Transmission, Distribution & Storage

We investigated hydrogen embrittlement in Fe20Mn20Ni20Cr20Co and Fe30Mn10Cr10Co (at.%) alloys pre-charged with 100 MPa hydrogen gas by tensile testing at three initial strain rates of 10⁻⁴ 10⁻³ and 10⁻² s⁻¹ at ambient temperature. The alloys are classified as stable and metastable austenite-based high-entropy alloys (HEAs) respectively. Both HEAs showed the characteristic hydrogen-induced degradation of tensile ductility. Electron backscatter diffraction analysis indicated that the reduction in ductility by hydrogen pre-charging was associated with localized plasticity-assisted intergranular crack initiation. It should be noted as an important finding that hydrogen-assisted cracking of the metastable HEA occurred not through a brittle mechanism but through localized plastic deformation in both the austenite and ε-martensite phases.

The heat transfer analysis in the filling process of compressed on-board hydrogen storage tank has been the focus of hydrogen storage research. The initial conditions mass flow rate and heat transfer coefficient have certain influence on the hydrogen filling performance. In this paper the effects of mass flow rate and heat transfer coefficient on hydrogen filling performance are mainly studied. A thermodynamic model of the compressed hydrogen storage tank was established by Matlab/Simulink. This 0D model is utilized to predict the hydrogen temperature hydrogen pressure tank wall temperature and SOC (State of Charge) during filling process. Comparing the simulated results with the experimental data the practicability of the model can be verified. The simulated results have certain meaning for improving the hydrogenation parameters in real filling process. And the model has a great significance to the study of hydrogen filling and purification.

The effect of different cathodic potentials applied to the X70 pipeline steel immersed in acidified and aerated synthetic soil solution under stress using a slow strain rate test (SSRT) and electrochemical impedance spectroscopy (EIS) was studied. According to SSRT results and the fracture surface analysis by scanning electron microscopy (SEM) the steel susceptibility to stress corrosion cracking (SCC) increased as the cathodic polarization increased (Ecp). This behavior is attributed to the anodic dissolution at the tip of the crack and the increment of the cathodic reaction (hydrogen evolution) producing hydrogen embrittlement. Nevertheless when the Ecp was subjected to the maximum cathodic potential applied (−970 mV) the susceptibility decreased; this behavior is attributed to the fact that the anodic dissolution was suppressed and the process of the SCC was dominated only by hydrogen embrittlement (HE). The EIS results showed that the cathodic process was influenced by the mass transport (hydrogen diffusion) due to the steel undergoing so many changes in the metallic surface as a result of the applied strain that it generated active sites at the surface.

Strain-induced martensite transformation (SIMT) commonly exists around a crack tip of metastable austenite stainless steels. The influence of the volume expansion of the SIMT on the hydrogen diffusion was investigated by hydrogen diffusion modelling around a crack tip in type 304L austenite stainless steel. The volume expansion changed the tensile stress state into pressure stress state at the crack tip resulting in a large stress gradient along the crack propagation direction. Compared to the analysis without considering the volume expansion effect this volume expansion further accelerated the hydrogen transport from the inner surface to a critical region ahead of the crack tip and further increased the maximum value of the hydrogen concentration at the critical position where the strain-induced martensite fraction approximates to 0.1 indicating that the volume expansion of the SIMT further increased the hydrogen embrittlement susceptibility.

In this paper we analyze the potential factors affecting the hydrogen sulfide type of stress corrosion cracking in C110 casing pipes. In order to further study these cracking factors the methods of material property testing scanning electron microscopy XRD TEM and 3D ultra-depth-of-field were applied in the experiments. Besides that an HTHP autoclave was independently designed by the laboratory to simulate the actual corrosion environment and the potential factors affecting the stress corrosion cracking of C110 casing pipes were determined. The test results showed that the chemical composition metallographic structure hardness and non-metallic inclusions of the two types of C110 casing pipes were all qualified. In fact there remains a risk of stress corrosion cracking when the two kinds of C110 casing pipes serve under long-term field-working conditions. It is considered in this paper that the precipitates on the material surface stress damage and pitting corrosion are all critical factors affecting the stress corrosion cracking of casing pipes.

The current energy system is subject to a fundamental transformation: A system that is oriented towards a constant energy supply by means of fossil fuels is now expected to integrate increasing amounts of renewable energy to achieve overall a more sustainable energy supply. The challenges arising from this paradigm shift are currently most obvious in the area of electric power supply. However it affects all areas of the energy system albeit with different results. Within the energy system various independent grids fulfill the function of transporting and spatially distributing energy or energy carriers and the demand-oriented supply ensures that energy demands are met at all times. However renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly.<br/>Energy storage technologies are one option for temporal matching of energy supply and demand. Energy storage systems have the ability to take up a certain amount of energy store it in a storage medium for a suitable period of time and release it in a controlled manner after a certain time delay. Energy storage systems can also be constructed as process chains by combining unit operations each of which cover different aspects of these functions. Large-scale mechanical storage of electric power is currently almost exclusively achieved by pumped-storage hydroelectric power stations.<br/>These systems may be supplemented in the future by compressed-air energy storage and possibly air separation plants. In the area of electrochemical storage various technologies are currently in various stages of research development and demonstration of their suitability for large-scale electrical energy storage. Thermal energy storage technologies are based on the storage of sensible heat exploitation of phase transitions adsorption/desorption processes and chemical reactions. The latter offer the possibility of permanent and loss-free storage of heat. The storage of energy in chemical bonds involves compounds that can act as energy carriers or as chemical feedstocks. Thus they are in direct economic competition with established (fossil fuel) supply routes. The key technology here – now and for the foreseeable future – is the electrolysis of water to produce hydrogen and oxygen.<br/>Hydrogen can be transformed by various processes into other energy carriers which can be exploited in different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system chemical energy storage technologies open up opportunities to link and interweave the various energy streams and sectors. Chemical energy storage not only offers means for greater integration of renewable energy outside the electric power sector it also creates new opportunities for increased flexibility novel synergies and additional optimization.<br/>Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. The article describes various technologies for energy storage and their potential applications in the context of Germany’s Energiewende i.e. the transition towards a more sustainable energy system. Therefore the existing legal framework defines some of the discussions and findings within the article specifically the compensation for renewable electricity providers defined by the German Renewable Energy Sources Act which is under constant reformation. While the article is written from a German perspective the authors hope this article will be of general interest for anyone working in the areas of energy systems or energy technology.

This study reports the investigative conclusions of parametric studies conducted to understand the effect of operating parameters on absorption and desorption characteristics of LaNi4.7Al0.3 metal hydride system for thermal management applications. Reactor with improved design containing 55 embedded cooling tubes is fabricated and filled with 4 kg of metal hydride alloy. Using water as heat transfer fluid (HTF) effects of supply pressure HTF temperature and HTF flow rate on absorption and desorption characteristics of the reactor are analyzed. Increasing supply pressure leads to prominent improvement in absorption capacity while the increase in HTF temperature enhanced desorption performance. At 20 bar and 20 °C 46.2877 g of hydrogen (1.16 wt%) was absorbed resulting in total energy output of 707.3 kJ for 300 s. During desorption at 80 °C with water flow rate of 8 lpm heat input of 608.1 kJ for 300 s resulted in 28.5259 g of hydrogen desorption.

A potential enabler of a low carbon economy is the energy vector hydrogen. However issues associated with hydrogen storage and distribution are currently a barrier for its implementation. Hence other indirect storage media such as ammonia and methanol are currently being considered. Of these ammonia is a carbon free carrier which offers high energy density; higher than compressed air. Hence it is proposed that ammonia with its established transportation network and high flexibility could provide a practical next generation system for energy transportation storage and use for power generation. Therefore this review highlights previous influential studies and ongoing research to use this chemical as a viable energy vector for power applications emphasizing the challenges that each of the reviewed technologies faces before implementation and commercial deployment is achieved at a larger scale. The review covers technologies such as ammonia in cycles either for power or CO₂ removal fuel cells reciprocating engines gas turbines and propulsion technologies with emphasis on the challenges of using the molecule and current understanding of the fundamental combustion patterns of ammonia blends.

The expansion of wind and solar power is creating a growing need for power system flexibility. Dispatchable power plants with CO₂ capture and storage (CCS) offer flexibility with low CO₂ emissions but these plants become uneconomical at the low running hours implied by renewables-based power systems. To address this challenge the novel gas switching reforming (GSR) plant was recently proposed. GSR can alternate between electricity and hydrogen production from natural gas offering flexibility to the power system without reducing the utilization rate of the capital stock embodied in CCS infrastructure. This study assesses the interplay between GSR and variable renewables using a power system model which optimizes investment and hourly dispatch of 13 different technologies. Results show that GSR brings substantial benefits relative to conventional CCS. At a CO₂ price of V100/ton inclusion of GSR increases the optimal wind and solar share by 50% lowers total system costs by 8% and reduces system emissions from 45 to 4 kgCO₂/MWh. In addition GSR produces clean hydrogen equivalent to about 90% of total electricity demand which can be used to decarbonize transport and industry. GSR could therefore become a key enabling technology for a decarbonization effort led by wind and solar power.

Hydrogen induced failure under uniaxial tension is simulated in a duplex stainless steel considering microstructural feature of the material. There are three key ingredients in the modelling approach: image processing and finite element representation of the experimentally observed microstructure stress driven hydrogen diffusion and diffusion coupled cohesive zone modelling of fracture considering mixed failure mode. The microstructure used as basis for the modelling work is obtained from specimens cut in the transverse and longitudinal directions. It is found that the microstructure significantly influences hydrogen diffusion and fracture. The austenite phase is polygonal and randomly distributed in the transverse direction where a larger effective hydrogen diffusion coefficient and a lower hydrogen fracture resistance is found compared to the specimen in the longitudinal direction where the austenite phase is slender and laminated. This indicates that the proper design and control of the austenite phase help improve hydrogen resistance of duplex stainless steel. The strength of the interface in the shear direction is found to dominate the fracture mode and initiation site which reveals the importance of considering mixed failure mode and calibrating the hydrogen induced strength reduction in shear.