Mining Science and Technology (China)最新文献

We determined a suitable gate road layout in slice mining in an ultra-thick unstable coal seam, using theoretical analysis and numerical calculations. Based on plasticity theory in terms of limiting equilibrium, the width of chain pillar in the upper slice was calculated to be 18 m. The stress distribution in the chain pillar after the upper slice was mined out was described with numerical simulation. The extent of the effect of stress on the upper chain pillar on the lower solid coal was obtained on the basis of an elastic solution of a distributed force loaded on a half-plane. Three layout designs for lower gate roads were proposed and a stability factor was introduced to analyze the stability of the lower pillar with numerical calculation. Gate road translation was determined as the most suitable layout method, which maximizes the extraction rate on the basis of the pillar stability.

We investigated the deformation failure mechanism of surrounding rock from the aspect of engineering support for a roadway in seams with soft roofs and soft floors and observed the large displacement of the roadway in these soft seams. The result shows that the deformation area is quite large, and settlement of the roof is evident and displacement of the side walls is also obvious. We considered rock bolt-cable coupling for roadway support in seams with soft roofs and floors, in which the cable should be fixed at key positions. As well, we designed an optimal scheme to support a roadway in soft seams of the Shizuishan Second Mine in Ningxia, China. Field monitoring results show that bolt-cable coupling support has achieved the aims of roadway stability control and minimizes deformation.

Na₂CO₃, Li₂CO₃, and K₂CO₃ were used as additives to Pingshuo (PS) coal that was subsequently gasified under a CO₂ stream. The catalytic gasification of coal samples by CO₂ in the presence single or mixed alkali carbonates was investigated by thermogravimetric analysis. The experimental results indicate that the catalytic effect of Li₂CO₃ is significantly larger than that of Na₂CO₃ or K₂CO₃. The catalytic effect of the mixed, bi-metal carbonate containing Li₂CO₃ and Na₂CO₃, or Li₂CO₃, and K₂CO₃, is related to the composition of the catalyst and the proportion of the two components. The bi-metal carbonates having a mole ratio of 9:1 (Li:X) has the largest catalytic effect for PS coal gasification. A synergistic effect between Li and K, or Na, carbonate appears at temperatures greater than 1300 K. An un-reacted shrinking core model is suitable for kinetic analysis of catalytic gasification of coal samples in the presence of alkali carbonates. It is inappropriate, however, to evaluate the catalytic effect only by the activation energy obtained from the kinetic calculations.

The long-term stability of backfill material is the key to retaining roadways successfully. In order to study the rheological deformation of backfill material and its long-term stability, given the visco-elastoplastic properties of this material, we introduced a softening and a hardening function for a new nonlinear rheological model with time-varying parameters. Based on this, we presented the instability condition of this model by using the principle of minimum potential energy. Combined with engineering practice, we calculated the unstable time period of backfill material. The results show that the time of instability of the backfill material relate to the initial parameters of the material, the coefficients decided by temperature and the ratio of the plastic zone of the backfill material. Based on the results of our analysis from the point of view of energy, we can quickly obtain the time of instability of this model from our graphical analysis. The time of instability of the backfill material obtained from our investigation coincides with an actual project.

One characteristic of electro-flotation is the presence of micro bubbles that are well known for improving the flotation performance of fine particles. An electro-flotation method was studied with fine scheelite and fluorite particles sized into three different fractions. Experiments were performed in a modified Hallimond tube. We investigated the effects of gas holdup, particle size, and different mesh electrode apertures on mineral recovery. Flotation results show that two size fractions show increased flotation recovery as the gas holdup increases. For the sized scheelite and fluorite, the flotation effect is diverse for different sizes of the cathode aperture. Pictures of the bubbles taken by a high speed CCD were used to determine the hydrogen bubble size distribution generated as a function of collector, current density, and electrode size. The diameters of the hydrogen bubbles ranged from 12 to 117 μm in alkaline conditions.

For a low permeability single coal seam prone to gas outbursts, pre-drainage of gas is difficult and inefficient, seriously restricting the safety and efficiency of production. Radical measures of increasing gas extraction efficiency are pressure relief and infrared antireflection. We have analyzed the effect of mining conditions and the regularity of mine pressure distribution in front of the working face of a major coal mine of the Jiaozuo Industrial (Group) Co. as our test area, studied the width of the depressurization zone in slice mining and analyzed gas efficiency and fast drainage in the advanced stress relaxation zone. On that basis, we further investigated and practiced the exploitation technology of shallow drilling, fan drilling and grid shape drilling at the working face. Practice and our results show that the stress relaxation zone is the ideal region for quick and efficient extraction of gas. By means of an integrated extraction technology, the amount of gas emitted into the zone was greatly reduced, while the risk of dangerous outbursts of coal and gas was lowered markedly. This exploration provides a new way to control for gas in working faces of coal mines with low permeability and risk of gas outbursts of single coal seams in the Jiaozuo mining area.

The auxiliary shaft is an important location for coal mine heating in the winter, where the main purpose of heating is to prevent icing of the shaft. Wellhead heating requires characteristics of openness, no-noise and big heat loads. The original coal-fired boiler heating mode causes significant waste of energy and environmental pollution due to the low efficiency of the heat exchange. Therefore, to solve these problems, we will use deep mine geothermal energy to heat the wellhead by making full use of its negative pressure field and design a low-temperature water and fan-free heating system. Through numerical calculations we will simulate temperature fields, pressure fields and velocity fields under different air supply temperatures, as well as different air supply outlet locations and varying number of radiators in the wellhead room of a new auxiliary shaft to find the proper layout and number of radiators that meet wellhead anti-frost requirements from our simulation results, in order to provide guidelines for a practical engineering design. Tests on the Zhangshuanglou auxiliary shaft wellhead shows good, look promising and appear to resolve successfully the problem of high energy consumption and high pollution of wellhead heating by a coal-fired boiler.

Based on multi-type, multi-temporal remote sensing data, we have monitored recent changes in cultivated land use and vegetation, in sandy areas and salinized desertification in the Green Corridor zone of the main channel of the Tarim River Basin. The results of our investigation show that the ecological environment in the Green Corridor of the main channel of the Tarim River Basin has conspicuously improved from 2002 to 2004. These improvements show up largely in such aspects as an increase in the rate of vegetation cover, a reduction in desertification land areas and a weakening in the intensity of sandy and the salinized land. On the other hand, the cultivated area in the Tarim River Basin significantly increased from 2002 to 2004. The rate of growth in cultivated areas during this period was significantly higher than that from 1999 to 2002. The increase in the use of irrigation resulting from the substantial increase in cultivated areas has a long-term potential restraining effect on the restoration of ecological functions of the Tarim River.

Determination of the capacity for explosion of gas mixtures in a sealed area is very important for mining engineers. If this capacity is high, it would be very dangerous for rescue workers to proceed with their rescue operations. A number of methods have been developed to determine the capacity for explosion of gas mixtures in sealed areas. One of the more popular methods is the Coward explosive triangle, published by Coward. He presented a fast and easy way to determine the capacity for explosion of gas mixtures, which has proved to be a very useful tool for mining engineers and members of rescue teams. However, due to few drawbacks in this method; potential errors would be introduced when it is applied. In a brief introduction we first describe the Coward method and then, we propose and discuss new calibrated explosive triangles. We demonstrate the method in two case studies where we compare our results with those of the old model. The results indicate that the calibrated method have improved accuracy and reliability. Therefore, assessments can be made more accurately.

As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage roadway in a certain coal mine is so broken and loose that the supporting is very difficult. Based on comprehensive analysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks. Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture development. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.