linear attenuation coefficients and gas holdup ... · linear attenuation coefficients and gas...

Linear Attenuation Coefficients and Gas Holdup Distributions in Bubble Column

with Vertical Internal for Fischer-Tropsch (FT) Synthesis

Abbas J. Sultan, Laith S. Sabri, and Muthanna H. Al-Dahhan† †Multiphase Reactors Engineering and Applications Laboratory (mReal)

† Department of Chemical and Biochemical Engineering, Missouri University of Science and

Technology, Rolla, MO 65409-1230. USA

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4/26/2017 2

Introduction

Motivations

Results and Discussion

Remarks

Acknowledgment

Multiphase Reactors Engineering and

Applications Laboratory (mReal)

Presentation Outline

4/26/2017 3

Coal

Biomass

Natural Gas

Fuel

& Chemicals

Gasification Syngas

Processing

Fischer-

Tropsch Synthesis

Syncrude

Refining & Upgrading

X L G

Introduction & Motivation

The conversion of natural and bio gas, coal, and biomass to liquid fuels and chemicals vis synthesis gas is currently of

interests to the energy and chemical industries which represents a valuable addition to diversifying in fuels and products

resources.

The key route for the conversion synthesis gas to liquid fuels and chemicals (GTL) technology is the Fisher-Tropsch

(FT) synthesis where the reaction of syngas (H2 and CO) over catalyst into liquid hydrocarbons takes place. FT synthesis

is highly exothermic and hence intense heat exchanging tubes (internals) are needed to control the temperature.

H2+CO (syngas) F-T waxes (C1-C100+)

H2O Water steam

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Bubble/Slurry bubble column reactor with vertical dense heat

exchanging tubes is one of the reactors of choice to conduct the highly

exothermic FT reaction.

The presence of the dense heat exchange tubes (internals) impacts the

hydrodynamics and mixing behavior of the reactor in a very complex

way and hence, it will affect the performance, selectivity and the yield.

The understanding of such complexity has been completely lacking

due to lack of implementing advanced measurement techniques.

Slurry bubble columns with vertical internals

Gas holdup distribution is the one of the important hydrodynamic

parameters governing the dynamic of the bubble/slurry bubble columns

where gas holdup drives the liquid circulation, and hence the rate of

mixing, mass, and heat transfer.

There is a lack of detailed investigation to understand the effect of the

intense internals on the gas holdup distribution.

Therefore, the focus of this work is to investigate, visualize, and quantify

for the first time the influence of the size, and configurations of the

intense heat exchanging tubes (internals) at wide range of the superficial

gas velocity on the time-averaged cross-sectional gas holdup distribution

and their radial/diametrical profiles by implementing non-invasive

gamma-ray computed tomography (CT) technique.

Industrial heat exchanging tubes (internals)

Dynamic level, L/D=10.3 (158 cm)

14 cm ID

183 cm

7.62 cm

Scan level, L/D=5.1 (78 cm) 2.54 cm O.D Plexiglas

internals Circular configuration

(supports)

Distributor

Drain

Compressed air in

30 cm

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Schematic diagram and photo of the stainless steel distributor (perforated plate)

Schematic diagrams and pictures of the circular configurations (spacers/supports)

for 0.5, and 1-inch internals

• The internals was designed to

cover 25% of the cross-

sectional area of the column to

mimic the bundle of heat

exchanging tubes used in FT

synthesis .

Experimental step up

Schematic diagram of 6-inch bubble column equipped with vertical internals



To the data

acquisition

system .60

samples at 10

Hz, which took

about 8.25 hours

for a full scan

Cs-137 source

Source collimator

Threaded rods

Aluminum

structure

Motor

Circular

plate

Square

plate

Steeper

motor

Chain

driver

15 NaI detectors

Detectors collimator

(2 mm × 5 mm)

Bubble column

with internals

Flowmeters

Cs-137 source

Source collimator

Bubble column with internals

Detectors collimator

NaI detector

CO-60 source

Source collimator

Detector collimator

15 NaI detectors

Bubble column with internals

Top supporter

Bottom supporter

Lead shield

CS-137 source

Schematic diagram of single gamma-ray computed tomography (CT) technique

with bubble column

Photo of dual-source gamma-ray computed tomography (CT) technique with

bubble column during CT scan

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Gamma–ray Computed Tomography (CT) Technique



Scanning a bubble column equipped with dense vertical internals

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Dual Source Computed Tomography (DSCT) Technique

6-inch Bubble Column without internals Bubble column reactor with 0.5-inch stainless

internals

6-inch Bubble Column reactor with 0.5” & 1” Plexiglas Internals



Electronics and data acquisition system for CT technique

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0

0.02

0.04

0.06

0.08

0.1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Lin

ear

att

enu

ati

on

co

effi

cien

t,cm

-

1

Dimensionless radius,r/R (-)

0

0.02

0.04

0.06

0.08

0.1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Lin

er a

tten

ua

tio

n c

oef

fici

ent,

cm-1

Dimensionless,radius,r/R (-)

0

0.02

0.04

0.06

0.08

0.1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Lin

ear

att

enu

ati

on

co

effi

cien

t,cm

-

1

Dimensionless radius,r/R(-)

0

0.02

0.04

0.06

0.08

0.1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Lin

ear

att

enu

ati

on

co

effi

cien

t,cm

-

1




CT Scan Validation by

Phantom

Cross-sectional linear attenuation coefficient distribution(cm-1), and

diameter profile for phantom Case I for case I (empty phantom)

Cross-sectional linear attenuation coefficient

distribution(cm-1), and diameter profile for phantom

case II (the inner cylinder filled with water)

Cross-sectional linear attenuation coefficient distribution(cm-1), and diameter

profile for phantom for case III (the outer cylinder filled with water)

Cross-sectional linear attenuation coefficient,

distribution (cm-1), and diameter profile of linear

for phantom for case IV (the inner and outer

cylinders filled with water)

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Results and Discussion

Linear attenuation coefficient distribution for a bubble column without internals: (a) empty column,

(b) column filled with water, and (c) column with air-water at superficial gas velocity 45 cm/s

Linear attenuation coefficient distribution for a bubble column equipped with 0.5-inch internals: (a) empty

column, (b) column filled with water, and (c) column with air-water at superficial gas velocity 45 cm/s

Linear attenuation coefficient distribution for a bubble column equipped with 1.0-inch internals: (a) empty

column, (b) column filled with water, and (c) column with air-water at superficial gas velocity 45 cm/s

Linear attenuation coefficient distribution (μ, cm-1 )for a bubble column with and without internals



The reconstructed linear

attenuation images clearly show

that the CT technique was able to

capture and reproduce the

arrangement and location of each

of the internals as well as of the

column wall.

These images confirm the quality

of this CT technique and also the

image reconstruction algorithm

(AM). Hence, the CT is capable

of capturing a small

maldistribution in the multiphase

reactor if it exists and it provides

reliable cross-sectional gas

holdup distribution to validate

CFD simulations and

hydrodynamics models.

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Effect the size of the internals on the time-averaged cross-sectional gas holdup distributions and their diameter profiles in a 6-inch bubble

column with or without internals at different superficial gas velocities (5, 20, and 45 cm/s) calculated based on the free cross-sectional area

(FCSA) for the flow

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Gas

hold

up (

-)


at 5 cm/s

at 20 cm/s

at 45 cm/s

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Gas

hold

up

(-)


at 5 cm/s at 20 cm/s at 45 cm/s

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1G

as

hold

up(-

)

Dimensional radius,r/R(-)

at 5 cm/s at 20 cm/s at 45 cm/s

Bubble column without internals

Bubble column with 0.5-inch internals

Bubble column with 1-inch internals



5 cm/s 20 cm/s 45 cm/s



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Impact of tubes bundle arrangements (hexagonal, circular, circular and one tube at center) on gas holdup

distribution and their radial profiles

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Gas

hold

up,(

-)


circular

circular & tube

hexagonal



0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Gas

ho

ldu

p,(

-)


circular

circular & tube

hexagonal

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Gas

hold

up

,(-)


circularcircular & tubehexagonal

5 cm/s

20 cm/s

45 cm/s

5 cm/s

20 cm/s

45 cm/s

5 cm/s

20 cm/s

45 cm/s

5 cm/s

20 cm/s

45 cm/s

Hexagonal configuration



Circular configuration



Circular & tube at center configuration



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0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Gas h

old

up(-

)


without internals

with 0.5-inch internals

with 1.0-inch internals

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Gas h

old

up,(

-)


circular

circular & tube

hexagonal

Comparison between the azimuthally averaged gas holdup profiles for

bubble columns with (0.5 and 1-inch) or without internals at superficial gas

velocity (45 cm/s) based on the free cross-sectional area (FCSA) for the flow

Comparison between the azimuthally averaged gas holdup profiles for

bubble columns with different configurations of internals at superficial gas

velocity (45 cm/s) based on the free cross-sectional area (FCSA) for the flow



Quantification the effect of the size and internals configurations on the gas holdup distribution and their diameter

profiles at superficial gas velocity 45 cm/s

4/26/2017 13

Remarks

For the first time, cross-sectional gas holdup distributions and their diametrical profiles were visualized and quantified at

different internal sizes, configurations, and superficial gas velocities to study and assess these parameters.

The reconstructed CT images show that the bubble columns equipped with or without internals displayed a symmetric

cross-sectional gas holdup distribution for all studied superficial gas velocities. However, the bubble column with 1-inch

internals (sparse arrangement) produced a more symmetric distribution than the bubble column equipped with 0.5-inch

internals (dense arrangement).

The design of the configurations of internals affect significantly on the gas holdup distribution especially at the core and

wall region of the reactor

The reconstructed linear attenuation coefficients (μ, cm-1 ) values are close to the theoretical values. The comparison

shows good agreement of these for empty columns and bubble column equipped with internals

The gamma-ray computed tomography technique was capable of capturing the wall thickness of a column and the

internals.

The present work provides, for the first time, benchmarking data to validate reactor models and computational fluid

dynamics (CFD) simulations and consequently will facilitate the design and scale-up of bubble column with internals.



The authors gratefully acknowledge the financial support in the form of a scholarship provided

by the Higher Committee for Education Development in Iraq (HCED), Ministry of Higher

Education and Scientific Research (Iraq), and the funds provided by Missouri S&T and

Professor Dr. Muthanna Al-Dahhan to develop the CT technique, the experimental set-up, and

to perform the present study. Also, the authors would like to thank Dr. Fadha Ahmed,and Mr.

Jianbin Shao for his help with the gamma-ray computed tomography (CT) technique.

Acknowledgements

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Computed Tomography (CT)

S10

For Phase Distribution Measurements

Radioactive Particle Tracking (RPT)

R1

R2

δ

Sc

Parylene N

Sc46 particle coated with

parylene-N, tracking solids

Sc46 particle in polypropylene ball,

tracking liquid

Picture of RPT

RPT

Calibration

Tracer particle

holding assembly

In Situ

Manual

35 cm

35 cm

0.625

35 cm

3.61

Detector

An On-line Technique Using NGD as Gamma Ray Densitometry (GRD)

Source

For Pinpointing Flow Pattern (Regime), Radial/Diameter Profile of Phases’ Holdups Mal-distribution identification & Reduced Tomography

Other Selected Sophisticated Techniques at Glance

Heat Transfer Coefficients

Heat transfer probe

DC

Power

PC

DA

Q

Amplifier

Mass Transfer Probes

Gas-Solid optical probes

Pressure Transducers

FID P

C

Am

Pebble bed unit

Gas/Liquid Dynamics – Tracer Techniques

Optical Probes in Packed bed

Light

going

to the

probe

tip (475

nm)

Sol-

Gel

Overcoat

Rigs

Radioisotope Laboratory for Advancing Industrial Multiphase Processes

Dual Source Computed Tomography (DSCT) Technique

Non-Radioisotope Laboratory for Advancing Industrial Multiphase Processes

Microalgae Laboratory

(Biological Lab)

4/26/2017 24



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