Academic literature on the topic 'H2- producing conditions'

ABSTRACT A series of molecular and geochemical studies were performed to study microbial, coal bed methane formation in the eastern Illinois Basin. Results suggest that organic matter is biodegraded to simple molecules, such as H2 and CO2, which fuel methanogenesis and the generation of large coal bed methane reserves. Small-subunit rRNA analysis of both the in situ microbial community and highly purified, methanogenic enrichments indicated that Methanocorpusculum is the dominant genus. Additionally, we characterized this methanogenic microorganism using scanning electron microscopy and distribution of intact polar cell membrane lipids. Phylogenetic studies of coal water samples helped us develop a model of methanogenic biodegradation of macromolecular coal and coal-derived oil by a complex microbial community. Based on enrichments, phylogenetic analyses, and calculated free energies at in situ subsurface conditions for relevant metabolisms (H2-utilizing methanogenesis, acetoclastic methanogenesis, and homoacetogenesis), H2-utilizing methanogenesis appears to be the dominant terminal process of biodegradation of coal organic matter at this location.

ABSTRACT Despite the fact that rice paddy fields (RPFs) are contributing 10 to 25% of global methane emissions, the organisms responsible for methane production in RPFs have remained uncultivated and thus uncharacterized. Here we report the isolation of a methanogen (strain SANAE) belonging to an abundant and ubiquitous group of methanogens called rice cluster I (RC-I) previously identified as an ecologically important microbial component via culture-independent analyses. To enrich the RC-I methanogens from rice paddy samples, we attempted to mimic the in situ conditions of RC-I on the basis of the idea that methanogens in such ecosystems should thrive by receiving low concentrations of substrate (H2) continuously provided by heterotrophic H2-producing bacteria. For this purpose, we developed a coculture method using an indirect substrate (propionate) in defined medium and a propionate-oxidizing, H2-producing syntroph, Syntrophobacter fumaroxidans, as the H2 supplier. By doing so, we significantly enriched the RC-I methanogens and eventually obtained a methanogen within the RC-I group in pure culture. This is the first report on the isolation of a methanogen within RC-I.

The eukaryotic green alga, Chlamydomonas reinhardtii, produces H2 under anaerobic conditions, in a reaction catalysed by an [FeFe]-hydrogenase. To identify genes that influence H2 production in C. reinhardtii, a library of 6000 colonies on agar plates was screened with sensitive chemochromic H2-sensor films for clones defective in H2 production. Two mutants of particular interest were fully characterized. One mutant, hydEF-1, is unable to assemble an active [FeFe]-hydrogenase. This is the first reported C. reinhardtii mutant that is not capable of producing any H2. The second mutant, sta7-10, is not able to accumulate insoluble starch and has significantly lowered H2-photoproduction rates in comparison with the wild-type. In hydEF-1, anaerobiosis induces transcription of the two reported C. reinhardtii hydrogenase genes, HydA1 and HydA2, indicating a normal transcriptional response to anaerobiosis. In contrast, the transcription of both hydrogenase genes in sta7-10 is significantly attenuated.

The preparation of hydrogen-producing microbial consortia from three anaerobic digested sludges were carried out by four different pretreatment methods (heat – shock, acid, base and aeration treatment) as well as untreatment. The obtained microbial seeds have been estimated for their stability in fermentative hydrogen production by three consecutive batch fermentations under the same conditions of pH 6.5, room temperature and cultivation time and also investigated the H2 fermentation from different concentrations of glucose and xylose. Three microbial seeds have the most effective H2 production at 5 g/l of glucose or xylose after 48 h cultivation time. The sewage sludge pretreated at 80oC for 30 minutes shows the hydrogen yield of 1.27 mol/mol glucose and 0.82 mol/mol xylose. The sludge in the biogas tank pretreated at 60oC for 30 minutes has the hydrogen yield of 1.27 mol/mol glucose and 0.71 mol/mol xylose. The sludge of the Hoa Binh waste treatment plant pretreated at 60oC for 30 minutes presents the hydrogen yield of 1.31 mol/mol glucose and 0.66 mol/mol xylose.

The proper strategy to establish efficient hydrogen-producing biosystems is the biochemical, physiological characterization of hydrogen-producing microbes followed by metabolic engineering in order to give extraordinary properties to the strains and, finally, bioprocess optimization to realize enhanced hydrogen fermentation capability. In present paper, it was aimed to show the utility both of strain engineering and process optimization through a comparative study of wild-type and genetically modifiedE. colistrains, where the effect of two major operational factors (substrate concentration and pH) on bioH2production was investigated by experimental design and response surface methodology (RSM) was used to determine the suitable conditions in order to obtain maximum yields. The results revealed that by employing the genetically engineeredE. coli(DJT 135) strain under optimized conditions (pH: 6.5; Formate conc.: 1.25 g/L), 0.63 mol H2/mol formate could be attained, which was 1.5 times higher compared to the wild-typeE. coli(XL1-BLUE) that produced 0.42 mol H2/mol formate (pH: 6.4; Formate conc.: 1.3 g/L).

Influence of different pretreatment methods applied on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H2) producing mixed culture using glucose as substrate. The cumulative H2 yield and H2 production rate were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. They could be increased by appropriate pretreatment methods, including use of heat, alkaline or acidic conditions. Along with the processing temperature and time of heat pretreatment and alkaline of alkali pretreatment increasing, the H2 yield increased and then declined, but it declined and then increased as the acidity of acid pretreatment increasing. Among the studied pretreatment methods, the heat pretreatment methods procedure enabled higher H2 yield and the maximum H2 production rate, then were alkali and acid pretreatment methods. When the inoculum was heat-treated at 80°C for 30 min, the highest cumulative H2 yield was obtained at 2152.0 mL, which was 53.20% higher than the control, and the maximum H2 production rate was 178.0 mL h-1, which was 122.0% higher than that of the Ctrl (138.0mL h-1).

A new system, that allowed the monitoring of hydrogen (H2) excretion by gnotobiotic rats without affecting their defined microbial status, was developed. The system consists of an isolator containing a chamber for an experimental animal, and a life-support system (LSS). with a sampling port outside the isolator connected to it. H2 accumulation in the system was measured by analysing a defined volume of gas after removal. H2 concentrations were determined with an electrochemical cell or by gas chromatography. To validate this technique, H2 excretion by germ-free (GF) and mono-associated rats fed a chemically defined diet was measured after oral application of lactulose. Mono-associated rats had been obtained by colonizing GF rats with a H2-producing Clostridium perfringens type A strain isolated from human faeces of a healthy volunteer. Application of 50 mg lactulose to the mono-associated rats resulted in a significant increase in H2 excretion. The net H2 excretion was 7.82±1.28 ml H2 in 12 h corresponding to a net maximal rate of 1.1±0.3 ml H2/h. In contrast, in experiments with GF rats, less than 0.13 ml H2 were detectable within 12 h. The technique presented is a useful tool for studying bacterial H2 metabolism in vivo under gnotobiotic conditions.

Before producing hydrogen plasma low pressure in experiment, it is necessary to know the density equilibrium process through a simulation. Hydrogen species densities of non-thermal plasma at low pressure is simulated using chemical kinetik model by Runge Kutta method. This simulation carried out to determine the equilibrium process of densities and reaction rates of hydrogen species in achieving equilibrium conditions. The equation used time-dependent continuity equation and Arrhenius form. The hydrogen species consist of electrons, H, H2, H+ and H2+. The results of show that electron density, H, H2, H+ and H2+ are respectively 1020,23m-3, 1019,69m-3, 1019,91m-3, 1019,39m-3 and 1018,43m-3 during of 23-24 ns. These describe that the density of each species of hydrogen very fast to achieve equilibrium conditions, while the value of the reaction rate obtained can be concluded that the value of the largest reaction rate is the impact ionization process with a value of 9.86x1052m-3 s-1and the smallest one is dissociation process with a value of 1.22x10-5m-3 s-1.

碩士
國立成功大學
化學工程學系碩博士班
93
Abstract 　In this study, an indigenous Clostridium butyricum CGS2 strain was isolated from highly efficient anaerobic hydrogen-producing sludge. Preliminary tests show that the C. butyricum CGS2 strain exhibited good hydrogen producing activity. Response surface methodology (RSM) was then applied to identify the optimal conditions for hydrogen production of C. butyricum CGS2 using carbon substrate concentration, temperature and pH as the primary operation parameters. First, one-level experiments were done in shake flasks to examine which type and concentration of carbon source was most efficient for hydrogen production. The results show that sucrose at a concentration of 20000 mg COD/l gave the highest hydrogen production rate (vH2) of 262.3 ml/h/l. Based on this result, the effect of pH and sucrose concentration on hydrogen production was further investigated in a fermenter to determine the center point for RSM experimental design. It was found that at a pH of 5.5 and a sucrose concentration of 20000 mg COD/l, the highest hydrogen yield (YH2) of 2.25 mol H2/mol sucrose was obtained, as total hydrogen production was nearly 4.9 l. Hence, the aforementioned conditions was used as the center point for RSM design. Using YH2 as the performance index, the optimum condition predicted from RSM was pH=5.2, temperature=35.1oC, and sucrose concentration=22.5 g COD/l. Under this condition, the hydrogen content was 58.5%, vH2 was 0.54 l/h/l, total hydrogen production was 7.2 l, and YH2 was 2.91 mol H2/mol sucrose. On the other hand, when vH2 was used as the performance index, the optimum condition was pH=5.36, temperature=35.1 oC, and sucrose concentration=26.1 g COD/l. This condition gave a hydrogen content of 63.3%, a YH2 of 3.26 mol H2/mol sucrose, total hydrogen production of 10.5 l, and a vH2 of 0.50 l/h/l. The validity of RSM predictions was confirmed by experimental results, suggesting that using RSM design could attain an optimal culture condition for C. butyricum CGS2 to enhance its hydrogen production performance. 　 　In the next experiments, the optimal culture condition predicted by RSM design was used to perform continuous hydrogen production in a CSTR process. It was found that the pH (5.36) was too low to limit cell grow, resulting in cell wash-out even at a high HRT of 12 h, whereas maximal hydrogen production performance was attained when the pH was controlled at 6.5. Therefore, the culture condition for continuous hydrogen fermentation was modified by using pH 6.5 instead of 5.36. With the modified condition, the reactor was operated at a progressively decreased HRT from 8 h to 2 h. The results show that operation at HRT=8 h allowed a 7 fold increase (from 0.70 to 5.31 mol H2/mol sucrose) in hydrogen yield when compared with control run. The hydrogen production also marked increased from 0.11 l/h/l to 0.90 l/h/l. The hydrogen content increased to 50%. As the HRT decreased, the hydrogen producing efficiency increased. The highest hydrogen production rate (1.34 l/h/l) and yield (4.40 mol H2/mol sucrose) was obtained when the system was operated at HRT=3 h. Finally, the experimental results were subject to numerical simulation with a steady-state kinetic models, and the model appeared to describe the data satisfactorily well.

This thesis is constituted of an introductive section given detailed information about the metabolic versatility of purple non sulfur bacteria. An exhaustive description of the photo-fermentation process in purple non sulfur bacteria is also offered, with particular consideration to the conditions needed to produce hydrogen. The acclimation (chromo-acclimation) to high light intensities in purple non sulfur bacteria is detailed described, and the role of photo-pigments into this process is highly considered. Moreover, a short description of all ways to dissipate the excess of energy by photosynthetic organisms, is included in this introduction. The use of different techniques to understand the molecular/ energetic status of the photosynthetic unit is presented, with particular attention to Pulse- Amplitude- modulation (PAM) fluorescence and Saturation Pulse Method of Quenching Analysis. In this section, a general view regarding the inhomogeneity problems of light distribution during the photo- fermentation process using purple non sulfur bacteria is offered. Furthermore, short statements about one topic with a few references in literature is described, i.e. production of hydrogen as a way to discard the excess of reducing power generated as a result of high light intensities exposure. The main aim of this thesis was to study the behavior of the purple non sulfur bacterium Rhodopseudomonas palustris strain 42OL to different culturing conditions illuminated at high light intensities, with particular interest to the production of hydrogen as a way to dispose the excess of reductants and as a mechanism to preserve a well physiological status. Besides, the acclimation to high light intensities in this strain was also one of the main objectives to be studied, particularly the trend of photo- pigments.

New business models in the solar PV business were pushed from government policies worldwide for reducing GHG emissions. Therefore, PV system installments increase exorbitant in the last years with the consequences of constant falling of prices for PV system and energy. All these quickly changed conditions, means new flexible BM. Power purchase agreements, Product Service Systems, demand resource provider, energy performance contracts are evolving rapidly in the renewable energy business. There is a variation of new PV BM for use. PV represent a new energy source for producing H2 as a storable renewable fuel in an overcapacity situation. Using H2 in combination with other systems, like hybrid systems, heat pumps gives new unique business opportunities. Decentralization will be the key to success. Other applications like mobility and long term storage are other further alternatives in connections or combination with the volatile renewable energy sources.

A cycle capable of generating both hydrogen and power with ‘inherent’ carbon capture is proposed and evaluated. The cycle uses chemical looping combustion (CLC) to perform the primary energy release from a hydrocarbon, producing an exhaust of CO. This CO is mixed with steam and converted to H2 and CO2 using the water-gas shift reaction (WGSR). Chemical looping uses two reactions with a re-circulating oxygen carrier to oxidise hydrocarbons. The resulting oxidation and reduction stages are preformed in separate reactors — the oxidiser and reducer respectively, and this partitioning facilitates CO2 capture. In addition, by careful selection of the oxygen carrier, the equilibrium temperature of both redox reactions can be reduced to values below the current industry standard metallurgical limit for gas turbines. This means that the irreversibility associated with the combustion process can be reduced significantly, leading to a system of enhanced overall efficiency. The choice of oxygen carrier also affects the ratio of CO vs. CO2 in the reducer’s flue gas, with some metal oxide reduction reactions generating almost pure CO. This last feature is desirable if the maximum H2 production is to be achieved using the WGSR reaction. Process flow diagrams of one possible embodiment using a zinc based oxygen carrier are presented. To generate power, the chemical looping system is operated as part of a gas turbine cycle, combined with a bottoming steam cycle to maximise efficiency. The WGSR supplies heat to the bottoming steam cycle, as well as helping to raise the steam necessary to complete the reaction. A mass and energy balance of the chemical looping system, the WGSR reactor, steam bottoming cycle and balance of plant, is presented and discussed. The results of this analysis show that the overall efficiency of the complete cycle is dependant on the operating pressure in the oxidiser, and under optimum conditions, exceeds 75%.

Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) as well as other forms of advanced combustion. During this event, at least a portion of the fuel hydrocarbons can be converted to products containing significant levels of H2 and CO, as well as other short chain hydrocarbons by means of thermal cracking, watergas shift, and partial oxidation reactions, depending on the availability of oxygen and the time-temperature-pressure history. The resulting products alter the autoignition properties of the combined fuel mixture for HCCI. Fuel-rich chemistry in a partial oxidation environment is also relevant to other high efficiency engine concepts (e.g., the dedicated EGR (D-EGR) concept from SWRI). In this study, we used a unique 6-stroke engine cycle to experimentally investigate the chemistry of a range of fuels injected during NVO under low oxygen conditions. Fuels investigated included iso-octane, iso-butanol, ethanol, and methanol. Products from NVO chemistry were highly dependent on fuel type and injection timing, with iso-octane producing less than 1.5% hydrogen and methanol producing more than 8%. We compare the experimental trends with CHEMKIN (single zone, 0-D model) predictions using multiple kinetic mechanisms available in the current literature. Our primary conclusion is that the kinetic mechanisms investigated are unable to accurately predict the magnitude and trends of major species we observed.

The operating range and wave speed performance of a Rotating Detonation Combustor (RDC) is characterized for hydrogen-air mixtures for three fuel injection schemes and two air injection schemes. The fuel injection scheme is altered by changing the total number of injection orifices and the individual orifice area, while maintaining the same fuel mass flux across the three schemes. The operability, performance and combustion-induced pressure rise due to the addition of a back-pressurizing convergent nozzle is also characterized. While the operating range is largely unaffected by changes in the length-to-diameter ratio of the fuel injector orifices, higher length-to-diameter ratios correspond to a lower number of pop-out events. Pop-out event is defined as a transitional RDC operation where there is a sudden abatement of the continuously propagating detonation wave, once established inside the combustor. Increased air injection area diminishes the operability, while producing high stochasticity in the performance of the RDC. The length-to-diameter ratio of the fuel orifices has a significant impact on the number of detonation waves that can exist in the chamber. For the highest length-to-diameter ratio of the fuel orifices, and at the highest air flow rates, the RDC supports multiple detonation waves inside the chamber. Without the convergent nozzle attachment, 80% of Chapman-Jouguet (C-J) detonation speed is achieved for all three fuel injection schemes. C-J detonation wave speed is achieved in the annulus when the RDC is back-pressurized using the nozzle. The ratio of reactant fill-height to the detonation cell-width tapers at the lean and rich operating conditions, while peaking at an equivalence ratio of around 1.2. The detonation-induced static pressure rise produced in the RDC is found to be dependent on the air flow rate and the equivalence ratio of the reactants.

Abstract There is growing interest in hydrogen (H2) as an energy carrier and fuel. Since H2 is a secondary or intermediate energy carrier, it is mainly produced from primary fossil fuels. To overcome the challenges of traditional reforming methods (such as high energy demands and CO2 emissions), this study investigates an alternative method, called tri-reforming, which combines the steam reforming of methane (SRM) and dry reforming of methane (DRM) with partial oxidation of methane (POM) in the same reactor. The energy requirement for this method is low since POM is an exothermic process that supplies the thermal energy for the endothermic SRM and DRM processes. Furthermore, the method can also potentially produce the desired quality of syngas (high H2/CO ratio) with low susceptibility to coking and high catalyst stability. A process model of a methane tri-reforming reactor is developed in Aspen Plus by employing the conservation of mass, momentum, and energy. In this study, we investigate the effect of the H2O/CO2/O2 feed ratio together with CH4 as fuel and find their optimum value to produce blue hydrogen (through an optimized H2/CO ratio) at different temperature conditions. The results present the specific O2/CH4 ratios at different temperatures (125–925°C), which would support the CO2/H2O conversion and achieve lower CO2 emissions (molCO2e/molCH4) with lower heat demand for producing hydrogen than the corresponding SRM and DRM processes.

Abstract Methanogenesis is the conversion of carbon dioxide (CO2) to methane (CH4) using microbes. In the context CO2 utilization, methanogenesis process in the utilizing native microbes from a particular reservoir can be a very slow process without any external intervention. To accelerate the conversion rate and methane yield, this study investigates the use of agriculture by-product such as palm oil mill effluent (POME) as substrates as well as potential microbial isolates that can produce biohydrogen at high temperatures. This paper covers the three laboratory assessments of microbes from anaerobic sludge from a local palm oil mill, use of POME to augment the microbial growth, and physicochemical manipulation to identify key parameters that increases CH4 yield and rate: i) biohydrogen production ii) biomethane production, and iii) syntrophic reactions. All experiments are conducted at 70°C which is considered a hyperthermophilic condition for many microbes. Biohydrogen production achieved with highest H2 production of 66.00 (mL/Lmedium). For biomethane production, the highest production rate achieved was 0.0768 CH4 µmol/mL/day which 10,000X higher than 19.6 pmol/mL/day used as a benchmark. Syntrophic reaction with both types of hydrogen-producing and methanogen in the same reactor, and pure H2 and CO2 supplemented externally was able to achieve the highest methane production of 10.095 µmol/mL and 2.524 µmol/ml/day. Methane production rate is 2.5 times faster than without external gasses being introduced. Introduction of external CO2 to the syntrophic reaction is to mimic actual carbon injection and storage in the reservoir. Our paper shows that stimulation of microbes using POME as substrates and H2/CO2 supplementation are important in accelerating the rate of methane production and yield. Future work will focus on optimizing the gas ratio, pH of growth media, and performing syntrophic reaction in porous media to emulate conditions of a reservoir.

This paper presents results of a steady-state thermodynamic model of a hybrid tubular solid oxide fuel cell (SOFC)-gas turbine (GT) cycle developed using commercial process simulation software, Aspen Plus®. The methane fueled hybrid cycle incorporates a 0-dimensional macro level SOFC model considering three chemical reactions: reaction of H2 with O2 producing H2O, methane steam-reforming reaction, and CO shift reaction. In this paper, all important thermodynamic properties, such as temperature, pressure, mass, volume and molar flow rates, and composition of all major streams in the cycle are investigated for two configurations: cycle with and without anode recirculation. In addition, operational conditions, like power output, specific work, efficiency, and heat duty of all equipments, such as SOFC stack, GT, fuel reformer, compressors, heat exchangers, and pump are evaluated. This work can help in better understanding of hybrid SOFC-GT cycle inner working.

Chemical-Looping Combustion (CLC) is a process where fuel oxidation is accomplished by the oxygen carried by a metal oxide, circulating across two reactors: a reduction reactor (reducing the metal oxide by oxidizing the natural gas fuel) and an oxidation reactor (re-oxidizing the metal by reacting with air, a strongly exothermic reaction). The system produces: (i) a stream of oxidation products (CO2 and H2O), ready for carbon sequestration after water separation and CO2 liquefaction; (ii) a stream of hot air (deprived of some oxygen) used as working fluid of a gas turbine cycle. Due to the moderate temperature (∼850°C) of this stream, sensibly lower than those adopted in commercial gas turbines, the combined cycle arranged around this concept suffers from poor conversion efficiency and, therefore, economics. In the present paper, the basic CLC arrangement is modified by inserting a third reactor in the loop. This reactor, by exploiting an intermediate oxidation state of the circulating metal, produces H2 used as decarbonized fuel to raise the temperature of the air coming from the oxidation reactor, up to the highest value allowed by the modern gas turbine technology (∼1350°C), thus achieving elevated efficiency and specific power output. This paper is aimed to assess the potential of power cycles based on the three reactors (CLC3) arrangement. More specifically, we will discuss the plant configuration, the process optimization and the performance prediction. Results show that the CLC3 system is very promising: the net LHV efficiency of the best configuration exceeds 51%, an outstanding figure for a natural gas power cycle producing liquid, disposal-ready CO2 and negligible NOx emissions. Commercial gas turbines can be easily adapted to operate in the specific conditions of the CLC3 arrangement which, apart from the reactors system, does not require the development of novel technologies and/or high-risk components. The paper also reports a final comparison with a rival technology based on natural gas partial oxidation, water-gas shift reaction and CO2 separation by MDEA absorption. This work has been performed within the research on the Italian Electrical System “Ricerca di Sistema”, Ministerial Decrees of January 26 – 2000, and April 17 – 2001.

Abstract Carbon Nanotube (CNTs) is a carbon-based nanoparticle regarded as the "Futuristic Materials" for advanced applications. With the initiative to produce CNTs from natural gas included the potential to reduce greenhouse gas emission in "Company X" assets, the Fluidized Bed Chemical Vapor Deposition (FBCVD) and chemical leaching was selected for production technology. During project execution, challenges in scaling up processes and equipment from laboratory data were discussed as a lesson learned for new technology development. The CNT project began with laboratory experiments of the reaction between mimic natural gas and custom catalysts, followed by purification with acidic mixtures. Based on synthesis recipes, the prototype unit was designed and installed at the onshore plant to test with real gas under various operating conditions such as different gas ratio (HC/H2/N2), temperature etc. to verify production technique. The FBVCD reactor improves overall reactions in a short time while the new acid mixture shows high leaching efficiency, resulting in high CNTs yield and purity. With the promising results, the larger scale plant has been designed with a lean facility concept for brownfield modification. CNTs quality is varied with production recipes which 65% yield and 95% purity for Multi-Walled CNTs with a diameter of 50 nm, approximately can be achieved by prototype unit which it is comparable with commercial grade product. Consequently, this production technique has high potential for producing CNTs from natural gas. However, some engineering points must be considered when scaling units. Some issues which had a significant impact on the initial design were encountered when scaling-up the plant. In large scale fluidized bed reactors, fluidization parameters such as velocity, flow pattern are important for equipment design. Computational fluid dynamics (CFD) based on the actual flow test is needed because the scale factor based on laboratory and prototype tests has shown different results in larger vessels. Based on CNTs purification, chemical kinetics and chain reactions are mandatory for system design. Because their effects may be undetected on a small scale, but it may lead to completely change the design concept due to more bulky mixing effects. While the examples mentioned have made the system more complex, a larger footprint with a higher project cost, but can be resolved with different approaches. CNTs synthesis using natural gas oil&gas plants as carbon source was firstly initiated with promising results from actual field tests. This production technology is proven with higher product yield and purity compared with other conventional methods and larger scale plant is considered highly feasible. In technology development, the new things with less data are considered risky for investment, but it is a challenge that could open the new horizon for oil and gas development.

Increased research into the chemistry, physics and material science of hydrogen cycling compounds has led to the rapid growth of solid-phase hydrogen-storage options. The operating conditions of these new options span a wide range: system temperature can be as low as 70K or over 600K, system pressure varies from less than 100kPa to 35MPa, and heat loads can be moderate or can be measured in megawatts. While the intense focus placed on storage materials has been appropriate, there is also a need for research in engineering, specifically in containment, heat transfer, and controls. The DOE’s recently proposed engineering center of expertise underscores the growing understanding that engineering research will play a role in the success of advanced hydrogen storage systems. Engineering a hydrogen system will minimally require containment of the storage media and control of the hydrogenation and dehydrogenation processes, but an elegant system design will compensate for the storage media’s weaker aspects and capitalize on its strengths. To achieve such a complete solution, the storage tank must be designed to work with the media, the vehicle packaging, the power-plant, and the power-plant’s control system. In some cases there are synergies available that increase the efficiency of both subsystems simultaneously. In addition, system designers will need to make the hard choices needed to convert a technically feasible concept into a commercially successful product. Materials cost, assembly cost, and end of life costs will all shape the final design of a viable hydrogen storage system. Once again there is a critical role for engineering research, in this case into lower cost and higher performance engineering materials. Each form of hydrogen storage has its own, unique, challenges and opportunities for the system designer. These differing requirements stem directly from the properties of the storage media. Aside from physical containment of compressed or liquefied hydrogen, most storage media can be assigned to one of four major categories, chemical storage, metal hydrides, complex hydrides, or physisorption. Specific needs of each technology are discussed below. Physisorption systems currently operate at 77K with very fast kinetics and good gravimetric capacity; and as such, special engineering challenges center on controlling heat transfer. Excellent MLVSI is available, its cost is high and it is not readily applied to complex shape in a mass manufacture setting. Additionally, while the heat of adsorption on most physisorbents is a relatively modest 6–10kJ/mol H2, this heat must be moved up a 200K gradient. Physisorpion systems are also challenged on density. Consequently, methods for reducing the cost of producing and assembling compact, high-quality insulation, tank design to minimize heat transfer while maintaining manufacturability, improved methods of heat transfer to and from the storage media, and controls to optimize filling are areas of profitable research. It may be noted that the first two areas would also contribute to improvement of liquid hydrogen tanks. Metal hydrides are currently nearest application in the form of high pressure metal hydride tanks because of their reduced volume relative to compressed gas tanks of the same capacity and pressure. These systems typically use simple pressure controls, and have enthalpies of roughly 20kJ/mol H2 and plateau pressures of at most a few MPa. During filling, temperatures must be high enough to ensure fast kinetics, but kept low enough that the thermodynamically set plateau pressure is well below the filling pressure. To accomplish this balance the heat transfer system must handle on the order of 300kW during the 5 minute fill of a 10kg tank. These systems are also challenged on mass and the cost of the media. High value areas for research include: heat transfer inside a 35MPa rated pressure vessel, light and strong tank construction materials with reduced cost, and metals or other materials that do not embrittle in the presence of high pressure hydrogen when operated below ∼400K. The latter two topics would also have a beneficial impact on compressed gas hydrogen storage systems, the current “system to beat”. Complex hydrides frequently have high hydrogen capacity but also an enthalpy of adsorption >30kJ/mol H2, a hydrogen release temperature >370K, and in many cases multiple steps of adsorption/desorption with slow kinetics in at least one of the steps. Most complex hydrides are thermal insulators in the hydrided form. From an engineering perspective, improved methods and designs for cost effective heat transfer to the storage media in a 5 to 10MPa vessel is of significant interest, as are materials that resist embrittlement at pressures below 10MPa and temperatures below 500K. Chemical hydrides produce heat when releasing hydrogen; in some systems this can be managed with air cooling of the reactor, but in other systems that may not be possible. In general, chemical hydrides must be removed from the vehicle and regenerated off-board. They are challenged on durability and recycling energy. Engineering research of interest in these systems centers around maintaining the spent fuel in a state suitable for rapid removal while minimizing system mass, and on developing highly efficient recycling plant designs that make the most of heat from exothermic steps. While the designs of each category of storage tank will differ with the material properties, two common engineering research thrusts stand out, heat transfer and structural materials. In addition, control strategies are important to all advanced storage systems, though they will vary significantly from system to system. Chemical systems need controls primarily to match hydrogen supply to power-plant demand, including shut down. High pressure metal hydride systems will need control during filling to maintain an appropriately low plateau pressure. Complex hydrides will need control for optimal filling and release of hydrogen from materials with multi-step reactions. Even the relatively simple compressed-gas tanks require control strategies during refill. Heat transfer systems will modulate performance and directly impact cost. While issues such as thermal conductivity may not be as great as anticipated, the heat transfer system still impacts gravimetric efficiency, volumetric efficiency and cost. These are three key factors to commercial viability, so any research that improves performance or reduces cost is important. Recent work in the DOE FreedomCAR program indicates that some 14% of the system mass may be attributed to heat transfer in complex hydride systems. If this system is made to withstand 100 bar at 450K the material cost will be a meaningful portion of the total tank cost. Improvements to the basic shell and tube structures that can reduce the total mass of heat transfer equipment while maintaining good global and local temperature control are needed. Reducing the mass and cost of the materials of construction would also benefit all systems. Much has been made of the need to reduce the cost of carbon fiber in compressed tanks and new processes are being investigated. Further progress is likely to benefit any composite tank, not just compressed gas tanks. In a like fashion, all tanks have metal parts. Today those parts are made from expensive alloys, such as A286. If other structural materials could be proven suitable for tank construction there would be a direct cost benefit to all tank systems. Finally there is a need to match the system to the storage material and the power-plant. Recent work has shown there are strong effects of material properties on system performance, not only because of the material, but also because the material properties drive the tank design to be more or less efficient. Filling of a hydride tank provides an excellent example. A five minute or less fill time is desirable. Hydrogen will be supplied as a gas, perhaps at a fixed pressure and temperature. The kinetics of the hydride will dictate how fast hydrogen can be absorbed, and the thermodynamics will determine if hydrogen can be absorbed at all; both properties are temperature dependent. The temperature will depend on how fast heat is generated by absorption and how fast heat can be added or removed by the system. If the design system and material properties are not both well suited to this filling scenario the actual amount of hydrogen stored could be significantly less than the capacity of the system. Controls may play an important role as well, by altering the coolant temperature and flow, and the gas temperature and pressure, a better fill is likely. Similar strategies have already been demonstrated for compressed gas systems. Matching system capabilities to power-plant needs is also important. Supplying the demanded fuel in transients and start up are obvious requirements that both the tank system and material must be design to meet. But there are opportunities too. If the power-plant heat can be used to release hydrogen, then the efficiency of vehicle increases greatly. This efficiency comes not only from preventing hydrogen losses from supplying heat to the media, but also from the power-plant cooling that occurs. To reap this benefit, it will be important to have elegant control strategies that avoid unwanted feedback between the power-plant and the fuel system. Hydrogen fueled vehicles are making tremendous strides, as can be seen by the number and increasing market readiness of vehicles in technology validation programs. Research that improves the effectiveness and reduces the costs of heat transfer systems, tank construction materials, and control systems will play a key role in preparing advanced hydrogen storage systems to be a part of this transportation revolution.