Energy efficiency and hazardous emission reduction have become industry priorities over the last decade. The pre-treatment of coal and other carbonaceous materials, such as biomass and organic wastes by means of low-temperature carbonization (LTC) can provide an effective means for producing clean fuels. With LTC technology, widely available low-grade fuels can be converted to high-grade and hazardous pollutants, such as sulphur, chlorine and mercury are effectively removed. In practical terms, LTC is a preventive environmental protection technology that may utilize available domestic fuels and contribute to compliance with environmental legislation in energy production.
Nevertheless LTC in practical configurations is a complex process involving fluid dynamics, turbulence, dense particle flow, heat transfer and chemical kinetics. As a consequence of the process general complexity, experimental and numerical studies in pilot configurations are extremely limited. In this context, the present work constitutes an attempt to formulate a compact mathematical model for the simulation of low-temperature solid fuels carbonization. A simple, yet comprehensive, chemical model is proposed, accounting for fuel drying, devolatilization and char gasification. The model solves for the heterogeneous reactions between gaseous and solid species and is incorporated in the general Eulerian multiphase framework. Computations were performed in a three dimensional geometry of an industrial scale rotating cement kiln and in a two dimensional cross section with the FLUENT6 CFD code, appropriately customized to incorporate the features of the proposed model. Results are reported in terms of gaseous and solids phase velocities, solid volume fractions, residence times, reaction rates and reactant and product concentrations as a function of the gasification temperature.
Further investigation and testing is required, particularly in comparing the model predictions with experimental measurements in industrial scale reactors. The simulations demonstrated the promising capabilities of the model and the CFD method in general, which may be applied to similar physico-chemical processes. The proposed model may be used as a tool for the design of industrial equipment and processes.