Delivery of cold hydrogen in glass fiber composite pressure vessels

We are proposing to minimize hydrogen delivery cost through utilization of glass fiber tube trailers at 200 K and 70 MPa to produce a synergistic combination of container characteristics with properties of hydrogen gas: (1) hydrogen cooled to 200 K is ∼35% more compact for a small increase in theoretical storage energy (exergy); and (2) these cold temperatures (200 K) strengthen glass fibers by as much as 50%, expanding trailer capacity without the use of much more costly carbon fiber composite vessels.     

Vehicular storage of hydrogen in insulated pressure vessels

This paper describes an alternative technology for storing hydrogen fuel onboard vehicles. Insulated pressure vessels are cryogenic capable vessels that can accept cryogenic liquid hydrogen, cryogenic compressed gas or compressed hydrogen gas at ambient temperature. Insulated pressure vessels offer advantages over conventional storage approaches. Insulated pressure vessels are more compact and require less carbon fiber than compressed hydrogen vessels. They have lower evaporative losses than liquid hydrogen tanks, and are lighter than metal hydrides.

The paper outlines the advantages of insulated pressure vessels and describes the experimental and analytical work conducted to verify that insulated pressure vessels can be safely used for vehicular hydrogen storage. Insulated pressure vessels have successfully completed a series of certification tests. A series of tests have been selected as a starting point toward developing a certification procedure. An insulated pressure vessel has been installed in a hydrogen fueled truck and tested over a six month period.     

Storage of cryo-compressed hydrogen in flexible glass capillaries

We present the results of the theoretical calculations and the corresponding experiments with compressed hydrogen storage in flexible glass capillaries both at room and liquid nitrogen temperatures. It was demonstrated that the strength of produced quartz capillaries can be high enough to withstand the internal hydrogen pressure up to 233 MPa and capillary vessels can have relatively high volumetric and gravimetric capacity.     

Polymer coated glass capillaries and structures for high-pressure hydrogen storage: Permeability and hydrogen tightness

The hydrogen tightness of high-pressure hydrogen storage is a basic criterion for long-term storage. The H₂ permeation coefficients of epoxy resin and a glass lacquer were determined to enable the geometric optimization of a glass capillary storage. It was found that the curing conditions have no significant influence on the H₂ permeation coefficient of resin. The H₂ permeation coefficient of epoxy resin is only about three orders of magnitude greater than that of borosilicate glass. This suggests that the initial pressure of 700 bar takes about 2.5 years to be halved in capillary array storage. Therefore, a high-pressure hydrogen storage tank based on glass capillaries is ideally suited for long-term storage in mobile applications.     

Safety approach for composite pressure vessels for road transport of hydrogen. Part 1: Acceptable probability of failure and hydrogen mass

Hydrogen is a promising alternative for current energy carriers. Compressed gas cylinders are the storage systems closest to the commercialization of hydrogen in vehicles. The safety factors in current standards are seen as restrictive for further growth and competitiveness of hydrogen infrastructure. A probabilistic approach can be employed in order to give a rational background to the safety factors. However, an acceptable probability of failure needs to be estimated before calculating the safety factors. The discussion of determining the acceptable probability must include the mass of hydrogen since this determines the consequences of an accident. It is concluded that an annual probability of failure of 10⁻⁷ would be appropriate for small pressure vessels containing a few kilograms of hydrogen. Larger pressure vessels of a few hundred kilograms or more should be designed for an annual probability 10⁻⁸.     

Dynamics of cryogenic hydrogen storage in insulated pressure vessels for automotive applications

A dynamic model is used to characterize cryogenic H₂ storage in an insulated pressure vessel that can flexibly hold liquid H₂ and compressed H₂ at 350 bar. A double-flow refueling device is needed to ensure that the tank can be consistently refueled to its theoretical capacity regardless of the initial conditions. Liquid H₂ charged into the tank is stored as supercritical fluid if the initial tank temperature is >120 K and as a subcooled liquid if it is <100 K. An in-tank heater is needed to maintain the tank pressure above the minimum delivery pressure. Even if H₂ is stored as a supercritical fluid, liquid H₂ will form as H₂ is withdrawn and will further transform to a two-phase mixture and ultimately to a superheated gas. The recoverable fraction of the total stored inventory depends on the minimum H₂ delivery pressure and the power rating of the heater. The dormancy of cryogenic H₂ is a function of the maximum allowable pressure and the pressure of stored H₂; the evaporative losses cannot deplete H₂ from the tank beyond 64% of the theoretical storage capacity.     

A transportation model approach for constructing the cost effective central hydrogen supply system in Korea

One of the major tasks in transition to a hydrogen economy is to build a cost-effective infrastructure of hydrogen supply. Building an infrastructure of hydrogen supply includes a series of logistical steps from production through delivery and storage to utilization of the hydrogen. This paper attempts to build the cost-effective central hydrogen supply system using a transportation model. As a case study, a hydrogen delivery plan for 2040 was established by dividing the Korean peninsula into two regions, northern and southern regions. Average hydrogen delivery distances for 2040 in the northern and the southern regions are estimated as 69.8 km and 85.2 km. The subsequently derived hydrogen supply network of centrally produced hydrogen in 2040 is expected to be similar to the liquefied natural gas pipeline network in 2005. The derived hydrogen supply network, delivery distances, and delivery costs are expected to provide a set of basic and indispensable information in building a cost-effective infrastructure of hydrogen supply in the Korean peninsula.     

Thermally moderated hollow fiber sorbent modules in rapidly cycled pressure swing adsorption mode for hydrogen purification

We describe thermally moderated multi-layered pseudo-monolithic hollow fiber sorbents entities, which can be packed into compact modules to provide small-footprint, efficient H₂ purification/CO₂ removal systems for use in on-site steam methane reformer product gas separations. Dual-layer hollow fibers are created via dry-jet, wet-quench spinning with an inner “active” core of cellulose acetate (porous binder) and zeolite NaY (69 wt% zeolite NaY) and an external sheath layer of pure cellulose acetate. The co-spun sheath layer reduces the surface porosity of the fiber and was used as a smooth coating surface for a poly(vinyl-alcohol) post-treatment, which reduced the gas permeance through the fiber sorbent by at least 7 orders of magnitude, essentially creating an impermeable sheath layer. The interstitial volume between the individual fibers was filled with a thermally-moderating paraffin wax. CO₂ breakthrough experiments on the hollow fiber sorbent modules with and without paraffin wax revealed that the “passively” cooled paraffin wax module had 12.5% longer breakthrough times than the “non-isothermal” module. The latent heat of fusion/melting of the wax offsets the released latent heat of sorption/desorption of the zeolites. One-hundred rapidly cycled pressure swing adsorption cycles were performed on the “passively” cooled hollow fiber sorbents using 25 vol% CO₂/75 vol% He (H₂ surrogate) at 60 °C and 113 psia, resulting in a product purity of 99.2% and a product recovery of 88.1% thus achieving process conditions and product quality comparable to conventional pellet processes. Isothermal and non-isothermal dynamic modeling of the hollow fiber sorbent module and a traditional packed bed using gPROMS^® indicated that the fiber sorbents have sharper fronts (232% sharper) and longer adsorbate breakthrough times (66% longer), further confirming the applicability of the new fiber sorbent approach for H₂ purification.     

Safety approach for composite pressure vessels for road transport of hydrogen. Part 2: Safety factors and test requirements

Composite pressure vessels for transporting hydrogen on roads are a promising and efficient solution for supplying refueling stations. The safety factors of current ISO design standards are perceived as being restrictive for design. In this paper, new safety factors are calculated based on a probabilistic approach and by extending the methods used in the DNV Offshore standard DNV-OS-C501 “Composite Components”. Short-term and long-term conditions are addressed.     

Safe,long range,inexpensive and rapidly refuelable hydrogen vehicles with cryogenic pressure vessels

Hydrogen storage is often cited as the greatest obstacle to achieving a hydrogen economy free of environmental pollution and dependence on foreign oil. A compact high-pressure cryogenic storage system has promising features to the storage challenge associated with hydrogen-powered vehicles. Cryogenic pressure vessels consist of an inner vessel designed for high pressure (350 bar) insulated with reflective sheets of metalized plastic and enclosed within an outer metallic vacuum jacket. When filled with pressurized liquid hydrogen, cryogenic pressure vessels become the most compact form of hydrogen storage available. A recent prototype is the only automotive hydrogen vessel meeting both Department of Energy's 2017 weight and volume targets. When installed onboard an experimental vehicle, a cryogenic pressure vessel demonstrated the longest driving distance with a single H₂ tank (1050 km). In a subsequent experiment, the vessel demonstrated unprecedented thermal endurance: 8 days parking with no evaporative losses, extending to a month if the vehicle is driven as little as 8 km per day. Calculations indicate that cryogenic vessels offer compelling safety advantages and the lowest total ownership cost of hydrogen storage technologies. Long-term (∼10 years) vacuum stability (necessary for high performance thermal insulation) is the key outstanding technical challenge. Testing continues to establish technical feasibility and safety.     

A comparative techno-economic and quantitative risk analysis of hydrogen delivery infrastructure options

The comparative techno-economic analysis and quantitative risk analysis (QRA) of the hydrogen delivery infrastructure covering the national hydrogen demands are presented to obtain a comprehensive understanding of the infrastructure of commercial hydrogen delivery. The cost calculation model, which was based on the hydrogen delivery scenario analysis model (HDSAM), was employed to estimate the costs of hydrogen fuel delivery in Seoul, Korea, whose area is small enough to not require intermediate delivery stations. The QRA methodology was modified to be suitable for the comparative analysis of the whole hydrogen infrastructure. The capacities of a hydrogen refueling station and the hydrogen market penetration were employed as the main variables and the two scenarios, viz. the gaseous and liquid hydrogen delivery options, were considered. The analysis results indicate that the delivery system of gaseous hydrogen was superior in terms of cost and that of liquid hydrogen was superior in terms of safety. Both delivery options were affected by the capacity of the station and the market penetration, and the cost and risk drastically changed, especially when the two variables were small. Thus, according to the results, the economic and safety issues of the hydrogen delivery infrastructure are critical to achieving a hydrogen energy society.     

On the physical differences between tensile testing of type 304 and 316 austenitic stainless steels with internal hydrogen and in external hydrogen

Seventeen metastable austenitic stainless steels (type 304 and 316 alloys) were tested in tension both with internal hydrogen and in external hydrogen. Hydrogen-assisted fracture in both environments is a competition between hydrogen-affected ductile overload and hydrogen-assisted crack propagation. In general, hydrogen localizes the fracture process, which results in crack propagation of particularly susceptible materials at an apparent engineering stress that is less than the tensile strength of the material. Hydrogen-assisted crack propagation in this class of alloys becomes more prevalent at lower nickel content and lower temperature. In addition, for the tests in this study, external hydrogen reduces tensile ductility more than internal hydrogen. External hydrogen promotes crack initiation and propagation at the surface, while with internal hydrogen surface cracking is largely absent, thus preempting hydrogen-assisted crack propagation from the surface. This is not a general result, however, because the reduction of ductility with internal and external hydrogen depends on the specifics of the testing conditions that are compared (e.g., hydrogen gas pressure); in addition, internal hydrogen can promote the formation of internal cracks, which can propagate similar to surface cracks.     

Composite pressure vessels for hydrogen storage in fire conditions: Fire tests and burst simulation

A type IV composite pressure vessel subjected to fire may burst because of the degradation of the outer layers, but when the inner pressure is less than a critical value, leak is observed instead of burst. This phenomenon is due to the heat transfer through the composite shell which leads to liner melting. In order to characterize this failure mechanisms, engulfing fire tests have been performed in the framework of the FireComp project whose objective is to understand and simulate the fire performance of hydrogen storage. An experimental set-up has been implemented to expose the cylinders to fire by the means of gas injectors. A simple FE model has been developed to simulate the coupled effects of mechanical damage and of temperature. This approach is found to accurately predict the time to burst of the composite tank, as well as the transition between burst and leak.     

Preparation, testing and modelling of a hydrogen selective Pd/YSZ/SS composite membrane

A palladium selective tubular membrane has been prepared to separate and purify hydrogen. The membrane consists of a composite material, formed by different layers: a stainless steel support (thickness of 1.9 mm), an yttria-stabilized zirconia interphase (thickness of 50 μm) prepared by Atmospheric Plasma Spraying and a palladium layer (thickness of 27.7 μm) prepared by Electroless Plating. The permeation properties of the membrane have been tested at different operating conditions: retentate pressure (1-5 bar), temperature (350-450 °C) and hydrogen molar fraction of feed gas (0.7-1). At 400 °C, a permeability of 1.1 × 10⁻⁸ mol/(s m Pa^0.5) and a complete selectivity to hydrogen were obtained. The complete retention of nitrogen was maintained for all tested experiment conditions, with both single and mixtures of gases, ensuring 100% purity in the hydrogen permeate flux.A rigorous model considering all the resistances involved in the hydrogen transport has been applied for evaluating the relative importance of the different resistances, concluding that the transport through the palladium layer is the controlling one. In the same way, a model considering the axial variations of hydrogen concentration because of the cylindrical geometry of the experimental device has been applied to the fitting of the experimental data. The best fitting results have been obtained considering Sieverts’-law dependences of the permeation on the hydrogen partial pressure.     

Three-dimensional modeling and simulation of hydrogen absorption in metal hydride hydrogen storage vessels

In this paper, a three-dimensional hydrogen absorption model is developed to precisely study the hydrogen absorption reaction and resultant heat and mass transport phenomena in metal hydride hydrogen storage vessels. The 3D model is first experimentally validated against the temperature evolution data available in the literature. In addition to model validation, the detailed 3D simulation results show that at the initial absorption stage, the vessel temperature and H/M ratio distributions are uniform throughout the entire vessel, indicating that hydrogen absorption is very efficient early during the hydriding process; thus, the local cooling effect is not influential. On the other hand, non-uniform distributions are predicted at the subsequent absorption stage, which is mainly due to differential degrees of cooling between the vessel wall and core regions. In addition, a parametric study is carried out for various designs and hydrogen feed pressures. This numerical study provides a fundamental understanding of the detailed heat and mass transfer phenomena during the hydrogen absorption process and further indicates that efficient design of the storage vessel and cooling system is critical to achieve rapid hydrogen charging performance.     

Safety criteria for the transport of hydrogen in permanently mounted composite pressure vessels

The recent growth of the net of hydrogen fuelling stations increases the demands to transport compressed hydrogen on road by battery vehicles or tube-trailers, both in composite pressure vessels. As a transport regulation, the ADR is applicable in Europe and adjoined regions, and is used for national transport in the EU. This regulation provides requirements based on the behaviour of each individual pressure vessel, regardless of the pressure of the transported hydrogen and relevant consequences resulting from generally possible worst case scenarios such as sudden rupture. In 2012, the BAM (German Federal Institute for Materials Research and Testing) introduced consequence-dependent requirements and established them in national transport requirements concerning the “UN service life checks” etc. to consider the transported volume and pressure of gases. This results in a requirement that becomes more restrictive as the product of pressure and volume increases. In the studies presented here, the safety measures for hydrogen road transport are identified and reviewed through a number of safety measures from countries including Japan, the USA and China. Subsequently, the failure consequences of using trailer vehicles, the related risk and the chance are evaluated. A benefit-related risk criterion is suggested to add to regulations and to be defined as a safety goal in standards for hydrogen transport vehicles and for mounted pressure vessels. Finally, an idea is given for generating probabilistic safety data and for highly efficient evaluation without a significant increase of effort.     

Analysis of jet flames and unignited jets from unintended releases of hydrogen

A combined experimental and modeling program is being carried out at Sandia National Laboratories to characterize and predict the behavior of unintended hydrogen releases. In the case where the hydrogen leak remains unignited, knowledge of the concentration field and flammability envelope is an issue of importance in determining consequence distances for the safe use of hydrogen. In the case where a high-pressure leak of hydrogen is ignited, a classic turbulent jet flame forms. Knowledge of the flame length and thermal radiation heat flux distribution is important to safety. Depending on the effective diameter of the leak and the tank source pressure, free jet flames can be extensive in length and pose significant radiation and impingement hazard, resulting in consequence distances that are unacceptably large. One possible mitigation strategy to potentially reduce the exposure to jet flames is to incorporate barriers around hydrogen storage equipment. The reasoning is that walls will reduce the extent of unacceptable consequences due to jet releases resulting from accidents involving high-pressure equipment. While reducing the jet extent, the walls may introduce other hazards if not configured properly. The goal of this work is to provide guidance on configuration and placement of these walls to minimize overall hazards using a quantitative risk assessment approach. The program includes detailed CFD calculations of jet flames and unignited jets to predict how hydrogen leaks and jet flames interact with barriers, complemented by an experimental validation program that considers the interaction of jet flames and unignited jets with barriers.     

Models,methods and approaches for the planning and design of the future hydrogen supply chain

The infrastructure of hydrogen presents many challenges and defies that need to be overcome for a successful transition to a future hydrogen economy. These challenges are mainly due to the existence of many technological options for the production, storage, transportation and end users. Given this main reason, it is essential to understand and analyze the hydrogen supply chain (HSC) in advance, in order to detect the important factors that may play increasing role in obtaining the optimal configuration. The objective of this paper is to review the current state of the available approaches for the planning and modeling of the hydrogen infrastructure. The decision support systems for the HSC may vary from paper to paper. In this paper, a classification of models and approaches has been done, and which includes mathematical optimization methods, decision support system based on geographic information system (GIS) and assessment plans to a better transition to HSC. The paper also highlights future challenges for the introduction of hydrogen. Overcoming these challenges may solve problems related to the transition to the future hydrogen economy.     

Enhanced dormancy due to para-to-ortho hydrogen conversion in insulated cryogenic pressure vessels for automotive applications

A dynamic model has been developed to characterize dormancy and hydrogen loss from an insulated cryogenic pressure vessel that is filled with 99.79%-para liquid hydrogen to reach supercritical conditions. The model considers the thermodynamics and kinetics of the endothermic para-to-ortho conversion that occurs when the stored H₂ heats after the vessel is exposed to ambient conditions for an extended time. The thermal, thermodynamic, and kinetic aspects of the model were validated against experimental data obtained on a 151-L tank designed for service at nominal pressures up to 350 bar. Depending on the initial pressure, temperature, amount of H₂, and the rate of heat gain from the ambient, the endothermic para-to-ortho conversion can extend the loss-free dormancy time by up to 85%. Under conditions in which the endothermic conversion does not materially affect dormancy, it can still significantly reduce the H₂ loss rate and it can even introduce a secondary dormancy period.