Flame propagation of a dust explosion in the MIKE 3 apparatus
Source: BAM, Division Safety of Energy Carriers
The increased use of hydrogen in industrial processes as well as the transformation of the energy sector away from the use of fossil raw materials and measures to reduce the release of CO2 into the atmosphere are associated with the use of new technologies. In many cases, these involve new risks that cannot be assessed in advance, such as the simultaneous occurrence of flammable dusts and gases, so-called hybrid mixtures, or the occurrence of atmospheres with increased oxygen content.
Hybrid mixtures pose a considerable risk with regard to the occurrence of undesired explosions and can lead to much more critical conditions in technical plants than dust/air mixtures. The use of new technologies can only succeed if the hazards they pose are known and suitable measures are taken to prevent accidents, in this case explosions.
Within the framework of the study presented here, the influence of the admixture of flammable gases (hydrogen and methane) as well as the increase of the oxygen content on the safety-related parameter minimum ignition energy were investigated. This parameter describes the ignition sensitivity of explosive mixtures and makes it possible to determine protective measures to prevent dust and gas explosions.
An increase in the oxygen content from 21 % to 50 %, as required, for example, for the so-called carbon capture process, already led to a considerable reduction in the minimum ignition energy of the dusts examined from values > 1000 mJ to a range between 10 mJ and 30 mJ. An admixture of 1 % to 2 % hydrogen or methane lowered the minimum ignition energy in some cases to values between 1 mJ and 3 mJ. Dusts that are non-sensitive to ignition when dispersed in air can exhibit very critical ignition behaviour in hybrid mixtures with flammable gases. In these cases, protective measures must be adapted to prevent dust explosions. Based on the experimentally determined data, various empirical models for estimating the minimum ignition energies of hybrid mixtures were furthermore compared and evaluated.
Effect of oxygen concentration, inert gas and CH4/H2 addition on the minimum ignition energy of coal dusts
Dejian Wua, Arne Krietsch, Martin Schmidt, Ulrich Krause
published in Journal of Loss Prevention in the Process Industries, Vol. 77, Article number 104772, page 1-10, 2022
BAM Chemical Safety Engineering department
BAM Safety of Energy Carriers division