Analysis of transport phenomena in a rotary-kiln hazardous waste incinerator

Processing of hazardous waste in a rotary kiln incinerator is a complex process. Since hazardous waste has often very complicated chemical compositions and physical forms, the transport phenomena within the incinerator are not well understood, and the incineration process expects large uncertainties in process chemistry and is difficult for emission control. For better understanding of the incineration process, various transport phenomena taking place in the rotary kiln were discussed and analysed in this paper. To get more quantitative understanding, process simulation was conducted by using Computational Fluid-Dynamics (CFD) to characterise gas and solid flow and mixing, temperature and species distribution in the incinerator. To include all the waste streams in a single CFD model is a difficult task, and how to define the different waste streams with different calorific values and chemical compositions is a challenge to the CFD modelling. In this study, hazardous waste in various forms is firstly converted to a hydrocarbon-based virtual fuel mixture based on an overall mass and energy balance. The combustion of the simplified waste was then simulated with a combustion model. The distribution of temperature and chemical species is broadly investigated under various conditions. The predicted temperature distribution has been validated with available measurement data from an operating rotary kiln waste incinerator, and reasonable agreement between the predicted and measured data has been reached.