223rd
ECS (Electrochemical Society) Meeting, 2013, Abstract #76
Novel
sulfur and carbon highly tolerant current collecting materials for SOFC
Ning Yan, Tong Gao, Jing-Li Luo & Karl T. Chuang
Department of Chemical and Materials Engineering, University of Alberta,
Edmonton, Alberta T6G 2G6, Canada
Introduction
Solid
oxide fuel cells (SOFC) have attracted increasingly attentions since they
exhibit excellent efficiency and fuel diversity. However, when using an
unpretreated feed such as sour gas (H2S+CH4), the conventional catalyst Ni will
suffer serious H2S poisoning and carbon deposition, both of which are extremely
detrimental to SOFC operation. Therefore, developing sulfur and carbon tolerant
anode catalyst has recently become one of the main focuses in SOFC study.
Although anode current collector is also a key component for SOFC,
little effort has been devoted to discover new candidate materials for anode
current collecting, which also resist both sulfur and coke. Researchers studied
a novel current collecting material based on transition metal carbide, which
should show high electrical conductivity and excellent stability in 0.5%H2S +
CH4.
source: https://ecs.confex.com/ecs/223/webprogram/Abstract/Paper12630/A1-0076.pdf
Showing posts with label Solid Oxide Fuel Cell. Show all posts
Showing posts with label Solid Oxide Fuel Cell. Show all posts
Thursday, November 14, 2013
Experimental Validation of Interval-Based Sliding Mode Control for Solid Oxide Fuel Cell Systems
2013
European Control Conference (ECC), July 17-19, 2013, Zürich, Switzerland.
Experimental Validation of Interval-Based Sliding Mode Control for Solid Oxide Fuel Cell Systems
Thomas D¨otschel, Andreas Rauh, Luise Senkel, and Harald Aschemann
Abstract
The utilization of solid oxide fuel cells (SOFCs) as well as other high-temperature fuel cells for a decentralized power supply demands for reliable and guaranteed stabilizing control strategies, that are capable of providing electrical and thermal energy. Moreover, it is essential to increase the number of possible thermal cycles of SOFCs by means of control laws which reduce temperature gradients in the space coordinates of a stack module during transient operating conditions. For this purpose, suitable control-oriented system models have been identified in previous work and parameterized reliably by means of both local and global optimization procedures. By exploiting these models, which can be extended to account for parameters that are subject to bounded uncertainty, intervalbased sliding mode controllers can be derived. These controllers simultaneously adjust the mass flow and temperature of air supplied to the cathode of the SOFC.
In this paper, a realtime capable implementation of the corresponding intervalbased sliding mode controller and selected experimental results are presented for an SOFC test rig available at the Chair of Mechatronics at the University of Rostock.
Introduction
The nonlinear, guaranteed stabilizing control design is restricted to a scalar system model. For this system model, a novel interval-based sliding mode controller is employed to account for bounded uncertainty of the parameters characterizing the dynamic behavior of the thermal subsystem and to account for disturbance variables estimated in real time. The presented system description can also be generalized to higher dimensions, see ,.
Free Full Text Source: http://www.nt.ntnu.no/users/skoge/prost/proceedings/ecc-2013/data/papers/0775.pdf
Experimental Validation of Interval-Based Sliding Mode Control for Solid Oxide Fuel Cell Systems
Thomas D¨otschel, Andreas Rauh, Luise Senkel, and Harald Aschemann
Abstract
The utilization of solid oxide fuel cells (SOFCs) as well as other high-temperature fuel cells for a decentralized power supply demands for reliable and guaranteed stabilizing control strategies, that are capable of providing electrical and thermal energy. Moreover, it is essential to increase the number of possible thermal cycles of SOFCs by means of control laws which reduce temperature gradients in the space coordinates of a stack module during transient operating conditions. For this purpose, suitable control-oriented system models have been identified in previous work and parameterized reliably by means of both local and global optimization procedures. By exploiting these models, which can be extended to account for parameters that are subject to bounded uncertainty, intervalbased sliding mode controllers can be derived. These controllers simultaneously adjust the mass flow and temperature of air supplied to the cathode of the SOFC.
In this paper, a realtime capable implementation of the corresponding intervalbased sliding mode controller and selected experimental results are presented for an SOFC test rig available at the Chair of Mechatronics at the University of Rostock.
Introduction
The nonlinear, guaranteed stabilizing control design is restricted to a scalar system model. For this system model, a novel interval-based sliding mode controller is employed to account for bounded uncertainty of the parameters characterizing the dynamic behavior of the thermal subsystem and to account for disturbance variables estimated in real time. The presented system description can also be generalized to higher dimensions, see ,.
Free Full Text Source: http://www.nt.ntnu.no/users/skoge/prost/proceedings/ecc-2013/data/papers/0775.pdf
Recent Progress of SOFC-GT Combined System with Tubular Type Cell Stack at MHI
ECS
Trans. 2013 volume 51, issue 1, 79-86
Recent Progress of SOFC-GT Combined System with Tubular Type Cell Stack at MHI
Yoshinori Kobayashia,
Yoshimasa Ando (a), Hiroshi Kishizawa (a), Kazuo Tomida (a) and Norihisa Matake (b)
a Mitsubishi Heavy Industries, Ltd. New Energy Systems Department, Power Systems
b Mitsubishi Heavy Industries, Ltd. Nagasaki Reserch & Development Center
Abstract
A solid oxide fuel cell (SOFC) can operate at high temperature. By applying its high-temperature exhaust heat to gas turbine (GT) combined-cycle power generation, an extremely high-efficiency thermal power system can be constructed.
Mitsubishi Heavy Industries, Ltd. (MHI) is one of the first companies to focus on the potential of the SOFC as a component of large-scale power generation systems. It has promoted both element and system development since the 1980s. New 250kW-class SOFC-MGT Hybrid System has been under trial operation since November 2012.
Full Text Source (Subscription or Fee): http://ecst.ecsdl.org/content/51/1/79.short
Recent Progress of SOFC-GT Combined System with Tubular Type Cell Stack at MHI
Yoshinori Kobayashia,
Yoshimasa Ando (a), Hiroshi Kishizawa (a), Kazuo Tomida (a) and Norihisa Matake (b)
a Mitsubishi Heavy Industries, Ltd. New Energy Systems Department, Power Systems
b Mitsubishi Heavy Industries, Ltd. Nagasaki Reserch & Development Center
Abstract
A solid oxide fuel cell (SOFC) can operate at high temperature. By applying its high-temperature exhaust heat to gas turbine (GT) combined-cycle power generation, an extremely high-efficiency thermal power system can be constructed.
Mitsubishi Heavy Industries, Ltd. (MHI) is one of the first companies to focus on the potential of the SOFC as a component of large-scale power generation systems. It has promoted both element and system development since the 1980s. New 250kW-class SOFC-MGT Hybrid System has been under trial operation since November 2012.
Full Text Source (Subscription or Fee): http://ecst.ecsdl.org/content/51/1/79.short
Multi-objective Optimization of PV-Bat-SOFC Hybrid System: Effect of different fuels used in Solid Oxide Fuel Cell (SOFC)
J.
Energy Eng., 10.1061/(ASCE)EY.1943-7897.0000170 (Oct. 24, 2013).
Multi-objective Optimization of PV-Bat-SOFC Hybrid System: Effect of different fuels used in Solid Oxide Fuel Cell (SOFC)
S. Sadeghi (1), (2) and M. Ameri (1), (2)
1 Department of Mechanical Engineering, Shahid Bahonar University, Kerman, Iran
2 Energy and Environmental Engineering Research Center, Shahid Bahonar University, Kerman, Iran
Abstract
Describes the multi-objective optimization of the combination of photovoltaic (PV) panels, batteries, and a solid oxide fuel cell (SOFC) according to different fuels for solid oxide fuel cell. The most desirable hybrid system is the one that has the least cost, the least emission, and the most reliability. Unfortunatelhy, these objectives are in conflict with each other.
Authors employ a multi-objective optimization evolutionary algorithm to obtain the optimum solutions. They compare various fuels as SOFC fuel in the hybrid system. They then compare results to specify the more favorable fuels for SOFC economically and ecologically. They opitimize for two categories of fuel price: international fuel prices and Iran fuel prices. The consider sensitivity analysis of fuel price. They explore the effect of change in SOFC power to determine enough auxiliary power for the hybrid system. Results reveal that the most appropriate fuel for SOFC in the hybrid system is natural gas. It causes low annualized cost (ANC) and low CO2 emission.
Full Text Source (Subscription or Fee): http://ascelibrary.org/doi/abs/10.1061/(ASCE)EY.1943-7897.0000170
Multi-objective Optimization of PV-Bat-SOFC Hybrid System: Effect of different fuels used in Solid Oxide Fuel Cell (SOFC)
S. Sadeghi (1), (2) and M. Ameri (1), (2)
1 Department of Mechanical Engineering, Shahid Bahonar University, Kerman, Iran
2 Energy and Environmental Engineering Research Center, Shahid Bahonar University, Kerman, Iran
Abstract
Describes the multi-objective optimization of the combination of photovoltaic (PV) panels, batteries, and a solid oxide fuel cell (SOFC) according to different fuels for solid oxide fuel cell. The most desirable hybrid system is the one that has the least cost, the least emission, and the most reliability. Unfortunatelhy, these objectives are in conflict with each other.
Authors employ a multi-objective optimization evolutionary algorithm to obtain the optimum solutions. They compare various fuels as SOFC fuel in the hybrid system. They then compare results to specify the more favorable fuels for SOFC economically and ecologically. They opitimize for two categories of fuel price: international fuel prices and Iran fuel prices. The consider sensitivity analysis of fuel price. They explore the effect of change in SOFC power to determine enough auxiliary power for the hybrid system. Results reveal that the most appropriate fuel for SOFC in the hybrid system is natural gas. It causes low annualized cost (ANC) and low CO2 emission.
Full Text Source (Subscription or Fee): http://ascelibrary.org/doi/abs/10.1061/(ASCE)EY.1943-7897.0000170
Numerical Modeling of the Sulfur Poisoning Effect on the Ni-YSZ Porous Anode of SOFCs
224th ECS (Electrochemical Society) Meeting, Abstract #346
Numerical Modeling of the Sulfur Poisoning Effect on the Ni-YSZ Porous Anode of SOFCs
Negar Manafi (a), Kunal Karan (b)
negar.manafi@chee.queensu.ca
kkaran@ucalgary.ca
a Queens-RMC Fuel Cell Research Centre 945 Princess Street, 2nd floor Kingston, Ontario K7L 5L9ıCanada
b Department of Chemical Engineering, University of Calgary, Calgary, Alberta T2N 1N4 Canada
Presence of H2S in the fuel can have adverse effect on the performance of Solid oxide fuel cells (SOFCs) because it can poison the Ni-based anodes. Poisoning occurs by sulfur adsorption on the electrochemically active sites on Ni. This study is aimed at predicting the effect of the sulfur poisoning on the performance of SOFC with porous Ni- YSZ anode.
The paper consists of two parts: (i) Modification of the kinetic expression for hydrogen electro-oxidation reaction at anode, and (ii) Implementation of the new kinetic formulation to an existing along-channel twodimensional porous Ni-YSZ half-cell model.
Full Text Source (Subscription or Fee): https://ecs.confex.com/ecs/224/webprogram/Abstract/Paper25417/B1-0346.pdf
Numerical Modeling of the Sulfur Poisoning Effect on the Ni-YSZ Porous Anode of SOFCs
Negar Manafi (a), Kunal Karan (b)
negar.manafi@chee.queensu.ca
kkaran@ucalgary.ca
a Queens-RMC Fuel Cell Research Centre 945 Princess Street, 2nd floor Kingston, Ontario K7L 5L9ıCanada
b Department of Chemical Engineering, University of Calgary, Calgary, Alberta T2N 1N4 Canada
Presence of H2S in the fuel can have adverse effect on the performance of Solid oxide fuel cells (SOFCs) because it can poison the Ni-based anodes. Poisoning occurs by sulfur adsorption on the electrochemically active sites on Ni. This study is aimed at predicting the effect of the sulfur poisoning on the performance of SOFC with porous Ni- YSZ anode.
The paper consists of two parts: (i) Modification of the kinetic expression for hydrogen electro-oxidation reaction at anode, and (ii) Implementation of the new kinetic formulation to an existing along-channel twodimensional porous Ni-YSZ half-cell model.
Full Text Source (Subscription or Fee): https://ecs.confex.com/ecs/224/webprogram/Abstract/Paper25417/B1-0346.pdf
Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co2−xFexO5+δ
Scientific
Reports 3,Article number:2426, doi:10.1038/srep02426, Published 15 August 2013
Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co2−xFexO5+δ
Convergence Technology Research Directorate, Agency for Defence Development, Daejeon, Republic of Korea
Jiyoun Kim
Department of Mechanical Engineering, Dong-Eui University, Busan 614–714, Korea
Jeeyoung Shin
UNIST Central Research Facilities and School of Mechanical and Advanced Materials Engineering, UNIST, Ulsan, 689–798, Korea
Hu Young Jeong
SABIC Technology Center, Riyadh, 11551, Saudi Arabia
YongMan Choi
School of Materials Science and Engineering, Center for Innovative Fuel Cell and Battery Technologies, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA
Meilin Liu
Abstract
Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures.
Authors report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co2−xFexO5+δ, which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm−2 at 600°C, representing an important step toward commercially viable SOFC technologies
Free Full Text Source: http://www.nature.com/srep/2013/130815/srep02426/full/srep02426.html?WT.ec_id=SREP-639-20130902
Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co2−xFexO5+δ
Convergence Technology Research Directorate, Agency for Defence Development, Daejeon, Republic of Korea
Jiyoun Kim
Department of Mechanical Engineering, Dong-Eui University, Busan 614–714, Korea
Jeeyoung Shin
UNIST Central Research Facilities and School of Mechanical and Advanced Materials Engineering, UNIST, Ulsan, 689–798, Korea
Hu Young Jeong
SABIC Technology Center, Riyadh, 11551, Saudi Arabia
YongMan Choi
School of Materials Science and Engineering, Center for Innovative Fuel Cell and Battery Technologies, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA
Meilin Liu
Abstract
Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures.
Authors report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co2−xFexO5+δ, which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm−2 at 600°C, representing an important step toward commercially viable SOFC technologies
Free Full Text Source: http://www.nature.com/srep/2013/130815/srep02426/full/srep02426.html?WT.ec_id=SREP-639-20130902
Stabilizing Nanostructured Solid Oxide Fuel Cell Cathode with Atomic Layer Deposition
Nano
Lett., 2013, 13 (9), pp 4340–4345, DOI: 10.1021/nl402138w
Stabilizing Nanostructured Solid Oxide Fuel Cell Cathode with Atomic Layer Deposition
Yunhui Gong †, Diego Palacio ‡, Xueyan Song *‡, Rajankumar L. Patel §, Xinhua Liang *§, Xuan Zhao †, John B. Goodenough , and Kevin Huang *†
kevin.huang@sc.edu
liangxin@mst.edu
xueyan.song@mail.wvu.edu
† Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina 29201, United States
‡ Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia 26506, United States
§ Department of Chemical and Biological Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409, United States
Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States
Abstract
Authors describe how a highly active but unstable nanostructured intermediate-temperature solid oxide fuel cell cathode, La0.6Sr0.4CoO3-δ (LSCo), can retain its high oxygen reduction reaction (ORR) activity with exceptional stability for 4000 h at 700 °C by overcoating its surfaces with a conformal layer of nanoscale ZrO2 films through atomic layer deposition (ALD).
The benefits from the presence of the nanoscale ALD-ZrO2 overcoats are remarkable: a factor of 19 and 18 reduction in polarization area-specific resistance and degradation rate over the pristine sample, respectively. The unique multifunctionality of the ALD-derived nanoscaled ZrO2 overcoats, that is, possessing porosity for O2 access to LSCo, conducting both electrons and oxide-ions, confining thermal growth of LSCo nanoparticles, and suppressing surface Sr-segregation is the key enabler for the observed stable and active nanostructured cathode.
Full Text Source (Subscription or Fee): http://pubs.acs.org/doi/abs/10.1021/nl402138w
Stabilizing Nanostructured Solid Oxide Fuel Cell Cathode with Atomic Layer Deposition
Yunhui Gong †, Diego Palacio ‡, Xueyan Song *‡, Rajankumar L. Patel §, Xinhua Liang *§, Xuan Zhao †, John B. Goodenough , and Kevin Huang *†
kevin.huang@sc.edu
liangxin@mst.edu
xueyan.song@mail.wvu.edu
† Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina 29201, United States
‡ Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia 26506, United States
§ Department of Chemical and Biological Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409, United States
Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States
Abstract
Authors describe how a highly active but unstable nanostructured intermediate-temperature solid oxide fuel cell cathode, La0.6Sr0.4CoO3-δ (LSCo), can retain its high oxygen reduction reaction (ORR) activity with exceptional stability for 4000 h at 700 °C by overcoating its surfaces with a conformal layer of nanoscale ZrO2 films through atomic layer deposition (ALD).
The benefits from the presence of the nanoscale ALD-ZrO2 overcoats are remarkable: a factor of 19 and 18 reduction in polarization area-specific resistance and degradation rate over the pristine sample, respectively. The unique multifunctionality of the ALD-derived nanoscaled ZrO2 overcoats, that is, possessing porosity for O2 access to LSCo, conducting both electrons and oxide-ions, confining thermal growth of LSCo nanoparticles, and suppressing surface Sr-segregation is the key enabler for the observed stable and active nanostructured cathode.
Full Text Source (Subscription or Fee): http://pubs.acs.org/doi/abs/10.1021/nl402138w
Cathode-supported tubular solid oxide fuel cell technology: A critical review
Journal
of Power Sources, Volume 237, 1 September 2013, Pages 84–97
Cathode-supported tubular solid oxide fuel cell technology: A critical review
Kevin Huang (a), , ,
Subhash C. Singhal (b),
a SmartState Center of Solid Oxide Fuel Cells, Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29201, USA
b Pacific Northwest National Laboratory, Richland, WA 99352, USA
Abstract
Over the decades, Siemens/Westinghouse has developed the cathode-supported tubular solid oxide fuel cell (SOFC) technology and demonstrated the world's first highly efficient, longest running 100-kWe class solid oxide fuel cell/combined heat and power (SOFC/CHP) system and the first highest-efficiency, 220-kWe class pressurized SOFC/gas turbine (PSOFC/GT) hybrid system based on this technology.
Authors review the technology from the perspectives of materials, manufacturing, cell design, system integration and electrical testing. They begin with the basic facts of a SOFC, describing the working principle, advantages, types and applications of SOFCs. Their focus then shifts to cathode-supported tubular SOFCs, providing detailed technical information on engineering innovations, materials advances, manufacturing processes and electrical performance of Siemens/Westinghouse's cylindrical and flattened ribbed tubular cells.
Full Text Source (Subscription or Fee): http://www.sciencedirect.com/science/article/pii/S0378775313003649
Cathode-supported tubular solid oxide fuel cell technology: A critical review
Kevin Huang (a), , ,
Subhash C. Singhal (b),
a SmartState Center of Solid Oxide Fuel Cells, Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29201, USA
b Pacific Northwest National Laboratory, Richland, WA 99352, USA
Abstract
Over the decades, Siemens/Westinghouse has developed the cathode-supported tubular solid oxide fuel cell (SOFC) technology and demonstrated the world's first highly efficient, longest running 100-kWe class solid oxide fuel cell/combined heat and power (SOFC/CHP) system and the first highest-efficiency, 220-kWe class pressurized SOFC/gas turbine (PSOFC/GT) hybrid system based on this technology.
Authors review the technology from the perspectives of materials, manufacturing, cell design, system integration and electrical testing. They begin with the basic facts of a SOFC, describing the working principle, advantages, types and applications of SOFCs. Their focus then shifts to cathode-supported tubular SOFCs, providing detailed technical information on engineering innovations, materials advances, manufacturing processes and electrical performance of Siemens/Westinghouse's cylindrical and flattened ribbed tubular cells.
Full Text Source (Subscription or Fee): http://www.sciencedirect.com/science/article/pii/S0378775313003649
Thermodynamic analysis of SOFC (solid oxide fuel cell)–Stirling hybrid plants using alternative fuels
Energy,
Volume 61, 1 November 2013, Pages 87–97
Thermodynamic analysis of SOFC (solid oxide fuel cell)–Stirling hybrid plants using alternative fuels
Masoud Rokni
Technical University of Denmark, Department of Mechanical Engineering, Thermal Energy System, Copenhagen, Denmark
Abstract
Presents an innovative hybrid power system (∼10 kW) for an average family home. The system is composed of a solid oxide fuel cell (SOFC) on top of a Stirling engine.
The off-gases produced in the SOFC cycle are fed to a bottoming Stirling engine, at which additional power is generated. Authors present results for natural gas (NG), ammonia, di-methyl ether (DME), methanol and ethanol. They compare the effects of key factors, including the utilization factor and the operating conditions under which the fuels are used. The combined system improves the overall electrical efficiency relative to that of a stand-alone Stirling engine or SOFC plant.
Full Text Source (Subscription or Fee): http://www.sciencedirect.com/science/article/pii/S0360544213004921
Thermodynamic analysis of SOFC (solid oxide fuel cell)–Stirling hybrid plants using alternative fuels
Masoud Rokni
Technical University of Denmark, Department of Mechanical Engineering, Thermal Energy System, Copenhagen, Denmark
Abstract
Presents an innovative hybrid power system (∼10 kW) for an average family home. The system is composed of a solid oxide fuel cell (SOFC) on top of a Stirling engine.
The off-gases produced in the SOFC cycle are fed to a bottoming Stirling engine, at which additional power is generated. Authors present results for natural gas (NG), ammonia, di-methyl ether (DME), methanol and ethanol. They compare the effects of key factors, including the utilization factor and the operating conditions under which the fuels are used. The combined system improves the overall electrical efficiency relative to that of a stand-alone Stirling engine or SOFC plant.
Full Text Source (Subscription or Fee): http://www.sciencedirect.com/science/article/pii/S0360544213004921
Anode recirculation behavior of a solid oxide fuel cell system: A safety analysis and a performance optimization
International Journal of Hydrogen Energy, Volume 38, Issue 6, 27 February
2013, Pages 2868–2883
Anode recirculation behavior of a solid oxide fuel cell system: A safety analysis and a performance optimization
Ming Liu (a), A. Lanzini (b), W. Halliop (c), V.R.M. Cobas (d), A.H.M. Verkooijen (a), P.V. Aravind (a)
a Delft University of Technology, Energy Technology Section, Leeghwaterstraat 44, 2628 CA Delft, The Netherlands
b Politecnico di Torino – Energetics Department, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
c Electrochemical Energy Systems and Technologies Ltd., 3314 Heska Court, Inverary, Ontario K0H 1X0, Canada
d Excellence Group in Thermal Power and Distributed Generation, Federal University of Itajubá, Av. BPS 1303, CP 50, Itajubá, Minas Gerais, Brazil
Abstract
Solid oxide fuel cell (SOFC) systems that operate with natural gas typically use anode recirculation. Researchers studied anode recirculation behavior to analyze its effect on safety issues regarding carbon deposition and nickel oxidation and the performance of an SOFC system fed with gasification syngas under steady state operation.
They constructed a detailed model including a recirculation model and an SOFC stack model for the investigation. Results reveal that the entrainment ratio with the gasification syngas is much smaller than that with the natural gas, and the gasification syngas does not have the tendency toward carbon deposition or nickel oxidation under the operating conditions studied.
Full Text Source (Subscription or Fee): http://www.sciencedirect.com/science/article/pii/S0360319912027401
Anode recirculation behavior of a solid oxide fuel cell system: A safety analysis and a performance optimization
Ming Liu (a), A. Lanzini (b), W. Halliop (c), V.R.M. Cobas (d), A.H.M. Verkooijen (a), P.V. Aravind (a)
a Delft University of Technology, Energy Technology Section, Leeghwaterstraat 44, 2628 CA Delft, The Netherlands
b Politecnico di Torino – Energetics Department, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
c Electrochemical Energy Systems and Technologies Ltd., 3314 Heska Court, Inverary, Ontario K0H 1X0, Canada
d Excellence Group in Thermal Power and Distributed Generation, Federal University of Itajubá, Av. BPS 1303, CP 50, Itajubá, Minas Gerais, Brazil
Abstract
Solid oxide fuel cell (SOFC) systems that operate with natural gas typically use anode recirculation. Researchers studied anode recirculation behavior to analyze its effect on safety issues regarding carbon deposition and nickel oxidation and the performance of an SOFC system fed with gasification syngas under steady state operation.
They constructed a detailed model including a recirculation model and an SOFC stack model for the investigation. Results reveal that the entrainment ratio with the gasification syngas is much smaller than that with the natural gas, and the gasification syngas does not have the tendency toward carbon deposition or nickel oxidation under the operating conditions studied.
Full Text Source (Subscription or Fee): http://www.sciencedirect.com/science/article/pii/S0360319912027401
Sulfur Poisoning of Anode-Supported SOFCs under Reformate Operation
Fuel Cells, Special Issue: 10th European SOFC Forum (EFCF2012), Volume
13, Issue 4, pages 487–493, August, 2013
Sulfur Poisoning of Anode-Supported SOFCs under Reformate Operation
A. Weber (1), S. Dierickx (1), A. Kromp (1), E. Ivers-Tiffée (1), (2)
andre.weber@kit.edu
1 Institut für Werkstoffe der Elektrotechnik (IWE), Karlsruher Institut für Technologie (KIT), Adenauerring 20b, 76131 Karlsruhe, Germany
2 DFG Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), D-76131 Karlsruhe, Germany
Abstract
Researchers analyzed the impact of sulfur-poisoning on reforming chemistry and electrochemistry of anode-supported solid oxide fuel cells using electrochemical impedance spectroscopy. Various anode supported cells were operated in hydrogen/steam – as well as simulated reformate – (H2 + H2O + CO + CO2 + N2) fuels containing 0.1–15 ppm of H2S.
Two main features were detected in the DRT: a decreased reaction rate of the electrochemical hydrogen oxidation and a deactivation of the catalytic conversion of CO via the water-gas shift reaction. By comparing the temporal characteristics of the polarization resistance of two different anode supported cells, researchers demonstrated that the accumulated H2S-amount divided by the Ni-surface area inside the anode substrate and anode functional layer determine the onset of the degradation.
Full Text Source (Subscription or Fee): http://onlinelibrary.wiley.com/doi/10.1002/fuce.201200180/abstract
Sulfur Poisoning of Anode-Supported SOFCs under Reformate Operation
A. Weber (1), S. Dierickx (1), A. Kromp (1), E. Ivers-Tiffée (1), (2)
andre.weber@kit.edu
1 Institut für Werkstoffe der Elektrotechnik (IWE), Karlsruher Institut für Technologie (KIT), Adenauerring 20b, 76131 Karlsruhe, Germany
2 DFG Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), D-76131 Karlsruhe, Germany
Abstract
Researchers analyzed the impact of sulfur-poisoning on reforming chemistry and electrochemistry of anode-supported solid oxide fuel cells using electrochemical impedance spectroscopy. Various anode supported cells were operated in hydrogen/steam – as well as simulated reformate – (H2 + H2O + CO + CO2 + N2) fuels containing 0.1–15 ppm of H2S.
Two main features were detected in the DRT: a decreased reaction rate of the electrochemical hydrogen oxidation and a deactivation of the catalytic conversion of CO via the water-gas shift reaction. By comparing the temporal characteristics of the polarization resistance of two different anode supported cells, researchers demonstrated that the accumulated H2S-amount divided by the Ni-surface area inside the anode substrate and anode functional layer determine the onset of the degradation.
Full Text Source (Subscription or Fee): http://onlinelibrary.wiley.com/doi/10.1002/fuce.201200180/abstract
Wednesday, July 10, 2013
Design and technoeconomic performance analysis of a 1 MW solid oxide fuel cell polygeneration system for combined production of heat, hydrogen, and power
CATEGORY: SOFC – SOLID OXIDE FUEL CELLS
Journal of Power Sources, Volume 200, 15 February 2012, Pages 34–44
Design and technoeconomic performance analysis of a 1 MW solid oxide fuel cell polygeneration system for combined production of heat, hydrogen, and power
W.L. Becker a, R.J. Braun a, M. Penev b, M. Melaina b
a Mechanical Engineering Department, Colorado School of Mines, Golden, CO, USA
b Hydrogen Technologies & Systems Center, National Renewable Energy Laboratory, Golden, CO, USA
Abstract
Authors focus on the design and performance estimation of a methane-fueled, 1 MW SOFC combined heat, hydrogen, and power (CHHP) system operating at steady-state. They studied two methods of hydrogen purification and recovery from the SOFC tail-gas: pressure swing adsorption (PSA) and electrochemical hydrogen separation (EHS).
Operating the system to produce additional hydrogen by flowing excess methane into the SOFC subsystem results in increased efficiency for both of the hydrogen separation design concepts. An economic analysis indicates that the expected cost of SOFC-based distributed hydrogen production (4.4 $ kg−1) is on par with other distributed hydrogen production technologies, such as natural gas reforming, electrolysis, and molten carbonate fuel cell CHHP systems. The study illustrates that ‘spark spreads’ (cost of electricity in ¢ kWh−1 minus cost of natural gas in $ MMBtu−1) of five or more offer near-zero or negative hydrogen production costs for distributed SOFC CHHP plants with total installed capital costs near 3950 $ kW.
Full Text Source (Subscription or Fee): http://www.sciencedirect.com/science/article/pii/S0378775311020325
Monday, October 24, 2011
Ceramic Materials for Solid Oxide Fuel Cells
Advances in Ceramics - Synthesis and Characterization, Processing and Specific Applications (2011)
Taroco, H. A., Santos, J. A. F., Domingues, R. Z. and Matencio, T.
Department of Chemistry, Universidade Federal de Minas Gerais, Brasil
Excerpt
Ceramics based on CeO2 are good examples of mixed conduction materials under a reducing atmosphere. The ceramics have an excellent catalytic activity for the hydrocarbon reforming reactions. In addition, they are resistant to carbon deposition. This allows for a direct supply of dry hydrocarbon fuels to the anode.
Free Full Text Source: http://www.intechopen.com/source/pdfs/17615/InTech-Ceramic_materials_for_solid_oxide_fuel_cells.pdf
///////
J. Fuel Cell Sci. Technol. -- June 2011 -- Volume 8, Issue 3, 031014 (8 pages)
Hedvig Paradis, Martin Andersson, Jinliang Yuan, and Bengt Sundén
Department of Energy Sciences, Faculty of Engineering, Lund University, P.O. Box 118, 221 00 Lund, Sweden
Abstract
This study develops an anode-supported SOFC theoretical model to enhance the understanding of the internal reforming reactions and their effects on the transport processes.. To unravel the interaction among internal reforming reactions, momentum, and heat and mass transport, a computational fluid dynamics approach, based on the finite element method, is implemented. The three different steam reforming reaction rates applied were developed and correlated with experimental studies found in the literature. Results indicate that the reaction rates are very fast and differ significantly in size. To fully understand the effect of the parameters connected to the internal reforming reaction, microscale modeling is needed.
Full Text Source (Subscription or Fee): http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFCSAU000008000003031014000001&idtype=cvips&gifs=yes&ref=no
Method For Operating Indirect Internal Reforming Solid Oxide Fuel Cell System
PATENT
European Patent Application EP2278650
Inventors:
Yokoyama, Shou (c/o JX Nippon Oil & Energy Corporation8 ChidorichoNaka-ku, Yokohama-shi Kanagawa 231-0815, JP)
Mizuno, Yasushi (c/o JX Nippon Oil & Energy Corporation8 ChidorichoNaka-ku, Yokohama-shi Kanagawa 231-0815, JP)
Ishida, Tomotaka (c/o JX Nippon Oil & Energy Corporation8 ChidorichoNaka-ku, Yokohama-shi Kanagawa 231-0815, JP)
Application Number: EP20090734655
Publication Date: 01/26/2011
Assignee: JX Nippon Oil & Energy Corporation (6-3, Otemachi 2-chome, Chiyoda-ku Tokyo 100-8162, JP)
Technical Field
Background Art
Usually, a hydrogen-containing gas (reformed gas) generated by reforming a hydrocarbon-based fuel (reforming raw material), such as kerosene and city gas, in a reformer is supplied to a solid oxide fuel cell (hereinafter sometimes referred to as SOFC). In the SOFC, electric power is generated by electrochemically reacting this reformed gas and air. The SOFC is usually operated at a high temperature of 550°C to 1000°C.
Various reactions, such as steam reforming and partial oxidation reforming, are used for reforming. Each of them requires a certain temperature or higher. Therefore, an indirect internal reforming SOFC has been developed in which a reformer is installed near an SOFC (at a position where the reformer receives thermal radiation from the SOFC), and the reformer is heated by radiant heat from the SOFC (see Patent Document 1). Also, in an indirect internal reforming SOFC, an anode off-gas (a gas discharged from the anode of the SOFC) containing a combustible component is combusted in an enclosure (module container) of the indirect internal reforming SOFC, and the reformer is heated using the combustion heat as a heat source (see Patent Document 2).
Not just in SOFCs, but in fuel cells, load following operation may be performed. In other words, the electric power generation output value may be varied according to an electric power requirement value from a consumer. Therefore, methods for controlling the output of a fuel cell with respect to a requested electric power value are studied (see Patent Documents 3 and 4).
Patent Document 3 describes a fuel cell electric power generation system including a fuel processing apparatus for reforming a reforming raw material to produce a fuel gas containing hydrogen as a main component, a fuel cell for generating electric power using the above fuel gas, an electric power generation amount measuring means for measuring the amount of electric power generation of the fuel cell, and a control part for controlling the speed of increase of the amount of electric power generation according to the amount of electric power generation measured by the electric power generation amount measuring means, when increasing the amount of electric power generation. This art aims to provide a method for generating electric power by a fuel cell, in which the stability during switching from low load operation to high load operation and during start-up is improved, and the switching time and the start-up time can be reduced.
Patent Document 4 describes controlling electric power generation according to a convergent type requested electric power following method in which a tentative electric current value or a tentative voltage value is calculated according to a requested electric power value, whether or not an effective electric power value corresponds to the requested electric power value suitably enough is determined after such a tentative electric current value or tentative voltage value is set, and the tentative electric current value or the tentative voltage value is appropriately increased or decreased when the effective electric power value does not correspond to the requested electric power value suitably enough. This art aims to provide a fuel cell system in which electric power generation can be controlled by controlling the fuel gas feed rate and the oxygen gas feed rate suitably enough, according to a requested electric power value, without installing a heating means for maintaining the temperature inside the electric power generation and combustion chamber substantially constant, and therefore without unnecessarily increasing the initial equipment cost and the operation cost.
Summary of the Invention
Problems to be Solved by the Invention
In an indirect internal reforming SOFC system, in a case where the electric power generation output value is increased according to a requested electric power value from a consumer, when the amount of electric power generation is instantaneously increased largely, the amount of combustion in the combustion region decreases, and the combustion heat generated in the combustion region becomes small. Therefore, the temperature of the reformer may decrease rapidly. When the temperature of the reformer decreases, the reformer cannot maintain the temperature required for reforming the fuel, and therefore, it is feared that unreformed fuel enters the cell and adversely affects the cell.
For example, in the cases of steam reforming and autothermal reforming in which an endothermic reaction is dominant, even if an attempt is made to address this fear by increasing the fuel input simultaneously with the increase of the electric power generation output value to increase the amount of reforming, the increase of the amount of reforming temporarily accelerates the decrease of the reformer temperature, before the temperature of the reformer is recovered by the increase of the amount of combustion in the combustion region, and the reformer temperature may fall below a reformer temperature desired to be maintained. On the other hand, in the case of a system using partial oxidation reforming in which an exothermic reaction is dominant, the reformer temperature may locally increase significantly by the increase of the amount of combustion on the reforming catalyst.
Not only when the electric power generation output value of the SOFC is increased, but also when the operation is continued with the electric power generation output value fixed, the temperature of the reformer may decreases due to some cause. Also in such a case, it is desired to avoid that unreformed fuel flows into the interior of the SOFC, or avoid that the reformer temperature locally increases significantly.
It is an object of the present invention to provide a method for operating an indirect internal reforming SOFC system, in which the temperature of a reformer can be maintained stably and suitably.
Free Full Text Source: http://www.freepatentsonline.com/EP2278650.html
Heat exchanger for fuel cell stack
PATENT
Inventors: Partho Sarkar, Hongsang Rho, Luis Yamarte, Gary Kovacik
Original Assignee: Alberta Innovates - Technology Futures
Patent number: 7892684
Issue date: Feb 22, 2011
Application number: 11/454,617
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
There is a class of fuel cells that operate at high elevated temperatures. One type of such fuel cell is a solid oxide fuel 2o cell (SOFC), which comprises two electrodes (anode and cathode) separated by a ceramic, solid-phase electrolyte. To achieve adequate ionic conductivity in such a ceramic electrolyte, the SOFC operates at elevated temperatures typically in the order of about 1000° C. The material in typical SOFC 25 electrolytes is a fully dense (i.e. non-porous) yttria-stabilized zirconia (YSZ) which is an excellent conductor of negatively charged oxygen (oxide) ions at high temperatures. Typical SOFC anodes are made from a porous nickel/zirconia cermet while typical cathodes are made from magnesium doped lan- 30 thanum manganate (LaMn03), or a strontium doped lanthanum manganate (also known as lanthanum strontium manganate (LSM)). In operation, hydrogen or carbon monoxide (CO) in a fuel stream passing over the anode reacts with oxide ions conducted through the electrolyte to produce water and/ 35 or C02 and electrons. The electrons pass from the anode to outside the fuel cell via an external circuit, through a load on the circuit, and back to the cathode where oxygen from an air stream receives the electrons and is converted into oxide ions which are injected into the electrolyte. The SOFC reactions 40 that occur include:
H2+0"-»H20+2(r CO+0"-»C02+2(T 45
CH4+40"-»2H20+C02+8(r Anode reaction:
02+4e~^20= Cathode reaction:
Known SOFC designs include planar and tubular fuel cells. Tubular fuel cells can be grouped together into a stack to 50 increase output. For example, a tubular stack design published by Siemens Westinghouse Power Generation features tubular fuel cells arranged in a side-by-side rectangular array. The large size of the Siemens Westinghouse fuel cells (typically >5 mm diameter) and the relatively low power density 55 (power output per unit volume) of the stack design makes such a fuel cell stack impractical for small scale applications such as portable electronic devices. Applicant's own PCT application no. PCT/CA01/00634 discloses a method of manufacturing small diameter tubular SOFC that are particu- 60 larly suitable for small-scale applications. Such fuel cells can be embedded in a solid phase foam matrix to form a stack, as disclosed in Applicant's PCT application no. PCT/CA03/ 00216.
One of the challenges for SOFC systems is efficient ther- 65 mal management. It is well known that larger SOFC systems (>5 kW) typically generate more heat than needed to keep the fuel cell stack at a suitable operating temperature, and therefore, need efficient heat removal techniques to prevent overshooting the temperature of the stack. In contrast, smaller SOFC systems generate less heat and consideration must be given in certain situations to retaining enough heat to keep the stack sufficiently warm. When a stack's size is reduced, the stack's ratio of outer surface area to volume tends to increase, which results in an increase in potential heat loss relative to rated power output. As SOFCs have to operate at high elevated temperatures, it is important to keep the stack and incoming reactant gases at suitable elevated operating temperatures. Inadequate thermal management can result in significant amounts of generated heat to be lost, such that heat from an external source must be used to heat the incoming reactant streams as well as to keep the stack within its operating temperature range. Such external heat sources constitute a parasitic load on the SOFC system which reduces the operating efficiency of the system.
A heat exchanger design known as a "Swiss roll" was conceived about thirty years ago by Felix Weinberg of Imperial College London. This heat exchanger had a supply fuel flowing in a channel running parallel with a channel carrying hot exhaust. The channels were rolled into a spiral, which had the effect of substantially increasing the internal surface area that was exchanging heat, as well as minimizing external surfaces that were losing heat. More recently, a team at the California Institute of Technology led by Sossina Haile has experimented with installing a fuel cell within a Swiss roll heat exchanger. Known Swiss roll heat exchangers are typically rigid structures having complex geometries that are fabricated from high-temperature tolerant materials such as titanium and ceramic. The manufacture of such heat exchangers and the integration of the fuel cell within the heat exchanger are laborious and not commercially practical for large scale manufacture.
SUMMARY OF THE INVENTION
It is a general object of the invention to provide effective thermal management of a fuel cell stack, and in particular, to effectively heat reactant gases using the heat created during electricity generation in the stack. It is a specific objective of the invention to provide a heat exchanger for a fuel cell stack that effectively transfers heat from exhaust reactant to supply reactant, provides thermal insulation to the stack, and is relatively cost-effective to manufacture.
According to one aspect of the invention, there is provided a fuel cell system comprising a fuel cell stack and a heat exchanger wrapped around the fuel cell stack. The stack has at least one fuel cell that operates at elevated temperatures above 150° C; a suitable such fuel cell is a solid oxide fuel cell (SOFC). The SOFC can be a tubular design having a pair of concentrically arranged electrode layers sandwiching a concentrically arranged electrolyte layer. The heat exchanger comprises a flexible thermally-conductive first layer and a flexible thermally-conductive second layer overlapping the first layer. The two layers are wrapped around the stack such that annular reactant supply and exhaust channels are defined with heated exhaust reactant flowing through the exhaust channel and heat radiating from the stack heating supply reactant flowing through the supply channel. In addition to exchanging heat between supply and exhaust reactant, the heat exchanger also serves to provide thermal insulation for the stack.
The heat exchanger can be a cross-flow type heat exchanger with the supply and exhaust channels respectively having an inlet and an outlet at the outer periphery of the heat exchanger, and respectively having an outlet and an inlet at the interface between the heat exchanger and the stack. The first and second layers can be rectangular sheets having a longitudinal dimension corresponding to the length of the fuel cell, and a transverse dimension corresponding to the 5 number of selected windings the heat exchanger wraps around the stack. The heat exchanger can wind one or more times around the stack; the transverse dimension can be selected so that there are enough windings around the stack that enough heat is absorbed by the layers that the outer 10 periphery of the heat exchanger is cool enough for human touch. The two heat exchanger layers can be of unequal transverse lengths, such that one of the layers can wrap at least one additional winding around the stack more than the other layer. 15
The reactant flowing through the supply and exhaust channels can be either air or fuel. When air, the outer electrodes of the fuel cells in the stack are cathodes, and when fuel, the outer electrodes are anodes. Alternatively, the heat exchanger can have multiple supply channels in which one of the supply 20 channels carries fuel and another carries air; the fuel supply channel is fluidly coupled to the anode side of the fuel cell stack, and the air supply channel is fluidly coupled to the cathode side of the fuel cell stack. In this case, the exhaust channel can be configured to carry a mixture of exhaust air 25 and unreacted fuel. The fuel supply channel can be coated with a reforming catalyst or filled with a porous reforming catalyst or a porous catalyst support coated with a reforming catalyst so that hydrocarbon fuel traveling through the fuel supply channel is reformed. 30
The heat exchanger can further comprise elongated flexible spacers mounted to a surface of each layer; the spacers cooperate with the layers to define the supply and exhaust channels when the layers are wrapped around the stack. Alternatively, the channels can be formed directly into the layers 35 themselves. The heat exchanger can also include a perforated distribution layer that surrounds the stack and is located inside of the first and second layers. The distribution layer is in fluid communication with an outlet of the supply channel such that supply reactant discharged from the supply channel 40 is radially distributed by the distribution layer to the stack. A perforated metal foil or a porous metal tube is particularly suitable as the distribution layer. This metal foil or tube can be coated with a heat reflective coating, or first coated with a glass, glass-ceramic, or ceramic thermal barrier coating then 45 optionally with a heat reflective coating.
The stack can be a plurality of tubular fuel cells that are embedded in spaced side-by-side arrangement within a solid phase porous foam matrix. In such case, the stack has an exhaust oxidant collector and the fuel cells surround the col- 50 lector; reactant supply air is fed through the distribution layer to the outer periphery of the stack, and unreacted air is collected by the collector located within the stack. The collector is fluidly coupled to an inlet of the reactant exhaust channel such that exhaust oxidant collected by the collector is trans- 55 mitted to the exhaust channel.
Instead of two separate sheets, the heat exchanger layers can be formed from a single folded metal foil sheet. The metal foil sheet can be the same material as used for the distribution layer. 60
The heat exchanger can have more than two layers. For example, the heat exchanger can further comprise a flexible thermally conductive third layer that overlaps and is spaced from the second layer, such that when wrapped around the stack with the first and second layers, a third reactant channel 65 is formed. Alternatively, the third layer can be a flexible thermally insulating layer that when wrapped around the stack with the first and second layers, contributes to retaining heat within the stack. This insulating layer can be a ceramic thermal insulating blanket, an aerogel blanket, or a sealed vacuum channel.
Free Full Text Source: http://www.google.com/patents/about?id=5_ooAQAAEBAJ&dq=solid+oxide+fuel+cell+hydrocarbon
Conversion Of Carbon Dioxide To Methanol And/Or Dimethyl Ether Using Bi-Reforming Of Methane Or Natural Gas
PATENT
Inventors: George A. Olah, G. K. Surya Prakash
Original Assignee: University of Southern California
Patent number: 7906559
Issue date: Mar 15, 2011
Application number: 11/850,501
BACKGROUND
Hydrocarbons are essential in modem life. Hydrocarbons are used as fuel and raw material in various fields, including the chemical, petrochemical, plastics, and rubber industries. Fossil fuels, such as coal, oil and natural gas, are composed of hydrocarbons with varying ratios of carbon to hydrogen. Despite their wide application and high demand, fossil fuels also have limitations and disadvantages, particularly due to 2o their finite reserve, irreversible combustion and contribution to air pollution (and thus to global warming). Regardless of these problems the more efficient use of still existing natural gas sources is highly desirable. Further new sources and ways for recyclable and environmentally benign carbon fuels are 25 needed.
One alternative frequently mentioned non-carbon fuel is hydrogen, and its use in the so-called "hydrogen economy." Hydrogen is thought to be beneficial as a clean fuel, producing only water when combusted. Free hydrogen, however, is 30 not a natural primary energy source on earth, due to its incompatibility with atmospheric oxygen. It must be generated from hydrocarbons or water is a highly energy-consuming process. Further, as hydrogen is produced from hydrocarbons or coal, any claimed benefit of hydrogen as a clean fuel is outweighed 35 by the fact that its generation, mainly by reforming of natural gas, oil or coal to synthesis gas ("syn-gas" a mixture of CO and H2), or the generation of electricity for the electrolysis of water is far from clean, besides hydrogen is difficult and costly to handle, transport and distribute. As it is extremely 40 light, volatile and potentially explosive, it requires high-pressure equipment. The needed non-existent infrastructure also necessitates special materials to minimize diffusion and leakage, and extensive safety precautions to prevent explosions.
The continued importation of natural gas from far away 45 and frequently difficult to access locations also necessitates its safe storage and transportation particularly when involving to LNG (liquefied natural gas). This necessities transporting LNG at low temperatures in its liquid form over the seas exposing it to serious environmental and safety hazards 50 including terrorism. It is suggested that a more practical and safe alternative for LNG is methanol, or dimethyl ether (DME), which are readily produced from natural gas (vide infra). Methanol, CH3OH, is the simplest liquid oxygenated hydrocarbon, differing from methane (CH4) by a single addi- 55 tional oxygen atom. Methanol, also called methyl alcohol or wood alcohol, is a colorless, water-soluble liquid with a mild alcoholic odor. It is easy to store and transport. It freezes at -97.6° C, boils at 64.6° C, and has a density of 0.791 at C. 60
Methanol is a convenient safe liquid easily obtained from existing coal or natural gas sources via methods developed and practiced since the 1920's. However, these methods using conversion (reforming) of coal and subsequently natural gas to syn-gas (a mixture of H2 and CO) are highly energy con- 65 suming and produce large amount of C02 as a by-product. This is notably an economic disadvantage but also represents a serious environmental problem by increasing a main greenhouse gas (causing global warming).
Methanol not only represent a convenient and safe way to store and transport energy, but together with its derived product dimethyl ether (DME), is an excellent fuel. Dimethyl ether is easily obtained from methanol by dehydration or from methane (natural gas) with C02 via bi-reforming. It is a particularly effective fuel for diesel engines because of its high cetane number and favorable combustion properties. Methanol and dimethyl ether exceedingly blend well with gasoline or diesel oil to be used as fuels in internal combustion engines or electricity generators. One of the most efficient use of methanol is in fuel cells, particularly in direct methanol fuel cells (DMFC), in which methanol is directly oxidized with air to carbon dioxide and water while producing electricity.
Contrary to gasoline, which is a complex mixture of many different hydrocarbons and additives, methanol is a single simple chemical compound. It contains about half the energy density of gasoline, meaning that two liters of methanol provide the same energy as a liter of gasoline. Even though methanol's energy content is lower, it has a higher octane rating of 100 (average of the research octane number (RON) of 107 and motor octane number (MON) of 92), which means that the fuel/air mixture can be compressed to a smaller volume before being ignited. This allows the engine to run at a higher compression ratio of 10-11 to 1 more efficiently than the 8-9 to 1 ratio of a gasoline-powered engine. Efficiency is also increased by methanol's (and oxygenate) higher "flame speed," which enables faster, more complete fuel combustion in the engines. These factors explain the high efficiency of methanol despite its lower energy density than gasoline. Further, to render methanol more ignitable even under the most frigid conditions, methanol is mixed with gasoline, and other volatile components or with a device to vaporize or atomize methanol. For example, an effective automotive fuel comprised by adding methanol to gasoline with the fuel having a minimum gasoline content of at least 15% by volume (M85 fuel) so that it can readily start even in low temperature environments were commercially used in the US in the 1980's. M20 fuel (with 20 volume % methanol) is also being introduced. Similarly, dimethyl ether (DME) mixed with diesel oil or in household use as a substitute of natural gas or LPG is of commercial interest. These mixtures are not only efficient fuels but conserve or replace decreasing oil resources. The amount of methanol or dimethyl ether added can be determined depending upon the specific condition and needs.
Methanol has a latent heat of vaporization of about 3.7 times higher than gasoline, and can absorb a significantly larger amount of heat when passing from liquid to gaseous state. This helps remove heat away from the engine and enables the use of an air-cooled radiator instead of a heavier water-cooled system. Thus, compared to a gasoline-powered car, a methanol-powered engine provides a smaller, lighter engine block, reduced cooling requirements, and better acceleration and mileage capabilities. Methanol and DME are also more environment-friendly than gasoline or diesel oil, and produce low overall emissions of air pollutants such as certain hydrocarbons, NOx, S02 and particulates.
Methanol is also one of the safest fuels available. Compared to gasoline, methanol's physical and chemical properties significantly reduce the risk of fire. Methanol has lower volatility, and methanol vapor must be four times more concentrated than gasoline for ignition to occur. Even when ignited, methanol burns about four times slower than gasoline, releases heat only at one-eighth the rate of gasoline fire, and is far less likely to spread to surrounding ignitable materials because of the low radiant heat output. It has been estimated by the EPA that switching from gasoline to methanol wouldreduce incidence of fuel-related fire by 90%. Methanol burns with a colorless flame, but additives can solve this problem. As methanol is completely miscible with water not only it is environmentally readily decomposed in nature but in contrast to ethanol there are no strict requirements needed to keep it dry to avoid phase separation from gasoline.
Methanol and/or DME also provide an attractive and more environmentally-friendly alternative to diesel fuel. They do not produce smoke, soot, or particulates when combusted, in contrast to diesel fuel, which generally produces polluting particles during combustion. They also produce very low emissions of NOx because they burn at a lower temperature than diesel. Furthermore, they have a significantly higher vapor pressure compared to diesel fuel, and the higher volatility allows easy start even in cold weather, without producing smoke typical of cold start with a conventional diesel engine. If desired, additives or ignition improvers, such as octyl nitrate, tetrahydrofurfuryl nitrate, peroxides or higher alky 1 ethers, can be added to bring methanol' s cetane rating to the level closer to diesel. Methanol is also used in the manufacture of biodiesel fuels by esterification of fatty acids.
As mentioned closely related and derived from methanol, and highly desirable alternative fuel is dimethyl ether. Dimethyl ether (DME, CH3OCH3), the simplest of all ethers, is a colorless, nontoxic, non-corrosive, non-carcinogenic and environmentally friendly chemical that is mainly used today as an aerosol propellant in spray cans, in place of the banned CFC gases. DME has a boiling point of -25° C, and is a gas under ambient conditions. DME is, however, easily handled as liquid and stored in pressurized tanks, much like liquefied petroleum gas (LPG). The interest in dimethyl ether as alternative fuel lies in its high cetane rating of 55 to 60, which is much higher than that of methanol and is also higher than the cetane rating of 40 to 55 of conventional diesel fuels. The cetane rating indicates that DME can be effectively used in diesel engines. Advantageously, DME, like methanol, is clean burning, and produces no soot particulates, black smoke or S02, and only very low amounts of NOx and other emissions even without after-treatment of its exhaust gas.
Free Full Text Source: http://www.google.com/patents/about?id=LXVQAQAAEBAJ&dq=solid+oxide+fuel+cell+hydrocarbon
Subscribe to:
Posts (Atom)