United Kingdom

Blue hydrogen is viewed as an important energy vector in a decarbonised global economy but its large-scale and capital-intensive production displays economic performance vulnerabities in the face of increased market and regulatory uncertainty. This study analyses flexible (modular) blue hydrogen production plant designs and evaluates their effectiveness to enhance economic performance under uncertainty. The novelty of this work lies in the development of a comprehensive techno-economic evaluation framework that considers flexible centralised and decentralised blue hydrogen plant design alternatives in the presence of irreducible uncertainty whilst explicitly considering the time value of money economies of scale and learning effects. A case study of centralised and decentralised blue hydrogen production for the transport sector in the San Francisco area is developed to highlight the underlying value of flexibility. The proposed methodological framework considers various blue hydrogen plant designs (fixed phased and flexible) and compares them using relevant economic indicators (net present value (NPV) capex value-at-risk/gain etc.) through a detailed Monte Carlo simulation framework. Results indicate that flexible centralised hydrogen production yields greater economic value than alternative designs despite the associated cost-premium of modularity. It is also shown that the value of flexibility increases under greater uncertainty higher learning rates and weaker economies of scale. Moreover sensitivity analysis reveals that flexible design remains the preferred investment option over a wide range of market and regulatory conditions except for high initial hydrogen demand. Finally this study demonstrates that major regulatory and market uncertainties surrounding blue hydrogen production can be effectively managed through the application of flexible engineering system design that protects the investment from major downside risks whilst allowing access to favourable upside opportunities.

Direct gaseous fuel injection in internal combustion engines is a potential strategy for improving in-cylinder combustion processes and performance while reducing emissions and increasing hydrogen energy share (HES). Through use of numerical modelling the current study explores combustion in a compression ignition engine utilising a late compression/early power stroke direct gaseous hydrogen injection ignited by a diesel pilot at up to 99% HES. The combustion process of hydrogen in this type of engine is mapped out and compared to that of the same engine using methane direct injection. Four distinct phases of combustion are found which differ from that of pure diesel operation. Interaction of the injected gas jet with the chamber walls is found to have a considerable impact on performance and emission characteristics and is a factor which needs to be explored in greater detail in future studies. Considerable performance increase and carbon-based emission reductions are identified at up to 99% HES at high load but low load performance greatly deteriorated when 95% HES was exceeded due to a much reduced diesel pilot struggling to ignite the main hydrogen injection.

Industry is the biggest sector of energy consumption and greenhouse gas emissions whose decarbonisation is essential to achieve the Sustainable Development Goals. Carbon capture energy efficiency improvement and hydrogen are among the main strategies for industrial decarbonization. However novel approaches are needed to address the key requirements and differences between sectors to ensure they can work together to well integrate industrial decarbonisation with heat CO2 and hydrogen. The emerging Calcium Looping (CaL) is attracting interest in designing CO2-involved chemical processes for heat capture and storage. The reversibility relatively high-temperature (600 to 900 ◦C) and high energy capacity output as well as carbon capture function make CaL well-fit for CO2 capture and utilisation and waste heat recovery from industrial flue gases. Meanwhile methane dry reforming (MDR) is a promising technology to produce blue hydrogen via the consumption of two major greenhouse gases i.e. CO2 and CH4. It has great potential to combine the two technologies to achieve insitu CO2 utilization with multiple benefits. In this paper progresses on the reaction conditions and performance of CaL for CO2 capture and industrial waste heat recovery as well as MDR were screened. Secondly recent approaches to CaL-MDR synergy have been reviewed to identify the advantages. The major challenges in such a synergistic process include MDR catalyst deactivation CaL sorbents sintering and system integration. Thirdly the paper outlooks future work to explore a rational design of a multi-function system for the proposed synergistic process.

This review presents a state-of-the-art of geochemical geomechanical and hydrodynamic modelling studies in the Underground Hydrogen Storage (UHS) domain. Geochemical modelling assessed the reactivity of hydrogen and res pective fluctuations in hydrogen losses using kinetic reaction rates rock mineralogy brine salinity and the integration of hydrogen redox reactions. Existing geomechanics studies offer an array of coupled hydromechanical models suggesting a decline in rock failure during the withdrawal phase in aquifers compared to injection phase. Hydrodynamic modelling evaluations indicate the critical importance of relative permeability hysteresis in determining the UHS performance. Solubility and diffusion of hydrogen gas appear to have minimal impact on UHS. Injection and production rates cushion gas deployment and reservoir heterogeneity however significantly affect the UHS performance stressing the need for thorough modelling and experimental studies. Most of the current UHS modelling efforts focus on assessing the hydrodynamic aspects which are crucial for understanding the viability and safety of UHS. In contrast the lesser-explored geochemical and geomechanical considerations point to potential research gaps. A variety of modelling software tools such as CMG Eclipse COMSOL and PHREEQC evaluated those UHS underlying effects along with a few recent applications of datadriven-based Machine Learning (ML) techniques for enhanced accuracy. This review identified several unresolved challenges in UHS modelling: pronounced lack of expansive datasets leading to a gap between model predictions and their practical reliability; need robust methodologies capable of capturing natural subsurface heterogeneity while upscaling from precise laboratory data to field-scale conditions; demanding intensive computational resources and novel strategies to enhance simulation efficiency; and a gap in addressing geological uncertainties in subsurface environments suggesting that methodologies from oil reservoir simulations could be adapted for UHS. This comprehensive review offers a critical synthesis of the prevailing approaches challenges and research gaps in the domain of UHS thus providing a valuable reference document for further modelling efforts facilitating the informed advancements in this critical domain towards the realization of sustainable energy solutions.

Renewable energies such as the wind energy and solar energy generate low-carbon electricity which can directly charge battery electric vehicles (BEVs). Meanwhile the surplus electricity can be used to produce the “green hydrogen” which provides zero-emission hydrogen fuels to those fuel cell electric vehicles (FCEVs). In order to charge/refuel multi-energy vehicles we propose a novel scheme of hybrid hydrogen/electricity supply using cryogenic and superconducting technologies. In this scheme the green hydrogen is further liquefied into the high-density and low-pressure liquid hydrogen (LH2) for bulk energy storage and transmission. Taking the advantage of the cryogenic environment of LH2 (20 K) it can also be used as the cryogen to cool down super conducting cables to realize the virtually zero-loss power transmission from 100 % renewable sources to vehicle charging stations. This hybrid LH2/electricity energy pipeline can realize long-distance large-capacity and high efficiency clean energy transmission to fulfil the hybrid energy supply demand for BEVs and FCEVs. For the case of a 100 MW-class hybrid hydrogen/electricity supply station the system principle and energy management strategy are analyzed through 9 different operating sub-modes. The corresponding static and dynamic economic modeling are performed and the economic feasibility of the hybrid hydrogen/electricity supply is verified using life-cycle analysis. Taking an example of wind power capacity 1898 MWh and solar power capacity 1619 MWh per day the dynamic payback period is 15.06 years the profitability index is 1.17 the internal rate of return is 7.956 % and the accumulative NPV is 187.92 M$. The system design and techno-economic analysis can potentially offer a technically/economically superior solution for future multi-energy vehicle charging/refueling systems.

Green energy is at the forefront of current policy research and engineering but some of the potential fuels require either a lot of deeper research or a lot of infrastructure before they can be implemented. In the case of hydrogen both are true. This report aims to analyse the potential of hydrogen as a future fuel source by performing a life-cycle assessment. Through this the well-to-tank phase of fuel production and the usage phase of the system have been analysed. Models have also been created for traditional fuel systems to best compare results. The results show that hydrogen has great potential to convert marine transport to operating off green fuels when powered through low-carbon energy sources which could reduce a huge percentage of the international community’s greenhouse gas emissions. Hydrogen produced through wind powered alkaline electrolysis produced emission data 5.25 g of CO2 equivalent per MJ compared to the 210 g per MJ produced by a medium efficiency diesel equivalent system a result 40 times larger. However with current infrastructure in most countries not utilising a great amount of green energy production the effects of hydrogen usage could be more dangerous than current fuel sources owing to the incredible energy requirements of hydrogen production with even grid (UK) powered electrolysis producing an emission level of 284 g per MJ which is an increase against standard diesel systems. From this the research concludes that without global infrastructure change hydrogen will remain as a potential fuel rather than a common one.

This document is phase 2 of the energy storage strategy study and it covers the storage challenges of the energy transition. We start in section 3 by covering historical and current natural gas imports into the UK and what these could look like in the future. In section 4 we explore what demand for hydrogen could look like – this has a high level of uncertainty and future policy decisions will have significant impacts on hydrogen volumes and annual variations. We generated two hydrogen storage scenarios based on National Grid’s Future Energy Scenarios and the Climate Change Committee’s Sixth Carbon Budget to assess the future need for hydrogen storage in the UK. We also looked at an extreme weather scenario resulting from an area of high-pressure settled over the British Isles resulting in very low ambient temperatures an unusually high demand for heating and almost no wind generation. In section 5 we investigate options for hydrogen storage and build on work previously carried out by SGN. We discuss the differences between the properties of hydrogen and natural gas and how this affects line pack and depletion of line pack. We discuss flexibility on the supply and demand side and how this can impact on hydrogen storage. We provide a summary table which compares the various options for storage. In section 5 we explore hydrogen trade and options for import and export. Using information from other innovation projects we also discuss production of hydrogen from nuclear power and the impact of hybrid appliances on gas demand for domestic heat. In section 7 we discuss the outputs from a stakeholder workshop with about 40 stakeholders across industry academia and government. The workshop covered UK gas storage strategy to date hydrogen demand and corresponding storage scenarios to 2050 including consideration of seasonal variation and storage options.

This paper presents the HEGIT (Heat Electricity and Gas Infrastructure and Technology) model for optimal infrastructure planning for decarbonising heating in buildings. HEGIT is an optimisation model based on Mixed Integer Linear Programming. The model co-optimises the integrated operation and capacity expansion planning of electricity and gas grids as well as heating technologies on the consumer side while maintaining the security of supply and subject to different environmental operational and system-wide constraints. The three main features of the HEGIT model are: • It incorporates an integrated unit commitment and capacity expansion problem for coordinated operation and long-term investment planning of the electricity and gas grids. • It incorporates the flexible operation of heating technologies in buildings and demand response in operation and long-term investment planning of gas and electricity grids. • It incorporates a multi-scale techno-economic representation of heating technologies design features into the whole energy system modelling and capacity planning. These features enable the model to quantify the impacts of different policies regarding decarbonising heating in buildings on the operation and long-term planning of electricity and gas grids identify the cost-optimal use of available resources and technologies and identify strategies for maximising synergies between system planning goals and minimising trade-offs. Moreover the multi-scale feature of the model allows for multi-scale system engineering analysis of decarbonising heating including system-informed heating technology design identifying optimal operational setups at the consumer end and assessing trade-offs between consumer investment in heating technologies and infrastructure requirements in different heat decarbonisation pathways.

This is a summary report of a study which aimed to understand the safety feasibility cost and impacts for 7 industrial sites to switch from natural gas to 100% hydrogen for heating. The volunteer industrial sites:<br/>♦ are located away from industrial clusters<br/>♦ use natural gas to meet most of their energy demand<br/>♦ will likely be most impacted by decisions on the future of the natural gas grid<br/>We have published the report in order to share its findings with other industrial sites and wider industry in particular those considering hydrogen as an option for decarbonisation.<br/>Note that:<br/>♦ some work was carried out on a non-hydrogen alternative energy source but to a lesser level of detail and not to determine the optimal decarbonisation solution<br/>♦ the findings do not apply to other end user environments because of differences between these environments and the consumption of gas<br/>The study was commissioned in 2022 by the former Department for Business and Energy and undertaken by AECOM and their safety sub-contractor ESR.<br/>The evidence will inform strategic decisions in 2026 on the role of low carbon hydrogen as a replacement for natural gas heating.

To achieve carbon neutrality in Japan by 2050 renewable energy needs to be used as the main energy source. Based on the constraints of various renewable energies the importance of hydrogen cannot be ignored. This study aimed to investigate the diffusion of hydrogen demand technologies in various sectors and used projections and assumptions to investigate the hydrogen supply side. By performing simulations with the E3ME-FTT model and comparing various policy scenarios with the reference scenario the economic and environmental impacts of the policy scenarios for hydrogen diffusion were analyzed. Moreover the impact of realizing carbon neutrality by 2050 on the Japanese economy was evaluated. Our results revealed that large-scale decarbonization via hydrogen diffusion is possible (90% decrease of CO2 emissions in 2050 compared to the reference) without the loss of economic activity. Additionally investments in new hydrogen-based and other low-carbon technologies in the power sector freight road transport and iron and steel industry can improve the gross domestic product (1.6% increase in 2050 compared to the reference) as they invoke economic activity and require additional employment (0.6% increase in 2050 compared to the reference). Most of the employment gains are related to decarbonizing the power sector and scaling up the hydrogen supply sector while a lot of job losses can be expected in the mining and fossil fuel industries.

Hydrogen is considered the fuel of the future due to its cleaner nature compared to methane and gasoline. Therefore renewable hydrogen production technologies and long-term affordable and safe storage have recently attracted significant research interest. However natural underground hydrogen production and storage have received scant attention in the literature despite its great potential. As such the associated formation mechanisms geological locations and future applications remain relatively under-explored thereby requiring further investigation. In this review the global natural hydrogen formation along with reaction mechanisms (i.e. metamorphic processes pyritization and serpentinization reactions) as well as the suitable geological locations (i.e. ophiolites organic-rich sediments fault zones igneous rocks crystalline basements salt bearing strata and hydrocarbon-bearing basins) are discussed. Moreover the underground hydrogen storage mechanisms are detailed and compared with underground natural gas and CO2 storage. Techno-economic analyses of large-scale underground hydrogen storage are presented along with the current challenges and future directions.

This paper presents a comprehensive review of existing explosion mitigation techniques for tunnels and evaluates their applicability in scenarios of hydrogen tank rupture in a fire. The study provides an overview of the current state of the art in tunnel explosion mitigation and discusses the challenges associated with hydrogen explosions in the context of fire incidents. The review shows that there are several approaches available to decrease the effects of explosions including wrapping the tunnel with a flexible and compressible barrier and introducing energy-absorbing flexible honeycomb elements. However these methods are limited to the mitigation of the action and do not consider either the mitigation of the structural response or the effects on the occupants. The study highlights how the structural response is affected by the duration of the action and the natural period of the structural elements and how an accurate design of the element stiffness can be used in order to mitigate the structural vulnerability to the explosion. The review also presents various passive and active mitigation techniques aimed at mitigating the explosion effects on the occupants. Such techniques include tunnel branching ventilation openings evacuation lanes right-angled bends drop-down perforated plates or high-performance fibre-reinforced cementitious composite (HPFRCC) panels for blast shielding. While some of these techniques can be introduced during the tunnel's construction phase others require changes to the already working tunnels. To simulate the effect of blast wave propagation and evaluate the effectiveness of these mitigation techniques a CFD-FEM study is proposed for future analysis. The study also highlights the importance of considering these mitigation techniques to ensure the safety of the public and first responders. Finally the study identifies the need for more research to understand blast wave mitigation by existing structural elements in the application for potential accidents associated with hydrogen tank rupture in a tunnel.

This paper presents work undertaken by the HSE as part of the Hytunnel-CS project a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces. The test programme investigating hydrogen dispersion in tunnels involved simulating releases analogous to Thermally activated Pressure Relief Devices (TPRDs) typically found on hydrogen vehicles into the HSE Tunnel facility. The releases were scaled and based upon four scenarios: cars buses and two different train designs. The basis for this scaling was the size of the tunnel and the expected initial mass flow rates of the releases scenarios. The results of the 12 tests completed have been analysed in two ways: the initial mass flow rates of the tests were calculated based upon facility measurements and the Able-Noble equations of state for comparison to the intended initial flow rate; and observations of the hydrogen dispersion in the tunnel were made based on 15 hydrogen sensors arrayed along the tunnel. The calculated mass flow rates showed reasonable agreement with the intended initial conditions showing that the scaling methodology can be used to interpret the data based on the full-scale tunnel of interest. Observations of the hydrogen dispersion show an initial turbulent mixing followed by a movement of the mixed hydrogen/air cloud down the tunnel. No vertical stratification of the cloud was observed but this effect could be possible in longer tunnels or tunnels with larger diameters. Higher ventilation rates in the tunnel resulted in a reduction of the residence time of the hydrogen and a slight increase in the dilution.

This study investigates methods for reducing air pollution in the shipping sector particularly in port areas. The study examines the use of fuel cells as an alternative to diesel generators. Environmental pollution at ports remains a critical issue so using fuel cells as an alternative to conventional energy systems warrants further research. This study compares commercial fuel cell types that can be used on a case study very large crude carrier (VLCC) vessel specifically although the technology is applicable to other vessels and requirements. Seven different fuel cell types were ranked based on five criteria to accomplish this. The proton-exchange membrane cell type was found to be the most suitable fuel cell type for the case study vessel. Based on the input fuel ammonia-based hydrogen storage has been identified as the most promising option along with using an ammonia reforming unit to produce pure hydrogen. Furthermore this study provides an integrated fuel cell module and highlights the economic environmental and maintenance aspects of implementing the proton-exchange membrane fuel cell module for this case study. It also calculates the required space as a crucial constraint of implementing fuel cell technology at sea.

With the growing demand for green technologies hydrogen energy devices such as Proton Exchange Membrane (PEM) fuel cells and water electrolysers have received accelerated developments. However the materials and manufacturing cost of these technologies are still relatively expensive which impedes their widespread commercialization. Additive Manufacturing (AM) commonly termed 3D Printing (3DP) with its advanced capabilities could be a potential pathway to solve the fabrication challenges of PEM parts. Herein in this paper the research studies on the novel AM fabrication methods of PEM components are thoroughly reviewed and analysed. The key performance properties such as corrosion and hydrogen embrittlement resistance of the additively manufactured materials in the PEM working environment are discussed to emphasise their reliability for the PEM systems. Additionally the major challenges and required future developments of AM technologies to unlock their full potential for PEM fabrication are identified. This paper provides insights from the latest research developments on the significance of advanced manufacturing technologies in developing sustainable energy systems to address the global energy challenges and climate change effects.

Distributed waste-to-hydrogen (WtH) systems are a potential solution to tackle the dual challenges of sustainable waste management and zero emission transport. Here we propose a concept of distributed WtH systems based on gasification and fermentation to support hydrogen fuel cell buses in Glasgow. A variety of WtH scenarios were configured based on biomass waste feedstock hydrogen production reactors and upstream and downstream system components. A cost-benefit analysis (CBA) was conducted to compare the economic feasibility of the different WtH systems with that of the conventional steam methane reforming-based method. This required the curation of a database that included inter alia direct cost data on construction maintenance operations infrastructure and storage along with indirect cost data comprising environmental impacts and externalities cost of pollution carbon taxes and subsidies. The levelized cost of hydrogen (LCoH) was calculated to be 2.22 GB P/kg for municipal solid waste gasification and 2.02 GB P/kg for waste wood gasification. The LCoHs for dark fermentation and combined dark and photo fermentation systems were calculated to be 2.15 GB P/kg and 2.29 GB P/kg. Sensitivity analysis was conducted to identify the most significant influential factors of distributed WtH systems. It was indicated that hydrogen production rates and CAPEX had the largest impact for the biochemical and thermochemical technologies respectively. Limitations including high capital expenditure will require cost reduction through technical advancements and carbon tax on conventional hydrogen production methods to improve the outlook for WtH development.

The growing need for hydrogen indicates that there is likely to be a demand for transporting hydrogen. Hydrogen pipelines are an economical option but the issue of hydrogen damage to pipeline steels needs to be studied and investigated. So far limited research has been dedicated to determining how the choice of inspection method for pipeline integrity management changes depending on the presence of a coating. Thus this review aims to evaluate the effectiveness of inspection methods specifically for detecting the defects formed uniquely in coated hydrogen pipelines. The discussion will begin with a background of hydrogen pipelines and the common defects seen in these pipelines. This will also include topics such as blended hydrogen-natural gas pipelines. After which the focus will shift to pipeline integrity management methods and the effectiveness of current inspection methods in the context of standards such as ASME B31.12 and BS 7910. The discussion will conclude with a summary of newly available inspection methods and future research directions.

Reducing industrial emissions to achieve net-zero targets by the middle of the century will require profound and sustained changes to how energy intensive industries operate. Preliminary activity is now underway with governments of several developed economies starting to implement policy and providing funding to support the deployment of low carbon infrastructure into high emitting industrial clusters. While clusters appear to offer the economies of scale and institutional capacity needed to kick-start the industrial transition to date there has been little systematic assessment of the factors that may influence the success of these initiatives. Drawing from academic and grey literature this paper presents a rapid evidence assessment of the approaches being used to drive the development of low carbon industrial clusters internationally. Many projects are still at the scoping stage but it is apparent that current initiatives focus on the deployment of carbon capture technologies alongside hydrogen as a future secondary revenue stream. This model of decarbonisation funnels investment into large coastal clusters with access to low carbon electricity and tends to obscure questions about the integration of these technologies with other decarbonisation interventions such as material efficiency and electrification. The technology focus also omits the importance that a favourable location and shared history and culture appears to have played in helping progress the most advanced initiatives; factors that cannot be easily replicated elsewhere. If clusters are to kick-start the low-carbon industrial transition then greater attention is needed to the social and political dimensions of this process and to a broader range of decarbonisation interventions and cluster types than represented by current projects.

To situate its low-carbon transition process in longer-term real-world business contexts this article makes a longitudinal analysis of the UK petrochemical industry focusing on changing economic and socio-political environments and company strategies in the last 50 years. Using the Triple Embeddedness Framework the paper identifies two parallel and conflicting reorientation processes in the UK petrochemical industry. The first one which started in the 1970s and is driven by long-standing competitiveness problems led to retrenchment in the 1980s exit of incumbent companies (BP Shell ICI) and the entry of new firms (INEOS SABIC) in the 1990s and 2000s and diversification into upstream fossil fuel production and ethane imports in the 2010s. The second reorientation process which started in the 2010s is driven by climate change considerations and has led petrochemical firms to reluctantly explore low-carbon alternatives. Despite advancing ambitious visions and plans companies are weakly committed to low-carbon reorientation because this is layered on top of and conflicts with the deeper economically-motivated reorientation process. The paper further concludes that the industry's low-carbon plans and visions are partial because they focus more on some innovations (hydrogen-as-fuel CCS) than on other innovations (recycling bio-feedstocks synthetic feedstocks). Despite exploring alternatives firms also use political resistance strategies to hamper and delay deeper low-carbon reorientation

This paper describes the performance of explosion free in fire self-venting (TPRD-less) composite tanks of Type IV in fires of realistic intensity HRR/A=1 MW/m2 in conditions of first responders’ intervention. This breakthrough safety technology does not require the use of thermally activated pressure relief devices (TPRD). It provides microleaks-no-burst (LNB) performance of high-pressure hydrogen storage tanks in a fire. Two fire intervention strategies are investigated one is the removal of a vehicle with LNB tank from the fire and another is the extinction of the fire. The removal from the fire scenario is investigated for one carbon-carbon and one carbon-basalt double-composite wall tank prototype. The fire extinction scenario is studied for four carbon-basalt prototypes. All six prototypes of 7.5 L volume and nominal working pressure of 70 MPa demonstrated safe release of hydrogen through microchannels of the composite wall after melting a liner. The technology allows fire brigades to apply standard intervention strategies and tactics at the fire scene with hydrogen vehicles if LNB tanks are used in the vehicle.

Green hydrogen is often promoted as a key facilitator for the clean energy transition but its implementation raises concerns around energy justice. This paper examines the socio-political and techno-economic challenges that green hydrogen projects may pose to the three tenets of energy justice: distributive procedural and recognition justice. From a socio-political perspective the risk of neocolonial resource extraction uneven distribution of benefits exclusion of local communities from decision-making and disregard for indigenous rights and cultures threaten all three justice tenets. Techno-economic factors such as water scarcity land disputes and resource-related conflicts in potential production hotspots further jeopardise distributive and recognition justice. The analysis framed by an adapted PEST model reveals that while green hydrogen holds promise for sustainable development its implementation must proactively address these justice challenges. Failure to do so could perpetuate injustices exploitation and marginalisation of vulnerable communities undermining the sustainability goals it aims to achieve. The paper highlights the need for inclusive and equitable approaches that respect local sovereignty integrate diverse stakeholders and ensure fair access and benefit-sharing. Only by centring justice considerations can the transition to green hydrogen catalyse positive social change and realise its full potential as a driver of sustainable energy systems.

The MultHyFuel project aims to develop evidence-based guidelines for the safe implementation of Hydrogen Refueling Stations (HRS) in a multi-fuel context. As a part of the generation of good practice guidelines for HRS Hazardous Area Classification (HAC) methodologies were analyzed and applied to case studies representing example configurations of HRS. It has been anticipated that Negligible Extent (NE) classifications might be applicable for sections of the HRS for instance a hydrogen generator. A NE zone requires that an ignition of a flammable cloud would result in negligible consequences. In addition depending on the pressure of the system IEC 60079-10-1:2020 establishes specific requirements in order to classify the hazardous area as being of NE. One such requirement is that a zone of NE shall not be applied for releases from flammable gas systems at pressures above 2000 kPag (20 barg) unless a specific detailed risk assessment is documented. However there is no definition within the standard as to the requirements of the specific detailed risk assessment. In this work an example for a specific detailed risk assessment for the NE classification is presented:<br/>• Firstly the requirements of cloud volume dilution and background concentration for a zone of NE classification from IEC 60079-10-1:2020 are analyzed for hydrogen releases from equipment placed in a mechanically ventilated enclosure.<br/>• Secondly the consequences arising from the ignition of the localized cloud are estimated and compared to acceptable harm criteria in order to assess if negligible consequences are obtained from the scenario.<br/>• In addition a specific qualitative risk assessment for the ignition of the cloud in the enclosure was considered incorporating the estimated consequences and analyzing the available safeguards in the example system.<br/>Recommendations for the specific detailed risk assessment are proposed for this scenario with the intention to support improved definition of the requirement in future revisions of IEC 60079-10-1.

This work investigated hydrogen production from biomass feedstocks (i.e. glucose starch lignin and cellulose) using a 100 mL h-type proton exchange membrane electrolysis cell. Biomass electrolysis is a promising process for hydrogen production although low in technology readiness level but with a series of recognised advantages: (i) lower-temperature conditions (compared to thermochemical processes) (ii) minimal energy consumption and low-cost post-production (iii) potential to synthesise high-volume H2 and (iv) smaller carbon footprint compared to thermochemical processes. A Lewis acid (FeCl3 ) was employed as a charge carrier and redox medium to aid in the depolymerisation/oxidation of biomass components. A comprehensive analysis was conducted measuring the H2 and CO2 emission volume and performing electrochemical analysis (i.e. linear sweep voltammetry and chronoamperometry) to better understand the process. For the first time the influence of temperature on current density and H2 evolution was studied at temperatures ranging from ambient temperature (i.e. 19 ◦C) to 80 ◦C. The highest H2 volume was 12.1 mL which was produced by FeCl3 -mediated electrolysis of glucose at ambient temperature which was up to two times higher than starch lignin and cellulose at 1.20 V. Of the substrates examined glucose also showed a maximum power-to-H2 -yield ratio of 30.99 kWh/kg. The results showed that hydrogen can be produced from biomass feedstock at ambient temperature when a Lewis acid (FeCl3 ) is employed and with a higher yield rate and a lower electricity consumption compared to water electrolysis.

Underground hydrogen storage (UHS) plays a critical role in ensuring the stability and security of the future clean energy supply. However the efficiency and reliability of UHS technology depend heavily on the careful and criteria-driven selection of suitable storage sites. This study presents a hybrid multi-criteria decision-making framework integrating the Analytical Hierarchy Process (AHP) and Preference Ranking Organisation Method for Enrichment of Evaluations (PROMETHEE) to identify and select the best hydrogen storage sites among depleted gas reservoirs in the UK. To achieve this a new set of site selection criteria is proposed in light of the technical and economic aspects of UHS including location reservoir rock quality and tectonic characteristics maximum achievable hydrogen well deliverability rate working gas capacity cushion gas volume requirement distance to future potential hydrogen clusters and access to intermittent renewable energy sources (RESs). The framework is implemented to rank 71 reservoirs based on their potential and suitability for UHS. Firstly the reservoirs are thoroughly evaluated for each proposed criterion and then the AHP-PROMETHEE technique is employed to prioritise the criteria and rank the storage sites. The study reveals that the total calculated working gas capacity based on single-well plateau withdrawal rates is around 881 TWh across all evaluated reservoirs. The maximum well deliverability rates for hydrogen withdrawal are found to vary considerably among the sites; however 22 % are estimated to have deliverability rates exceeding 100 sm3 /d and 63 % are located within a distance of 100 km from a major hydrogen cluster. Moreover 70 % have access to nearby RESs developments with an estimated cumulative RESs capacity of approximately 181 GW. The results highlight the efficacy of the proposed multicriteria site selection framework. The top five highest-ranked sites for UHS based on the evaluated criteria are the Cygnus Hamilton Saltfleetby Corvette and Hatfield Moors gas fields. The insights provided by this study can contribute to informed decision-making sustainable development and the overall progress of future UHS projects within the UK and globally.

This paper presents work undertaken by the HSE as part of the Hytunnel-CS project a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces.<br/>Hydrogen vehicles typically have a Thermally activated Pressure Release Device (TPRD) providing protection to the on-board storage of the vehicle. Upon activation the content of the vessel is released in a blowdown. The release of this hydrogen gas poses a significant hazard of ignition. The consequences of such an ignition could also be compounded by confinement or congestion.<br/>HSE undertook a series of experiments investigating the consequences of these events by releasing hydrogen into a tunnel and causing ignitions. A sub-section of these tests involved steel structures providing congestion in the tunnel. The mass of hydrogen released into the tunnel prior to ignition was varied by storage pressure (up to 59 MPa) release diameter and ignition delay. The ignition delays were set based on the expected worst-case predicted by pre-simulation models. To assess the consequences overpressure measurements were made down the tunnel walls and for the tests with congestion at the face and rear of the congestion structures. The flame arrival time was also measured using exposed-tip thermocouples resulting in an estimate for flame speed down the tunnel. The measured overpressure and flame extent results are presented and compared against overpressure levels of concern.