(9a) Flammability Limits of HYDROGEN and ITS MIXTURES with Hydrocarbons In AIR AT Atmospheric and SUB-Atmospheric PRESSURES

FLAMMABILITY LIMITS
OF HYDROGEN AND ITS MIXTURES WITH HYDROCARBONS IN AIR AT ATMOSPHERIC AND
SUB-ATMOSPHERIC PRESSURES

Hai Le, Subramanya Nayak, M. Sam Mannan

The knowledge of hydrogen flammability characteristics,
especially flammability limits, is of particular importance and interest
because of the following reasons: i) ARIA (Analysis, Research and Information
on Accidents)  database showed that approximately 84%
of the studied incidents involving hydrogen resulted in fires and/ or
explosion, and the consequences of the accidents were tremendously serious with
25% of the cases resulted in deaths or serious injuries [1]; and ii) hydrogen is currently produced and used in various industrial processes ranging from the oil and gas industry to the food manufacturing with the annual amount generated worldwide estimated in the magnitude of million tons a year and worth billions of U.S. dollars [2].

This research aims at investigating the flammability limits
of hydrogen and its mixtures with hydrocarbons at both atmospheric and
sub-atmospheric pressures. Specifically, the upper flammability limit (UFL) and
lower flammability limit (LFL) of pure hydrogen in air are determined
experimentally in a closed cylindrical steel vessel
(inner diameter 10.22 cm, length 100 cm) with upward flame propagation at
ambient temperature and initial pressures of 1 atm, 0.7 atm, 0.5 atm, 0.3 atm,
0.1 atm. It was found that the flammability zone of hydrogen first widens when
the initial pressure decreased below 1 atm until 0.3 atm, then the zone narrows
when the initial pressure was further reduced. The UFLs and LFLs of binary
mixtures of hydrogen and hydrocarbons are also determined experimentally by the
same method. The application of Le Chatelier's rule to the flammability
limits of hydrogen mixtures will be evaluated using the obtained data. In
addition, the evaluation on the fire hazards and risk  of hydrogen at
atmospheric and sub-atmospheric pressures will be discussed.

REFERENCES

[1] ARIA. Accidentology involving
hydrogen.

[2] Winter C-J. Hydrogen energy,  Abundant,
efficient, clean: A debate over the energy-system-of-change. International
journal of hydrogen energy. 2009;34:S1-S52.