Transmission, Distribution & Storage

In a fuel cell electric vehicle (FCEV) powered by a metal hydride tank the performance of the tank is an indicator of the overall health status which is used to predict its behaviour and make appropriate energy management decisions. The aim of this paper is to investigate how to evaluate the effects of charge/discharge cycles on the performance of a commercial automotive metal hydride hydrogen storage system applied to a real FCEV. For this purpose a mathematical model is proposed based on uncertain physical parameters that are identified using the stochastic particle swarm optimisation (PSO) algorithm combined with experimental measurements. The variation of these parameters allows an assessment of the degradation level of the tank’s performance on both the quantitative and qualitative aspects. Simulated results derived from the proposed model and experimental measurements were in good agreement with a maximum relative error of less than 2%. The validated model was used to establish the correlations between the observed degradations in a hydride tank recovered from a real FCEV. The results obtained show that it is possible to predict tank degradations by developing laws of variation of these parameters as a function of the real conditions of the use of the FCEV (number of charging/discharging cycles pressures mass flow rates temperatures).

It is a common belief that embedded expanding inclusions are subjected to an internal homogeneous compressive hydrostatic stress. Still cracks that appear in precipitates that occupy a larger volume than the original material are frequently observed. The appearance of cracks has since long been regarded as a paradox. In the present study it is shown that matrix materials that increases its volume even several percent during the precipitation process develop a tensile hydrostatic stress in the centre of the precipitate. This is the result of a complicated mechanical-chemical phase transformation process. The process is here studied using a Landau phase feld model. Before the material is transformed and incorporated in a precipitate it undergoes stretching beyond the elastic strain limit because of the presence of already expanded material. During the phase transformation the accompanying volumetric expansion cannot be fully accommodated which instead creates an internal compressive stress and adds tension in the surrounding material. As the growth of the precipitate proceeds a region with increasing tensile stress develops in the interior of the precipitate. This is suggested to be the most probable cause of the observed cracks. First the mechanics that lead to the tension is computed. The infuence of elastic-plastic properties is studied both for cases both with and without cracks. The growth history from microscopic to macroscopic precipitates is followed and the result is compared with observations of so called hydride blisters that are formed on surfaces of zirconium alloys in the presence of hydrogen. A common practical situation is when the zirconium is in contact with an object of lower temperature. Then the cooled spot attracts hydrogen that make the zirconium transform to a metal hydride with the shape of a blister. The simulations predicts a final size and position of the growing crack that compares well with the experimental observations.

The decarbonization of the industrial sector is imperative to achieve a sustainable future. Carbon capture and storage technologies are the leading options but lately the use of CO2 is also being considered as a very attractive alternative that approaches a circular economy. In this regard power to gas is a promising option to take advantage of renewable H2 by converting it together with the captured CO2 into renewable gases in particular renewable methane. As renewable energy production or the mismatch between renewable production and consumption is not constant it is essential to store renewable H2 or CO2 to properly run a methanation installation and produce renewable gas. This work analyses and optimizes the system layout and storage pressure and presents an annual cost (including CAPEX and OPEX) minimization. Results show the proper compression stages need to achieve the storage pressure that minimizes the system cost. This pressure is just below the supercritical pressure for CO2 and at lower pressures for H2 around 67 bar. This last quantity is in agreement with the usual pressures to store and distribute natural gas. Moreover the H2 storage costs are higher than that of CO2 even with lower mass quantities; this is due to the lower H2 density compared with CO2 . Finally it is concluded that the compressor costs are the most relevant costs for CO2 compression but the storage tank costs are the most relevant in the case of H2.

After nearly 25 years of service some of the wires of the tendons of “La Arena” bridge (Spain) started to exhibit the effects of environmental degradation processes. “La Arena” is cable-stayed bridge with 6 towers and a reference span between towers of about 100 meters. After a maintenance inspection of the bridge evidences of corrosion were detected in some of the galvanized wires of the cables. A more in-deep analysis of these wires revealed that many of them exhibited loss of section due to the corrosion process. In order to clarify the causes of this degradation event and to suggest some remedial actions an experimental program was designed. This program consisted of tensile and fatigue tests on some strand samples of the bridge together with a fractographic analysis of the fracture surfaces of the wires its galvanized layer thickness and some hydrogen measurements (hydrogen embrittlement could be another effect of the environmental degradation process).Once the type and extension of the flaws in the wires was characterized a structural integrity assessment of the strands was performed with the aim of quantifying the margins until failure and establishing some maintenance recommendations.

Pressure vessels operating in sour service conditions in refinery environments can be subject to the risk of H₂S cracking resulting from the hydrogen entering into the material. This risk which is related to the specific working conditions and to the quality of the steel used shall be properly managed in order to maintain the highest safety at a cost-effective level.<br/>Nowadays the typical management strategy is based on a risk based inspection (RBI) evaluation to define the inspection plan used in conjunction with a fitness for service (FFS) approach in defining if the vessel although presenting dangerous defects such as cracks can still be considered “fit for purpose” for a given time window based on specific fracture mechanics analysis.<br/>These vessels are periodically subject to non-destructive evaluation typically ultrasonic testing. Phased Array (PA) ultrasonic is the latest technology more and more used for this type of application.<br/>This paper presents the design and development of an optimized Phased Array ultrasonic inspection technique for the detection and sizing of hydrogen induced cracking (HIC) type flaws used as reference for comparison. Materials used containing natural operational defects were inspected in “as-service” conditions.<br/>Samples have then been inspected by means of a “full matrix capture” (FMC) acquisition process followed by “total focusing method” (TFM) data post processing. FCM-TFM data have been further post-processed and then used to create a 3D geometrical reconstruction of the volume inspected. Results obtained show the significant improvement that FMC/TFM has over traditional PA inspection techniques both in terms of sensitivity and resolution for this specific type of defect. Moreover since the FMC allows for the complete time domain signal to be captured from every element of a linear array probe the full set of data is available for post-processing.<br/>Finally the possibility to reconstruct the geometry of the component from the scans including the defects present in its volume represents the ideal solution for a reliable data transferring process to the engineering function for the subsequent FFS analysis.

In this study highly porous carbon fiber was prepared for hydrogen storage. Porous carbon fiber (PCF) and activated porous carbon fiber (APCF) were derived by carbonization and chemical activation after selectively removing polyvinyl alcohol from a bi-component fiber composed of polyvinyl alcohol and polyacrylonitrile (PAN). The chemical activation created more pores on the surface of the PCF and consequently highly porous APCF was obtained with an improved BET surface area (3058 m² g⁻¹) and micropore volume (1.18 cm³ g⁻¹) compare to those of the carbon fiber which was prepared by calcination of monocomponent PAN. APCF was revealed to be very efficient for hydrogen storage its hydrogen capacity of 5.14 wt% at 77 K and 10 MPa. Such hydrogen storage capacity is much higher than that of activated carbon fibers reported previously. To further enhance hydrogen storage capacity catalytic Pd nanoparticles were deposited on the surface of the APCF. The Pd-deposited APCF exhibits a high hydrogen storage capacity of 5.45 wt% at 77 K and 10 MPa. The results demonstrate the potential of Pd-deposited APCF for efficient hydrogen storage.

Strength hardness and ductility characteristics were determined for a series of palladium-copper alloys that compositionally vary from 5 to 25 weight percent copper. Alloy specimens subjected to vacuum annealing showed clear evidence of solid solution strengthening. These specimens showed as a function of increasing copper content increased yield strength ultimate strength and Vickers microhardness while their ductility was little affected by compositional differences. Annealed alloy specimens subsequently subjected to exposure to hydrogen at 323 K and PH² = 1 atm showed evidence of hydrogen embrittlement up to a composition of ~15 wt. % Cu. The magnitude of the hydrogen embrittlement decreased with increasing copper content in the alloy.

Power-to-Gas technologies offer a promising approach for converting renewable electricity into a molecular form (fuel) to serve the energy demands of non-electric energy applications in all end-use sectors. The technologies have been broadly developed and are at the edge of a mass roll-out. The barriers that Power-to-Gas faces are no longer technical but are foremost regulatory and economic. This study focuses on a Power-to-Gas pathway where electricity is first converted in a water electrolyzer into hydrogen which is then synthetized with carbon dioxide to produce synthetic natural gas. A key aspect of this pathway is that an intermittent electricity supply could be used which could reduce the amount of electricity curtailment from renewable energy generation. Interim storages would then be necessary to decouple the synthesized part from hydrogen production to enable (I) longer continuous operation cycles for the methanation reactor and (II) increased annual full-load hours leading to an overall reduction in gas production costs. This work optimizes a Power-to-Gas plant configuration with respect to the cost benefits using a Monte Carlo-based simulation tool. The results indicate potential cost reductions of up to 17% in synthetic natural gas production by implementing well-balanced components and interim storages. This study also evaluates three different power sources which differ greatly in their optimal system configuration. Results from time-resolved simulations and sensitivity analyses for different plant designs and electricity sources are discussed with respect to technical and economic implications so as to facilitate a plant design process for decision makers.

Hydrogen energy is a very attractive option in dealing with the existing energy crisis. For the development of a hydrogen energy economy hydrogen storage technology must be improved to over the storage limitations. Compared with traditional hydrogen storage technology the prospect of hydrogen storage materials is broader. Among all types of hydrogen storage materials solid hydrogen storage materials are most promising and have the most safety security. Solid hydrogen storage materials include high surface area physical adsorption materials and interstitial and non-interstitial hydrides. Among them interstitial hydrides also called intermetallic hydrides are hydrides formed by transition metals or their alloys. The main alloy types are A2B AB AB2 AB3 A2B7 AB5 and BCC. A is a hydride that easily forms metal (such as Ti V Zr and Y) while B is a non-hydride forming metal (such as Cr Mn and Fe). The development of intermetallic compounds as hydrogen storage materials is very attractive because their volumetric capacity is much higher (80–160 kgH2m−3 ) than the gaseous storage method and the liquid storage method in a cryogenic tank (40 and 71 kgH2m−3 ). Additionally for hydrogen absorption and desorption reactions the environmental requirements are lower than that of physical adsorption materials (ultra-low temperature) and the simplicity of the procedure is higher than that of non-interstitial hydrogen storage materials (multiple steps and a complex catalyst). In addition there are abundant raw materials and diverse ingredients. For the synthesis and optimization of intermetallic compounds in addition to traditional melting methods mechanical alloying is a very important synthesis method which has a unique synthesis mechanism and advantages. This review focuses on the application of mechanical alloying methods in the field of solid hydrogen storage materials.

Numerous reviews on hydrogen storage have previously been published. However most of these reviews deal either exclusively with storage materials or the global hydrogen economy. This paper presents a review of hydrogen storage systems that are relevant for mobility applications. The ideal storage medium should allow high volumetric and gravimetric energy densities quick uptake and release of fuel operation at room temperatures and atmospheric pressure safe use and balanced cost-effectiveness. All current hydrogen storage technologies have significant drawbacks including complex thermal management systems boil-off poor efficiency expensive catalysts stability issues slow response rates high operating pressures low energy densities and risks of violent and uncontrolled spontaneous reactions. While not perfect the current leading industry standard of compressed hydrogen offers a functional solution and demonstrates a storage option for mobility compared to other technologies.