Journal of China University of Mining and Technology最新文献

In order to understand the fundamentals of a high energy vibrating type milling process, the energy transfer during mechanical alloying of molybdenum disilicide is investigated based on the Magini-Iasonna energy transfer method, amended by Murty. The efficiency factor and total energy of milling are calculated. MoSi2 synthesized by a mechanically induced self-propagating reaction has also been studied according to different milling parameters, such as the number of balls and the ball to powder weight ratio. The results indicate that the efficiency factor is between 1.944 and 8.507 J/(g·s). A total milling energy of about 19.38-26.47 kJ/g is found to be necessary for the mechanically induced self-propagating reaction of a Mo:2Si powder mixture. The efficiency of milling energy transfer is about 3.3%-4.5%. The experiment and modeling show that the optimum condition for mechanical alloying is a half full vial of balls.

The kinetics and mechanism of methylene blue (MB) adsorption onto activated carbon fibers (ACFs) have been studied. The effects of various experimental parameters, such as the initial MB concentration and the ACF mass, on the adsorption rate were investigated. Equilibrium data were fit well by a Freundlich isotherm equation. Adsorption measurements show that the process is very fast. The adsorption data were modeled using first- and second-order kinetic equations and intra-particle diffusion models. It was found that the first-order kinetic equation could best describe the adsorption kinetics. The adsorption process was found to be complex and controlled by both surface and pore diffusion with surface diffusion at the earlier stages, followed by pore diffusion at the later stages. The thermodynamic parameters ΔG₀, ΔS₀ and ΔH₀, have been calculated. The thermodynamics of the MB-ACF system indicate that the adsorption process is spontaneous.

Mining subsidence pools are water bodies formed by soil subsidence near mines. We studied the impact the surrounding coal production activities and power plants have on these waters by measuring the concentrations of harmful trace elements in these waters. The concentration of the four elements F, Hg, Se and As increased by 0.92%, 0.78%, 0.70% and 0.81%, respectively, in the Datong mining subsidence pool from November 2004 to November 2006. The four elements increased by 1.58%, 1.23%, 1.08% and 0.92%, respectively, in the Xie'er mining subsidence pool and 1.16%, 1.06%, 1.02% and 1.01%, respectively, in the Pansan mining subsidence pool over the same time period. The absolute levels of F, Hg, Se and As in the pool are related to the background levels of the elements. A close relationship between nearby coal mines and power plants and increasing levels of the measured elements is noted.

In the period of the first twenty years after World War II the number of fires in Polish hard coal mines reached annually the value of several thousands of cases. About 80% of fires constituted spontaneous fires. Investigations into the development of new methods of fire hazard prediction and implementation of new methods and means of fire prevention as well as the introduction of prohibition concerning the use of products manufactured of combustible organic materials in underground mine workings reduced considerably the hazard of underground fire rise. The worked out at the Central Mining Institute (GIG) new method of underground fire prediction allows the correct selection of fire prevention means. The introduction into common use of fire-resistant conveyor belts, the main factor giving rise to spontaneous fires, and methods of assessment of their fire resistance eliminated practically the fire hazard. These activities contributed in an efficient way to the reduction of the number of underground fires to a satisfactory level.

GIS- or CAD-based technology has been widely used for cartographic maps in coal mines, but structural gaps between such maps make it difficult to provide an integrated map service, for any specific purpose, at higher levels. There is no uniform platform that can be used to manage all involved maps. The main reason for this is that datasets are submitted by individual coal mines using their individual, diverse software. No consistent model is used within the software for data abstraction and symbolization. This paper first reviews all the essential specifications concerning OGC (Open Geospatial Consortium) interoperability. Then an OGC standard-oriented architecture is proposed to provide distributed coal mine map services. Within this new architecture the management of spatial data archives, and the integration of coal mine maps, are achieved through the interfaces of geospatial services. Finally an open source geospatial approach is suggested to implement the proposed scheme. A case study of the Huaibei Coal Group is used to demonstrate the proposal.

When, in a coal mine distribution network whose neutral point is grounded by an arc suppression coil (ASC), a fault occurs in the ASC, compensation cannot be properly realized. Furthermore, it can damage the safe and reliable run of the network. We first introduce a three-phase five-column arc suppression coil (TPFCASC) and discuss its autotracking compensation theory. Then we compare the single phase to ground fault of the coal mine distribution network with an open phase fault at the TPFCASC using the Thévenin theory, the symmetrical-component method and the complex sequence network respectively. The results show that, in both types of faults, zero-sequence voltage of the network will appear and the maximum magnitude of this zero-sequence voltage is different in both faults. Based on this situation, a protection for the open phase fault at the TPFCASC should be established.

The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings produced by high velocity arc spray (HVAS) were studied. Several different conditions were studied under simulated boiler conditions at 650°C. The protection effect of an Al coating deposited by HVAS onto the Ni-Cr coating was also investigated. Microscope, X-ray diffraction and corrosion rate curves have been used to analyze corrosion mechanisms. The experimental results show that: 1) The oxidation rates are almost superposed in both air (no SO₃) and in simulated coal-fired gas (containing SO₃) as long as no salt was present on the surface. These rate curves show a logarithmic relationship. 2) When the surface is coated with salt (75%K₂SO₃ + 25%Na₂SO₃) the rate curve for LTHC of the Ni-Cr coated surface shows a parabolic shape in the simulated coal-fire flue gas. In air only the oxidation reaction takes place, the second type of LTHC was not seen. And 3) the Al over coating on the Ni-Cr enhances resistance to LTHC because an inter-metallic compound, Al₃Ni₂, forms at the Al/Ni-Cr interface and because of the increase in coating thickness.

Permeability of coal reservoirs in China is in general low. Injection of CO₂ into coal seams is one of the potential approaches for enhancing coalbed methane (CBM) production. The feasibility of this technology has been investigated in China since the 1990s. Advances in mechanism of CO₂ enhanced CBM recovery (CO₂-ECBM) in China are reviewed in light of certain aspects, such as the competitive multi-component gas adsorption, sorption-induced coal swelling/shrinkage and its potential effect on CBM production and numerical simulation for CO₂-ECBM recovery. Newer investigations for improving the technology are discussed. It is suggested that a comprehensive feasibility demonstration in terms of geology, technology, economics and environment-carrying capacity is necessary for a successful application of the technology for CBM recovery in China. The demonstration should be carried out after more investigations into such facets as the control of coal components and structure to a competitive multi-component-gas adsorption, the behavior and essence of supercritical adsorption by coal of gas, environmental and safe feasibility of coal mining after CO₂ injection and more extensive pilot tests for CO₂-ECBM recovery.

A new method based on principal component analysis (PCA) and support vector machines (SVMs) is proposed for fault diagnosis of mine hoists. PCA is used to extract the principal features associated with the gearbox. Then, with the irrelevant gearbox variables removed, the remaining gearbox, the hydraulic system and the wire rope parameters were used as input to a multi-class SVM. The SVM is first trained by using the one class-based multi-class optimization algorithm and it is then applied to fault identification. Comparison of various methods showed the PCA-SVM method successfully removed redundancy to solve the dimensionality curse. These results show that the algorithm using the RBF kernel function for the SVM had the best classification properties.

To solve the problem of water loss during mining of shallow, buried coal seams, we have first analyzed the mechanism and suitability of solid-liquid coupling, i.e., we used the FLUID-MECHANICS system of 3-Dimensional Distinct Element Code (3DEC) in simulating dynamic water crannies in overlying strata, under mining conditions of a large longwall coalface. Next the dynamic initiation of a water cranny, its propagation and close phases were studied with 3DEC, along with the overlying strata breakage and recombination as the mining space of the shallow, buried coal seam increased. Combined with the change in the stress and displacement fields, the distribution features of the mining cranny were systematically studied. The effect of regularities and their effective measures of local filling and mine slicing technology in controlling mine crannies were investigated and the potential danger areas of water loss identified. Our results can be applied to decrease water loss during the exploitation of shallow, buried coal seams with a thin bedrock. The results also prove that 3DEC is a credible numerical analytical method to predict initiations of dynamic water crannies, their propagation, their closure phases and other concomitant hazards.