A Model of CO2 Absorption in Aqueous K2CO3/PZ
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Transcript A Model of CO2 Absorption in Aqueous K2CO3/PZ
Jorge M. Plaza
The University of Texas at Austin
January 10-11, 2008
Outline
Previous Work
Intercooling effect
Conclusions
Future Work
Modeling
+
K /PZ
Cullinane K+/PZ (2005)
e-NRTL to predict VLE and speciation
Equilibrium and interactions regressed in FORTRAN
Experimental rate constants and diffusion coefficients
Hilliard K+ /PZ(2005)
Thermodynamics into ASPEN Plus ®
Chen
Pilot plant testing (2004 – 2006)
4 Campaigns 5m/2.5m, 6.4m/1.6m K+/PZ and 7m MEA
Absorber Model developed for K+/PZ (2006)
System Modeling
Freguia MEA (2002) - Ratefrac
Aspen Plus® rate-based model based on Dang (2001)
Equilibrium by Jou et al. (1995)
Intercooling for MEA absorber
Ziaii MEA (2006) - RateSepTM
Developed rate-based model for MEA in Aspen Plus ® based
on Freguia (2002), Hikita (1977) and Aboudheir (2002)
Plaza K +/PZ(2006 – 2007)
Activity based kinetics for 4.5m/4.5m K+/PZ
Intercooling with split feed
Approaches to Absorber modeling
Mass Transfer
Gj
Lj-1
Gj
Lj-1
Enh
Gj
R
Gj+1
Lj
Gj+1
R
Lj
Rate
Based
Rate-based
Approach
Rate-based
Approach
Rate
Based
Reaction equilibrium
Reaction equilibrium
Reaction Kinetics
Reaction
kinetics
Enhancement Factor
Enhancement factor
Gj
Lj-1
Gj
Lj-1
Gj+1
Lj
Gj+1
Lj
Equilibrium
Equilibrium Approach
Equilibrium
Equilibrium Approach
Reaction Equilibrium
Reaction
equilibrium
Reaction Kinetics
Reaction
kinetics
Lj-1
R
Lj
Gj+1
Rate
Based
Rate-based Approach
Reaction Kinetics
Reaction
kinetics
Film Reactions
Film Reactions
Reaction
Kenig et al. Reactive Absorption: Optimal Process Design Via Optimal Modeling. Chem. Eng. Sci. 2001, 56, 343-350.
Film Discretization
PG
Pi = H[CO2]i
Gas Film
Rxn Film
Liquid Film
P*i
[CO2]*i
Bulk Gas
Interface
P*B
[CO2]*B
Bulk Liquid
Absorber Reactions
PZCOO-
PZ CO2 b
PZCOO bH
PZ(COO-)2
PZCOO CO2 b
PZ COO
2
b= OH-, H2O, PZ, CO3-2, PZCOO HCO3-
CO2 b
HCO3 bH
b=PZ, PZCOO-, OH-
bH
Effect of Intercooling for 4.5m K+/4.5m PZ
Lean
Variable
ldg & flow
Gas Out
90% removal
H=15 m D=9.8 m
CMR-MTL metal NO-2P
Q
5% V. Liquid Hold up
5.48 kmol/s
12.7% mol CO2
(500 MW Plant)
Gas in
Rich
Intercooling with 4.5m K+/ 4.5 m PZ
Capacity (Kg CO2 removed/Kg Solvent)
0.12
0.1
0.08
0.06
0.04
Capacity-no cool
0.02
Capacity-single cool-0.5 H
Capacity-single cool-opt
0
0.15
0.2
0.25
0.3
Lean ldg
0.35
0.4
0.45
Rich loading vs. lean loading. 4.5m K+/ 4.5 m PZ
0.52
0.51
Rich ldg
0.5
0.49
0.48
Rich ldg
Rich ldg-single cool-0.5
H
Rich ldg-single cool-opt
0.47
0.46
0.45
0.15
0.2
0.25
0.3
Lean ldg
0.35
0.4
0.45
T and CO2 rate profiles 4.5m/4.5 m K+/ PZ . Loading = 0.44
72
-0.12
68
-0.1
64
-0.08
T (oC)
60
CO2 rate
56
-0.06
52
-0.04
Liquid T
48
-0.02
44
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
0.6
Z/ZTotal
0.7
0.8
0.9
1.0
Bottom
CO2 absorption rate (kmol/s)
No Intercooling
T and CO2 rate with intercooling 4.5m/4.5 m K+/ PZ.
Loading=0.44
Intercooling
-0.12
68
-0.1
64
T (oC)
-0.08
60
56
-0.06
CO2 rate
52
-0.04
48
-0.02
Liquid T
44
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
0.6
Z/ZTotal
0.7
0.8
0.9
1.0
Bottom
CO2 absorption rate (kmol/s)
72
T and CO2 rate profiles. 4.5m/4.5 m K+/ PZ. Loading = 0.21
-0.12
No Intercooling
68
-0.1
T (oC)
64
-0.08
60
56
-0.06
Liquid T
52
-0.04
48
-0.02
CO2 rate
44
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
Z/ZTotal
0.6
0.7
0.8
0.9
Bottom
CO2 absorption rate (kmol/s)
72
T and CO2 rate with intercooling. 4.5m/4.5 m K+/ PZ
Loading=0.21
Intercooling
-0.12
68
-0.1
Temperature (oC)
64
-0.08
60
56
-0.06
52
-0.04
48
Liquid T
CO2 rate
44
40
-0.02
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
0.6
Z/ZTotal
0.7
0.8
0.9
1.0
Bottom
CO2 Absorption rate (kmol/s)
72
T and CO2 rate profiles. 4.5 m K+/ 4.5 m PZ. Loading=0.315
No Intercooling
-0.12
68
Liquid T
T (oC)
64
-0.08
60
56
52
-0.04
48
44
CO2 rate
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
Z/ZTotal
0.6
0.7
0.8
0.9
1.0
Bottom
CO2 Absorption Rate (kmol/s)
72
T and CO2 rate with intercooling. 4.5m/4.5 m K+/ PZ
Loading=0.315
Intercooling
-0.12
68
-0.1
T (oC)
64
-0.08
60
56
-0.06
52
CO2 rate
-0.04
Liquid T
48
-0.02
44
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
0.6
Z/ZTotal
0.7
0.8
0.9
1.0
Bottom
CO2 absorption Rate (kmol/s)
72
Effect of Intercooling for 11m MEA
Lean
0.40
Q
H=15 m D=10.6 m
Semi
Lean
0.46
CMR-MTL metal NO-2P
1% V. Liquid Hold up
Q
5.48 kmol/s
12.7% mol CO2
(500 MW Plant)
Gas Out
Variable
removal
Gas in
Rich
T and CO2 rate profiles for no intercooling. 11 m MEA.
Semilean Feed
56
-0.04
85% Removal
T (oC)
54
-0.03
52
50
-0.02
48
Liquid T
46
-0.01
44
CO2 rate
42
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
0.6
Z/ZTotal
0.7
0.8
0.9
1.0
Bottom
CO2 Absorption rate (kmol/s)
58
T and CO2 rate profiles with intercooled semilean feed.
11 m MEA.
56
-0.04
Semilean Feed
92.3% Removal
T (oC)
54
-0.03
52
CO2 rate
50
-0.02
48
46
-0.01
44
Liquid T
42
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
0.6
Z/ZTotal
0.7
0.8
0.9
1.0
Bottom
CO2 absorption rate (kmol/s)
58
T and CO2 rate profiles with intercooled semilean feed & intercooling.
11 m MEA.
56
-0.04
Semilean Feed
93.0% Removal
2nd
Intercooling
T (oC)
54
-0.03
52
50
-0.02
CO2 rate
48
46
-0.01
44
Liquid T
42
40
0
0.0
Top
0.1
0.2
0.3
0.4
0.5
0.6
Z/ZTotal
0.7
0.8
0.9
1.0
Bottom
CO2 Absorption rate (kmol/s)
58
CO2 removal results for MEA absorber with split feed
Intercooling
CO2 Removal (%)
None
85.0
Single
92.3
Double
93.0
Conclusions
Optimum intercooling is related with T bulge position
Tbulge = pinch then intercooling efficient
Tbulge away from pinch then not much improvement
Conclusions
For a simple absorber system intercooling allows increase in
solvent capacity as high as 45%.
Intercooling improves performance for MEA split feed as
high as 10%
Intercooling offers a benefit in energy consumption in the
stripper thanks higher rich solvent loading
Intercooling is most effective for operations in the range of
0.27 to 0.40 loading for the lean feed.
Future Work
Substitute new Hilliard (2007) thermodynamics
Model Aboudheir laminar jet to extract kinetics with
RateSepTM
Fix ASPEN to represent physical properties : ρ, D, H
Regress MEA pilot plant data to validate model