Flammability limit behavior of methane with the addition of gaseous fuel at various relative humidities

Investigation on the overpressure of methane-air mixture gas explosions in straight large-scale tunnels

Study of flame distribution laws and the hazard effects in a tunnel gas explosion accident is of great importance for safety issue. However, it has not yet been fully explored. The object of present work is mainly to study the effects of premixed gas concentration on the distribution law of the flame region and the hazard effects involving methane-air explosion in a tube and a tunnel based on experimental and numerical results. The experiments were conducted in a tube with one end closed and the other open. The tube was partially filled with premixed methane-air mixture with six different premixed methane concentrations. Major simulation works were performed in a full-scale tunnel with a length of 1000 m. The first 56 m of the tunnel were occupied by methane–air mixture. Results show that the flame region is always longer than the original gas region in any case. Concentration has significant effects on the flame region distribution and the explosion behaviors. In the tube, peak overpressures and maximum rates of overpressure rise (dp/dt) max for mixtures with lower and higher concentrations are great lower than that for mixtures close to stoichiometric concentration. Due to the gas diffusion effect, not the stoichiometric mixture but the mixture with a slightly higher concentration of 11% gets the highest peak overpressure and the shock wave speed along the tube. In the full-scale tunnel, for fuel lean and stoichiometric mixture, the maximum peak combustion rates is achieved before arriving at the boundary of the original methane accumulation region, while for fuel rich mixture, the maximum value appears beyond the region. It is also found that the flame region for the case of stoichiometric mixture is the shortest as 72 m since the higher explosion intensity shortens the gas diffusion time. The case for concentration of 13% can reach up to a longest value of 128 m for longer diffusion time and the abundant fuel. The “serious injury and death” zone caused by shock wave may reach up to 3–8 times of the length of the original methane occupied region, which is the widest damage region.

Effects of premixed methane concentration on distribution of flame region and hazard effects in a tube and a tunnel gas explosion

Explosion Flame Acceleration over Obstacles: Effects of Separation Distance for a Range of Scales

In this study, experiments of explosions and flame characteristics in methane/air mixtures are performed in a 10-m3 vessel. Pressure gauges and a high-speed camera are utilized to record the pressure trajectories and the flame propagation process of ignition growth. The experimental results show that the maximum value of overpressure and the maximum rate of the explosion pressure rise are 0.596 MPa and 1.82 MPa/s for the methane (9.5% in volume)/air mixture at atmospheric conditions, respectively. Both values are higher than for other mixtures with different compositions. The results also indicate that the overpressure from the large-scale vessel in this study is lower than that of a smaller apparatus (e.g., 5-L closed cylindrical vessel). This difference occurs due to the cooling effect and because the reflected sonic disturbances by the vessel wall affect the explosion process and weaken the energy during the pressure attenuation stage, thus rendering the value of overpressure in the large-scale apparatus lower than in the tiny cylindrical vessels. The maximum overpressure is observed at 0.75 m for C = 7% (“C” means the methane concentration) and 9.5% but at 1.3 m for C = 5%, 6.5%, 11.2%, and 13%. These results indicate that methane/air is an easier means to generate overpressure and that the overpressure is higher near the stoichiometric condition. Based on the analysis of the flame propagation process, the mean value of the flame speed of methane (C = 9.5%)/air is calculated to be approximately 2.43 m/s because the nonuniformity of the chemical reaction at the flame front results in a maximum fluctuation of flame speed of approximately 28.5%. The flame thickness (θ) of methane (C = 9.5%)/air fluctuates between 9.84 and 10.95 mm, with a mean value of 10.53 mm. © 2014 American Institute of Chemical Engineers Process Saf Prog 33: 362–368, 2014

Explosion and flame characteristics of methane/air mixtures in a large-scale vessel

Influence of laneway support spacing on methane/air explosion shock wave

Nonlinear distribution characteristics of flame regions from methane–air explosions in coal tunnels

Based on numerical methods and theoretical analysis, the influence of the tunnel wall surface conditions on the methane-air explosion is evaluated. A rough tunnel wall causes stronger turbulence in the methane-air explosion. In a straight tunnel where some part of the space is filled with the methane-air mixture, the turbulence intensity varies with distance along the tunnel axis: it is higher in the methane-air premixing region and also in the far region of air shock wave propagation; between these regions, the turbulence intensity is lower. In the methane-air premixing region, the effect of turbulence is manifested as a significant increase in the explosion pressure. In the far region of air shock wave propagation, turbulence makes the shock wave strength decrease, but its effect is indistinctive among others. In the original methane-air premixing region, the explosion pressure of the methane-air mixture in a tunnel with rough walls is higher than that in a tunnel with smooth walls. However, the air shock wave beyond the premixing region in a tunnel with rough walls is weaker than that in a tunnel with smooth walls.

Influence of the tunnel wall surface condition on the methane-air explosion

Methane-air explosion is one of the main accidents in coal mines. In this paper, the hazard effects of the gas explosion in a long straight coal laneway were studied by virtue of numerical simulation. Distribution characteristics of the shock wave overpressure, the flame speed and the temperature field were obtained. Along the increasing axial distance, shock wave overpressure increases in original methane-air area and decreases beyond the original methane-air area. Range of flame exceeds original methane-air area. Flame accelerates continually in original methane-air area and decelerates beyond the original methane-air area. The temperature attenuates slowly along the increasing distance in the flame area by virtue of flame front, and attenuates quickly along the increasing distance beyond the flame region. High temperature hazard involves farther area beyond original methane-air area.

Lei Pang

Papers

Influence of laneway support spacing on methane/air explosion shock wave

Nonlinear distribution characteristics of flame regions from methane–air explosions in coal tunnels

Influence of the tunnel wall surface condition on the methane-air explosion

Study on Hazard Effects of Gas Explosion in Coal Laneways