Safety
Controlling the Pressure of Hydrogen-natural Gas Mixture in an Inclined Pipeline
Feb 2020
Publication
This paper discusses the optimal control of pressure using the zero-gradient control (ZGC) approach. It is applied for the first time in the study to control the optimal pressure of hydrogen natural gas mixture in an inclined pipeline. The solution to the flow problem is first validated with existing results using the Taylor series approximation regression analysis and the Runge-Kutta method combined. The optimal pressure is then determined using ZGC where the optimal set points are calculated without having to solve the non-linear system of equations associated with the standard optimization problem. It is shown that the mass ratio is the more effective parameter compared to the initial pressure in controlling the maximum variation of pressure in a gas pipeline.
A Comparative Study of CFD-Modelling for Lean Premixed Hydrogen Deflagrations in Large-scale Vented Vessels
Sep 2021
Publication
Hydrogen combustion inside a post-accident nuclear reactor containment may pose a challenge to the containment integrity which could alter the fission-product release source term to the public. Combustion-generated overpressures may be relieved by venting to adjacent compartments through relief panels or existing openings. Thus an improved understanding of the propagation of lean hydrogen deflagrations in inter-connected compartments is essential for the development of appropriate management strategies. GOTHIC is a general purpose lumped parameter thermal-hydraulic code for solving multi-phase compressible flows which is accepted as an industry-standard code for containment safety analyses. Following the Fukushima accident the application of three-dimensional computational fluid dynamics methods to high-fidelity detailed analysis of hydrogen combustion processes has become more widespread. In this study a recently developed large-eddy-simulation (LES) capability is applied to the prediction of lean premixed hydrogen deflagrations in large-scale vented vessels of various configurations. The LES predictions are compared with GOTHIC predictions and experimental data obtained from the large-scale vented combustion test facility at the Canadian Nuclear Laboratories. The LES methodology makes use of a flamelet- or a progress-variable-based combustion model. An empirical burning velocity model is combined with an advanced finite-volume framework and a mesh-independent subfilter-scale model. Descriptions of the LES and GOTHIC modelling approaches used to simulate the hydrogen reactive flows in the vented vessels along with the experimental data sets are given. The potential and limitations of the lumped parameter and LES approaches for accurately describing lean premixed hydrogen deflagrations in vented vessels are discussed.
Worst Case Scenario for Delayed Explosion of Hydrogen Jets at a High Pressure: Ignition Position
Sep 2021
Publication
Delayed explosion of free field hydrogen releases at a high pressure is subject of multiple investigation performed by various authors in the past years. These studied considered various parameters such as pressures flow rates etc. and their influence on the resulting overpressure. However the influence of the ignition position on the maximum overpressure was not fully explored. Current investigation addressed by computational fluid dynamics (CFD) simulations and experimental measurement fills this gap. This work demonstrates that the ignition positions corresponding to 55%-65% of H2/air mixture give the maximum overpressure. This observation initially observed numerically and afterword confirmed experimentally. A simple model is also suggested.
Studies on the Impact of Hydrogen on the Results of THT Measurement Devices
Dec 2021
Publication
An essential prerequisite for safe transport and use of natural gas is their appropriate odorization. This enables the detection of uncontrolled gas leaks. Proper and systematic odorization inspection ensures both safe use of gas and continuity of the process itself. In practice it is conducted through among others measuring odorant concentrations in gas. Control devices for rapid gas odorization measurements that are currently used on a large scale in the gas industry are equipped with electrochemical detectors selective for sulfur compounds like tetrahydrothiophene (THT). Because the selectivity of electrochemical detector response to one compound (e.g. THT) the available declarations of manufacturers show that detector sensitivity (indirectly also the quality of the measurement result) is influenced by the presence of increased e.g. sulfur or hydrogen compound content in the gas. Because of the lack of sufficient source literature data in this field it was necessary to experimentally verify this impact. The results of studies on experimental verification of suspected influence of increased amounts of hydrogen in gas on the response of electrochemical detector was carried out at the Oil and Gas Institute—National Research Institute (INiG—PIB). They are presented in this article. The data gathered in the course of researching the dependence between THT concentration measurement result quality and hydrogen content in gas composition enabled a preliminary assessment of the threat to the safety of end users of gaseous fuels caused by the introduction of this gas into the distribution network. Noticing the scope of necessary changes in the area of odorization is necessary to guarantee this safety.
Nanotechnology Enabled Hydrogen Gas Sensing
Sep 2019
Publication
An important contribution to industry standards and to effective installation of hybrid renewable energy systems is evaluation of hydrogen (H2) monitoring techniques under pilot-scale and/or real-world conditions. We have designed a hybrid system to integrate solar power electrolysis and hydrogen fuel cell components in a DC micro-grid with capacity to evaluate novel nanomaterials for enhanced H2 gas sensing performance. In general enhanced hydrogen sensing performance is evaluated by high sensitivity selectivity and stability as well as low power consumption. Unique properties such as high surface area to volume ratio a large number of surface active sites high specific surface area and reactivity are key attributes of nanomaterials used for gas sensing. These attributes enable sensors to be embedded in Internet-of-Things applications or in mobile systems. With rapid development of hydrogen-based technologies for clean energy applications there remains a requirement for faster accurate and selective H2 sensors with low cost and low power consumption. Operating principles for these sensors include catalytic thermal conductivity electrochemical resistance based optical and acoustic methods. In this paper we review performance of H2 gas sensors based on conductometric devices operating at room temperature up to 200 °C. The focus of this work includes nanostructured metal oxides graphene materials and transition metal dichalcogenides employed as sensing materials.
Modelling of Ventilated Hydrogen Dispersion in Presence of Co-flow and Counter-flow
Sep 2021
Publication
In the framework of the EU-funded project HyTunnel-CS an inter-comparison among partners CFD simulations has been carried out. The simulations are based on experiments conducted within the project by Pro-Science and involve hydrogen release inside a safety vessel testing different ventilation configurations. The different ventilation configurations that were tested are co-flow counter-flow and cross-flow. In the current study co-flow and counter-flow tests along with the no ventilation test (m' = S g/s d = 4 mm ) are simulated with the aim to validate available and well-known CFD codes against such applications and to provide recommendations on modeling strategies. Special focus is given on modeling the velocity field produced by the fan during the experiments. The computational results are compared with the experimental results and a discussion follows regarding the efficiency of each ventilation configuration.
On the Evaluation of ALD TiO 2 , ZrO 2 and HfO 2 Coatings on Corrosion and Cytotoxicity Performances
May 2021
Publication
Magnesium alloys have been widely studied as materials for temporary implants but their use has been limited by their corrosion rate. Recently coatings have been proven to provide an effective barrier. Though only little explored in the field Atomic Layer Deposition (ALD) stands out as a coating technology due to the outstanding film conformality and density achievable. Here we provide first insights into the corrosion behavior and the induced biological response of 100 nm thick ALD TiO2 HfO2 and ZrO2 coatings on AZ31 alloy by means of potentiodynamic polarization curves electrochemical impedance spectroscopy (EIS) hydrogen evolution and MTS colorimetric assay with L929 cells. All three coatings improve the corrosion behavior and cytotoxicity of the alloy. Particularly HfO2 coatings were characterized by the highest corrosion resistance and cell viability slightly higher than those of ZrO2 coatings. TiO2 was characterized by the lowest corrosion improvements and though generally considered a biocompatible coating was found to not meet the demands for cellular applications (it was characterized by grade 3 cytotoxicity after 5 days of culture). These results reveal a strong link between biocompatibility and corrosion resistance and entail the need of taking the latter into consideration in the choice of a biocompatible coating to protect degradable Mg-based alloys.
Australians’ Considerations for Use of Hydrogen in the Transport Sector
Sep 2019
Publication
Hydrogen fuel cells power a range of vehicles including cars buses trucks forklifts and even trains. As fuel cell electric vehicles emit no carbon emissions and only produce water vapor as a by-product they present an attractive option for countries who are experiencing high pollution from transport. This paper presents the findings of ten focus groups and a subset of a national survey which focused specifically on use of hydrogen in the transport sector (N=948). When discussing hydrogen transport options Australian focus group participants felt that rolling out hydrogen fuel cell buses as a first step for fuel cell electric vehicle deployment would be a good way to increase familiarity with the technology. Deploying hydrogen public transport vehicles before personal vehicles was thought to be a positive way to demonstrate the safe use of hydrogen and build confidence in the technology. At the same time it was felt it would allow any issues to be ironed out before the roll out of large-scale infrastructure on a to support domestic use. Long haul trucks were also perceived to be a good idea however safety issues were raised in the focus groups when discussing these vehicles. Survey respondents also expressed positive support for the use of hydrogen fuel cell buses and long-haul trucks. They reported being happy to be a passenger in a fuel cell bus. Safety and environmental benefits remained paramount with cost considerations being the third most important issue. Respondents supportive of hydrogen technologies were most likely to report purchasing a hydrogen vehicle over other options
The Challenges of Hydrogen Storage on a Large Scale
Sep 2021
Publication
With the growing success of green hydrogen the general trend is for increased hydrogen production and large quantities of storage. Engie’s projects have grown from a few kilos of hydrogen to the quest for large scale production and associated storage – e.g. several tons or tens of tons. Although a positive sign for Engie’s projects it does inevitably result in challenges in new storage methods and in risks management related to such facilities; particularly with hydrogen facilities being increasingly placed in the vicinity of general public sites. For example a leak on hydrogen storage can generate significant thermal and overpressure effects on surrounding people/facilities in the event of ignition. Firewalls can be installed to protect individuals / infrastructure from thermal effects but the adverse result is that this solution can increase the violence of an explosion in case of delayed ignition or confinement. The manner of emergency intervention on a pool fire of hydrogen is also totally different from intervention on compressed gaseous hydrogen. The first part of this presentation will explain different means to store hydrogen in large quantities. The second part will present for each storage the specific risks generated. The third and final part will explain how these risks can be addressed on a technical point of view by safety devices or by other solutions (separation distance passive/active means …).
A Flammability Limit Model for Hydrogen-air-diluent Mixtures Based on Heat Transfer Characteristics in Flame Propagation
May 2019
Publication
Predicting lower flammability limits (LFL) of hydrogen has become an ever-important task for safety of nuclear industry. While numerous experimental studies have been conducted LFL results applicable for the harsh environment are still lack of information. Our aim is to develop a calculated non-adiabatic flame temperature (CNAFT) model to better predict LFL of hydrogen mixtures in nuclear power plant. The developed model is unique for incorporating radiative heat loss during flame propagation using the CNAFT coefficient derived through previous studies of flame propagation. Our new model is more consistent with the experimental results for various mixtures compared to the previous model which relied on calculated adiabatic flame temperature (CAFT) to predict the LFL without any consideration of heat loss. Limitation of the previous model could be explained clearly based on the CNAFT coefficient magnitude. The prediction accuracy for hydrogen mixtures at elevated initial temperatures and high helium content was improved substantially. The model reliability was confirmed for H2-air mixtures up to 300 C and H2-air-He mixtures up to 50 vol % helium concentration. Therefore the CNAFT model developed based on radiation heat loss is expected as the practical method for predicting LFL in hydrogen risk analysis.
CFD Simulations of Large Scale LH2 Dispersion in Open Environment
Sep 2021
Publication
An inter-comparison among partners’ CFD simulations has been carried out within the EU-funded project PRESLHY to investigate the dispersion of the mixture cloud formed from large scale liquid hydrogen release. Rainout experiments performed by Health and Safety Executive (HSE) have been chosen for the work. From the HSE experimental series trial-11 was selected forsimulation due to its conditions where only liquid flow at the nozzle was achieved. During trial-11 liquid hydrogen is spilled horizontally 0.5 m above a concrete pad from a 5 barg tank pressure through a 12 mm (1/2 inch) nozzle. The dispersion takes place outdoors and thus it is imposed to variant wind conditions. Comparison of the CFD results with the measurements at several sensors is presented and useful conclusions are drawn.
Flammability Reduction in a Pressurised Water Electrolyser Based on a Thin Polymer Electrolyte Membrane through a Pt-alloy Catalytic Approach
Jan 2019
Publication
Various Pt-based materials (unsupported Pt PtRu PtCo) were investigated as catalysts for recombining hydrogen and oxygen back into water. The recombination performance correlated well with the surface Pt metallic state. Alloying cobalt to platinum was observed to produce an electron transfer favouring the occurrence of a large fraction of the Pt metallic state on the catalyst surface. Unsupported PtCo showed both excellent recombination performance and dynamic behaviour. In a packed bed catalytic reactor when hydrogen was fed at 4% vol. in the oxygen stream (flammability limit) 99.5% of the total H2 content was immediately converted to water in the presence of PtCo thus avoiding safety issues. The PtCo catalyst was thus integrated in the anode of the membrane-electrode assembly of a polymer electrolyte membrane electrolysis cell. This catalyst showed good capability to reduce the concentration of hydrogen in the oxygen stream under differential pressure operation (1–20 bar) in the presence of a thin (90 μm) Aquivion® membrane. The modified system showed lower hydrogen concentration in the oxygen flow than electrolysis cells based on state-of-the-art thick polymer electrolyte membranes and allowed to expand the minimum current density load down to 0.15 A cm−2 . This was mainly due to the electrochemical oxidation of permeated H2 to protons that were transported back to the cathode. The electrolysis cell equipped with a dual layer PtCo/IrRuOx oxidation catalyst achieved a high operating current density (3 A cm−2 ) as requested to decrease the system capital costs under high efficiency conditions (about 77% efficiency at 55 °C and 20 bar). Moreover the electrolysis system showed reduced probability to reach the flammability limit under both high differential pressure (20 bar) and partial load operation (5%) as needed to properly address grid-balancing service
Large-eddy Simulation of Tri-fuel Combustion: Diesel Spray Assisted Ignition of Methanol-hydrogen Blends
May 2021
Publication
Development of marine engines could largely benefit from the broader usage of methanol and hydrogen which are both potential energy carriers. Here numerical results are presented on tri-fuel (TF) ignition using large-eddy simulation (LES) and finite-rate chemistry. Zero-dimensional (0D) and three-dimensional (3D) simulations for n-dodecane spray ignition of methanol/hydrogen blends are performed. 0D results reveal the beneficial role of hydrogen addition in facilitating methanol ignition. Based on LES the following findings are reported: 1) Hydrogen promotes TF ignition significantly for molar blending ratios βX = [H2]/([H2]+[CH3OH]) ≥0.8. 2) For βX = 0 unfavorable heat generation in ambient methanol is noted. We provide evidence that excessive hydrogen enrichment (βX ≥ 0.94) potentially avoids this behavior consistent with 0D results. 3) Ignition delay time is advanced by 23–26% with shorter spray vapor penetrations (10–15%) through hydrogen mass blending ratios 0.25/0.5/1.0. 4) Last adding hydrogen increases shares of lower and higher temperature chemistry modes to total heat release.
Combustion Characteristics of Premixed Hydrogen/Air in an Undulate Microchannel
Jan 2022
Publication
This work reports a numerical investigation of microcombustion in an undulate microchannel using premixed hydrogen and air to understand the effect of the burner design on the flame in order to obtain stability of the flame. The simulations were performed for a fixed equivalence ratio and a hyperbolic temperature profile imposed at the microchannel walls in order to mimic the heat external losses occurred in experimental setups. Due to the complexity of the flow dynamics combined with the combustion behavior the present study focuses on understanding the effect of the fuel inlet rate on the flame characteristics keeping other parameters constant. The results presented stable flame structure regardless of the inlet velocity for this type of design meaning that a significant reduction in the heat flux losses through the walls occurred allowing the design of new simpler systems. The increase in inlet velocity increased the flame extension with the flame being stretched along the microchannel. For higher velocities flame separation was observed with two detected different combustion zones and the temperature profiles along the burner centerline presented a non-monotonic decrease due to the dynamics of the vortices observed in the convex regions of the undulated geometry walls. The geometry effects on the flame structure flow field thermal evolution and species distribution for different inlet velocities are reported and discussed.
Hydrogen Jet Structure in Presence of Forced Co-, Counter- and Cross-flow Ventilation
Sep 2021
Publication
This paper presents results of experimental investigations on unignited horizontal hydrogen jets in air in presence of co- cross- and counter-flow. Hydrogen concentration distributions are obtained as functions of distance to the hydrogen release nozzle. The H2-jet variables are two nozzle diameters 1 mm and 4 mm and two H2-jet mass flow rates 1 g/s up to 5 g/s. A propeller fan is used to provide forced ventilation compared to the case with no ventilation three different airflow velocities up to 5 m/s were studied systematically. It was found that any forced ventilation in co- cross- and counter-flow direction reduces the size of the burnable mixture cloud of the H2-jet compared to a free jet in quiescent air.
CFD Model Based Ann Prediction of Flammable Vapor Colour Formed by Liquid Hydrogen Spill
Sep 2021
Publication
Unintended releases can occur during the production storage transportation and filling of liquid hydrogen which may cause devastating consequences. In the present work liquid hydrogen leak is modeled in ANSYS Fluent with the numerical model validated using the liquid hydrogen spill test data. A three-layer artificial neural network (ANN) model is built in which the wind speed ground temperature leakage time and leakage rate are taken as the inputs the horizontal diffusion distance and vertical diffusion distance of combustible gas as the outputs of the ANN. The representative sample data derived from the detailed calculation results of the numerical model are selected via the orthogonal experiment method to train and verify the back propagation (BP) neural network. Comparing the calculation results of the formula fitting with the sample data the results show that the established ANN model can quickly and accurately predict the horizontal and vertical diffusion distance of flammable vapor cloud relatively. The influences of four parameters on the horizontal hazard distance as well as vertical hazard height are predicted and analyzed in the case of continuous overflow of liquid hydrogen using the ANN model.
Hydrogen Dispersion and Ventilation Effects in Enclosures under Different Release Conditions
Apr 2021
Publication
Hydrogen is an explosive gas which could create extremely hazardous conditions when released into an enclosure. Full-scale experiments of hydrogen release and dispersion in the confined space were conducted. The experiments were performed for hydrogen release outflow of 63 × 10−3 m3/s through a single nozzle and multi-point release way optionally. It was found that the hydrogen dispersion in an enclosure strongly depends on the gas release way. Significantly higher hydrogen stratification is observed in a single nozzle release than in the case of the multi-point release when the gas concentration becomes more uniform in the entire enclosure volume. The experimental results were confirmed on the basis of Froud number analysis. The CFD simulations realized with the FDS code by NIST allowed visualization of the experimental hydrogen dispersion phenomenon and confirmed that the varied distribution of hydrogen did not affect the effectiveness of the accidental mechanical ventilation system applied in the tested room.
Experimental Study of the Explosion Severity of Vented Methane/Hydrogen Deflagrations
Sep 2021
Publication
Adding hydrogen to mains natural gas has been identified as one of the main strategies to reduce CO2 emissions in the United Kingdom. This work aims to characterise the explosion severity of 80:20 v./v. methane/hydrogen blends (‘a blend’) and methane vented deflagrations. The explosion severity of homogenous mixtures was measured in a 15 m3 cubic steel chamber in which the relief area was provided by four windows and a door covered with polypropylene sheet. The pressure increase over time was characterised using piezo-resistive pressure transducers and the flame speed was estimated using ionisation probes installed in the walls of the enclosure. The explosion severity of both mixtures was determined for different equivalence ratios from lean to rich mixtures. The pressure over time presented very similar behaviour for both mixtures comprising multiple peaks divided into three main stages: a first stage related to a spherical confined explosion until the opening of the vent a second stage generated by increased combustion during venting and an oscillatory peak generated by acoustic disturbances with the enclosure. A slight increase in the first stage overpressure was observed for the blend in comparison with methane regardless of the equivalence ratio but no general trend in pressure was observed for other stages of the propagation. The effect of the blockage ratio on explosion severity was studied by adding metallic elements representing furniture in a room.
Behavior of Barrier Wall under Hydrogen Storage Tank Explosion with Simulation and TNT Equivalent Weight Method
Mar 2023
Publication
Hydrogen gas storage place has been increasing daily because of its consumption. Hydrogen gas is a dream fuel of the future with many social economic and environmental benefits to its credit. However many hydrogen storage tanks exploded accidentally and significantly lost the economy infrastructure and living beings. In this study a protection wall under a worst-case scenario explosion of a hydrogen gas tank was analyzed with commercial software LS-DYNA. TNT equivalent method was used to calculate the weight of TNT for Hydrogen. Reinforced concrete and composite protection wall under TNT explosion was analyzed with a different distance of TNT. The initial dimension of the reinforced concrete protection wall was taken from the Korea gas safety code book (KGS FP217) and studied the various condition. H-beam was used to make the composite protection wall. Arbitrary-Lagrangian-Eulerian (ALE) simulation from LS-DYNA and ConWep pressure had a good agreement. Used of the composite structure had a minimum displacement than a normal reinforced concrete protection wall. During the worst-case scenario explosion of a hydrogen gas 300 kg storage tank the minimum distance between the hydrogen gas tank storage and protection wall should be 3.6 m.
Spherically Expanding Flame Simulations in Cantera Using a Lagrangian Formulation
Sep 2021
Publication
A Lagrangian-based one-dimensional approach has been developed using Cantera to study the dynamics of spherically expanding flames. The detailed reaction model USC-Mech II has been employed to examine flame propagating in hydrogen-air mixtures. In the first part our approach has been validated against laminar flame speed and Markstein number data from the literature. It was shown that the laminar flame speed was predicted within 5% on average but that discrepancies were observed for the Markstein number especially for rich mixtures. In the second part a detailed analysis of the thermo-chemical dynamics along the path of Lagrangian particles propagating in stretched flames was performed. For mixtures with negative Markstein lengths it was found that at high stretch rates the mixture entering the reaction-dominated period is less lean with respect to the initial mixture than at low stretch rate. This induces a faster rate of chemical heat release and of active radical production which results in a higher flame propagation speed. Opposite effects were observed for mixtures with positive Markstein lengths for which slower flame propagation was observed at high stretch rates compared to low stretch rates."
No more items...