Experimental Study of Circulating Fluidized Bed Using Radioactive Particle Tracking Technique
Experimental Study of Circulating Fluidized Bed
Using Radioactive Particle Tracking Technique Premkumar Kamalanathan,
Trilok Tribedi, Rajesh Kumar
Upadhyay*
of Technology (IIT) ? Guwahati Assam 781039, India Circulating fluidized bed (CFB) finds
application in industrial process like cracking, combustion, gasification,
drying, etc. The major reasons cited being operation flexibility, efficiency,
short residence time, etc. Even though, CFB is in use for more than two
decades, fundamental understanding of flow characteristics in CFB is still
insufficient. Therefore, the design and scale up of CFB is still based on
empirical equations and experience. This is mainly due to the complexity of gas
? solid, solid ? solid and solid wall interactions. Multi-scale nature of these
interactions makes it more difficult to delineate the hydrodynamics. Several numerical and experimental efforts have
been made in literature to understand the hydrodynamics. Numerical efforts have
been largely suffering from lack of experimental data. Further, most of the
experimental work carried out in CFB is based on invasive measurements which
can disturb the flow particularly if velocity is very high as in CFB. In literature
very few data is available based on non-invasive measurements particularly at
relatively higher solid flux which is of interest to industry. In current work,
attempt has been made to augment the previous work to understand the hydrodynamics
of gas-solids flows CFB. Radioactive particle tracking (RPT), a non-invasive technique,
is used to study the hydrodynamics of CFB at industrially operated solid
fluxes. In RPT, a radioactive particle is used
as a marker of the phase. Marker is made similar to shape and density of solids
to be tracked. Motion of marker is traced using scintillation detectors placed
strategically around the column. Path of the tracer (instantaneous position) is
reconstructed using Monte Carlo based reconstruction algorithm from the
recorded photon count time series on each detectors. From the instantaneous
positions, instantaneous velocities are calculated. Ensemble averaged
velocities are obtained by averaging over the instantaneous velocities. Lab scale CFB of 0.05 m diameter and 3 m
height is used for current study. A Glass bead of 500 µm diameter is used as
solids. Investigations are conducted at different solid fluxes and inlet gas
velocities. Particle trajectories, instantaneous velocities, pdf of
instantaneous velocities, mean velocities are quantified to understand the
hydrodynamics of CFB. Particle occurrences along the investigation zone for the
two solid fluxes are shown in the Figure 1. Occurrence is high near the wall,
indicating the solid volume fraction near the wall is high. With increase in solid flux, zone of high
solids occurrences decreases. This may be due to solids distribution is more
uniform. Further results will be discussed in the full manuscript.Â
(a)
                                         (b)
Using Radioactive Particle Tracking Technique Premkumar Kamalanathan,
Trilok Tribedi, Rajesh Kumar
Upadhyay*
Department of Chemical Engineering, Indian Institute
of Technology (IIT) ? Guwahati Assam 781039, India Circulating fluidized bed (CFB) finds
application in industrial process like cracking, combustion, gasification,
drying, etc. The major reasons cited being operation flexibility, efficiency,
short residence time, etc. Even though, CFB is in use for more than two
decades, fundamental understanding of flow characteristics in CFB is still
insufficient. Therefore, the design and scale up of CFB is still based on
empirical equations and experience. This is mainly due to the complexity of gas
? solid, solid ? solid and solid wall interactions. Multi-scale nature of these
interactions makes it more difficult to delineate the hydrodynamics. Several numerical and experimental efforts have
been made in literature to understand the hydrodynamics. Numerical efforts have
been largely suffering from lack of experimental data. Further, most of the
experimental work carried out in CFB is based on invasive measurements which
can disturb the flow particularly if velocity is very high as in CFB. In literature
very few data is available based on non-invasive measurements particularly at
relatively higher solid flux which is of interest to industry. In current work,
attempt has been made to augment the previous work to understand the hydrodynamics
of gas-solids flows CFB. Radioactive particle tracking (RPT), a non-invasive technique,
is used to study the hydrodynamics of CFB at industrially operated solid
fluxes. In RPT, a radioactive particle is used
as a marker of the phase. Marker is made similar to shape and density of solids
to be tracked. Motion of marker is traced using scintillation detectors placed
strategically around the column. Path of the tracer (instantaneous position) is
reconstructed using Monte Carlo based reconstruction algorithm from the
recorded photon count time series on each detectors. From the instantaneous
positions, instantaneous velocities are calculated. Ensemble averaged
velocities are obtained by averaging over the instantaneous velocities. Lab scale CFB of 0.05 m diameter and 3 m
height is used for current study. A Glass bead of 500 µm diameter is used as
solids. Investigations are conducted at different solid fluxes and inlet gas
velocities. Particle trajectories, instantaneous velocities, pdf of
instantaneous velocities, mean velocities are quantified to understand the
hydrodynamics of CFB. Particle occurrences along the investigation zone for the
two solid fluxes are shown in the Figure 1. Occurrence is high near the wall,
indicating the solid volume fraction near the wall is high. With increase in solid flux, zone of high
solids occurrences decreases. This may be due to solids distribution is more
uniform. Further results will be discussed in the full manuscript.Â
(a) Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â (b)
Figure
1: Contours of occurrences (a) Ug=8.8 m/s, Gs=110 kg/m2s (b) Ug=8.8
m/s, Gs=121 kg/m2s
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