Two-dimensional computational fluid dynamics simulation of coal combustion in a circulating fluidized bed combustor

A computational fluid dynamics (CFD) approach was applied to simulate the air-coal two-phase flow and combustion characteristics in a 50 kW circulating fluidized bed (CFB) combustor. Eulerian–Granular multiphase model with a drag coefficient correction based on the extended energy-minimization multi-scale (EMMS/matrix) model was used to study the gas–solid hydrodynamics. One energy conservation equation was applied to the mixture of gases and solids, considering heat conduction, heat convection and heat sources from chemical reactions. Reactions during coal combustion included moisture evaporation, dry coal devolatilization, volatile combustion, char combustion and char gasification. The model predicted the main features of the complex gas–solid flow, including the cluster formation of the solid phase along the walls, the flow structure of upward flow in the core and downward flow in the annular region. The voidage and temperature profiles in the furnace and the concentrations of gas components from the riser were validated with experimental data. Distributions of reaction rates in the riser were also obtained. This indicates a promising way to simulate the coal combustion in CFB to help understanding the combustion mechanism and designing new combustion technologies.