Power-to-Gas: Safety Characteristics of Hydrogen/Natural- Gas Mixtures

Abstract

Safety characteristics for explosion protection of natural gas/hydrogen mixtures relevant in connection with the Power2Gas technology were studied in this work. Lower explosion limits (LEL) and upper explosion limits (UEL), limiting oxygen concentrations (LOC), maximum experimental safety gaps (MESG), maximum explosion pressures (p_max) and maximum rates of pressure rise (dp/dt)_max were determined experimentally in dependence of the hydrogen fraction. Adding hydrogen did mainly effect the UEL, LOC, MESG and (dp/dt)_max. The mixtures become more "critical" concerning the explosion hazards with increasing hydrogen fraction. However, the dependency of the safety characteristics from the hydrogen fraction is mainly not linear. Adding up to 10% hydrogen to natural gas had nearly no effect on the safety characteristics. More significant effects on the safety characteristics were observed at hydrogen fractions of more than 25%. For example the explosion group changes from IIA to IIB. Considering the huge explosion region and very high (dp/dt)_max of hydrogen compared to natural gas, even adding 50% hydrogen to natural gas has a rather small effect on these characteristics. Furthermore p_max of hydrogen/natural-gas mixtures can be calculated with good accuracy assuming ideal adiabatic conditions. EL and LOC of natural gas/hydrogen mixtures in ternary systems with inert gas and air were calculated in dependence of the type of inert gas with the so called “model of constant adiabatic flame temperature profiles” (Askar et al./2010).