Upload
voxuyen
View
220
Download
3
Embed Size (px)
Citation preview
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
4 -
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
7 -
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
8 -
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
9 -
Simulation tool
• Excel based process simulator, thermodynamic calculations in dll
10 -
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
11 -
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
13 -
Modelling of liquid- vapor- solid equilibria in the NH3- CO2- H2O system
Maria G. Lioliou
TNE RD NEH [email protected], tel: +47 94424249www.statoil.com
Thank you
14 -
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
16 -
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)