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With technological development, the transport units for compressed gases are becoming larger and their number is increasing. Simultaneously, the filling pressure for hydrogen in transport has increased far beyond the 200 bar, which has been the common European standard for decades. In total, this increases the potential consequences of an incident, which needs to get limited for ensuring acceptance in current practice with pressure vessels from large serial production.
Consequently, the measures for new developments of extremely large and highly pressurised pressure vessels should meet a risk based higher level of requirements. For this purpose, the so-called pressure-volume product was proposed as a safety related criteria to the relevant regulatory bodies in 2020. The approach was accepted, and a working group was set up at the United Nations for developing a broadly accepted limitation of today's established pressure vessels compared to future units with even more gas content. The path to the finally decided limit value of 1.5 million bar litres is presented here for hydrogen with its individual steps: ‘Boundary between major accident and disaster’, ‘The effect of pressure waves on the human body’, ‘The propagation of pressure waves’, ‘The reference value for population density’ and ‘Impact of pressure waves’. This result of the UN working group has been accepted in December 2023 and will lead to a binding limitation of the pressure volume product for the so called pressure receptacles by 2027. The work on units larger than this pV-limit is going on at ISO level.
We analyse electromotive force measurements of concentration cells using non-equilibrium thermodynamics, and determine the transference coefficients of ion-exchange membranes in aqueous KCl solutions. By taking advantage of the analytical expression for the permselectivity, we extract transport coefficients with high accuracy. The transport number of K+ and the transference coefficient of water in the Selemion CMVN cationexchange membrane are found to be 100𝑡K+ = 99.59 ± 0.56 and 𝑡𝑤 = 3.69 ± 0.40 respectively, while for the Selemion AMVN anion-exchange membrane they are 100𝑡Cl− = 100.21 ± 0.37 and 𝑡𝑤 = −3.75 ± 0.27. These results suggest that the membranes are perfectly selective to the target ion, and that each ion carries 3-4 water molecules through the membrane, which reduces the membrane permselectivity. In these concentration cells, the electrical potential contribution of the membrane alone was more easily isolated with bare Ag/AgCl electrodes without reference solutions and liquid junction plugs. Additionally, we find a large contribution to the measured concentration cell voltage from concentration gradients across the porous plug of the reference electrode, which cannot be explained by Henderson’s equation alone. For most of the concentration range, the transport number of the porous plug is determined to be 100𝑡K+ = 49.43 ± 0.78 with negligible water transport, similar to literature values for bulk electrolyte. In dilute electrolyte solutions with concentrations below 0.1 mol kg−1, the plug shows anomalous behaviour consistent with an increase in K+ selectivity and water co-transport.
Monte-Carlo-Analysis of Minimum Burst Requirements for Composite Cylinders for Hydrogen Service
(2021)
For achieving Net Zero-aims hydrogen is an indispensable component, probably the main component. For the usage of hydrogen, a wide acceptance is necessary, which requires trust in hydrogen based on absence of major incidents resulting from a high safety level. Burst tests stand for a type of testing that is used in every test standard and regulation as one of the key issues for ensuring safety in use. The central role of burst and proof test is grown to historical reasons for steam engines and steel vessels but - with respect for composite pressure vessels (CPVs) - not due an extraordinary depth of outcomes. Its importance results from the relatively simple test process with relatively low costs and gets its importance by running of the different test variations in parallel. In relevant test und production standards (as e. g. ECE R134) the burst test is used in at least 4 different meanings. There is the burst test on a) new CPVs and some others b) for determining the residual strength subsequent to various simulations of ageing effects. Both are performed during the approval process on a pre-series. Then there is c) the batch testing during the CPVs production and finally d) the 100% proof testing, which means to stop the burst test at a certain pressure level. These different aspects of burst tests are analysed and compared with respect to its importance for the resulting safety of the populations of CPVs in service based on experienced test results and Monte-Carlo simulations. As main criterial for this the expected failure rate in a probabilistic meaning is used. This finally ends up with recommendations for relevant RC&S especially with respect to GTR 13.
Die Bundesanstalt für Materialforschung und -prüfung (BAM) ist eine wissenschaftlich-technische Bundesoberbehörde mit Sitz in Berlin, die zum Geschäftsbereich des Bundesministeriums für Wirtschaft und Klimaschutz gehört. Unsere Hauptaufgabe besteht darin, durch Forschung, Prüfung und Beratung zum Schutz von Mensch, Umwelt und Sachgütern beizutragen. Dies umfasst die Bewertung der Sicherheit von Materialien, Stoffen und Produkten sowie die Entwicklung von Methoden und Standards in Bereichen wie Materialwissenschaft, Werkstofftechnik und Chemie. Wir forschen und prüfen an drei Standorten in Berlin, sowie auf unserem Testgelände Technische Sicherheit in Horstwalde in Brandenburg. Hier haben wir weitreichende Möglichkeiten, Versuche im Realmaßstab durchzuführen. Besonderes Augenmerk möchten wir heute auf das Reallabor Wasserstofftankstelle richten. Diese voll digitalisierte technische Anlage, die die Wertschöpfungskette von Wasserstoff abbildet, wurde gerade eröffnet und steht nun Partnern aus Industrie und Forschung sowie kleinen mittelständischen Unternehmen oder Start-Ups zum gemeinsamen Forschen und Erproben neuer Technologie zur Verfügung. Ihre Besonderheiten umfassen z.B. eine umfassende Prozessüberwachung nach Industrie 4.0, die dafür nötige IT/OT Infrastruktur, Digitale Zwillinge auf verschiedenen Ebenen, großflächige Aufstellung und baulicher Schutz, Gas-Probenahmestellen auf dem Weg durch die Anlage und H2-Sensornetzwerke zur frühzeitigen Erfassung und Ortung von Leckagen.
This presentation highlights some key points in hydrogen safety related to compressed HYDROGEN STORAGE. It explains some needs concerning the Market ramp-up: cost and safety related aspects like Risk-control by consequence and/or frequency limitation. Other aspects are the optimization of design and test standards by using Monte-Carlo based assessments and the Generation of probabilistic data as input for risk management tools during the design type approval and periodic inspection. Further safety aspects of design and manufacturing have to be taken into account as well as aspects of operational safety with material degradation, non-destructive testing and appropriate tools for operational files.
Based on the preliminary presentations in this task force it is repeated how a basic population scatters and its degradation influences properties statistically. There is a remainder on the issue of accepting borderline populations due to the minimum burst ratio requirement.
Then it is explained in detail how the analysis of minimum requirements by a Monte-Carlo-simulation works. The result with respect to the further reduced minimum burst ratio of 2.0 is summarised and means a two-step approach of two scatter levels requiring two different minimum burst ratios.
The methods for evaluating batch tests are analysed. A proposal for integration a statistical analysis is described in detail.
Finally, the positive effect of proof testing is shown and its dependence from the real ageing is shown.
This ends in the recommendation to have a stronger and quantitative look on real ageing and to follow the 2 proposed sets of criteria for a safe usage of hydrogen storage systems.
The reverse electrodialysis heat engine (REDHE) is a promising salinity gradient energy technology, capable of producing hydrogen with an input of waste heat at temperatures below 100 °C. A salinity gradient drives water electrolysis in the reverse electrodialysis (RED) cell, and spent solutions are regenerated using waste heat in a precipitation or evaporation unit. This work presents a non-equilibrium thermodynamics model for the RED cell, and the hydrogen production is investigated for KCl/water solutions. The results show that the evaporation concept requires 40 times less waste heat and produces three times more hydrogen than the precipitation concept. With commercial evaporation technology, a system efficiency of 2% is obtained, with a hydrogen production rate of 0.38 gH2 m−2h−1 and a waste heat requirement of 1.7 kWh g−1H2. The water transference coefficient and the salt diffusion coefficient are identified as membrane properties with a large negative impact on hydrogen production and system efficiency. Each unit of the water transference coefficient in the range tw=[0–10] causes a −7 mV decrease in unit cell electric potential, and a −0.3% decrease in system efficiency. Increasing the membrane salt diffusion coefficient from 10−12 to 10−11 leads to the system efficiency decreasing from 2% to 0.6%
Photopolymer derived carbon grows in popularity, yet the range in available feature sizes is limited. Here we focus on expanding the field to low surface to volume ratio (SVR) structures. We describe a high temperature acrylic photopolymerizable precursor with FTIR and DSC and develop a thermal inert-gas treatment for producing architected carbon in the mm scale with SVR of 1.38 x10-3 μm-1. Based on TGA and MS, we distinguish two thermal regimes with activation energies of ~79 and 169 kJ mol-1, which we reason with mechanisms during the polymer’s morphologic conversion between 300 - 500 °C. The temperature range of the major dimensional shrinkage (300-440 °C, 50%) does not match the range of the largest alteration in elemental composition (440-600 °C, O/C 0.25-0.087%). The insights lead to an optimized thermal treatment with an initial ramp (2 °C min-1 to 350 °C), isothermal hold (14h), post hold ramp (0.5 °C min-1 to 440 °C) and final ramp (10 °C min-1 to 1000 °C). The resulting carbon structures are dimensionally stable, non-porous at the μm scale, and comprise an unprecedented variation in feature sizes (from mm to μm scale). The findings shall advance architected carbon to industrially relevant scales.
With the fast development in the field of additive manufacturing, triply periodic minimal surface (TPMS) based porous media have recently found many uses in mechanical property tuning. However, there is still a lack of understanding in their porosity-dependent permeability and electrical as well as thermal conductivity. Here, we perform finite volume simulations on the solid and void domains of the Schoen gyroid (SG), Schwarz primitive (SP) and Schwarz primitive beam (SPB) TPMS with porosities between 63% and 88% in Ansys Fluent. A simple cubic lattice (CL) of equivalent porosity served as reference. The SPB and CL showed up to one order of magnitude higher permeabilities than the SG and SP. However, SG and SP have about 1.3 and 2.6 times the electrical and thermal conductivity of SPB and CL, respectively. Furthermore, the properties of SPB and CL are largely affected by the surface area density, whereas tortuosity variation does not impact permeability and conductivity to a major extent. Finally, empirical relations are adapted to describe the presented data and thus, they may enable future designers of TPMS based porous structures to fine-tune the geometries according to the requirements on permeability and electrical as well as thermal conductivity.
