Investigating the concentration distribution characteristics of methane in large storage facility using desorption-concentration gradient method and CFD simulation

Abstract

The continuous methane emission from the coal piles is associated with many environmental problems and safety risks, in large storage facility. The methane emission parameters of coal piles and the concentration distribution characteristics of methane, which are the basis of ventilation design, are rarely reported in large storage facilities. In this study, based on the mass-transfer diffusion theory, desorption-concentration gradient method for determining methane emission parameters of coal piles in large facilities is proposed. In this method, firstly, the coal pile methane diffusion coefficient was deduced by conducting the coal particles absorption-desorption experiments and the particle-size distribution. Then, combing the diffusion coefficient and methane concentration-gradient on the coal pile surface, the coal pile methane diffusion flux was calculated. Further, when methane diffusion flux was utilized as the source item for CFD calculations, the results were consistent with the onsite measured values, which demonstrated the accuracy of this method. The CFD simulation results show that methane has diffusion characteristics that adhere upward along the slope of the coal pile and converge on the coal ridge. The methane flow reaches the dome upwards, where a higher concentration is formed. Both the coal pile volume and the methane diffusion flux will affect the concentration distribution of methane in large storage facility. For a larger diffusion flux, the explosion limit will be exceeded, and measures need to be taken to eliminate the safety risk. These findings provide principal data and analysis guide for optimized design of ventilation performance in closed industrial building.