Journal of Coal Science and Engineering (China)

Operating principle of water three-way valve with high flow for individual hydraulic prop in coal was presented in this paper, its strict and precise mathematical model was established, its flow field was simulated numerically by software Fluent, and its dynamic characteristics were analyzed during the work process such as raising leg, loading and overflow, the influence of the related parameters on high-flow water three-way valve was determined. The results as follows: during the raising leg stage and early raising leg stage, when the damping ratio increases, the overshoot of system decreases and the setting time reduces, and the dynamic response performance has a significant improvement. During the loading stage and the overflow stage, the pressure in plunger chamber of single hydraulic prop, the output flow and the displacement of the high-flow water three-way valve decrease with the decreasing of the external load. The spring stiffness of the safety valve directs the flow and the spool’s displacement of the safety valve, and it can be used to control the high-flow three-way valve’s sensitivity.

Using a 20 L spherical explosion suppressing test system, the largest gas explosion pressure and maximum pressure rising rate with additives of ultra-fine ABC dry powder and diatomite powder were tested and compared, and the explosion suppression effect of the two kinds of powder was analyzed. Experimental results show that both powders can suppress gas explosion and ABC dry powder is superior to diatomite powder. Adding two powders under the same experimental conditions, when methane concentration is 7.0%, the maximum explosion pressure decreased 39% and 4%, respectively, while the rising rate of the maximum pressure decreased 80% and 53%, respectively. When methane concentration is 9.5%, the maximum explosion pressure decreased 14% and 12%, respectively, the rising rate of maximum pressure decreased 62% and 27%, respectively, the maximum explosion pressure decreased 23% and 18%, respectively, while the rising rate of the maximum pressure decreased 77% and 70%, respectively. When methane concentration is 12.0%, the explosion suppression effect of ultra-fine ABC dry powder is not affected by the methane concentration, and the explosion suppression effect of diatomite powder under high methane concentrations is more obvious.

The three-dimensional (3D) deformation effect of the slope engineering under the step-by-step excavation for the Antaibao surface mine was analyzed using the FLAC3D technique. An optimal excavated scheme with a relatively steeper slope angle of 47° instead of 30° was successfully implemented at the west wall in the geological section 73200 of the mine area, where the 3D effect of the nonlinear large deformation of the slope was taken into account. Based on the above research conclusion, put forward the countermeasures of shortening mining length, excavating by different regions, timely foot backfilling to protect the excavated slope, and monitoring and feedback adjustment by studying the nonlinear effect. The results show that these countermeasures are effective in controlling maximum deformation and increasing the stability of the slope.

A two-dimensional numerical model of a large (1 000 m × 200 m) section of mine strata in the vicinity of seam 349 in longwall panel 802 in part B of the Murcki Colliery in the Upper Silesian Coal Basin, Poland, was built using the Universal Distinct Element Code UDEC. Longwall extraction of seam 349 with roof caving was simulated in the model over a length of 450 m. Mining-induced changes in displacements, strains and stresses in the mine strata were investigated. Under the assumptions that (1) methane-bearing strata occur 15.6 m beneath seam 349 and include seam 350 and the strata lying beneath, and (2) the methane reservoir pressure is equal to 2 MPa, a fully coupled mechanical hydraulic analysis was performed in which joint conductivity was dependent on the mechanical deformation and, conversely, the mechanical behavior of rock masses was affected by joint fluid pressure. It was shown that migration of methane from coal seams lying beneath the mined seam is possible under conditions where the floor strata deform to a great extent, undergo separation, fracture and break into blocks.

Red mud will flow in paste form under high pressure during pipeline transport. It belongs to a two-phase flow of materials with high viscosity and a high concentration of non-sedimentation, homogeneous solid-liquids. In pipeline transport, its resistance characteristics will be influenced by such factors as grain size, velocity, concentration, density, grain composition and pipe diameter etc.. With the independently developed small-sized tube-type pressure resistance test facility, studied the resistance characteristics of red mud concerning the three influencing factors, paste concentration, velocity and pipe diameter, which attract the most attention in projects. The fine grain size of the red mud is d 50= 13.02 μm. According to the experimental results, the pressure loss in transport will increase along with the increase of velocity and will fall along with the increase of pipe diameter. A 1% difference in paste concentration will result in a 50%∼100% difference in pipeline resistance loss. These experimental data is hoped to be direct guidance to the design of high concentration and viscous material pipeline transport system.

In order to explore the reason for the frequency explosion of spontaneous combustion coal gangue dump and get to know their explosion mechanism, established the experiment platform about spontaneous combustion coal gangue dump interoperable water. The gangue dump was heated using the external heat source, and rainy weather through water mist was simulated. Simulated experiment about explosion of spontaneous combustion coal gangue dump was carried out on the different conditions of the rainfall or not. The unusual gases produced in the course of gangue combustion and the changes in temperature were observed, and their impacts on the explosion of gangue dump were analyzed. The experimental results show that overall warming phenomenon of the gangue dump after watering occurred, the amount of H2 is three times than that before watering, and the amount of CO is far greater than that on the conditions of no-watering, at the same time combining with local observation and tests. It is found that the content of the oxygen reduce with the temperature increasing; however, gangue dump internal hydrogen content increase unusually on the rainfall conditions at 90°C, but the local measuring points reach the explosion limit. The existence of the CO and H2 is the main reason for inducing the explosion of spontaneous combustion coal gangue dump.

Triaxial creep tests on CCG specimens were systematically performed using a self-made creep seepage experimental apparatus for determining the creep law of CCG. An improved triaxial creep model of CCG was established on the basis of a Nishihara model and another visco-elasto-plastic model, parameters of which were fitted on test data. Furthermore, the creep model is validated according to the result of triaxial creep experiments, and the outcome shows that the proposed triaxial creep model can properly characterize the properties of various creep deformation phases of CCG, especially the accelerating creep phase. At the same time, the instability conditions of CCG were presented based on the discussion of the improved model’s stability in terms of stability theories of differential equation solution.

It is of great significance to forecast high yield of CBM wells and analyze dynamic production by having an overall study on the characteristics of the produced CBM and determining the main factors influencing the productivity of CBM. With the test report and the related geological parameters of a single well, methods of combining the productivity data and typical production curves were used to analyze different geological factors and how to influence the capacity of a single layer. Then, the paper proposed a new understanding about capacity characteristics of the study area and geological control factors: First, the Shanxi formation production capacity characteristics was divided into two-stages, showing signs of gas and gas breakthrough for 100 days. Second, two parameters, which include potential of gas production and gas production capacity, were better than the single parameter, such as gas content, coal thickness, and penetration to analyze affecting factors of single well production. Finally, comprehensive analysis concluded that the ratio of critical desorption pressure to reservoir pressure has greater influence on the production of vertical CBM wells. Besides, the potential of gas production capacity has greater impact at stage of showing gas signs; the coal reservoir pressure and gas production capacity have greater impact at stage of gas breakthrough for 100 days. Thus, to seek the coal bed methane with high ratio of critical desorption pressure to reservoir pressure and high yield of gas will be important guarantee to the success of the coal bed methane exploration and development.