Discrete particle simulations of high pressure fluidization


Godlieb, W. and Deen, N.G. and Kuipers, J.A.M. (2006) Discrete particle simulations of high pressure fluidization. In: CHISA 17th international congress of chemical and process engineering, 27-31 August 2006, Prague.

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Abstract:Low density polyethylene and polypropylene are produced at large scale via the Unipol
process. In this process catalyst particles are fluidized with monomer gas which reacts with
the catalyst particles to form polymeric particles up to a size of 1 mm. The process is
typically operated at pressures of 20 to 25 bar. Pressure impacts the hydrodynamics of the
fluidized bed as it influences the bubble behaviour, particle mixing and heat transfer
characteristics. Despite decades of research on fluid beds these effects are not completely
In order to gain more insight in the effects of operating pressure on the fluidization behaviour
we have performed full 3D discrete particle simulations. We use a state-of-the art discrete
particle model (DPM) to simulate fluidization behaviour at different pressures. In our model
the gas phase is described by the volume-averaged Navier-Stokes equations, whereas the
particles are described by the Newtonian equations of motion. The DPM accurately accounts
for the gas-particle interaction, which is necessary for capturing the pressure effect.
The simulation results were analysed with spectral analysis of the pressure drop fluctuations
and analysis of the porosity field. In order to study the bubble behaviour, a sophisticated
bubble detection algorithm was developed. From this algorithm, gas bubble characteristics,
such as bubble velocity and bubble size are obtained.
The simulation results show increasing emulsion porosity and decreasing bubble porosity
with increasing pressure. In other words, the bubble-emulsion structure becomes less distinct.
The determined bubble velocity is very well in accordance with empirical correlations for
low pressures, and decreases at elevated pressures.
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Link to this item:http://purl.utwente.nl/publications/69258
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