The viability of thermochemically-derived biofuels can be greatly enhanced by reducing the process parasitic energy loads. Integrating renewable power into biofuels production is one method by which these efficiency drains can be eliminated. There are a variety of such potentially viable "hybrid-renewable" approaches; one is to integrate concentrated solar power (CSP) to power biomass-to-liquid fuels (BTL) processes. Barriers to CSP integration into BTL processes are predominantly the lack of fundamental kinetic and mass transport data to enable appropriate systems analysis and reactor design. A novel design for the reactor has been created that can allow biomass particles to be suspended in a flow gas, and be irradiated with a simulated solar flux. Pyrolysis conditions were investigated and a comparison between solar and non-solar biomass pyrolysis was conducted in terms of product distributions and pyrolysis oil quality. A novel method was developed to analyse pyrolysis products, and investigate their stability.
Automakers and fuel providers have made public commitments to commercialize light duty fuel cell electric vehicles and fueling infrastructure in select US regions beginning in 2014. The development, implementation, and advancement of meaningful codes and standards is critical to enable the effective deployment of clean and efficient fuel cell and hydrogen solutions in the energy technology marketplace. Metrics pertaining to the development and implementation of safety knowledge, codes, and standards are important to communicate progress and inform future R&D investments. This document describes the development and benchmarking of metrics specific to the development of hydrogen specific codes relevant for hydrogen refueling stations. These metrics will be most useful as the hydrogen fuel market transitions from pre-commercial to early-commercial phases. The target regions in California will serve as benchmarking case studies to quantify the success of past investments in research and development supporting safety codes and standards R&D.
The US Department of Energy (DOE) Energy Efficiency and Renewable Energy (EERE) Office of Fuel Cell Technologies Office (FCTO) is establishing the Hydrogen Fueling Infrastructure Research and Station Technology (H2FIRST) partnership, led by the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (SNL). FCTO is establishing this partnership and the associated capabilities in support of H2USA, the public/private partnership launched in 2013. The H2FIRST partnership provides the research and technology acceleration support to enable the widespread deployment of hydrogen infrastructure for the robust fueling of light-duty fuel cell electric vehicles (FCEV). H2FIRST will focus on improving private-sector economics, safety, availability and reliability, and consumer confidence for hydrogen fueling. This whitepaper outlines the goals, scope, activities associated with the H2FIRST partnership.
In an attempt to mitigate the hazards associated with storing large quantities of reactive metal hydrides, polymer composite materials were synthesized and tested under simulated usage and accident conditions. The composites were made by polymerizing vinyl monomers using free-radical polymerization chemistry, in the presence of the metal hydride. Composites with vinyl-containing siloxane oligomers were also polymerized with and without added styrene and divinyl benzene. Hydrogen capacity measurements revealed that addition of the polymer to the metal hydride reduced the inherent hydrogen storage capacity of the material. The composites were found to be initially effective at reducing the amount of heat released during oxidation. However, upon cycling the composites, the mitigating behavior was lost. While the polymer composites we investigated have mitigating potential and are physically robust, they undergo a chemical change upon cycling that makes them subsequently ineffective at mitigating heat release upon oxidation of the metal hydride. Acknowledgements The authors would like to thank the following people who participated in this project: Ned Stetson (U.S. Department of Energy) for sponsorship and support of the project. Ken Stewart (Sandia) for building the flow-through calorimeter and cycling test stations. Isidro Ruvalcaba, Jr. (Sandia) for qualitative experiments on the interaction of sodium alanate with water. Terry Johnson (Sandia) for sharing his expertise and knowledge of metal hydrides, and sodium alanate in particular. Marcina Moreno (Sandia) for programmatic assistance. John Khalil (United Technologies Research Corp) for insight into the hazards of reactive metal hydrides and real-world accident scenario experiments. Summary In an attempt to mitigate and/or manage hazards associated with storing bulk quantities of reactive metal hydrides, polymer composite materials (a mixture of a mitigating polymer and a metal hydride) were synthesized and tested under simulated usage and accident conditions. Mitigating the hazards associated with reactive metal hydrides during an accident while finding a way to keep the original capability of the active material intact during normal use has been the focus of this work. These composites were made by polymerizing vinyl monomers using free-radical polymerization chemistry, in the presence of the metal hydride, in this case a prepared sodium alanate (chosen as a representative reactive metal hydride). It was found that the polymerization of styrene and divinyl benzene could be initiated using AIBN in toluene at 70°C. The resulting composite materials can be either hard or brittle solids depending on the cross-linking density. Thermal decomposition of these styrene-based composite materials is lower than neat polystyrene indicating that the chemical nature of the polymer is affected by the formation of the composite. The char-forming nature of cross-linked polystyrene is low and therefore, not an ideal polymer for hazard mitigation. To obtain composite materials containing a polymer with higher char-forming potential, siloxane-based monomers were investigated. Four vinyl-containing siloxane oligomers were polymerized with and without added styrene and divinyl benzene. Like the styrene materials, these composite materials exhibited thermal decomposition behavior significantly different than the neat polymers. Specifically, the thermal decomposition temperature was shifted approximately 100 °C lower than the neat polymer signifying a major chemical change to the polymer network. Thermal analysis of the cycled samples was performed on the siloxane-based composite materials. It was found that after 30 cycles the siloxane-containing polymer composite material has similar TGA/DSC-MS traces as the virgin composite material indicating that the polymer is physically intact upon cycling. Hydrogen capacity measurements revealed that addition of the polymer to the metal hydride in the form of a composite material reduced the inherent hydrogen storage capacity of the material. This reduction in capacity was observed to be independent of the amount of charge/discharge cycles except for the composites containing siloxane, which showed less of an impact on hydrogen storage capacity as it was cycled further. While the reason for this is not clear, it may be due to a chemically stabilizing effect of the siloxane on the metal hydride. Flow-through calorimetry was used to characterize the mitigating effectiveness of the different composites relative to the neat (no polymer) material. The composites were found to be initially effective at reducing the amount of heat released during oxidation, and the best performing material was the siloxane-containing composite which reduced the heat release to less than 50% of the value of the neat material. However, upon cycling the composites, all mitigating behavior was lost. The combined results of the flow-through calorimetry, hydrogen capacity, and thermogravimetric analysis tests lead to the proposed conclusion that while the polymer composites have mitigating potential and are physically robust under cycling, they undergo a chemical change upon cycling that makes them ineffective at mitigating heat release upon oxidation of the metal hydride.
Two of the most daunting problems facing humankind in the twenty-first century are energy security and climate change. This report summarizes work accomplished towards addressing these problems through the execution of a Grand Challenge LDRD project (FY09-11). The vision of Sunshine to Petrol is captured in one deceptively simple chemical equation: Solar Energy + xCO{sub 2} + (x+1)H{sub 2}O {yields} C{sub x}H{sub 2x+2}(liquid fuel) + (1.5x+.5)O{sub 2} Practical implementation of this equation may seem far-fetched, since it effectively describes the use of solar energy to reverse combustion. However, it is also representative of the photosynthetic processes responsible for much of life on earth and, as such, summarizes the biomass approach to fuels production. It is our contention that an alternative approach, one that is not limited by efficiency of photosynthesis and more directly leads to a liquid fuel, is desirable. The development of a process that efficiently, cost effectively, and sustainably reenergizes thermodynamically spent feedstocks to create reactive fuel intermediates would be an unparalleled achievement and is the key challenge that must be surmounted to solve the intertwined problems of accelerating energy demand and climate change. We proposed that the direct thermochemical conversion of CO{sub 2} and H{sub 2}O to CO and H{sub 2}, which are the universal building blocks for synthetic fuels, serve as the basis for this revolutionary process. To realize this concept, we addressed complex chemical, materials science, and engineering problems associated with thermochemical heat engines and the crucial metal-oxide working-materials deployed therein. By project's end, we had demonstrated solar-driven conversion of CO{sub 2} to CO, a key energetic synthetic fuel intermediate, at 1.7% efficiency.
Sandia National Laboratories has developed a vehicle-scale demonstration hydrogen storage system as part of a Work for Others project funded by General Motors. This Demonstration System was developed based on the properties and characteristics of sodium alanates which are complex metal hydrides. The technology resulting from this program was developed to enable heat and mass management during refueling and hydrogen delivery to an automotive system. During this program the Demonstration System was subjected to repeated hydriding and dehydriding cycles to enable comparison of the vehicle-scale system performance to small-scale sample data. This paper describes the experimental results of life-cycle studies of the Demonstration System. Two of the four hydrogen storage modules of the Demonstration System were used for this study. A well-controlled and repeatable sorption cycle was defined for the repeated cycling, which began after the system had already been cycled forty-one times. After the first nine repeated cycles, a significant hydrogen storage capacity loss was observed. It was suspected that the sodium alanates had been affected either morphologically or by contamination. The mechanisms leading to this initial degradation were investigated and results indicated that water and/or air contamination of the hydrogen supply may have lead to oxidation of the hydride and possibly kinetic deactivation. Subsequent cycles showed continued capacity loss indicating that the mechanism of degradation was gradual and transport or kinetically limited. A materials analysis was then conducted using established methods including treatment with carbon dioxide to react with sodium oxides that may have formed. The module tubes were sectioned to examine chemical composition and morphology as a function of axial position. The results will be discussed.
This paper describes mitigation technologies that are intended to enable the deployment of advanced hydrogen storage technologies for early market and automotive fuel cell applications. Solid State hydrogen storage materials provide an opportunity for a dramatic increase in gravimetric and volumetric energy storage density. Systems and technologies based on the advanced materials have been developed and demonstrated within the laboratory [1,2], and in some cases, integrated with fuel cell systems. The R&D community will continue to develop these technologies for an ever increasing market of fuel cell technologies, including, forklift, light-cart, APU, and automotive systems. Solid state hydrogen storage materials are designed and developed to readily release, and in some cases, react with diatomic hydrogen. This favorable behavior is often accomplished with morphology design (high surface area), catalytic additives (titanium for example), and high purity metals (such as aluminum, Lanthanum, or alkali metals). These favorable hydrogen reaction characteristics often have a related, yet less-desirable effect: sensitivity and reactivity during exposure to ambient contamination and out-of-design environmental conditions. Accident scenarios resulting in this less-favorable reaction behavior must also be managed by the system developer to enable technology deployment and market acceptance. Two important accident scenarios are identified through hazards and risk analysis methods. The first involves a breach in plumbing or tank resulting from a collision. The possible consequence of this scenario is analyzed though experimentally based chemical kinetic and transport modeling of metal hydride beds. An advancing reaction front between the metal hydride and ambient air is observed to proceed throughout the bed. This exothermic reaction front can result in loss of structural integrity of the containing vessel and lead to un-favorable overheating events. The second important accident scenario considered is a pool fire or impinging fire resulting from a collision between a hydrocarbon or hydrogen fueled vehicle. The possible consequence of this scenario is analyzed with experimentally-based numerical simulation of a metal hydride system. During a fire scenario, the hydrogen storage material will rapidly decompose and release hydrogen at high pressure. Accident scenarios initiated by a vehicular collision leading a pipe break or catastrophic failure of the hydride vessel and by external pool fire with flame engulfing the storage vessel are developed using probabilistic modeling. The chronology of events occurring subsequent to each accident initiator is detailed in the probabilistic models. Technology developed to manage these scenarios includes: (1) the use of polymer supports to reduce the extent and rate of reaction with air and water, (2) thermal radiation shielding. The polymer supported materials are demonstrated to provide mitigation of unwanted reaction while not impacting the hydrogen storage performance of the material. To mitigate the consequence of fire engulfment or impingement, thermal radiation shielding is considered to slow the rate of decomposition and delay the potential for loss-of-containment. In this paper we explore the use of these important mitigation technologies for a variety of accident scenarios.
Mitigating and overcoming environmental problems brought about by the current worldwide fossil fuel-based energy infrastructure requires the creation of innovative alternatives. In particular, such alternatives must actively contribute to the reduction of carbon emissions via carbon recycling and a shift to the use of renewable sources of energy. Carbon neutral transformation of biomass to liquid fuels is one of such alternatives, but it is limited by the inherently low energy efficiency of photosynthesis with regard to the net production of biomass. Researchers have thus been looking for alternative, energy-efficient chemical routes inspired in the biological transformation of solar power, CO2 and H2O into useful chemicals; specifically, liquid fuels. Methanol has been the focus of a fair number of publications for its versatility as a fuel, and its use as an intermediate chemical in the synthesis of many compounds. In some of these studies, (e.g. Joo et al., (2004), Mignard and Pritchard (2006), Galindo and Badr (2007)) CO2 and renewable H2 (e.g. electrolytic H2) are considered as the raw materials for the production of methanol and other liquid fuels. Several basic PFD diagrams have been proposed. One of the most promising is the so called CAMERE process (Joo et al., 1999 ). In this process, carbon dioxide and renewable hydrogen are fed to a first reactor and transformed according to: H2 + CO2 <=> H2O + CO Reverse Water Gas Shift (RWGS) After eliminating the produced water the resulting H2/CO2/CO mixture is then feed to a second reactor where it is converted to methanol according to: CO2 + 3.H2 <=> CH3OH + H2O Methanol Synthesis (MS) CO + H2O <=> CO2 + H2 Water Gas Shift (WGS) The approach here is to produce enough CO to eliminate, via WGS, the water produced by MS. This is beneficial since water has been proven to block active sites in the MS catalyst. In this work a different process alternative is presented: One that combines the CO2 recycling of the CAMERE process and the use of solar energy implicit in some of the biomass-based process, but in this case with the potential high energy efficiency of thermo-chemical transformations.
The use of risk information in establishing code and standard requirements enables: (1) An adequate and appropriate level of safety; and (2) Deployment of hydrogen facilities are as safe as gasoline facilities. This effort provides a template for clear and defensible regulations, codes, and standards that can enable international market transformation.
Objectives are to enable development and implementation of codes and standards for H{sub 2} containment components: (1) Evaluate data on mechanical properties of materials in H{sub 2} gas - Technical Reference on Hydrogen Compatibility of Materials; (2) Generate new benchmark data on high-priority materials - Pressure vessel steels, stainless steels; and (3) Establish procedures for reliable materials testing - Sustained-load cracking, fatigue crack propagation. Summary of this presentation are: (1) Completed measurement of cracking thresholds (K{sub TH}) for Ni-Cr-Mo pressure vessel steels in high-pressure H{sub 2} gas - K{sub TH} measurements required in ASME Article KD-10 (2) Crack arrest test methods appear to yield non-conservative results compared to crack initiation test methods - (a) Proposal to insert crack initiation test methods in Article KD-10 will be presented to ASME Project Team on Hydrogen Tanks, and (b) Crack initiation methods require test apparatus designed for dynamic loading of specimens in H{sub 2} gas; and (3) Demonstrated ability to measure fatigue crack growth of pressure vessel steels in high-pressure H{sub 2} gas - (a) Fatigue crack growth data in H{sub 2} required in ASME Article KD-10, and (b) Test apparatus is one of few in U.S. or abroad for measuring fatigue crack growth in >100 MPa H{sub 2} gas.
A permeability model for hydrogen transport in a porous material is successfully applied to both laboratory-scale and vehicle-scale sodium alanate hydrogen storage systems. The use of a Knudsen number dependent relationship for permeability of the material in conjunction with a constant area fraction channeling model is shown to accurately predict hydrogen flow through the reactors. Generally applicable model parameters were obtained by numerically fitting experimental measurements from reactors of different sizes and aspect ratios. The degree of channeling was experimentally determined from the measurements and found to be 2.08% of total cross-sectional area. Use of this constant area channeling model and the Knudsen dependent Young & Todd permeability model allows for accurate prediction of the hydrogen uptake performance of full-scale sodium alanate and similar metal hydride systems.
Advances are reported in several aspects of clathrate hydrate desalination fundamentals necessary to develop an economical means to produce municipal quantities of potable water from seawater or brackish feedstock. These aspects include the following, (1) advances in defining the most promising systems design based on new types of hydrate guest molecules, (2) selection of optimal multi-phase reactors and separation arrangements, and, (3) applicability of an inert heat exchange fluid to moderate hydrate growth, control the morphology of the solid hydrate material formed, and facilitate separation of hydrate solids from concentrated brine. The rate of R141b hydrate formation was determined and found to depend only on the degree of supercooling. The rate of R141b hydrate formation in the presence of a heat exchange fluid depended on the degree of supercooling according to the same rate equation as pure R141b with secondary dependence on salinity. Experiments demonstrated that a perfluorocarbon heat exchange fluid assisted separation of R141b hydrates from brine. Preliminary experiments using the guest species, difluoromethane, showed that hydrate formation rates were substantial at temperatures up to at least 12 C and demonstrated partial separation of water from brine. We present a detailed molecular picture of the structure and dynamics of R141b guest molecules within water cages, obtained from ab initio calculations, molecular dynamics simulations, and Raman spectroscopy. Density functional theory calculations were used to provide an energetic and molecular orbital description of R141b stability in both large and small cages in a structure II hydrate. Additionally, the hydrate of an isomer, 1,2-dichloro-1-fluoroethane, does not form at ambient conditions because of extensive overlap of electron density between guest and host. Classical molecular dynamics simulations and laboratory trials support the results for the isomer hydrate. Molecular dynamics simulations show that R141b hydrate is stable at temperatures up to 265K, while the isomer hydrate is only stable up to 150K. Despite hydrogen bonding between guest and host, R141b molecules rotated freely within the water cage. The Raman spectrum of R141b in both the pure and hydrate phases was also compared with vibrational analysis from both computational methods. In particular, the frequency of the C-Cl stretch mode (585 cm{sup -1}) undergoes a shift to higher frequency in the hydrate phase. Raman spectra also indicate that this peak undergoes splitting and intensity variation as the temperature is decreased from 4 C to -4 C.
An entirely new class of light-weight reversible hydrides was recently discovered (the Ti-doped alanates)[1]. These NaAIH{sub 4}-based materials have demonstrated reversible hydrogen storage capacities of up to 5 wt%, nearly 4 times the gravimetrically density of commercial metal hydrides. For this reason, they have been considered a breakthrough for hydrogen storage in fuel cell vehicles. This project is the first to publish the use of alanates for the generation of electrical power and the first demonstration of a hydride-fueled elevated-temperature PEM Fuel Cell. Because the kinetics of hydrogen uptake and release by the alanate improves with elevated temperatures, novel concepts were tested for the purpose of developing a highly efficient stand-alone power system. A major focus of this work was on the modeling, design, construction and testing of an integrated fuel cell stack and hydrogen storage system that eliminates the need of complicated heat transfer systems and media. After extensive modeling efforts, a proof-of-concept system was built that employs an integrated fuel cell stack and hydride beds that balancing the generation of fuel cell waste heat with the endothermic release of hydrogen from the alanates. Our demonstration unit was capable of greater than one hour of operation on a single charge of hydrogen from the integrated 173 gram alanate bed. In addition, composite hydride materials with synergistic reaction heats were evaluated and tested to enhance the operational performance of the alanates. The composites provide a unique opportunity to utilize the heat produced from hydriding classic metal hydrides to improve both absorption and desorption rates of the alanates. A particular focus of the mixed storage materials work was to balance the thermodynamics and kinetics of the hydrides for start-up conditions. Modeling of the sorption properties proved invaluable in evaluating the optimum composition of hydrides. The modeling efforts were followed by full validation by experimental measurements. This project successfully completed the proof-of-concept goals and generated a powerful set of tools for optimizing the complete power-generation system. It has also created a new direction for hydrogen power generation as well the potential for new R&D based on this work.