China, People’s Republic

Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The “Magnesium group” of international experts contributing to IEA Task 32 “Hydrogen Based Energy Storage” recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures kinetics and thermodynamics of the systems based on MgH₂ nanostructuring new Mg-based compounds and novel composites and catalysis in the Mg based H storage systems. Finally thermal energy storage and upscaled H storage systems accommodating MgH₂ are presented.

In this paper the effects of hydrogen blending radio and EGR rate on combustion and emission characteristics of a PFI gasoline engine with hydrogen direct-injection have been investigated by numerical modelling methods using a new generation of CFD simulation software CONVERGE. Results showed that compared with original engine hydrogen direct-injection PFI gasoline engine had a better performance on combustion characteristics but it also had a disadvantage of increasing NOx emissions. With the increase of hydrogen blending radio combustion duration shortened and CA50 advanced and was closer to TDC. And CO and THC emissions decreased however NOx emission increased. The variations of the combustion and emission characteristics followed by the increase of the EGR rate were exactly the opposite to the change of hydrogen blending radio. Considering both the combustion and emission characteristics using moderate EGR rate (15%~20%) under high hydrogen blending radio (15%~20%) condition can realize the simultaneous improvement of combustion and emission performance.

Microgrid with hydrogen storage is an effective way to integrate renewable energy and reduce carbon emissions. This paper proposes an optimal operation method for a microgrid with hydrogen storage. The electrolyzer efficiency characteristic model is established based on the linear interpolation method. The optimal operation model of microgrid is incorporated with the electrolyzer efficiency characteristic model. The sequential decision-making problem of the optimal operation of microgrid is solved by a deep deterministic policy gradient algorithm. Simulation results show that the proposed method can reduce about 5% of the operation cost of the microgrid compared with traditional algorithms and has a certain generalization capability.

Hydrogen generation by the reaction of pure Al powder in water with the addition of Al(OH)3 γ- Al2O3 α-Al2O3 or TiO2 at mild temperatures was investigated. It was found that the reaction of Al with water is promoted and the reaction induction time decreases greatly by the above hydroxide and oxides. X-ray diffraction analyses revealed that the hydroxide and oxide phases have no any change during the Al-water reaction indicating that they are just as catalysts to assist the reaction of Al with water. A possible mechanism was proposed which shows that hydroxide and oxides could dissociate water molecules and promote the hydration of the passive oxide film on Al particle surfaces.

During the World Expo Shanghai there were one hundred fuel-cell sight-seeing cars in operation at the Expo Site. The sight-seeing cars were not allowed to drive out of the Expo Site and the stationary hydrogen refuelling station was not permitted to build at the Expo Site for the sake of safety. A flexible solution to refuel the cars was the application of mobile hydrogen refuelling stations. To better understand the hazards and risks associated with the mobile hydrogen refueling stations a risk analysis was preformed to improve the safety of the operations. The risks to the station personnel and to the public were discussed separately. Results show that the stationary risks of the mobile stations to the personnel and refueling customers are lower than the risk acceptance criteria over an order of magnitude so occupational risks and risks to customers are completely acceptable. The third party risks can be acceptable as long as the appropriate mitigation measures are implemented especially well designed parking area and operation time. Leak from boosters is the main risk contributor to the stationary risks because of its highest failure rates according to the generic data and its worst harm effects based on the consequence evaluations. As for the road risks of the mobile stations they can be acceptable as long as the appropriate mitigation measures are implemented especially well-designed moving path and transportation time.

The potential of catalytic pyrolysis of biomass for hydrogen and bio‐oil production has drawn great attention due to the concern of clean energy utilization and decarbonization. In this paper the catalytic pyrolysis of pine sawdust with calcined dolomite was carried out in a novel moving bed reactor with a two‐stage screw feeder. The effects of pyrolysis temperature (700–900 °C) and catalytic temperature (500–800 °C) on pyrolysis performance were investigated in product distribution gas composition and gas properties. The results showed that with the temperature increased pyrolysis gas yield in‐ creased but the yield of solid and liquid products decreased. With the increase in temperature the CO and H2 content increased significantly while the CO2 and CH4 decreased correspondingly. The calcined dolomite can remove the tar by 44% and increased syngas yield by 52.9%. With the increasing catalytic temperature the catalytic effect of calcined dolomite was also enhanced.

Wet dust removal systems used to control dust in the polishing or grinding process of Mg alloy products are frequently associated with potential hydrogen explosion caused by magnesium-water reaction. For purpose of avoiding hydrogen explosion risks we try to use a combination of chitosan (CS) and sodium phosphate (SP) to inhibit the hydrogen evolution reaction between magnesium alloy waste dust and water. The hydrogen evolution curves and chemical kinetics modeling for ten different mixing ratios demonstrate that 0.4% wt CS + 0.1% wt SP yields the best inhibition efficiency with hydrogen generation rate of almost zero. SEM and EDS analyses indicate that this composite inhibitor can create a uniform smooth tight protective film over the surface of the alloy dust particles. FTIR and XRD analysis of the chemical composition of the surface film show that this protective film contains CS and SP chemically adsorbed on the surface of ZK60 but no detectable Mg(OH)2 suggesting that magnesium-water reaction was totally blocked. Our new method offers a thorough solution to hydrogen explosion by inhibiting the hydrogen generation of magnesium alloy waste dust in a wet dust removal system.

The deterioration of the mechanical properties of metal induced by hydrogen absorption threatens the safety of the equipment serviced in hydrogen environments. In this study the hydrogen concentration distribution in 2.25Cr-1Mo-0.25V steel after hydrogen charging was analyzed following the hydrogen permeation and diffusion model. The diffusible hydrogen content in the 1-mm-thick specimen and its influence on the mechanical properties of the material were investigated by glycerol gas collecting test static hydrogen charging tensile test scanning electron microscopy (SEM) test and microhardness test. The results indicate that the content of diffusible hydrogen tends to be the saturation state when the hydrogen charging time reaches 48 h. The simulation results suggest that the hydrogen concentration distribution can be effectively simulated by ABAQUS and the method can be used to analyze the hydrogen concentration in the material with complex structures or containing multiple microstructures. The influence of hydrogen on the mechanical properties is that the elongation of this material is reduced and the diffusible hydrogen will cause a decrease in the fracture toughness of the material and thus hydrogen embrittlement (HE) will occur. Moreover the Young’s modulus E and microhardness are increased due to hydrogen absorption and the variation value is related to the hydrogen concentration introduced into the specimen.

The safety issues related to explosion venting of hydrogen-air mixtures are significant and deserve more detailed investigation. Vented hydrogen-air explosion has been studied extensively in vessels with a single vent. However little attention has been paid to the cases with more than one vent. In this paper experiments about explosion venting of rich hydrogen-air mixtures were conducted in a cylindrical vessel with two symmetrical vents to investigate the effect of vent area and distribution on pressure build up and flame behaviours. Venting accelerates the flame front towards the vent but has nearly no effect on the opposite side. The maximum internal overpressure decreases and the maximum external flame length increases with the increase of vent area. Two pressure peaks can be identified outside of vessel which correspond to the external explosion and the burnt gas jet respectively. Compared with single vent two vents with same total vent area leads to nearly unchanged maximum internal and external overpressure but much smaller external flame length.

The number of hydrogen refuelling stations worldwide is growing rapidly in recent years. The first large capacity hydrogen refuelling station in China is under construction. A 3D quantitative risk assessment QRA）is conducted for this station. Hazards associated with hydrogen systems are identified. Leakage frequency of hydrogen equipment are analyzed. Jet flame explosion scenarios and corresponding accident consequences are simulated. Risk acceptance criteria for hydrogen refuelling stations are discussed. The results show that the risk of this refuelling station is acceptable. And the maximum lethality frequency is 6.3*10-6. The area around compressors has the greatest risk. People should be avoided as far as possible from the compressor when the compressor does not need to be maintained. With 3D QRA the visualization of the evaluation results will help stakeholders to observe the hazardous areas of the hydrogen refuelling station at a glance.