Transmission, Distribution & Storage

A systematic study of different ratios of CO CO₂ N₂ gas components on the hydrogen storage properties of the Na₃AlH₆ complex hydride with 4 mol% TiCl3 8 mol% aluminum and 8 mol% activated carbon is presented in this paper. The different concentrations of CO and CO₂in H₂ and CO CO₂ N₂ in H₂ mixture were investigated. Both CO and CO₂gas react with the complex hydride forming Al oxy-compounds NaOH and Na₂CO₃ that consequently cause serious decline in hydrogen storage capacity. These reactions lead to irreversible damage of complex hydride under the current experimental condition. Thus after 10 cycles with 0.1 vol % CO + 99.9 vol %H₂ and 1 vol % CO + 99 vol %H₂ the dehydrogenation storage capacity of the composite material decreased by 17.2% and 57.3% respectively. In the case of investigation of 10 cycles with 1 vol % CO₂ + 99 vol % H₂ gas mixture the capacity degradation was 53.5%. After 2 cycles with 10 vol % CO +90 vol % H₂  full degradation was observed whereas after 6 cycles with 10 vol % CO₂+ 90 vol % H₂ degradation of 86.8% was measured. While testing with the gas mixture of 1.5 vol % CO + 10 vol % CO₂+ 27 vol % H₂ + 61.5 vol % N2 the degradation of 94% after 6 cycles was shown. According to these results it must be concluded that complex aluminum hydrides cannot be used for the absorption of hydrogen from syngas mixtures without thorough purification.

The safety and convenience of hydrogen storage are significant for fuel cell vehicles. Based on mass conservation equation and energy conservation equation two thermodynamic models (single zone model and dual zone model) have been established to study the hydrogen gas temperature and tank wall temperature for compressed hydrogen storage tank. With two models analytical solution and Euler solution for single zone (gas zone) charge-discharge cycle have been compared Matlab/Simulink solution and Euler solution for dual zone (gas zone wall zone) charge-discharge cycle have been compared. Three charge-discharge cycle cases (Case 1 constant inflow temperature; Case 2 variable inflow temperature; Case 3 constant inflow temperature variable outflow temperature) and two compressed hydrogen tanks (Type III 25L Type IV 99L) charge-discharge cycle are studied by Euler method. Results show Euler method can well predict hydrogen temperature and tank wall temperature.

A study of open literature was performed to determine the effects of high hydrogen purity and gas pressure (in the range of 700-1000 bar) on the hydrogen embrittlement of several metallic materials. A particular focus was given to carbon low-alloy and stainless steels but information on embrittlement of aluminum and copper was included in the study. Additionally the most common test methods were studied and results from similar tests are presented in a manner so as to simplify comparisons of materials. Finally suggestions are provided for future testing necessary to ensure the safety of hydrogen storage at 700 bar.

The objective of this work was to enable the safe design of hydrogen pressure vessels by measuring the fatigue crack growth rates of ASME code-qualified steels in high-pressure hydrogen gas. While a design framework has recently been established for high-pressure hydrogen vessels a material property database does not exist to support the design calculations. This study addresses such voids in the database by measuring the fatigue crack growth rates of three different heats of ASME SA-372 Grade J steel in 100 MPa hydrogen gas. Results showed that the fatigue crack growth rates were similar for all three steel heats although the highest-strength steel appeared to exhibit the highest growth rates. Hydrogen accelerated the fatigue crack growth rates of the steels by as much as two orders of magnitude relative to anticipated crack growth rates in inert environments. Despite such dramatic effects of hydrogen on the fatigue crack growth rates measurement of these properties enables reliable definition of the design life of steel hydrogen containment vessels.

The UK government has committed to reducing greenhouse gas emissions to net zero by 2050. All future energy modelling identifies a key role for hydrogen (linked to CCUS) in providing decarbonised energy for heat transport industry and power generation. Blending hydrogen into the existing natural gas pipeline network has already been proposed as a means of transporting low carbon energy. However the expectation is that a gas blend with maximum hydrogen content of 20 mol% can be used without impacting consumers’ end use applications. Therefore a transitional solution is needed to achieve a 100% hydrogen future network.

Deblending (i.e. separation of the blended gas stream) is a potential solution to allow the existing gas transmission and distribution network infrastructure to transport energy as a blended gas stream. Deblending can provide either hydrogen natural gas or blended gas for space heating transport industry and power generation applications. If proven technically and economically feasible utilising the existing gas transmission and distribution networks in this manner could avoid the need for investment in separate gas and hydrogen pipeline networks during the transition to a future fully decarbonised gas network.

The Energy Network Association (ENA) “Gas Goes Green” programme identifies deblending could play a critical role in the transition to a decarbonised gas network. Gas separation technologies are well-established and mature and have been used and proven in natural gas processing for decades. However these technologies have not been used for bulk gas transportation in a transmission and distribution network setting. Some emerging hydrogen separation technologies are currently under development. The main hydrogen recovery and purification technologies currently deployed globally are:

• Cryogenic separation
• Membrane separation
• Pressure Swing Adsorption (PSA)

The technologies noted above require an energy input to drive the separation of gas components in the form of compression to provide a pressure differential. The configuration of the GB gas transmission and distribution networks provides a possible source of available energy through the pressure let-down in the network pressure tiers which could be used to drive the gas component separation processes. This study evaluated the gas separation technologies noted above against a selection of case studies based on actual network operating conditions to assess the technical andeconomic feasibility of hydrogen deblending in the GB gas network context. This study constitutes the first stage (proof of concept) in a programme of works that should provide the critical evidence for hydrogen deblending as a necessary component to enable the use of GB gas networks to transport and distribute hydrogen.

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The influence of the addition of refractory metals (molybdenum and tantalum) on the hydrogenation properties of FeTi intermetallic phase-based alloys was investigated. The suspended droplet alloying technique was applied to fabricate FeTiTa-based and FeTiMo-based alloys. The phase composition and hydrogen storage properties of the samples were investigated. The samples modified with the refractory metals exhibited lower plateau pressures and lower hydrogen storage capacities than those of the FeTi reference sample due to solid solution formation. It was observed that the equilibrium pressures decreased with the amount of molybdenum which is in good agreement with the increase in the cell parameters of the TiFe phase. Suspended droplet alloying was found to be a practical method to fabricate alloys with refractory metal additions; however it is appropriate for screening samples with desired chemical and phase compositions rather than for manufacturing purposes.

Transition metal carbides are a class of materials widely known for both their interesting physical properties and catalytic activity. In this work we have used plane-wave DFT methods to study the interaction with increasing amounts of molecular hydrogen on the low-index surfaces of four major carbides – TiC VC ZrC and NbC. Adsorption is found to be generally exothermic and occurs predominantly on the surface carbon atoms. We identify trends over the carbides and their surfaces for the energetics of the adsorption as a function of their electronic and geometrical characteristics. An ab initio thermodynamics formalism is used to study the properties of the slabs as the hydrogen coverage is increased.

Development of technologically and economically feasible solutions for hydrogen storage stimulates progress in hydrogen economy. High gravimetric and volumetric capacities of magnesium hydride makes it promising material capable to accelerate implementation of hydrogen-based technologies in our daily life. However widely discussed limitations of sorption kinetics and thermodynamic properties must be managed in MgH2. This work investigates two steps hydrogenation when process of hydrogen absorption is followed after hydrogen plasma activation. Such technique initiates creation of new channels for enhanced hydrogen sorption. Moreover synthesis of negligible amount of hydride acts as positive factor for further hydrogenation.

Correlating hydrogen embrittlement phenomenon with the metallic microstructural features holds the key for developing metals resistant to hydrogen-based failures. In case of fatigue failure of hydrogen charged metals in addition to the hydrogen-based failure mechanisms associated with monotonic loading such as HELP HEDE etc. microstructural features such as grain size type of grain boundary (special/random) fraction of special grain boundaries; their network and triple junctions can play a complex role. The probable sites for fatigue crack initiation in such metals can be identified as the sites of highest hydrogen concentration or accumulated plastic strain. To this end we have developed an experimental framework based on in-situ fatigue crack initiation and propagation studies under scanning electron microscope (SEM) to identify the weakest link in the metallic microstructure leading to failure. In-situ fatigue experiments are performed on carefully designed polycrystalline nickel (99.95% pure) specimens (miniaturised shallow-notched & electro-polished) using a 10 kN fatigue stage inside the SEM. Electron Back Scattering Diffraction (EBSD) map of the notched region surface helps identify the distribution of special/random grain boundaries triple junctions and grain orientation. The specimen surface in the shallow notched region for both the hydrogen charged and un-charged specimens are then carefully studied to correlate the microstructural feature associated with fatigue crack initiation sites. Such correlation of the fatigue crack initiation site and microstructural feature is further corroborated with the knowledge of hydrogen trapping and grain’s elastic anisotropicity to be either the site of high hydrogen concentration accumulated plastic slip or both.

Significant challenges still remain in the development of suitable materials for storing hydrogen for practical applications. Clathrate hydrates as a special inclusion compounds could be tailored by changing the storage pressure and temperature to adapt ambient conditions. In this work the hydrates were adopted to encage hydrogen in tetrahydrofuran (THF) aqueous solution with concentration of 3.0 mol%. The formation and dissociation behaviours were investigated by a high pressure micro-differential scanning calorimeter at the operating pressure of 18 MPa 25 MPa and 34 MPa. Experimental results show that the memory water only affects the hydrate formation behaviour instead of the hydrate dissociation behaviour. The dissociation temperature of the THF-H2 hydrate increases with the increase of the operating pressure and its dissociation equilibrium data can be obtained. The dissociation temperatures of the THF-H2 hydrate are 9.26 ℃ 10.94 ℃ and 12.67 ℃ at the operating pressure of 18 MPa 25 MPa and 34 MPa respectively. It is fundamental for performing the kinetics and microscopic experiments.