Methane is one of the most common gaseous fuels that also exist in nature as the main part of the natural gas, the flammable part of biogas or as part of the reaction products from biomass pyrolysis. In this respect, the biogas and biomass installations are always subjected to explosion hazards due to methane. Simple methods for evaluating the explosion hazards are of great importance, at least in the preliminary stage. The paper describes such a method based on an elementary analysis of the cubic law of pressure rise during the early stages of flame propagation in a symmetrical cylindrical vessel of small volume (0.17 L). The pressure–time curves for lean, stoichiometric and rich methane–air mixtures were recorded and analyzed. From the early stages of pressure–time history, when the pressure increase is equal to or less than the initial pressure, normal burning velocities were evaluated and discussed. Qualitative experiments were performed in the presence of a radioactive source of 60Co in order to highlight its influence over the explosivity parameters, such as minimum ignition energy, maximum rate of pressure rise, maximum explosion pressure and normal burning velocity. The results are in agreement with the literature data.
The naturally or industrially occurring flammable mixtures containing combustible gases or/and dusts represent a potential risk of explosion with major consequences on the environment and human personnel. Methane and coal dust are among the best known components able of leading to the formation of such mixtures either in coal mining activities or in different industries using coal dust as fuel. In order to assess the risk of explosion and the explosion evolution in such composite mixtures, the knowledge of the characteristic explosion parameters under standardized conditions is necessary. In this paper the maximum explosion pressure p max , maximum rate of pressure rise (dp/dt) max and explosion severity factor for methane-air mixtures, air-coal dust mixture and hybrid air-methane-coal dust mixture were determined in a standard 20 dm 3 spherical explosion vessel.
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