X-ray tomography : a tool for revealing local distribution of liquid in structured packed columns

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X-ray tomography :

a tool for revealing local distribution of

liquid in structured packed columns

Dominique TOYE

dominique.toye@ulg.ac.be

Products, Environment, and Processes (PEPs) Department of Chemical Engineering

Université de Liège www. chemeng.ulg.ac.be

Introduction

Experimental setup

Results

Global hydrodynamic quantities

Influence of viscosity

Flow morphology

Conclusions

2

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Structured packed columns

Gas/Vapor Gas/ Vapor Liquid Liquid

Packed column applications

Gas-liquid absorption CO

₂

capture

Solvent stripping regeneration

Distillation

High performance structured packings

High void fraction

low pressure drop high capacity

High specific surface area

high mass transfer properties

LIEGE - 11 May 2017 3

Structured packed columns

Gas/Vapor

Gas/ Vapor

Liquid

Liquid flow hydrodynamics

Liquid holdup

Gas – liquid interfacial surface area

Liquid flow morphology

(films, rivulets…)

Reliable predictive models

Characterisation of the fluid distribution

down to a very local scale

X-ray tomography

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5 X-ray source Voltage : 30 - 420 kV Current : 2 - 8 mA Focal spot : 0.8 mm Collimator : Pb Fan beam geometry Angle : 40° - Thickn.: 1 mm

Linear detector

1280 high energy photodiodes Pitch : 0.4 mm – H : 0.6 mm 12-bit (4096 intensity levels)

Rotating table 360° object rotation (t_mes= 45 s)

Max diam. : 0.45 m Max. height: 3.80 m Toye et al., Meas. Sci. Technol.,

2005,16, 2213-2220

ULG X-ray tomograph

Packed column Operating modes 1- tomographic mode 2- radiographic mode LIEGE - 11 May 2017

Packed column

Liquid distributor Pall rings (H_Pall= 800 mm) 4 MellapakPlus 752.Y elements rotated by 90° (H_Mellapak= 800 mm)

Radiography of the column

(transparent PVC) Dbed= 100 mm H_bed= 1600 mm Operating conditions Liquid - Water (µ = 1 mPa.s) - Glycerine solutions (µ = 10 – 20 mPa.s) Flowrate : uL= 0 – 25 m3/m2.h Gas = Air LIEGE - 11 May 2017 6

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Structured packing

MellapakPlus 752.Y geometrical properties

Packing element height 0.2 m Packing element diameter 0.10 m

(0.09 m) Specific surface area 510 m²/m³

Void fraction 97.5 % Corrugation angle 41° Corrugation base 9.85 mm Corrugation height 6.50 mm (Sulzer Chemtech) LIEGE - 11 May 2017 7 8

Image of dry packing image

Mellapak 752Y

(1)Column wall (2)Corrugated sheet (3) Wall wiper

(4) Hole Aferka et al., 2010, Chem. Eng. Sci., 65, 511–516

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Methodology

u_L= 23 m³m-²hWater -1

no gas flow

Grey = solid (binary image)

Blue = liquid (binary image) Aferka et al., 2007, Chem. Eng. Sci., 62, 6076-6080

Images of liquid distribution

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Liquid distribution in cross sections

LIEGE - 11 May 2017 Uniform liquid distribution Film flow predominates At contact points between sheets, rivulets and/or flooded channels Mellapak 752Y Water u_L= 23 m³m-²_h-1 No gas flow H =500 mm H =800 mm H =600 mm H =700 mm

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Image processing

Objective = quantitative analysis

1. Normalisation(partial volume effect)

convert grayscale values into liquid holdup values divide each pixel value by the value of a pixel

completely filled by liquid

Distribution of liquid holdup

2.

Counting of interfacial pixels

(liquid – gas) Distribution of gas-liquid interfacial area

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Viva et al., 2011, Flow Meas Instrum, 22, 279-290

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Method validation : liquid holdup

Comparison to experimental data

(global values averaged on 70 sections)

Viva, 2008, PhD thesis, University of Pisa

Very different methods: - quick closing valves + weighing - Tomo + geometrical LIEGE - 11 May 2017

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13 LIEGE - 11 May 2017 Very different methods: - chemical - geometrical

Method validation : G-L interfacial area

Comparison to experimental data

(global values averaged on 70 sections)

Aferka et al., 2011, Chem. Eng. Sci. , 66, 3413-3422

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Influence of liquid viscosity

Mellapak 752Y H = 300 mm u_L= 17 m³m-²_h-1 u_G= 0 Water µ = 1 mPa.s

Aqueous solution of glycerine µ = 10 mPa.s Uniform liquid distribution Thicker liquid films Larger number of flooded channels between sheets

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0 0,05 0,1 0,15 0,2 0 5 10 15 20 25 hL,t o t (-) uL(m³/m²h)

Water Glycerine 10 cP Glycerine 20 cP

On liquid holdup

µ

Each point = one operating condition

= averaged value over the whole packed bed (70 sections)

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Bradtmöller et al., 2015, Ind. Eng. Chem. Res., 52, 2015, 2803-2815

On G-L interfacial area

0 100 200 300 400 500 0 5 10 15 20 25 aG L (m ²/ m ³) uL(m³/m²h)

Water Glycerine 10 cP Glycerine 20 cP

µ 

Each point = one operating condition

= averaged value over the whole packed bed (70 sections)

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On axial profiles

Liquid hold-up uL= 17 m³/m²h E le va ti o n [m m ] Hold-up [-]

1 mPas 10 mPas 20 mPas

-17-K o lo n n e n h ö h e [ m m ] aeff[m²/m³]

1 mPas 10 mPas 20 mPas

uL= 17 m³/m²h

Gas-liquid interfacial surface area

E le va ti o n [ m m ]

70 cross-section images for each operating condition LIEGE - 11 May 2017

Liquid flow morphology

Flow structures

Films

Ideal morphology

Contact point flow

Liquid mixing

Flooded channels

No transfer

-18-Liquid distribution Binary image LIEGE - 11 May 2017 Janzen et al., 2013, Chem. Eng. Sci., 102, 451-460

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= Iterative method

Step 1 = Separation and labelling of each flow structure Step 2 = Classification based on the size and shape

-19-SIZE

Minimum and maximum Feret diameters (F_minand F_max) computed on all flow structures

F_min and F_max= dimensions of the minimal enclosing parallelogram

LIEGE - 11 May 2017 Janzen et al., 2013, Chem. Eng. Sci., 102, 451-460

Flow structure classification

Step 1 = Separation and labelling of flow structures

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Janzen et al., 2013, Chem. Eng. Sci., 102, 451-460

Limited spatial resolution of the ULG X-ray CT Distinct flow structures may be adjacent « seen » as a single structure

Criterion for structure splitting

Elimination of pixels with the smallest number of neighbors

(erased pixels not lost = arbitrarily added to the main flow pattern = film flow)

5 . 0 _ < rect Feret t Flow_struc S S

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Step 2 = Classification based on the size and shape

Flooded channels

Thickness ≥ distance between packing sheets

F

_min

> 9 mm

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Flow structure classification

Step 2 = Classification based on the size and shape

Contact point flow

« Round » shape and

F_min< 9 mm

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Flow structure classification

2 min max < F F

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Step 2 = Classification based on the size and shape

Film flow

Elongated thin shape

and

F_min< 9 mm

+ all remaining pixels (including erased pixels from structure separation)

-23-2 min max > F F LIEGE - 11 May 2017

Flow structure classification

Flow morphology: results

- 24 µ= 1 mPa.s uL= 17 m³/m²h µ= 10mPa.s uL= 17 m³/m²h µ= 20 mPa/s uL= 17 m³/m²h Films

Flooded channels Contact points

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Flow morphology

-25-Films

µ  µ  LIEGE - 11 May 2017

Flooded

channels

Contact

points

Janzen et al., 2013, Chem. Eng. Sci., 102, 451-460

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Influence of liquid flowrate

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Flooded channels Contact points Films

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Influence of liquid viscosity

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Flooded channels Contact points Films

u_L= 17 m/h

Hydrodynamic Analogy model

dH α α α α zL zG

G-L interfacial surface area

Wetting efficiency

⇒ fraction of irrigated and

non-irrigated channels

Liquid holdup

=> total amount of liquid

Liquid flow morphology

⇒ Flooded channels fraction ⇒ Contact point flow fraction

( mixing length : ZL)

zG= gas mixing length (packing geometry) fraction flow point contact points contact between dist. = L z LIEGE - 11 May 2017 28

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0 0,002 0,004 0,006 0,008 0,01 0,012 5 10 15 20 25 30 kL a [ 1 /s ] Flüssigkeitsbelastung [m³/m²h]

F-Faktor=0,63

Experiment Simulation

Model validation :

mass transfer

Liquid load (m3_/m2_.h) F-factor = u_G.ρρρρ_G0.5= 0.63 Pa0.5 CO₂desorption from water         − − = _* * ln bot bot top top pack L L x x x x H u a k Satisfying agreement LIEGE - 11 May 2017 29

Conclusions

Tomographic measurements

Quantitative assesment of the influence

of liquid load and liquid viscosity on

G-L interfacial surface area

Liquid holdup

Flow morphology

(films, rivulets, flooded)

Mass-transfer model

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Based on an Hydrodynamic Analogy

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Validated by mass transfer experiments

Global values

Spatial distributions

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LIEGE - 11 May 2017

Acknowlegments

Saïd Aferka, Michel Crine, Pierre Marchot, Aurora Viva, Elisabetta Brunazzi, Julia Steube, Anna Janzen, Evgeny Kenig

X-ray tomography : a tool for revealing local distribution of liquid in structured packed columns

X-ray tomography :

a tool for revealing local distribution of

liquid in structured packed columns

Contents

Introduction

Experimental setup

Results

Global hydrodynamic quantities

Influence of viscosity

Flow morphology

Conclusions

Structured packed columns

Packed column applications

Gas-liquid absorption CO

capture

Solvent stripping regeneration

Distillation

High performance structured packings

High void fraction

low pressure drop high capacity

High specific surface area

high mass transfer properties

Structured packed columns

Liquid flow hydrodynamics

Liquid holdup

Gas – liquid interfacial surface area

Liquid flow morphology

(films, rivulets…)

Reliable predictive models

Characterisation of the fluid distribution

down to a very local scale

X-ray tomography

ULG X-ray tomograph

Packed column

Radiography of the column

Structured packing

Image of dry packing image

Methodology

Images of liquid distribution

Liquid distribution in cross sections

Image processing

Objective = quantitative analysis

Counting of interfacial pixels

Method validation : liquid holdup

Comparison to experimental data

Method validation : G-L interfacial area

Comparison to experimental data

Influence of liquid viscosity

On liquid holdup

On G-L interfacial area

On axial profiles

Liquid flow morphology

Flow structures

Films

Ideal morphology

Contact point flow

Liquid mixing

Flooded channels

No transfer

Flow structure classification

Flow structure classification

Step 1 = Separation and labelling of flow structures

Step 2 = Classification based on the size and shape

Flooded channels

F

> 9 mm

Flow structure classification

Step 2 = Classification based on the size and shape

Contact point flow

Flow structure classification

Step 2 = Classification based on the size and shape

Film flow

Flow structure classification

Flow morphology: results

Flow morphology

-25-Films

Flooded

channels

Contact