Spontaneous combustion characteristics of hydrothermal eroded coal in deep mining

In the process of deep mining, the temperature of mine water is significantly higher than that of shallow coal seams. The erosion of high-temperature hydrothermal fluids affects the physical and chemical characteristics of coal, which in turn affects its spontaneous combustion process. To study the spontaneous combustion characteristics and influencing mechanisms of coal under the influence of hydrothermal erosion in deep mining, through low-field nuclear magnetic resonance, molecular dynamics simulation, mechanical test and C600 trace heat experiment, the influence of hydrothermal erosion on coal porosity, pore size distribution, mechanical strength and oxidation heat characteristic parameters was analyzed. Combined with correlation analysis, the correlation between various parameters was quantitatively described. The study results show that under the dual influence of thermal stress and swelling, the internal pore structure of hydrothermal eroded coal changes significantly. There is a significant positive correlation between hydrothermal temperature and total porosity of coal, and the correlation coefficient is 0.97. With the increase of hydrothermal temperature, the total porosity of coal increases from 0.24% to 1.35%, the proportion of micropores decreases from more than 69% to less than 60%, and the proportion of mesopores and macropores increases. Coal body pore size significantly affects the oxygen diffusion coefficient, which increases exponentially with a linear increase in coal body pore size. Under the influence of hydrothermal erosion, the development of coal pores and the dissolution of some organic matter significantly reduce the mechanical strength of coal. From raw coal to 80 ℃ hydrothermal eroded coal, the average compressive strength decreases from 23 MPa to 11.6 MPa, which is reduced by 50%. Compared with raw coal, the heat release intensity of hydrothermal erosion coal is higher and the heat release is greater. The heat release of TH40, TH50, TH60, TH70 and TH80 increase by 12.61%, 16.63%, 17.32%, 19.36% and 25.02%, respectively. The correlation coefficient between hydrothermal temperature and coal oxidation heat release is 0.92. Hydrothermal erosion significantly affects the porosity and oxidation process of coal. As the hydrothermal temperature increases, the porosity of the coal body increases, the mechanical strength weakens, the oxygen consumption and oxidation rate of the oxidation process accelerate, and the heat release increases. Hydrothermal erosion coal has a higher risk of spontaneous combustion, and the higher the hydrothermal temperature is, the greater the risk is

Optimization of Operating Parameters for Coal Low-Temperature Ashing: A Suitable and Efficient Treatment Method for Mineral Analysis in Coal

Low-temperature oxygen-plasma ashing plus X-ray diffraction analysis is one of the effective techniques to identify minerals in coal. However, previous publications have not provided any details of the exact low-temperature degrees and corresponding working conditions of ashers, and this could lead to two adverse effects without proper operating guidance: (1) a relatively high temperature (e.g., >150 °C) may cause alteration of minerals (particularly clay minerals), and (2) a relatively low temperature (e.g., (004) and kaolinite d(002) can be clearly distinguished by LTAs-XRD analysis. In addition, different low temperatures have certain influence on the crystal structure of minerals. When the power rises to above 300 W (about 150 °C), the crystal structure of minerals undergoes changes. The symmetry and integrity of the mineral peaks became worse, and destructive interference occurred between the spacing of reflection planes, resulting in significant decrease in diffraction peak intensity; thus, some trace minerals were unable to be identified. The study on the working parameters of the instrument would be helpful to ash coals more effectively and make qualitative and quantitative analysis of minerals more accurate

Petrographic and geochemical characteristics of selected coal seams from the Late Cretaceous-Paleocene Guaduas Formation, Eastern Cordillera Basin, Colombia

Petrographic, geochemical and carbon isotopic determinations were conducted on five samples from four seams within the Late Cretaceous-Paleocene of the Guaduas Formation in Colombia. The individual coal seams are thin, ranging from 0.59 to 1.2 m, and occur over a 157 m interval. The average weighted ash yield is 13.7% (dry basis), although one sample presented values >35%. Vitrinite reflectance increases from 1.33% in the stratigraphically uppermost seam (La Cuarta) to 1.44% in the lower most coal seam (Cisquera), indicating their rank to be medium volatile bituminous. The studied sequence of the Guaduas Formation represents a peat environment influenced by shifting depositional settings, particularly in relation to the proximity of marine/brackish water environments as indicated by Sr/Ba values, sulfur, pyrite, δ13C and the proportion of telinite. A decrease in inertinite indicates that the peat mires were becoming relatively ‘wetter’ stratigraphically upwards. This trend, unlike that of Sr/Ba and telinite, may be driven by climatic shifts rather than only changes in depositional environment. Both trace and rare earth elements, plus yttrium (REY) are related to the inorganic fraction of the coal. All rare earth elements are depleted relative to average worldwide hard coals (for trace elements) and average upper continental crust (for REY) with the notable exception of Li and Sb for the high ash yield sample (the La Cuarta lower coal seam). The abundance of some REY elements (i.e. Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) may be more influenced by the presence of illite rather than just the quantity of total ash yield. Based on the relationship between SiO2 and Nb/Y, the provenance of the inorganics changed from a rhyolitic source at the lowest seam (Cisquera) to a dacite source in the middle layer (El Tesoro) to an andesite source in the stratigraphically uppermost seams (La Gemela and La Cuarta).</p

Intrinsic or Interface Clustering-Induced Ferromagnetism in Fe-Doped In₂O₃‑Diluted Magnetic Semiconductors

Five percent Fe-doped In₂O₃ films were deposited using a pulsed laser deposition system. X-ray diffraction and transmission electron microscopy analysis show that the films deposited under oxygen partial pressures of 10^–3 and 10^–5 Torr are uniform without clusters or secondary phases. However, the film deposited under 10^–7 Torr has a Fe-rich phase at the interface. Magnetic measurements demonstrate that the magnetization of the films increases with decreasing oxygen partial pressure. Muon spin relaxation (μSR) analysis indicates that the volume fractions of the ferromagnetic phases in PO₂ = 10^–3, 10^–5, and 10^–7 Torr-deposited samples are 23, 49, and 68%, respectively, suggesting that clusters or secondary phases may not be the origin of the ferromagnetism and that the ferromagnetism is not carrier-mediated. We propose that the formation of magnetic bound polarons is the origin of the ferromagnetism. In addition, both μSR and polarized neutron scattering demonstrate that the Fe-rich phase at the interface has a lower magnetization compared to the uniformly distributed phases

CEPC Conceptual Design Report: Volume 2 - Physics & Detector

The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed by the Chinese particle physics community to explore the Higgs boson and provide critical tests of the underlying fundamental physics principles of the Standard Model that might reveal new physics. The CEPC, to be hosted in China in a circular underground tunnel of approximately 100 km in circumference, is designed to operate as a Higgs factory producing electron-positron collisions with a center-of-mass energy of 240 GeV. The collider will also operate at around 91.2 GeV, as a Z factory, and at the WW production threshold (around 160 GeV). The CEPC will produce close to one trillion Z bosons, 100 million W bosons and over one million Higgs bosons. The vast amount of bottom quarks, charm quarks and tau-leptons produced in the decays of the Z bosons also makes the CEPC an effective B-factory and tau-charm factory. The CEPC will have two interaction points where two large detectors will be located. This document is the second volume of the CEPC Conceptual Design Report (CDR). It presents the physics case for the CEPC, describes conceptual designs of possible detectors and their technological options, highlights the expected detector and physics performance, and discusses future plans for detector R&D and physics investigations. The final CEPC detectors will be proposed and built by international collaborations but they are likely to be composed of the detector technologies included in the conceptual designs described in this document. A separate volume, Volume I, recently released, describes the design of the CEPC accelerator complex, its associated civil engineering, and strategic alternative scenarios