11 Experimental Study and Modelling of Particle …
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reached if 100% of the lightweight material is discharged as light product and 100%
of the heavyweight material is delivered as heavy product.
The operational efficiency of ZACs at low particle concentrations has been investigated by Senden [5] who used square pieces of paper and porous polystyrene
spheres as test materials during the experiments. He analyzed the influence of different channel depths and bending angles (90°, 120°, 150°) and found the 150° case
showing the highest separation efficiency associated with an enormous increase of
particle residence time. Furthermore, he developed a stochastic model to describe
the separation behavior based on observations of every single stage. Rosenbrand [8]
extended Senden’s model [5] for high particle concentrations using a dimensionless
correlation.
Vesilind and Henrikson [9] studied the influence of feed rate on the separation
performance in a zigzag channel with a bending angle of 120° using square-shaped
plastic and aluminum pieces. It was shown that particle residence times decrease
with increasing feed rate; the same applies to separation efficiency. Both effects
were ascribed to an increased particle-particle collision frequency.
For performance comparison of different air classifiers, Biddulph and Connor
[10] developed a simple test based on the estimation of effective diffusivity; good
separation efficiencies were assumed to be connected with low diffusivities.
The research group around Tomas [11, 12] developed a model to describe the
separation performance in a ZAC. This model agreed well with experimental data
measured by separation experiments of glass beads, sand, split, and gravel at low mass
loadings of the air. One important advantage of their model is a flexible application
concerning separation by size, density, or shape. The zigzag air classifier was found
to deliver satisfactory to good separations, and this at low energy consumption.
The separation of PET flakes by particle shape in a zigzag separator has been
studied in several studies [4, 13, 14]. Using a low mass loading of the air, the process
showed good separation efficiency.
Several investigations can also be found in the literature (e.g., [13, 15]) concerning the simulation of one- and multi-phase flows in zigzag-shaped channels using
Computational Fluid Dynamics (CFD). However, only few of these publications
attempted to quantify separation performance.
The aim of the present investigation was to investigate in a systematic manner the
processes leading to particle separation in a ZAC, by combining in a suitable manner
theoretical, experimental and numerical investigations.
The installation used for all studies is shown in Fig. 1. The pilot-scale air separator used in this research consists of the zigzag channel featuring four exchangeable
channel modules aligned vertically and housing two segments each, which are connected under a prescribed inclination angle. A controllable blower drives the air in a
closed circuit through the apparatus. Air flows through the inflow pipe and then from
bottom to top through the zigzag channel, through an aero-cyclone and a filter before
it re-enters the blower. Particles are fed to the system through a small square duct
at mid-height of the zigzag channel by means of a controllable vibration conveyer
connected to a hopper. The separated material is collected in two containers, one for
393
reached if 100% of the lightweight material is discharged as light product and 100%
of the heavyweight material is delivered as heavy product.
The operational efficiency of ZACs at low particle concentrations has been investigated by Senden [5] who used square pieces of paper and porous polystyrene
spheres as test materials during the experiments. He analyzed the influence of different channel depths and bending angles (90°, 120°, 150°) and found the 150° case
showing the highest separation efficiency associated with an enormous increase of
particle residence time. Furthermore, he developed a stochastic model to describe
the separation behavior based on observations of every single stage. Rosenbrand [8]
extended Senden’s model [5] for high particle concentrations using a dimensionless
correlation.
Vesilind and Henrikson [9] studied the influence of feed rate on the separation
performance in a zigzag channel with a bending angle of 120° using square-shaped
plastic and aluminum pieces. It was shown that particle residence times decrease
with increasing feed rate; the same applies to separation efficiency. Both effects
were ascribed to an increased particle-particle collision frequency.
For performance comparison of different air classifiers, Biddulph and Connor
[10] developed a simple test based on the estimation of effective diffusivity; good
separation efficiencies were assumed to be connected with low diffusivities.
The research group around Tomas [11, 12] developed a model to describe the
separation performance in a ZAC. This model agreed well with experimental data
measured by separation experiments of glass beads, sand, split, and gravel at low mass
loadings of the air. One important advantage of their model is a flexible application
concerning separation by size, density, or shape. The zigzag air classifier was found
to deliver satisfactory to good separations, and this at low energy consumption.
The separation of PET flakes by particle shape in a zigzag separator has been
studied in several studies [4, 13, 14]. Using a low mass loading of the air, the process
showed good separation efficiency.
Several investigations can also be found in the literature (e.g., [13, 15]) concerning the simulation of one- and multi-phase flows in zigzag-shaped channels using
Computational Fluid Dynamics (CFD). However, only few of these publications
attempted to quantify separation performance.
The aim of the present investigation was to investigate in a systematic manner the
processes leading to particle separation in a ZAC, by combining in a suitable manner
theoretical, experimental and numerical investigations.
The installation used for all studies is shown in Fig. 1. The pilot-scale air separator used in this research consists of the zigzag channel featuring four exchangeable
channel modules aligned vertically and housing two segments each, which are connected under a prescribed inclination angle. A controllable blower drives the air in a
closed circuit through the apparatus. Air flows through the inflow pipe and then from
bottom to top through the zigzag channel, through an aero-cyclone and a filter before
it re-enters the blower. Particles are fed to the system through a small square duct
at mid-height of the zigzag channel by means of a controllable vibration conveyer
connected to a hopper. The separated material is collected in two containers, one for