Hongtu Zhang’s research while affiliated with Henan Polytechnic University and other places

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Publications (7)


Intelligent identification of coal fractures using an improvedU-shaped networ
  • Article
  • Full-text available

December 2024

ADVANCES IN GEO-ENERGY RESEARCH

Dengke Wang

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Lu Li

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Hongtu Zhang

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[...]

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Yuling Xia
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Spatial–Temporal Evolution of Temperature and Gas Pressure in Soft and Hard Coal During Cryogenic Treatment: An Experimental and Theoretical Investigation

December 2023

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6 Reads

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2 Citations

Natural Resources Research

An experimental apparatus was custom-designed to scrutinize the evolution of temperature and methane pressure during the freezing process in both soft and hard coal samples. Additionally, a thermal–hydrological–mechanical coupling theoretical model was developed, and temperature and methane pressure evolutions were simulated using COMSOL software. It was observed that methane pressure and temperature within the coal samples underwent two distinct phases during the freezing process: an initial rapid decline followed by a more gradual reduction. An exponential function was found to describe aptly the correlation of methane pressure or temperature in the coal samples with both freezing time and radial direction. Moreover, it was discerned that the thermal conductivity of soft coal is inferior to that of hard coal, and the radial decay coefficient of methane pressure or temperature in both types of coal is inversely proportional to freezing time. Significantly, it was revealed that, in post-freezing treatment, ethane pressure in both soft and hard coal could be reduced to 0.74 MPa. This finding elucidates the potential applicability of cryogenic methods for the theoretical elimination of coal seam outbursts. The results furnish a vital understanding of the physical properties of coal under cryogenic conditions, and they can inform the optimization of cryogenic treatment procedures for industrial applications.


Modeling and experiment for effective diffusion coefficient of gas in water-saturated coal

January 2021

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41 Reads

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120 Citations

Fuel

The diffusion of gas in water-saturated porous media plays a significant role in CO2 geological sequestration and mine gas prevention and control. However, it is lack of an accurate model to calculate the effective diffusion coefficient of gas in a water-saturated coal core. In this work, an improved model was constructed to calculate the effective diffusion coefficient of gas in a water-saturated coal core by considering both the gas adsorption in residual pore and the gas dissolution in pore water. By using a PVT (Pressure-Volume-Temperature) test method, the calculation results of improved model are in the range of 1.03 × 10⁻¹² ~ 30.40 × 10⁻¹²m²/s, which are 5 ~ 6 orders of magnitude lower than those calculated by traditional model, because the traditional model only considers the gas dissolution in pore water. Therefore, the results of improved model are more in line with the actual situation. Furthermore, the saturated moisture, equilibrium moisture and NMR experiments were carried out. Results shows that, the saturated moisture and equilibrium moisture decreases with the rising coal rank. The pore size changes from micropore/mesopore-dominated to micropores-dominated as the coal rank rise. In addition, the proportion of open porosity gradually reduces with the rising coal rank, while the closed porosity increases, indicating that the pore connectivity decreases with the growing coal rank. Finally, the influences of adsorbability, pore structure, pressure and liquid properties on the effective diffusion coefficient were analyzed.


Quantitative analysis of fracture dynamic evolution in coal subjected to uniaxial and triaxial compression loads based on industrial CT and fractal theory

January 2021

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104 Reads

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80 Citations

Journal of Petroleum Science and Engineering

The dynamic evolution characteristics of fractures in coal under different compressive loads are of great significance to the recovery of coalbed methane (CBM). In this paper, the X-ray computer tomography (CT) detections of coal samples under uniaxial and triaxial compressive loading conditions were performed by using a developed triaxial in situ rig and an industrial CT scanner. The image processing technique, three-dimensional reconstruction method and statistical principles were employed to describe two-dimensional and three-dimensional fracture evolution in coal under uniaxial and triaxial compressive loads. The results showed that the developed triaxial in situ rig has an enough scanning resolution and is suitable to carry out CT scanning inspections under uniaxial and triaxial compressive loads for porous materials of coal and rock. The two-dimensional cross-sectional CT images effectively reflect the dynamic evolution of two-dimensional fractures during the deformation of coal. Confining pressure and minerals have a significant effect on fracture propagation in coal. The evolution characteristics of three-dimensional fractures can be clearly revealed by the reconstructed three-dimensional digital fracture models of coal. Euler number effectively reflects the fracture connectivity in coal at different deformation stages. During the deformation of coal, the fracture volume, fracture rate, fracture density and fracture connectivity mainly undergo a slow decrease stage, a slow increase stage and a sharp increase stage, display a good linear correlation with fractal dimension, and quantitatively characterize the evolution process of the three-dimensional fractures in coal. The fractal dimension calculated by the box-counting method effectively mirrors fracture propagation and fracture geometric complexity and can be employed to uncover the fracture dynamic evolution in coal under different compressive loading conditions.


The sampling locations of coal specimens in China
The test process of permeability changes and internal crack evolution under thermal shocks
The SEM test process of coal particles under thermal shocks
Effect of thermal shocks on coal permeability (TD of 180 °C means the temperature difference of 180 °C)
The reconstructed 3D crack structures in the examined coal specimens before and after thermal shocks

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Microcrack evolution and permeability enhancement due to thermal shocks in coal

May 2020

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247 Reads

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16 Citations

To understand the effects of thermal shock on microcrack propagation and permeability in coal, thermal shock tests were conducted on coal specimens by using a constant temperature drying oven (105 °C) and a SLX program controlled cryogenic tank. The growth and propagation of microcracks were measured with computer tomography (CT) scanning and scanning electron microscope (SEM) tests. Results showed that thermal shocks improved the permeability of coal significantly. Notably, the permeability of coal after thermal shocks increased from 211.31% to 368.99% and was positively correlated with temperature difference. CT scanning images revealed that thermal shocks increased the crack number, crack volume and crack width as well as smoothened and widened the gas flow paths, thereby enhancing coal permeability. Moreover, SEM images showed that heating-cooling shocks created more new microcracks, forming more complex crack propagation paths and better connectivity among microcracks in coal compared to cooling shocks. We proposed a crack propagation criterion for coal to explain the mechanism of crack failure and propagation during thermal shocks. Our experiment results and theoretical analysis indicate that the heating-cooling shock is more effective in damaging and breaking coal than the cooling shock. Thus, it can be used as an alternative approach to enhance coal permeability in the production of coalbed methane (CBM).


Pressure drop characteristic of dilute negative pressure pneumatic conveying

September 2019

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48 Reads

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6 Citations

Particulate Science And Technology

The pressure drop characteristics of negative pressure sampling drill pipe were studied experimentally in this work. The pressure drop was measured by a customized designed negative pressure sampling test system. The effects of the inner diameter of the drill pipe, the solid-gas rate and the inlet air velocity on the internal pressure drop of the drill pipe were analyzed. When the drill pipe is loaded under the same inner diameter and air velocity, the pressure drop of the drill pipe increases as the solid-gas rate increases. With the same inner diameter and solid-gas rate, the rate of gas phase pressure drop to solid phase pressure drop increases with the increase of air velocity. Through the experimental pressure drop data, the additional pressure drop coefficient model is established by dimension analysis method, which can accurately predict the pressure drop of the drill pipe. The maximum error between the modeled value and the measured value is –16.2%.


Proactive inertisation in longwall goaf for coal spontaneous combustion control-A CFD approach

March 2019

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53 Reads

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60 Citations

Safety Science

Spontaneous combustion of coal has long been a thermal dynamic hazard during coal mining, storage, and transport, posing a great threat to coal mine safety. Especially coal spontaneous combustion in longwall goaf poses a great threat to underground working crew. To investigate such a mine safety issue with more insights and “what if” scenarios, this study employs CFD technique to develop a proactive inertisation plan in a longwall goaf. Based on real on-site conditions of the longwall goaf, a three-dimensional transient non-equilibrium thermal CFD model was developed to study heating evolution and proactive inertisation plans of the longwall goaf. The theoretical model incorporated a set of governing equations including low temperature kinetics of coal oxidation, energy and mass conservation, momentum balance, and continuity equation. After the base model (1000 m) was validated and calibrated with field gas monitoring data, another model (500 m model) was studied to obtain an optimum inertisation plan. Both steady state and transient simulations were conducted to study the flow dynamics of air velocity, oxygen ingress, dispersion of gaseous products and heating evolution in the longwall goaf. Based on the flow dynamics field, proactive inertisation plans using nitrogen to suppress the onset and development of goaf heatings were then developed and studied.

Citations (4)


... The large coal blocks were processed into cylindrical specimens, each with a 25-mm diameter and 50mm height. The industrial CT rock scanning system proposed by Wang et al. (2021) was employed to scan four coal samples. ...

Reference:

Intelligent identification of coal fractures using an improvedU-shaped networ
Quantitative analysis of fracture dynamic evolution in coal subjected to uniaxial and triaxial compression loads based on industrial CT and fractal theory
  • Citing Article
  • January 2021

Journal of Petroleum Science and Engineering

... In addition to self-diffusion, cross-diffusion can also drive Turing instability (Fellner et al., 2023;Si et al., 2021;Pal et al., 2023). Several studies had analyzed the role of cross-diffusion and discussed its impact on pattern formation and pattern types in these systems. ...

Modeling and experiment for effective diffusion coefficient of gas in water-saturated coal
  • Citing Article
  • January 2021

Fuel

... Lastly, permeability values augmented exponentially with increasing inlet pressure under constant confining stress [35]. Zhang et al. (2020) [36] examined anthracite and bituminous coals subjected to both LN 2 cold shock and heating-cooling shock. Their specimens were from the Jiaozuo mining region of Henan province in China. ...

Microcrack evolution and permeability enhancement due to thermal shocks in coal

... The width of the self-ignition area is related to the air leakage intensity. The surrounding rock temperature affects the timing of coal spontaneous combustion, with a higher temperature indicating a shorter time to self-ignition (Zhang et al., 2019). ...

Proactive inertisation in longwall goaf for coal spontaneous combustion control-A CFD approach
  • Citing Article
  • March 2019

Safety Science