Investigation into Hydrodynamics, Dispersion and Mass-Transfer in a Bubble Column

Chemical Engineering Research Presentation

• Applications in both the Oil & Gas Industry, Bulk Chemical Manufacture as well as Industrial Microbiology

• Fischer-Tropsch Applied Study

Study conducted under academic supervision in Dublin, Ireland.

Self-Published to Promote Engineering on the Interweb.

ii) Scope of Review

1. Hydrodynamics [60]– Impingement Plate Study– Instrument Noise Characterisation– Directionality in Measurements

2. Dispersion [30]– Characterisation of Mixing in a Bubble Column

3. Mass-Transfer [10]– Study of Mass-Transfer in a Bubble Column

1. Hydrodynamics

• Study of Fluid Properties/Flow– Conservation Laws– Newtonian Fluid Behaviour– Enhanced Process Understanding

• Focused upon Measuring Dispersion– Standard Inert Test …the black-box approach

• Optimise & Control Sources of Error– Tracer Injection– Tracer Measurement Recordings

1.1 Impingement Plate Study

• Description

• D.O.E

• Challenges– An efficient Injection Pulse– Optimise Radial Dispersion

1.1 Impingement Plate Study

• Gaussian Plume Modelled

• Dissipation of Mass/Energy

1.1 Results, Conclusions, Caveats

Effects of Critical Variables:

• Gas Flow Rate Changing Mechanisms of Dispersion

• Plate Separation Buoyant Effects, Dispersion Ratio

• Plate Geometry Impingement Characteristics

• Tracer Concentration Viscosity, Density Effects

• Plate Size Energy Losses, Liquid Pooling

1.2 Instrument Signal Analysis

0.12

0.14

0.16

0.18

200 210 220 230 240 250 260 270 280 290 300

Time [s]

Vo

ltag

e [V

]

Comment : Un-Filtered Data

1.2 Noise Characterisation

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6

Pro

bab

ility

[%

]

3 L/min

4 L/min

6 L/min

8 L/min

10 L/min

12 L/min

14 L/min

15 L/min

16 L/min

Average

1.3 Optimum Conductivity Probe Orientation in Two-Phase Flow

Position

Window

N NE H SE

0 0.89 1.06 1.74 1.10

-60 0.29 0.89 1.14 1.41

-45 0.54 0.49 0.22 0.35

60 1.29 1.30 1.65 1.04

45 0.67 1.35 1.60 1.03

1.3 Directionality in Readouts

0

20

40

60

80

0 1 2 3 4 5 6

Per

cent

age

[ % ]

1.3 Window Projection Residence Time Theory

WindowPositi

on45o 60o 90o 120o 135o

0o 2.12 1.5 3 1.38 0.64

45o 3.18 2.25 4.5 2.25 3.18

90o 4.24 3 6 2.75 1.28

135o 3.18 2.25 4.5 2.25 3.18

1.3 Results, Conclusions, Caveats

• Optimum Probe Position and Window Orientation

• Bubble Column:– Variability Consistent– Linked with theory

• Similarity between Columns established– Noise analysis– Geometrical Scales

Two parameters characterised

RTD could be interpreted with a degree of understanding

2. Dispersion

• Dispersion helps us to understand the flow behaviour of certain materials

• It occurs in this study as a fluid-fluid interaction

• Characterisation of dispersion would allow a rigorous mathematical model to be applied

2. Axial Dispersion Model

0

0.5

1

1.5

2

2.5

3

0 0.1 0.2 0.3 0.4 0.5

CL/C

0

0.2

0.3

0.5

0.8

/L

Time

Comment : Notable Similarities to Control Theory

2. Dispersion

0.8

0.85

0.9

0.95

1

1.05

0 0.2 0.4 0.6 0.8 1

Time

Co

ncen

trati

on

/L0.450.8

2. Dispersion

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7 8

Selected RTD for Pulse Injection

Dispersion mechanisms evident – Expected Result ?

3. Mass Transfer

• Mass Transfer is concerned with the analyses of behaviour on a molecular level

• Bubble Columns are understood to relate primarily to macroscopic phenomena

• Measurement of kLa

• Dissolved Oxygen Measurements

3. Mass Transfer of CO2

Exponential Model to fit Data, Regression Coefficient of 0.9995

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Time

Conce

ntr

atio

n

3. Improved Dispersion Model

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Dimensionless Time

Dim

ensio

nle

ss C

oncentr

ation C

/C0

Comment : Agreement of Experimental Data with Predictive Theory

Questions ?

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