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The engineering background of this paper is the upper protecting seams exploitation of Huangsha Mine, By use of CFD software to analyze the methane delivery law in U type ventilation work face gob. By analyzing the density distribution, pressure distribution, velocity field and mash methane concentration of air-methane mixed gas, obtained the locat...
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... of natural packing zone is 20m; length of mining infection zone is 60m; length of re-compaction zone is 140m; width of intake airflow roadway and return airway is 3m On the basis of previous researches [2] , the permeability, viscosity coefficient and porosity of upper 2# seam are presented in Table 1, numerical model is presented in Figure 1. where A is intake airflow roadway; B is return airway; C is roof control area; D is natural packing zone ; E is infection zone of coal mining; F is re-compaction zone. ...
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Citations
... There are also some valuable studies on this subject. The largest number of works in the area of the risk of coal spontaneous combustion concern goafs [70][71][72][73]. Furthermore, a large number of papers related to the methane release hazard are also devoted to goafs. ...
... In this respect, Karacan, in his work [70], pointed out that methane emissions from the longwall ventilation system are an important indicator of how much methane a mine produces and how much air needs to be provided to keep methane levels below the regulatory limits, including goafs. Zhang, in his paper [71], presented the results of the study on the distribution of air and gases in the sheared goafs of a longwall with the U-type ventilation system. Tutak and Brodny, in their work [72], studied the effect of the auxiliary devices used for the U-type ventilation system on the methane concentration in the upper corner of the longwall. ...
Various types of natural hazards are inextricably linked to the process of underground hard coal mining. Ventilation hazards-methane and spontaneous combustion of coal-are the most dangerous; they pose a major threat to the safety of the workers and decrease the effectiveness of the whole coal production process. One of the methods designed to limit the consequences of such hazards is based on the selection of a ventilation system that will be suitable for the given mining area. The article presents a case study of an active longwall area, where-due to increasing ventilation hazard (methane and spontaneous combusting of coal)-the whole system was rebuilt. The U-type ventilation system was used in the initial stage of the extraction process, however, it often generated methane in amounts that exceeded the allowable values. Consequently, such conditions forced the change of the ventilation system from a U-type to Y-type system. The new system was installed during the ongoing mining process, unlike the usual practice. The article presents the results of tests on mine gas concentrations and descriptive statistics for both types of ventilation system. The results clearly demonstrate that the U-type longwall ventilation system, in the case of high methane release hazard, prevents safe and effective operation. At the same time, the use of this system limits the carbon oxidation reactions in the goaf, leading to spontaneous heating and combustion, which is confirmed by the low concentrations of gases-by-products of these reactions. In turn, the use of the Y-type longwall ventilation system ensures safe and effective operation in areas with high methane release hazard, but at the same time deteriorates the safety associated with the spontaneous combusting of coal. The presented case-both from a scientific and practical perspective-is quite interesting and greatly broadens the knowledge in the scope of an efficient ventilation system for underground workings.
... Gao et al. (2012) simulated the air leakage distribution between working face and gob area and the migration of gob gas by using Fluent software. Zhang (2012) used CFD software to analyze the methane migration law in a U type ventilation working face gob. Zhu and Liu (2012) performed a theoretical qualitative analysis to understand the influence of tail methane drainage pattern on methane and oxidation concentration distribution. ...
Large areas of gob containing a considerable amount of methane in China are produced annually. The practice of injecting CO2 into gobs to extract methane could not only reduce the greenhouse gas emission, but also exploit clean methane resource. In this paper, an experimental apparatus was built to conduct the simulation of injecting CO2 into gob. The results show that the gob volume can be orderly divided into three zones from bottom to top: the residual coal zone (RCZ), the gas transitive zone (GTZ) and the methane enrichment zone (MEZ). The gob methane concentration exhibits an increasing trend before and after CO2 injection, and the methane concentration in the MEZ is obviously higher than that in the RCZ and GTZ. After CO2 injection, the methane concentration in RCZ decreases, while the methane concentration in the MEZ significantly increases. Meanwhile, the methane concentration in the RCZ would decrease as the total amount of CO2 injected increases and that the methane concentration in the MEZ would increase as the methane concentration in the RCZ increases. Based on the simulation results, a new in-situ technology was proposed and applied in a gob of Yiyuan mine in China to improve its methane extraction concentration by arranging a highly-located roadway in the MEZ and injecting CO2 into the GTZ. The field testing shows that this technology can increase the gob methane concentration by 22% for the highly-located roadway with an original low methane concentration of 20%-25%.
With the spreading of the green environmental protection concept, increasing attention has been paid to improving the tunneling environment. In this paper, the distribution characteristics of airflow fields, the diffusion laws of pollutants, and the influence of airflow rate changes on pollutants in tunnels under single-forced ventilation conditions were simulated according to the computational fluid dynamics (CFD) theory. In addition, the reliability of the simulation results was verified through field measurements. A three-stage distribution was observed once the dust concentration stabilized: we noticed areas with relatively low dust concentrations (< 300 mg/m³), high dust concentrations (> 500 mg/m³), and medium dust concentrations ( ~ 400 mg/m³, near the tunnel exit). Meanwhile, after stabilizing, the gas concentration was 0.67%. Properly increasing the airflow rate (Q) can effectively improve the tunnel environment: when Q reached 600 m³/min, the air in the tunnel was effectively purified. However, under a continuous increase of the airflow rate, there is a risk of pollution rebound.We conclude that, to effectively improve the tunnel environment and achieve a sustainable utilization of resources, the optimal operation airflow rate should be 600 m³/min.
