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Modeling Ammonia
Absorption of CO2
Alex Bonsu
OLI Simulation Conference
Whippany, NJ
Nov 16-17, 2010
Modeling CO2 Absorption with
Ammonia
• Basis for Process and Model
• Types of OLI Models Used
• Results
• Conclusions
Basis for Process and Model
•Process Basis
Stable solvent
Non-foaming solvent
High loading capacity solvent
High solvent regeneration pressure
Low CO2 compression energy
Unique gas-liquid contacting device
•Model Basis
Ammonia chemistry complex
Products unstable
Difficult to prepare standard solutions
Confidential and Proprietary
Absorption & Regeneration
Routes
Minor route: Ammonium carbonate
2NH3 + H2O + CO2 (NH4)2CO3
(NH4)2CO3 + H2O + CO2 2NH4 HCO3
Major route: Ammonium carbamate
2NH3 + CO2 (NH3)2CO2
(NH3)2CO2 + 2H2O + CO2 2NH4 HCO3
Confidential and Proprietary
Models Used
•Bench Scale Stirred Tank Reactor
• DynaChem: Gas and liquid phase composition
•Analyzers Calibration – Chemical species
• Stream Analyzer
• DynaChem
•Equilibrium Model – Pressure versus
Temperature
• Stream Analyzer
•Steady State Commercial Process
Modeling
• ESP
• OLIPRO
Confidential and Proprietary
Stirred Tank Reactor
Fixed head
Reactor vessel Heating jacket
Pneumatic lift
Guide rail
for heater
Split-ring
assembly
Confidential and Proprietary
Stirred Tank Reactor
Stirred Tank Reactor
Dynamic Model
Solvent
Gas
Thermal Energy
Electrical Signal
Unit 1
Unit 2 Unit 4
Unit 3
Unit 6
Unit 5
V3
V7
V5
1
2
Raw Gas
Treated Gas
3 V4
4
Rich Solvent
Cooler
10
CO2
Condensate
9
7
8
5
Absorber Regenerator
12 6
13
11
TC TC
Heater
CL3 CL5
Measured versus Predicted CO2
Capture Efficiencies and R values
0
4
8
12
16
20
24
28
32
36
40
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100 120
CO
2 C
ap
ture
Eff
.
Time, mins
Model Eff. Exp Eff Model R Exp R NH4HCO3PPT
R an
d A
BC
Crystals, w
t%
Measured versus Predicted Ammonia Slip
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
0 20 40 60 80 100
Time, mins
Am
mo
nia
Sli
p,
pp
m
0
5
10
15
20
25
30
35
OLI Model NH3 Exp NH3 OLI Model ABC PPT
Confidential and Proprietary
Liquor Composition Predicted by OLI Model
0
10
20
30
40
1 2 3 4
Molar Ratio, R, (NH3/CO2)
Ch
em
ical
Sp
ec
ies,
g m
ols
Aqueous ammonia Bicarbonate ions Ammonium ions Carbamate ions ABC crystals
Confidential and Proprietary
Nuclear Magnetic Resonance
Analysis
• Left-hand peak allows direct
determination of ammonium
carbamate.
• Right-hand peak determines
combination of ammonium
carbonate and bicarbonate.
• Greater the horizontal
separation of peaks the
greater the bicarbonate
content.
Frequency shift
Confidential and Proprietary
Measured vs. Predicted Ammonium
Carbamate
Confidential and Proprietary
y = 0.988x
R 2 = 0.9947
0
2
4
6
8
10
12
14
0 2 4 6 8 10
OLI predicted, wt. %
NM
R m
ea
su
red
, w
t. %
Measured vs. Predicted Ammonium
Carbonate
Confidential and Proprietary
y = 1.7339x
R 2 = 0.9911
0
1
2
3
4
5
6
0 1 2 3 4
OLI predicted, wt. %
NM
R m
ea
su
red
, w
t. %
Measured versus Predicted Ammonium
Bicarbonate
Confidential and Proprietary
y = 0.9622x
R 2 = 0.9906
0
10
20
30
40
0 10 20 30 40
OLI prediction, wt. %
NM
R m
ea
su
red
, w
t. %
Comparing NMR Data and OLI
Model
Raman Spectra Basics
• Raman spectroscopy
uses vibrational and
rotational energy to
identify and quantify
molecules.
• Peak wave numbers
identify the compound .
• Intensity of the energy
or the peak heights
determine the
concentration of the
compound.
Raman Spectral Correlation
to Carbamate
Correlation (R2) = 0.9777
5 Factors
Raman Spectral Correlation to
Bicarbonate
Correlation (R2) = 0.985
5 Factors
Equilibrium Pressure vs.
Temperature
0.00
200.00
400.00
600.00
800.00
1000.00
1200.00
0 20 40 60 80 100 120 140 160 180
Pre
ssu
re,
psia
Temperature, C
Model Pres psia Exp Pres
Conventional CO2 Capture System
CO2 Compression
& Dehydration
Lean solvent
pump
Syngas
Treated Gas
Reboiler
Regenerator Absorber
Lean solvent
cooler
Rich solvent
pump
Lean/rich
exchanger
Condenser
Gas-liquid
separator
ESP Model for CO2 Capture with Ammonia
NH3
LS = Lean Solvent
RS = Rich Solvent
SV = Syngas Vapor
SC = Syngas Cool
NH3
Valve
MIX
104
MIX
102 E-102
RSH
E-103
V-102
CSM
V-103
FSPLIT
Regen H2O
Va
lve
H2O
MIX
H2O
LRH
Lean
Cooler
V-100
RCGH Raw
Syngas
Clean
Syngas H
E-6
Purge
Lean Solvent
RS4 RS3 RS1 RS2
Ric
h S
olv
en
t 5
Ric
h S
olv
en
t 5
A
Ric
h S
olv
en
t 6
Ric
h S
olv
en
t M
Raw SC
Raw
SV
Clean Syngas M
Clean Syngas 2
Clean Syngas 3
Final Acid
Gas
Condensate 1
LRH = Lean Rich Heat Exchanger
CSM = Clean Syngas Mix
RSH = Rich Solvent Heat
Exchanger
RCGH = Raw & Clean Gas Heat Exchanger
FSPLIT = Flow Splitter
NH3
CNTL
C+4
CNTL
H2O
CNTL
A-NH3 LS2
A-H
2O
Conclusion
• Using a bench scale stirred tank reactor
we successfully validated the OLI Mixed
Solvent Electrolyte (MSE) data and
established that the reaction between CO2
and ammonia is equilibrium controlled .
• MSE and ESP will be used to model and
establish the economic viability of the
steady state commercial process for CO2
capture with ammonia.
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