Key technologies for extraction and identification of gas target area for pressure relief in inclined thick coal seam

In order to study the dip angle effect on the evolution law of the target area for pressure relief gas drainage in inclined thick coal seams, the physical similarity simulation test and theoretical analysis were combined to study the fracture evolution in the target area under different coal seam dip angles. The evolution law of broken fracture’s width, the area proportion of bed-separated fracture, and the fractal dimension of fracture with the change of coal seam dip angle in the target area were obtained, and then the coal seam dip angle effect model of the targeted area evolution was established. The results showed that the broken fracture’s width presented the distribution characteristics that the boundary area on both sides of the goaf was greater than that in the middle, and the low horizon was greater than that in the higher horizon. What’s more, the broken fracture’s width was strongly affected by the hinged beam. With the increase of the coal seam dip angle (0° < 15° < 30°), the broken fracture’s width in the upper region of the first layer of hinged beam is significantly reduced compared with that in the lower region, which is only 52.8%, 64.3%, and 71.1%, respectively. The area proportion of bed-separated fracture in the dominant gas migration channel zone was the largest at the bottom, followed by the top, and the smallest in the middle. The fractal dimension of overlying fractures decreased first and then increased as a whole. The fracture evolution laws were obviously different on both sides of the layer where the hinged beam of the first layer and the minimum fractal dimension of the fracture were located. Therefore, the dominant channel belt of gas migration was divided into low-layer target areas, middle-layer target areas, and high-layer target areas according to the level of the spatial horizon. Finally, based on the theory of mining fracture ellipse belts and the dominant gas migration channel zone at the working face side, the mathematical equation of the target area in inclined thick coal seams was established considering the coal seam dip angle, and the basis for selection of pressure relief gas drainage methods in the targeted area was formed. It provided a reference for optimizing the parameters of pressure relief gas drainage in an inclined, thick coal seam working face

Experimental study on the influence of surfactant foam properties on the slow release of gas in coal

In the process of mining coal resources, the abnormal emission of gas associated with coal may lead to serious gas overrun, and trigger problems such as gas disaster or greenhouse effect. Many studies have shown that injecting surfactant solutions into coal seam is one of the effective and important means of gas management. Surfactant mixed with gas is easy to form stable foam. However, there are few studies on the influence of foam properties on gas desorption. Therefore, this paper studied the influence of surfactant foam properties on the slow release law of gas. Two surfactants, sodium dodecyl benzene sulfonate (SDBS) and alkyl glycoside (APG0810), were selected to test the surface tension, viscosity, foaming, stability and foam morphology of solutions. The effects of surfactant foam properties on gas release was investigated using a self-developed experimental apparatus. The experimental results shown that with the increase of surfactant mass fraction, the surface tension of liquid decreased greatly at first, the foaming rate increased obviously, and the foaming stability increased gradually. When approaching the critical micelle concentration, the decrease amplitude of surface tension slowed down, and the foaming and foaming stability increased gently. At a mass fraction of 0.15%, the foaming heights of SDBS and APG0810 after air injection were 44 mm and 40 mm, respectively, and the maximum half-life of SDBS foam was 786.5 s. The slow release effect of solution foam on gas was well correlated with its foaming rate and half-life. At the same mass fraction, SDBS was generally better than APG0810 in the slow release of gas. At a mass fraction of 0.15%, the gas slow release rate of APG0810 and SDBS within 10 min were about 37.4% and 12.7%, respectively, and that of SDBS within 2 h was still about 50.84%. This study can provide a new perspective to investigate the inhibition and its mechanism of gas desorption in coal by surfactants, and also a certain theoretical support for the prevention and control of gas in mines and the green mining of coal

Study on energy dynamic change law in the process of water-contained coal caused by liquid nitrogen freezing

To study the energy dynamic change law of moisture-contained coal in the process of liquid nitrogen freezing, a self-developed acoustic emission (AE) experimental system for the whole process of liquid nitrogen frozen coal was utilized to analyze the characteristics and the change laws of AE energy dissipation in the whole process of liquid nitrogen freezing in coal with different moisture contents. The results shown that AE energy during liquid nitrogen freezing of coal was divided into steep, fluctuating and calm periods in the time domain. The primary and secondary peaks of energy were both positively linearly related to moisture content, and the primary and secondary energy peak of 5.96% moisture content were 1.66 and 2.26 times higher than those of dry coal. The cumulative energy of liquid nitrogen frozen coal, divided into three stages of steep increase, slow growth and stabilization versus time, was positively linearly related to moisture content, which of 5.96% moisture contained coal was 2.88 times higher than that of dry coal. The energy amplitude of different moisture content coals was mostly concentrated in the range of 40-50 dB, accounting for 94.39%-99.11% of the total, and decreased linearly with the increasing moisture content of coal. The time series of acoustic emission ringing counts in liquid nitrogen frozen coals had chaotic fractal characteristics, and the correlation dimensions of the steep increase, slow growth and stable stages were positively exponentially, linearly and linearly correlated with the moisture content, respectively. Furthermore, the correlation dimension in the steep increase stage of 5.96% moisture contained coal was 2.00 and 5.78 times higher than that of the slow growth and stable stage, respectively. The type of coal cracks produced by the liquid nitrogen freezing was mainly tensile, its proportion with the increasing moisture content was a negative exponential decrease, and the proportion of shear cracks positively linearly increased with the increasing moisture content. The increase of moisture in coal strengthened the freezing and expansion force generated by the water-ice phase transition during the liquid nitrogen freezing process, and the increase of energy dissipation contributed to the rapid development of pore-crack and the structural damage and plastic deformation of coal. However, the structural damage was difficult to detect in real time and can be inverted by AE energy

pH-Responsive Dual Drug-Loaded Nanocarriers Based on Poly (2-Ethyl-2-Oxazoline) Modified Black Phosphorus Nanosheets for Cancer Chemo/Photothermal Therapy

Synergistic cancer therapy, such as those combining chemotherapeutic and photothermal methods, has stronger treatment effect than that of individual ones. However, it is challenging to efficiently deliver nanocarriers into tumor cells to elevate intracellular drug concentration. Herein, we developed an effective pH-responsive and dual drug co-delivery platform for combined chemo/photothermal therapy. An anticancer drug doxorubicin (DOX) was first loaded onto the surface of black phosphorus (BP). With poly(2-ethyl-2-oxazoline) (PEOz) ligand conjugated onto the polydopamine (PDA) coated BP nanosheets, targeted long circulation and cellular uptake in vivo was significantly improved. With another anticancer drug bortezomib (BTZ) loaded onto the surface of the nanocapsule, the platform can co-deliver two different drugs. The surface charge of the nanocapsule was reversed from negative to positive at the tumor extracellular pH (∼6.8), ionizing the tertiary amide groups along the PEOz chain, thus facilitating the cell internalization of the nanocarrier. The cytotoxicity therapeutic effect of this nanoplatform was further augmented under near-infrared laser irradiation. As such, our DOX-loaded BP@PDA-PEOz-BTZ platform is very promising to synergistic cancer therapy

Study on synergistic water-resisting stability of upper and lower soil layers and bedrock layer in shallow coal seam group

The roof water inrush of shallow buried coal seam is caused by the water flowing fractured zone through the aquifuge. With the downward mining of coal seam group, the mechanism of synergistic water isolation between soil layer and bedrock layer needs to be clarified. In order to analyze the failure mechanism of aquiclude under the background of downward mining of coal seam group, so as to accurately predict the water inrush problem of coal mine roof, taking the downward mining of 2−2, 3−1 and 4−2 coal seams in Han Jiawan Coal Mine of Shenfu Mining Area in Northern Shaanxi as the research background, the differences in the properties of aquiclude at different depths were obtained by in-situ borehole coring experiments. The development form of cracks is described by establishing the mechanical model of seepage expansion of upper aquifuge soil layer. Using the mechanical model of soil-rock composite aquiclude, the mechanical criterion of the lower aquiclude in the overall stable state is calculated under the condition of ‘given deformation’. The research shows that the aquiclude can be divided into upper aquiclude and lower aquiclude according to its different properties. By comparing the total load with the tensile strength of the upper aquifuge, when the total load is less than or equal to the tensile strength of the upper aquifuge, the crack no longer develops downward to obtain the crack development length. Under the condition of ‘given deformation’, when the tensile stress generated at the middle position of the long side of the aquiclude is less than or equal to the tensile strength threshold, the overall structure of the lower aquiclude is in a stable state, and no tensile failure will occur. According to the geological conditions of Han Jiawan coal mine, the numerical simulation results are consistent with the theoretical analysis results. The research can provide reference for roof water inrush prediction under similar geological conditions

Experimental study on the influence of middle and low rank coal functional groups on coal wettability

Coal seam water injection can effectively inhibit gas gushing in the process of coal mining, and its inhibition effect mainly depends on the wetting characteristics of coal seam. The chemical structure of coal is one of the important factors affecting the wettability of coal. In order to study the relationship between the functional groups of medium and low rank coal and its wettability, the coal quality characteristics of typical medium and low rank coal samples were analyzed, and the parameters of different coal samples were obtained by Nicolet iN10 Fourier Transform microscopic infrared spectrometer. In this paper, the size of the contact Angle of deionized water at the solid-liquid-gas junction on the coal surface is used to characterize the wettability of coal. JC2000D contact Angle measuring instrument is used to obtain the contact Angle of different coal samples. Zeta potential can reflect wettability and ionization degree of coal surface functional groups, so as to establish the relationship between hydrophilic functional groups (hydroxyl functional groups, other oxygen-containing functional groups), contact Angle and Zeta potential of coal samples. The experimental results show that with the deepening of coal metamorphism, the strength of hydrophilic functional groups of coal samples decreases gradually, the peak height of hydrophilic functional groups of middle rank coal decreases by 0.13 compared with that of low rank coal, and the absorption peak area decreases by 58.91. The hydrophilic functional groups are negatively correlated with the contact Angle of coal samples, that is, the contact Angle decreases gradually with the increase of absorption peak intensity of hydrophilic functional groups, and the contact Angle decreases by 8.27 ° from middle rank coal samples to low rank coal samples. The relationship between hydrophilic functional groups and Zeta potential of coal samples shows a first-order exponential decay function, and the correlation coefficient is as high as 0.95. That is to say, the absolute value of Zeta potential increases gradually with the increase of absorption peak area of hydrophilic functional groups. The surface electronicity of coal samples is strong, and the hydrophilicity of coal is good. Among them, the hydroxyl functional group has a great influence on the wettability of coal, and the hydrogen bond formed by self-associating hydroxyl group is the main factor affecting the wettability of coal. Other oxygen-containing functional groups, such as carboxyl and ether bond hydrophilic functional groups, combine with water molecules under intermolecular force, showing strong vitality and improving the hydrophilicity of coal

A Remarkable New Species of <i>Liparis</i> (Orchidaceae) from China and Its Phylogenetic Implications

<div><p>In the present study, we formally describe <i>Liparis pingxiangensis</i> as a new species from Guangxi, China on the basis of morphological and molecular phylogenetic analyses. It is easily distinguished from closely related species by strongly curved column without column wings, and broadly rhombic-elliptic lip with 2 uncinate calli at the base. In particular, it differs most markedly from its congeners in possessing two pollinia attached by long and prominent caudicles (not stipes), to a distinct sticky disc. This type of pollinarium, as far as we know, is not found in any other species of <i>Liparis</i>, and is also unique among the orchids with waxy pollinia. We then proceeded to a phylogenetic analysis to ascertain the systematic position of this enigmatic species. Molecular study based on nuclear ribosomal ITS and plastid <i>mat</i>K DNA sequence data supports <i>L. pingxiangensis</i> as a distinct species, which forms an independent lineage sister to <i>L. nervosa</i> and its allies (93% BS, 1.00 BPP). In the light of previous work, the findings have important implications for a better understanding of the well-supported pattern mainly based on vegetative features in Malaxideae.</p></div

Phylogenetic tree.

<p>Strict consensus tree of the 1932 most parsimonious trees obtained from sequences of the combined nrITS and plastid <i>mat</i>K DNA sequence data (2280 steps, CI = 0.53, RI = 0.89), showing the position of <i>Liparis pingxiangensis</i>. Parsimony bootstrap proportions higher than 50% and Bayesian posterior probabilities (BPP) more than 0.95 are shown above and below branches, respectively.</p

Morphology of <i>Liparis pingxiangensis</i> (A–D, G) and allied species <i>L. nervosa</i> (E–F).

<p>A. inflorescence, B. flower, front view, C. flower, lateral view, D. gynostemium including anther, clinandrium and viscidium attached to apex of rostellum, lateral view, E. two pairs of close pollinia, F. two pairs of separate pollinia, G. pollinarium including pollinia, caudicles and viscidium. Scale bars, 3(B–C); 1 mm (D); 0.3 mm (E–G).</p

Liparis pingxiangensis.

<p>A. habit, B. flower, frontal view, C. flower, lateral view, D. bract, E. dorsal sepal, F. petal, G. lateral sepal, H. lip, I. column, lateral view, J. column without anther cap, ventral view, K. anther cap, L. pollinarium. Drawn by Yun-Xiao Liu.</p