Numerical simulation on the premix properties and explosion process of methane / coal dust mixture in a vertical pipeline under turbulent flow

To reveal the pre-mixed turbulent characteristics and flame propagation process for methane / coal dust mix- ture in a vertical tube,the physical and mathematical models for dust diffusion and explosion in the vertical pipeline were constructed,respectively. Based on fluid mechanics and heat-mass transfer,Fluent,a commercial code was ap- plied to simulate the dispersion characteristics and explosion process for methane / coal dust hybrid mixture. The char- acteristic stages for coal dust diffusion in the vertical pipelines were analyzed and divided. Besides,the influence of ini- tial vacuum degree and gas intake pressure on the turbulent characteristic was analyzed,and the evolution mechanism of flow field and temperature field in coal dust / methane explosion in the vertical pipeline was revealed. Moreover,the influence law of methane concentration,coal dust concentration and coal particle size on Pmax and(dP / dt) max were in- vestigated,in addition,the flame propagation characteristics and explosion process were revealed. Results showed that: discrete phase diffuses in the vertical pipe can be divided into four consecutive stages:fast injection,decelerated dis- persion,stability and sedimentation. Besides,both the initial vacuum degree and gas intake pressure have an influence on turbulence intensity. The pressure field inside the pipe was basically evenly distributed at different times during the explosion process. The relationships between methane concentration,coal dust concentration,and coal particle size and Pmax and(dP / dt) max showed a quadratic function. The flame structure,flame height,and flame propagation velocity ob- tained by simulation and experiment are consistent at different time,the flame structure showed a “crescent-S-concave crescent-finger” variation trend till the end of the explosion. However,the temperature distribution was uneven,and the high temperature zone was concentrated in the upper and middle of the pipeline. The flame propagation velocity in- creased quickly at first and then decreased,and finally showed concussion characteristics in the later period.