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The energy hazard criteria of ASTM program CHETAH have been tested as criteria of flammability of gaseous mixtures containing an hydrocarbon vapour and air as oxidiser, at lean concentrations. A method for calculating the lower flammability limits in air, at atmospheric pressure and ambient temperature, is proposed as a result of a statistical study, which involved 67 combustible compounds. CHETAH's fourth energy hazard criterion was found to be the most reliable flammability criterion. The method is predictive since all the input data may be obtained with very good accuracy using a group contribution method. It is reliable, predicted limits being more frequently underevaluated, by 0. 11 mol% on average, than overevaluated. The method is also precise, with a standard deviation of the estimates of 0. 14 mol%. It is easily applicable to fuel mixtures and gives the same results as Le Chatelier's law.

Abstract: The dissociation of gas and model hydrates was studied using a classical thermodynamic method and a calorimetric method, in various aqueous media including pure water, high concentration calcium chloride solutions and water-in-oil emulsions. Methane hydrate dissociation temperatures vs. pressure curves were determined using pressure vs. temperature measurements in a constant volume cell (PVT), and high pressure differential scanning calorimetry (DSC), at 5 to 10 MPa gas pressure and at temperatures ranging from -10 to +12°C. PVT and DSC results are in good agreement, and concordant with data available in literature. From a thermodynamic point of view, there are no measurable differences between bulk solutions and emulsions. From a kinetic point of view, due to the considerable surface of interface between the two phases, emulsions allow the formation of much greater amounts of hydrate than solutions, without any agitation. Model hydrate of trichlorofluoromethane was studied in 9 to 27 mass% calcium chloride solutions in emulsion in oil, using DSC under atmospheric pressure, at temperatures ranging from -20 to +5°C. A diagram of dissociation temperature vs. salt concentration is proposed.