Institute of Thermal Engineering Chair of Gas and Heat Technology Flame stability of ultra-lean methane and synthesisgas combustion in inert porous burners presented by Stefan Voss Friday, 15 th of June 2012 TU Bergakademie Freiberg I Gustav-Zeuner-Str. 7 I 09596 Freiberg Tel. 0 37 31 / 39-39 41 I Fax 0 37 31 / 39-39 42 I www.tu-freiberg.de
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Motivation Utilization of lean gas mixtures low calorific value gas mixtures hydrogen synthetic gas mixtures are applicable in several fields: Gasification/Reforming Fuel Cell Technology Power to Gas Scenarios Pyrolysis Landfill Gases Characterization of global stability of premixed sustained flame in porous inert media Gasification Reforming Fuel Cell Technology Power to Gas Source: Gräbner (2010) Source: Sunfire (2012) Source: OPAL
Technological attractiveness +2 0-2 +2 Question Mark Strategy R&D Withdrawal Technology Portfolio Post-Combustion Systems in Fuel Cell 1 2 3 4 0 Answers (Required) R&D Effort Strategy of Technology Leadership R&D Rationalization -2 1) Premixed Combustion 2) Non-premixed Combustion 3) Catalytic Combustion 4) Direct Combustion (on the stack) Technological Risk very high high average low very low
Premixed Combustion Premixed flames their realization as flexible and controllable flames with adjustable flame temperature and with comparable opportunities of reducing high-temperature based pollutants to non-premixed flames. F. Weinberg (1986)
Ultra-Lean combustion low reaction rates low flame temperatures leads to low emissions! burning velocity S L influenced by H 2 and inert fractions moderate flame stability hydro-dynamic instabilities thermo-diffusive instabilities, for Le < 1 Le D thermal diffusivity molecular diffusivity T. Poinsot (2005)
Combustion within Porous Inert Media Flow stabilization (change in cross-sectional area) Thermal stabilization (Peclet-criteria) (Pe s 65) for CxHy L dp,eff ρf cpf heat production (Pe Pe= 20) for H = 2 based fuels λ f heat release Structure of a lean premixed flame: δ T = preheating zone δ r = reaction zone δ ε =post combustion zone Silicium infiltrated Silicium Carbide foam/sponge (SiSiC) Global Properties 10 ppi ( 3 mm pore size) macro porosity 0.8 to 0.9 T 1540 C high thermal shock resistance
Dimensions of the Model Burner 80 76 54 18 [mm]
Regulations/Directives of Emissions for stationary CHP systems NO x CO Regulation 260 mg/kwh 50 mg/kwh 1000 ppm (dry, O 2 -free) 60 mg/kwh DIN EN 50465 Blue Angel RAL-ZU 61 --- 300 ppm (dry, O 2 -free) IEC 62282-3
SOFC System FlameSOFC Combined Heat and Power CHP system FlameSOFC EC. Grant no 019875-SES6
SOFC mode Ultra-lean gas mixtures Fuel Cell FlameSOFC EC. Grant no 019875-SES6 Start-up/Load rejection mode (Reformate) CO < 35 mg/kwh NO x < 24 mg/kwh CO < 30 mg/kwh NO x < 20 mg/kwh
SOFC mode Ultra-lean gas mixtures Fuel Cell FlameSOFC EC. Grant no 019875-SES6 Start-up/Load rejection mode (Reformate)
SOFC mode Ultra-lean gas mixtures Fuel Cell FlameSOFC EC. Grant no 019875-SES6 Temperature Distribution Temperature Distribution at the outlet plane of the burner 340 kw/m², = 1.4 (ϕ =0.5), T u = 673 K
[1] L. Bobrova et al., Catalysis Today (2009) [2] J. Requies et al., Catalysis Today (2009) [3] Z. Al-Hamamre, S. Voss, D. Trimis, Int. J. Hydrogen Energy (2009) [4] M. Zahedi nezhad et al., Int. J. Hydrogen Energy (2009) [5] Thinh X. Ho et al., Chemical Eng. Sci. (2009) [6] C. Cremers te al., Fuel Cells (2007) Reforming Scenarios for SOFC systems H 2 CO N 2 CO 2 H 2 /CO Dilution H u vol. % molar % MJ/kg A1 13,3 6,7 70 10 2 80 1,954 A2 10,0 5,0 75 10 2 85 1,419 A3 8,6 4,4 77 10 2 87 1,214 A4 6,7 3,3 80 10 2 90 0,916 B1 15,0 5,0 70 10 3 80 1,961 B2 11,2 3,8 75 10 3 85 1,417 B3 9,7 3,3 77 10 3 87 1,210 B4 7,5 2,5 80 10 3 90 0,911 C1 16,0 4,0 70 10 4 80 1,964 C2 12,0 3,0 75 10 4 85 1,415 C3 10,4 2,6 77 10 4 87 1,208 C4 8,0 2,0 80 10 4 90 0,908 Synthetic gas mixtures (H 2 /CO) for different reforming strategies with a post utilization in a fuel cell (SOFC) system (Methan (CH 4 ) primary fuel) H 2 /CO (molar): 2 11 Dilution (inert fraction in the fuel stream): 35 90 %
Ultra-lean gas mixtures Hydrogen Carbon Monoxide 400 kw/m² = 2.0 (ϕ =0.5) T u = 673 K 1000 kw/m² = 2.0 (ϕ =0.5) T u = 673 K
Ultra-lean gas mixtures Hydrogen - Nitrogen
Ultra-lean gas mixtures Methane - Carbon Dioxide
Ultra-lean gas mixtures Methane T u =298K
Conclusion The flame stabilization within porous inert media offers the possibility to operate over a wide range and to utilize specific gas mixtures and to achieve extremely low emissions. Source: ITM Power (2012) Further details of the complexity in the flame structure are given in: S. Voss et al., Investigation on the thermal flame thickness for lean premixed combustion of low calorific H 2 /CO mixtures within porous inert media, Proceedings of the Combustion Institute, Vol. 34, paper accepted
Thank you for your attention contact details Stefan Voss TU Bergakademie Freiberg Institute of Thermal Engineering Germany stefan.voss@iwtt.tu-freiberg.de BMBF (2012) happy to take questions!