An Innovative Finite Tube Method for Coupling of Mine Ventilation Network and Gob Flow Field: Methodology and Application in Risk Analysis

Explosions and fires originated from longwall gob due to the formation of methane-air mixture have been a severe threat to coal miner's lives. Many numerical studies on coal mine fire and explosion hazards have focused on the airflow in roadways and mine gobs. However, most of these studies isolate the gob from its surrounding roadways, and the network analysis and the CFD method are applied independently to model the two classes of airflows. This approach greatly limits the ability of simulating mine ventilation flow, especially unable to consider the effects of gob boundary conditions on air exchange between the gob and the surrounding airways. An innovative finite tube method (FTM) is developed to couple the one-dimensional mine ventilation network (MVN) and the 2D/3D gob flow field (GFF). In FTM, GFF is discretized into a finite number of flow tubes each of which is formed by any two adjacent stream lines. These tubes, representing the gob's field flow, connect the MVN into a new coupling network. To solve the coupling model between MVN and GFF, an iterative solution technique is developed in which the MVN analysis is used to evaluate the boundary pressures for GFF simulation and in turn the FTM feeds the GFF results back to the coupling network. Based on the FTM approach, a model for gas migration in gob has been established for delineating the hazard zones of explosive methane concentration and spontaneous combustion. A computer program is developed to implement the FTM simulation. An illustrative example with five flow tubes representing the GFF is created to verify the stability and convergence of the FTM solution process. A simulation example also indicates that the accuracy of FTM is improved by 12% compared with previous method. Results of an application case show that the program is capable of quantitatively evaluating the gob's risk zones prone for spontaneous combustion and gas explosion as well as performing risk analysis for various ventilation scenarios.