Power generation capacity. Ref: «Fuel Conditioning System for Ammonia-Fired Power Plants » By Arif KarabeyoÄlu , Brian Evans, 2012 ...
2015 International Conference on Power and Energy Systems (ICPES 2015)
Ammonia as a renewable energy source and development of reduced chemical mechanisms
Hadi Nozari and Arif Karabeyoğlu Department of Mechanical Engineering Koç University İstanbul, Turkey
•
Why ammonia?
•
Challenges
•
Study Scope
•
Some Results
• Extensive use of fossil fuels • Major problems: Human health and welfare, environmental issues • A hot concern: Replacing current energy carriers • The Intergovernmental Panel on Climate Change (IPCC) report: Atmospheric CO2 levels rose almost twice as fast in the first decade of this century
«THE WORLD MUST RAPIDLY MOVE AWAY FROM CARBON-INTENSIVE FUELS»
Clean
Energy Dense
Ideal Energy Carrier
Safe
Cost Effective
NH3 as a Green Energy Source
SUSTAINABLE, RENEWABLE, NO CARBON INCLUDED FUEL
WELL DEVELOPED
AND EFFICIENT SYNTHESIS PROCESS
Haber-Bosch Process
EXISTING PRODUCTION, STORAGE AND TRANSPORT INFRASTRUCTURE
• High energy density
Ref: «Ammonia and related chemicals as potential indirect hydrogen storage materials», By R. Lan et al., 2012
Power generation capacity
Ref: «Fuel Conditioning System for Ammonia-Fired Power Plants » By Arif Karabeyoğlu , Brian Evans, 2012
Drawbacks also exist!
•
Slow kinetics (low flame speed)
•
NH3 , a source of fuel NOx in flames
Flame Speed (cm/sec)
200
150
145 H2
100 50
CH4 NH3
40 10
0 Standard Temperature and Pressure Air as oxidizer
«Ammonia – It’s Transformation and Effective Utilization» AIAA 2008 Ref: Miller, J. A. et al. , Combust. Sci. Tech., 34:149–176 (1983)
A simplified reaction mechanism
8
x 10
-3
2100 Temerature 2000
4
1900
2
1800
Effect of H2 addition to the mixture 0
•
Constant Inlet T (400°C) • Thermal NOx and Fuel NOx; the only players?
0
20
40
60
1700 100
80
%E H2 8
x 10
-3
Constant Flame T 7
•
Decoupling thermal NOx from total NOx
[NOx Level @Const. Inlet T of 400℃ ] – [NOx Level @ Const. Flame T of 1730 K] × 100 = 𝑻𝒉𝒆𝒓𝒎𝒂𝒍 𝑵𝑶𝒙 𝑺𝒉𝒂𝒓𝒆 [NOx Level @ Const.Inlet T of 400℃ ]
•
Thermal NOx share increase with increasing H2 % (Flame T)
NOx Mole Fraction
Constant Flame T (1730 K) • General expectation: decrease in Total NOx (decreasing fuel bond N) • Total NOx still increasing (despite const. thermal NOx)! • Effect of H and HNO accumulation → Increasing ROP of some key reactions • NO2+H↔NO+OH • HNO+H↔NO+H2 • HNO+OH↔NO+H2O
5 4 3 2 1 0
a 0
20
40
60
100
90 80 70 Extra H2 to be added
60 50 40 30 20 10
b 0
0
20
40
60 %E H2
ɸ=0.5
80
%E H2
% Thermal NOx Share in Total NOx
•
Constant Inlet T
6
80
100
Flame Temperature (K)
NOx Formation
Total NOx Mole Fraction
NOx 6
NOx Formation 0.01 Pure NH3 0.009
Effect of equivalence ratio variation
80% NH3 60% NH3
0.008
•
Increasing / Decreasing trend
Two opposite effects: 1) Increase in thermal NOx by increase in adiabatic flame T
NOx Mole Fraction
20% NH3 0.007
10% NH3 Pure H2
0.006 0.005 0.004 0.003 0.002
2) Decreasing fuel NOx by decreasing O/F ratio 𝑁𝐻𝑖 + 𝑂𝑋 → 𝑁𝑂 + 𝐻𝑖 𝑋
0.001 0 0.4
0.6
0.8 1 Equivalence Ratio
OX: Oxygenated species
Noticeable reduction in NOx emission under the rich conditions P=17 bar, T=673 K
1.2
1.4
Reduced Mechanism NOx Emission Prediction
P=17 bar, T=673 K
Reduced Mechanism Comparison with Experiments
Full Konnov Red. Mech.1 Red. Mech.2 Red. by Duynslaegher et al. Exp. Van Wonterghem et al. Exp. Duynslaegher et al.
140
Flame Speed (cm/s)
120 100 80 60 40 20 0
10
20
DuynslaegherC., PhD dissertation, Universit_ecatholique de Louvain; 2011. Wonterghem JV,Tiggelen AV., Bulletin des SocietesChimiquesBelges1955; 64:99-121
30 Dilution (%N2) STP Condition
40
50
60
Reduced Mechanism Efficiency Chart Full Konnov Mech.
1
Red. Mech.1 Red. Mech.2 Duynslaegher et al.
• •
CPU Time • Reference: Konnov Mech. (unity) Precision • Reference: Experimental Data
Normalized CPU time
0.8
0.6
0.4
0.2
0
4
5
6 7 8 9 10 Average deviation from experimental data (%)
11
0.02
•
•
Ignition delay time not captured accurately
The final NOx emission very well predicted by the two reduced mechanisms
NO Mole Fraction
•
0.015
0.01
0.005
Concentration time profiles very well predicted (once the time scale is translated to account for the differences in the delay times between the reduced mechanism and the full Konnov mechanism)
Konnov Red. Mech. #1 Red. Mech. #2
0 8
0 -3 x 10
1
2
3
t (sec)
-4
x 10 Konnov
Needed
OH Mole Fraction
Red. Mech. #1 Red. Mech. #2
6
4
2
Reduced mechanism applicable to non-steady conditions 0
0
1
2 t (sec)
ɸ=0.5, P=17 bar, 80 %E NH3
3 -4
x 10
•
Controlling role of radicals in laminar flame speed and autoignition process with OH as the most influential radical
•
Adding H2 to the fuel mixture improved laminar flame speed and autoignition process
•
Despite improving flame speed and autoignition process, adding H2 does not necessarily decrease the NOx level
•
Total NOx formation is highly dependent on the competition between fuel NOx and thermal NOx levels
•
Localized rich combustion seems to minimize NOx. Ammonia slip may be the compromise
•
The obtained reduced mechanisms give reliable predictions for flame speed and exhaust emissions
•
About the same accuracy of Konnov mechanism with nearly 5 times less CPU time expense
Thank You
Objective •
To burn NH3 in a power generation system in efficient and environmentally friendly way: –
Low NOx emission
–
Low NH3 slip
Approach •
Chemical kinetics study of NH3/H2/Air under practical combustion conditions
•
Developing a reduced mechanism capable of predicting combustion characteristics with an acceptable accuracy
•
CFD simulation of combustion
•
Experimental study to examine the validity of results
NH3/H2/Air
𝑥𝑁𝐻3 + 𝑦𝐻2 + 𝑎𝑠𝑡𝑜𝑖 𝑂2 + 3.76 𝑁2 → 𝑏 𝐻2 𝑂 + 𝑐 𝑁2
P=17 atm ɸ=0.5-1.8
Studied Cases % E of NH3
NH3
H2
O2
N2
100
0.1228
0
0.1843
0.6929
80
0.0958
0.0382
0.1819
0.6840
60
0.0701
0.0745
0.1797
0.6757
40
0.0456
0.1091
0.1776
0.6677
20
0.0223
0.1421
0.1755
0.6600
Reactants’ Composition
%𝐸 𝑁𝐻3 =
•
Major Combustion Properties
Steady – –
•
𝑋𝑁𝐻3 × 𝐿𝐻𝑉𝑁𝐻3 × 100 𝑋𝑁𝐻3 × 𝐿𝐻𝑉𝑁𝐻3 + 𝑋𝐻2 × 𝐿𝐻𝑉𝐻2
Burning velocity (laminar flame speed) Emission (NOx formation)
Non-steady –
* A.A.Konnov, Combust. Flame 156 (2009) 2093–2105
Ignition delay time
Konnov Mechanism*
Elements: N/H/O Species: 30 Reactions: 240
Ammonia decomposition analysis Aim: To identify the contribution of each reaction in molar conversion of NH3
80%NH3
100% NH3
Study Cases
ɸ = 0.5, P=17 bar, T= 673 K
60%NH3
The most important reactions and their contribution (%)
Fuel mixture
NH3+OH↔NH2+H2O
NH3+O↔NH2+OH
NH3+NH2↔N2H3+H2
Pure NH3 80%NH3 60%NH3
95%
4.64%
0.23%
94.8%
5.04%
0.11%
94.5%
5.45%
ignorable
Importance of OH radical in flame speed
Correlation
ɸ = 0.5, P=17 bar, T= 673 K
Average Flame Speed Prediction Error (%)
Reduced Mechanism • •
2 Versions Obtained Applicable to steady state conditions
Red. Mech. 1
Red. Mech. 2
Red. Belgium
0.5
8.4
5.6
30
1
4.8
6
19.6
1.1
4.9
5.9
18.3
1.2
4.6
6
19.4
1.5
4.4
6.7
18.3
Konnov (full)
Belgium Red.*
Red. Mech. 1
Red. Mech. 2
1.8
4.2
7.7
16.8
# elements
3
3
3
3
3
7.8
8.8
4.7
# species
30
19
21
18
# reactions
240
80
91
80
Reduction based on: -
ɸ
Contribution of rections in form/decomp of species Tracking form./decomp. of imp radicals in flame speed (OH,H,O, …) Tracking form./decomp. of imp radicals in NOx emmision (NO,NH,NH2, …)
P=17 bar, T=673 K * Duynslaegher C, Contino F,Vandooren J, Jeanmart H., Combust Flame 2012.
Average NOx Formation Prediction Error (%) ɸ
Red. Mech. 1
Red. Mech. 2
Red. Belgium
0.5
7.5
5.6
10.6
1
2.8
1.8
2.5
1.1
5
2.8
5.5
1.2
3
2.7
2.8
1.5
3.2
4.5
10
1.8
3.2
12.8
29.7
3
7.5
23.6
51.4
Reduced Mechanism Flame Speed Prediction
P=17 bar, T=673 K
Reduced Mechanism Flame Speed Prediction Error (%)
Experiments of Duynslaegher etal.
Experiments of Van Wonterghem et al.
Comparison with Experiments
STP Condition
% N2
Konnov
Red. Mech.1
Red. Mech.2
Red. By Duynslaegher et al.
0
1.2
0.4
0.8
10.3
5
1.5
0.6
1.3
11.2
10
3.6
2.9
3.5
13.1
15
4.7
3.8
4.8
13.8
20
7.1
6.3
7.1
15.6
25
11.3
10.0
10.7
19.2
30
15.1
14.7
15.2
22.8
35
1.4
1.1
1.9
7.9
40
5.9
6.0
4.5
1.4
45
9.5
9.1
10.5
12.6
50
3.8
3.6
5.8
4.7
55
1.9
1.2
3.6
3.1
60
12.1
14.0
15.5
12.8
61.7
3.9
5.6
7.8
5.6
Autoignition
Importance of radicals in autoignition and ignition initiation
100%NH3
Accumulation of influential radicals close to the ignition time ɸ=0.5, T=1300 K, P=17 bar
80%NH3
Autoignition -
Effect of initial mixture T
-
Effect of NH3 content
ɸ=0.5, P=17 bar
