Research on hydrogen distribution characteristics in town hydrogen-doped methane pipeline.

The study of hydrogen concentration distribution law of hydrogen-doped methane pipeline is directly related to the safety and stability of hydrogen-doped methane pipeline network. Based on the theory of fluid dynamics, this paper established a model of hydrogen-doped methane pipeline and simulated the operation and shutdown status of hydrogen-doped methane pipeline by adopting the computational fluid dynamics method and selecting the mixture multiphase model and standard k - ε turbulence model. This paper investigates the hydrogen concentration distribution law in hydrogen-doped methane pipelines as well as the influence law of different hydrogen-doping ratios, operating flow velocities, operating pressures, shutdown time and gas usage on the hydrogen concentration distribution in gas pipeline. The results show that: under the operation condition, there is a weak uneven distribution of hydrogen in the pipeline, the hydrogen-doping ratio, flow velocity, pressure on the hydrogen volume fraction of the change in the 0.9% or less, the effect can be ignored; in the shutdown status, there is a clear stratification phenomenon, the hydrogen-doping ratio increased from 10 to 25%, the change in the volume fraction of hydrogen in the 11.2% or less, a positive correlation; with the extension of the shutdown time to 900s, the pipeline firstly appeared obvious stratification phenomenon in the branch pipe, the thickness of the gas with hydrogen volume fraction above 40% on the upper wall surface of the branch pipe increased to 0.7 mm, and after the shutdown time was extended to 10 h, obvious stratification phenomenon appeared in the main pipeline, and the volume fraction of hydrogen near the top of the main pipe of about 16.5 mm was above 30%, which was positively correlated; In the shutdown status, the shutdown time has the greatest effect on the stratification phenomenon in the pipe, followed by the hydrogen-doping ratio, and the gas usage has the least effect.

Evolution Path of Precursor-Induced High-Temperature Lithiation Reaction during the Synthesis of Lithium-Rich Cathode Materials.

High-temperature lithiation is one of the crucial steps for the synthesis of Li- and Mn-rich layered metal oxide (LMLO) cathodes. A profound insight of the micromorphology and crystal structure evolution during calcination helps to realize the finely controlled preparation of final cathodes, finally achieving a desired electrochemical performance. In this work, two typical precursors (hydroxide and oxalate) were selected to prepare LMLO. It is found that the influence of the lithium source on reaction pathways is determined by the properties of precursors. In the case of hydroxide as a precursor, whatever lithium sources it is, the flake morphology of LMLO is inherited from hydroxide precursors. This is because the crystal structure of cathode products has a high similarity with its precursor in terms of the oxygen array arrangement, and the topological transformation occurs from hydroxide (P-3ml) to LMLOs (C/2m and R3m). Thus, the morphology and microstructure of LMLO cathodes could be well controlled only by tuning the properties of hydroxide precursors. Conversely, the decomposition of a lithium source has a great influence on the intermediate transformation when oxalate is used as the precursor. This is because a large amount of CO2 is released from the oxalate precursor after the decomposition reaction, resulting in drastic structural changes. At this time, the diffusion ability of the lithium source leads to the competition between the spinel phase and layered phase. Based on this point, the formation of a spinel intermediate phase can be reduced by accelerating the decomposition of the lithium source, contributing to the generation of a highly pure layered phase, thus exhibiting higher electrochemical performance. These insights provide an exciting cue to the rational selection and design of raw materials and lithium sources for the controlled synthesis of LMLO cathodes.

Research Progress on Replacement and Production Technology for Long-Distance Liquefied Ethane Pipelines.

Ethane is used as raw material to produce ethylene, which is the most important basic raw material for the petrochemical industry. The liquid phase ethane transportation method has the advantages of large transportation capacity and high economy. In this paper, the research progress of long-distance ethane pipelines is reviewed from the aspects of construction, phase change characteristics, standards and specifications, replacement, and production technology. The phase change characteristics of ethane-nitrogen mixed gas in the replacement process are discussed. In addition, the applicability of existing standards, specifications, and related replacement production technologies to liquefied ethane pipelines was analyzed, and operational recommendations have been given. Suggestions for future research are put forward to promote the application of pipeline replacement and production technology for ethane long transportation.