The distribution of multiscale pores and fractures in coal and rock is an important basis for reflecting the capacity of fluid flow in coal seam seepage passages. Accurate extraction and qualitative and quantitative analysis of pore-fracture structures are helpful in revealing the flow characteristics of fluid in seepage channels. The relationship between pore and fracture connectivity can provide a scientific reference for optimizing coal seam water injection parameters. Therefore, to analyse the change in permeability caused by the variability in the coal pore-fracture network structure, a CT scanning technique was used to scan coal samples from the Leijia District, Fuxin. A total of 720 sets of original images were collected, a median filter was used to filter out the noise in the obtained images, and to form the basis of a model, the reconstruction and analysis of the three-dimensional pore-fracture morphology of coal samples were carried out. A pore-fracture network model of the coal body was extracted at different scales. Using the maximum sphere algorithm combined with the coordination number, the effect of different quantitative relationships between pore size and pore throat channel permeability was studied. Avizo software was used to simulate the flow path of fluid in the seepage channels. The change trend of the fluid velocity between different seepage channels was discussed. The results of the pore-fracture network models at different scales show that the pore-fracture structure is nonuniform and vertically connected, and the pores are connected at connecting points. The pore size distribution ranges from 104 μm to 9425 μm. The pore throat channel length distribution ranges from 4206 μm to 48073 μm. The size of the coordination number determines the connectivity and thus the porosity of the coal seam. The more connected pore channels there are, the larger the pore diameters and the stronger the percolation ability. During flow in the seepage channels of the coal, the velocity range is divided into a low-speed region, medium-speed region and high-speed region. The fluid seepage in the coal seam is driven by the following factors: pore connectivity > pore and pore throat dimensions > pore and pore throat structure distribution. Ultimately, the pore radius and pore connectivity directly affect the permeability of the coal seam.
To solve the problem
of poor dust wettability during coal mine
dust treatment, sodium dodecyl sulfate (SDS) and alkyl glycoside (APG1214)
were selected for compounding. An efficient, environmentally friendly,
economical wetting agent was prepared. First, through molecular dynamics
simulation studies, it was determined that the tail group C of SDS
and APG1214 was adsorbed on the surface of bituminous coal, and the
head groups S and O were adsorbed on the surface of water. The simulation
result is found to be consistent with the surfactant solution dust
removal theory, which proves the confidence of simulation. Then, by
comparing the interaction of water–SDS and APG1214–bituminous
coal and water–bituminous coal systems and the number of hydrogen
bonds, the wetting mechanism of the SDS and APG1214 solution on bituminous
coal was revealed. Finally, the surface tension, contact angle, and
wetting time of different SDS and APG1214 solutions were determined
by experiments and they decreased with decreasing mass fraction of
SDS at the same concentration. The surface tension of the SDS and
APG1214 solution and the number of micelles affected the wettability
of bituminous coal. The optimal concentration of the SDS and APG1214
solution was 0.7%, and the optimal ratio was SDS/APG1214 = 1:3.
To improve the efficiency
of coal dust removal by water spray technology,
the addition of wetting agents in water becomes the main dust removal
method. The influence of sodium dodecyl sulfate (SDS), sodium dodecyl
sulfonate (SDDS), and sodium dodecylbenzene sulfonate (SDBS) on the
wettability of coal dust is studied by experimental and molecular
dynamics (MD) simulation. Measurement of the contact angle and surface
tension was accomplished via relevant experiments for the three wetting
agents, and their adhesion work, spreading work, and wetting work
were also calculated. A preferred experimental method of conventional
coal dust wetting agent is optimized. The wettability of the three
wetting agents upon bituminous coal follows the trend: SDS > SDDS
> SDBS. The simulation was performed based on MD to derive the
intermolecular
interaction energy, diffusion coefficient of water molecules, and
water molecule count in the vicinity of the hydrophilic groups of
the wetting agents. The wetting mechanism and performance of the wetting
agent solution on bituminous coal were identified. The simulation
results of the wetting performance of the wetting agents are consistent
with the experimental results, which verifies the reliability of the
simulation method. An easy, time-saving, and labor-saving MD simulation
method is proposed, which provides a novel insight for choosing various
wetting agents of coal dust.
The structural characteristics of
coal at the molecular level are
important for its efficient use. Bituminous coal from the Baozigou
Coal Mine is investigated, using elemental analysis,
13
C nuclear magnetic resonance, X-ray photoelectron spectroscopy, and
Fourier transform infrared. The molecular structure was determined.
The aromatic compounds of bituminous coal molecules are primarily
two- and three-ring structures, and the aliphatic structures are primarily
in the form of methyl, ethyl side chains, and naphthenic hydrocarbons.
The ratio of aromatic bridge carbon to peripheral carbon in the molecular
structure is 0.279. Oxygen atoms in the form of carbonyl, phenolic
hydroxyl and C–O, and nitrogen atoms in pyrroles. Thus, the
average structure model of bituminous coal macromolecules was constructed;
the molecular formula was C
169
H
128
O
10
N
2
S, and the molecular weight was 2378. The aromatic structural
units in the macromolecular structure of coal include four naphthalenes,
three anthracenes, two tetracenes, and heteroatoms in the form of
three carbonyl groups, one phenolic hydroxyl group, one pyrrole, and
one pyridine. The structure optimization and annealing kinetic simulation
of a single macromolecular structure model were performed. Chemical
bonds such as bridge bonds and aliphatic bonds were found to be twisted,
and π–π interactions between the aromatic sheets
in the molecule produced adjacent aromatic sheets. This arrangement
tends to be approximately parallel, and the total energy decreases
from 6713.401 to 2667.595 kJ/mol, among which the bond stretching
energy and van der Waals energy dominate. We used 20 bituminous coal
macromolecular models to construct aggregated structural models. After
optimization by molecular dynamics simulation, the macromolecules
were constrained by the surrounding molecules, and the sheet-like
aromatic carbon structures that were originally approximately parallel
were distorted. The macromolecular structure model of bituminous coal
constructed in this study provides a theoretical model basis for the
optimal surfactant.
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