Angela Violi, University of Michigan. University Coal ... + OH: ab initio .... Li et al. Davis et al. GRI-Mech 3.0. O'Conaire et al. Ig nitio n. D e lay, Ï (ms). 1000/T (1/K).
Syngas and Hydrogen Combustion: Ignition and Flame Propagation Grant Number: DE-FG26-06NT42717 Development of Comprehensive Detailed and Reduced Reaction Mechanisms for Syngas and Hydrogen Combustion
Principal Investigator: Chih-Jen Sung Department of Mechanical and Aerospace Engineering Case Western Reserve University Cleveland, Ohio 44106 Collaborators: Hai Wang, University of Southern California Angela Violi, University of Michigan University Coal Research Contractors Review Conference June 5-6, 2007
Objectives • This project aims to develop the tools necessary for the design of future synthesis-gas and hydrogen (SGH) fueled combustion turbines. – Generate a detailed experimental database of SGH combustion at IGCC-like conditions. – Investigate fundamental chemical kinetics of H2/CO/O2/N2/H2O/CO2 at pressures, temperatures, and concentrations typical of SGH combustion in gas turbines – Develop detailed and reduced chemical mechanisms based on this database, capable of predicting NOx formation during SGH combustion.
Scope of Work • Obtain benchmark experimental characteristics of syngas
data
for
combustion
– Conterflow Burner Apparatus • Laminar flame speeds • Extinction limits • Flame structure – Rapid Compression Machine • Ignition delays at elevated pressures
• Develop comprehensive and computationally-efficient chemical models – – – –
Assessment of available kinetic mechanisms Theoretical calculations to determine critical rate constants Mechanism optimization Mechanism simplification and reduction
Accomplishments - Year 1 • Autoignition of dry H2/CO mixtures at elevated pressures in a rapid compression machine. • Assessment of kinetics of syngas combustion at elevated pressures using global uncertainty analysis methods. • Reaction kinetics of CO+HO2 − ab initio calculations. • 3 journal publications and 1 under review. • Preliminary experimentation on autoignition of wet H2/CO mixtures at elevated pressures in a rapid compression machine. • Preliminary experimentation to determine combustion characteristics of wet H2/CO mixtures in a counterflow configuration.
Outline • Autoignition of Dry H2/CO Mixtures – – – –
Characterization of Rapid Compression Machine Ignition Delay Results “Brute Force” Sensitivity Analysis Global Uncertainty Analysis
• Reaction Kinetics of CO+HO2 → CO2 + OH: ab initio Study and Master Equation Modeling • Laminar Flame Speeds of Wet H2/CO Mixtures with Preheat – Counterflow Burner Apparatus – Preliminary Results
• Conclusions • Future Work
Autoignition of Dry H2/CO Mixtures
High-Pressure Ignition and Oxidation Rapid Compression Machine (RCM)
Rapid sampling apparatus
Reactor Cylinder end region Cylinder with quartz window, pressure transducer, thermocouple & gas line
Hydraulic piston seal Hydraulic Chamber
Piston stopping groove
Spacers for adjusting stroke
Air line from tank Hydraulic line for filling, draining, and solenoid release Hydraulic Piston
Port for gas inlet/outlet valve
Ports for quartz windows
Pressure transducer
Thermocouple
End Reaction Chamber
Driver Piston
Creviced Piston
Features of the Present RCM • RCM simulates a single compression stroke of an engine – simple and relatively easy to operate
• Adjustable stroke and clearance • Fast compression (< 30 ms) • Compressed pressure up to 60 bar • Temperature – 500 to 1100 K • Elevated pressure condition is sustained up to 100 ms • Optimized creviced piston for ensuring homogeneity of reacting mixture • Optically accessible • GC/MS and a fast sampling apparatus for species measurement • Direct measurement of ignition delay • Study of low-to-intermediate temperature chemistry
RCM Operation • Pneumatically driven
• Hydraulically actuated and stopped
Reproducibility 60
Pressure (bar)
50 40
Ignition Delay, τ
PC = 30 bar TC = 999 K
30 20 10 0 -30
-20
-10 Time (ms)
0
10
Molar composition: H2/CO/O2/N2/Ar = 9.375/3.125/6.25/18.125/63.125 Initial conditions – T0 = 298.7 K and P0 = 661 Torr
Comparison of RCM Experiment and Model Simulation using CHEMKIN and SENKIN – with volume specified as a function of time in a homogeneous adiabatic system. 50
Pressure (bar)
40
PC= 30 bar TC= 977 K
Experiment
Model
30 Nonreactive (experiment and model)
20 10 0 -15
-10
-5
0 5 Time (ms)
10
15
20
Dry H2/CO Experiments − Specifications • Temperature (TC): 950 – 1100K
• Pressure (PC): 15 − 50 bar
• Equivalence ratio (φ): 0.36 – 1.6
• RCO=[CO]/([H2]+[CO]): 0 – 0.80
Mixture #
φ
RCO
H2
CO
O2
N2
Ar
1
1.0
0
12.5%
0%
6.25%
18.125%
63.125%
2
1.0
0.25
9.375%
3.125%
6.25%
18.125%
63.125%
3
1.0
0.50
6.25%
6.25%
6.25%
18.125%
63.125%
4
1.0
0.65
4.375%
8.125%
6.25%
18.125%
63.125%
5
1.0
0.80
2.5%
10%
6.25%
18.125%
63.125%
6
0.36
0.25
6.667%
2.222%
12.345%
14.418%
64.348%
7
0.72
0.25
6.667%
2.222%
6.173%
21.586%
63.352%
8
1.0
0.25
6.667%
2.222%
4.444%
23.600%
63.067%
9
1.3
0.25
6.667%
2.222%
3.419%
24.782%
62.910%
10
1.6
0.25
6.667%
2.222%
2.777%
25.511%
62.823%
Hydrogen Ignition Delay (1) • Stoichiometric hydrogen mixtures (H2/O2/N2/Ar = 2/1/2.9/10.1) 50
Pressure (bar)
40
P0= 705.8 Torr TC= 977 K
P0 = 640 Torr TC = 1010.5 K
30 T0 = 298 K
20
Experimental O'Conaire et al. (2004)
10
Davis et al. (2005) Li et al. (2004)
0 -15
-10
-5
0 5 Time (ms)
10
15
20
Hydrogen Ignition Delay (2) • H2/O2/N2/Ar = 12.5/6.25/18.125/63.125 100
}
Ignition Delay, τ (ms)
PC=15 bar
Ignition Delay, τ (ms)
100 Experimental Li et al. Davis et al.
PC=30 bar
0.96
0.98 1 1.02 1000/T (1/K)
10 Experimental Li et al. Davis et al. GRI-Mech 3.0 O'Conaire et al.
0.94
10
1 0.94
PC=50 bar
1
GRI-Mech 3.0 O'Conaire et al.
1.04
1.06
}
0.96
0.98
1 1.02 1000/T (1/K)
1.04
1.06
“Brute Force” Sensitivity Analysis Reaction Number
22
TC = 1010.5 K PC = 30 bar
20
H2O2+H=HO2+H2 H2O2(+M)=OH+OH(+M)
19
HO2+HO2=H2O2+O2
18
HO2+HO2=H2O2+O2
17
HO2+OH=H2O+O2
13
H+O2(+M)=HO2(+M)
1
H+O2=OH+O -60
-40
-20
0
20
40
60
Percent Sensitivity
Reactions involving formation and consumption of HO2 and H2O2 are important.
H2/CO Ignition Delay (1) Effect of increasing RCO
100 Ignition Delay, τ (ms)
PC = 50 bar
0.80 0.65
0.50 0.25 RCO=0
10
1 0.96
0.98 1 1000/TC (1/K)
1.02
1.04
Replacement of even small amounts of H2 with CO leads to an inhibition of autoignition.
H2/CO Ignition Delay (2) 100
100
0.50 0.80 0.65
RCO=0
Ignition Delay, τ (ms)
Ignition Delay, τ (ms)
PC = 30 bar
0.25
10
RCO 0 0.25 0.50 0.65
10
0.80
PC = 15 bar
1
1 0.96
0.98
1 1.02 1000/TC (1/K)
1.04
1.06
0.94
0.96 0.98 1000/TC (1/K)
1
The inhibition effect of CO addition is seen to be much more pronounced at higher pressures.
1.02
H2/CO Ignition Delay (3) • Existing mechanisms fail to describe the inhibition effect of CO addition. • From mechanisms, inhibition effect of CO is not observed until it constitutes 80% of the total fuel mole fraction.
4 Ignition Delay, τ (ms)
30 Ignition Delay, τ (ms)
Li et al.
25
PC = 30 bar TC = 1010.5 K
GRI-Mech 3.0
GRI-Mech 3.0
3
PC = 50 bar TC = 1044 K
Davis et al.
2.5
Experimental
2 1.5 1 0.5
Davis et al.
20
Li et al.
3.5
Experimental
0
15
0
0.2
0.4
0.6
0.8
1
RCO
10
(H2+CO)/O2/N2/Ar = 12.5/6.25/18.125/63.125
5 0
0
0.2
0.4
0.6 RCO
0.8
1
“Brute Force” Sensitivity Analysis 29 28
Reaction Number
27
TC = 1010.5 K PC = 30 bar
26
CO+OH=CO2+H CO+HO2=CO2+OH CO+O2=CO2+O CO+O(+M)=CO2(+M)
22
H2O2+H=HO2+H2
20
H2O2(+M)=OH+OH(+M)
19
HO2+HO2=H2O2+O2
RCO
18
HO2+HO2=H2O2+O2 HO2+OH=H2O+O2
0 0.50 0.80
17 13
H+O2(+M)=HO2(+M) H+O2=OH+O
1
-60
-40
-20
0
20
40
60
Percent Sensitivity
CO+HO2=CO2+OH appears to be the primary reaction responsible for the mismatch of experimental and calculated ignition delays.
Global Uncertainty Analysis • “Brute force” local sensitivity analysis is a useful linear analysis, but this cannot reveal interactions between kinetic parameter values. • Uncertainties have to be assigned to all relevant parameters and the response to variations within the assigned ranges must be tested. • Global, non-linear, uncertainty analysis which simultaneously considers variations in all kinetic parameters is required to interpret the origins of the discrepancy (e.g. Morris-one-at-atime and Monte-Carlo methods). in collaboration with Prof. J. F. Griffiths, University of Leeds
Morris Analysis (1) • The overall importance ranking of reactions is determined by the absolute mean perturbation of the predicted ignition delay across all simulations when rate parameters are varied in a prescribed way within their ranges of uncertainty. • The standard deviation reflects non-linear effects, i.e. the extent to which the sensitivity of the ignition delay may change if other parameters are adjusted.
Morris Analysis (2) 0.8CO + 0.20H2 at 50 bar and1040 K using 76 irreversible reaction scheme (Davis et al., 2005) 0.5
CO + HO -> CO + OH
standard deviation / ms
2
H + O + M -> HO + M
HO + OH -> H O+ O2 2 2
0.4
2
2
HO + H2 -> H2O + H 2 2
REACTION
0.3
H + O -> OH + O 2
H2O + M -> 2OH + M 2
0.2
0.1
2
CO + OH -> CO + OH 2
CO+HO2 → CO2+OH
(-10.702 → -9.902)
H+O2+M → HO2+M
(-11.272 → -10.871)
H+O2 → OH+O
(-7.207 → -7.507)
H2O2+M → 2OH+M
(19.146 → 19.546)
HO2+OH → H2O+O2
(-10.905 → -9.905)
HO2+H2 → H2O2+H
(-19.667 → -19.047)
0.0 0.0
0.2
0.4
0.6
0.8
1.0
1.2
absolute mean perturbation / ms
1.4
Range of log A (cm molecule s)
1.6
Monte Carlo Analysis (1) Significance of k of CO+HO2 in predicting ignition delay 12
10
log A in primary
t/ms
8
Experimental tign at 50 bar and 1040 K
data set The experimental value for tign is predicted in only a few cases regardless of all other parameter values
6
4
2
0 -12.0
-11.5
-11.0
-10.5 -1
3
-1
log(A/molecule cm s )
This is why we think k for CO + HO2 is wrong.
-10.0
Monte Carlo Analysis (2) Relationship of various values of k of CO+HO2 with predicted ignition delays
Normalised frequency
1.0
tign for log A = -10.3 and all other rate parameters are allowed to vary over their uncertainty ranges (s.d ~ + 60%)
0.8
tign for log A = -11 and all other rate parameters are allowed to vary over their uncertainty ranges (s.d ~ + 40%)
0.6
0.4
These variations arise even in a 76 reaction scheme for which the data are
0.2
generally “well known”. BE WARNED! 0.0 0.0
2.5
5.0
7.5
tign / ms
10.0
12.5
15.0
Conclusions from Global Uncertainty Analysis • The currently accepted parameter values for CO + HO2 are obviously not right. • Log A < -11 would fix it but the present analysis does not permit us to do more than indicate that the overall reaction rate is too fast. • This constraint arises from the uncertainty in other rate parameters that gives the scatter in the predicted ignition delays – which is problem for any model validation using ignition delay data. • Corrected parameters cannot be generated for this reaction solely from ignition delay evaluations • Direct experimental or theoretical approaches are required to determine the rate parameters.
Reaction Kinetics of CO+HO2 → CO2 + OH ab initio Study and Master Equation Modeling
Motivation (1) 1011
Vandooren et al. Azatyan et al. Colket et al. Atri et al. Baldwin (1970) Baldwin (1965) Vardanyan Mittal et al. Burrows et al. Davis et al. Howard Gramham Simonaitis Bohn et al. Arustamyan et al. Wyrsch et al. Khachatrian et al. Hoare and Patel Hastie Volman and Gorse
Sun et al. Tsang and Hampson
109
107
Mueller et al. 105
Lloyd 103
101
10-1
CO+HO2=CO2+OH 10-3 0.5
1.0
1.5
2.0
1000K/T
2.5
3.0
3.5
Motivation (2) • Prior theoretical efforts are insufficient to ensure an accurate rate coefficient. • In all cases, the hindered internal rotations in the HOOC•O adduct and the critical geometries were inadequately treated. • The complexity of the potential energy surface due to the trans- and cis-conformers and their mutual isomerization was not considered. • In addition, the calculations of the potential energy barriers may not be sufficiently reliable to obtain accurate rate constant values.
Approach • A more detailed analysis of the potential energy surface of CO+HO2 reaction using several high-level quantum chemistry methods. • Our best estimates for the saddle point energies are then incorporated in transition state theory simulations that consider the full complexity of the hindered rotational motions. • Furthermore, the possibility of collisional stabilization and the dissociation of the adduct back to CO + HO2• along the trans pathway is examined via master equation simulations.
Quantum Chemistry Calculation • CCSD(T)/CBS energy (Halkier, 1998) ECCSD(T)/CBS ≈ ECCSD(T)/cc-pVQZ +
27 ⎡ × ⎢ ECCSD(T)/cc-pVQZ − ECCSD(T)/cc-pVTZ ⎤⎥ ⎦ 37 ⎣
• FCC/CBS energy (He, 2000)
Basis set correction
1 EFCC/CBS ≈ ECCSD(T)/CBS + × ⎡⎢ ECCSD(T)/cc-pVTZ − ECCSD/cc-pVTZ ⎤⎥ ⎦ 5 ⎣ Configuration Interaction truncation error
• Energies (kcal/mol) at 0 K relative to CO + HO2• Products/ G3B3 transition state CO2+OH HOOC•O TS1 TS2 TS3 TS4 HC•O+O2
-63.3 6.3 18.3 12.0 19.3 15.5 33.3
CCSD(T)/ CCSD(T)/ CCSD(T)/ FCC/CBS cc-pVTZ cc-pVQZa CBS -59.9 8.1 18.8 14.4 19.9 17.2 33.1
-61.0 7.2 18.3 13.4 19.3 16.4 33.7
-61.8 6.5 17.9 12.7 18.9 15.8 34.1
-61.7 6.0 17.3 11.8 18.2 15.3 34.0
Literature value -61.6±0.1
33.6±0.1
Potential Energy Surface •
CO+HO2→products (CCSD(T)/CBS//CCSD(T)/cc-pVTZ, kcal/mol)
TS3 (cis)
TS1 (trans)
18.9
17.9
TS2 (trans) 12.7
trans-HOOC•O 6.5
CO+HO2 0
Theory
TS1
PT2(5e,5o)/CBS
17.1
PT2(9e,8o)/CBS
18.2
PT2(11e,11o)/CBS
18.4
cis-HOOC•O
CO2+OH -61.8
Internal Rotation Asymmetric characteristics TS1↔TS3 Potential Energy
• •
V03 V02 V01
V04 1.149 1.758
1.150
TS3 1.742 0.968
TS1
TS1
π/2
0
π
3π/2
2π
Rotation Angle, φ
TS1 1.391
12 4
1 ⎛ π kBT ⎞ Qh ( T ) = ⎜ ⎟ 2π ⎝ B ⎠
iπ / 2
∑ ∫( i =1
i −1)π 2
d φ e −V
TS3
1.400
0.969
kBT
Density of States •
Hindered internal rotation contributions ρh ( E ) = ρh 1 ( E ) + ρh 2 ( E ) + ρh 3 ( E ) + ρ h 4 ( E )
•
Total density of states
Treatment of the Moment of Inertia • At lower level approximation
I
( 2, n )
=
I L (1, n )I R (1, n )
I L (1, n ) + I R (1, n )
• At higher level approximation (East and Radom, 1997) I
(3, 4 )
(
)
2 ⎡ 2⎤ 3 α U iy βi ⎥ (1,1) ⎢ =I −∑ + ⎢ m L + mR ⎥ I i i =1 ⎢ ⎥⎦ ⎣
Results (1) •
Effects of internal rotor and I treatment on k (cm3/mol·s) Hindered rotor
T(K)
Harmonic oscillator
Free rotor with I(3,4)
I(2,1)
I(2,3)
I(3,4)
500
2.1×103
3.8×104
2.9×103
1.5×103
1.7×103
1000
5.6×107
6.1×108
1.1×108
6.3×107
6.5×107
1500
2.6×109
2.1×1010
5.5×109
3.4×109
3.2×109
2000
2.2×1010
1.4×1011
4.7×1010
2.9×1010
2.7×1010
2500
8.8×1010
4.6×1011
1.9×1011
1.2×1011
1.1×1011
Results (2) Vandooren et al. Azatyan et al. Colket et al. Atri et al. Baldwin (1970) Baldwin (1965) Vardanyan Mittal et al. Burrows et al. Davis et al. Howard Gramham Simonaitis Bohn et al. Arustamyan et al. Wyrsch et al. Khachatrian et al. Hoare and Patel Hastie Volman and Gorse
1011
109
107
105
103
this work 101
10-1
CO+HO2=CO2+OH 10-3 0.5
1.0
1.5
2.0
2.5
3.0
3.5
1000K/T • No pressure dependence up to 500 atm. • Supports the notion advanced in RCM studies that the literature rate values are too large.
Uncertainty Analysis 1011
Sources of Uncertainty: Upperlimit (this work)
• TS1, TS3 barrier: ± 1 kcal/mol
k (cm3/mol-s)
1010
• Internal rotation barrier: ± 1 kcal/mol 109
• State counting: 50% This work
108
107
Rate constant Uncertainty:
Lowerlimit (this work)
• 300 K, a factor of 8; 106
• 1000 K, a factor of 2; 0.6
0.8
1.0
1.2
1.4
1000K/T • The error bars reject almost all of the rate values reported in earlier studies.
• 2000 K, a factor of 1.7.
Modeling vs. RCM Experiments 15
Pc = 15 Bar Tc = 1028.5 K
Molar composition: (H2+CO)/O2/N2/Ar =12.5/6.25/18.125/63.125.
10
5
0
• Dashed lines: Model of Davis et al. (2005)
25
Pc = 30 Bar Tc = 1010.5 K
20 15
• Solid lines: updated model.
10 5 0 5
1. CO+HO2=CO2+OH (this work)
Pc = 50 Bar Tc = 1044 K
4
2. CO+OH=CO2+H (Joshi and Wang)
3
3. HO2+OH=H2O+O2 (Sivaramakrishnan et al.)
2 1 0
0.0
0.2
0.4
0.6
RCO
0.8
1.0
Summary • The current theoretical analysis supports lower rate value for CO+HO2=CO2+OH. • Recommended rate expression:
(
)
k cm3 mol ⋅ s = 1.57 ×105T 2.18e−9030 T (300≤T≤2500 K, P≤ 500 atm)
Laminar Flame Speeds of Wet H2/CO Mixtures with Preheat
Counterflow Twin-Flame Configuration Sonic Nozzle
Bypass
Nebulizer Air
Mixing Chamber
O2 N2 Syringe Pump
Temperature Controller Nozzle Heating Pad
N 2 Coflow
Heating Rope
Counterflow Twin Flames
Z
Uz
DPIV System for Velocity Measurement Gemini PIV-Nd:YAG Dual Lasers 15 Hz repetition rate 120 mJ/pulse at 532 nm 3-5 ns pulse width
Laser Head
Dantec PIV 2100 Processor
Burner
Dantec HiSense CCD Camera 1280×1024 pixels 6.7 μm ×6.7 μm 9 frames/sec
DPIV Measurement
1
0.5
Reference Speed
Radial Velocity at Reference Point (m/s)
Axial Velocity (m/s)
1.5 0.6 Radial Velocity Gradient
0.4 0.2
Î stretch rate, K
0 -0.2 -0.4 -0.6
Reference Point 0
-3
0 0.5 1 1.5 2 2.5 3 Distance from Nozzle Exit, z (mm)
-2 -1 0 1 Radial Axis, r (mm)
2
3
Linear Extrapolation φ=0.7, RCO=0.95, ξH2O=15%, Tu=323 K
100
Reference Flame Speed (cm/s)
Reference Flame Speed (cm/s)
100
80
60
Laminar Flame Speed
40
20
0
0
200
400
600
Stretch Rate (s-1)
800
φ=0.7, RCO=0.95, ξH2O=25%, Tu=323 K
80
60
Laminar Flame Speed 40
20
0
0
200
400
600
Stretch Rate (s-1)
ξH2O=[H2O]/([H2]+[CO]+[H2O])
800
Effect of Water Addition on Flame Propagation Fixed Volumetric Flow Rate φ=0.7, RCO=0.75, Tu=323 K
Fixed Volumetric Flow Rate φ=1.3, RCO=0.95, Tu=323 K
ξH2O=0%
ξH2O=0%
ξH2O=25%
ξH2O=25%
laminar flame speed decreases with increasing ξH2O
laminar flame speed increases with increasing ξH2O
Conclusions • Need comprehensive detailed and reduced mechanisms for syngas and hydrogen combustion. • Discrepancies between simulations and the newly obtained experimental data are discussed. • Comparison of experimental and computational results will enable the re-evaluation and optimization of current mechanisms. • The lack of accurate/meaningful experimental data has in the past hampered the progress in the development of kinetic mechanism. – Need extensive benchmark data of high fidelity.
Future Work • Obtain detailed experimental data for combustion characteristics of SGH mixtures using rapid compression machine and counterflow burner. – Effects of CO2 and H2O addition on the autoignition of H2/CO mixtures. – Measurements of laminar flame speeds and strain-induced extinction limits of premixed SGH flames.
• Assess kinetic mechanism against the newly acquired experimental data, thereby enabling re-evaluation and optimization of rate constants and mechanism. • Conduct ab initio quantum chemistry calculation and master equation modeling for certain key reactions, including HO2+HO2→H2O2+O2 and HO2+OH→H2O+O2. – Notable influence on SGH oxidation rates under high-pressure, low-tointermediate temperature conditions. – Complex temperature and pressure dependences that cannot be easily resolved through mechanism optimization.
Acknowledgements • Work supported by DOE/NETL − Contract Monitor: Rondle E. Harp. • Former and current graduate students: Gaurav Mittal, Kamal Kumar, Xiaoqing You, and Apurba Das.
