The Effect of Solid Inhibitors on Hydrogen-air Combustion

The use of hydrogen as an energy carrier is a promising solution for enabling the transition towards increased use of renewable energy sources in the global energy mix. However, hydrogen-air mixtures are highly reactive, and conventional technologies for explosion protection have limited applicability for hydrogen systems. As such, it is not straightforward to achieve the same level of safety for hydrogen energy systems, compared to systems based on conventional hydrocarbon fuels. The last decades have seen the development of innovative solutions for chemical inhibition of vapour cloud explosions with solid inhibitors, such as sodium bicarbonate and potassium carbonate (Roosendans and Hoorelbeke, 2019). Both substances are non-toxic, non-flammable, lowcost and relatively harmless to the environment, compared to for example halons. Although solid suppressants can be highly effective for hydrocarbons (Babushok and Tsang, 2000), experiments indicate that the same compounds are not very effective for the inhibition of hydrogen-air mixtures. The absence of carbon implies that hydrogen combustion is inherently different from hydrocarbons, however, the combustion of hydrocarbons includes the elementary reactions involved in combustion of hydrogen-air mixtures. These elementary reactions change when exposed to solid inhibitors like sodium or potassium compounds (Roosendans, 2018). Simulations of chemical kinetics based on these elementary reactions show that potassium compounds should yield a significant reduction of flame velocity. The same simulations show a significantly higher generation of radicals for hydrogen combustion compared to hydrocarbon combustion. Thus, more inhibitor is needed for effective inhibition of premixed hydrogen-air flames. For a solid inhibitor to be effective, the compound must evaporate in the flame zone, and this process appears to be the main hurdle for effective inhibition of hydrogen explosions. This paper presents results from dedicated experiments and simulations with chemical kinetics software that elaborate on previous findings and improve the understanding of the underlying mechanics of solid inhibitors in hydrogen-air combustion.publishedVersio

An Experimental Investigation on Fire Extinguishing Powder Efficiency

International audienceA series of large-scale tests were carried out to evaluate the effectiveness of using extinguishing powder (Purple K) to supress propane or petrol fire or to reduce emitted radiative heat flux. Three sets of different fire were carried out: a petrol leakage fire, a petrol pool fire and a liquid propane jet fire impinging a horizontal cylinder. In these tests, the powder was not able to extinguish the liquid hydrocarbons fire, but in some cases was able to extinguish the propane jet fire. In all cases, powder spray had excellent properties to reduce radiative heat flux

Flame Inhibition by Potassium-Containing Compounds

<p>A kinetic model of inhibition by the potassium-containing compound potassium bicarbonate is suggested. The model is based on the previous work concerning kinetic studies of suppression of secondary flashes, inhibition by alkali metals, and the emission of sulfates and chlorides during biomass combustion. The kinetic model includes reactions with the following gas-phase potassium-containing species: K, KO, KO₂, KO₃, KH, KOH, K₂O, K₂O₂, (KOH)₂, K₂CO₃, KHCO₃, and KCO₃. Flame equilibrium calculations demonstrate that the main potassium-containing species in the combustion products are K and KOH. The main inhibition reactions, which comprise the radical termination inhibition cycle are KOH + H=K + H₂O and K + OH + M=KOH + M with the overall termination effect: H + OH=H₂O. Numerically predicted burning velocities for stoichiometric methane/air flames with added KHCO₃ demonstrate reasonable agreement with available experimental data. A strong saturation effect is observed for potassium compounds: approximately 0.1% volume fraction of KHCO₃ is required to decrease burning velocity by a factor of 2; however, an additional 0.6% volume fraction is required to reach a burning velocity of 5 cm/s. Analysis of the calculation results indicates that addition of the potassium compound quickly reduces the radical super-equilibrium down to equilibrium levels, so that further addition of the potassium compound has little effect on the flame radicals.</p