Modeling of gas emission in coal mine excavation workface: a new insight into the prediction model.

Coalbed methane (CBM) is a clean energy source, but its utilization is inefficient due to the complexity and low accuracy of its emission prediction model. In this research, we constructed a mathematical model of gas emission from the excavation workface, and combined the experimental results to propose a new model for accurate and concise prediction. The new model was validated in the field workface and compared with the traditional prediction model. Moreover, the sensitivity of gas emission parameters and the participation ratio of gas emission sources were analyzed. The study results show that the new model has higher calculation accuracy than the old model prediction, with an average error reduction of 4.693%. In the excavation workface, the coal fall gas emission conforms to the negative power function equation, and the coal wall gas emission conforms to the negative exponential function equation. In the early stage of excavation, the proportion of coal fall gas emission is higher than that of coal wall gas emission, and the peak proportion reaches 58.5%. In the later stage, the proportion of coal fall gas emission gradually decreases to below 30%. The order of the sensitivity of gas emission parameters is coal wall gas initial velocity > coal fall gas decay coefficient > coal fall gas initial velocity > coal wall gas decay coefficient. The new model is successfully applied in engineering, which helps to improve the efficiency of coal mine gas disaster control and utilization.

Pressure Measurement of Coal Seam with Active Nitrogen Injection: Model and Experimental Analysis.

Coal seam gas pressure is the core index of coal mine gas disaster prevention and control. Research on active nitrogen injection pressure measurement can effectively shorten the pressure measurement time and is of great significance to improve the pressure measurement efficiency. The purpose of this paper is to study the variation in gas pressure in the process of active nitrogen injection and the influence of different gas injection pressures on pressure measurement. Through the design of active pressure test device, pressure measurement experiments with different nitrogen injection pressures were carried out. The multicomponent gas migration model of active pressure measurement was constructed, and the active pressure numerical solver was developed based on OpenFOAM and C++ language. The borehole gas pressure equation was verified by field pressure data. The results show that when the injected nitrogen pressure is closer to the original coal seam gas pressure, the borehole gas pressure balance time is shorter. The gas change rate in this process depends on the pressure difference and concentration difference between the borehole and the surrounding coal. When the nitrogen injection pressure is greater than the gas pressure around the borehole, N2 will percolate, diffuse, and adsorb into the coal. In contrast, it is dominated by the desorption, diffusion, and seepage of CH4 to the borehole. The correlation coefficient R 2 between the borehole gas pressure equation and the field pressure measurement data is more than 0.88. Therefore, the equation can verify the reliability of the measurement results of active gas injection pressure in the field. The research results provide a reference for further understanding the mechanism and application of pressure measurement in coal seam injected with active nitrogen.

Discrimination Method of Gas Pressure Measurement in Coal Seams: Physical Experiment and Model Development.

Coal seam gas pressure is a key parameter of gas accident control and gas drainage. At present, there are some problems in field pressure measurement, such as long period, and there is often a need to drill more holes to ensure the reliability of pressure measurement. In this research, a physical gas pressure measurement experiment in a coal sample borehole was carried out, and a mathematical model of gas pressure evolution with time was constructed. Based on the OpenFOAM platform and C++ language, a numerical solver was developed, and the mathematical model was verified by the data of gas pressure in coal seam boreholes. The results show that the evolution process of gas pressure in coal seam boreholes can be divided into two stages. In the first stage, the gas pressure increases rapidly, and the pressure change rate decreases continuously. In the second stage, the gas pressure is slow and stable, and the pressure change rate tends to 0. The correlation coefficients between the mathematical model and the field-measured data are more than 0.94, and the calculation and prediction accuracy are high. Therefore, the model can be used to verify the field data during pressure measurement, which has better field significance and application value.

Analysis of the Correlation between Occupational Accidents and Economic Factors in China.

One of the important factors affecting the production safety of a country or region is the level of economic development. Avoiding accidents under the condition of ensuring economic development is a problem that needs in-depth research. On the basis of collecting the data of occupational accidents and economic development indicators in China from 2000 to 2020, this paper studies the relationship between occupational accidents and five economic indicators, such as resident consumption, energy consumption, education funds, wage level and research input. The grey working accident model of Gaussian function is established, the occurrence trend of occupational accidents is quantitatively analyzed, and the accident reduction measures are suggested based on the relationship between accidents and economy. The results show that there is a strong correlation between accident and economic indicators, and the comprehensive correlation coefficient among scientific research investment, education funds and accident indicators is significantly higher than that of other economic indicators. Increasing investment in scientific research and education is conducive to improving the quality of workers and training safety professionals and can effectively reduce workplace accidents.

Maternal genetic structure in ancient Shandong between 9500 and 1800 years ago.

Archaeological and ancient DNA studies revealed that Shandong, a multi-culture center in northern coastal China, was home to ancient populations having ancestry related to both northern and southern East Asian populations. However, the limited temporal and geographical range of previous studies have been insufficient to describe the population history of this region in greater detail. Here, we report the analysis of 86 complete mitochondrial genomes from the remains of 9500 to 1800-year-old humans from 12 archaeological sites across Shandong. For samples older than 4600 years before present (BP), we found haplogroups D4, D5, B4c1, and B5b2, which are observed in present-day northern and southern East Asians. For samples younger than 4600 BP, haplogroups C (C7a1 and C7b), M9 (M9a1), and F (F1a1, F2a, and F4a1) begin to appear, indicating changes in the Shandong maternal genetic structure starting from the beginning of the Longshan cultural period. Within Shandong, the genetic exchange is possible between the coastal and inland regions after 3100 BP. We also discovered the B5b2 lineage in Shandong populations, with the oldest Bianbian individual likely related to the ancestors of some East Asians and North Asians. By reconstructing a maternal genetic structure of Shandong populations, we provide greater resolution of the population dynamics of the northern coastal East Asia over the past nine thousand years.