Seepage properties of crushed coal particles

Gas release from the crushed coal formation during coal mining poses a threat to the normal storage and gas transport within coal seam. This sort of release is largely related with the evolution of gas seepage properties of crushed coal, namely, the evolution of gas seepage properties plays an important role in the gas extraction and the outburst prevention of coal seam. Meanwhile, the evolution is directly related to the volume and geometry of fractures within the crushed coal and strongly influenced by particle size and porosity (axial displacement). In order to investigate the effect, a gas flow apparatus connecting with the MTS815.02 system was designed. The gas seepage properties of crushed coal specimens with five particle sizes of a (2.5-5 mm), b (5-10 mm), c (10-15 mm), d (15-20 mm) and e (mixed sizes) under the variable axial displacement of 10, 15, 20, 25, 30, 35, and 40 mm, respectively are measured by the revised MTS815.02 system. The results of test show that: The porosity decreases with the increase of axial displacement and the weight loss of larger particle size, respectively. Particle crushing during compaction is a main reason to increase small-size and emerge size 0-2.5 mm. Gas flow seepage properties of crushed coal are found to be strongly influenced by particle size and axial displacement. The permeability decreases and non-Darcy coefficient increases with the increase of axial displacement (decreases of porosity) and the decrease of larger particle size, respectively. The permeability and non-Darcy coefficient are controlled by the fracture among the coal particles. The seepage properties of crushed coal are not only related to particle size, loading levels (axial displacement), but also the compound mode. Based on the regression analysis, the relationship between the permeability and non-Darcy coefficient and porosity shows that the exponential function can fit the experimental data well.