Chemical Inhibition of Premixed Hydrogen-air Flames: Experimental Investigation using a 20-litre Vessel

Throughout the history of the mining, petroleum, process and nuclear industries, continuous efforts have been made to develop and improve measures to prevent and mitigate accidental explosions. Over the coming decades, energy systems are expected to undergo a transition towards sustainable use of conventional hydrocarbons and an increasing share of renewable energy sources in the global energy mix. The variable and intermittent supply of energy from solar and wind points to energy systems based on hydrogen or hydrogen-based fuels as the primary energy carriers. However, the safety-related properties of hydrogen imply that it is not straightforward to achieve and document the same level of safety for hydrogen systems, compared to similar systems based on established fuels such as petrol, diesel and natural gas. Compared to the conventional fuels, hydrogen-air mixtures have lower ignition energy, higher combustion reactivity, and a propensity to undergo deflagration-to-detonation-transition (DDT) under certain conditions. To achieve an acceptable level of safety, it is essential to develop effective measures for mitigating the consequences of hydrogen explosions in systems with certain degree of congestion and confinement. Extensive research over the last decade have demonstrated that chemical inhibition, or partial suppression, can be used for mitigating the consequences of vapour cloud explosions (VCEs) in congested process plants. Total and cooperation partners have demonstrated that solid flame inhibitors injected into flammable hydrocarbon-air clouds represent an effective means of mitigating the consequences of VCEs involving hydrocarbons. For hydrogen-air explosions these same chemicals inhibitors have not proved effective. It is however well-known that hydrocarbons can affect the burning velocity of hydrogen-air mixtures greatly. This paper gives an overview over previous work on chemical inhibitors. In addition, experiments in a 20-litre vessel have been performed to investigate the effect of combinations of hydrocarbons and alkali salts on hydrogen/air mixtures.