Research On Critical Technology For Multilayer Safety Protection System In Gas Drainage Pipeline

Coal resources are important materials for industrial production and human life. To ensure the rapid development of national economy, our coalmine output and depth are increased every year. The mining conditions are deteriorating constantly and high gas outburst coalmines are grown with the gas content increased. Gas Control has become the most important issue for coalmine safety, and gas drainage is the most effective way to control gas.There are significant security risks in the process of gas drainage, since gas concentration often being explosive limit in gas drainage pipelines, and gas fire or explosion is often occured when equipments suffered abnormal operations, static electricity or lightning, seriously harmed coal mine production safety and the safety of miners. To ensure the safety of coal mine gas drainage pipelines, safety facilities such as explosion venting, suppression and resistance devices should be installed in gas drainage pipelines nearby the possible ignition sources. There is significance for reliable mine gas drainage, eliminating security risks during emissions and transport process of low-density gas. The principles of original venting, suppression and resistance technologies are feasible, but gas drainage safety facilities are Low reliability due to the lack of comprehensive and systematic studies for explosion flow field characteristics and influencing factors in gas drainage pipelines, which a reliable gas drainage safety protection system is required for coal mine gas safety extraction. In this dissertation, the general idea of multilayer safety protection system is proposed for gas drainage pipelines. Water sealing of barriering&explosion venting technology, explosion suppression technology based on inert gas to extinguish flames, and rapid blocking technology based on fast closing butterfly value are studyed to develop a gas drainage multilayer safety protection system, using theoretical research, design calculations and industrial test methods, which solved the problem of low reliability of gas explosion safety protection devices with single safety equipment.Receach on gas explosion flow field characteristics variation are the basis to develop the multilayer satety protection system for gas drainage pipeline. Based on computational fluid dynamics theory, variations of temperature, pressure, reaction rate, and gas flow rate of gas explosion are receached in pipelines, and characteristics of gas explosion are analyzed in straight pipes of different diameters and lengths, as well as a bend pipe of actual drainage pipelines in a domestic coal mine. Results showed that the maximum reaction rate, the maximum relative pressure and maximum flow rate are all acceleration processes with increasing acceleration. Because the degree of fluid turbulence is exacerbated in the corner, the maximum reaction rate, the maximum relative pressure and maximum flow rate are higher and the combustion completion time is shorter than the same diameter straight pipe. Explosion pressure is changed greatly by diameters, the smaller the diameter, and the greater the explosion pressure. In straight pipelines of different length, reaction rate, pressure and velocity are all increased slowly at the beginning of gas explosion, but rapid growth at120ms, lead to huge explosion energy. Based on the theoretical analysis, an overall scheme of gas drainage multilayer safety protection system is proposed, combining with explosion venting, explosion suppression, and explosion resistance technology.Because of lacking the research on characteristics of explosion venting and the liquid level compensation technology, the original explosion venting technology is esay to lead explosion venting failure. The unsteady analysis of gas explosion and venting process is carried out at the different liquid levels in common gas drainage pipeline with the diameter of500mm, based on computational fluid dynamics theory. The results shown that, the explosion energy rushed out from the bends of venting pipe when the gas was ignited at explosion venting port with the central pressure of5MPa and central temperature of3350K, so that the explosion energy was released, and explosion pressure and temperature were reduced rapidly. If the height of water level is higher than50mm, explosion flame can be barriered by the venting device effectively when the reaction rate is0mol/m3·s above the liquid surface. Explosion venting device with adaptive level control is developed based on the research of water level automatic control system.Because the extinguishing media suspension time is short, so the original gas explosion suppression technology is easy to cause explosion failure. First of all, the distance between the position of inert gas sprayed and pipe import is defined according to the flame sensor response speed, explosion flame propagation speed and so on. The numerical simulation of gas explosion flame extinguished process is studied in the pipe, which diameter of500mm, and length of30m. The results showed that the temperature of combustion gas greatly reduced, and concentration of methane and oxygen is diluted gradually, with the injection of the carbon dioxide. When the spray rate of carbon dioxide is more than20kg/s, the fire can be extinguished within100ms, and the greater carbon dioxide sprayed, the shorter time flame extinguished. Through the above research, the explosion suppression device was developed based on carbon dioxide inert gas extinguishing fire.Gas explosion should be resistant by a faster explosion resistance speed. Because origal resistence valve closed slowly, a method of explosion resistance by hydraulically driven butterfly valve is proposed in gas drainage with the diameter of500mm. Using the method of finite element analysis, the dynamic characteristic and strength of explosion resistance device driven by hydraulic butterfly valve is analyzed, and a explosion resistance device is designed which could satisfy the requirement of gas explosion resistance parameters. A multilayer safety protection system is designed in a gas drainage pipeline, combining with explosion venting, suppression and resistance, and the industrial test of single-layer, double-layer and multilayer are carried out based on the research of multi-sensor and monitoring systems. The test result proved that, the multilayer safety protection system can realize multilevel correlation, and protect the gas drainage pipelines and underground coal mine safe effectively. The multilayer safety protection system which is of great significance to assure the safety of the coal mine production and the miners’lives have been applied in many gas drainage pipelines of china such as Xiangyuan Qiyi new coal industry Co. Ltd, Shougang Fushan Resources Group Limited, Datong Coal Mine Group, etc.