234
G. Fragnière et al.
In case of the unresolved CFD-DEM simulations, the product of stressing frequency and energy showed good correlation with experimental grinding results. For
the validation different particles were investigated using microcompression, including yeast cells, to experimentally determine the respective breakage probability. Correlating these breakage probabilities with the collision frequencies gained from the
simulations allowed for a direct comparison with experimentally gained breakage
rates from performing grinding experiments.
For the systematic analysis of fine particle breakage via compression between
grinding beads a breakage tester was constructed. Material specific fracturing properties were investigated in dependence of the original particle size and the gap size
between the rolls. Force and torque were captured for an energetic evaluation. The
device enabled the prediction of material specific breakage behavior which, in a
normalized form, should enable the prediction within flow sheet simulations.
The temporal development of particle size distribution was modeled with population balance equations. On this basis the impact of various operating and machine
parameters on the breakage rate was examined. It could be verified that collision
frequency and thereby load frequency has a linear dependence of the stirrer speed
and the number of grinding beads. The so determined breakage rates showed a good
correlation with experimental results. The product transport through the mill was
simulated via a cell model with mixing flow.
Additionally, circular mode grinding experiments were performed to investigate
the impact of operation parameters. For instance, it was shown, that only viscosities
high enough to impact the kinetic energy have an impact on the grinding process.
Additionally, radiometric densitometry was used to investigate grinding media transport. A high correlation between tip speed and volume flow on the grinding media
transport along the horizontal axis could be detected.
The results from these experiments and simulations were included in Dyssol as
a flow sheet simulation. The implemented model was then examined by performing
simulations and comparing them with experimental results for the particle size at the
outlet of a stirred media mill.
References
1. Tavares, L.M., de Carvalho, R.M.: Modeling breakage rates of coarse particles in ball mills.
Miner. Eng. 22(7–8), 650–659 (2009)
2. Capece, M., Bilgili, E., Davé, R.: Insight into first-order breakage kinetics using a particle-scale
breakage rate constant. Chem. Eng. Sci. 117, 318–330 (2014)
3. Theuerkauf, J.: Numerische und experimentelle Untersuchungen von Fluid- und Mahlkörperbewegungen in Rührwerkskugelmühlen, Zugl.: Braunschweig, Techn. Univ., Diss., 2000, 1.
Aufl., Cuvillier Göttingen, 2000, ISBN 3897128039
4. Conway-Baker, J., Barley, R.W., Williams, R.A., et al.: Measurement of the motion of grinding
media in a vertically stirred mill using positron emission particle tracking (PEPT). Miner. Eng.
15(1), 53–59 (2002)
5. Jankovic, A.: Variables affecting the fine grinding of minerals using stirred mills. Min. Eng.
16(4), 337–345 (2003)
G. Fragnière et al.
In case of the unresolved CFD-DEM simulations, the product of stressing frequency and energy showed good correlation with experimental grinding results. For
the validation different particles were investigated using microcompression, including yeast cells, to experimentally determine the respective breakage probability. Correlating these breakage probabilities with the collision frequencies gained from the
simulations allowed for a direct comparison with experimentally gained breakage
rates from performing grinding experiments.
For the systematic analysis of fine particle breakage via compression between
grinding beads a breakage tester was constructed. Material specific fracturing properties were investigated in dependence of the original particle size and the gap size
between the rolls. Force and torque were captured for an energetic evaluation. The
device enabled the prediction of material specific breakage behavior which, in a
normalized form, should enable the prediction within flow sheet simulations.
The temporal development of particle size distribution was modeled with population balance equations. On this basis the impact of various operating and machine
parameters on the breakage rate was examined. It could be verified that collision
frequency and thereby load frequency has a linear dependence of the stirrer speed
and the number of grinding beads. The so determined breakage rates showed a good
correlation with experimental results. The product transport through the mill was
simulated via a cell model with mixing flow.
Additionally, circular mode grinding experiments were performed to investigate
the impact of operation parameters. For instance, it was shown, that only viscosities
high enough to impact the kinetic energy have an impact on the grinding process.
Additionally, radiometric densitometry was used to investigate grinding media transport. A high correlation between tip speed and volume flow on the grinding media
transport along the horizontal axis could be detected.
The results from these experiments and simulations were included in Dyssol as
a flow sheet simulation. The implemented model was then examined by performing
simulations and comparing them with experimental results for the particle size at the
outlet of a stirred media mill.
References
1. Tavares, L.M., de Carvalho, R.M.: Modeling breakage rates of coarse particles in ball mills.
Miner. Eng. 22(7–8), 650–659 (2009)
2. Capece, M., Bilgili, E., Davé, R.: Insight into first-order breakage kinetics using a particle-scale
breakage rate constant. Chem. Eng. Sci. 117, 318–330 (2014)
3. Theuerkauf, J.: Numerische und experimentelle Untersuchungen von Fluid- und Mahlkörperbewegungen in Rührwerkskugelmühlen, Zugl.: Braunschweig, Techn. Univ., Diss., 2000, 1.
Aufl., Cuvillier Göttingen, 2000, ISBN 3897128039
4. Conway-Baker, J., Barley, R.W., Williams, R.A., et al.: Measurement of the motion of grinding
media in a vertically stirred mill using positron emission particle tracking (PEPT). Miner. Eng.
15(1), 53–59 (2002)
5. Jankovic, A.: Variables affecting the fine grinding of minerals using stirred mills. Min. Eng.
16(4), 337–345 (2003)