86,526 research outputs found
On the Mechanical Energy Involved in the Catastrophic Rupture of Liquid Hydrogen Tanks
No full textHydrogen can play a central role in the energy transition thanks to its unique properties. However, its low density is one of the main drawbacks. The liquefaction process can drastically increase its density up to virtually 71 kg m-3 at atmospheric pressure and -253°C (NIST, 2019). The safety knowledge gap on physical explosions is still broad in the case of liquid hydrogen (LH2). For instance, it is unclear what are the consequences yields as well as the probabilities of a catastrophic rupture of an LH2 tank. A boiling liquid expanding vapour explosion (BLEVE) might arise after this top event. In this case, the expansion of the compressed gaseous phase is followed by the flashing of a fraction of the liquid. Moreover, combustion may occur for hydrogen since it is highly flammable. This complex phenomenon was not widely explored for LH2 yet. This study focused on the physical explosion by also considering the combustion process. Many integral models were adopted to estimate the mechanical energy developed by the explosion. The tank pressure prior to the rupture was considered below the critical one (1.298 MPa (NIST, 2019)). It was assumed that both liquid and gaseous phases are present inside the tank. The influences of the filling degree of the tank (liquid level) and the temperatures of the liquid and gaseous phases on the explosion energy were analysed. The results were compared with the ones of a previous study where similar models were employed to estimate the mechanical energy of an LH2 tank with different initial conditions (Ustolin et al., 2020a). In particular, the effect of the combustion process on the explosion energy and shock wave overpressure was not accounted for. The aim of this study is to conduct a comparison between different models and assess which are the most and the least conservative. The outcomes of this work provide critical suggestions on the consequence analysis of cryogenic liquefied gas vessels explosions
Loss of integrity of hydrogen technologies: A critical review
No full textHydrogen is one of the main candidates in replacing fossil fuels in the forthcoming years. However, hydrogen technologies must deal with safety aspects due to the specific substance properties. This study aims to provide an overview on the loss of integrity (LOI) of hydrogen equipment, which may lead to serious consequences, such as fires and explosions. Substantial information regarding the hydrogen lifecycle, its properties, and safety related aspects has gathered. Furthermore, focus has placed on the phenomena responsible for the LOI (e.g. hydrogen embrittlement) and material selection for hydrogen services. Moreover, a systematic review on the hydrogen LOI topic has conducted to identify and connect the most relevant and active research group within the topic. In conclusion, a significant dearth of knowledge in material behaviour of hydrogen technologies has highlighted. It is thought that is possible to bridge this gap by strengthening the collaborations between scientists from different research fields. © 2020 The Author(s
Fuel cells for airborne usage: Energy storage comparison
No full textThe global drone market is growing every year. The number of applications is increasing: from search and rescue, security, surveillance to science and research and unmanned cargo systems.
A limiting factor for drone exploitation is that for the energy storage, normally, a battery is used and this solution affects flight time. A possible solution could be the utilization of fuel cells. This paper focuses on the utilization of fuel cells power as an alternative solution for drone propulsion.
The aim of the study is to determine when it is more appropriate, in terms of mass, to use a battery or a hybrid (fuel cell þ battery) system to power drones. To compare the different systems, a numerical simulation model has been developed in order to choose the best power system once the drone operation profile has been defined.
The model allows comparing different type of fuels and battery systems. The data to tune the model have been taken from commercial products, today already available. The simulation model considers a light-weight open-air cathode PEM (Polymer Exchange Membrane) fuel cell. The stack power output is chosen according to the mission profile and rages from 200 W to 1000 W.
The presented results show that, for the considered drone segment, multi-rotor drones with weight of 7 kg at take-off, lithium batteries are still the best choice for time flight shorter than about 1 h. A hybrid system, appears to be interesting for longer flights. For example, it has been calculated that a hybrid quadcopter drone with a mass of 7 kg, considering a flight profile that requires 1089 Wh can be powered with a 4.4 kg hybrid system composed by a 500 W and 1.4 kg PEM fuel cell system, 1.9 kg hydrogen composite pressure vessel and a 0.8 kg lithium battery. The same amount of energy can be stored in a lithium battery with a weight of about 6.6 kg. These means a weight saving of more than 30%. The hybrid system, in term of weight, is even more convenient for flight profiles that require more energy
An innovative and comprehensive approach for the consequence analysis of liquid hydrogen vessel explosions
No full textHydrogen is one of the most suitable solutions to replace hydrocarbons in the future. Hydrogen consumption is expected to grow in the next years. Hydrogen liquefaction is one of the processes that allows for increase of hydrogen density and it is suggested when a large amount of substance must be stored or transported. Despite being a clean fuel, its chemical and physical properties often arise concerns about the safety of the hydrogen technologies. A potentially critical scenario for the liquid hydrogen (LH2) tanks is the catastrophic rupture causing a consequent boiling liquid expanding vapour explosion (BLEVE), with consequent overpressure, fragments projection and eventually a fireball. In this work, all the BLEVE consequence typologies are evaluated through theoretical and analytical models. These models are validated with the experimental results provided by the BMW care manufacturer safety tests conducted during the 1990's. After the validation, the most suitable methods are selected to perform a blind prediction study of the forthcoming LH2 BLEVE experiments of the Safe Hydrogen fuel handling and Use for Efficient Implementation (SH2IFT) project. The models drawbacks together with the uncertainties and the knowledge gap in LH2 physical explosions are highlighted. Finally, future works on the modelling activity of the LH2 BLEVE are suggested
Modelling liquid hydrogen bleves: A comparative assessment with hydrocarbon fuels
No full textHydrogen is one of the best candidates in replacing traditional hydrocarbon fuels to decrease environmental pollution and global warming. Its consumption is expected to grow in the forthcoming years. Hence its liquefaction becomes necessary to store and transport large amounts of this fuel. However, a liquid hydrogen (LH2) boiling liquid expanding vapor explosion (BLEVE) is a potential accident scenario for these technologies, despite the fact it may be considered as atypical. A BLEVE is a physical explosion resulting from the catastrophic rupture of a tank of a liquid at a temperature above its boiling point at atmospheric pressure. Its consequences are the pressure wave, the missiles, which are the tank debris thrown away by the explosion, and a fireball if the substance is flammable and an ignition source is present. The aim of this paper is to estimate the consequences associated with BLEVEs from LH2 storage and transport systems by means of integral models. Both ideal and real gas behavior models were considered to calculate the explosion overpressure. The physical models were employed to analyze the consequences of analogous fuel BLEVEs, in order to provide a comparative assessment of the results. BLEVE experimental results for LH2 are not available in literature yet. For this reason, the developed models will be validated during the SH2IFT project in which LH2 BLEVE experimental tests will be conducted
Lessons Learned from Experimental Tests concerning Liquid Hydrogen Releases
No full textIn recent years, the adoption of liquid hydrogen (LH2) in industrial and transport applications is becoming increasingly widespread. The high volumetric energy density of LH2 compared to gaseous or compressed hydrogen allows for efficient storage of the fuel. In particular, LH2 is gaining success in the maritime sector because it allows to reduce carbon emissions with respect to fossil fuels and increase the quantity of hydrogen stocked on board. However, the implementation of such emerging technology is still an open issue in terms of safety. Actually, LH2 shares many of the characteristics of liquified natural gas (LNG), both with respect to chemical and physical properties, and to loss of containment scenarios. Therefore, as there is historical evidence of localized explosions (e.g., rapid phase transition (RPT)) in the case of LNG spills on water, the occurrence of severe consequences when LH2 is released onto water must be investigated. In this respect, several large-scale experiments have been performed to analyse the potential consequences of accidental releases of LH2 in or over water. Specifically, more than 80 single spill events have been carried out at release rates of approximately 0.25 kg/s, 0.50 kg/s, and 0.80 kg/s either above or below the water surface with different orientations. The results showed that the RPT phenomenon was not observed. However, the ignition of the released gas cloud with a blast wave overpressure and heat radiation to the surrounding environment was detected. The unexpected ignition of the flammable cloud is not a well-understood event. Few theories have been proposed to explain the reason behind this phenomenon, but, to date, uncertainty is still present. Based on these considerations, in the present paper, the data collected from the experimental campaign have been considered to investigate the relevance of the outcomes in view of their possible use in real applications. A comparison between the experimental set-up and operating conditions with specific industrial applications has been carried out in order to identify potential lessons learned. Overall, the present study will help laying the foundations for a safe implementation of LH2 infrastructure in the foreseeable future
Digital moka: Small-scale condition monitoring in process engineering
No full textIn this letter, we present a data-driven condition-monitoring system for a moka pot aiming at anomaly detection in the coffee-preparation process. A data-acquisition system and the corresponding generation process of a comprehensive dataset (including data from ideal and anomalous brewing scenarios) are described. Supervised and unsupervised machine learning algorithms are trained and tested on the dataset aiming at detecting anomalies in the process and showing the relevance of the considered framework
Design and Operation of Liquid Hydrogen Storage Tanks
No full textLiquid hydrogen (LH2) is a versatile and efficient energy carrier with numerous applications in space exploration, hydrogen fuel cell vehicles, industrial processes, and the maritime sector. However, its extremely low boiling point and low density present unique challenges in handling, storage, and transportation, particularly in the prevention of loss of containment scenarios. At present, there is still limited knowledge available on the thermodynamics of liquid hydrogen contained in cryogenic storage tanks. This scientific paper delves into an examination of insulation techniques and the operation of liquid hydrogen tanks. Also, self-pressurization is explained and set into context. Furthermore, modelling of specific parameters such as temperature distribution, pressure increase and liquid level play an important role in understanding the thermodynamics inside of LH2 tanks and enable to draw conclusions for the efficient operation when avoiding the loss of hydrogen by releasing boil off gas. The ramifications of this study hold critical importance for industries reliant on hydrogen. The insights gained will facilitate the development of prediction models to enhance operational directives, and the development of effective storage systems
Experimental analysis on the influence of operating profiles on high temperature polymer electrolyte membrane fuel cells
No full textThe Energy System lab at the University of Trieste has carried out a study to investigate the reduction in performance of high temperature polymer electrolyte membrane (HTPEM) fuel cell membrane electrode assemblies (MEAs) when subjected to different ageing tests. In this study, start and stop cycles, load cycles, open circuit voltage (OCV) permanence and constant load profile were considered. Polarization curves (PC) together with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) data were recorded during the ageing tests to assess the fuel cell per-formance. In this paper, experimental data are presented to confirm the test methodology previ-ously proposed by the authors and to quantitatively correlate the performance degradation to the operational profiles. It was demonstrated that OCV condition, start and stop and load cycling in-crease degradation of the MEAs with respect to constant load operation. As expected, the OCV is the operational condition that influences performance degradation the most. Finally, the MEAs were analyzed with synchrotron small angle X-ray scattering (SAXS) technique at the Austrian SAXS beamline at Elettra-Sincrotrone Trieste to analyze the nano-morphological catalyst evolution. As for the catalyst morphology evolution, the ex situ SAXS methodology proposed by the authors is confirmed in its ability to assess the catalyst nanoparticles aggregation
Machine learning-aided risk-based inspection strategy for hydrogen technologies
No full textAlthough technically challenging, effective, safe, and economical transport is crucial for enabling a widespread rollout of hydrogen technologies. A promising option to transport large amounts of hydrogen lies in employing retrofitted natural gas pipelines. Nevertheless, H2-rich environments tend to degrade pipeline steels, reducing their load-bearing capability and accelerating crack propagation. Regular inspection and maintenance activities can preserve the pipelines’ integrity and guarantee safe operations. The risk-based inspection (RBI) approach is based on estimating the risk for each component item. It focuses most inspection activities on high-risk components to reduce costs while maximizing the plant's safety and availability. However, the RBI standards do not consider hydrogen-induced degradations and cannot be adopted for industrial equipment operating in H2 environments. This study proposes a novel ad-hoc methodology for the risk-based inspection planning of hydrogen handli..
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