United Kingdom

Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The “Magnesium group” of international experts contributing to IEA Task 32 “Hydrogen Based Energy Storage” recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures kinetics and thermodynamics of the systems based on MgH₂ nanostructuring new Mg-based compounds and novel composites and catalysis in the Mg based H storage systems. Finally thermal energy storage and upscaled H storage systems accommodating MgH₂ are presented.

This paper studies the economic feasibility of installing hydrogen networks for decarbonizing heat in urban areas. The study uses the Heat Infrastructure and Technology (HIT) spatially resolved optimization model to trade-off energy supply infrastructure and end-use technology costs for the most important heat-related energy vectors: gas heat electricity and hydrogen. Two model formulations are applied to a UK urban area: one with an independent hydrogen network and one that allows for retrofitting the gas network into hydrogen. Results show that for average hydrogen price projections cost-effective pathways for heat decarbonization toward 2050 include heat networks supplied by a combination of district-level heat pumps and gas boilers in the domestic and commercial sectors and hydrogen boilers in the domestic sector. For a low hydrogen price scenario when retrofitting the gas network into hydrogen a cost-effective pathway is replacing gas by hydrogen boilers in the commercial sector and a mixture of hydrogen boilers and heat networks supplied by district-level heat pumps gas and hydrogen boilers for the domestic sector. Compared to the first modelled year CO₂ emission reductions of 88% are achieved by 2050. These results build on previous research on the role of hydrogen in cost-effective heat decarbonization pathways.

This is a Network Innovation Allowance funded project overseen by a steering group comprising the UK and Ireland gas network operators (Cadent Gas Networks Ireland National Grid Northern Gas Networks SGN Wales and West). The project follows on from previous studies that modelled the role of green gases in decarbonising the GB economy. The role of this study is to understand the transition from the GB economy today to a decarbonised economy in 2050 focusing on how the transition is achieved and the competing and complementary nature of different low and zero emission fuels and technologies over time.

While the project covers the whole economy it focuses on  transport especially trucks as an early adopter of green gases and as a key enabler of the transition. The study and resulting report are aimed at the gas industry and government and tries to build a green gas decarbonisation narrative supported by a wide range of stakeholders in order clarify the path ahead and thereby focus future efforts on delivering decarbonisation through green gases as quickly as possible.

The objectives of the study are:

• Analyse the complete supply chain production distribution and use of electricity biomethane bio-SNG and hydrogen to understand the role of each fuel and the timeline for scaling up of their use.
• Develop a narrative based on these findings to show how the use of these fuels scales up over time and how they compete and complement one another.

Once a clear narrative to 2050 was developed put togethera series of policy asks and stakeholder actions to show what is required to achieve the narrative. The study included analysis of two scenarios a High Green Gas scenario and a Low Green Gas scenario. The narrative presented here focuses on the High Green Gas scenario with commentary on the Low Green Gas scenario covered in Chapter 6.

Green gases

This report discusses the future role of ‘green gases’ which are biomethane and hydrogen produced from low- and zero-carbon sources each produced via two main methods:

Biomethane from Anaerobic Digestion (AD): A mature technology for turning biological material into a non-fossil form of natural gas (methane). AD plants produce biogas which must then be upgraded to biomethane.

Biomethane from Bio-Substitute Natural Gas (Bio-SNG): This technology is at an earlier stage of development than AD but has the potential to unlock other feedstocks for biomethane production such as waste wood and residual household waste.

Blue Hydrogen: Hydrogen from reformation of natural gas which produces hydrogen and carbon monoxide. 90-95% of the carbon is captured and stored making this a low-carbon form of hydrogen.

Green Hydrogen: Water is split into hydrogen and oxygen via electrolysis using electricity generated by renewables. No carbon emissions are produced so this is zero-carbon hydrogen."

When looking out to 2050 there is huge uncertainty surrounding how gas will be consumed transported and sourced in Great Britain (GB). The extent of the climate change challenge is now widely accepted and the UK Government has introduced a legislative requirement for aggressive reductions in carbon dioxide (CO2) emissions out to 2050. In addition at European Union (EU) level a package of measures has been implemented to reduce greenhouse gas emissions improve energy efficiency and significantly increase the share of energy produced from renewable sources by 2020. These policy developments naturally raise the question of what role gas has to play in the future energy mix.



To help inform this debate the Energy Networks Association Gas Futures Group (ENA GFG) commissioned Redpoint and Trilemma to undertake a long-range scenario-based modelling study of the future utilisation of gas out to 2050 and the consequential impacts of this for gas networks. Our modelling assumptions draw heavily on the Department of Energy and Climate Change (DECC) 2050 Pathways analysis and we consider that our conclusions are fully compatible with both DECC‟s work and current EU policy objectives.



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Numerical simulations are carried out for a highly under-expanded hydrogen jet resulting from an accidental release of high-pressure hydrogen into the atmospheric environment. The predictions are made using two independent CFD codes namely CFX and KIVA. The KIVA code has been substantially modified by the present authors to enable large eddy simulation (LES). It employs a oneequation sub-grid scale (SGS) turbulence model which solves the SGS kinetic energy equation to allow for more relaxed equilibrium requirement and to facilitate high fidelity LES calculations with relatively coarser grids. Instead of using the widely accepted pseudo-source approach the complex shock structures resulting from the high under-expansion is numerically resolved in a small computational domain above the jet exit. The computed results are used as initial conditions for the subsequent hydrogen jet simulation. The predictions provide insight into the shock structure and the subsequent jet development. Such knowledge is valuable for studying the ignition characteristics of high-pressure hydrogen jets in the safety context.

Experimental studies were carried out to examine the lift-off and blow-out stability of H2/CO2 H2/Ar H2/C3H8 and H2/CH4 jet flames. The experiments were carried out using a burner with a 2mm inner diameter. The flame structures were recorded by direct filming and also by a schlieren apparatus. The experiments showed that the four gases affected the lift-off and blow-out stability of the hydrogen differently. The experiments showed that propane addition to an initially attached flame always produced lifted flame and the flame was blown out at higher jet velocity. The blow-out velocity decreased as the increasing in propane concentration. Direct blow-off of hydrogen/propane was never observed. Methane addition resulted in a relatively stable flame comparing with the carbon dioxide and propane addition. Comparisons of the stability of H2/C3H8 H2/CH4 and H2/CO2 flames showed that H2/C3H8 produced the highest lift-off height. Propane is much more effective in lift-off and blow out hydrogen flames. The study carried out a chemical kinetic analysis of H2/CO2 H2/Ar H2/C3H8 and H2/CH4 flames for a comparison of effect of chemical kinetics on flame stability.

This paper presents a compilation and discussion of the results supplied by HySafe partners participating in the Standard Benchmark Exercise Problem (SBEP) V1 which is based on an experiment on hydrogen release mixing and distribution inside a vessel. Each partner has his own point of view of the problem and uses a different approach to the solution. The main characteristics of the models employed for the calculations are compared. The comparison between results together with the experimental data when available is made. Relative deviations of each model from the experimental values are also included. Explanations and interpretations of the results are presented together with some useful conclusions for future work.

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:

• Cryogenic separation
• Membrane separation
• Pressure Swing Adsorption (PSA)

The technologies noted above require an energy input to drive the separation of gas components in the form of compression to provide a pressure differential. The configuration of the GB gas transmission and distribution networks provides a possible source of available energy through the pressure let-down in the network pressure tiers which could be used to drive the gas component separation processes. This study evaluated the gas separation technologies noted above against a selection of case studies based on actual network operating conditions to assess the technical andeconomic feasibility of hydrogen deblending in the GB gas network context. This study constitutes the first stage (proof of concept) in a programme of works that should provide the critical evidence for hydrogen deblending as a necessary component to enable the use of GB gas networks to transport and distribute hydrogen.

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.

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 %).

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.