Study on deposition pattern of coal rock particles in the pumping gas flow at the back end of mining fissure shrinkage

Coal particles carried by the gas extraction flow are easy to be deposited in the mining-induced fracture, which seriously reduces the flow rate of gas extraction. Mastering the deposition characteristics of particles in the fracture is an important basis for improving the flow rate of gas extraction. In this paper, we carried out a particle transport and deposition experiment in the fracture with a shrinkage, and studied the particle deposition bed evolution law after crossing the shrinkage under the influence of the gas extraction flow. In addition, we analyzed the influence of the gas velocity and shrinkage structure parameter on the particle deposition law of the back end of the shrinkage of the fracture and the local resistance of the gas flow. The results show that the granular sedimentary bed at the back end of the fracture shrinkage shows two kinds of evolution patterns. When the particle deposition bed is distributed in a “V” shape along the airflow direction, the deposition height of the granular deposition bed shows an evolution pattern of rapid increase followed by a slow decrease. When the depositional zone is a “Ʌ” shaped deposition along the direction of flow, the depositional height shows an evolutionary pattern of slow increase and then slow decrease. In addition, with the development of the particle bed in the fracture, the local resistance changes at the back end of the fracture shrinkage can be divided into the initial stabilization stage, the rapid development stage and the final stabilization stage. The evolution time of the initial stabilization stage is shortened with the increase of the pumping rate or the decrease of the shrinkage ratio. The evolution time of the rapid development stage is shortened with the increase of the pumping rate or the increase of the shrinkage ratio.