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Modeling of Sudden Hydrogen Expansion from Cryogenic Pressure Vessel Failure
Sep 2011
Publication
We have modelled sudden hydrogen expansion from a cryogenic pressure vessel. This model considers real gas equations of state single and two-phase flow and the specific “vessel within vessel” geometry of cryogenic vessels. The model can solve sudden hydrogen expansion for initial pressures up to 1210 bar and for initial temperatures ranging from 27 to 400 K. For practical reasons our study focuses on hydrogen release from 345 bar with temperatures between 62 K and 300 K. The pressure vessel internal volume is 151 L. The results indicate that cryogenic pressure vessels may offer a safety advantage with respect to compressed hydrogen vessels because i) the vacuum jacket protects the pressure vessel from environmental damage ii) hydrogen when released discharges first into an intermediate chamber before reaching the outside environment and iii) working temperature is typically much lower and thus the hydrogen has less energy. Results indicate that key expansion parameters such as pressure rate of energy release and thrust are all considerably lower for a cryogenic vessel within vessel geometry as compared to ambient temperature compressed gas vessels. Future work will focus on taking advantage of these favourable conditions to attempt fail-safe cryogenic vessel designs that do not harm people or property even after catastrophic failure of the inner pressure vessel.
Hydrogen Safety and Permitting Hydrogen Fueling Stations
Sep 2007
Publication
Two key aspects of hydrogen safety are (1) incorporating data and analysis from research development and demonstration (RD&D) into the codes and standards development process; and (2) adopting and enforcing these codes and standards by state and local permitting officials. This paper describes work that the U.S. Department of Energy (DOE) is sponsoring to address these aspects of hydrogen safety. For the first DOE is working with the automobile and energy industries to identify and address high priority RD&D to establish a sound scientific basis for requirements that are incorporated in hydrogen codes and standards. The high priority RD&D needs are incorporated and tracked in an RD&D Roadmap adopted by the Codes and Standards Technical Team of the FreedomCAR and Fuel Partnership. DOE and its national laboratories conduct critical RD&D and work with key standards and model code development organizations to help incorporate RD&D results into the codes and standards process. To address the second aspect DOE has launched an initiative to facilitate the permitting process for hydrogen fueling stations (HFS). A key element of this initiative will be a Web-based information repository a toolkit that includes information fact sheets networking charts to encourage information exchange among code officials who have permitted or are in the process of permitting HFS templates to show whether a proposed station footprint conforms to requirements in the jurisdiction and a database of requirements incorporated in key codes and standards. The information repository will be augmented by workshops for code officials and station developers in jurisdictions that are likely to have HFS in the near future.
Predictions of Solid-State Hydrogen Storage System Contamination Processes
Sep 2009
Publication
Solid state materials such as metal and chemical hydrides have been proposed and developed for high energy density automotive hydrogen storage applications. As these materials are implemented into hydrogen storage systems developers must understand their behavior during accident scenarios or contaminated refueling events. An ability to predict thermal and chemical processes during contamination allows for the design of safe and effective hydrogen storage systems along with the development of appropriate codes and standards. A model for the transport of gases within an arbitrary-geometry reactive metal hydride bed (alane -AlH3) is presented in this paper. We have coupled appropriate Knudsen-regime permeability models for flow through packed beds with the fundamental heat transfer and chemical kinetic processes occurring at the particle level. Using experimental measurement to determine and validate model parameters we have developed a robust numerical model that can be utilized to predict processes in arbitrary scaled-up geometries during scenarios such as breach-in-tank or contaminated refueling. Results are presented that indicate the progression of a reaction front through a compacted alane bed as a result of a leaky fitting. The rate of this progression can be limited by; 1) restricting the flow of reactants into the bed through densification and 2) maximizing the rate of heat removal from the bed.
Hydrogen Deblending in the GB Network - Feasibility Study Report
Nov 2020
Publication
The UK government has committed to reducing greenhouse gas emissions to net zero by 2050. All future energy modelling identifies a key role for hydrogen (linked to CCUS) in providing decarbonised energy for heat transport industry and power generation. Blending hydrogen into the existing natural gas pipeline network has already been proposed as a means of transporting low carbon energy. However the expectation is that a gas blend with maximum hydrogen content of 20 mol% can be used without impacting consumers’ end use applications. Therefore a transitional solution is needed to achieve a 100% hydrogen future network.
Deblending (i.e. separation of the blended gas stream) is a potential solution to allow the existing gas transmission and distribution network infrastructure to transport energy as a blended gas stream. Deblending can provide either hydrogen natural gas or blended gas for space heating transport industry and power generation applications. If proven technically and economically feasible utilising the existing gas transmission and distribution networks in this manner could avoid the need for investment in separate gas and hydrogen pipeline networks during the transition to a future fully decarbonised gas network.
The Energy Network Association (ENA) “Gas Goes Green” programme identifies deblending could play a critical role in the transition to a decarbonised gas network. Gas separation technologies are well-established and mature and have been used and proven in natural gas processing for decades. However these technologies have not been used for bulk gas transportation in a transmission and distribution network setting. Some emerging hydrogen separation technologies are currently under development. The main hydrogen recovery and purification technologies currently deployed globally are:
This report and any attachment is freely available on the ENA Smarter Networks Portal here. IGEM Members can download the report and any attachment directly by clicking on the pdf icon above.
Deblending (i.e. separation of the blended gas stream) is a potential solution to allow the existing gas transmission and distribution network infrastructure to transport energy as a blended gas stream. Deblending can provide either hydrogen natural gas or blended gas for space heating transport industry and power generation applications. If proven technically and economically feasible utilising the existing gas transmission and distribution networks in this manner could avoid the need for investment in separate gas and hydrogen pipeline networks during the transition to a future fully decarbonised gas network.
The Energy Network Association (ENA) “Gas Goes Green” programme identifies deblending could play a critical role in the transition to a decarbonised gas network. Gas separation technologies are well-established and mature and have been used and proven in natural gas processing for decades. However these technologies have not been used for bulk gas transportation in a transmission and distribution network setting. Some emerging hydrogen separation technologies are currently under development. The main hydrogen recovery and purification technologies currently deployed globally are:
- Cryogenic separation
- Membrane separation
- Pressure Swing Adsorption (PSA)
This report and any attachment is freely available on the ENA Smarter Networks Portal here. IGEM Members can download the report and any attachment directly by clicking on the pdf icon above.
Risk-Informed Separation Distances For Hydrogen Refuelling Stations
Sep 2007
Publication
The development of an infrastructure for the future hydrogen economy will require the simultaneous development of a set of codes and standards. As part of the U.S. Department of Energy Hydrogen Fuel Cells & Infrastructure Technologies Program Sandia National Laboratories is developing the technical basis for assessing the safety of hydrogen-based systems for use in the development/modification of relevant codes and standards. This work includes experimentation and modelling to understand the fluid mechanics and dispersion of hydrogen for different release scenarios including investigations of hydrogen combustion and subsequent heat transfer from hydrogen flames. The resulting technical information is incorporated into engineering models that are used for assessment of different hydrogen release scenarios and for input into quantitative risk assessments (QRA) of hydrogen facilities. The QRAs are used to identify and quantify scenarios for the unintended release of hydrogen and to identify the significant risk contributors at different types of hydrogen facilities. The results of the QRAs are one input into a risk-informed codes and standards development process that can also include other considerations by the code and standard developers. This paper describes an application of QRA methods to help establish one key code requirement: the minimum separation distances between a hydrogen refuelling station and other facilities and the public at large. An example application of the risk-informed approach has been performed to illustrate its utility and to identify key parameters that can influence the resulting selection of separation distances. Important parameters that were identified include the selected consequence measures and risk criteria facility operating parameters (e.g. pressure and volume) and the availability of mitigation features (e.g. automatic leak detection and isolation). The results also indicate the sensitivity of the results to key modelling assumptions and the component leakage rates used in the QRA models.
Measurement Challenges for Hydrogen Vehicles
Apr 2019
Publication
Uptake of hydrogen vehicles is an ideal solution for countries that face challenging targets for carbon dioxide reduction. The advantage of hydrogen fuel cell electric vehicles is that they behave in a very similar way to petrol engines yet they do not emit any carbon containing products during operation. The hydrogen industry currently faces the dilemma that they must meet certain measurement requirements (set by European legislation) but cannot do so due to a lack of available methods and standards. This paper outlines the four biggest measurement challenges that are faced by the hydrogen industry including flow metering quality assurance quality control and sampling.
Safety Considerations for Hydrogen Test Cells
Sep 2009
Publication
The properties of hydrogen compared to conventional fuels such as gasoline and diesel are substantially different requiring adaptations to the design and layout of test cells for hydrogen fuelled engines and vehicles. A comparison of hydrogen fuel properties versus conventional fuels in this paper provides identification of requirements that need to be adapted to design a safe test cell. Design examples of actual test cells are provided to showcase the differences in overall layout and ventilation safety features fuel supply and metering and emissions measurements. Details include requirements for ventilation patterns the necessity for engine fume hoods as well as hydrogen specific intake and exhaust design. The unique properties of hydrogen in particular the wide flammability limits and nonvisible flames also require additional safety features such as hydrogen sensors and flame cameras. A properly designed and implemented fuel supply system adds to the safety of the test cell by minimizing the amount of hydrogen that can be released. Apart from this the properties of hydrogen also require different fuel consumption measurement systems pressure levels of the fuel supply system additional ventilation lines strategically placed safety solenoids combined with appropriate operational procedures. The emissions measurement for hydrogen application has to be expanded to include the amount of unburned hydrogen in the exhaust as a measurement of completeness of combustion. This measurement can also be used as a safety feature to avoid creation of ignitable hydrogen-air mixtures in the engine exhaust. The considerations provided in this paper lead to the conclusion that hydrogen IC engines can be safely tested however properly designed test cell and safety features have to be included to mitigate the additional hazards related to the change in fuel characteristics.
Natural and Forced Ventilation Study In An Enclosure Hosting a Fuel Cell
Sep 2009
Publication
The purpose of the experimental work is to determine the conditions for which an enclosure can guest a fuel cell for civil use. Concerning the installation permitting guide this study allows the safe use of the fuel cell in case of small not catastrophic leakages. In fact the correct plan of the vents in the enclosure guarantees the low concentration of hydrogen (H2) below the LFL.
Experimental Study of Hydrogen Release Accidents in a Vehicle Garage
Sep 2009
Publication
Storing a hydrogen fuel-cell vehicle in a garage poses a potential safety hazard because of the accidents that could arise from a hydrogen leak. A series of tests examined the risk involved with hydrogen releases and deflagrations in a structure built to simulate a one-car garage. The experiments involved igniting hydrogen gas that was released inside the structure and studying the effects of the deflagrations. The “garage” measured 2.72 m high 3.64 m wide and 6.10 m long internally and was constructed from steel using a reinforced design capable of withstanding a detonation. The front face of the garage was covered with a thin transparent plastic film. Experiments were performed to investigate extended-duration (20–40 min) hydrogen leaks. The effect that the presence of a vehicle in the garage has on the deflagration was also studied. The experiments examined the effectiveness of different ventilation techniques at reducing the hydrogen concentration in the enclosure. Ventilation techniques included natural upper and lower openings and mechanical ventilation systems. A system of evacuated sampling bottles was used to measure hydrogen concentration throughout the garage prior to ignition and at various times during the release. All experiments were documented with standard and infrared (IR) video. Flame front propagation was monitored with thermocouples. Pressures within the garage were measured by four pressure transducers mounted on the inside walls of the garage. Six free-field pressure transducers were used to measure the pressures outside the garage.
Estimation of an Allowable Hydrogen Permeation Rate From Road Vehicle Compressed Gaseous Hydrogen Storage Systems In Typical Garages- Part 3
Sep 2009
Publication
The formation of a flammable hydrogen-air mixture is a major safety concern especially for closed space. This hazardous situation can arise when considering permeation from a car equipped with a composite compressed hydrogen tank with a non-metallic liner in a closed garage. In the following paper a scenario is developed and analysed with a simplified approach and a numerical simulation in order to estimate the evolution of hydrogen concentration. The system is composed of typical size garage and hydrogen car’s tank. Some parameters increasing permeation rate (i.e. tank’s material thickness and pressure) have been chosen to have a conservative approach. A close look on the top of tank surface showed that the concentration grows as square root of time and does not exceed 8.2×10-3 % by volume. Also a simplified comparative analysis estimated that the buoyancy of hydrogen-air mixture prevails on the diffusion 35 seconds after permeation starts in good agreement with simulation where time is at about 80 seconds. Finally the numerical simulations demonstrated that across the garage height the hydrogen is nearly distributed linearly and the difference in hydrogen concentration at the ceiling and floor is negligible (i.e. 3×10-3 %).
Roadmap to Hydrogen in the NTS - National Grid Gas Transmission
Jan 2020
Publication
DNV GL believes that the National Transmission System (NTS) will be central to the future of decarbonised energy in the UK. The future NTS could transmit natural gas hydrogen blends of the two and carbon dioxide. New pipelines will be built however a large cost-saving is available if the existing NTS assets can also be re-purposed. To move towards this future National Grid Gas Transmission wants to develop a project to trial injection hydrogen into the NTS. This is an opportunity to show that National Grid is part of the solution to achieving Net Zero. The trial will demonstrate to the Government and public that re-purposing the NTS is cost-effective safe and involves minimal disruption.
This report sets out a roadmap of projects to provide the knowledge needed for the trial. The roadmap was developed by assessing the knowledge required and how much of it already existed. The knowledge already available is summarised in this report with references to where further details can be found. Gaps in the knowledge are then described. The roadmap consists of projects to conduct work to close the knowledge gaps. The results are summarised in the figures below and in the box to the right.
This report and any attachment is freely available on the ENA Smarter Networks Portal here. IGEM Members can download the report and any attachment directly by clicking on the pdf icon above.
This report sets out a roadmap of projects to provide the knowledge needed for the trial. The roadmap was developed by assessing the knowledge required and how much of it already existed. The knowledge already available is summarised in this report with references to where further details can be found. Gaps in the knowledge are then described. The roadmap consists of projects to conduct work to close the knowledge gaps. The results are summarised in the figures below and in the box to the right.
This report and any attachment is freely available on the ENA Smarter Networks Portal here. IGEM Members can download the report and any attachment directly by clicking on the pdf icon above.
For a Successful Arrival of the Hydrogen Economy Improve Now the Confidence Level of Risk Assessments
Sep 2009
Publication
For large-scale distribution and use of energy carriers classified as hazardous material in many countries as a method to assist land use planning to grant licenses to design a safe installation and to operate it safely some form of risk analysis and assessment is applied. Despite many years of experience the methods have still their weaknesses even the most elaborated ones as e.g. shown by the large spread in results when different teams perform an analysis on a same plant as was done in EU projects. Because a fuel as hydrogen with its different properties will come new in the daily use of many people incidents may happen and risks will be discussed. HySafe and other groups take good preparatory action in this respect and work in the right direction as appears from various documents produced. However already a superficial examination of the results so far tells that further cooperative work is indispensable. To avoid criticism skepticism and frustration not only the positive findings should be described and general features of the methods but the community has also to give strong guidance with regard to the uncertainties. Scenario development appears to be very dependent on insight and experience of an individual analyst leak and ignition probability may vary over a wide range of values Computational Fluid Dynamics or CFD models may lead to very different result. The Standard Benchmark Exercise Problems SBEPs are a good start but shall produce guidelines or recommendations for CFD use or even perhaps certification of models. Where feasible narrowing of possible details of scenarios to the more probable ones taking into account historical incident data and schematizing in bowties more explicit use of confidence intervals on e.g. failure rates and ignition probability estimates will help. Further knowledge gaps should be defined.
Spontaneous Ignition of Hydrogen Leaks, a Review of Postulated Mechanisms
Sep 2005
Publication
Over the last century there have been reports of high pressure hydrogen leaks igniting for no apparent reason and several ignition mechanisms have been proposed. Although many leaks have ignited there are also reported leaks where no ignition has occurred. Investigations of ignitions where no apparent ignition source was present have often been superficial with a mechanism postulated which whilst appearing to satisfy the conditions prevailing at the time of the release simply does not stand up to rigorous scientific analysis. Some of these proposed mechanisms have been simulated in a laboratory under superficially identical conditions and appear to be rigorous and scientific but the simulated conditions often do not have the same large release rates or quantities mainly because of physical constraints of a laboratory. Also some of the release scenarios carried out or simulated in laboratories are totally divorced from the realistic situation of most actual leaks. Clearly there are gaps in the knowledge of the exact ignition mechanism for releases of hydrogen particularly at the high pressures likely to be involved in future storage and use. Mechanisms which have been proposed in the past are the reverse Joule-Thomson effect; electrostatic charge generation; diffusion ignition; sudden adiabatic compression; and hot surface ignition. Of these some have been characterized by means of computer simulation rather than by actual experiment and hence are not validated. Consequently there are discrepancies between the theories releases known to have ignited and releases which are known to have not ignited. From this postulated ignition mechanisms which are worthy of further study have been identified and the gaps in information have been highlighted. As a result the direction for future research into the potential for ignition of hydrogen escapes has been identified.
A Safety Assessment of Hydrogen Supply Piping System by Use of FDS
Sep 2017
Publication
At least once air filling a piping from main hydrogen pipe line to an individual home end should be replaced with hydrogen gas to use the gas in the home. Special attention is required to complete the replacing operation safely because air and supplied hydrogen may generate flammable/explosive gas mixture in the piping. The most probable method to fulfill the task is that at first an inert gas is used to purge air from the piping and then hydrogen will be supplied into the piping. It is easily understood that the amount of the inert gas consumed by this method is much to purge whole air especially in long piping system. Hence to achieve more economical efficiency an alternative method was considered. In this method previously injected nitrogen between air and hydrogen prevents them from mixing. The key point is that how much nitrogen is required to prevent the dangerous mixing and keep the condition in the piping safe. The authors investigated to find the minimum amount of nitrogen required to keep the replacing operation safe. The main objective of this study is to assess the effect of nitrogen and estimate a pipe length that the safety is maintained under various conditions by using computational fluid dynamic (CFD). The effects of the amount of injected nitrogen hydrogen-supply conditions and the structure of piping system are discussed.
Hydrogen-air Deflagrations in Open Atmosphere- Large Eddy Simulation Analysis of Experimental Data
Sep 2005
Publication
The largest known experiment on hydrogen-air deflagration in the open atmosphere has been analysed by means of the large eddy simulation (LES). The combustion model is based on the progress variable equation to simulate a premixed flame front propagation and the gradient method to decouple the physical combustion rate from numerical peculiarities. The hydrodynamic instability has been partially resolved by LES and unresolved effects have been modelled by Yakhot's turbulent premixed combustion model. The main contributor to high flame propagation velocity is the additional turbulence generated by the flame front itself. It has been modelled based on the maximum flame wrinkling factor predicted by Karlovitz et al. theory and the transitional distance reported by Gostintsev with colleagues. Simulations are in a good agreement with experimental data on flame propagation dynamics flame shape and outgoing pressure wave peaks and structure. The model is built from the first principles and no adjustable parameters were applied to get agreement with the experiment.
CFD Modeling OF LH2 Dispersion Using the ADREA-HF Code
Sep 2011
Publication
In the present work the computational fluid dynamics (CFD) code ADREA-HF has been applied to simulate the very recent liquefied hydrogen spill experiments performed by the Health Safety Laboratory (HSL). The experiment consists of four LH2 release trials over concrete at a fixed rate of 60 lt/min but with different release direction height and duration. In the modeling the hydrogen source was treated as a two phase jet enabling simultaneous modeling of pool formation spreading as well as hydrogen vapor dispersion. Turbulence was modeled with the standard k- model modified for buoyancy effects. The effect of solidification of the atmospheric humidity was taken into account. The predicted concentration at the experimental sensors? locations was compared with the observed one. The results from the comparison of the predicted concentration with and without solidification of the atmospheric humidity indicate that the released heat from the solidification affects significantly the buoyant behavior of the hydrogen vapor. Therefore the simulation with solidification of the atmospheric humidity is in better agreement with the experiment.
Numerical Simulation of Hydrogen Explosion Tests with a Barrier Wall for Blast Mitigation
Sep 2005
Publication
We have investigated hydrogen explosion risk and its mitigation focusing on compact hydrogen refuelling stations in urban areas. In this study numerical analyses were performed of hydrogen blast propagation and the structural behaviour of barrier walls. Parametric numerical simulations of explosions were carried out to discover effective shapes for blast-mitigating barrier walls. The explosive source was a prismatic 5.27 m3 volume that contained 30% hydrogen and 70% air. A reinforced concrete wall 2 m tall by 10 m wide and 0.15 m thick was set 2 or 4 m away from the front surface of the source. The source was ignited at the bottom centre by a spark for the deflagration case and 10 g of C-4 high explosive for two detonation cases. Each of the tests measured overpressures on the surfaces of the wall and on the ground displacements of the wall and strains of the rebar inside the wall. The blast simulations were carried out with an in-house CFD code based on the compressive Euler equation. The initial energy estimated from the volume of hydrogen was a time-dependent function for the deflagration and was released instantaneously for the detonations. The simulated overpressures were in good agreement with test results for all three test cases. DIANA a finite element analysis code released by TNO was used for the structural simulations of the barrier wall. The overpressures obtained by the blast simulations were used as external forces. The analyses simulated the displacements well but not the rebar strains. The many shrinkage cracks that were observed on the walls some of which penetrated the wall could make it difficult to simulate the local behaviour of a wall with high accuracy and could cause strain gages to provide low-accuracy data. A parametric study of the blast simulation was conducted with several cross-sectional shapes of barrier wall. A T-shape and a Y-shape were found to be more effective in mitigating the blast.
Fire Prevention Technical Rule for Gaseous Hydrogen Refuelling Stations
Sep 2005
Publication
In the last years different Italian hydrogen projects provided for gaseous hydrogen motor vehicles refuelling stations. Motivated by the lack of suitable set of rules in the year 2002 Italian National Firecorps (Institute under the Italian Ministry of the Interior) formed an Ad Hoc Working Group asked to regulate the above-said stations as regards fire prevention and protection safety. This Working Group consists of members coming from both Firecorps and academic world (Pisa University). Throughout his work this Group produced a technical rule covering the fire prevention requirements for design construction and operation of gaseous hydrogen refuelling stations. This document has been approved by the Ministry’s Technical Scientific Central Committee for fire prevention (C.C.T.S.) and now it has to carry out the “Community procedure for the provision of information”. This paper describes the main safety contents of the technical rule.
Mixing of Dense or Light Gases with Turbulent Air- a Fast-Running Model for Lumped Parameter Codes
Sep 2005
Publication
The release of gases heavier than air like propane at ground level or lighter than air like hydrogen close to a ceiling can both lead to fire and explosion hazards that must be carefully considered in safety analyses. Even if the simulation of accident scenarios in complex installations and long transients often appears feasible only using lumped parameter computer codes the phenomenon of denser or lighter gas dispersion is not implicitly accounted by these kind of tools. In the aim to set up an ad hoc model to be used in the computer code ECART fluid-dynamic simulations by the commercial FLUENT 6.0 CFD code are used. The reference geometry is related to cavities having variable depth (2 to 4 m) inside long tunnels filled with a gas heavier or lighter than air (propane or hydrogen). Three different geometrical configurations with a cavity width of 3 6 and 9 m are considered imposing different horizontal air stream velocities ranging from 1 to 5 m/s. A stably-stratified flow region is observed inside the cavity during gas shearing. In particular it is found that the density gradient tends to inhibit turbulent mixing thus reducing the dispersion rate. The obtained data are correlated in terms of main dimensionless groups by means of a least squares method. In particular the Sherwood number is correlated as a function of Reynolds a density ratio modified Froude numbers and in terms of the geometrical parameter obtained as a ratio between the depth of the air-dense gas interface and the length of the cavity. This correlation is implemented in the ECART code to add the possibility to simulate large installations during complex transients lasting many hours with reasonable computation time. An example of application to a typical case is presented.
Large Scale Experiments- Deflagration and Deflagration to Detonation within a Partial Confinement Similar to a Lane
Sep 2005
Publication
About 20 years ago Fraunhofer ICT has performed large scale experiments with premixed hydrogen air mixtures [1]. A special feature has been the investigation of the combustion of the mixture within a partial confinement simulating some sort of a “lane” which may exist in reality within a hydrogen production or storage plant for example. Essentially three different types of tests have been performed: combustion of quiescent mixtures combustion of mixtures with artificially generated turbulence by means of a fan and combustion of mixtures with high speed flame jet ignition. The observed phenomena will be discussed on the basis of measured turbulence levels flame speeds and overpressures. Conditions for DDT concerning critical turbulence levels and flame speeds as well as a scaling rule for DDT related to the detonation cell size of the mixture can be derived from the experiments for this special test setup. The relevance of the results with respect to safety aspects of future hydrogen technology is assessed. Combustion phenomena will be highlighted by the presentation of impressive high speed film videos.
Numerical Modelling of Hydrogen Release, Mixture and Dispersion in Atmosphere.
Sep 2005
Publication
The method of the numerical solution of a three-dimensional problem of atmospheric release dispersion and explosion of gaseous admixtures is presented. It can be equally applied for gases of different densities including hydrogen. The system of simplified Navie-Stocks equations received by truncation of viscous members (Euler equations with source members) is used to obtain a numerical solution. The algorithm is based on explicit finite-difference Godunov scheme of arbitrary parameters breakup disintegration. To verify the developed model and computer system comparisons of numerical calculations with the published experimental data on the dispersion of methane and hydrocarbons explosions have been carried out. Computational experiments on evaporation and dispersion of spilled liquid hydrogen and released gaseous hydrogen at different wind speeds have been conducted. The largest mass concentrations of hydrogen between the bottom and top limits of flame propagation and cloud borders have been determined. The problem of the explosion of a hydrogen-air cloud of the complex form generated by large-scale spillage of liquid hydrogen and instant release of gaseous hydrogen has been numerically solved at low wind speed. Shock-wave loadings affecting the buildings located on a distance of 52 m from a hydrogen release place have been shown.
The Hydrogen Safety Program of the US Department of Energy
Sep 2005
Publication
Demonstrated safety in the production distribution and use of hydrogen will be critical to successful implementation of a hydrogen infrastructure. Recognizing the importance of this issue the U.S. Department of Energy has established the Hydrogen Safety Program to ensure safe operations of its hydrogen research and development program as well as to identify and address needs for new knowledge and technologies in the future hydrogen economy. Activities in the Safety Program range across the entire safety spectrum including: R&D devoted to investigation of hydrogen behaviour physical characteristics materials compatibility and risk analysis; inspection and investigation into the safety procedures and practices of all hydrogen projects supported by DOE funds; development of critical technologies for safe hydrogen systems such as sensors and design techniques; and safety training and education for emergency responders code inspectors and the general public. Throughout its activities the Safety Program encourages the open sharing of information to enable widespread benefit from any lessons learned or new information developed.
This paper provides detailed descriptions of the various activities of the DOE Hydrogen Safety Program and includes some example impacts already achieved from its implementation.
This paper provides detailed descriptions of the various activities of the DOE Hydrogen Safety Program and includes some example impacts already achieved from its implementation.
1D Phenomenological Model Estimating the Overpressure which could be Generated by Gas Explosion in a Congested Space
Sep 2005
Publication
A phenomenological approach is developed to calculate the velocity of flame propagation and to estimate the value of pressure peak when igniting gaseous combustible mixtures in a congested space. The basic idea of this model is afterburning of the remanent fuel in pockets of congested space behind the flame front. The estimation of probable overpressure peak is based on solution of one-dimensional problem of the piston (having corresponding symmetry) moving with given velocity in polytropic gas. Submitted work is the first representation of such phenomenological approach and is realized for the simplest situation close to one-dimensional.
On Numerical Simulation of Liquefied and Gaseous Hydrogen Releases at Large Scales
Sep 2005
Publication
The large eddy simulation (LES) model developed at the University of Ulster has been applied to simulate releases of 5.11 m3 liquefied hydrogen (LH2) in open atmosphere and gaseous hydrogen (GH2) in 20-m3 closed vessel. The simulations of a spill of liquefied hydrogen confirmed the advantage of LES application to reproduce experimentally observed eddy structure of hydrogen-air cloud. The inclination angle of simulated cloud is close to experimentally reported 300. The processes of two phase hydrogen release and heat transfer were simplified by inflow of gaseous hydrogen with temperature 20 K equal to boiling point. It is shown that difference in inflow conditions geometry and grid resolution affects simulation results. It is suggested that phenomenon of air condensationevaporation in the cloud in temperature range 20-90 K should be accounted for in future. The simulations reproduced well experimental data on GH2 release and transport in 20-m3 vessel during 250 min including a phenomenon of hydrogen concentration growth at the bottom of the vessel. Higher experimental hydrogen concentration at the bottom is assumed to be due to non-uniformity of temperature of vessel walls generating additional convection. The comparison of convective and diffusion terms in Navie-Stokes equations has revealed that a value of convective term is more than order of magnitude prevail over a value of turbulent diffusion term. It is assumed that the hydrogen transport to the bottom of the vessel is driven by the remaining chaotic flow velocities superimposed on stratified hydrogen concentration field. Further experiments and simulations with higher accuracy have to be performed to confirm this phenomenon. It has been demonstrated that hydrogen-air mixture became stratified in about 1 min after release was completed. However one-dimensional models are seen not capable to reproduce slow transport of hydrogen during long period of time characteristic for scenarios such as leakage in a garage.
Experimental Study of Jet-formed Hydrogen-air Mixtures and Pressure Loads from their Deflagrations in Low Confined Surroundings
Sep 2007
Publication
To provide more practical data for safety assessments a systematic study of explosion and combustion processes which can take place in mixtures produced by jet releases in realistic environmental conditions is required. The presented work is aimed to make step forward in this direction binding three inter-connected tasks: (i) study of horizontal and vertical jets (ii) study of the burnable clouds formed by jets in different geometry configurations and (iii) examination of combustion and explosion processes initiated in such mixtures. Test matrix for the jet experiments included variation of the release pressure and nozzle diameter with the aim to study details of the resulting hydrogen concentration and velocity profiles depending on the release conditions. In this study the following parameters were varied: mass flow rate jet nozzle diameter (to alter gas speed) and geometry of the hood located on top of the jet. The carried out experiments provided data on detailed structure for under-expanded horizontal and buoyant vertical jets and data on pressure loads resulted from deflagration of various mixtures formed by jet releases. The data on pressures waves generated in the conditions under consideration provides conservative estimation of pressure loads for realistic leaks.
Stress Corrosion Cracking Of Stainless Steels In High Pressure Alkaline Electrolysers
Sep 2005
Publication
Hydrogen-producing high-pressure electrolysers operating with 40% potassium hydroxide solution and an applied oxygen pressure up to 30 barg have been developed. Austenitic stainless steels of type AISI316L are deemed resistant to stress corrosion cracking (SCC) in concentrated KOH solutions. However SCC has on some occasions been observed on the oxygen side of the high-pressure electrolysers thereby representing a safety risk in the operation. Several materials have been tested for resistance to SCC using C-ring specimens in autoclaves under conditions similar to the high-pressure electrolysers and at temperatures up to 120°C. The tests confirmed the observed susceptibility of austenitic stainless steels to SCC in concentrated KOH solutions. Higher alloyed austenitic stainless steels also showed SCC. Duplex stainless steel and nickel based Alloy 28 showed good resistance to SCC in the given environment. Further tests are needed to define the optimum weld procedure.
A Survey Among Experts of Safety Related to the Use of Hydrogen as an Energy Carrier
Sep 2005
Publication
Based on the increasing need of energy for the future and the related risks to the environments due to burning of fossils fuels hydrogen is seen as an efficient and application related clean energy carrier that may be derived from renewable energy sources. A variety of applications connected with production and use of hydrogen and the related risks have been identified and a survey has been conducted among a number of experts as an internet exercise for unveiling the potential lack of necessary knowledge in order to handle hydrogen in a safe way concerning the various applications. The main results concern hazardous situations related to release and explosions of hydrogen in confined and semi-confined areas tunnels and garages and mitigation of hazardous situations i.e. preventions of accidents and reduction of consequences from accidents happening anyway.
Consequence Assessment of the BBC Hydrogen Refuelling Station, Using The Adrea-Hf Code
Sep 2009
Publication
Within the framework of the internal project HyQRA of the HYSAFE Network of Excellence (NoE) funded by the European Commission (EC) the participating partners were requested to apply their Quantitative Risk Assessment (QRA) methodologies on a predefined hypothetical gaseous H2 refuelling station named BBC (Benchmark Base Case). The overall aim of the HyQRA project was to perform an inter-comparison of the various QRA approaches and to identify the knowledge gaps on data and information needed in the QRA steps specifically related to H2. Partners NCSRD and UNIPI collaborated on a common QRA. UNIPI identified the hazards on site selected the most critical ones defined the events that could be the primary cause of an accident and provided to NCSRD the scenarios listed in risk order for the evaluation of the consequences. NCSRD performed the quantitative analysis using the ADREA-HF CFD code. The predicted risk assessment parameters (flammable H2 mass and volume time histories and maximum horizontal and vertical distances of the LFL from the source) were provided to UNIPI to analyze the consequences and to evaluate the risk and distances of damage. In total 15 scenarios were simulated. Five of them were H2 releases in confined ventilated spaces (inside the compression and the purification/drying buildings). The remaining 10 scenarios were releases in open/semi-confined spaces (in the storage cabinet storage bank and refuelling hose of one dispenser). This paper presents the CFD methodology applied for the quantitative analysis of the common UNIPI/NCSRD QRA and discusses the results obtained from the performed calculations.
Agent-Based as an Alternative to Prognostic Modelling of Safety Risks in Hydrogen Energy Scenarios
Sep 2005
Publication
Interest in the future is not new. Economic constraints and acceptability considerations of today compel decision-makers from industry and authorities to speculate on possible safety risks originating from a hydrogen economy developed in the future. Tools that support thinking about the long-term consequences of today's actions and resulting technical systems are usually prognostic based on data from past performance of past or current systems. It has become convention to assume that the performance of future systems in future environments can be accommodated in the uncertainties of such prognostic models resulting from sensitivity studies. This paper presents an alternative approach to modelling future systems based on narratives about the future. Such narratives based on the actions and interactions of individual "agents" are powerful means for addressing anxiety about engaging the imagination in order to prepare for events that are likely to occur detect critical conditions and to thus achieve desirable outcomes. This is the methodological base of Agent-Based Models (ABM) and this paper will present the approach discuss its strengths and weaknesses and present a preliminary application to modelling safety risks related to energy scenarios in a possible future hydrogen economy.
Safety Study of Hydrogen Supply Stations for the Review of High Pressure Gas Safety Law in Japan
Sep 2005
Publication
A safety study of gaseous hydrogen supply stations with 40MPa storage system is undertaken through a risk based approach. Accident scenarios are identified based on a generic model of hydrogen station. And risks of identified accident scenarios are estimated and evaluated comparing with risk acceptance criteria. Also safety measures for risk reduction are discussed. Especially for clearance distance it is proposed that the distance from high-pressurized equipment to site borders should be at least 6 meters. As a result of the study it is concluded that risks of accidental scenarios can be mitigated to acceptable level under the proposed safety measures with several exceptions. These exceptional scenarios are very unlikely to occur but expected to have extremely severe consequence once occurred.
Heading for Hydrogen - The Oil and Gas Industry’s Outlook for Hydrogen, From Ambition to Reality
May 2020
Publication
The future of hydrogen energy is wrapped up with the future of natural gas renewable energy and carbon capture and storage (CCS). This yields useful synergies but also political economic and technical complexity. Nevertheless our survey of more than 1000 senior oil and gas professionals suggests a more certain future for hydrogen and that the time is right to begin scaling the hydrogen economy.
Risk Assessment of Hydrogen Explosion for Private Car with Hydrogen-driven Engine
Sep 2009
Publication
The aim of the study is to identify and quantify the additional risks related to hydrogen explosions during the operation of a hydrogen-driven car. In a first attempt the accidents or failures of a simple one-tank hydrogen storage system have been studied as a main source of risk. Three types of initiators are taken into account: crash accidents fire accidents without crash (no other cars are involved) and hydrogen leakages in normal situation with following ignition. The consequences of hydrogen ignition and/or explosion depend strongly on environmental conditions (geometry wind etc.) therefore the different configurations of operational and environmental conditions are specified.<br/>Then Event Tree/Fault Tree methods are applied for the risk assessment.<br/>The results of quantification permit to draw conclusions about the overall added risk of hydrogen technology as well as about the main contributors to the risk. Results of this work will eventually contribute to the on-going pre-normative research in the field of hydrogen safety.
Study of Potential Leakage on Several Stressed Fittings for Hydrogen Pressures Up To 700 Bar
Sep 2011
Publication
In order to improve risk analyses and influence the design of the future H2 systems an experimental study on “real” leaks qualification and quantification was performed. In H2 energy applications fittings appeared as a significant leakage potential and subsequently explosion and flame hazards. Thus as a part of the “Horizon Hydrogène Energie” French program four kinds of commercial fittings usually employed on H2 systems were tested thanks to a new high pressure test bench – designed setup and operated by INERIS – allowing experiments to be led for H2 pressures until 700 bar. The fittings underwent defined stresses representative of H2 systems lifetime and beyond. The associated leaks – when existing – are characterized in terms of flow rate.
Enhancing the Efficiency of Power- and Biomass-to-liquid Fuel Processes Using Fuel-assisted Solid Oxide Electrolysis Cells
Apr 2022
Publication
Power- and biomass-to-liquid fuel processes (PBtL) can utilize renewable energy and residual forestry waste to produce liquid synthetic fuels which have the potential to mitigate the climate impacts of the current transportation infrastructure including the long-haul aviation sector. In a previous study we demonstrated that implementing a solid oxide electrolysis cell (SOEC) in the PBtL process can significantly increase the energy efficiency of fuel production by supplying the produced hydrogen to a reverse water gas shift (RWGS) reactor to generate syngas which is then fed downstream to a Fischer–Tropsch (FT) reactor. The tail gas emitted from the FT reactor consists primarily of a mixture of hydrogen carbon monoxide and methane and is often recycled to the entrained flow gasifier located at the beginning of the process. In this analysis we investigate the efficiency gains of the PBtL process as a result of redirecting the tail gas of the FT reactor to the anode of an SOEC to serve as fuel. Supplying fuel to an SOEC can lower the electrical work input required to facilitate steam electrolysis when reacting electrochemically with oxide ions in the anode which in turn can reduce oxygen partial pressures and thus alleviate material degradation. Accordingly we develop a thermodynamic framework to reveal the performance limits of fuel-assisted SOECs (FASOECs) and provide strategies to minimize oxygen partial pressures in the SOEC anode. Additionally we elucidate how much fuel is required to match the heating demands of a cell when steam is supplied to the cathode over a broad range of inlet temperatures and demonstrate the influence of a set of reaction pathways of the supplied fuel on the operating potential of an FASOEC and the corresponding efficiency gain of the PBtL process. Based on preliminary calculations we estimate that implementing an FASOEC in the PBtL process can increase the energy efficiency of fuel production to more than 90% depending on the amount of FT tail gas available to the system.
Estimation of an Allowable Hydrogen Permeation Rate From Road Vehicle Compressed Gaseous H2 Storage Systems In Typical Garages, Part 2: CFC Dispersion Calculations Using the ADREA-HF Code and Experimental Validation Using Helium Tests at the Garage Facility
Sep 2009
Publication
The time and space evolution of the distribution of hydrogen in confined settings was investigated computationally and experimentally for permeation from typical compressed gaseous hydrogen storage systems for buses or cars. The work was performed within the framework of the InsHyde internal project of the HySafe NoE funded by EC. The main goal was to examine whether hydrogen is distributed homogeneously within a garage like facility or whether stratified conditions are developed under certain conditions. The nominal hydrogen flow rate considered was 1.087 NL/min based on the then current SAE standard for composite hydrogen containers with a non-metallic liner (type 4) at simulated end of life and maximum material temperature in a bus facility with a volume of 681m3. The release was assumed to be directed upwards from a 0.15m diameter hole located at the middle part of the bus cylinders casing. Ventilation rates up to 0.03 ACH were considered. Simulated time periods extended up to 20 days. The CFD simulations performed with the ADREA-HF code showed that fully homogeneous conditions exist for low ventilation rates while stratified conditions prevail for higher ventilation rates. Regarding flow structure it was found that the vertical concentration profiles can be considered as the superposition of the concentration at the floor (driven by laminar diffusion) plus a concentration difference between floor and ceiling (driven by buoyancy forces). In all cases considered this concentration difference was found to be less than 0.5%. The dispersion experiments were performed at the GARAGE facility using Helium. Comparison between CFD simulations and experiments showed that the predicted concentrations were in good agreement with the experimental data. Finally simulations were performed using two integral models: the fully homogeneous model and the two-layer model proposed by Lowesmith et al. (ICHS-2 2007) and the results were compared both against CFD and the experimental data.
Evaluation of Heat Decarbonization Strategies and Their Impact on the Irish Gas Network
Dec 2021
Publication
Decarbonization of the heating sector is essential to meet the ambitious goals of the Paris Climate Agreement for 2050. However poorly insulated buildings and industrial processes with high and intermittent heating demand will still require traditional boilers that burn fuel to avoid excessive burden on electrical networks. Therefore it is important to assess the impact of residential commercial and industrial heat decarbonization strategies on the distribution and transmission gas networks. Using building energy models in EnergyPlus the progressive decarbonization of gas-fueled heating was investigated by increasing insulation in buildings and increasing the efficiency of gas boilers. Industrial heat decarbonization was evaluated through a progressive move to lowercarbon fuel sources using MATLAB. The results indicated a maximum decrease of 19.9% in natural gas utilization due to the buildings’ thermal retrofits. This coupled with a move toward the electrification of heat will reduce volumes of gas being transported through the distribution gas network. However the decarbonization of the industrial heat demand with hydrogen could result in up to a 380% increase in volumetric flow rate through the transmission network. A comparison between the decarbonization of domestic heating through gas and electrical heating is also carried out. The results indicated that gas networks can continue to play an essential role in the decarbonized energy systems of the future.
CFD Simulation Study to Investigate the Risk from Hydrogen Vehicles in Tunnels
Sep 2007
Publication
When introducing hydrogen-fuelled vehicles an evaluation of the potential change in risk level should be performed. It is widely accepted that outdoor accidental releases of hydrogen from single vehicles will disperse quickly and not lead to any significant explosion hazard. The situation may be different for more confined situations such as parking garages workshops or tunnels. Experiments and computer modelling are both important for understanding the situation better. This paper reports a simulation study to examine what if any is the explosion risk associated with hydrogen vehicles in tunnels. Its aim was to further our understanding of the phenomena surrounding hydrogen releases and combustion inside road tunnels and furthermore to demonstrate how a risk assessment methodology developed for the offshore industry could be applied to the current task. This work is contributing to the EU Sixth Framework (Network of Excellence) project HySafe aiding the overall understanding that is also being collected from previous studies new experiments and other modelling activities. Releases from hydrogen cars (containing 700 bar gas tanks releasing either upwards or downwards or liquid hydrogen tanks releasing only upwards) and buses (containing 350 bar gas tanks releasing upwards) for two different tunnel layouts and a range of longitudinal ventilation conditions have been studied. The largest release modelled was 20 kg H2 from four cylinders in a bus (via one vent) in 50 seconds with an initial release rate around 1000 g/s. Comparisons with natural gas (CNG) fuelled vehicles have also been performed. The study suggests that for hydrogen vehicles a typical worst-case risk assessment approach assuming the full gas inventory being mixed homogeneously at stoichiometry could lead to severe explosion loads. However a more extensive study with more realistic release scenarios reduced the predicted hazard significantly. The flammable gas cloud sizes were still large for some of the scenarios but if the actual reactivity of the predicted clouds is taken into account very moderate worst-case explosion pressures are predicted. As a final step of the risk assessment approach a probabilistic QRA study is performed in which probabilities are assigned to different scenarios time dependent ignition modelling is applied and equivalent stoichiometric gas clouds are used to translate reactivity of dispersed nonhomogeneous clouds. The probabilistic risk assessment study is based on over 200 dispersion and explosion CFD calculations using the commercially available tool FLACS. The risk assessment suggested a maximum likely pressure level of 0.1-0.3 barg at the pressure sensors that were used in the study. Somewhat higher pressures are seen elsewhere due to reflections (e.g. under the vehicles). Several other interesting observations were found in the study. For example the study suggests that for hydrogen releases the level of longitudinal tunnel ventilation has only a marginal impact on the predicted risk since the momentum of the releases and buoyancy of hydrogen dominates the mixing and dilution processes.
Effect of Hydrogen–diesel Dual-fuel Usage on Performance, Emissions and Diesel Combustion in Diesel Engines
Jul 2016
Publication
Diesel engines are inevitable parts of our daily life and will be in the future. Expensive after-treatment technologies to fulfil normative legislations about the harmful tail-pipe emissions and fuel price increase in recent years created expectations from researchers for alternative fuel applications on diesel engines. This study investigates hydrogen as additive fuel in diesel engines. Hydrogen was introduced into intake manifold using gas injectors as additive fuel in gaseous form and also diesel fuel was injected into cylinder by diesel injector and used as igniter. Energy content of introduced hydrogen was set to 0% 25% and 50% of total fuel energy where the 0% references neat diesel operation without hydrogen injection. Test conditions were set to full load at 750 900 1100 1400 1750 and finally 2100 r/min engine speed. Variation in engine performance emissions and combustion characteristics with hydrogen addition was investigated. Hydrogen introduction into the engine by 25% and 50% of total charge energy reveals significant decrease in smoke emissions while dramatic increase in nitrogen oxides. With increasing hydrogen content a slight rise is observed in total unburned hydrocarbons although CO2 and CO gaseous emissions reduced considerably. Maximum in-cylinder gas pressure and rate of heat release peak values raised with hydrogen fraction.
An Intercomparison Exercise on the Capabilities of CFD Models to Predict Deflagration of a Large-Scale H2-Air Mixture in Open Atmosphere
Sep 2005
Publication
This paper presents a compilation of the results supplied by HySafe partners participating in the Standard Benchmark Exercise Problem (SBEP) V2 which is based on an experiment on hydrogen combustion that is first described. A list of the results requested from participants is also included. The main characteristics of the models used for the calculations are compared in a very succinct way by using tables. The comparison between results together with the experimental data when available is made through a series of graphs. The results show quite good agreement with the experimental data. The calculations have demonstrated to be sensitive to computational domain size and far field boundary condition.
HyDeploy Gas Safe Webinar
Nov 2020
Publication
HyDeploy is a pioneering hydrogen energy project designed to help reduce UK CO2 emissions and reach the Government’s net zero target for 2050.
As the first ever live demonstration of hydrogen in homes HyDeploy aims to prove that blending up to 20% volume of hydrogen with natural gas is a safe and greener alternative to the gas we use now. It is providing evidence on how customers don’t have to change their cooking or heating appliances to take the blend which means less disruption and cost for them.
As the first ever live demonstration of hydrogen in homes HyDeploy aims to prove that blending up to 20% volume of hydrogen with natural gas is a safe and greener alternative to the gas we use now. It is providing evidence on how customers don’t have to change their cooking or heating appliances to take the blend which means less disruption and cost for them.
Fire Prevention Technical Rule for Gaseous Hydrogen Transport in Pipelines
Sep 2007
Publication
This paper presents the current results of the theoretical and experimental activity carried out by the Italian Working Group on the fire prevention safety issues in the field of the hydrogen transport in pipelines. From the theoretical point of view a draft document has been produced beginning from the regulations in force on the natural gas pipelines; these have been reviewed corrected and integrated with the instructions suitable to the use with hydrogen gas. From the experimental point of view a suitable apparatus has been designed and installed at the University of Pisa; this apparatus will allow the simulation of hydrogen releases from a pipeline with or without ignition of the hydrogen-air mixture. The experimental data will help the completion of the above-mentioned draft document with the instructions about the safety distances. However in the opinion of the Group the work on the text contents is concluded and the document is ready to be discussed with the Italian stakeholders involved in the hydrogen applications.
A Review of Synthetic Fuels for Passenger Vehicles
May 2019
Publication
Synthetic fuels produced with renewable surplus electricity depict an interesting solution for the decarbonization of mobility and transportation applications which are not suited for electrification. With the objective to compare various synthetic fuels an analysis of all the energy conversion steps is conducted from the electricity source i.e. wind- solar- or hydro-power to the final application i.e. a vehicle driving a certain number of miles. The investigated fuels are hydrogen methane methanol dimethyl ether and Diesel. While their production process is analyzed based on literature the usage of these fuels is analyzed based on chassis dynanometer measurement data of various EURO-6b passenger vehicles. Conventional and hybrid power-trains as well as various carbon dioxide sources are investigated in two scenarios. The first reference scenario considers market-ready technology only while the second future scenario considers technology which is currently being developed in industry and assumed to be market-ready in near future. With the results derived in this study and with consideration of boundary conditions i.e. availability of infrastructure storage technology of gaseous fuels energy density requirements etc. the most energy efficient of the corresponding suitable synthetic fuels can be chosen.
Can the Current EU Regulatory Framework Deliver Decarbonisation of Gas?
Jun 2020
Publication
This Energy Insight examines the current regulatory framework and challenges facing the natural gas industry (producers transporters suppliers and consumers) during the transition to a zero-carbon economy. The EU has declared its intention to be climate neutral by 2050 which means that the current level of natural gas usage will no longer be possible. However natural gas is a crucial component of energy supply representing 24 per cent of primary energy supply for the EU27+UK and 36 per cent of residential energy consumption. In some countries the use of natural gas is much higher – around 40 per cent of primary energy supply in Netherlands UK and Italy. The current framework impacting gas addresses two different market failures – natural monopolies for gas transportation and the externalities of Greenhouse Gas Emissions. The framework will not deliver decarbonisation of gas as it does not stimulate either supply or demand for alternatives such as hydrogen nor create the conditions to enable gas networks to transition to a decarbonised future. Policy makers need to prioritise their objectives to take account of the trade-offs involved in designing a new framework. Exclusion of certain low carbon technologies risks driving away investors and reduces the chances of targets being met whilst “picking winners” involves risks because of the many uncertainties involved such as future costs and time required to build new value chains.
Link to Document on Oxford Institute for Energy Studies website
Link to Document on Oxford Institute for Energy Studies website
Planning, Optimisation and Evaluation of Small Power-to-Gas-to-Power Systems: Case Study of a German Dairy
May 2022
Publication
In the course of the energy transition distributed hybrid energy systems such as the combination of photovoltaic (PV) and battery storages is increasingly being used for economic and ecological reasons. However renewable electricity generation is highly volatile and storage capacity is usually limited. Nowadays a new storage component is emerging: the power-to-gas-to-power (PtGtP) technology which is able to store electricity in the form of hydrogen even over longer periods of time. Although this technology is technically well understood and developed there are hardly any evaluations and feasibility studies of its widespread integration into current distributed energy systems under realistic legal and economic market conditions. In order to be able to give such an assessment we develop a methodology and model that optimises the sizing and operation of a PtGtP system as part of a hybrid energy system under current German market conditions. The evaluation is based on a multi-criteria approach optimising for both costs and CO2 emissions. For this purpose a brute-force-based optimal design approach is used to determine optimal system sizes combined with the energy system simulation tool oemof.solph. In order to gain further insights into this technology and its future prospects a sensitivity analysis is carried out. The methodology is used to examine the case study of a German dairy and shows that PtGtP is not yet profitable but promising.
The Effect of Hydrogen Content and Yield Strength on the Distribution of Hydrogen in Steel a Diffusion Coupled Micromechanical FEM Study
Mar 2021
Publication
In this study we investigate the effect of the heterogeneous micromechanical stress fields resulting from the grain-scale anisotropy on the redistribution of hydrogen using a diffusion coupled crystal plasticity model. A representative volume element with periodic boundary conditions was used to model a synthetic microstructure. The effect of tensile loading initial hydrogen content and yield strength on the redistribution of lattice (CL) and dislocation trapped (Cx) hydrogen was studied. It was found that the heterogeneous micromechanical stress fields resulted in the accumulation of both populations primarily at the grain boundaries. This shows that in addition to the well-known grain boundary trapping the interplay of the heterogeneous micromechanical hydrostatic stresses and plastic strains contribute to the accumulation of hydrogen at the grain boundaries. Higher yield strength reduced the amount of Cx due to the resulting lower plastic deformation levels. On the other side the resulting higher hydrostatic stresses increased the depletion of CL from the compressive regions and its diffusion toward the tensile ones. These regions with increased CL are expected to be potential damage initiation zones. This aligns with the observations that high-strength steels are more susceptible to hydrogen embrittlement than those with lower-strength.
Modeling of a High Temperature Heat Exchanger to Supply Hydrogen Required by Fuel Cells Through Reforming Process
Sep 2021
Publication
Hydrogen as a clean fuel and a new energy source can be produced by various methods. One of these common and economical methods of hydrogen production is hydrocarbon vapor modification. This research studies hydrogen production using a propane steam reforming process inside a high temperature heat exchanger. The application of this high temperature heat exchanger in the path of the power supply line is a fuel cell stack unit to supply the required hydrogen of the device. The heat exchanger consists of a set of cylindrical tubes housed inside a packed-bed called a reformer. The energy required to perform the reaction is supplied through these tubes in which high temperature gas is injected and the heat exchanger is insulated to prevent energy loss. The results show that at maximum temperature and velocity of hot gases (900 K and 1.5 m s−1 ) complete consumption of propane can be observed before the outlet of the reformer. Also in the mentioned conditions the maximum hydrogen production (above 92%) is obtained. The best permeability under which the system can perform best is 1×10−9 m2.
Coordinated Control Scheme of a Hybrid Renewable Power System Based on Hydrogen Energy Storage
Aug 2021
Publication
An all-weather energy management scheme for island DC microgrid based on hydrogen energy storage is proposed. A dynamic model of a large-scale wind–solar hybrid hydrogen-generation power generation system was established using a quasi-proportional resonance (QPR). We used the distributed Nautilus vertical axis wind power generation system as the main output of the system and it used the photovoltaic and hydrogen energy storage systems as alternative energy sources. Based on meeting the load power requirements and controlling the bus voltage stability we can convert the excess energy of the microgrid to hydrogen energy. With a shortage of load power we can convert the stored hydrogen into electrical energy for the load. Based on the ANSYS FLUENT software platform the feasibility and superiority over large-scale distributed Nautilus vertical axis wind power generation systems are verified. Through the MATLAB/Simulink software platform the effectiveness of the energy management method is verified. The results show that the large-scale distributed Nautilus vertical axis wind power generation system runs well in the energy system produces stable torque produces energy better than other types of wind turbines and has less impact on the power grid. The energy management method can ensure the normal operation of the system 24 h a day under the premise of maintaining the stable operation of the electric hydrogen system without providing external energy.
Green Synthetic Fuels: Renewable Routes for the Conversion of Non-Fossil Feedstocks into Gaseous Fuels and Their End Uses
Jan 2020
Publication
Innovative renewable routes are potentially able to sustain the transition to a decarbonized energy economy. Green synthetic fuels including hydrogen and natural gas are considered viable alternatives to fossil fuels. Indeed they play a fundamental role in those sectors that are difficult to electrify (e.g. road mobility or high-heat industrial processes) are capable of mitigating problems related to flexibility and instantaneous balance of the electric grid are suitable for large-size and long-term storage and can be transported through the gas network. This article is an overview of the overall supply chain including production transport storage and end uses. Available fuel conversion technologies use renewable energy for the catalytic conversion of non-fossil feedstocks into hydrogen and syngas. We will show how relevant technologies involve thermochemical electrochemical and photochemical processes. The syngas quality can be improved by catalytic CO and CO2 methanation reactions for the generation of synthetic natural gas. Finally the produced gaseous fuels could follow several pathways for transport and lead to different final uses. Therefore storage alternatives and gas interchangeability requirements for the safe injection of green fuels in the natural gas network and fuel cells are outlined. Nevertheless the effects of gas quality on combustion emissions and safety are considered.
Electrosynthesized Ni-P Nanospheres with High Activity and Selectivity Towards Photoelectrochemical Plastics Reforming
May 2021
Publication
Photoelectrochemical reforming of plastic waste offers an environmentally-benign and sustainable route for hydrogen generation. Nonetheless little attention was paid to develop electrocatalysts that can efficiently and selectively catalyze oxidative transformation of valueless plastic wastes into valued chemicals. Herein we report on facile electrosynthesis of nickel-phosphorus nanospheres (nanoNi-P) and their versatility in catalyzing hydrogen generation water oxidation and reforming of polyethylene terephthalate (PET). Notably composite of nanoNi-P with carbon nanotubes (CNT/nanoNi-P) requires −180 mV overpotential to drive hydrogen generation at -100 mA cm−2. Besides CV-activated nanoNi-P (nanoNi-P(CV)) was shown to be capable of reforming PET into formate with high selectivity (Faradic efficiency= ∼100 %). Efficient and selective generation of hydrogen and formate from PET reforming is realized utilizing an Earth-abundant photoelectrochemical platform based on nanoNi-P(CV)-modified TiO2 nanorods photoanode and CNT/nanoNi-P cathode. This work paves a path for developing artificial leaf for simultaneous environmental mitigation and photosynthesis of renewable fuels and valued chemicals.
In Situ Neutron Radiography Investigations of Hydrogen Related Processes in Zirconium Alloys
Jun 2021
Publication
In situ neutron radiography experiments can provide information about diffusive processes and the kinetics of chemical reactions. The paper discusses requirements for such investigations. As examples of the zirconium alloy Zircaloy-4 the hydrogen diffusion the hydrogen uptake during high-temperature oxidation in steam and the reaction in nitrogen/steam and air/steam atmospheres results of in situ neutron radiography investigations are reviewed and their benefit is discussed.
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