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 ; 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 .
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.
 ARIA. Accidentology involving hydrogen.
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