China, People’s Republic

Underground hydrogen storage in aquifers is a promising solution to address the imbalance between energy supply and demand yet its practical implementation requires optimized strategies to ensure high efficiency and economic viability. To improve the storage and production efficiency of hydrogen it is essential to select the appropriate cushion gas and to study the influence of reservoir and process parameters. Based on the conceptual model of aquifer with single-well injection and production three potential cushion gas (carbon dioxide nitrogen and methane) were studied and the changes in hydrogen recovery for each cushion gas were compared. The effects of temperature initial pressure porosity horizontal permeability vertical to horizontal permeability ratio permeability gradient hydrogen injection rate and hydrogen production rate on the purity of recovered hydrogen were investigated. Additionally the impact of different well pattern on the purity of recovered hydrogen was studied. The results indicate that methane is the most effective cushion gas for improving hydrogen recovery in UHS. Different well patterns have significant impacts on the purity of recovered hydrogen. The mole fractions of methane in the produced gas for the single-well line-drive pattern and five-spot pattern were 16.8% 5% and 3.05% respectively. Considering the economic constraints the five-spot well pattern is most suitable for hydrogen storage in aquifers. Reverse rhythm reservoirs with smaller permeability differences should be chosen to achieve relatively high hydrogen recovery and purity of recovered hydrogen. An increase in hydrogen production rate leads to a significant decrease in the purity of the recovered hydrogen. In contrast hydrogen injection rate has only a minor effect. These findings provide actionable guidance for the selection of cushion gas site selection and operational design of aquifer-based hydrogen storage systems contributing to the large-scale seasonal storage of hydrogen and the balance of energy supply and demand.

The use of rare earth elements in hydrogen storage processes offers significant advantages in terms of increasing technological efficiency and ensuring system security. However this process also creates some serious problems in terms of environmental and economic sustainability. It is necessary to determine the most critical indicators affecting the sustainable use of these elements. Studies on this subject in the literature are quite limited and this may lead to wrong investment decisions. The main purpose of this study is to determine the most important indicators to increase the sustainable use of rare earth elements in hydrogen storage processes. An original decision-making model in which Siamese network logarithmic percentage-change driven objective weighting (LOPCOW) fractal fuzzy numbers and weighted influence super matrix with precedence (WISP) approaches are integrated in the study. This study provides an original contribution to the literature by identifying the most critical indicators affecting the sustainable use of rare earths in hydrogen storage processes by presenting an innovative model. Fractal structures such as Koch Snowflake Cantor Dust and Sierpinski Triangle can model complex uncertainties more successfully. Fractal structures are particularly effective in modeling linguistic fuzziness because their recursive nature closely mirrors the layered and imprecise way humans often express subjective judgments. Unlike linear fuzzy sets fractals can capture the patterns of ambiguity found in expert evaluations. Hydrogen storage capacity and government supports are determined as the most vital criteria affecting sustainability in rare earth use.

Driven by the global energy transition and the dual carbon goals developing low-carbon and zero-carbon alternative fuels has become a core issue for sustainable development in the internal combustion engine sector. Ammonia is a promising zero-carbon fuel with broad application prospects. However its inherent combustion characteristics including slow flame propagation high ignition energy and narrow flammable range limit its use in internal combustion engines necessitating the addition of auxiliary fuels. To address this issue this paper proposes a composite injection technology combining “ammonia duct injection + hydrogen cylinder direct injection.” This technology utilizes highly reactive hydrogen to promote ammonia combustion compensating for ammonia’s shortcomings and enabling efficient and smooth engine operation. This study based on bench testing investigated the effects of hydrogen direct injection timing (180 170 160 150 140◦ 130 120 ◦CA BTDC) hydrogen direct injection pressure (4 5 6 7 8 MPa) on the combustion and emissions of the ammonia–hydrogen engine. Under hydrogen direct injection timing and hydrogen direct injection pressure conditions the hydrogen mixture ratios are 10% 20% 30% 40% and 50% respectively. Test results indicate that hydrogen injection timing that is too early or too late prevents the formation of an optimal hydrogen layered state within the cylinder leading to prolonged flame development period and CA10-90. The peak HRR also exhibits a trend of first increasing and then decreasing as the hydrogen direct injection timing is delayed. Increasing the hydrogen direct injection pressure to 8 MPa enhances the initial kinetic energy of the hydrogen jet intensifies the gas flow within the cylinder and shortens the CA0-10 and CA10-90 respectively. Under five different hydrogen direct injection ratios the CA10- 90 is shortened by 9.71% 11.44% 13.29% 9.09% and 13.42% respectively improving the combustion stability of the ammonia–hydrogen engine.

Activated carbon as a hydrogen storage material possesses advantages such as low cost high safety lightweight and good cycling performance. Zhundong coal characterized by low calorific value high volatility and elevated reaction activity stands out as an exceptional raw material for the production of activated carbon. This study employed Zhundong coal for the synthesis of hydrogen storage activated carbon exploring the impact of acid treatment and varied activation conditions on Zhundong coal. The specific surface area of sample ZD-HK3-AC is 1980 m2 /g and the gravimetric hydrogen storage density reaches 0.91 wt% under the condition of 80bar at room temperature. The adsorption–desorption isotherms nearly overlapped demonstrating excellent cycling performance and high mechanical strength. At the same time the relationship between the pore structure parameters of activated carbon and hydrogen storage density was explored revealing the mechanism of activated carbon adsorption and hydrogen storage. These findings hold significant guiding implications for the preparation and research of hydrogen storage materials utilizing activated carbon.

The gas equation of state (EOS) serves as a critical tool for analyzing the thermal effects within the hydrogen storage tank during refueling processes. It quantifies the dynamic relationships among pressure temperature and volume playing a vital role in numerical simulations of hydrogen refueling the development of refueling protocols and ensuring refueling safety. This study first establishes a lumped-parameter thermodynamic model for the hydrogen refueling process which combines a zero-dimensional gas model with a one-dimensional tank wall model (0D1D). The model’s accuracy was validated against experimental data and will be used in combination with different EOSs to simulate hydrogen temperature and pressure. Subsequently parameter values are derived for the van der Waals EOS and its modified forms—Redlich–Kwong Soave and Peng–Robinson. The accuracy of the modified forms is evaluated using the Joule–Thomson inversion curve. A polynomial EOS is formulated and its parameters are numerically determined. Finally the hydrogen temperatures and pressures calculated using the van der Waals EOS Redlich– Kwong EOS polynomial EOS and the National Institute of Standards and Technology (NIST) database are compared. Within the initial and boundary conditions set in this study the results indicate that among the modified forms for van der Waals EOS the Redlich– Kwong EOS exhibits higher accuracy than the Soave and Peng–Robinson EOSs. Using the NIST-calculated hydrogen pressure as a benchmark the relative error is 0.30% for the polynomial EOS 1.83% for the Redlich–Kwong EOS and 17.90% for the van der Waals EOS. Thus the polynomial EOS exhibits higher accuracy followed by the Redlich–Kwong EOS while the van der Waals EOS demonstrates lower accuracy. This research provides a theoretical basis for selecting an appropriate EOS in numerical simulations of hydrogen refueling processes.