Safety

In the current work the combustion behavior of hydrogen-carbon monoxide-air mixtures in semiconfined geometries is investigated in a large horizontal channel facility (dimensions 9 m x 3 m x 0.6 m (L x W x H)) as a part of a joint German nuclear safety project. In the channel with evenly distributed obstacles (blockage ratio 50%) and an open to air ground face homogeneous H2-CO-air mixtures are ignited at one end. The combustion behavior of the mixture is analyzed using the signals of pressure sensors modified thermocouples and ionization probes for flame front detection that are distributed along the channel ceiling. In the experiments various fuel concentrations (cH2 + cCO = 14 to 22 Vol%) with different H2:CO ratios (75:25 50:50 and 25:75) are used and the transition regions for a significant flame acceleration to sonic speed (FA) as well as to a detonation (DDT) are investigated. The conditions for the onset of these transitions are compared with earlier experiments performed in the same facility with H2-air mixtures. The results of this work will help to allow a more realistic estimation of the pressure loads generated by the combustion of H2-CO-air mixtures in obstructed semi-confined geometries.

Building  the  international  hydrogen  supply  chain  requires  the  large-scale  liquefied   hydrogen(LH2) carrier. During shipping LH2 with LH2 Carrier the tank is pressurized by LH2 evaporation due to heat ingress from outside. Before unloading LH2 at the receiving terminal reducing the tank pressure is essential for the safe tank operation. However pressure reduction might cause flashing leading to rapid  vaporization  of liquefied  hydrogen  liquid  leakage.   Moreover  it  was  considered  that  pressure recovery phenomenon which was not preferred in terms of tank pressure management occurred at the beginning  of  pressure  reduction.  Hence  the   purpose  of  our  research  is  to  clarify  the phenomenon inside  the  cargo  tank  during   pressure  reduction.  The  CFD  analysis  of  the  pressure  reduction phenomenon was conducted with the   VOF based in-house CFD code utilizing the C-CUP scheme combined  with  the  hybrid   Level  Set  and  MARS  method.  In  our  previous  research  the  pressure reduction  experiments   with  the  30  m³  LH2  tank  were  simulated  and  the  results  showed  that  the pressure   recovery  was  caused  by  the  boiling  delay  and  the  tank  pressure  followed  the   saturation pressure  after  the  liquid  was  fully  stirred.  In  this  paper  the  results  were re-evaluated  in  terms  of temperature.  While  pressure  reduction  was  dominant  the  temperature  of  vapor-liquid  interface decreased.  Once  the  boiling  bubble  stirred  the  interface  its  temperature  reached  the  saturation temperature  after  pressure  recovery  occurred.  Moreover  it  was  found  that  the  liquid  temperature during  pressure  reduction  could  not  be  measured  because  of  the  boiling  from  the  wall  of  the thermometer. The CFD analysis on pressure reduction of 1250 m³ tank for the LH2 Carrier was also very could occur in the case of the 1250 m³ tank in a certain condition. These results provide new insight into the development of the LH2 carrier.

Hydrogen has the physical and chemical characteristics of being flammable explosive and prone to leakage and its safety is the main issue faced by the promotion of hydrogen as an energy source. The most common scene in vehicle application is the longitudinal wind generated by driving and the original position of hydrogen concentration sensors (HCSs) did not consider the influence of longitudinal wind on the hydrogen leakage trajectory. In this paper the computational fluid dynamics (CFD) software STAR CCM 2021.1 is used to simulate the hydrogen leakage and diffusion trajectories of fuel cell vehicles (FCVs) at five different leakage locations the longitudinal wind speeds of 0 km/h 37.18 km/h and 114 km/h and it is concluded that longitudinal wind prolongs the diffusion time of hydrogen to the headspace and reduces the coverage area of hydrogen in the headspace with a decrease of 81.35%. In order to achieve a good detection effect of fuel cell vehicles within the longitudinal wind scene based on the simulated hydrogen concentration–time matrix the scene clustering method based on vector similarity evaluation was used to reduce the leakage scene set by 33%. Then the layout position of HCSs was optimized according to the proposed multi-scene full coverage response time minimization model and the response time was reduced from 5 s to 1 s.

The development of safe dispensing equipment for the fueling of heavy duty (HD) vehicles is critical to the expansion of this newly and quickly expanding market. This paper discusses the development of a HD dispenser and nozzles assembly (nozzle hose breakaway) for these new larger vehicles where flow rates are more than double compared to light duty (LD) vehicles. This equipment must operate at nominal pressures of 700 bar -40o C gas temperature and average flow rate of 5-10 kg/min at a high throughput commercial hydrogen fueling station without leaking hydrogen. The project surveyed HD vehicle manufacturers station developers and component suppliers to determine the basic specifications of the dispensing equipment and nozzle assembly. The team also examined existing codes and standards to determine necessary changes to accommodate HD components. From this information the team developed a set of specifications which will be used to design the dispensing equipment. In order to meet these goals the team performed computational fluid dynamic pressure modelling and temperature analysis in order to determine the necessary parameters to meet existing safety standards modified for HD fueling. The team also considered user operational and maintenance requirements such as freeze lock which has been an issue which prevents the removal of the nozzle from LD vehicles. The team also performed a failure mode and effects analysis (FMEA) to identify the possible failures in the design. The dispenser and nozzle assembly will be tested separately and then installed on an innovative HD fueling station which will use a HD vehicle simulator to test the entire system.

This paper presents an experimental study of a hydrogen fusible link developed for use in the detection of hydrogen and in the activation of passive ventilation or other safety systems. Fusible links are commonly used to passively close fire dampers in the event of a fire; they generally consist of two pieces of metal joined together by a low temperature alloy to form a single device. When exposed to fire the link will heat up and eventually melt the alloy causing the metal pieces to separate. The same principle has been adopted for the hydrogen fusible link in which hydrogen recombiner catalyst was coated onto small rectangular brass plates. These plates were then soldered together to create prototypes of the hydrogen fusible link. When the resulting link is exposed to a hydrogen-air mixture an exothermic reaction occurs on the catalyst surface that will heat up the link and melt the solder separating the two sections of the hydrogen fusible link. A series of experiments was performed to characterize the thermal response of the hydrogen fusible links to various hydrogen-air mixtures. The effect of both hydrogen concentration and its rate of accumulation on the increase of catalyst temperature was examined. This study demonstrated the applicability of the hydrogen fusible link for managing hydrogen risk.

Hydrogen has the potential as an energy solution to contribute to decarbonisation targets as it has the capability to deliver low-carbon energy at the scale required. For this to be realised the suitability of the existing natural gas pipeline networks for transporting hydrogen must be established. The current paper describes a feasibility study that was undertaken to assess the potential for repurposing the UK’s Local Transmission System (LTS) natural gas pipelines for hydrogen service. The analysis focused on SGN’s network which includes 3000 km of LTS pipelines in Scotland and the south of England. The characteristics of the LTS pipelines in terms of materials of construction and operation were first evaluated. This analysis showed that a significant percentage of SGN’s LTS network consists of lower strength grades of steel pipeline that operate at low stresses which are factors conducive to a pipeline’s suitability for hydrogen service. An assessment was also made of where existing approaches in pipeline operation may require modifications for hydrogen. The effects of changes in mechanical properties of steel pipelines on integrity and lifetime as a result of potential hydrogen degradation were demonstrated using fitness-for-purpose analysis. A review of pipeline risk assessment and Land-Use Planning (LUP) zone calculations for hydrogen was undertaken to identify any required changes. Case studies on selected sections of the LTS pipeline were then carried out to illustrate the potential changes to LUP zones. The work concluded with a summary of identified gaps that require addressing to ensure safe pipeline repurposing for hydrogen which cover materials performance inspection risk assessment land use planning and procedures.

Hydrogen fuel cell vehicle (HFCV) technology poses great promise as an alternative to significantly reduce the environmental impact of the transport sector’s emissions. However hydrogen fuel cell technology is relatively new therefore confirmation of the reliability and safety analysis is still required particularly for fire scenarios within confined spaces such as tunnels. This study applied the computational fluid dynamics (CFD) simulations in conjunction with probabilistic calculation methods to determine the associated thermal risk of a hydrogen jet fire in a tunnel and its dependency on scenarios with different tunnel slopes longitudinal and transverse ventilation velocities and fire positions. A large-scale model of 102 m in which the effects of outlined parameter variations on the severity of the fire incident were analysed. It is found that both tunnel ventilation techniques and slope were critical for the effective ejection of accumulated heat. With ventilation playing a primary role in the ejection of heat and gas and slope ensuring the stability of the ejected heat probabilities of thermal burns were found to be reduced by up to approximately 35% with a strong suggestion of critical combinations to further reduce the dangers of hydrogen tunnel fires.

In the case of a severe nuclear power plant accident hydrogen gas formation may occur from the core degradation and cooling water evaporation and subsequent oxidation of zircaloy. These phenomena increase the risk of hazardous combustion events in the reactor especially when combined with an ignition source. If not handled carefully these types of accidents can cause severe damage to the reactor building with potential radioactive effects on the environment. Although hydrogen-air combustion has been investigated before hydrogen-air-steam mixtures remain unstudied under reactor-like conditions. Thus this study investigated such mixtures’ combustion regimes. A closed tube of 318 liters (7.65m tall and 0.23m inner diameter) measures the flame speed flame propagation and shock wave behaviors for 11-15 %vol hydrogen mixtures combined with 0 20 or 30 %vol steam and air. Thus both the effect of steam and hydrogen content was investigated and compared. The experimental setup combined photomultiplier tubes pressure sensors and shock detectors to give a full view of the different combustion regimes. A number of obstacles changed the in-chamber turbulence during flame propagation to provide further reactor-like environments. This changed turbulence affected the combustion regimes and enhanced the flame speed for some cases. The results showed varying combustion behaviors depending on the water vapor concentration where a higher concentration meant a lower flame speed reduced pressure load and sometimes combustion extinction. At 0 %vol steam dilution the flame speed remained supersonic for all H2 concentrations while at 30 %vol steam dilution the flame speed remained subsonic for all H2 concentrations. Thus with high levels of steam dilution the risk for shock waves leading to potential reactor building destruction decreases."

Hydrogen is an environmentally friendly source of renewable energy. Energy generation from hydrogen has not yet been widely commercialized due to issues related to risk management in its storage and transportation. In this paper the authors propose a hybrid multiple-criteria decision-making (MCDM)-based method to manage the risks involved in the storage and transportation of hydrogen (RSTH). First we identified the key points of the RSTH by examining the relevant literature and soliciting the opinions of experts and used this to build a prototype of its decision structure. Second we developed a hybrid MCDM approach called the D-ANP that combined the decision-making trial and evaluation laboratory (DEMENTEL) with the analytic network process (ANP) to obtain the weight of each point of risk. Third we used fuzzy evaluation to assess the level of the RSTH for Beijing China where energy generation using hydrogen is rapidly advancing. The results showed that the skills of the personnel constituted the most important risk-related factor and environmental volatility and the effectiveness of feedback were root factors. These three factors had an important impact on other factors influencing the risk of energy generation from hydrogen. Training and technical assistance can be used to mitigate the risks arising due to differences in the skills of personnel. An appropriate logistics network and segmented transportation for energy derived from hydrogen should be implemented to reduce environmental volatility and integrated supply chain management can help make the relevant feedback more effective.

Throughout the history of the mining petroleum process and nuclear industries continuous efforts have been made to develop and improve measures to prevent and mitigate accidental explosions. Over the coming decades energy systems are expected to undergo a transition towards sustainable use of conventional hydrocarbons and an increasing share of renewable energy sources in the global energy mix. The variable and intermittent supply of energy from solar and wind points to energy systems based on hydrogen or hydrogen-based fuels as the primary energy carriers. However the safety-related properties of hydrogen imply that it is not straightforward to achieve and document the same level of safety for hydrogen systems compared to similar systems based on established fuels such as petrol diesel and natural gas. Compared to the conventional fuels hydrogen-air mixtures have lower ignition energy higher combustion reactivity and a propensity to undergo deflagration-to-detonation-transition (DDT) under certain conditions. To achieve an acceptable level of safety it is essential to develop effective measures for mitigating the consequences of hydrogen explosions in systems with certain degree of congestion and confinement. Extensive research over the last decade have demonstrated that chemical inhibition or partial suppression can be used for mitigating the consequences of vapour cloud explosions (VCEs) in congested process plants. Total and cooperation partners have demonstrated that solid flame inhibitors injected into flammable hydrocarbon-air clouds represent an effective means of mitigating the consequences of VCEs involving hydrocarbons. For hydrogen-air explosions these same chemicals inhibitors have not proved effective. It is however well-known that hydrocarbons can affect the burning velocity of hydrogen-air mixtures greatly. This paper gives an overview over previous work on chemical inhibitors. In addition experiments in a 20-litre vessel have been performed to investigate the effect of combinations of hydrocarbons and alkali salts on hydrogen/air mixtures.