CALCULATION OF DEGRADATION MECHANISM OF FREON 227EA IN THE FLAME OF METHANE-OXYGEN MIXTURE

Abstract

На основании известных кинетических данных выполнен расчет механизма превращения C3F7H в пламени смеси метан – кислород. Показано, что C3F7H в пламени смеси СН4 / О2 деструктурирует в реакциях с H, О и ОН без регенерации. В богатой смеси стадии с участием С3F7H и С2F4 в основном протекают за счет взаимодействия с атомарным водородом и ответственны за ингибирование горения метана в кислороде. Полученная схема качественно описывает всю известную экспериментальную картину, наблюдаемую при горении смесей СН4 / O2 / С3F7H. Fluorinated hydrocarbons with the general formula СnF2n+1H are widely used as gaseous fire extinguishing agents. However, these substances have a significant global warming potential, and their production must be phased out by 85 % by 2036 under the Kigali Amendment to the Montreal Protocol on Substances that Deplete the Earth’s Ozone Layer. Since it is impossible to completely abandon the use of fluorinated alkanes in fire extinguishing, one way to reduce their consumption is to increase their fire extinguishing efficiency by creating mixtures with other agents. The implementation of this approach is possible if the mechanism of transformation of compounds of the type СnF2n + 1H in a flame is known. This work is a continuation of the study of the mechanism of transformation of fluorinated hydrocarbons in a flame and is devoted to the consideration of heptafluoropropane (freon 227ea, C3F7H). Based on known experimental data on the concentrations of intermediate substances and taking into account only those elementary reactions whose kinetic parameters are known, the mechanism of the conversion of C3F7H in the flame of mixtures of methane with oxygen of various compositions was calculated. It has been shown that C3F7H in the flame of a СН4 / О2 mixture destructs in reactions with H, O and OH without regeneration, which refutes the hitherto widespread classical idea that the transformation of initial reagents in a flame proceeds along a molecular path. In a rich mixture, the stages involving С3F7H and С2F4 mainly occur through interaction with atomic hydrogen and are responsible for inhibiting the combustion of methane in oxygen. In a stoichiometric and especially in a lean mixture, the role of reactions of С3F7H and С2F4 with atomic hydrogen decreases, and the role of oxidative processes with the participation of O and OH increases, i.e. in a lean mixture, the inhibition effect weakens. The resulting scheme qualitatively describes the entire known experimental picture observed during the combustion of СН4 / O2 / С3F7H mixtures and can be used in the creation of highly effective gas fire extinguishing compositions based on freon 227ea.