Study On Superposition Method Of Air Leakage And Gas Delivery In Cave-in Gobs

Air leakage in an exhausted gob is the most important inducement of two main hazards in a working face:gas overrun in the upper corner of working face and spontaneous combustion of abandoned coals in the gob, therefore it becomes especially significant to make clear the seeping field of a gob under different complex boundary conditions. In view of the impossibility for persons to get into a gob,it is very difficulty to obtain exactly the distribution of different physical variables by field measurement. Furthermore,not only does the practical similitude simulation need a lot of manpower and material resources,but also are its results difficulty to be verified,so nowadays many scholars have adopted a CFD method to numerically simulate the flow field of different gobs behind different working faces and have achieved some aims.In one hand,however,different gobs have different boundary conditions,even in the same gob various working periods also mean various boundary conditions;in other hand it will occupy plenty of computer resources to numerically simulate all kinds of boundary conditions in all kinds of gobs.Based on the relevant theory of PDEs and the analysis of controlling equations of the seeping field and gas concentration field in a gob, this paper introduced the linear superposition theory to the numerical calculation of gob flow field, and then simplified the determination of flow field with complex boundary conditions and sources and reduced the necessary numerical test as well as simulation time. In the area of numerical simulation of gob's flow field,this method realized the transformation from individuality to commonness,from particularity to generalization,from embodiment to abstract,thus established the theory base of on-line analysis of gob's flow field and provided technical supports.During the research,this paper deduced a series of formulas,such as the general formula of superposition theory,the calculation formula of gas concentration in gobs,relations between permeability and gas concentration in gobs as well as formulas connecting the airflow rate of working face and the air leakage of gobs,which simplified to some extent the flow field calculation of gobs in different ways respectively. As to the distribution styles of permeability,this paper put forward the hypothesis of"free falling permeability",which equipped a reasonable boundary condition for the change of permeability in gobs and helpt to depict and research more exactly the distribution of gob's permeability. The distribution of oxidization and heat accumulation zone, which is deduced from the hypothesis of"free falling permeability", can explain to some extent the sporadic spontaneous combustion phenomenon of a gob after a rapid working face. These formulas and hypothesis themselves and their application composed the core elements of this paper.Based on the tracking data of 416# working face of Chen Jia-Shan mine in Nov.2006, this paper employed the superposition theory and relevant formulas deduced in the same paper to analyze and calculate the coupled flow field of the working face and its gob under different gas pumping conditions, and then proved that the integrated gas pumping measures equipped in 416# working face were rather effective.