Download Detailed Chemical Kinetic Modelling of Pollutant

Detailed Chemical Kinetic Modelling
of Pollutant Conversion in Flue
Gases from Oxycoal
y
Plant
R.K. Robinson and R.P. Lindstedt
Thermofluids Section, Department of Mechanical Engineering,
Imperial
p
College
g London,, Exhibition Road,,
London SW7 2AZ
Outline
 Motivation
 Model Development
 Calculation of Thermodynamic Data
 Results, Sensitivities and Product Distributions
 Conclusions
 Future Work and Acknowledgements
Motivation
 Carbon Capture and Storage (CCS) aims to capture CO2 emissions from
large scale energy generators. Strongly corrosive impurities such as oxides
off nitrogen
it
and
d sulphur
l h need
d tto b
be separated
t d ffrom other
th exhaust
h
t gases.
 Experimental methodologies to remove these impurities have been
developed[1,2]. However the chemistry behind these processes is poorly
understood.
 The current work outlines computational methods that attempt to model the
relevant conversion processes and the distribution of subsequent products
in flue gases.
1. White V. and Allam R.J., Purification of Oxyfuel-Derived CO2 for Sequestration or EOR, Proceeding of the 8th
International Conference on Greenhouse Gas Control Technologies, Trondheim, Norway, (2006).
2. Allam R.J., White V. and Miller J., Purification of Carbon Dioxide, US Patent 7,416,716.
Background
 The sulphur
p
chemistry
y is based on detailed high
g temperature
p
chemical
kinetics obtained from the following studies:

F.G. Cerru, A. Kronenburg and R.P. Lindstedt “A systematically reduced mechanism for
sulphur oxidation”
oxidation Proc.
Proc Combust
Combust. Inst
Inst. 30 (2005) 1227-1235
1227 1235.

F.G. Cerru, A. Kronenburg and R.P. Lindstedt “Systematically reduced chemical
mechanisms for sulphur oxidation and pyrolysis” Combust. Flame 146 (2006) 437-455.
 The nitrogen chemistry is based on the following studies:

Lindstedt, R.P., Lockwood, F.C. and Selim, M. A., “Detailed Kinetic Modelling of Chemistry
and Temperature Effects on Ammonia Oxidation” Combust. Sci. and Technol., 99 (1994),
253-276.

Lindstedt, R.P., Lockwood, F.C. and Selim, M.A., 'Detailed Kinetic Study of Ammonia
Oxidation', Combust. Sci. Technol., 108, (1995) 231-254.
 In both cases subsequent updates have been performed and validated in
combustion applications.
Background
 Work has taken p
place in 3 key
y areas:

Current kinetic models of combustion involving both sulphur and
nitrogen species have been extended to low temperature ranges via
th addition
the
dditi off key
k species
i and
d reactions.
ti

An aqueous phase mechanism has been developed to model
reactions occurring in solution
solution. A mass transfer coefficient has been
estimated to allow movement of species between the gaseous and
aqueous phases.

Accurate quantum mechanical methods have been used to update
thermodynamic data for species involved in the model and to
calculate new data for aqueous species by taking into account the
enthalpy of dissolution.
Model Development
 The original Sulphur mechanism featured 12 sulphur containing species
and 70 reversible reactions. The nitrogen mechanism featured 21
species and 95 reversible chemical reactions.
 The above mechanisms are here combined with hydrocarbon chemistry
for C1-C2 species that permit the additional interactions with burnt gas
products such as CO, CO2 and H2O as well as any remaining
hydrocarbon fragments.
 16 additional reactions for nitrogen and sulphur gas phase chemistry.
 10 mass transfer rates added to allow movement of species between
gaseous and aqueous phases.
 8 aqueous phase
h
reaction
ti used
d tto create
t a basic
b i aqueous phase
h
mechanism.
Model Development

Additions to reaction Mechanism rates taken from NIST Chemical Kinetics
Database or CAPRAM Aqueous Mechanism for Troposheric chemistry or
extrapolated there from.
Gaseous Phase Additions with rates shown in modified Arrhenius form
PRODUCTS
NH3
NO2
NO2
O2
N3
N3
O2
NO2
NO2
NO2
NO
N2O3
N2O5
NO2
H2O
SO3
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
REACTANTS
NO2
N3
N3
N3
O
N3
NO
O
O
NO3
NO2
H2O
H2O
NO2
NO
H2O
+ M
+ NO2
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
HNO2
N2O
N2
N2O
N2
N2
NO3
NO3
NO3
N2O5
N2O3
HNO2
HNO3
N2O4
HNO2
H2SO4
+
+
+
+
+
+
A
NH2
N2O
NO
NO
NO
N2
+ M
+ HNO2
+ HNO3
+ HNO2
;
;
+ NO ;
;
;
+ N2 ;
;
;
;
;
;
;
;
;
;
;
n
2.4510E-03 3.410E+00
1.2040E+08 0.000E+00
3
3.6130E+08
6130E+08 0
0.000E+00
000E+00
3.6130E+01 0.000E+00
6.7450E+09 0.000E+00
9.0330E+08 0.000E+00
3.4030E-16 -1.750E+00
4
4.0990E-07
0990E 07 -1.500E+00
1 500E+00
3.5240E+09 0.240E+00
3.7300E+07 0.600E+00
1.6050E+06 0.000E+00
1.2900E+07 0.000E+00
5
5.1000E-05
1000E 05 0.000E+00
0 000E 00
6.0220E+05 0.000E+00
5.1530E-10 0.000E+00
7.2270E+05 0.000E+00
Ea
1.250E+05;
0.000E+00;
0
0.000E+00;
000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0
0.000E+00;
000E+00
0.000E+00;
0.000E+00;
0.000E+00;
3.717E+04;
0
0.000E+00;
000E 00
0.000E+00;
0.000E+00;
0.000E+00;
Model Development

Mass Transfer Rates between Gaseous and Aqueous Phase taken to be 0.01
kmol m-3 s-1 after sensitivity analysis performed.
Basics Aqueous Phase Mechanism with rates shown in modified Arrhenius form
PRODUCTS
REACTANTS
SO2
=
SO2(A)
;
NO2
=
NO2(A
;
NO
=
NO(A)
;
HNO3
=
HNO3(A)
;
HNO2
=
HNO2(A)
;
NO3
=
NO3(A)
;
N2O5
=
N2O5(A)
;
N2O3
=
N2O3(A)
;
N2O4
=
N2O4(A)
;
H2SO4
=
H2SO4(A)
;
SO2(A) + H2O(L)
=
H2SO3(A)
;
NO2(A + NO2(A + H2O(L)
=
HNO2(A) + HNO3(A)
;
HNO2(A) + HNO2(A) + HNO2(A) = HNO3(A) + NO(A) + NO(A) + H2O(L);
N2O5(A) + H2O(L)
=
HNO3(A) + HNO3(A)
;
N2O4(A) + H2O(L)
=
HNO2(A) + HNO3(A)
;
HNO2(A) + OH(A)
=
NO2(A + H2O(L)
;
NO(A) + NO2(A + H2O(L)
=
HNO2(A) + HNO2(A)
;
NO2(A + NO2(A + NO2(A +H2O(L)=
HNO3(A) + HNO3(A) + NO(A)
;
A
0.010E+00
0.010E+00
0.010E+00
0.010E+00
0.010E+00
0.010E+00
0.010E+00
0.010E+00
0.010E+00
0.010E+00
0 010E+00
6.270E+04
1.000E+08
6.000E+00
5.100E-05
5.100E-05
5.100E 05
1.000E+09
1.000E+08
1.000E+08
n
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0 000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
0.000E+00
Ea
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0 000E+00
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
0.000E+00;
Calculation Method for Thermodynamic data
Molecular Mechanics
Mi i i ti and
Minimisation
d
Conformational
Analysis used to
locate starting
structure
Program locTorsion
ran to locate all
internal rotations
and create input files
Program polyScript ran to
harvest data from G3B3 and
scanCalc log files,
files calculate
Enthalpies of Formation and
Moments of Inertia, and
produce input for next stage
High Accuracy
Q
Quantum
t
Mechanics
G3B3/G3MPB3
Energy
Calculation
DFT Quantum
Mechanics
used to scan
and analyse
Internal
Rotations
Statistical Mechanics
Package PAC 99 used
to calculate
thermodynamic values
from 200K to 6000K
Atomization Energies,
E th l i and
Enthalpies
d
Vibration Frequencies
produced in G3B3 log
file
Program scanCalc ran to
harvest internal rotation
data fit
data,
V = ½ ∑Vn(1 – cos(nθ)) and
calculate IR symmetry
numbers and Moments of
Interia
7 Term JANAF
Polynomials
produced by
regression of
calculated data
Examples of NOx Thermodynamic Data

Thermodynamic data calculated for species where data were not
available or required updating and fitted to 7 term JANAF polynomials.

For aqueous species enthalpy of dissolution were taken into account by
modifying the enthalpy of formation at 298K.
NO2(Aq)Calculated Data
N2O3 Calculated Data
∆fH298
22.6 kJ/mol
∆fH298
81.7 kJ/mol
S298
239.9 J/mol/K
S298
317.0 J/mol/K
Cp298
36 9 kJ/mol
36.9
Cp298
69 2 kJ/mol
69.2
HNO2(A)
200K-6000K REF :
R.ROBINSON 03-Dec-08
5.83337654E+00 3.92942470E-03 -1.49885436E-06 2.43940583E-10 -1.45404150E-14
-1.64746315E+04 -3.02996870E+00 4.73508766E+00 6.07796919E-03 -2.03586709E-06
-9.22492080E-10 6.38649372E-13 -1.61106404E+04 2.90221746E+00
N2O3
200K-6000K REF : G3B3
R.ROBINSON 16-Dec-08
8.75695849E+00 3.70515651E-03 -1.41680841E-06 2.34798620E-10 -1.42777213E-14
6.73047701E+03 -1.35522821E+01 4.90534181E+00 1.63782898E-02 -2.10621083E-05
1.70161360E-08 -5.97183185E-12 7.79013682E+03 6.09886939E+00
Examples of NOx + SOx Thermodynamic Data
HNO2 Calculated Data
HNO2(Aq) Calculated Data
∆fH298
-76.7 kJ/mol
∆fH298
-120.1 kJ/mol
S298
249 3 J/mol/K
249.3
J/ l/K
S298
249 3 J/mol/K
249.3
J/ l/K
Cp298
45.4 kJ/mol
Cp298
45.4 kJ/mol
SO2 Calculated Data
SO2(Aq)Calculated Data
∆fH298
-296.8
296 8 kJ/mol
kJ/ l
∆fH298
-323.8
323 8 kJ/mol
kJ/ l
S298
248.2 J/mol/K
S298
248.2 J/mol/K
Cp298
39.9 kJ/mol
Cp298
39.9 kJ/mol
Results : Experiment 1 - Conversion Evolution
Conditions :
Pressure - 2.7
2 7 Atmospheres
Species
ppm
%
SO2
9 81E+02
9.81E+02
0 10%
0.10%
09
0.9
NO
3.22E+02
0.03%
0.8
NO2
3.58E+01
0.00%
0.7
O2
5.50E+04
5.50%
0.6
CO
2.00E+02
0.02%
CO2
8.34E+05
82.35%
NH3
1.00E+04
1.00%
N2
9.00E+04
9.00%
0.2
H2O
1.00E+04
1.00%
0.1
H2O
Liquid
1.00E+04
1.00%
Temperature - 300 K
% Conversion
1
0.5
0.4
0.3
SO2
NOx
Experimental SO2
Experimental NOx
0
0
50
100 Time (s) 150
200
250
% Conve
ersion
Results : Experiment 1 – Mass Transfer Sensitivity
1
0.9
0.8
0.7
0.6
0.5
04
0.4
0.3
0.2
0.1
0
SO2 Mass Transfer x5
SO2 Mass Transfer 0.01 kmol3 m3 s-1
SO2 Mass Transfer x 0.2
% Conversion
0
50
100
Time (s)
150
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0
3
0.2
0.1
0
200
250
NOx Mass Transfer x5
NOx Mass Transfer 0.01 kmol3 m3 s-1
NOx Mass Transfer x 0.2
0
50
100
Time (s)
150
200
250
Results : Experiment 1 – NOx Ratio Evolution
The Ratio of NO to NO2 is known to change from approximately 9:1 to 3:1 after the
compressor/receiver the current model reproduces this affect.
1
0.9
0.8
% Conversion
0.7
0.6
NO
NO2
Experimental NO
Experimental NO2
0.5
0.4
0.3
0.2
0.1
0
0
50
100
Time (s)
150
200
250
Results : Experiment 1 – NOx Ratio Sensitivity
NO2 is more readily absorbed into the aqueous phase due its larger negative enthalpy
of dissolution, therefore the ratio of NO to NO2 influences conversion time for NOx.
1
09
0.9
0.8
% Conversion
0.7
0.6
0.5
0.4
0
0.3
0.2
90%-NO 10%-NO2
0.1
75% NO 25%-NO2
75%-NO
25% NO2
50%-NO 50%-NO2
0
0
50
100
Time (s)
150
200
250
Results : Experiment 1 – Pressure Sensitivity
NOx conversion also pressure dependent as higher pressures lead to greater conversion
from NO to NO2 in the gaseous phase.
1
0.9
0.8
% Conversion
n
0.7
0.6
0.5
0.4
0.3
SO2 All Pressures
NOx 1 Bar
NO 3 B
NOx
Bar
NOx 7 bar
0.2
0.1
0
0
50
100
Time (s)
150
200
250
Results : Experiment 2 - Conversion Evolution
Conditions :
Pressure - 5 Atmospheres
p
Species
ppm
%
SO2
7.61E+02
0.08%
NO
2.99E+02
0.03%
NO2
3.32E+01
0.00%
O2
5 50E+04
5.50E+04
5 50%
5.50%
CO
2.00E+02
0.02%
CO2
8.34E+05
83.37%
NH3
0.00E+00
0.00%
N2
9.00E+04
9.00%
0.2
H2O
9.98E+03
1.00%
01
0.1
H2O
Liquid
9.98E+03
1.00%
0
Temperature
p
- 300 K
1
09
0.9
0.8
% Conversion
0.7
0.6
0.5
0.4
0.3
SO2
Nox
Experimental SO2
Experimental NOx
0
100
200
300
Time (s)
400
500
Results : Experiment 2 – NOx Ratio Evolution
The Ratio of NO to NO2 is known to change from approximately 9:1 to 3:1 after the
compressor/receiver ,the current model reproduces this affect.
1
09
0.9
0.8
% Conversion
0.7
0.6
NO
NO2
Experimental NO
Experimental NO2
0.5
04
0.4
0.3
0.2
0.1
0
0
50
100
150
200
250
Time (s)
300
350
400
450
Results : Experiment 2 – Product Distribution
800
NO
NO2
SO2
700
600
NO(A)
NO2(A)
SO2(A)
500
400
ppm
500
ppm
600
300
400
300
200
200
100
100
0
0
0
100
200
300
0
400
100
300
0.1
200
180
160
140
120
100
80
60
40
20
0
01
0.1
HNO2(A)
HNO3(A)
H2SO3(A)
H2SO4(A)
0
100
200
Time (s)
300
400
400
N2O4
N2O4(A)
N2O3
N2O3(A)
0.1
ppm
ppm
200
Time (s)
Time (s)
0.0
0.0
0.0
0.0
0.0
0
100
200
Time (s)
300
400
Conclusions

The current work shows that detailed models based on chemical kinetics
can be of significant help in interpreting experimental data.

The approach of not heuristically fitting individual rate constants allows
the separation of validation and simulation.

Key sensitivities are also identified as part of the modelling process.

SO2 and NOx conversion predominately occurs in the aqueous phase.

NOx conversion residence times are highly dependent on the initial ratio
of NO/NO2 and the pressure of system while the SO2 conversion is less
pressure dependent.

Anyy model needs to simulate both g
gaseous and aqueous phases and the
differing conditions of both the compressor and the receiver.
Future Work and Acknowledgements

Mass transfer rates need to be considered in more detail, and are likely to vary
throughout the apparatus. Rates may be estimated from interfacial areas.

Currently ionic species are modelled as molecules.
molecules A detailed aqueous phase
mechanism would include ionic species and the pH of the system.

Expansion of the aqueous phase mechanism in line with current findings.

We would like to thank Air Products and Doosan Babcock for their support. Also Dr.
L.Torrente-Murciano and Prof. D.Chadwick, Imperial College, for the experimental
data.
Results : Experiment 3 - Conversion Evolution
Conditions :
Pressure - 5 Atmosphere
Temperature - 300 K
1
ppm
%
SO2
6.22E+02
0.06%
09
0.9
NO
1.70E+01
0.00%
0.8
NO2
1.89E+00
0.00%
0.7
O2
5.50E+04
5.50%
CO
2.00E+02
0.02%
CO2
8 34E+05
8.34E+05
83 42%
83.42%
NH3
0.00E+00
0.00%
N2
9.00E+04
9.00%
H2O
9.98E+03
1.00%
H2O
Liquid
% Conversion
Species
0.6
0.5
0.4
0.3
0.2
SO2
01
0.1
NOx
0
9.98E+03
1.00%
0
50
100
150
200
250
Time (s)
300
350
400
450
Results : Experiment 3 – Product Distribution
700
NO
600
NO2
SO2
500
ppm
ppm
400
300
200
100
0
0
100
200
Time (s)
300
NO(A)
NO2(A)
( )
SO2(A)
0
400
180
0.0
160
0.0
140
100
200
Time (s)
300
ppm
100
80
60
HNO2(A)
HNO3(A)
H2SO3(A)
H2SO4(A)
40
20
0
400
N2O4
N2O4(A)
N2O3
N2O3(A)
0.0
0
0
120
ppm
500
450
400
350
300
250
200
150
100
50
0
0.0
0.0
0.0
0.0
0.0
0
100
200
Time (s)
300
400
0
100
200
Time (s)
300
400