OCR Text |
Show combustion/ oxidation reactions leads to the familiar concept of the flamability limit. The second reason for the rapidity of combustion/oxidation processes is that with rare exception they occur via chain branching mechanisms. The fact that these mechanisms can cause the number of free radical chain carriers to increase exponentially means that, even under isothermal conditions very high rates of reaction are possible, these high rates of reaction being caused by concentrations of free radical chain carriers orders of magnitude greater than thermodynamic equilibrium would provide. This, however, is possible only if the initial fuel concentration is high enough to generate the superequilibrium concentration of free radicals. Thus it can be argued that even for an isothermal oxidation reaction there is a threshold for the initial concentration for the fuel below which the extent to which the reaction generates a superequilibrium concentration of free radicals is reduced and the reaction is correspondingly slower. Studies by the author and J. E. Hardy (6,7,8) showed the existence of a second threshold for combustion for the wet oxidation of CO, i.e. it was found that the specific rate of CO oxidation decreased rapidly with decreasing initial concentrations of CO for values of [COJi less than lOOOppm. The present research was undertaken with two goals, the first being to demonstrate the existence of second threshold effects for the kinds of organic molecules that are of concern in hazardous waste incineration. The molecules chosen form this purpose were methyl chloride, benzene and chlorobenzene. The seco nd purpose of this study was to demonstrate, on a laboratory scale, a novel method of improving incinerator efficiency, Clean Fuel Injection. EXPERIMENTAL PROCEDURES Experiments were done using EER's Precision Gas Kinetics Flow System which has been described previously (9). This apparatus consists of three sUbsystems: a system for preparing flowing mixtures of fixed gases and vaporized liquids, a reactor, and an -analytical train. The reactor consists of a quartz tube with capillary inlet and outlet legs in a three zone electric furnace and was operated at 50KPA. Previous studies with this reaction system of the kinetics of wet oxidation of CO have produced results in close agreement with computer modeling, indicating an absence of significant wall effects (6,7,8). Similarly studies of the kinetics of the Thermal DeNOx reaction with this system gave results in accord with the NO reductions observed in the application of Thermal DeNOx to large utility boilers and industrial furnaces (i.e. systems large enough to be wallless)(lO). This also indicates an absence of significant wall effects. 4 |