Chapter 9
Impact Comminution in Jet Mills
Alexander Strobel, Benedikt Köninger, Stefan Romeis, Karl-Ernst Wirth,
and Wolfgang Peukert
Abstract Modelling the comminution in jet mills with respect to the complex twophase flow and the dynamic process behaviour is still a challenging task. The processed solids pass through several stages in the mill: The comminution process in
the lower part, the pneumatic transport towards the classifier in the middle section,
and the classification step at the top. In this contribution, the grinding kinetics and
process behaviour during quasi-batch and fed-batch operational mode for different
holdups, classifier speeds, and particle sizes are examined in detail. A previously
developed method using well-characterized aluminium particle probes to access the
stressing conditions is adapted for application in the investigated jet mill: The relative particle impact velocity is linked to the geometric changes of the particles upon
impact. A high number of impact events happen in the mill, while at the same time,
the average particle velocity is comparatively low. Besides the stressing conditions,
breakage probabilities for the used glass beads are determined by single particle
impact experiments and described by the model of Vogel and Peukert. Solids concentration measurements and high-speed imaging reveal the formation of particle
clusters at the classifier and its periphery. These clusters have a massive impact on
the classification step itself: Fine particles are trapped inside the clusters and are not
discharged. Based on an adaption of the breakage model, and using the mean relative
particle impact velocity determined by the particle probes, a model for the product
mass flow is introduced.
Nomenclature
(1 − ε)
Solid volume fraction [–]
(1 − ε) r Solid volume fraction at radius r [–]
(1 − ε) jet Solid volume fraction in the jet [–]
a
Particle acceleration [m s
−2 ]
A. Strobel · B. Köninger · S. Romeis · K.-E. Wirth · W. Peukert (B)
Institute of Particle Technology, Friedrich-Alexander-Universität
Erlangen-Nürnberg, Erlangen, Germany
e-mail: wolfgang.peukert@fau.de
© Springer Nature Switzerland AG 2020
S. Heinrich (ed.), Dynamic Flowsheet Simulation of Solids Processes,
https://doi.org/10.1007/978-3-030-45168-4_9
305
Impact Comminution in Jet Mills
Alexander Strobel, Benedikt Köninger, Stefan Romeis, Karl-Ernst Wirth,
and Wolfgang Peukert
Abstract Modelling the comminution in jet mills with respect to the complex twophase flow and the dynamic process behaviour is still a challenging task. The processed solids pass through several stages in the mill: The comminution process in
the lower part, the pneumatic transport towards the classifier in the middle section,
and the classification step at the top. In this contribution, the grinding kinetics and
process behaviour during quasi-batch and fed-batch operational mode for different
holdups, classifier speeds, and particle sizes are examined in detail. A previously
developed method using well-characterized aluminium particle probes to access the
stressing conditions is adapted for application in the investigated jet mill: The relative particle impact velocity is linked to the geometric changes of the particles upon
impact. A high number of impact events happen in the mill, while at the same time,
the average particle velocity is comparatively low. Besides the stressing conditions,
breakage probabilities for the used glass beads are determined by single particle
impact experiments and described by the model of Vogel and Peukert. Solids concentration measurements and high-speed imaging reveal the formation of particle
clusters at the classifier and its periphery. These clusters have a massive impact on
the classification step itself: Fine particles are trapped inside the clusters and are not
discharged. Based on an adaption of the breakage model, and using the mean relative
particle impact velocity determined by the particle probes, a model for the product
mass flow is introduced.
Nomenclature
(1 − ε)
Solid volume fraction [–]
(1 − ε) r Solid volume fraction at radius r [–]
(1 − ε) jet Solid volume fraction in the jet [–]
a
Particle acceleration [m s
−2 ]
A. Strobel · B. Köninger · S. Romeis · K.-E. Wirth · W. Peukert (B)
Institute of Particle Technology, Friedrich-Alexander-Universität
Erlangen-Nürnberg, Erlangen, Germany
e-mail: wolfgang.peukert@fau.de
© Springer Nature Switzerland AG 2020
S. Heinrich (ed.), Dynamic Flowsheet Simulation of Solids Processes,
https://doi.org/10.1007/978-3-030-45168-4_9
305