of particle size distributions by means of chord length transformation

For a wide range of applications in fluidized bed technologies particle size is of utmost interest. The product size of agglomeration and granulation processes impacts directly the disperse bulk characteristics such as conveyance, miscibility and solubility concerning for instance instantised foods. Being an internal process coordinate, the particle size also exerts a significant influence on growth kinetics as well as fluidization behaviour.
The progress of recent years achieved in the fields of microelectronic, material science and signalling technique facilitated the development of highly integrated fibre-optical probes. Their two distinct functional principles base upon shading of fibre-optical grids or backscattering, comprising the detection of the particle size distribution (PSD), velocity and concentration of disperse media as in case of crystallisation or fluidized and spouted beds.

In order to implement an adaptive control loop for the particle properties (e.g. size, moisture content) in particle forming processes, a fibre-optical probe of the Parsum Company is investigated. In contrast to conventional measurement devices (offline) the inline-particle-probe features a high sampling rate and minor fluid-dynamical perturbations within the process, thus qualifying for the use in a control loop. Like the majority of inline particle size analysers the Parsum probe is restricted to the dynamic detection of chord length distributions (CLD), which derives most obviously from the depicted measurement principle: Similar to a light barrier the particles traverse a LASER-lit fiber-optical lattice, triggering a shading sequence, which relates to the particle velocity. Combined with the  shading interval of each particle, precisely detected by an additional single fiber, this yields a particle size. Due to the  random particle orientation and offset to the optical lattice the detected lengths are likewise randomly distributed, hence being chord lengths. As a result of the stochastic properties chord length distributions are not compliant with mass balances and in turn inapplicable to any model-based process control. Therefore specially devised algorithms are used to perform a real-time transformation of the chord length distribution into its corresponding particle size distribution. The applicability of this technique had been validated for spherical particles during fluidized bed granulation and coating. For that purpose offline-samples had been drawn at constant intervals during the process and analysed afterwards with a digital image analyser (Retsch GmbH).

        

Impact of the particle shape on the chord length distribution

The effect of the particle shape on the generation of chord lengths marks a particularly challenging aspect of transforming the chord length distribution into nonrandom characteristic lengths such as diameter, Feret-diameter etc. An analytical solution, necessary for the real-time transformation, only exists for few simple convex particle shapes such as sphere, ellipsoid and cuboid. Since numerous fluidizsed bed processes in practice involve the formation of aspherical particles, the main focus is on expanding the transformation algorithm to irreguarly shaped particles. These include agglomerates as one common representative of major industrial relevance. By dint of an agglomerate constructor, which provides a particle formation with adjustable characteristics, typical chord length distributions are generated and will be associated to characteristic lengths. The primary objective of ongoing investigations constitutes the development of a general inversion of agglomerate chord lengths combined with a dynamic shape evolution model, enabling an inline-detection of particle size, that is mass conservative and therefore applicable to model-based process control.

Inline-detection of particle concentration and velocity

The fiber-optical inline-probe QRV (BASF AG) is based on the concept of backscattering of lit particles facilitating the detection of solid concentration and particle velocities in disperse media.The device is employed for the survey of bubble formation and spatial porosity distribution within fluidized beds. Additionally a systematic mapping of a fluidized bed is performed to identify and delineate functional zones in regard to local solid concentration and velocities. Accordingly both particle properties require special attention to characterize spray cones of nozzles due to the intense quality affecting mechanisms. As a consequence the detected residence time of particles within the spraying zone serves to determine the aggregation efficiency of the binder.     
         



The research project is funded by the German Federal Ministry of Science and Education (BMBF) as part of the InnoProfile-Transfer project "Unternehmen Region".

Contact

Dipl.-Ing. Christian Fischer
Dates
University Course Drying 2020
30.03.2020 - 02.04.2020 in Magdeburg
University Course Fluidization Technology 2019
04.11.2019 - 07.11.2019 in Hamburg
News
Appreciation of the research work at the chair with title page of the journal Processes (MDPI)
First project meeting Wigratec InterSpiN
Award for Maciej Jaskulski
Cluster WIGRATEC enters the next round
Arun S. Mujumdar Medal for Prof. E. Tsotsas
Award for best oral presentation
Award for best oral presentation for Christoph Neugebauer on Population Balance Modeling Conference 2018
Faculty Prize 2018
Award for Prof. E. Tsotsas
Honorary Professorship of UCTM, Sofia, for Prof. Tsotsas
University Course Drying 2018
19. March -- 22. March 2018 in Magdeburg
University Course Fluidization Technology 2017
6. - 9. November 2017 in Hamburg
Award on Conference
Best Research Award for Sayali Zarekar on IDS in Gifu, Japan
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Best Poster Award for Christian Rieck at PARTEC 2016 in Nuremberg, Germany
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Best poster award for Vesselin Idakiev at national conference
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Best Presentation Awards on Nordic Baltic Drying Conference 2015
ECCE 2015
27. September - 01. October 2015 in Nice, France
Granulation Workshop 2015
1st July - 3rd July 2015 in Sheffield, UK
University Course Drying 2016
29. March -- 01. April 2016 in Magdeburg
Extension of the Research Training Group 1554
Extension of the funding period for 4.5 years
Award on annual conference
Award for best poster presentation goes to Maryam Dadkhah
Modern Drying Technology Vol. 3
Prof. E. Tsotsas in CES Top 20 Reviewer 2010
Award on Asia Pacific Drying Conference
VDI Ehrenring für Jun.-Prof. Mirko Peglow
University Course Drying 2014
Fundamentals and Applications of Drying Technology