Experimental research on the venting characteristics of methane and coal dust two-phase system mixture explosions

This research focused on the venting characteristics and influence factor of methane and coal dust mixture explosions. The corresponding relationship between the venting parameters was analyzed and the effect of methane concentration was obtained. Results indicate that the venting flame propagation and pressure rise of vessel interior and exterior presented the clear corresponding relationship. The venting flame underwent the evolution process of “mushroom”, “spherical” and “strip” structures. At 6% methane concentration, the venting flame was longest and its propagation velocity was fastest. During the extinguishing stage, the flame exhibited an obvious oscillation. The venting flame appeared a secondary venting phenomenon at 6% and 8% methane concentrations, and the phenomenon was more evidently at 8% methane concentration. The pressure at the venting pipe was the greatest and its change was also most significant, even appeared a larger negative value. Compared with the vessel interior, the pressure of vessel exterior was continuously decreased as the venting distance increased. The venting pressure was the greatest at 6% methane concentration, followed by 8% methane concentration. The pressures of four points at 4% methane concentration were respectively reduced by 25.0%, 34.9%, 43.8% and 81.8%. The corresponding flame temperature also presented the same change trend. Besides, the venting flame image showed a good correspondence with the temperature field distribution and the highest temperature appeared in the center of spherical flame. The secondary venting resulted in the recurrence of high temperature flame at the venting port (500℃-650℃) and was affected by the methane concentration inside the vessel.