The relation of cool flames and auto-ignition phenomena to process safety at elevated pressure and temperature.
The cool-flame phenomenon can occur in fuel-oxygen (air) mixtures within the flammable range and outside the flammable range, at fuel-rich compositions, at temperatures below the auto-ignition temperature (AIT). It is caused by chemical reactions occurring spontaneously at relatively low temperatures and is favoured by elevated pressure. The hazards that cool flames generate are described. These vary from spoiling a product specification through contamination and explosive decomposition of condensed peroxides to the appearance of unexpected normal (hot) flame (two-stage ignition).
On the cool flames of methane
ABSTRACT Methane is an attractive alternate fuel. It bums cleanly and is resistant to “knock.” For many years methane was believed not to give rise to the phenomenon of cool flame, a process basic to the problem of “knock” in internal combustion engine. This paper shows that methane exhibits the same combustion events as those observed in higher hydrocarbons: slow combustion; production of hydrogen peroxide; multistage, low temperature ignition; single and multiple cool flames; regions of negative temperature coefficient; and high temperature ignition. The ignition diagrams are normal, but the cool-flames regions are found at higher temperatures and are much narrower than for higher hydrocarbons. This is the reason why the methane cool flames escaped experimental observation for such a long time. These findings give a rationale for the high, but not absolute, resistance of methane to “knock.”
Oxygen effect in the photochlorination of ethane
The inhibitory effect of oxygen on the photochlorination of ethane has been studied between 253 and 423°K. It can be explained by the removal of ethyl radicals by molecular oxygen: C2H5+O2→ C2H5O2 k9. The value k9 = 0.63 × 109 mole-1 l. sec-1 is in good agreement with literature data. The dependence of the rate on concentrations and light intensity is discussed and permits one to discard an alternative explanation involving the reaction Cl+O2→ClO2.