Mohammed Jabbar Ajrash

Impact of suspended coal dusts on methane deflagration properties in a large‐scale straight duct

Knowledge about flame deflagrations in mixtures of methane and diluted coal dust assists in the prediction of fires and explosions, and in the design of adequate protective systems. This vital lack of information on the role of hybrid mixtures (methane/coal dust) is covered in this work by employing a novel Large-Scale Straight Duct (LSSD) designed specifically for this purpose. The hybrid fuel was injected along the first 8m of the 30m long LSSD. The results revealed that a 30gm-3 coal dust concentration boosted the flame travel distance, from 6.5m to 28.5m, and increased the over pressure rise profile to 0.135bar. The over pressure rise (OPR), pressure wave velocity, flame intensity and the flame velocity were significantly boosted along the LSSD in the presence of 10gm-3 or 30gm-3 coal dust concentrations in the methane flame deflagrations. Finally, the high speed camera showed that the presence of the coal dust enhanced the turbulence in the front flame. Consequently, the pressure wave and flame velocities were both increased when a 10gm-3 coal dust concentration coexisted with a 9.5% methane concentration in the deflagration.

Flame Deflagration In Side-on Vented Detonation Tubes: a Large Scale Study

Venting is often used in process industries to reduce the possibility of dangerous rises in pressure levels and the severity of explosions. To date, the effectiveness of side-on venting on methane flame deflagration in large scale operations has not been clearly addressed. This work explicitly investigates the influences of side-on venting on varied methane flame deflagration concentrations in a 30m long Detonation Tube (DT). RESULTS corresponding to this study prove the existence of a significant correlation between the fire and explosion driving parameters such as pressure rise and flame propagation velocity with the vent location. It observed venting the explosion at distance between 6.5m and 20.5m from the ignition source resulted in reducing the explosion total pressure by about 33% to 56%. For methane concentration of 7.5% the dynamic and static pressures reduced by about 66% and 33%, respectively. The reduced pressure observed to decelerate the flame velocity by about 70%. Significant pressure rise and flame deflagration velocity reductions were observed in both upstream and downstream of the DT corresponding to the location of the vent. For high methane concentrations vacuum effect observed to drawback the flame into the vent and trigger the secondary pressure rise.

Experimental evaluation and analysis of methane fire and explosion mitigation using isolation valves integrated with a vent system

There has been a surge of interest from the extractive industries in the application of mechanical means to the mitigation of flame deflagration. To verify the implementation and performance of passive and active mitigation protection, a comprehensive experimental investigation has been conducted on a large scale detonation tube, 30m long and 0.5m in diameter, with two mitigation valves (passive and active) and a burst panel venting system. The valves were used alternately to mitigate the flame deflagration of methane in concentrations ranging from 1.25% to 7.5%. The experimental work revealed that locating the passive mitigation valve at 22m distance from the ignition source mitigates the flame by fully isolating the tube. However, closing the valve structure in the axial direction generated another pressure wave upstream, which was approximately the same value as for the original pressure wave upstream. In the case of the active mitigation system, the system perfectly isolated upstream from downstream with no further pressure wave generation. When the vent was located at 6.5m from the ignition source, the total pressure was reduced by 0.48bar. Due to the counter flow of the reflected pressure wave the flame was extinguished at 12.5m from the ignition source.