(732d) Numerical Verification and Validation of the Particle Tracking Technique in Predicting Particle Velocity and Solids Distribution in a Travelling Fluidized Bed with CFD-DEM

Numerical verification and validation of
the particle tracking technique in predicting particle velocity and solids
distribution in a travelling fluidized bed with CFD-DEM

Yupeng Xu^1,8, Tingwen Li²,
Sina Tebianian³, Jamal Chaouki⁴, Thomas W. Leadbeater⁷,
Rouzben Jafari⁴, David J. Parker⁵, Jonathan Seville⁵,
Naoko Ellis⁶, John R. Grace⁶

 
¹
National Energy Technology Laboratory, U.S. Department of Energy, Morgantown, WV, USA

 
²
SABIC Corporate Research and Development

 
³ IFP
Energies Nouvelles, Process Design and Modeling division, Lyon, France

 
⁴
Département de génie chimique, Ecole Polytechnique, Montréal, QC Canada H3T
1J4.

 
⁵
Positron Imaging Centre, University of Birmingham, Birmingham, B15 2TT, UK

 
⁶
Department of Chemical & Biological Engineering, University of British
Columbia, Vancouver, Canada V6T1Z3  

 
⁷
Department of Physics, University of Cape Town, South Africa

 
⁸
West Virginia University Research Corporation, Morgantown, WV 26506, USA

Abstract

Gas-solid
fluidized beds are widely used in energy and chemical industry applications due
to their good mixing and heat transfer ability. However, the design and
scale-up of the reactor and improvement of reactor performance are still
hindered by the lack of fundamental knowledge of physical phenomena in these
systems due to the opaque and abrasive nature of the solid particles,
turbulence, and multiple scales of motion and flow structure. Several
non-invasive techniques such as radioactive particle tracking (RPT) and
positron emission particle tracking (PEPT) have been deployed to measure the average
particle velocity and the mean solid distribution in recent years in a “travelling
fluidized bed”. These techniques require the use of tracer particles
which differ in size, density and/or shape from the bulk particles of interest.
In determining averaged velocities based on such techniques, a choice must be
made between averaging velocities of particles crossing a virtual plane over a
period of time (“face-average” approach) and those passing through a defined
volume over time (the “volume-average” approach).  Moreover, different
methods have been developed to calibrate the particle tracking measurements in order
to quantify the mean solid concentration in fluidized beds.

In the current
research, CFD-DEM simulations were conducted to study the gas-solid flows in
the traveling fluidized bed and the behavior of different particles, including bulk
sand particles and tracer particles for radioactive particle tracking and
positron emission particle tracking. The general flow hydrodynamics of
numerical simulation are compared with measured values obtained using different
experimental techniques. As shown in Figure 1, the formation, movement and
burst of a typical square nosed slug for a superficial gas velocity of 0.4 m/s are
well captured.

Analyses were
carried out to derive particle velocity and mean solid concentrations from the
tracer particle data. The different averaging techniques for particle velocity
and different calibration approaches for solids volume fraction are also
compared.  It is shown that both the particle velocity and the mean solid
concentration can be measured reliably based on representative tracer
particles. As an example, comparison of the cross-section averaged solids
volume fraction along the bed height between simulation and different
experimental techniques are shown in Figure 2 for superficial velocities of 0.40
and 0.60 m/s.

Figure 1.  Simulation results of the formation,
movement and burst of a typical square-nosed slug for a superficial gas
velocity of 0.4 m/s.

Figure 2. Comparison of cross section averaged
solids volume fraction along the bed height between simulation and different
experimental techniques at (a) U_g=0.40 m/s, (b) U_g=0.60
m/s.