Explosion characteristics and energy utilisation of coal mine ultra-lean methane

Abstract

Reasonable recycling low concentration methane, especially the ultra-lean methane (the concentration lower than 5%), is significant to resource saving and environment protection. Nowadays, low concentration gas power generation technology is well developed. Notwithstanding this, ultra-lean methane has not been applied in large scale mainly due to the high utilisation costs. Therefore, to address this issue, we break through the empirical thinking to make ultra-lean methane combustion by blending with combustible substances other than only increasing the methane concentration. Its feasibility was analysed from theoretical analysis, especially the cost analysis. Dimethyl ether (DME) was selected as the additive from a range of combustible substances. Then experimental study on the explosion parameters of coal mine ultra-lean methane blending with DME was carried out in a standard 20-L explosion spherical vessel; the lower explosion limits (LEL) at different initial temperatures (ambient temperature, 40°C, 60°C and 80°C) were tested at methane concentration of 0.5%, 1%, 2%, 3% and 4%, respectively. The experimental results indicate that the addition of DME can significantly reduce the minimum explosion concentration of methane, and both P max and (dP/dt)max increase with an increase of DME content in the total fuel. The overall trend of P max and (dP/dt)max increases first and reaches to the maximum. In addition, both CO and CO2 in explosion tail gases are consistent with the decrease trend with increasing in gas mixture. The explosion solid product contained a large number of aromatic hydrocarbon structures, and the solid particles were mainly two types of spherical and blocky with the diameter between 30 and 50 µm. The explosion phenomenon and data provide a reference for assessing the hazards of practical energy system, and guiding the designs of fuel formula and engine safety.