Explosion Risks of Hydrogen/Methane Blends

Abstract

Hydrogen is the next frontier and there is a concerted push to include hydrogen as an energy carrier. The main benefit is emissions reduction—eventually by 100 %. When used as a fuel, hydrogen supplies more energy per unit mass than the popular fuels used today. However, in the near term, there is a very significant cost differential between fossil fuels and hydrogen. Therefore, proposals have been made for the use of hydrogen as an additive to hydrocarbon fuels as a practical approach to the introduction of hydrogen in the energy mix. Enriched Methane (EM, a blend of hydrogen and natural gas) can presage a gradual transition to an eventual hydrogen economy. Besides the techno-commercial challenges for introducing hydrogen (or for that matter a hydrogen-methane blend), another key issue is that of the comparative safety between natural gas and hydrogen concerning the application, storage, transport, etc. Due to prior experience with, e.g. the process or petrochemical industries, it is well known that accidental releases of flammable substances are one of the largest contributors to the hazards of most industrial, domestic, and infrastructure facilities. Assessing the consequences and risks of such accidental releases is thus crucial. The consequences of a release such as cloud size and subsequent explosion like overpressure are dependent on several parameters such as fuel type, concentration, leak rate/direction, environmental conditions, cloud size, ignition location, and presence of any mitigation measures. More importantly, geometrical effects—including congestion and confinement, as well as layout of objects and walls—plays a key role in determining the magnitudes of gas cloud size (following a release) and overpressure/drag loads (following an explosion). Therefore, simple analysis techniques are generally not applicable as these may provide inaccurate results. 3D modelling based on Computational Fluid Dynamics (CFD) needs to be used. The current chapter describes the safety aspects of EM. In general, it can be expected that EM is relatively safer to handle (compared to hydrogen), thus significantly reducing the risk of fire and explosion. This chapter also seeks to evaluate whether EM may be safer than both hydrogen and methane under certain conditions. This is due to the fact EM combines the positive safety properties of hydrogen (strong buoyancy, high diffusivity) and methane (much lower flame speeds and narrower flammability limits as compared to hydrogen). Nonetheless, the explosion risk is by no means insignificant. The work is performed using the CFD software FLACS that has been well validated for safety studies of both natural gas/methane and hydrogen systems. Validation for EM-air explosions is also demonstrated. Practical systems such as vehicular tunnels, garages, etc., are used to demonstrate positive safety benefits of EM with comparisons to similar simulations for both hydrogen and methane.