Colloquia on Reaction Engineering January 24, 2014 Pyrolysis and Combustion of Complex Hydrocarbon Mixtures: Detailed Kinetics and Lumping Procedures. Eliseo Ranzi Dipartimento di Chimica, Materiali e Ingegneria Chimica. Politecnico di Milano (Italy) Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta” Politecnico di Milano
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Colloquia on Reaction Engineering January 24, 2014
Pyrolysis and Combustion
of Complex Hydrocarbon Mixtures:Detailed Kinetics and Lumping Procedures.
Eliseo Ranzi
Dipartimento di Chimica, Materiali e Ingegneria Chimica.
Politecnico di Milano (Italy)
Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”Politecnico di Milano
Colloquia on Reaction Engineering January 24th, 2014
C2H6
C2H5
C2H4
C2H3
C2H2
Aromatics
Soot
Pyrolysis
O2
CHi
O2
OH
Oxidation
CH3OOH
CH3OH
CH2OH
CH3OO
CH3
CH3O
CH2O
HCO
CO
CO2
CH4
NOx
Detailed Kinetics of Methane CombustionCH4+ 2 O2 ���� CO2 + 2 H2O
More than the correct rate parameters of
specific reaction, it is important to include
all the relevant reactions and the proper
relative selectivity of parallel reaction paths.
Colloquia on Reaction Engineering January 24th, 2014
Outlines
Complexity of Pyrolysis and Combustion Systems� Complexity of Chemical Mechanisms
� Complexity of Liquid Fuels
� Dimension of Detailed Kinetic Mechanisms
� Coupling of Detailed kinetics and Complex Hydrodynamics
� Time Scales in Combustion Processes
Automatic Generation of Reaction Mechanisms
Simplifications (QSS) and Lumping Procedures
� Pyrolysis and High Temperature Mechanisms
• Steam Cracking Process (SPYRO)
• Extension to Complex Mixtures
� Low Temperature Oxidation Mechanisms
Conclusions
3
Colloquia on Reaction Engineering January 24th, 2014
4
Detailed Oxidation Mechanism of n-pentane
E.Ranzi, T.Faravelli, P.Gaffuri, G.Pennati “Low Temperature combustion: Automatic generation of primary oxidation reactions and
Combustion ReactionsAutomatic Generation of Detailed Reaction SchemesPrimary propagation reactions of n-dodecane pyrolysis
(Units are: m kmol s kcal).
Colloquia on Reaction Engineering January 24th, 2014
Detailed Mechanisms of n-Alkane Oxidation58
E. Ranzi, A. Frassoldati, S. Granata, and T. Faravelli ‘Wide-Range Kinetic Modeling Study of the Pyrolysis, Partial Oxidation,
and Combustion of Heavy n-Alkanes’ Ind. Eng. Chem. Res. 2005, 44, 5170-5183
Colloquia on Reaction Engineering January 24th, 2014
59
n-dodecane Primary Oxidation Reactions
Detailed Scheme
258 Primary reactions
72 Intermediate radicals
58 Primary products
(retaining nC12 structure)
6 n-dodecenes
16 O-cyclic-ethers
6 hydroperoxides
30 keto-hydroperoxides
Low and High Temperature
oxidation mechanisms are
conveniently simplified by grouping
intermediate Species and Reactions.
Colloquia on Reaction Engineering January 24th, 2014
Low Temperature Combustion
60
, Lumping of Alkyl, Peroxy,
Alkyl-hydroperoxy and
Peroxy-alkyl-hydroperoxy
Lumping of Alkenes, Cyclic
ethers, Peroxides and
Ketohydroperoxides
Lumping of Alkenes, Cyclic
ethers, Peroxides and
Ketohydroperoxides
60
Colloquia on Reaction Engineering January 24th, 2014
61Lumped Scheme of
n-alkane Primary Oxidation Reactions
Colloquia on Reaction Engineering January 24th, 2014
62
n-dodecane Primary Oxidation Reactions
Detailed Scheme
258 Primary reactions
72 Intermediate radicals
58 Primary products
(retaining nC12 structure)
6 n-dodecenes
16 O-cyclic-ethers
6 hydroperoxides
30 keto-hydroperoxides
Lumped Scheme
15 Primary lumped reactions
4 Intermediate radicals
4 Primary lumped products
1 lumped n-dodecene
1 lumped O-cyclic-ether
1 lumped hydroperoxide
1 lumped keto-hydroperoxides
E. Ranzi, A. Frassoldati, S. Granata, and T. Faravelli ‘Wide-Range Kinetic Modeling Study of the Pyrolysis, Partial
Oxidation, and Combustion of Heavy n-Alkanes’ Ind. Eng. Chem. Res. 2005, 44, 5170-5183
Significant mechanism reductions relate to the primary products (retaining the
structure of the original fuel).
Secondary reactions (primary reactions of lumped products) can be better analysed.
Kinetic Models always require a reasonable and well balanced presence
of ‘primary’ and ‘secondary’ reactions.
Colloquia on Reaction Engineering January 24th, 2014
63Lumped Mechanisms of Heavy n-Alkane Oxidation
E. Ranzi, A. Frassoldati, S. Granata, and T. Faravelli ‘Wide-Range Kinetic Modeling Study of the Pyrolysis, Partial
Oxidation, and Combustion of Heavy n-Alkanes’ Ind. Eng. Chem. Res. 2005, 44, 5170-5183
Low and High temperature primary mechanism
of different n-alkanes heavier than n-heptane are always described with
4 lumped radicals (R, ROO, QOOH, and OOQOOH) and
15 similar reactions, with the same lumped kinetic parameters
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64
Overall Oxidation Mechanism
Hierarchy and Modularity
are the main features of Detailed Kinetic Schemes
• GRI scheme for Gases
• PRF (nC7-iC8) and additives for Gasolines
•Alcohols
•Diesel and Jet Fuels
•Biofuels – FAME – FAEE CO
C3
CH4
C2
nC7-iC8
H - O2 2
Bio Diesel Fuels Alcohols
Ranzi, E., Frassoldati, A., Grana, R., Cuoci, A., Faravelli, T., Kelley, A. P., & Law, C. K. (2012).
Hierarchical and comparative kinetic modeling of laminar flame speeds of hydrocarbon and oxygenated fuels.
Progress in Energy and Combustion Science, 38(4), 468-501.
Colloquia on Reaction Engineering January 24th, 2014
N-Heptane OxidationLow and High Temperature Ignitions
E. Ranzi, P. Gaffuri, T. Faravelli, P. Dagaut ‘A Wide-Range Modeling Study of n-Heptane Oxidation’ (1995) Combust. Flame 103: 91-106
0.01
0.1
1
10
100
0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
ign
itio
n t
ime
[ms]
1000/T [K]
P = 6.5 barP = 13.5 barP = 42 bar
Pressure effect on the NTC region
Colloquia on Reaction Engineering January 24th, 2014
66Gasoline and Primary Reference FuelsMixtures n-heptane / iso-octane (1,2,3)
Lille RCM
Total ignition time [ms]
0
20
40
60
80
100
600 700 800 900
Temperature [K]
ON 100ON 95ON 90
Princeton PFR
Released Heat [T(i) – T]
0
20
40
60
80
100
120
140
500 600 700 800 900Initial Temperature [K]
n-heptane (0 ON)62 ON PRF87 ON PRF
iso-octane (100 ON)
(1) Callahan C. V., Held T. J., Dryer F. L., Minetti R., Ribaucour M., Sochet L. R., Faravelli T., Gaffuri P. and Ranzi E., (1996) 26th Symposium (International) on combustion, The Combustion Institute, Pittsburgh, pp. 739-746
(2) Minetti R., Ribaucour M., Carlier M., Fittschen C and Sochet L. R., (1994). Combust. Flame 96:201
(3) Held T. J. and Dryer F. L., (1994) 25th Symposium (International) on combustion, The Combustion Institute, Pittsburgh, 901
Colloquia on Reaction Engineering January 24th, 2014
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Size of Detailed and Semi-detailed Mechanisms
T.F. Lu, C.K. Law ‘Toward accommodating realistic fuel chemistry in large-scale computations’
Progress in Energy and Combustion Science 35 (2009) 192–215
67
Lumped kinetic models allow an easier and
CFD applications.
Lumped kinetic models allow an easier and
more effective successive reduction, for
CFD applications.
Oxidation
POLIMI
2011
Pyrolysis
SPYRO
1980Oxidation
C1-C4
1995
L=25 K
Colloquia on Reaction Engineering January 24th, 2014
Reduction of Detailed Kinetics68
Detailed Kinetics always require a successive lumping phase
in order to significantly reduce the number of species
A skeletal kinetic mechanism of n-dodecane oxidation derived from a lumped scheme
involves ~120 species, while the one obtained via a detailed scheme involves ~ 300 species.
Colloquia on Reaction Engineering January 24th, 2014
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Reduction of Detailed KineticsSkeletal Mechanisms of n-dodecane and Bio-Diesel Fuels
Stagni, A., Cuoci, A., Frassoldati, A., Faravelli, T., & Ranzi, E. (2013). Lumping and reduction of detailed kinetic schemes:
an effective coupling. Industrial & Engineering Chemistry Research (in press).
Colloquia on Reaction Engineering January 24th, 2014
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Colloquia on Reaction Engineering January 24th, 2014
71
CRECK Modeling Group at Politecnico di Milano
Thanks for the attention
Colloquia on Reaction Engineering January 24th, 2014
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Colloquia on Reaction Engineering January 24th, 2014
Chemical lumping procedures are applied to the development of detailed kinetic
schemes of pyrolysis and combustion of complex hydrocarbon mixtures, such as
naphtha, gasoline, gasoil and diesel fuels.
The automatic generation of detailed kinetic schemes of pyrolysis and combustion of
primary reference fuels (n-heptane and iso-octane) is discussed, advantages and
limitations of chemical lumping are analysed. The extension of the lumping
approach towards heavier and more complex mixtures in case of steam cracking
process is also addressed.
It is not of interest to automatically generate detailed mechanisms with several
thousands of species and elementary reactions. A compromise has to be found
between computation efforts and prediction accuracy.
From a modeling point of view, it is more convenient to directly link a post-processor to
the kinetic generator with the purpose of lumping intermediate and final products
into a limited number of lumped components.
A further advantage of semi-detailed kinetic models, reduced with a chemical lumping,
is that it is easier and more effective to apply further reduction techniques.
73
Abstract
Colloquia on Reaction Engineering January 24th, 2014
Time Scales in Combustion Processes
time [s]
no
rma
lize
d m
ass
fra
ctio
nInlet mixture: C3H8 + Air
Temperature: 1800 K
fuel
Prompt
NOx
Thermal
NOx
A wide range of time
scales are involved in
Combustion Chemistry
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H-abstraction reaction on n-decane
800 K 1000 K 1200 K
C9H18 + CH3• 0.0424 0.0516 0.0588
C8H16 + C2H5• 0.1478 0.1332 0.1193
C7H14 + C3H7• 0.1519 0.1475 0.1346
C6H12 + C4H9• 0.1519 0.1475 0.1346
C5H10 + C5H11• 0.1479 0.1332 0.1193
C4H8 + C6H13• 0.1492 0.1412 0.1359
C3H6 + C7H15• 0.1526 0.1569 0.1677
C2H4 + C8H17• 0.0563 0.0889 0.1300
Temperature effect on primary product distribution
from β-decomposition reaction of n-decyl radical
The product distribution and The product distribution and
corresponding ‘lumped’
stoichiometry shows a weak
T dependence
Colloquia on Reaction Engineering January 24th, 2014
76
n-dodecane Primary Oxidation Reactions
Detailed Scheme
258 Primary reactions
72 Intermediate radicals
Lumped Scheme
15 Primary lumped reactions
4 Intermediate radicals
Low and High temperature primary mechanism of n-alkanes heavier than n-heptane
are described with
4 lumped radicals (R, ROO, QOOH, and OOQOOH) and
15 similar reactions, with the same lumped kinetic parameters
E. Ranzi, A. Frassoldati, S. Granata, and T. Faravelli ‘Wide-Range Kinetic Modeling Study of the Pyrolysis, Partial
Oxidation, and Combustion of Heavy n-Alkanes’ Ind. Eng. Chem. Res. 2005, 44, 5170-5183
Colloquia on Reaction Engineering January 24th, 2014
77Knocking Propensity of Primary Reference Fuels
Isomerization reactions of peroxy radicals
explain the different ignition times of the two PRF
iso-octane ON=100n-heptane ON=0
O
OH
H
H
H
Peroxy
radicals
4 secondary
(1-5) H-abstractions
k=4 1011.0exp(-20000/RT)
O
OH
H
2 secondary
(1-4) H-abstractions
k= 2 1011.8 exp (-26000/RT)
k(700)= 105.4 [s-1]
OH
O
H
H
H
Alkyl-
hydroperoxy-
radicalsH
k(700)= 104.0 [s-1]
OH
O
Colloquia on Reaction Engineering January 24th, 2014