innovative method to measure solids circulation in spouted fluidized beds 2009 aiche national...
TRANSCRIPT
Innovative Method to Measure Solids Circulation in Spouted
Fluidized Beds
2009 AIChE National MeetingNashville, TN
November 9, 2009
Time121.8 122.0 122.2 122.4 122.6
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Objectives
• Develop method for directly measuring solids circulation in particulate systems
• Apply to experimental spouted beds to better understand solids circulation dynamics
• This study- Demonstrate potential for a particular approach using magnetic tracking
Background
Several other solids tracking methods have been developed over the past several decades:
•Visual observations in 2D or half-round columns
•In bed capacitance, momentum or optical probes
•Radioactive particle tracking (CARPT)
•MRI/NMRI methods
•Positron emission tomography(PET)
•Various residence time distribution methods
Advantages of Magnetic Tracer• True 3D tracking of single particles without in-bed probes
• Simpler and more general than MRI and PET
• Safer than CARPT and PET
• Much cheaper that CARPT, MRI and PET
• Adaptable to various bed configurations
Limitations• Small size beds (more sensitive probes are available to
study larger beds)
• Non-Magnetic bed structure required
• Low Temperature (< 300F)
Approach
Measure magnetic field from ‘tracer’ particle with an embedded magnet:
•Tracer particle made from neodymium magnet embedded in polymer (similar size and density to particles of interest)
•Externally mounted detectors monitor magnetic field from tracer in bed
•Algorithm calculates position from magnetic field readings•3D spatial trajectory provides detailed circulation statistics• Variations in vertical position used to calculate particle recirculation frequency
Experimental Setup
Small air-fluidized spouted bed at ambient temperature and pressure with multi-channel digital data acquisition
Spouted Bed & Probe Details
Magnetic Probes
Magnetic Probes
Magnetic Tracer Preparation
• Neodymium magnets available as cubes, cylinders and discs down to about 1 mm
• Three methods – Solid polymer coating
– Imbedding in plastic bead
– Foaming polymer coating
• Sizes 1 to 4 mm
• Densities 1.5 to 5.5 g/cc
Magnetic Field signals
Each probe records a time varying signal as the tracer moves
Tracking Algorithm (1)• Normal (perpendicular orientation) field strength-distance
relationship calibrated for each tracer and probe type
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1/sqrt(magnetic field strength in milli- teslas)
Tracking Algorithm (2)
Md
)cos(
||
1
||
1
||
1
||
1
MsMn
MsMnY
||
1|
||
1
||
1|
||
1
MwMe
MwMeX
2222 )1(||
)cos(YXR
Mn
nZ
2222 )1(||
)cos(YXR
Ms
sZ
2222 )1(||
)cos(YXR
Me
eZ
2222 )1(||
)cos(YXR
Mw
wZ
• Tracer magnetic axis aligns with earth magnetic field in bed
• Probe signal function of tracer distance & magnetic axis angle
• Probe orientation and geometric construct eliminates angle dependence for X & Y
• Vertical position (Z) from Pythagorean Theorem
3-D TrajectoriesNet result is reconstruction of 3D tracer trajectory versus time
Time121.8 122.0 122.2 122.4 122.6
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Analysis (1)
Lag - 0.01 seconds
0 1000 2000 3000 4000 5000
Cor
rela
tion
Coe
ffic
ent
-0.5
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1.0090708T15.csv
Many statistics can be computed from the dynamic trajectories
Vertical tracer position versus time
Fourier Power Spectrum
Autocorrelation
Direct visual tracking appears to validate magnetic tracer results
Legend
Video of surfaceTracer
Us- cm/sec100 105 110 115 120 125 130
Rec
ircu
lati
on
Fre
qu
enci
es -
1/s
ec
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Analysis (2)
Experimental Conditionsfor Recirculation Study
•Glass beads: 0.8, 1.0, 1.2, 1.5, 2.0 mm : 2.5 g/cc•ZrSiO4: 1.0 and 2.0 mm : 4.1 g/cc•ZrO2: 1.0 mm : 5.7 g/cc•Millet Seed : 1.8 mm : 1.2 g/cc•Nylon Sphere : 3.1 mm 1.1 g/cc•Pasta : 2.8 mm : 1.2 g/cc•Each material: 5 air rates at each of three bed depths•45 and 60 degree cone angles for some materials•3 and 4 mm air inlets for 60 degree cone•Experiments sampled at 100 or 200 hertz•Each run 5 minutes long•Total of 500 runs
Velocity Effect on Recirculation- 1.2 mm glass beads -
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0 5 10 15 20 25 30 35 40
Us-Ums - cm/sec
Rc
- g
/sec
Bed Height Effect On Recirculation- 1.2 mm glass beads -
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Us-Ums - cm/sec
Rc -
g/se
c 4 cm bed
5.8 cm bed
6.5 cm bed
Recirculation Rate Correlation
-60
-40
-20
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0 20 40 60 80 100 120 140 160 180 200 220 240 260
(U-Ums)((phobulk*particle size)^1/2)(Hfac) -g^0.5 /sec
Rc
-Rc
ms
- g
/se
c
1.2 mm glass,45,4
1.5 mm glass,45,4
2.0 mm glass,45,4
1.0 mm ZrSiO4,45,4
1.0 mm ZrO2,45,4
2.8 mm Pasta,45,4
3.14 mm Nylon,45,4
1.85 mm Millet Seed,45,4
1.2 mm Glass.60.3
1.5 mm Glass,60,3
1.0 mm ZrSiO4,60,3
1.0 mm ZrO2,60,3
2.0 mm Glass,60,3
1.85 mm millet Seed, 60,3
1.2 mm Glass, 60,4
1.5 mm glass, 60,4
1.2 mm Glass, Bifurcation Ser
1.85 MilletSeed,60,4
1 mm ZrO2,60,4
Rcms Correlation
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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Minimun spouting air was rate - gr/s
Rcm
s-g
r/s
1.2 mm glass,45,4
1.5 mm glass,45,4
2 mm glass,45,4
1.0 mm ZrSiO4,45,4
1.0 mm ZrO2,45.4
0.8 mm Glass, 4,45
2.8 mm Pasta,45,4
3.15 mm Nylon,45,4
Millet Seed,45,41.2 mm Glass,60,3
1.5 mm glass, 60,3
1.0 mm ZrSiO4,60,3
1.0 mm ZrO2,60,3
2.0 mm Glass,60,3
Millet Seed,60,3
1.2 mm Glass,60,4
1.5 mm Glass, 60,4
Recirculation Rate at Minimum Spouting
Work Plans
• More sensitive magnetic probes• Larger diameter beds (e.g., 70 mm)• Slugging beds (limited tests done)• Beds of mixed particle sizes (limited tests done)• Simulated biomass particles• Tracking algorithms for different sensor
configurations• Stochastic-deterministic models for particle motion
Acknowledgement
The author wish to acknowledge Waynesburg University’s Center for Research and
Economic Development for their financial support and encouragement of this research.
More Information
On-line publication: Ind. Eng. Chem. Res.Sept 23, 2009doi: 10:1021/ie9008698
Or
Email: [email protected]