Fubao Zhou

Practice of Fighting Fire and Suppressing Explosion for a Super-Large and Highly Gassy Mine

Abstract The Baijigou Mine fire in Ningxia Province, which broke out on October 24, 2003, affected more than 10 8 m 3 of the mine and was probably the largest underground fire in China in recent years. In addition to its size, the fire was also characterized by excessive air leakage and the potential for violent methane explosions. A series of new measures were taken to fight the fire, including sealing intake tunnels with water, injecting three-phase foam through boreholes, and flushing with a large volume of nitrogen. The fire was successfully extinguished and production resumed soon afterwards; not one single methane explosion occurred during fire-fighting and afterwards.

Gas drainage efficiency: an input–output model for evaluating gas drainage projects

Gas drainage not only ensures safety in coal mine but also produces clean energy and reduces emission of greenhouse gases. However, a good method to evaluate the efficiency of gas drainage is still absent. In this study, we firstly propose a definition of gas drainage efficiency which is defined as the ratio of the real output–input efficiency to the ideal output–input efficiency. The definition combines both engineering parameters such as radius, length of borehole and economical parameters such as drilling cost to develop a comprehensive index for the assessment of the engineering–economical efficiency. Then, three important factors to determine gas drainage efficiency including the difficulty level, the input and output, namely investment and production, and the attenuation characteristic of gas drainage are discussed. Based on the relative standards, the index can reasonably evaluate gas drainage projects with different difficulty levels, thereby avoiding dependence on an absolute standard for the evaluation of overall difficulty levels. The indicator can also take both input and output into consideration and reflect the reduction of gas drainage flow with time. Besides, we investigate the relationship between gas drainage efficiency and several engineering parameters, including borehole radius, borehole length and the quality of borehole sealing. The results show the possibility of optimizing engineering parameters to maximize gas drainage efficiency. Finally, the evaluation method is proven efficient by performing case studies.

CO2 storage in coal to enhance coalbed methane recovery: a review of field experiments in China

ABSTRACT Coal reservoirs especially deep unminable coal reservoirs, are viable geological target formations for CO2 storage to mitigate greenhouse gas emissions. An advantage of this process is that a large amount of CO2 can be stored at relatively low pressure, thereby reducing the cost of pumping and injection. Other advantages include the use of existing well infrastructure for CO2 injection and to undertake enhanced recovery of coalbed methane (ECBM), both of which partially offset storage costs. However, ECBM faces difficulties such as low initial injectivity and further permeability loss during injection. Although expensive to perform, ECBM field experiments are essential to bridge laboratory study and large-scale implementation. China is one of the few countries that have performed ECBM field experiments, testing a variety of different geological conditions and injection technologies. These projects began more than a decade ago and have provided valuable experience and knowledge. In this article, we review past and current CO2 ECBM field trials in China and compare with others performed around the world to benefit ECBM research and inform future projects. Key aspects of the ECBM field projects reviewed include the main properties of target coal seams, well technologies, injection programmes, monitoring techniques and key findings.

Experimental investigation on blockage boundary for pneumatic conveying of powders in narrow bifurcation slits

ABSTRACT To investigate the blockage characteristics for dense-phase pneumatic conveying in narrow bifurcation slits, a study on the blockage boundary conditions of powders was undertaken. The results show that the solid mass flow rate for blockage increases with superficial air velocity, and the variation trend can be divided into three typical stages. Besides the relationship between the solid loading ratio and superficial air velocity for blockage in the bifurcation slit displays a “S” shape with the increase of air velocity, the solid loading ratio increases, then decreases, finally increases, and in each stage above, the relationship between the two approximately meets power function, respectively. According to the “S” shape relationship, the formula used for blockage boundary [Setia, Mallick, Wypych, and Pan (2013). Validated scale-up procedure to predict blockage condition for fluidized dense-phase pneumatic conveying systems, Particuology, 11, 657–663] was modified into piecewise function for bifurcation slits. In addition, with the increase of the bifurcation angle and conveying pressure, the superficial air velocity decreases, while the solid mass flow rate and the critical solid loading ratio increase. The research work could help understand the blockage theory of the dense-phase pneumatic conveying.

An investigation of the key factors influencing methane recovery by surface boreholes

The paper deals with key factors influencing surface borehole gas drainage. Herein, the surface borehole drilled through the overburden of gobs, which was commonly operated in China, has been investigated. By building a mathematical model, the literature probed into the issue that how such factors as permeability coefficient and pressure of coal seams affected the flow of pure methane under standard conditions. The results indicated that a key factor was the distance between mining face and borehole (reflecting the gas permeability coefficients of overlying coal seams and gobs). The data measured from surface gas drainage practice at Wulan Coal Mine verified the conclusions of the theoretical research.

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.