Modelling of liquid-vapor-solid equilibria in the NH3-CO2-H2O systemMaria G. Lioliou, Statoil ASA

2 -

Introduction

• CO2 capture by amines is state-of-the-art technology

• Characteristics of a desired technology− Temperature stability over a temperature range− High selectivity for CO2

− Non-corrosive− High cycle life− Low energy regeneration (stripping)− Rapid kinetics for scrubbing and stripping

• Can ammonia processes challenge amines with respect to− energy requirements− reduced environmental impact

Photo: Marit Hommedal, Statoil

3 -

Ammonia for CO2 capture

• Used in De-NOx processes & to remove SO2 and HCl

• Low environmental impact

• Several approaches on the thermodynamics− Edwards (1978), Pawlikowski (1982), Bieling (1989), Kurz (1995), Krop (1999)

• Tool to predict phase behavior, mass & energy balances

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Components & equilibrium reactions

Soave-Redlich-Kwong EOS for gas fugacitiesVapour

Aqueous

Solids

2CO

2CO

3NH

3NH

2H O

2H O

2 2 3CO H O H HCO+ −+ ↔ +

23 3HCO H CO− + −↔ +

4 3NH H NH+ +↔ +

3 3 2 2NH HCO NH COO H O− −+ ↔ +

2H O H OH+ −↔ +

4 3 4 3 ( )NH HCO NH HCO s+ −+ ↔

4 3 ( )NH HCO s

4 2 2, , ,CH N O Ar

Pitzer model & equilibrium constants

Pure solids

Solubility product

Henry’s law

5 -

Thermal model• Heat capacities, standard state enthalpies & entropies were used

− For water:

− Aqueous & dissolved species:

− Solid(s): treated as particles/species in a water stream

− Gas components:

0( )0

• • ( )TT

f f p iH H C T dt= + ∫

,( ) , , 200

p Cp i p A p B

CC C C T

T= + ⋅ +

−

2

5, 6 2

( ) , , ,2

1010p C

p H O p A p B p D

CC C C T C T

T

−−⋅

= + ⋅ + + ⋅

( ) ( ) ( )id res

p i p i p iC C C= +

( ) ( )id idp m i p i

i

C x C= ⋅∑2 3

( ) , , , ,idp i p A p B p C p DC C C T C T C T= + ⋅ + ⋅ + ⋅

residual term:calculated through the EOS

6 -

Data

• Model is based entirely on open literature data• Approximately 3500 experimental data on:

− VLE− SLE− heat capacities, enthalpies, entropies

• Scattered SLE data• NH4HCO3(s) of primary importance• Other possible salts: (NH4)2CO3

NH4CO2NH4

NH4HCO3-NH4CO2NH2

(NH4)2CO3-NH4HCO3-H2O

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Model testing – NH3-CO2-H2O system

Data from: Pexton and Badger (1938), Van Krevelen et al. (1949),

Otsuka et al. (1960), Kurz et al. (1995), Verbrugge (1979), Göppert

and Maurer (1988), Müller et al. (1988), Pawlikowski et al. (1982),

Mezger and Payer (1925)

0.0 0.3 0.6 0.9 1.2 1.5 1.80.00

0.04

0.08

0.12

0.16

0.20

Temp=20oC NH3=0.49752

NH3=0.5078

NH3=1.02846

NH3=0.1288

NH3=1.56242

NH3=2.11016

p

()

0.0 2.5 5.0 7.5 10.0 12.5 15.0

0

20

40

60

80

Temp=60oC NH3=0.721 NH3=0.728 NH3=0.966 NH3=1.0285 NH3=1.129 NH3=2.1102 NH3=2.186 NH3=2.658 NH3=3.837 NH3=3.977 NH3=8.14 NH3=11.69 NH3=11.79

0 2 4 6 8 10 120

25

50

75

100

NH3=0.591

NH3=1.087

NH3=2.006

NH3=4.14

NH3=5.93

NH3=9.03

NH3=12.17

Temp=80oC

0 2 4 6 8 10 120

20

40

60

80

NH3=1.079 NH3=3.12 NH3=9.57 NH3=11.2 NH3=14.19

p

()

Temp=100oC

Vap

or

pre

ssu

re (

bar)

CO2 concentration (mole/kgH2O)

T=20oC

T=80oC T=100oC

T=60oC NH3: 0.5-13 mole/kg H2O

CO2: up to 15 mole/kg H2O

Reliable results at least up to 100oC

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Model testing – NH4HCO3 solubility

Data from:Jänecke (1927), Jänecke (1929)

Su

pers

atu

rati

on

, SR

Temperature (oC)

0 20 40 60 80 100 1200.5

1.0

1.5

2.0

2.5

3.0

( )4 3

4 3sp

NH HCOSR

K NH HCO

+ − =

SR=1 perfect match

SR>1 model predicts too low solubility

SR<1 model predicts too high solubility

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Simulation tool

• Excel based process simulator, thermodynamic calculations in dll

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Application in a generic ammonia process

• Chilled Ammonia Process patented by Eli Gal (2006)

• Powerspan’s ECO2® technology• CSIRO’s ammonia PCC• CAER pilot studies (Univ. of

Kentucky)Flue gas

CO2 rich

CO2 lean

Pure CO2

Cleaned gas

Air cooler

Heatexchanger

Desorber

Absorber

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0 5 10 15 20 25 30 35 40 45

5

10

15

20

25

30

Solvent: (NH4)2CO

3

3 mol/L 4 mol/L 6 mol/L

NH

3 slip

(mm

ole/

s)

Temperature in absorber (oC)

Simulation results

NH3 in cleaned gasFlue gas CO2

rich

Cleaned gas Solven

t

3.5% CO2, G: 10 kg/s, L: 200 kg/s, (NH4)2CO3: 3,4,6 mol/L

Absorber

Cooling duty of flue gas

3.5% CO2, G: 10 kg/s, L: 200 kg/s, (NH4)2CO3: 4 mol/L

0 5 10 15 20 25 30 35 40 45

400

800

1200

1600

2000

2400

Flue gas temperature 80oC 90oC 120oC

Coo

ling

duty

of f

lue

gas

(kJ/

s)

Temperature in absorber (oC)

12 -

Simulation results

CO2

lean

Pure CO2

Desorber

60 65 70 75 80 85 900

50

100

150

200

250

Hea

ting

duty

(kJ/

s)

Temperature in desorber (oC)

T in absorber 15oC 20oC 35oC

Energy needed to heat CO2 rich stream

T(regen): 60, 70, 80, 90oC, T(abs): 12, 20, 35oC

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Modelling of liquid- vapor- solid equilibria in the NH3- CO2- H2O system

Maria G. Lioliou

TNE RD NEH CCAmlio@statoil.com, tel: +47 94424249www.statoil.com

Thank you

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Backup slides

15 -

Calculations

• Calculate thermodynamic equilibrium and other P-T constants• EOS solved for gas fugacity coefficients• Pitzer solved for aqueous components activity coefficients• Equilibria, mass balances for CO2, NH3, H2O & alkalinity equation• Update EOS and SRK with new values

• Typically 3-6 iterations

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Parameters & simplifications in Pitzer model

• Similar to Bieling et al. (1995)

• Theoretically: 36 binary and 120 ternary parameters• Interactions neglected:

− H+/[OH-] << NH3/NH4+ and CO2/HCO3

-/CO32-

− CO2 and NH3 cannot coexist− ions of the same sign− ion and a neutral

• Ternary parameters: important only at very high concentrations• Same approach for triple interactions

17 -

NH3 solubility –Comparison with HYSYS

20 30 40 50 60 70-1.5x107

-1.0x107

-5.0x106

0.0

5.0x106

1.0x107

1.5x107

2.0x107

2.5x107

3.0x107

HYSYS 40% NH3

Model 40% NH3

HYSYS 60% NH3

Model 60% NH3

HYSYS 80% NH3

Model 80% NH3

Hea

t Flo

w (J

/s)

Temperature (oC)

Water: 10 kg/sGas: 20 kg/s

x% NH3

20 kg/s• oC

Water10 kg/s

• oCQ

Gas out, ToC

Liquid out, ToC

10 20 30 40 50 60 70 80-2.10x106

-1.95x106

-1.80x106

-1.65x106

-1.50x106

-1.35x106

-1.20x106

-1.05x106

-9.00x105

Peng Robinson EOS model developed model Redlich Kwong

Hea

t Flo

w (J

/s)

Temperature (oC)

• Different fluid packages in HYSYS – non ideal behaviour of NH3 in water

• Solubility of NH3 is calculated and compared to various models

0 10 20 30 40 50 60 70 80 90 100

0

10

20

30

40

50

experimental points developed model Peng-Robinson NRTL

NH

3 sol

ubili

ty

Temperature (oC)