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Proton exchange membranes
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Proceedings Papers
Proc. ASME. ES2012, ASME 2012 6th International Conference on Energy Sustainability, Parts A and B, 217-226, July 23–26, 2012
Paper No: ES2012-91471
Abstract
Pacific Northwest National Laboratory (PNNL) is working with industry to independently monitor up to fifteen distinct 5 kilowatt-electric (kWe) combined heat and power (CHP) high temperature (HT) proton exchange membrane (PEM) fuel cell systems (FCSs) installed in light commercial buildings. This research paper discusses an evaluation of the first six months of measured performance data acquired at a one-second sampling rate from real-time monitoring equipment attached to the FCSs at building sites. Engineering performance parameters are independently evaluated. Based on an analysis of the first few months of measured operating data, FCS performance is consistent with manufacturer-stated performance. Initial data indicate that the FCSs have relatively stable performance and a long term average production of about 4.57 kWe of power. This value is consistent with, but slightly below, the manufacturer’s stated rated electric power output of 5 kWe. The measured system net electric efficiency has averaged 33.7%, based on the higher heating value (HHV) of natural gas fuel. This value, also, is consistent with, but slightly below, the manufacturer’s stated rated electric efficiency of 36%. The FCSs provide low-grade hot water to the building at a measured average temperature of about 48.4°C, lower than the manufacturer’s stated maximum hot water delivery temperature of 65°C. The uptime of the systems is also evaluated. System availability can be defined as the quotient of total operating time compared to time since commissioning. The average values for system availability vary between 96.1 and 97.3%, depending on the FCS evaluated in the field. Performance at Rated Value for electrical efficiency (PRV eff ) can be defined as the quotient of the system time operating at or above the rated electric efficiency and the time since commissioning. The PRV eff varies between 5.6% and 31.6%, depending on the FCS field unit evaluated. Performance at Rated Value for electrical power (PRV p ) can be defined as the quotient of the system time operating at or above the rated electric power and the time since commissioning. PRV p varies between 6.5% and 16.2%. Performance at Rated Value for electrical efficiency and power (PRV t ) can be defined as the quotient of the system time operating at or above both the rated electric efficiency and the electric power output compared to the time since commissioning. PRV t varies between 0.2% and 1.4%. Optimization to determine the manufacturer rating required to achieve PRV t greater than 80% has been performed based on the collected data. For example, for FCS unit 130 to achieve a PRV t of 95%, it would have to be down-rated to an electrical power output of 3.2 kWe and an electrical efficiency of 29%.The use of PRV as an assessment metric for FCSs has been developed and reported for the first time in this paper. For FCS Unit 130, a 20% decline in electric power output was observed from approximately 5 kWe to 4 kWe over a 1,500 hour period between Dec. 14th 2011 and Feb. 14th 2012.
Proceedings Papers
Proc. ASME. ES2012, ASME 2012 6th International Conference on Energy Sustainability, Parts A and B, 885-890, July 23–26, 2012
Paper No: ES2012-91338
Abstract
In this study, a novel flow-based method is presented to place catalytic nanoparticles into a reactor by solgelation of a porous ceramic consisting of copper-based nanoparticles, silica sand, ceramic binder, and a gelation agent. This method allows for the placement of a liquid precursor containing the catalyst into the final reactor geometry without the need of impregnating or coating of a substrate with the catalytic material. The so generated foam-like porous ceramic shows properties highly appropriate for use as catalytic reactor material, e.g., reasonable pressure drop due to its porosity, high thermal and catalytic stability, and excellent catalytic behavior. The catalytic activity of micro-reactors containing this foam-like ceramic is tested in terms of their ability to convert alcoholic biofuel (e.g. methanol) to a hydrogen-rich gas mixture with low concentrations of carbon monoxide (up to 75% hydrogen content and less than 0.2% CO, for the case of methanol). This gas mixture is subsequently used in a low-temperature fuel cell, converting the hydrogen directly to electricity. A low concentration of CO is crucial to avoid poisoning of the fuel cell catalyst. Since conventional Polymer Electrolyte Membrane (PEM) fuel cells require CO concentrations far below 100 ppm and since most methods to reduce the mole fraction of CO (such as Preferential Oxidation or PROX) have CO conversions of up to 99%, the alcohol fuel reformer has to achieve initial CO mole fractions significantly below 1%. The catalyst and the porous ceramic reactor of the present study can successfully fulfill this requirement. The results of the present study confirm that product gas mixtures with up to 75% hydrogen content and less than 0.2% CO content can be achieved, which is an excellent result. The reactor temperature can be kept as low as 220°C while obtaining a methanol conversion of up to 70%. The used PROX catalyst showed selective CO conversion rates above 99.5% for temperatures between 80 and 100°C in presence of large molar fractions of H 2 O and CO 2 .
Proceedings Papers
Proc. ASME. ES2011, ASME 2011 5th International Conference on Energy Sustainability, Parts A, B, and C, 1631-1640, August 7–10, 2011
Paper No: ES2011-54389
Abstract
The present study investigates the feasibility, efficiency, and system design of a hybrid solar system generating electric power for stationary applications such as residential buildings. The system is fed by methanol and combines methanol steam reforming and Proton Exchange Membrane (PEM) fuel cells with solar collectors to generate the required heat for the steam reforming. The synergies of these technologies lead to a highly efficient system with significantly larger power densities compared to conventional systems and generate tremendous advantages in terms of installation and operation costs. The present investigation describes the entire proposed system and its components and presents first analytical, numerical, and experimental results of a larger project to prove the feasibility of such a system by analyzing first a bench test demonstrator generating around 10 W of electric power and finally a prototype for an entire single family household. It is shown that the methanol-to-electricity efficiency of the entire system is above 50%.
Proceedings Papers
Proc. ASME. ES2010, ASME 2010 4th International Conference on Energy Sustainability, Volume 1, 879-888, May 17–22, 2010
Paper No: ES2010-90255
Abstract
The idea of this study is to investigate possibilities to use sunlight as the main energy source to generate and store electrical energy via different methods and technologies. Several systems consisting of photovoltaics, photoelectrolytic converters and solarthermal reformers in combination with fuel cells have been investigated in terms of efficiency and costs. A simple energetic approach would not account for these different kinds of energy and their differing availabilities (radiant, thermal, chemical, and electrical energy). To consider different forms of energy and compare them in a fair manner, exergy as the useful part of energy (the part that can theoretically be completely converted to work) provides a perfect instrument for dealing with complex energy conversion systems. In this study, four different scenarios have been investigated: Scenario A describes the direct conversion of sunlight to electricity by photovoltaics. The electric power is used in a Polymer Electrolyte Membrane (PEM) electrolyzer to split water to hydrogen which is stored in a pressure tank. A PEM fuel cell converts hydrogen to electricity on demand. Scenario B deals with a photoelectrolytic cell splitting water to hydrogen by solar irradiation combined with a storage tank and a fuel cell. In Scenario C, solar radiation is converted by photovoltaic cells to electricity which is stored in different types of batteries. Scenario D combines a methanol steam reformer heated by solar power with a PEM fuel cell to generate electricity. The reformate gas mixture can be stored at elevated pressure in a gas tank. In contrast to routes A–C, scenario D has two exergy inputs: Solar radiation and chemical exergy in form of methanol as fuel. All systems are analyzed for an average day in July and February in Central California, including a storage device sufficient to store the energy for one week. Scenario D reaches an overall exergetic efficiency of more than 25% in summer at the expense of an additional exergy input in the form of methanol. The exergetic efficiency of scenario C amounts to 10–17% in summer (4–6% in winter) depending on the battery type and scenarios A and B achieve less than 10% efficiency even in summer. The systems of scenarios A and C would cost around $20k–$45k per 1 kW average electricity generation during the day in July. Scenario D leads to significantly lower costs and scenario B is the most expensive design due to the current immaturity of photoelectrolytic devices.
Proceedings Papers
Proc. ASME. ES2010, ASME 2010 4th International Conference on Energy Sustainability, Volume 1, 1055-1061, May 17–22, 2010
Paper No: ES2010-90387
Abstract
This paper deals with the construction and implementation of the Off-Grid Zero Emissions Building (OGZEB), a project undertaken by the Energy Sustainability Center (ESC), formally the Sustainable Energy Science and Engineering Center (SESEC), at the Florida State University (FSU). The project involves the design, construction and operation of a completely solar-powered building that achieves LEED-NC (Leadership in Energy and Environment Design-New Construction) platinum certification. The 1064 square foot building is partitioned such that 800 square feet is a two bedroom, graduate student style flat with the remaining 264 square feet serving as office space. This arrangement allows the building to serve as an energy efficient model for campus designers in student living and office space. The building also serves as a prototype for developing and implementing cutting edge, alternative energy technologies in both residential and commercial settings. For example, hydrogen is used extensively in meeting the energy needs of the OGZEB. In lieu of high efficiency batteries, the excess electricity produced by the buildings photovoltaic (PV) panels is used to generate hydrogen via water electrolysis for long term energy storage. The hydrogen is stored on-site until needed for either generating electricity in a Proton Exchange Membrane (PEM) fuel cell stack or combusted in natural gas appliances that have been modified for hydrogen use. The use of hydrogen in modified natural gas appliances, such as an on-demand hot water heater and cook top, is unique to the OGZEB. This paper discusses the problems and solutions that arose during construction and includes detailed schematics of the OGZEBs energy system.
Proceedings Papers
Proc. ASME. ES2008, ASME 2008 2nd International Conference on Energy Sustainability, Volume 2, 483-488, August 10–14, 2008
Paper No: ES2008-54307
Abstract
A model is presented to simulate the energy production from a solar photovoltaic (PV) array in Southern Nevada and its energy produced for hydrogen production at a hydrogen filling station. A solar PV array composed of four single axis tracking units provides power to a Proton Exchange Membrane (PEM) electrolyzer, which produces hydrogen that is stored on site for use in hydrogen converted vehicles. The model provides the ability to predict possible hydrogen production at the site, as well as the amount of hydrogen required to sustain a prescribed level of vehicle usage. Together, these results made it possible to determine the energy required to produce sufficient hydrogen to sustain the vehicles, and the percentage of that energy generated by the solar PV array. For an average year in Las Vegas and a travel requirement of 57 miles/day, this percentage was found to be 33 percent. This simulation has the potential to be modified for different locations, array size, amount of storage, or usage requirement.
Proceedings Papers
Proc. ASME. ES2008, ASME 2008 2nd International Conference on Energy Sustainability, Volume 1, 537-547, August 10–14, 2008
Paper No: ES2008-54197
Abstract
The present work presents a three-dimensional, non-isothermal computational model of PEMFC, implemented in the CFD code Fluent. The model accounts for all major transport phenomena, including: water and proton transport through the membrane; electrochemical reaction; transport of electrons; transport and phase change of water in the gas diffusion electrodes; diffusion of multi-component gas mixtures in the electrodes; and mass transport in the gas flow channels. First, the polarization behavior or steady state performance of the PEMFC has been simulated and then the transient response subjected to a variable load has been studied. In the steady state analysis, the polarization curves, obtained by single phase and two-phase numerical simulations, have been compared with the experimental data given in literature. A good agreement is evident for the curve given by the two-phase simulations, while the single-phase model is unable to reproduce the experimental data at the high current densities. A parametric study has been done to validate the model and the predicted polarization curves have been compared with experiments. Finally unsteady simulations have been performed. The effect of the rate of change in cell voltage on cell performance for three different rates have been shown. The transient results demonstrate that current density overshoots the stabilized state value when cell voltage is abruptly decreased.
Proceedings Papers
Proc. ASME. ES2007, ASME 2007 Energy Sustainability Conference, 573-580, July 27–30, 2007
Paper No: ES2007-36170
Abstract
This paper deals with the Off-Grid Zero Emissions Building (OGZEB), a project undertaken by the Sustainable Energy Science & Engineering Center (SESEC) at Florida State University (FSU). The project involves the design, construction and operation of a completely solar-powered building that achieves LEED-NC (Leadership in Energy and Environment Design-New Construction) platinum certification. The resulting 1000 square foot building will be partitioned such that 750 square feet will be a two bedroom, graduate student style flat with the remaining 250 square feet serving as office space. This arrangement will allow the building to serve as an energy efficient model for campus designers in student living and office space. The building will also serve as a prototype for developing and implementing cutting edge, alternative energy technologies in both residential and commercial settings. For example, hydrogen will be used extensively in meeting the energy needs of the OGZEB. In lieu of high efficiency batteries, the excess electricity produced by the building’s photovoltaic (PV) panels will be used to generate hydrogen via water electrolysis. The hydrogen will be stored on-site until needed for either generating electricity in a Proton Exchange Membrane (PEM) fuel cell stack or combusted in natural gas appliances that have been modified for hydrogen use. Although commercial variants already exist, a highly efficient water electrolysis device and innovative PEM fuel cell are currently under development at SESEC and both will be implemented into the OGZEB. The use of hydrogen in modified natural gas appliances, such as an on-demand hot water heater and cook top, is unique to the OGZEB.
Proceedings Papers
Proc. ASME. ES2007, ASME 2007 Energy Sustainability Conference, 31-38, July 27–30, 2007
Paper No: ES2007-36108
Abstract
Numerical simulations of proton exchange water electrolysis for hydrogen production were performed for the purpose of examining the phenomena occurring within the proton exchange membranes (PEM) water splitting cell. A two-dimensional steady-state isothermal model of the cell has been developed. Finite element method was used to solve the multicomponent transport model coupled with flow in porous medium, charge balance and electrochemical kinetics. The Maxwell-Stefan equation is applied for the multi-component diffusion and convection in water distribution electrodes. The Butler-Volmer kinetic equation is used to obtain the local current density distribution at the catalyst reactive boundaries. Darcy’s law was applied for the flow of species in the porous electrodes. Parametric studies are performed based on appropriate mass balances, transport, and electrochemical kinetics applied to the electrolysis cell. There are significant current spikes present at the corners of the current collector. The current density varies significantly in the cell, being highest at the corners of the current collector. As the water on the anode side flows from the inlet to the outlet, the mass fraction of oxygen increases. This is the effect of oxygen concentration due to the effect oxidation of water. On the cathode side, as the mass fraction of water decreases there is little variation in the hydrogen mass fraction content due to the effect of hydrogen reduction.