Ammonia as a potential energy vector for future energy application/蔡偉翔教授

Transcript

1. Ammonia as a potential energy vector for future energy application Dr. Wai Siong CHAI 蔡偉翔 11th October 2022 NCKU, Tainan
2. Self-introduction University of Nottingham Malaysia, BEng (Hons.) in Chemical Engineering (2012) & PhD in Engineering (2017) 2 Postdocs in China (2018-2022) Assistant Professor in Department of Mechanical & Electro- Mechanical Engineering, National Sun Yat-Sen University (Aug 2022- Present)
3. Outline Energy and environmental issues Shipping sector Hydrogen and ammonia Limitations of ammonia systems and relevant strategies Ammonia/hydrogen and ammonia/methane Summary and future perspectives
4. National Sun Yat-Sen University
5. History of NSYSU Co-exist with the monkeys on- campus
6. Energy issue Conventional fuels – major energy generator Taiwan mostly conventional ↑ global worldwide population, industrial processes ↑ global energy demand
7. Environmental issue Increased global energy demand → huge carbon and greenhouse gas (GHG) emission Environmental and pollution issues Most harmful GHG is carbon dioxide (CO2 ), 74% of total GHG & 30% warming potential on its own
8. Asia Pacific region contributes >50% carbon emission Shanghai and Jakarta (Nusantara) are sinking and vulnerable to sea level rises What about Taiwan??
10. Combustion is GHG emission important contributor Renewable sources cut down carbon emission but has intermittency Conventional industrial burners are difficult to replace Zero-carbon emission target Usage of alternative carbon- free fuel is necessary
11. Shipping sector issue Transports > 80% of world trade by volume 6th highest carbon emission worldwide Carbon cuts are of pressing importance 2030 is the mid- term decarbonization deadline
12. Four critical questions (Steven Chu) 1. H2 source – natural gas. Not ideal 2. High density storage 3. Distribution infrastructure 4. Fuel cell maturity
13. Alternative fuel – hydrogen (H2 ) Most popular carbon-free fuels High energy content Simple structure Reduces climate change impacts High costs to in liquifying and transportation of liquid hydrogen H H
14. Ammonia Carbon-free Efficient hydrogen carrier Higher hydrogen density per unit volume (108 kg/m3) than liquid hydrogen and metal hydrides (25 kg/m3) Lower storage space than liquid H2 Lower storage pressure (8 vs 700 bars) than hydrogen Lower liquefaction temperature (-253 °C) than H2 (-253 °C) Saved about 10 and 47 times in storage and transportation cost H H H N Fuel H2 content (wt%) Volumetric energy density Ammonia 17.7 4325 Methanol 12.5 4600 Ethanol 13 6100 Gasoline 15.8 9700 Hydrogen 100 1305
15. Ammonia Haber-Bosch process N2 + 3H2 -> 2NH3 High temperature, high pressure! Been here for more than a century Main usage as fertilizer, feeding more than half the population Current distribution infrastructure >100 M tonnes/year Minimal investment and increased confidence Safer: lighter density, pungent odor, narrow flammability Shipping sector: promising alternative fuel, related safety is industrial practice
16. Limitations of pure NH3 combustion Low laminar burning velocity (LBV) Low reactivity, high auto-ignition temperature <10 cm/s, ~20% of CH4 /air flames ↓ with pressure, insignificant change with equivalence ratio High fuel NOx emissions Overall reaction: 4NH3 + 3O2 -> 2N2 + 6H2 O NOx inevitably produced in actual combustion Fuel Flammability limit (vol% in air) Auto-ignition temp (K) Gasoline 1.4-7.6 573 Diesel 0.6-5.5 503 Natural gas 5-15 723 Hydrogen 4-75 844 Ammonia 16-25 924 0 5 10 15 20 25 30 35 40 0.7 0.8 0.9 1 1.1 1.2 1.3 Burning velocity (cm/s) Equivalence ratio NH3/air CH4/air
17. Strategies in tackling limitations of NH3 comb 1. Low LBV Improved oxygen content NH3 /air flames with O2 content of 0.35, similar performance as CH4 /air flames Additive fuel addition Other additive fuels such as methane and hydrogen can increase the LBV 0 5 10 15 20 25 30 35 0.7 0.8 0.9 1 1.1 1.2 1.3 Burning velocity (cm/s) Equivalence ratio NH3/air NH3/CH4 NH3/H2 ER = 1, stoichiometric ER < 1, Fuel lean ER > 1, Fuel rich
18. Strategies in tackling limitations of NH3 comb 2. High fuel NOx emissions Burn under rich condition NO peaks at ER=0.9, negligible at ER=1.3 Unburned NH3 after ER=1.1 Burn under pressured conditions NO halved from 1 to 5 bar, OH radicals reduction Burn with steam  ↑ NO consumption Additive fuel addition Other additive fuels such as methane and hydrogen can decrease the NOx, competing reactions
19. Strategies in tackling limitations of NH3 comb Wide range of NH3 combustion studies, kinetics, NOx, rich, lean burn, ignition delay Accurate model is still lacking Most methods can only solve single issue Additive fuel strategy to be adopted Tackle both issues simultaneously Additive fuel ratio, pressure → LBV, NOx NH3 comb NH3 /H2 NH3 /CH4
20. NH3 /H2 comb (LBV) ↑ over wide range of ER and entire H2 range Similar trend as NH3 /air O+H2 = OH + H H+O2 = OH+O (most enhancing) H2+OH = H2O + H (most inhibiting) ↓ with pressure N-based elementary reactions dominated over H-based ones Reaction between NH3 and OH radical preferred over H Others ↑ Flame temperature & heat release rate IDT ↓ more pronouncedly at 10-30 atm than 1.4-10 atm
21. NH3 /H2 comb (NOx) ↑ when molar ratio of H2 < 0.8 Presence of OH and O radicals at high T NOx negligible once ER > 1.05 Very concentration dependent ↓O2 in comb ↓NO Thermal NOx HNO, N and NH oxidation ↓ with pressure 5 and 1 ppm at P = 10 and 20 atm Steam addition mitigates thermal NO O+H2O=2OH promoted over N2+O=NO+N NO consumption through NH2 mechanism
22. NH3 /CH4 comb (LBV) ↑ over wide range of ER and entire CH4 range Similar trend as NH3 /air and NH3 /H2 Sensitive to CH4 ratio Addition of C component complicates the reactions H+O2 = OH+O (most important) HCO=H+CO, CH2OH+H=CH3+OH Under fuel-rich, flame propagation dominated by methane chemistry ↓ with pressure Increased unburned mixture density Significant: H+O2=OH+O, H+CH3(+M)=CH4(+M) Important with P: 2CH3(+M)=C2H6)+M), CH4+NH2=CH3+NH3 More responsive towards NH3 and hydrocarbon species
23. NH3 /CH4 comb (NOx) CO2 halved, CO ↓ when NH3 ratio > 0.6 ↑ CH4 ratio ↓ NOx CH4 complete oxidation all ER ER>1↑CO, ER≥1↑CO2 , ER≤1 ↑NO Fuel-rich reduce NOx CO and NOx↓ with pressure NOx higher sensitivity than CO H+O2+M=HO2+M suppresses OH radical NH+NO=HNO+H at high pressure Steam addition ↑NO ↓ CO O+H2O=2OH promoted over N2+O=NO+N NO consumption through NH2 mechanism H+H2O=OH+H2, O+H2O=2OH Others ↑ Flame temperature IDT ↑ with ER, ↓ with T, P and CH4
24. Preliminary findings For NH3 /H2 and NH3 /CH4 blended fuels: ↑ fuel proportion and ER ↑ LBV ↑ ER and pressure ↓ NOx production Slight fuel rich and high pressure conditions are beneficial for maximizing LBV and minimizing NOx production 24 0 500 1000 1500 2000 2500 3000 3500 0 5 10 15 20 25 30 35 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 NOx (ppm) LBV (cm/s) ER xCH4=0.2 xCH4=0.8 xH2=0.15 xH2=0.40 NOx,CH4 (2 bar) NOx,CH4 (1 bar) NOx,H2 (1 bar)
25. NH3 /H2 , NH3 /CH4 comb model & challenges Mathieu, Otomo, Tian – IDT, LBV, NOx of NH3 combustion Mathieu, Klippenstein, Okafor & San Diego - Pure NH3, NH3 /H2 , NH3 /CH4 Tian, Okafor- NOx and CO of NH3 /CH4 Hydrogen enriches O/H radical pool Methane introduces hydrocarbon species, parallel oxidation of individual fuel in mixture, sharing same radical pool C-N interactions negligible in NH3 /CH4 Current models are not capturing reaction kinetics of many species compared to real combustion systems Applicability of an accurate reaction model towards multi- parameter not realized yet
26. Ammonia color codes Five categories Brown – coal gasification Grey – natural gas reforming Blue – Additional carbon capture and storage unit Green – Renewable electricity Pink – Nuclear
27. Future trends Blue and green NH3 set to replace grey NH3 in 2025 and 2030 Staged movement - Mixed combustion with coal → carbon-free green NH3 Strong collaboration between industry, governments, supply & demand country – successful large-scale reformation Global efforts involving regional, intercontinental accelerate NH3 reformation as fuel in various industries Public perception, risk/health and safety/regulation advancements, infrastructure developments, material resistance to ammonia corrosiveness,
28. Current and future directions for NH3 • NH3 can be produced renewably • Further improvements on low LBV of ammonia combustion and NOx generation • Improvements on detailed chemical kinetics of NH3 combustion • Molecular understanding to practical applications in combustion systems before commercialization of NH3 -blends
29. The Royal Society (2020) Ammonia: zero-carbon fertilizer, fuel and energy store
31. 台灣2050氫應用發展技術藍圖 Taiwan's 2050 Hydrogen Application Development Technology Blueprint • Hydrogen 9-12% • 750 M tonnes by 2050 (hydrogen 435 M tonnes, NH3 315 M tonnes) • Import 75% • Three directions: Strengthened technology applications, Complete transportation and storage infrastructures, Expand hydrogen import sources
32. Summary & future perspectives • Conventional fuels – pollution and environmental problems • NH3 as zero-carbon fuel, highly sought after • Limited by low LBV and high fuel NOx • Hydrogen and methane studied as additive fuel • ↑LBV and↓ NOx for both mixtures • Slight-fuel rich and pressured conditions for max LBV and min NOx
33. Co-existence is the key Future is from the past Thank you for your attention Wai Siong Chai Email: wschai@mail.nsysu.edu.tw 33