Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”
Politecnico di Milano
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)
Colloquia on Reaction Engineering
January 24, 2014
Detailed Kinetics of Methane Combustion
CH4+ 2 O2
CO2 + 2 H2O
CH4
C2H6
C2H5
O2
C2H4
C2H3
C2H2
Aromatics
Soot
Pyrolysis
Colloquia on Reaction Engineering
O2
CH3
CHi
CH3OO
CH3OOH
CH3O
CH3OH
CH2O
CH2OH
HCO
NOx
More than the correct rate parameters of
specific reaction, it is important to include
CO
all the relevant reactions and the proper
OH
relative selectivity of parallel reaction paths.
CO2
Oxidation
January 24th, 2014
3
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
Colloquia on Reaction Engineering
January 24th, 2014
4
Detailed Oxidation Mechanism of n-pentane
Combustion of large molecules
Complex kinetic mechanisms.
E.Ranzi, T.Faravelli, P.Gaffuri, G.Pennati “Low Temperature combustion: Automatic generation of primary oxidation reactions and
Lumping Procedures” Combust. Flame 102: 179-192. 1995.
Colloquia on Reaction Engineering
January 24th, 2014
Simplified Scheme of n-alkane (nC10H22)
Primary Oxidation Reactions
5
Alkyl radicals
forms Peroxy radicals
Succesive reactions
of Peroxy Radicals explain
the system reactivity
Colloquia on Reaction Engineering
January 24th, 2014
6
Detailed Oxidation Mechanism of n-pentane
Pyrolysis Mechanism
Pyrolysis reactions hierarchically
preced oxidation reactions.
Combustion of large molecules
Complex kinetic mechanisms.
E.Ranzi, T.Faravelli, P.Gaffuri, G.Pennati “Low Temperature combustion: Automatic generation of primary oxidation reactions and
Lumping Procedures” Combust. Flame 102: 179-192. 1995.
Colloquia on Reaction Engineering
January 24th, 2014
7
High temperature Reactions of n-pentane
Decomposition and dehydrogenation reactions of alkyl radicals
kDEC = 1013.5 * exp[(-32000 )/RT]
kDeHyd= 1014 * exp[(-40000 )/RT]
[s-1]
[s-1]
At High Temperatures, life time of alkyl
radicals is lower than 10-6 -10-8 s.
Colloquia on Reaction Engineering
January 24th, 2014
8
High Temperature Oxidation Mechanism
Decomposition of Large Molecules
Alkanes
Alkyl-radicals
Alkenes
Small radicals
High Temperature mechanism mainly involves interactions amongst
small and stable radicals (H, CH3, C2H3, C3H3, …)
and small stable species such as C2H4 and C2H2
as well as oxigenated species ( O2, O, OH, HO2, …..)
High Temperature mechanism is not very sensitive
to the structure of the hydrocarbon fuel
Colloquia on Reaction Engineering
January 24th, 2014
Liquid fuels are Complex
Hydrocarbon Mixtures
9
Liquid fuels are mostly constituted by
complex mixtures of large
hydrocarbons derived from refinery
Typical composition
of a kerosene
GC distribution of alkanes
in a liquid fraction
J.F.Griffiths, J.A.Barnard ‘Flame and Combustion’ Blackie Academic London 1994
Colloquia on Reaction Engineering
January 24th, 2014
10
Liquid fuels are complex mixtures
of large hydrocarbons derived from the refinery
The complexity of these mixtures
calls for lumping and simplifications
Altgelt and Boduszynski 1994
Colloquia on Reaction Engineering
January 24th, 2014
Size of Detailed Kinetic Mechanisms
11
Large Methyl esters:
Rapeseed and soybean oil
Methyl
decanoate
Detailed
kinetic
mechanism
is consists
a biomass
fuelspecies
surrogate.
4800
and
~20,000
Detailed
kineticreactions
mechanism
C K Westbrook
et al.species
Comb. Flame
consists
of 3036
and
158 (2011):
8555742-755.
reactions.
Automatic Generation of
kinetic mechanisms easily produces
Large Kinetic Models
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
Colloquia on Reaction Engineering
January 24th, 2014
12
Strong interactions amongst
Thermodynamics, Chemistry and Fluidodynamics
in Combustion Processes
– Chemistry
Huge Number of
Species and
Elementary Reactions
– Fluidodynamics
Different description
scales
– Materials
Wall and Catalyst
reactions
(*) Joseph Grcar ‘Combustion Simulation and Modeling ‘ CSET – Scientific Applications Meeting
Argonne National Laboratory May 3-4, 1999
Colloquia on Reaction Engineering
January 24th, 2014
13
Time Scales in Combustion Processes
Physics
Kinetics
Kinetic post-processor
Slow Processes:
100 s
NOx Formation
10 -2 s
Intermediate Processes
PAH Formation
Soot Formation
Fast Processes:
Partial Equilibrium
10 -4 s
10 -6 s
10 -8 s
Steady State Cond.
Colloquia on Reaction Engineering
flux,
transport,
turbulence
Mixed = Burned
CFD
January 24th, 2014
C.K. Law ‘Dryden Lecture’ 2011 AIAA Aerospace Science Meeting
Colloquia on Reaction Engineering
January 24th, 2014
14
15
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
Colloquia on Reaction Engineering
January 24th, 2014
Detailed Oxidation Mechanism of n-C5
Pyrolysis Mechanism
High temperature mechanism is simply
constituted by pyrolysis reactions.
Only then, oxidation reactions of small
olefins and radicals take place.
Pyrolysis reactions hierarchically
preced oxidation reactions.
Colloquia on Reaction Engineering
January 24th, 2014
16
17
High temperature Reactions of n-pentane
Decomposition and dehydrogenation reactions of alkyl radicals
kDEC = 1013.5 * exp[(-32000 )/RT]
kDeHyd= 1014 * exp[(-40000 )/RT]
[s-1]
[s-1]
At High Temperatures, life time of alkyl
radicals is lower than 10-6 -10-8 s.
High Temperature mechanism requires the analysis
of H-abstraction reactions to form alkyl radicals
and their successive decomposition paths.
Colloquia on Reaction Engineering
January 24th, 2014
H-Abstraction Reactions on n-dodecane18
The Six nC12H25 Radicals
can isomerize and/or decompose
Pyrolysis mechanism and/or High temperature oxidation
mechanism require to define the kinetic parameters of:
- H-abstraction
- Isomerization
- Decomposition Reactions
Colloquia on Reaction Engineering
January 24th, 2014
Isomerization Reactions
(Internal H-abstraction of 2methyl-pentyl radicals)
log A
(1-5) H transfer
[s-1]
H
H
H
E
[kcal/kmol]
10.2
14500
11.0
19800
(six membered ring intermediate)
(1-4) H transfer
H
H
H
(five membered ring intermediate)
Difference in activation energy reflects the strain of the five membered ring.
Difference in frequency factor is due to the # rotors blocked in the transition phase.
Colloquia on Reaction Engineering
January 24th, 2014
Decomposition and Isomerization Reactions
of Large Alkyl Radicals
1e+09
kISOM=3 1010.2*exp(-14500/RT) [1/s]
kISOM
kDEC
1e+08
H
kISOM
1e+07
H
kDEC
1e+06
kDEC = 1 1014 * exp(-30000/RT) [1/s]
Kinetic constants vs T [K]
1e+05
800
900
1000
1100
At Temperatures higher than 1000 K
decomposition prevails on isomerization reactions
Colloquia on Reaction Engineering
January 24th, 2014
1200
Reference Kinetic Parameters
21
Reference Kinetic Parameters
mainly depends on
- the type of radicals
- the type of H
Reference Kinetic Parameters
are known since several years.
E.Ranzi, M.Dente, S.Pierucci, G.Biardi "Initial product distributions from pyrolisis of normal and branched paraffins"
Ind.Eng.Chem. Fundam, 22, 132 (1983).
Colloquia on Reaction Engineering
January 24th, 2014
22
Outlines
Complexity of Pyrolysis and Combustion Systems
Complexity of Chemical Mechanisms
Complexity of Liquid Fuels
Coupling of Detailed kinetics and Complex Hydrodynamics
Time Scales in Combustion Processes
Dimension of Detailed Kinetic Mechanisms
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
Colloquia on Reaction Engineering
January 24th, 2014
Automatic generation of Kinetic Scheme
Classes of reactions
1. H abstraction Reactions
2. isomerization Reactions R
R’
3. Decomposition of alkyl radicals
R → CnH2n+R’
Reference kinetic parameters
•H-Abstraction Reactions (Primary H-Atoms)
log A
E
- Primary radical
8.3
13500
- Secondary radical
8.3
14500
- Tertiary radical
8.3
15000
•Isomerization Reactions
(Primary on primary internal H-abstraction)
- (1-5) H Transfer
- (1-4) H Transfer
•Decomposition Reactions
10.2
11.0
14500
19800
(to form Primary Radicals)
- Primary radical
- Secondary radical
- Tertiary radical
Colloquia on Reaction Engineering
14
14
14
30000
31000
32000
January 24th, 2014
AUTOMATIC GENERATION OF
Primary elementary reactions
Detailed Reaction Scheme
Automatic Generation of Detailed Reaction Schemes 24
Primary propagation reactions of n-dodecane pyrolysis
(Units are: m kmol s kcal.)
H-abstraction reactions
β-decomposition reactions
A
E
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
Automatic Generation of Detailed Reaction Schemes
25
Primary propagation reactions of n-dodecane pyrolysis
(Units are: m kmol s kcal.)
Isomerization (H-transfer) reactions
A
Dimension of these detailed kinetic
schemes calls for simplifications.
It is not of interest to generate detailed mechanisms
with thousands of species and reactions.
A compromise has to be found between
computation efforts and prediction accuracy.
Colloquia on Reaction Engineering
January 24th, 2014
E
26
Outlines
Complexity of Pyrolysis and Combustion Systems
Complexity of Chemical Mechanisms
Complexity of Liquid Fuels
Coupling of Detailed kinetics and Complex Hydrodynamics
Time Scales in Combustion Processes
Dimension of Detailed Kinetic Mechanisms
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
Colloquia on Reaction Engineering
January 24th, 2014
Automatic generation of Lumped Reactions
Classes of reactions
1. H abstraction Reactions
2. isomerization Reactions R
R’
3. Decomposition of alkyl radicals
R → CnH2n+R’
Reference kinetic parameters
MAMA
MAMAProgram
Program
•H-Abstraction Reactions (Primary H-Atoms)
log A
E
- Primary radical
8.3
13500
- Secondary radical
8.3
14500
- Tertiary radical
8.3
15000
•Isomerization Reactions
1-Generation
ofof
Primary
Reactions
1-Generation
Primary
Reactions
2- QSS Assumption for Large Alkyl Radicals
3- Generation of Lumped Reactions
(Primary on primary internal H-abstraction)
- (1-5) H Transfer
- (1-4) H Transfer
•Decomposition Reactions
10.2
11.0
(to form Primary Radicals)
- Primary radical
- Secondary radical
- Tertiary radical
Colloquia on Reaction Engineering
14
14
14
14500
19800
It is convenient to directly link a post-processor
processor to
30000
the kinetic generator with the purpose of lumping
31000
32000 intermediate and final products into a limited
January 24th, 2014
number of lumped components.
MAMA PROGRAM
generates ‘lumped reactions’ (at 1040K)
28
H-abstractions on large molecules are lumped into a single equivalent reaction.
Intermediate radicals larger than C4 are linearly transformed
(QSSA -isomerized and decomposed) into their final products.
Interactions of alkyl radicals with the reacting mixture
(Additions and H-Abstractions) are negligible
Large Alkyl Radicals (Rj ) , initially formed at rate Pj , are involved in
Decomposition ( kD) and Isomerization ( kI) Reactions.
Continuity equations of isomer radicals give rise to a system of linear equations:
Colloquia on Reaction Engineering
January 24th, 2014
H-Abstraction Reactions on n-dodecane
The linear system of continuity
equations (SSA) of the six nC12H25
radicals gives the first
decomposition path.


I
D
R j  ∑ k j ,i + ∑ k j ,i  = ∑ k I i , j ⋅Ri + Pɺj
i∈DJ
 i∈I J
 i∈I J
( j = 1, 6)
Colloquia on Reaction Engineering
January 24th, 2014
29
Chain radical propagation reactions of n-decane
RH +
C2H4 +
+
RH +
+ C2H5
+
R +
RH +
+
+ CH3
RH +
+
RH +
+
Primary H-abstraction reactions on n-decane produce 5 n-decyl radicals.
Again, successive reactions include isomerization and β-decomposition reactions
Colloquia on Reaction Engineering
January 24th, 2014
Lumped Pyrolysis Mechanism of n-decane
Intermediate radicals (larger than C4) are transformed into their final
products (QSSA).
Colloquia on Reaction Engineering
January 24th, 2014
Lumped Reactions of n-decane
On the basis of detailed kinetics and SSA of large Alkyl Radicals,
it is possible to generate the ‘lumped reactions’
R• + nC10H22
RH + {mixC10H21•}
{mixC10H21•}
.0205 H• + .0803 CH3• + .2593 C2H5• + .4061 nC3H7• + .2339 1C4H9•
+ .3785 C2H4 + .3127 C3H6 + .2114 1- C4H8 + .1870 1-C5H10 + .1815 1-C6H12
+ .1461 1-C7H14 +.1284 1-C8H16 + .0540 1-C9H18 + .0025 1-C10H20
+ .0006 2-C5H10 + .0012 C6H12s + .0013 C7H14s + .0005 C8H16s + .0100 C10H20s
Together with a similar ‘lumped’ initiation reaction,
these are the ‘new’ reactions needed to extend the overall kinetic scheme.
These stoichiometries, i.e.the slate
of products of the decomposition of
large radicals, are evaluated at a
given temperature ( T=1040 K).
Colloquia on Reaction Engineering
January 24th, 2014
At low temperatures (T<900 K),
alkyl radicals also add on oxygen to form
peroxyl radicals, before decomposition.
Other reactions need to be included.
33
‘Lumped Reactions’
are generated at a fixed Temperature (@ 1040K)
Intermediate radicals larger than C4 are transformed
(QSSA - isomerized and decomposed) into their final products.
Lumped H-abstraction Reactions on large molecules become:
R + nC12H26
RH + [mix C12H25]
.0226 H + .0735 CH3 + .2518 C2H5 + .4283 1C3H7 + .2238 1C4H9
+ .4529 C2H4 + .2936 C3H6 + .1935 1C4H8 + .1857 1C5H10 + .00054 2C5H10
+ .2056 1C6H12 + .00091 2C6H12 + .00023 3C6H12 + .1352 1C7H14 + .00121 C7H14s
+ .1179 1C8H16 + .00088 C8H16s + .1057 1C9H18 + .00081 C9H18s + .1002 1C10H20
+ .00042 C10H20s + .04506 1C11H22 + .00194 1C12H24 + .01005 C12H24s
[mixC12H25]
Similarly, in pyrolysis conditions or at high temperatures, decyl radicals decomposes:
[mixC10H21]
.0205 H• + .0803 CH3• + .2593 C2H5• + .4061 nC3H7• + .2339 1C4H9•
+ .3785 C2H4 + .3127 C3H6 + .2114 1- C4H8 + .1870 1-C5H10
+ .1815 1-C6H12 + .1461 1-C7H14 +.1284 1-C8H16 + .0540 1-C9H18 + .0025 1-C10H20
+ .0006 2-C5H10 + .0012 C6H12s + .0013 C7H14s + .0005 C8H16s + .0100 C10H20s
Significant reduction of both species and reactions, but …
…..
weak temperature dependence
Colloquia on Reaction Engineering
January 24th, 2014
34
Temperature effect:
At different T, different ‘lumped reactions’ of n-heptane are obtained:
At 1040 K: {mixC7H15•}= .0211 H + .0806 CH3+.2297 C2H5+.3629 1-C3H7+.3057 1-C4H9
Despite of the large difference in the
+.2277 C2H4+ .3463 C3H6+.2705 C4H8+.1912 C5H10+.0806 C6H12 + .0189 C7H14
temperatures (1040 vs 1500 K),
fuel decomposition,
intermediate
At 1500 K: {MixC7H15•}= .0747
H + .0920 CH3+.1722
C2H5+.3819 1-C3H7+.2792 1-C4H9
and radicals formations are
+.3623 C2H4+ .2939 Cproducts,
3H6+.2129 C4H8+.1671 C5H10+ .0920 C6H12 + .0651 C7H14
very similar in both the conditions
Pyrolysis of n-heptane at 1300 K
0.001
0.01
C2H4
0.006
CH3
C2H2
Mole fractions
Mole fractions
0.008
nC7H16
0.004
C3H6
0.0001
1e-05
C3H3
0.002
0
1e-06
1e-6
0.0001
0.01
1
10
Time [s]
1e-6
0.0001
0.01
1
Time [s]
Predicted mole fractions of relevant species.
Lumped kinetics at 1040 K (lines) and 1500 K (dashed lines)
Colloquia on Reaction Engineering
January 24th, 2014
10
Reliability of QSSA and lumped reactions.
35
‘Methyl concentration time-histories during
iso-octane and n-heptane oxidation and pyrolysis’
Model predictions (lines) vs experimental measurements (points).
Davidson D.F., M.A. Oehlschlaeger, R.K. Hanson (2007) Proc. Comb. Inst. 31:321-328
Colloquia on Reaction Engineering
January 24th, 2014
Reliability of QSSA and lumped reactions.
Mole Fractions [ppm]
10000
C2H4
1000
10
1
1e-006
Initial reflected shock conditions:
1410 K, 2.37 atm,
457 ppm nC12, 7577 ppm O2/Ar
nC12H26
100
OH
1e-005
0.0001
0.001
Time [s]
Species time-histories for ndodecane, OH and C2H4.
Points: experiments. Lines: simulations.
D.F. Davidson et al. / Proceedings of the Combustion Institute 33 (2011) 151–157
Colloquia on Reaction Engineering
January 24th, 2014
36
37
Outlines
Complexity of Pyrolysis and Combustion Systems
Complexity of Chemical Mechanisms
Complexity of Liquid Fuels
Coupling of Detailed kinetics and Complex Hydrodynamics
Time Scales in Combustion Processes
Dimension of Detailed Kinetic Mechanisms
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
Colloquia on Reaction Engineering
January 24th, 2014
38
STEAM CRACKING OF HYDROCARBONS
Operating Conditions
Hydrocarbons
Steam
C2H4
C3H6
Butadiene
BTX
•Temperature 900-1150 K
•Pressure: 1.5-2.5 bar
•Contact
time:
100-400
ms
The proper
knowledge
of ethylene
selectivity first requires the correct
knowledge of the feed
Complexity of the Liquid Mixtures
Feeds
Pyrolysis Coils in
Conventional Furnaces
•Ethane and gases E/P
•Naphthas (C4-C10)
•Gasoils
M.Dente, E.Ranzi "Mathematical modelling of pyrolisis reactions" in "Pyrolysis: Theory and Industrial Practice" Chap. 7
(L.F.Albright, B.L.Crines, W.H.Corcoran Eds), Academic Press (1983).
Colloquia on Reaction Engineering
January 24th, 2014
Complexity of the Liquid Feedstocks:
Naphthas, Kerosene, and Gasoils
Carbon
Number
Boiling
Number of
Temperature Paraffin
Isomers
[°C]
8
10
12
15
20
25
30
35
126
174
216
271
344
402
449
489
18
75
355
4347
3.66 105
3.67 107
4.11 109
4.93 1011
Altgelt and Boduszynski 1994
Colloquia on Reaction Engineering
January 24th, 2014
39
Petroleum Fraction
Gasoline and Naphthas
Kerosene
Jet Fuels
Diesel Fuels
Light Gasoil
Gasoil
Heavy Gasoil
Atmospheric Residue
40
Naphtha Fractions
17 Isomers of branched paraffines C8H18
3MEC7
2MEC7
23DMEC6
3ETC6
24DMEC6
22DMEC6
4MEC7
25DMEC6
33DMEC6
34DMEC6
234MEC5
2ME3ETC5
223MEC5
224MEC5
233MEC5
3ME3ETC5
Colloquia on Reaction Engineering
January 24th, 2014
2233MEC4
41
Pyrolysis of Different C8 Isomers.
Equivalent stoichiometries evaluated by MAMA Program @ 1040 K
R• + 2MEC7 = RH + 0.152 CH3• + 0.111 C2H5• + 0.159 nC3H7•
+ 0.258 iC3H7• + 0.196 1C4H9• + 0.122 1iC4H9• + 0.211 C2H4
+ 0.272 C3H6 + 0.116 1C4H8 + 0.208 iC4H8 + 0.148 1C5H10
+ 0.101 3me1C4H8 +0.053 me1C5H10 + 0.030 1C7H14 + 0.114 oleC7
R• + 3MEC7 = RH + 0.172 CH3• + 0.251 C2H5• + 0.211 nC3H7•+ 0.018 iC3H7•
+ 0.147 1C4H9• + 0.201 2C4H9• + .175 C2H4 + .219 C3H6 + .235 1C4H8
+ 0.106 2C4H8 + 0.002 1C5H10 + 0.002 2C5H10 + 0.164 2me1C4H8
+ 0.035 1C6H12 + 0.068 noleC6 +0.068 me1C5H10 + 0.144 oleC7
R• + 4MEC7 = RH + 0.131 CH3• + 0.533 C2H5• + 0.309 nC3H7•+ 0.019 iC3H7•
+ 0.008 1iC4H9• + 0.135 C2H4 + .677 C3H6+ .007 iC4H8 + 0.073 1C5H10
+ 0.164 2C5H10 + 0.238 me1C5H10 + 0.120 oleC7
R• + 23DC6 = RH + 0.370 CH3• + 0.233 C2H5• + 0.180 nC3H7•+ 0.217 iC3H7•
+ 0.056 C2H4 + 0.421 C3H6 + 0.168 2C4H8 + .06 1C5H10 + .123 2C5H10
+ 0.026 3me1C4H8+ 0.140 2me2C4H8 +0.133 me2C5H10 + 0.197 oleC7
R• + 3ETC6 = RH + 0.315 CH3• + 0.507 C2H5• + 0.159 nC3H7•+ 0.009 1C4H9•
+ 0.011 2C4H9• + 0.187 C2H4 + 0.179 C3H6+ 0.271 1C4H8 + 0.002 2C4H8
+ .03 1C5H10 + .148 2C5H10+ .271 noleC6 + .130 me1C5H10 + .117 oleC7
R• + TRMC5 = RH + 0.525 CH3• +0.475 iC3H7• + 0.212 C3H6 + 0.212 2C4H8
+ 0.071 3me1C4H8 + 0.405 2me2C4H8 +0.313 oleC7
Colloquia on Reaction Engineering
January 24th, 2014
42
Pyrolysis of Different C8 Isomers.
Yields predictions (wt. %) @ Reference Cracking Conditions
2MEC7
3MEC7
4MEC7
23DIME
C6
234-TRI
ME C5
3ETC6
H2
0.79
0.75
0.81
0.78
0.82
0.86
CH4
12.73
14.45
13.00
16.45
18.48
14.83
C2H4
30.84
30.44
32.16
22.28
14.95
31.71
C3H6
21.44
18.88
21.61
21.22
20.98
14.94
BTD
4.54
5.58
5.28
6.69
7.12
7.16
1C4H8
2.38
2.81
2.01
2.18
2.15
2.92
2C4H8
0.76
1.45
0.57
2.41
3.83
0.88
iC4H8
5.56
2.20
1.88
2.04
3.63
1.31
C5-
84.75
82.46
83.97
79.09
76.00
81.69
1.19
0.72
1.45
2.03
0.50
ISOPR
0.63
Colloquia on Reaction Engineering
January 24th, 2014
Relative Amount of Branched Isomers
in iso-C8H18 fraction of Virgin Feeds
Isomers (wt%)
Ponca
Occidental
Texas
Default
mono-methyl >
di-methyl
45.8
2-methylheptane
46.3
36.9
42.1
3-methylheptane
15.4
28.5
23.4
4-methylheptane
10.3
10.2
9.3
2,3-dimethylhexane
3.6
5.4
6.3
2,4-dimethylhexane
3.1
5.5
4.2
2,5-dimethylhexane
3.1
5.7
4.0
3.4
3,4-dimethylhexane
6.7
2.6
3.7
3.4
2,2-dimethylhexane
0.5
-
0.3
-
3,3-dimethylhexane
1.5
1.7
0.4
-
2,3,4-trimethylpentane
0.3
-
1.1
1.2
2,2,3-trimethylpentane
0.2
-
-
2,3,3-trimethylpentane
0.3
-
0.6
-
3-ethylhexane
4.6
3.5
3.1
3.8
2-methyl-3-ethylpentane
3.1
-
1.5
1.2
3-methyl-3-ethylpentane
1.0
-
-
-
22.9
11.5
2-methyl
heptane is more abundant
3.4
than
3.4 other methyl-heptanes
quaternary
C atoms are negligible
methyl >
ethyl-substitutions
A relative regularity is observed in the virgin feedstocks.
A single ‘lumped’ or equivalent component can substitute the mixture.
Colloquia on Reaction Engineering
January 24th, 2014
43
Relative Amount of Branched Isomers
in iso-C8H18 fraction of Virgin Feeds
Isomers (wt%)
Ponca
Occidental
Texas
Default
45.8
2-methylheptane
46.3
36.9
42.1
3-methylheptane
15.4
28.5
23.4
22.9
4-methylheptane
10.3
10.2
9.3
11.5
2,3-dimethylhexane
3.6
5.4
6.3
3.4
2,4-dimethylhexane
3.1
5.5
4.2
3.4
2,5-dimethylhexane
3.1
5.7
4.0
3.4
3,4-dimethylhexane
6.7
2.6
3.7
3.4
2,2-dimethylhexane
0.5
-
0.3
-
3,3-dimethylhexane
1.5
1.7
0.4
-
2,3,4-trimethylpentane
0.3
-
1.1
1.2
2,2,3-trimethylpentane
0.2
-
-
2,3,3-trimethylpentane
0.3
-
0.6
-
3-ethylhexane
4.6
3.5
3.1
3.8
2-methyl-3-ethylpentane
3.1
-
1.5
1.2
3-methyl-3-ethylpentane
1.0
-
-
-
A relative regularity is observed in the virgin feedstocks.
A single ‘lumped’ or equivalent component can substitute the mixture.
Colloquia on Reaction Engineering
January 24th, 2014
44
45
Pyrolysis of Different C8 Isomers.
A single ‘lumped’ or equivalent component MIXC8 substitutes the mixture
R• + C8ISO = RH + 0.180 CH3• + 0.218 C2H5• + 0.169 nC3H7• + 0.166 iC3H7• + 0.124 1iC4H9•
+ 0.074 1C4H9• + 0.069 2C4H9•+ 0.175 C2H4 + 0.290 C3H6 + 0.124 1C4H8
+ 0.047 2C4H8+ 0.118 iC4H8 + 0.080 1C5H10 + 0.034 2C5H10 + 0.045 2me1C4H8
+ 0.058 3me1C4H8 + 0.010 2me2C4H8 + 0.008 1C6H12 + 0.026 noleC6
+ 0.074 me1C5H10 +0.019 me2C5H10+ 0.014 1C7H14 + 0.135 oleC7
MIX C8
2MEC7
3MEC7
4MEC7
23DIMEC6
H2
0.79
0.79
0.75
0.81
0.78
0.82
0.86
CH4
13.87
12.73
14.45
13.00
16.45
18.48
14.83
C2H4
29.09
30.84
30.44
32.16
22.28
14.95
31.71
C3H6
20.54
21.44
18.88
21.61
21.22
20.98
14.94
BTD
5.29
4.54
5.58
5.28
6.69
7.12
7.16
1C4H8
2.43
2.38
2.81
2.01
2.18
2.15
2.92
2C4H8
1.10
0.76
1.45
0.57
2.41
3.83
0.88
iC4H8
4.04
5.56
2.20
1.88
2.04
3.63
1.31
C5-
82.84
84.75
82.46
83.97
79.09
76.00
81.69
1.19
0.72
1.45
2.03
0.50
ISOPR
0.91
0.63
234,TRIMC5
The ‘lumped’ component with a ‘default’ composition
represents the overall mixture of isomers C8 .
Colloquia on Reaction Engineering
January 24th, 2014
3ETC6
Distribution of pseudocomponents
CnH2n-z
46
Number of C atoms vs. Z (dehydrogenation degree)
SPYRO 2000
60
Horizontal and Vertical Lumping
50
H/C=0.5
allows to reduce the total number of species
C/H=1
Z
40
7
6
5
4
3
2
1
30
20
Alkyl-Phenanthrenes
Alkyl-Naphtalenes
10
Alkyl-Benzenes
0
N- and iso-Paraffins
0
10
20
C ATOMS
Colloquia on Reaction Engineering
January 24th, 2014
30
40
50
Only 240 molecular and radical species
characterize the pyrolysis system.
Wide Range Naphtha - Pyrolysis Yields (wt)
H2
CH4
C2H2
C2H4
C2H6
Allene
Propyne
C3H6
C3H8
nC4H10
iC4H10
iC4H8
1C4H8
trans-2C4H8
cis-2C4H8
1,3-butadiene
nC5H12
C5ISO
CycloC5H10
1C5H10
2C5H10
2me-1butene
3me-1butene
2me-2butene
1,3-pentadiene
isoprene +
(cyclopentadiene)
Exp.
0.48
8.45
0.09
19.57
3.33
0.12
0.22
15.50
0.62
1.73
0.28
3.19
3.63
0.79
0.62
4.06
2.57
2.03
0.00
0.74
0.61
0.68
0.19
0.22
0.81
1.84
Colloquia on Reaction Engineering
Pred.
0.54
8.64
0.09
19.74
3.34
0.09
0.12
15.71
0.58
1.92
0.30
3.02
3.34
0.78
0.57
3.93
2.73
2.16
0.07
0.75
0.40
0.57
0.19
0.16
0.71
0.95
1.23
Exp.
0.61
10.54
0.17
23.76
3.57
0.19
0.31
16.62
0.65
1.31
0.23
3.17
3.09
0.72
0.59
4.91
1.71
1.33
0.00
0.40
0.44
0.53
0.10
0.18
0.75
2.09
Pred.
0.67
10.65
0.18
23.64
3.44
0.15
0.20
16.73
0.57
1.44
0.23
2.94
2.84
0.71
0.52
4.59
1.79
1.42
0.05
0.41
0.29
0.45
0.12
0.10
0.65
0.89
1.55
Exp.
0.77
12.88
0.27
27.49
3.67
0.27
0.00
16.21
0.60
0.82
0.15
2.73
1.98
0.57
0.47
5.25
0.85
1.03
0.00
0.18
0.19
0.28
0.04
0.12
0.62
2.19
January 24th, 2014
Pred.
0.83
12.97
0.31
27.46
3.38
0.21
0.30
16.16
0.51
0.90
0.15
2.49
1.93
0.55
0.40
4.85
0.90
0.70
0.02
0.16
0.14
0.26
0.05
0.04
0.51
0.67
1.61
Exp.
0.89
14.86
0.45
29.97
3.41
0.32
0.00
13.88
0.48
0.42
0.08
1.92
0.98
0.36
0.30
5.00
0.32
0.72
0.01
0.07
0.08
0.11
0.01
0.06
0.48
2.00
Pred.
0.98
14.93
0.51
30.25
3.22
0.27
0.39
14.12
0.43
0.49
0.08
1.85
1.13
0.37
0.27
4.68
0.35
0.26
0.01
0.06
0.05
0.12
0.01
0.01
0.39
0.42
1.33
Exp.
1.01
16.55
0.68
31.75
3.08
0.33
0.60
11.24
0.35
0.17
0.03
1.21
0.44
0.23
0.18
4.51
0.08
0.00
0.01
0.03
0.03
0.04
0.01
0.03
0.34
1.81
47
Pred.
1.10
16.58
0.79
31.97
2.97
0.31
0.46
11.46
0.33
0.22
0.04
1.24
0.65
0.23
0.17
4.28
0.10
0.06
0.00
0.03
0.02
0.05
0.00
0.00
0.30
0.24
0.94
48
Naphtha Feed
Product yields (wt%) vs CH4
C5-C6 species
0.5
0.25
2-pentenes
0.4
0.2
0.3
0.15
0.2
0.1
0.1
0.05
Despite of all the0.8simplifications, also minor
2me-2butene
1-pentene
species are well0.6predicted by the model.
0.4
0
5
10
15
20
0.8
0
5
0.2
10
2
15
20
0.6
1.5
0.4
1
5
2.5
iso-hexanes
2me-1butene
0
10
15
20
isoprene+C5H6
2
1.5
CycloC5H6
1
0.2
0
5
0.5
10
15
20
2
0
5
0.5
10
15
20
0.25
5
10
0.8
Me-cyclo
pentene
n-hexane
0.2
1.5
0
isoprene
15
20
1,3- pentadiene
0.6
0.15
1
0.4
0.1
0.5
0
5
0.2
0.05
10
Colloquia on Reaction Engineering
15
20
0
5
10
January 24th, 2014
15
20
0
5
10
15
20
49
Size of SPYRO Mechanism
for the simulation of Steam Cracking Process
2010
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
Colloquia on Reaction Engineering
January 24th, 2014
50
Outlines
Complexity of Pyrolysis and Combustion Systems
Complexity of Chemical Mechanisms
Complexity of Liquid Fuels
Coupling of Detailed kinetics and Complex Hydrodynamics
Time Scales in Combustion Processes
Dimension of Detailed Kinetic Mechanisms
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
50
Colloquia on Reaction Engineering
January 24th, 2014
51
High Temperature Oxidation Mechanism
Decomposition of Large Molecules
Alkanes
Alkyl-radicals
Alkenes
Small radicals
High Temperature mechanism mainly involves interactions amongst
small and stable radicals (H, CH3, C2H3, C3H3, …)
and small stable species such as C2H4 and C2H2
as well as oxigenated species ( O2, O, OH, HO2, …..)
High Temperature mechanism is not very sensitive
to the structure of the hydrocarbon fuel
Colloquia on Reaction Engineering
January 24th, 2014
Low Temperature Oxidation Mechanism
52
Low Temperature oxidation mechanism requires
to define new reaction classes
Colloquia on Reaction Engineering
January 24th, 2014
Simplified Scheme of n-alkane (nC10H22)
Primary Oxidation Reactions
53
Alkyl radicals
forms Peroxy radicals
Peroxy radicals isomerize
to form Alkyl-hydroperoxy radicals
Succesive reactions
of these radicals explain
the system reactivity
Colloquia on Reaction Engineering
January 24th, 2014
Reaction Classes
54
High temperature mechanism
Reaction class 1:
Reaction class 2:
Reaction class 3:
Reaction class 4:
Reaction class 5:
Reaction class 6:
Reaction class 7:
Reaction class 8:
Reaction class 9:
Unimolecular fuel decomposition
H-atom abstractions
Alkyl radical decomposition
Alkyl radical+O2=olefin+HO2
Alkyl radical isomerization
H atom abstraction from olefins
Addition of radical species to olefins
Alkenyl radical decomposition
Olefin decomposition
Low temperature (high pressure) mechanism
Reaction class 10:
Reaction class 11:
Reaction class 12:
Reaction class 13:
Reaction class 14:
Reaction class 15:
Reaction class 16:
Reaction class 17:
Reaction class 18:
Reaction class 19:
Reaction class 20:
Reaction class 21:
Reaction class 22:
Reaction class 23:
Reaction class 24:
Reaction class 25:
Alkyl radical addition to O2
R+R′O2=RO+R′O
Alkylperoxy radical isomerization
RO2+HO2=ROOH+O2
RO2+H2O2=ROOH+HO2
RO2+CH3O2=RO+CH3O+O2
RO2+R′O2=RO+R′O+O2
RO2H=RO+OH
Alkoxy radical decomposition
QOOH decomposition and production of cyclic ethers
QOOH beta decomposition to produce olefin+HO2
QOOH decomposition to small olefin, aldehyde and OH
Addition of QOOH to molecular oxygen O2
O2QOOH isomerization to carbonylhydroperoxide + OH
Carbonylhydroperoxide decomposition
Reactions of cyclic ethers with OH and HO2
CK Westbrook et al. "A comprehensive detailed chemical kinetic reaction mechanism for combustion of nalkane hydrocarbons from n-octane ton-hexadecane." Combustion and Flame 156.1 (2009): 181-199.
Colloquia on Reaction Engineering
January 24th, 2014
Automatic generation
55
Classes of reactions
1. Decomposition of alkyl radicals R → CnH2n+R’
2. O2 addition to alkyl radicals R+O2
ROO
3. Internal isomerization ROO QOOH
4. O2 addition to hydroperoxyalkyl radicals
QOOH +O2
OOQOOH
5. Decomposition of hydroperoxyalkyl peroxy radicals
OOQOOH
OOQOOH + OH
AUTOMATIC GENERATION OF PRIMARY
OXIDATION REACTIONS
………
Reference kinetic parameters
H-Abstraction Reactions
Primary H atom
Primary radical
108.0 exp (-13.5/RT)
Secondary H atom
108.0 exp (-11.2/RT)
Tertiary H atom
108.0 exp (-9/RT)
108.0 exp (-12.2/RT)
108.0 exp (-12.7/RT)
108.7 exp (-18.8/RT)
108.0 exp (-10/RT)
108.0 exp (-10.5/RT)
108.7 exp (-16.5/RT)
Isomerization Reactions (Transfer of a Primary H-atom)
1-4 H Transfer
1-5 H Transfer
Primary radicalb
1011.0 exp (-20.6/RT) 1010.2 exp (-14.5/RT)
1-6 H Transfer
109.7 exp (-14.5/RT)
Secondary radical
Tertiary radical
Peroxyl radical
108.0 exp (-14.5/RT)
108.0 exp (-15/RT)
108.7 exp (-21.5/RT)
MAMOX Program
Peroxyl radical
1011.8 exp (-29.1/RT) 1011.0 exp (-23.0/RT) 1010.6 exp (-23.0/RT)
Alkyl Radical Decomposition Reactions to form Primary Radicals
Primary radical
Secondary radical
Tertiary radical
1014.0 exp (-30/RT)
1014.0 exp (-31/RT)
1014.0 exp (-31.5/RT)
Hydroperoxy-Alkyl Radical Decomposition Reactions to form
HO2•• and Conjugate Olefins
Smaller Olefins
1014.0 exp (-23/RT)
1013.2 exp (-22.5/RT)
to form Cyclic Ethers
Oxetans
Furans
1012.0 exp (-18/RT)
1011.2 exp (-17/RT)
1010.4 exp (-8.5/RT)
Corrections in Activation Energy to form:
Methyl radical
Secondary radical
Tertiary radical
+ 2.
- 2.
- 3.
Xirans
E. Ranzi, T. Faravelli, P. Gaffuri, E. Garavaglia, A. Goldaniga Ind. Eng. Chem. Res. 36, 3336-3344 (1997)
Colloquia on Reaction Engineering
January 24th, 2014
56
Combustion Reactions
Automatic Generation of Detailed Reaction Schemes
Primary propagation reactions of n-dodecane pyrolysis
(Units are: m kmol s kcal).
R5a -Isomerization of ROO•• to •QOOH radicals
COO*-C-C-C-C-C-C-C-C-C-C-C ==> COOH-*C-C-C-C-C-C-C-C-C-C-C
COO*-C-C-C-C-C-C-C-C-C-C-C ==> COOH-C-*C-C-C-C-C-C-C-C-C-C
COO*-C-C-C-C-C-C-C-C-C-C-C ==> COOH-C-C-*C-C-C-C-C-C-C-C-C
C-COO*-C-C-C-C-C-C-C-C-C-C ==> *C-COOH-C-C-C-C-C-C-C-C-C-C
C-COO*-C-C-C-C-C-C-C-C-C-C ==> C-COOH-*C-C-C-C-C-C-C-C-C-C
C-COO*-C-C-C-C-C-C-C-C-C-C ==> C-COOH-C-*C-C-C-C-C-C-C-C-C
C-COO*-C-C-C-C-C-C-C-C-C-C ==> C-COOH-C-C-*C-C-C-C-C-C-C-C
C-C-COO*-C-C-C-C-C-C-C-C-C ==> C-*C-COOH-C-C-C-C-C-C-C-C-C
C-C-COO*-C-C-C-C-C-C-C-C-C ==> C-C-COOH-*C-C-C-C-C-C-C-C-C
C-C-COO*-C-C-C-C-C-C-C-C-C ==> *C-C-COOH-C-C-C-C-C-C-C-C-C
C-C-COO*-C-C-C-C-C-C-C-C-C ==> C-C-COOH-C-*C-C-C-C-C-C-C-C
C-C-COO*-C-C-C-C-C-C-C-C-C ==> C-C-COOH-C-C-*C-C-C-C-C-C-C
C-C-C-COO*-C-C-C-C-C-C-C-C ==> C-C-*C-COOH-C-C-C-C-C-C-C-C
C-C-C-COO*-C-C-C-C-C-C-C-C ==> C-C-C-COOH-*C-C-C-C-C-C-C-C
C-C-C-COO*-C-C-C-C-C-C-C-C ==> C-*C-C-COOH-C-C-C-C-C-C-C-C
C-C-C-COO*-C-C-C-C-C-C-C-C ==> C-C-C-COOH-C-*C-C-C-C-C-C-C
………………….
………………….
Colloquia on Reaction Engineering
January 24th, 2014
A
1.26E+12
2.00E+11
8.00E+10
2.00E+12
1.26E+12
2.00E+11
8.00E+10
1.26E+12
1.26E+12
3.00E+11
2.00E+11
8.00E+10
1.26E+12
1.26E+12
2.00E+11
2.00E+11
E
26800
20700
20700
29100
26800
20700
20700
26800
26800
23000
20700
20700
26800
26800
20700
20700
57
Combustion Reactions
Automatic Generation of Detailed Reaction Schemes
Primary propagation reactions of n-dodecane pyrolysis
(Units are: m kmol s kcal).
R5b -Isomerization of •QOOH to ROO•• radicals
COOH-*C-C-C-C-C-C-C-C-C-C-C ==> COO*-C-C-C-C-C-C-C-C-C-C-C
COOH-C-*C-C-C-C-C-C-C-C-C-C ==> COO*-C-C-C-C-C-C-C-C-C-C-C
COOH-C-C-*C-C-C-C-C-C-C-C-C ==> COO*-C-C-C-C-C-C-C-C-C-C-C
*C-COOH-C-C-C-C-C-C-C-C-C-C ==> C-COO*-C-C-C-C-C-C-C-C-C-C
C-COOH-*C-C-C-C-C-C-C-C-C-C ==> C-COO*-C-C-C-C-C-C-C-C-C-C
C-COOH-C-*C-C-C-C-C-C-C-C-C ==> C-COO*-C-C-C-C-C-C-C-C-C-C
C-COOH-C-C-*C-C-C-C-C-C-C-C ==> C-COO*-C-C-C-C-C-C-C-C-C-C
*C-C-COOH-C-C-C-C-C-C-C-C-C ==> C-C-COO*-C-C-C-C-C-C-C-C-C
C-*C-COOH-C-C-C-C-C-C-C-C-C ==> C-C-COO*-C-C-C-C-C-C-C-C-C
C-C-COOH-*C-C-C-C-C-C-C-C-C ==> C-C-COO*-C-C-C-C-C-C-C-C-C
C-C-COOH-C-*C-C-C-C-C-C-C-C ==> C-C-COO*-C-C-C-C-C-C-C-C-C
C-C-COOH-C-C-*C-C-C-C-C-C-C ==> C-C-COO*-C-C-C-C-C-C-C-C-C
*C-C-C-COOH-C-C-C-C-C-C-C-C ==> C-C-C-COO*-C-C-C-C-C-C-C-C
C-*C-C-COOH-C-C-C-C-C-C-C-C ==> C-C-C-COO*-C-C-C-C-C-C-C-C
C-C-*C-COOH-C-C-C-C-C-C-C-C ==> C-C-C-COO*-C-C-C-C-C-C-C-C
………………….
………………….
Colloquia on Reaction Engineering
January 24th, 2014
A
E
9.45E+10
1.50E+10
6.00E+09
9.45E+10
9.45E+10
1.50E+10
6.00E+09
1.50E+10
9.45E+10
9.45E+10
1.50E+10
6.00E+09
6.00E+09
1.50E+10
9.45E+10
19100
13000
13000
18100
19100
13000
13000
12000
19100
19100
13000
13000
12000
13000
19100
Detailed Mechanisms of n-Alkane Oxidation
58
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
Lumping of Alkenes, Cyclic
ethers, Peroxides and
Ketohydroperoxides
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Lumping of Alkyl, Peroxy,,
Alkyl-hydroperoxy and
Peroxy-alkyl-hydroperoxy
60
January 24th, 2014
Lumped Scheme of
n-alkane Primary Oxidation Reactions
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January 24th, 2014
61
62
n-dodecane Primary Oxidation Reactions
Detailed Scheme
Lumped Scheme
258 Primary reactions
15 Primary lumped reactions
72 Intermediate radicals
4 Intermediate radicals
58 Primary products
(retaining nC12 structure)
4 Primary lumped products
6 n-dodecenes
16 O-cyclic-ethers
6 hydroperoxides
30 keto-hydroperoxides
1 lumped
1 lumped
1 lumped
1 lumped
n-dodecene
O-cyclic-ether
hydroperoxide
keto-hydroperoxides
Significant mechanism reductions relate to the primary products (retaining the
Kinetic Models
always
require a reasonable and well balanced presence
structure
of the original
fuel).
of ‘primary’ and ‘secondary’ reactions.
Secondary reactions (primary reactions of lumped products) can be better analysed.
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
Lumped Mechanisms of Heavy n-Alkane Oxidation
63
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
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
64
Overall Oxidation Mechanism
• GRI scheme for Gases
Bio Diesel
Fuels Alcohols
• PRF (nC7-iC8) and additives for Gasolines
nC7-iC8
•Alcohols
•Diesel and Jet Fuels
C3
C2
•Biofuels – FAME – FAEE
CH4
CO
H -O
2 2
Hierarchy and Modularity
are the main features of Detailed Kinetic Schemes
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 Oxidation
Low and High Temperature Ignitions
Pressure effect on the NTC region
ignition time [ms]
100
10
1
P = 6.5 bar
P = 13.5 bar
P = 42 bar
0.1
0.01
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1000/T [K]
E. Ranzi, P. Gaffuri, T. Faravelli, P. Dagaut ‘A Wide-Range Modeling Study of n-Heptane Oxidation’ (1995)
Combust. Flame 103: 91-106
Colloquia on Reaction Engineering
January 24th, 2014
Gasoline and Primary Reference Fuels
66
Mixtures n-heptane / iso-octane (1,2,3)
Lille RCM
Princeton PFR
Total ignition time [ms]
Released Heat [T(i) – T]
100
140
ON 100
ON 95
ON 90
80
120
100
60
80
40
60
n-heptane (0 ON)
62 ON PRF
87 ON PRF
iso-octane (100 ON)
40
20
20
0
600
700
800
900
Temperature [K]
0
500
600
700
Initial Temperature [K]
800
900
(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
67
Size of Detailed and Semi-detailed Mechanisms
Oxidation
POLIMI
2011
Pyrolysis
SPYRO
1980
L=25 K
Oxidation
C1-C4
1995
Lumped kinetic models allow an easier and
more effective successive reduction, for
CFD applications.
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
Colloquia on Reaction Engineering January 24th, 2014
Reduction of Detailed Kinetics
68
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.
Detailed Kinetics always require a successive lumping phase
in order to significantly reduce the number of species
Colloquia on Reaction Engineering
January 24th, 2014
Reduction of Detailed Kinetics
69
Skeletal 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).
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Colloquia on Reaction Engineering
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Thanks for the attention
CRECK Modeling Group at Politecnico di Milano
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Colloquia on Reaction Engineering
January 24th, 2014
Abstract
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
Colloquia on Reaction Engineering
January 24th, 2014
Time Scales in Combustion Processes
normalized mass fraction
Inlet mixture: C3H8 + Air
Temperature: 1800 K
fuel
Prompt
NOx
Thermal
NOx
A wide range of time
scales are involved in
Combustion Chemistry
time [s]
Colloquia on Reaction Engineering
January 24th, 2014
H-abstraction reaction on n-decane
75
Temperature effect on primary product distribution
from β-decomposition reaction of n-decyl radical
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
Colloquia on Reaction Engineering
January 24th, 2014
The product distribution and
corresponding ‘lumped’
stoichiometry shows a weak
T dependence
n-dodecane Primary Oxidation Reactions
76
Detailed Scheme
Lumped Scheme
258 Primary reactions
15 Primary lumped reactions
72 Intermediate radicals
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
Knocking Propensity of Primary Reference Fuels
n-heptane ON=0
H
H
O
O
77
iso-octane ON=100
Peroxy
radicals
H
H
H
H
O
O
4 secondary
2 secondary
(1-5) H-abstractions
(1-4) H-abstractions
k=4 1011.0exp(-20000/RT)
k= 2 1011.8 exp (-26000/RT)
OH
O
H
Alkylhydroperoxyradicals
H
H
k(700)= 105.4 [s-1]
OH
O
H
k(700)= 104.0 [s-1]
Isomerization reactions of peroxy radicals
explain the different ignition times of the two PRF
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Colloquia on Reaction Engineering
January 24th, 2014