Jianhong Kang

A fully coupling coal–gas model associated with inertia and slip effects for CBM migration

Although inertia and slip effects of gas flow that may impose significant influences on Coalbed methane (CBM) well and reservoir performance have been widely confirmed and studied, and some mathematical models have also been proposed to quantitatively evaluate these two effects, the combined inertia and slip effects on CBM migration were seldom considered in the previous models. In this study, a fully coupled finite element (FE) model of non-Darcy gas flow and coal deformation process with sorption and Klinkenberg effects in the coalbed is developed to quantify CBM migration mechanism. The FE model is validated by comparison with available analytical and numerical solutions. The results indicate that the evolution of coalbed permeability and gas transport in CBM reservoir not only relate with the sorption-induced coal deformation and the pore pressure change, but also closely depend on the coupling inertia (non-Darcy) effect and slip (Klinkenberg) effects. Based on the simulation, it is found that CBM production can be significantly enhanced due to gas slip (Klinkenberg) effect. But when slip effect is significant, the inertia effect will be ignored. The simulation results can improve the understanding of the coal–gas interactions during underground CBM migration and provide a scientific basis for evaluation of the gas-drainage efficiency, design and optimization of drainage systems, etc. However, the different pressure and permeability thresholds corresponding to prominent response of inertia or slip effect should be further determined through experiments and theoretical models in the future.

An anomalous subdiffusion model with fractional derivatives for methane desorption in heterogeneous coal matrix

Methanedesorption in coal matrix is one of the fundamental gas transport processes during coalbed methane extraction, the mechanism of which is commonly described by Fickian diffusiontheory. Here, an anomalous subdiffusion model with fractional derivatives is developed to explore the methanedesorption in coal matrix with a highly heterogeneous pore structure. Numerical simulations reproduce the volume fraction of gas desorbed over the entire timescale of experimental desorption. It is suggested that the diffusion of methane in heterogeneous coal matrix may obey the anomalous time and space subdiffusion, rather than Fickian second law. The physical reason is perhaps due to the basic topological complexity inherent to porous coal matrix and the strong adsorption effect of coal on methane molecules.

Progress in Ni-based anode materials for direct hydrocarbon solid oxide fuel cells

Ni-based anode materials of solid oxide fuel cells (SOFCs) are susceptible to carbon deposition and deactivation in direct hydrocarbon fuels, greatly limiting the commercialization. Extensive studies on finding new alternative anode materials have been developed; however, new problems such as low electrochemical performance and complex cell preparation process destroyed the further research passion of Ni-free anode materials. Considering the superior catalytic activity and mature technology of Ni-based anode materials, a large number of recent research results proved that it is still important and promising to solve the carbon coking of Ni-based anode materials. In this review, progress in four typically promising Ni-based anode materials free from carbon coking has been summarized, including the noble metals, ceria, Ba-containing oxides and titanium oxide. Correspondingly, the mechanisms that improve the carbon tolerance of Ni-based modified SOFCs anodes are clearly concluded, providing the materials and theoretical basis for the use of direct hydrocarbon SOFCs as early as possible.

Evaluation of gas drainage and coal permeability improvement with liquid CO2 gasification blasting

With the increasing mining depths of underground coal mines, gas drainage and coal permeability improvement with conventional coal seam fracture stimulating methods have shown some deficiencies. In this work, an application of liquid CO2 gasification blasting is proposed for increasing gas drainage and fracturing coal seam with high-gas content and low permeability. The methods of theoretical analysis, numerical simulation as well as field experiments are involved to build up a comprehensive understanding of this promising application. The variation of gas pressure for the gasification blasting is quantitatively determined by using a modified van der Waals equation of state. It is shown that the maximum pressure generated by the rapid thermal expansion of liquid CO2 could induce the initiation and propagation of coal cracks and fractures. To testify the fracturing effects of liquid CO2 gasification blasting on gas drainage, field experiments were carried out on two transportation roadways of Yuwu coal mine in China. It is found that (a) the effective fracturing radius could be about 3 m around the blasting borehole, (b) the quantities of gas extraction and gas emission are increased significantly, and (c) the outburst risk indices for drilling cutting fall below their critical values.

Charge-Transfer Modeling and Polarization DRT Analysis of Proton Ceramics Fuel Cells Based on Mixed Conductive Electrolyte with the Modified Anode–Electrolyte Interface

A charge-transfer model considering the mixed conductivities of proton, oxygen ion, and free electron in interface-modified La2Ce2O7 (LCO) electrolyte is designed to analyze the characteristics of proton ceramics fuel cell in the field of the open-circuit voltage, internal short-circuit current, proton-transfer number, discharging curves, oxygen/hydrogen partial pressure, and cell efficiencies. The properties of anode-supported single cells with the modified anode-electrolyte interface containing an in situ formed doped BaCeO3 reaction layer are compared to those of unmodified cells at various temperatures T and H2O partial pressures. Besides, the electrochemical impedance spectroscopies of both cells were investigated by the relaxation time distribution to distinguish different polarization processes. The results indicated that the reaction interface layer can effectively reduce the internal short-circuit current density and increase the proton-transfer number of electrolytes. Importantly, the NiO-BaZr0.1Ce0.7Y0.2O3-δ anode can also make more protons transfer from anode to cathode and participate in the cathodic reaction for LCO-based proton ceramics fuel cell. The polarization of the cell decreases with the increase of water partial pressure, which leads to the increase of open-circuit voltage and cell efficiency.

Numerical modeling of gas flow in deformed well casing for the prediction of local resistance coefficients pertinent to longwall mining and its engineering evaluation

During gob gas venthole (GGV) drainage, the borehole casing is to withstand various forces induced by the movement of overlying strata of the longwall panel so as to become deformed. Tensile deformation, compressive deformation and shear deformation are the most typical deformation modes of the casing. Once deformation of the casing occurs, the flow resistance of gas in casing increases sharply, which causes the volumetric flow of gob gas recovery to decrease. Through an analysis of the cross-sectional shapes of three typical casing deformations, the characteristic parameters of each kind of deformation were determined. In addition, a numerical simulation of the gas flow field was carried out using the four casing models, i.e., one without deformation and three with typical deformations. The changing characteristics of the local resistance coefficient of the deformed casing with varying characteristic parameters of corresponding deformation were analyzed. In addition, this study compared the local resistance coefficient of casings for the three deformation models and deduced that the local resistance coefficient resulting from shear deformation is the largest. Furthermore, by considering the flow field characteristics of gas in the three models, this study determined that the vortex induced by the separation of the boundary layer in the areas of deformation was a major cause of local resistance. Finally, a method for predicting the characteristic parameter values of casing deformation was proposed, and a case study was performed. The research results provide a theoretical basis for predicting the influence of casing deformation on GGV drainage.