Study On The Law Of Movement And Distribution Of Gas In Goaf On The Condition Of Surface Hole Drainage

As one important method in extracting coalbed methane, the technology of surface hole drainage has been tried in some coal mine and gotten approving effection. During the course of field experiment, some pivotal problems such as optimization about hole position and forecast about gas output etc emerged out. Paper studied the law of movement and distribution of gas in goaf and the extraction principium of surface hole drainage, and ascertained the reasonable hole position from the angle in favor of gas extraction in the end.The law of movement and distribution of gas in goaf are dissertated detailedly in this paper. First, the principle of surface hole drainage is analyzed, the mathematic model on dynamical dispersion of gas in goaf is given and the numerical result is gived. Then choose longwall panels 13118 at Xieqiao and longwall panels 11418 at Zhangbei, and apply CFD fluent progress to simulate the dispersion law of goaf gas of longwall panels chosen, which educes the dispersion law of goaf gas when gas actived or not actived. Finally,tracer gas is released from longwall panel and correlative data mensurated is taken order with, and the law about movement and dispersion of gas in goaf is analyzed primarily, which proves it reliable that using CFD fluent progress analyzing goaf gas movement and dispersion. The research result of this paper can be as the basis of surface hole designing.The mostly conclusions of theses are shown in the next content:(1) The conclusion can be drown from the mathematics model that the quantity of gas extracted and released in goaf is equal ,which makes the chroma and pressure of gas steady at initial stage. As the persistence of extraction, the gas released from dump reduces and the direct result is the accelerative falling of thickness in the goaf. The thickness of gas in goaf will reach balance gagin and maintain the level in the end when it decreases to some certain extent. (2) From the numerical simulation and field SF6 tracer gas experiment, the density distribution rule of gas can be found that it is low near to work face and rises in goaf deep, the tiptop density zone occurs 500m in goaf and it becomes low again as expending farther in goaf. Added to this,gasses strength upper site presented to goaf middle laying return airway side aboard without surface hole drainage.(3) The gasses strength in site laying return airway side aboard decreased during the runtime of surface hole. Oxygen would infiltrate into the goaf farther and be sucked into tube when plural holes run simultaneously which maked the strength of gas from the hole nearer to working face decrease, which means we need strengthen detection force to PH indicator of gas and oxygen in pipeline and adjust the draining parameters duly.(4) We can draw the conclusion from the result of SF6 tracer gas experiment that sampling data attenuated submitting negative exponent regular with time, which were alike among all holes (5) According to the analysis about theory and numerical simulation, surface hole should be layed in site laying return airway side aboard and expended into crack zone. It is shown from the field experiment data that the output in such hole mentioned above could come to a head of 33.8 m3/min.