A discrete element study of moisture dependent particle-particle interaction during granulation in a spout fluidized bed

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Buijtenen van, Maureen S. and Deen, Niels G. and Heinrich, Stefan and Antonyuk, Sergiy and Kuipers, J.A.M. (2008) A discrete element study of moisture dependent particle-particle interaction during granulation in a spout fluidized bed. In: 6th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries, CFD 2008, 10-12 June 2008, Trondheim, Norway.

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Abstract:process industry in granulation processes, in which efficient
contacting between large particles, droplets and gas is of
paramount importance. However, detailed understanding of
the complex behavior of these systems is lacking. In this
paper we study the effect of the inter-particle interaction on
the bed dynamics, by investigating the bed height, pressure
drop and vertical particle velocity as function of the variable
restitution coefficient, which varies in time and space as
function of the moisture content due to the particle-droplet
interaction. This is done computationally, by using the
extended discrete element model (DEM) which describes the
dynamics of the continuous gas-phase and the discrete
particles and droplets. The objective of this work is to gain
insight in the effect of the variable restitution coefficient on
the flow behavior of spout fluidized beds at different flow
regimes using DEM. The three flow regimes comprise the
intermediate / spout-fluidization regime (B1), spouting-withaeration
regime (B2) and the jet-in-fluidized-bed regime
(B3). The simulation results with variable restitution
coefficients were compared to simulations with constant
restitution coefficients reported by Van Buijtenen et al.
(2007). The trend of increasing average bed height with
decreasing restitution coefficient is also valid for the variable
restitution coefficient. However, the average bed height is
larger for the variable restitution coefficient for all flow
regimes. This is also observed for the pressure drop, showing
a lower value compared to the constant restitution coefficient.
These results suggest a significant influence of the variable
restitution coefficient on the bed dynamics, since the variable
restitution coefficient provides regions in the bed with
particles having different collision properties. The presence
of these distinctive regions causes different behavior of the
bed dynamics, which is also shown in the time-averaged
vertical particle velocity. The velocity in the spout region for
the variable restitution coefficient is lower than for the
constant restitution coefficient for case B1 and B2. However,
for case B3 these regions are less pronounced, due to the
larger mixing capacity caused by the larger interaction
between the spout channel and the bubbles in the annulus
region. As a result, the particle velocity for the variable
restitution coefficient complies with the particle velocity for
the constant restitution coefficient.
These findings reveal the significant impact of the influence
of the variable restitution coefficient on the dynamics of the
bed, which is clearly different compared to the constant
restitution coefficient. This is due to the presence of
distinctive regions with different restitution coefficient,
which can only be simulated when the dependency of the
moisture content on the restitution coefficient is accounted
for.
Currently, only the wetting process on the particles has been
simulated without evaporation and crystallization of the
deposited granulate solution, which are phenomena that are
very important in the granulation process. It is therefore
desirable to further improve the discrete element model, by
solving mass and energy balances for the particles and the gas
phase
Item Type:Conference or Workshop Item
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Link to this item:http://purl.utwente.nl/publications/68588
Organisation URL:http://www.sintef.no/Projectweb/CFD2008
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