Combustion modeling of the solid fuel bed and its application

Abstract

Combustion of bulky solid fuel particles usually occurs in the form of a bed. According to the flow direction of solid fuel and an oxidizer, the bed can be classified as either a batch type packed bed, a co-current and counter-current beds, or a cross-current moving bed. This list excludes beds that contain very complicated physical phenomena such as rotation of the furnace or fluidization. Bed combustion is understood based on similar combustion processes and modes of heat transfer. Various bed configurations and ignition methods can be considered numerically as boundary conditions. However, the bed combustion models which have been reported treat the sub-models and boundary conditions application-specifically, even though the governing equations and basic combustion procedures have much in common. Additionally, previous models have treated the solid material as a single phase, which has one specific particle size and uniform composition. This assumption has problems that the model cannot reflect the various sizes and kinds of the material mixed in the solid bed to the simulation. In this study, an unsteady 1-dimensional model of bed combustion, which can be applied to a variety of bed combustion cases, is proposed. Based on the assumption that the bed material is homogeneous and continuum, the governing mechanisms of the solid and the gas phases are modeled. Solid material are treated as multiple solid phases. These mechanisms include solid-gas reaction, gaseous reaction, various modes of heat transfers, and geometric changes of the solid particles. The numerical model is applied to an iron ore sintering bed, which can be characterized as a relatively uniform process of solid material, coke combustion, various modes of heat transfer, and the complicated physical changes of solid particles. Solid material is treated as three phases: iron ore, coke and limestone. Drying, condensation, coke combustion, limestone decomposition, generation of the macroscopic inter...