Molecular Dynamics Simulation of Coal Structure Damage Under the Action of Surfactant

An anionic surfactant, sodium dodecyl sulfate (SDS) was used to modify the coal structure. This was done to improve the compactness of the coal structure, promote the damage of coal structure, improve the efficiency of gas drainage, and prevent shock pressure disasters. The mercury intrusion experiment and uniaxial compression experiments were used to determine the changes in the pore structure and mechanical properties of coal after modified by surfactant. This work established six groups of water / surfactant / coal simulation systems with different concentrations. Based on the energy behavior and dynamics characteristics ( interaction energy, relative concentration distribution, radial distribution function, mean square displacement) of each system, the effects of surfactants with different concentrations on the structural damage of coal were analyzed by molecular dynamics simulation, and the mechanism of coal structural damage was revealed. The results show that the SDS solution can significantly reduce the mechanical strength of the coal. When the solution concentration is 0.6%, the degree of damage to the coal structure is the maximum. SDS molecules can be detected at the water / coal interface. SDS molecules are adsorbed to the coal surface through intermolecular interactions, and -SO3 groups are preferentially adsorbed to the oxygen-containing functional groups on the coal surface. The difference in SDS adsorption on the coal surface is caused by the difference in the number and spatial distribution of alkyl chains in the SDS molecule. The main modification mechanisms of surfactants on coal are that when SDS is adsorbed on the coal surface, a large number of secondary pores and cracks are generated on the surface and inside of the coal, and cracks are formed under the action of tensile stress. The cracks continue to expand, extend, which ultimately promotes damage to the coal structure. The results are expected to provide a theoretical basis for the structure damage of coal modified by surfactant, and provide a new method for the prevention of rockburst disasters and gas outburst control.

Prediction of gas pressure in thin coal seams in the Qinglong Coal Mine in Guizhou Province, China

Thin coal seams in mines usually lack gas data. Thus, preventing and controlling gas outbursts of thin coal seams are difficult. In this study, a coal structure index, which is used to express the damage degree of coal, was estimated by logging curve. In accordance with the contour line of the floor of the coal seam, structural curvature was calculated to express the complexity of the coal seam structure quantitatively. Subsequently, relationships among the burial depth, thickness, coal structure index, structural curvature were analyzed on the basis of the gas pressure of coal seam. The gas pressure values of the coal seams of Nos. 22, 24, and 27 in the study area were predicted by multiple linear regression (MLR) and were then verified and analyzed. The deviation rate of the MLR method was 6.5%–19.7%, with an average of 13.0%. The average deviation rate between the predicted value and the measured value was 11.6%, except for the measuring point of No. 2, which had a large deviation. Results show that the prediction accuracy of the aforementioned method is acceptable and has practical value in the prediction of gas pressure in thin coal seams without measured data. The results in the gas pressure prediction provide a basis for evaluating the risk of gas outbursts in thin coal seams.

Solubility Property of Baganuur Coal: Performance Assessment by FTIR Spectroscopic Analysis

In the present work, the extraction of Mongolian Baganuur coal in solvents as pyridine and ionic liquid with 1-butyl-3-methyl-imidazolium chloride ([Bmim]Cl) anion was first applied. The as recieved coal, its extracts and insoluble residues were then characterized using the Fourier transform infrared (FTIR) spectroscopy. The obtained FTIR spectra have revealed many new features in the field of coal study. An appearance or sharpening of the particular bands after the chemical treatment allow a determination of inactive or weak fundamental vibrations precisely. Some emphasis are as follows, substantial quantitative change, the integrated area decrease of water molecule band at 3260 cm−1 comparing to as received sample and ionic liquid treated extract, can be seen for the extract spectrum in the pyridine treatment. Pyridine react to coal structure particularly in long-wave frequency zone means very susceptible to the oxygen containing functional group. Upon interaction between acidic group of the coal and the basic solvent as pyridine, the inter-fragment hydrogen and ester bonding in the coal structure is breaking, thus increasing the solubility of the individual fragments via producing new components. Towards forming H bond in the short wave zone Cl− anion shows a strong effect on the coal molec-ular structure. A stabilization of hydrogen bonds show well fluidization and a strong intermolecular interaction of the process via its powerful spectral intensity that is followed many new bands and con-siderable strengthening of band spectral integral area in this frequency region. In long-wave vibrational region there are appearances of many new bands, shift in frequency and depletion of the as recieved coal bands. [Bmim]Cl treatment exhibits the highest effect of the disruption on the carboxylic acids dimer.

Investigations of Coal-Rock Parting-Coal Structure (CRCS) Slip and Instability by Excavation

Slip and instability of coal-rock parting-coal structure (CRCS) subjected to excavation disturbance can easily induce coal-rock dynamic phenomena in deep coal mines. In this paper, the failure characteristics and influencing factors of CRCS slip and instability were investigated by theoretical analysis, numerical simulations, and field observations. The following main results are addressed: (1) the slip and instability of CRCS induced by excavation are due to stress release, and the damage of the rock parting is partitioned into three parts: shear failure zone, slipping zone, and splitting failure zone from inside to outside with slip; (2) the slip and instability process of CRCS is accompanied by initiation, expansion, and intersection of shear and tensile cracks. The development of the cracks is dominated by shear behaviour, while the tensile crack is the main factor affecting fracture and instability of CRCS; and (3) slip and instability of CRCS are characterized by stick-slip first and then stable slip, accompanied with high P-wave velocity and rockburst danger coefficient based on microseismic tomography.