Innovative Method to Measure Solids Circulation in Spouted

Fluidized Beds

2009 AIChE National MeetingNashville, TN

November 9, 2009

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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

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Analysis (1)

Lag - 0.01 seconds

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Cor

rela

tion

Coe

ffic

ent

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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

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qu

enci

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1/s

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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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Us-Ums - cm/sec

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/sec

Bed Height Effect On Recirculation- 1.2 mm glass beads -

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Us-Ums - cm/sec

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c 4 cm bed

5.8 cm bed

6.5 cm bed

Recirculation Rate Correlation

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(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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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: halow@windstream.net