Modeling the Thermal Decomposition of Chlorinated Hydrocarbons in an Ideal Turbulent Incinerator

Abstract

Combustion of wastes is an effective disposal technology. Although there are many examples of application in industry, severe environmental concerns are raised regarding the emissons from incinerators. Thermal treatment plants are usually comprised of a primary combustion chamber followed by a second combustion chamber, as schematically described in Fig. 1. During the oxidation of solid and liquid wastes in the primary chamber the mixing and the reaction conditions are inhomogeneous. Thus, the wastes undergo incomplete combustion and the gases traveling to the secondary stage of the reactor are rich in potentially hazardous products of incomplete combustion (PICs) together with unreacted wastes. For instance, incineration of chlorinated hydrocarbons can lead to highly toxic chemical species like polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The secondary chamber is the component of the plant which most strongly influences the air quality of the exhaust. Additionally, fuel (usually a waste) is injected to raise the temperature, promote better mixing of the reactants, and thus complete the oxidation of wastes. Formation of large droplets, quenching due to the existence of cold zones, and poor turbulent mixing of the gaseous reactants are examples of faults which may lead to unwanted emissions. In Germany, for instance, the BImSchG law (Bundes-Immissionsschutzgesetz) requires a residence time of 2s at a temperature of 1200°C for the combustion of chlorinated hydrocarbons to achieve their complete conversion. Nonetheless, the current regulation is not based on an adequate knowledge of the oxidation of halogenated species in the incineration systems [3].