CHARACTERIZATION OF FOAMING BEHAVIOR IN
AMINE-BASED CO2 CAPTURE PLANTS
Research Review Meeting
January 10 – 11, 2008
University of Texas at Austin, Texas
BHURISA THITAKAMOL AND AMORNVADEE VEAWAB
Faculty of Engineering, University of Regina
CANADA
1
OUTLINE

Introduction

Objectives

Experiment

Results and discussions

Foam model

Conclusions

Future works

Acknowledgements
INTRODUCTION
Foaming problem in the CO2 absorption process
One of the most severe operational problems causing extra expenditures
 Occurring in both an absorber and a regenerator during plant start-up and
operation
 Causing many adverse impacts on the plant operation
Impacts based on plant experiences
 Excessive loss of alkanolamine solvents
 Premature flooding
 Reduction in plant throughput
 Off-spec products
 High alkanolamine carryover to downstream plants
5
6
9
INTRODUCTION
Research on foaming problem: For the CO2 absorption process in gas treating services
Research group
Alkanolamine type
Contaminant
Operating
condition
Pauley et al.,
1989
MEA
DEA
MDEA
Two formulated
MDEA (with non
specified additives)
Formic acid
Acetic acid
Propionic acid
Butyric acid
Pentanoic acid
n-hexanoic acid
Octanoic acid
Decanoic acid
Dodecanoic acid
Liquid hydrocarbon
Atmospheric
pressure
McCarthy and
Trebble, 1996
DEA
Methanol
Corrosion inhibitor
Antifoam agent
Lubrication oil
Organic acid
Degradation product
Suspended solid
20 - 85oC
0.1 - 3 MPa
Harruff, 1998
DGA
93oC
up to 6.9 MPa
Current foaming knowledge in the CO2 absorption process
for a coal-fired power plant is limited:
The application of the CO2 absorption process is relatively new for a coal-fired power plant.
 No reports of plant experiences and research work has published.
OBJECTIVES

To obtain comprehensive foaming information from bench-scale
experiments under well-simulated environments.


To reveal the parametric effects as listed below on foaming

Gas flow rate

Solution volume

CO2 loading

Alkanolamine concentration

Solution temperature

Degradation product

Corrosion inhibitor

Alkanolamine type
To establish the foam model to predict a steady-state pneumatic foam
height (H) from the physical properties and operating conditions
7
EXPERIMENTS
The pneumatic method modified from
the standard ASTM D892 (ASTM, 1999)
Recorded foam
volume
Emitted to
atmosphere
Drying column
F
Gas mass
flowmeter
Flowmeter
N2 cylinder
Test Cell
Immerse heater
with
thermometer
Temperature bath
8
9
EXPERIMENTS
 Recorded data: Foam volume (cm3) vs. Time (min) for each minute during the 25minute blowing time
150
3
300
Average steady foam volume (cm )
Recored foam volume (cm3)
350
Raw data
250
200
150
100
50
120
0
0
5
10
15
20
o
(average steady
foam volume)
90
60
30
0
25
5
Time (min)
 The foaminess coefficient () (Bikerman, 1973)
o

G
; o = Average foam volume (cm3)
G = Gas flow rate (cm3/min)
10
15
Time (min)
20
25
10
RESULTS AND DISCUSSIONS
EFFECT OF GAS FLOW RATE
 At 20 – 80 cm3/min, N2 flow rate
, 
 At 80 – 110 cm3/min, N2 flow rate
, 
CONSTANT
Foaminess cofficient (min)
6.0
3
kmol/m3
2.0
kmol/m MEA
2.0
5.0
kmol/m3
5.05.0
kmol/m3 MEA
4.0
3.0
Working flow rate at 94 cm3/min
2.0
1.0
0.0
0
20
40
120
100
80
60
3
Nitrogen flow rate (cm /min)
140
160
(Test condition: 2.0 & 5.0 kmol/m3 MEA, 400 cm3 solution volume, 0.40 mol/mol CO2 loading and 40oC)
11
RESULTS AND DISCUSSIONS
EFFECT OF SOLUTION VOLUME
 At 200 – 400 cm3, solution volume
, 
 At 400 – 700 cm3, solution volume
,  CONSTANT
Foaminess coefficient (min)
1.0
0.8
0.6
0.4
Working Volume
at 400 cm3
0.2
0.0
0
200
400
600
800
3
Solution volume (cm )
(Test condition: 2.0 kmol/m3 MEA, 94 cm3/min N2, 0.40 mol/mol CO2 loading and 40oC)
12
RESULTS AND DISCUSSIONS
EFFECT OF MONOETHANOLAMINE (MEA) CONCENTRATION
 MEA concentration
,  initially
and then
25oC
40oC
50oC
70.00
60.00
50.00
40.00
0.80
0.0
Decreased
surface
tension
0.60
Increased
bulk liquid
absorber
Absorber
toptopviscosity
Absorber
bottom
absorber
bottom
0.40
0.0
2.0
4.0
6.0
MEA concentration (kmol/m3)
(Test condition: MEA, 94 cm3/min N2, 400 cm3 solution volume,
absorber top: 0.20 mol/mol CO2 loading/ 40oC & absorber bottom:
0.40 mol/mol CO2 loading/ 60oC)
8.0
2.0
4.0
6.0
MEA concentration (kmol/m3)
8.0
Surface tension of CO2-unloaded aqueous MEA solution
replotted from experimental data [Vázquez et al., 1997]
4.0
Predicted viscosity (mPa.s)
Foaminess coefficient (min)
1.00
Surface tension (mN/m)
80.00
absorber top
3.5
absorber bottom
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.0
2.0
4.0
6.0
8.0
MEA concentration (kmol/m3)
Predicted viscosity of CO2-loaded aqueous MEA solutions
from correlation [Weiland et al., 1998]
RESULTS AND DISCUSSIONS
65.000
,  initially
Surface tension (mN/m)
EFFECT OF CO2 LOADING
 CO2 loading
and then
1.50
40 40o C
60.000
55.000
50.000
60 60o C
45.000
90 90o C
40oC 3, 40o C
22,kmol/m
60oC 3, 60o C
22,kmol/m
33,kmol/m
40oC 3, 40o C
33,kmol/m
60oC 3, 60o C
0.00
0.20
0.40
0.60
CO2 loading in solution (mol CO2/mol MEA)
1.00
Surface tension of CO2-loaded aqueous MEA solution
measured by Spinning Drop Interfacial Tensiometer Model 510
0.50
Increased
bulk liquid
viscosity
Decreased
surface
tension
0.00
0.00
0.10
0.20
0.30
0.40
0.50
CO2 loading in solution (mol CO2/mol MEA)
0.60
Predicted viscosity (mPa.s)
Foaminess coefficient (min)
13
4.0
3.5
3.0
40oC
40oC
60oC
60oC
90oC
90oC
2.5
2.0
1.5
1.0
0.5
0.0
(Test condition: 5.0 kmol/m3 MEA, 94 cm3/min N2, 400 cm3
solution volume and 40, 60 and 90oC)
0.00
0.20
0.40
0.60
CO2 loading in solution (mol CO 2/mol MEA)
Predicted viscosity of 5.0 kmol/m3 MEA solution from
correlation [Weiland et al., 1998]
RESULTS AND DISCUSSIONS
14
EFFECT OF SOLUTION TEMPERATURE
, 
1.60
0.20
0.20 mol CO2/mol MEA
1.40
0.40 mol CO2/mol MEA
0.40
Reduced
bulk
viscosity
1.20
Decreasing 
1.00
0.80
0.60
0.40
0.20
0.00
40.0
50.0
60.0
70.0
80.0
90.0
Solution temperature (o C)
(Test condition: 5.0 kmol/m3 MEA, 94 cm3/min N2, 400 cm3
solution volume and 0.20 & 0.40 mol/mol CO2 loading)
Predicted viscosity (mPa.s)
Foaminess coefficient (min)
 Solution temperature
2.5
2.0
1.5
1.0
0.5
0.0
40.0
0.20 mol/mol CO2 loading
0.40 mol/mol CO2 loading
50.0 60.0 70.0 80.0
Solution temperature (oC)
90.0
Predicted viscosity of 5.0 kmol/m3 MEA solution
from correlation [Weiland et al., 1998]
RESULTS AND DISCUSSIONS
EFFECT OF DEGRADATION PRODUCT
 Most degradation products added into aqueous MEA solution induce foam.
Degradation product
Average  (min)
None
0.80  0.015
Ammonium thiosulfate
0.97  0.049
Glycolic acid
0.94  0.028
Sodium sulfite
0.92  0.042
Malonic acid
0.92  0.016
Oxalic acid
0.90  0.038
Sodium thiocyanate
0.90  0.015
Sodium chloride
0.89  0.004
Sodium thiosulfate
0.85  0.018
Bicine
0.85  0.015
Hydrochloric acid
0.83  0.037
Formic acid
0.83  0.033
Acetic acid
0.82  0.043
Sulfuric acid
0.77  0.034
(Test condition: 10,000 ppm of degradation product, 5.0 kmol/m3 MEA, 94 cm3/min N2, 400 cm3 solution
volume, 0.40 mol/mol CO2 loading and 60oC)
15
16
RESULTS AND DISCUSSIONS
EFFECT OF CORROSION INHIBITOR
1.20
70.000
1.00
Surface tension (mN/m)
Foaminess coefficient (min)
 Corrosion inhibitors added into aqueous MEA solution enhance .
0.80
0.60
0.40
0.20
0.00
1
MEA
2 3
NaVO
3 3 Na24SO3
CuCO
Corrosion inhibitor
(Test condition: 1,000 ppm of corrosion inhibitor, 5.0
kmol/m3 MEA, 94 cm3/min N2, 400 cm3 solution volume,
0.40 mol/mol CO2 loading and 60oC)
65.000
60.000
55.000
MEA w/o inhibitor
MEA+NaVO3
MEA+CuCO3
MEA+Na2SO3
50.000
45.000
40.000
0
0.5
1
1.5
Corrosion inhibitor
Surface tension of 5.0 kmol/m3 MEA solutions containing no CO2
loading at 25oC with/without 1000 ppm corrosion inhibitor
(measured by KrÜss Tensiometer K100 using the Wihelmy plate’s
principle)
17
RESULTS AND DISCUSSIONS
EFFECT OF ALKANOLAMINE TYPE
 Foam formation in MEA and MDEA but not in DEA
 Only small amount of foam in AMP+MEA solution
with the mixing ratio of 1:2 mol/mol
Average 
MEA
0.85  0.004
DEA
No foam
MDEA
4.0
2.0
0.0
0.32  0.019
AMP
No foam
MEA + MDEA (1:1)
No foam
MEA + MDEA (2:1)
No foam
MEA + MDEA (1:2)
No foam
DEA + MDEA (1:1)
No foam
DEA + MDEA (2:1)
No foam
DEA + MDEA (1:2)
No foam
MEA + AMP (1:1)
No foam
MEA + AMP (1:2)
No foam
MEA + AMP (2:1)
0.13  0.001
(Test condition: 4.0 kmol/m3 total alkanolamine conc., 94 cm3/min N2, 400
cm3 solution volume, 0.40 mol/mol CO2 loading, 60oC and mixing ratio of
blended solution = 1:1, 2:1 and 1:2 (mole:mole))
MEA (Maham et al., 2002)
DEA (Teng et al., 2002)
MDEA (Teng et al., 2002)
AMP (Henni et al., 2003)
6.0
0.0
2.0
Alkanolamine conc.
4.0
(kmol/m3)
6.0
Viscosity of CO2-unloaded aqueous alkanolamine solution
at 60o replotted from experimental data
Predicted viscosity (mPa.s)
Type of alkanolamine
Viscosity (mPa.s)
and AMP solutions
Single alkanolamine
8.0
2.5
Blended alkanolamine
1:2
1:1
2:1
2.0
1.5
1.0
0.5
0.0
MEA+MDEA DEA+MDEA
MEA+AMP
Type of blended alkanolamine
Predicted viscosity of the CO2-unloaded aqueous blended alkanolamine solution
(4.0 kmol/m3 total alkanolamine conc. and 60oC)
from Grunberg and Nissan’s equation (Mandal et al., 2003))
18
FOAM MODEL: LITERATURE
Researcher
Foaming system
Solution
Method
Proposed equation
Gas


Ito and Fruehan
(1989)
28%Cao-42%SiO230%FeO slags
Argon
Dimensional analysis
=  (, , )
  5.7  102
Jiang and
Fruehan (1991)
30%FeO
(Cao/SiO2=1.25) and
0%FeO (Cao/SiO2=1.25)
slags
Argon
Dimensional analysis
=  (, , , g)
  359
Zhang and
Fruehan (1995)
40%Cao-40%SiO215%Al2O3-5%FeO slags
Argon
Dimensional analysis
=  (, , , g, Db)
1.2
  115 0.2 0.9
 Db
Ghag et al
(1998)
Water + 78 – 95%
glycerinate +SDBS
N2
Dimensional analysis
1. =  (, , , g, Db);  is surface
tension depression
2. =  (g, , Db, EM); EM is surface
elasticity
3. =  (g, , Db, Eeff); Eeff is effective
elasticity

g
  2.02  106 
1.32
g2.32 Db3.64
  5.43  105 
EM0.89
g1.89 Db2.78
  1 106
Eeff
g2 Db3
Pilon et al
(2001)
Results from other research
works
Dimensional analysis of the
governing equation for the
pneumatic foam layer proposed by
(Bhakta and Ruckenstein, 1997)
  j  jm 
H  2905 2.6
ro
g1.8
Pilon and
Viskanta (2004)
Results from other research
works
Dimensional analysis of the
governing equation for the
pneumatic foam layer proposed by
(Bhakta and Ruckenstein, 1997) +
Prediction of minimum superficial
gas velocity (jm)
H  2905
0 .8
  j  jm 
2 .6
ro
g1.8
0 .8
16
19
FOAM MODEL: DEVELOPMENT
START
Process parameter:
1. MEA concentration (M)
2. Solution temperature (T)
3. Superficial gas velocity (j)
4. Minimum superficial gas velocity (jm)
5. Initial liquid volume (Vlig)
6. CO2 loading (aCO2)
Physical properties:
1. Surface tension ()
2. Gas density (G)
3. Liquid density (L)
4. Liquid viscosity (L)
5. Water viscosity (w)
Surface tension prediction
using Wilson equation
(Chunxi et al., 2000)
Liquid density prediction
using Weiland’s correlation
(Weiland et al., 1998)
Liquid viscosity prediction
using Weiland’s correlation
(Weiland et al., 1998)
Define the control surface for
the pneumatic foam layer
END
Governing equation
Pilon et al (2001)
YES
Dimensional analysis
Find K and n:
 
H
 Re 
Ca    K 

 Fr 
 ro 
R2 à 1.0
Sr à 0.0
Initial guess
for bubble
radius (ro)
n
Modified Laplace equation
Pc  Pin  Pout  
Hpredict’s trend @ Hexp’s trend
Adjust new ro
NO
END
R2 à 1.0 and Sr à0.0
Hpredict’s trend @ Hexp’s trend
Recalculating ro
NO
YES
YES
NO
2
ro
20
FOAM MODEL: RESULTS
Foaming height equation
1.22

  j  j m 
H  172059 3.44
ro
g 2.22

where
ro 
2
101.325  Pout 
INSIGNIFICANT
Pout = Pdispersion + Pfoam + P*
80.00
Parity chart
110.30M 1.1210 T 2.5210 j 3.2610
3
*
Hexp (mm)
P 
60.00
P 
40.00
R² = 0.84
20.00
104.01M 7.9110 T 3.6210 j 3.0210
0.00
0.00
3
20.00
40.00
60.00
Hpredicted (mm)
80.00
3
9.6510  3 1.3710  3
Vlig
aCO
2
4
2
7.1110 4.8310
Vlig
j
2
2
 L  w
 L
when %

  53%

when 53  % L   w   73%



1.4110
104.06M 9.0410 T 1.1810 aCO
3
P* 
3
1.6810  2 5.9410  4
Vlig
aCO
2
3
*
3
L

3
when
   w 
  73%
% L

L


21
35.00
70.00
30.00
60.00
Foam height (mm)
25.00
20.00
15.00
10.00
Experiment
Predicted
5.00
200
400
600
40.00
30.00
Experiment - 2M
Predicted - 2M
Experiment - 5M
Predicted - 5M
20.00
10.00
0.00
0.00
0
50.00
0
800
40.00
60.00
35.00
50.00
30.00
25.00
20.00
15.00
Experiment - Bottom
Predicted - Bottom
Experiment - Top
Predicted - Top
10.00
5.00
0.00
0.0
2.0
4.0
6.0
MEA concentration (kmol/m3)
8.0
Foam height (mm)
Foam height (mm)
Solution volume (cm3)
50
100
Experiment - 40
Experiment - 60
Experiment - 90
200
60.00
Predicted - 40
Predicted - 60
Predicted - 90
40.00
30.00
20.00
10.00
50.00
40.00
30.00
20.00
Experiment - 0.2
Predicted - 0.2
Experiment - 0.4
Predicted - 0.4
10.00
0.00
0.00
0.0
150
Gas flow rate (cm3/min)
Foam height (mm)
Foam height (mm)
FOAM MODEL: RESULTS
0.2
0.4
CO2 loading (mol/mol)
0.6
0.0
20.0
40.0
60.0
80.0 100.0
Solution temperature (oC)
CONCLUSION
22
 Solution volume affects  when it is small. Increasing the solution volume to a certain quantity
results in a constant foam volume or .
 An increase in gas flow rate decreases . The gas flow rate can lead to a constant  when
increases to a certain value.
 Ranges of solution volume and gas flow rate that lead to a constant  were found for the CO2aqueous alkanolamines. These ranges enable the generation of foam data that do not depend
on solution volume, gas flow rate, pore size of gas disperser, and dimension of test cell.
 Variations in MEA concentration, CO2 loading and solution temperature affect .
 An increase in temperature decreases .
  increases and then declines with increasing MEA concentration and CO2 loading.
 Most degradation products and corrosion inhibitors enhance .
 MEA, MDEA and AMP + MEA (1:2 mixing mole ratio) generate apparent foams
 FOAM MODEL is established to predict the steady-state pneumatic foam height from the
physical properties and operating conditions and also to identify the important dimensionless
numbers for a scaling-up hydrodynamic experiment.
23
FUTURE WORK
FOAM MODEL
 Sensitivity analysis of input parameters on the predicted foam height.
 Model improvement by incorporating the minimum superficial gas velocity predicted
based on the one-dimensional drift-flux model (Pilon and Viskanta, 2004)
HYDRODYNAMIC
 Study the foaming behavior occurred in the packed absorber during absorption
process based on dimensionless numbers in terms of the foaming tendency and the
foam stability by measuring  and foam half-life, respectively.
 Investigate the effect of foaming on the hydrodynamic parameter s (e.g., pressure
drop, liquid holdup and flooding point) of the packed CO2 absorption column based
on dimensionless numbers. à FOAMING CHART
21
ACKNOWLEDGEMENT
 Faculty of Graduate Studies and Research (FGSR), University of
Regina
 Faculty of Engineering, University of Regina
 The Natural Sciences and Engineering Research Council (NSERC)
24