| Coal seam gas extraction is one of the most effective methods in coal mine gas control and prevention of coal and gas outburst, it is not only the needs of safe production, but also an urgent needs to save energy, protect the environment. The gas concentration in borehole and the pipeline is not only influence mine safety, and is prerequisites if the gas that drained out can be used, how to improve the concentration in drainage pipe and control the gas concentration in drained gas pipeline outside the explosion limit is recognized as problems in underground gas extraction technical field, achieve detection monitoring, and automated regulation the gas extraction concentration in the gas pipe has an important significance in the gas extraction field. A moment of drained gas concentration depends on the level of gas flow and gas leakage flow in the borehole, around this basic question, the controlling factors that impact borehole gas flow and affecting the borehole air leakage are analyzed,a theoretical basis for the study of concentration automation control system in drainage pipe is provided, research results are as follows:1) Based on the analysis of gas deposit and flow theory in coal seam, the borehole gas flow formula was deduced use Darcy's law, and the factors affecting the size of gas flow is carried on theoretical analysis, consider that under the same conditions,different seams raw gas pressure,if negative pressure changes in the same amount value range, the flow change is a fixed value; the concept of borehole gas flow change rate and unit negative pressure flow changes rate are proposed based on this analysis, and through the simplified theoretical analysis and assignment formulas, indicate that optimize its reasonable extraction negative press size improve the flow of gas flow and borehole gas concentration by calculating the size of the unit negative press flow change rate has practical significance;2) On the basis analysis of strain and displacement of coal and rock around the borehole, the concept of drilling leak lap is proposed, under the same conditions, the larger the leak circle area is, the greater the amount of leakage, and the factors that impact the borehole leak circle area size is carried theoretical analysis, by investigating coal permeability changes around the borehole, a formula for calculating the amount of borehole leak flow and gas concentration by the application of air percolation theory is deduced;3) The concept of base concentration,import concentration and immediate concentration is proposed,noting that change imported concentration is the key to adjust the size of the immediate concentration in borehole,and factors that influence imported concentration is analyzed, including the effective length of borehole,the hole diameter, the radius of the plastic ring,force of sealing supporting, length of sealing section,negative press in extraction process;4) The view of flow acceleration is proposed, which pointing out that concentration in borehole Increased or decreased with negative press changes, depending on the ratio W between he amount of gas emission flow acceleration and borehole leakage flow acceleration in borehole, when W>1, improved negative press in sealing units can improve gas extraction concentration, reduce the negative press in gas sealing unit will reduce drainage concentration; when W<1, improve drainage negative pressure will reduce the gas concentration in sealing unit, while reduce the negative pressure of gas extraction will increase the gas concentration, reasonable approach and proposals use W to optimize gas concentration based on this opinion is put forward;5) based on supporting sealing principle, capsular bag sealing grouting equipment is developed and engineering applications is carried out, the experiment proved that the new method can improve gas drilling concentration and extraction flow compared with the existing sealing polyurethane sealing method;6)Test experimental device gas concentration changes with drainage negative when parameters of the coal seam different was designed, experimental analyzes that gas concentration changes with negative pressure in different coal seam gas pressure and air leakage change with negative pressure were carried out, experimental analysis show that gas extraction concentration trend change with negative pressure increasing mainly depends on coal seam gas pressure, borehole sealing quality and tiny particles motion state in leak fractured, accordingly, the best extraction negative view was proposed, which point that negative pressure is not as high as possible, nor is it as low as possible in the process of gas extraction, but there is an optimal value, and best vacuum extraction classified analysis was carried out, best gas extraction concentration can be explored by adjusting the negative pressure, ensuring the highest possible gas extraction while minimize the air leakage. was put forward;7) Research ideas of gas concentration automatic control system is proposed based on the analysis of theoretical and laboratory experiments, this system use computer, sensors and movement actuators can detect and adjust the gas extraction negative pressure to the best condition. Three programs were designed depending on different actions actuators, by comparison, to finalize the plan of electric valve as actuators action. Main control system,sensors, and action actuators is discussed respectively, hardware selection, PLC program design, touch screen configuration interface design, PC configuration interface design are completed, a comprehensive online test is conducted at last;8) The gas concentrations automatic regulation and warning system installed and testing in Jiulishan coal mine, system defaults is identified according to the coal seam geological conditions and parameters of borehole sealing in engineering practice sites, the best extraction negative pressure and optimum gas concentration of the test roadway was searched out, theoretical analysis correctness and feasibility were proved, reliability and availability of the system is showed in industrial experiments. |
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