Syngas and Hydrogen Combustion: Ignition and ...

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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, τ (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



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.