Can the addition of hydrogen to natural gas reduce the explosion risk?

摘要

One of the main benefits sought by including hydrogen in the alternative fuels mix is emissions reduction - eventually by 100%. However, in the near term, there is a very significant cost differential between fossil fuels and hydrogen. Hythane (a blend of hydrogen and natural gas) can act as a viable next step on the path to an ultimate hydrogen economy as a fuel blend consisting of 8-30% hydrogen in methane can reduce emissions while not requiring significant changes in existing infrastructure. This work seeks to evaluate whether hythane may be safer than both hydrogen and methane under certain conditions. This is due to the fact hythane 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). For this purpose, several different mixture compositions (e.g. 8%, 20% and 30% hydrogen) are considered. The evaluation of (a) dispersion characteristics (which are more positive than for methane), (b) combustion characteristics (which are closer to methane than hydrogen), and (c) Combined dispersion + explosion risk is performed. This risk is expected to be comparable to that of pure methane, possibly lower in some situations, and definitely lower than for pure hydrogen. 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. The first part of the work will involve validating the flame speeds and flammability limits predicted by FLACS against values available in literature. The next part of the work involves validating the overpressures predicted by the CFD tool for combustion of premixed mixtures of methane and hydrogen with air against available experimental data. In the end, practical systems such as vehicular tunnels, garages, etc. is used to demonstrate positive safety benefits of hythane with comparisons to similar simulations for both hydrogen and methane.