Molecular simulations, which can explain macroscopic phenomena from a microscopic molecular perspective, are currently receiving considerable attention. The key to this is how to characterize molecular structural parameters and construct realistic numerical models of molecules. In this paper, 13 C NMR tests were performed on ten coal samples, the macromolecular carbon skeleton structure of different coal samples was calculated and analyzed, and the macromolecular structure model of coal was constructed and modified using Materials Studio (MS). According to the principles of molecular mechanics and molecular dynamics, the energy stabilization model of coal macromolecular structure was geometrically optimized. Also, based on the quantum chemical calculations, the bond lengths and other parameters of the molecular structure model were obtained. Finally, combined with the fragmentation of chemical bonds after breaking, the main reactive groups in coal and the types of free radicals generated were summarized. The results show that the coal metamorphism degree is positively correlated with aliphatic structure stability. The constructed molecular model of coal has a reasonably good fit after correction by comparing the experimental spectra. The molecular structure model after energy optimization has a strong spatial three-dimensionality and lower total molecular energy. The molecular structure we built is more stable and closer to that of real coal samples. The more branched C−C bonds have longer bond lengths and lower bond energies. In addition, the breakage of C−C reactive chemical bonds in coal molecules results in the formation of a number of different types of reactive radicals, which in turn lead to the formation of gases such as carbon monoxide and carbon dioxide. This work has the potential to be applied to investigate the microscopic properties of the initial active chemical bond breakage behind macroscopic phenomena such as coal powder explosion or combustion.
The problem of low efficiency of coal mine methane utilization is caused by the concentration of methane of less than 10%, or a concentration that varies dramatically directly emitted into the atmosphere. This work deals with the concept of a co-production system that blends lean methane and biogas to produce electric energy. It is recommended to add the biogas generated by straws around the mines in a controlled manner to the lean methane flow to obtain the desired gas concentration in order to generate electricity. Potential electricity generation and reduced greenhouse gas emissions were also evaluated. The result shows that the co-production system can significantly improve the utilization efficiency of lean methane in coal mines; the average use of pure methane in three coal mines is 0.18, 1.12, and 5.32 million m3 every year, respectively, and the emission reduction effect of carbon dioxide (CO2) equivalent is, respectively, 3081, 18,796, and 89,050 tons. The electricity generated and the economic environmental benefits of the co-production system are remarkable, and it has economic feasibility and broad perspectives for popularization. It not only has the advantage of improving the utilization rate of methane and biomass and providing power supply and heat source for mines, but also has practical significance in terms of saving energy, reducing environmental pollution, adjusting the energy structure, and achieving the target of carbon emission peak and carbon neutrality.
Recycling methane from ventilation air is an effective means of reducing greenhouse gas emissions, improving gas utilization efficiency, and developing green mines. Regenerative oxidation properties of ventilation air methane (VAM) blending with dimethyl ether (DME) in a thermal reverse flow reactor were investigated. By analyzing the operating conditions, the influence of key process parameters on methane conversion was determined. The results showed that the addition of DME could greatly shorten the ignition delay time, lower the ignition temperature, and significantly enhance methane conversion. The initial temperature had the greatest influence on methane conversion, followed by methane concentration, whereas the effect of VAM flow on methane oxidation does not increase with an expanded flow rate, and there is an optimal flow rate range adapted to the reactor size. Additionally, methane conversion increases gradually as the equivalent ratio increases, but the temperature field does not change noticeably. Furthermore, understanding the reaction characteristics and mechanism of the CH4/DME mixture is critical for improving methane conversion and thermal utilization efficiency. Temperature sensitivity and rate of production during the oxidation process were analyzed, which revealed that R145 and R1 show positive effects, while R189 and R146 have an inhibitory effect at different DME mixing ratios and initial temperatures. For OH, the most significant promotional reaction was R1, while R27 had the reverse effect. In general, regenerative oxidation of the VAM/DME mixture contributes to an increase in methane conversion and stability of the self-sustaining operation of the system. Therefore, it is feasible to recover the thermal energy produced during the oxidation process for comprehensive utilization. This technology is of great practical importance for the improvement of methane utilization rates and the promotion of the objective of zero gas emissions in coal mines.
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