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

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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

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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

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Stirred Tank Reactor

Fixed head

Reactor vessel Heating jacket

Pneumatic lift

Guide rail

for heater

Split-ring

assembly

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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

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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

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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

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Measured vs. Predicted Ammonium

Carbamate

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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

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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

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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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